U.S. patent application number 09/083004 was filed with the patent office on 2001-08-09 for apparatus and method for printing.
Invention is credited to KOREM, AHARON.
Application Number | 20010011507 09/083004 |
Document ID | / |
Family ID | 11068223 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010011507 |
Kind Code |
A1 |
KOREM, AHARON |
August 9, 2001 |
APPARATUS AND METHOD FOR PRINTING
Abstract
A printing method and system which includes at least one
printing apparatus is provided. Each printing apparatus includes a
printing member for selectively receiving ink into an ink receptive
portion, the ink receptive portion includes a plurality of ink
receptive dots forming a pattern in a desired resolution and an ink
repelling portion, the ink repelling portion includes the entire
area of the printing member except the ink receptive dots. Each
printing apparatus includes at least one printing unit, preferably
but not necessarily an ink-jet printing unit, the printing unit for
applying ink onto the printing member in accordance with a pattern
representing an image to be printed, thereby forming an ink image
on a portion of the ink receptive dots, and a transfer system for
transferring the ink image onto a printing substrate.
Inventors: |
KOREM, AHARON; (HERZLIA,
IL) |
Correspondence
Address: |
EITAN, PEARL, LATZER & COHEN-ZEDEK
ONE CRYSTAL PARK, SSUITE 210
2011 CRYSTAL DRIVE
ARLINGTON
VA
22202-3709
US
|
Family ID: |
11068223 |
Appl. No.: |
09/083004 |
Filed: |
May 21, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09083004 |
May 21, 1998 |
|
|
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PCT/IL96/00150 |
Nov 13, 1996 |
|
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Current U.S.
Class: |
101/217 |
Current CPC
Class: |
B41F 7/02 20130101; B41J
3/546 20130101; B41C 1/1075 20130101; B41J 29/17 20130101; B41J
3/543 20130101; B41P 2227/70 20130101 |
Class at
Publication: |
101/217 |
International
Class: |
B41L 023/00; B41L
025/00; B41F 007/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 23, 1995 |
IL |
116123 |
Claims
1. A printing system comprising: at least one printing apparatus,
said printing apparatus comprising: a printing member for
selectively receiving ink comprising an ink receptive portion, said
ink receptive portion comprising a plurality of ink receptive dots
forming a pattern in a desired resolution and an ink repelling
portion, said ink repelling portion comprising the entire area of
said printing member except said ink receptive dots; at least one
printing unit for applying ink onto said printing member in
accordance with a pattern representing an image to be printed,
thereby forming an ink image on a portion of said ink receptive
dots; and a transfer system for transferring said ink image onto a
printing substrate.
2. The printing system of claim 1 wherein said pattern is either
randomly generated or comprises a plurality of grid points.
3. The printing system of claim 1 wherein said printing unit is an
ink-jet printing unit.
4. The printing system of either of claims 1 or 3 and also
comprising a cleaning system, said cleaning system for cleaning
said printing member after the operation of said transfer
system.
5. The printing system of claim 4 and further comprising at least
one heating system, said heating system for heating said printing
member.
6. The printing system of claim 1 wherein said ink is a UV curable
ink and wherein said printing system further comprises a UV curing
system downstream said at least one transfer system, said UV curing
system for curing said UV curable ink transferred to said printing
substrate.
7. The printing system of claim 1 wherein said printing apparatus
comprises a plate cylinder, said plate cylinder for mounting said
printing member thereon and wherein said transfer system comprises:
a blanket cylinder for transferring said applied ink to a printing
substrate; and an impression cylinder for impressing said printing
substrate against said blanket cylinder.
8. The printing system of claim 1 wherein said printing member is a
gravure like cylinder having depressions forming said ink receptive
dots and elevated portions forming said ink repelling portion and
wherein said transfer system comprises an impression cylinder for
impressing said printing substrate against said gravure like
cylinder.
9. The printing system of claim 1 wherein said printing member is a
cylinder having elevated portions forming said ink receptive
portion and depressions forming said ink repelling portion.
10. The printing system of claim 9 wherein said transfer system
comprises a blanket cylinder for transferring said applied ink to a
printing substrate and an impression cylinder for impressing said
printing substrate against said blanket cylinder.
11. The printing system of claim 9 wherein said transfer system
comprises an impression cylinder for impressing said printing
substrate against said gravure like cylinder.
12. The printing system of claim 1 wherein said printing member is
a rotatable belt having elevated portions forming said ink
receptive portion and depressions forming said ink repelling
portion.
13. The printing system of claim 12 wherein said transfer system
comprises a blanket cylinder for transferring said applied ink to a
printing substrate and an impression cylinder for impressing said
printing substrate against said blanket cylinder.
14. The printing system of claim 1 wherein said transfer system
comprises an impression cylinder for impressing said printing
substrate against said rotatable belt.
15. The printing system of claim 14 wherein said at least one
ink-jet unit comprises a line array of ink jet nozzlesoperating to
apply said ink onto said printing member substantially
simultaneously.
16. The printing system of claim 15 comprising a plurality of said
line array connected therebetween by a support said support capable
of shaping it self in accordance to the shape of said printing
member so as to position each line array in a substantially equal
distance from said printing member.
17. The printing system of claim 15 wherein the resolution of said
ink receptive dots is higher than the resolution of said
nozzles.
18. The printing system of claim 1 wherein said ink is an aqueous
based ink and wherein said ink receptive dots are hydrophilic and
said ink repelling portion is hydrophobic.
