DE102009023160A1 - Gravure printing method for producing catalyst layers on e.g. ionomer membranes, involves utilizing printing plate that exhibits print image with interrupted line grid pattern whose longitudinal lines are arranged against pressure direction - Google Patents

Abstract

The method involves utilizing a printing plate that exhibits a print image with an interrupted line grid pattern whose longitudinal lines are arranged against a pressure direction in an angle between 20 to 70 degree. The image exhibits drawing volume in a range of 150 to 250 milli liter per meter square, and exhibits corroding depth in a range of 120 to 200 micrometer. Produced catalyst layers possess a dry coating weight in a range of 2 to 15 micrometer. The longitudinal lines exhibit line length (L) in a range of 0.1 to 20 mm and width (B) of the lines in a range of 0.1 to 0.5 mm. An independent claim is also included for a low printing plate for production of catalyst layers on substrate materials.

Description

The The present invention relates to a process for the preparation of Fuel cell components, in particular a gravure printing method for the preparation of catalyst layers, electrodes and membrane-electrode assemblies ("MEEs") for Polymer Electrolyte Membrane Fuel Cells ( "PEM fuel cell").

fuel cells locally convert a fuel and an oxidizer separated from each other on two electrodes in electricity, heat and water around. As fuel is usually hydrogen or a hydrogen-rich gas, as an oxidant oxygen or Air. The process of energy conversion in the fuel cell draws characterized by a very high efficiency. For this reason gain fuel cells in combination with electric motors increasingly Meaning as an alternative for conventional internal combustion engines. The PEM fuel cell is suitable due to its compact design, their power density and high efficiency for the use as an energy converter in motor vehicles.

The PEM fuel cell consists of a stacked arrangement ("stack") of membrane-electrode assemblies ("MEE"), between which arranged bipolar plates for gas supply and current dissipation are. A membrane-electrode assembly consists of a solid polymer electrolyte membrane, on both sides with catalyst-containing reaction layers is provided. One of the reaction layers is as an anode for the oxidation of hydrogen and the second reaction layer as Cathode designed for the reduction of oxygen. On These reaction layers become so-called gas distribution structures ("Gas diffusion layers", GDLs) made of carbon fiber paper or carbon fleece applied, the good access of the reaction gases to allow the electrodes and a good dissipation of the cell current. Anode and cathode contain so-called electrocatalysts, the the respective reaction (oxidation of hydrogen at the anode or reduction of oxygen at the cathode) catalytically support. As catalytically active components are usually the precious metals, preferably the metals of the platinum group of the periodic table of the Elements (PGMs) used. The majority become so-called supported catalysts used in which the catalytically active platinum group metals in highly dispersed form on the surface of a conductive Carrier material were applied.

The polymer electrolyte membrane consists of proton-conducting polymer materials. These materials will also be referred to as ionomers for short. Preference is given to using a tetrafluoroethylene-fluorovinyl ether copolymer having acid functions, in particular sulfonic acid groups. Such materials are, for example, under the trade name Nafion ^® (EI du Pont) or Flemion ^® (Asahi Glass Co.) sold. However, other, in particular fluorine-free, ionomer materials, such as sulfonated polyether ketones or aryl ketones or polybenzimidazoles can also be used. In addition, ceramic membranes and other high temperature materials are also usable.

The Performance data of a fuel cell are crucial from the quality of the polymer electrolyte membrane applied catalyst layers from. These layers are mostly highly porous and usually consist of an ionomer and a finely divided electrocatalyst dispersed therein. Together with the polymer electrolyte membrane form in these layers so-called three-phase interfaces, wherein the ionomer in direct contact with the electrocatalyst and the over brought the pore system to the catalyst particles Gases (hydrogen at the anode, air at the cathode) is.

in the With a view to broad market penetration of fuel cell technology In the mobile sector is a significant reduction in the cost of the Production of fuel cells, in particular of electrodes and Membrane electrode units necessary.

So far become standard methods for the production of membrane electrode units used, the coating speeds (or production speeds) in the range of 0.5 m / min to 2 m / min (= 0.008 to 0.03 m / s). These are z. For example, by screen printing or knife coating method. For an application for mass production are significantly higher Production speeds required.

Out In the field of print media, coating processes are evident higher speed known. In this context In particular, the gravure printing technology is of interest. The gravure finds as a mass printing method in magazine printing with high Editions as well as in packaging, decor and security printing. In the standard gravure printing process become raster patterns or dot patterns, but not contiguous ones Created surfaces.

