EP0170078A1 - Support for lithograhic printing plates made from an aluminium alloy, and printing plate of this material - Google Patents

Abstract

An aluminum alloy suitable as a base for printing plates consists essentially of aluminum containing iron (Fe) and manganese (Mn), the Fe content being 1.2 to 2.1% by weight, the Mn content being 0.1 to 0.9% by weight and the sum of the Fe and Mn contents being 1.3 to 2.2% by weight. A printing plate can be produced with such a base, the base being mechanically, chemically and/or electrochemically roughened and if required, anodically oxidized and hydrophilized. The printing plate includes at least one radiation-sensitive reproduction layer applied on the base.

Description

The invention relates to a carrier material for printing plates made of a specific aluminum alloy containing iron and manganese and a printing plate based on such a carrier material and at least one reproduction layer.

Reproduction layers sensitive to radiation (light) are used, for example, in the production of offset printing forms or photoresists, ie they are generally applied to a layer support by the consumer or by the industrial manufacturer. Metals such as zinc, magnesium, chromium, copper, brass, steel, silicon, aluminum or combinations of these metals, plastic films, paper or similar materials are used as layer supports in these copying materials. These supports can be modified without a modifying pretreatment, but preferably after carrying out a surface modification such as mechanical, chemical and / or electrochemical roughening, oxidation and / or treatment with hydrophilizing agents (especially in the case of supports for offset printing plates made of aluminum or one of its alloys) radiation-sensitive reproduction layer can be coated. The usual radiation-sensitive reproduction layers usually contain an organic binding in addition to at least one radiation-sensitive compound agents (resins or the like) and optionally also plasticizers, pigments, dyes, wetting agents, sensitizers, adhesion promoters, indicators and other customary auxiliaries. These reproduction layers are developed after their irradiation (exposure) in order to produce an image from them, for example a printing form is obtained in this way.

Als besondere Vorteile der jeweiligen Legierungen bzw. der daraus hergestellten Druckplattenträgermaterialien werden angegeben:

• - hohe Reckbarkeit bei einer nach dem Reckvorgang bleibenden Dehnung, günstiges Streckgrenzenverhältnis durch niedrige Streckgrenze und hohe Festigkeit, gute Formbeständigkeit der Druckplatten bei der Lagerung (DE-B 11 60 639);
• - gute Schmiegsamkeit beim Einspannen auf Druckzylinder, gute Abkantbarkeit an den Einspann-Enden der Druckplatten (DE-A 19 29 146);
• - verbesserter Widerstand gegen Ermüdung, hohe Zerreißfestigkeit, gute Dehnbarkeit und leichte Biegbarkeit (DE-A 25 37 819);
• - hohe Ermüdungsbeständigkeit bei gleichmäßig aufgerauhter Oberfläche (DE-A 32 32 810) durch spezielle Herstellung in den Stufen: Wärmebehandlung bei 450 bis 600 °C, Warmwalzen, Kaltwalzen mit einer Reduktion (Verformungsrate) von wenigstens 70 %, Tempern bei 150 bis 250 ^*C während wenigstens 1 h;
• - gleichmäßig aufgerauhte Oberfläche, gute mechanische Eigenschaften beim Drucken auch bei hohen Druckgeschwindigkeiten, gute Dimensionsstabilität auch bei dünneren Platten (EP-A 0 067 056) durch eine Korngröße der intermetallischen Verbindungen von weniger als 3 µm, wobei diese direkt unterhalb der äußeren Oberfläche der heiß- und kaltgewalzten, getemperten und abschließend kaltgewalzten Trägermaterialien angeordnet sind; ähnliche Eigenschaften und Herstellungsstufen nennt auch die EP-A 0 067 632;
• - bessere Aufrauheigenschaften und Oberflächentopographie durch die Anwesenheit von Sn, In, Ga und/oder Zn in der Legierung (EP-A 0 096 347);
• - bessere Aufrauheigenschaften und Oberflächentopographie durch die Reduzierung des Cu-Anteils (EP-A 0 097 318).

The following aluminum alloys for use in the printing plate field are known from the prior art, the alloys mentioned in the first three sources being commercial products to be found on the European, American and / or Japanese market.

