JP2001014648A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium that improves a problem due to electrification caused by friction, has good traveling performance and does not cause a problem such as the generation of a discharge noise as a magnetic recording medium used for a high density magnetic recording. SOLUTION: A nonmagnetic layer containing a nonmagnetic powder, carbon black and a binder and a magnetic layer containing a magnetic powder and a binder are successively laminated on a nonmagnetic substrate to obtain the objective magnetic recording medium. The nonmagnetie powder such as hematite or titanium dioxide and the carbon black in the nonmagnetic layer have been chemically bonded. Since the carbon black is previously bonded to the nonmagnetic powder and dispersed in the binder, a good C-N ratio and superior surface properties are ensured and surface resistance can be lowered even in the case of a low carbon black content. A defective traveling due to electrification is prevented and a problem such as the generation of a discharge noise is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium used for high-density magnetic recording, and more particularly, to a high-density magnetic recording medium having reduced surface resistance, good running properties, and no discharge noise. And its manufacturing method.

[0002]

2. Description of the Related Art In recent years, development of coating type magnetic recording media has been actively studied with the aim of increasing the density and the capacity, and the performance has been promoted. Under such circumstances, the recording wavelength is becoming shorter.

The coating type magnetic recording medium conventionally has a non-magnetic support and a magnetic layer formed on the non-magnetic support. The magnetic layer is formed by applying a magnetic coating material in which a magnetic powder, a binder and the like are dispersed in a solvent on a non-magnetic support.

[0004] In such a coating type magnetic recording medium, a magnetic powder, a binder and the like have been studied for the purpose of achieving high dispersibility and high density recording of the magnetic powder. However, even when high-density recording is achieved by using a magnetic powder having a high dispersibility or a binder that highly disperses the magnetic powder, wear and the like occur when the magnetic recording medium runs. In many cases, sufficient results were not obtained in terms of durability, reliability and the like. For this reason,
At present, magnetic recording media are put into practical use by adding a dispersant, a lubricant, a curing agent, and the like to a magnetic paint as needed.

[0005] Incidentally, in such a magnetic recording medium, its electrical resistance is also a serious problem from the viewpoints of running properties and electrical conversion characteristics. If the electric resistance of the magnetic recording medium is high, the magnetic recording medium is charged, and the tape is stuck to a traveling system such as a guide or a cassette or cartridge containing a magnetic recording medium and a wall adjacent to the medium. Or discharge noise may occur. In this case, the problem has been solved by adding carbon or the like having a small particle size (several tens of nm) to the magnetic layer in order to reduce the electric resistance.

However, fillers (inorganic fillers, large-diameter carbon, etc.) added for the purpose of controlling the surface and preventing abrasion, and carbon for reducing the electric resistance, etc., are not suitable for polymers due to their surface properties. Further, it is known that the interaction with the functional group and the dispersant is small and the dispersibility is inferior to that of the magnetic powder.

Heretofore, the above-described problem of charging generated in a magnetic recording medium has been improved by adding low-resistance carbon black having a small particle diameter to a magnetic layer. Also,
In particular, in JP-A-10-269558, a magnetic powder used for a magnetic layer is treated with a titanate coupling agent or an aluminate coupling agent as a countermeasure against electric charges generated in a magnetic recording medium. Attempts have been made to deposit carbon black on the magnetic powder in advance by depositing carbon or graphite such as carbon black on the magnetic powder. By bonding carbon black to the magnetic powder in advance in this way, when the carbon black is dispersed together with the magnetic powder, the production process becomes complicated due to the dispersibility of the carbon black, which has conventionally occurred, and the surface is reduced to the required degree. Problems such as a decrease in magnetic recording density due to carbon black added to reduce resistance have been improved.

Further, in recent years, as the recording wavelength is shortened with the increase in density, the problem of self-demagnetization loss at the time of recording and thickness loss at the time of reproduction, in which the output is reduced when the magnetic layer is thick, is increasing. For this reason, attempts have been made to reduce the thickness of the magnetic layer. However, when a magnetic layer having a thickness of 2 μm or less is directly applied to the support, the influence of the nonmagnetic support tends to appear on the surface of the magnetic layer, and the electromagnetic conversion characteristics and the dropout tend to deteriorate.

As one means for solving this problem, JP-A-63-191315 and JP-A-63-1874 are known.
As described in JP-A No. 18, a method in which a non-magnetic layer is provided as a lower layer using a simultaneous multi-layer coating method and a high-concentration magnetic coating solution is thinly applied has been put to practical use. This technology has dramatically improved the yield and made it possible to obtain good electromagnetic conversion characteristics. However, the track width has been narrowed since then to further increase the recording density. Correspondingly, a magnetoresistive head (MR
It is proposed that the data be reproduced using a head) and that it be put to practical use in a hard disk or the like.

As described above, the magnetic recording medium is required to have a higher density every year. for that reason,
It is necessary to develop a technology for making the magnetic layer thinner by using a magnetic material having a smaller particle size. In this case, the problem of charging of the magnetic recording medium is more problematic than in the related art. In a conventional magnetic recording medium having no nonmagnetic layer, the charging of the magnetic recording medium is dealt with simply by lowering the resistance of the magnetic layer as described above. However, by providing a non-magnetic layer on a support as described above, good magnetic conversion characteristics are obtained, and in the case of a magnetic recording medium with improved yield, the non-magnetic layer generally has a high electric resistance. Electric charges generated by running of the recording medium and the like are more likely to be accumulated than before. Therefore, there is a case where it is not possible to cope with the problem that merely lowering the resistance of the magnetic layer as in the related art causes sticking of the magnetic recording medium to a traveling system or the like or generation of discharge noise. there were.

[0011]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve a problem caused by electrification caused by friction in a magnetic recording medium having a magnetic layer provided on a non-magnetic layer, which is suitable for high-density magnetic recording. It is an object of the present invention to provide an excellent magnetic recording medium having good running properties and free from problems such as discharge noise. Still another object of the present invention is to provide a method suitable for manufacturing the magnetic recording medium.

[0012]

Means for Solving the Problems The present inventors have intensively studied the constitution of the magnetic layer and the non-magnetic layer in order to achieve the above-mentioned object. As a result, in a magnetic recording medium in which a nonmagnetic layer mainly containing a nonmagnetic powder and a binder is provided on a nonmagnetic flexible support, and a magnetic layer containing at least a ferromagnetic powder and a binder is provided thereon. It has been found that, by chemically bonding a material having a low electric resistance such as carbon black to the non-magnetic powder, the problem of charging generated in the magnetic recording medium having the above-described configuration can be improved, and the present invention has been accomplished. .

[0013] That is, the present invention provides a method for manufacturing a magnetic recording medium comprising:
In a magnetic recording medium comprising a non-magnetic powder, a non-magnetic layer containing carbon black and a binder, and a magnetic layer containing a magnetic powder and a binder sequentially laminated, the non-magnetic powder and carbon The present invention relates to a magnetic recording medium characterized by being chemically bonded to black.

It is preferable that the non-magnetic powder is selected from hematite and titanium oxide. Further, it is preferable that the nonmagnetic powder and the carbon black are chemically bonded using a treating agent selected from a silane coupling agent and a titanate coupling agent.

Further, the present invention provides a coating for a non-magnetic layer containing a non-magnetic powder, carbon black and a binder on a non-magnetic support, and a coating for a magnetic layer containing a magnetic powder and a binder. A method for producing a magnetic recording medium, comprising sequentially or simultaneously multi-layer coating with a coating material, wherein the non-magnetic layer coating material is chemically bonded using a treatment agent selected from a silane coupling agent and a titanate coupling agent. The present invention relates to a production method characterized by being obtained by dispersing non-magnetic powder and carbon black in a binder.

