EP0719873A1 - Process for manufacturing a shadow mask, made from an iron-nickel alloy - Google Patents

Abstract

Process for the mfr. of an iron-nickel alloy shadow mask comprises: (a) providing a metal sheet pierced with uniformly distributed hole, the metal sheet comprising an alloy comprising (in wt.%): 35.5-37 Ni; max. 0.5 Co; max. 0.1 Cr; max. 0.1 Cu; max. 0.1 Mo; max. 0.1 V; max. 0.1 Nb; max. 0.1 Mn; 0.03-0.15 Si; max. 0.001 S; 0.0001-0.002 Ca; 0.0001-0.002 Mg; max. 0.005 Al; max. 0.01 O; max. 0.002 C; max. 0.005 N; max. 0.003 P; 0.001 H; max. 0.001 B; balance Fe plus usual impurities, the following relationships satisfied: max. S = 0.02 x Mn + 0.8 x Ca + 0.6 x Mg Cr + Cu + Mo + V + Nb + Si = max. 0.15; (b) heat treating the sheet to obtain a grain size which defined by ASTM E112-88,12.4 is greater or equal to 7 ASTM; and (c) forming the sheet to the required shape. The shadow mask is also claimed.

Description

The invention relates to the manufacture of an iron / nickel alloy shadow mask for cathode-ray tube for color display.

A color display cathode ray tube generally comprises an envelope having a glass display window comprising a display screen on which phosphors in red, green and blue are arranged. A shadow mask or "Shadow mask" pierced with a very large number of small holes is mounted in the tube, facing the display screen and at a short distance from it. When the tube is in operation, three electron beams are generated inside of it by three electron guns, the electron beams pass through the holes of the shadow mask and bombard the phosphorescent areas.

The relative positions of the holes and the phosphors are such that each electron beam bombards the phosphorescent areas corresponding to a particular color to form an image.

However, a significant part of the electrons is intercepted by the shadow mask and the kinetic energy of these electrons is transformed into heat which raises the temperature of the shadow mask. The thermal expansion of the shadow mask caused by this rise in temperature can cause a local deformation of the shadow mask which causes a disturbance in the relative arrangement of the holes and the associated phosphors.

This results in errors in the colors of the image and these errors are all the more important as the shadow mask is flatter, which is more and more the case in current generations of cathode ray display tubes, the viewing windows are becoming increasingly flat.

It is well known that such problems caused by thermal effects can be avoided by making shadow masks from a material having a very low coefficient of expansion. Such a material is for example an Iron / Nickel alloy containing about 36% of Nickel. However, the high mechanical characteristics and the difficulties of rolling such materials limit their use for this application.

It is known from US Pat. No. 4,685,321 (EP-A 179 506) to first subject a sheet of such a material intended for the manufacture of a shadow mask, to a heat treatment to reduce its elastic limit at 0.2% at room temperature and then carry out the shaping above room temperature so as to further reduce its elastic limit to 0.2%. The Iron / Nickel alloy used in this product has a linear expansion coefficient between 1x10 ^{-6 / o} K and 1.5x10 ^{-6 / o} K. A lower expansion coefficient can be obtained by replacing part of the Nickel with Cobalt in contents of between 2% and 12% by weight.

However, the substitution of Nickel with Cobalt has several disadvantages. On the one hand, Cobalt is a very expensive element, on the other hand, Cobalt pollutes the chemical attack reagents used for drilling the holes in the shadow mask by chemical etching.

The object of the present invention is to provide a method of manufacturing a shadow mask made of an Iron / Nickel alloy containing no or very little Cobalt, having a coefficient of linear expansion less than 0.9 × 10 ^{-6 / o} K and easy to laminate.

