Automatic Stripping Of Electrodeposited Starting Sheets

Abstract

Starting sheets (copper sheets electrolytically deposited on cathode base sheets) can be readily stripped from their base sheets by pulling with suction disk when a layer of air is formed in the interface between each starting sheet and its base sheet by a simple physical process such as rolling or vibration applied to one part of the sheet. Stripping is further facilitated and the starting and base sheets are protected by the application on the base sheets before electrolysis of at least one coating agent containing an organic compound of an acid such as phosphoric acid, xanthic acid, thiocarbonic acid, or thiocarbamic acid or an organic ester such as organic phosphorous ester.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to electrolytic processing of copper and more particularly to a new method and apparatus for automatic stripping of starting sheets in electrolytic refining and winning of copper (hereinafter referred to as "copper electrolysis").

Starting sheets for use in copper electrolysis are ordinarily prepared by electrodeposition of copper on cathode base sheets of smooth rolled copper sheets or stainless steel sheets. In the case of rolled copper sheets, if their surfaces are clean, the electrodeposited copper, i.e., the starting sheets, will adhere intimately to their cathode base sheets and be bonded firmly thereto and give rise to great difficulty in stripping of the starting sheets. Accordingly, it has been the common practice to apply onto the surfaces of the rolled copper sheets coating materials such as oils, fats, asphalts, and soaps thereby to prevent excessively strong adhesion. In the case of stainless steel sheets, polishing has been resorted to in order to prevent such bonding of the starting sheets.

Heretofore, starting sheets which have been electrodeposited on cathode base sheets have been stripped by a manual procedure which comprises inserting a knife-edged tool between each starting sheet and its cathode base sheet and prying open a gap between the two sheets thereby to separate them by manually applied force. In this procedure, the resistance to stripping, i.e., the force necessary for stripping the starting sheet from the cathode base sheet, differs extremely depending on the nature of the coating material. For example, when a mixture of 90 percent of a boiled oil and 10 percent of asphalt primer is applied, this stripping force is from 1.0 to 2.5 kg. per 25 mm. of width.

Such a manually stripping procedure depending on human power, however, is accompanied by extreme danger and, moreover, by the risk of damaging the surfaces of the cathode base sheets since a knife-edged tool is used. Since starting sheets adhere strongly to damaged surfaces of the cathode sheets, the subsequent stripping operations after succeeding electrodepositions are more difficult.

Furthermore, when starting sheets are stripped by hand, curvatures and warping to a certain extent in the stripped starting sheets cannot be avoided. According to our experience, it is not possible to accomplish practical stripping by hand without inserting a knife-edged tool between the starting sheet and the cathode base sheet. On the other hand, however, a mechanical stripping procedure is difficult because of the thinness of the starting sheets and is accompanied by the risk of applying excessive force and thereby damaging the cathode base sheets and other parts.

With the aim of overcoming these difficulties, we attempted to accomplish mechanical stripping by attaching low-pressure or vacuum suction cups of disks to starting sheets electrodeposited on cathode base sheet and applying pulling force away from and perpendicularly to each cathode base sheet. However, we found it impossible to separate the starting sheets from their cathode base sheets, irrespective of the size of the suction disks and the magnitude of the pulling force.

The reason for this is that, since the bond between the cathode base sheet and the starting sheet with a layer of a coating agent for facilitating stripping interposed therebetween is due to electrodeposition, no layer of air, whatsoever, exists in the interface parts related to this bond, and a powerful adhesion due to vacuum acts between the cathode base sheet and the starting sheet to resist separation thereof.

Therefore, one solution to this problem is to cause an air layer to be created between the cathode base sheet and each starting sheet to eliminate the adhesion therebetween due to the absence of an air layer.

Another expedient for facilitating stripping is to use a greatly improved coating agent for stripping. Examples of coating agents used or known heretofore are sodium sulfide, calcium sulfide, mercurous chloride, silver nitrate, chain hydrocarbons such as fuel oils, light oils, and paraffin, fatty acids, sodium soaps, boiled oils, asphalts, and emulsions containing light oils.

These coating agents, however, have numerous disadvantages such as short life, the tendency to produce copper powder on the cathode, and the tendency to impair the properties of the electrolytic copper sheets. While oily coating agents are particularly excellent for facilitating the stripping action, they impair the electrodeposition of the copper. While the use of water-soluble coating agent results in good electrodeposition, the subsequent stripping is caused to be somewhat difficult.

