SOLVENT SYSTEMS FOR REMOVAL OF INK AND IMAGED COATING FROM PRINTING PLATES AND METHOD OF USING SAME

Abstract: A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether ester and water, with or without ammonia or aminoethanol, and with or without a solubility enhancer. A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether ester and aminoethanol. A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether, water and ammonia or aminoethanol, with or without a solubility enhancer. A method of simultaneously removing adsorbed ink and imaged polymer coating from printing plates using these solvent systems. A method of cleaning used printing plates in-situ using these solvent systems.

Description: SOLVENT SYSTEMS FOR REMOVAL o OF INK AND IMAGED COATING FROM PRINTING PLATES AND METHOD OF USING SAME 5 This application claims priority to provisional patent application serial no. 60/133,576, herein incorporated by reference. BACKGROUND OF THE INVENTION 1. Technical Field ^ The present invention relates generally to chemical solvent systems for cleaning printing plates used in printing presses, and more particularly to chemical solvent systems for removing adsorbed ink and imaged polymer coating from printing plates so as to permit the recycling of printing press plates. 15 2. Background Art In the commercial printing press industry, printing plates are used for the transfer of images to various media such as cloth and paper. An image on a printing plate is created when a water soluble polymer is applied to a printing plate 20 and the polymer is converted into a water insoluble product via a laser imaging process. The imaged polymer coating will accept ink and transfer the same for printing. Due to the vast number and wide variety of images used in the commercial printing press industry, the practice of discarding a printing plate after 25 there is no longer a need to print the image it bears has become neither economically feasible nor environmentally conscious. Furthermore, the removal and replacement of printing plates is a time-intensive process. Thus, there is a need for a method and medium which will aid in the accomplishment of printing plate 30 recycling. In order to render a printing plate reusable for many cycles of recoating, re-imaging, and printing, both adsorbed ink and the imaged coating must be removed from the surface of the plate without causing damage to the surface of 35 the plate or nearby printing press components. Previously, such removal had been accomplished in two separate steps, with one solvent being used to remove the ink, and a different solvent being used to remove the image. Such solvents were often harmful to other printing press components such as those made of rubber or metal. Furthermore, such a sequential process was both inefficient and tedious, requiring - twice the work and twice the materials in comparison to use of one solvent system capable of simultaneously removing both ink and imaged coating. However, there existed no known solvent system which could safely and effectively accomplish such simultaneous removal. BRIEF SUMMARY OF THE INVENTION 10 It is an object of the invention to provide a chemical solvent system which will safely and effectively remove both adsorbed ink and imaged polymer coating from printing plates without harming the plates or other components of the printing press. 15 It is a further object of the invention to allow for the reuse of printing plates via removal of the adsorbed ink and imaged coating to prepare the plates for recoating, re-imaging and printing. We, the inventors, have found that while many single organic 20 solvents, when used in isolation, effectively remove adsorbed ink from the surface of used printing plates, these single solvents have no effect on the removal of the imaged coating. However, we have discovered that when such single organic solvents, such as glycol ether esters or glycol ethers are combined with water, „- aminoethanol and/or ammonia a surprising synergism results whereby the resulting solvent systems exhibit not only excellent ink removing abilities, but exhibit excellent imaged coating removing abilities. The invention includes the following solvent systems: (1) mixtures of a glycol ether ester and water, with or without ammonia or aminoethanol, and with 30 or without a solubility enhancer and (2) mixtures of a glycol ether, water and ammonia or aminoethanol, with or without a solubility enhancer. 