The following are stated as particular advantages of the respective alloys or the printing plate carrier materials produced therefrom:

• - High stretchability with a stretch remaining after the stretching process, favorable yield ratio due to low yield strength and high strength, good dimensional stability of the printing plates during storage (DE-B 11 60 639);
• - Good flexibility when clamping on printing cylinders, good bendability at the clamping ends of the printing plates (DE-A 19 29 146);
• - Improved resistance to fatigue, high tensile strength, good elasticity and easy flexibility (DE-A 25 37 819);
• - High fatigue resistance with a uniformly roughened surface (DE-A 32 32 810) through special production in the following stages: heat treatment at 450 to 600 ° C, hot rolling, cold rolling with a reduction (deformation rate) of at least 70%, annealing at 150 to 250 ^* C for at least 1 hour;
• uniformly roughened surface, good mechanical properties when printing even at high printing speeds, good dimensional stability even with thinner plates (EP-A 0 067 056) due to a grain size of the intermetallic compounds of less than 3 μm, these being arranged directly below the outer surface of the hot and cold-rolled, tempered and finally cold-rolled carrier materials; similar properties and production stages are also mentioned in EP-A 0 067 632;
• - better roughening properties and surface topography due to the presence of Sn, In, Ga and / or Zn in the alloy (EP-A 0 096 347);
• - Better roughening properties and surface topography due to the reduction of the Cu content (EP-A 0 097 318).

Of the aluminum alloys listed above, those with a high Al content of more than 99.0%, in particular at least 99.5%, are generally distinguished by good to very good roughening properties, but they are often not suitable for modern processing methods from printing plates to printing forms are sufficiently temperature-stable, i.e. they tire, for example as a result of the high temperatures of more than 180 ^* C, in particular also of more than 240 ^* C, which are required when baking positive reproductive layers, although aluminum alloys with a lower Al content can often have one show better temperature stability, but are usually inferior in their roughening properties, especially in the uniformity of the roughening topography.

Without a reference to the printing plate area, in DE-C 24 23 597 (= US Pat. No. 3,989,548) describes aluminum alloy sheets with uniformly distributed intermetallic particles (compounds), the alloy containing at least two elements from the group Fe, Ni, Mn and Si. At least 1.2% Fe, 1.1% Ni, 0.3% Mn and 0.5% Si must be present in the alloy. The alloy is produced by casting the alloy with a certain growth rate on the solidification front and a certain temperature gradient in the liquid metal near the solidification front and a subsequent hot and / or cold working of the cast alloy with the aim of reducing the cross section by at least 60%. A preferred range for an Al-Fe-Mn alloy has an Fe content of 1.4 to 2.0% and an Mn content of 0.3 to 1.2%, this special alloy also containing Zn, Li, Cu, Mg and Si contains up to 1.5% in total and up to a maximum of 1.0% individually (single component), as well as other elements such as Ni, Cr, Co or B up to 1.0% in total and up to at a maximum of 0.3% each.

The object of the present invention is to develop a carrier material for printing plates which at least corresponds to the better materials of the prior art in the quality of the surface topography after the roughening, in particular the electrochemical roughening, without, however, having their disadvantages in the thermal treatment.

The invention is based on the known carrier materials lien for printing plates made of an aluminum alloy containing iron (Fe) and manganese (Mn), the Fe content being greater than the Mn content. The carrier material according to the invention is then characterized in that the Fe content is 1.2 to 2.1%, the Mn content is 0.1 to 0.9 and the sum of the Fe and Mn content is 1.3 to 2 , Amount to 2%. In a preferred embodiment, the sum of the Fe and the Mn content is 1.5 to 2.2%. In a further preferred embodiment, the Fe content is 1.45 to 1.6%, the Mn content is 0.35 to 0.5% and the sum of the Fe and Mn content is 1.8 to 2.1 %. Another object of the invention is a printing plate based on such a carrier material and at least one radiation-sensitive reproduction layer applied to the carrier material, the carrier material being in mechanically, chemically and / or electrochemically roughened and optionally anodically oxidized and hydrophilized form.

