JPH01185828A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enable uniform dispersion of Ba-ferrite powder and to improve electromagnetic conversion characteristics by using Ba-ferrite powder in which part of Fe is substd. with Co and Zn and, if necessary, Nb and other elements as the Ba-ferrite powder and using a vinyl chloride/vinyl acetate copolymer as a binder. CONSTITUTION:The Ba-ferrite powder is the Ba-ferrite is which a part of the Fe is substd. with the Co and Zn and which has 400-900Angstrom average grain size (length of the diagonal line of the plate face of hexagonal ferrite), 2.0-6.0 planar ratio (the value obtd. by dividing the length of the diagonal line of the plate face of the hexagonal ferrite by the plate thickness) and 350-2,000 Oe coercive force. Resin binder contains the vinyl chloride/vinyl acetate copolymer contg. a sulfonic group. The high dispersibility of the Ba-ferrite powder and the high stability to prevent the magnetic reflocculation of a coating compd. after dispersion are thereby obtd. and the reproduced output and electromagnetic conversion characteristics which are better than those of the magnetic recording medium formed by using Co- and Ti-substd. Ba-ferrite powder are obtd.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an improved magnetic recording medium, and more particularly to improved dispersibility of magnetic powder and excellent electromagnetic conversion characteristics of the magnetic recording medium. The present invention relates to magnetic recording media.

(Prior Art) Magnetic recording media such as magnetic tapes and magnetic disks for audio, video, and combination 1-9 use magnetic powder, a resin binder, a solvent, and a non-magnetic support such as polyester. Many media are used in which a magnetic recording layer is formed by uniformly applying a magnetic paint made of various additives.

Further, as video tapes become more compact and magnetic recording media become more compact, there is a demand for higher density recording, and ferromagnetic Ba-ferrite powder is used as a magnetic powder suitable for high-density recording.

By the way, the Ba-ferrite powder used for such applications is a magnetic powder with high saturation magnetization, and the one-finger binder of Ba-ferrite powder has good dispersibility and is suitable for magnetic recording media. It is necessary to select a material that provides excellent electromagnetic conversion characteristics.

For this reason, various attempts have been made to improve the Ba-ferrite powder and the binder used in combination with the Ba-ferrite powder. Ti-substituted Ba
- Ferrite powder and vinyl chloride as a binder -
A combination of a vinyl acetate-vinyl alcohol copolymer and a polyurethane resin has been proposed.

(Problems to be Solved by the Invention) Although the combination of 8a-ferrite powder and binder improves the dispersibility of the magnetic powder and the electromagnetic conversion characteristics as a magnetic recording medium, it is not always sufficient. In particular, it is used for DAT magnetic tapes that require high-density recording, video tapes with high image quality, and extremely excellent dispersibility of magnetic powder, high playback output, and high C/N.
When used in a magnetic recording medium that requires specific characteristics, there is a problem in that fully satisfactory electromagnetic conversion characteristics cannot be obtained.

The present invention was made to solve these problems, and an object of the present invention is to provide a magnetic recording medium that enables uniform dispersion of 8a-ferrite powder and has improved electromagnetic conversion characteristics.

[Structure 1 of the Invention (VL & Means for Solving the Problems) The magnetic recording medium of the present invention is a magnetic recording medium made by coating a support with a magnetic paint in which ferromagnetic Ba-ferrite powder is dispersed in a resin binder. In the recording medium, the Ba-ferrite powder has an average grain size (the length of the diagonal line of the hexagonal ferrite plate surface) of 400 to 900 Å, in which a part of Fe is replaced with at least C0J3 and Zn, and a plate ratio (hexagonal The value obtained by dividing the quality of the 1-square wire by the plate thickness) 2.0 to 6
．． 8a-ferrite with a coercive force of 350 to 2000 Oe, and is characterized in that the resin binder contains a vinyl-enriched-vinyl acetate copolymer containing at least sulfone U in the molecule.

