JP2856852B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a high recording density magnetic recording medium having excellent recording characteristics in a wide wavelength range from a short wavelength range to a long wavelength range.

(Prior art) A coating type magnetic recording medium is obtained by coating a magnetic powder such as γ-Fe ₂ O ₃ , CrO ₂ , CO-γ-Fe ₂ O ₃ or iron powder on a polyester film base together with a resin binder. It is configured to be applied. This binder is added to ensure the dispersibility of the magnetic powder and the running durability of the medium, and the amount of the binder is required to be at least 10 parts by weight or more based on 100 parts by weight of the magnetic powder. I have.

In recent years, magnetic recording media have been required to have higher recording densities as the amount of information to be recorded has increased. As one of means for meeting such a demand, there is a method of reducing the particle size of the magnetic powder. As a magnetic powder for magnetic recording media corresponding to high recording density by miniaturization, at present, part of Fe can be replaced with Co, Ti, etc., and coercive force can be recorded and reproduced with ordinary recording and reproducing head 200-200
There is an ultrafine hexagonal ferrite powder such as Ba-ferrite having a particle size of 0.2 μm or less, which is defined as 0 Oe.

Such ultrafine hexagonal ferrite powder is a hexagonal plate-like crystal with a very small particle size and an easy axis of magnetization in the direction perpendicular to the plate surface, making it suitable for high-density magnetic recording media. Known as suitable.

(Problems to be Solved by the Invention) By the way, in a magnetic recording medium using such a magnetic powder, in order to obtain excellent recording characteristics for signal recording in a wide wavelength range from a short wavelength range to a long wavelength range, It is necessary to improve the surface smoothness of the magnetic recording layer and to increase the saturation magnetization (Ms) as much as possible. However, for example
Since ultrafine hexagonal ferrite powder such as Ba-ferrite originally has a small saturation magnetization, there is a limit from the viewpoint of sufficiently extending long wavelength characteristics.

As one of means for increasing the saturation magnetization of the magnetic recording layer, there is a method of increasing the packing density of magnetic powder in the magnetic layer, that is, the so-called packing ratio. However, the increase in the packing ratio tends to cause a decrease in the durability of the coating film, and it is difficult to balance the durability of the coating film with the electromagnetic conversion characteristics. is not.

On the other hand, in order to enhance the surface smoothness of the magnetic recording layer, it is generally necessary to disperse the magnetic powder in the magnetic layer to a high degree, but the dispersion tends to become difficult as the particles become finer.

The present invention has been made in order to solve such a conventional problem, and it is intended to increase the packing ratio without impairing the dispersibility of the magnetic powder and the durability of the coating film, thereby increasing the saturation magnetization of the magnetic recording layer. It is an object of the present invention to provide a magnetic recording medium having excellent recording characteristics in both a short wavelength range and a long wavelength range and capable of high density recording.

[Constitution of the Invention] (Means for Solving the Problems) The magnetic recording medium of the present invention is a magnetic recording medium provided with a magnetic layer formed by applying hexagonal ferromagnetic powder on a substrate together with a resin binder. The amount of the binder is not less than 1 part by weight and not more than 5 parts by weight based on 100 parts by weight of the hexagonal ferromagnetic powder, and at least a part of the resin binder has a molecular weight of 20,000 or less, and is 0.1 to 1.0 mmol / g) a resin having at least one polar group selected from among a sulfone group, a phosphoric acid group, a carboxyl group, a metal base thereof, an amino group, and an ammonium group.

As described above, in the conventional magnetic powder medium, at least 10 parts by weight or more is required as the resin binder in order to secure the dispersibility of the ferromagnetic powder and the running durability of the medium. However, according to the present invention, particularly in a medium using a hexagonal ferrite powder that can be highly filled, the excessive addition of the resin binder not only lowers the output characteristics of the medium but also reduces the durability. It was also found that this was unfavorable in that it caused an increase in the friction coefficient and made it difficult to replenish the lubricant. Therefore,
Improving the output characteristics and further studying the addition amount of the resin binder that can ensure the running durability required for the magnetic recording medium, the hexagonal ferrite powder was 100 parts by weight of the magnetic powder. Thus, it was found that sufficient dispersibility and durability can be ensured with an extremely small addition amount of the resin binder of 1 to 5 parts by weight, which has not been considered conventionally.