The aluminum alloy used for the carrier material according to the invention, which is in strip, plate or foil form, can be produced in particular according to the information in DE-C 24 23 597. In the production of the starting melt, it is expedient to start from a eutectic alloy with the addition of the alloy elements. To make the casting alloy, the metal is cast so that there is essentially no nucleation of intermetallic particles in the molten metal in front of the front between the liquid and solid metals. The term "eutectic alloy" is used in the this context also mean a range of compositions of the alloys in the vicinity of the eutectics, in which it is possible to achieve the simultaneous deposition of the metallic aluminum phase and one or more fibrous intermetallic phases. After the casting alloy has been produced, its further processing can be carried out by hot and / or cold machining (for example rolling), a cross-section reduction of at least 60% being achieved. In the production of rolled products, it is preferred to achieve the greater part of the reduction in cross-section of the original cast ingot by hot rolling, the further reduction then being carried out by a subsequent cold rolling process. In this context, "cold processing" means processing at a temperature of less than 250 ^* C. Instead of the preferred rolling ingot casting at the beginning of the alloy processing, strip casting can also take place. For example, the cast alloy is heated to about 500 ° C and the hot rolling of the billet begins to descend to about 260 to 330 ° C at that temperature. After the cold rolling, in which the strip thickness is reduced, for example, from approximately 3.0 mm to approximately 0.8 or approximately 0.3 mm, after an intermediate annealing of the cold-rolled material to approximately 340 ° C., a further cold rolling can follow, in which the about 0.8 mm thick tape is also reduced to about 0.3 mm. In practice, the carrier materials used have a thickness of 0.1 to 0.5 mm in particular, but deviations downwards and upwards are also possible.

In addition to the elements Al, Fe and Mn listed above, the alloy can also contain Si (but preferably not more than 0.1%), Cu (preferably but not more than 0.3%), Mg (but preferably not more than 0.1%) X), Ti (but preferably not more than 0.1%), Zn (preferably but not more than 0.1%), Ni (preferably but not more than 0.3%) and / or Co (but preferably not more than 0.3%), the sum of these elements should preferably not exceed 0.4%. Otherwise, the alloy used according to the invention can also contain a maximum of 0.15% and individually a maximum of 0.05% of the elements B, Be, Bi, Ca, Cr, Ga, Li, Na, Pb, Sb, Sn, V and / or Zr included. The alloy used according to the invention differs from the prior art in the field of carrier materials for printing plates on the one hand by a high Fe content and a relatively high Mn content for a high Fe content and on the other hand by a high sum of both components.

When used in practice, the carrier materials for printing plates are preferably mechanically (e.g. by brushing and / or with abrasive treatments), chemically (e.g. by means of) in tape form or also in plate or film form before the reproduction layer is applied Etching agent) or electrochemically (eg by alternating current treatment in aqueous HC1 or HN0 ₃ solutions) roughened on one or both sides; in particular, they are roughened mechanically and electrochemically or only electrochemically. The average roughness depth R _{z of} the roughened surface is in the range from about 1 to 15 pm, especially in the range of 1.5 to 10 pm. The roughness depth is determined in accordance with DIN 4768 in the version from October 1970, the roughness depth R _z is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections.

Before the roughening, the flat support material can be pre-cleaned; it includes, for example, treatment with aqueous NaOH solution with or without degreasing agent and / or complexing agents, trichlorethylene, acetone, methanol or other commercially available aluminum stains. The roughening or, in the case of several roughening stages, also between the individual stages, an abrasive treatment can additionally be carried out, in particular a maximum of 2 g / m ^{2 being} removed (up to 5 g / m ² between the stages); In general, aqueous solutions of alkali metal hydroxide or aqueous solutions of alkaline salts or aqueous acid solutions based on HN0 ₃ , H ₂ SO ₄ or H ₃ PO ₄ are used as abrasive solutions. In addition to an abrasive treatment stage between the roughening stage and a subsequent anodizing stage, non-electrochemical treatments are also known which essentially have only a rinsing and / or cleaning effect and, for example, for removing deposits formed during roughening ("Schmant") or simply for removal serve from leftovers; For example, dilute aqueous alkali hydroxide solutions or water are used for these purposes.

