JPH0417115A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve high frequency characteristics and low frequency characteristics in good balance by using a ferromagnetic powder which satisfies a specified relation as the ferromagnetic powder to be incorporated into the magnetic layer. CONSTITUTION:Such a ferromagnetic powder which satisfies the relation expressed by formulae I, II, III is used as the ferromagnetic powder to be incorporated into the magnetic layer. Namely, the ferromagnetic powder has specified sigmaS, Fe<2+>/Fe<3+> (weight ratio), and Hc. When plural magnetic layers are provided on a nonmagnetic supporting body, the low frequency (chroma) characteristics can be further improved by incorporating this ferromagnetic powder into the lowest layer, namely the layer adjacent to or the nearest to the supporting body. When a layer containing dispersion of a conductive material is provided as a lower layer, dropout can be reduced. Thus, both of high frequency characteristics and low frequency characteristics can be improved in good balance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium in which both high-frequency and low-frequency characteristics are improved in a well-balanced manner.

[Prior Art and Problems to be Solved by the Invention] Coercive force ( Ferromagnetic powder with high Hc) is used.

However, when such ferromagnetic powder is contained in the magnetic layer, the characteristics in the low range deteriorate.

In this way, with conventional technology, it is difficult to obtain a magnetic recording medium with well-balanced improvements in both high-frequency and low-frequency characteristics.
It was extremely difficult.

The present invention has been made to improve the above situation.

That is, an object of the present invention is to provide a magnetic recording medium with improved high-frequency characteristics and low-frequency characteristics in a well-balanced manner.

[Means for Solving the Problems] To achieve the above objects, the present invention provides a coating-type magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, in which a ferromagnetic powder is contained in the magnetic layer. This magnetic recording medium is characterized by using ferromagnetic powder that satisfies the following formula (%).

The present invention will be explained in detail below.

Layer Structure - The magnetic recording medium of the present invention is basically formed by laminating a single layer or a plurality of magnetic layers on a nonmagnetic support.

Regardless of whether it is a single layer or multiple layers, the magnetic layer is made by dispersing ferromagnetic powder in a binder.

Note that an adhesive layer may be provided between the nonmagnetic support and the magnetic layer closest to it, or a protective layer may be provided on the outermost magnetic layer. A back coat layer can also be provided on the back side of the body.

1. Ferromagnetic Powder What is important in the present invention is to use ferromagnetic powder with specified σs, Fe2''''/Fc:l+ (weight ratio), and Hc as the ferromagnetic powder contained in the magnetic layer.

In other words, this ferromagnetic powder must satisfy the following formula.

Hc≧l190 (Oe)...[engine] U . It is possible to obtain a well-balanced magnetic recording medium with excellent range characteristics.

On the other hand, if any of the above formulas [I], [II], and [m1] are not satisfied, the effects of the present invention cannot be achieved.

In the present invention, when a plurality of magnetic layers are provided on a non-supporting body, the magnetic layer corresponding to the lower layer, that is, the magnetic layer that is in contact with the non-supporting body or closest to it, contains the ferromagnetic powder specified above. , it is possible to further improve low frequency (chroma) characteristics.

Further, as will be described later, when a layer in which a conductive substance is dispersed is provided in the lower layer, dropouts are reduced, so that a highly reliable magnetic recording medium can be provided.

That is, the tape specific resistance is usually 1. Ox 106~1
．． The range is preferably 0x109.

The ferromagnetic powder used in the present invention can be appropriately selected from the following as long as it satisfies each of the above formulas.

For example, Go-containing y-Fe2O3 powder, Goo-containing Fe
3O4 powder, Co-containing FedX (4/3 < x <
3/2) powder or Fe-A11j metal powder, F
e-Ni metal powder, FeAn-Ni metal powder, Fe-A
n-P metal powder, Fe-N15i-A9. Metal powder, FeFe-Ni-3i-AJJ-metal powder, Fe-M
n-Zn metal powder, Fe-Ni-Zn metal powder, Fe-
Examples include fine ferromagnetic metal powders such as Co-Ni-Cr metal powder and Fe-Co-Ni-P metal powder.

These ferromagnetic powders can be used alone or in combination of two or more.

Among these, preferred is fine Go-containing -Fe
J: + powder.

Such ferromagnetic powder has large σs and Hc, and is excellent in high-density recording.

Further, the specific surface area of the ferromagnetic powder used in the present invention is usually B
ET value: 25-70 m2/g, preferably 35-60 m
2/g.