• on approvisionne une feuille percée de trous uniformément répartis, constituée d'un alliage Fer/Nickel dont la composition chimique comprend, en poids : $$\text{35,5\% ≤ Ni ≤37\%}$$
  
  $$\text{Co ≤ 0,5\%}$$
  
  $$\text{Cr ≤0,1\%}$$
  
  $$\text{Cu ≤ 0,1\%}$$
  
  $$\text{Mo ≤ 0,1\%}$$
  
  $$\text{V ≤ 0,1\%}$$
  
  $$\text{Nb ≤ 0,1\%}$$
  
  $$\text{Mn ≤ 0,1 \%}$$
  
  $$\text{0,03\% ≤ Si ≤ 0,15\%}$$
  
  $$\text{S ≤ 0,001\%}$$
  
  $$\text{0,0001\% ≤ Ca ≤ 0,002\%}$$
  
  $$\text{0,0001\% ≤ Mg ≤ 0,002\%}$$
  
  $$\text{Al ≤ 0,005\%}$$
  
  $$\text{O ≤ 0,01\%}$$
  
  $$\text{C ≤ 0,02\%}$$
  
  $$\text{N ≤ 0,005\%}$$
  
  $$\text{P ≤ 0,003\%}$$
  
  $$\text{H ≤ 0,001\%}$$
  
  $$\text{B ≤ 0,001\%}$$
  

To this end, the subject of the invention is a method of manufacturing a shadow mask according to which,

• we supply a sheet pierced with uniformly distributed holes, made of an Iron / Nickel alloy whose chemical composition comprises, by weight: $$\text{35.5\% ≤ Ni ≤37\%}$$
  
  $$\text{Co ≤ 0.5\%}$$
  
  $$\text{Cr ≤0.1\%}$$
  
  $$\text{Cu ≤ 0.1\%}$$
  
  $$\text{Mo ≤ 0.1\%}$$
  
  $$\text{V ≤ 0.1\%}$$
  
  $$\text{Nb ≤ 0.1\%}$$
  
  $$\text{Mn ≤ 0.1\%}$$
  
  $$\text{0.03\% ≤ If ≤ 0.15\%}$$
  
  $$\text{S ≤ 0.001\%}$$
  
  $$\text{0.0001\% ≤ Ca ≤ 0.002\%}$$
  
  $$\text{0.0001\% ≤ Mg ≤ 0.002\%}$$
  
  $$\text{Al ≤ 0.005\%}$$
  
  $$\text{O ≤ 0.01\%}$$
  
  $$\text{C ≤ 0.02\%}$$
  
  $$\text{N ≤ 0.005\%}$$
  
  $$\text{P ≤ 0.003\%}$$
  
  $$\text{H ≤ 0.001\%}$$
  
  $$\text{B ≤ 0.001\%}$$
  

The remainder being iron and unavoidable impurities resulting from processing;

et $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0,15\%}$$

• on soumet la feuille à un traitement thermique pour obtenir un grain dont la taille telle que définie par la norme ASTM E 112-88,12.4 est égale ou supérieure à 7 ASTM ;
• on forme la feuille pour lui donner la forme du masque d'ombre.

The chemical composition satisfying relationships: $$\text{S ≤ 0.02 x Mn + 0.8 x Ca + 0.6 x Mg}$$

and $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0.15\%}$$

• the sheet is subjected to a heat treatment to obtain a grain whose size as defined by standard ASTM E 112-88,12.4 is equal to or greater than 7 ASTM;
• we form the sheet to give it the shape of the shadow mask.

$$\text{Cr ≤ 0,07\%}$$

$$\text{Cu ≤ 0,05\%}$$

$$\text{Mo ≤ 0,05\%}$$

$$\text{Mn ≤ 0,05\%}$$

$$\text{O ≤ 0,005\%}$$

$$\text{N ≤ 0,003\%}$$

$$\text{S ≤ 0,0005\%}$$

$$\text{C ≤ 0,005\%}$$

$$\text{B ≤ 0,0004\%}$$

Preferably, the chemical composition must be chosen so that: $$\text{If ≤ 0.08\%}$$

$$\text{Cr ≤ 0.07\%}$$

$$\text{Cu ≤ 0.05\%}$$

$$\text{Mo ≤ 0.05\%}$$

$$\text{Mn ≤ 0.05\%}$$

$$\text{O ≤ 0.005\%}$$

$$\text{N ≤ 0.003\%}$$

$$\text{S ≤ 0.0005\%}$$

$$\text{C ≤ 0.005\%}$$

$$\text{B ≤ 0.0004\%}$$

In order for the coefficient of expansion to be as low as possible, the nickel content must be between 35.9% and 36.2%.

