Method and apparatus for handling printed sheet materials

Abstract: A support cylinder (10) for guiding freshly processed substrate material (S) between printing units (20A, 20B, 20C, 20D) or at the delivery end of a printing press is provided with a low coefficient of friction, semi-conductive base covering (56, 60, 70, 80, 90, 100, 106) for supporting and guiding the freshly processed substrate material without smearing the ink or causing indentations on the surface of the substrate. Radially projecting surface portions (56A, 56B, 74, 84, 94) of the semi-conductive base covering define electrostatic precipitation points and reduce the surface area available for frictional engagement. The low friction and semi-conductive properties of the cylinder base covering permit free movement of the freshly processed substrates (S) relative to the support cylinder (34). Electrostatic charges carried by the freshly processed substrates are discharged through the semi-conductive base covering into the support cylinder 34, thus eliminating electrostatic cling attraction between the freshly processed substrate and the base covering.

Description: This invention concerns improvements to transfer cylinders for preventing smearing and marking of freshly printed sheet material in a printing press. In the operation of a multi-unit rotary offset printing press, freshly printed sheets are transported by transfer devices from one printing unit to another, and then they are delivered to a sheet stacker. Sheet transfer devices are known by various names including transfer cylinders, support rollers, delivery wheels, delivery cylinders, skeleton wheels, transfer drums, support wheels, guide wheels and the like. The ink marking problems inherent in transferring freshly printed sheets have been longstanding. In order to minimize the contact area between the transfer cylinder and the printed sheet, conventional support wheels have been modified in the form of relatively thin disks having a toothed or serrated circumference, referred to as skeleton wheels. However, those thin disk wheels have not overcome the problems of smearing and marking the printed surface of the freshly printed sheet material due to sliding action between the sheet material and the projections or serrations. Moreover, attempts to minimize the surface support area in contact with the sheet material have resulted in actual indenting or dimpling of the material itself. Various efforts have been made to overcome the limitations of thin disk skeleton wheels. One of the more successful solutions has been completely contrary to the concept of minimizing the surface area of contact. That improvement is disclosed and claimed in US Patent 3,791,644 wherein there is provided a substantially cylindrical wheel or roller coated with an improved ink repellent surface formed by a layer of polytetrafluoroethylene (PTFE). During the use of the PTFE coated cylinder in high speed commercial printing press, the surface of the coated cylinder must be washed relatively frequently with a solvent to remove any ink accumulation. EP 0687561 discloses transfer cylinders having a conductive layer and also comprising a flexible jacket between the transfer cylinder support surface and the transported substrate. The limitations on the use of the conventional skeleton wheel and the PTFE coated transfer cylinder have been overcome with a transfer cylinder having an ink repellent and supportive flexible jacket covering for handling the freshly printed sheet material. It is now well recognized and accepted in the printing industry world-wide that marking and smearing of freshly printed sheets caused by engagement of the wet printed surface against the supporting surface of a conventional press transfer cylinder is substantially eliminated by using the anti-marking flexible covering system as disclosed and claimed in US Patent No 4,402,267 entitled "Method and Apparatus for Handling Printed Sheet Material". That system, which is marketed under license by Printing Research, Inc of Dallas, Texas under the registered trademark SUPER BLUE®, includes a movable covering or jacket of flexible material, referred to as a "flexible jacket covering". The flexible jacket covering provides yieldable, cushioning support for the freshly printed side of the sheet such that any relative movement between the printed sheet and the transfer cylinder surface takes place between the surface of the flexible jacket covering and the support surface of the cylinder so that marking and smearing of the freshly printed surface is substantially reduced. Although the improved SUPER BLUE® transfer cylinder has achieved world-wide commercial success, with continuous use such as is common in many printing operations, there is over a period of time a slight accumulation of ink on the surface of the flexible jacket covering. Moreover, some printing presses do not have sufficient cylinder clearance to accommodate the flexible jacket covering. Investigation and testing has identified the accumulation of an electrostatic charge on the freshly printed sheets as a significant factor that tends to impede completely free movement of the printed sheets as they are pulled around the transfer cylinder. The electrostatic charge build-up also appears to cause a faster accumulation of ink so that the support surface of the transfer cylinder becomes ink encrusted, thus requiring replacement more frequently. The build-up of the static electric charge on the freshly printed sheets is believed to be caused by "frictional electricity", which is the transfer of electrons from one material to another as they are pressed or rubbed together. According to one theory, the transfer of an electrostatic charges between two contacting dielectric materials, such as the metal printing press parts and a paper or other substrate sheet, is proportional to the difference between their dielectric constants, with the electrostatic charge moving from the material having the lower dielectric constant to the material having the higher dielectric constant. Since metal has a lower dielectric constant as compared with paper, an electrostatic charge is transferred to the sheets of paper as a result of frictional contact with metal press parts as the sheets travel through the press. Those transfer cylinders whose transfer surfaces are covered by a synthetic or natural organic resin, for example, as disclosed in my U.S. Patent 4,402,267, have a low-friction transfer surface but also have electrically insulating, dielectric properties which make the cylinder base covering an accumulator of electrostatic charges. That is, the electrical charges which are transferred to the printed sheets are also transferred to the underlying low friction, electrically insulating dielectric cylinder base