CA 02226966 l998-0l-l3 W O 97/03382 PCTrUS96/11185 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 CA 02226966 l998-0l-l3 W O 97/03382 PCT~US96/11185 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 CA 02226966 l998-0l-l3 W O 97/03382 PCTrUS96/11185 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, W 097/03382 PCTrUS96/11185 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 -W O 97/03382 PCT~US96/11185 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 . W O 97/03382 PCTAUS96/11185 ; - 6 -invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.