EP2328754B1 - Doctor blade - Google Patents

Abstract

A doctor blade (1), particularly for wiping printing ink off a surface of a printing plate, comprising a flat and elongated main body (11) having a working edge region (13) configured in a longitudinal direction, the working edge region (13) being covered with a first coating (20) on the basis of a nickel-phosphorus alloy applied by electroless deposition, and hard material particles (20.1) being dispersed in the first coating (20), characterized in that the first coating (20) is covered with a second coating (21) on the basis of galvanically deposited nickel.

Description

Technical area

The invention relates to a squeegee, in particular for doctoring ink from a surface of a printing form, comprising a flat and elongated base body having a working edge region formed in a longitudinal direction, the working edge region having a first coating based on a nickel-phosphorus electroless alloy is coated and wherein in the first coating hard material particles are dispersed. Furthermore, the invention relates to a method for producing a doctor blade.

State of the art

In the printing industry, scrapers are used, in particular, for scraping off excess printing ink from the surfaces of printing cylinders or printing rollers. Especially with intaglio and flexographic printing, the quality of the squeegee has a decisive influence on the print result. Unevenness or irregularities of the standing with the impression cylinder working edges of the doctor blade lead z. B. to incomplete stripping of the ink from the webs of the printing cylinder. This can lead to an uncontrolled release of ink on the print carrier.

The working edges of the doctor are pressed during stripping to the surfaces of the impression cylinder or pressure rollers and are moved relative to these. Thus, the working edges, especially in rotary printing machines, exposed to high mechanical loads, which bring a corresponding wear. Squeegees are therefore basically consumables, which must be replaced periodically.

Squeegees are usually based on a steel body with a specially shaped working edge. To improve the life of the doctor blade, the working edges of the doctor blade can also be provided with coatings or coatings of metals and / or plastics. Metallic coatings often contain nickel or chromium, which may be mixed or alloyed with other atoms and / or compounds. The material properties of the coatings in particular have a significant influence on the mechanical and tribological properties of the doctor blade.

In the WO 2003/064157 (Nihon New Chrome Co. Ltd.) are z. B. squeegee for printing described, which have a first layer of chemically nickel with dispersed therein hard material particles and a second layer with a low surface energy. The second layer preferably consists of a coating of chemically nickel with fluorine-based resin particles or of a purely organic resin.

Such coated doctor blades have an improved wear resistance compared to uncoated doctor blades. The lifetime is still not completely satisfactory. In addition, it has been shown that uncontrolled banding can occur when using such doctor blades, especially in the running-in phase, which is likewise undesirable.

There is therefore still a need for an improved squeegee, which in particular has a longer life and at the same time allows optimal wiping.

Presentation of the invention

The object of the invention is therefore to provide a the technical field mentioned above squeegee, which has an improved wear resistance and during the entire life of a precise scraping, in particular of printing ink allows.

The solution of the problem is defined by the features of claim 1. According to the invention, the first coating is coated with a second coating based on electrodeposited nickel.

Under a electroless deposited nickel-phosphorus alloy, which forms the basis for the first coating, is understood in this context, a mixture of nickel and phosphorus, wherein the phosphorus content is in particular 1-15 wt .-%. Such alloys are deposited without current or without external current and are also referred to as chemical nickel. The term "electroless nickel-phosphorous alloy based" means that the electroless nickel-phosphorus alloy is the main constituent of the first coating. In this case, in addition to the electrolessly deposited nickel-phosphorus alloy, other types of atoms and / or chemical compounds which have a smaller proportion than the electrolessly deposited nickel-phosphorus alloy may well be present in the first coating. The proportion of electrolessly deposited nickel-phosphorus alloy in the first coating is preferably at least 50% by weight, particularly preferably at least 75% by weight and very particularly preferably at least 95% by weight. Ideally, the first coating is unavoidable Impurities exclusively from a currentless deposited nickel-phosphorus alloy with dispersed therein hard material particles.

