JP2826661B2 - Magnetic recording media - Google Patents

Description

The present invention relates to a magnetic recording medium such as a magnetic tape, a magnetic sheet, and a magnetic disk.

[Background of the Invention]

Recently, higher density of magnetic recording media such as magnetic tape,
With the adoption of N, magnetic powder having a smaller particle diameter has been used.

Generally, it is said that the S / N ratio of a magnetic recording medium is proportional to the square root of the number of particles of magnetic powder in a recording material related to recording / reproducing.
The use of a magnetic powder having a smaller particle diameter is more advantageous for improving the S / N. Also, when the magnetic powder is finely divided and its BET value is increased,
Since the surface of the magnetic layer becomes smoother and the spacing loss is reduced, it is advantageous in obtaining high electromagnetic conversion characteristics. However, if the limit is too small, it will enter the superparamagnetic region and lose ferromagnetism.

Further, needle-like small particles which form a single magnetic domain in the magnetic particles and give a high coercive force (Hc) are preferably used. At this time, if the ratio of the major axis length l and the minor axis length d defining the needle shape; l / d is the axis ratio (aspect ratio) as, as is large and l is long in the single magnetic domain formation range. forgiven. However, the volume of the particles (Kl ² / as; k is a constant) has a preferable range, and l and as are regulated.

Further, in a magnetic tape having a laminated configuration in which high and low frequency recording is shared by a plurality of magnetic layers, the radius of curvature of the magnetic flux lines leaking from the head formed in the magnetic layer is small in the upper layer close to the head, and away from the head. Since l and as become larger in the lower layer, it is necessary to match l and as to the radius of curvature of the magnetic field lines to prevent a decrease in SN.

It is generally considered that the higher the packing ratio of the magnetic particles, the better. However, it is known that the coercive force decreases when the particles are too dense and come into contact with each other.

Further, the size, the axial ratio, the filling rate, etc. of the magnetic particles directly affect the magnetic conditions of the magnetic tape, as well as the running durability, other film physical properties, and the interlayer adhesion.

As described above, at present, the design of magnetic tapes has been advanced while groping in the dark with causal relationships related to magnetic particles being unarranged or without finding the appropriate combination.

For example, in the case of a laminated configuration, it is preferable that the axial ratio as is also discriminated by the magnetic layer.However, an attempt to make as equal in all layers causes an interlayer adhesion failure, reduces as, and reduces electromagnetic conversion characteristics. The conditions for increasing the driving durability are degraded, and conversely, attempts to increase the driving durability by increasing as have encountered problems such as lowering of the electromagnetic conversion characteristics.

[Object of the invention]

An object of the present invention is to provide a magnetic tape having a laminated structure having good electromagnetic conversion characteristics, strong interlayer adhesion, and excellent running durability in view of the above technical situation.

[Structure and operation and effect of the invention]

It is another object of the present invention to provide a magnetic recording medium having at least two layers in a laminated constitution layer provided on a non-magnetic support, and having a major axis length of magnetic particles contained in an uppermost magnetic layer of the at least two magnetic layers. Is 0.3 μm or less, and the axial ratio is 3 to 8
Less than, the axial ratio of the magnetic grains of the magnetic layer of at least one layer other than the uppermost layer is at 8 to 12, and, the laminated magnetic _{layer, -SO 3 M, -OSO 2 M} , -COOM and, - (M ¹ O) P (OM
² ) = O (wherein, M is a hydrogen atom, lithium or sodium, and M ₁ and M ² are each a hydrogen atom, lithium, potassium, sodium or an alkyl group. M ¹ and M ² may be different from each other or may be the same.) As a binder, any one of a vinyl chloride resin, a polyester resin and a polyurethane resin having at least one functional group This is achieved by a magnetic recording medium characterized by containing.

In the embodiment of the present invention, the BET value of the magnetic particles contained in the uppermost magnetic layer and at least one magnetic layer other than the uppermost layer is preferably 40 m ² / g or more and 30 m ² / g or more, respectively. Practically, up to about 70 m ² / g and 50 m ² / g are sufficient. In the above BET value range, the upper BET layer is preferably larger than the lower BET value.

The magnetic layer of the magnetic tape of the present invention is a dispersion type magnetic layer in which a magnetic powder or the like is dispersed and suspended in a binder, and further a dispersion, a lubricant, and the like are used.

