Printing – Antismut device – Contact preventers
Reexamination Certificate
1995-05-26
2001-08-07
Yan, Ren (Department: 2854)
Printing
Antismut device
Contact preventers
C101S183000, C101S231000
Reexamination Certificate
active
06269743
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to printing press equipment, and in particular to anti-marking sheet transfer apparatus for conveying printed sheets between successive stations in a sheet-fed rotary printing press.
BACKGROUND OF THE INVENTION
It has been traditional in the art of sheet-fed printing press machines to provide devices for supporting freshly inked sheet material when transferring the sheet material from one printing station to another or when handling the sheets as they are transferred from the final printing station to a delivery station where the sheets are released and stacked. Typically, a transfer system denotes an apparatus disposed between the several printing stations in the press and which functions to receive a freshly printed sheet from one impression cylinder and move the sheet to the next printing station for additional printing by a further impression cylinder. A delivery system typically denotes an apparatus which receives the freshly printed sheet from the last impression cylinder of the press, and delivers the sheet to the press delivery station, typically a sheet stacker. As used hereinafter, the term transfer is intended to include both apparatus used to transfer a sheet between printing stations of the press and an apparatus used for delivering the sheets to the press delivery stacking station.
In sheet-fed rotary printing presses, it is customary to transfer the sheets from the impression cylinder of one printing station to the impression cylinder of the next by means of one or more successively coacting transfer cylinders, each of which is provided with grippers for engaging the leading edge of the sheet. These cylinders usually are formed with substantially continuous peripheral surfaces for supporting and controlling the body of the sheet during its travel between stations. This transfer apparatus has proven to be effective for transferring sheets in precise registration, but has a tendency to cause the sheets to be marked or smeared.
Marking and smearing of the freshly printed ink occurs as follows. As each sheet is removed from the impression cylinder, and after having received an inked impression, it is immediately conveyed in a reverse curvilinear path with its printed face in contact with the surface of the transfer cylinder. Movement of the sheet is so rapid that the ink on the sheet does not have time to set before it contacts the transfer cylinder surface; consequently, a portion of the ink accumulates on the transfer cylinder surface. As the next sheet and all subsequent sheets are transferred, they may become marked or smeared by the ink accumulation on the cylinder surface.
Marking or smearing of the printed side of the sheet is sometimes caused by fluttering displacement of the sheet as it transfers through the reverse curvilinear path from the impression cylinder to the next transfer cylinder. Slight lateral fluttering in the nip region between the impression cylinder surface and the transfer cylinder surface occurs because of the sudden reversal in the direction of forces acting on the mass of the sheet as it is pulled through the nip region along the reverse curvilinear path. Moreover, the trailing and portion of the wet, printed side of the sheet may be slapped against the transfer cylinder as it is pulled through the nip region. Both the fluttering movement and the tail slap can cause marking or smearing as the freshly imprinted side of the sheet is contacted against the transfer cylinder.
DESCRIPTION OF THE PRIOR ART
Various make-ready methods and devices have been proposed for reducing or eliminating smudges and smears. One such method, for example, involves the use of Emory cloth or the like abrasive material on the surface of the transfer drum to reduce the area of contact with the wet, printed side of the sheet. Other such devices which engage the wet side of the sheet include sawtooth or serrated bands, star wheels, sheets with pointed staples or tacks, whereby the printed side of the sheets are supported at spaced intervals by the respective projecting points.
One of the more common of such devices are wheels of relatively narrow width which have circumferentially spaced teeth. Such devices are known in the trade as “skeleton wheels”. The problems inherent in handling freshly inked printed sheets and the like by skeleton wheels have been longstanding. Typically, a set of grippers pulls a printed sheet from an adjacent printing station across a rotating set of as many as seven or more skeleton wheels for subsequent stacking and delivery. The sheet is subjected to high tension and stresses as it is pulled by the grippers, and the skeleton wheels support the sheet to prevent it from buckling or warping. The freshly printed, undried sheets present their wet, inked surface to the skeleton wheels, and this contact between the inked surface and wheels has been a continuing source of marking problems.
Marking occurs as ink is deposited from each sheet onto the skeleton wheels and is subsequently transferred from the skeleton wheels to succeeding sheets. In addition, if the peripheral sheet contacting surface of the skeleton wheels is traveling at a different speed relative to the sheet, then it is likely that the inked sheet will be smeared. The problem is particularly acute in conventional high speed presses which have high output, for example, from 4,000 to 18,000 sheets per hour. In any event, marked sheets must be rejected and the job run again, resulting in additional expense and delay.
There have been a variety of expedients developed in attempts to overcome the skeleton wheel marking problem, the attempts typically being directed toward minimizing the amount of surface area contact between the inked areas of each sheet and the skeleton wheels. In general, however, it is evident that a reduction in contact area between the skeleton wheels and the printed surface correspondingly reduces the amount of support provided for each sheet by the skeleton wheels. As a result, these prior attempts have not been satisfactory.
In one such prior art arrangement, the skeleton wheels are in the form of thin discs having a fluted or serrated circumference presenting a series of very narrow, curved projections for engaging and supporting the printed side of the sheet. However, these projections still mark and smear the printed surface as previously described. Moreover, the force of the narrow projections against the sheet often produces a corresponding series of concave depressions along the sheet. The depressions alone mar the printing job, and also further cause “fan out” of the sheet and prevent accurate registration. In a “fan out” condition, the depressions cause slight changes in the dimensions of the sheet. If the sheet is to be run through a press a second time, as is often the case in multicolor jobs, it must be in precise registration or else the second printing will be blurred. “Fan out” from the skeleton wheel depressions causes misregistration.
Various efforts have been made to overcome the limitations of thin disc skeleton wheels. One of the more successful approaches has been completely contrary to the concept of minimizing the surface area contact. This more successful approach is disclosed and claimed by Howard W. DeMoore in U.S. Pat. No. 3,791,644 entitled “Sheet Handling Apparatus” wherein a substantially cylindrical drum or cylinder is coated with an improved ink repellent surface comprising a layer of polytetrafluoroethylene. Although this improved transfer cylinder has been commercially successful, under continuous use conditions such as is common in many commercial printing operations, there is over a period of time a slight accumulation of ink on the surface of the transfer cylinder which must be removed.
In high speed commercial printing equipment, for example, it has been determined that in order to provide satisfactory printing quality, the surface of the coated transfer cylinder must be washed occasionally with a solvent to remove ink accumulation. Moreover, it has also been determin
DeMoore Howard W.
Secor Howard C.
Locke Liddell & Sapp LLP
Yan Ren
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