After the roughening process or processes, an anodic oxidation of the carrier material can then optionally follow in a further process step to be used, for example in order to improve the abrasion and adhesion properties of its surface (s). The usual electrolytes such as H ₂ S0 ₄ , H ₃ P0 ₄ , H ₂ C ₂ 0 ₄ , amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof can be used for anodic oxidation; in particular, H ₂ S0 ₄ and H ₃ P0 _{4 are used} alone, in a mixture and / or in a multi-stage anodizing process. The layer weights of aluminum oxide range from 1 to 10 g / m ² , corresponding to a layer thickness of approximately 0.3 to 3.0 μm.

The stage of anodic oxidation of the carrier material can also be followed by one or more post-treatment stages. Aftertreatment is understood to mean in particular a hydrophilizing chemical or electrochemical treatment of the aluminum oxide layer, for example immersion treatment of the material in an aqueous polyvinylphosphonic acid solution according to DE-C 16 21 478 (= GB-A 1 230 447), an immersion treatment in an aqueous alkali silicate Solution according to DE-B 14 71 707 (= US-A 3 181 461) or an electrochemical treatment (anodization) in an aqueous alkali silicate solution according to DE-A 25 32 769 (= US-A 3 902 976). These post-treatment stages serve in particular to additionally increase the hydrophilicity of the aluminum oxide layer, which is often sufficient, while at least the other known properties of this layer are retained.

Reproduction layers sensitive to radiation (light) are to be understood in principle as those which, after irradiation (exposure), possibly with subsequent development and / or fixation, provide an imagewise surface from which printing can take place.

• positiv-arbeitende, o-Chinondiazide, insbesondere o-Naphthochinondiazide wie Naphthochinon-(1,2)-diazid-(2)-sulfonsäureester oder -amide, die nieder- oder höhermolekular sein können, als lichtempfindliche Verbindung enthaltende Reproduktionsschichten, die beispielsweise in den DE-C 854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273, 1 124 817 und 2 331 377 und den EP-A 0 021 428 und 0 055 814 beschrieben werden;
• negativ-arbeitende Reproduktionsschichten mit Kondensationsprodukten aus aromatischen Diazoniumsalzen und Verbindungen mit aktiven Carbonylgruppen, bevorzugt Kondensationsprodukte aus Diphenylamindiazoniumsalzen und Formaldehyd, die beispielsweise in den DE-C 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, den US-A 2 679 498 und 3 050 502 und der GB-A 712 606 beschrieben werden;
• negativ-arbeitende, Mischkondensationsprodukte aromatischer Diazoniumverbindungen enthaltende Reproduktionsschichten, beispielsweise nach der DE-C 20 65 732, die Produkte mit mindestens je einer Einheit aus a) einer kondensationsfähigen aromatischen Diazoniumsalzverbindung und b) einer kondensationsfähigen Verbindung wie einem Phenolether oder einem aromatischen Thioether, verbunden durch ein zweibindiges, von einer kondensationsfähigen Carbonylverbindung abgeleitetes Zwischenglied wie einer Methylengruppe aufweisen;
• positiv-arbeitende Schichten nach der DE-A 26 10 842, der DE-C 27 18 254 oder der DE-A 29 28 636, die eine bei Bestrahlung Säure abspaltende Verbindung, eine monomere oder polymere Verbindung, die mindestens eine durch Säure abspaltbare C-0-C-Gruppe aufweist (z. B. eine Orthocarbonsäureestergruppe oder eine Carbonsäureamidacetalgruppe) und gegebenenfalls ein Bindemittel enthalten;
• negativ-arbeitende Schichten aus photopolymerisierbaren Monomeren, Photoinitiatoren, Bindemitteln und gegebenenfalls weiteren Zusätzen; als Monomere werden dabei beispielsweise Acryl- und Methacrylsäureester oder Umsetzungsprodukte von Diisocyanaten mit Partialestern mehrwertiger Alkohole eingesetzt, wie es beispielsweise in den US-A 2 760 863 und 3 060 023 und den DE-A 20 64 079 und 23 61 041 beschrieben wird;
• negativ-arbeitende Schichten gemäß der DE-A 30 36 077, die als lichtempfindliche Verbindung ein Diazoniumsalz-Polykondensationsprodukt oder eine organische Azidoverbindung und als Bindemittel ein hochmolekulares Polymeres mit seitenständigen Alkenylsulfonyl- oder Cycloalkenylsulfonylurethan-Gruppen enthalten.