Examples of the magnetic material include γ-Fe ₂ O ₃ and Co-containing γ-Fe ₂
O ₃ , Co-deposited γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-deposited Fe ₃
O ₄ , Co-containing magnetism Oxide magnetic materials such as Fe, Ni, Co, Fe-Ni alloy, Fe-
Co alloy, Fe-Ni-P alloy, Fe-Ni-Co alloy, Fe-Mn-Zn alloy, F
e-Ni-Zn alloy, Fe-Co-Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-N
Various ferromagnetic materials such as a magnetic metal powder mainly composed of Fe, Ni, and Co, such as an i-alloy, a Co-P alloy, and a Co-Cr alloy. Additives for these metallic magnetic materials include Si, Cu, Zn, Al,
Elements such as P, Mn, and Cr or compounds thereof may be contained. Hexagonal ferrites such as barium ferrite and iron nitride are also used.

Of the above, Co-containing FeOx magnetic powder is preferably used.

Next, the “cobalt-containing iron oxide magnetic powder” will be described.

When the ferromagnetic iron oxide particles are generally represented by FeOx, those having a value of x in the range of 1.33 ≦ x ≦ 1.50, ie, maghemite (γ-Fe ₂ O ₃ ; x = 1.50), magnetite (Fe ₃
O ₄ ; x = 1.33) and their solid solutions (FeOx; 1.33 <x <
1.50).

γ-Fe ₂ O ₃ and Fe ₃ O ₄ are usually obtained by the following production method.

An alkali is added to the ferrous salt solution to produce ferrous hydroxide, and air is blown and oxidized at a predetermined temperature and pH to obtain needle-like hydrous iron oxide, which is heated at 250 to 400 ° C in air. It is heated and dehydrated, and then heated and reduced at 300 to 450 ° C. in a reducing atmosphere to obtain acicular magnetite particles. If necessary, the magnetite is reoxidized at 200 to 350 ° C. to obtain acicular magnetite (γ
−Fe ₂ O ₃ ).

Among these ferromagnetic iron oxides, the cobalt-containing iron oxide magnetic powder according to the present invention is roughly classified into two types: a doped type and an adhered type.

The method of producing Co-doped iron oxide particles includes: (1) a method in which ferric hydroxide containing cobalt hydroxide is subjected to hydrothermal treatment in an alkaline atmosphere to reduce and oxidize the generated powder; At the time of synthesis, a method of adding a cobalt salt solution in advance, synthesizing goethite containing cobalt while adjusting the pH, and reducing and oxidizing it, (3) using goethite containing no Co as a nucleus, A method in which a reaction similar to the reaction of (2) is performed on the nucleus to grow and reduce and oxidize goethite containing Co. (4) An alkali containing a Co salt is added to the surface of acicular goethite or magnetite. There is a method in which treatment is performed in an aqueous solution to adsorb the Co compound, followed by reduction / oxidation or heat treatment at a relatively high temperature.

Also, Co-coated iron oxide magnetic particles are mixed with an acicular magnetic iron oxide and a cobalt salt in an alkaline aqueous solution and heated to adsorb a cobalt compound such as cobalt hydroxide on the iron oxide particles.
This can be obtained by washing and drying, collecting, and then heat-treating in a non-reducing atmosphere such as air or N ₂ gas.

Co-coated particles are superior to Co-doped particles in heating and / or depressurization of the medium magnetic layer, and it is preferable to use Co-coated particles except in special fields.

It is preferable that the content of cobalt is 1.0 to 5.0 wt% of the whole magnetic powder. The coercive force (Hc) of the magnetic powder is 600 to 1100 Oe
It is preferable that

The specific surface area represented by the above BET value refers to the surface area per unit weight, is a physical quantity completely different from the average particle diameter, for example, even if the average particle diameter is the same, a large specific surface area, Some have a small specific surface area. The specific surface area is measured by a specific surface area measurement method generally called a BET method (for details, see J. Ame. Chem. Soc. 60 309 (1.
938)).

The binder used in the present invention is a resin modified by introducing a functional group or a functional group that forms an internal salt, particularly a modified vinyl chloride resin, a modified polyurethane resin, in view of dispersion of magnetic particles and other fillers. Resin or modified polyester resin is used.

Examples of the functional groups in the resins, -SO ₃ M, -OSO ₂
M, -COOM, and (Wherein, M is a hydrogen atom, any of lithium and sodium, and M ¹ and M ² are each a hydrogen atom, lithium, potassium, sodium and an alkyl group.

Also the M ¹ and M ^2, may be different from each other, it may be the same. ).

These functional groups are combined with resins such as vinyl chloride resins, polyester resins, and polyurethane resins, for example. (However, M, M ¹ and M ² have the same meanings as described above, respectively.) The compound can be obtained by condensing a compound containing a negative functional group and chlorine in the molecule by a dehydrochlorination reaction.