The Gravure printing is particularly high due to the achievable Production speeds for a mass production of Fuel cell components interesting. Allows a continuous process for substrate coating, above In addition, the substrates can be gravure printed in discrete patterns (Printed images) or in full-surface, coherent Form are coated.

The operation of the gravure printing process is well known to those skilled in the printing art. A detailed essay on this can be found in Helmut Kipphan (ed.), Handbuch der Printmedien - Technologie und Produktionsverfahren, Springer-Verlag, Berlin (2000) , The general principle of gravure is in the 1 shown.

Herein mean (cf. DIN 16528 - terms for gravure printing):

1

Plate cylinder (Print form)

2

print image

3

print motif (printed catalyst layer)

4

substrate material

5

Impression cylinder (Impression roller)

6

doctor with doctor blade

7

paint tray (Inking)

8th

printing paste (Ink, dispersion)

9

direction of rotation pressure cylinder

10

direction of rotation Impression cylinder

11

movement direction Substrate material (printing direction)

In principle, gravure printing takes place in a paint tray ( 7 ) located on a cylinder-shaped printing forme cylinder ( 1 ), which rotates in the direction of rotation ( 9 ) emotional. In the present application, this cylinder is referred to as a "printing form" or "sleeve". On the printing form ( 1 ) are printed images or grids ( 2 ) introduced as depressions. The printing paste / ink ( 8th ) flows into the depressions of the printed image ( 2 ) and fill them out. With the help of a squeegee with doctor blade ( 6 ), the excess print paste / ink ( 8th ) stripped from the printing form. Thereafter, the in the wells of the printed image ( 2 ) remaining printing paste / ink by means of a counter-pressure cylinder ( 5 ) on the surface of a substrate ( 4 ) transfer. The impression produced by the printing process or the layer produced ( 3 ) on the substrate ( 4 ) is used in the present application as a print motif ( 3 ) designated.

Alternatively, the squeegee ( 6 ) and the ink tray ( 7 ) and formed as a closed Einfärbesystem (for example, as a "chamber doctor blade"). The ink supply then takes place via a pressure pot. Protruding material is stripped off with a doctor blade, which is placed directly on the surface of the plate cylinder ( 1 ) running. Arrangement of chamber doctor blade and doctor blade are freely variable.

How out 2 can be seen on the printing plate cylinder ( 1 ) several print images ( 2 ) are introduced. The number of print images depends on the available area of the plate cylinder and the size of the individual print images.

3 shows a single print image ( 2 ) in detail. One recognizes the different webs ( 12 ), which form a grid or a grid structure. This figure shows an example of a line grid with additional cross lines, but all other grid structures according to the invention are also possible. The bridges ( 12 ) represent partitions which delimit the depressions of a gravure form from each other and when doctored off by the doctor blade ( 6 ) serve as an edition.

The gravure allows a variable geometry of the desired print motif ( 3 ), ie it can be generated in addition to rectangular and elliptical or circular catalyst layers (print motifs). The amount of transferred ink / paste is determined by the volume of the printing form ( 1 ) or the individual print images ( 2 ) certainly. This gives a high reproducibility of the layer thickness of the individual print motifs.

The use of gravure printing processes for the production of electrodes and fuel cell components has already been proposed. That's how it teaches DE 195 48 422 continuous production of composite materials (ie MEE laminates) for fuel cells, using screen printing, high-pressure and gravure printing as coating methods. Also from the EP 1,037,295 B2 is a method of applying Electrode layers on a band-shaped polymer electrolyte membrane for fuel cells known. As the printing method, the screen printing is preferably used. In both documents the gravure printing process is mentioned, but not further described.

In the US Pat. No. 6,967,038 B2 and US 7,316,794 describes the preparation of catalyst-coated membranes with a raised relief printing process. This method involves the use of preformed panels with raised surfaces that define the print motif. Catalyst paste is applied to the raised surface and then transferred to the membrane.

disadvantage This printing process are the inhomogeneous layer thickness and the lack of edge sharpness of the print motifs.

From the US 6,280,879 For example, a method of making electrode current collector laminates for electrochemical devices, particularly Li-polymer batteries, is known. The patent teaches a method of forming thick layers of electrode material on a current collector foil by means of the gravure printing process.

