DE3628874A1 - Magnetic powder for high density magnetic recording, and a magnetic recording medium using the magnetic powder - Google Patents

Abstract

A magnetic powder for high density magnetic recording contains hexagonal ferrite particles having an average particle diameter in the range from 0.01 to 0.2 mu m and having a coercivity field strength in the range from 200 to 2000 Oe. The ferrite particles contain 0.05 to 1.0 Sn in the chemical formula. A magnetic recording medium has a coating of this magnetic powder on the surface of a substrate.

Description

The invention relates to a magnetic powder for a magnetic High density record and a magnetic Recording medium using the magnetic powder.

A magnetic layer memory consists of a non-magnetic one Substrate such as polyethylene terephthalate and a magnetic layer made of fine magnetic particles and a wood binder as main components on the substrate.

So far, acidic magnetic particles of γ-Fe ₂ O ₃ , CrO ₂ , Co-γ-Fe ₂ O ₃ , etc. have been widely used as fine magnetic particles. Recently, in view of a substantial improvement in the magnetic recording density, the need to make a magnetic recording medium with vertical magnetization available is emphasized. Magnetic recording media using fine hexagonal magnetic ferrite particles have been investigated as products corresponding to this aim. These have been shown to enable high density recording. A magnetic powder for high density recording in which a part of the Fe atoms of a hexagonal ferrite is substituted by divalent Co and a trivalent element selected from Ti, Zr and Ge or a pentavalent element selected from V, Nb, Sb and Ta through the US-PS 43 41 648 known.

Incidentally, the magnetic recording medium using a hexagonal ferrite in the form of fine magnetic particles is also required that the magnetic properties remain stable with changes in temperature. If the magnetic properties are significantly affected by temperature changes, the reproducing properties of the magnetic recording medium change depending on temperature changes in the environment during use of the magnetic recording medium. The magnetic recording medium using hexagonal ferrite is relatively stable against temperature changes and has a special temperature characteristic, according to which the size of the magnetic coercive force ( H _c ) increases in proportion to the temperature. In practice, however, a higher temperature stability than the hexagonal ferrite mentioned is desirable.

The inventors struggled with an improvement in temperature characteristics the magnetic coercive force of magnetic recording material, the hexagonal ferrite used, dealt with and eliminated the deficiency described. You have found that an improvement in Temperature characteristics can be obtained if hexagonal Ferrite is used, which is a predetermined amount Contains tin. The journal Applied Physics 21 (1966) Pages 282 following describes that the substitution of a Part of the elements in barium ferrite possible through tin ions is. However, the impact of this substitution is not described anywhere.

The object of this invention is to produce a magnetic powder for a to make available high density magnetic recording, which is an improved temperature characteristic of the magnetic Has coercive field strength. This improved temperature characteristic the magnetic coercive force should be without significant loss of saturation magnetization be available. A magnetic powder should be made available be one for magnetic recording high density suitable magnetization and coercive force having.  

Another object of this invention is a magnetic To make available recording medium that the has properties mentioned.

The magnetic powder according to the invention is characterized by the features of claim 1, the magnetic according to the invention Recording medium by the features of claim 6 featured. Further refinements of the invention are the other claims.

Specific examples of for the purposes of this invention Hexagonal ferrite crystals that can be used are hexagonal Barium ferrite of the M (magnetoplumbite) type and the W type with uniaxial magnetic anisotropy (strontium ferrite, Lead ferrite, calcium ferrite, solid solutions thereof and Ion substitution products).

Any of the following divalent to hexavalent elements is suitable as the substitution element of the hexagonal barium ferrite mentioned:
Divalent elements - Mn, Co, Zn and Ni
Trivalent elements - In and Cr
Tetravalent elements - Ti, Ge and Zr
Pentavalent elements - V, Nb, Sb and Ta
Hexavalent elements - Mo and W

Because this element is used instead of the trivalent Fe ion the average valence per atom of the substituting element with the valency of 3 by the substitution of the Fe atom to be removed match. Trivalent metal can be used alone, however, preferably divalent, tetravalent, pentavalent and hexavalent metals are used in combination, so that the average value is 3. If the substitution by combining a divalent and a tetravalent  Metal is to be brought about, it suffices the two metals use in the atomic ratio 1/2 to 1/2. If the Substitution by combining a divalent and one pentavalent metal, it suffices to this Use metals in an atomic ratio of 2/3 to 1/3.