If the BET value is less than 25 m 27 g, the output will be extremely low, and if the BET value exceeds 70 m 2 / g, it will be very difficult to achieve uniform dispersion and it may not be possible to obtain sufficient characteristics, so it is preferable. do not have.

In particular, if ferromagnetic powder with a BET value of 40 m27 g or more is used, it is possible to easily realize a medium that enables high-density recording and has an excellent S/N ratio.

- Binder In the present invention, it is preferable to use a resin modified by introducing a functional group, particularly a modified vinyl chloride resin, a modified polyurethane resin, or a modified polyester resin, as the binder contained in the magnetic layer.

Examples of the functional group include -3o3M, -0302
M, -COOM and OM'/M2 may be the same or different. ) etc. are preferred.

If the modified resin contains such a functional group, the compatibility between the modified resin and the ferromagnetic powder will be improved, and the dispersibility of the ferromagnetic powder will not only be further improved, but also its agglomeration will be prevented. The stability of the working fluid is further improved, and the frequency characteristics from high to low frequencies are improved in a well-balanced manner, and in addition to the electromagnetic conversion characteristics, the durability of the magnetic recording medium is also improved.

The modified resins can be used alone or in combination of two or more.

The modified resin is a compound having a vinyl chloride resin, a polyurethane resin, or a polyester resin and a negative functional group and chlorine in the molecule, for example (where M is a hydrogen atom or an alkali metal such as lithium or sodium,
Ml and M2 are each a hydrogen atom, lithium, potassium, sodium, or an alkyl group, and Ml and 6-CH2CH25OJ, C-CH2CH,
0302M, CJlj-CH2C00M.

(M, M', M2 have the same meanings as above) and the like by condensation through a dehydrochloric acid reaction.

In the present invention, thermoplastic resins, thermosetting resins, reactive resins, electron beam curable resins, or mixtures thereof, which are conventionally known in the field of magnetic recording media, may be used as the binder. Alternatively, these may be used in combination with the modified resin.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, and acrylic ester-vinylidene chloride copolymer. copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl sotyral,
Cellulose derivative (cellulose acetate tstylate)
, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.)
, styrene-butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, amino resin, and synthetic rubber-based thermoplastic resin.

These may be used alone or in combination of two or more.

Examples of the thermosetting resin or reactive resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reactive resin, high molecular weight polyester resin, and isocyanate prepolymer. mixtures of methacrylate copolymers and diisocyanate prepolymers, urea formaldehyde resins, and polyamine resins.

These may be used alone or in combination of two or more.

Examples of the electron beam curable resin include unsaturated prepolymers such as maleic anhydride type, urethane acrylic type, epoxy acrylic type, polyester acrylic type, polyether acrylic type, polyurethane acrylic type, polyamide acrylic type; ether acrylic type; , urethane acrylic type, epoxy acrylic type, phosphoric acid ester acrylic type, aryl type, and hydrocarbon type.

These may be used alone or in combination of two or more.

In the present invention, the amount of the binder contained in the magnetic layer is generally 1 to 200 parts by weight, preferably 1 to 50 parts by weight, per 100 parts by weight of the ferromagnetic powder.

If the amount of binder blended is too high, the amount of ferromagnetic powder blended will be reduced, which may reduce the recording density of the magnetic recording medium, and if the amount blended is too small, the strength of the magnetic layer will decrease. However, the running durability of the magnetic recording medium may be reduced.

In the present invention, an aromatic or aliphatic polyisocyanate can be used in combination with the binder resin as a curing agent.

Examples of aromatic polyisocyanates include tolylene diisocyanate (TD I ) and adducts of this with active hydrogen compounds, and have an average molecular weight of 100 to 3.
A value in the range of 000 is preferred.

Examples of aliphatic polyisocyanates include hexamethylene diisocyanate (I (MD I )) and adducts of this with active hydrogen compounds, and have an average molecular weight of 1
00 to 3000 is preferred, and non-alicyclic polyisocyanates and adducts of these with active hydrogen compounds are more preferred.

The amount of the aromatic or aliphatic polyisocyanate added is usually 1/20 to 1/20 by weight relative to the binder resin.
It is 7/10, preferably 1/10 to 1/2.

-Other components In the magnetic recording medium of the present invention, various additive components such as a lubricant, nonmagnetic abrasive particles, conductive powder, and surfactant can be contained in the magnetic layer as necessary.

Examples of the lubricant include silicone oil, taraphite, molybdenum disulfide, and
About 0 monobasic fatty acids (for example.

Examples include fatty acid esters consisting of stearic acid) and a monohydric alcohol having about 3 to 26 carbon atoms.