The US 2004 / 0221755A1 describes a gravure printing process for the production of multilayer ceramic capacitors. Here, electrode paste is applied in the form of rectangular print motifs on a ceramic foil. Each print image ("image area") has boundary lines both parallel and perpendicular to the print direction. As a result, individual cells are formed in the printed images; nothing is known about the scum volume or etch depth of these cells. The method is particularly suitable for high-viscosity, metal powder-containing pastes.

In the WO 03/054991 A1 describes a gravure printing method for coating a fuel cell membrane with catalyst. The catalyst layers produced are not homogeneous, but have a plurality of three-dimensional structural units. The individual screen structures of the printed image can be found in the catalyst layer again. Due to the lack of a continuous structure and the inhomogeneous layer thickness, the catalyst layers thus produced are not very suitable for PEM fuel cells.

It is therefore an object of the present invention, an improved To provide gravure printing process, with the catalyst layers with a coherent, continuous structure can be produced. The procedure should be continuous be operated, a high printing speed or production speed and for the direct coating of ionomer membranes as well as for coating other substrate materials (decal substrates, Decals, PET films, coated papers, carbon fiber nonwovens etc) can be used. The produced by the process Catalyst layers should in the fuel cell a good electrical Show performance.

These The object is achieved by the method according to the present invention Claims solved. Preferred embodiments of the method are mentioned in the subclaims. Farther If a printing form according to the invention claimed.

The The present invention relates to a gravure printing process for the production of catalyst layers on substrate materials with the aid of catalyst-containing Inks, wherein a printing form is used, the at least one Print image contains a broken line grid having. The longitudinal lines of this interrupted line grid are at an angle α of 10 ° to 80 °, preferably at an angle α of 20 ° to 70 ° to the Arranged printing direction.

In one possible embodiment of the method, the printing form (or the print image) has a scoop volume in the range from 100 to 300 ml / m ² , preferably in the range from 150 to 250 ml / m ² . In a further possible embodiment, the printing form (or the printed image) has an etching depth in the range from 100 to 250 μm, preferably in the range from 120 to 200 μm.

The generated by the method according to the invention Catalyst layers should be continuous or continuous be. They should have a dry film thickness in the range of 1 to 20 μm, preferably in the range of 2 to 15 microns and more preferably in the range of 5 to 10 microns.

It has been found that this task by the provision of suitable printing forms or Print images can be achieved. The experiments showed that the necessary dry film thickness for the catalyst layer can be achieved if a sufficient amount of catalyst ink is transferred to the substrate. As a result, it was found that the printing form (or the printed image) should have a certain scoop volume. The printing plates (or printed images) suitable for the process according to the invention have scoop volumes in the range from 100 to 300 ml / m ² ; Particularly suitable are scoop volumes in the range of 150 to 250 ml / m ² . This causes a sufficient volume of catalyst ink to be transferred to the substrate. If the pumping volumes are too high, the ink can hardly be doctored off, which leads to unclean printed images (eg, fog outside the printed images).

As was further demonstrated in the experiments of the present invention, is a printing form (or a printed image) with an etching depth in the range of 100 to 250 μm, preferably in the range from 120 to 200 microns necessary to the desired To achieve dry film thicknesses. These values are significantly higher the gravure printing plates used, their etching depths in the range of 10 to 50 microns.

Conventional intaglio printing forms such as cross grid or dot matrix usually have a scoop volume of up to 40 ml / m ² . Such rasters have a large number of regularly arranged wells filled with ink. During printing, the ink that has flowed into the cups is transferred to the substrate. In the course of the work, it has been shown that such conventional cross lattices or dot patterns are less suitable for achieving the necessary dry layer thicknesses.

One Another essential aspect is the provision of a suitable Raster structure or raster geometry for the printing form. The for the inventive method suitable grid structure should only have a minimal volume in the transmission area on the printing form (or in the printed image) occupy, but a sufficient Support function for the squeegee (or doctor blade) and a good transfer of the ink to the Substrate enable.

L

= Länge eine Längslinie

B

= Breite einer Längslinie

A1, A2

= Linienabstände

Z

= Zwischenraum zwischen zwei Linien einer Reihe

V, V1, V2

= Reihenversatz (positiv und/oder negativ)

α

= Winkel zwischen Druckrichtung und Längslinie.

