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Description  |
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REFERENCE TO RELATED PUBLICATION
Wolfgang Walenski: "Einfuhrung in den Offsetdruck" ("Introduction to Offset
Printing"), pages 143,148 and 155.
The present invention relates to printing machinery, and more particularly
to a printing system for a sheet printing machine of the rotary offset
printing type, having a plate cylinder, with which an inker and damper are
associated, at least one blanket cylinder and an impression cylinder, and
so arranged that prime and verso printing can be carried out, in which the
verso print is applied over the impression cylinder.
BACKGROUND
The referenced literature Wolfgang Walenski: "Einfuhrung in den
Offsetdruck"("Introduction to Offset Printing") describes a printing
machine for offset printing in which a sheet is passed between two blanket
cylinders, each one of which has a plate cylinder associated therewith,
and each plate cylinder has its own inker and damper. Prime-and-verso
printing is carried out by this machine at the same time. This type of
machine requires a separate printing arrangement for prime printing and
for verso printing. Some printing machines only include a system for prime
printing, and expansion of such a system to permit double-sided printing
is not possible since machines designed for prime printing only do not
provide space for an additional plate cylinder. Constructing printing
machines to be universally applicable for prime and verso printing is
frequently uneconomical if, usually, only prime printing is to be
effected, and double-sided printing only occasionally. The substantially
higher price of a machine having two separate printing systems, one for
each side of the sheet, mitigates against such an arrangement unless it is
to be used continuously.
Attempts have been made to design machines which are primarily arranged for
one mode of printing, but which are more versatile in that change-over to
different modes of printing is also possible. The machine described in
U.S. Ser. No. 353,235, now U.S. Pat. No. 4,414,896, Nov. 15, 1983, by the
inventor hereof, describes a sheet rotary offset printing machine which,
selectively, can be used for prime printing or prime-and-verso printing.
The machine is so constructed that change-over from prime printing to
double-sided printing causes the output per unit time to be half of that
of prime printing only. The number of colors which are available for prime
printing is decreased by the number of colors which are used for verso
printing. Thus, if the machine is used for two-color prime printing,
change-over for double-sided printing enables printing on the prime and
verso sides only with one color.
A different type of machine is described in German Patent DE-PS No. 21 39
830, based on an invention by the inventor hereof, which describes a
multiple printing machine system in which substrate sheets are supplied
from a make-ready table to a first printing station having a plate
cylinder, a rubber blanket cylinder and an impression cylinder, as is
customary in the field. To permit multi-color printing, a group of such
printing stations is arranged serially between the make-ready table and a
removal apparatus with itermediate transfer drums providing for transport
of sheets between the respective printing stations. One or more of such
transfer drums may be provided and, additionally, the sheets transported
to the respective printing stations, or removed therefrom, are supplied
by, respectively, supply drums or removal drums. Each one of the printing
stations has its own respective plate and blanket cylinder, with the
associted inkers and dampers, and an impression cylinder. The sheet is
transferred or passed from a supply drum, transfer drums, and removed from
a removal drum after having been printed between the blanket cylinders and
the respective impression cylinders of the respective printing stations.
In accordance with the disclosure of this patent, it is additionally
possible to apply verso printing by so arranging one or more of the
transport drums, that is, the supply drum, the transfer drums and the
removal drum, that it can carry a printing plate, and to associate an
inker with the printing plate.
Double prime-and-verso printing using the direct lithographic printing mode
in which the plate cylinder engaging, for example, the prime side of the
printing substrate sheet forms the impression cylinder for the plate
cylinder applied to the verso side of the sheet--and vice versa--has been
described in British Pat. No. 1,328,257, Dahlgren, to which U.S. patent
application Ser. No. 862,789, filed Oct. 1, 1969, corresponds. In order to
permit double-sided printing, the printing plate applied to the plate
cylinder has a hard, durable surface into which ink-receptive image areas
are etched to form recesses. These recesses are etched into a dampening
fluid receptive surface. Ink is suplied to the recessed image areas of the
printing plate, and dampening fluid is supplied to the remaining surface
area of the printing plate, such that the surface rejects ink. The
printing image is deep-etched into a metal printing plate, for example a
trimetal plate.