19. The printing system of claim 1 wherein said ink is a
non-aqueous based ink and wherein said ink receptive dots are
oleophilic and said ink repelling portion is oleophobic.
20. The printing system of claim 1 wherein the number of printing
apparatus corresponds to the number of printing inks forming said
ink image.
21. The printing system of claim 20 wherein said printing system
comprises four printing apparatus, each for inking one of the four
process colors CMYK.
22. A printing method comprising: providing a printing member for
selectively receiving ink in ink receptive portion, said ink
receptive portion comprising a plurality of ink receptive dots
forming a pattern in a desired resolution and an ink repelling
portion, said ink repelling portion comprising the entire area of
said printing member except said ink receptive dots; applying ink
onto said printing member in accordance with a pattern representing
an image to be printed so as to form an ink image on a portion of
said ink receptive dots; and transferring said ink image onto a
printing substrate.
23. The printing method of claim 22 further comprising cleaning
said printing member after said transferring.
24. The printing method of claim 22 further comprising heating said
printing member.
25. The printing method of claim 22 wherein said ink is a UV
curable ink and wherein said printing method further comprising
curing said UV curable ink after said transferring.
26. The printing method of claim 22 wherein said forming comprising
forming said ink receptive dots in a higher resolution than the
resolution of said applying.
27. A printing member for selectively receiving ink comprising: an
ink receptive portion, said ink receptive portion comprising a
plurality of points forming a pattern of ink receptive dots in a
desired resolution; and An ink repelling portion, said ink
repelling portion comprising the entire area of said printing
member except said ink receptive dots, said printing member for
selectively receiving an ink image on a portion of said ink
receptive dot, said ink image corresponding to a digital
representation of an image.
28. The printing member of claim 27 wherein said printing member
comprises at least two layers, a first layer forming said ink
receptive dots and a second different layer forming said ink
repelling portion.
29. The printing member of claim 27 wherein said printing member
having depressions forming said ink receptive dots and elevated
portions forming said ink repelling portion.
30. The printing member of claim 27 wherein said printing member
having elevated portions forming said ink receptive dots and
depressions forming said ink repelling portion.
31. The printing member of claim 27 wherein said pattern is
randomly generated or comprises a plurality of grid points.
Description
RELATED APPLICATION
[0001] This application is a continuation in part application of
International Patent Application Ser. No. PCT/IL 96/00150 filed
Nov. 13, 1996.
FIELD OF THE INVENTION
[0002] The present invention relates generally to digital printing
systems and more particularly to an indirect digital printing
system in which an ink image is formed on a printing member for
subsequent transfer onto a printing substrate.
BACKGROUND OF THE INVENTION
[0003] Two general types of printing systems are known in the art
for printing digitally stored images, namely direct printing
systems and indirect printing systems.
[0004] In direct printing systems, one copy of the stored digital
image is printed per one output of the digital data, the digital
data being employed to control the flow of ink or other colorant,
so as to form the printed image on the printing substrate. An
example of a direct printing system is ink-jet printing
systems.
[0005] Ink-jet printing systems in which ink is applied directly to
the printed substrate have many deficiencies, inter alia, the
following:
[0006] (1) Dust carried by the printing substrate and, when the
substrate is paper, lint may also clog the orifices of the ink-jet
nozzles. To minimize clogging, the substrate is placed at a
relatively large distance from the nozzles, the large distance
resulting in larger inaccuracy of the applied ink and leads to
deficient quality of the printed image.
[0007] (2) For proper jetting, the ink must be of low viscosity,
but this may cause undesirable spreading or penetration of the ink
droplets on the medium and may also make the drying process lengthy
or complex.
[0008] In indirect printing systems, on the other hand, the digital
image is recorded on a printing plate, the printing plate includes
a pattern of ink-receptive areas representing the recorded image
within non-ink-receptive areas, and the printing process consists
of applying ink to the entire surface of the printing form, wherein
only the recorded image areas, i.e. the ink-receptive areas, retain
the applied ink, and transferring the retained ink by contact to
the printing substrate so as to form the printed image. The
indirect printing process, carried out in a printing press, is
classified according to the type of printing plate utilized, the
three primary classes being salient, also known as letterpress or
flexo; planographic, also known as lithographic or offset; and
intaglio, also known as gravure.
[0009] Salient and planographic printing plates are usually
configured as plates that are mounted around a cylinder in the
printing press, while intaglio is usually formed on the surface of
a solid cylinder.
[0010] The terms letter press, offset and gravure are used
hereinbelow to indicate the three types of printing plates in any
form, such as in the form of a plate or as a part of the printing
cylinder.
[0011] In conventional printing presses, the image is recorded on
the printing plate or cylinder off-press. In digital presses, in
particular in digital offset presses, such as the Quick Master
D146-4, commercially available from Heidelberg Drachmachinen of
Germany, the image is recorded on printing plate on-press, i.e.
while the printing plate is mounted on the printing press.
[0012] In another indirect printing system known in the art,
described in U.S. Pat. No. 4,855,768 to lino et al a printing
member is formed from ink receptive dots forming a grid and from an
ink repelling portion of ink repelling dots therebetween. Ink is
applied onto the entire printing member and retained by all the ink
receptive dots and then selectively transferred therefrom using
electrostatic force so as to form the printed image.
