JPH11345416A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent surface property, good electromagnetic conversion characteristics and excellent durability. SOLUTION: In the magnetic recording medium having a magnetic layer on a nonmagnetic supporting body with a nonmagnetic layer interposed, a polyvinyl chloride resin containing carboxylic acids and amine polar groups and a polyurethane resin containing phosphobetaine and/or phosphamine as polar groups are used as a binder in the nonmagnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium having improved electromagnetic conversion characteristics and durability.

[0002]

2. Description of the Related Art In recent years, digitization of magnetic recording media has been advanced for the purpose of releasing signal deterioration due to repeated copying. In addition, the recording density is required to increase as the recording data amount increases. For this purpose, it has been practically used to use finer metal magnetic powder having a high saturation magnetic flux density or hexagonal plate-like barium ferrite powder as the magnetic powder. On the other hand, in order to increase the recording density, it is necessary to consider the thickness loss and the self-demagnetization loss of the medium. From such a viewpoint, it is desired to reduce the thickness of the magnetic layer. However, when the magnetic layer becomes thinner, the surface properties of the support are reflected on the surface of the magnetic layer, and the electromagnetic conversion characteristics are deteriorated. For this reason, it has been conventionally proposed to provide a nonmagnetic layer using, for example, a thermosetting resin as an undercoat on the surface of a support, and to provide a magnetic layer through the nonmagnetic layer. However, there is a problem that such a nonmagnetic layer has insufficient durability. In addition, when a nonmagnetic layer and a magnetic layer are applied, a method of forming the magnetic layer after coating and drying the nonmagnetic layer is used. Therefore, depending on the resin used, the surface property of the nonmagnetic layer may be reduced. The problem of worsening occurs. For these reasons, Japanese Patent Application Laid-Open No. 63-19 / 1988
No. 1315 and JP-A-63-191318 disclose a nonmagnetic lower layer in which a nonmagnetic powder is dispersed in, for example, a thermoplastic resin binder, and the lower layer and the magnetic layer are wetted with a coating solution for each layer. It discloses a method of applying in a state of being layered, and describes that the electromagnetic conversion characteristics, durability and head wear are improved by this. In addition, JP
In Japanese Patent Application Laid-Open No. 6-259751, a non-magnetic lower layer is formed using granular α-iron oxide / carbon black as an inorganic pigment in order to improve the surface properties, and coating is performed by the above-described method. By using granular α-iron oxide, acicular α-
The effect of improving the surface properties as compared with a material such as titanium oxide is obtained even in the case of iron oxide or granular. On the other hand, when we turn our attention to the binder for preparing the nonmagnetic layer paint, α-
In the case of using an iron oxide / carbon black pigment, JP-A-06-259751 discloses an example in which a resin containing a sulfonic acid group is used. JP-A-08-017035 discloses a chloride having only an amine polar group. Examples of using a urethane resin having a vinyl-based resin and a sulfonic acid-based polar group are described in JP-A-09-265623. Examples of the urethane resin having a metal salt of sulfamic acid as a polar group are described in Examples and Claims. Has been stated.

[0003]

However, in magnetic recording media such as digital recording video tapes and floppy disks, the magnetic layer is required to be thinner with the increase in recording density. JP-A-2595751, JP-A-08-017035, JP-A-09-2
Dispersion is not sufficient with only the pigment / binder disclosed in Japanese Patent No. 65623, and as a result, the surface properties are not sufficient. For example, since α-iron oxide and carbon black have different properties, a binder having a sulfonic acid-based polar group that disperses α-iron oxide and aluminum oxide well is inferior in dispersion of carbon black, and conversely disperses carbon black well. It is conventionally known that a binder having an amine-based polar group is inferior in dispersion of iron oxide, and a vinyl chloride-based resin having only an amine-based polar group and a sulfonic acid-based resin as disclosed in JP-A-08-017035. Even when a urethane resin having a polar group is used, bad points of each other appear and a satisfactory dispersion state cannot be obtained. Therefore, in order to obtain the required surface properties, it is necessary to further improve the dispersion level. That is, the object of the present invention is α
-To improve the dispersion of pigments having different properties, such as iron oxide, carbon black, and aluminum oxide, to obtain a magnetic recording medium having excellent surface properties, good electromagnetic conversion characteristics, and excellent durability.

