Printing – Printing members – Blanks and processes
Reexamination Certificate
1999-02-22
2001-06-12
Yan, Ren (Department: 2854)
Printing
Printing members
Blanks and processes
C101S415100, C101S493000
Reexamination Certificate
active
06244178
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns method and apparatus for reducing marking and smearing of freshly printed substrate material in a printing press.
BACKGROUND OF THE INVENTION
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 wheels, guide rollers and the like. The ink marking problems inherent in transferring freshly printed substrates have been longstanding. In order to minimize the contact area between the transfer means and the freshly printed substrate, 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 disc transfer means have not overcome the problems of smearing and marking the freshly printed substrate due to moving contact between the freshly printed substrate and the projections or serrations. Moreover, the attempts to minimize the surface support area in contact with the freshly printed substrate material has also resulted in actual indenting or dimpling of the substrate itself.
DESCRIPTION OF THE PRIOR ART
Various efforts have been made to overcome the limitations of thin disk skeleton wheels. One of the most important improvements has been completely contrary to the concept of minimizing the surface area of contact. That improvement is disclosed and claimed in my U.S. Pat. No. 3,791,644 to Howard W. DeMoore wherein the support surface of a transfer cylinder in the form of a wide wheel or cylinder is coated with an improved ink repellent surface formed by a layer of polytetrafluoroethylene (PTFE).
During the use of the PTFE coated transfer cylinders in high speed commercial printing presses, the surface of the coated cylinders must be washed too frequently with a solvent to remove any ink accumulation. Moreover, it has also been determined that the PTFE coated cylinders do not provide a critically needed cushioning effect and relative movement.
The limitations on the use of the PTFE coated transfer cylinders have been overcome with an improved transfer cylinder having an ink repellent, cushioning and supportive fabric covering or the like for transferring the freshly printed sheet. 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 with the supporting surface of a conventional press transfer cylinder is substantially eliminated by using the anti-marking fabric covering system as disclosed and claimed in my U.S. Pat. No. 4,402,267 entitled “Method and Apparatus for Handling Printed Substrate Material”, the disclosure of which is incorporated herein by reference.
That system, which is marketed under license by Printing Research, Inc. of Dallas, Tex., U.S.A. under the registered trademark SUPER BLUE®, includes the use of a low friction coating on the supporting surface of the transfer cylinder, and over which is loosely attached a movable fabric covering. The original fabric covering provided a yieldable, cushioning support for the freshly printed side of the substrate such that relative movement between the freshly printed substrate and the transfer cylinder surface would take place between the original fabric covering and the support surface of the transfer cylinder so that marking and smearing of the freshly printed surface was substantially reduced.
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. The original SUPER BLUE® fabric covering is constructed of a stretchable cotton cheesecloth material that has ridges, furrows, rows and wrinkles. Alter extended use, the original stretchable cotton cheesecloth covering requires re-adjustment and tightening to provide the proper amount of relative movement of the fabric covering relative to the transfer cylinder surface. 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.
Modern printing presses have been constructed with closer clearance between the impression cylinder and the transfer cylinder in the expectation that sheet registration will improve. However, the close cylinder clearance has not improved registration and has actually made the marking problem worse. Consequently, there has been continuing development in the design of the fabric covering to eliminate the problems caused by static electricity, stretchability of the fabric covering and close cylinder clearances.
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. The electrostatic charge build-up also appears to accelerate the accumulation of ink deposits so that the fabric covering becomes ink encrusted faster. The build-up of the static electric charge on the fabric covering is caused by “frictional electricity”, which is the transfer of electrons from one material to another when they are pressed or rubbed together. This occurs in a printing press as the moving substrate contacts the stationary parts of the press.
According to one theory, the transfer of electrostatic charges between two contacting dielectrics, such as a fabric covering and paper, plastic or other printed material, 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 a fabric covering of the woven type typically used in the original SUPER BLUE® cylinder covering system has a higher dielectric constant as compared to the dielectric constant of a sheet of paper, for example, the electrostatic charge picked up by the freshly printed sheet from frictional contact with press parts as the sheet material travels through the press is conducted onto the fabric covering as the sheet is transferred over the transfer cylinder.
Transfer cylinders whose transfer surfaces are covered by a synthetic or natural organic resin, for example as disclosed in my U.S. Pat. No. 4,402,267, have a low-friction surface and also have insulating, dielectric properties which make them an accumulator of electrostatic charges carried by the freshly printed sheet material. That is, the electrical charges that are conducted from the freshly printed sheets to the fabric covering are also conducted to the underlying low friction, cylinder base covering. As a result of such electrostatic charge transfer and accumulation on both the fabric covering and the cylinder base covering, the fabric covering clings to the underlying cylinder base covering and cannot move freely because of the force of electrostatic attraction between the fabric covering and the cylinder base covering.
The resultant build-up of electrostatic charges on the fabric covering also appears to make the fabric covering more attracted to the freshly printed image area, with the result that the ink accumulation and encrusting action is accelerated. Consequently, the original SUPER BLUE® fabric covering must be replaced more frequently. 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.
I
Branson John Andrew
DeMoore Howard W.
DeMoore Howard W.
Locke Liddell & Sapp LLP
Yan Ren
LandOfFree
Anti-static, anti-smearing pre-stretched and pressed flat,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Anti-static, anti-smearing pre-stretched and pressed flat,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Anti-static, anti-smearing pre-stretched and pressed flat,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2467148