It is generally considered that the low resistance obtained by carbon black is due to the fact that carbon black aggregates to some extent and the aggregates of carbon black contact each other to form a conductive path. Therefore, carbon black is inherently difficult to disperse, and if it is excessively dispersed, the resistance is rather increased. As a result, it is necessary to increase the amount of carbon black to be added, and it is difficult to reduce the resistance. became. Such problems in the prior art have been studied by the present inventors, and as a result, a structure in which carbon black is chemically bonded in advance to a nonmagnetic powder, specifically, hematite or titanium oxide, and then dispersed with a binder. By using the same, even with a small amount of carbon black added, a reduction in the resistance of the magnetic recording medium can be achieved, and furthermore, adverse effects due to charging can be prevented.

That is, according to the present invention, it is possible to lower the resistance of a magnetic recording medium by chemically bonding carbon black to a powder added to a nonmagnetic layer such as titanium oxide in advance, and at the same time, The surface roughness of the non-magnetic layer can be further reduced, and as a result, a synergistic effect that a higher recording density can be achieved by making it possible to apply a thinner magnetic layer has been found. It has been reached. The reason why such a synergistic effect can be obtained is not out of the range of estimation, but since carbon black is chemically strongly bonded to the surface of the non-magnetic powder, even if the amount of carbon black added is small, carbon black can be obtained even with a small amount of carbon black added. It is considered that it is possible to provide a pseudo aggregation effect such that a single aggregate is formed, and as a result, a sufficient conductive path can be formed even with a small amount of carbon black added.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The magnetic recording medium of the present invention is a magnetic recording medium in which a non-magnetic layer and a magnetic layer are sequentially laminated on a non-magnetic support, and is particularly contained in the non-magnetic layer. The non-magnetic powder and the carbon black are chemically bonded.

In the magnetic recording medium of the present invention, the non-magnetic layer containing a non-magnetic powder to which carbon black is chemically bonded is contained in the non-magnetic layer. Can be improved. By combining carbon black with non-magnetic powder, while avoiding the problem of poor dispersion of carbon black,
The chargeability of the magnetic recording medium of the present invention can be improved. More specifically, it can be considered as follows. Carbon black has extremely poor dispersibility, and tends to aggregate when dispersed together with nonmagnetic powder. Therefore, it is necessary to add a considerable amount of carbon black to obtain a desired antistatic effect. However, when a large amount of carbon black is added to the non-magnetic layer, the surface roughness of the non-magnetic layer further increases due to the aggregation of the carbon black, and it becomes difficult to apply a thin magnetic layer thereon. . Therefore, it is necessary to effectively reduce the resistance of the non-magnetic layer with as little carbon black as possible. In the magnetic recording medium of the present invention, by chemically bonding carbon black to non-magnetic powdered sugar such as hematite or titanium oxide added to the non-magnetic layer, the above-described problem of aggregation of carbon black is not caused. In addition, the resistance of the nonmagnetic layer can be reduced.

Non-magnetic layer [Chemical bond between non-magnetic powder and carbon black] For the non-magnetic powder to which carbon black is chemically bonded, for example, the non-magnetic powder is treated with a silane coupling agent or a titanate coupling agent. It can be obtained by treating and then binding carbon black to a silane coupling agent or a titanate coupling agent bound to the nonmagnetic powder.

The silane coupling agent preferably used in the present invention has the following general formula:

[0022]

Embedded image XRSi (OR ₁ ) ₃ or

[0023]

## STR2 ## may be those having a XRSi (Y) _3. In the above formula, R represents a substituted or unsubstituted alkylene group, and R ₁ represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aralkyl group. As the alkyl group for R ₁ , an alkyl group having 2 to 7 carbon atoms is preferable. X is a phosphate residue, and examples thereof include the following groups.

[0024]

Embedded image _{-P (= O) (OH 2} ), -P (= O) (H) (OH), -P (= O) (R 2) (OH), -P (= O) (R ₂ ) ₂ , -P (= O) (OR ₂ ) ₂ , -P (= O) (OH) -OP (= O) (OR ₂ ) ₂ , -OP (= O) (OR ₂ ) ₂ , —OP (＝ O) —P (＝ O) (OR ₂ ) _{2 where} R ₂ is a substituted or unsubstituted alkyl group;
It is a substituted or unsubstituted aralkyl group. Y represents a halogen atom such as a chlorine atom and a bromine atom. Hereinafter, specific examples of the silane coupling agent used in the present invention are shown, but the present invention is not limited to these silane coupling agents, and two or more silane coupling agents can be used in combination.

[0025]

Exemplified Compound 1 (HO) ₂ -P (= O)-(CH ₂ ) ₄ ? Si- (OC ₂ H _{5) 3} Example Compound _{2 (HO) 2 -P (=} O) - (CH 2) 4 -Si- (OC 3 H 7) 3 Exemplified Compound _{3 (HO) 2 -P (=} O _{) - (CH 2) 4 -Si-} (OC 4 H 9) 3 exemplified compound _{4 (HO) 2 -P (=} O) - (CH 2) 4 -Si- (OC 5 H 11) 3 exemplified compound 5 ( (HO) ₂ -P (= O)-(CH ₂ ) ₄ -Si- (OC ₆ H ₁₃ ) ₃ Exemplary compound 6 (HO) ₂ -P (= O)-(CH ₂ ) ₄ -Si- (OC ₇ H ₁₅ ) ₃ exemplified compound 7 (HO) ₂ -P (-O)-(CH ₂ ) ₃ -Si- (OC ₂ H ₅ ) ₃ exemplified compound 8 (HO) (H) -P (= O)-( CH ₂ ) ₃ -Si- (OC ₂ H ₅ ) ₃ exemplified compound 9 (HO) (C ₃ H ₇ ) -P (= O)-(CH ₂ ) ₈ -Si- (OC ₂ H ₅ ) ₃ exemplified compound _{10 (C 3 H 7) 2} -P (= O) - (CH 2) 8 -Si- (OC 2 H 5) 3 example compound _{11 (C 5 H 11 O)} (C 3 H 7 O) -P ( _{= O) - (CH 2)} 13 -Si- (OC 2 H 5) 3 example compound _{12 (C 8 H 17 O)} 2 -P (= O) -O-P (= O) (OH) -Si ( OC ₂ H ₅ ) ₃ exemplified compound 13 (C ₈ H ₁₇ O) ₂ -P (= O) -O-Si- (OC ₂ H ₅ ) ₃ exemplified compound 14 (C ₈ H ₁₇ O) ₂ -P (= O) -P (= O) -O -Si (OC 2 H 5) 3

The titanate coupling agent which can be used in the present invention includes those represented by the following general formula.

[0027]

(RO) _n -Ti- (OR ') _{4-n wherein} RO is a hydrophilic group, R is an alkyl group and forms a ring with Ti. Often, OR 'is a hydrophobic group such as an amino acid, a phosphate group or an acyl group. Specific examples of the titanate coupling agent are shown below, but the titanate coupling agent is not limited to these.

[0028]

Embedded image

[0029]

Embedded image

[0030]

Embedded image

[0031]

Embedded image

[0032]

Embedded image

[0033]

Embedded image

[0034]

Embedded image

[0035]

Embedded image

[0036]

Embedded image

However, in the above structure, "Ti." Represents a lone electron in a titanium atom. In each of the above structural formulas, the functional group bonded to the left side of Ti is a hydrophilic group that interacts with the non-magnetic powder (this is considered to generate a hydroxyl group or active functional group having a strong affinity with the magnetic powder surface by hydrolysis. The functional group bonded to the right side is a hydrophobic group containing an amino group, a phosphate group or an acyl group that interacts with a binder or a solvent. Further, a plurality of the above functional groups may be contained in one molecule. Also, two or more of the above titanate coupling agents can be used in combination.