covering. As a consequence of such electrostatic charge transfer and accumulation, the freshly printed sheets tend to cling to the underlying cylinder base covering surface and do not move as freely because of the force of electrostatic attraction between the printed sheet material and the electrically insulating cylinder base covering. It has been discovered that virtually smear-free sheet transfer can be obtained without using a flexible jacket covering as disclosed in U.S. Patent 4,402,267. According to the present invention, smear-free sheet transfer is accomplished by a substrate contacting base covering of electrically semi-conductive material having a frictional coefficient that is less than the frictional coefficient of the transfer cylinder sheet support surface. The detrimental effect of electrostatic charge accumulation on the freshly printed sheets is prevented by interposing a layer or covering of semi-conductive material having a low coefficient of friction that is less than the frictional coefficient of the transfer cylinder surface, whereby electrostatic charges carried by the freshly printed sheet material are discharged through the semi-conductive layer or covering into the grounded transfer or delivery-cylinder. Consequently, the accumulation of electrostatic charges on the semi-conductive covering cannot occur, since such charges are conducted immediately from the printed sheet through the semi-conductive base covering into the transfer cylinder and into the grounded frame of the printing press. According to one aspect of the present invention, radially projecting surface portions on the semi-conductive base covering define electrostatic precipitation points and reduce the surface area available for frictional engagement. The low friction properties of the semi-conductive base covering permit free movement of the freshly printed sheets relative to the transfer cylinder surface. Electrostatic charges carried by the printed sheet material are discharged into the transfer cylinder through the semi-conductive base covering. The structurally differentiated, radially projecting surface portions are provided by weft and warp strands of woven material in one embodiment, and by nodes or beads in an alternative embodiment. According to another aspect of the present invention, the low coefficient of friction, semi-conductive base covering for the transfer cylinder comprises a woven fabric of polyamide fiberglass strands coated with an organic fluoropolymer which contains a conductive agent such as carbon black, graphite or the like. The freshly printed sheets engage radially projecting strand portions of the woven covering without marking the freshly printed surface or damaging the sheet material itself. In accordance with another embodiment of the present invention, the cylindrical support surface of the transfer cylinder is covered by a layer of semi-conductive fluoropolymer resin which forms a low friction, electrically semi-conductive supporting surface. In that embodiment, the surface of the semi-conductive layer is structurally differentiated by nodes or beads. The invention will now be described by way of example only, reference being made to the accompanying drawings in which:- FIGURE 1 is a schematic side elevational view in which multiple transfer cylinders of the present invention are installed at interstation positions in a four color rotary offset printing press; FIGURE 2 is a perspective view of a delivery cylinder; FIGURE 3 is a sectional view showing a semi-conductive base covering installed on the sheet support surface of the delivery cylinder, taken along the line 3-3 of FIGURE 2; FIGURE 4 is a top plan view of a semi-conductive base covering; FIGURE 5 is a simplified sectional view thereof showing weft and warp strands; FIGURE 6 is an enlarged sectional view, partially broken away, of the delivery cylinder of FIGURE 2 having a semi-conductive base covering in the form of a layer of fluorinated polymer resin which is impregnated by a conductive agent; FIGURE 7 is a perspective view showing an alternative embodiment of a semi-conductive base covering having radially projecting nodes; FIGURE 8 is a sectional view showing the semi-conductive base covering of FIGURE 7 installed on a delivery cylinder; FIGURE 9 is a perspective view of a portion of the delivery cylinder of FIGURE 2 whose transfer surface is covered by a layer of semi-conductive beads; FIGURE 10 is a longitudinal sectional view thereof; FIGURE 11 is a sectional view showing an alternative embodiment of a semi-conductive base covering having radially projecting nodes; FIGURE 12 is a sectional view showing the conductive base covering of FIGURE 11 installed on a delivery cylinder; FIGURE 13 is an enlarged sectional view, partially broken away, of a delivery cylinder having a semi-conductive transfer surface which is infused with low friction polymeric particles; FIGURE 14 is an enlarged sectional view, partially broken away, of a delivery cylinder having a semi-conductive transfer surface which is infused with low friction polymeric particles; and, FIGURE 15 is a greatly enlarged pictorial representation of a microscopic section taken through a semi-conductive surface region of the delivery cylinder of FIGURE 14. As used herein, the term "processed" refers to various printing methods which may be applied to either side or both sides of a substrate, including the application of aqueous inks, protective coatings and decorative coatings. The term "substrate" refers to sheet material or web material. Also, as used herein, "fluoropolymer" means and refers to fluorocarbon polymers, for example polytetrafluoroethylene, polymers of chlorotrifluoroethylene, fluorinated ethylene-propylene polymers, polyvinylidene fluoride, hexafluoropropylene, and other elastomeric high polymers containing fluorene, also known and referred to as fluoroelastomers. The term "semi-conductive" refers to a conductive material whose surface resistivity at room temperature 20°C (70°F) is in the range 10 -2 ohms-centimeter to 10 9 ohms-centimeter, which is between the resistivity of metals and insulators. The term "support cylinder" as used herein refers to transfer cylinders, delivery cylinders, support rollers, guide wheels, transfer drums and the like. For exemplary purposes, the invention is described with reference to sheet material. However, it will be understood that the principles of the invention are equally applicable to continuous web substrates. The improved method and apparatus for handling a processed substrate in accordance with the present invention may be practiced in combination with high speed printing press equipment of the type used, for example, in offset printing. Such equipment may include one or more transfer cylinders 10 for handling a processed