Preferably, the heat treatment must be carried out by maintaining at a temperature between 750 ° C and 850 ° C, in a non-oxidizing atmosphere.

$$\text{Co ≤ 0,5\%}$$

$$\text{Cr ≤ 0,1\%}$$

$$\text{Cu ≤ 0,1\%}$$

$$\text{Mo ≤ 0,1\%}$$

$$\text{V ≤ 0,1\%}$$

$$\text{Nb ≤ 0,1\%}$$

$$\text{Mn ≤ 0,1 \%}$$

$$\text{0,03\% ≤ Si ≤ 0,15\%}$$

$$\text{S ≤ 0,001\%}$$

$$\text{0,0001\% ≤ Ca ≤ 0,002\%}$$

$$\text{0,0001\% ≤ Mg ≤ 0,002\%}$$

$$\text{Al ≤ 0,005\%}$$

$$\text{O ≤ 0,01 \%}$$

$$\text{C ≤ 0,02\%}$$

$$\text{N ≤ 0,005\%}$$

$$\text{P ≤ 0,003\%}$$

$$\text{H ≤ 0,001 \%}$$

$$\text{B ≤ 0,001\%}$$

The invention also relates to a shadow mask made of an Iron / Nickel alloy having a coefficient of linear expansion between 20 ° C and 100 ° C less than 0.9x10 ^{-6 o} K, and preferably less than 0.8x10 ^{-6 o} K in which, the chemical composition of the Iron / Nickel alloy includes by weight: $$\text{35.5\% ≤ Ni ≤37\%}$$

$$\text{Co ≤ 0.5\%}$$

$$\text{Cr ≤ 0.1\%}$$

$$\text{Cu ≤ 0.1\%}$$

$$\text{Mo ≤ 0.1\%}$$

$$\text{V ≤ 0.1\%}$$

$$\text{Nb ≤ 0.1\%}$$

$$\text{Mn ≤ 0.1\%}$$

$$\text{0.03\% ≤ If ≤ 0.15\%}$$

$$\text{S ≤ 0.001\%}$$

$$\text{0.0001\% ≤ Ca ≤ 0.002\%}$$

$$\text{0.0001\% ≤ Mg ≤ 0.002\%}$$

$$\text{Al ≤ 0.005\%}$$

$$\text{O ≤ 0.01\%}$$

$$\text{C ≤ 0.02\%}$$

$$\text{N ≤ 0.005\%}$$

$$\text{P ≤ 0.003\%}$$

$$\text{H ≤ 0.001\%}$$

$$\text{B ≤ 0.001\%}$$

et $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0,15\%}$$

The remainder being iron and unavoidable impurities resulting from the processing; the chemical composition satisfying the relationships: $$\text{S ≤ 0.02 x Mn + 0.8 x Ca + 0.6 x Mg}$$

and $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0.15\%}$$

$$\text{Cr ≤ 0,07\%}$$

$$\text{Cu ≤ 0,05\%}$$

$$\text{Mo ≤ 0,05\%}$$

$$\text{Mn ≤ 0,05\%}$$

$$\text{O ≤ 0,005\%}$$

$$\text{N ≤ 0,003\%}$$

$$\text{S ≤ 0,0005\%}$$

$$\text{C ≤ 0,005\%}$$

$$\text{B ≤ 0,0004\%}$$

Preferably, the chemical composition of the Iron / Nickel alloy constituting the shadow mask is such that: $$\text{If ≤ 0.08\%}$$

