MAKING A PHOTOPOLYMER PRINTING PLATE

FABRICATION D'UNE PLAQUE D'IMPRESSION PORTANT UN PHOTOPOLYMERE

English Abstract

A process of making a photopolymer printing plate includes steps of exposing a
photopolymer material to light that is applied in a predetermined image
pattern, washing the plate with a processing solution in order to cause
polymeric material from portions of the plate that are determined by the image
pattern to dissolve from the plate into the processing solution, and removing
the dissolved polymeric material from the processing solution on the molecular
level by ultrafiltration. The use of ultrafiltration permits the polymeric
material to be efficiently recovered without the need for conventional
recovery techniques such as distillation or flocculation, and allows reuse of
the filtrate to process additional photopolymer plates. A system (10) for
performing the process is also disclosed. The system is comprised of a plate
making system (12), and an ultrafiltration system (24) with an ultrafilter
(26) and a recirculation conduit (32).

French Abstract

L'invention concerne un procédé de fabrication d'une plaque d'impression portant un photopolymère, consistant à exposer le photopolymère à de la lumière, l'exposition se faisant suivant un motif image prédéterminé, à laver la plaque avec une solution de traitement pour faire en sorte que le matériau polymère des parties de la plaque délimitées par le motif image se dissolve dans la solution de traitement et à séparer le matériau polymère dissous de la solution de dissolution par ultrafiltration, à l'échelle moléculaire. L'utilisation de l'ultrafiltration permet de récupérer le polymère d'une manière efficace, sans avoir besoin de recourir à des techniques de récupération traditionnelles telles que la distillation ou la floculation, le filtrat étant utilisé à nouveau pour traiter d'autres plaques portant un photopolymère. L'invention concerne également un appareillage (10) permettant de mettre en oeuvre le procédé. L'appareillage comprend un système (12) pour fabriquer les plaques, un système d'ultrafiltration (24) avec un ultrafiltre (26) et une conduite (32) de recirculation.

Claims

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WHAT IS CLAIMED IS:
1. An improved process of making a photopolymer
printing plate, comprising steps of:
(a) exposing a plate comprising photopolymer
material to light that is applied in a predetermined image
pattern;
(b) washing the plate with a processing solution
in order to cause polymeric material from portions of the
plate that are determined by the image pattern to dissolve
from the plate into the processing solution; and
(c) removing the dissolved polymeric material
from the processing solution on the molecular level by
ultrafiltration, whereby the polymeric material may be
efficiently recovered without the need for conventional
recovery techniques such as distillation or flocculation.
2. A process according to claim 1, wherein step
(c) is performed so as to remove substantially all of the
polymeric material from the processing solution.
3. A process according to claim 1, wherein steps
(b) and (c) are performed with a processing solution that is
acidic.
4. A process according to claim 3, wherein steps
(b) and (c) are performed with a processing solution that
has a ph that is substantially within the range of 1.0 to
4Ø
5. A process according to claim 3, wherein steps
(b) and (c) are performed with a processing solution that
has a pH of about 2.0 to about 2.5.
6. A process according to claim 1, wherein step
(c) is performed at a temperature that is substantially
within the range of about 75 to 95 degrees Fahrenheit.

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7. A process according to claim 1, wherein step
(c) is performed with an ultrafiltration membrane that is
designed to preclude passage therethrough of polymeric
molecules having a weight average molecular weight of within
the range of about 10,000 to about 100,000.
8. A process according to claim 7, wherein step
(c) is performed with an ultrafiltration membrane that is
designed to preclude passage therethrough of polymeric
molecules having a weight average molecular weight of within
the range of at least 50,000 to at least 100,000, but that,
as a result of a dynamic layer that forms against the
membrane, achieves excellent filtration of polymeric
molecules having molecular weights of lower than 50,000.
9. A process according to claim 8, wherein step
(c) is performed with an ultrafiltration membrane that is
designed to preclude passage therethrough of substantially
all polymeric molecules having a weight average molecular
weight of at least 70,000.
10. A process according to claim 1, wherein step
(c) is performed with an ultrafiltration membrane that is
designed to preclude passage therethrough of substantially
all polymeric molecules having a weight average molecular
weight of about 70,000.
11. A process according to claim 1, wherein step
(c) is performed with a filter that comprises polyether
sulfone.

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12. An improved system for recovering effluent
from a photopolymer printing plate, comprising:
exposure means for exposing a plate comprising
photopolymer material to light that is applied in a
predetermined image pattern;
washout means for washing the surface with a
processing solution in order to cause polymeric material
from portions of the plate that are determined by the image
pattern to dissolve from the plate into the processing
solution; and
ultrafiltration means for removing the dissolved
polymeric material from the processing solution on the
molecular level by ultrafiltration, whereby the polymeric
material may be efficiently recovered without the need for
conventional recovery techniques such as distillation or
flocculation, and filtrate may be reused to process
additional plates.
13. A system according to claim 12, wherein said
ultrafiltration means is constructed and arranged to remove
substantially all of the polymeric material from the
processing solution.
14. A system according to claim 12, wherein said
processing solution is acidic.
15. A system according to claim 14, wherein said
processing solution has a ph that is substantially within
the range of 1.0 to 4Ø
16. A system according to claim 14, wherein said
processing solution has a ph of about 2.0 to about 2.5.
17. A system according to claim 11, wherein said
ultrafiltration means operates at a temperature that is
substantially within the range of about 75 to 95 degrees
Fahrenheit.