In accordance with the invention, hard material particles include, in particular, metal carbides, metal nitrides, ceramics and intermetallic phases, which preferably have a hardness of at least 1000 HV. These include, for example, diamond (C), cubic boron nitride (BN), boron carbide (BC), chromium oxide (Cr ₂ O ₃ ), titanium diboride (TiB ₂ ), zirconium nitride (ZrN), zirconium carbide (ZrC), titanium carbide (TiC), silicon carbide ( SiC), titanium nitride (TiN), corundum (Al ₂ O ₃ ), tungsten carbide (WC), vanadium carbide (VC), tantalum carbide (TaC), zirconium dioxide (ZrO ₂ ) and / or silicon nitride (Si ₃ N ₄ ).

The expression "based on electrodeposited nickel" means that the electrodeposited nickel, which is deposited by means of electricity from an electrolyte bath, forms the main component of the second coating. In this case, in addition to the electrodeposited nickel, other types of atom and / or chemical compounds may still be present in the second coating, which have a smaller proportion than the electrodeposited nickel. In particular, a nickel alloy with other types of atoms and / or chemical compounds may also be present. The proportion of the electrodeposited nickel in the second coating is preferably at least 50% by weight, particularly preferably at least 75% by weight and very particularly preferably at least 95% by weight.

In a first variant of the invention, the second coating is in particular substantially free of phosphorus. However, in this case, phosphorus can be present as an unavoidable impurity in the smallest amounts, in particular in a proportion of less than 0.1% by weight, also in the second coating. Ideally, the second coating, except for unavoidable impurities, consists exclusively of electrodeposited nickel.

In a further advantageous variant of the invention, the second coating comprises a galvanically deposited nickel-phosphorus alloy. Under a galvanically deposited nickel-phosphorus alloy is understood in this context, a mixture of nickel and phosphorus, wherein the phosphorus content especially at 12-15 wt .-% and the remaining portion is preferably made of pure nickel. The phosphorus content of the galvanically deposited nickel-phosphorus alloy can in principle also be less than 12% by weight or more than 15% by weight, which however has a partially disadvantageous effect in the context according to the invention. The deposition of the electrodeposited nickel-phosphorus alloy is carried out with the aid of electricity from an electrolyte bath.

The electroformed nickel-phosphorus alloy of the second coating differs in particular with respect to the microstructure and elasticity of the electroless deposited nickel-phosphorus alloy of the first coating.

The term "nickel-phosphorous alloy based" means that the electrodeposited nickel-phosphorus alloy is the main constituent of the second coating. In this case, in the second coating, in addition to the galvanically deposited nickel-phosphorus alloy, there may well be other types of atoms and / or chemical compounds which have a smaller proportion than the galvanically deposited nickel-phosphorus alloy. The proportion of the electrodeposited nickel-phosphorus alloy in the second coating is preferably at least 50% by weight, particularly preferably at least 75% by weight and very particularly preferably at least 95% by weight. Particularly suitable is the second coating except for unavoidable impurities exclusively from a galvanically deposited nickel-phosphorus alloy.

It has been found that the inventive doctor have a high wear resistance and, accordingly, a long life. Comparative experiments have shown that the combination of a first coating of electroless nickel-phosphorus alloy with dispersed therein hard material particles and a second coating based on electrodeposited nickel causes a positive synergistic effect with respect to the wear resistance. If doctor blades are used for comparison purposes with a comparable overall layer thickness as the doctor blade according to the invention either only with the first coating (electroless nickel-phosphorus alloy with dispersed hard material particles) or only with the second coating (coating based on electrodeposited nickel) provided, resulting in significantly lower wear resistance and service life than in the inventive doctor blades.

Furthermore, the working edges are optimally stabilized by the combination of the first coating of electrolessly deposited nickel-phosphorus alloy with dispersed hard material particles and the second coating based on electrodeposited nickel. This results in a sharply defined contact zone between the doctor blade and the printing cylinder or the pressure roller, which in turn allows extremely accurate ink stripping. The contact zone remains largely stable over the entire printing process.

In addition, it has been found that the doctoring devices according to the invention do not form any stripes during the running-in phase in the printing process or otherwise cause effects which impair the printing process. The doctor according to the invention therefore makes it possible to achieve a substantially constant printing quality during the entire printing process.

