US2429107A - Method of producing a stainless - Google Patents

Description

Patented Oct. 14, 1947 STEEL LITHOGRAPHIC PLATE WITH A COPPER IMAGE THEREON Torsten Seved Alexander Petrn, Fullesta, Huddinge, and Erich Karl Willi Sternherg, Ahra-' hamsberg, Sweden, ass gnors to Ahlen 8r Akerlunds Forlag, Stockholm, Sweden Nb Drawing. Application May 25, 1943, Serial No. 488,436. In Sweden June 4, 1940 3 Claims. 1

The present invention relates to the manufacture of a printing plate for offset printing, 1. e., a printing plate of the type where the ink transferring and the ink repellent portions lie in the same plane or have a level difference insufficient for relief-process printing or intaglio printing. In the manufacture of such printing plates it is known to use plates consisting of or coated with rust-resisting steel, a rust-resisting steel alloy, chromium, chromium alloy-s or similar rustresisting material with good colour repelling properties. It is further known to apply to such plate, for instance galvanically, a coating of copper, nickel or another metal which in itself has great adhesion relatively to the printing ink. After the plate has been provided with a photographic layer, exposed and developed the copper layer is etched away at the portions which shall not form the image, the surface of the base plate being laid bare at said portions.

The use of plates of corrosion-proof metallic material, such as rust-resisting steel is very beneficial in offset-printing. The abundant supply of water which is necessary when using plates of an oxidising material is avoided. A very small supply of water is suflicient whereby the quality of the prints will be improved. During occasional standstills of the printing machine it is not necessary-as otherwise when using plates of an oxidising materialto protect the plate by applying gum arabic solution or the like. Moreover the resistance of the plate is considerably improved in comparison with that of the heretofore widely used plates of zinc or aluminium, and as a result, in the printing of large editions, the quality of the prints will also be improved.

In the known methods for the manufacture of printing plates having an ink repellent surface of rust-resisting steel, chromium or alloys thereof and an ink receptive image surface of copper, nickel or the like a galvanizing apparatus has been indispensable. Another drawback is that the consumption of copper has been high because it was necessary to coat the entire base plate with the other metal, subsequently in most cases etchity 0.91.

loys or similar corrosionproof materials, develop"- ing the image and treating the portions of the plate laid bare by the development with a solution which contains a metal compound the metal of which has a lower electrolytical dissolution pressure than has the metal of the base surface of the plate, the metal of the compound of the said solution having greater adhesion relatively to water-insoluble offset printing inks than has the material whereof the base surface of the plate consists.

The treating solution may comprise a metal compound, the metal of which will form an alloy with the base metal, said alloy having a greater adhesion relatively to water-insoluble offsetprinting inks than has the material whereof the base surface of the plate consists.

If corrosion-proof metallic plates, e. g., of rustresisting steel, are used, the etching solution should preferably contain cuprous chloride.

In the following the invention will be described more fully with reference to a non-limitative example of the'manufacture of a printing plate.

A plate consisting of rust-resisting steel is subjected in known manner to a roughening or graining process by mechanical means in order to secure a larger surface on the plate for the image and to increase the lasting qualities of the latter. The plate is subsequently cleansed in order to prevent the adhesion of grease at places which shall be water-receptive. To this end one may use a solution containing about 2% of formic acid, about 5% of alum and nitric acid.

The plate is coated with a photographic layer containing for example the following chemicals: 75 grams of ammonium bichromate and 10 grams of manganese sulfate dissolved in 325 cm. of water, 50 grams of albumin dissolved in 150 cm. of water, 1 litre solution of gum arabic of 14.5 B. and cm. of ammonia of the specific grav- After the layer has been applied the plate is exposed. Then the image is developed by means of an aqueous solution. When employing ing away the largest portion of the layer formed thereof.

These inconveniences are obviated by the method according to the present invention which is mainly characterized by applying a photographic layer to a plate consisting of or coated with a metal or metal alloy with ink repellent properties, preferably a corrosio-nproof metal or metal alloy, such as rust-resisting steel, a rustr'esistlngsteel alloy, chromium or chromium althe photographic layer above described one may use a calcium chloride solution of 36 B., 1 litre of which contains 50 grams of lactic acid and 40 cm. of 96% alcohol.

After the development those portions of the plate which are laid bare and which shall be ink-receptive are treated with an etching solution which may be composed as follows: 1 litre calcium chloride solution having a specific gravity of 1.2-1.4 (about 39 36.), about 25 grams of ferric chloride, about 10 cm. of nitric acid, about 30 cm! of hydrochloric acid as well as about 2'5 grams of cuprous chloride. The addition of cuprous chloride may of course vary, for instance within the range to 100 grams; the said quantity of about 25 grams has, however, proved to be especially suitable and sufiicient for the purpose.

After this procedure the plate after corrections, if any, is ready to be prepared for printing in the same way as with usual zinc plates, i. e., by greasing the image surface and washing away the hardened photographic layer which covers those portions of the plate which shall be water receptive and ink repellent. Through the treatment with the said etching solution there has formed on the image surface an extremely thin copper layer which has good adhesive properties relatively to the grease and printing-ink. In the following the formation of the copper coat and the conditions with respect thereto will be touched upon.