The Ba-ferrite powder used for making wooden blocks has Fc and C
By partially replacing with o, the coercive force is controlled to an appropriate value, and further by partially replacing with In, C
It is possible to achieve a high saturation magnetization that cannot be obtained by O substitution alone, and to obtain a magnetic recording medium with excellent electromagnetic conversion characteristics and a high reproduction output. Furthermore, by roughly replacing a portion of Fe with Nb, a magnetic recording medium with higher reproduction output and excellent electromagnetic conversion characteristics can be obtained. Also,
In the Ba-ferrite of the present invention, a part of Fe is roughly Ti.
, In, Hn.

There is no problem even if it is substituted with a transition metal such as Cu, GO, or Sn.

In addition, when Ba-ferrite used in the present invention is expressed by the following general formula, H is substituted gold ji), BaO-n ((Fa
l-, H,) 203)->0.36 (However, Co
+zn-o, oa ~0.3, Co/Zn-0,5~1
0), n = 5.4 to 6.0, and H is preferably a combination of two or more elements having an average valence of 3.

In the present invention, the reason why the average particle size, plate ratio, and coercive force are limited as described above is as follows. In other words, if the average particle size is less than 400, the reproduction output when used as a magnetic recording medium will be insufficient, and conversely, if the average particle size is less than 400,
If the number exceeds 0.00, the surface smoothness of the magnetic recording medium will deteriorate significantly and the noise level will become too high. In addition, if the platelet ratio is less than 20, a perpendicular orientation ratio suitable for Pi polishing recording cannot be obtained when used as a magnetic recording medium, and conversely, if the platelet ratio exceeds 6.0, when used as a magnetic recording medium. surface smoothness deteriorates significantly and the noise level becomes too high.

Furthermore, if the coercive force is less than 3,500a, it becomes difficult to retain the recording signal, and if it exceeds 200,000, the head magnetic field decreases to saturation, making recording difficult.

As a method for producing the magnetic powder used in the present invention, for example, oxides and carbonates of each element necessary to form the target Ba-ferrite are melted together with a glass-forming substance such as boric acid. , the resulting melt is rapidly cooled to form a glass, and then this glass is heat treated at a predetermined temperature 1! In addition to the glass crystallization method, in which the target Ba-ferrite crystal powder is precipitated by plating and the glass component is finally removed by heat treatment, coprecipitation-calcination methods, hydrothermal synthesis methods, etc. can be applied. be.

The sulfone group-containing vinyl chloride-vinyl acetate copolymer used in the present invention is obtained, for example, by copolymerization with sulfone group-containing monomers vinyl chloride and vinyl acetate,
The average molecular ffi is about 5,000 to 50,000, and the m suspension of the sulfone group-containing monomer in the molecule is 0.1 to 3.
A content of about 0% by weight is preferable.

Moreover, -01-11 can be introduced at any arbitrary step 11 by hydrolysis of vinyl acetate in the copolymer.

When the average molecular weight is less than 5,000, the resin becomes brittle and it becomes difficult to form a strong coating film, and when it exceeds 50,000, the solubility decreases, making it poorly soluble in solvents during the preparation of magnetic paints, making it impractical. If the weight of the sulfonic group-containing monomer in the molecule is less than 011 [z], the adsorption of the resin to the magnetic powder is insufficient and the dispersibility is poor;
If it exceeds %, the viscosity of the paint increases significantly at the stage of forming the paint, making it impossible to obtain a good paint film.

The Ba-ferrite powder used in the present invention has high saturation magnetization because a part of Fe is replaced with Co and 2n, but magnetic reagglomeration due to dispersion is very likely to occur during the dispersion process. , ordinary vinyl chloride-vinyl acetate-
Resin binder systems, such as vinyl alcohol copolymers and urethane combinations, cannot produce coatings with dispersibility and stability up to the application step. Here, when the sulfonic group-containing vinyl chloride-vinyl acetate copolymer of the present invention is used as the resin binder, the strong polarity of the sulfonic groups will cause a strong bond to the surface of the highly dispersed 8a-ferrite powder during the dispersion process. is formed, and a resin layer is formed on the surface of the Ba-ferrite powder. This suppresses the magnetic re-agglomeration of Ba-ferrite powder, making it possible to produce a paint with improved dispersibility and stability, which in turn allows for high reproduction output and A magnetic recording medium having excellent electromagnetic conversion characteristics can be obtained.

