US716306A - Process of electrolytically preparing metals and alloys for lithographic purposes. - Google Patents

Description

No. 716,306. Patnted Dec. I6, I902.

l 0. c; STBECKEB. PROCESS OF ELECTROLYTIGALLY PREPARING METALS AND ALLOYS FOR LITHOGBAPHIG PURPOSES.

(Application filed Apr. 19, 1900.) (No Model.)

. a subject of the German Emperor, and aresii r STATES.

.ATENT FFicE.

OTTO CARL memes; OF COLOGNE, GERMANY.

PROCESS OF ELECTROLYTICALLY PREPARING M ETALS AND ALLOYS FOR LlTHOGRAPHlC PURPOSES.

ESZPZECIFIGATION forming part of Letters Patent No. 716,306, dated December 16, 1902.

Application filed April 19; 1900. Serial No. 13,466. (No specimens.)

T0 (LZZ whom itmay concern: i I 3 Be it known that'l, OTTO CARL Strnncldnnf,

(lent ofCologne, Germany, have invented cer; tain new and useful Improvements in the Process ofElectrolytically Preparing Metals or Alloys for Lithographic Purposes, of which the following is aspecification. L Metal plates for printing purposes have been hitherto Iprepared by coatingthe plates with a layer of hygroscopic materials directlyor by brushing, powdering, &c., in a mechanical way orby coating the plates with materials capable toform such layers by chemical ref action with the metal of the plate. I

My inventionconsists in employing electrolysis or an electrolytic process for the same purpose in such manner that the plate before or after transferring the drawing serves as an electrode and as an electrolyte the watery solution of a substance or mixture of substances whose ion going to the plate is capable of forming a layer which is either hygroscopic (having great affinity to water) or may be changed .into a hygroscopic layer by fur ther process.

For the purpose of my invention it does not matter whether the materialemployed will act as anode or as cathode, nor does it make any difierence whether the greasy drawing has been already transferred to the plate or not. Further, the plates prepared for reprinting maybecleaned that is, the layers may be taken off 'partly or fully by the same process, but proceeding in reversed order. In this case the plates are used as cathodes in a direct current, and it will make no dif ference whether the greasy drawing is adher ing yet to the plate or not or whether the plate has been prepared according to my process or by the old process.

The desired effect can be reached by electrolysis in different ways, either generally by an electric current, continuonsor alternate, generated from the source of energy, or in special casesby forming a galvanic element for which the printing-plateis used as an electrode. Different electrolytes will give different results, but to a certain point such difference will not alter the procedure. In the casesdescribed below the electrolyte will not have any influence upon the plate nor upon the drawing as long as the circuit is I opened. The action commences with the closing and ends with the opening of the circuit; but, as described later onyelectrolyte decompositions may occur, whereby the contact of the electrolyte with the plate to be treated will cause an electrochemical reaction, which has to be influenced and guided in a defined sense in order to reach the same effect 'asin the two first-described cases.

The plates may consist of metals or alloys of such color, density, consistence, and chemical qualities as to allow their practical use.

A metal plate of zinc is ground by means of apad of steel turniugs and pumice powder in the manner described later on, the metal is rinsed with water and then made dry, and

is ready for use. On this plate a lithographic design or transfer, the negative of the intended print, is fixed. After this the plate is gummed with a solution of gum-arabic of medium strength, and this is made dry. After being perfectly dry the greasy substance is washed out by lithophine, (a solution chiefly consisting of asphaltum in benzene or spirits of turpentine,) the excess is wiped 01f, and the plate made dry. Then the gumarabic is washed off the plate by water, and the negative is left on the plate as a layer of asphaltum. The negative is properly .inked by means of the roller, and then the plate is cleaned from spots and the like, alterations and corr =ns are done by lithographic ink after the method well-known to lithographic printers, and the plate is ready for my process, in which it will be used as the anode.

The reaction of the process may be given as specified in the equation below, the elec trolyte being a solution of 2.5 percent. fluorid of sodium. The density of the continuous current applied is 0.5 to 0.9 ampere to the square foot, and the action of it may last from two to live minutes, according to the density. For instance, a plate two feet by three feet requires 0.5 6 5:3 amperes for five minutes or 0.9 6 3.3:5.4 amperes for fore using the electrolyte again.

In the drawings, Figure 1 is a perspective for attaching the positive Wire.

view illustrating the practice of my invention in connection with an electrolytic cell, and Fig. 2 a like view illustrating the use of a brush instead of a cell.