SUMMARY OF THE INVENTION
[0013] A primary object of the present invention is to provide an
indirect digital printing system and method for selectively
applying ink on a printing member in accordance with the digital
data representing the image to be printed so as to form an ink
image thereon, the ink image subsequently transferred to a printing
substrate, such as paper.
[0014] A further object of the present invention is to provide an
improved digital printing press which employs an ink-jet printing
unit for applying ink on a printing member so as to form an ink
image thereon and a transfer system for transferring the ink image
onto a printing substrate.
[0015] Still another further object of the present invention is to
provide an indirect ink-jet printing system which employs an
ink-jet printing unit for selectively applying ink on a printing
member so as to form an ink image thereon and a transfer system for
transferring the ink image onto a printing substrate.
[0016] Yet another object of the present invention is to provide an
ink-jet printing system having improved accuracy and resolution
with respect to prior art ink-jet printing systems.
[0017] There is thus provided, according to a preferred embodiment
of the present invention, a printing system which includes at least
one printing apparatus. Each printing apparatus includes a printing
member for selectively receiving ink into an ink receptive portion,
the ink receptive portion includes a plurality of ink receptive
dots forming a pattern in a desired resolution and an ink repelling
portion, the ink repelling portion includes the entire area of the
printing member except the ink receptive dots. Each printing
apparatus includes at least one printing unit, preferably but not
necessarily an ink-jet printing unit, the printing unit for
applying ink onto the printing member in accordance with a pattern
representing an image to be printed, thereby forming an ink image
on a portion of the ink receptive dots, and a transfer system for
transferring the ink image onto a printing substrate.
[0018] Further, in accordance with a preferred embodiment of the
present invention, each printing apparatus also includes a cleaning
system, the cleaning system for cleaning the printing member after
the operation of the transfer system.
[0019] Still further, the printing apparatus may include at least
one heating system, the heating system for heating the printing
member.
[0020] Additionally, where the ink used in the printing system is a
UV curable ink, the printing system may further include a UV curing
system downstream the at least one transfer system, the UV curing
system for curing the UV curable ink transferred to the printing
substrate.
[0021] In accordance with a preferred embodiment of the present
invention, each printing apparatus includes a plate cylinder, the
plate cylinder for mounting the printing member thereon and the
transfer system includes a blanket cylinder for transferring the
applied ink to a printing substrate and an impression cylinder for
impressing the printing substrate against the blanket cylinder.
[0022] According to an alternative preferred embodiment of the
present invention, the printing member is a gravure like cylinder
having depressions forming the ink receptive dots and elevated
portions forming the ink repelling portion and the transfer system
includes an impression cylinder for impressing the printing
substrate against the gravure like cylinder.
[0023] According to yet another alternative embodiment of the
present invention, the printing member is a cylinder having
elevated portions forming the ink receptive portion and depressions
forming the ink repelling portion. Further, The printing apparatus
may include a blanket cylinder for transferring the applied ink to
a printing substrate and an impression cylinder for impressing the
printing substrate against the blanket cylinder. Alternatively, the
transfer system includes an impression cylinder for impressing the
printing substrate against the gravure like cylinder.
[0024] In accordance with yet another preferred embodiment of the
present invention, the printing member is a rotatable belt having
elevated portions forming the ink receptive portion and depressions
forming the ink repelling portion. Further, the transfer system
includes a blanket cylinder for transferring the applied ink to a
printing substrate and an impression cylinder for impressing the
printing substrate against the blanket cylinder. Alternatively, the
transfer system includes an impression cylinder for impressing the
printing substrate against the rotatable belt.
[0025] Further, according to any of the preferred embodiments of
the present invention, the at least one ink-jet unit includes a
line array of ink jet nozzles operating to apply the ink onto the
printing member substantially simultaneously. The resolution of the
ink receptive dots may be substantially similar to or higher than
the resolution of the nozzles.
[0026] Still further, according to any of the preferred embodiments
of the present invention, the ink is an aqueous based ink, the ink
receptive dots are hydrophilic and the ink repelling portion is
hydrophobic. Alternatively, the ink is a non-aqueous based ink, the
ink receptive dots are oleophilic and the ink repelling portion is
oleophobic.
[0027] Further, in accordance with a preferred embodiment of the
present invention, each printing apparatus also includes a cleaning
system, the cleaning system for cleaning the printing member after
the operation of the transfer system.
[0028] Still further, the printing apparatus may include at least
one heating system, the heating system for heating the printing
member.
[0029] Additionally, where the ink used in the printing system is a
UV curable ink, the printing system may further include a UV curing
system downstream the at least one transfer system, the UV curing
system for curing the UV curable ink transferred to the printing
substrate.
[0030] In accordance with a preferred embodiment of the present
invention, each printing apparatus includes a plate cylinder, the
plate cylinder for mounting the printing member thereon and the
transfer system includes a blanket cylinder for transferring the
applied ink to a printing substrate and an impression cylinder for
impressing the printing substrate against the blanket cylinder.
[0031] According to an alternative preferred embodiment of the
present invention, the printing member is a gravure like cylinder
having depressions forming the ink receptive dots and elevated
portions forming the ink repelling portion and the transfer system
includes an impression cylinder for impressing the printing
substrate against the gravure like cylinder.