German Patent Publication Document DE-OS No. 21 34 397, Brodin et al,
describes a printing machine which is primarily designed for two-color
prime and single-color verso printing, in which a substrate sheet is
passed between two rubber blanket cylinders, each having their own inkers
and dampers associated with respective plate cylinders, to effect,
simultaneously, prime and verso printing from the plate cylinders
associated with the two rubber blanket cylinders. A further prime printing
image can be transferred by an additional rubber blanket cylinder in
engagement--with the substrate sheet between--with one of the rubber
blanket cylinders. The additional rubber blanket cylinder has its own
plate cylinder, and damper and inker associated therewith. The disclosure
includes the comment that, upon use of another method customary in offset
printing, the so-called lithographic printing, three impressions can be
applied to one side, and no impressions to the other. In this type of
operation, the path of the paper web will have to be changed to wrap
around one of the rubber blanket cylinders--for example the one previously
applying the verso printing, and utilizing the previously used rubber
blanket cylinder as an impression cylinder for the plate, which previously
was associated with the rubber blanket cylinder now functioning as the
impression cylinder.
Various types of printing machines--see, for example, the above-referenced
literature--utilize sheet turning drums between successively located
printing stations. In such apparatus, a sheet which is passed between two
serially arranged printing stations is turned over, so that the second
printing station, rather than printing on the same side--for example the
prime side--of a sheet, will then print on the reverse, that is, the verso
side. Such sheet turning apparatus, in some machines, can be added
subsequently as attachments. They have some disadvantages since set-up of
the machine for dual-sided printing is much more time-consuming than
set-up for single-sided printing only. Further, in order to prevent
increased production of scrap, attachments which control the path of the
sheet, and utilizing compressed air or suction zones, must be installed.
The sheets tend to smear at the turn-over region. The coverage of printed
material on the substrate sheet is decreased since a margin must be left
not only on the top side, for example, but a similar margin on the bottom
in order to permit gripping at the two ends of the sheets by grippers of
the turn-over apparatus. Thus, the overall format and coverage of the
sheet is not utilized as efficiently as coverage in single-sided printing.
THE INVENTION
It is an object to provide a printing machine which is versatile in that it
permits, selectively, prime-only printing, or, if necessary, prime and
verso printing, without decrease in output per unit time, which is simple
and which can be constructed by using standard and previously used
printing system arrangements, if necessary, prime-and-verso printing.
Briefly, a standard offset printing system is provided for prime printing
in which a printing station has a plate cylinder, an inker and damper
associated therewith, and a rubber blanket cylinder, positioned in image
transfer relationship to the plate cylinder. Printing is effected between
the rubber cylinder and an impression or counter cylinder, located for
passage of a sheet to be printed between the plate cylinder and the
impression or counter cylinder.
In accordance with the present invention, the impression or counter
cylinder itself forms a support cylinder on which, selectively, various
covers including a planographic plate which applies the printing image can
be applied. The support cylinder thus can function as an impression or
counter cylinder. It includes attachment means to attach thereto,
selectively, a flexible planographic printing plate or another surface
cover. An inker is provided, positioned in operative relationship to the
flexible planographic printing plate.
If the planographic printing plate is a direct lithographic plate, a damper
is additionally provided for engagement with the planographic printing
plate.
In accordance with a feature of the invention, the diameter of the support
cylinder is slightly smaller than the diameter of an associated
dimensioning or bearer ring; the difference in diameter should be at least
twice the thickness of the planographic plate to be applied to the
impression cylinder. The attachment elements for the plate on the support
cylinder are so arranged that, selectively, a cover from a set of covers
including a wet or dry planographic printing plate, an elastic or a stiff
cover can be applied, thereby permitting, selectively, prime-only or
prime-and-verso printing.
DRAWINGS
FIG. 1 is a schematic side view of the printing system of the present
invention;
FIG. 2 is a part-pictorial, part-sectional view through the support
cylinder; and
FIG. 3 is a schematic side view of the support cylinder and the associated
dimensioning or bearer ring.
DETAILED DESCRIPTION
Referring first to FIG. 1, showing the printing system in schematic
representation: Two plate cylinders 1, 2 each have an inker 3, 4, and a
damper 5, 6 associated therewith. The plate cylinders transfer the
respective images to rubber blanket cylinders 7, 8. A support cylinder
which may function, on one mode of operation, as an impression cylinder is
provided, which--see FIG. 2--includes sheet grippers 10.
In accordance with a feature of the invention, the diameter of the cylinder
9 is smaller by the dimension 2a than the diameter of an associated
dimensioning ring or bearer ring 11. The dimension a corresponds at least
to the thickness of a planographic plate 12 (FIG. 2) which can be
stretched over the circumference of the cylinder 9.
Two clamping strips 13, 14, 15, 16, attached to the respective ends of the
planographic plate 12 (see FIG. 2), are attached to the plate by screws
17, 18. The pair of strips 13, 14 can be inserted and retained within a
groove 20 in the cylindrical circumference 21 of the cylinder 9.
