CA1057105A - Developing and stripping of binder-containing presensitized coatings - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A composition, method and apparatus for removing a presensitized, photosensitive coating, containing a resin-ous binder, form a lithographic plate substrate, including;
contacting the coated substrate with a solution of a nonvola-tile glycol or glycol derivative, such as, high boiling gly-col, ether derivative thereof and liquid polymeric deriva-tives thereof, a surfactant, such as a non-ionic or anionic surfactant and, optionally, a high boiling solvent for such coating, such as an organic solvent, and/or an acid, for ex-ample, an organic acid or a mineral acid, at a temperature above ambient temperature, preferably about 60 to 110°C, and thereafter rinsing the plate with water, with or without brushing action, and preferably at a temperature above ambi-ent temperature, for example, 50 to 60°C.

Description

~057105 DEVELOPING AND STRIPPING OF BINDER-CONTAINING, PRESENSITIZED COATINGS
Background of the Invention This invention relates to presensitized litho-graphic plates. More specifically, the present invention relates to the removal of photosensitive, binder-containing coatings used in the manufacture of said plates.
In the present day art, many of the commercially available presensitized, offset lithographic plates consist of an aluminum plate or foil coated with a water-insoluble, light-sensitive compound, SUch as a diazo compound, contain-ed in a resinous binder.
In practical use, the light-sensitive coating is exposed to light under a master and the image is developed by utilizing a developer WhiCh removes the exposed, coated area, when light exposure is made through a negative master.
After development, in accordance with known pro-cedures, the printing image is prepared for receiving a greasy ink and the non-image areas are made hydrophilic by such known operations as rinsing and acid and salt fixing.
An imaged planographic printing plate prepared in such a manner will effectively maintain a good diferentiation between the hydrophilic metal surface and the oleophilic image, during offset printing.
Photosensitive, binder-containing plates came into existence as an advance over the practice of lacquer-ing plates to put a protective cap over the image (U. S.
Patent 3,136,637, Larson; U. S. Patent 3,679,419, Gillich).

,~

Current plates are, in effect, pre-lacquered, and uniform factory coating insures higher quality and more consistent, longer runs with less effort than was possible with previous post-lacquered plates.
The commercial developers used for development of the imagedphotosensitive coatings, particularly of those sensitive to light exposure through a negative master, are composed of solvents which soften and dissolve the unexposed resinous areas, so that these areas can be cleaned by mechani-cal and water rinsing action. Examples of such developers are given in the U. S. Patents just referred to above.
The metallic surface is thus exposed and then de-sensitized, following any of the known procedures to make these metallic surfaces more hydrophilic. The main disad-vantage in using present developers, espe~ially with current negative-working developers (using negative image masters), is that these developers are composed of volatile solvents such as alcohols, esters, and ethers. Usually, the volatil-ity of the solvent i9 9uch as to create formulation diffi-culties, necessitating adjustments in order to minimize flammability and combustion hazards. The use of volatile solvents also necessitates that room areas where the plate development is performed be well ventilated, to protect per-sonnel from toxic effects. Furthermore, the direct washing of such solvents into sanitary sewers creates environmental, ecological problems which require that such disposal in sew-erage systems be monitored to meet locally acceptable pollu-tion standards.

