Anti-static, anti-smearing pre-stretched and pressed flat, precision-cut striped flexible coverings for transfer cylinders

Abstract

Freshly printed sheets are transferred from one printing unit to another by transfer cylinders each having an ink repellent, electrically conductive, striped flexible jacket covering that is movable relative to the sheet support surface of the transfer cylinder. The jacket covering is made of a flexible fabric material that is pre-stretched, pressed flat, cut to size and treated with an ink repellent compound and is also treated with an anti-static ionic compound or is otherwise rendered electrically conductive by one or more conductive strands. Electrostatic charges carried by the freshly printed sheets are discharged through the ink repellent, electrically conductive, flexible jacket covering into the grounded transfer cylinder. A low friction, electrically conductive cylinder base covering that includes center alignment marks is secured to the transfer cylinder for engaging the flexible jacket covering. The ink repellent, electrically conductive flexible jacket covering is provided with alignment center marks and alignment stripes so that the flexible jacket covering can be precisely aligned with ease and secured over the gripper edge, tail edge and side edges of the transfer cylinder. The low frictional coefficient of the conductive cylinder base covering is further reduced by nodes and / or openings.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application is a continuation of prior U.S. patent application Ser. No. 08 / 581,068 filed Dec. 29, 1995, now U.S. Pat. No. 5,907,998 entitled as above by the same inventors for which benefit under 35 USC § 120 is claimed.FIELD OF THE INVENTION[0002]This invention concerns method and apparatus for reducing marking and smearing of freshly printed substrate material in a printing press.BACKGROUND OF THE INVENTION[0003]In the operation of a multi-unit rotary offset printing press, freshly printed substrates such as sheets or web material are guided by transfer cylinders or the like from one printing unit to another, and then they are delivered to a sheet stacker or to a sheet folder / cutter unit, respectively. Transfer cylinders are known by various names including delivery cylinders, transfer rollers, support rollers, delivery wheels, skeleton wheels, segmented wheels, transfer drums, support drums, spider wheels, support wheels, guide wh...

AI Technical Summary

Benefits of technology

[0015]The present invention provides an improved method and apparatus for transferring substrate material in sheet form or in web form that has been freshly printed on at least one side wherein the substrate material is supported by a movable, ink repellent and electrically conductive covering or jacket of flexible material is attached to the transfer cylinder. In accordance with one aspect of the present invention, the build-up of electrostatic charges on the movable, flexible jacket covering is prevented by including one or more conductive elements in the jacket covering material, or by treating the jacket covering with an anti-static ionic polymer compound, that make the jacket covering electrically conductive. According to these improvements, electrostatic charges delivered to the flexible jacket covering by frictional contact with the freshly printed substrate material are in turn drawn off and discharged through the low frictional coefficient, conductive cylinder base covering into the transfer or delivery cylinder. Consequently, the build-up or accumulation of electrostatic charges on the flexible, ink repellent conductive jacket covering cannot occur, since such charges are conducted immediately through the conductive cylinder base covering into the transfer cylinder and into the grounded frame of the printing press.

[0016]In accordance with another aspect of the present invention, movement of the ink repellent, conductive flexible jacket covering relative to the transfer cylinder is improved by a cylinder base covering of a conductive material, such as a metal foil or sheet, that is coated with a low frictional coefficient, semiconductive material. The cylinder base covering material has a frictional coefficient that is less than the frictional coefficient of the bare cylinder support surface. The frictional coefficient is further reduced by radially projecting surface portions, or by openings or holes formed in the cylinder base covering, that reduce the surface area of frictional engagement. In one embodiment, the surface of the cylinder base covering material is structurally differentiated and is characterized by radially projecting portions that reduce the amount of surface area for contact with the ink repellent, conductive flexible jacket 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 another embodiment. The structurally differentiated cylinder base covering embodiments are useful for further reducing the frictional drag that occurs as a result of movement of the flexible jacket covering relative to the cylinder base covering.

[0017]According to yet another aspect of the present invention, an ink repellent, conductive and flexible jacket covering for the transfer cylinder comprises a woven fabric material having at least one conductive strand that makes the flexible jacket covering conductive, and the at least one conductive strand also defines a stripe for alignment purposes. The ink repellent, conductive jacket covering is supported on the low friction, conductive cylinder base covering to gently cushion any slight relative movement between the freshly printed substrate and the transfer cylinder surface without marking the freshly printed surface or damaging the substrate material itself.

[0021]According to a related aspect of the present invention, the flexible jacket covering material is cotton cheesecloth that has been pre-stretched, pressed flat and pre-cut to predetermined length and width dimensions, and is marked with one or more alignment stripes and one or more center alignment marks for simple and easy installation of the flexible jacket covering onto the transfer cylinder, without requiring measuring or trimming of the flexible jacket covering as it is being precisely aligned and attached onto the transfer cylinder. In this pre-cut embodiment, the transfer cylinder and / or the base cylinder covering is also marked with center alignment marks for facilitating proper attachment of the flexible jacket covering to the transfer cylinder in an operative position with the flexible jacket covering being precisely aligned and having the proper amount of relative movement or end play of the flexible jacket covering relative to the transfer cylinder support surface.

Problems solved by technology

Moreover, it has also been determined that the PTFE coated cylinders do not provide a critically needed cushioning effect and relative movement.

The original SUPER BLUE® transfer cylinder and fabric covering system has achieved world-wide commercial success; however, with continuous use such as is common in printing presses, there is over a period of use an accumulation of ink on the fabric covering, which is now believed to be caused in major part by static electricity.

After extended use without such re-adjustment, the cotton cheesecloth fabric covering becomes so loose that it will be caught on press parts and torn off of the cylinder.

However, the close cylinder clearance has not improved registration and has actually made the marking problem worse.

Lengthy investigation and testing have revealed the build-up of electrostatic charges on the fabric covering as the handicapping factor that has prevented completely free movement of the fabric covering.

Additionally, the build-up of electrostatic charges on the fabric covering makes it cling to the cylinder base covering, thereby preventing completely free movement of the fabric covering.

However, in some press installations the side and tail edges of the original SUPER BLUE® fabric covering have become encrusted with dried ink, particularly where small size sheets have been printed.

The dried ink accumulation on the side edges and tail of the fabric covering and cause the fabric covering to be unusable for transferring freshly printed larger size sheets without marking or smearing, therefore requiring replacement of the original fabric covering.

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