substrate such as a freshly printed sheet between printing units and upon delivery of the printed sheet to a delivery stacker. The particular location of the improved support cylinder 10 of the present invention at an interstation transfer position (T1, T3) or at a delivery position (T4) in a typical rotary offset printing press 12 is believed to be readily understandable to those skilled in the art. In any case, reference may be made to my earlier U.S. Patents 3,791,644 and 4,402,267 that disclose details regarding the location and function of a sheet support cylinder in a typical multi-unit printing press. The present invention may, of course, be utilized with conventional printing presses having any number of printing units or processing stations. Referring to FIGURE 1, the press 12 includes a press frame 14 coupled on its input end to a sheet feeder 16 from which sheets, herein designated S, are individually and serially fed into the press. At its delivery end, the press 12 is coupled to a sheet stacker 18 in which the printed sheets are collected and stacked. Located between the sheet feeder 16 and the sheet stacker 18 are four substantially identical sheet printing units 20A, 20B, 20C, and 20D that are capable of printing different color inks onto the sheets as they are transferred through the press. As illustrated in FIGURE 1, each printing unit is of conventional design, and includes a plate cylinder 22, a blanket cylinder 24 and an impression cylinder 26. Freshly printed sheets S from the impression cylinder are transferred to the next printing unit by a transfer cylinder 10. The initial printing unit 20A is equipped with a sheet in-feed roller 28 which feeds individual sheets one at a time from the sheet feeder 16 to the initial impression cylinder 26. The freshly printed sheets S are transferred to the sheet stacker 18 by a delivery conveyor system, generally designated 30. The delivery conveyor 30 is of conventional design and includes a pair of endless delivery gripper chains 32 carrying transversely disposed gripper bars, each having gripper elements for gripping the leading edge of a freshly printed sheet S as it leaves the impression cylinder 26 at the delivery position T4. As the leading edge of the printed sheet S is gripped by the grippers, the delivery chains 32 pull the gripper bars and sheet S away from the impression cylinder 26 and transport the freshly printed sheet S to the sheet delivery stacker 18. An intermediate transfer cylinder 11 receives sheets printed on one side from the transfer cylinder 10 of the preceding printing unit. Each intermediate transfer cylinder 11, which is of conventional design, typically has a diameter twice that of the transfer cylinder 10, and is located between two transfer cylinders 10, at interstation transfer positions T1, T2 and T3, respectively. The impression cylinders 26, the intermediate transfer cylinders 11, the transfer cylinders 10, as well as the sheet in-feed roller 28, are each provided with sheet grippers which grip the leading edge of the sheet to pull the sheet around the cylinder in the direction as indicated by the associated arrows. The transfer support cylinder 10 in the delivery position T4 is not equipped with grippers, and includes instead a large longitudinal opening A that provides clearance for passage of the chain-driven delivery conveyor gripper bars. The function and operation of the transfer cylinders and associated grippers of the printing units are believed to be well known to those familiar with multicolor sheet fed presses, and need not be described further except to note that the impression cylinder 26 functions to press the sheets against the blanket cylinders 24 which applies ink to the sheets, and the transfer cylinders 10 guide the sheets away from the impression cylinders with the freshly printed side of each sheet contacting the support surface of the transfer cylinder 10. Since each transfer cylinder 10 supports the printed sheet with the wet, freshly printed side facing the transfer cylinder support surface, the transfer cylinder 10 is provided with a low coefficient of friction, electrically semi-conductive cylinder base covering 56 as described below. Referring now to FIGURE 1, FIGURE 2 and FIGURE 3, an improved transfer support cylinder 10 constructed for use in the delivery position (T4) is characterized by a cylindrical rim portion 34 which is mountable on the press frame 14 by a shaft 36. The external cylindrical surface 38 of the cylindrical rim portion 34 has an opening A extending along the longitudinal length of the transfer delivery cylinder between leading and trailing edges 38A, 38B, respectively. The transfer delivery cylinder 10 includes longitudinally spaced hub portions 40, 42, 44 which are integrally formed with the cylindrical rim portion 34. Each hub portion is connected to the cylinder 34 by webs 46, 48 and 50, and support the transfer delivery cylinder 10 for rotation on the shaft 36 on a printing press in a manner similar to the mounting arrangement disclosed in U.S. Patent 3,791,644. As shown in FIGURE 2, the transfer delivery cylinder 10 includes opposed elongated integral flange members 52, 54 which extend radially inwardly from the surface of the cylinder 34. The flange portions 52 and 54 include elongated flat surfaces for securing a low coefficient of friction, semi-conductive base covering 56. Referring now to FIGURE 2 and FIGURE 3 of the drawings, there is illustrated in detail the improved construction of the transfer delivery cylinder 10 of the present invention including the semi-conductive base covering 56 for providing supporting contact for the printed side of a sheet S while guiding the printed sheet to the next printing unit or to the press delivery stacker. Although the ink repellent flexible jacket covering disclosed in U.S. Patent 4,402,267 provided improvements in transferring freshly printed sheet material, it has been discovered that virtually smear-free sheet transfer can be obtained without using the flexible jacket covering. Instead, an electrically semi-conductive, low friction base covering on the supporting surface 38 of the delivery cylinder supports and guides successive sheets of printed material without transferring the wet ink from a previous sheet to successive sheets and without marking or indenting the surface of the freshly printed sheet. In accordance with one aspect of the present invention, a semi-conductive resin compound, preferably a dielectric resin containing a conductive agent, has produced a substantial improvement in the transferring of printed sheet material that has wet ink on one surface thereof as it passes over and is supported by the transfer delivery cylinder 10. A suitable semi-conductive base covering 56 in accordance with the present invention