In addition to the layers containing silver halides used in many fields, various others are also known, such as e.g. As described in "Light-Sensitive Systems" by Jaromir Kosar, John Wiley & Sons Verlag, New York 1965: the colloid layers containing chromates and dichromates (Kosar, Chapter 2); the layers containing unsaturated compounds in which these compounds are isomerized, rearranged, cyclized or crosslinked during exposure (Kosar, Chapter 4); the layers containing photopolymerizable compounds, in which monomers or prepolymers optionally polymerize during exposure by means of an initiator (Kosar, Chapter 5); and the layers containing o-diazo-quinones such as naphthoquinonediazides, p-diazo-quinones or diazonium salt condensates (Kosar, Chapter 7). The suitable layers also include the electrophotographic layers, ie those which contain an inorganic or organic photoconductor. In addition to the radiation-sensitive substances, these layers can of course also other components such. B. contain resins, dyes or plasticizers. In particular, the following radiation-sensitive masses or compounds can be used in the reproduction layers:

• positive-working, o-quinonediazides, in particular o-naphthoquinonediazides such as naphthoquinone- (1,2) -diazid- (2) -sulfonic acid esters or amides, which can be of low or higher molecular weight, as a photosensitive compound-containing reproduction layers, for example in the DE-C 854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273, 1 124 817 and 2 331 377 and EP-A 0 021 428 and 0 055 814;
• negative working reproduction layers with condensation products from aromatic diazonium salts and compounds with active carbonyl groups, preferably condensation products from diphenylamine diazonium salts and formaldehyde, which are described, for example, in DE-C 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, US-A 2,679,498 and 3,050,502 and GB-A 712,606;
• Reproductive layers containing negative-working, mixed condensation products of aromatic diazonium compounds, for example according to DE-C 20 65 732, the products with at least one unit each of a) a condensable aromatic diazonium salt compound and b) a condensable compound such as a phenol ether or an aromatic thioether, connected by have a double bonded intermediate derived from a condensable carbonyl compound such as a methylene group;
• positive-working layers according to DE-A 26 10 842, DE-C 27 18 254 or DE-A 29 28 636, which contain a compound which cleaves off under irradiation, a monomeric or polymeric compound which has at least one C-cleavable by acid -0-C group (z. B. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally contain a binder;
• negatively working layers made of photopolymerizable monomers, photoinitiators, binders and optionally other additives; the monomers used are, for example, acrylic and methacrylic acid esters or reaction products of diisocyanates with partial esters of polyhydric alcohols, as described, for example, in US Pat. Nos. 2,760,863 and 3,060,023 and DE-A 20 64 079 and 23 61 041;
• Negative-working layers according to DE-A 30 36 077, which contain a diazonium salt polycondensation product or an organic azido compound as a photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as a binder.

It can also be photoconductive layers such as z. B. in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 can be used.

The substrate materials according to the invention have properties for the printing plate application area that exceed the qualities of the prior art, that is to say they are in particular temperature-stable and at the same time, even after roughening, preferably after electrochemical roughening, they show a practical surface topography which is required for contemporary high-performance printing plates; This combination of properties has not yet been achieved with the aluminum alloys previously used and / or described in the lithography field. This offers particular advantages in the production of printing plates with positive-working reproduction layers, which are often burned in to achieve longer print runs, ie the exposed and developed printing plate is heated to a temperature of more than 180 ^* C before printing in order to make the image areas more resistant close. If these printing plates have a carrier material with the alloy composition according to the invention, strength problems in the carrier material occur to a reduced extent after baking.

In the following examples and the description above, the percentages are by weight, unless otherwise stated.