In carrying out the improved process I may employ (a) the method of dipping explained by the first figure of the drawings. A is the cell; 1), is the anode with the design; 0, the cathode; d, is the electrolyte, and f+f are the copper wires connecting b and c with the source B of electric energy. The plate provided with the drawing is secured as an anode by suitable means. The said platesay about two feet by three feet-is completely dipped into the liquid, except at the usual curved edge, which carries a binding-post The cathode is suspended and connected ina similar way. An ampere-meter C may be inserted in one of the conducting-wires.

The method of sponging shown in Fig. 2 makes a the anode and cthecathode,(therotative plate with an insulated handle) (1, the electrolyte, is on the plate invisible, and f+ fare the copper wires connecting a, and c with the sou rce of electric energy. The plate provided with the drawing or transfer is brought to a horizontal position and connected to the positive pole of the supply of electricity. Upon this electrode I pour liquid, While the negative pole is brought into contact with the electrolyte by means of a fiat metal plate provided with an insulated handle. The metal plate is faced with a layer (four to five millimeters) of cotton and constitutes the cathode, which is passed (in accordance with the tension of the current) over the anode. The intensity of the continuous current applied is 0.1 ampere to four inches square, which is the size of the rotative plate, and the duration is, according to the size of the printing-plate, five to ten minutes.

Instead of using the expensive copper or nickel plates I might use alloys of them with zinc or with other metals; but I prefer zinc on account of its cheapness and the exceedingly good results obtained by it. Such a zinc plate (best No. 12 of the Belgian gage) is ground by means of a coarse 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 order to prevent the fingers being hurt. Before grinding, the plate is washed with a solution of acid fluorid of ammonia, three ounces to the gallon of water, and one-fourth of a pint of ammoniain 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. Afterhavingdonesoforabout twenty to twenty-five minutes, the size of the plate being a yard square, the plateis washed ofi and then fifteen hundred cubic centimeters of water acidulated with about five cubic centimeters of nitric acid of 1.185 specific gravity are formed and distributed upon it, and it is,

. now a soft whitish appearance,

then left for about three minutes. After this the plate is washed and made dry and has and is ready for use. The negative (the lithographic design or transfer) is now fixed on the plate by the method well known to lithographers and printers and is gummed as soon as it has been dried properly with a solution of gumarabic of medium strength sifted that no pieces of wood or grit may be left in it. The gum is dried, and in doing so is wiped witha moist piece of cotton in order to have a good and 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 oif, so that only very little of-it is left on the plate, and then the plate is dried again. The plate is Washed with water to free it from the gum arabic, and the design appears as a layer of asphaltum on the plate. 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 gummed and dried, the gum washed 01f, and the plate inked up afresh and dried again. Finally the negative is dusted in with powdered colophane and this rubbed off with talc. Then the plate is ready for the process or processes. In the case that an alternating current has been used the electrolyte may consist, for instance, of a solution of borax neutralized with boric acid two per cent. strong. -By using the alternating current the current oxidizes the plate only and zinc so forms zinc oxid, (ZnO,) which reaction cannot be given by a chemical equation. This plate, covered with hydroxid, is then treated with a weak solution of acid, preferably phosphoric acid, and a phosphate of zinc is formed, as may be seen from the following equation, or it may be done otherwise: i

The tension of the current is the same as previously and the proceedings may be carried out in the same way as under a and b.

When aluminium plates are used, aluminium oxid would be produced, which cannot be transformed into phosphate by this process. The processes as described above are carried out in the most simple electrochemical way. Special circumstances, however, will occur in the following proceedings. By employing for the same purpose the salts of complex acidsas, for instance, silico fluorid of am monia-these salts in regard to their complex anion will be reduced on closing the circuit to their c0mponents-that is, simpler anions of the hydrofluoric and silicic acidsand the insoluble layer will be formed only in an imperfect manner or under some circumstances not at all, because soluble salts will be produced by hhGSB PIOCGSSGSr The complex salts will also show a similar electrolytic disintegration and effect if they are poured or applied inan aqueous solution upon the plate to be prepared and serving as electrode of a galvanic or electrolytical process. A vehement reaction and development ofgases will occur, although this might not be expected; but in most cases no layer will be formed. In special cases only a difficult soluble layer is formed having caustic qualities, and therefore the printing-plates will not be fit for practical use. The gas developing during this reaction is hydrogen, which will cause the acid complicated reactions, and therefore it has to be eliminated by adding oxidizing substances which will be reduced by hydrogen, and thereby an absolute solid layer will be produced upon the metal or alloys, as described. The adding of said substances will have the result that in the reaction the complex anion is divided into simple ions, of which one part will be ineffective,while the other part will form with the metal of the electrode an insoluble layer. Easily-reduced substances will be preferable to obtain this. In most cases nitrate of ammonia will be suitable, as all the ammonium salts are easily soluble in water. I will, however, not limit my process in this respect, as other oxidizing means or salts may be used to advantage. The reaction expressed by an equation is as follows:

The solution is then distributed by means of a fine-hair brush and allowed to act upon the zinc or other metal for 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, the remaining solution is washed off. The plate is made dry and is then gummed. The process of coating may be repeated and finally the plate after gumming is made dry and is then ready for use.