$$\text{Cr ≤ 0.07\%}$$

$$\text{Cu ≤ 0.05\%}$$

$$\text{Mo ≤ 0.05\%}$$

$$\text{Mn ≤ 0.05\%}$$

$$\text{O ≤ 0.005\%}$$

$$\text{N ≤ 0.003\%}$$

$$\text{S ≤ 0.0005\%}$$

$$\text{C ≤ 0.005\%}$$

$$\text{B ≤ 0.0004\%}$$

It is also preferable that the nickel content is between 35.9% and 36.2%.

Finally, it is desirable that the grain of the Iron / Nickel alloy has a size measured according to standard ASTM E112-88,12.4 greater than the index 7 ASTM.

The invention will now be described in more detail, but without limitation.

$$\text{Co ≤ 0,5\%}$$

$$\text{Cr ≤ 0,1\%}$$

$$\text{Cu ≤ 0,1\%}$$

$$\text{Mo ≤ 0,1\%}$$

$$\text{V ≤ 0,1\%}$$

$$\text{Nb ≤ 0,1\%}$$

$$\text{Mn ≤ 0,1 \%}$$

$$\text{0,03\% ≤ Si ≤ 0,15\%}$$

$$\text{S ≤ 0,001\%}$$

$$\text{0,0001\% ≤ Ca ≤ 0,002\%}$$

$$\text{0,0001\% ≤ Mg ≤ 0,002\%}$$

$$\text{Al ≤ 0,005\%}$$

$$\text{O ≤ 0,01 \%}$$

$$\text{C ≤ 0,02\%}$$

$$\text{N ≤ 0,005\%}$$

$$\text{P ≤ 0,003\%}$$

$$\text{H ≤ 0,001 \%}$$

$$\text{B ≤ 0,001 \%}$$

A strip having a thickness of approximately 150 μm is obtained by hot rolling then cold rolling of an ingot or a slab of iron / nickel alloy containing by weight: $$\text{35.5\% ≤ Ni ≤ 37\%}$$

$$\text{Co ≤ 0.5\%}$$

$$\text{Cr ≤ 0.1\%}$$

$$\text{Cu ≤ 0.1\%}$$

$$\text{Mo ≤ 0.1\%}$$

$$\text{V ≤ 0.1\%}$$

$$\text{Nb ≤ 0.1\%}$$

$$\text{Mn ≤ 0.1\%}$$

$$\text{0.03\% ≤ If ≤ 0.15\%}$$

$$\text{S ≤ 0.001\%}$$

$$\text{0.0001\% ≤ Ca ≤ 0.002\%}$$

$$\text{0.0001\% ≤ Mg ≤ 0.002\%}$$

$$\text{Al ≤ 0.005\%}$$

$$\text{O ≤ 0.01\%}$$

$$\text{C ≤ 0.02\%}$$

$$\text{N ≤ 0.005\%}$$

$$\text{P ≤ 0.003\%}$$

$$\text{H ≤ 0.001\%}$$

$$\text{B ≤ 0.001\%}$$

et $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0,15\%}$$

The remainder being iron and unavoidable impurities resulting from processing; the chemical composition satisfying the relationships: $$\text{S ≤ 0.02 x Mn + 0.8 x Ca + 0.6 x Mg}$$

and $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0.15\%}$$

The composition of this alloy is chosen so as to obtain a coefficient of linear expansion less than 0.9 × 10 ^{-6 / o} K and preferably less than 0.8 × 10 ^{-6 / o} K; a good ability to hot and cold rolling, a good ability to obtain very fine and very close holes distributed over the strip by chemical etching and a good ability to cold forming by stamping.