The radiation-sensitive layer is either a negative-working layer containing a reaction product of polyvinyl butyral with propylene sulfonyl isocyanate, a polycondensation product composed of 1 mol of 3-methoxy diphenylamine-4-diazonium sulfate and 1 mol of 4,4'-bismethoxymethyl-diphenyl ether precipitated as mesitylene sulfonate, H ₃ P0 ₄ , Victoriareinblau FGA and phenylazodiphenylamine or a positive working with a content of a cresol-formaldehyde novolak, 4- (2- Phenyl-prop-2-yl) -phenyl ester of naphthoquinone- (1,2) -diazide- (2) -sulfonic acid- (4), polyvinylbutyral, naphthoquinone- (1,2) -diazid- (2) -sulfonic acid chloride- ( 4) and crystal violet applied to the carrier material according to the invention. Practical printing plates and printing forms can be created from it.

example 1

An aluminum alloy strip produced on the production route of rolled ingot casting, hot rolling and cold rolling with an Fe content of 1.6% and a Mn content of 0.35% (the remaining elements are a maximum of 0.3%, the rest is aluminum) in one degreased aqueous NaOH solution and electrochemically roughened in an aqueous 0.9% solution of HCl with alternating current (115 A / dm ² at 35 ° C.) and in an aqueous solution containing H ₂ SO ₄ and A1 ³⁺ ions with direct current anodized.

Comparative Example V1

The procedure of Example 1 is followed, but a strip made of the aluminum alloy "pure aluminum" (or "1050") is used as the starting material (Fe content 0.4%, practically no Mn content).

Comparative example V2

The procedure of Example 1 is followed, but a strip made of the aluminum alloy "1100" is used as the starting material (Fe content 0.375%, practically no Mn content).

Comparative Example V3

The procedure of Example 1 is followed, but a strip made of the aluminum alloy "3003" is used as the starting material (Fe content 0.15%, Mn content 0.7%).

Example 2

The procedure is as described in Example 1, but the starting material is an aluminum alloy strip with an Fe content of 1.6% and a Mn content of 0.5% (the remaining elements are a maximum of 0.35%) The rest is aluminum).

Example 3

The procedure is as described in Example 1, but as a starting material a strip made of an aluminum alloy with an Fe content of 1.5% and a Mn content of 0.5% (the remaining elements are a maximum of 0.35%) The rest is aluminum).

Example 4

The procedure is as described in Example 1, but as a starting material a band made of an aluminum alloy with an Fe content of 1.45% and a Mn content of 0.5% (the remaining elements are a maximum of 0.3%) The rest is aluminum).

Example 5

The procedure is as described in Example 1, but as a starting material a band made of an aluminum alloy with an Fe content of 1.45% and a Mn content of 0.35% (the remaining elements are a maximum of 0.3%) The rest is aluminum).

Roughening topography

The roughening topography is most uniform (i.e. uniformity of the hole distribution, little to no scars) with V1 and Examples 1 to 5 according to the invention, with V2 and V3 the quality is already significantly poorer.

Mechanical properties after heating

To investigate the mechanical properties after heating as a function of the temperature, the yield strength and the tensile strength at room temperature and between 100 and 300 ° C. are determined at specific temperature intervals.

With regard to the yield point and the tensile strength, the carrier materials according to the invention are at the level of V3. V1 and V2 are significantly below these values.

Claims (4)

1. Support material for printing plates made of an aluminum alloy containing iron (Fe) and manganese (Mn), the Fe content being greater than the Mn content, characterized in that the Fe content is 1.2 to 2.1 % By weight, the Mn content 0.1 to 0.9% by weight and the sum of the Fe and Mn content 1.3 to 2.2% by weight. 2. Support material according to claim 1, characterized in that the sum of the Fe and the Mn content is 1.5 to 2.2 wt .-%. 3. Support material according to claim 1 or 2, characterized in that the Fe proportion 1.45 to 1.6 wt.%, The Mn proportion 0.35 to 0.5 wt.% And the sum of the Fe - And the Mn content 1.8 to 2.1 wt .-%. 4. Printing plate on the basis of a mechanically, chemically and / or electrochemically roughened and optionally anodically oxidized and hydrophilized support material made of an aluminum alloy containing Fe and Mn, the Fe content being greater than the Mn content, and at least one the radiation-sensitive reproduction layer applied to the carrier material, characterized in that the Fe content is 1.2 to 2.1% by weight, the Mn content 0.1 to 0.9% by weight and the sum of the Fe and the Mn content 1.3 to 2.2 wt .-%.