When an Sn atom substitutes part of the Fe atom should receive the substitution product for which Substitution uses a combination of Co-Ti or Co-Nb has been particularly beneficial properties.

Among all types of magnetic powders for a magnetic High density recording according to this invention a typical variety arises from the general Formula:

AFe _{(12- X - Y )} M _X Sn _Y O ₁₉

where A is at least one element from the group consisting of Ba, Sr, Ca and Pb, M is at least one element from the group Mn, Co, Zn, Ni, In, Cr, Ti, Ge, Zr, V, Nb, Sb, Ta, Mo and W, X for a number between 1 and 2.5 and Y for a number between 0.05 and 1.0, preferably between 0.1 and 0.5.

Of all the hexagonal barium ferrite crystals that meet the above description, those having a magnetic coercive force in the range between 200 and 2,000 Oe (15.9 × 10 ³ to 159.2 × 10 ³ A / m) are suitable for the purposes of the invention .

The invention limits the magnetic coercive force to the above range for the following reasons. If the magnetic coercive force is less than 200 Oe (15.9 × 10 ³ A / m), it is difficult to maintain the recorded information against the demagnetizing field in the generated recording medium. On the other hand, if the value of 2,000 Oe (159.2 × 10 ³ A / m) is exceeded, the coercive force is so excessive that an existing recording-reproducing head made of a material consisting of ferrite, sendust, an amorphous alloy, etc. It is difficult to record information to be recorded and it is difficult to erase the recorded information.

Furthermore, in this invention, the average Particle diameter of the hexagonal barium ferrite crystals to the range of 0.02 to 0.2 µm for the following reasons limited. Is the average particle diameter less than 0.02 µm, then the magnetization and the magnetic coercive force insufficient and that reproduced signal of the magnetic recording medium is insufficient. On the other hand, exceeds the particle diameter 0.2 µm, then the magnetic coercive force reduced and the noise during reproduction high density recording is prohibited large.

In general, the temperature coefficient of the coercive force Hc , namely ( Δ Hc / Hc ) / Δ T of a hexagonal barium ferrite, has a positive value ( Δ Hc denotes the change in Hc corresponding to the change Δ T in the measured temperature). When Sn is added to the hexagonal barium ferrite, the temperature coefficient of Hc decreases and changes to a negative value in the ratio in which the amount of Sn added is increased. By controlling the Sn content to fall within the range provided by this invention, the magnetic powder produced has a smaller temperature change of Hc (not more than 2.5 × 10 ^-3 / ° C in absolute value) , as the well-known hexagonal barium ferrite.

This invention sets the upper limit for X , that is, the amount of the substituting metal in said hexagonal barium ferrite, at 2.5 for the following reason. If the amount exceeds 2.5, the magnetic powder has such a low magnetic coercive force that it is insufficient for the magnetic recording material. The invention limits the amount Y of Sn used for the substitution to the range of 0.05 to 1.0 for the following reason. If the Sn content is below 0.05, a sufficient improvement in the temperature coefficient of Hc is not obtained. If the Sn content exceeds 1.0, this results in an improved temperature coefficient of Hc for the magnetic powder, but it has an insufficiently low saturation magnetization for the magnetic recording material.

The hexagonal barium ferrite according to this invention is generally in combination with a resin binder applied to the surface of a substrate to be as Medium to be used for magnetic recording. As for the formation of the magnetic layer from the magnetic powder suitable resin binder can be a vinyl chloride-vinyl acetate Copolymer, a vinylidene type copolymer Acrylic ester copolymer, a polyvinyl butyral resin Polyurethane resin, a polyester resin, a cellulose derivative, an epoxy resin or a mixture of two or more of the mentioned substances are used.

In addition to the fine magnetic powder and the synthetic resin binder mentioned can the magnetic layer suitable additives such as a Dispersant, a lubricant, an abrasive or contain an antistatic agent.

