WO2016075287A1

WO2016075287A1 - Production of chromium layers on intaglio printing cylinders

Info

Publication number: WO2016075287A1
Application number: PCT/EP2015/076551
Authority: WO
Inventors: Thilo VON VOPELIUS; Christoph Gschossmann
Original assignee: Maschinenfabrik Kaspar Walter Gmbh & Co. Kg; Vopelius Chemie Ag
Priority date: 2014-11-14
Filing date: 2015-11-13
Publication date: 2016-05-19
Also published as: EP3250733A1; ES2893649T3; DE102014116717A1; EP3250733B1; PL3250733T3

Abstract

The invention relates to the use of an electrolyte for the electrolyte deposition of chromium as metal on an intaglio printing cylinder, comprising (a) a chromium(III)-salt, (b) a compound of formula (I), wherein R represents NH₂, OH or SO₃H and n is a whole number between 1 - 3, (c) formic acid, and (d) at least one additive. The invention also relates to a method for the deposition of a chromium layer, to an intaglio printing cylinder coated with chromium and obtained according to said method, and to an electrolytic cell for coating intaglio printing cylinders with chromium.

Description

MANUFACTURING

FROM CHROMIUM LAYERS TO LOW PRESSURE CYLINDERS

The invention relates to the use of an electrolyte for the electrolytic deposition of chromium as metal on gravure cylinders, in particular as a hard chrome layer or wear protection layer, a process for producing chromium layers, in particular hard chrome layers, on gravure cylinders, a gravure cylinder with a chromium layer obtainable by this process and a Electrolysis cell, which is designed to coat a gravure cylinder containing the electrolyte.

With gravure cylinders, the printing form for gravure printing is called. The base cylinder is generally a steel tube core which is first coated with copper in an electrolytic bath and then with chromium after application of the image data. This process takes place by means of a galvanic coating of the gravure cylinder with chromium.

Galvanic processes for surface coating on objects have long been known. By means of such galvanic processes, articles can be given specific functional and / or decorative surface properties, for example hardness, corrosion resistance, metallic appearance, gloss, etc.

In this case, from a galvanic bath, which contains the metal to be deposited as a salt in solution, this metal is deposited by means of direct current on the cathode connected object. The object to be coated is usually a metallic material. If this object is not electrically conductive, a metallization of the surface is carried out beforehand.

Galvanic baths containing chromium are used in technical applications usually for the production of particularly hard mechanically resistant layers.

The application of chromium to objects is of particular technical relevance, with the resulting chromium layer serving either for decorative applications or as a hardcoat on objects for technical applications. In decorative applications, in particular a bright and highly reflective chromium layer is desired. For such technical applications, the applied chromium layers are to be wear-resistant, abrasion-resistant and heat-resistant and corrosion resistant. Such items to be chromed are, for example, pistons, cylinders, liners or axle bearings.

Galvanic plating is usually carried out in plating baths containing chromium (VI) salts and sulfuric acid using insoluble lead / antimony or lead / tin anodes. As chromium (VI) salt in particular Cr0 _{3 is} used. A major problem in galvanic applications, such as chromium plating using chromium (VI) solutions, is gas evolution, particularly of hydrogen, due to the low efficiency of 15% to 25% and, to a lesser extent, formation of anodic oxygen acidic, corrosive and sometimes also toxic spray mist leads. As a result of this evolution of gas, for example, a chromic acid mist is entrained, which is severely detrimental to health and requires intensive extraction of the surface of the galvanic bath. To limit this occurring chromic acid mist, surface-active substances are used in chromium plating baths, which reduce the surface tension to form a foam blanket. Such surfactants are also referred to as wetting agents. The chromium (VI) electrolytes also have the disadvantage that highly toxic and carcinogenic Cr0 ₃ is used.

In order to avoid these disadvantages of chrome plating, numerous efforts have been made in the past.

For example, methods for depositing chromium layers from baths containing non-toxic chromium (III) salts are known.

But all these methods have significant disadvantages. Either only layers of chromium can be deposited in too low layer thickness, or the system structure is so complicated that industrial use is not possible.

WO 2008/014987 A2 discloses an electrolyte for the electrodeposition of chromium layers as hard chrome layers for protection against wear and corrosion and / or as decorative chrome layers comprising a catholyte having at least one chromium (III) salt and at least one chromium (II) ion-stabilizing compound, and an anolyte comprising a Bronsted acid, wherein the catholyte and the anolyte by an anion-selective membrane Q

are separated from each other. In this case, the anolyte circulation from the catholyte circuit is separated from one another by this membrane. This is to ensure that the chromium (III) salts contained in the electrolyte are not oxidized to chromium (VI). The disadvantage of the technical teaching from WO 2008/014987 A2 is that it is not possible to deposit chromium layers which satisfy the industrially required requirements, since the quality of the chromium layers is not sufficient, i. they have pores, smallpox and craters.

