Printing – Rolling contact machines – Rotary
Reexamination Certificate
1999-08-10
2001-06-26
Hilten, John S. (Department: 2854)
Printing
Rolling contact machines
Rotary
C101S484000, C101S488000, C101SDIG029
Reexamination Certificate
active
06250220
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a system and method for preventing wrinkling of a web in a web-offset press. More particularly, the invention relates to a system and method for preventing wrinkling, tearing, and web-breaks of a web as the web contacts a first chill roller after passage through a dryer, to thereby minimize press down-time.
BACKGROUND OF THE INVENTION
In a web-fed printing system such as a web-offset press, a series of repeating images are printed on a web of material, typically paper. In the typical process, the web is fed to sequential printing units, wherein each printing unit prints a different color ink on the web to produce a multi-color image. The web is subsequently fed to a thermal dryer which dries the ink and is then routed to a series of chill rollers which operate to cool the web and set the ink. The web is next slit in the longitudinal direction (the direction of web movement) by a slitting mechanism to produce a plurality of continuous ribbons. The ribbons are directed to a folder wherein the ribbons are aligned one on top of the other, folded longitudinally, and then cut laterally to produce a plurality of multi-page, approximately page-length segments, each of which is termed a “signature”. The signatures are subsequently bound together to produce magazines, catalogs, or other printed products.
As the art of web-offset high-volume printing has progressed, publishers have migrated to the usage of lighter basis-weight paper for the printing of magazines, catalogs, and coupons. Lightweight paper has a lower cost per impression, as well as lower postal mailing costs.
SUMMARY OF THE INVENTION
Such lightweight paper has been found to yield an acceptable level of quality in terms of print density and opacity, and is gaining popularity. As schematically illustrated in
FIG. 2
, however, a serious problem in the usage of this paper is the formation of wrinkles or creases
44
or the like as the web emerges from the dryer and wraps around the first chill roller
33
during start-up of the press. Because the web
14
is unsupported in the long span of the dryer, it tends to form corrugations
48
. These corrugations
48
decrease the effective width of the web.
During start-up, when the web
14
moves to contact the first chill roller
33
, these corrugations
48
must flatten out. Because the width of the web as laid down on the chill roller is slightly less than the true width of the web, the excess paper manifests as creases
44
substantially parallel to the long axis
46
of the web
14
. A crease is raised in a direction away from the center of the chill roller
33
. As the paper wraps around the circumference of the chill roller
33
, the raised portion of the paper is now describing a semicircle whose radius is larger than the paper which is lying flat on the surface of the chill roller
33
. The creased paper is consequently stretched, and lighter weight paper is often sufficiently weak such that it will rip. The crease
44
can create a series of small rips
50
in the paper, every few inches along the crease.
The numerous small rips
50
in the paper can be the initial point of a web-break, especially if the rip happens to occur in the region of the web which will be longitudinally slit to form ribbons of lesser width. A rip encountering the slitting mechanism can result in a failure of the slitting mechanism with resultant web-break, or a ribbon with a torn edge can be greatly weakened, resulting in a higher probability of breakage under tension as the rip passes through the folder.
During normal running of the press, creases in the web present a much lesser problem. When the press is running at full speed, the web travels from the dryer to the first chill roller so quickly that the web is still hot. The web is cooled and resultant thermal shrinkage occurs quickly on the first chill roller. The shrinkage to a large extent eliminates the creases before ripping occurs.
Spreader rollers are commonly used on printing press in-feeds to remove wrinkles from the web before the web is fed to the printing units. Spreader rollers are well known in the art; see, for example, U.S. Pat. Nos. 4,566,162, 5,607,039, and 5,729,878. The design of a spreader roller can be as simple as a handmade application of adhesive tape, wound in two separate helical patterns on an existing roller. The helical patterns operate to carry wrinkles toward the edges of the web.
Another problem, particularly severe in the case of lightweight paper, is poor lateral stability of the paper under conditions of low web tension. During normal operation of the press, if the web should break, the web is subsequently re-threaded through the press, with a handmade splice at the point of breakage. Such splices have poor strength and would pull apart if subjected to a tension typically used for the paper. Thus, a lower tension is used until the splice has passed through the press. The combination of lightweight paper and lower tension causes poor lateral stability of the web. During slow speed operation of the press, the web may slowly creep off-center to either side of the chill rollers, falling partially off the edge of the roller. The wrinkled paper will generally break, causing additional downtime re-webbing the press. During start-up, a pressman may manually hold the paper and pull it to remove creases and prevent crawling toward either side, but this action requires valuable manpower, and requires skill to avoid accidentally ripping the paper.
There is a need to prevent the formation of creases on the web and prevent lateral instability of the web during the period of press start-up when the web is moving too slowly for the paper to remain hot enough at the point that the web first contacts the first chill roller.
An object of the present invention is to provide a mechanism for the restoration of web width prior to the first chill roller during start-up, to prevent wrinkling and tearing of the web with resultant web-breaks and press downtime.
A further object of the invention is to retract the web-width restoration mechanism during normal running of the press, to avoid marring the hot ink on the web.
A yet further object of the invention is to pull the web in a manner that prevents the paper from traveling off-center of the rollers far enough to reach the edges of the chill rollers and the various other rollers in the web path after the dryer.
Other features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description, claims, and drawings.
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Lasecki Alan D.
Peglow Craig J.
Sainio Jeffrey W.
Hilten John S.
Michael & Best & Friedrich LLP
Quad Graphics, Inc.
Williams Kevin D.
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