Surprisingly, the use of broken line grids has been found to be advantageous. Such broken line rasters have geometric structural units having different length and width dimensions and different angles, optionally in combination. Within a printed image, these structural units are repeated both one behind the other (ie in the x-direction) and one above the other (ie in the y-direction). The catalyst ink is in the spaces between the individual lines or webs ( 12 ) of the printed image ( 2 ) and is transferred to the substrate during the printing process. The 4 . 5 . 6 and 7 show schematically the structure of the printing forms according to the invention or printed images with linear raster structures. In the following mean:

L

= Length a longitudinal line

B

= Width of a longitudinal line

A1, A2

= Line distances

Z

= Space between two lines of a row

V, V1, V2

= Row offset (positive and / or negative)

α

= Angle between printing direction and longitudinal line.

For the angle α, which is the angle between the printing direction and the longitudinal lines are defined, in principle, two angle specifications possible, which differ in the respective direction of rotation (+ α and -α). They result from the Reflection of this angle on the printing direction as an axis. In the The present patent application comprises the angle indication α both Turning directions or possibilities, especially since there are no observable ones Differences in the arrangement of the line grid in the original or in the mirrored angle α result against the pressure direction to have.

4 shows an example of a broken line grid having only parallel longitudinal lines, but no cross lines. In this example, the row offset V of the longitudinal lines is respectively positive, ie formed as an overlap.

5 shows an example of a broken line grid with longitudinal lines having both a positive offset (V1) and a negative offset (V2), ie a gap.

QL

= Länge der Querlinie

QB

= Breite der Querlinie

QZ

= Zwischenraum zwischen Querlinie und Längslinie

β

= Winkel zwischen Querlinie und Längslinie

6 illustrates an example of a broken line grid with longitudinal lines and cross lines. The longitudinal lines are aligned with the angle α in the printing direction, while the transverse lines are arranged at a certain angle β to the longitudinal lines. Hereby additionally mean:

QL

= Length of the cross line

QB

= Width of the cross line

QZ

= Space between transverse line and longitudinal line

β

= Angle between transverse line and longitudinal line

7 also shows a line grid with longitudinal lines and cross lines. The longitudinal lines are aligned with the angle α against the printing direction, while the transverse lines connect at a certain angle β to the longitudinal lines and there is no gap QZ between the transverse line and the longitudinal line (ie QZ = 0).

L

= 1 bis 20 mm, bevorzugt 1 bis 15 mm

B, QB

= 0.1 bis 0.5 mm

A1, A2

= 0.5 bis 2 mm

Z

= 0.1 bis 10 mm

V

= (+/–) 0.1 bis 10 mm

QL

= 0.1 bis 4.5 mm

QZ

= 0 bis 2.5 mm

α

= 10° bis 80°, bevorzugt 20° bis 70°

β

= 5° bis 175°, bevorzugt 60° bis 120°.

In principle, all parameters, in particular length L and width B and the row offset V, the gap Z and the angles α and β are variable. Within a printed image, these raster structures are repeated, but they can also be varied within a printed image in order to achieve, for example, better edge sharpness at the edge of the printed image (for example in edge / middle variations). In extreme cases, all these parameters can be arranged stochastically, comparable to stochastic frequency-modulated grids ("FM grid") in the graphics industry. For the parameters, the following ranges have proven to be advantageous:

L

= 1 to 20 mm, preferably 1 to 15 mm

B, QB

= 0.1 to 0.5 mm

A1, A2

= 0.5 to 2 mm

Z

= 0.1 to 10 mm

V

= (+/-) 0.1 to 10 mm

QL

= 0.1 to 4.5 mm

QZ

= 0 to 2.5 mm

α

= 10 ° to 80 °, preferably 20 ° to 70 °

β

= 5 ° to 175 °, preferably 60 ° to 120 °.

In the rule are in the process of the invention to prefer thinner line structures to wider structures, because the broader structures of the formation of a self-leveling, to oppose homogeneous film. The line widths B (longitudinal lines) and QB (cross lines) should be in the range of 0.1 to 0.5 mm. Furthermore, it has been found that at line lengths L of the longitudinal lines in the range of 0.1 to 20 mm, preferably in the range of 1 to 15 mm, a good support of the squeegee and thus a good print result is achieved. For the Line lengths of the cross lines (QL) have values in the range best proven from 0.1 mm to 4.5 mm. (Minimum value for QL: width of a longitudinal line (B); Maximum value for QL: sum of the values B + A1 + A2). Too long line structures have proved unfavorable. They cause a transport movement the ink in the printing direction due to the adhesion of the ink at the squeegee.