Examples of the non-magnetic abrasive particles include alumina [
α-A x 20 :+ (corantum) etc.], artificial corundum, fused alumina, silicon carbide, chromium oxide,
Examples include diamond, synthetic diamond, garnet, and emery (main components: corundum and magnetite). The content of this abrasive particle is 2% relative to the ferromagnetic powder.
The amount is preferably 0 parts by weight or less, and the average particle size is preferably 0.5 gm or less, and even more preferably 0.4 p-m or less.

Incidentally, when the lubricant and nonmagnetic abrasive particles are contained particularly in the outermost magnetic layer, the contact characteristics with the head (sliding performance, wear resistance, etc.) can be significantly improved.

Examples of the conductive powder include carbon black, graphite, silver powder, and nickel powder, and examples of the surfactant include natural, nonionic, anionic, and
Examples include cationic and amphoteric surfactants.

When these conductive powders are contained especially in the lower layer, the surface electrical resistance can be effectively lowered, and the generation of noise due to the discharge of the withstanding electric charge and the occurrence of dropouts due to the adhesion of dust can be prevented.

Non-magnetic support - Examples of materials for forming the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose tiacetate, polyamide,
Plastics such as polycarbonate, Cu, Ai, Zn
Examples include metals such as, glass, boron nitride, Si carbide, ceramics, etc.

The form of the non-magnetic support is not particularly limited, and main forms include tape, film, sheet, cart, disk, and drum.

Is there any particular restriction on the thickness of the non-magnetic support? For example, in the case of a film or sheet, it is usually 3 to 11,007 mm.
, is preferably 5 to 50 JLm, approximately 3QILm to IDmm in the case of a disk or card shape, and appropriately selected depending on the recorder etc. in the case of a drum shape.

Note that this nonmagnetic support may have a single layer structure or a multilayer structure.

Further, this non-magnetic support may be subjected to surface treatment such as corona discharge treatment.

Manufacture of Magnetic Recording Medium The method of manufacturing the magnetic recording medium of the present invention is not particularly limited, and may be manufactured in accordance with the method used for manufacturing known single-layer or multi-layer magnetic recording media. I'll come.

For example, generally, a magnetic coating material is prepared by cross-dispersing magnetic layer-forming components such as ferromagnetic powder and a binder in a solvent, and then the magnetic coating material is coated on the surface of a non-magnetic support and dried.

Examples of the solvent include acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone (MIBK).
Ketones such as , cyclohexanone, alcohols such as methanol, ethanol, propatool, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester systems such as ethylene glycol monoacetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, dioxane, etc. Aromatic hydrocarbons such as benzene, toluene, xylene, etc.: methylene chlorite, ethylene chloride carbon tetrachloride chloroform, ethylene chloride Halogenated hydrocarbons such as hydrin and dichlorobenzene can also be used.

When preparing a magnetic paint, the ferromagnetic powder and other magnetic layer forming components are charged into a kneader simultaneously or individually.

For example, adding the ferromagnetic powder to a solution containing a dispersant,
After kneading for a predetermined time, the remaining components are added and kneading is continued to form a magnetic paint.

Various kneaders can be used for cross-dispersing the magnetic layer-forming components.

Examples of this mixer include a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a sight grinder, a Sqegvari attritor, a high-speed impeller splitter, a high-speed stone mill, a high-speed impact mill, a disper kneader-1 high-speed mixer homogenizer, Examples include ultrasonic dispersion machines.

Examples of application methods include wet-on-wet (
wet-on-wet method, wet-on-dry method, dry-on-wet method, try-on-dry method -on-dry) method.

Among these, the wet-on-wet method and the wet-on-dry method are preferred, and the wet-on-wet method is particularly preferred.

The wet-on-wet method has advantages over other coating methods in that it is easier to control the film thickness and the coating properties are very stable.

Application methods for magnetic paint include, for example, gravure coating method, knife coating method, wire bar coating method, doctor blade coating method, reverse roll coating method, dip coating method, air knife coating method, calendar coating method, and squeegee coating method. , the kiss coach ink method, and the fantin coating method.

After a magnetic paint is applied to the surface of a non-magnetic support, the undried paint film is generally subjected to a magnetic field orientation treatment, and then a surface smoothing treatment is performed using a supercalendar roll or the like to achieve the desired shape. By cutting into shapes,
A magnetic recording medium can be obtained.

[Example] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

In addition, in the following, "part" means "part by weight".

Moreover, the method of measuring the physical properties is as explained below.

