US731082A - Process of preparing metals or alloys for lithographic printing. - Google Patents

Description

UNITED STATES Patented June 16, 1903.

PATENT OFFICE.

' PROCESS OF PREPARING METALS OR ALLOYS FOR LITHOGRAPHIC PRINTING.

SPECIFICATION forming part of Letters Patent N 0. 731,082, dated J une 16, 1903.

Original application filed April 19. 1900, Serial lib-13,466. Divided and this application filed May 21,1902. Serial No. 108,308. (No specimens.)

To to whom it may concern:

Be it known that I, Orro CARL STRECKER, a subject of the Emperor of Germany, and a resident of Darmstadt, Germany, have invented certain new and useful Improvements in the Process of Preparing Metals or Alloys for Lithographic Printing, of which the following is a specification, this being a division of my prior pending application, Serial No. 13,466, filed April 19, 1900.

Metal plates for printing purposes may be coated with a hygroscopic layer by submitting them as electrodes to an electrolytic process, which conveys thereto in the form of ions the molecules necessary for the formation of the layer. The desired effect may be obtained by electrolysis in different ways by an electric current; but it is difficult to obtain this result by such salts, which as electrolytes are decomposed by the current and which will produce soluble acid salts on account of certain secondary proceedings, and which therefore must be applied with precaution. The same result can be obtained by applying these electrolytes to the metal plates to be treated, in which cases decomposition of the solutions applied take place in the same way as in the electrolysis. Such reactions occur when certain complex snbstancesfor instance, the complex salts in a watery solution-are poured upon the 'plate to be prepared. A vehement reaction and development of gases will occur, although this could not be expected from the nature of these salts. The complex salt will be reduced to the components, but in most cases no layer will be formed. In special cases onlya difficult soluble layer is formed having caustic qualities,

and therefore the printing-plates will not be fit for practical use. By employing a salt of complex acids, the acids of which would singly form insoluble compounds with the metals employedfor instance, the complex salt silico-fiuorid of ammonia-this salt when applied to zinc will be decomposed in radicals of hydrofluoric acid and silicic acid and ammonia, and the silicic acid will neutralize the ammonia. The gas developing during this reaction, as described before, is hydrogen, which will cause complicated processes, on account of which soluble acid salts occur, and,

as stated above, no useful layer is obtained; but these reactions cannot be given by simple equations. Therefore the hydrogen has to be eliminated by adding oxidizingsubstances, which will be reduced by the nascent hydrogen, and thereby an absolute solid layer will be produced upon the metal oralloys, as described. The adding of said substances will have the result that in the reaction the complex salt is divided into simple radicals, of which-one part will be ineffective, While the other part will form with the metal of the plate an insoluble layer. Easily-reduced substances will be preferable to obtain this. In most cases nitrate of ammonia will be suitable. I will, however, not limit my process in this respect, as other oxidizing means or salts may be used to advantage. The reaction of these proceedings expressed by an equation is as follows, when using silico-fluorid of ammonia and nitrate of ammonia:

The process is carried out as follows: A plate, preferably of zinc, although I may use any metal or alloys, which by their color density and chemical quality allow their practical use, is selected. A zinc plate, best No. 12 of the Belgian gage, is ground by means of a course emery and pumice powder, equal parts, and a pad made of steel turnings of the finest and selectest shape. This pad is covered with a soft leather in orderto prevent the fingers from being hurt by cutting them with the sharp edges of thesteel tu rnings. Before grinding, the plate is washedwith a solution of acid fiuorid of ammonia, three ounces to the gallon of water, and one-fourth of a pint of ammonia in order to remove grease or oxid. Then the zinc is rinsed properly and the plate is ground by passing the pad with a slight pressing and rotative movement over the plate. After having done so for about twenty to twenty-five minutes, the size of the plate being a yard square, the plate is washed 0E and then poured and distributed on it two pints of water acidulatedwith about eighty drops of nitric acid and then left for about three minutes. After this the plate is washed well-prepared surface,so that the gum touches and fits the greasy substance. On the dried plate lithophine, a solution of asphalt in benzene and spirits of turpentine, is poured and the greasy substance dissolved. The liquid is wiped off so that only very little of it is left on the plate and then the latter is dried again. The plate is washed with water to free it from gu'm-arabic, and then appears with a layer of.

asphaltum on its face. The design is properly inked with printing-ink by the usual method until a good black negative is obtained. The plate is made dry and alterations or corrections are made. The plate is again gummed and dried, the gum washed off, and the plate inked up afresh and dried again. Finally, the negative is dusted in with powdered colophane, and this is rubbed ed with talc. Then the plate is ready for the process. The zinc plate thus obtained with a copy, or simply ground and without a copy, is used for the printing-plate, and the said solution is poured on the plate. The solution is then distributed by means of a fine hair-brush and allowed to act upon the zinc or other metal in the course of two to three minutes, while the solution is brushed frequently over the plate to cause it to improve and strengthen the layer. When the time of action for the chemical substances has passed over, the remaining solution is washed 0E, the plate is made dry, and is then gummed. The process of coating may berepeated, and finally the plate after gumming is made dry and is then ready for use.

In the case that a plate was furnished with its coating before printing thereon a transfer or design it will be necessary to free it from the gum .which adheres yet and wash the plate well, or wash first with a solution of alum and then with water when zinc was used or with other means on other metals, or zinc plates may also be washed with a weak solution of soda to neutralizethe gum or the reaction of salts used. Then the plate is provided with a design or transfer or the like and treated with the solution, as before, and is then ready for printing after having been washed, gummed, and dried subsequently.

The solution applied contains a mixture of salts composed of three ounces of complex salts and three ounces of an oxidizing means and three ounces of gum-arabic in one pint and a half of water, or about four per cent. of the salts. The time of the action and the composition of the solution depends upon the kind of work. When the lithographic negative or transfer has been well protected by resinous substances, a comparatively strong solution' may be used. As to the complex salts and the substances which may be applied in these processes, I preferably use of the salts of the complex acids chiefly silicofluorid of ammonia mixed with nitrate of ammonia in equal parts, by weight.

The result in all cases is the production of an insoluble hygroscopic layer on the metal employed.

In carrying out my improved process one must be careful to attend to the rules given in this specification for producing transfers, as otherwise it inadvertently occurs that the negative is easily smeared or daubed before even my process may be applied.

Having now particularly described and ascertained my invention, what I claim, and desire to secure by Letters Patent, is-

The process for preparing'metal plates or alloys for lithographic designs, transfers and printing, consisting in submitting the prepared plates to the treatment of a solution containing two to four per cent. of a mixture of salts of complex acids whose constituent acids singly would form insoluble compounds with the metals employed, and an oxidizing means, which solution, acting on the metal and the latter on the chemicals applied in the process, forms on the plate an insoluble and hygroscopic layer which is firmly adherent to the surface of the metals or alloys employed, substantially as described.

In testimony whereof I have hereunto set my hand in presence of two witnesses.

, OTTO CARL STREOKER. Witnesses:

' J EAN GRUND,

CARL GRUND.