US3481738A - Presensitized photoengraving plate and method of making same - Google Patents

Description

United States Patent PRESENSITIZED PHOTOENGRAVING PLATE AND METHOD OF MAKING SAME Robert L. Eissler, Peoria, Ill., assignor to Ball Brothers Company Incorporated, Mnncie, Ind., a corporation of Indiana No Drawing. Filed Sept. 21, 1966, Ser. No. 580,898

Int. Cl. G03c 5/00, 1/94, N70 US. Cl. 96-86 9 Claims ABSTRACT OF THE DISCLOSURE A method of preparing a presensitized photoengraving plate by applying to a zinc base a mixture of a photosensitive polymer and a thermosetting resin, examples of the former including the cinnamoyl groups and the lat-' ter melamine-formaldehyde and urea-formaldehyde, and heating the coated plate to a temperature which hardens the coating but does not cross-link the photosensitive polymer, and photoengraving plates so prepared.

This invention relates to a novel presensitized photoengraving plate and to a new and improved method for producing such a plate.

In recent years, the powderless etching of photoengraving plates has become widespread. In powderless etching, an etching bath containing nitric acid in combination with surface active agents of various types is commonly employed. Since powderless etching methods have been widely accepted, it has been proposed to use presensitized plates to free the printing shop from the task of applying the photosensitive resin to a metal plate. However, the use of presensitized photoengraving plates has not been completely successful.

Attempts have been made to produce presensitized engraving plates which will perform successfully with powderless etching baths, but heretofore none of the plates have been completely successful. Some of the plates proposed were not successful because they did not have sufficiently long storage life while with other plates it has been necessary to change the conventional bath formulation in order to achieve an etch. Thus, none of the previous attempts to produce a presensitized photoengraving plate which can be used with commercial bath formulations has been successful.

The presensitized photoengraving plate of the present invention overcomes many of the deficiencies of previously employed presensitized photoengraving plates and also provides additional advantages and benefits. For example, the presensitized photoengraving plate of the invention has a long storage life and press life and produces plates with sharp images. Also, the method for producing the presensitized plate of the invention is simple and relatively low in cost.

The presensitized photoengraving plate of the present invention comprises a zinc base plate and a substantially uniform photosensitive coating on a surface thereof comprising a melamine-formaldehyde or urea-formaldehyde thermosetting resin and a photosensitive vinyl polymer. The photoengraving plate of the invention advantageously is prepared by graining a surface of a zinc base plate, applying to the grained surface a mixture comprising the thermosetting resin and a photosensitive vinyl polymer, and heating the coated plate to an elevated temperature.

The base plate employed in the preparation of the presensitized photoengraving plate may be a conventional zinc or zinc alloy engraving plate and advantageously has a thickness of between about 0.03 and 0.3 inch.

To provide a proper surface for the photosensitive coating, it is important that the surface of the plate be 'ice properly prepared. Advantageously, the plate is grained to provide a roughened surface and to remove residual dirt and oils from the surface. Preferably, the graining is accomplished by employing an acid solution and particularly in combination with scrubbing such as the use of a rotating brush. Suitable acid solutions for use in the chemical graining include solutions of acids such as acetic acid, hydrochloric, nitric, and chromic acid. Advantageously, the acid solution is made up of mixtures of the above acids. Preferably, the chemical graining is preceded by a mechanical graining step using a brush and an abrassive slurry.

The photosensitive coating applied to the plate as set forth above, comprises a mixture of the specified thermosetting or cross-linking resins and a photo sensitive vinyl polymer. The thermosetting resin is a melamine-formaldehyde resin or urea-formaldehyde resin.

The photosensitive polymer employed is a water-insoluble vinyl polymer and, advantageously, is a substituted vinyl polymer. Preferably, the polymer contains arylkenoxy groups such as cinnamoyl groups, for example, cinnamic acid esters of polyvinyl alcohol, ar-vinyl-benzalacetophenone polymers, ar-vinylcinnamalacetophenone polymers, hydroxyalkyl cellulose cinnamates, etc., such as disclosed in US. Patent No. 2,756,143.

Advantageously, the specified thermosetting resins and the photosensitive polymer are dissolved in an organic solvent. Preferably a small amount of a dispersing agent or surface-active agent is also added to the solution. Examples of suitable solvents for the resin and polymer include methyl Cellosolve acetate, benzene, methylene chloride, toluene, etc.

The proportions of resin and polymer in the solution are advantageously controlled to form a solution of a viscosity which permits spraying of the solution onto the plate. Advantageously, the total resin and polymer comprises between about 4% and 20% by weight of the solution and preferably between about 6%. and 12%. The thermosetting resin advantageously comprises between about 16% and 33% by Weight of the total of the resinpol ymer mixture and preferably between about 20% and 26 0.

