DE2403366C2 - Process for the production of ferromagnetic particles coated with a protective layer - Google Patents

Description

The invention relates to a method for producing ferromagnetic ones coated with a protective layer Particle in which the ferromagnetic particles are mixed with a salt of a long chain fatty acid will.

A method of this type is known from DD-PS 91 017. The alkali salts of the stearic, Palmitic or oleic acid should be used.

It is known that ferromagnetic powders, such as. B. cobalt cobalt-nickel alloys, iron-cobalt alloys, iron-nickel alloys, iron-nickel-cobalt alloys and similar ferromagnetic powders, have better magnetic properties compared to magnetic oxide powders, such as iron oxide or cobalt oxide . However, the oxidation resistance of magnetic metal powders in air is small. If ferromagnetic powders are left in air, their magnetic properties gradually deteriorate as they oxidize. A spontaneous combustion occurs therein due to an external thermal shock and / or a mechanical shock, its electrostatic discharge, etc. To avoid this, it is usual to take magnetic metal powders out of a furnace by dipping the powder in an organic solvent, then exposing it to air, and then gradually evaporating the organic solvent to slowly air the magnetic metal powders and gradually form an oxide layer on the surface of the magnetic metal powder. In this process, heat is generated gradually by oxidation. The heat generated is absorbed by evaporation of the organic solvent, or the organic solvent is heated until it evaporates, thus avoiding spontaneous combustion. The organic solvents are selected such that they have a boiling point of about 10 ⁰ C up to a few 100 ⁰ C and in that they are inert to the gastric tables metal powders substantially. Such solvents are e.g. B. benzene, toluene, xylene, hexane, cyclohexane uiw. The oxide layer formed is relatively hard and prevents an oxidation reaction from proceeding in the magnetic metal powder to a certain extent. However, such oxidized magnetic metal powders have a relatively short life. This means that the magnetic properties of the magnetic metal powders coated with an oxide layer deteriorate and cannot be maintained.

Another reason why these ferromagnetic powders produced by the above method are not practically used for the production of magnetic tapes is that these magnetic metal powders are low in dispersion property when coated on a tape and are difficult to get in a binder can be dispersed. This low dispersion property is caused by the fact that the magnetic moment of the metal powder a _s · 1.89 ΙΟ- ⁴ to 2.51 · lO ^ TmVkg (150 to 200 emu / g) at Eisenoxydpulver 1.01 x 10- ⁴ to 1 and , 13 x 10 ~ ⁴ Tm ³ / kg (80 to 90 emu / g) is at Chromdioxydpulver. Since the interparticle interaction of magnetic metal powder is expressed by (m) (m'Xr ² (where m and m 'represent the magnetized amount of the particles and r the distance between the particles), the interparticle interaction is the magnetic one Metal powder four to nine times larger than that of the magnetic oxide powder, so that the known magnetic metal particles easily coagulate in a binder and are therefore difficult to disperse in the binder.

When a surfactant with a long molecular chain in the known magnetic metal particles is used, a significant degree of dispersion can be achieved. A surfactant such as lecithin used in a commercially available magnetic tape, however, decomposes when cs.with comes into contact with a magnetic metal body and therefore cannot assist the dispersion.

Another known dispersing method for magnetic oxide powders is the use of a water solution with a mixture of an alkaline metal salt and a fatty acid, which with magnetic Oxydpulverp is mixed to form a monomolecular film on the surface of the particles of the magnetic oxide powder of the radical of the fatty acid. When this method is applied to magnetic metal powders, its dispersing property and oxidation resistance become sufficiently large, but it is a drying process necessary as a result of treatment in water. When the drying process by heating is carried out, there is a risk that spontaneous combustion may occur during, if the Drying process is carried out by ventilation, the magnetic metal particles by water and Oxygen oxidize, which leads to a deterioration in magnetic properties, so that the material cannot be used as a magnetic material.

It is known that spontaneous combustion often occurs even when the above dehydration and / or Drying processes can be carried out in a vacuum.

The invention is intended to provide a method according to the preamble of claim 1 for the production of fine ferromagnetic particles are created with a protective layer that has a high resistance to oxidation and which can be easily dispersed in an organic solvent, so that they are particularly good are suitable for the production of magnetic tapes

This object is achieved by the features specified in the characterizing part of claim 1. Refinements of the invention emerge from the subclaims.