Preferably, strip 13 is formed with a projecting ridge 19 which engages
the groove 20. Similarly, the pair of strips 15, 16 is arranged so that
one of the strips, for example strip 16 is formed with a projecting ridge
22 which can hook into a groove of a tensioning shaft 24, which is
rotatably retained between the side walls of the cylinder 9. Upon rotation
of the shaft 24 in the direction of the arrow b, and then clamping the
shaft 24 in the rotating position by any suitable means, for example
compression nuts, the plate 12 can be securely stretched over the
circumference of the cylinder 9. The system is so arranged that the plate
12, upon loosening of the shaft 24, can be readily removed and exchanged
for different plates to which similar end strips 13-16 have been attached.
The grippers 10 are essentially conventional. In order to permit easy
insertion of the end strips 13, 14, grippers 10 together with a gripper
engagement or counter strip 26, and the respective operating shaft 25
therefor, are all retained between two end plate elements 27; only one
such axially positioned plate element 27 is visible in FIG. 2. The plate
elements 27 are rotatably secured on or in the end face walls of the
cylinder 9. The pivoting shaft 28 can be rotated, for example by a worm
drive (not shown) in the direction of the arrow c, so that the entire
gripper assembly is rocked out of position and permits easy insertion of
the strips 13, 14 and the associated end portion of the element 12 in the
groove of the cylinder, and engagement of the ridge 19 in the groove
portion 20.
In accordance with a feature of the invention, the planographic printing
plate 12 has an inker 29 associated therewith, which can be selectively
engaged with the printing plate on the cylinder 9. Further, a damper 30
can be engaged with the cylinder 9.
A transport chain system 31, having grippers 31a, is provided to remove
sheets fed from a sheet feeding apparatus 11--which can be of conventional
type--to a subsequent printing system, or to a stacking arrangement. The
subsequent printing system could be constructed similar to that described
in connection with FIG. 1.
Operation: In the arrangement shown in FIG. 1, blanket cylinders 7, 8 can
apply prime printing on one side of a sheet fed from the sheet feeder 11
with respectively two different colors. The additional possibility
presents itself, however, to apply additional printed subject matter on
the verso side by stretching a planographic directly lithographic printing
plate 12 on the cylinder 9. Since the sheet then will be printed between a
planographic printing plate of hard surface, and the blanket cylinders 7,
8 will have an elastic surface, clean printing will be obtained regardless
of the quality or the thickness of paper which is fed from the paper
feeder 11.
The planographic printing plate applied to the cylinder 9 may be one
designed to dry offset printing; for this printing mode, the damper 30 may
not be needed, or selectively, can be left out of operation.
The printing system is highly versatile, and the additional components and
elements necessary over and beyond the system permitting only prime
printing are minor; it is only necessary to provide an additional inker
and, if necessary, a damper, and means to clamp the cover--as desired--on
the cylinder 9. Thus, the printing system is particularly suitable for
print shops which have to carry out prime-and-verso printing only
occasionally, but which desire the capability to do so. If the printing
system is used only for prime printing, that is, if the inker 29 and the
damper 30 are placed out of operation or out of operative engagement from
the impression cylinder 9, then a further advantage of the system will be
apparent: The cylinder 9, now functioning as an impression cylinder, may
have different types of surfaces applied thereto, for example an elastic
cover which, in one form, may be a rubber blanket; or a stiff or rigid, or
essentially unyielding cover, such as a metal plate. The cylinder 9, thus,
can be selectively equipped in accordance with the printing results
desired by the customer of the printer, so that the printer can then
select a cylinder surface for optimum results, with easy and ready
interchange of the surface structure.
The grippers 10 of the cylinder 9 transfer the sheets to the grippers 31a
of the transport chain system 31 which can be conventional and of any well
known and suitable construction. No turning of the sheet is necessary, and
smearing of the freshly printed subject matter is thus effectively
prevented. The transport chain system transports the sheets either to a
stacking or receiving apparatus, or may transport the sheets to a further
printing system which, for example, may be identical to the one described.
Various changes and modifications may be made within the scope of the
inventive concept.
The usual and customary drive arrangements for the respective rubber
cylinders, plate cylinders, cylinder 9 and the chain removal system have
been omitted from the drawings for clarity, and can be of any appropriate
construction.
The invention has been described in connection with a sheet-fed printing
machine; it is equally applicable to web-fed machines, in which case the
sheet supply system will be replaced by a web guidance system, and the
removal gripper chain by suitable web guide rollers for subsequent
transport to folding, cutting, and other utilization apparatus.
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