Examples of resin binders used in the present invention include polyurethane resins, polynisder resins, polyamide resins, acrylic resins, epoxy resins, A resin component such as phenoxy resin, melamine resin, vinyl butyral resin, vinyl alcohol resin, or a copolymer resin thereof may be used in combination.In this case, a sulfonic group-containing vinyl chloride-vinyl acetate copolymer may be used. It is desirable that the content of m is 1% by weight or more, more preferably 5% by weight or more.If the content m of the sulfonic group-containing vinyl chloride-vinyl acetate copolymer is less than 1% by weight, the effect of improving the dispersibility of the magnetic powder will decrease. is significantly reduced.

The method for manufacturing the magnetic recording medium of the present invention includes, for example, 8
a- Ferrite powder, resin binder, and additives are kneaded together with a solvent to create a magnetic paint, and this magnetic paint is applied onto a support, and then subjected to orientation treatment, drying treatment, etc. to form a magnetic layer. A commonly used method of manufacturing a recording medium can be applied.

The mixing ratio of the ferromagnetic powder and the binder in the present invention is 5 to 400 parts by weight, preferably 6 to 20 parts by weight, of the binder per 10,011 parts of the ferromagnetic powder. The recording density of magnetic recording media with too much binder decreases,
If it is too small, the strength of the magnetic layer will be poor, resulting in undesirable situations such as decreased durability and powder falling off.

In addition, in the magnetic paint, if necessary, per 100 parts by weight of magnetic powder, 40 parts by weight or less of a dispersant, 40 parts by weight or less of a lubricant,
Additives such as up to 400 parts by weight of a curing agent and up to 40 parts by weight of an ω1 abrasive material may be added.

Examples of the dispersant include lecithin,
Examples of lubricants include higher fatty acids and fatty acid esters, examples of curing agents include bifunctional or higher-functional isocyanates, and examples of abrasives include Cr, 03, AJ2.203, α-Fe
203 etc. are mentioned.

As the support used in the present invention, any non-magnetic support that is commonly used as a support for magnetic recording media, such as a film made of polyethylene terephthalate, polyolefin sulfide, etc., may be used.

(Function) In the magnetic recording medium J5 of the present invention, Ba-ferrite powder in which a part of Fe is replaced with Co and In or [a part of e is replaced with C01] is used as the ferromagnetic Ba-ferrite powder.
Since Ba-ferrite powder substituted with zn or Nb or other metal elements as necessary is used, and a vinyl chloride-vinyl acetate copolymer containing a sulfone group is used as the resin binder, high dispersion of the 8a-ferrite powder is achieved. It provides high stability and prevents magnetic reaggregation of the paint after dispersion, and also provides higher reproduction output and excellent electromagnetic conversion characteristics compared to magnetic recording media using conventional C01Till 6a-ferrite powder. Obtainable.

(Example) Next, examples of the present invention will be described.

Example 1 A Ba-ferrite powder of CoX7nji expressed by the chemical formula % was prepared by a glass crystallization method.

First, BaO1FeO, which was formulated to constitute the above Ba-ferrite composition, was added to the BO.8aO glass.
Add CoO, Tie, , lnO at the same time to 1350
A glass containing the above-mentioned components was prepared by melting at ℃, rolling and quenching.

Next, this glass was heated at 850°C for 4 hours to form Co, Ti12nrfi! in the matrix. Replaced 8a-
Ferrite was precipitated. Finally, wash with acetic acid and CO
1Ti, In-substituted 88-ferrite magnetic powder was obtained.