and illustrated in the embodiment of FIGURE 5 comprises a woven material having warp and weft strands 56A, 56B that are covered with a low friction, semi-conductive compound 58. The semi-conductive base covering 56 is attached to the flanges 52 and 54 and is wrapped around the cylinder support surface 38, as shown in FIGURE 3. The semi-conductive base covering 56 is preferably of rectangular shape as shown in FIGURE 4 and FIGURE 5, and is dimensioned to completely cover the external support surface 38 of the cylinder 34. Preferably, the semi-conductive compound 58 is polytetrafluoroethylene resin (PTFE), for example as sold under the trademarks TEFLON and XYLAN, that is impregnated with a conductive agent such as carbon black or graphite. The cylinder base covering material 56 comprises warp and weft (fill) strands 56A, 56B of polyamide fiberglass, woven together in a base fiber thickness of approximately 0.2mm(.007inch). The woven material is coated with semi-conductive PTFE to a finished thickness in the range of 0.2mm-0.3mm(.009-.011 inch), a finished weight in the range of 56-63 dynes/sq.cm (17-20 ounces per square yard), with a tensile strength of approximately 281 x 10 3 - 175 x 10 3 kg/m 2 (400 - 250 pounds per square inch) warp and weft (fill). In one embodiment, the polyamide fiber comprises woven fiberglass filaments 56A, 56B covered by semi-conductive PTFE according to MIL Standard Mil-W-18746B. The PTFE resin compound 58 contains electrically conductive carbon black, or some other equivalent conductive agent such as graphite or the like, preferably in an amount sufficient to provide a surface resistivity not exceeding approximately 100,000 ohms-centimeter. While polyamide fiber covered or coated with polytetrafluoroethylene (PTFE) resin or a fluorinated ethylene propylene (FEP) resin impregnated with carbon black is preferred, other synthetic or natural organic resins including linear polyamides such as that sold under the trade name NYLON, linear polyesters such as polyethylene terephthlate sold under the trade name MYLAR, hydrocarbon or halogenated hydrocarbon resins such as polyethylene, polypropylene or ethylene-propylene copolymers, and acrylonitrile butadinene styrene (ABS) have a low coefficient of friction surface and can also be combined with a conductive agent, such as carbon black, graphite or the like, to render the compound electrically conductive. In the preferred embodiment, the surface resistivity of the conductive base covering 56 is approximately 75,000 ohms-centimeter. Other surface resistivity values may be used to good advantage, for example in the surface resistivity range of 50,000 ohms-centimeter to 100,000 ohms-centimeter. The coefficient of friction and conductivity of the base covering material are influenced by the presence of the conductive agent. Consequently, the amount of conductive agent included in the fluoropolymer resin for a given conductivity or surface resistivity will necessarily involve a compromise with the coefficient of friction. Generally, high conductivity (low surface resistivity) and low coefficient of friction are desired. The amount of conductive agent contained in the fluoropolymer resin preferably is selected to provide a surface resistivity not exceeding approximately 75,000 ohms-centimeter and a coefficient of friction not exceeding approximately .110. Referring to FIGURE 2 and FIGURE 3, the semi-conductive base covering 56 is secured to the transfer delivery cylinder 10 by ratchet clamps 59, 61. An important aspect of the present invention concerns reducing the coefficient of friction of the support surface 38 of the cylinder 34. The improved cylinder base support surface has a coefficient of friction less than the frictional coefficient of the cylinder surface 38 such as may be provided by coating the external surface 38 of the cylinder 34 with a fluoropolymer, but which has structurally differentiated surface portions that reduce the surface area available for frictional contact against the freshly printed sheets. It has been discovered that the radially projecting surface portions of the embodiments of FIGURES 5, 7, 8, 9 10, 11 and 12 provide improved, low frictional slip surfaces which perform substantially better in reducing accumulation of ink deposits on the base support surface 38 of the transfer cylinder 10. Referring to FIGURE 6, a low friction, semi-conductive base covering is also provided by a semi-conductive coating layer 60 applied directly on the cylinder support surface 38. The coating layer 60 is a composite fluorocarbon coating material containing a conductive agent. A preferred semi-conductive composition for providing the layer 60 is a polytetrafluoroethylene (PTFE) resin made under the trademark XYLAN by the Whitford Corporation, Westchester, Pennsylvania, impregnated with carbon black. A satisfactory coating type is XYLAN 1010 composite coating material which is curable at low oven temperatures, for example 121°C (250°F). The semi-conductive base layer 60 as described provides a substantially glazed surface having a low coefficient of friction of about 0.110, which is semi-conductive (surface resistivity of about 75,000 ohms-centimeter) and also provides for free movement of the freshly printed sheets by eliminating electrostatic cling. Although the low friction, conductive fluoropolymer layer 60 is particularly advantageous, other semi-conductive coatings can be applied to the transfer cylinder surface 38 to produce a comparable low friction, semi-conductive support surface. Both the woven semi-conductive base covering 56 (FIGURE 3) and the semi-conductive base layer 60 (FIGURE 6) have provided the improvement of reducing ink smearing and marking in high speed printing equipment and have also eliminated depressions and indentations on the printed surface of the sheets. Referring now to FIGURE 7 and FIGURE 8, an alternative embodiment of a cylinder base covering is illustrated. In that embodiment, a base covering 70 comprises a carrier sheet 72, formed of a moldable material such as plastic or the like. According to an important aspect of this alternative embodiment, the carrier sheet 72 is molded or pressed to produce multiple nodes or radial projections 74 on the sheet engaging side of the carrier sheet 72. Each node 74 has a curved, sheet engageable surface 74S which is radially offset with respect to the curved transfer path of the sheet S. Preferably, the nodes 74 and the surface of the carrier sheet 72 are covered by a layer 78 of a semi-conductive, low friction resin compound, for example, a fluoropolymer impregnated with a conductive agent such as carbon black or graphite. Polytetrafluoroethylene (PTFE) impregnated with carbon black is preferred for this embodiment, and is applied in a layer directly onto the surface of the