The composition of the second coating based on electrodeposited nickel depends essentially on the intended application of the doctor blade. This plays z. B. the material and the surface condition of the printing cylinder or the pressure roller an essential role. A second coating comprising an electrodeposited nickel-phosphorous alloy is generally somewhat harder and more corrosion resistant than a nickel-based nickel-based coating which is substantially free of phosphorus.

Preferably, at least one jacket region of the main body which is present with respect to the longitudinal direction is completely and completely covered with the second coating. In this case, at least the working edge, the upper side, the lower side and the rear edge of the main body opposite the working edge are covered with the second coating. The side surfaces of the main body that are perpendicular to the longitudinal direction may be uncoated. But it is also within the scope of the invention that the second coating the body completely and Covered on all sides, so also the present perpendicular to the longitudinal direction side surfaces of the body are covered with the second coating. In this case, the second coating surrounding the body so all around.

Because at least the jacket region of the main body which is present in the longitudinal direction is completely and completely covered with the second coating, the essential regions of the main body which do not belong to the working edge and are not covered with the first coating are also provided with the second coating. This is particularly advantageous in order to protect the main body from the water-based or slightly acidic printing inks and / or other fluids coming into contact with the doctor blade. In particular, with base bodies made of steel so optimal rust protection for the doctor blade is created. Thus, the constancy of the print quality during the printing process is further improved, since the printing cylinder or printing roller in contact with the doctor blade during the printing process is not contaminated by rust particles, for example. Furthermore, the basic body is best protected against rust formation by a second coating applied in the jacket area during storage and / or transport.

If, in addition to the cladding region provided with respect to the longitudinal direction, the side surfaces of the main body which are perpendicular to the longitudinal direction are also covered with the second coating, the quality of the doctor blade further improves.

In principle, it is also possible to cover the main body, apart from the working edge, only partially or not at all with the second coating. This can be z. B. be advantageous if the body z. B. made of a stainless steel or other resistant to printing inks material.

It has also proved to be particularly advantageous when hard material particles of SiC and / or Al ₂ O ₃ and / or diamond and / or BN are present. In this case, it is also possible for a plurality of hard material particles of different materials to be present at the same time. The hard material particles preferably have particle sizes of less than 1 .mu.m, in particular from 0.3 to 0.5 .mu.m. A volume fraction of the hard material particles in the first Coating is especially at 5-20%. Squeegees with such hard particles are characterized in particular by an extremely good wear resistance and long life. At the same time, however, when using such hard materials, there is also a very sharply delimited contact zone between doctor blade and pressure cylinder or pressure roller, the contact zone remaining essentially constant or stable over the entire service life of the doctor blade.

It is also possible in principle to provide hard material particles of other materials and of other sizes or volume fractions. However, under certain circumstances, the wear resistance and / or the stability of the doctor during the printing process may be impaired.

In particular, a phosphorus content of the first coating is 7-12% by weight. Such coatings have proven to be optimal in combination with the second coating based on electrodeposited nickel or the second coating based on the electrodeposited nickel-phosphorus alloy, since both a high wear resistance and the best possible and constant stability during the entire life of the squeegee is obtained.

In principle, however, the phosphorus content of the first coating can also be less than 7% by weight or greater than 12% by weight. However, the aforementioned advantageous properties of the doctor are thereby impaired.

Advantageously, the first coating has a hardness of 750-1400 HV. As a result, in particular the wear resistance of the doctor is increased. Although lower hardnesses than 750 HV are also possible, the wear resistance of the doctor blade decreases. If the hardness is higher than 1400 HV, the printing cylinder or roller may be damaged, reducing the print quality.

A thickness of the first coating preferably measures 5 to 30 μm, in particular 7 to 20 μm. Such thicknesses of the first coating provide optimum wear resistance for the inventive doctor blade. Thicknesses of 7-20 μm have proven to be particularly suitable. Thicknesses of less than 5 microns are possible, but the wear resistance decreases rapidly. Greater thicknesses than 30 microns are also feasible. These are one hand but not economically and in part have a negative impact on the quality of the working edge.