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18. A system according to claim 11, wherein said
ultrafiltration means comprises an ultrafiltration membrane
that is designed to preclude passage therethrough of
polymeric molecules having a weight average molecular weight
of within the range of at about 10,000 to about 100,000.
19. A system according to claim 18, wherein said
ultrafiltration membrane is designed to preclude passage
therethrough of polymeric molecules having a weight average
molecular weight of within the range of at least 50,000 to
at least 100,000, but that, as a result of a dynamic layer
that forms against the membrane, achieves excellent
filtration of polymeric molecules having molecular weights
of lower than 50,000.
20. A system according to claim 19, wherein said
ultrafiltration means comprises an ultrafiltration membrane
that is designed to preclude passage therethrough of
substantially all polymeric molecules having a weight
average molecular weight of at least 70,000.
21. A system according to claim 12, wherein said
ultrafiltration means comprises an ultrafiltration membrane
that is designed to preclude passage therethrough of
substantially all polymeric molecules having a weight
average molecular weight of about 70,000.
22. A system according to claim 12, wherein said
ultrafiltration means comprises a filter that comprises
polyether sulfone.

Description

CA 02226966 l998-0l-l3
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MAKING A PHOTOPOLYMER PRINTING PLATE.
FIELD OF ~1~ lNV~NllON
This invention relates broadly to the commercial
printing industry, and more specifically to systems o~ the
photopolymer type ~or making printing plates.
DESCRIPTION OF THE RTIT.~TF.n TECHNOLOGY
Photopolymer printing technology, such as the
FLEX-LITE SPLASH7M brand systems recently introduced by the
owner o~ this invention, Poly~ibron Technologies, Inc.,
involves making a ~lexographic printing plate by exposing a
predetermined image onto a photosensitive polymeric
material, which is then etched with a process solution to
expose the image in a raised pattern on the printing plate.
Polymer that is removed ~rom the plate during the etching
process becomes dissolved in a process or wash solution that
is used to ~lush the printing plate.
Removing the dissolved polymer ~rom the process
solution is currently an expensive and laborious process,
but one that is necessary ~or environmental reasons.
Current processes to remove the dissolved polymer include
distillation or chemical addition and ~locculation o~ the
polymer. Distillation units are costly and time consuming
to operate. Flocculation involves the addition o~ a
chemical such as borax to the solution, which raises the pH
and renders the polymer insoluble in the washout solution.
The stickiness o~ ~locculated polymer, however, makes it
very di~icult to mechanically remove ~rom the solvent;
mechanical separators ~oul almost immediately.

i
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It is clear that a long and un~llled need exists
for an improved process and system ~or removing dissolved
polymer ~rom solution in a photopolymer printing plate
making ~acility that is less laborious and expensive than
the systems and processes that are currentiy in use.
SU~ RY OF I~E lNV~N-llON
Accordingly, it is an object o~ the invention to
provide an improved process and system ~or removing
dissolved polymer ~rom solution in a photopolymer printing
plate making ~acility that is less laborious and expensive
than the systems and processes that are currently in use.
In order to achieve the above and other objects o~
the invention, an improved process o~ making a photopolymer
printing plate includes steps o~ (a) exposing a photopolymer
material to light that is applied in a predetermined image
pattern; (b) washing the polymer with a processing solution
in order to cause polymeric material ~rom portions o~ the
polymer that are determined by the image pattern to dissolve
from the polymer into the processing solution; and (c)
removing the dissolved polymeric material ~rom the
processing solution on the molecular level by
ultra~iltration, whereby the polymeric material may be
e~iciently recovered without the need for conventional
recovery techniques such as distillation or ~locculation.
This allows the filtrate to be reused to process additional
photopolymer plates.
An improved system for making and recovering
e~luent ~rom a photopolymer printing plate includes,
according to a second aspect o~ the invention, an exposure
system ~or exposing a sur~ace o~ a photopolymer material to
light that is applied in a predetermined image pattern; a
washout system ~or washing the unexposed polymer with a
processing solution in order to cause polymeric material
~rom portions o~ the polymer that are determined by the
image pattern to dissolve ~rom the sur~ace into the
processing solution; and an ultra~iltration system ~or
removing the dissolved polymeric material ~rom the