Accordingly, the object of the present invention is to make it possible to provide chromium layers which do not have the disadvantages known from the prior art and which satisfy the requirements which have been made especially for chromium coatings on gravure printing cylinders.

According to the invention this is achieved by the use of an electrolyte for the electrolytic deposition of chromium as metal on a gravure cylinder, wherein the electrolyte comprises:

(a) a chromium (III) salt,

(b) a compound of the formula (I)

OH

R- (CH ₂ ) _n -C = O

(I) wherein R is NH ₂ , OH or SO ₃ H and n is an integer from 1 to 3,

(c) formic acid and

(d) at least one additive.

The formic acid present in the electrolyte serves, in particular, to remove the oxygen formed from the chromium (III) salt by the reaction being carried out to CO ₂ and H ₂ O.

The amount of formic acid in the electrolyte is favorably 1, 0 mol / 1 to 3.0 mol / 1, based on the electrolyte. With this amount of formic acid in the electrolyte is a particularly favorable removal of oxygen. This quantity refers to the electrolyte before the chromium deposition. In the course of chromium deposition, it is possible that the pH of the electrolyte changes. To adjust the pH, it is also possible to add further formic acid. This added amount should not be taken into account for the amount of formic acid in the electrolyte, ie before the beginning of the deposition. Preferably, the compound of formula (I) is glycine, glycolic acid, sulfoacetic acid or a mixture of these. Further, it is preferable that in the electrolyte, the amount of the compound of the formula (I) is 0.5 mol / 1 to 1.5 mol / l based on the electrolyte.

The compound of formula (I) is used to adjust the pH of the electrolyte, wherein the pH can be adjusted in a particularly favorable manner with the indicated amounts.

In one embodiment of the electrolyte according to the invention, the chromium (III) salt comprises an inorganic and / or an organic chromium (III) salt. The term "chromium (III) salt" as used herein means any chromium (III) salt with which chromium can be deposited as a metal layer on articles. Preferably, the inorganic chromium (III) salt is potassium chrome alum, ammonium chrome alum, chromium sulfate, chromium nitrate, chromium chloride and mixtures of two or more thereof. The organic chromium (III) salt may preferably be chromium citrate, chromium formate, chromium oxalate and mixtures of two or more thereof.

Conveniently, the amount of the chromium (III) salt is 0.25 mol / 1 to 2.0 mol / 1, based on the electrolyte. With these amounts, chromium layers can be produced on metallic objects by electrolytic deposition in a particularly favorable manner.

In the electrolyte is present as component (d) an additive. Preferably, it comprises a complexing agent and / or a wetting agent. As wetting agents, wetting agents used in the production of chromium layers by electrodeposition can usually be present in the electrolyte. These wetting agents cause the lowering of the surface tension, thus allowing H ₂ bubbles to detach from the cathode. As a result, pore formation can be avoided in a simple and favorable manner and thus uniform chromium layers can be produced.

The complexing agents are preferably compounds with short-chain alkyl chains (1 - 4 C-atoms) with 1 or 2 carboxyl groups or their Derivatives and having 1 or 2 thio and / or sulfone groups or the following compound

S

in which

n is an integer from 1 to 5, in particular 3,

Ri is a C 1 -C 5 -alkyl radical, in particular CH ₃ CH ₂ -, and

X is a metal ion to balance the negative charge, in particular Na ⁺ , K ⁺ , Ca ²⁺ , Mg ²⁺ .

Particularly preferred complexing agent is the compound N, N-dimethyl-dithiocarbamylpropylsulfonic acid sodium salt (DPS). When using DPS particularly good chromium layers are obtained.

The amount of the additive present in the electrolyte may be 0.01 g / 1 to 2.0 g / l, based on the electrolyte. The amount of the complexing agent may be 0, 5 mol / 1 to 4, 0 mol / 1. The amount of wetting agent may be 0 mol / 1 to 0, 5 mol / 1.

The subject of the application is also a method for producing a chromium layer on a gravure cylinder. In this case, the electrolyte can be used in the process according to the invention.