A thickness of the second coating preferably measures 1-8 μm, in particular 1.5-5 μm. Such thicknesses of the second coating, in particular in combination with a first coating having a thickness of 5 to 30 μm, or preferably 7 to 20 μm, provide optimum wear resistance and stability of the working edge of the doctor blade according to the invention.

In principle, however, the second coating may also have a thickness less than 1 μm or a thickness greater than 8 μm. However, the quality of the working edge decreases.

If the doctor blade is completely and completely covered with the second coating, the thickness of the second coating in the region of the working edge is advantageously approximately twice as thick as in the region of the center of the doctor blade surface or in a region behind the working edge.

The second coating preferably comprises a base layer of pure nickel adjoining the first coating and a cover layer arranged above it, a thickness of the base layer measuring 0.2-0.8 μm, in particular 0.4-0.6 μm, and wherein the cover layer comprises saccharin and / or a saccharin salt contains. The base layer of pure nickel is, except for unavoidable impurities, preferably exclusively of nickel.

On the one hand, such a second coating has high adhesion to the first coating and possibly also to the main body. In addition, the second coating due to the top layer with saccharin and / or a saccharin salt on a very flat surface with a low surface roughness, which favors the formation of a sharply defined contact zone between doctor blade and impression cylinder or pressure rollers.

In principle, however, it is possible with the second coating to dispense with the formation of a base layer and a cover layer and to provide only a single and substantially homogeneous layer.

For producing a doctor according to the invention, in particular in a first step, a first coating based on a nickel-phosphorus alloy with hard material particles dispersed therein can be deposited without current on a working edge region of the doctor blade formed in a longitudinal direction of a flat and elongate base body. In a second step, a second coating based on nickel is deposited by means of a galvanic process at least on the first coating.

By electroless deposition of the nickel-phosphorus alloy with dispersed therein hard material particles, a high-quality first coating can be produced, which in particular has a high contour accuracy with respect to the working edge of the doctor blade or with respect to the main body of the doctor blade and a very uniform layer thickness distribution. In other words, an extremely uniform nickel-phosphorus alloy with hard particles dispersed therein is formed by the electroless deposition, which optimally follows the contour of the working edge of the doctor blade or the base body, which decisively contributes to the quality of the doctor blade. Furthermore, a first coating can be formed by the electroless deposition, which is compatible in the best possible way in particular with the second coating based on galvanic nickel to be applied in the second step. This ensures sufficient adhesion of the second coating on the first coating. For electroless plating, the working edge or optionally the entire body of the doctor blade is immersed in a suitable electrolyte bath with hard material particles suspended therein and coated in a manner known per se. The hard particles suspended in the electrolyte bath are incorporated into the nickel-phosphorus alloy during the coating or deposition process and are present essentially randomly distributed in the formed nickel-phosphorus alloy.

Due to the electroless deposition of the nickel-phosphorus alloy, in principle, plastics can also be used as the base body for the doctor blade and provided in a simple manner with the first coating of the nickel-phosphorus alloy.

The galvanic process carried out in the second step can be carried out in a manner known per se. The areas of the doctor blade to be coated, that is to say at least the working edge provided with the first coating, are immersed, for example, in a suitable galvanic electrolyte bath. The areas to be coated act as a cathode, while for example a soluble consumable electrode with nickel serves as the anode. It is, depending on the material to be deposited, but in principle also possible to use insoluble anodes. By applying a suitable electrical voltage between the cathode and anode, an electric current flows through the galvanic electrolyte bath, whereby elemental nickel or, for example, a nickel-phosphorus alloy is deposited on the areas of the doctor blade to be coated and forms the second coating. The second coatings produced by the galvanic process are pure and of high quality. In principle, additives can be added to the electrolyte bath to further improve the quality of the second coating, which additives may also be incorporated into the second coating.