Accordingly, the ordinary practice when using new cathode base sheets has been to use, first, an oily coating agent. For example, a coating mixture of a boiled oil and asphalt primer (10 percent) is initially applied, and then, from the succeeding operation, the cathode base sheets are dipped in a 5-percent solution of a water-soluble soap each time electrolytic copper sheets are produced. Ordinarily, after from 7 to 10 cycles of use, copper particles and other impurities are formed as electrolytic copper is electrodeposited on the cathode base plates. Accordingly, an oily coating agent as, for example, a light oil or a boiled oil, is again applied for stripping.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for automatically stripping starting sheets from cathode base sheets in a safe manner without damaging the sheets and thereby to decrease the rate or rejection of defective starting sheets and increase production efficiency and economy.

Another object of the invention is to provide a relatively simple apparatus for thus automatically stripping starting sheets from cathode base sheets.

Still another object of the invention is to provide effective coating agents for application on the surfaces of cathode base sheets to prevent strong bonding thereto of electrodeposited starting sheets thereby to facilitate stripping.

A further object of the invention is to provide coating agents of the above stated character which will not adversely affect the state, properties, and uniformity of the copper starting sheets electrolytically deposited on the cathode base sheets.

According to the present invention, briefly summarized, there is provided a method, and apparatus for automatically stripping starting sheets from cathode base sheets in the preparation of starting sheets in copper electrolysis, the method being characterized by the steps of creating an air layer in one part of the adhering part of each starting sheet electrodeposited on a corresponding cathode base sheet by a physical process such as vibration, percussion, or rolling between rolls and thereafter separating the two sheets by means of low-pressure or vacuum suction disks.

According to the present invention there is further provided a simple apparatus for carrying out the above described method in a practical manner.

According to the present invention, in a further aspect thereof, there is provided a group of new coating agents for application on cathode base sheets before electrolysis which coating agents not only reduce the resistance to stripping of the starting sheets but also cause substantial improvement in the state, properties, and uniformity of the electrodeposited copper.

The nature, principle, details, and utility of the invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawing, in which like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a side elevational view showing one example of a stripping apparatus constituting an embodiment of the invention;

FIG. 2 is an elevational view orthogonal to FIG. 1;

FIG. 3 is a fragmentary elevational view showing one example of a rotating hammer device for creating an air layer between each starting sheet and its cathode base sheet; and

FIGS. 4, 5, and 6 are, respectively, a fragmentary plan view, a fragmentary elevational view, and an elevational view showing one example of a roll device for imparting rolling action to starting sheets and cathode base sheets thereby to create air layers therebetween.

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2, the apparatus shown therein is provided with a suitable horizontally moving conveyor 10 (fragmentarily shown in FIG. 1) supporting a number of cathode base sheets 1 (only one sheet shown) suspended therefrom and moved thereby at a constant speed in the arrow direction of FIG. 1. Each cathode base sheet 1, which bears starting sheets 2, 2 electrodeposited on opposite sides thereof, is thus caused to pass through or by an air layer creating device 3, which may be a vibration percussion device or a rolling device, whereby air layers are created between the cathode base sheet 1 and the starting sheets 2, 2 at one part thereof.

The cathode base sheet 1 and starting sheets 2, 2 thus provided with air layers thereafter move into position between opposed groups of suction disks 4 supported on arms 5 on respective transverse sides of the travel path of the sheets, the arms 5 being pivotally supported on a carriage or bogie truck 7, which can travel in the same direction as the sheets, and being in their closed (inward) position at this time. With the arms 5 thus closed, the suction disks 4 are then caused by a hydraulic (oil-pressure) cylinder for suction attachment to move perpendicularly to the electrodeposited surface and thereby be attached by suction to the surfaces of the starting sheets 2,2.

At the same time, the speed of the truck 7 is synchronized with that of the traveling cathode base sheet 1. Then, as the truck 7 is thus moved, the arms 5 are caused to open transversely and outwardly with a pivotal movement by a hydraulic (oil-pressure) cylinder 8 and gears 9, and, since the cathode base sheet 1 is held by guide rollers 10a and thereby prevented from moving transversely, the starting sheets 2, 2 are stripped from the cathode base sheet 1.

The starting sheets 2, 2 thus stripped and still held by suction by the suction disks 4 are conveyed to suitable means (not shown) for temporary storage, while the cathode base sheet 1 is conveyed at constant speed by the conveyor 10. Each truck 7 is returned to its original position upon completion of one stripping operation to repeat the operation.