The invention is illustrated below with reference to FIGS. 1 to 3 explained. It shows

F i g. 1 is a diagram showing the changes in the magnetic moment of ferromagnetic particles emerge as a function of the time which are known by the method according to the invention and na ^ ii Process to be produced;

F i g. 2 is a diagram showing the influence on the square-wave ratio of a ferromagnetic Particle-made magnetic tape is evident when the proportion of the salt of fatty acid is changed;

F i g. 3 is a diagram showing the influence of the length of the carbon chain in salts of fatty acids on the Rectangular ratio of a magnetic tape is shown

In general, salts of a fatty acid have a high solubility in water, especially in hot water, however, very little or almost no solubility in an organic solvent. It did, however found that a chemical compound is made by mechanically mixing a powder of a salt one Fatty acid is achieved with a magnetic metal powder in an organic solvent, so that the ferromagnetic particles are coated with a layer of the radical of the fatty acid. It can be accepted That the radical of the fatty acid chemically bonds with the ferromagnetic particles forms. The nature of such an unexpected mechano-chemical reaction between metal particles and salt particles a fatty acid produced by mechanical contact or mechanical impact is not previously known. It is known that a time interval is required for this reaction is. which depends on the contact frequency of both particles. It is generally a ferromagnetic powder consists of acicular particles that have a length of about 0.02 to 0.5 μΐη, it is desirable that the The size or diameter of the fatty salt particles is small, e.g. B. less than about 500 μιτι, so that an increase the contact frequency between the ferromagnetic particles and the fatty salt particles is achieved. In in practice, the time interval required for the reaction described above is more than 20 hours. in the hereinafter the above treatment is sometimes referred to as "fatty acid salt treatment in an organic solvent" designated

Organic solvents that can be used are aromatic hydrocarbons such as benzene, toluene and xylene, which have no chemical reactivity with magnetic metal particles and / or are not decomposed by contact with such metal particles, ring-shaped hydrocarbons such as cyclohexane etc. and straight-chain carbons such as η -Hexane, etc. On the other hand, ketones such as acetone, esters such as ethyl acetate, alcohol, halogenated hydrocarbons such as trichlorethylene are not suitable solvents because there is a risk that these solvents will decompose due to the catalytic effect of the ferromagnetic powder.

After the fatty acid salt treatment in an organic solvent is finished, since evaporation and drying must be carried out without increasing the temperature of the organic solvent, an organic solvent having a high boiling point is undesirable from a practical point of view, that is, the drying period for such an organic one Solvent is quite long. An organic solvent with a boiling point in the range from 50 to 160 ^° C. is therefore preferred.

An alkaline. Metal salt such as sodium, potassium, ammonium combined with a straight-chain Gj-Qzb-Fe ·, ».- acid is suitable as a salt of a fatty acid for coating the ferromagnetic powder. Preferably Cio-C26 straight-chain fatty acids are used to have fatty acids with fewer than six carbon atoms a short carbon chain, and the length between its salt particles cannot be great, so that no suitable dispersing effect can be achieved, and fatty acids with more than 26 carbon atoms come do not exist naturally and are expensive to synthesize so that they are unsuitable. aside from that almost all naturally produced fatty acids have an even number of carbon atoms, and Fatty acids with an odd number of carbon atoms in the range of 26 are synthetically produced. As is to be expected, synthetic fatty acids are rarer and more expensive than naturally occurring fatty acids, so that the synthetic fatty acids, although suitable, are not considered from an economic standpoint come. Fatty acids that are naturally produced are a mixture of several different ones Species with different amounts of carbon atoms, however, such a mixture of fatty acids can be without Obstacles are applied.

Moreover, even with one or more fatty acids are Doppelverbir.dungen (CC = C ...) or with one or more side chains such as hydroxyl group (-OH) in the straight C ₆ -C ₂ 6 main chain in the

Also useful in the practice of the invention, and the dispersing and stabilizing effect will not become changed.

Fig. 1 is a graph showing the change in magnetic moment of ferromagnetic particles with time when the ferromagnetic particles are left in the atmosphere. In the diagram of Fig. I, the abscissa represents the time fo in days of the residence time of the ferromagnetic particles in air and the ordinate represents the magnetic moment σ, of the ferromagnetic particles in TmVkg.

The curve I in FIG. Fig. 1 shows the properties of the ferromagnetic particles that of the fatty acid salt treatment in an organic solvent according to the invention. The curve II in FIG. 1 shows the properties of the ferromagnetic particles subjected to a fatty acid salt in water, such as this is known from the prior art, and curve III in FIG. 1 shows the properties of the ferromagnetic Particles that are only subjected to an oxidation treatment in toluene.

