Printing – Printing members – Rolling contact
Reexamination Certificate
2001-10-03
2004-02-10
Eickholt, Eugene H. (Department: 2854)
Printing
Printing members
Rolling contact
C101S401100, C101S217000, C492S048000
Reexamination Certificate
active
06688226
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sleeve for an indirect or offset printing machine and in particular to an offset blanket cylinder.
As is well known, an offset machine or a lithographic rotary machine with indirect printing mainly comprises three cylinders. A first cylinder carries lithographic plates and is in contact with inking rollers and wetting rollers. A second, subsidiary cylinder (or blanket cylinder) receives the inked data to be printed (i.e., “the impression”) from the first cylinder. These data are transferred to a substrate or web of paper or other material (for example plastic), interposed between the blanket cylinder and a third cylinder or pressing (or printing) cylinder. After transforming the inked data to the substrate, the surface of the blanket cylinder passes through a bath of solvents that wash the residual ink from the surface of the blanket cylinder.
The blanket cylinder is usually covered with a natural rubber blanket, which can have either a “compressible” structure, i.e., with a compressible layer, or a “conventional” structure, i.e., without a compressible layer. Various methods (and corresponding products) for producing the blanket cylinder are known. One of these uses a blanket of flat natural rubber with a yieldable (compressible) structure. The cylinder has an axial slot disposed parallel to the longitudinal axis. The rubber is wrapped about the blanket cylinder with its ends inserted into the slot and fixed to the cylinder by inserting a bar into the axial slot to retain the ends of the rubber therein.
The use of this type of blanket cylinder gives rise to various problems. For example, the presence of said slot results in mechanical imbalance of the cylinder structure. When the slot passes through the contact region between the respective cylinders, the pressure exerted between the blanket cylinder and the printing cylinder (or plate cylinder) varies. This cyclic pressure variation leads to vibration and stresses on the blanket cylinder and results in poor print quality on the substrate.
Said imbalance also limits the maximum rotational speed of the cylinder. Exceeding the maximum rotational speed generates stresses that can mechanically damage the printing machines. This limitation in rotational speed in turn limits the amount of printed substrate that can be produced in a given amount of time.
The presence of the slot also results in wastage of the substrate by creating a void in the print on the substrate.
This known method and resultant solution was later overtaken by other solutions. For example, offset presses began using a rotary support or mandrel that carries a cylindrical blanket sleeve, which together with the mandrel function as the blanket cylinder. This blanket sleeve includes an inner cylindrical portion or core that is formed as a hollow cylindrical body or sleeve. The core is typically formed of a thin-walled nickel tube that has a radial thickness in the range of seven thousandths of an inch thick to ten thousandths of an inch. The core is configured to be selectively drawn over the mandrel and locked to the mandrel. Thus, the blanket sleeve can be mounted on and dismounted from the mandrel, as by pressurized air for example, and therefore is independent from the rotary mandrel of the offset press. The blanket sleeve includes a compressible layer positioned on the inner cylindrical portion (core), a substantially incompressible reinforcement layer positioned on the compressible layer, and finally a printing layer that receives the inked data.
The compressible layer comprises a first continuous tubular body (without joints) of elastomeric material (natural rubber) presenting internally a plurality of cavities that determine the “compressibility” of the layer. To produce this compressible layer on the inner cylinder (core) first requires placing the natural rubber material into solution to form a liquid. This is accomplished by adding solvents to the solid natural rubber to provide the rubber in liquid solution. Then microspheres (that ultimately will produce the desired cavities in the compressible layer) are mixed into that rubber solution. Then, in a very time consuming process that requires considerable operator skill, the natural rubber solution with the microspheres is applied to the surface of the inner cylinder (core) by a knife coating technology or ring coating technology for example to build up a precursor layer of about one millimeter in radial thickness. However, because natural rubber does not adhere well to nickel surfaces, when the core is formed of nickel, an adhesive preparation must be provided. For example, a two-sided adhesive tape is typically first wound around the nickel core, and the rubber solution is applied to the exposed surface of the tape rather than to the bare nickel surface.
The use of a knife coating technology to produce this precursor layer requires an operator to mount the core onto a rotating mandrel. As the mandrel rotates, the operator must apply the liquid rubber solution with the microspheres to the surface of the rotating core. At the same time, a knife blade rises automatically to even out the surface being created while heated air is applied to remove the solvent from the solution as the core is rotating. The amount of solution being applied by the operator will vary depending on the consistency of the solution. If the solution is running it will not form the solid layer around the core. The consistency of the solution depends on the atmospheric ambient conditions of temperature, humidity and barometric pressure. These conditions also affect whether the solvent is removed completely during each revolution of the core on the mandrel. The solvent, which is volatile, must be completely removed prior to the next step, which is subjecting the precursor layer to heat that is sufficient (100 to 130 degrees centigrade) to cure the rubber. The generation of the precursor layer using the knife coating technology takes on the order of two to three hours for a typical sleeve or cylinder.
Once this preliminary thickness of the precursor layer has been attained, the natural rubber forming the precursor layer must be cured by the application of heat and pressure in another time-consuming process that requires operator manipulation of the cylinder. First, a tape that shrinks when subjected to curing temperatures (noted above) is wound around the precursor layer. The taped sleeve may be placed into an oven and maintained at curing temperatures (noted above) for two to three days. As the tape shrinks, the necessary pressure is applied to the precursor layer in order to effect curing of the natural rubber. Once the curing step is done, the cylinder must be manipulated to another station where the surface of the precursor layer can be ground down to the desired thickness (typically three tenths to seven tenths of a millimeter) of the compressible layer forming a tubular body.
Reinforcement structures such as threads or meshes (of cotton or other material) can be built on top of the compressible layer. The reinforcement layer can be defined by an elastomeric matrix containing threads, preferably of cotton. The threads can be continuous or discontinuous. These reinforcement structures can be applied spirally or linearly on the compressible layer. The function of this reinforcement layer is to form a support structure with physical and mechanical characteristics that are far superior to those of the elastomeric natural rubber matrix that forms the compressible layer and the outer printing layer (now to be described).
Finally, the surface printing layer is formed of elastomeric material (natural rubber) on top of the tubular body with the reinforced structure. The surface printing layer can be formed like the compressible layer, except without the use of microspheres and the voids created thereby. Alternatively, the surface printing layer can be formed by another technology such as by extrusion of a natural rubber sleeve onto and around the reinforcing layer. The final surf
Castelli Francesco
Rossini Felice
Dority & Manning P.A.
Eickholt Eugene H.
Erminio Rossini S.p.A.
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