In accordance with the invention as mentioned briefly hereinbefore, an air layer is created between each starting sheet 2 and its cathode base sheet 1 by the application thereto of a physical action such as vibration, percussion, or rolling action. Example of devices 3 for applying such action are illustrated in FIGS. 3 through 6.

In one example of a device as shown in FIG. 3 vibratory percussion is applied to the starting sheets and cathode base sheet by a rotating hammer which comprises a shaft 11 rotated at high speed by motive power means 3a and rings 12 having large inner diameters and adapted to be forced outward by centrifugal force due to the rotation of the shaft 11. By suitably positioning this rotating hammer device with respect to the path of the cathode base sheet and starting sheets, it is possible to create an air layer at one part of the bond therebetween.

In one instance of actual practice, a rotating hammer device of the above described organization was operated at a rotational speed of 162,000 r.p.m. to impart vibratory percussion to starting sheets each measuring 680.times.760 mm. (approximately 3.0 kg./sheet) and conveyed at a speed of 16 cm./sec. by a conveyor. As a result, it was possible to carry out fully automatic stripping with a stripping time of 15 seconds/sheet with maximum stripping force of 300 kg. at the upper part and 200 kg. at the lower part.

An example of a roll device suitable for creating air layers between starting sheets and cathode base sheets according to the invention is illustrated in FIGS. 4, 5, and 6. This device comprises, essentially, a pair of opposed rolls 13, 13 rotatable about vertical axes at a peripheral speed equal to the linear speed of each cathode base sheet 1 and deposited starting sheet passed therebetween and therepast, force applying means 14, 14 such as hydraulic piston cylinder motors rotatably supporting respective rolls 13, 13 and being operable to move the rolls toward and away from the sheet 1 on respectively opposite sides thereof, and driving means for rotating the rolls 13, 13.

The driving means comprises an electric motor 15, the output power of which is transmitted through shafts and gears 16, 16 to the rolls 13, 13.

Each of the rolls 13, 13 may be of a cylindrical shape with a straight-line generatrix or with a generatrix of suitable curvature. The roll surface may be knurled with a certain pattern to prevent slipping, or it may be provided with gearlike teeth. Furthermore, a plurality of rows of similar rolls may be used in combination.

In operation the rolls 13, 13 press against and impart rolling action simultaneously to the starting sheets and the cathode base sheet, whereby metallographical strain is produced in these sheets and gives rise to strain in the bond interface between the starting sheets and the cathode base sheet. As a result, a layer of air forms in the interface at one part of the sheets. This rolling action is advantageous in that it does not generate excessive noise, as in the case of vibratory and percussive action, and in that the rolling force can be readily adjusted.

Thus, the present invention provides a method and apparatus whereby air layers can be created between cathode base sheets and starting sheets deposited thereon without stopping the moving sheets, and the operation of stripping starting sheets in copper electrolysis, which operation comprises attaching suction disks onto the starting sheet surfaces by vacuum or low pressure, stripping, and moving and conveying the cathode base sheets and starting sheets, can be made fully continuous and automatic.

It is possible, of course, to carry out discontinuous or successive but intermittent operation also in accordance with the invention. Furthermore, the teachings of the invention can be applied also to the stripping of other metals such as zinc and cadmium which are also processed electrolytically by electrodeposition onto cathode base sheets and stripping therefrom.

The present invention, in another aspect thereof, provides a new group of coating agents for application on the surfaces of cathode base sheets for the purpose of preventing excessively strong bonding between the base sheets and starting sheets deposited thereon. The nature and utility of these coating agents will be apparent from the following detailed description beginning with general considerations and concluding with specific examples of embodiment of the invention.

We have found that organic compounds of phosphoric acid and of thiophosphoric acid, organic phosphorous esters, organic thiophosphorous esters, organic compounds of thiocarbonic acid, compounds of thiocarbamic acid, and thiazole compounds having properties as described hereinafter and used in accordance with the invention as described hereinafter are highly suitable as coating agents.

We have found that by applying one or more of these coating agents on the surfaces of cathode base sheets, it is possible to prevent strong bonding of electrolytic copper to the cathode base sheets and thereby to reduce remarkably the rate of rejection of electrolytic sheets due to defective stripping and the force necessary for stripping.