The reason why the magnetic powder can be bonded to each other with such a small amount of the resin binder is not always clear, but the hexagonal ferrite powder has a hexagonal plate surface, and a fan working between the surfaces. It is considered that the Waals force works effectively. In addition, it is possible to hold lubricant in small voids existing between adjacent particles, and in this respect, it becomes easy to replenish lubricant. It is. Furthermore, in such a medium having a small amount of the resin binder added, the hardness of the coating film can be increased regardless of the glass transition point Tg of the resin, and the durability can be more easily achieved. Seem.

The resin binder used in the present invention contains at least one polar group selected from a sulfone group, a phosphate group, a metal base thereof, an amino group, and an ammonium group. Group 0.1-1.0
mmol / g and at least partly with a molecular weight of 20,000
These are: Here, the reason why the molecular weight of the resin is set to 20,000 or less is that when the amount of addition is 5 parts by weight or less, it is difficult to sufficiently disperse the magnetic paint with all the resins having the molecular weight of 20,000 or more. The preferred molecular weight for obtaining sufficient dispersion is 2,000 to 15,000. Further, the reason for setting the magnetic group content to 0.1 mmol / g or more is that each molecule adsorbed on the surface of the hexagonal ferromagnetic powder has at least 0.5
This is because it has a maximum of about 5 polar groups, which requires more complete adsorption. That is,
By using a resin having a molecular structure as described above as a binder component, the finely divided magnetic powder is well dispersed, and the bond between the magnetic powder and the non-magnetic powder and the resin binder becomes strong.

Such a resin binder according to the present invention is obtained as follows. That is, when the resin binder containing a polar group is a resin obtained by vinyl polymerization, the resin binder is usually obtained by copolymerizing a vinyl monomer containing such a polar group with a normal vinyl monomer. When the resin binder containing a polar group is a polyester resin or a polyurethane resin, a polybasic acid or a polyhydric alcohol as a component thereof and a polybasic acid or a polyhydric acid into which the polar group is introduced are used. It is obtained by mixing an alcohol and performing a condensation reaction.

Examples of monomers having these groups and polybasic acids or polyhydric alcohols used in the production of resins containing sulfone groups and these metal bases include vinyl sulfonic acid, vinyl benzene sulfonic acid soda,
Acrylamide-2-methylpropanesulfonic acid and vinyl monomers containing these metal bases, and And so on.

Further, as a monomer used in the production of a resin having a phosphoric acid group or this metal base, or an amino group,
Vinyl monomers having respective polar groups or polybasic acids or polyhydric alcohols having respective polar groups are used.

Typical vinyl resin monomers copolymerized with vinyl monomers having a polar group such as a sulfone group include:
Examples include various monomers such as vinyl chloride, vinyl alcohol, maleic anhydride, vinyl acetate, various acrylate monomers, vinylidene chloride, vinyl acetal, vinyl butyral, acrylates, acrylonitrile, and styrene.

Examples of ordinary polyhydric alcohol copolymerized with a vinyl monomer having a polar group such as a sulfone group include 1,4-butanediol, 1,6-hexamethylenediol, cyclohexanediol, ethylene glycol, diethylene glycol, and triene glycol. Tylene glycol, propylene glycol and the like, and polybasic acids include terephthalic acid, isophthalic acid, adipic acid, sebacic acid, oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid and the like. The ratio of the monomer having a polar group such as a sulfone group or a polybasic acid or a polyhydric alcohol in these resins has a molecular weight of 20,0.
When it is less than 00, it is introduced so as to be 0.1 mmol / g or more as described above.

These resin binders having a polar group may be used alone, but in combination with other resin binders having no sulfone group or the like, it is possible to improve the mechanical strength of the coating film and the running property. .

Examples of the resin binder that can be used in combination with such a resin binder having a sulfone group include a polyurethane resin, a polyester resin, a polycarbonate resin, a polyacryl resin, a polyamide resin, an epoxy resin, a phenol resin, a polyether resin, a phenoxy resin, and a melamine resin. , Vinyl butyrate resin, furan resin, vinyl chloride resin, vinyl acetate resin, vinyl alcohol resin, and mixtures or copolymers thereof.