Following the application of the solution, the coating is advantageously allowed to level for a short interval such as one minute or so and then permitted to air dry for a few additional minutes. Thereafter, the plate is heated, such as, for example, in an oven to an elevated temperature for several minutes, e.g., about 1 to 5 minutes. The temperature during the heating step is selected to partially harden the photosensitive polymer but to avoid crosslinking of the thermosetting resin. Advantageously, the temperature is between about and 250 F., and preferably between about and 225 F., although the exact temperature will depend to some extent upon the duration of the heating period and the particular thermosetting resin used. The thickness of the final coating is relatively thin and comprises between about 0.002 and 0.007 gram of solids applied per square inch of surface. If desired, the coating may be dyed.

The finished plate can be subjected to conventional exposure and developing treatments prior to the etching process. After the plate has been exposed, developed and cleaned with aplate cleaner, the plate again is heated to an elevated temperature, preferably somewhat above the temperature of the previous heating step to cross-link the thermosetting resin. Advantageously, a heating period of between about 1 and 4 minutes at a temperature of between about 250 and 400 F. provides sufiicient crosslinking of the thermosetting resin. Following the heating or burn-in step, the plate is descummed and etched according to conventional powderless etching procedures.

Advantageously, the etching bath is a nitric acid solution containing one or more surface-active agents. The resulting plates show improvements in the sharpness of the image and rate of etching as compared with conventional plates and show good dye retention after etching. Also, the shoulder angle is satisfactory. In addition, the length of the runs and storage life between runs are of acceptable length.

The following examples illustrate specific embodiments of the invention and are not intended to restrict or limit the scope of the invention. In the examples, parts and percentages are by weight.

EXAMPLE I A zinc plate of a size of about 18 inches by 24 inches and a thickness of about 0.064 inch was processed as follows: The plate was first cleaned by brushing the surface of the plate with an aqueous slurry of pumice. This cleaning both roughened the surface of the plate and removed residual dirt and oils. The cleaned surface was rinsed with water and given three passes through a single brush machine. The roughened surface of the plate was sprayed at a point immediately preceding the contact of the brush with the plate surface, with a soluiton containing by volume 20 parts of glacial acetic acid, 1 part of concentrated hydrochloric acid, 1 part of concentrated nitric acid, 240 parts of water, to which was added approximately 20 grams of chromic acid (technical grade) for each liter of the above solution.

Following each pass through the brush machine, the plate surface was rinsed with water. After the third pass, the plate was dried prior to the application of the photosensitive coating.

The photosensitive coating solution was made by mixing 4 parts of a 50% solution of melamine-formaldehyde resin in butanol and 20 parts of a polyvinyl cinnamate resist lacquer sold under the name of Kodak Photo Lacquer by Eastman Kodak Company. The melamine-formaldehyde resin used is sold by Rohm and Haas Company as UFORMITE MM57. The resulting mixture was diluted to a sprayable viscosity of about 50 centipoises with about 75 parts of methyl Cello solve acetate and 0.3 part of a dispersing agent sold under the name Nuosperse 657 by Nuodex Corp. The resulting solution was filtered and then sprayed onto the grained surface of the zinc plate. The application of the solution was sufficient to provide about 0.5 gram of solids per square foot of surface. Following application of the solution to the surface, about four minutes were allowed for the coating to level and air dry. The resulting plate was then dyed with KPR dyes, a commercial dyestutf vended by Eastman Kodak Co., and placed in an oven maintained at a temperature of about 230 F. After about four minutes, the plate was removed and inspected.

The resulting plate was exposed using a 2% minutes exposure on a Nu Arc platemaker and then developed for one minute in a vapor developer. In the developer, liquid trichloroethylene is vaporized and rises over the surface of the plate until it contacts cooling coils above the plate where the vapor condenses and washes back down over the surface of the plate into the tank of the developer. The combination of vapor and liquid quickly removes the unexposed photosensitive coating from the plate.

After being developed, the plate was cleaned with a plate cleaner solution of xylene-heptyl alcohol and then burned in for about one minute at 400 F. using an immersion burner. Following the burn-in step, the plate was descummed with a mixture of nitric and sulfuric acids and then etched in a bath containing 13 /2 parts by volume of 42 Baume nitric acid, 3.6 parts by volume of a commercial engraving mix and sufficient water to produce a total of 100 parts by volume. The commercial engraving mix included 20.5 parts of sulfated castor oil with specifications including 5.8 to 6.5% combined S0 12 to 21% free fatty acid calculated as oleic acid, 1.0 to 2.3% alkalinity calculated as NaOH, 21 to 26% moisture, 62 to 68% total fatty matter, and a pH of 6.0 to 8.0, 10.5 parts of sulfated castor oil having specifications of 4.9 to 5.5% combined S0 18 to 25% free fatty acid calculated as oleic acid, 1.0 to 2.3% alkalinity calculated as NaOH, 21 to 26% moisture, 62 to 68% total fatty matter and a pH of 6.0 to 8.0, 68.5 parts of an aromatic hydrocarbon petroleum solvent and 0.35 part of dodecyl benzene sulfonic acid.