As can be seen from the diagram of FIG. 1, the ferromagnetic particles according to the invention improved antioxidant properties. This property becomes a major disadvantage of the prior art Avoided technology. The ferromagnetic particles having the properties shown by curve II are subject no change with the passage of time, however, have and can have too low a magnetic moment cannot be used as magnetic material. The ferromagnetic particles used in this investigation were used were acicular iron-cobalt alloy powders obtained by a later described Method and later referred to as Sample I. All particles of sample I are the same magnetic properties, before discussing them, that are not necessarily mentioned.

F i g. Fig. 2 is a graph showing the fact that the dispersing property of ferromagnetic powders treated according to an embodiment of the invention is better. The abscissa represents the amount Λ / (ίη percent by weight) of a fatty acid salt added to the ferromagnetic powder during the fatty acid salt treatment in an organic solvent, and the ordinate represents the stretching percentage /? Of a magnetic tape on which the ferromagnetic powder is coated. Like F i g. 2 shows, if the added amounts of fatty acid salt exceed one percent by weight, the rectangular ratio Λ, 70%, which is from a practical point of view. " out is necessary. This means that the addition of an amount of M higher than 1% by weight is practically necessary. The fact that the squareness ratio Ri is improved shows that as a result of the improvement in the dispersing property, the orientation by the magnetic field is improved.

When adding more than 6% fatty acid salt, the mechanical properties of the magnetic tape, in particular the tearing off of the ferromagnetic particles from the magnetic tape base material is noticeable increases, and thus a crack or the like is likely to be on the surface of the magnetic tape is formed. Although a ferromagnetic powder treated with more than 6% fatty acid salt in the magnetic properties is better. it is therefore difficult to use in practice. It can be accepted be that. when the amount of fatty acid salt exceeds 6%, radicals of fatty acid in excess around the monomolecular film of fatty acid radicals that covers the ferromagnetic powder.

Fig. J is a diagram showing the rectangular ratio R ₅ (as the ordinate) of a magnetic tape on which the ferromagnetic powder subjected to the treatment of the fatty acid salt in an organic solvent in relation to the number N of carbon atoms (as the abscissa) in emerges from the fatty acid salt.

As can be seen from the diagram in FIG. 3, the rectangular ratio R i increases when the number N of carbon atoms exceeds 6, and the rectangular ratio P _s exceeds 75% when the number N of carbon atoms exceeds 10. However, if the number Λ / νοη of carbon atoms exceeds 14, the square ratio remains essentially constant and remains between 75 and 76%.

So it is. in order to improve the dispersing property of ferromagnetic powders, it is preferable to use the To have the surface of the ferromagnetic powder firmly coated with a fatty acid radical that is one carbon chain length Has. which is greater than a predetermined value, which is greater than 6 and preferably greater than 10 is.

As described above, however, a fatty acid with more than 26 carbon atoms or a / odd number of carbon atoms not or almost not found in nature, and synthetically produced Fatty acids are expensive so they are not so valuable from a practical standpoint.

Working examples

With the previous general discussion in mind, a number of detailed Examples are illustrated which show how the invention can be carried out. The ferromagnetic powder, used in the examples is an iron-cobalt alloy powder (80% Fe and 20% Co im Atomic weight), which was prepared in the following way:

1566 g of a needle-shaped goethite powder («-FeOOH with a molecular weight of about 89). the particle with a length of 3 to 0.4 microns and a needle ratio of 7 to 8 was placed in 40 liters of water dispersed. to form a pulp. 1047 g cobalt chloride hexahydrate (CoCb · 6 H2O) was added to the slurry and the mixture was stirred until the hexahydrate was uniformly dissolved. After that it became resulting pulp vigorously stirred and mixed with 2.4 liters of 7 normal ammonia water, so that the resulting slurry had a pH of 9.8.

The resulting slurry then went through filtering, water washing, drying and pulverizing operations subject. Then 1950 g of goethite powder with a colloid of cobalt hydroxide Co (OH) 2 on the Get the surface of the powder particles. The modified goethite powder was then subjected to a heating treatment

treatment in an atmosphere of 700 ° C for two hours, and thereafter 1,800 g of acicular was obtained Oxide of the Fe-Co system.