(a) RF specific output RF-OUT), Lumi-3N (L-O
UT), chroma output (C-OUT), chroma-AM (
C-AM) Using Shibaku noise meter 925C, JVC HR
- Measured using S 7000 deck.

(B) Dropout (Dlo) Run the sample in HR-S 7000 deck, 1
5ILS, signal loss of −15 dB or more was measured every minute for 20 minutes, and the average value per minute was calculated.

(Examples 1 to 10, Comparative Examples 1 to 5) After cross-dispersing the following composition for the first layer, polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Kogyo Co., Ltd.)
Magnetic paint A was prepared by adding 5 parts.

1st iL m-product Go-γ-FeOx・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・・ toO part (1,34≦X≦1.5, physical properties are listed in Table 1) Sulfonic acid metal salt-containing vinyl chloride system Resin...Conflict...1
0 parts (MRIIO5 day Thursday Zeon day type Zeo 2 ester polyurethane...5 parts (XE-1
(manufactured by Takeda Pharmaceutical Co., Ltd.) Alumina (average particle size 0.2 ILm) 5 parts Carbon black 1 part Myristic acid
・・・・・・・・・1 part stearic acid・・・・・・・
...1 part butyl stearate...
1 part Methyl ethyl ketone 100 parts Cyclohexanone 100 parts Toluene 100 parts Next, apply magnetic paint A to a thickness of 14 g. , m on a polyethylene terephthalate base and dried to form a single magnetic layer with a thickness of 3.01 parts m. The magnetic recording medium thus obtained was slit into samples with a width of 2 inches, and the electromagnetic conversion characteristics thereof were measured. Table 2 shows the results.

As mentioned above, Table 1 shows the physical properties of ferromagnetic powder, among which Fe 2 + / Fe:
A graph of the relationship between the 14 weight ratio and HC is shown in Figure 1, and a graph of the relationship between σ1 and HC is as shown in Figure 2. ,
The code attached to the Δ mark indicates the NO of the ferromagnetic powder).

(Examples 11 to 19) After cross-dispersing the following composition for the second layer, polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Kogyo Co., Ltd.)
Magnetic paint B was prepared by adding 5 parts.

IU good quality Co-γ-F eOX for 1st L 100
parts (1,34≦X≦1.5, physical properties are listed in Table 3)
10 parts of vinyl chloride resin containing sulfonic acid metal salt (MRIIO1 manufactured by Nippon Zeon Co., Ltd.) Polyester polyurethane 5 parts (XE-1
(Manufactured by Takeda Pharmaceutical Co., Ltd.) Myristic acid・・・・・・・・・ Stearic acid・・・・・・・・・ Butyl stearate・・・・・・ Methyl ethyl ketone・・・・・・... Cyclohexanone ...... Toluene ...... 1 part 1 part 1 part 100 parts 100 parts 100 parts Also for the third layer below Paint C (not a magnetic paint) was prepared by cross-dispersing the composition.

10 parts (average particle size 20m JL) Sodium sulfonate-containing polyester 10 parts Methyl ethyl ketone 100 parts Toluene ...... 100 parts Next, the magnetic paint B and paint C thus prepared and the magnetic paint A prepared in Examples 5, 7, and 10 were combined as appropriate, Two or three coating layers (each film thickness is shown in Table 4) were coated on a polyethylene terephthalate base with a thickness of 14 JLm, and the magnetic recording medium thus obtained was slit into 172 inch width samples. , and measured its physical properties.

The results are shown in Table 5.

Table 1 [Effects of the Invention] According to the present invention, it is possible to provide a magnetic recording medium in which both high-frequency characteristics and low-frequency characteristics are improved in a well-balanced manner.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between Fe''/Fe'+ weight ratio of ferromagnetic powder and Hc, and FIG. 2 is a graph showing the relationship between σ8 and Hc of ferromagnetic powder.

Claims (2)

[Claims] (1) In a coated magnetic recording medium in which a magnetic layer is provided on a non-magnetic support, the ferromagnetic powder to be contained in the magnetic layer has the following formula [I], [II], [III] Hc (coercive force) ≧69
0 (Oe)...[I]σs (saturation magnetization) ≧7
3+ {(Hc-690)^1^/^2/2}...
...[II] (Fe^2^+/Fe^3^+) x 100≧4.0+(
Hc/20)...[III] A magnetic recording medium characterized by using ferromagnetic powder that satisfies the following. (2) The magnetic recording medium according to claim 1, wherein the magnetic layer consists of multiple layers.