[0004]

According to the present invention, as a result of repeated studies to solve the above-mentioned problems, a vinyl chloride resin having an amine-based polar group and a carboxylic acid-based polar group in the same molecule and phosphobetaine and / or phosphobetaine are used. It has been found that α-iron oxide, aluminum oxide, and carbon black contained in a polyurethane resin having phosphamine as a polar group can all be well dispersed, and it has been extremely difficult to achieve conventionally by combining these two resins. The present inventors have found that a magnetic recording medium having excellent smooth surface properties and excellent durability and electromagnetic conversion characteristics can be obtained, and have reached the present invention. That is, the present invention provides (1) a magnetic recording medium having a magnetic layer on a nonmagnetic support via a nonmagnetic layer, wherein the nonmagnetic layer is a vinyl chloride resin containing a carboxylic acid and an amine polar group as a binder; And (2) a magnetic recording medium comprising using a polyurethane resin containing phosphobetaine and / or phosphamine as a polar group.
Α-Fe ₂ O ₃ , BET =
60-250 (m ² / g), DBP oil absorption = 40-15
(1) The magnetic recording medium according to the above (1), wherein the nonmagnetic layer contains 0 (ml / 100 g) carbon black, and (3) the nonmagnetic layer is a particulate α-Fe ₂ O ₃ , α-Al ₂ O ₃ , and B
ET = 60 to 250 (m ² / g), DBP oil absorption = 40
(1) The magnetic recording medium according to the above (1), wherein the magnetic powder contains carbon black of from 150 to 150 (ml / 100 g), and (4) the magnetic powder contained in the magnetic layer is a metal magnetic powder or a hexagonal ferromagnetic powder. (5) The magnetic recording medium according to (1), wherein the average thickness of the magnetic layer is 1.0 μm or less, and the average thickness of the nonmagnetic layer is 1 to 3 μm. The magnetic recording medium according to the above (1) or (5), wherein the non-magnetic layer is applied, and the non-magnetic layer is applied simultaneously or sequentially in a wet state, and (7) the carboxyl contained in the vinyl chloride resin. When the amount of the acid polar group is 0.1
The magnetic recording medium according to the above (1), wherein
(8) The magnetic recording medium according to (1), wherein the amount of the amine-based polar group contained in the vinyl chloride-based resin is 50 ppm or more, (9) the average degree of polymerization of the vinyl chloride-based resin is 100 to 7.
(1) the magnetic recording medium according to the above (1), wherein
0) The polyurethane resin has a number average molecular weight of 5,000 to 20
(1) the magnetic recording medium according to the above (1), wherein
1) The magnetic recording medium according to (1) above, wherein the mixing ratio of the vinyl chloride resin and the polyurethane resin is from 9/1 to 5/5 (weight ratio), and (12) the particle size of the granular α-Fe ₂ O ₃ . Is 100
(3) the magnetic recording medium according to (2) or (3), wherein the amount of carbon black added is granular α-Fe
(2) or (3), wherein the magnetic recording medium is 20 to 80 parts by weight with respect to 100 parts by weight of ₂ O _3;
4) The magnetic recording medium according to the above (3), wherein the amount of α-Fe ₂ O ₃ added is 10 to 40 parts by weight based on 100 parts by weight of the total amount of α-Fe ₂ O ₃ and carbon black.