[0032] According to yet another alternative embodiment of the
present invention, the printing member is a cylinder having
elevated portions forming the ink receptive portion and depressions
forming the ink repelling portion. Further, the printing apparatus
may include a blanket cylinder for transferring the applied ink to
a printing substrate and an impression cylinder for impressing the
printing substrate against the blanket cylinder. Alternatively, the
transfer system includes an impression cylinder for impressing the
printing substrate against the gravure like cylinder.
[0033] In accordance with yet another preferred embodiment of the
present invention, the printing member is a rotatable belt having
elevated portions forming the ink receptive portion and depressions
forming the ink repelling portion. Further, the transfer system
includes a blanket cylinder for transferring the applied ink to a
printing substrate and an impression cylinder for impressing the
printing substrate against the blanket cylinder. Alternatively, the
transfer system includes an impression cylinder for impressing the
printing substrate against the rotatable belt.
[0034] Further, according to any of the preferred embodiments of
the present invention, the at least one ink-jet unit includes a
line array of ink jet nozzles operating to apply the ink onto the
printing member substantially simultaneously. The resolution of the
ink receptive dots may be substantially similar to or higher than
the resolution of the nozzles.
[0035] Still further, according to any of the preferred embodiments
of the present invention, the ink is an aqueous based ink, the ink
receptive dots are hydrophilic and the ink repelling portion is
hydrophobic. Alternatively, the ink is a non-aqueous based ink, the
ink receptive dots are oleophilic and the ink repelling portion is
oleophobic.
[0036] According to yet another preferred embodiment of the present
invention, the number of printing apparatus corresponds to the
number of printing inks forming the ink image. Preferably, but not
necessarily, the printing system includes four printing apparatus,
each for inking one of the four process colors CMYK.
[0037] There is also provided, according to a preferred embodiment
of the present invention, a printing method which includes the
following steps:
[0038] a. providing a printing member for selectively receiving ink
onto an ink receptive portion, the ink receptive portion includes a
plurality of ink receptive dots forming a pattern in a desired
resolution; and an ink repelling portion, the ink repelling portion
includes the entire area of the printing member except the ink
receptive dots;
[0039] b. applying ink onto the printing member in accordance with
a pattern representing an image to be printed so as to form an ink
image on a portion of the ink receptive dots; and
[0040] c. transferring the ink image onto a printing substrate.
[0041] Further, the method may also include the step of cleaning
the printing member after the transferring. Still further, the
method may also include the step of heating the printing
member.
[0042] According to a preferred embodiment of the present
invention, the ink is a UV curable ink and the printing method
further includes the step of curing the UV curable ink after the
transferring.
[0043] Further, according to yet another preferred embodiment of
the present invention, the method also include the step of forming
the ink receptive dots in a higher resolution than the resolution
provided in the step of applying.
[0044] Finally, there is provided in accordance with a preferred
embodiment of the present invention, a printing member for
selectively receiving ink, the printing member includes an ink
receptive portion, the ink receptive portion includes a plurality
of points forming a pattern of ink receptive dots in a desired
resolution and an ink repelling portion, the ink repelling portion
includes the entire area of the printing member except the ink
receptive dots, the printing member for selectively receiving an
ink image on a portion of the ink receptive dot, the ink image
corresponding to a digital representation of an image. Preferably,
the printing member includes at least two layers, a first layer
forming the ink receptive dots and a second different layer forming
the ink repelling portion.
[0045] In accordance with one preferred embodiment of the present
invention, the printing member having depressions forming the ink
receptive dots and elevated portions forming the ink repelling
portion. According to an alterative embodiment of the present
invention, the printing member having elevated portions forming the
ink receptive dots and depressions forming the ink repelling
portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The present invention will be understood and appreciated
more fully from the following detailed description taken in
conjunction with the appended drawings in which:
[0047] FIGS. 1A-1C are schematic illustrations of three printing
members for selectively receiving ink, constructed according to
three preferred embodiments of the present invention;
[0048] FIGS. 1D-1F are schematic cross sections of the printing
members of FIGS. 1A-1C, respectively;
[0049] FIGS. 1F and 1G are schematic illustrations and a cross
section thereof, respectively, of a printing member for selectively
receiving ink, constructed according to a further preferred
embodiment of the present invention;
[0050] FIGS. 2A-2C illustrate two configurations of an ink-jet
printing unit applying ink on the printing member of FIGS.
1A-1F;
[0051] FIG. 3A-3C illustrate certain advantages of the use of the
printing member of FIGS. 1A-1F;
[0052] FIG. 4 is a schematic isometric illustration of a belt based
indirect digital printing system having a printing member similar
to that of any of FIGS. 1A-1F;
[0053] FIG. 5 is a schematic isometric illustration of a printing
cylinder having a printing member similar to any of the printing
members of FIGS. 1A-1F and an ink-jet printing unit suitable for
applying ink thereon;
[0054] FIGS. 6-8 are schematic isometric illustrations of three
indirect digital printing systems; and
[0055] FIGS. 9-10 are schematic isometric illustrations of two
printing systems, comprising a plurality of printing cylinders and
a single impression cylinder.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0056] Reference is now made to FIGS. 1A-1F. FIGS. 1A-1F illustrate
a schematic portion of three alternative printing members for
selectively receiving ink, referenced 10 (FIGS. 1A and 1D), 20
(FIGS. 1B and 1E) and 30 (FIGS. 1C and 1F), respectively.