The galvanic deposition of a nickel-phosphorus alloy also has process engineering advantages over electroless plating. For example, the phosphorus content is very easy to control and the deposits can be carried out at high deposition rates. Likewise, the galvanic deposition of a nickel-phosphorus alloy over the galvanic deposition of nickel has the advantage that even insoluble anodes can be used.

Preferably, in the second step, during the galvanic process, nickel is deposited on all sides or, for example, a nickel-phosphorus alloy, on all sides, at least on a jacket region of the base body that is in the longitudinal direction, in particular on the entire base body. Apart from the fact that the main body of the doctor blade is best protected against environmental influences and in particular the partially chemically aggressive inks, thereby simplifying the galvanic process in the second step. The main body can z. B. be completely immersed in the electrolyte bath. This is not possible with the sole coating of the working surface provided with the first coating, since Under certain circumstances, the main body then has to be aligned in a complex manner with respect to the liquid surface of the electrolyte bath.

In principle, however, only the working edge provided with the first coating can also be provided with the second coating.

Advantageously, in a third step, which is carried out after the second step, a heat treatment is carried out to cure the first coating. The heat treatment induces solid state reactions in the nickel-phosphorus alloys which increase the hardness of the nickel-phosphorus alloys. Since the heat treatment takes place only after the deposition or the application of the second coating, in particular an oxide formation on the surface of the first coating is prevented. On the one hand, this entails a high adhesion between the first coating and the second coating, and on the other hand the uniformity of the doctor in the area of the working edge is improved overall.

In principle, however, can also be dispensed with a heat treatment. However, this is at the expense of the wear resistance or service life of the doctor blade produced according to the invention.

In particular, during the heat treatment, the coated base body is heated to a temperature of 100-500 ° C, particularly preferably to a temperature of 170-300 ° C. In particular, these temperatures are held for a holding time of 0.5 to 15 hours, preferably 0.5 to 8 hours. Such temperatures and hold times have been found to be optimal to achieve sufficient hardness of the nickel-phosphorus alloys.

Temperatures of less than 100 ° C are also possible. In this case, however, very long and mostly uneconomical holding times are required. Higher temperatures than 500 ° C, depending on the material of the body, in principle also feasible, but the curing process of the nickel-phosphorus alloy is more difficult to control.

Advantageously, during the galvanic process in the second step, first a base layer of nickel at a pH of less than 1.5, in particular at a pH of less than 1, and then it is preferred to deposit a covering layer of nickel using saccharin at a pH of 2-5, in particular at a pH of 3.4-3.9.

Due to the acidic conditions, the surface of the working edge to be coated or the surface of the base body is chemically activated and the base layer forms an extremely stable adhesive bond with the working edge or the base body. The base layer forms an optimal base for the covering layer to be deposited over it. Maintaining a pH of 2-5 and the use of saccharin provide an optimal topcoat with a smooth and even surface.

In principle, however, the base layer and the outer layer can also be deposited under other conditions.

From the following detailed description and the totality of the claims, further advantageous embodiments and feature combinations of the invention result.

Brief description of the drawings

Fig. 1

Einen Querschnitt durch eine Lamellenrakel mit einer Zweifachbeschichtung im Bereich der Arbeitskante;

Fig. 2

Eine schematische Darstellung eines Verfahrens zur Herstellung einer Rakel.

The drawings used to explain the embodiment show:

Fig. 1

A cross-section through a lamellar blade with a double coating in the region of the working edge;

Fig. 2

A schematic representation of a method for producing a doctor blade.

Basically, the same parts are provided with the same reference numerals in the figures.

Ways to carry out the invention

In Fig. 1 a slat blade 1 according to the invention is shown in cross-section. The lamella blade 1 includes a base body 11 made of steel, which on the in Fig. 1 left Side has a rear portion 12 having a substantially rectangular cross-section. A squeegee thickness, measured in from the top side 12.1 to the bottom side 12.2 of the rear area, is about 0.2 mm. A length of the base body 11 or the lamella blade 1 measured perpendicular to the plane of the sheet is, for example, 1000 mm.

