US2258956A - Steel plate for lithographic printing - Google Patents

Description

d- 1941- w. N1 ,MlsuRAcA 2,258,956

STEEL PLATE FOR L ITHOGRAPHIC PRINTING Filed Sept. 14, 1938' FIG. 3

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' INVENTOR WILLIAM N. ISURACA ATTORNEY Patented Oct. 14, 1941 UNITED STATESPATENT OFF-ICE 2,258,956 S'TEEL PLATE FOR r rr noeaarmc ram William N. Misuraca, Merrick, N. Y., assignor to Misuraca, Inc., Branchville, N. J., a corporation of New Jersey Application September 14, 1938, Serial No. 229,809

4 Claims.

1 formed of a substance having a definite aflinity for grease or a greasy type of marking material, while the non-printing areas of the plate are prepared to accept water so. as to restrict the application of the greasy marking material to the printing areas only. At present, the'only metals that have been successfully used for lithographic printing plates are zinc and aluminum. Although there are many ways in which such plates are prepared for printing, one method which is widely used includes the following steps: (1) Making a print on a grained zinc or aluminum plate sensitized with'a dichromated colloid; (2) developing the print to expose the metal surface in theprinting areas; (3) etching if desired, and treating the printing areas with an ink receptive substance; (4) removing thedichromated colloid coating fromthe non-printing areas; (5) treating the baremetal non-printing areas with a desensitizing acid. solution so as to make such resistance than zinc and aluminum and has the design or printing areas thereof coated with a material having substantially as great a wearing life as the harder or more wear-resistant metal, and the non-printing areas treated with a des'ensitizing solution which will adhere to the harder metal.

In accordance with my invention a grained plate comprising a metalharder or more wearresistant than zinc and aluminum is first coated with a light sensitive solution and exposed to the light through a positive or negative film. Theexposed plate is then developed so as to eliminate areas receptive to water and, hence, repellant to v grease. I

When plates prepared in this manner, or one of the many modifications thereof, are used in printing, difiiculties are encountered in retaining the grease repellant properties of the non-printing areas of the plate and in preventing the wearing probably due'both to friction and to the fact that the plate surface is grained or roughened. Such wearing is also increased by the fact that the greasy base of the design is not entirely resistthe coating from the unexposed printing areas of the plate. Following this I coat the plate with a resinous material which, when baked at a relatively high temperature, will polymerize to form an extremely hard film; and then remove both the light-hardened sensitive solution and the resinous material from the non-printing areas of the plate so as to leave the resinous material adhering only to the printing or work areas. In this condition the plate is baked at a suitable temperature to polymerize the resinous material and render it hard andhighly resistant to the chemical action eration of the following description and the accompanying drawing, in which:

Fig. 1 is a plan view of a finished lithographic plate embodying my invention;

Fig. 2 is an enlarged vertical sectional view taken substantially along the line 2-2 of Fig. 1,

ant; to the corrosiveaction of the acids usually difliculties encountered in the use of prior lithographic plates may be overcome by providing ametal plate which is harder or has greater wear the thickness of the various layers applied to the plate being exaggerated for the sake of clarity;

Fig. 3 is a greatly. enlarged vertical section through a portion of a grained plate prior to treatment; and

Figs. 4, 5, 6 and .7 are enlarged sectional views, similar to Fig. 2, showing the plate during certain stages of its production.

Referring now to the drawing, it will he noted that in Fig, 3 I have shown an enlarged-section through a portion of a plate It! the upper sur-' face of which has been roughened or grained, as

indicated at H, by the use of an abrasive which covers the entire surface with microscopic scratches in a well known manner. The plate used in practicing my invention comprises a metal or alloy such as stainless steel, Monel metal, copper and other special alloys all of which are harder or more wear-resistant than either zinc or aluminum, so that the grained surface, which is necessary for the retention of water on the non-printing areas and for the adhesion of the various coatings applied during the course of preparation to both printing and non-printing areas, will have a considerably longer wearing life than any lithographic plate that has heretofore been successfully used. The metal employed should alsopreferably be of a type that will not oxidize readily when subjected to water.

After graining the plate in the usual maimer, the grained surface thereof is coated with a light sensitive colloidal solution. The colloids usually employed are egg albumen, animal glue, gum arabic, etc., and these aretreated with a soluble bichromate or other salt which is light-sensitive so as to render the colloid substantially insoluble in water after exposure. Such a solution is suitably spread over the surface, as by whirling, to form a thin uniform layer l2 (Fig. 4) which is free from spots and streaks. When th coating is dry, it is exposed to light through a positive (or negative) film I3 (Fig. 4). This is generally 'done-by placing the plate 10 in a printing frame or photocomposing machine and printing with the positive film l3 in good contact with the sensitized layer l2. In this manner, the sensive coating [2 is exposed to light only in those areas which correspond with the clear portions of the positive (or negative) film. Following the printing, the exposed plate is developed in any suitable manner so that those parts of the design which have become hardened by the light will adhere firmly to the surface of the plate and the coating on those portions which have not been exposed to light will wash away, leaving the original metal exposed. In Fig. 5 I have shown the plate at this stage of the preparation and it will be observed that the coating l2 has been removed from a portion II but is left on the remaining areas I5 of the plate. The portion I4 is a part of the design or printing area of the plate and is additionally treated in the novel manner now to be described.