In this case, the chromium layer has proven to be particularly favorable for gravure cylinder, since it meets the high demands on chrome layers on such gravure cylinders.

The electrolytic deposition of chromium layers can be carried out in an electrolysis cell which is filled with the electrolyte. This is the electrolyte described above. In the electrolyte anode and cathode are immersed. When a DC voltage is applied to these two electrodes, ie anode and cathode, the chromium is deposited on the gravure cylinder. In this case, this is connected as a cathode, that is, in the object to be coated is the cathode. If it is not metallically conductive, it can be made electrically conductive by a pretreatment. In some cases, this structure is varied so that an electrolysis cell is ready. - G -

in which the electrolyte is separated by a semipermeable membrane into a cathode (electrolyte in the cathode space) and an anolyte (electrolyte in the anode space). The substrate, i. The cathode as the object to be coated, immersed in the catholyte containing the deposited chromium ions. When a voltage is applied, a current flows through the membrane through the membrane into the catholyte. Such a system of catholyte and anolyte is described, for example, in WO 2008/014987 A2, with full reference being made to WO 2008/014987 A2 with regard to the further details of this type of electrolysis cell.

The anode used in the electrolytic cell may be an insoluble anode, e.g. be a Mischoxidanode. The anode may have a pocket, e.g. is designed as an anode basket. The pocket may be open at the top and serves to receive metallic chrome elements, e.g. Chrome pellets.

In one embodiment of the method according to the invention, the preparation of the chromium layer can be carried out at a pH of 2.0 to 4.5. As already described above in connection with the composition of the electrolyte, the adjustment of the pH can be carried out by the above compound of the formula (I).

In another embodiment of the method according to the invention, the preparation of the chromium layer can be carried out at a temperature of 20 ° C to 60 ° C. This can be achieved, for example, by setting the temperature of the electrolyte to a value within this range by means of corresponding heating and cooling devices.

In another embodiment of the method according to the invention, the chromium layer can be produced at a current density of 5 to 60 A / dm ² .

In a further embodiment of the method according to the invention, the electrolyte can be moved, for example so that a circulation of five bath volumes, ie volume of the electrolyte, takes place per hour. Since devices known per se for depositing chromium layers on articles can be used for the method according to the invention, the volumes of the electrolyte baths of these devices known per se serve as a basis for determining the bath volumes in the method according to the invention. In another embodiment of the method according to the invention, the gravure cylinder can be moved at a speed of 1 to 20 cm / s.

With the use according to the invention and the process according to the invention, chromium coatings of particularly outstanding quality are obtained, which surprisingly satisfy the requirements imposed on gravure cylinders. In particular, smooth, uniform surfaces are obtained which have substantially no pores, smallpox or craters. The layer thickness of the chromium layers obtained can be thicker than previously available layers. In particular, layer thicknesses of 100 μνΆ and more can be obtained. Furthermore, chromium layers of high hardness can be produced, in particular of more than 900 HV. The chromium layers obtainable using the electrolyte or using the method according to the invention are corrosion-resistant, wear-resistant, have favorable frictional properties and are thermally and chemically resistant. Furthermore, the available chrome layers are bright and well reflective, so they are also suitable for decorative purposes. Furthermore, the chromium coating can be applied using the electrolyte according to the invention or with the method according to the invention in a simpler, faster and more cost-effective manner.

As already stated above, has a chromium layer, which was prepared using the electrolyte or using the method according to the invention, a greater thickness than previously available layers, a smooth, uniform surface, which is in particular free of pores, smallpox and Kra- ter , as well as a very high hardness. With a conventional X-ray diffractometry investigation it was possible to show that the chromium layers obtained with the electrolyte or the method according to the invention have a lattice constant of 2.92 angstroms or more and can thus be termed amorphous layers. Thus, the chromium layers obtainable with the electrolyte or with the method according to the invention differ from chromium layers, which can be produced with other electrolytes and / or other processes according to the prior art.

To determine the lattice constant of the chromium coating, X-ray diffractometry studies were carried out on a chromed brass sample (18 μm layer thickness). The measurement took place in the smoother area of the chromium deposition in the middle of the sample. FIG. 1 shows the diffractogram of the chromed brass sample. The chromium layer thickness (18 μιη) is so large that no signals appear from the ground (brass). The upper curve is the trace without subtraction of the ground, the lower one with. Only a broad peak at an angle 29 = 43, 76 ° can be seen, corresponding to the lattice planes (1 10), for the lattice planes (200), (21 1) and (220) no peaks could be observed. From the width of the peak (100), the crystallite size was calculated to be 2-3 nm, ie the chromium is X-ray amorphous. The lattice constant was calculated from the interplanar spacing: 292.32 pm (JCPDF database: 288.39 pm). The lattice constant of 292.32 pm corresponds to 2, 9232 Å as stated above.