sont imposées pour que le coefficient de dilatation linéaire soit inférieur à 0,9x10^-6/oK. Il est préférable que la teneur en Nickel soit comprise entre 35,9% et 36,2% en poids, et que la teneur, en poids, du Chrome soit inférieure à 0,07%, les teneurs en Cuivre, Molybdène, Manganèse soient inférieures à 0,05% et la teneur en Silicium inférieure à 0,08%; on obtient ainsi un coefficient de dilatation inférieur à 0,8x10^-6/oK.The contents of Nickel, Chromium, Copper, Molybdenum, Vanadium, Niobium, Silicon and Manganese as well as the relationship: $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0.15\%}$$

are imposed so that the coefficient of linear expansion is less than 0.9 × 10 ^{-6 / o} K. It is preferable that the nickel content is between 35.9% and 36.2% by weight, and that the content, in weight, chromium is less than 0.07%, the contents of copper, molybdenum, manganese are less than 0.05% and the silicon content less than 0.08%; this gives a coefficient of expansion of less than 0.8x10 ^{-6 / o} K.

The Cobalt content must remain below 0.5% to avoid polluting the attack fluid used for the chemical etching operation.

sont imposées afin d'obtenir une bonne aptitude au laminage malgré la très basse teneur en Manganèse. De préférence, la teneur en Oxygène doit être inférieure à 0,005%, la teneur en Soufre inférieure à 0,0005%.Sulfur, Silicon, Calcium, Magnesium, Oxygen and Phosphorus content limits as well as the relationship $$\text{S ≤ 0.02 x Mn + 0.8 x Ca + 0.6 x Mg}$$

are imposed in order to obtain a good rolling ability despite the very low manganese content. Preferably, the oxygen content must be less than 0.005%, the sulfur content less than 0.0005%.

The aluminum content must be less than 0.005% and the nitrogen content less than 0.005% and preferably less than 0.003% in order to avoid the formation of aluminum nitrides which is unfavorable for the ability to be deformed when hot.

The carbon content must remain less than 0.02% and preferably less than 0.005% in order to reduce the elastic limit which is favorable for the ability to stamp.

The hydrogen content is limited to 0.001% to avoid the formation of blisters.

The boron content must remain less than 0.001% and preferably less than 0.0004% to avoid the formation of powdery nitrides on the surface of the strip during the heat treatment.

Fine holes are created on the strip by a chemical photoengraving process. These holes can have any desirable shape, for example round or elongated.

After etching the holes, the strip on which the dividing lines have also been etched is cut into sheets, each of these sheets forming a shadow mask sheet comprising a network of holes.

The material constituting the shadow mask sheet thus obtained has an elastic limit of 0.2% of between 580MPa and 640MPa at ambient temperature, which is too important to obtain a shadow mask sheet having the curvature. wanted. To reduce this elastic limit, the shadow mask sheet is annealed for approximately 15 minutes in a hydrogenated atmosphere (approximately 10% H ₂ , the rest N ₂ ) at a temperature between 750 ° C and 850 ° C. thus a material having a grain size of approximately 15 μm, a coercive force of approximately 40 Am and a coefficient of linear expansion between 20 ° C and 100 ° C less than or equal to 0.9 × 10 ^{-6 / o} K.

The elastic limit of 280 MPa, although reduced, however remains too high for the process of shaping the shadow mask to be reproducible. It is therefore necessary to further reduce the elastic limit. For this, the shadow mask sheet is shaped at a temperature between 50 ° C and 250 ° C. At 200 ° C the elastic limit is around 130 MPa.