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-- 3
processing solution on the molecular level by
ultrafiltration, whereby the polymeric material may be
e~ficiently recovered without the need for conventional
recovery techniques such as distillation or flocculation.
These and various other advantages and features of
J novelty which characterize the invention are pointed out
with particularity in the claims annexed hereto and ~orming
a part hereof. However, for a better understanding of the
invention, its advantages, and the objects obtained by its
use, reference should be made to the drawings which form a
further part hereof, and to the accompanying descriptive
matter, in which there is illustrated and described a
pre~erred embodiment of the invention.
BRIEF DESCRIPTION OF '1'~ DRAWINGS
FIG. 1 is a schematic diagram depicting an
improved system for recovering effluent from a photopolymer
printing plate according to the preferred embodiment o~ the
invention.
DET~TT.T~.n DESCRIPTION OF '1'~ PR~K~ EMBODIMENT(S)
Re~erring now to Figure 1, an improved system 10
~or making a photopolymer type printing plate includes the
actual plate making system 12, which includes, in an
arrangement that is well known in this area of technology,
an exposure system ~or exposing a photopolymer material
plate to light that is applied in a predetermined image
pattern, and a washout system for washing the plate with a
processing solution in order to cause polymeric material
~rom portions o~ the plate that are determined by the image
pattern to dissolve from the plate into the processing
solution. System 10 further includes a conduit 14 ~or
passing the process solution that has the dissolved
polymeric material therein to a holding tank 40, as may be
seen in FIGURE 1. A ~ill control valve 16 having a ~loat
member 18 is provided in the conduit 14 to prevent over-
filling of the holding tank 40. System 10 further includes,

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as may also be seen in FIGURE 1, an ultrafiltration system
24 for removing the dissolved polymeric material from the
processing solution on the molecular level by
ultrafiltration, so that the polymeric material may be
efficiently recovered without the need for conventional
recovery techniques, such as distillation or flocculation.
Ultrafiltration system 24 includes an intake conduit 22,
through which processing solution is drawn from the tank 40
by means of pump 28 and ~orced into an intake port of an
ultrafilter 26, as may also be seen in FIGURE 1. The
pressure at the intake port of the ultxafilter 26 is
monitored by a pressure gauge 30. A second, recirculation
conduit 32 is communicated at a first end with a
recirculation port of the ultrafilter 26, which.is of the
cross ~low type, and at a second end with a holding tank 40.
A pressure gauge 34 and temperature gauge 36 is interposed
within the conduit 32, as may be seen in FIGURE 1.
Ultrafilter 26 further has a permeate port to which a third
conduit 38 is communicated, as may be seen in FIGURE 1. As
is known in filtration technology, a large volume of
processing fluid is circulated within one side of the
ultra~ilter 26 thorough the intake conduit 22 and the
recirculation conduit 32. A relatively small amount of
clean, filtered permeate fluid is emitted from the permeate
port and is taken away for reuse by the permeate conduit 38.
The processing solution used in the plate making
system 12 is preferably acidic, having a pH that is
substantially within the range of 1.0 to 4.0, with a more
preferred range of about 2.0 to 2.5 and a most preferred
level of about 2Ø The temperature of the solution at the
ultrafilter 26 is preferably within the range of about 75 to
about 95 degrees Fahrenheit.
In the most preferred embodiment, plate making
system 12 utilizes photo sensitized plates that are
predominantly polyurethane, and that produce polymers in the
processing solution that have a number average molecular
weight (Mn) of about 29,500, and a weight average molecular
-

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5 - - -
weight of about 80,200. The invention embraces the concept
o~ using ultrafiltration to remove such molecules from the
processing solution, meaning that a membrane having a
nominal molecular weight cut-off of about 10,000 to about
40,000 could be used. However, the inventors have also
discovered that, for unknown reasons, near perfect
filtration can be achieved with a membrane that has a
nominal molecular weight cut-off that is substantially
greater than 40,000. This is a result of the product
forming a second dynamic layer over the initial membrane
material.
The inventors have determined that ultrafilter 26
can produce optimal filtration of the processing solution at
a nominal molecular weight cut-of~ that is within the range
of about 50,000 to about 100,000. Most preferably, filter
26 has a nominal molecular weight cut off of 60,000 to
70,000. A membrane having a nominal molecular weight cut
off of 60,000 can be obtained as Model AES 100 from Advanced
Membrane Technologies of San Diego, California. Advanced
Membrane Technologies also supplies a membrane having a
nominal molecular weight cut off of 70,000 under the Model
Code AF 100. By increasing the nominal molecular weight cut
off of the membrane that is used in ultrafilter 26, the flow
capacity of ultra~ilter 26 and the life of the membrane
itself are increased when compared to a membrane that has a
lower nominal molecular weight cut o~f. For example, it has
been determined that an ultrafilter 26 based upon the Model
AES 100 membrane described above will have a life of 1 year
or greater, which is considered to be outstanding in this
area of technology.
It is to be understood, however, that even though
numerous characteristics and advantages of the present
invention have been set forth in the foregoing description,
together with details of the structure and function of the
invention, the disclosure is illustrative only, and changes
may be made in detail, especially in matters of shape, size
and arrangement of parts within the principles of the

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invention to the full extent indicated by the broad general
meaning of the terms in which the appended claims are
expressed.

Representative Drawing