Such a silane coupling agent or a titanate coupling agent forms a strong chemical bond between the nonmagnetic powder and carbon black. The amount of these coupling agents used is, per 1000 g of non-magnetic powder,
For example, a range of 1 g to 20 g is appropriate,
Preferably, it is 1 g to 10 g.

The treatment of the non-magnetic powder with the coupling agent and the preparation of the coating solution include the following steps: (1) diluting the coupling agent with water to obtain a 0.5 to 1% by weight aqueous solution, A method of mixing well with a blender and then mixing with carbon black to form a coating solution, (2) dissolving a coupling agent in an appropriate organic solvent, mixing with a non-magnetic powder, and then mixing with carbon black. And the like to obtain a coating solution. At the time of the above-mentioned treatment, heating may be appropriately performed at the time of mixing the coupling agent with the non-magnetic powder and further mixing with the carbon black. The preparation method will be described later in detail.

[Non-Magnetic Powder] As the non-magnetic powder chemically bonded to carbon black, known ones can be used. For example, Japanese Patent Nos. 2,571,351 and 2,566,096 can be used.
Nos. 1 to 3 can be cited. Specifically, the nonmagnetic powder can be a needle-shaped metal oxide having a pH of 5 or more. These have high adsorptivity to functional groups, so that even a small amount of binder can be dispersed well, and the mechanical strength of the coating film can be increased. Further, the present invention is characterized in that the thixotropy of the coating solution required in the present invention is easily obtained from the shape effect. The particle size may be that described in the above-mentioned publication, but it is preferred that the particle size be as small as possible. Specific examples of these particles include particles such as titanium oxide and hematite.

The nonmagnetic powder has an oil absorption of 5 using DBP.
~ 100ml / 100g, preferably 10-80ml /
100 g, more preferably 20 to 60 ml / 100 g. Specific gravity is 1 to 12 g / cc, preferably 3 to 6 g / cc.
cc. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape. The ignition loss is preferably 20% by weight or less.

The nonmagnetic powder preferably has a Mohs hardness of 4 or more. The roughness factor of these powder surfaces is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2. The stearic acid (SA) adsorption amount is 1 to 20 μmol / m ² , more preferably ² to 15 μmol / m ² . The heat of wetting of the nonmagnetic powder in water at 25 ° C. is 200 erg / cm ² -60.
It is preferably in the range of 0 erg / cm ² . Also,
Any solvent can be used as long as it is within the range of the heat of wetting. The amount of water molecules on the surface at 100 to 400 ° C is suitably 1 to 10/100 °. Also,
The pH of the isoelectric point in water is preferably between 5 and 10, more preferably between 7 and 10.

At least a part of the surface of the nonmagnetic powder is made of Al
It is preferably coated with ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO. Among them, Al ₂ O ₃ , SiO ₂ , TiO
₂ , those coated with ZrO ₂ are particularly preferred. These coating compounds may be used in combination of two or more, or may be used alone.

[Carbon Black] Examples of the carbon black chemically bonded to the nonmagnetic powder in the present invention include:
Examples thereof include furnace for rubber, thermal for rubber, black for color, and acetylene black. Carbon black has a specific surface area of 5 to 500 m ² / g, DB
P oil absorption is 10 to 1500 ml / 100 g, particle size is 5
mμ to 300mμ, more preferably 5mμ to 100mμ,
More preferably, it is 5 mμ to 50 mμ. The pH of the carbon black is 2 to 10, the water content is 0.1 to 10% by weight, and the tap density is 0.1 to 1 g /
It is preferably ml. Specific examples of carbon black used in the present invention include those manufactured by Cabot Corp.
LACKPEARLS 2000, 1300, 100
0, 900, 800, 700, VULCAN XC-7
2. # 80, # 60, # 55, # 5 manufactured by Asahi Carbon Co., Ltd.
0, # 35, manufactured by Mitsubishi Chemical Corporation, # 3950B, # 24
00B, # 2300, # 900, # 1000, # 30,
# 40, # 10B, manufactured by Columbia Carbon, COND
UCTEX SC, RAVEN 150, 50, 40,
15 and the like. In addition, Ketjen Black EC and Ketjen Black ECD manufactured by Lion Aguso
-500, Ketjen Black ECDJ-600 and the like can be used in the same manner.

Among the above-mentioned carbon blacks, in particular, Conductex of Colombia Carbon Japan Co., Ltd.
ductex) 975 (BET value 250 m ² / g, particle size 24 m
μ), Conductex 900 (BET value 125 m ² /
g, particle size 24 mμ), Conductex 40-220
(Particle size 20mμ), Conductex SC (BET value 2
20 m ² / g, particle size 20 mμ), Cabot Valcan XC-72 manufactured by Cabot Corporation (BET value 25
4m ² / g, particle size 30mμ), Vulcan P (BET value 14
3 m ² / g, particle size 20 mμ), raben 1040, 42
0, black pearls 1000 (particle diameter 16 mμ), black pearls L, and conductive carbon black such as # 44 manufactured by Mitsubishi Chemical Corporation are preferred. When these carbon blacks have an oil absorption (DBP) of 90 ml / 100 g or more, it is preferable in that the carbon black easily has a structure structure and exhibits higher conductivity, but is preferably 110 to 200 ml / 100 g.
It is even more preferred that the value be g. The amount of carbon black chemically bonded to the non-magnetic powder depends on the amount of the non-magnetic powder 1
0.1 to 10 parts by weight, preferably 0.1 to 10 parts by weight, per 100 parts by weight.
It is in the range of 1 to 5 parts by weight.

Carbon black has the functions of preventing the non-magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength. These functions differ depending on the type of carbon black used. Therefore, carbon black used for the non-magnetic layer is
The type, amount, and combination of the particles can be appropriately changed, and the particle size, the oil absorption, the conductivity, the pH, and the like can be appropriately selected according to the purpose based on the above-described various properties. Carbon black that can be used in the nonmagnetic layer of the present invention is, for example, "Carbon black".
Bon Black Handbook "Carbon Black Association Edition" can be referred to. Carbon black may be used by grafting it with a resin, or one obtained by graphitizing a part of the surface. These carbon blacks can be used alone or in combination.

[Binder] The binder used in the nonmagnetic layer is as follows:
It may be the same as the magnetic layer described below, but more preferably contains a functional group that improves dispersibility. Further, it is more effective to use an aromatic phosphorus compound as a dispersing aid for accelerating dispersion in the inorganic powder. In addition, these techniques are described in more detail in Japanese Patent Nos. 25666088 and 2634792.

The weight B (L) of the binder in the non-magnetic layer is set to 25 parts or less, preferably 20 parts or less with respect to 100 parts by weight of the non-magnetic powder as the main component. The ratio with B (U) is 0.1 ≦ B (L) / B (U) ≦ 1.0, preferably 0.3
It is preferable that ≦ B (L) / B (U) ≦ 0.7. B (L) is 2
If it exceeds 5 parts, the degree of filling of the magnetic layer is reduced. Also B (L) / B
When (U) is larger than 1, not only the surface roughness increases, but also it becomes impossible to apply a thin magnetic layer by simultaneous multilayer coating.
If less than 0.1, the amount of the binder in the nonmagnetic layer is too small, and the mechanical strength of the coating film cannot be secured,
Powder fall occurs.

In the non-magnetic layer of the present invention, as a binder, the following polyisocyanate, tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-
Isocyanates such as toluidine diisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, products of these isocyanates and polyalcohol, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Ltd., Takenate D-102, Takenate D- 1
10N, Takenate D-200, Takenate D-20
2. Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc., manufactured by Sumitomo Bayer Co., Ltd., and these are used alone or in combination of two or more using the difference in curing reactivity. Can be used. These polyisocyanates can also be used as a binder for a magnetic layer described later.

