DE3628874C2 - - Google Patents

Description

The invention relates to a magnetic recording medium for recordings high density.

A magnetic layer memory consists of a non-magnetic substrate, such as Polyethylene terephthalate and a magnetic layer of fine magnetic Particles and a resin binder as main components on the Substrate.

As fine magnetic particles are so far widely acicular magnetic particles of γ -Fe₂O₃, CrO₂, Co- γ -Fe₂O₃, etc. used. Recently, in view of a substantial improvement in the magnetic recording density, the need to make available a magnetic recording medium having vertical magnetization is emphasized. As products corresponding to this aspect, magnetic recording media using fine hexagonal magnetic ferrite particles have been studied. These have been shown to enable high density recording. A magnetic powder for a high-density recording in which a part of 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, has become known from US-PS 43 41 648. For example, according to column 3, lines 62 and 63 AFe _{12-2 x} Co _x M _x O₁₉ (M is Ti, among others) and AFe _{12-3 / 2 x} Co _x M _{1/2 x} O₁₉ (M is, inter alia, Nb) in question ,

From DE-OS 34 43 049 is a magnetic powder of hexagonal ferrite particles known with a content of tin. There, however, a salary is mandatory Al and / or Ga prescribed.

Further, the above-mentioned magnetic recording medium using a hexagonal ferrite in the form of fine magnetic particles requires that the magnetic properties remain stable with temperature changes. When the magnetic properties are significantly affected by temperature changes, the reproducing characteristics of the magnetic recording medium change depending on temperature changes of the environment during use of the magnetic recording medium. The magnetic recording medium using hexagonal ferrite is relatively stable to temperature changes and has a specific temperature characteristic, whereafter the magnitude of the coercive magnetic field strength (H _c ) increases in proportion to the temperature. In practice, however, a higher temperature stability is desirable than having the mentioned hexagonal ferrite.

The inventors have come up with an improvement in temperature Characteristic of the magnetic coercive force of magnetic recording material, the hexagonal ferrite used, dealt with and eliminated the deficiency described above. They have found that an improvement in the Temperature characteristic can be obtained when hexagonal Ferrite is used, which is a predetermined amount Tin contains. The Journal of Applied Physics 21 (1966) Pages 282 to 286 describes that the substitution of a Part of the elements in barium ferrite possible by tin ions is. The impact of this substitution, however, is nowhere described.

The object of this invention is to provide a magnetic recording medium for to make high density magnetic recordings available an improved temperature characteristic of the magnetic Having coercive field strength, without significant losses of saturation magnetization enter.  

The magnetic recording medium of the present invention is characterized by the features of claim 1 ge features. Further embodiments of the invention are to take the remaining claims.

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

As represented by M substitution element of said hexagonal barium ferrite is suitable the following two- to six-valued elements:

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
Six-valued elements - Mo and W

Because this element is used instead of the trivalent Fe ion should, the average valence per atom of the Substituting element with the valency 3 of the substitution to be removed Fe atoms agree. Although trivalent metal can be used alone, but preferably should be bivalent, tetravalent, pentavalent and hexavalent metals can be used in combination, so that the average weight is 3. If the substitution by combination of a bivalent and a quadrivalent  Metal is to be effected, it is sufficient, the two metals in the atomic ratio ½ to ½ use. If the substitution by combining a divalent and a pentavalent metal, it is sufficient, this Use metals in the atomic ratio of ² / ₃ to ¹ / ₃.

When an Sn atom substitutes part of the Fe atom is replaced by the substitution product, in which at the Substitution uses a combination of Co-Ti or Co-Nb has been particularly favorable properties.

Among all the hexagonal barium ferrite crystals, the satisfy the above description, are for the purposes of Invention suitable for those having a magnetic coercive force in the range between 200 and 2000 Oe (15.9 × 10³ to 159.2 × 10³ A / m).

The invention limits the magnetic coercivity to the mentioned area for the following reasons. is the magnetic coercivity is less than 200 Oe (15.9 × 10³ A / m), it is difficult to record Information opposite the demagnetizing field in  to maintain the recorded recording medium. Becomes on the other hand, the value exceeded 2000 Oe (159.2 × 10³ A / m), then the coercivity is so excessive that an existing recording-playback head from a Material consisting of ferrite, sendust, an amorphous alloy, etc. the information to be recorded only below Difficulties and records the information recorded only with difficulty deletes.

Furthermore, in this invention, the average Particle diameter of hexagonal barium ferrite crystals to the range of 0.02 to 0.2 μm for the following reasons limited. Is the average particle diameter smaller than 0.02 μm, then the magnetization and the magnetic coercivity insufficient and the re produced signal of the magnetic recording medium is insufficient. Exceeds the particle diameter 0.2 μm, then the magnetic coercive field strength lowered and the noise during reproduction a high-density recording becomes inadmissible large.

In general, the temperature coefficient of the coercive force H _c, namely, (Δ H _c / H _c) / Δ t of a hexagonal barium ferrite has a positive value (Δ H _c denotes the change in H _c corresponding to the change Δ T of the measured temperature). When Sn is added to the hexagonal barium ferrite, the temperature coefficient of H _c 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 in this invention, it is achieved that the generated magnetic powder has a smaller temperature change of H _c than the known hexagonal barium ferrite.

This invention sets the upper limit of x , that is, the amount of the substituted metal in said hexagonal barium ferrite, to 2.5 for the following reason. When the amount exceeds 2.5, the magnetic powder has such a low coercive magnetic field that it is insufficient for the magnetic recording medium. 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, then sufficient improvement in the temperature coefficient of H _c is not obtained. If the Sn content exceeds 1.0, although this gives an improved temperature coefficient of H _c for the magnetic powder, it has an insufficiently low saturation magnetization for the magnetic recording medium.