In the case that a plate should be furnished with its coating, which might be done by one of the described ways, 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 is used, or with other means on other metals. Zinc plates may also be washed with a weak solution of soda to neutralize the gum or the reaction of the salts used.

The solution applied, the electrolyte contains a mixture of salts composed of three ounces of ammonium silico fluorid and three ounces of ammonium nitrate and three ounces of gum-arabic in one pint and a half of water, or an equivalent mixture of other complex salts and gum. The time of the action and the composition of the electrolyte the solution applied depends upon the kind of work. hen the lithographic negative or transfer has been well protected by resinous substances, a comparatively strong solution and long duration may be used. As to the electrolyte, which is used for the electrolysis under a and b, I use the solution of salts of those acids which form insoluble salts with the metals applied or other efficient solutions, such as very weak solutions of acids, which are electrolytically decomposed, and for the electrolytes, which are applied in the electrolytical or galvanic processes under 0, I preferably use salts of the complex acids, such as ammonium silico fluorid. The density of the solution varies in strength from two to four per cent. of the operative and efficient mixture of the said substances. The result in all cases is the production of an insoluble hygroscopic layer of the metal employed'and the anion of the acid.

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.

I do not herein claim a process for preparing metal plates or alloys for lithographic printing with an insoluble and hygroscopic layer of salts of the metals used, consistingin the employment of electrolysis or electrolytical or galvanic action, wherein the plates to be prepared serve as electrodes and the anion of the described substances applied go to the said plates and form with the metal of the plates said layer which is adhesive to the plate, or a process for preparing metal plates or alloys for lithographic printing and other purposes by submitting the plates with a design to electrolysis of preferably watery solutions of salts, whereby the continuous current passes from the cathode to the anode constituting the said plate and forms thereon an insoluble layer with the anion of the salt, such being the subject-matter of an application filed by me on the 12th day of May, 1902, Serial No. 1065,9601}, as a division hereof, nor do I claim a process for preparing metal plates or alloys for lithographic and printing purposes consisting in submittingthe plate to the action of an alternating current by which a layer of oxids is formed on the metals employed, which layer is transformed by chemical means, according to chemical reactions well known,into an insoluble layer of salts adhering firmly to the metal, or a process for preparing metal plates or alloys for lithographic and printing purposes consisting in first submitting the plate to the action of an alternating current :in'iwatery and preferably neutral solutions of salts, whereby the current passing from the electrodes through the electrolyte forms on the anodea layer adhering firmly to the plate and insoluble in water, and then submitting said plate to a secondary chemical treatment by which the neutral or basic layer Will be rendered fit for lithographic purposes and still adhere firmly to the surface of the metal, such being the subject-matter of an application filed by me on the 19th day of April, 1902, Serial No. 103,308, also as a division hereof, nor yet do I claim a process for preparing metal plates or alloys for lithographic printing and other purposes consisting in submitting the well-ground plates to the treatment of an electrolyte containing, preferably, two to four per cent. of an efficient mixture of salts of the complex acids and an oxidizing means, such as nitrate of ammonia, and acting in such a Way on the metal and the chemicals applied that an insoluble and hygroscopic layer is formed, which is firmly adherent to the plate of the metals or alloys applied, such being the subject-matter of an application filed by me on the 21st day of May,

1902, Serial No. 108,308, likewise as a division hereof; but

That I do claim, and desire to secure by Letters Patent, is-

The process for preparing metal plates or alloys for lithographic printing, consistingin preparing the plate by preliminary grinding, rinsing, subjecting to an 'acidulated Watery solution, washing and drying, fixing the negative upon the surface thus prepared, coating With gum-arable, treating with lithophine after the gum-arabic has dried, to dissolve the greasy substance, washing the plate with water to free it from the gum-arabic, dusting With powdered colophaneand rubbing thisoff, then submitting the plate as an electrode to electrolytic action in a solution of salts and gum-arabic.

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

OTTO CARL STRECKER.

Witnesses:

L. BARNES, F. E. MALLETT.

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