[0057] Each of the printing members 10, 20 and 30 comprises an ink
receptive portion, the ink receptive portion comprising a plurality
of grid points forming a pattern of ink receptive dots 12, 22, and
32 respectively, and an ink repelling portion, referenced 14, 24
and 34, respectively, which forms the entire area of the printing
member except the ink receptive dots 12, 22 and 32,
respectively.
[0058] In the illustrated embodiments only exemplary ink receptive
dots 12, 22 and 32 are referenced.
[0059] The printing members 10, 20 and 30 are particularly useful
for receiving ink applied by ink-jet printing units and minimize
the deficiencies associated with direct ink-jet printing as
described hereinbelow with reference to FIGS. 2A-2C and 3A-3C.
[0060] As shown in FIG. 1D, the printing member 10 (FIG. 1A)
comprises at least two layers, one being an ink receptive layer 16
and the other being an ink repelling layer 14 wherein the ink
receptive layer is exposed in the dots 12 which form a grid pattern
19 on the printing member 10.
[0061] It will be appreciated that the grid pattern 19 as well as
the grid patterns 29 and 39 of printing members 20 and 30 are
illustrated in FIGS. 1A-1C, respectively, only for explanatory
purposes. The printing members 10, 20 and 30 need not include any
marking of the grid pattern thereon.
[0062] It will be further appreciated that the pattern of ink
receptive dots 12, 22, and 32 and ink repelling portion, referenced
14, 24 and 34, (of the ink receptive portion of printing members
10, 20 and 30, respectively) may comprise any pattern including
random patterns (to be described hereinbelow) and is not restricted
to a pattern composed of grid points. The description of grid
points in FIGS. 1A-1F is given by way of example only.
[0063] The printing member 10 may be similar to any offset printing
plate in having an ink receptive portion and an ink repelling
portion. However, unlike prior art offset printing plates, the
printing member 10 comprises a predefined grid 19 of ink receptive
dots 12 which receive the ink applied by an ink jet printing
unit.
[0064] For example, if the ink-jet ink is an oil based ink, the
printing member 10 may be produced from an oleophilic polyester
substrate and a silicone oleophobic coating. An example of a
printing plate having a polyester substrate and silicone coating
thereon is described in U.S. Pat. No. 5,378,580 to Leenders. By
ablating the silicone coating of the printing member and exposing
its oleophilic polyester substrate in accordance to the desired
grid 19, oleophilic dots 12 are formed.
[0065] The grid pattern of ink receptive dots 12 of the printing
member 10 may be produced by any suitable method known in the art
for producing printing plates. It may be produced by producing a
film by an image setter, such as the Dolev 800 image setter,
commercially available from Scitex Corporation Ltd. of Herzlia,
Israel, and transferring the grid recorded on the film onto the
printing member 10. Alternatively, the grid may be produced
directly by a plate setter operating to record the grid 19 of dots
12 directly on the printing member 10. An example of a suitable
plate setter is the Raystar, commercially available from Scitex
Corporation Ltd. of Herzlia, Israel.
[0066] It will be appreciated that the printing member 10 is
produced substantially similarly to any other prior art printing
plate. However, unlike prior art printing plates on which the image
is recorded, the grid 19 of ink receptive dots 12 is recorded to
form the printing member 10.
[0067] The printing member 20 (FIGS. 1B and 1E) may be similar to a
gravure printing plate in that it has ink receptive material 26
having depressions 22 and ink repelling elevated portions 24.
However, in contrast to any prior art gravure cylinder which
includes a recorded image thereon, the printing member 20 comprises
a grid 29 of ink receptive depressions 22 for selectively receiving
ink so as to form the ink image thereon.
[0068] It will be appreciated that the printing member 20 may be
produced by any suitable method for producing prior art engraved
cylinders, such as gravure cylinders. However, according to the
present invention, a grid 29 of dots 22 is produced to form the
printing member 20 while prior art gravure cylinders include a
recorded image thereon.
[0069] The printing member 30 (FIGS. 1C and 1F) may be similar to a
letter press printing plate in that it has ink receptive elevated
portions 32 and ink repelling depressions 34. However, in contrast
to any prior art letter press cylinder which has a recorded image
thereon, the printing member 30 comprises a grid 39 of ink
receptive elevated portions 32.
[0070] It will be appreciated that the printing member 30 may be
produced by any suitable method for producing prior art letter
press cylinders. However, according to the present invention, a
grid 39 of dots 32 is produced to form the printing member 30 while
prior art letter press cylinders include a latent image
thereon.
[0071] The ink attraction of the cells is based on one of two known
physical phenomena; either surface tension or capillary force. In
the case of printing member 10 (similar to an offset printing
plate--FIGS. 1A and 1D), and printing member 30 (similar to a
letter press printing plate--FIGS. 1C and 1F), the cells 12 and 32,
respectively attract the ink due to surface tension while the
backgrounds 14 and 34, respectively, reject the ink due to the
relatively low surface tension.
[0072] In the case of printing member 20 (similar to a gravure
printing plate--FIGS. 1B and 1E), the ink attraction is due to the
capillary force produced and is related to the size and shape of
the holes and the viscosity of the ink. The outer surface can be
coated with an ink reductive coating which will further improve the
process.
[0073] Unlike prior art printing plates, the printing members 10,
20 and 30 are usable for receiving ink thereon a large number of
times so as to form different ink images thereon.