The acicular oxide of Fe-Co system was then subjected to a reduction process in a furnace at 420 ° C. for seven hours while supplying hydrogen in an amount of 50 liters to produce an acicular alloy powder. The needle-shaped alloy powder thus obtained was cooled to room temperature in the furnace, completely immersed in 7 liters of toluene while it was still in the furnace, and then removed from the furnace to the atmosphere. The toluene was gradually evaporated over a period of 72 hours so that a thin layer of oxide was formed on the surface of the needle alloy powder particle. The amount of the alloy powder obtained after drying was 1,300 g. The Fe-Co alloy powder thus obtained had the following magnetic properties: its coercive force H ₁ - was 79,600 A / m (at a density of 0.8), its stretching ratio / ?, was 53% and its magnetic moment </, was 2.26 x 10- ^ TmVkg (180 emu / g). The above alloy powder is referred to below as “sample I” and / or as untreated alloy particles.

Example I.

1300 g of sample I and 39 g of sodium oleate (Ci ₇ H ₃ SCOONa) were placed in a cylindrical stainless steel container with an internal volume of 101 together with 1500 g of toluene. The container was then placed on a ball mill and rotated to achieve mechanical mixing. The mixture in the container was kept in the coagulation state for 48 hours after the container was started to rotate, but shows fluidity thereafter. After about 120 hours the mixture in the container became a perfect slurry. It is believed that the chemical bond between oleic acid iron and oleic acid cobalt is formed on the surface of the untreated alloy particles, making the alloy particles hydrophobic and thus well dispersed in the toluene. The magnetic alloy particles subjected to the above surface treatment were then treated in a centrifugal dryer to remove the toluene therefrom, and thereafter were rinsed with 2 kg of new toluene and recovered as a semi-wet cake, which was then subjected to a drying treatment in air for 24 hours became. The amount of the alloy particles after drying was 1335 g; these particles are hereinafter referred to as "the magnetic alloy particles after surface treatment".

The magnetic properties of the magnetic alloy particles after surface treatment were as follows:

H ₁ - = 75 620 A / m (density 1.60),

ih = 2.19 · 10- ⁴ tm ³ /kg(174e.m.uyg).

LriC lliagllCU ^ ClICll L-CgICl Ullg3Lrai UHCI liani v ^ iyvi I ia \ .ll \ .l! Lf \, llalluiui iiati \ .u \ -iiiv. .iv.111 itisii \. iijuivpiivi / ibL.! '

property, and it was found that the density as a powder compared to that of untreated Alloy particles was higher by a factor of about 2.

If the magnetic alloy particles were left in the atmosphere after surface treatment, 4t there was almost no change over time. The magnetic alloy particles after surface treatment are hereinafter referred to as "sample II".

If another organic solvent instead of toluene such as benzene, xylene, cyclohexane, hexane, the has no reactivity with untreated magnetic alloy particles, were used obtained the same magnetic properties.

In addition, when another alkali metal is used instead of sodium to form an oleic acid salt such as potassium salt or an ammonium salt was used, the same results were also obtained.

Example II

A mixture of the following materials was made:

Probell 5335 g

Vinyl chloride vinyl acetate copolymer 150 g

Polyurethane rubber 150 g

Lubricant 30 g

Cyclohexanone (solvent) 2500 g

The above materials were mixed in a ball mill for 72 hours and then on a polyester resin film given. The mixture on the polyester resin film was subjected to a lengthwise orientation treatment exposed in a magnetic field of 131 340 A / m and then dried the coated surface was subjected to calendering treatment after the drying process, and the thickness obtained was Layer was 3.0 μm. The magnetic properties of the magnetic tape thus produced were as follows:

H _c = 71 640 A / m,

Rs = 76%,

Br = 035Tesla,

S _m = 0.46 Tesla.

10

15th

20th

25th

30th

As can be seen from the above magnetic properties, drs has magnetic tape according to this example a very high square ratio and a very high residual magnetic flux density.

Example IH

A procedure substantially the same as that of Example II was followed; H. the skin acid salt treatment in organic solvent medium! was carried out, but with the exception that the added Amount of sodium oleate was changed between 6.5 g and 130 g. The magnetic properties of the magnetic alloy particles obtained after the above surface treatment were as follows:

Amount of sodium oleate Amount of sodium oleate Hc (ing) (in %) (At the) 6.5 0.5 77 212 13th 1.0 77 212 26th 2.0 76416 39 3.0 75 620 52 4.0 75 620 65 5.0 74 824 78 6.0 74 824 104 8.0 74 824 130 10.0 74 824

(TmVkg) / (e.m.u./g)

53
54
54
55
55
55
55
55
55

2.25
2.24
2.21
2.19
2.16
2.15
2.13
2.07
2.04

N- ⁴ (179) 10- ⁴ (178) 1O- ⁴ (176)

10- ⁴ (169)

When the ferromagnetic particles are coated on a tape in the same manner as in Example II the magnetic tapes obtained had the same as shown in FIG. 2 rectangle ratio shown.