In addition, an abrasive may be added to the non-magnetic layer. As an abrasive, α-alumina, β-alumina having an α conversion of 90% or more, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium, carbide, Titanium oxide,
Known materials having a Mohs hardness of 6 or more, such as silicon dioxide and boron nitride, are used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% by weight or more. The tap density is 0.3-2 g / ml, and the water content is 0.1.
1-5% by weight, pH 2-11, specific surface area 1-30m
It is preferably in the range of ² / g. The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specific examples of the abrasive include AKP-20, AKP-30, and AKP-50, manufactured by Sumitomo Chemical Co., Ltd.
HIT-50, HIT-100, manufactured by Nippon Chemical Industry Co., Ltd., G
5, G7, S-1, Toda Kogyo KK, TF-100, TF
-140 and the like. The abrasive used in the present invention can be of different types, amounts and combinations for the magnetic layer and the non-magnetic layer, and it is of course possible to selectively use them according to the purpose. These abrasives may be added to the magnetic paint after dispersion treatment with a binder in advance. A known lubricant can be added to the non-magnetic layer. The lubricant will be described in detail when describing the magnetic layer.

Magnetic Layer The magnetic layer of the magnetic recording medium of the present invention is not particularly limited except that it contains a magnetic powder and a binder. [Magnetic powder] As the magnetic powder contained in the magnetic layer, γ-
FeOx (x = 1.33-1.5), Co-modified γ-FeO
x (x = 1.33-1.5), Fe or Ni or Co
Well-known ferromagnetic powders such as ferromagnetic alloy fine powder containing barium as a main component (75% or more), barium ferrite, and strontium ferrite can be used. However, ferromagnetic alloy powder containing α-Fe as a main component and hexagonal ferrite such as barium ferrite are preferable. In particular, as described above, the ferromagnetic powder contained in the upper magnetic layer is an alloy magnetic powder mainly composed of Fe or a magnetoplumbite-type hexagonal ferrite, and the ferromagnetic powder contained in the lower magnetic layer is mainly composed of Fe. It is preferable from the viewpoint of improving the reproduction output in short-wavelength recording that the magnetic powder is an alloy magnetic powder. These ferromagnetic powders include Al, Si, S, Sc, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B. These ferromagnetic fine powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. To be more specific,
No. 4090, JP-B-45-18372, JP-B-47-22062, JP-B-47-22513, JP-B-46-28466,
JP-B-46-38755, JP-B-47-4286, JP-B-4
No. 7-12422, Japanese Patent Publication No. 47-17284, Japanese Patent Publication No. 47-1850
No. 9, JP-B-47-18573, JP-B-39-10307, JP-B-48-39639, U.S. Patent No. 3026215, U.S. Patent No. 3031341, U.S. Patent No. 3,100,194, and U.S. Patent No. 324200
No. 5, 3,389,014 and the like.

Among the above ferromagnetic powders, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy fine powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low-pressure inert gas And how to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

The ferromagnetic powder of the magnetic layer of the present invention is subjected to the BET method.
25-80m in terms of specific surface area ^Two/ G, preferred
Or 40-70m^Two/ G. 25m^Two/ G or less
Noise rises, 80m^Two/ G or more gives good surface properties
Unfavorable. The ferromagnetic powder particles of the magnetic layer of the present invention
The crystallite size is 450 to 100 angstroms,
Preferably it is 350 to 100 angstroms. acid
Σs of the iron oxide magnetic powder is 50 emu / g or more, preferably
70 emu / g or more, in the case of ferromagnetic metal fine powder
Is preferably 100 emu / g or more, more preferably
It is 110 emu / g to 170 emu / g. Upper layer magnetism
When ferromagnetic powders with different σs are used for the lower layer and the lower magnetic layer
Is 50 to 140 emu / g for the upper layer and 100 to 1 for the lower layer.
It is preferably in the range of 70 emu / g. Coercive force is
The upper layer is preferably 2,000 Oe or more and 4000 Oe or less.
Preferably it is 2000 Oe or more and 3000 Oe or less. strength
The needle ratio of the magnetic powder is 18 or less, more preferably 12 or less.
It is.

The ferromagnetic powder preferably has an r3000 of 1.5 or less. More preferably, r3000 is 1.
0 or less. r3000 indicates the% of the amount of magnetization remaining without being reversed when a magnetic field of 3000 Oe is applied in the opposite direction after the magnetic recording medium is saturated. The water content of the ferromagnetic powder is preferably 0.01 to 2% by weight. It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. Tap density of gamma iron oxide is 0.5g
/ Ml or more, more preferably 0.8 g / ml or more. In the case of an alloy powder, the amount is preferably 0.2 to 0.8 g / ml, and if it is used at 0.8 g / ml or more, oxidation tends to proceed in the process of compacting the ferromagnetic powder, and it becomes difficult to obtain a sufficient σs. If the tap density is 0.2 g / ml or less, dispersion tends to be insufficient.

When γ iron oxide is used, the ratio of divalent iron to trivalent iron is preferably 0 to 20%, more preferably 5 to 10%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 2 to 8%. Preferably, the pH of the ferromagnetic powder is optimized by the combination with the binder used. Its range is from 4 to 12, preferably from 6 to 10. A ferromagnetic powder can be used if necessary.
Surface treatment may be performed with l, Si, P, or an oxide thereof. The amount is 0.1 to
When the surface treatment is performed, the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less, which is preferable. The ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr, but if it is 500 ppm or less, there is no particular effect on the characteristics.

The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of acicular, granular, rice granular, and plate-like shapes as long as the above-mentioned characteristics regarding the particle size are satisfied. In the case of acicular ferromagnetic powder, the acicular ratio is preferably 12 or less. SFD (Swiching Field Distribution) of this ferromagnetic powder
In order to achieve 0.6 or less, it is necessary to reduce the distribution of Hc in the ferromagnetic powder. For this purpose, there are methods such as improving the particle size distribution of goethite, preventing sintering of γ-hematite, and lowering the deposition rate of cobalt on cobalt-modified iron oxide as compared with the conventional method.

The present invention also provides barium ferrite, strontium ferrite as plate-like hexagonal ferrite,
Substitutes of lead ferrite and calcium ferrite, Co
Hexagonal Co powder such as a substituted body can be used. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, and further include a magnetoplumbite-type barium ferrite and strontium ferrite that further contain a spinel phase, and particularly preferred are barium ferrite and strontium ferrite. It is a Co substitute. Further, in order to control the coercive force, Co-Ti, Co-Ti-Zr,
A material to which an element such as Co-Ti-Zn, Ni-Ti-Zn, Ir-Zn is added can be used. Hexagonal ferrite is usually hexagonal plate-like particles, and the particle size means the width of the plate of hexagonal plate-like particles, and is measured using an electron microscope.

In the present invention, the particle diameter is 0.01 to 0.2 μm.
m, particularly preferably in the range of 0.03 to 0.1 μm. The average thickness (plate thickness) of the fine particles is about 0.001 to 0.2 μm, and particularly 0.003 to 0.2 μm.
~ 0.05 μm is preferred. Further, the tabular ratio (particle size / plate thickness) is 1 to 10, preferably 3 to 7. The specific surface area (SBET) of these hexagonal ferrite fine powders by the BET method is preferably from 25 to 70 m ² / g.

The average value d of the magnetic layer thickness is 0.01 to 0.3.
μm, preferably 0.01 to 0.2 μm, more preferably 0.01 to 0.1 μm. The present invention can be used with a single magnetic layer or a plurality of magnetic layers.