It is therefore an object of this invention to provide non-toxic developers of very low volatility so that the image development of the lithographic plates can be accomplished without hazard to human health and with a mini-mum deleterious effect on the environment.
Another object of this invention is to economi-cally reclaim photosensitive-coated aluminum or other metal-lic foils, which have been rejected for commercial use be-cause the coatings do not meet quality assurance, specifica-tion standards. The rejected metal foils can be in the form of webs or sheets.
Still another object of this invention is to use the principle described below to provide economical litha-graphic plate developing processors. The mechanism for such development is simple, since only a very brief (seconds) immersion of the imaged plate is required, followed by a spray rinse with water under pressure, with or without slight mechanical action.
~rief Summary of Invention In order to strip unwanted coating, a simple pro-cessing machine is used. The operation of the process is best understood by reference to Fig. 1, which shows the pro-cess utilized for stripping coating. This machine provides means for transporting a web or plate of coated metal through a chamber kept filled with the novel developer composition of the present invention, which is maintained at an elevated temperature. The coating comes in contact with the develop-ing solution, absorbs a portion of it and swells. Further, Aæ-743 `` 1057105 the adhesion of the coated layer to the carrier metal, which it is desired to strip, weakens materially (deadhesion~. Sur-plus developer is returned to the chamber by squeegee rollers, although other means may be used for this purpose. ~o more developer is needed than the amount which will be absorbed and swell the coating, there being no benefit in permitting "drag-out". The total dwell time may be measured in seconds.
After the web has passed the squeegee, it is led to a zone, in which it is subjected to the action of a high pressure water spray (with or without brushing action), to flush off the swelled coating. By simple filtration, the rinse water may be made reusable or the water slurry of coating particles may be disposed of in the drain.
When it is desired to develop an exposed plate, the apparatus of Fig. 2 will be found more useful. This apparatus provides means for transporting an exposed, cut plate through the developing bath, squeegee rollers, and, finally, a high intensity water spray, with or without brushing action.
The developer in the chamber consists principally of:
a. a high boiling glycol or glycol ether, or ethoxylated or propoxylated alcohol.
b. a non-ionic or anionic surfactant.
c. optionally, a high boiling solvent, and d. optionally, a small amount of acid.
Brief Description of the Drawings Figure 1 of the drawings is a perspective view of apparatus for stripping a presensitized coating from a web of lithographic plate substrate,and ~057105 AZ-743 Figure 2 is a perspective view of apparatus for developing, an exposed, presensitized lithographic plate.
Detailed Description of the Invention For stripplng coating from a presensitized web of lithographic substrate, the device of Fig. 1 is employed.
In Fig. 1, a metal roll of coated substrate 1 is disposed on an unwind stand 2. Guide rollers 3 and 4 lead the web of coated metal into developing or stripping chamber 5. Follow-ing immersion in the developing chamber, the web passes through a set of squeegee rollers 6 which squeegee off excess decoating solution and return the surplus to the developing chamber 5. The web is then led into rinse section 11 of the apparatus. Here, a set of high pressure sprays 7, one on each side of the web, impinge upon it to remove the coating (if on both sides). If only one side is coated, one spray may be dispensed with but it will normally remove residual developer from the uncoated side. Tha brushes 8, and addi-tional sprays 9, are optional and may be used when the action of sprays 7 i9 not complete. The axe~ of guide rollers 10 are tilted away from the horizontal to permit rapid flow of rinse fluid from the web. Following the final rinse, the web passes through squeegee rollers 12 and drying zone 13, and is then recoiled at rewind station 14.
For developing or stripping coated, cut sheets of lithographic substrate, on a continuous basis, the apparatus of Fig. 2 is employed. Inasmuch as a continuous web of metal is not available to be pulled through the various stations of the apparatus, driven pinch rollers, at suitable intervals, are relied on to grip the leading edge of the sheet and keep it in continuous motion until it leaves the exit end of the machine. The cut sheet 15 is carried by rollers 16, 17 and 18 through developing chamber 19. Upon leaving chamber 19, the sheet passes through squeegee rollers 20 and then through the pressure spray rinse means 21. As before, optional brush-es 22 and a second spray rinse 23 may be used. Pinch rollers 24 pull the plate through and propel it into drying zone 25.
Pinch rollers 26 pull the plate out of the machine.
A simple device for developing or stripping cut sh-eets consists of a heated tank, containing suitable developer, in which the plates are immersed. After removal from the tank, they are spray rinsed.
The compositions of stripper or developer consist, as noted above, of high boiling glycol, surfactant, and op-tionally, a high boiling water miscible solvent and/or a small amount of acid.
GlYcol The glycol portion can be as high as 95% of the total compo9ition with the other ingredient9 forming the re-mainder of the composition. As examples of the type of gly-cols which can be used in this invention, it has been found that ethylene glycol is satisfactory as well as the ethylene oxide condensates of ethylene glycol. Such glycols as die-thylene glycol, triethylene glycol and the higher ethoxylated and propoxylated polymers can be used. I prefer to select those glycols of a non-toxic nature, such as diethylene gly-col. of course, propylene glycol ~an be used as well as its ~057105 derivatives. In the selection of the high boiling component, the controlling factors o~ selection are non-toxicity and cost of materials.
Surfactants Non-ionics: Ethylene oxide condensates of:
Trade Name Manufacturer Nonylphenol "Igapal CO" GAF Corporation "Triton" . Rohm & Haas Iso-octyl cresols "Triton X-100" Rohm & Haas "Igepal CA" GAF Corporation Tridecyl alcohol "Emulphogenes" GAF Corporation Sorbitol "Spans, Tweens" Atlas Sec. Alcohols "Tergitols" UCC
Fatty acid "Emulphors" GAF Corporation Alkylamides "Ethomides" Armour Alkylamines "Ethomeens" Armour Modified linear aliphatic polyeth~r "Antarox BL 240" GAF Corporation Phosphate esters o~
above: "Gafac" GAF Corporation "Tryfac" Trylon Chemical9 Anionics:
Fatty acid taurates "Igepon T" GAF Corporation Alkyl naphthalene sulfonates "Nekal BX, A" GAF Corporation Alkyl benzene sulfonates "Nacconol" Allied Chemical Corporation ~ci~
Citric Phosphoric Glycollic Nitric Acetic Other mineral acids Other organic acids Solvents Gamma-butyrolactone N-methyl pyrrolidone Dimethyl formamide Ethylene carbonate The surfactants, acids and solvents enumerated above are merely examples, not intended to restrict the scope of the invention.
The compositions which are useful, according to the present invention, include from 95% glycol to as low as 25% glycol, with the balance surfactant. It is preferred, however, to use compositions in which the glycol ranges from 95% to 85% of the total composition, with the balance surfac-tant. The optional solvent, when added, may constitute up to 60% of the composition. The optional acid similarly may be added in amounts up to 10% of the composition.
The principle described in this invention has been found particularly applicable to commercial, negative-working, presensitized, lithographic plates manufactured by such com-panies as Azoplate - Division of American Hoechst Corporation, DuPont, Polychrome, Eastman Kodak, and Minnesota Mining and Manufacturing Company.
The boiling point of the glycol and the temperature of treatment with the glycol-containing solution are interrela-ted to the extent that the boiling point of the glycol should be above the treatment temperature. The boiling point of the high boiling solvent should likewise be above the treatment temperature.