Among the resins thus obtained, a resin obtained by introducing a negative functional group into a vinyl chloride resin or a polyurethane resin is preferable.

Further, as the vinyl chloride resin, for example, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl maleate-vinyl alcohol copolymer, And vinyl chloride-vinyl propionate-vinyl maleate-vinyl alcohol copolymer.

In the present invention, in addition to the binder, a non-modified vinyl chloride resin, polyurethane resin or polyester resin conventionally used can be used, if necessary, and further, a cellulose resin, a phenoxy resin or a specific resin can be used. May be used in combination with a thermoplastic resin, a thermosetting resin, a reactive resin, an electron beam irradiation-curable resin, or the like having the above method.

The above-mentioned resins are complementary in length and length, and can be used by selecting the optimum point of the kind and amount as the constituent binder of the constituent layers of the present invention, for example, the magnetic layer, the back coat layer, the protective layer or the adhesive layer.

In order to improve the durability of the constituent layers such as the magnetic layer of the magnetic tape of the present invention, various curing agents can be contained, for example, isocyanate can be contained.

Aromatic isocyanates that can be used include, for example, tolylene diisocyanate (TDI) and adducts of these isocyanates with active hydrogen compounds, and those having an average molecular weight in the range of 100 to 3,000 are suitable.

Examples of the aliphatic isocyanate include hexamerenedene diisocyanate (HMDI) and the like and adducts of these isocyanates and active hydrogen compounds. Among these aliphatic isocyanates and adducts of these isocyanates and active hydrogen compounds, those having a molecular weight of 10
It is in the range of 0-3,000. Of the aliphatic isocyanates, non-alicyclic isocyanates and adducts of these compounds with active hydrogen compounds are preferred.

In the present invention, conventional techniques can be utilized to form a magnetic layer, a back coat layer or other constituent layers of the magnetic tape of the present invention.

A dispersant is used in the magnetic paint used to form the magnetic layer, and if necessary, additives such as a lubricant, an abrasive, a matting agent, and an antistatic agent may be contained.

As the dispersant used in the present invention, in addition to the phosphate according to the present invention, amine compounds, alkyl sulfates, fatty acid amides, higher alcohols, polyethylene oxide, sulfosuccinic acid, sulfosuccinates, known surfactants And salts thereof, and a salt of a polymer dispersant having a negative organic group (for example, -COOH) can also be used. Even if these dispersants are used alone,
Alternatively, two or more kinds may be used in combination. Examples of the lubricant include silicone oil, graphite, carbon black graft polymer, molybdenum disulfide, tungsten disulfide, lauric acid, myristic acid, and C12 to C16.
Resin acid esters (so-called waxes) composed of a monobasic fatty acid and a monohydric alcohol having 21 to 23 carbon atoms in total with the number of carbon atoms of the fatty acid can also be used. These lubricants are added in the range of 0.2 to 20 parts by weight based on 100 parts by weight of the binder.

As the abrasive, generally used materials such as fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, artificial diamond, garnet, emery (main components: corundum and magnetite) and the like are used. These abrasives have an average particle size of 0.05 to 5 μm, and particularly preferably 0.1 to 2 μm. These abrasives are added in the range of 1 to 20 parts by weight based on 100 parts by weight of the binder.

As the matting agent, an organic powder or an inorganic powder is used individually or as a mixture.

As the organic powder used in the present invention, acrylic styrene-based resin, benzoguanamine-based resin powder, melamine-based resin powder, and phthalocyanine-based pigment are preferable, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, and polyimide-based resin are preferable. Powders, polyfluorinated ethylene resin powders and the like can also be used. As inorganic powders, silicon oxide, titanium oxide, aluminum oxide, calcium carbonate, barium sulfate, zinc oxide, tin oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, α-Fe ₂ O
₃ , talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide.

Examples of antistatic agents include conductive powders such as carbon black, graphite, tin oxide-antimony oxide compounds, titanium oxide-tin oxide-antimony oxide compounds; natural surfactants such as saponin; alkylene oxides; glycerin And glycidol-based nonionic surfactants; higher alkylamines, quaternary ammonium salts, pyridine, other heterocycles, cationic surfactants such as phosphonium or sulfoniums; carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid Anionic surfactants containing an acidic group such as an ester group or a phosphoric ester group; amphoteric surfactants such as amino acids, aminosulfonic acids, and sulfuric acid or phosphoric esters of amino alcohol;

Examples of the solvent to be blended in the paint or a diluting solvent at the time of applying the paint include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone;
Alcohols such as methanol, ethanol, propanol and butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and ethylene glycol cenoacetate; ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane and tetrahydrofuran; benzene , Toluene and xylene; and halogenated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and dichlorobenzene.