$$\text{Co = 0,015\%}$$

$$\text{Cr = 0,02\%}$$

$$\text{Cu < 0,01 \%}$$

$$\text{Mo = 0,0055\%}$$

$$\text{V < 0,005\%}$$

$$\text{Nb < 0,005\%}$$

$$\text{Si = 0,078\%}$$

$$\text{Mn = 0,024\%}$$

$$\text{S < 0,0005\%}$$

$$\text{Ca = 0,0003\%}$$

$$\text{Mg = 0,0004\%}$$

$$\text{Al < 0,005\%}$$

$$\text{O = 0,0042\%}$$

$$\text{C = 0,003\%}$$

$$\text{N = 0,0033\%}$$

$$\text{P < 0,003\%}$$

$$\text{H < 0,001 \%}$$

$$\text{B < 0,0004\%}$$

By way of example, a shadow mask was made with a material according to the invention, the chemical composition by weight of which comprises: $$\text{Ni = 36.13\%}$$

$$\text{Co = 0.015\%}$$

$$\text{Cr = 0.02\%}$$

$$\text{Cu <0.01\%}$$

$$\text{Mo = 0.0055\%}$$

$$\text{V <0.005\%}$$

$$\text{Nb <0.005\%}$$

$$\text{If = 0.078\%}$$

$$\text{Mn = 0.024\%}$$

$$\text{S <0.0005\%}$$

$$\text{Ca = 0.0003\%}$$

$$\text{Mg = 0.0004\%}$$

$$\text{Al <0.005\%}$$

$$\text{O = 0.0042\%}$$

$$\text{C = 0.003\%}$$

$$\text{N = 0.0033\%}$$

$$\text{P <0.003\%}$$

$$\text{H <0.001\%}$$

$$\text{B <0.0004\%}$$

The levels indicated as being "less than" are levels below the sensitivity threshold of the analysis methods used.

The shadow mask thus obtained had a blister defect that was at least 15% lower than the defect of the same kind observed on a comparable shadow mask made of an Iron / Nickel alloy according to the prior art.

Due to the low Cobalt content, the chemical etching process is not affected by this element. The coercive field less than 55 A / m is particularly favorable to the process of demagnetization of the shadow masks implemented each time the tube is turned on.

One of the advantages of the invention is that the shadow mask does not need to be coated with a layer such as a layer of Bi ₂ O _3, Al ₂ O ₃ or glass or lead borate, to inhibit overheating due to electronic bombardment.

The invention relates to shadow masks having circular holes or elongated holes extending both over a small part of the height of the mask and over the entire height of the mark. It is particularly suitable for the manufacture of shadow masks for color display cathode ray tubes, brands having a very large number of holes with very small spaces between holes.

It can be noted that the sheet for shadow masks according to the invention, containing very small amounts of Si, Mn and Cr in particular, has a more homogeneous crystal structure which improves the aptitude for chemical etching. This is very important for shadow masks intended for color tubes whose masks must have a very large number of closely spaced holes.

Claims (8)

Method for manufacturing an Iron / Nickel alloy shadow mask characterized in that: - we supply a sheet pierced with uniformly distributed holes, made of an Iron / Nickel alloy whose chemical composition comprises, by weight: $$\text{35.5\% ≤ Ni ≤37\%}$$

$$\text{Co ≤ 0.5\%}$$

$$\text{Cr ≤0.1\%}$$

$$\text{Cu ≤ 0.1\%}$$

$$\text{Mo ≤ 0.1\%}$$

$$\text{V ≤ 0.1\%}$$

$$\text{Nb ≤ 0.1\%}$$

$$\text{Mn ≤ 0.1\%}$$

$$\text{0.03\% ≤ If ≤ 0.15\%}$$

$$\text{S ≤ 0.001\%}$$

$$\text{0.0001\% ≤ Ca ≤ 0.002\%}$$

$$\text{0.0001\% ≤ Mg ≤ 0.002\%}$$

$$\text{Al ≤ 0.005\%}$$

$$\text{O ≤ 0.01\%}$$

$$\text{C ≤ 0.02\%}$$

$$\text{N ≤ 0.005\%}$$

$$\text{P ≤ 0.003\%}$$

$$\text{H ≤ 0.001\%}$$

$$\text{B ≤ 0.001\%}$$

the remainder being iron and unavoidable impurities resulting from processing; the chemical composition satisfying the relationships: $$\text{S ≤ 0.02 x Mn + 0.8 x Ca + 0.6 x Mg}$$