The coating agents according to the invention have the following characteristics and properties. ##SPC1## ##SPC2##

The above specified compounds are respectively applied on the surfaces of cathode base sheets to produce electrolytic copper sheets in the following manner.

A solution or emulsion of one or more coating agents selected from organic phosphoric acid compounds and organic thiophosphoric acid compounds, with or without one or more known coating agents, is applied onto the cathode base sheets by brushing, swabbing, dipping, spraying, or any other suitable method, and electrolytic copper sheets are produced in an electrolyte of a sulfuric acid and copper sulfate solution.

For the second application and applications thereafter, the above described coating agent or a solution or emulsion of one or more compounds selected from organic phosphoric acid or thiophosphoric acid compounds is ordinarily applied by the above described procedure each time. By this simple procedure, the electrolytic copper sheets can be readily stripped from their cathode base sheets over a long period of operation. We have found that a concentration of the organic phosphoric acid or thiophosphoric acid compounds of at least 0.2 percent is suitable.

When an organic phosphoric acid or thiophosphoric acid compound is used as a coating agent, the resulting resistance to stripping between the cathode base sheet and each electrolytic copper sheet differs with the number of carbon atoms in the chain hydrocarbon radical of the compound. In general, the resistance to stripping decreases with increase in this number of carbon atoms. However, as this number of carbon atoms increases, the compound becomes oleophilic. Therefore, in contrast to a compound in which this number of carbon atoms is small, and which can be used in the form of an aqueous solution, a compound in which this number is large must be dissolved in an organic solvent.

A coating agent in which n=2, R is an alkyl radical, X is ethanol amine, and the number of carbon atoms is 10 or higher is soluble in oils and, in general, is suitable for use as a coating agent for new cathode base sheets. In contrast, such a coating agent in which the above-mentioned number of carbon atoms is eight or less is water soluble or water dispersible and, therefore, is generally suitable as a coating agent for regular stripping, i.e., for the second coating agent application and thereafter.

The aforementioned organic phosphorous ester or organic thiophosphorous esters are ordinarily used in the form of solutions of at least 0.2-percent concentration, being applied on cathode base sheets either singly or as a mixture of two or more thereof. Electrolytic copper sheets are then produced on the cathode sheets in an electrolyte consisting of a sulfuric-acid and copper sulfate solution. By merely applying this coating agent in this manner each time on the cathode base sheets, electrolytic copper sheets can be easily stripped from the cathode base sheets over a long period of operation.

When one of the above-mentioned esters is used thus as a coating agent, the resulting resistance to stripping, in general, decreases with an increase in the number of carbon atoms in the hydrocarbons of the radicals R.sub.1, R.sub.2, and R.sub.3, particularly the chain hydrocarbons. As this number increases, however, the solubility of the ester in organic solvents decreases. We have found that, when R.sub.2 and R.sub.3 are not chain or aromatic hydrocarbon radicals and the radical forming R.sub.1 does not contain more than eight carbon atoms, stripping cannot be readily accomplished when R.sub.2 and R.sub.3 are hydrogen unless there are at least eight carbon atoms in the radical forming R.sub.1.

The aforementioned organic thiocarbonic acid compounds, thiocarbamic acid compounds, and thiazole compounds produce equally effective stripping results when applied either singly or as a mixture of two or more thereof as a coating agent on cathode base sheets. These coating agents are ordinarily used in concentrations of at least 0.2 percent.

When one of these coating agents is used, the resulting resistance to stripping between each cathode base sheet and electrolytic copper sheet deposited thereon differs with the hydrocarbon radical R. In general, with the same number of carbon atoms, a chain hydrocarbon radical results in a lower resistance to stripping than an aromatic hydrocarbon radical, the minimum resistance to stripping resulting from the use of a coating agent with a straight chain.

An important feature of the present invention is that, by producing electrolytic copper sheets with the use of the above described coating agents according to the invention, not only is the stripping greatly facilitated, but the resulting electrodeposition surface is extremely smooth and uniform, and the purity of the product is comparable to that obtained by known methods wherein boiled oil and asphalt primer (10 percent) or soap solutions are used. The cell voltage of the electrolyte and current efficiency also do not vary from those of conventional practice.

Furthermore, when a conventional coating agent is used, the electrolytic copper sheets become firmly bonded to their cathode base sheets unless the sheets are placed in the main electrolytic cell, and electrolysis is started immediately after immersion of the cathode base sheets into soap solution. However, when a coating agent according to the present invention is used, stripping can be easily carried out even when the starting sheets are dried, after the coating is applied thereto, placed in the electrolytic cell, and subjected to electrolysis.