[0074] Further, unlike prior art printing plates which do not
determine the resolution of the image recorded thereon, the
printing members 10, 20 and 30 determine the resolution of the
images recorded thereon. The resolution of each of the printing
members 10, 20 and 30 is set in accordance with the spacing between
the dots forming the grids 19, 29 and 39.
[0075] According to a preferred embodiment of the present
invention, the printing members 10, 20 and 30 are used as printing
members in any indirect digital printing system. Five preferred
embodiments of printing systems utilizing a suitable printing
member, such as the printing members 10, 20 and 30 are illustrated
with reference to FIGS. 4-10 hereinbelow.
[0076] The printing members 10, 20 and 30 are particularly useful
for receiving ink from any suitable printing unit capable of
selectively applying ink on the printing member in accordance with
a pattern representing the image to be printed so as to form an ink
image thereon. A preferred printing unit for selectively applying
ink on the printing members 10, 20 and 30 is an ink-jet printing
unit. The ink-jet printing unit may be any suitable ink-jet
printing unit. Non limiting examples are a moving ink-jet printing
unit having a single nozzle, a moving ink-jet printing unit having
an array of ink-jet nozzles, such as the ones produced by Hewlett
Packard of California, U.S.A or a series of arrays one beside the
other so as to simultaneously apply ink on any of the printing
members 10, 20 and 30.
[0077] It will be appreciated that the term nozzle is used herein
in a broad sense to indicate any suitable mechanism known in the
art for ejecting ink droplets from an ink-jet printing unit. A non
limiting example of such mechanism is described in published
European Patent Application Number 640481 assigned to the assignee
of the present application.
[0078] Reference is now made to FIGS. 1G-1H which illustrate a
printing member, referenced 90, for selectively receiving ink,
constructed according to a further preferred embodiment of the
present invention.
[0079] The printing member 90 comprises an ink receptive material
92 having a random pattern, generally referenced 94, formed
thereon. The random pattern 94, which covers approximately 70% of
the material 92, comprises a plurality of ink repelling 96 and a
plurality of ink receptive portions 98. In this case, printing
member 90 acts similar to offset (FIGS. 1A and 1D) or letter press
printing plates (FIGS. 1C and 1F).
[0080] Alternatively, printing member 90 may comprise a plurality
of ink repelling (elevated) portions and a plurality of ink
receptive depressions, in which case, printing member 90 acts
similar to a gravure plate (FIGS. 1B and 1E). The random pattern
may be generated by any suitable randomization function such as the
screen frequent modulation FM screen (stochastic ) technique
described in U.S. Pat. No. 5,508,828 assigned to the present
applicants, or using error diffusion technique described in U.S.
Pat. No. 4,920,501 assigned to Eastman Kodak Company of New York,
USA.
[0081] The generated pattern is then engraved or otherwise formed
on the printing member 90 by known in the art process such as,
laser engraving or ablation, chemical etching or contact with a
prepared film. Preferably for each color being printed, a separate
randomization pattern is generated.
[0082] A grid pattern (described hereinabove with respect to FIGS.
1A-1F) compensates for inaccuracies in the alignment of the ink-jet
ejectors caused by clogging and/or by manufacturer's tolerances.
The random pattern reduces the effect of regular pattern error,
such as missing, faint or dark lines.
[0083] Both the random pattern and the grid pattern overcome the
deficiencies of direct to paper ink-jet printing.
[0084] While any suitable printing unit, in particular any ink-jet
printing unit falls within the scope of the present invention, two
preferred configurations of an ink-jet printing unit are
illustrated with reference to FIGS. 2A-2C hereinbelow.
[0085] FIGS. 2A and 2C are schematic illustrations of two ink-jet
printing units capable of applying ink onto the printing member of
FIG. 2B. In the illustrated embodiment the printing member 10 is
illustrated as a non limiting example of any of the printing
members 10, 20 and 30.
[0086] FIG. 2A illustrates a printing unit 40 having an array of
nozzles 42A-42H which may simultaneously apply ink on the ink
receptive dots 44A-44H of a corresponding row of the printing
member 10.
[0087] It will be appreciated that with the printing unit 40, the
resolution of the ink image is determined by the resolution of the
ink-jet nozzles.
[0088] In accordance with a preferred embodiment of the present
invention, the resolution of the ink receptive dots determines the
resolution of the ink image formed on the printing members. The ink
receptive dots may be formed on the printing member in any desired
resolution, including high resolutions, such as 600 ink receptive
dots per inch (dpi).
[0089] It will be appreciated that using the printing members of
the present invention provides an improvement over the art inter
alia since there is a limitation son how small the ejected ink-jet
droplets may be made, since smaller droplets are increasingly
subject to aerodynamic forces that tend to increase their deviation
from normal trajectory and because of cross talk effects between
the nozzles themselves. Thus, the achievable resolution of the
printed image when determined by the resolution of the nozzles is
limited.
[0090] Ink-jet printing unit 50 (FIG. 2C) is a suitable printing
head for applying ink on a printing member having a resolution
larger than that of its nozzles.
[0091] The printing unit 50 comprises an array of staggered nozzles
referenced 52A-52H. In the illustrated embodiment, each row of
nozzles includes nozzles sufficiently spaced apart from each other
so as to minimize cross talk effects therebetween. Accordingly, the
ink image is formed by a relative movement between the printing
unit 50 and the printing member 10 so as to enable each row of the
unit 50 to apply ink on the corresponding ink receptive dot.