The suitable dimensions for the parameter Z (= gap between two lines of a row) are in the range of 0.1 to 10 mm; suitable values for V (= row offset between the rows of lines) are in the range of 0.1 to 10 mm. It can the row offset V both as an overlap (i.e., positive) as also be designed as a gap (ie negative).

The broken line grids are arranged in the longitudinal direction (ie, based on the length L) at an angle α of 10 ° to 80 °, preferably at an angle α of 20 ° to 70 ° to the printing direction. The optional transverse lines QL are arranged at an angle β to the longitudinal lines L, wherein the angle β is in the range of 5 ° to 175 °, preferably in the range of 60 ° to 120 ° Be. However, longitudinal lines and transverse lines can also meet at an angle β, with a hook-shaped grid being formed (cf. 7 ).

It was found that by the invention Raster structures the transport movement of the ink within the printing form or the printed image is reduced and a uniform Print motif is achieved. Further advantages are the higher ones Edge sharpness of the print motif, the stabilization of the squeegee as well as the lower wear (eg abrasion, damage of webs etc) of the printing plate cylinder.

The catalyst layers produced with the printing forms or printed images according to the invention are continuous or continuous. They generally have a dry film thickness in the range of 1 to 20 microns, preferably in the range of 2 to 15 microns and more preferably in the range of 5 to 10 microns. Standard gravure printing typically produces raster patterns or dot patterns but no contiguous areas. By contrast, catalyst layers having a coherent, continuous structure can be produced by the process according to the invention. In the resulting Print motif is to recognize only a negligible surface structure; the catalyst layers have a low surface roughness.

The Production of printing forms, printing cylinders, printed images and Raster structures is the expert in the field of gravure printing known. The for the inventive Method required printed images with broken line grids are exposed on a plate cylinder (or sleeve sleeve) and then to the desired etch depth in the range of 50 to 250 microns, preferably in the range of 100 to 200 μm, etched out. Diameter and circumference the printing form or sleeve cylinder are of the type of gravure printing machine dependent and can be varied within wide limits become. The finished printing sleeve is used for the printing process mounted on the sleeve sleeve, so that for the Printing process necessary dimensional stability is given.

in principle can for the inventive Process any catalyst pastes or catalyst inks with be used in a variety of compositions. The containing suitable for the process catalyst inks in principle at least one catalyst material, at least one ionomer material and at least one solvent. As catalyst materials can all known in the field of fuel cells Catalysts, in particular electrocatalysts are used. In the case of supported electrocatalysts is called Carrier usually a finely divided, electrically conductive Material used, with preference carbon blacks or graphites but also conductive oxides can be used. The catalytically active component used are the noble metals, preferably the elements of the platinum group of the periodic table (Pt, Pd, Ru, Rh, Os, Ir) or alloys thereof. The catalytically active metals can add other alloying additives such as Cobalt (Co), chromium (Cr), tungsten (W) or molybdenum (Mo) contain. As a rule, supported catalysts are used (eg 40 wt.% Pt / C) in which the catalytically active platinum group metals in highly dispersed form on the surface of a conductive Soot carrier are applied. For the Production of the electrode layers can also be carrier-free Catalysts such as platinum-black or platinum powder be used with a high surface.

The ionomer material used is generally proton-conducting polymer materials. Preference is given to using a tetrafluoroethylene-fluorovinyl ether copolymer having acid functions, in particular having sulfonic acid groups. Such materials are sold, for example under the trade names Nafion ^® (Du Pont) or Flemion ^® (Asahi Glass Co.). Many fluorine-containing ionomer materials are available in the form of solutions or dispersions in different concentrations. In addition, ionomers with different equivalent weights (EW) are also available from different manufacturers.

to Achieving a homogeneous layer with a uniform Layer structure should be a good flow or "spreading" of individual ink deposits can be achieved after the order. For the gravure printing method according to the invention are therefore Catalyst inks with adapted rheological properties (i.e. H. adapted viscosity). advantageously, should the viscosity of the inks not be too high, so that after application some bleeding on the substrate material is possible. The solids content of the catalyst ink should but not too low, so that the required dry film thickness can be achieved.