35 Other objectives, advantages and features of the invention will become apparent from the following detailed description of the invention, and from the claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The solvent systems of the invention comprise mixtures of a linear or 5 branched chain glycol ether ester (Formula I) and water, with or without ammonia or aminoethanol, and with or without a solubility enhancer: O I I CH 3 - (CH 2 ) m - O - ((CH 2 ) q - O) n - C - (CH 2 ) P - CH 3 10 (I) where m, n, p and q are integers The solvent systems of the invention also comprise mixtures of a 15 linear or branched chain glycol ether of the general Formula II, water and ammonia or aminoethanol, with or without a solubility enhancer: CH 3 - (CH 2 ) m - O - ((CH 2 ) q - O) n - H (II) where m, n and q are integers 20 Preferred glycol ether esters include those of Formula I in which m = 0-7, n = 1-4, p = 0-7, and q = 2-3. The most preferred glycol ether esters include: ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, and propylene glycol methyl ether acetate. Preferred 25 glycol ethers include those of Formula II in which m = 0-7, n = 1-4, and q = 2-3. The most preferred glycol ethers include ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol 2-ethyl-hexyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol -.„ butyl ether, and propylene glycol methyl ether. The solvent systems of the invention are compatible with printing press components, including rubber, polymer and metal components. When used alone, glycol ether esters exhibit excellent ink removing characteristics, but do not remove the imaged coating. However, when glycol ether esters are combined with water, aminoethanol, aminoethanol and water, or ammonia and water, solvent systems result which will not only remove ink, but will also remove the imaged coating. Glycol ethers and glycol ether esters have limited water solubility. For example, diethylene glycol butyl ether acetate has a maximum water solubility of about 6-7% by weight. Thus, preferred solvent systems of the present invention in which diethylene glycol butyl ether acetate is fully solubilized and which contain only diethylene glycol butyl ether acetate and water comprise about 1-7% by weight diethylene glycol butyl ether acetate and about 93-99% by weight water, more preferably about 5-7% by weight diethylene glycol butyl ether acetate and about 93- 95% by weight water. Solvent systems of the present invention include those in which the glycol ether or glycol ether ester is not fully solubilized due to its presence in an amount exceeding its water solubility. While the presence of these higher levels of glycol ethers or glycol ether esters may not further enhance the ability of the solvent system to remove the imaged coating, the presence of higher levels of the glycol ethers or the glycol ether esters has the potential of enhancing the ability of the solvent system to remove ink. The solubility of a glycol ether or a glycol ether ester in water in the solvent systems of the invention may be enhanced via the addition of a solubility enhancer, such as a linear or branched chain solvent of the general Formula III: O I I CH 3 - (CH 2 ) P - C - O - ((CH 2 ) q - O)„ - (CH 2 ) m - OH (III) where m, n, p and q are integers Solvents of the Formula III are structurally similar to glycol ethers and glycol ether esters, and are compounds (or mixtures) of esters made up of fatty acids reacted with polyglycols. Preferred solvents of Formula III include ethoxylated tall oils such as Akzo's Ethofat®, wherein m = 2, n - 14, q = 2 and p may be any integer. Such ethoxylated solvents not only serve as solubility enhancers in the solvent systems of the invention, but are also ink removers, and thus increase the ink removing ability of the solvent systems. Thus, the present invention also encompasses solvent systems comprising mixtures of a glycol ether or a glycol ether ester, a compound capable of enhancing the solubility of the glycol ether or the glycol ether ester (such as an ethoxylated solvent or a detergent), water, and, optionally, ammonia, particularly