In the case of a plurality of magnetic layers, see, for example,
A technique such as 39555 can be applied. In the present invention, since the magnetic layer thickness is small and the recording state is saturated, it is ideal that the magnetic layer thickness does not fluctuate.
If the relationship between d and d is σ / d ≦ 0.5, it is practically acceptable. More preferably, σ / d ≦ 0.3.

A specific means for reducing σ is disclosed in Japanese Patent No. 256
No. 6096, a needle-like nonmagnetic powder is used for the lower layer so as to impart thixotropic properties to the nonmagnetic layer coating solution. In addition to the method and the like, in the present invention, the amount of the binder in the non-magnetic layer and the amount of the binder in the magnetic layer, which will be described later, are specified, so that a magnetic recording medium can be obtained more favorably.

The residual magnetization of the magnetic layer is 0.0005 to 0.0005.
It is preferably 0.005 emu / cm ² . This residual magnetization amount can be optimized according to the recording / reproducing method. Various methods can be used to set the amount of residual magnetization in the above range. For example, when reproducing the medium with a conventional inductive head, it is preferable to set a relatively large value in the range of the residual magnetization. Set the magnetic layer thinner (for example, 0.1μ
m) or less, the magnetic powder has a large σs (140
~ 160 emu) It is preferable to use alloy powder.

On the other hand, when reproducing with an MR head, it is preferable to increase the number of particles and set the amount of residual magnetization to a smaller value in the above range.

In this case, the σs of the magnetic powder is 50
It is preferable to use a material having a particle size of ~ 130 emu / g and improve the packing density as much as possible by reducing the amount of the binder in the upper layer / lower layer. The magnetic powder used has a σs of 100
Alloy powder of １３０130 emu / g, σs of 50 to 80 em
u / g hexagonal ferrite, magnetite, and Co-ferrite.

The coercive force Hc of the magnetic layer is 1500 to 40
00 Oe, preferably 1800 to 3500 Oe, more preferably 2000 to 3000 Oe, and the magnetic powder preferably has the same Hc.

The size of the magnetic particles is preferably reduced as far as the influence of thermal fluctuation does not occur, and this does not depend on the type of reproducing head used.

When needle-like particles are practically used, the average major axis length is 0.05 to 0.2 μm, and the minor axis diameter is 0.01 to 0.2 μm.
025 μm is the current state. For hexagonal ferrite,
Plate diameter 0.01-0.2μm, thickness 0.001-0.1μm
Is the current situation. The preferred range is not limited to the above range, and it can be used if it becomes smaller as the technology advances.

The magnetic powder contains Al, S,
i, S, Sc, Ti, V, Cr, Cu, Y, Mo, R
h, Pd, Ag, Sn, Sb, Te, Ba, Ta, W,
Re, Au, Hg, Pb, Bi, La, Ce, Pr, N
It may contain atoms such as d, P, Co, Mn, Zn, Ni, Sr, and B. Al, S for improving thermal stability
i, Ta, Y, etc. can be adhered to the surface or solid-solved. In particular, in order to increase Hc, Co, Sm, Nd
And the like can be added in an amount of 5 to 40% by weight based on Fe.

These magnetic powders include a dispersant, a lubricant,
A treatment with a surfactant, an antistatic agent or the like may be performed before dispersion.

[Binder] Known binders can be used as the binder contained in the magnetic layer. For example, Japanese Patent No. 256
No. 6096 and No. 2571351 can be used. These binders preferably contain a functional group (SO ₃ M, PO ₃ M, etc.) that promotes adsorption to the magnetic powder, and those containing an epoxy group are also preferable. The molecular weight of the binder used is 10,000 to 100,000, preferably 20,000 in weight average molecular weight.
６０60,000. The weight average molecular weight of the binder resin was determined by gel permeation chromatography (G
PC) or the like. The amount of the binder resin used is 5 to 25 parts per 100 parts by weight of the magnetic powder.
Parts, preferably 5 to 20 parts, more preferably 5 to 15 parts.
It is preferable to use a part.

Specifically, examples of the above-mentioned binder include the following resins, and resins obtained by modifying the following resins by bonding the above-described functional groups thereto. Specifically, as these resins, for example,
For thermoplastic resin, polyvinyl chloride, ethylene vinyl acetate copolymer, polyvinyl acetate, polyvinyl acetal such as polyvinyl alcohol, vinyl butyral, polyvinyl formal, polyvinyl benzal of various degrees of saponification, polystyrene, acrylonitrile styrene copolymer Styrene butadiene rubber (SBR) and carboxylated styrene butadiene rubber;
Acrylonitrile butadiene styrene copolymer (AB
S), various acrylic copolymer resins, styrene acrylic copolymers, methacrylic resins such as polymethyl methacrylate, polycarbonate resins, copolymerized polycarbonate resins, copolymerized polyarylate resins, polyester resins, and polyamide resins. These resins are
Two or more kinds may be appropriately used in combination.

Examples of the thermosetting resin used as the above-mentioned binder include an epoxy resin, a urethane resin, a thermosetting polyester resin and the like, and those obtained by appropriately modifying these. It is also possible to use these thermoplastic resins and thermosetting resins in an appropriate mixture.

Further, in the present invention, the magnetic layer may contain a known abrasive; α-alumina, Cr ₂ O _3, etc., and the average particle size of these particles is wet-on-wet coating. Preferably, the thickness is 1/3 or more and 5 times or less of the thickness, and in wet on dry coating, it is 1/3 or more and 2 times or less of the thickness of the magnetic layer. If it is too large, it causes thermal asperity. Particularly in the case of wet-on-dry coating, the abrasive is liable to become projections, so that fine particles are preferred. Known techniques can be used for pH and surface treatment.

The magnetic layer may further include a solid lubricant, specifically, carbon or carbon black having a particle size of 30 μm or more.
Liquid lubricants such as Teflon powder and fatty acids and fatty acid esters can be added. Carbon black can be appropriately selected from those described above. However, carbon black has the functions of preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, improving the film strength, and the like, and these differ depending on the carbon black used. Therefore, the carbon black used for the magnetic layer, the kind, the amount, the combination is appropriately changed, the particle size,
Of course, it is possible to use differently according to the purpose based on the above-mentioned various properties such as oil absorption, conductivity, pH and the like. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

[Additives] Various additives other than those described above can be added to the magnetic layer and the nonmagnetic layer of the present invention. As the additive used, for example, those having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, silicone with polar groups, fatty acid-modified silicone, fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and Its alkali metal salts, alkyl sulfates and its alkali metal salts, polyphenyl ethers,
Fluorine-containing alkyl sulfates and alkali metal salts thereof, monobasic fatty acids having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched), and metal salts thereof (Li, Na, K , Cu, etc.) or carbon number 1
Monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent alcohols of 2 to 22 (which may contain an unsaturated bond or may be branched), alkoxy alcohols having 12 to 22 carbon atoms , A monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and monovalent, divalent, trivalent, tetravalent, pentavalent having 2 to 12 carbon atoms Mono- or di-fatty acid esters, tri-fatty acid esters, or monoalkyl ethers of alkylene oxide polymers consisting of any one of a hexavalent alcohol (which may contain an unsaturated bond and may be branched) And fatty acid amides having 8 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms.

Specific examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, Isooctyl stearate, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol-ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums or sulfoniums , Such as cationic surfactants, carboxylic acids, sulfonic acids,
Anionic surfactants containing acidic groups such as phosphoric acid, sulfate ester groups and phosphate ester groups, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and amphoteric surfactants such as alkyl betaine type can also be used.