Suitable catalyst inks or catalyst dispersions have a viscosity in the range of 50 to 1000 mPas, preferably in the range of 50 to 900 mPas and particularly preferably in the range of 150 to 400 mPas (at a shear rate of D = 1000 s ^-1 , measured with a plate / cone viscometer). For the measurements for the present application, a plate / cone viscometer type MCR 300 from Physica (Anton Paar GmbH, D-73760 Ostfildern) was used. However, devices from other manufacturers can also be used.

suitable Inks have a solids content (i.e., the sum of catalyst content and ionomer content) of 3 to 20% by weight, preferably 5 to 20% by weight. and particularly preferably a solids content of 7 to 16% by weight (measured in each case by the loss of drying relative to the Total weight of ink). The loss of drying occurs during drying in a convection oven at 120 ° C for 60 minutes certainly.

When Solvents can basically all organic solvents are used for Catalyst inks that are useful in coating processes, in particular printing processes are processed. Hydrous catalyst inks are preferred from an environmental point of view and with regard to occupational safety.

The present invention provides a gravure printing process for the production of continuous, zusam Menhängenden catalyst layers on a variety of substrate materials ready. The printing parameters which are advantageous for the method according to the invention, such as production speed, doctor blade setting angle, doctor blade contact pressure, impression press pressure and press hardness, are indicated below.

Of the Impression cylinder (impression roller) is pressurized from 2 to 10 bar, preferably 3 to 6 bar pressed on the printing form cylinder. The hardness of the press is usually in the range from 50 to 100 shore. As a rule, with a doctor blade pressure worked from 1 to 2 bar. The web speed (or printing speed) is in the range of 0.02 to 3 m / s, preferably in the range of 0.1 to 1 m / s. As material for the doctor blade or doctor blade Usually stainless steel or plastic is used. The squeegee angle is in the range of 50 to 85 °, preferably in the range from 60 to 83 ° (measured to the cylinder tangent of the plate cylinder). Such squeegee angles provide good results when using the Inventive catalyst inks.

In a particular embodiment is a gravure printing system with a closed inking system (i.e. used. As a result, evaporation effects due to volatile Solvents avoided in the printing ink.

When Substrate materials can in principle all band-shaped Ionomermembranen (in supported as well as unsupported Shape, as composites, as composite membranes or as multilayer membranes), treated or untreated plastic films (polyester, PET, Polyamides, polyimides, etc), decal substrates, coated and / or treated papers, composite films, but also Carbon fiber substrates (such as carbon fiber webs, carbon fiber webs or carbon fiber papers). Suitable substrate materials should have a low surface roughness as well as a have low thermal expansion to a stable web run during printing and subsequent drying.

The Drying after printing can be done in batch and / or continuous Procedure done. For discontinuous operation Drying ovens or drying cabinets are suitable; for continuous operation z. B. Belt pass dryers are used in the gravure press can be integrated. Preferably, the drying is done drying the substrate web in in-line process with hot air or IR dryers. The temperature of the drying is typically between 20 and 150 ° C, the drying parameters are the respective method and generally lie between a few seconds and seconds several minutes.

As already stated, the catalyst layers produced by the process according to the invention are continuous. They are usually light-tight, ie they have a low light transmittance in the transmitted light observation. As a measure of the homogeneity and the continuous structure of the applied catalyst layer, surface roughness is used in the present application. The measurement of the surface condition is carried out by the stylus method DIN EN ISO 4287 (October 1998) on the determination of the R _a value (= the arithmetic mean of the profile coordinates). For this purpose, the surface roughness is determined over a measuring section of 1 mm in length on a smooth substrate (PET film) and the R _a value is determined in each case. The mean of three measurements is calculated and given as a value. The device used is a tactile profilometer (tactile roughness meter). The measurements for the present application were made with Veeco Dektak 8 (Veeco Instruments Inc., Plainview, NY 11803, USA). However, other devices are usable for this purpose.

The Catalyst layers produced continue to have a dry film thickness in the range of 1 to 20 microns, preferably in the range of 2 to 15 μm, and more preferably in the range of 5 to 10 μm. The determination of the dry film thickness also takes place with a profilometer (Veeco).

The layers produced according to the invention are continuous and continuous and have a low surface roughness. Typically, the R _a value is in the range of <10% of the respective dry film thickness. This means that catalyst layers having a thickness of 1 .mu.m have an R _a value of <0.1 .mu.m, while catalyst layers having a thickness of max. 20 microns have an R _a value in the range <2 microns. The layers produced in the examples with a thickness of approximately 8 μm accordingly have R _a values in the range of <0.8 μm.