The invention furthermore relates to a chromium layer obtainable by the process according to the invention, as described in detail above.

Further, an electrolytic cell containing an anode, a cathode and an electrolyte, as described in detail above, the subject of the invention, wherein the electrolytic cell according to the invention is designed so that gravure cylinder can be coated, in particular gravure cylinder or gravure rolls, such as They are used for example in printing processes.

An example of an electrolyzer specifically designed for gravure coating will be described below. It shows

FIG. 2 shows a bath apparatus in a schematic illustration during a cylinder change phase; FIG. and

3 shows the bath apparatus according to FIG. 2 during a galvanization phase.

2 and 3 show a bath apparatus in different process states, namely firstly at the time of a cylinder change (FIG. 2), when a gravure cylinder 21 has just been inserted into the bath apparatus by means of a crane (not shown) and through storage facilities belonging to a storage facility. bridge 22 is held and in a Galvanisierungsphase (Fig. 3), in which the lateral surface of the gravure cylinder 21 is to be coated with chromium. Since the components in FIGS. 2 and 3 are substantially identical, they are identified by the same reference numerals. The bath apparatus has an upper tub 23 and a lower tub 24 arranged underneath. In the upper tub 23 and in the lower tub 24 is a liquid electrolyte 25 which is pumped by means of a pump 26 from the lower trough 24 in the upper trough 23 and via a vertically movable in at least two positions overflow 27 back into the lower trough 24 flows. Alternatively, it is also possible to arrange two mutually apparent overflows at different height levels. In the upper tub 23, a vertically movable anode device is further arranged, which essentially consists of an anode rail 28 and an anode basket 29, which is electrically and mechanically coupled to the anode rail 28 and serves as a metal holding device. The anode basket 29 may also consist of a plurality of assembled anode baskets or grids or be designed as an anode pocket. Usually, the anode basket 29 is made of titanium and filled with chromium pellets as metal elements 29a. When current is applied, the chromium decomposes, so that chromium ions migrate via the electrolyte 25 to the surface of the gravure cylinder 21 connected as cathode and settle there in the form of a chromium coating.

The anode basket 29 may also be part of an insoluble anode. The metallic chromium available at the anode is dissolved in the electrolyte 25 and thus enriches the electrolyte 25. Of the bearing bridges 22 is shown in Figs. 2 and 3, only one. The two bearing bridges 22 are movable on rails 30a, 30b in the axial direction of the gravure cylinder 21 by means of spindles or other suitable adjusting mechanisms, so that they clamp the rotogravure cylinder 21 between them and keep them rotatable.

As can be seen in FIGS. 2 and 3, about one half of the upper trough 23 remains freely accessible at the top by the bearing bridges 22 supporting on one side, so that the anode rail 28 extending there parallel to the axial direction of the gravure cylinder 21 is freely vertically movable. The vertical movement of the anode rail 28 to the anode basket 29 is otherwise known, so that a further description and illustration is not required. The degree of filling of the electrolyte 25 in the upper tub 23, that is, the height level of the electrolyte 25, can be adjusted by means of the vertically movable overflow 27 between a height level 31 in the cylinder change phase and a height level 32 in the plating phase.

Fig. 3 shows the bathing apparatus in the plating phase in which the gravure cylinder 21 is almost completely submerged. In particular, immersion depths can be greater than 65% for large cylinders (1500 mm in circumference) and up to 80% for smaller cylinders (800 mm in circumference).

The anode basket 29 is pulled up laterally, so that it forms an approximately 50% larger Korboberfläche compared to the known semi-submersible bath.

After completion of the electroplating phase, the anode rail 28 is moved with the anode basket 29 down into the upper trough 23, as shown in Fig. 2. At the same time or with a time delay, the overflow 27 is lowered, so that the electrolyte 25 flows down to the height level 31 into the lower sump 24.

As can be seen in Fig. 2, thereby can reach a state in which the anode basket 29 is still completely covered by the electrolyte 25, while the gravure cylinder 21 is completely free above the electrolyte level 31 and there dug easily with the crane, not shown can be.