The invention is now based on exemplary embodiments described:  

Example 1:

It was made according to the manufacturing process described below four kinds of fine ferrite particles of the following Formula made:

BaFe _{12-2 ( X + Y )} Ti _X Sn _Y Co _{X + Y} O ₁₉

in which the amount of cobalt for the substitution (number of Atoms in the empirical formula) is fixed at 0.85 and the Amount of tin for the substitution to four values in Range between 0.1 and 0.7 is set. There were Ferrites where Sn is a part of Ti of the hexagonal M-type barium ferrite substituted with Ti and Co according to the formula:

BaFe _{12-2 X} Ti _X Co _X O ₁₉

was substituted.

BaO, Fe ₂ O ₃ , TiO ₂ , SnO ₂ and CoO components calculated for the barium ferrite compositions mentioned were first added to a B ₂ O ₃ BaO glass. The resulting mixture was melted at a temperature above 1,300 ° C. The melt was rolled and then suddenly cooled to provide a jar containing the above components. Then, by heating this glass to 800 ° C for 4 hours, a barium ferrite in which Sn and Co are substituted as described above was precipitated within the matrix. Finally, a barium ferrite magnetic powder was obtained by washing the glass with acetic acid. The average particle diameter of the magnetic powder obtained was about 800 Å (80 nm).

Then, using this fine barium ferrite powder  a magnetic coating material of the following Composition (the components are in parts by weight specified).

Ti-Sn-Co substituted barium ferrite paritles 100 parts vinyl chloride-vinyl acetate copolymer 10 parts polyurethane 10 parts aluminum oxide 2 parts lubricant 1.5 parts dispersant (lecithin) 2 parts methyl ethyl ketone 70 parts toluene 70 parts cyclohexanone 40 parts hardener 5 parts

The five obtained in the manner described above Coating materials were each on one Polyethylene terephthalate film applied with a thickness of 15 microns and then subjected to a calendering and cutting treatment, to get a magnetic tape that has a magnetic layer with had a thickness of 3.5 microns.

Example 2:

Four types of fine barium ferrite particles were produced in accordance with the process described in Example 1, the amounts X , of Co and Sn for the substitution in the Co-Sn-substituted barium ferrite of the formula:

BaFe _{12-2 X} Co _X Sn _X O ₁₉

were set to four values in the range between 0.5 to 1.20 (the value 1.20 was used for comparison purposes). The Powders obtained had an average particle diameter from 800 to 900 Å (80 to 90 nm). The powder were converted into coating materials and the Coating materials applied to a substrate to  To produce magnetic tapes according to Example 1.

Comparative example:

Five types of magnetic powders, in which the amounts X of Co and Ti for the substitution in the Co-Ti substituted barium ferrite of the formula:

BaFe _{12-2 X} Ti _X Co _X O ₁₉

set to five values in the range between 0.71 and 0.84 were, according to the previously described Manufactured embodiments. The powders obtained had an average particle diameter of about 800 Å (80 nm). The powders were in coating materials converted and applied to a substrate, around magnetic tapes in the same way as with the generate previous embodiments.

The magnetic tapes obtained according to Example 1, Example 2 and the comparative example were tested for Hc at room temperature and for the changes ( Δ Hc / Hc ) / Δ T of Hc at 20 to 100 ° C. The results are shown in Table 1, Table 2 and Table 3.

Table 1, Table 2 and Table 3 show the test results the magnetic tapes of Example 1, Example 2 and the Comparative example.  

Table 1

Table 2

Table 3

When the temperature coefficients of Hc of the ferrite powders according to Table 1 (Example 1) and Table 1 (Example 2) to which Sn has been added are compared with those of the Ti-Co-substituted barium ferrite powders according to Table 3 (comparative example), which have essentially the same values of Hc then it is found that the barium ferrite powders with Sn added have a smaller absolute value of the temperature coefficient of Hc than the barium ferrite powders according to the comparative example, whereby it is shown that the addition of Sn significantly improves the temperature coefficient of Hc .

Table 4 shows the dependence of the saturation magnetization of fine powder on BaFe _{12-2 X} Co _X Sn _X O ₁₉ of Example 2 with a substitution amount ( X ).