[0092] In the illustrated embodiment, the nozzles 52A and 52D apply
ink on the ink receptive dots 54A and 54D, the unit 50 or the
printing member is than moved so as to enable nozzles 52B and 52E
to apply ink on dots 54B and 54E. Similarly, the nozzles 52C and
52F apply ink on dots 54C and 54F and the nozzles 52D and 52G apply
ink on the dots 54D and 54G.
[0093] It will be appreciated that the arrays 40 and 50 may be
formed from any suitable ink-jet printing array known in the art, a
non limiting example being the array described in the above
mentioned European Patent Application Number 640481.
[0094] Reference is now made to FIGS. 3A-3C. FIGS. 3A-3C illustrate
advantages associated with the use of the printing members of the
present invention in terms of the accuracy and uniformity of the
applied ink-jet drops.
[0095] Typically, the distance of a fibrous printing substrate,
such as paper, from the ink-jet nozzles is on the order of one to
few millimeters and this distance can be substantially reduced
employing the printing members of the present invention since they
are not based on fibrous material whose lint may clog the orifices
of the nozzles.
[0096] FIG. 3A illustrates four schematic ink-jet nozzles,
referenced 70A-70D which apply ink on two groups of substrates,
referenced 72A-72D and 74A-74D, placed at the distances denoted Dl
and D2, respectively. The substrates 72 represent for example the
printing members of the present invention which can be located in
closer distance to the nozzles 70 than the distance of conventional
printing substrates 74, such as paper.
[0097] Since the substrates 72A-72D are closer to the nozzles 70,
the inaccuracy resulting from a deviation from normal trajectory of
ink droplets applied by the nozzles 70 is smaller then for the
substrates 74 which are placed at a larger distance. This is shown
in particular for the drop 76D vs. drop 78D and to a lesser extent
for the drops 76B-76C vs. drops 78B-78C. Drops 76A and 78A are
drawn with no deviation for reference.
[0098] A further advantage of the printing members of the present
invention, shown in FIGS. 3B and 3C is their self centering
property which improves both accuracy and uniformity of the ink
droplets. As shown in FIG. 3B ink droplets applied with an
inaccuracy as shown for drops 80B-80D, are attracted by the ink
receptive dots and rejected by the ink repelling surroundings so as
to center themselves in the ink receptive dots 82A-82D (FIG. 3C).
In the illustrated embodiment the ink receptive dots 32 (FIG. 1C)
are shown as a non limiting example.
[0099] The resulting dots are more uniformly and accurately placed
than dots resulting from application of ink directly on printing
substrates, such as paper. The uniformity of the dots during their
transfer to the printing substrate employing the printing members
of the present invention may also be improved by heating the ink
image as described with reference to the printing system of FIG. 4
hereinbelow, thereby increasing the viscosity of the ink and
minimizing undesired spreading of the ink when transferred to the
printing substrate.
[0100] FIG. 4 illustrates an indirect digital printing system,
generally referenced 100, constructed and operative in accordance
with a preferred embodiment of the present invention. The printing
system 100 comprises a belt 102, forming a printing member similar
to the printing member 10. The belt 102 rotates about rollers 104
and 106 in the direction of arrow 108 in any suitable known
mechanism, such as a capstan arrangement.
[0101] The system 100 also comprises an ink-jet printing unit 112
which preferably comprises a plurality of linear arrays, of which
four 114A-114D are shown herein, arranged in staggering
relationship therebetween as described in detail hereinabove with
respect to FIG. 2C. Each of the arrays 114 includes a plurality of
nozzles for applying ink drops on the belt 102. Two exemplary
nozzles are referenced 115.
[0102] The ink-jet printing unit 112 selectively applies ink onto
the belt 102 so as to form an ink image 116 in a resolution defined
by the grid of ink receptive dots 118 on the belt 102. Ink image
116 is formed in accordance to digital data representing the image
stored in the control system 120. The control system 120 may by any
suitable computer operating to store the digital representations of
the images to be printed, to output them so as to control the
ink-jet printing unit which applies ink in accordance with the
digital representation and which further operates to control the
operation of the system components.
[0103] The ink image 116 is transferred to the printing substrate
122 impressed against an impression cylinder 124, the cylinder 124
rotating in the direction designated by arrow 126, so as to form a
printed image 128 thereon. It will be appreciated that the image
128, is on the other side of substrate 122 and shown through the
printing substrate for illustration purposes.
[0104] The printing substrate can be fed between the impression
cylinder 124 and the belt 102 by any suitable mechanism, such as
the rollers mechanism schematically illustrated by rollers 130 and
132.
[0105] Once the image is transferred to the sheet 122 from the belt
102, the belt is cleaned in a cleaning station 134 and is then
ready for receiving ink so as to form a new ink image thereon.
[0106] The cleaning station 134 may be any suitable cleaning
station known in the art, for example, a cleaning station based on
high pressurized gas, such as a high pressured air based cleaning
station.
[0107] As optional features, the printing system 100 may include a
heating system 136 for heating the belt 102, thereby drying the ink
applied on thereon as described hereinabove and an Ultra violet
(UV) curing system 138 for curing the ink in case UV curable inks
are used by the ink-jet printing unit 112.
[0108] The UV curing system may be any UV curing system known in
the art. A non limiting example is the DRS UV curing system
commercially available from Fusion Inc. of the United States.