Corrosion-proof metals, e. g., rust-resisting steel, are sometimes passive, i. e., they have such an electrolytical dissolution pressure that copper cannot deposit on same. Nor is there formed any adsorptive copper layer because the places where adsorption could take place are occupied by passivating atoms. It is assumed that these atoms are oxygen atoms. Only after the activation of the corrosion-proof metal a copper coat can form on the surface of the plate. The develop-ing solution has an activating influence on the corrosionproof plate, e. g., the steel plate, because it consists of a calcium chloride solution which contains lactic acid. It is known that chlorine ions exercise a strongly activating effect, and that organic acids, such as formic acid, acetic acid and citric acid act in the same way. To the same class of organic acids also lactic acid belongs. Through the treatment with the developing solution the plate, e. g., the steel plate is thus prepared for the reception of copper present in the etching solution.

It should further be observed that the chemicals present in the treating bath in addition to the copper salt are so selected that the plate is kept active through the bath. It is believed that this efiect should be mainly attributed to the high chloride concentration of the bath. The iron content of the bath is beneficial in that it' suppresses the deposition of copper, at the beginning thereby exercising a controlling influence. The potential between the plate and the treating bath depends upon the ratio between iron ions and copper ions. If there were no iron ions present the potential at the beginning would be so high as to cause irregular distribution of the copper when the bath is poured. The specific gravity of the solution previously stated (1.2-1.4) is convenient to prevent the precipitation of the iron as hydroxide by hydrolysis.

Nitric acid normally acts passivating but in the present case there is no risk of its having any detrimental effect because the concentration is too small to produce passivity. The concentration may for instance be kept at about 0.6% by weight. The importance of the nitric acid in the treating bath resides mainly therein that it causes a protraction of the time of treatment which may be of advantage.

Apart from the difference in the manufacture a printing plate produced by the method according to the invention differs considerably from known printing plates having a copper coat produced galvanically or by spraying. A plate of the latter type has a copper base formed by many millions of atom layers which is consequently distinctly perceivable and measurable. The

printing plate produced according to the inven-' tion on the contrary has a copper base which is very nearly mono-atomic and mostly quite invisible.

Experiments have shown that prints obtained with the use of a printing plate manufactured according to th invention are of very good quality. With respect to the quality the plate is riot inferior to any of the known types. In contradi'stinction to the known bimetallid printing plates it can be produced by simple methods, as previously pointed out. The consumption of copper, nickel or the like becomes very slight in the manufacture of the printing plate by the novel process in comparison with such methods where at first a copper coat, produced for instance galvanically, has to be disposed over the entire plate. The galvanic treatment is completely dispensed with whereby much time is saved and the printery becomes independent of galvano-technical equipment. The ink receptive coating is formed simultaneously with the etching procedure which is necessary in any event, simply by the addition to the etching bath of a copper salt or another compound of a metal suitable for the purpose.

What we claim is:

1, A method of manufacturing a printing plate for offset printing, the ink repellent and ink transferring surface portions of which lie in the same plane or have a level difference insufiicient for such printing processes as relief process printing and intaglio printing, the plate comprising a stainless steel surface with greasy ink repellent and water receptive properties, characterized by applying a photographic light-sensitive layer to said plate, exposing said plate, developing the resulting image and treating the portions of the .plate laid bare by the development with an etching solution which contains copper chloride capable of producing a deposit of copper on said bare portions by metal displacement, said copper forming an alloy with the stainless steel having a greater adhesion relatively to water-insoluble offset printing inks than the stainless steel of the plate, and washing away the hardened remainder of the light-sensitive layer; said etching solution containing cuprous chloride and ferric chloride.

2. A method of manufacturing a printing plate for offset printing, the ink repellent and ink transferring surface portions of which lie in the same plane or have a 1eve1 difference insufiicient for such printing processes as relief process printing and intaglio printing, the plate comprising a stainless steel surface with greasy ink repellent and water receptive properties, characterized by applying a photographic light-sensitive layer to said plate, exposing said plate, developing the resulting image and treating the portions of the plate laid bare by the development With an etching solution which contains copper chloride capable of producing a deposit of copper on said bare portions by metal displacement, said copper forming an alloy with the stainless steel having a greater adhesion relatively to water-insoluble offset printing inks than the stainless steel of the plate, and washing away the hardened remainder of the light-sensitive layer; said etching solution containing calcium chloride, ferric chloride, nitric acid, hydrochloric acid and cuprous chloride.

3. A method of manufacturing a printing plate for offset printing, the ink repellent and ink transferring surface portions of which lie in the same plane or have a leve1 difierence insufficient for such printing processes as relief process printing and intaglio printing, the plate comprising a 5 stainless steel surface with greasy ink repellent and water receptive properties, characterized by applying a photographic light-sensitive layer to said plate, exposing said plate, developing the resulting image and treating the portions of the plate laid bare by the development with an etching solution which contains copper chloride capable of producing a deposit of copper on said bare portions by metal displacement, said copper forming an alloy with the stainless steel having a greater adhesion relatively to water-insoluble offset printing inks than the stainless steel of the plate, and washing away the hardened remainder of the light-sensitive layer; said etching solution having the following composition: 1 litre calcium chloride solution of a specific gravity of 1.2-1.4 (about-39 B.), about 25 grams of ferric chloride, about 10 cm. of nitric acid, about 30 cm. of hydrochloric acid and about 25 grams of cuprous chloride.

TORSTEN SEVED ALEXANDER PE'I'REN. ERICH KARL WILLI S'I'ERNBERG,

file of this patent: I

UNITED STATES PATENTS Number Name Date 992,898 Payne May 23, 1911 160,177 Friedlander Feb. 23, 1875 2,203,849 Trist June 11, 1940 2,097,831 Backelman Nov, 2, 1937 2,270,712 Wood Jan. 20, 1942 1,704,523 Ullmann Mar. 5, 1929 2,042,003 Huebner May 26, 1936 FOREIGN PATENTS Number Country Date 483,349 Great Britain Apr. 19, 1938