carrier sheet 72 as previously described. The nodes 74 have a radial projection with respect to the carrier sheet 72 of approximately 0.1 mm (4 mils) with a circumferential spacing between each node of approximately 0.05 mm (2 mls). The carrier sheet 72 is electrically connected to the cylinder 34 through the ratchet clamps 59, 61. The low friction, semi-conductive coating 78 is applied directly to the carrier sheet, whereby electrical charges delivered by the printed sheet S are conducted through the carrier sheet 72 into the cylinder 34 and into the grounded press frame 14. The carrier sheet 72 should have a gauge thickness which is sufficient to provide strength and dimensional stability and yet be flexible enough to easily wrap around the ratchet wheel and the support cylinder 34. Generally, gauge thicknesses in the range of about 0.05 mm (2 mls) to about 0.6 mm (24 mils) may be used to good advantage, depending on press clearance and press design. Referring again to FIGURE 8, one advantage provided by the node embodiment is reduced surface contact between the freshly printed sheets and the cylinder base covering 70. Because of the curved contour of the nodes 74 and the node spacing, there is less surface area available for contact by the freshly printed sheets. Consequently, the force of frictional engagement is substantially reduced, thus permitting free movement of the freshly printed sheets relative to the transfer cylinder base covering. Referring now to FIGURE 9 and FIGURE 10, yet another semi-conductive base covering embodiment is illustrated. In this embodiment, a low friction, semi-conductive base covering 80 comprises a metallic carrier sheet 82, constructed of a malleable metal such as aluminum, copper, zinc or the like. The conductive carrier sheet 82 has multiple beads 84 secured to its external surface, for example by electrical weld unions W. The surface of the conductive carrier sheet 82 and the beads 84 are covered by a layer 86 of a fluoropolymer resin that contains a semi-conductive agent, for example polytetrafluoroethylene resin (PTFE) containing carbon black, as previously specified. The beads 84 may be formed of a metal such as aluminum, copper, zinc or the like, or other material such as nylon polyamide resin. The beads 84 have a diameter of approximately 0.15 mm (6 mils), and the thickness of the low friction, semi-conductive coating layer 86 is approximately 0.05 mm (2 mils). Preferably, the coated beads are arranged in a rectilinear pattern and are circumferentially spaced with respect to each other by approximately 0.076 mm (3 mils). The gauge thickness of the conductive carrier sheet 82 is in the range of approximately 0.05 mm (2 mils) to approximately 0.6 mm (24 mils), depending on press clearance and design. The spacing and curvature of the coated beads reduces the amount of surface available for contact with the freshly printed sheets. The low friction surface provided by the PTFE resin layer 86, together with the circumferential spacing, and radially projecting portions of the beads substantially reduce the area of frictional engagement, thus reducing surface contact between the freshly printed sheets and the underlying cylinder base covering 80. Yet another embodiment of a low frictional slip, semi-conductive base covering is shown in FIGURE 11 and FIGURE 12. In this alternative embodiment, a semi-conductive base covering 90 comprises a base carrier sheet 92 of a moldable plastic material having integrally formed spherical projections 94 arranged in a rectilinear array. The base carrier sheet 92 and the spherical projections 94 are covered by a semi-conductive layer or coating 96 of a fluoropolymer resin which contains a conductive agent, for example polytetrafluoroethylene resin (PTFE) mixed with carbon black or graphite, as previously specified. In the molded carrier sheet embodiment shown in FIGURE 11 and FIGURE 12, the semi-conductive layer or coating 90 is secured in electrical contacting engagement with the cylinder 34 by a linking portion 98. The coated, spherical projections 94 are spaced with respect to each other by approximately 0.076 mm (3 mils). The gauge thickness of the base carrier sheet 92 is in the range of approximately 0.05 mm (2 mils) to as much as 0.6 mm (24 mils) or more, subject to press clearance. The spherical projections 94 have a radius of approximately 0.076 mm (3 mils), and the thickness of the low friction, conductive coating layer 96 is approximately 0.05 mm (2 mils). The radially projecting portions 94 substantially reduce the surface area available for contact, thus reducing frictional engagement between the freshly printed sheets and the base covering 90. The woven embodiment of FIGURE 5 and the node embodiments of FIGURE 7 through FIGURE 12 reduce the amount of surface are available for contact with the freshly printed sheets. For example, the overlapping warp and weft (fill) strands 56A, 56B of the woven embodiment shown in FIGURE 5A provide a lattice-like framework of radially projecting lattice portions that reduce the surface area available for frictional engagement. The low frictional coefficient support function is also provided by the radially projecting node embodiments of FIGURES 7-12. An additional advantage provided by the foregoing embodiments is that the structurally differentiated and radially projecting surface portions provided by the woven material and by the nodes concentrate or focus the area of electrostatic discharge between the freshly printed sheets and the semi-conductive, low friction base covering. The raised or projecting surfaces provided by the woven material and by the nodes provide reduced area discharge points or electrostatic precipitation points where the electric field intensity is increased, thus increasing the transfer of electrostatic charges from the freshly printed sheets to the semi-conductive base covering 56, and thereafter through the cylinder 34 and into the grounded press frame 14. Referring now to FIGURE 13, yet another semi-conductive base covering embodiment is illustrated. In this alternative embodiment, a low friction, semi-conductive base covering 100 comprises an infusion of organic lubricant particles 102, preferably polytetrafluoroethylene (PTFE), that are infused into the support surface 38 of the cylinder 34. The support surface 38 is covered or plated by a porous, thin metal film 104, with the PTFE particles being infused through the porous metal film, and partially into the cylinder 34, thus providing a semi-conductive base support surface 38E which has a low coefficient of friction, and which has a surface resistivity in the range of from 50,000 ohms-centimeter to about 100,000 ohms-centimeter. The infusion of a low friction coefficient, organic lubricant material such as PTFE is carried