Table 4

From Table 4 it follows that if the amount of Sn for the Substitution exceeds 1.0, the saturation magnetization of the magnetic powder drops considerably and the property of the powder as a material for a magnetic High density recording is deteriorated.

Example 3:

There were barium ferrite magnetic powders with an average Particle diameter of about 450 Å (45 nm) accordingly obtained the method of Example 1, wherein  however, the conditions for the crystallization of the glass were varied. Magnetic powders were produced which had the same compositions as the magnetic powders of example 1.

Then the magnetic powder was in coating materials converted and applied to a substrate to in the same way as in Example 1 magnetic tapes to manufacture.

The magnetic tapes were tested for Hc at room temperature and for changes ( Δ Hc / Hc ) / Δ T in the temperature range from 20 to 100 ° C. The results are shown in Table 5.

Table 5

Example 4

There were four types of fine ferrite particles according to the Formula:

BaFe _{12-3 / 2 ( X + Y )} Nb _{X 1/2} Sn _Y Co _{X + Y} O ₁₉

prepared, the amount of Co for the substitution (number of atoms in the empirical formula) X + Y was set to 0.85 and the amount of Sn for the substitution was set to four values in the range between 0.1 and 0.7 . The preparation was carried out according to the procedure of Example 1, with the exception that Nb was used instead of Ti. The magnetic powders thus obtained, which had the same compositions as those of Example 1, were converted into coating materials and applied to a substrate to prepare magnetic tapes according to the method of Example 1. The magnetic tapes were tested for Hc at room temperature and for the change ( Δ Hc / Hc ) / Δ T in the temperature range from 20 to 100 ° C. The results are shown in Table 6.

Table 6

Claims (11)

1. Magnetic powder for high density magnetic recording, characterized in that it contains hexagonal ferrite particles with 0.05 to 1.0 Sn in the sum formula, the average particle diameter in the range from 0.02 to 0.2 µm and the coercive force in the range is between 200 to 2,000 Oe. 2. Magnetic powder according to claim 1, characterized in that the hexagonal ferrite is represented by the general formula AFe _{(12- X - Y )} M _X Sn _Y O ₁₉ , wherein
A represents at least one element from the group Ba, Sr, Ca and Pb,
M for at least one element from the group Mn, Co, Zn, Ni, In, Cr, Ti, Ge, Zr, V, Nb, Sb, Ta, Mo and W,
X for a number in the range between 1 and 2.5 and
Y for a number in the range between 0.05 and 1.0. 3. Magnetic powder according to claim 2, characterized in that that Ba stands for A. 4. Magnetic powder according to claim 2 or 3, characterized characterized in that M is a combination of Represents Co-Ti or a combination of Co-Nb. 5. Magnetic powder according to one of claims 2 to 4, characterized in that Y is a value in the range from 0.1 to 0.5. 6. High density magnetic recording medium, thereby characterized in that on the surface of a A hexagonal ferrite is applied to the substrate of the chemical formula contains 0.05 to 1.0 Sn and one average particle diameter in the range of 0.02 up to 0.2 µm and a coercive field strength in the range of 200 to 2,000 Oe. 7. Magnetic recording medium according to claim 6, characterized in that the hexagonal ferrite is represented by the general formula AFe _{(12- X - Y )} M _X Sn _Y O ₁₉ , wherein
A represents at least one element from the group Ba, Sr, Ca and Pb,
M for at least one element from the group Mn, Co, Zn, Ni, In, Cr, Ti, Ge, Zr, V, Nb, Sb, Ta, Mo and W,
X for a number in the range between 1 and 2.5 and
Y for a number in the range between 0.05 and 1.0. 8. A magnetic recording medium according to claim 7, characterized characterized in that Ba stands for A. 9. A magnetic recording medium according to claim 7 or 8, characterized in that M is a combination of Co-Ti or a combination of Co-Nb represents. 10. Magnetic recording medium according to one of claims 6 to 8, characterized in that the value of Y is in the range from 0.1 to 0.5. 11. Magnetic recording medium according to one of the  Claims 6 to 10, characterized in that the hexagonal ferrite in combination with a binder resin applied to the surface of a substrate is.