The compounding amount of the resin binder that can be used in combination is appropriately set within 80% by weight with respect to all the resin binders.

In the magnetic recording medium according to the present invention, a polyamine or polyisocyanate compound is usually added to the resin binder together with the ferromagnetic powder. In other words, when the ferromagnetic powder-resin binder system is applied on a support, when a required magnetic recording medium is manufactured, by crosslinking, the mechanical strength of the coating film is further increased and the durability is increased.

Such compounds include, for example, polyamine compounds such as tolylenediamine (TDA), 4,4'-diaminodiphenylmethane (MDA), 4,4'-diamino-3,
3'-dichlorodiphenylmethane and the like. Examples of polyisocyanate compounds include toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), naphthalene diisocyanate (NDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), Adducts of trimethylolpropane and water, such as xylylene diisocyanate (XDI), and isocyanurates are used.

In addition, as novel compounds, 1,4-diisocyanatocyclohexane, 1,3-bis (α, α-dimethylisocyanatomethyl) benzene (TMXDI), isocyanatomethylmethylcyclohexyl isocyanate (IMCI)
Can be used.

(Function) In the magnetic recording layer of the magnetic recording medium of the present invention, by using a resin binder containing a predetermined amount of a polar group such as a sulfone group with respect to the hexagonal ferromagnetic powder, the dispersibility thereof is significantly improved, Reduces surface roughness during alignment. In addition, by setting the resin binder to 5 parts by weight or less per 100 parts by weight of the ferromagnetic powder, the filling rate of the magnetic powder is improved, and excellent running durability is secured.

(Example) Hereinafter, an example of the present invention will be described.

Prior to the description of the specific example, a general description will be given of the configuration of the magnetic recording medium according to the present invention.

Examples of the hexagonal ferromagnetic powder usable in the present invention include M-type (magnet plumbite type) and W-type hexagonal Ba ferrite, Sr ferrite, Pb ferrite, and Ca ferrite represented by the following general formulas. Alternatively, a solid solution or ion-substituted product thereof can be used.

MaO · n (Fe _1-x Mb _x ) ₂ O ₃ (In the formula, Ma represents any one element of Ba, Sr, Ca, and Pb, and Mb represents Co, Zn, Ni, Cu, Mg, Mn , In, Ti, Sn, Ge,
It represents at least two elements selected from the group consisting of Zr, Hf, V, Nb, Sb, Ta, Cr, Mo and W, one of which is Nb. n represents the number of 5.4-6.0. More specifically, the hexagonal ferrite powder used in the present invention includes a part of Fe atoms, which are constituent elements of these uniaxial hexagonal ferrite crystals, with a divalent metal and a pentavalent metal, Nb. And further substituted with 0.05 to 0.5 Sn atoms per chemical formula are suitable, and the amount of substitution is set to an amount such that the coercive force becomes 200 to 2000 Oe.

Among the substitution elements, the divalent metal mainly acts to lower the coercive force of the hexagonal ferrite powder to an appropriate range, the pentavalent metal Nb acts to increase the saturation magnetization, and the tetravalent metal Sn acts as This is preferable because it acts to reduce the change in the temperature characteristic of the coercive force.

In the hexagonal ferrite used in the present invention, 2
The appropriate substitution amount of the valent metal (MII) and the pentavalent metal (MV) is M
Although it depends on the combination of II and MV, the substitution amount per chemical formula of MII is generally 0.5 to 1.2.

As for the relationship between the substitution amounts of these substitution elements, for example, regarding magnetoplumbite-type Ba ferrite, the chemical formula of the substitution product is BaFe _{12- (x + y (+ z))} MII _x MV _y (MIV _z ) O Represented by ₁₉ . Where x, y, and z are MII, MV, and M
It is the substitution amount per one chemical formula of IV element.

MII, MV, and MIV are divalent, pentavalent, and tetravalent, respectively, and the substituted Fe atom is trivalent. Therefore, the relationship of y = (x−z) / 2 is established in consideration of valence compensation. . That is, the replacement amount of the MV is uniquely determined from the replacement amount of the MIV.