[0109] It will be appreciated that while the illustrated embodiment
has been described with respect to a belt forming a printing member
similar to the printing member 10, the belt 102 may be similar to
either of the printing members 10, 20 and 30.
[0110] Reference is now made to FIG. 5 which illustrates the
application of a plurality of linear ink-jet arrays for applying
ink on a printing cylinder as shown for the printing systems of
FIGS. 6-10.
[0111] The printing cylinder of FIG. 5, referenced 150 is either
formed in the shape of a printing member or is capable for mounting
thereon a printing member. In the illustrated embodiment, the
cylinder 150 is formed so as to have the ink receptive dots 152
thereon.
[0112] An ink-jet printing unit 154 for applying ink on the
cylinder 150 so as to form an ink image thereon is preferably
similar to the ink-jet printing unit 112 (FIG. 4), i.e. it includes
a plurality of linear arrays of which three 154A-154C are shown, in
a staggered arrangement therebetween.
[0113] Each of the arrays 154 includes a plurality of nozzles of
which only one is referenced 156. A particular feature of the
arrays 154 is their similar radial distance from the printing
cylinder 150.
[0114] In the illustrated embodiment, for illustration purposes
only, the printing cylinder is similar to the printing member 10.
It will be appreciated that the printing cylinder can be formed in
the shape of or being capable for mounting thereon any of the
printing members of the present invention as illustrated with
respect to the indirect digital printing systems illustrated with
reference to FIGS. 6-8 hereinbelow.
[0115] FIGS. 6-8 illustrate a gravure like, a letter press like and
an offset like printing presses, referenced 200, 300 and 400,
respectively.
[0116] The indirect digital printing system 200 comprises a
printing cylinder 202 forming a printing member similar to that of
printing member 20, an impression cylinder 204 and a printing
substrate 206 cut away so as to expose an ink image 208 formed on
the printing cylinder by employing an ink-jet printing unit 210.
The ink jet printing unit is preferably but not necessarily similar
to the ink-jet printing unit 154.
[0117] Once the ink image 208 is formed and transferred to the
substrate 206 so as to form a printed image 212 on the substrate
206, the cylinder 202 is cleaned in a cleaning station 214 so that
it can receive a new ink image thereon. The image 212 is on the
other side of the substrate 206 and shown therethrough for
illustration purposes.
[0118] The printing system 200 also include a control system 216
and may include a UV curing station 218 in case a UV curable ink is
applied to form the ink image 208. It may also include a heating
system (not shown) similar to the heating system 136 (FIG. 4).
[0119] The printing system 300 (FIG. 7) is generally similar to the
printing system 200, and therefore, similar reference numerals are
used in FIGS. 6 and 7. However, the printing member of the printing
system 300 is a printing member similar to the printing member 30
mounted on the printing cylinder 302 or forming the printing
cylinder itself.
[0120] FIG. 8 illustrates an offset like indirect printing system
having an offset like printing member 402 mounted thereon or
forming the printing cylinder itself. The printing system 400
comprises in addition to the elements of the printing systems 200
and 300 referenced by similar reference numerals, a blanket
cylinder 404 for receiving the ink image formed on the cylinder 402
and for transferring it to the printing substrate 206 as printed
image 212.
[0121] It will be appreciated that the printing systems 100, 200,
300 and 400 may be utilized as a stand alone printing system or as
a printing apparatus forming part of a larger printing system as
illustrated in FIGS. 9-10 hereinbelow.
[0122] Also, it will be appreciated that as a stand alone printing
system the printing systems 100, 200, 300 and 400 may be utilized
for multicolor or monochrome color printing.
[0123] FIG. 9 illustrates a multi color printing system, generally
referenced 500. The printing system 500 comprises a plurality of
printing stations, each being similar to the printing system 400
(FIG. 8) except the impression cylinder 502 which is common to all
printing stations.
[0124] In the illustrated embodiment, four printing stations
designated 400A-400D are used to apply the four process colors
Cyan, Magenta, Yellow and Black, known in the art as CMYB or CMYK
colors.
[0125] FIG. 10 illustrates a multicolor printing system directed to
a gravure or letter press like configuration. The printing system,
generally referenced 600, comprises a plurality of printing
stations, each being similar to that of the printing systems 200
and 300, respectively, except the impression cylinder 602 which is
common to all printing stations.
[0126] In the illustrated embodiment, four printing stations in a
gravure like configuration are shown and referenced 200A-200D for
printing the image with the CMYK colors.
[0127] A further advantage of the printing systems of the present
invention is that they provide improved registration, i.e. correct
positional overlap between corresponding printed dots of different
colors. Since the printing members are used in a cyclic fashion,
separable set-up for each image is not required.
[0128] It will be appreciated that the present invention is not
limited by what has been described hereinabove and that numerous
modifications, all of which fall within the scope of the present
invention, exist. For example, while the present invention has been
described with respect to ink-jet printing, it equally applicable
to any printing method capable of selectively applying ink so as to
form the ink image. Examples for such printing methods are thermal
wax transfer, thermal sublimation and toner jet. Furthermore, while
the present invention has been described with respect to ink, it is
equally applicable to any other colorant, such as toners, which may
be applied to form an ink image by various processes, such as
electrography, electrophotography, and iongraphy.
[0129] It will be appreciated by persons skilled in the art that
the present invention is not limited by what has been particularly
shown and described hereinabove. Rather the scope of the invention
is defined by the claims which follow:
* * * * *