An advantage of the gravure printing method according to the invention is the achievement of high printing speeds (or web speeds), values of 0.02 to 3 m / s, preferably in the range of 0.1 to 1 m / s being achieved. Furthermore, the process can be operated continuously and the drying process in the process is integrated (for example as a roll-to-roll process). In this case, production speeds of 0.02 to 3 m / s, preferably from 0.1 to 1 m / s can be achieved. In addition, a continuous, automated MEE production is possible in which further steps such as, for example, singulation, cutting and lamination of the substrates are included.

With produced by the process according to the invention Catalyst layers were prepared membrane-electrode assemblies and tested in PEM fuel cells. The electrical performance of the MEU produced according to the invention are with the Comparable to those obtained with MEEs in the conventional Manufacturing process to be manufactured.

The inventive method is intended in the following Examples are described in more detail.

Examples

General preliminary remarks

The experiments are carried out on a self-developed laboratory gravure press at room temperature and a rel. Humidity of 30-50% rel. Humidity. In the case of the tests carried out here, the sleeve cylinder produced has a diameter of 220 mm and thus a circumference of 691.2 mm. The finished printing sleeve is mounted on the sleeve cylinder for the printing process with the help of compressed air. Printed images (raster segments) with a geometric size of 3 × 3 cm ² and 3 × 5 cm ² are used. The printing plates used were produced by the Sächsische Walzengravur GmbH (SWG, D-09669 Frankenberg). The web width is 35 mm. The gravure printing is done with a chamber doctor blade, with an angle of attack of 60 ° to Zylindertangente is used. The ink supply is made via a pressure pot with a container pressure of 1.0 bar.

example 1

Production of Pt catalyst layers on a decal substrate

A Pt-containing catalyst ink "DS4 / type 31" (containing a soot-supported type 20 Pt catalyst Wt .-%. Pt / C, as well as ionomer and organic solvents) is applied on the laboratory gravure press at a temperature of 21 ° C and rel. Humidity of 30% processed.

The viscosity of the ink is 350 mPas @ D = 1000 s ^-1 (measured with Physica MCR 300). The solids content is 13 wt .-%. Test Parameters: substrate: Decal film (polyester film, 80 μm thickness) Web speed: 0.125 m / s Etching depth printing form: 180 μm Grid structure: long line grid Angle α = 45 ° A1 = 0.5 mm A2 = 2 × A1 = 1.0 mm B = 0.3 mm L = 12 mm Z = 8 mm V1 = 5 mm V2 = -0.5 mm (negative offset) drying: 40 s at 100 ° C (continuous dryer) Active area: about 10 cm ² (after pressure) Dry film thickness: 8 μm roughness: continuous, light-tight layer R _a = 0.66 μm (PET substrate, mean value) (Veeco Dektak 8) Active area: about 10 cm ² (after pressure)

Electrochemical test:

Two to Decalfolie printed printing motifs (active area 10 cm ²⁾ on the front and back side of an ionomer membrane (type Nafion ^® 112, thickness 50 micron, H ⁺ form) translaminated. The catalyst-coated membrane is processed with suitable GDLs ("gas diffusion layers") to a 5-layer membrane electrode assembly (MEU) and measured in a PEM fuel cell (single cell) in the hydrogen / air mode (pressure 1 bar abs). The electrochemical performance of this MEE is comparable to the performance of a MEE made in the standard printing process.

Example 2

Production of Pt catalyst layers in gravure printing

The catalyst ink "DS4 / type 31" is processed as described in Example 1 on the laboratory gravure printing machine. The printing form used is a short line grid. The geometric dimensions are given below. Grid structure: short line grid Angle α = 25 ° A1 = A2 = 0.4 mm B = 0.3 mm L = 1.5 mm Z = 0.5 mm V = 0.4 mm

The decal substrate used is a 125 μm thick polyester film (PET). After drying in a continuous dryer, coherent, light-tight catalyst layers are obtained which have a dry film thickness of 7-8 μm. The roughness R _a is about 0.6 μm.