Examples of the support include polyethylene terephthalate, polyethylenes such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose derivatives such as cellulose diacetate, polyamides, and plastics such as polycarbonate. Metals such as Cu, Al and Zn, glass, ceramics such as boron nitride BN and Si carbide can also be used.

The thickness of these supports is about 3 to 100 μm, preferably 5 to 50 μm in the case of a film or a sheet, about 30 μm to 10 mm in the case of a disk or a card, and is cylindrical in the case of a drum. The type is determined depending on the recorder used.

An intermediate layer for improving adhesion may be provided between the support and the magnetic layer.

As a coating method for forming the laminated magnetic layer on the support, in the case of wet on wet, simultaneous and sequential application of extrusion, river scroll + extrusion, gravure roll + extrusion, and the like are conceivable.

Further, it is also conceivable to combine any one of air doctor coat, blade coat, air knife coat, squeeze coat impregnated coat, transfer roll coat, kiss coat, cast coat and spray coat.

In the case of wet on dry, any combination of the above coating methods may be used.

〔Example〕

 The present invention will be specifically described with reference to examples.

Examples 1 to 3 and Comparative Examples (1) to (5) Magnetic tape samples were prepared according to the following magnetic paint formulations A (for the upper layer) and B (for the lower layer), and the characteristics were measured. still,
Table 1 shows the average major axis length and the axial ratio. The major axis length of the lower magnetic particles is not particularly specified.

 “Parts” in the examples indicate all parts by weight.

Magnetic coating formulation A (for upper layer) and formulation B (for lower layer) Co-γ-Fe ₂ O ₃ 100 parts Sulfo-modified vinyl chloride / vinyl acetate / vinyl alcohol copolymer 13 parts Polyester polyurethane resin 7 parts α-Al ₂ O ₃ (Average particle size 0.1 μm) 6 parts Carbon black 12 parts Myristic acid 4 parts Stearic acid 1 part Butyl stearate 1 part Cyclohexanone 180 parts Methyl ethyl ketone 120 parts Toluene 120 parts The paint of the above formulation is coated on a 14.5 μm polyethylene terephthalate support. , And an upper layer of 1.5 μm and a lower layer of 2.0 μm were applied to obtain video tape samples of Examples and Comparative Examples.

The performance of the obtained sample was evaluated, and the results are shown in Table 1.

As is clear from Table 1, the sample of the present invention was a comparative sample (1).
Compared with (3), it has excellent electromagnetic characteristics (RF output, Lumi S / N, squareness ratio), and does not hinder running performance even after 200 passes.

Evaluation method of characteristics (1) Squareness ratio: Using VSM (measuring magnetic field 10KOe), residual magnetic flux density (Br)
The ratio (Bm / Br) between the saturation magnetic flux density and the saturation magnetic flux density (Bm) was measured.

(2) RF output: The output during reproduction of a 100% white signal was determined by comparing the reference tape (Comparative Example (3)) with OdB.

(3) Lumi-S / N: Using a noise meter (manufactured by Shibasoku Co., Ltd.), the difference between the S / N of the sample at 100% white signal was determined in comparison between the reference tape and the sample tape.

(4) Video running performance: Using a commercially available video cassette deck (VHS type), performing a running test of 200 passes at 40 ° C and 80% RH, RF
The decrease and the state of the front and back surfaces of the tape were observed.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 5/716 G11B 5/702

Claims (1)

(57) [Claims] In a magnetic recording medium having at least two magnetic layers in a laminated magnetic layer provided on a non-magnetic support, a length of magnetic particles contained in an uppermost magnetic layer of the at least two magnetic layers is defined. The axial length is 0.3 μm or less, the axial ratio is 3 or more and less than 8, the axial ratio of the magnetic particles of at least one magnetic layer other than the uppermost layer is 8 or more and 12 or less, and the laminated magnetic layer is _{-SO 3 M, -OSO 2 M,} -COOM, and - (M ¹ O) P
(OM ² ) = O (wherein, M is a hydrogen atom, any of lithium and sodium, and M ₁ and M ² are each a hydrogen atom, lithium, potassium, sodium and an alkyl group. And M ¹ and M ² may be different from each other or the same.) A vinyl chloride resin having at least one functional group
A magnetic recording medium comprising a binder resin containing either a polyester resin or a polyurethane resin.