The hexagonal barium ferrite according to this invention becomes generally in combination with a resin binder applied to the surface of a substrate as a Medium for the magnetic recording to be used. As for forming the magnetic layer of the magnetic powder suitable resin binder may 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 mentioned resin binder The magnetic layer may contain suitable additives such as Dispersant, a lubricant, an abrasive or an antistatic agent.

The invention will now be described with reference to exemplary embodiments described:  

Example 1

It was after the manufacturing process described below Four kinds of fine ferrite particles of the following Formula produced:

BaFe _{12-2 (x + y)} Ti _x Sn _y Co _{x + y} O₁₉

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 substitution to four values in the range is set between 0.1 to 0.7. There were Ferrites where Sn is a part of Ti of hexagonal Barium ferrites of the M-type substituted with Ti and Co according to the formula:

BaFe _{12-2 x} Ti _x Co _x O₁₉

was substituted.

At first, for the abovementioned barium ferrite Composition calculated BaO, Fe₂O₃, TiO₂, SnO₂ and CoO Components added to a B₂O₃ BaO glass. The obtained Mixture was melted at a temperature above 1300 ° C. The melt was rolled and then cooled suddenly, to deliver a glass containing the said components. Then, by heating this glass to 800 ° C for a period of 4 hours a barium ferrite, in which Sn and Co are substituted as described above, within eliminated from the matrix. Finally it was through Washing the glass with acetic acid, a magnetic barium obtained ferrite powder. The average particle diameter of the obtained magnetic powder 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 indicated).

Ti-Sn-Co-substituted barium ferrite particles 100 parts Vinyl chloride-vinyl acetate copolymer 10 parts polyurethane 10 parts alumina 2 parts lubricant 1.5 parts Dispersing agent (lecithin) 2 parts methyl ethyl ketone 70 parts toluene 70 parts cyclohexanone 40 parts Harder 5 parts

The five coating materials obtained in the above-described manner were each on a polyethylene Terephthalatfilm applied to a thickness of 15 microns and then subjected to a calendering and cutting treatment, to obtain a magnetic tape having a magnetic layer with had a thickness of 3.5 microns.

example 2

Four types of fine barium ferrite particles were prepared according to the method described in Example 1, the amounts of x , on Co and Sn for the substituents in the Co-Sn-substituted barium ferrite of the formula:

BaFe _{12-2 x} Co _x Sn _x O₁₉

set to four values were in the range between 0.5 to 1.20 (1.20 for comparison purposes). The obtained powders had an average particle diameter from 800 to 900 Å (80 to 90 nm). The powders 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 quantities x of Co and Ti for substitution in the Co-Ti-substituted barium ferrite of the formula:

BaFe _{12-2 x} Ti _x Co _x O₁₉

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

According to Example 1, Example 2 and magnetic tapes obtained the comparative example were tested for H _c at room temperature and with respect to the changes (Δ H _c / H _c) / Δ T H _c of from 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 H _{c of} the Sn-added ferrite powders of Table 1 (Example 1) and Table 1 (Example 2) are compared with those of the Ti-Co-substituted barium ferrite powders of Table 3 (Comparative Example), the substantially the same values H _c , it is found that the Sn-added barium ferrite powders have a smaller absolute value of the temperature coefficient of H _c than the barium ferrite powders of the comparative example, thereby demonstrating that the addition of Sn significantly improves the temperature coefficient of H _c .

Table 4 shows the dependence of the saturation magnetization of the fine powder of BaFe _{12-2 x} Co _x Sn _x O₁₉ of Example 2 at a substitution amount (x).

Amount of substituted Co-Sn, x Saturation magnetization, (emu / g) 0.50 59.0 0.75 54.0 1.00 48.0 1.20 33.0

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

Then the magnetic powders were in coating materials converted and applied to a substrate in order to the same way as in Example 1 to produce magnetic tapes.

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

Table 5

example 4

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

BaFe _{12-3 / 2 (x + y)} Nb _{x 1/2} Sn _y Co _{x + y} O₁₉

wherein the amount of Co for substitution (number of atoms in the empirical formula) x + y was set to 0.85 and the amount of Sn for substitution was set to four values in the range of 0.1 to 0.7 , The preparation was carried out according to the procedure of Example 1, except that Nb was used instead of Ti. The thus-obtained magnetic powders having the same compositions as those of Example 1 were converted into coating materials and applied to a substrate to produce magnetic tapes according to the method of Example 1.

The magnetic tapes were tested for H _c at room temperature and with respect to the changes (Δ H _c / H _c) / Δ T in the temperature range of 20 to 100 ° C. The results are shown in Table 6.

Table 6

Claims (3)

1. A magnetic recording medium having a coercive field strength between 16 and 160 kA / m of hexagonal ferrite particles of the general formula AFe₁₂O₁₉, where A is Ba, Sr, Ca and / or Pb and the iron content by Co, Ti, Nb, Ge, V, Sb and / or Ta, characterized in that the composition is determined by the formula AFe _{12- xy} M _x Sn _y O₁₉, wherein the tin content is 0.05 y 1 and M is Co, Ti, Nb, Ge , V, Sb, Ta, Mn, Zn, Ni, In, Cr, Zr, Mo and / or W in a proportion of 1 x 2.5. 2. A magnetic recording medium according to claim 1, characterized in that the tin content is 0.1 y 0.5. 3. A magnetic recording medium according to claim 1 or 2, characterized, that it has the composition Ba (Fe, Co, Ti, Sn) ₁₂O₁₉ or Ba (Fe, Co, Nb, Sn) has ₁₂O₁₉.