in solvent systems wherein the percent glycol ether or glycol ether ester present is near, at the limit or exceeds the limit of its solubility in water. Thus, these solvent systems of the invention include an amount of a solubility enhancing agent (such as an ethoxylated solvent) sufficient to solubilize the glycol ether or the glycol ether ester, e.g. about 4-10.5% by weight Akzo's Ethofat®. The addition of ammonia to the solvent systems of the invention, and, to a lesser extent, the addition of the ammonia-like additive aminoethanol (ethanolamine), has been shown to greatly enhance the imaged coating removing ability of the solvent systems. Thus, the glycol ether ester-based solvent systems of the invention also comprise mixtures of a glycol ether ester and aminoethanol; a glycol ether ester, aminoethanol and water; and a glycol ether ester, ammonia, and water. Preferable glycol ether ester-based solvent systems include: about 30-99% diethylene glycol butyl ether acetate and about 1 -70%) aminoethanol, more preferably about 33-95% diethylene glycol butyl ether acetate and about 5-67%) by weight aminoethanol; about 0-80% diethylene glycol butyl ether acetate, about 10- 90%) aminoethanol and about 10-90% water; about 0-50% diethylene glycol butyl ether acetate, about 0.1-4% ammonia, and about 50-99% water, more preferably about 3% diethylene glycol butyl ether acetate, about 0.12% ammonia, and about 97%) water, all by weight. Ammonia is introduced into the solvent systems of the invention using an aqueous ammonia solution having a preferable concentration of about 1-4%) by weight ammonia, more preferably about 3% by weight ammonia. When used alone, glycol ethers of Formula II such as ethylene glycol butyl ether exhibit excellent ink removing characteristics, but do not remove the imaged coating. However, when glycol ethers such as ethylene glycol butyl ether are combined with aminoethanol (ethanolamine) and water or ammonia and water, a solvent system results which will not only remove ink, but will also remove the imaged coating. Thus, the glycol ether-based solvent systems of the invention comprise mixtures of a glycol ether, aminoethanol and water; and mixtures of a glycol ether, ammonia, and water. Preferable glycol ether-based solvent systems include: about 10-40% ethylene glycol butyl ether, about 10-30%) aminoethanol, about 50-80%) water, more preferably about 10-40%> ethylene glycol butyl ether, about 10-20%) aminoethanol, about 50-70% water; about 10-40%) ethylene glycol butyl ether, about 0.1-4% ammonia, about 50-80% water. Ammonia is introduced into the solvent systems of the invention using an aqueous ammonia solution having a preferable concentration of about 1 -4% by weight ammonia, more preferably about 3% by weight ammonia. The benefits and advantages of the solvent systems of the invention will become further evident via presentation of the following non-limiting Examples. In the following Examples, solvent systems were tested on printing plates which had an accumulation of adsorbed ink from being run through a full run of prints. The imaged polymer coating to be removed was, on average, 2 microns thick. The solvent systems were formulated on a percent weight basis, using commercially available solvents. In each test, one drop of the solvent system was applied to the surface of the printing plate. The solvent system was allowed to remain on the printing plate for approximately 15 seconds before it was wiped off by hand, using a Baldwin® cloth. With respect to ink and imaged coating removal, the effectiveness of the solvent systems were graded on the following seven point scale: none, very slight, slight, fair, good, very good, excellent. Unless otherwise indicated, all the % data relate to weight percentage. EXAMPLE ONE Five solvents ~ diethylene glycol butyl ether acetate (solvent #1), ethylene glycol butyl ether (solvent #2), aminoethanol (ethanolamine) (solvent #3), N-Methylpyrrolidone (solvent #4), and Ammoniacal aqueous solutions (solvent #5) ~ were tested for their individual ability remove ink and imaged coating from the surface of the printing plates. Table 1 summarizes the results obtained when each of these solvents was used in isolation. Table 1 Ink Image No. Solvent Removal Removal 1 diethylene glycol