out by providing a thin metal layer 104 of a porous alloy of nickel or cobalt, or the like, with boron or the like, which is electrochemically deposited on the cylinder surface 38. The cylinder 34 is immersed in a catalytic nucleation plating bath containing a nickel salt and a borohydrite reducing agent, with the plating rate being adjusted to provide a nickel-boron coating layer 104 at a plating deposition rate on the order of approximately 0.05 mm-0.076 mm per hour (1-2 mils/hour). The plating nucleation is terminated after the coating layer 104 has formed a metallurgical union with the cylinder surface 38, but where the coating layer 104 still retains voids that provide a porosity of the order of about 20%-50%, and having a radial thickness of approximately 0.025 m (one mil) or less. After rinsing and drying, the nickel-boron thin metal layer 104 is heat treated to improve metal bond integrity and to increase the hardness of the porous thin metal layer 104 from about 58-62 Rockwell "C" to about 70-72 Rockwell "C". The heat treatment is preferably carried out at a temperature of approximately 343°C (650°F). A low friction coefficient organic lubricant material, for example PTFE, is then applied to the porous surface 38E, and is further heat treated to cause the organic lubricant material to flow into the voids of the porous metal alloy layer 104. Preferably, the organic lubricant material is infused during the heat treatment at higher temperatures above the melting point of the organic lubricant (preferably at a temperature in the range of approximately 308°C (580°F) to approximately 315°C (600°F) for polytrafluoroethylene to cause mixing, flow and infusion until the voids of the porous metal alloy layer 104 are completely filled, thus providing a reservoir of organic lubricant material. After infusion of the organic lubricant 102, the surface 38E is burnished and polished to remove excess material, exposing the bare metal alloy surface 38E and pores which have been filled with the organic lubricant. The result is a hardened surface 38E which has a coefficient of friction lower than that of the cylinder surface 38 and is electrically semi-conductive. Referring now to FIGURE 14 and FIGURE 15, an alternative semi-conductive base covering 106 is illustrated. In this embodiment, the cylinder 34 itself is constructed of a porous metal, for example cast iron. Cast iron is considered to be relatively porous as compared with the porosity extruded aluminum, for example. The organic lubricant particles 102 are infused directly into the porous surface region R underlying the support surface 38. The infusion of lubricant 102 is concentrated in the porous surface region R, preferably to a penetration depth of about 0.05 mm (.001 inch). The organic lubricant particles 102 preferably comprise polytetrafluoroethylene (PTFE). After cleaning, rinsing and drying the surface 38 of the cylinder 34, the cylinder is heated in an oven at a pre-bake burn-off temperature of about 343°C (650°F) to drive off oils and other volatiles from the porous surface region R. The heating step opens and expands the pores in the surface region of the cylinder. While the cylinder 34 is still hot, an organic lubricant, for example PTFE particles suspended in a liquid carrier, are sprayed onto the heated surface 38. After the surface 38 has been thoroughly wetted by the liquid organic lubricant solution, it is placed in an oven and heated at a temperature above the melting point of the organic lubricant, preferably at a temperature on the order of approximately 548°C (580°F) to approximately 568°C (600°F) for polytetrafluoroethylene, to cause mixing, flow and infusion into the surface pores of the cylinder 34 until the voids in the surface region R are completely filled with the PTFE particles 102. As a result of such heating, the PTFE particles melt and coalesce, while the solvent is boiled and removed by evaporation. After cooling, the surface pores of the cylinder 34 are completely filled with solidified organic lubricant, substantially as shown in FIGURE 15. After infusion and solidification of the organic lubricant 102, the surface 38 is burnished and polished to remove excess material so that the bare metal surface 38 is exposed and the solid lubricant material 102 in each pore is flush with the bare metal surface 38. That is, any lubricant material 102 or other residue that forms a bridge over the metal surface 38 is removed and the external face of the solidified organic lubricant deposit 102 is leveled with the exposed metal surface 38. The porous near surface region R that is filled with solidified organic lubricant material 102 provides a semi-conductive zone for conducting electrostatic charges from the freshly printed sheets through the conductive transfer cylinder 34 and into the grounded press frame 14. The freshly processed substrates and the low coefficient of friction, semi-conductive base covering on the cylinder surface are electrostatically neutralized with respect to each other, so that the freshly processed substrates remain freely movable and do not cling to the semi-conductive base support surface of the cylinder. Another beneficial result of the neutralizing action is that the underlying base support surface becomes more resistant to ink accumulation and encrustation. Yet another advantage of the electrostatically neutralized substrate material is that it retains its natural flexibility and movability in the absence of electrostatic charge accumulation. Because of the selected polymeric materials used in the construction of the semi-conductive base covering, the transfer support cylinder has longer wear life, requires less cleaning, and provides greater operating efficiencies. Since the fluorocarbon polymer surface of the semi-conductive base covering is both oleophobic and hydrophobic, it resists wetting. It is not necessary to wash the semi-conductive base support surface of the cylinder since the semi-conductive covering is ink repellent and resists the accumulation of ink, thus reducing maintenance time and labor, while improving quality and increasing productivity. Moreover, removal of the electrostatic charges from freshly printed sheets makes sheet handling easier at the delivery unit. By eliminating the electrostatic charges on the freshly printed sheet, the printed sheets are more easily jogged to achieve a uniform stack of sheets. Another advantage is that offset or set-off in the delivery stacker is reduced because the electrostatically neutralized printed sheets are delivered gently and uniformly into the delivery stacker. The electrostatic charges are removed from the freshly printed sheets as they are transferred through the press, so that each printed sheet is electrically neutralized as it is delivered to the stacker.