Hereinafter, a specific configuration of the present invention will be described in detail. The vinyl chloride resin, which is one of the binders of the nonmagnetic layer of the present invention, preferably has a vinyl chloride content of 60 to 95%. As such a vinyl chloride resin, vinyl chloride-vinyl acetate-vinyl alcohol Copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-
Maleic acid copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-maleic acid copolymer, and the like. Furthermore, in the present invention, it is necessary to simultaneously have, as one component of the vinyl chloride resin, a carboxylic acid having good dispersion of α-iron oxide and aluminum oxide and an amine polar group having good dispersion of carbon black in one molecule. . Without a carboxylic acid, the paint lacks stability and deteriorates in surface properties during multi-layer coating, and when it does not have an amine-based polar group, carbon dispersibility is poor and satisfactory surface properties cannot be obtained. . As the introduction of a carboxylic acid group, a polymerizable monomer such as maleic acid, maleic anhydride, or acrylic acid may be copolymerized with another polymerizable monomer. Among them, maleic anhydride is preferred. The introduction of the amine-based polar group is carried out by adding an amine compound to the vinyl chloride copolymer and causing it to react. Primary, secondary and tertiary amines such as aliphatic, alicyclic amines and aromatic amines are used as the amine compound. For example, ethylamine, ethanolamine, diethylamine, diethanolamine, dimethylethanolamine, diethylethanolamine and the like can be mentioned. Among them, dimethylethanolamine is preferred.

The amount of the carboxylic acid contained in the vinyl chloride resin is preferably 0.1 to 2.0 wt%, more preferably 0.2 to 2.0 wt%.
The range is 1.0% by weight. If the amount is less than 0.1 wt%, a sufficient effect on the dispersibility tends to be not recognized,
If it is more than 2.0% by weight, the paint will thicken and the dispersibility and applicability will tend to decrease. Similarly, the amount of the amine polar group is 50
ppm or more, preferably 100 ppm or more.
If it is less than 50 ppm, a sufficient effect on the dispersibility tends not to be recognized. The average degree of polymerization of the vinyl chloride resin is preferably in the range of 100 to 700, and more preferably in the range of 200 to 500. If it is less than 200, the strength of the coating film decreases and the durability is adversely affected. Conversely, if it exceeds 700, the paint becomes thick and the dispersion becomes insufficient.

Further, the polyurethane resin must have, as a polar group, phosphobetaine or phosphamine, which has both properties of a phosphoric acid system having good dispersion of α-iron oxide and aluminum oxide and an amine system having good dispersion of carbon black. It may be a mixture of the two or a mixture of the two. Phosphobetaine is an inner salt having quaternary ammonium and phosphonic acid, phosphinic acid, an anion of an acid phosphate compound as a cation in one molecule, and phosphamine is a phosphoric acid, a phosphinic acid, a hydroxyl group of an acid phosphate compound. Amide substitution. When one polar group does not have a phosphoric acid-based and amine-based polar group at the same time, such as phosphobetaine or phosphamine, the dispersion is poor and the surface properties at the time of multilayer coating are deteriorated, and the object of the present invention is not achieved. The polyurethane resin used in the present invention is synthesized by the reaction of a high molecular weight polyol and a polyisocyanate with other copolymers as required, similarly to the usual polyurethane synthesis method. Any of the isocyanate components may be contained, or a method of introducing a polar group into a polymer as a polymer reactive component may be used. However, in consideration of the unreacted components and the introduction ratio, it is easier to control the polymer monomer having a polar group. This polymerized monomer is synthesized by the reaction of aminodiol with phosphonic acid, phosphinic acid, and acid phosphate. Its structural formula is

[0008]