When the developed plate has been properly dried, I coat at least the printing area N thereof with a thin layer l6 of a heat reactive synthetic resinous composition having the property of polymerizing into a hard film which'ls resistant to strong acids and alkalis when the film is baked at an elevated temperature. Such a solution may comprise a suitable phenolic resin varnish, for example, so that it may be applied with a brush, spray or any other suitable coating device in the desired thin layer I6. The following are typical examples of compositions which may be used to advantage in practicing this phase of my invention:

Example I Parts by weight Heat reactive phenol formaldehyde resin 35 Drying oil acid modified glycerol phthalate resin 10 Solvent naphtha Butyl acetate 7 15 Ethyl acetate 15 Butyl alcohol- 1 10 This material will form a hard film satisfactory for the purposes of my invention by baking it at a temperature of about 375 F. for about 22 minutes.

Example II Parts by weight Heat reactive phenol formaldehyde resin Butyl aceta Ethyl acetate 25 Butyl alcohol 15 This composition forms a hard film when baked at a temperature of about 380 F. for about minutes.

This material also will form a suitable hard film when baked for about 25 minutes at a temperature of about 325 F.

I have also found that urea formaldehyde resins, plasticized with alkyd resins, and other similarheat hardenable compositions may be satisfactorily used for the layer IS.

The next step in the preparation of the plate is to eliminate all coating material from the non-printing portions I5 of the plate so as to leave only the thin resinous layer l6 on the printable to heat the plate slightly so as to dry the layer [6 sufliciently that it will adhere to the surface of the plate when said plate is washed and brushed in the usual manner with a solution in which the lightsensitive layer i2 is soluble. After the grained surface on the non-printing portions l5 of the metal plate has been exposed, the plate is baked in a suitable oven to polymerize the resin completely and render the film IE on the printing area I4 hard and alkali and acid resistant. Such a hardened filmwill have a wearing quality substantially equal to that of the grained surface of a stainless steel plate. The platein this condition is shown in Fig. '7. Because of the baking necessary to render the film l6 hard and resistant to acids and alkalis, care should be taken to avoid the use of metals which crystallize or become otherwise unsuitable as printing members when subjected to such treatment. The commonharder metals mentioned above do not exhibit any detrimental change of structure when baked at the necessary temperature.

Finally, the plate may be completely prepared for printing by applying to the bare metal nonprinting portions I5, a thin layer ll (Fig. 2) of a solution which will thoroughly desensitize these parts so that they will retain water and repel grease. A solution which I have found exceptionally desirable for desensitizing all metals harder than zinc and aluminum is a composition comprising chrome alum and gum arabic as disclosed in my copending application Ser. No. 194,075, filed March 5, 19,38. As explained in that application, the chrome alum acts as a'hardener for the gum arabic. so as to render it insoluble without exposure or further treatment.

When th finished lithographic printingmember consists of a plate of one of the harder metcustomary in prior metal plates, these difiiculties may be obviated; and I consider this a part of my present invention.

From the foregoing description, it will be understood that the lithographic plate embodying my invention will have harder printing and nonprinting areas and consequently a longer useful life than lithographic plates heretofore known. Moreover, various changes may be made in the construction and preparation of the plate and certain features thereof may be employed without others, without departing from my invention or sacrificing any of its advantages.

What I claim is: 1

1. A method of preparing a lithographic printing member, which comprises graining the surface of a thin steel plate, applying a light sensitive film to the grained surface, exposing said film to light through a film having a design thereon, developing th exposed plate to eliminate the sensitive film from the unexposed printing areas, coating at least the bare printing areas with a heat reacting synthetic resinous composition which may be converted to the insoluble state at atemperature above 300 F., removing all coating material from the non-printing areas of the plate, and applying a desensitizing solution including gum. arabic and chrome alum to the non-printing areas of the plate.

2. A lithographic printing member, comprising a stainless steel plate having a grained surface including printing and non-printing areas, said printing areas being coated with a hard set film of resin which does not attack the stainless steel, and said non-printing areas being treated with a solution including gum arabic and chromealum.

3. A lithographic printing member comprising a stainless steel plate both surfaces of which are grained by covering said surfaces with a plurality of microscopic scratches, one of said surfaces having printing and non-printing areas thereon, said printing surfaces being coated with a hard set film of resin of the group consisting of phenol-formaldehyde, urea formaldehyde and vinyl resins, and said non-printing'areas being treated with a solution including gum arabic and chrome alum.

4. A method of preparing a lithographic printing member, which comprises graining the surface of a thin steel plate; applying a light sensiterial from the printing areas of the plate; and

applying a desensitizing solution including gum arabic "and chrome alum to the non-printing areas of the plate.

' WILLIAM N. MISURACA.

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