These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
Instead of being 0% pure, impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. may be contained in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

These lubricants and surfactants used in the present invention can be used in a non-magnetic layer and a magnetic layer in different types and amounts as needed. For example, controlling bleeding to the surface using fatty acids with different melting points in the non-magnetic layer and magnetic layer, controlling bleeding to the surface using esters with different boiling points and polarities, adjusting the amount of surfactant It is possible to improve the stability of application by doing, to improve the lubrication effect by increasing the amount of lubricant added in the non-magnetic layer, etc., but is not limited to the examples shown here . All or some of the additives used in the present invention may be added at any step of the production of the magnetic paint. For example, when mixing with ferromagnetic powder before the kneading step,
When added in the kneading step with ferromagnetic powder, binder and solvent, when added in the dispersion step, when added after dispersion,
In some cases, it is added immediately before coating. In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Further, depending on the purpose, a lubricant can be applied to the surface of the magnetic layer after calendering or after slitting.

Commercial examples of these lubricants used in the present invention include NAA-102 and NAA-4 manufactured by NOF Corporation.
15, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, Cation SA, Cation MA, Cation A
B, cation BB, Nymin L-201, Nymin L-202, Nymin S-202, Nonion E-20
8, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-6
0, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku, oleic acid, manufactured by Takemoto Yushi, FAL-205, FAL-123,
NJRUB LO, NJRUBIP manufactured by Shin Nippon Rika Co., Ltd.
M, Sansocizer-E4030, manufactured by Shin-Etsu Chemical Co., Ltd., TA-
3, KF-96, KF-96L, KF96H, KF41
0, KF420, KF965, KF54, KF50, K
F56, KF907, KF851, X-22-819,
X-22-822, KF905, KF700, KF39
3, KF-857, KF-860, KF-865, X-
22-980, KF-101, KF-102, KF-1
03, X-22-3710, X-22-3715, KF
-910, KF-3935, manufactured by Lion Armor, Armide P, Armide C, Armoslip CP, manufactured by Lion Yushi, Duomin TDO, manufactured by Nisshin Oil, BA
-41G, manufactured by Sanyo Kasei Co., Ltd., Profan 2012E, Newpole PE61, Ionet MS-400, Ionet MO-200, Ionet DL-200, Ionet DS-300, Ionet DS-1000, Ionet DO-200 and the like. it can.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol and isopropyl alcohol. , Alcohols such as methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate,
Ester such as glycol acetate, glycol dimethyl ether, glycol monoethyl ether, glycol ether such as dioxane, benzene, toluene, xylene, cresol, aromatic hydrocarbons such as chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, Chlorinated hydrocarbons such as chloroform, ethylene chlorohydrin, dichlorobenzene, and the like, N, N-dimethylformamide, hexane, and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The kind of the organic solvent used in the present invention is preferably the same for the magnetic layer and the non-magnetic layer, but the amount thereof may be changed. Use a solvent with a high surface tension (cyclohexanone, dioxane, etc.) for the non-magnetic layer to improve coating stability. Specifically, the arithmetic average of the surface tension of the upper solvent composition is the arithmetic average of the surface tension of the lower solvent composition It is preferable not to fall below. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that the solvent composition contains 50% or more of a solvent having a dielectric constant of 15 or more. Further, the solubility parameter is preferably from 8 to 11.

The thickness of the magnetic recording medium of the present invention will be described.
It is preferably from 100 to 100 μm, more preferably from 4 to 80 μm. The total thickness of the magnetic layer and the nonmagnetic layer is used in a range of 1/100 to 2 times the thickness of the nonmagnetic support.
It is also possible to provide an undercoat layer between the nonmagnetic support and the nonmagnetic layer for improving adhesion.

The undercoat layer has a thickness of 0.01 to 2
μm, and more preferably 0.02 to 0.5 μm. Further, a back coat layer may be provided on the side of the non-magnetic support opposite to the side of the magnetic layer. This thickness is 0.1 to 2 μm, preferably 0.3 to 1.0 μm. Known undercoat layers and backcoat layers can be used.

[Non-magnetic support] Examples of the non-magnetic support used in the present invention include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide and polyamide. Known films such as imide, polysulfone, aramid, and aromatic polyamide can be used. These supports have a corona discharge treatment, a plasma treatment, an easy adhesion treatment,
Heat treatment, dust removal treatment, or the like may be performed.

To achieve the object of the present invention, a non-magnetic support
In the surface roughness spectrum measured by AFM as a body
Roughness intensity of 1 nm to 5 μm is 0.2 nm^TwoBelow, preferably
Is 0.15 nm^TwoHereinafter, more preferably 0.1 nm^TwoLess than
Below, the roughness intensity of wavelength 0.5 μm to 1 μm is 0.02 to
0.1nm^Two, Preferably 0.04 nm^Two~ 0.08 nm
^TwoYou need to use what is. Surface roughness shape
Depends on the size and amount of filler added to the support.
It can be controlled for any reason. These fillers
Specifically, for example, oxidation of Ca, Si, Ti, etc.
In addition to organic substances and carbonates, organic fine powders such as acrylic
be able to. The non-magnetic support used in the present invention is
In the case of a loop, the F-5 value in the running direction is preferably 5 to 50.
kg / mm^Two, The F-5 value in the width direction is preferably 3 to 3
0 kg / mm^TwoAnd the F-5 value in the longitudinal direction of the tape is
-Generally, the value is higher than the F-5 value in the width direction.
When it is necessary to increase the strength in the width direction,
Absent.

The heat shrinkage of the support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and 80 ° C. for 30 minutes. The heat shrinkage is preferably 1% or less, more preferably 0.5% or less. Breaking strength 5-100 in both directions
kg / mm ^2, it is preferable that the elastic modulus is the 100 to 2,000 kg / mm ^2.

[Manufacturing Method of Magnetic Recording Medium] The magnetic recording medium of the present invention basically comprises a coating for a non-magnetic layer containing a non-magnetic powder, carbon black and a binder on a non-magnetic support. And a magnetic layer paint containing a magnetic powder and a binder are sequentially applied. In particular, the present invention provides a method for dispersing a non-magnetic powder and carbon black in a binder in which the non-magnetic layer paint is chemically bonded using a treating agent selected from a silane coupling agent and a titanate coupling agent. It is characterized in that it is obtained by performing The chemical bond between the non-magnetic powder and carbon black is
As described above, for example, a non-magnetic powder is treated with a silane coupling agent or a titanate coupling agent, and then carbon black is added to the silane coupling agent or the titanate coupling agent bonded to the non-magnetic powder. It can be performed by bonding. The step of producing the paint for the magnetic layer and the paint for the non-magnetic layer of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each of the steps may be performed in two or more stages. Raw materials such as a ferromagnetic powder, a binder, carbon black, an abrasive, an antistatic agent, a lubricant, and a solvent used in the present invention may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, the polyurethane may be separately charged in the kneading step, the dispersing step, and the mixing step for adjusting the viscosity after dispersion. A nonmagnetic powder abrasive chemically bonded to ferromagnetic powder or carbon black may be dispersed in a binder before being added to the paint.

In order to achieve the object of the present invention, it is needless to say that a conventional known manufacturing technique can be used as a part of the process. However, in the kneading process, a continuous kneader or a pressure kneader is used. It is preferable to use a material having a strong kneading force in order to obtain a higher residual magnetic flux density (Br). When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (however, preferably 30% or more of the total binder) and 100 parts by weight of the ferromagnetic powder are used. The kneading treatment is performed in the range of 15 to 500 parts by weight. The details of these kneading treatments are described in JP-A-1-10633.
No. 8 and JP-A-64-79274. When preparing the non-magnetic layer liquid, it is desirable to use a dispersion medium having a high specific gravity, and zirconia beads are suitable.