On the in Fig. 1 right side of the base body 11 is tapered to form a working edge 13 of the top 12.1 of the rear portion 12 ago stepwise. An upper side 13.1 of the working edge 13 lies on a plane below the plane of the upper side 12 of the rear region 12, but is essentially parallel or plane-parallel to the upper side 12. 1 of the rear region 12. Between the rear portion 12 and the working edge 13 is a concave shaped transition region 12.5 before. The bottom 12.2 of the rear portion 12 and the bottom 13.2 of the working edge 13 lie in a common plane, which is plane-parallel to the top 12.1 of the rear portion 12 and plane parallel to the top 13.1 of the working edge 13 is formed. A width of the main body 11, measured from the left end of the rear area to the end face 14 of the working edge 13 measures, for example, 40 mm. A thickness of the working area 13, measured from the upper side 13.1 to the lower side 13.2 of the working area, is for example 0.060-0.150 mm, which corresponds to approximately half the thickness of the squeegee in the rear area 12. A width of the working area 13, measured at the top 13.1 of the working area 13 from the end face 14 to the transition area 12.5, is for example 0.8-5 mm.

A free end face 14 of the right-hand free end of the working edge 13 extends from the top 13.1 of the working edge obliquely to the bottom left to the bottom 13.2 of the working edge 13 out. The end face 14 has an angle of approximately 45 ° or 135 ° with respect to the upper side 13.1 of the working edge 13 or with respect to the lower side 13.2 of the working edge 13. An upper transition region between the upper side 13.1 and the end face 14 of the working edge 13 is rounded. Likewise, a lower transition region between the end face 14 and the bottom 13.2 of the working edge 13 is rounded.

The working edge 13 of the lamella blade 1 is further surrounded by a first coating 20. The first coating 20 covers the upper side 13.1 of the Working edge 13, the transition region 12.5 and a subsequent to this subsection of the top 12.1 of the rear portion 12 of the body completely. Likewise, the first coating 20 covers the end face 14, the underside 13.2 of the working edge 13 and a subregion of the underside 12.2 of the rear region 12 of the base body 11 adjoining the underside of the working edge 13.

The first coating 20 is z. B. from a nickel-phosphorus alloy with a phosphorus content of 9 wt .-%. Therein, hard material particles 20.1 are dispersed from silicon carbide (SiC). The volume fraction of the hard material particles 20.1 is for example 16% and an average particle size of the hard material particles 20.1 is about 0.4 μm. The layer thickness of the first coating 20 measures in the region of the working edge 13 z. B. 15 microns, while the hardness z. B. 1200 HV. In the area of the upper side 12. 1 and the lower side 12. 2 of the rear area 12, the layer thickness of the first coating 20 decreases continuously, so that the first coating 20 ends in a wedge shape in a direction away from the working edge 13.

The first coating 20 and the remaining regions of the main body 11, which are not covered by the first coating 20, are completely surrounded by a second coating 21. Thus, the top 12.1 and the bottom 12.2 of the rear portion 12 and the rear end face of the main body 11 with the second coating 21 are covered. The lateral region of the main body 11 with respect to the longitudinal direction of the main body 11 or of the doctor blade 1 perpendicular to the plane of the page is thus completely and completely surrounded by at least one of the two coatings 20, 21. The plane parallel to the leaf level and in Fig. 1 invisible front and rear side surfaces of the base body 11 may also be covered with the second coating 21.

The second coating 21 consists of a base layer 21.1, which consists of electrodeposited pure nickel and has a layer thickness of about 0.5 microns. Over the base layer 21.1 a cover layer 21.2 is arranged. The cover layer 21.2 also consists of an electrodeposited pure nickel, but which is additionally mixed with saccharin.

A layer thickness of the second coating 21, ie the layer thickness of the base layer 21.1 and the layer thickness of the cover layer 21.2 together, in the region of the working edge 13, for example, 4 microns, while the layer thickness in the rear region 12 z. B. 2 microns.