As a result, the present invention affords improvement in the electrolytic conditions relative to those of known practice. For example, since the adhesivity of these coating agents of the invention with respect to cathode base sheets is excellent, there is almost no change in the resistance to stripping even when the electrolyte temperature is raised. This is only one example of the indirect advantages that are afforded. Furthermore, while expedients such as covering the peripheral parts of cathode base sheets with electrically insulative material and providing grooves are resorted to in order to facilitate physically or electrochemically the stripping of electrolytic copper sheets, the present invention has further advantageous features such as the remarkable reduction of damage to these parts.

In order to indicate still more fully the nature and utility of the invention, the following specific examples of procedure constituting preferred embodiments of the invention and comparisons with conventional practice are set forth, it being understood that these examples are presented as illustrative only, and that they are not intended to limit the scope of the invention, which is defined in the appended claims.

EXAMPLE 1

With an electrolyte composed of a solution of 42 grams/liter of copper and 175 grams/liter of free sulfuric acid and under the conditions of a temperature of 55.degree. C. and a cathode current density of 207 A/dm.sup.2, values such as resistance to stripping in the case of electrolysis for 24 hours with the use of rolled copper sheets (measuring 40.times.80 mm.) for cathode base sheets were measured for cases wherein coating agents of the invention were used and compared with the results of cases wherein conventional coating agents were used. The comparative results are set forth in table 1.

The resistance of stripping (or bond strength between each starting sheet and its cathode sheet) is represented in the unit of kg. per 40 mm. of width, by the force required to separate an electrolytic copper sheet deposited on a 40.times.80 mm. cathode from one end of a width of 40 mm. by means of vacuum suction disks (this definition being applicable to all other examples set forth hereinafter). ##SPC3##

This example indicates the results in the case wherein new cathode base sheets are used. While the coating agents of the organic phosphoric or thiophosphoric series according to the invention do not differ greatly from conventional coating agents on the point of resistance to stripping, they are superior in interior appearance and properties as well as uniformity of electrodeposition. Furthermore, aqueous solutions of organic compounds of phosphoric acid, in general, produce better properties of electrodeposition than coating agents having oiliness.

EXAMPLE 2

Under the same electrolytic conditions as in example 1, values of resistance to stripping (kg./40 mm. width) were measured over a long period of operation. The results are indicated in table 2. ##SPC4##

The electrodeposition with the use of a mixture of boiled oil and asphalt primer as the coating agent for the initial application was slightly poor, but the use of coating agents of organic phosphoric acid compounds resulted in good electrodeposition and also somewhat low stripping resistance. As a regular coating agent, a conventional soap produced a stripping resistance of more than 5 kg./40 mm. of width on the 11th stripping (after 11th day) and thereafter, while coating agents of organic phosphoric acid compounds produced stripping resistances of 1 kg./40 mm. of width or less.

In the case of a soap used as a regular coating agent, the stripping resistance increased in all instances at the seventh application and thereafter. However, when the coating agent for a new cathode base sheet was a thiophosphoric acid compound, its life was relatively long. Furthermore, when the regular coating agent was an organic phosphoric acid or thiophosphoric acid compound, a substantially constant stripping resistance was produced over a long period.

EXAMPLE 3

Under the same electrolytic conditions as those set forth in example 1, the following emulsion was used as a coating agent according to present invention. In 80 percent of fluid paraffin, 20 percent of dilauryl triethanolamine phosphate was thoroughly dissolved, and an oil-in-water emulsion containing 10 percent of the solution thus obtained was prepared and used as the coating agent for the second application and subsequent applications by dipping. The values of stripping resistance in this case over a long period are shown in table 3. ##SPC5##

These results indicate that an emulsion is also effective as a coating agent.

EXAMPLE 4

Under the same electrolytic conditions as in example 1, stripping resistances were measured with respect to cathode base sheets of stainless steel (each measuring 40.times.80 mm.). The stainless steel was of Japanese Industrial Standards designation SUS 36 (containing max. 0.03 percent C, 12.00-16.00 percent Ni, 17.00-19.00 percent Cr, 1.20-2.75 percent Mo, and 1.00-2.50 Cu) which was polished with No. 80 emery (sieve number according to Japanese Industrial Standard K-6001, corresponding to sieve No. 80-85 of ASTM). The results are shown in table 4. ##SPC6##

These results indicate that similar effective results can be attained also in the case wherein a stainless steel sheet is used as a cathode base sheet and coated with an organic phosphoric acid compound.