The following configuration can be proposed as an example of an apparatus and method for applying a magnetic recording medium having a multilayer configuration as in the present invention.

1. First, a non-magnetic layer is applied by a gravure coating, roll coating, blade coating, extrusion coating device or the like generally used in the application of a magnetic paint, and the non-magnetic layer is wet while the non-magnetic layer is in a wet state. And JP-A-60-238179,
1. coating a magnetic layer with a support pressure type extrusion coating apparatus disclosed in Japanese Patent No. 65672; JP-A-63-88080, JP-A-2-179
No. 71, Japanese Unexamined Patent Publication No. 2-265672, and the like, in which the upper and lower layers are coated almost simultaneously by one coating head having two built-in coating liquid passage slits; An example in which the upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll disclosed in Japanese Patent Application Laid-Open No. 174965/1990.

Incidentally, in order to prevent a decrease in the electromagnetic conversion characteristics and the like of the magnetic recording medium due to the aggregation of the magnetic particles, Japanese Patent Application Laid-Open No.
It is desirable to apply shear to the coating liquid inside the coating head by a method disclosed in Japanese Patent Application Laid-Open No. 95174 or Japanese Patent Application Laid-Open No. 1-236968. Further, the viscosity of the coating solution preferably satisfies the numerical range disclosed in JP-A-3-8471. In order to obtain the magnetic recording medium of the present invention, it is necessary to perform strong orientation.
Therefore, it is preferable to use a solenoid of 1000 G or more and a cobalt magnet of 2000 G or more in the same polarity facing each other, and it is preferable to provide an appropriate drying step before orientation so that the orientation after drying is the highest. . When the present invention is applied to a disk medium, an orientation method for randomizing the orientation is required. Further, the direction of orientation for changing the orientation direction of the magnetic layer and the non-magnetic layer does not necessarily have to be the longitudinal direction and the in-plane direction, but can be oriented in the vertical direction and the width direction.

Further, it is preferable to use a heat-resistant plastic roll such as epoxy, polyimide, polyamide or polyimide amide as the roll for calendering. Further, the treatment can be carried out with metal rolls. The processing temperature is preferably 70 ° C. or higher, more preferably 8 ° C.
0 ° C. or higher. The linear pressure is preferably 200 kg / c
m, more preferably 300 kg / cm or more. In the magnetic recording medium of the present invention, the friction coefficient of the magnetic layer surface and the opposite surface to SUS420J is preferably 0.5 or less, more preferably 0.3 or less, and the surface resistivity is preferably 10 ⁴ to 10 ¹² ohm / □. The elastic modulus at 0.5% elongation of the magnetic layer in the running direction and the width direction is preferably 100 to 2000 kg / mm ² , the breaking strength is preferably 1 to 30 kg / cm ² , and the elastic modulus of the magnetic recording medium is 100 to 1500 kg, preferably in the length direction
/ Mm ² , the residual elongation is preferably 0.5% or less, 100% or less.
The heat shrinkage at any temperature below ℃ is preferably below 1%, more preferably below 0.5% and most preferably below 0.1%. The glass transition temperature of the magnetic layer (110
Hz), the maximum point of the loss elastic modulus in the dynamic viscoelasticity measurement is preferably from 50 ° C to 120 ° C, and the glass transition temperature of the nonmagnetic layer is preferably from 0 ° C to 100 ° C. The loss modulus is preferably in the range of 1 × 10 ⁸ to 8 × 10 ⁹ dyne / cm ² , and the loss tangent is preferably 0.2 or less. This is because if the loss tangent is too large, adhesion failure is likely to occur.

The residual solvent contained in the magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ^2.
m ² or less, and the residual solvent contained in the second layer is preferably smaller than the residual solvent contained in the first layer. The porosity of both the nonmagnetic layer and the magnetic layer is preferably 30% by volume or less, more preferably 20% by volume or less. The porosity is preferably small in order to achieve high output, but it may be better to secure a certain value depending on the purpose. For example, in a magnetic recording medium for data recording in which repetitive use is emphasized, a higher porosity is often preferable in running durability. When the magnetic properties of the magnetic recording medium of the present invention were measured at a magnetic field of 5 KOe, the squareness ratio in the tape running direction was 0.70 or more.
Preferably it is 0.80 or more, more preferably 0.90 or more.

The squareness ratio in two directions perpendicular to the tape running direction is preferably 80% or less of the squareness ratio in the running direction. SFD (Swiching Field Distribution) of magnetic layer
Is preferably 0.6 or less.

In the roughness spectrum, the surface of the magnetic layer has a roughness component intensity of 0.2 nm ² or less at a wavelength of 1 to 5 μm,
The intensity of the roughness component at a wavelength of 0.5 to 1.0 μm is 0.02 to
0.1 nm ² . To improve the CNR (C / N), the smaller the roughness intensity is, the more preferable it is. However, to improve the running durability, the roughness intensity in the wavelength range of 0.5 to 1.0 μm is 0.1 μm. it is necessary to keep in 02~1.0nm ^2.

Although the magnetic recording medium of the present invention has a non-magnetic layer and a magnetic layer, it is easily presumed that the physical properties of the non-magnetic layer and the magnetic layer can be changed according to the purpose.
For example, the elastic modulus of the magnetic layer is increased to improve running durability, and at the same time, the elastic modulus of the non-magnetic layer is made lower than that of the magnetic layer to improve the contact of the magnetic recording medium with the head. What kind of physical properties are to be provided to each of the two or more magnetic layers can be referred to a known technique regarding the magnetic layer. For example, when a multilayer magnetic layer is used, many inventions such as Japanese Patent Publication No. 37-2218 and Japanese Patent Application Laid-Open No. 58-56228 disclose making the Hc of the upper magnetic layer higher than the Hc of the lower magnetic layer. However, by making the magnetic layer thinner as in the present invention, recording becomes possible even with a higher Hc magnetic layer.

[0096]

Next, the details of the present invention will be specifically described with reference to examples. In the examples, "parts" indicates "parts by weight".
Means

Adhesion treatment of non-magnetic powder to carbon black 1) Coupling agent treatment 100 parts by weight of the non-magnetic powder described in Table 1 were put into a planetary mixer, and the coupling agent was added to the mixture while rotating the blade. 0.5 parts by weight were added as described.
The water-cooled jacket of the planetary mixer container has 50
Mixing was carried out for 2 hours while flowing hot water at ℃. As the coupling agent, one having the following chemical structure was used.

[0098]

Embedded image (HO) ₂ -P (= O)-(CH ₂ ) ₄ -Si- (OC ₂ H ₅ ) ₃

[0099]

Embedded image

2) Carbon Attachment Treatment 100 parts by weight of the nonmagnetic powder subjected to the coupling agent treatment and 5 parts by weight of carbon black were treated with a hybridizer to attach carbon black to the surface of the nonmagnetic powder. In the above-mentioned coupling treatment and carbon attachment treatment, powder having the following characteristics was used. Carbon black (A) (# 3030B, manufactured by Mitsubishi Chemical Corporation) Average primary particle size 55 nm DBP oil absorption 130 ml / 100 g Non-surface area by BET method 29 m ² / g A: Titanium oxide Long axis length: 0.08 μm Crystal type: Rutile TiO ₂ content 90% or more Surface treatment layer: Al ₂ O ₃ specific surface area: 80 m ² / g B: hematite Long axis length: 0.15 μm Surface treatment layer: Al ₂ O ₃ , SiO ₂ specific surface area: 52 m ² / G pH 8

[0101]

[Table 1]

(Example 1) Manufacture of single-layer magnetic layer Ferromagnetic metal fine powder 100 parts Composition Fe / Co = 70/30 Hc 2250 Oe, specific surface area by BET method 45 m ² / g Crystal size 170Å Surface treatment agent Al ₂ O ₃ , Y ₂ O ₃ particles Size (major axis diameter) 0.09 μm Needlelike ratio 8 σs: 150 emu / g

Vinyl chloride copolymer 10 parts (MR-110 manufactured by Nippon Zeon) Polyurethane defatting (UR-8200 manufactured by Toyobo) 6 parts α-Al ₂ O ₃ (average particle size 0.15 μm) 5 parts carbon black ( 0.5 part Butyl stearate 1 part Stearin Shun 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts Toluene 60 parts

The components having the above composition were kneaded with an open kneader, and then dispersed using a sand mill. 5 parts of a polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to the obtained dispersion, and 40 parts of a mixed solvent of methyl ethyl ketone-cyclohexanone was added to the dispersion, followed by filtration using a filter having an average particle diameter of 1 μm. Then, a coating solution was prepared.