In Fig. 2 is a method 100 for producing a lamellar blade, as z. In Fig. 1 is shown, shown schematically. In this case, in a first step 101, the working edge 13 of the base body 11 to be coated with the nickel-phosphorus alloy or the first coating 20 is immersed, for example, in a suitable and known aqueous electrolyte bath with hard material particles 20.1 suspended therein, wherein nickel ions consist of a nickel salt , z. For example, nickel sulfate, by a reducing agent, for. As sodium hypophosphite, reduced in aqueous environment to elemental nickel and deposited on the working edge 13 under Aubildung a nickel-phosphorus alloy and simultaneous embedding of the hard material particles 20.1. This is done without the application of an electrical voltage or completely de-energized under moderately acidic conditions (pH 4 - 6.5) and at elevated temperatures of for example 70 - 95 ° C.

In a second step 102 z. For example, first a first galvanic electrolyte bath on an aqueous basis with nickel chloride and hydrochloric acid at a pH of about 1 presented. Subsequently, the base body 11 with the first coating 20 already applied in the first step is completely immersed in the electrolyte bath in a manner known per se with externally supplied electrical current, a base layer 21.1 of the second coating 21 is deposited. Subsequently, in a second galvanic electrolyte bath on an aqueous basis with nickel, nickel sulfate, nickel chloride, boric acid and saccharin, a covering layer 21.1 is deposited in a manner known per se at a pH of 3.7.

In a third step 103, the base body 11 provided with the first coating 20 and the second coating 21 is subjected to a heat treatment during, for example, two hours and at a temperature of 300 ° C. Finally, the finished lamellae 1 is cooled and ready for use.

As has been shown in test experiments, the in Fig. 1 lamella blade 1 shown a very high wear resistance and stability over the entire life. For comparison, an identical body was as in the lamellae 1 off Fig. 1 provided in a first comparative experiment only with a first coating 20 and dispensed with the attachment of a second coating. In a second test, an identical base body as in the lamellae blade 1 was made Fig. 1 only with a second coating 21 provided with a comparable with the first coating from the first test layer thickness, but was dispensed with the attachment of a first coating. Both lamellar blades produced for the test tests showed 1 compared to the lamellar blade Fig. 1 lower wear resistance or life on.

The above-described embodiment and the manufacturing method are to be understood as illustrative examples only, which may be modified as desired within the scope of the invention.

Thus, the main body 11 in Fig. 1 also from another material, such. As stainless steel or carbon steel, be made. In this case, it may be advantageous for economic reasons to attach the second coating 21 only in the region of the working edge 13 in order to reduce the material consumption in the coating. In principle, the base body 11 but also made of a non-metallic material such. As plastics exist. This may be advantageous in particular for applications in flexographic printing.

But it is also possible, instead of the main body 11 from Fig. 1 to use a basic body with a different shape. In particular, the base body may have a wedge-shaped working edge or a non-tapered cross-section with a rounded working edge. The free end face 14 of the right-hand free end of the working edge 13 may for example also be formed completely rounded.

Furthermore, the inventive doctor blade Fig. 1 also be different dimensions. For example, the thickness of the working area 13, measured from the Top 13.1 to the bottom 13.2 of the work area, varying in a range of 0.040 - 0.200 mm.

Likewise, the first coating 20 of Fig. 1 other alloying components and / or additional substances, such. As metal atoms, non-metal atoms, inorganic compounds and / or organic compounds.

Instead of or in addition to the hard material particles of silicon carbide (SiC), other hard material particles may also be present.

In the second coating 21 21.2 and in the outer layer 21.2 other substances, for. As metal atoms, non-metal atoms, inorganic compounds and / or organic compounds can be added.

It is also within the scope of the invention to omit the base layer 21.1 of the second coating 21 and, for example, to form the cover layer 21.2 thicker. It is likewise possible to dispense with the saccharin in the case of the covering layer 21.2 or to replace it with a different and equally active substance.

In addition to or instead of the base layer 21.1 and / or the cover layer 21.2 of the second coating 21 Fig. 1 It is also possible for further layers to be based on galvanic nickel. This can be particularly advantageous in order to adapt the properties of the doctor blade according to the invention to specific requirements.