The average particle size of the 1q magnetic powder was 500 Å, and the plate ratio was 3.
01 coercive force was 650 Oe. Also, the saturation magnetization first
It was as shown in the table.

Next, as a binder, sulfonated vinyl-vinyl chloride-vinyl acetate (sulfone group is Na salt) was produced by polymerization. The average molecular weight of the obtained copolymer was 18,000,
The ffuhl ratio of each heptamine in the molecule is sulfonated vinyl (Na salt): 1.0%, J-pinyl: 8
0% vinyl acetate: 19. OL [461%. After sufficiently mixing and dispersing the following composition using this sulfonated vinyl-vinyl chloride-vinyl acetate copolymer in a ball mill, trifunctional isocyanate Coronate C-3041 (F-1 Honpolyurethane Co., Ltd.) was used as a curing agent. A magnetic paint was prepared by adding 5 ffiffi parts of vA (trade name) and mixing and stirring until uniform.

Co-Ti-7n substituted Ba-7x light magnetic powder 100 parts by weight Sulfonated vinyl-vinyl chloride-10 Vinegar Im vinyl copolymer (sulfonic Ha salt) polyurethane resin/N
-230110II manufactured by Nippon Polyurethane Co., Ltd. Carbon black (average particle size 30μ) 5 Lecithin 1 Butyl stearate 4 α-AJ2203
5.

Methyl ethyl ketone 50〃Cyclohexanone 50〃Toluene
After applying the 50-year-old magnetic paint to a polyester film in an unoriented state and a vertically oriented state (m < 2k Oe) using a reverse roll coater, the surface was smoothed using a super calender, and a magnetic recording layer with a magnetic layer thickness of 2 μ- A medium was prepared.

Regarding this magnetic recording medium, the surface gloss, saturation magnetization Hs, output C, and C/N (dB: relative value) perpendicular alignment ability of the coating film were measured. The results are shown in Table 1.

Example 2 Co, In, Hb'll-converted Ba-ferrite powder (average particle size 520 Å, platelet ratio 31, coercive force 60
A magnetic recording medium was produced in the same manner as in Example 1 using 000> as magnetic powder. Table 1 shows the properties of the magnetic powder used in this example and the properties of the magnetic recording medium obtained.

Comparative Example 1 By the same method as in Example 1, Co-Ti substituted Ba-ferrite (average particle size 560 Å, plate ratio 3.01, coercive force 590 Oe) represented by the chemical formula % was used as a magnetic material, and a binder was 1 as VAGII (UCC
A magnetic recording medium was produced in the same manner as in Example 1, except that a 10-fold opening was used (vinyl chloride-vinyl acetate-vinyl alcohol copolymer, average molecular weight 1i23000, manufactured by Co., Ltd.). Table 1 shows the properties of the magnetic powder used in this example and the properties of the magnetic recording medium obtained.

(The following is a blank space) [Effect of the invention 1 As is clear from the above examples, the magnetic recording medium of the present invention is a Ba-ferrite powder in which a part of Fe is replaced with Co and In and Nb and other elements as necessary. B replaced with
a By using ferrite powder and using a sulfonic group-containing vinyl chloride-vinyl acetate copolymer as a binder, the dispersibility and dispersion stability of the magnetic powder are improved, which improves the output characteristics and C/N characteristics. This enables high-density recording.

Claims (1)

[Claims] (1) A magnetic recording medium formed by coating a non-magnetic support with a magnetic paint in which ferromagnetic Ba-ferrite powder is dispersed in a resin binder, wherein the Ba-ferrite powder contains at least a portion of Fe. C
o and Zn substituted average particle size 400-900 Å,
It is Ba-ferrite with a plate ratio of 2.0 to 6.0 and a coercive force of 350 to 2000 Oe, and the resin binder contains at least a vinyl chloride-vinyl acetate copolymer containing a sulfone group in the molecule. Features of magnetic recording media.