The treatment temperatures, with glycol-containing solution, which are most effective depend upon whether stripping or develop-ing operations are being conducted, upon whether the treating solution contains solvent, upon the temperature employed in the rinsing step and upon the nature and thickness of the coating.
Considering all these factors, the treatment temperature may vary between about 60 and 110 C. The following discussion and examples illustrate these relatlonships as they affect the treating temperature .
When decoating ENCO N-50 plates (products of Azo-plate - Division of American Hoechst Corporation), with or without added solvent, a temperature ranglng from approxlmately 65 C to 95 C ls suitable . Below the lower temperature the coating is not sufficiently removed after rinsing. Above the upper temperature, the coating is removed, but begins to come off in the treatment solution, which results ln premature depletlon of the treatlng solu-tlon. The preferred temperature range, for the most effectlve cleanlng in most cases, ls approxlmately 80 C to 100 C .
When uslng the treatlng solutlon as a developer tto remove unwanted non-lmage areas) for Enco N-50 plates, the addltlon of solvent ls preferable. If 25% of butyrolactone ls added, a tem-perature range from approximately 75 C to 95 C ls sultable, but best results are obtained at the upper end of this range. Agaln, hlgher temperatures provlde good development, but are less economl-cal because removal of non-lmage areas occurs ln the treatlng solutlon, resultlng in lts premature depletlon. Thls composltlon w111 not satlsfactorily develop Enco N-100 and N-200 plates (products of Azoplate - Dlvlsion of American Hoechst ~L057105 AZ-743 Corporation) which have thicker coatings and progressively longer press lives than ENCO N-50 plates. The addition of butyrolactone to the level of about 6~/o is necessary to accomplish this purpose, (although the 25%
level is sufficient to strip Enco N-100 and N-200 plates). When developing with the 6~/o butyrolactone-containing solution, the Enco N-50 plate can be developed at temperatures ranging from approximately 65C to 85C with the upper end of the range pre-ferred. Enco N-100 and N-200 plates can be developed within a temperature range of approximately 85C to 105C.
In general, it has been found that elevation of the temperature or an increase of solvent concentration, with conse-quent lowering of the glycol level, for a given operation with a given plate, shortens the time required for treatment. The water wash may be carried out at ambient temperature but is also preferably above ambient temperature. However, it need not be as high as the treating temperature and is preferably above about 50C and in the range of about 50 to 60C.
It is further evident that, in view of the numerous factors of composition and proce9s alr~ady discussed and the following examples, together with a correct and proper under-standing of them, with ordinary skill in their application, a very wide range of commercially available presensitized litho-graphic plates may be successfully treated and are within the scope of this invention.
The following examples serve to illustrate the principle of this invention:
ExamPle 1 A solution, of the following composition:
Diethylene Glycol 57%