[0105] 2. Manufacture of lower coating layer (non-magnetic) Non-magnetic powder 80 parts Carbon black (A) 0 parts Carbon black (B) 12 parts Average primary particle diameter 16 nm DBP oil absorption 120 ml / 100 g pH 8.0 Specific surface area by BET method 250 m ² / g Volatile content 1.5%

Vinyl chloride copolymer 12 parts (MR-104 manufactured by Zeon Corporation) Polyester polyurethane resin having a cyclic structure and a polyether group 5 parts α-Al ₂ O ₃ (average particle size 0.2 μm) 1 part Ethyl steer Rate 1 part Stearin Hayao 1 part Ethyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts

For each of the above paints, each component was kneaded with an open kneader and then dispersed using a sand mill. 5 parts of a polyisocyanate (Coronate L manufactured by Nippon Polyurethane) was added to the obtained nonmagnetic layer dispersion, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone was added to the dispersion, followed by filtration using a filter having an average pore diameter of 1 μm. Then, a lower layer coating layer and a coating solution for forming a magnetic layer were respectively prepared. The obtained lower layer coating solution was applied so that the thickness after drying was 1.5 μm. Immediately after that, a 5.2 μm thick magnetic layer coated surface and a center line surface roughness of 0.001 μm on the polyethylene naphthalate support were simultaneously overlaid thereon so that the magnetic layer thickness would be 0.2 μm. Coating, and while both layers are still wet, a cobalt magnet with a magnetic force of 5000 G and 4000
It was oriented by a solenoid having a magnetic force of G. After drying,
200m / mi / min at a temperature of 100 ° C using a seven-stage calender composed of a metal roll and an epoxy resin roll.
n. Thereafter, a back layer having a thickness of 0.5 μm was applied. After slitting to a width of 8 mm, a sample was prepared.

Using the sample prepared as described above, the electromagnetic conversion characteristics, surface properties, and surface electric resistance were evaluated.
The conditions for each measurement are as follows. 1. Electromagnetic conversion characteristics: A 7 MHz signal was recorded on a sample tape using a VTR (FJIX8, manufactured by Fuji Photo Film) and reproduced. 7MH recorded on the reference tape of Comparative Example 7
The relative playback output of the tape when the playback output of z was 0 dB was measured. For C / N, the noise spectrum was measured using a spectrum analyzer manufactured by Shibasoku. For the output of 7MHz carrier signal,
The ratio to the noise level 1 MHz away was taken as C / N. 2. Surface Ra (nm) Measured using 3d-MIRAU, which is measured in a non-contact manner by a light sweating method. Ra of an area of 250 nm square was measured using TOPO3D (trade name) manufactured by WYKO. The measurement wavelength is
Spherical and cylindrical corrections were made at 650 nm. 3. Surface electric resistance (Ω / □) 10 m of 8 mm wide sample was measured using a digital surface electric resistance meter TR-8611A (manufactured by Takeda Riken, trade name).
Measurements were taken between two electrodes with a cross section of m quadrants and spaced 8 mm apart. Table 2 shows the measurement results. As shown in Table 2, the magnetic recording medium of the present invention has a good C / N ratio, excellent surface properties, sufficiently low surface electric resistance, and can prevent charging of the magnetic recording medium. Met.

(Examples 2 to 5) Table 1
Non-magnetic powder C, using titanium oxide, hematite, silane coupling agent and titanate coupling agent shown in
D, E, and F were prepared, a magnetic recording medium was prepared using these powders in the same manner as in Example 1, and the evaluation was performed in the same manner as in Example. As shown in Table 2, good characteristics were obtained. Obtained.

Comparative Examples 6 to 10 As comparative examples, magnetic recording media were prepared in the same manner as in Example 1 except that nonmagnetic powder was not treated with a coupling agent as in the present invention. Evaluation was performed in the same manner as in Example 1. Table 2 shows the results. As shown in Table 2, it was shown that all the magnetic recording media using no nonmagnetic powder of the present invention had high resistance and were inferior in chargeability. Comparative Example 8 is a comparative example in which a non-magnetic powder and a silane coupling agent were simply mixed without being treated as in the present invention as a sample to prepare a magnetic recording medium. As shown in Table 2, Comparative Example 8 has a higher surface resistance than Examples 1 to 5 of the present invention obtained by treating a nonmagnetic powder with a coupling agent.

4. Confirmation that carbon black is chemically bonded to non-magnetic powder The non-magnetic layer coating solution used in Example 1 and Comparative Example 8 of the present invention was subjected to ultracentrifugation at 15,000 rpm. On this occasion,
The nonmagnetic powder having a large specific gravity settled at the bottom. The nonmagnetic powder was taken out, 4 g of methyl ethyl ketone was added to 1 g of the nonmagnetic powder, and ultracentrifugation was performed again under the same conditions. After the nonmagnetic powder was taken out and the solvent was removed by vacuum degassing, the powder was examined for fluorescent X-rays. As a result, although carbon was detected from the powder obtained from Example 1 of the present invention, carbon was not detected from the powder obtained from Comparative Example 8.

[0112]

[Table 2]

[0113]

According to the present invention, it is preferable to use a structure in which carbon black is previously bonded to a non-magnetic powder such as hematite or titanium oxide added to the non-magnetic layer and dispersed in a binder. High C / N ratio, excellent surface properties, and low surface resistance even with a small amount of carbon black added. A superior magnetic recording medium can be provided.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 4J037 AA02 AA15 AA22 CB23 CB26 CC26 DD05 DD07 DD17 EE02 EE28 EE43 EE48 FF05 FF11 5D006 BA01 CA02 CA04 CA05 5D112 AA03 AA22 BD02 BD03 BD07 BD09

Claims (4)

[Claims] 1. A non-magnetic support comprising a non-magnetic layer containing a non-magnetic powder, carbon black and a binder, and a magnetic layer containing a magnetic powder and a binder sequentially laminated on a non-magnetic support. In a magnetic recording medium, the nonmagnetic powder and carbon black are chemically bonded. 2. The magnetic recording medium according to claim 1, wherein the non-magnetic powder is selected from hematite and titanium oxide. 3. The method according to claim 1, wherein the nonmagnetic powder and the carbon black are chemically bonded using a treating agent selected from a silane coupling agent and a titanate coupling agent. The magnetic recording medium according to the above. 4. A coating for a non-magnetic layer containing a non-magnetic powder, carbon black and a binder, and a coating for a magnetic layer containing a magnetic powder and a binder are successively provided on a non-magnetic support. Or a method for producing a magnetic recording medium including simultaneous multi-layer coating, wherein the non-magnetic layer paint is non-magnetic chemically bonded using a treatment agent selected from a silane coupling agent and a titanate coupling agent. A production method characterized by being obtained by dispersing powder and carbon black in a binder.