Furthermore, it is possible to provide a galvanically deposited nickel-phosphorus alloy instead of electrodeposited pure nickel for the second coating 21, wherein a phosphorus content is preferably 12-15%. As a result, in particular the hardness of the second coating can be increased, which may be advantageous depending on the application.

In summary, it can be stated that a novel doctor blade construction has been found which guarantees a long service life and quality of the doctor blade and in particular enables more economical printing processes.

Claims (15)

1. A doctor blade (1), in particular for doctoring off printing ink from a surface of a printing form, comprising a flat and elongated main body (11) having a working edge region (13) formed in a longitudinal direction, wherein the working edge region (13) is covered with a first coating (20) on the basis of an electrolessly deposited nickel-phosphorus alloy, and wherein hard material particles (20.1) are dispersed in the first coating (20), characterized in that the first coating (20) is covered with a second coating (21) on the basis of electrodeposited nickel.
2. The doctor blade (1) as claimed in claim 1, characterized in that at least a lateral surface region of the main body (11) that is present with regard to the longitudinal direction is covered entirely and all around with the second coating (21).
3. The doctor blade (1) as claimed in either of claims 1-2, characterized in that the hard material particles (21.1) of SiC and/or Al₂O₃ and/or diamond and/or cubic BN are present.
4. The doctor blade (1) as claimed in one of claims 1-3, characterized in that the phosphorus content of the first coating (20) is 7-12% by weight.
5. The doctor blade (1) as claimed in one of claims 1-4, characterized in that the first coating (20) has a hardness of 750-1400 HV.
6. The doctor blade (1) as claimed in one of claims 1-5, characterized in that the thickness of the first coating (20) measures 5-30 µm, in particular 7-20 µm.
7. The doctor blade (1) as claimed in one of claims 1-6, characterized in that the thickness of the second coating (21) measures 1-8 µm, in particular 1.5-5 µm.
8. The doctor blade (1) as claimed in one of claims 1-7, characterized in that the second coating (21) comprises a base layer (21.1), which adjoins the first coating (20) and consists of pure nickel, and a top layer (21.2) arranged thereabove, wherein the thickness of the base layer (21.1) measures 0.2-0.8 µm, in particular 0.4-0.6 µm, and wherein the top layer (21.2) contains saccharin and/or a saccharin salt.
9. The doctor blade (1) as claimed in one of claims 1-8, characterized in that the second coating (21) comprises an electrodeposited nickel-phosphorus alloy.
10. The doctor blade (1) as claimed in claim 9, characterized in that the electrodeposited nickel-phosphorus alloy has a phosphorus content of 12-15%.
11. A process (100) for producing a doctor blade, in particular a doctor blade (1) as claimed in one of claims 1-10, wherein, in a first step (101), a first coating (20) on the basis of a nickel-phosphorus alloy with hard material particles (20.1) dispersed therein is electrolessly deposited on a working edge region (13) of the doctor blade (1), which is formed in a longitudinal direction of a flat and elongated main body (11), characterized in that, in a second step (102), a second coating (21) on the basis of nickel is deposited by an electroplating process at least on the first coating (20).
12. The process (100) as claimed in claim 11, characterized in that, in the second step (102), during the electroplating process, nickel is deposited on all sides of and all around at least a lateral surface region of the main body (11) that is present with regard to the longitudinal direction, in particular the entire main body (11).
13. The process (100) as claimed in either of claims 11-12, characterized in that, in a third step (103) carried out chronologically after the second step (102), heat treatment is carried out in order to harden the first coating (20) and/or the second coating (21).
14. The process (100) as claimed in claim 11, characterized in that the coated main body (11) is heated to a temperature of 100-500°C, in particular 170-300°C, during the heat treatment.
15. The process (100) as claimed in one of claims 11-14, characterized in that, during the electroplating process in the second step, firstly a base layer (21.1) consisting of nickel is deposited at a pH of less than 1.5, in particular at a pH of less than 1, and in that this is followed by the deposition of a top layer (21.2) consisting of nickel using saccharin at a pH of 2-5, in particular at a pH of 3.4-3.9.

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