To reduce the amount of electrolyte in the upper tub 23, the upper tub 23 is tapered in the lower region. The rejuvenation can z. B. with the help of additionally inserted sheets 33 or by appropriate adaptation of the walls of the upper tub. Furthermore, it is possible to use blocks or boxes to displace volume. The limitation or reduction of the volume of the upper trough 23 has the advantage that not too much electrolyte 25 has to be pumped up from the lower trough 24. Accordingly, there is no risk that the sub-tub 24 is completely emptied and the pump 26 runs dry.

In one embodiment of the electrolysis cell, the latter has a catholyte and an anolyte, the electrolyte according to the invention being present in the catholyte.

The electrolysis cell according to the present invention is expressly understood as an electrolytic cell containing the electrolyte as detailed above is described contains. As a container that can be used as an electrolytic cell, any suitable for the skilled person in question vessel can be used, as it is in particular commonly used in electroplating. The cathode used is usually the object to be coated, on which the chromium layer is to be deposited, ie the gravure cylinder. Anodes which are known to the person skilled in the art can be used as the anode. The anode may be a sheet, plate material, sintered material or expanded material. Examples of insoluble anodes are those made from a material selected from the group consisting of platinized titanium, graphite, stainless steel, titanium coated with iridium-transition metal mixed oxide, tantalum or niobium or special carbon material and combinations of these anodes. It is possible if the anode material used is a titanium, niobium or tantalum sheet coated with mixed metal oxides. Furthermore, mixed metal oxide anodes, in particular of iridium-ruthenium mixed oxide, iridium-ruthenium-titanium mixed oxide or iridium-tantalum mixed oxide can be used. Further, the anode may be a mixed oxide anode in which titanium as the anode base material is coated with platinum, iridium or palladium oxide. The shape of the anode can be adapted by the skilled person according to the respective purpose. The anode system may, for example, be one in which the anode is in direct contact with a membrane, ie the anode is coated with a membrane. It is a so-called direct contact membrane anode, as it is known from DE 10 2010 055 143 AI. The following polymers can be used in a favorable manner as polymer membrane: polypyrene membranes, olefin polymer membranes, sulfonated polystyrene membranes, fluorinated / perfluorinated sulfonated polymer membranes (PFSA membranes), S-PEEK-S-PSU, PSU-CI, ICVT membranes, aryl polymer membranes, polyether ketone membranes, polybenzimidazole membranes, thermoplastic polymer membranes, perfluorosulfonic acid polymer membranes, perfluoro carboxylate ionomers, polyamides, polyamines, poly (vinyl alcohol) membranes and perfluorophosphonate membranes. It can be used for cations permeable membranes. With regard to the further details of these membranes, reference is made to DE 10 2010 055 143 A1, to which reference is made in its entirety. With the device according to the invention, the electrolyte can be used in a particularly favorable manner or the process according to the invention can be carried out in a particularly favorable manner, so that chromium layers with above-mentioned intrinsic properties can be obtained. Shafts on gravure cylinders can be obtained in a particularly favorable manner.

The following examples are intended to further illustrate the invention. It should be understood that these examples are only intended to illustrate the present invention. They should in no case be understood to limit the invention to these examples.

Examples 1 to 9

An electrolyte of the following composition was provided:

- 0, 77 mol / 1 Kaliumchromalaun-dodecahydrate

- 1, 5 mol / 1 formic acid and

- 1, 0 mol / 1 glycine.

Further, the additives (brightener and wetting agents) indicated in the table were added to the electrolyte in the amounts shown in the table.

The Verchromungsanlage had a container in which the gravure cylinder to be coated could be hung vertically so that they can be moved at different rotational speed. Three anodes (direct contact anodes) were mounted in a ring around the cylinder so that the distance between anode and cylinder could be varied. Direct contact anodes are anodes in which an ion-permeable membrane is applied directly to the anode sheet. The following polymers can be used in a favorable manner as polymer membrane: polypyrole membranes, olefin polymer membranes, sulfonated polystyrene membranes, fluorinated / perfluorinated sulfonated polymer membranes (PFSA membranes), S-PEEK-S-PSU, PSU-CI, ICVT membranes, aryl polymer membranes, polyether ketone membranes, polybenzimidazole membranes, thermoplastic polymer membranes, perfluorosulfonic acid polymer membranes, perfluoro carboxylate ionomers, polyamides, polyamines, poly (vinyl alcohol) membranes, and perfluorophosphonate membranes. In this case, permeable membranes can be used for cations. With regard to the further details of these membranes, reference is made to DE 10 2010 055 143 A1, to which reference is made in its entirety. Furthermore, a circulation pump for the electrolyte was installed in the system, whose pumping capacity could also be varied. To keep the electrolyte clean, a filter is installed in the electrolyte circuit. A heating and cooling device is used to keep the temperature constant. A pH sensor permanently measures the pH, which is kept within the desired range by the addition of formic acid. The actual temperature and pH are given in the table.