Comparative Example 1 (VB1)

Production of layers on a decal substrate in the gravure printing process (cross grid)

A model ink of the type HWD 06 is on the laboratory gravure printing machine at a room temperature of 21 ° C and a rel. Humidity of 30% processed. The substrate used is a decal film (polyester film, 80 μm thick). The viscosity of the ink is 250 mPas @ 1000 s ^-1 (measured with Physica MCR 300). The solids content is 14 wt .-%. Test Parameters: Print speed: 0.4 m / s Printing form: Well depth 53 μm Cell Volume: 17 ml / m ² Grid structure: Printing form DF 1, four-lane cross grid Grid width 54 L / cm Layer thickness: approx. 0.7 μm (not homogeneous)

To Drying in a continuous dryer does not give coherent, light-tight catalyst layers. The layer is translucent, wherein the individual grid points are recognizable as a pattern.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19548422 [0017]
• - EP 1037295 B2 [0017]
• - US 6967038 B2 [0018]
• US7316794 [0018]
• - US 6280879 [0020]
• US 2004/0221755 A1 [0021]
• WO 03/054991 A1 [0022]

Cited non-patent literature

• - Helmut Kipphan (ed.), Handbuch der Printmedien - Technologie und Produktionsverfahren, Springer-Verlag, Berlin (2000) [0010]
• - DIN 16528 [0011]
• - DIN EN ISO 4287 (October 1998) [0056]

Claims (17)

Gravure printing process for the production of catalyst layers on substrate materials with a catalyst-containing ink, wherein a printing form is used, the at least one printed image with a broken line grid whose longitudinal lines at an angle α of 10 ° to 80 °, preferably at an angle α of 20 ° to 70 ° against the printing direction are arranged. The method of claim 1, wherein the printed image has a scoop volume in the range of 100 to 300 ml / m ² , preferably in the range of 150 to 250 ml / m ² . The method of claim 1 or 2, wherein the printed image etching depths in the range of 100 to 250 μm, preferably in the range from 120 to 200 microns. Method according to one of claims 1 to 3, wherein the generated catalyst layers have a dry film thickness in the range of 1 to 20 microns, preferably in the range of 2 to 15 microns own. Method according to one of claims 1 to 4, wherein the longitudinal lines of the line grid line lengths L in the range of 0.1 to 20 mm and line widths B in the range of 0.1 to 0.5 mm. Method according to one of claims 1 to 5, wherein the broken line grid at least one space Z has between two lines of a row whose dimensions in Range from 0.1 to 20 mm. Method according to one of claims 1 to 6, where the print image is a line grid with additional cross lines has, where the cross lines line lengths (QL) in the range from 0.1 mm to 4.5 mm and those with an angle β im Range from 5 ° to 175 ° to the longitudinal lines are arranged. A method according to any one of claims 1 to 7, wherein the prepared catalyst layers have a low surface roughness and the R _a value is <10% of the respective dry layer thickness. Method according to one of claims 1 to 8, wherein as substrate materials ionomer membranes (in supported or unsupported form), composite membranes, composite membranes, Multi-layer membranes, treated or untreated plastic films (such as polyesters, polyamides or polyimides), decal substrates, Decal substrates, coated or treated papers, composite films and carbon fiber substrates (such as carbon fiber nonwovens, Carbon fiber fabric or carbon fiber papers) can be used. Method according to one of claims 1 to 8, wherein the catalyst-containing ink comprises at least one electrocatalyst, at least one ionomer and at least one solvent contains. Method according to one of claims 1 to 9, wherein the catalyst-containing ink has a solids content in the range from 3 to 20% by weight (measured as loss on drying at 120 ° C / 60 minutes). Method according to one of claims 1 to 10, wherein the catalyst-containing ink has a viscosity in the range of 50 to 1,000 mPas, preferably in the range of 150 up to 400 mPas (measured with a plate / cone system). Method according to one of claims 1 to 12, wherein the ink supply takes place via a chamber doctor blade. Method according to one of claims 1 to 13, characterized in that it is continuous, preferably in a roll-to-roll process. Method according to one of claims 1 to 14, wherein the printing speed in the range of 0.02 to 3 m / s lies. Use of the method according to one of the claims 1 to 15 for the production of electrodes and membrane-electrode assemblies for fuel cells. Thermoforming mold for the production of catalyst layers on substrate materials, characterized in that it comprises at least one printed image with a broken line grid, whose Längsli nien at an angle α of 10 ° to 80 °, preferably at an angle α of 20 ° to 70 ° are arranged against the printing direction.