Abstract:
A developer composition for positive working lithographic printing plates and photoresists comprising an aqueous alkaline solution with a non-ionic surfactant.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to developer compositions for lithographic printing plates. More particularly, the invention relates to developers for printing plates of the so-called positive type which are sensitized with o-quinone diazide photosensitive materials. 
     It is known that the diazo groups of o-quinone diazides are removed by irradiation to actinic light, and that the compound itself changes to a compound with a carboxyl group. When the photosensitive coating containing o-quinone diazide is exposed to the light and developed with an alkaline developer, the part exposed to light is removed while the part not exposed to light remains as the image. Because of this characteristic, it is known as a positive-type photosensitive component for printing plates or for photoresist compositions. Compositions of o-quinone diazide are usually mixed with alkali-soluble resins having economical and practical advantages in such uses. Mixtures of phenol formaldehyde resins, or cresol formaldehyde resins, are generally used as the alkali soluble resins. Trisodium phosphate, sodium hydroxide, or sodium silicate alone, or their mixed aqueous solutions are used as a developer for sensitive films containing these o-quinone diazides. However, aqueous solutions of these developers tend to have detrimental etching effects on such printing plate substrate metals as aluminum. Also, the results of development vary considerably. In extreme cases, even a slight excess of developing time causes failure in image formation. If alkalinity is decreased, development speed decreases unacceptably. If alkalinity is increased, the aluminum or aluminum oxide substrate etches away, thus undesirably undermining and removing image as well as non-image areas. 
     Japanese Pat. No. 75-51324 suggests one method of attacking this problem. It teaches the addition of both an anionic and a dipolar surfactant to the aqueous alkaline developer solution. 
     Surfactants have also been used in other types of developers. U.S. Pat. No. 3,891,438 teaches the development of negative working printing plates sensitized by diazonium salts with aqueous solutions of organo-lithium salts to which anionic, cationic or non-ionic surfactants have been added. 
     SUMMARY OF THE INVENTION 
     The present invention provides a developer solution for positive working photographic elements such as lithographic printing plates and photoresists which comprises an aqueous solution of hydroxide ions such as from an alkali and a compatible non-ionic surfactant. 
     This composition has been determined to substantially preserve the development speed as compared to an element developed with the alkali alone in solution and yet effectively, substantially acts as a barrier to the etching action of the aluminum. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As hereinbefore mentioned the developer of the present invention comprises an aqueous solution of an alkali and a compatible non-ionic surfactant. 
     Any composition capable of releasing hydroxide ions in solution is a suitable alkali useful for the practice of this invention. These include compounds which directly ionize in water or salts which generate hydroxide ions in water. 
     Non-limiting examples of alkalis useful for the practice of the present invention include sodium silicate, sodium metasilicate, trisodium phosphate, monosodium phosphate and sodium hydroxide. 
     Non-limiting examples of non-ionic surfactants useful for the practice of the present invention are those which are compatible with the alkali solution. That is, those which do not cause a precipitate when mixed with the aqueous alkali solution. Examples include ethoxylated phenols, tetramethyl decynediol, ethoxylated tetramethyl decynediol, ethoxylated aliphatic alcohols, alkylene oxide block copolymers, fatty acid amides, and ethoxylated diols. Especially preferred surfactants include Triton X-100 available from Rohm &amp; Haas of Philadelphia, Pa; Tergitol Min Foam 1x available from Union Carbide Corporation; Antarox BL-330 available from GAF and Amidox C-5 available from Stepan Chemical Co. of Northfield, Ill. 
     Other preferred surfactants are the Surfynols available from Air Products and Chemicals, Inc. of Allentown, Pa. These generally have the formula ##STR1## where R=methyl 
     R&#39;=isobutyl 
     R&#34;=OH or (--O--CH 2  --CH 2 ) x  --OH 
     These surfactants are believed to act as a barrier to aluminum etching while maintaining the speed of the aqueous alkaline developer. 
     Commonly, salts are used in addition to the source of hydroxide ions. These are capable of forming hydrophilic water-insoluble coatings on the metal, produce alkaline-reacting systems themselves in water or help buffer the system. These may be present in the range of 0.2-10% by weight with the preferred salt content in the range of 0.5-5% by weight. 
     Representative of these salts are the following in aqueous alkaline solution: 
     salts of hydrofluosilicic acid M I   2  (SiF 6 ) and M II  (SiF 6 ) 
     salts of hydrofluotitanic acid M II  (TiF 6 ) and M III  (TiF 6 ) 
     salts of hydrofluostannic acid M I  (SnF 6 ) 
     salts of hydrofluoboric acid M I  (BF 6 ) 
     salts of orthosilicic acid or metasilicic acid M I  O.xSiO 2 .xH 2  O 
     salts of orthotitanic acid 2M I   2  O.TiO 2  and 
     salts of stannic acid M I  (Sn(OH) 6 ) 
     wherein M is a metal ion. These salts are more fully described in U.S. Pat. No. 3,110,596 which is incorporated herein by reference. 
     In the preferred embodiment, the alkali may be present in the developer in an amount of from about 0.2 to about 12 parts by weight; more preferably 0.2 to about 10; most preferably 3 to about 8. 
     In the preferred embodiment, the non-ionic surfactant may be present in the developer of the present invention in an amount of from about 0.1% to about 10% by weight; more preferably 0.5 to 3% by weight of the developer. 
     The pH of the developers of this invention generally range from about above 7.0 to about 14, more preferably about 11 to about 13. 
     Preferred developer formulations comprise the Triton X-100 surfactant in any of the following developers: 
     