In the case where Sn is used as the MIV element in the magnetic powder used in the present invention, the proper range of the substitution amount is 0.05 to 0.5 per hexagonal ferrite chemical formula. Note that Ti having the same valence may be used in place of Sn.

Further, in the magnetic recording medium of the present invention, more preferable results can be obtained by providing an undercoat layer having a pigment / resin binder ratio of 10/100 or more on the substrate surface. Such pigments include organic pigments including carbon black, titanium oxide, calcium carbonate, and γ-
Use non-magnetic and magnetic inorganic pigments composed of metal powder mainly composed of ferrite and iron, and use polyurethane resin, polyester resin, vinyl chloride-vinyl acetate copolymer resin, polyacryl resin, epoxy resin, etc. as the resin binder. Can be. Further, it is desirable to add a polyisocyanate or polyamine-based curing agent to these resin binders to impart appropriate solvent resistance.

Alternatively, the magnetic recording medium of the present invention can be subjected to a corona or plasma treatment on the surface of the substrate to obtain the same favorable results as in the case where the undercoat layer is provided. In corona treatment or plasma treatment, the surface molecules of the substrate are stabilized, radicals are generated by the surface molecules, fine irregularities are generated on the surface, or molecules that are favorable for adhesion are bonded to the generated radicals. To increase the adhesiveness,
All of these have proven to be effective means.

If desired, a dispersant, a lubricant, an abrasive, or a conductivity-imparting agent such as carbon black may be added to the components of the magnetic coating film.

As the dispersant, an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. For example, a phosphate anionic surfactant such as lecithin or gaffax is particularly desirable. As the lubricant, fatty acid or fatty acid alkyl ester type, silicone type, fluorinated hydrocarbon type, or a mixture or compound thereof can be used. Further, inorganic powders having a Mohs' hardness of 5 or more, such as TiO ₂ , Cr ₂ , O ₃ , Al ₂ , O ₃ , SiC, and ZrO ₂ , are suitable as the abrasive.

It is desirable that the amount of these additives is as small as possible. For 100 parts by weight of the hexagonal ferromagnetic powder, for example, the dispersant and the lubricant are each 4 parts by weight or less, the abrasive is 6 parts by weight or less, The amount of carbon black is suitably not more than 3 parts by weight.

In obtaining the magnetic recording medium of the present invention, the hexagonal ferromagnetic powder, the resin binder and, if necessary, various additives are sufficiently mixed with a solvent, and a curing agent such as a polyisocyanate compound is further added to the substrate. After coating on the top, an orientation treatment and a drying treatment are performed according to a conventional method, and the obtained coating film may be subjected to a smoothing treatment by a calendar. It is to be noted that a conductive primer layer may be formed on the substrate as necessary, and a magnetic recording layer may be formed on the primer layer.

Example 1 Co, Ti, Nb-substituted Ba-ferrite powder 100 parts by weight Polyurethane resin * 1 3.8 {toluene / cyclohexanone = 1/2 mixed solution 180} lecithin 2 {alumina (average particle size 0.3 μm) 3} stearic acid 2 〃 * 1 Aliphatic polyurethane resin having a So ₃ Na group, molecular weight: 10,000, sulfone group content: 0.5 mmol / g After mixing the above ingredients, they were further dispersed by a sand grinder for 2 hours. After adding 1 part by weight of Coronate L (polyisocyanate trade name: manufactured by Nippon Polyurethane Co.) to 100 parts by weight of the obtained magnetic paint, an undercoat layer with a pigment / resin binder of 10/100 was applied by a reverse coater. A 2.5μm-thick coating on a polyester film with a magnetic field perpendicular to the substrate surface (strength: 4k Oe)
It was dried while passing under.

After the obtained coating film was cured at 40 ° C. for 3 days, it was cut into イ ン チ inch width to prepare a magnetic tape, which was used for measurement.