The etching was done in a machine having a paddle speed of about 500 rpm. The temperature of the etching bath was F. and the time of etching was fifteen minutes. The bottom depth of the etch was 0.031 inch and the shoulder angle was 32 from the vertical. No pimples were present on the etched surface. The etched image was sharp and clean and no softening of the top could be observed. Also, there was less loss of fine halftone color than was found with commercially available presensitized photoengraving plates, which had been etched with the same bath.

EXAMPLE II The procedure of this example was the same as that of Example I, except that urea-formaldehyde resin was used in place of the melamine-formaldehyde resin.

Presensitized plates made according to the procedure of this example had press runs which were similar to the runs of the plate of Example I.

EXAMPLE III The procedure of this example was the same as that of Example I, except that the presensitizing solution contained 5.5 parts of melamine-formaldehyde resin and 20 parts of the polyvinyl cinnamate resist lacquer.

The plate produced by the procedure of this example showed the same results as the plates of Examples I and II.

The above description and examples show that the present invention provides a new and improved presensitized photoengraving plate. Furthermore, the plate has long storage and press life and produces sharp, clean images when etched with conventional powderless etching baths. Moreover, the method for producing the presensitized engraving plate of the invention is simple and relatively low in cost.

From the above description it will be apparent that various modifications and changes in the procedures and formulations may be made within the scope of the invention. Therefore, the invention is not intended to be limited to the specific examples and detailed procedures described except as may be required by the following claims.

What is claimed is:

1. A presensitized photoengraving plate comprising a zinc base plate and a substantially uniform, photosensitive coating on a surface of said plate, said coating comprising a mixture of a cinnamate photosensitive polymer and a thermosetting resin selected from a group consisting of melamine-formaldehyde resin and urea-formaldehyde resin.

2. A presensitized photoengraving plate as set forth in claim 1 wherein said coating comprises a mixture of melamine-formaldehyde resin and a water-insoluble photosensitive polymer containing cinnamoyl groups.

3. A presensitized photoengraving plate as set forth in claim 1 wherein said coating comprises a mixture of urea-formaldehyde resin and a water-insoluble photosensitive polymer containing cinnamoyl groups.

4. A presensitized photoengraving plate as set forth in claim 1 wherein said zinc base plate is grained and said coating comprises a mixture of between about 16% and 33% by weight of melamine-formaldehyde resin and between about 67% and 84% by weight of a waterinsoluble photosensitive polymer containing cinnamoyl groups.

5. A presensitized photoengraving plate comprising a mechanically and chemically grained zinc base plate, a substantially uniform, photosensitive coating on said grained surface, said coating comprising a mixture of between about and 26% by weight of melamineformaldehyde resin and between about 74% and by weight of a water-insoluble photosensitive polymer containing cinnamoyl groups.

6. A method for preparing a presensitized photoengraving plate comprising graining a surface of a zinc base plate, applying a photosensitive coating to said grained surface, and heating said coated plate to an elevated temperture above about F. which hardens but does not cross-link the coating, said coating comprising a mixture of a cinnamate photosensitive polymer and a thermosetting resin selected from the group consisting of melamine-formaldehyde resin and urea-formaldehyde resin.

7. A method as set forth in claim 6 wherein said coating solution comprises between about 4% and 20% by Weight of a mixture of a cinnamate photosensitive polymer and a formaldehyde condensation resin selected from the group consisting of a melamine-formaldehyde and urea-formaldehyde.

8. A method for preparing a presensitized photoengraving plate comprising chemically graining a surface of a zinc base plate, applying a photosensitive coating solution to said grained surface, and heating said coated plate to a temperature between about 100 and 250 F. to harden but not cross-link the coating, said solution com- 'of a zinc base plate, applying a photosensitive coating solution to said grained surface, and heating said coated plated to a temperature between about 100 and 250 F. to harden but not cross-link the coating, said solution -comprising a mixture of between about 20% and 26% by weight of melamine-formaldehyde resin and between about 74% and 80% by weight of a photo-sensitive polymer containing cinnamoyl groups.

References Cited UNITED STATES PATENTS 3,128,204 4/1964 Schaum et a1. ll734 X 3,218,168 11/1965 Workman 96l15 X 3,396,019 8/1968 Uhlig 9675 X OTHER REFERENCES Kodak industrial data book P-7, Kodak Photosensitive Resists for Industry, 1962, pp. 21-22.

GEORGE F. LESMES, Primary Examiner R. E. MARTIN, Assistant Examiner US. Cl. X.R.