butyl ether acetate excellent none 2 ethylene glycol butyl ether excellent none 3 aminoethanol excellent none 4 N-Methylpyrrolidone excellent excellent 5 Ammoniacal aqueous solutions very slight very slight As can be seen from Table 1 , although solvents 1 through 4 were excellent at the removal of ink from the printing plates, only solvent 4 (N- Methylpyrrolidone) was excellent at the removal of the imaged coating. Solvents 1 through 3 removed none of the imaged coating. While solvent 4 exhibited both excellent ink and imaged coating removing abilities, it is also an extremely strong solvent capable of dissolving a variety of highly polymerized materials, and is thus not of practical use in the commercial printing press industry where many printing press components are polymer-based. Solvent 5 removed both ink and imaged coating only very slightly. EXAMPLE TWO The effect of the presence of ammonia was studied in the diethylene glycol butyl ether acetate-based solvent systems of the invention. A three (3%) aqueous ammonia solution of ammonia in water was employed in the formulation of the solvent systems. Reported percent ammonia is the weight percentage of the ammonia present in the resultant solvent system. Table 2 summarizes of the results of this study. Table 2 % % % Ink Image solvent water ammonia Removal Removal 1% diethylene glycol butyl ether 99 slight none acetate 1 % diethylene glycol butyl ether -99 0.12 fair fair acetate 3%> diethylene glycol butyl ether 97 slight slight acetate 3%> diethylene glycol butyl ether -97 0.12 excellent excellent acetate 3% ethylene glycol butyl ether -97 0.12 slight slight 5.5% diethylene glycol butyl 84% very very good ether acetate and 10.5% Ethofat ® good 5.5% diethylene glycol butyl -84% 0.06 excellent excellent ether acetate and 10.5% Ethofat ® As can be seen from Table 2, the addition of ammonia improved the imaged coating removing abilities of the diethylene glycol butyl ether acetate-based solvent systems of the invention. The addition of about 0.12% ammonia to a solvent system comprising about 1% diethylene glycol butyl ether acetate and about 99%) water improved the imaged coating removing ability of the solvent system from none to fair. The addition of about 0.12% ammonia to a solvent system comprising about 3% diethylene glycol butyl ether acetate and about 97% water improved the imaged coating removing ability of the solvent system from slight to excellent. The addition of about 0.06% ammonia to a solvent system comprising about 5.5%) diethylene glycol butyl ether acetate, about 10.5%o Ethofat® and about 84%) water improved the imaged coating removing ability of the solvent system from very good to excellent. The addition of ammonia also improved the ink removing abilities of the diethylene glycol butyl ether acetate-based solvent systems of the invention. The addition of about 0.12%> ammonia to a solvent system comprising about 1% diethylene glycol butyl ether acetate and about 99% water improved the ink removing ability of the solvent system from slight to fair. The addition of about 0.12% ammonia to a solvent system comprising about 3% diethylene glycol butyl ether acetate and about 97% water improved the ink removing ability of the solvent system from slight to excellent. The addition of about 0.06%> ammonia to a solvent system comprising about 5.5% diethylene glycol butyl ether acetate, about 10.5% : Ethofat® and about 84%) water improved the ink removing ability of the solvent system from very good to excellent. It will be readily apparent to those skilled in the art that a number of modifications or changes may be made without departing from the spirit and scope of the present invention. Therefore, the invention is only to be limited by the claims. 5 0 5 0 5