EXAMPLE 5

A copper electrolysis plant having two electrolytic cells was operated in accordance with the new method of the invention and the former conventional method each for 10 days with the use of rolled-copper cathode base sheets for producing electrolytic copper sheets measuring 680.times.760 mm. under the operational conditions of Cu 40 to 44 g./liter, free sulfuric acid 170 to 180 g./liter, and electrolyte temperature of from 51.degree. to 54.degree. C.

A mixture of a boiled oil and asphalt primer was used as a coating agent for the first application of all new base sheets. From the second application, a conventional aqueous soap solution was used in the former method, and an aqueous solution (1.3 percent) of dilauryltriethanolamine phosphate, which is an organic phosphoric acid compound, was used in the new method, these coating agents being applied by dipping the base sheets therein.

The comparative results of these two operations are shown in table 5. ##SPC7##

These results indicate that the use of coating agent containing an organic phosphoric acid compound results in a stripping efficiency which is approximately 5 percent higher and an electrolytic copper sheet rejection rate which is approximately 0.8 percent lower than corresponding values attainable through the use of a conventional coating agent. Furthermore, since the quantity of organic phosphoric acid compound adhering to the electrolytic copper sheets is extremely minute, it has no effect whatsoever on the quality of the product.

EXAMPLE 6

Under the same electrolytic conditions as those set out in example 1, stripping resistances and other conditions were measured with respect to the coating agent and organic phosphorus ester after application of the present invention. The following table 6, shows a comparison between them. The value of the stripping resistance is denoted in units of force (Kg./40 mm. width) required for stripping the electrolytic copper starting sheet off the cathode base sheet of 40.times.80 mm. by means of vacuum suction discs from the end of the base sheet of 40 mm. width. ##SPC8##

This example indicates the effectiveness of the coating agents when used on new cathode base sheets. Even when the alkyl radical in the organic phosphorous ester is an octyl radical, a mere 1 percent of the ester results in a stripping resistance which approximately the same as that attainable with a conventional coating agent, and an organic phosphorous ester having an alkyl radical with a larger number of carbon atoms has an even higher performance, producing excellent results in the state, properties, and uniformity of the electrodeposition.

EXAMPLE 7

The same performance values as those of example 6 were determined for coating agents containing organic thiophosphorous esters by carrying out electrolysis under the same electrolytic conditions as in example 1, whereupon the results shown in table 7 were obtained. ##SPC9##

As indicated in table 7, coating agents containing organic thiophosphorous esters are superior in performance to conventional coating agents on the points of stripping resistance and electrodeposition state, properties, and uniformity.

EXAMPLE 8

Organic thiophosphorous esters as indicated in table 8 were tested, and the resulting values of stripping resistance (kg./40 mm. width) were measured over a long period under the same electrolytic conditions as in example 1. The values of stripping thus measured are shown in table 8. ##SPC10##

As indicated in table 8, coating agents containing organic thiophosphorous esters are superior to the conventional mixture of boiled oil and asphalt primer in stripping resistance also over a long period of operation.

Example 9

The performance of coating agents containing compounds of xanthic (xanthogenic) acid represented by the general formula

in which radical X represents an oxygen atom, and Y and Z represent atoms of sulfur and potassium, respectively, were compared with those of a conventional coating agent by carrying out electrolysis under the same electrolytic conditions as in example 1 and with new cathode base sheets, whereupon the results shown in table 9, were obtained. ##SPC11##

It can be observed from table 9 that the stripping resistance decreases somewhat as the alkyl radical R increases in size and that the stripping resistance also decreases with increases in the concentration of the xanthogenate solution.

EXAMPLE 10

The procedure of example 9 was carried out with coating agents containing dixanthic acid compounds represented by the general formula

in which radical X represents an oxygen atom, and Y and Z, respectively, represent a sulfur atom and

under the same electrolytic conditions as in example 1 and with new cathode base sheets, whereupon the results shown in table 10 were obtained. ##SPC12##

These dixanthogenates are insoluble in water but are soluble in organic solvents. As indicated in table 10, these dixanthogenates are superior to a conventional coating agent of boiled oil and asphalt primer, with respect to outer appearance properties and uniformity of electrodeposition.