Example IV

Treatment similar to Example I was carried out with the following fatty acid salts. The amount of salt added to sample I was selected to be 3.0 percent by weight.

number of

35 carbon atoms in the fatty acid radical

description

Molecular formcl

40

45

50

55

60

4 6 8 10 12 14 16 18 20 22 24 26

Butyric acid sodium salt

Caproic acid sodium salt

Caprylic acid sodium salt

Capric acid sodium salt

Lauric acid sodium salt

Myristic acid sodium salt

Palmitic acid sodium salt

Stearic acid sodium salt

Arachidic acid sodium salt

Behenic acid sodium salt

Lignoceric acid sodium salt

Cerotic acid sodium salt

CH ₃ (CH ₂ J ₂ COONa

CH ₃ (CH ₂ J ₄ COONa

CH ₃ (CH ₂ J ₆ COONa

CH ₃ (CH ₂ J ₈ COOUa

CH ₃ (CHj) ₁₀ COONa

CH ₃ (CH ₂ ) I ₂ COONa

CH ₃ (CH ₂ ) _H COONa

CH ₃ (CH ₂ J ₁₆ COONa

CH ₃ (CH ₂ J ₁₈ COONa

CH ₃ (CH ₂ J ₂₀ COONa

CH ₃ (CH ₂ J ₂₂ COONa

CH ₃ (CH ₂ J ₂₄ COONa

The magnetic properties of the magnetic alloy particles thus obtained were as follows: W ₁ - was in the range of 74 824 to 75 620 A / m, R _s in the range of 54 to 55%, and o _s in the range of 2.17 · 10 ^"4 to 2.20 ■ 10- ⁴ Tm ³ / kg (173-175 ema / g). the magnetic alloy particles were coated on a base material of a magnetic tape in the same manner as described in example II. the rectangle ratio R _{One of} the magnetic tapes was the same as that shown in FIG.

Example V

Investigations were carried out using the following fatty acid salts to determine whether the effect can also be achieved with fatty acid salts that have a side chain such as a hydroxyl group or a had unsaturated double bond in their carbon chain. The treatment method used was same as that described in Example I.

number of
Double bonds 24 03 366 description number of
Kohlensti -f ^r atomc 0
1
2
3
1 Side chain Stearic acid sodium salt
oleic acid sodium salt
Linolic acid sodium salt
Linolenic acid sodium salt
Ricinoleic acid sodium salt 00 00 00 OC OC -OH

The magnetic properties of the obtained magnetic alloy particles, those of the surface treatment were subjected to were as follows:

W ₁ - = 74 824 to 75 620 A / m,

R, = 54 to 55%,

<h = 2.17 · 10 "to 20.2 ■ 10- ⁴ Tm ³ / kg (173 to 175 emu / g).

= 54 to 55%, _{| 5}

As the above results show, there is not much difference between the magnetic properties the magnetic alloy particle with respect to the magnetic alloy spariikci, which are saturated with, straight-chain fatty acid salts have been treated.

The magnetic properties of a magnetic tape made with the above magnetic alloy particles by a procedure similar to that of Example II were in the following range:

H ₁ . = 70 844 to 71 640 A / m,

R, = 75 to 76%,

B _r = 0.34 to 0.35 Tesla,

B _n , = 0.44 to 0.45 Tesla.

The above results are different from those of Example I! not very different, and the magnetic field shows better electromagnetic conversion properties than audio or video tape.

Comparative example Vl

1300 g of untreated magnetic alloy powder (Sample I) and 39 g of sodium oleate were mixed in 10 L of water and stirred well for 5 hours to form an oleic acid monomolecular radical film on the surface of the magnetic alloy particles. The ferromagnetic particles obtained were η · η *% " * 7nn * " - "f iir * nlti-Anl / niinn untomtinpfan > ins4 ηΐ« 1 / i.nlinn _nlir yjrt _rt «. ^ NrtinllnriAn k-ilkti-A ^ bfttiftn Doi -t'il> nln iwiifs-lft

dried by air at room temperature for 120 hours. The amount of the dried ferromagnetic particles was 1,350 g and showed high hydrophobicity. The nadelföiinigen alloy particles hold after the above surface treatment, the following magnetic characteristics: H _c was 74028 A / m, R _s was 54%, and a ₅ was ί, 748 x 10 ~ ⁴ Tm ³ / kg (142 emu / g); these results are almost the same as those obtained by practicing the invention.