and $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0.15\%}$$

the sheet is subjected to a heat treatment in order to obtain a grain whose size as defined by standard ASTM E112-88,12,4 is greater than or equal to 7 ASTM, - we form the sheet to give it the shape of the shadow mask. Process according to Claim 1, characterized in that the chemical composition of the iron / nickel alloy comprises, by weight: $$\text{If ≤ 0.08\%}$$

$$\text{Cr ≤ 0.07\%}$$

$$\text{Cu ≤ 0.05\%}$$

$$\text{Mo ≤ 0.05\%}$$

$$\text{Mn ≤ 0.05\%}$$

$$\text{O ≤ 0.005\%}$$

$$\text{N ≤ 0.003\%}$$

$$\text{S ≤ 0.0005\%}$$

$$\text{C ≤ 0.005\%}$$

$$\text{B ≤ 0.0004\%}$$

Process according to Claim 1 or Claim 2, characterized in that the chemical composition of the iron / nickel alloy comprises by weight: $$\text{35.9\% ≤ Ni ≤ 36.2\%}$$

Process according to any one of Claims 1 to 3, characterized in that the heat treatment is carried out by maintaining at a temperature between 750 ° C and 850 ° C, in a non-oxidizing atmosphere. Shadow mask made of an Iron / Nickel alloy having a coefficient of linear expansion between 20 ° C and 100 ° C, less than 0.9x10 ^{-6 / o} K, and preferably less than 0.8x10 ^{-6 / o} K characterized in that the chemical composition of the Iron / Nickel alloy includes. in weight : $$\text{35.5\% ≤ Ni ≤37\%}$$

$$\text{Co ≤ 0.5\%}$$

$$\text{Cr ≤ 0.1\%}$$

$$\text{Cu ≤ 0.1\%}$$

$$\text{Mo ≤ 0.1\%}$$

$$\text{V ≤ 0.1\%}$$

$$\text{Nb ≤ 0.1\%}$$

$$\text{Mn ≤ 0.1\%}$$

$$\text{0.03\% ≤ If ≤ 0.15\%}$$

$$\text{S ≤ 0.001\%}$$

$$\text{0.0001\% ≤ Ca ≤ 0.002\%}$$

$$\text{0.0001\% ≤ Mg ≤ 0.002\%}$$

$$\text{Al ≤ 0.005\%}$$

$$\text{O ≤ 0.01\%}$$

$$\text{C ≤ 0.02\%}$$

$$\text{N ≤ 0.005\%}$$

$$\text{P ≤ 0.003\%}$$

$$\text{H ≤ 0.001\%}$$

$$\text{B ≤ 0.001\%}$$

The remainder being iron and unavoidable impurities resulting from processing; the chemical composition satisfying the relationships: $$\text{S ≤ 0.02 x Mn + 0.8 x Ca + 0.6 x Mg}$$

and $$\text{Cr + Cu + Mo + V + Nb + Si ≤ 0.15\%}$$

Shadow mask according to claim 5 characterized in that: $$\text{If ≤ 0.08\%}$$

$$\text{Cr ≤ 0.07\%}$$

$$\text{Cu ≤ 0.05\%}$$

$$\text{Mo ≤ 0.05\%}$$

$$\text{Mn ≤ 0.05\%}$$

$$\text{O ≤ 0.005\%}$$

$$\text{N ≤ 0.003\%}$$

$$\text{S ≤ 0.0005\%}$$

$$\text{C ≤ 0.005\%}$$

$$\text{B ≤ 0.0004\%}$$

Shadow mask according to claim 5 or claim 6 characterized in that the chemical composition of the iron / nickel alloy preferably comprises, by weight: $$\text{35.9\% ≤ Ni ≤ 36.2\%}$$

Shadow mask according to any one of claims 5 to 7, characterized in that the grain of the iron / nickel alloy has a size measured according to standard ASTM E112-88,12.4 greater than the index 7 ASTM.