~B~ -lo-~057105 AZ 743 Triton X-100 10%
Gamma Butyrolactone 25%
Phosphoric Acid (85%) 8%, was heated to 70 - 80 C and a negative-working, presensitized plate was subjected to a dwell time in the solution of approximately 30 seconds, then removed from the solution, squeegeed and sprayed for about 3 minutes with water at 50 - 60 C, with and without slight brushing action .
This solution was found effective for Enco N -5 0, Kodak LN-M , and Kodak LN-L presensitized and exposed sub-strates. Full development of the image was obtained, with the background satisfactorlly desensltized.
Example 2 Following the procedure of Example 1, a solutlon of:
Diethylene Gl,y~ol 85%
Triton X-100 5%
Phosphoric Acid (85%) 10%
was used to completely decoat an exposed Enco N-50 lithographlc plate .
Example 3 Similarly, a compositlon of:
Dlethylene Glycol50%
~ .
Antarox BL 240 45%
Phosphorlc Ac1d (85%) 5%
completely decoated an unexposed Enco N-50 negative-working, presensitized lithographic plate, following the procedure of Example 1 above.
Example 4 In a composition of:

...~ .i~, ~e~ ' ~ 11 ~

Diethylene Glycol 45%
Igepon T-77 7%
Phosphoric Acid (85%) 8%
Enco N-50 , Lydel I , Lydel II--', and Polychrome LS II
presensitized substrates were decoated, at 70 - 90C, after a dwell time of approximately 30 seconds and washing, while brush-ing, with a spray of water at 50 - 60 C.
Examples_5 to 8 An unexposed Enco N-5 0 plate was divided into four por-tions and immersed in a solution composed of:
Diethylene glycol 9 0%
Triton X-100 10%
for varying lengths of time at progressively higher temperatures to determine stripping actlvity. Following immersion, a water rlnse was applied for 60 seconds at 30 psi and at 55 - 60 C.
Example No. Solution Tem. C Dwell Time, Sec. Strlppinç~
80 30 - 60 none 6 90 30 complete 7 100 30 complete 8 110 30 complete, with coating dissolv-ed before rlnsing Example 9 Following the procedure of Example 1 above, a compositlon of:
Dlethylene Glycol 82%
Igepal DM 970 10%
Phosphoric Acld 8%

! ~ ~
,J1 ~05710~ AZ-743 was used to decoat an Enco N-50 lithographic plate after a 30 second dwell time at 70-90C and a water (50-60C) spray, with slight brushing action.
The above experiments serve to illustrate the applicability of the novel principle used for the develop-ment of imaged presensitized lithographic plates.
As shown in Examples 5 to 8, the same principle can be applied to the decoating of metallic webs or plates which, during their production, are found unacceptable for market release because standards of quality are not met.
This method permits the reclaiming of such substrates which can be made into acceptable products by further processing Thus, economies can be realized.
Example 10 A solution of the composition of Example 1 was heated to 90C and an Enco ~-100 plate was subjected to a dwell time of 30 seconds, removed from the solution, squee-geed and then sprayed with water for about one minute at 30 psi and 55C. The coating survived the immersion in the treatment bath but was completely flushed off in the rinse.
When the temperature was lowered to 70C and the dwell time increased to 60 seconds, the coating was only incompletely removed. By raising the temperature to ilOC, the coating was removed in the treatment bath, without need for rinse;
thus a temperature of 110C is too high, as it results in undue contamination of the treatment bath.
Example 11 A solution of the composition:

Diethylene Glycol 22%
Triton X-100 l~/o H3Po4 (85%) 8/~
Gamma Butyrolactone 6~/o was heated to 90C, and imagewise exposed Enco N-100 and Enco ~-200 plates were immersed in it for 30 seconds, squeegeed af-ter removal and rinsed with water for 120 seconds at 55C and 30 psi with slight brushing action. Both plates were found to be properly developed. In contrast, use of the solution of Example 10 at temperatures ranging from 60C to 110C was unsat-isfactory, due to incomplete development up to 100C and re-moval of imageareas at 110C.
ExamPle 12 Three solutions of the formula of Example 1 were r made up, in which ethylene glycol, hexylene glycol and poly-ethylene glycol (average molecular weight 380-420), respect-ively, replaced diethylene glycol. Each of these solutions was used to decoat Enco N-50 and N-100 plates by immersion for 30 seconds at 80C followed by squeegeeing and rinsing with water at 60C. for two to three minutes. The samples were evaluated for completeness of decoating and the results are summarized in the following table:
EncoEthylene Hexylene Polyethylene*
PlateGlYCol Glycol GlY
N-50 Good Good Good N-100Incomplete Good Good *Decoating temperature 90C.
Example 13 The solutions of Example 12 were used to develop imagewise exposed Enco ~-50, N-100, and N-200 plates at 80C
for 30 seconds followed by squeegeeing and rinsing as in Example 12. The samples were evaluated for completeness of development and the results are sùmmarized in the following table:

Enco Ethylene Hexylene Polyethylene Plate Glycol GlYcol Glycol ~~50 Good Incomplete Undeveloped N-100 Good Good at 95C Good at 95C
for 60 seconds. for 60 seconds.
Some coating Some coating attack. attack.
N-200 Good at Incomplete Incomplete (30 sec.) In the above examples, there was no image area attack, except as noted.
The above cited experiments also illustrate the non-polluting, non-toxic and non-hazard composition of the developer media used.
It will be obvious to those skilled in the art that many modifications may be made within the ~cope o~
the present invention without departing from the spirit thereof and the invention includes all such modifications.

Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composition for removing a presensitized, photosensitive coating, containing a resinous binder, from a lithographic plate substrate comprising a surfactant and a nonvolatile glycol selected from the group consisting of glycols, alkoxylated glycol derivatives and mixtures thereof, having a boiling point above ambient tempera-ture, said composition containing from 95% to 25% glycol.

2. A composition in accordance with claim 1 wherein the non-volatile glycol is selected from the group consisting of glycols, ether derivatives of glycols, liquid, polymeric alkoxylated deriva-tives of glycols and mixtures thereof.

3. A composition in accordance with claim 1 wherein the non-volatile glycol is selected from the group consisting of ethylene glycols, alkoxylated ethylene glycol derivatives and mixtures thereof.

4. A composition in accordance with claim 1 wherein the non-volatile glycol is selected from the group consisting of propylene glycols, alkoxylated propylene glycol derivatives and mixtures thereof.

5. A composition in accordance with claim 1 wherein the sur-factant is selected from the group consisting of nonionic surfac-tants, anionic surfactants and mixtures thereof.

6. A composition in accordance with claim 1 which additionally includes a high boiling solvent for the coating.

7. A composition in accordance with claim 6 wherein the high boiling solvent is an organic solvent.

8. A composition in accordance with claim 6 which additionally includes an acid.

9. A composition in accordance with claim 1 which additionally includes an acid.

10. A method for removing a presensitized, photosensitive coat-ing, containing a resinous binder, from a lithographic plate sub-strate, comprising; immersing said substrate in a solution of a surfactant and a nonvolatile glycol selected from the group con-sisting of glycols, alkoxylated glycol derivatives and mixtures thereof, having a boiling point above ambient temperature, said solution containing from 95% to 25% glycol.

11. A method in accordance with claim 10 wherein the substrate is completely decoated.

12. A method in accordance with claim 10 wherein a plate of the substrate is exposed imagewise, through a master, prior to immersing the same in the solution and the imaged plate is developed.

13. A method in accordance with claim 12 wherein the solution additionally contains a high boiling solvent for the coating.

14. A method in accordance with claim 10 wherein the excess solution is removed by squeegeeing.

15. A method in accordance with claim 10 wherein the substrate is rinsed with a pressurized spray of water.

16. A method in accordance with claim 15 wherein the water is at an elevated temperature above ambient temperature.

17. A method in accordance with claim 10 wherein the water is at an elevated temperature above ambient temperature.

18. A method in accordance with claim 10 wherein the substrate is subjected to brushing action during the rinsing step.