Example 2 100 parts by weight of Co, Ti, Nb-substituted Ba-ferrite powder Amino group-added vinyl chloride * 12 2 polyurethane resin * 2 1.8 {toluene / cyclohexanone = 1/2 mixed solution 180 {lecithin 2} alumina (average) Particle size: 0.3 μm) 3 {stearic acid 2} * 1 Molecular weight: 8,000, amino group content: 0.2 mmol / g * 2 Aliphatic polyurethane resin, molecular weight: 10,000 A magnetic paint was prepared in the same manner as in Example 1. . After applying the obtained coating material to a polyester film having a surface treatment by corona discharge with a thickness of 2 μm, the coating film surface is dried while passing through a magnetic field in a direction perpendicular to the film surface while the coating surface is not dried. A magnetic tape was produced in the same manner as in Example 1.

Example 3 In Example 1, a sulfonated polyester (molecular weight: 15,000, sulfone group content:
0.4 mmol / g) and a plasma-treated polyester film was used as the substrate.
A magnetic tape was produced in the same manner as in the above case.

Example 4 In Example 1, a polyvinyl chloride-vinyl acetate copolymer resin (molecular weight: 15,000, sulfone group content: 0.2 m) was used in place of the polyurethane resin.
mol / g, epoxy equivalent: 1000) 3.5 parts by weight and tolylenediamine (TDA) as curing agent (amine equivalent: 400)
Was prepared in the same manner as in Example 1 except that 1.4 parts by weight was mixed.

Example 5 A magnetic tape was prepared in the same manner as in Example 1 except that a polyurethane having a carboxyl group (molecular weight: 10,000, carboxyl group content: 0.3 mmol / g) was blended in place of the polyurethane resin in Example 1. Was prepared.

Example 6 In Example 1, the molecular weight of the polyurethane resin was 10,000.
0. A magnetic material having a sulfone group content of 0.5 mmol / g was used in the same manner as in Example 1 except that the addition amount was 3 parts by weight and the addition amount of the curing agent was 1.5 parts by weight. A tape was made.

Example 7 In Example 1, the molecular weight of the polyurethane resin was 5,000.
A magnetic tape was prepared in the same manner as in Example 1 except that the amount of the sulfone group was 0.7 mmol / g, the addition amount was 2 parts by weight, and the addition amount of the curing agent was also 2 parts by weight. Produced.

Comparative Examples 1 and 2 Magnetic tapes were prepared in the same manner as in Examples 1 and 2, except that the amounts of resin added were 6 and 12, respectively, and that 3 parts by weight of a curing agent were added. did.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1, except that a polyurethane resin having no sulfone group was used as the resin.

Comparative Example 4 In the case of Example 1, the resin had a molecular weight of 30,000
A magnetic tape was produced in the same manner as in Example 1 except that the polyurethane resin was used.

Comparative Example 5 A magnetic tape was produced in the same manner as in Example 1 except that the resin of Comparative Example 5 was used in an amount of 8 parts by weight and a curing agent was added in an amount of 3 parts by weight.

As described above, the surface properties, packing rate (saturated magnetization), still durability, and the like of the tapes obtained in Examples 1 to 7 and Comparative Examples 1 to 5
The results of the output measurements are shown in the following table.

Note that the packing ratio is indicated by saturation magnetization since the same magnetic powder was used in both the examples and comparative examples, and the still durability was 1 d
The time until B dropped was shown, and the recording / reproducing output was shown as the Y signal output when recording was performed at a frequency of 7 MHz.

[Effects of the Invention] As is clear from the above examples, according to the present invention, the recording characteristics in a wide wavelength range from short wavelength to long wavelength are excellent in surface property and running durability, large in saturation magnetization, and large. It functions as an excellent magnetic recording medium.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-280217 (JP, A) JP-A-1-251420 (JP, A) JP-A-3-252918 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G11B 5/702 G11B 5/706 G11B 5/70

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer formed by applying hexagonal ferromagnetic powder on a substrate together with a resin binder, wherein the amount of the resin binder is 100 parts by weight of the hexagonal ferromagnetic powder. 1 part by weight or more and 5 parts by weight or less, and at least a part of the resin binder has a molecular weight of 20,000 or less and has a sulfone group, a phosphate group, a carboxyl group of 0.1 to 1.0 mmol / g, a metal base thereof, A magnetic recording medium comprising a resin having at least one kind of polar group selected from an amino group and an ammonium group.