In order to improve the quality of the chromium layer and to avoid the formation of pores, on the one hand various wetting agents were added as an additive and, on the other hand, different deposition parameters, such as the temperature of the electrolyte or the rotational speed of the gravure cylinder, were varied. The table below gives an overview of the experiments:

DPS = N, N-dimethyl-dithiocarbamyl-propyl-sulfonic acid sodium salt

For all experiments, the above-mentioned base electrolyte was used. The layer thickness was always about 10 μνΆ deposited.

It could be deposited in all these experiments shiny chrome layers. Also, each wetting agent used significantly reduced pore formation, i. Chrome layers were obtained which were uniform and had no pores. The number of pores decreased with increasing wetting agent content.

The anodes used were coated with a special ion-selective membrane (Navion ^®). This prevented the oxidation of Cr (III) to Cr (VI), which arrests the chromium deposition.

The chromium (III) salts used, the necessary complexing agents, buffering agents and wetting agents for lowering the surface tension of the electrolyte lead, in particular in their entirety, to hard chrome layers, which are characterized by high gloss and hardness and excellent abrasion resistance, as well as the qualitative requirements for the industrial application suffice. The above examples show that the chromium layers obtained are particularly well suited for coating gravure cylinders.

Claims

claims

Use of an electrolyte

full:

(a) a chromium (III) salt,

(b) a compound of the formula (I)

OH

R- (CH ₂ ) _n -C = O (I) where R is NH ₂ , OH or SO ₃ H and n is an integer from 1 to 3,

(c) formic acid and

(d) at least one additive,

for the production of chrome layers on gravure cylinders.

Use according to claim 1, wherein the compound of formula (I) comprises glycine, glycolic acid or a mixture thereof.

Use according to any one of the preceding claims, wherein the chromium (III) salt comprises an inorganic and / or organic chromium (III) salt, in particular wherein the inorganic chromium (III) salt is selected from potassium chrome alum, ammonium chrome alum, chromium sulfate, chromium nitrate, Chromium chloride and mixtures of two or more thereof, or wherein the organic chromium (III) salt is selected from chromite, Chromformiat, Chromoxalat and mixtures of two or more of these.

Use according to one of the preceding claims, wherein the additive comprises a complexing agent and / or a wetting agent, in particular wherein the complexing agent is a compound having short-chain alkyl chains (1-4 C-atoms) with 1 or 2 carboxyl groups or derivatives and 1 or 2 thio and / or sulfone groups or the following compound

S

I i

Ri -O-C- (CH ₂ ) "- S0 ₃ ^2" X in which

n is an integer from 1 to 5, in particular 3,

Ri is a C 1 -C 5 -alkyl radical, in particular CH ₃ CH ₂ - and

A method of forming a chrome layer on gravure cylinders by electrolytic deposition of chromium, wherein the chromium layer is deposited on the gravure cylinders using an electrolyte as defined in any one of claims 1 to 4.

The method of claim 5, wherein the preparation of the chromium layer at a pH of 2, 0 to 4, 5 takes place.

Method according to one of claims 5 or 6, wherein the preparation of the chromium layer is carried out at a temperature of 20 ° C to 60 ° C.

Method according to one of claims 5 to 7, wherein the preparation of the chromium layer is carried out at a current density of 5 to 60 A / dm ² .

Method according to one of claims 5 to 8, wherein an electrolyte movement takes place by circulation of 5 bath volumes per hour.

Method according to one of claims 5 to 9, wherein the gravure cylinder is moved at 1 to 20 cm / s.

Gravure printing cylinder with a chromium layer, produced by the method according to one of claims 5 to 10.

An electrolytic cell comprising an anode, a cathode and an electrolyte as defined in any one of claims 1 to 4, wherein the electrolytic cell is adapted for chromium plating gravure cylinders.

An electrolytic cell according to claim 12, wherein the electrolytic cell comprises a catholyte and an anolyte, the electrolyte being present in the catholyte.

14. An electrolytic cell according to any one of claims 12 or 13, wherein the anode is an insoluble anode and having a pocket for receiving metallic chromium elements. 15. An electrolytic cell according to any one of claims 12 to 14, wherein the anode is a Mischoxidanode.