Claims: A method for supporting a processed substrate (S) as it is transferred from a processing unit (20A, 20B, 20C, 20D) of a printing press (12), characterized by the steps of:- (i) providing a rotatable member (34) having a substrate support surface (38) thereon; (ii) providing a base covering (56, 60, 70, 80, 90, 100, 106) of electrically semi-conductive material (58, 60, 78, 86, 96, 102) having a frictional coefficient that is less than the frictional coefficient of the substrate support surface; (iii) securing the base covering to the substrate support surface (38) and in electrical contact with the rotatable member (34); and (iv) rotating the base covering in contact with a processed substrate (S) and discharging electrostatic charges carried on the processed substrate into the base covering as the processed substrate is transferred from the processing unit. A method as claimed in Claim 1 wherein the base covering (56) comprises a sheet of woven material having warp and weft strands (56A, 56B) defining a lattice framework of radially projecting portions, the method comprising engaging the processed substrate (S) against the radially projecting lattice portions. A method as claimed in Claim 1 or Claim 2 wherein the base covering (56) comprises a sheet of woven material having strands (56A, 56B) that are covered with the semi-conductive material (58), the method comprising securing the semi-conductive base covering to the rotatable member by wrapping the sheet of woven material around the substrate support surface (38). A method as claimed in any one of Claims 1 to 3 wherein securement of the base covering to the rotatable member is performed by forming a layer (60) of the semi-conductive material directly onto the substrate support surface (38). A method as claimed in Claim 1 wherein:- 5.1 the base covering (56) comprises a woven material having warp and weft strands (56A, 56B), and the warp and weft strands are covered with a coating (58) of the semi-conductive material, the method comprising engaging the coated warp and weft strands against the processed substrate (S) to bring the substrate and base covering into electrostatic discharging contact with each other; or 5.2 the base covering (70) comprises a carrier sheet (72) having radially projecting nodes (74) and the nodes are coated by a coating (78) of semi-conductive material, the method comprising contacting the coated nodes against the processed substrate (S) to bring the substrate and base covering into electrostatic discharging contact with each other; or 5.3 the base covering (80) is a carrier sheet (82) having an array of beads (84) disposed on the surface of the carrier sheet and the beads are covered by a coating (86) of the semi-conductive material, the method comprising engaging the coated beads against the processed substrate (S) to bring the substrate and the base covering into electrostatic discharging contact with each other. A method as claimed in Claim 1 wherein:- 6.1 the base covering (56, 70, 80, 90) comprises a sheet of material having radially projecting portions (56A, 56B, 74, 84, 94) that are covered by the semi-conductive material (58, 78, 86, 96), the method including concentrating the electrostatic discharge between the processed substrate and the base covering by engaging the processed substrate (S) against the radially projecting portions; or 6.2 the base covering (70, 80, 90) comprises a carrier sheet (72, 82, 92) having radially projecting nodes (74, 84, 94) that are coated with the semi-conductive material (78, 86, 96), the electrostatic discharge being concentrated by engaging the freshly processed substrate against the coated nodes; or 6.3 the conductive base covering (80) is a carrier sheet (82) having an array of beads (84) that project from the surface of the carrier sheet, the beads being beads coated with the semi-conductive material (84), the method including concentrating the electrostatic discharge by engaging the processed substrate (S) against the coated beads. A method as claimed in any preceding claim wherein the semi-conductive base covering (56, 70, 80, 90) has structurally differentiated surface portions (56A, 56B, 74, 84, 94) defining electrostatic precipitation points, the discharge of electrostatic charges carried on the processed substrate (S) being discharged through the electrostatic precipitation points. A method as claimed in any preceding claim wherein the printing press (12) includes a grounded press frame (14) and a cylinder (10) mounted on the press frame for guiding a processed substrate (S), the electrostatic discharge from the substrate being performed by conducting the electrostatic charges from the base covering through the transfer cylinder into the grounded press frame as the semi-conductive base covering (56, 60, 70, 80, 90, 100, 106) engages the processed substrate. A method as claimed in any preceding claim wherein the printing press (12) is a rotary offset press having multiple printing units (20A, 20B, 20C, 20D), each printing unit employing a blanket cylinder (24) and an impression cylinder (26) for applying a printed image or a protective coating on one side of a processed substrate (S) transferring between, the method comprising the following steps performed at eaching printing unit in succession:- (i) applying printing ink or coating material from the blanket cylinder (24) to a substrate (S) as the substrate is transferred through the nip between the impression cylinder (26) and the blanket cylinder; (ii) transferring the processed substrate (S) from the impression cylinder; and (iii) discharging an electrostatic charge carried on the processed substrate into the semi-conductive base covering (56, 60, 70, 80, 90, 100, 106) as the substrate is transferred from the impression cylinder (26). A transfer cylinder (10) having a substrate support surface (38) for guiding a processed substrate (S) as it is transferred from one printing unit (20A, 20B, 20C, 20D) to another, characterized in that the substrate support surface (38) is the exposed surface of either:- (i) a peripheral integral thickness (R) of the electrically conductive cylinder material (34), said material being penetrable by an organic lubricant (102) and impregnated therewith so that the substrate support surface (38) is the substrate contact surface and is of reduced frictional coefficient and electrically semi-conductive, or (ii) an applied base covering (56, 60, 70, 80, 90, 100, 104) which is the substrate contact surface and is of electrically semi-conductive material (58, 60, 78, 86, 96, 102) which is disposed on the surface (38) of the transfer cylinder (10), the semi-conductive material (58, 60, 78, 86, 96, 102) having a frictional coefficient that is less than the frictional coefficient of said cylinder surface (38). A transfer cylinder (10) as claimed in Claim 10 wherein the semi-conductive material (58, 60, 78, 86, 96, 102) comprises a dielectric resin. A transfer cylinder (10) as claimed in Claim 11 wherein the dielectric resin comprises a linear polyamide, a polyethylene terephthalate or other linear polyester, a hydrocarbon or halogenated hydrocarbon resin or an acrylonitrile-butadiene-sytrene copolymer. A transfer cylinder (10) as claimed in Claim 12 wherein the halogenated hydrocarbon resin is a fluorocarbon homo- or co-polymer. A transfer cylinder (10) as claimed in Claim 13 wherein the fluorocarbon polymer is a fluorinated ethylene-propylene copolymer or polytetrafluoroethylene. A transfer cylinder (10) as claimed in Claim 12 wherein the hydrocarbon or halogenated hydrocarbon resin is an optionally halogenated polyethylene, polypropylene or ethylene-propylene copolymer. A transfer cylinder (10) as claimed in any one of Claims 10 to 15 wherein the semi-conductive material contains an electrically-conductive agent. A transfer cylinder (10) as claimed in Claim 16 wherein the conductive agent comprises carbon black or graphite. A transfer cylinder (10) as claimed in any one of Claims 10 to 17 wherein the base covering comprises semi-conductive material which comprises a dielectric resin and an amount of an electrically-conductive agent contained in the dielectric resin, the resin, the conductive agent and the amount thereof being selected to provide the base covering (56, 60, 70, 80, 90) with a surface resistivity not exceeding approximately 75,000 ohms-centimeter and a coefficient of friction not exceeding approximately 0.11. A transfer cylinder (10) as claimed in any one of Claims 10 to 18 wherein the semi-conductive base covering (60) comprises:- 19.1 a dielectric resin containing a conductive agent disposed in a solid layer on the substrate support surface (38) of the transfer cylinder (10); 19.2 a woven or non-woven stranded component covered with a semi-conductive covering; 19.3 a carrier sheet (72, 82, 92) having radially projecting nodes (74, 84, 94), the semi-conductive material (78, 86, 96) being in the form of a coating layer on the nodes; 19.4 a metallic carrier sheet (82) and an array of beads (84) disposed on the surface of the carrier sheet, the semi-conductive material (86) forming a coating layer on the beads; or 19.5 a layer (104, 106) of porous metallic material disposed on the substrate support surface, the porous metallic material layer containing an infusion of an organic lubricant (102). A transfer cylinder (10) as claimed in Claim 19 wherein the base covering (56) comprises a sheet of woven material having warp strands (56A) and weft strands (56B) covered with the semi-conductive material (58). A transfer cylinder (10) as claimed in Claim 19 or Claim 24 wherein the semi-conductive material comprises woven polyamide strands (56A, 56B) covered with a fluoropolymer resin (58) that contains a conductive agent. A transfer cylinder (10) as claimed in Claim 19 wherein the porous metallic material layer (104) comprises boron alloyed with nickel and/or cobalt. A transfer cylinder (10) as claimed in Claim 19 wherein the porous metallic material layer (104) comprises an electrochemical plating deposition (104) of a porous metal alloy on the substrate support surface (38). A transfer cylinder (10) as claimed in any one of Claims 19 to 23 wherein the organic lubricant (102) comprises polytetrafluoroethylene (PTFE). A transfer cylinder (10) as claimed in any one of Claims 19 to 24 wherein the organic lubricant (102) is disposed within the pores of the porous metallic material. A transfer cylinder (10) as claimed in Claim 10 wherein the transfer cylinder (34) comprises a cast iron or other porous metallic material (that is relatively porous as compared with the porosity of extruded aluminium), characterized in that an organic lubricant (102) is infused into the porous metal substrate support surface (38). A transfer cylinder (10) having a substrate support surface (38) for guiding a processed substrate (S) as it is transferred from one printing unit (20A, 20B, 20C, 20D) to another, characterized by a surface cylinder thickness (56, 60, 70, 80, 90, 100, 104) of electrically semi-conductive material (58, 60, 78, 86, 96, 102) forming the substrate support surface (38) of the transfer cylinder (10), the semi-conductive material (58, 60, 78, 86, 96, 102) forming the substrate contact surface and having a frictional coefficient that is less than the frictional coefficient of a sub-surface of said cylinder exposable by removal of said thickness.

Inventors: BRANSON JOHN A, DEMOORE HOWARD W, BRANSON, JOHN A., DEMOORE, HOWARD W.
Applicants: DEMOORE HOWARD W, DEMOORE, HOWARD W.
Application year: 1996
Main classification: B41F22
IPC codes: B41F22, B65H29, B65H5, B65H27, B41F30, B41N10