Claims: What is claimed is: 1. A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether ester of the formula O I I CH 3 - (CH 2 ) m - O - ((CH 2 ) q - O) n - C - (CH 2 ) P - CH 3 wherein m, n, p and q are integers; and water. 2. The solvent system of claim 1 further comprising ammonia. 3. The solvent system of claim 1 further comprising aminoethanol. 4. The solvent system of claim 1 further comprising a solubility enhancer. 5. The solvent system of claim 2 further comprising a solubility enhancer. 6. The solvent system of claim 3 further comprising a solubility enhancer. 7. The solvent system of claim 1 wherein m is an integer from 0 to 7, n is an integer from 1 to 4, p is an integer from 0 to 7, and q is an integer from 2 to 3. 8. The solvent system of claim 1 wherein the glycol ether ester is selected from the group consisting of ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, and propylene glycol methyl ether acetate. 9. The solvent system of claim 4 wherein the solubility enhancer has the formula O I I CH 3 - (CH 2 ) P - C - O - ((CH 2 ) q - O) n - (CH 2 ) m - OH where m, n, p and q are integers. o 10. The solvent system of claim 5 wherein the solubility enhancer has the formula O 5 I ' D CH 3 - (CH 2 ) P - C - O - ((CH 2 ) q - O)„ - (CH 2 ) m - OH where m, n, p and q are integers. 11. The solvent system of claim 6 wherein the solubility enhancer has the 0 formula O I I CH 3 - (CH 2 ) P - C - O - ((CH 2 ) q - O)„ - (CH 2 ) m - OH where m, n, p and q are integers. 5 12. The solvent system of claim 9 wherein m is 2, n is 14, q is 2, and p is any integer. 0 13. The solvent system of claim 10 wherein m is 2, n is 14, q is 2, and p is any integer. 14. The solvent system of claim 11 wherein m is 2, n is 14, q is 2, and p is any -- integer. 15. A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether ester of the formula O 0 | | CH 3 - (CH 2 ) m - O - ((CH 2 ) q - O)„ - C - (CH 2 ) P - CH 3 wherein m, n, p and q are integers; and aminoethanol. 16. The solvent system of claim 15 wherein m is an integer from 0 to 7, n is an integer from 1 to 4, p is an integer from 0 to 7 and q is an integer from 2 to 3. 17. A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether of the formula CH 3 - (CH 2 ) m - O - ((CH 2 ) q - O) n - H wherein m, n and q are integers; water; and ammonia. 18. A solvent system for removing ink and imaged coating from printing plates comprising a glycol ether of the formula CH 3 - (CH 2 ) m - O - ((CH 2 ) q - O) n - H wherein m, n and q are integers; water; and aminoethanol. 19. The solvent system of claim 17 further comprising a solubility enhancer. 20. The solvent system of claim 18 further comprising a solubility enhancer. 21. The solvent system of claim 17 wherein m is an integer from 0 to 7, n is an integer from 1 to 4, and q is an integer from 2 to 3. 22. The solvent system of claim 18 wherein m is an integer from 0 to 7, n is an integer from 1 to 4, and q is an integer from 2 to 3. 23. The solvent system of claim 17 wherein the glycol ether is selected from the group consisting of ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol 2-ethyl-hexyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol butyl ether, and propylene glycol methyl ether. 24. The solvent system of claim 18 wherein the glycol ether is selected from the group consisting of ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol 2-ethyl-hexyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol butyl ether, and propylene glycol methyl ether. 25. The solvent system of claim 19 wherein the solubility enhancer has the formula O I I CH 3 - (CH 2 ) P - C - O - ((CH 2 ) q - O) n - (CH 2 ) m - OH where m, n, p and q are integers. 26. The solvent system of claim 20 wherein the solubility enhancer has the formula O I I CH 3 - (CH 2 ) P - C - O - ((CH 2 ) q - O) n - (CH 2 ) m - OH where m, n, p and q are integers. 27. The solvent system of claim 25 wherein m is 2, n is 14, q is 2 and p is any integer. 28. The solvent system of claim 26 wherein m is 2, n is 14, q is 2 and p is any integer. 29. A method of simultaneously removing adsorbed ink and imaged polymer coating from printing plates comprising the steps of: applying the solvent system of claim 1 to a used printing plate; and wiping the printing plate clean of adsorbed ink and imaged polymer coating. 0. A method of cleaning a used printing plate in-situ comprising the steps of: applying the solvent system of claim 1 to the plate while the plate is still in the printing press; and wiping the plate clean of adsorbed ink and imaged polymer coating.

Inventors: BEN-PORAT AVI, STEADLY HARVEY, WOJTOWICZ STEPHEN G, BEN-PORAT, AVI, STEADLY, HARVEY, WOJTOWICZ, STEPHEN, G.
Applicants: BALDWIN GRAPHIC PRODUCTS
Application year: 2000
Main classification: C11D3
IPC codes: B41N3, C09D10, C11D1, C11D7