However, in the case of the magnetic tape obtained with the above magnetic alloy particles according to a procedure similar to that of Example II, R _{s was} 75%, which is higher than that of a tape treated with ferromagnetic particles according to the invention. however, H _{c was} 70 048 A / m and B _{r was} 0.285 Tesla, which is lower. It can therefore be seen that the magnetic tape of this example cannot be used practically as an audio tape or a video tape because it cannot provide a large output signal level.

Comparative Example VII

Not treated magnetic

Alloy powder (sample I) 1300 g

Vinyl chloride vinyl acetate copolymer 150 g

Polyurethane rubber 150 g

Lubricant 30 g

Cyclohexanone 2500 g

oleic acid sodium 39 g

The above materials were mixed in a ball mill for 72 hours and then coated on a base material by a method similar to that of Example II to form a magnetic tape. The magnetic properties of the resulting magnetic tape were as follows: H _c was 69 252 A / m, R < 59%, S _r = 0.26 Tesla and β _m = 0.44 Tesla. It can be seen that the alloy particles, after being coated with radicals of fatty acids, must be mixed with a binder in order to obtain the desired dispersing effect.

Comparative Example VIII

Untreated magnetic

Alloy powder (sample I) 130Og

5 oleic acid 39 g

Tbluen 1700 g

The above materials were mixed for 120 hours and then the toluene was filtered off. The particles obtained had a dark brown color and the following magnetic properties: H _c was ίο 74 824 A / m, A _s = 55%, ft = Z16 - 10- "Tm ³ / ^ (172 ejn.lL / g); the particles The amount of the finally obtained particles was 1,330 g, and the particles were coated on a base material to form a magnetic tape by a method similar to that of Example II. The magnetic properties of the magnetic tape thus produced were as follows:

15 Hc = 70 844 A / m,

R _s = 66%,

B _r - 0.3 Tesla.

B _m = 0.46 Tesla.

It can therefore be seen that the above magnetic tape owing to the poor dispersibility of the particles has a low square ratio and is difficult to use in practice.

Comparative Example IX

25 Untreated Magnetic

Alloy powder (sample I). 1300 g

Lecithin (dispersant) 39 g

Toluene (solvent) 2000 g

The above materials were mixed for 120 hours. The treated ferromagnetic particles gave off an odor, indicating that the lecithin had decomposed. The amount finally obtained particles was 1330 g, and the magnetic properties thereof were as follows: H _c was / m 74 824 A, Ä = 54%, and oil = Z15 - 10- ⁴ Tm ³ / kg (171 emu7g). The magnetic tape with these ferromagnetic particles thereon (prepared by the same method as that of Example II) had an R ₁ of 61%, which shows that

35 no dispersing effect was obtained. The magnetic properties of this tape were as follows:

H _c = 70 844 A / m,
Br = 0.275 Tesla.
B _m = 0.45 Tesla.

For this purpose 3 sheets of drawings

Claims (8)

Patent claims: 1. Process for the production of ferromagnetic particles coated with a protective layer which the ferromagnetic particles are mixed with a salt of a long-chain fatty acid, d a by characterized in that the ferromagnetic particles and the salt particles in an organic Solvent to be mixed until a monomolecular layer of the radical of the Fatty acid forms on every ferromagnetic particle and that the salt with a particle size of smaller is used as 500 μηι. 2. The method according to claim 1, characterized in that the fatty acid has a carbon chain with 10 to ίο contains 26 carbon atoms 3. The method according to claim 1, characterized in that the organic solvent consists of a aromatic hydrocarbon, cyclic hydrocarbon and straight chain hydrocarbon containing group is selected. 4. The method according to claim 3, characterized in that the organic solvent has a boiling point ! 5 point in the range from 50 to 160 ° C 5. The method according to claim 1, characterized in that the ferromagnetic particles from one Material consist of a cobalt, cobalt-nickel alloys, iron-cobalt alloys, iron-nikkei alloys and iron-nickel-cobalt alloys. 6. The method according to claim 1, characterized in that the fatty acid has a carbon chain has at least one unsaturated double bond 7. The method according to claim 1, characterized in that the fatty acid has a carbon chain has at least one side chain 8. The method according to claim 7, characterized in that the side chain comprises a hydroxyl group.