EXAMPLE 11

Coating agents consisting of aqueous solutions of dithiocarbamates of the general formula

, where the radical X is a nitrogen atom, and Y and Z are respective atoms of sulfur and sodium, were tested under the same electrolytic conditions as in example 1 and with the use of new cathode base sheets, whereupon the results shown in table 11 were obtained. ##SPC13##

As indicated in table 11, these dithiocarbamates are superior to conventional coating agents.

EXAMPLE 12

Coating agents containing a compound of thiazole of the general formula

, in which the radical X represents a sulfur atom, and Y and Z represent, respectively, atoms of sodium and hydrogen, were tested on new cathode base sheets under the same electrolytic conditions as in example 1, whereupon the results shown in table 12 were obtained. ##SPC14##

EXAMPLE 13

The stripping resistances (kg./40 mm. width) of coating agents containing a dixanthogenate and a dithiocarbamate were compared with those of a conventional coating agent under the same electrolytic conditions as in example 1 over a long period, whereupon the results shown in table 13 were obtained. ##SPC15##

As indicated in table 13 these coating agents according to the present invention are superior to the conventional mixture of boiled oil and asphalt primer in stripping resistance over a long period of operation.

It should be understood, of course that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

Claims

We claim:

1. In the preparation of starting sheets for cathode base sheets by electrolysis of metal, including the step of first coating the surface of each cathode base sheet with a coating agent to prevent strong bonding of a starting sheet to the surface thereof, then carrying out electrolysis to deposit the starting sheet on the surface of the cathode base sheet, subsequently forming a layer of air by a physical process at one portion between the starting sheet thus deposited and the cathode base sheet upon completion of the electrolysis, and stripping the starting sheet from the cathode base sheet by means of lower pressure or vacuum suction discs, an improvement comprising

performing said coating step with said coating agent selected from the group consisting of solutions and emulsions of organic compounds of phosphoric acid and thiophosphoric acid, organic phosphorus esters, organic thiophosphorus esters, compounds of xanthic acid, organic compounds of thiacarbonic acid, compounds of thiacarbonic acid, and thiazole compounds.

2. The method as claimed in claim 1 in which the layer of air is formed by applying vibration to a part of the starting sheets.

3. The method as claimed in claim 1 in which the layer of air is formed by applying percussion to a part of the starting sheets.

4. A method as claimed in claim 1 in which the coating agent is at least one member selected from the group consisting of solutions and emulsions of organic compounds representable by the general formulas:

(RO).sub.n PO (OX).sub.3.sub.-n

where

R is a chain hydrocarbon radical,

X is a member selected from the group consisting of hydrogen, sodium, potassium, and amino alcohol, and

n assumes the values of 1, 2, and 3; (RO).sub.n PO (SX).sub.3.sub.-n

where

R is a chain or aromatic hydrocarbon radical,

X is a member selected from the group consisting of hydrogen, sodium, potassium, and amino alcohol, and

n assumes the values of 1, 2, and 3;

where

R.sub.1 is a chain hydrocarbon radical and has eight or more carbon atoms when R.sub.2 and R.sub.3 are hydrogen,

each of R.sub.2 and R.sub.3 is a member selected from the group consisting of chain and ring hydrocarbon radicals, hydrogen, sodium, potassium, amines, and

each of Z.sub.1, Z.sub.2, and Z.sub.3 is a member selected from the group consisting of oxygen and sulfur; and

where

R is a hydrocarbon radical,

X is a nucleophilic reagent selected from the group consisting of oxygen, sulfur, nitrogen, and imino group,

Y is a radical selected from the group consisting of sulfur, nitrogen, and imino radicals, and

Z is a radical selected from the group consisting of hydrogen, metal, and hydrocarbon radicals,

5. A method of preparing starting sheets for cathode base sheets by electrolysis of metal, comprising the steps of first coating the surface of each cathode base sheet with a coating agent to prevent strong bonding of a starting sheet to the surface thereof, then carrying out electrolysis to deposit the starting sheet on the surface of the cathode base sheet, said coating agent being selected from the group consisting of solutions and emulsions of organic compounds of phosphoric acid and thiophosphoric acid, organic phosphorus esters, organic thiophosphorus esters, compounds of xanthic acid, organic compounds of thiocarbonic acid, compounds of thiocarbonic acid, and thiazole compounds.