         ______________________________________                       Weight Percent1.   Soft Water             91.545Sodium Metasilicate-5 H.sub.2 O                       3.988Trisodium Phosphate-12 H.sub.2 O                       3.423Monosodium Phosphate   0.337Sodium Hydroxide (Reagent Grade)                       0.707                       100.000                       Weight Percent2.   Soft Water             92.196Sodium Metasilicate-5 H.sub.2 O                       4.016Trisodium Phosphate-12 H.sub.2 O                       3.448Monosodium Phosphate   0.340                       100.0003.   7.5 g. of tertiary sodium orthophosphate-12H.sub.23.5 g. of sodium metasilicate2.0 g. of primary sodium orthophosphate-1H.sub.2 O1.0 g. of water-soluble methyl cellulose of mediumviscosity985.0 g. of distilled waterThe pH value of the solution is 11.14.   4.5 g. of sodium metasilicate0.9 g. of sodium hexametaphosphate994.6 g. of distilled waterThe pH value of the solution is 11.355.   56.0 g. of sodium metasilicate10.0 g. of sodium hexametaphosphate934.0 g. of distilled waterThe pH value of the solution is 11.656.   58.0 gms. of sodium metasilicate18.0 gms. of tertiary sodium orthophosphate-12H.sub.2 O4.0 gms. of primary sodium orthophosphate920.0 gms of distilled waterThe pH value of the solution is 11.8                       Weight Percent7.   Distilled water        95.9%Sodium metasilicate    2.0Monosodium phosphate   0.8Sodium hydroxide       0.88.   Distilled water        95.835%Sodium metasilicate    1.912Monosodium phosphate   0.765Sodium hydroxide       1.149______________________________________ 
    
     The following non-limiting examples demonstrate the invention. 
    
    
     EXAMPLE 1 
     5×7&#34; samples of P-150 (positive printing plates available from the Azoplate Division of American Hoechst Corporation, Branchburg, N.J.) are exposed in a vacuum frame for a fixed number of time units (30 secs. e.g.). In a small tray ˜750 ml. of positive developer is used to develop a plate. The tray is rocked on a rocker attached to a timer. The developer composition may be as follows: 
     
         ______________________________________Water             92.196%Sodium metasilicate             4.016%trisodium phosphate             3.448%monosodium phosphate             0.340%             100.000%______________________________________ 
    
     Development is fixed at 15 minutes. The plate is rinsed and blotted dry. This is a control sample. Sample plates are then successively developed in a similar fashion with 7.5 ml. (1%) of the surfactant under study. plates are rinsed and dried and compared to the control. Table 1 demonstrates the results effected with several surfactant types. 
     Comparison is based on (1) Stauffer 21 step scale (a higher clear step indicates more aggressive development. (2) Half tone dot sharpening (reduction) or loss. (3) Attack of non-image area oxide as well as the intermediate steps of the Stauffer scale, as evidenced by formation of a white powdery oxide which can be wiped off readily. 
     
                                           TABLE 1__________________________________________________________________________  Manu-       Stouffer                    Dot shar-                         oxide                             imageSurfactant  facturer        Type  step wedge                    pening                         attack                             attack__________________________________________________________________________Surfynol 440  Air Pro-        Non-ionic              clear 3                    none none                             slight  ducts &amp;     ghost 6  ChemicalsSurfynol 465 &#34;     clear 4                    none none                             slight              ghost 7Surfynol 485 &#34;     clear 4                    none none                             slight              ghost 7Triton X-100 &#34;     clear 3                    none none                             none              ghost 6Gafac BI-750  GAF   anionic              clear 6                    severe                         severe                             moderate              ghost 10Control  none  N/A   clear 8                    severe                         severe                             moderate              ghost 11__________________________________________________________________________ 
    
     EXAMPLE 2 
     The procedure of Example 1 may be repeated using the following developer: 
     
         ______________________________________Water             91.545%Sodium metasilicate             3.988%trisodium phosphate             3.423%monosodium phosphate             0.337%sodium hydroxide  0.707%             100.000%______________________________________ 
    
     Since this is a more aggressive developer, the samples are rock developed for only 7 mins. All other aspects of the procedure were similar. The following results are noticed when the indicated surfactant is added at 1% by weight. 
     
                                           TABLE 2__________________________________________________________________________  Manu-      Stouffer                   Dot shar-                        oxide                            imageSurfactant  facturer        Type step wedge                   pening                        attack                            attack__________________________________________________________________________None control  N/A   --   plate almost devoid of coating with             severe attack of aluminum surface.Aerosol 05  American        anionic             clear 9                   moderate                        yes yes  Cyanamid   ghost 13Triton X-100  Air Pro-        non-ionic             clear 5                   slight                        slight                            slight  ducts &amp;    ghost 9  Chem.Gafac RE-610  GAF   anionic             clear 9                   severe                        severe                            moderate             ghost 10Aerosol C-61  American        cationic             almost complete loss of image &amp; severe  Cyanamid   oxide attack__________________________________________________________________________