Embedded image

[0009] (Where R ₁ and R ₃ constitute a diol, R ₂ is a phenyl group and has 1 to 40 carbon atoms.
Is an alkyl group or an alkylphenyl group. X represents the above-mentioned phosphonic acid, phosphinic acid or acid phosphate. Examples of aminodiols include, but are not limited to, N 2
-Methyldiethanolamine, N-ethyldiethanolamine, N-phenyldiethanolamine, diethanolamine and the like. On the other hand, examples of phosphonic acids include, but are not limited to, methylphosphonic acid, ethylphosphonic acid, phenylphosphonic acid, methylenediphosphonic acid, octadecylphosphonic acid, and the like.Examples of phosphinic acids include phenylphosphinic acid, diphenylphosphinic acid, Examples include dimethyl phosphinic acid, and examples of the acid phosphate include amyl acid phosphate, 2-ethylhexyl acid phosphate, methyl acid phosphate, ethyl acid phosphate, and polyoxyethylene nonylphenyl ether phosphate. Above all, N
It is preferred to use a polymerized monomer obtained by the reaction of methyldiethanolamine with phenylphosphonic acid, octadecylphosphonic acid, methyl acid phosphate or polyoxyethylene nonylphenyl ether phosphate. The amount of these polar groups is 0.01 to 1.0 mmol
1 / g is good, more preferably 0.03 to 0.5.
It is in the range of mmol / g. The amount of polar group is 0.01mm
When the amount is less than ol / g, there is a tendency that a sufficient effect on the dispersibility is not recognized.
Intermolecular or intramolecular aggregation is likely to occur, adversely affecting the dispersibility and making it difficult to obtain the effects of the present invention. The number average molecular weight of the polyurethane resin is 5,000 to 200,0
00 is good, preferably 10,000 to 100,0
00 range. If it is less than 5,000, the strength of the coating film decreases and the durability is adversely affected. Conversely, if it exceeds 200,000, problems may occur in the production of the paint and in the coating process.

The above-mentioned polyurethane resin or vinyl chloride resin may be a thermoplastic resin, a thermosetting or reactive resin, an electron beam (EB) sensitive modified resin, or the like. In particular, those having a hydroxyl group at the terminal and / or the side chain are preferable because the electron beam-sensitive group can be easily introduced and crosslinking using isocyanate can be easily used. As a curing agent for crosslinking these resins with isocyanate, Coronate L, HL, 3041 (manufactured by Nippon Polyurethane Co., Ltd.), 24A-100, TPI-100 (manufactured by Asahi Chemical Industry Co., Ltd.) and the like can be used. . The resins used in Examples and Comparative Examples of the present invention are all cross-linking reaction (thermosetting) resins having a hydroxyl group. The most desirable mode of the present invention is to use a vinyl chloride resin having at least a carboxylic acid and an amine polar group and a polyurethane resin having phosphobetaine and / or phosphamine as a polar group at the same time in the non-magnetic lower layer. When a mixture of the vinyl chloride resin and the polyurethane resin is used, the weight ratio is 9 / vinyl chloride resin / polyurethane resin.
It is 1/5/5, preferably 8 / 2-6 / 4. When this ratio is larger than 9/1, the coating film tends to become brittle.
When this ratio is smaller than 5/5, the coating film becomes soft,
Durability tends to deteriorate. If necessary, it may be used in combination with a polyurethane resin having another polar group. In this case, the content of the polyurethane resin containing phosphobetaine and / or phosphamine as a polar group is desirably 10% to 50% of the total resin components. By using these resins, the dispersion becomes good and a coating film having good surface properties can be obtained.

The non-magnetic lower layer of the present invention preferably contains a non-magnetic pigment. In particular, the particle shape has an aspect ratio of 1
Α-Fe ₂ O ₃ having a BET value of 60 to 250
(M ² / g) and the DBP oil absorption is 40 to 150 (ml / 1
It is preferable to use a mixture of carbon black (00 g). By using granular α-Fe ₂ O ₃ , high dispersibility can be achieved, and the filling rate of ultrafine particles in the nonmagnetic layer can be increased. Therefore, the surface properties of the nonmagnetic layer itself are improved, and the surface properties of the magnetic layer are also improved. This effect is difficult to obtain with α-Fe ₂ O ₃ having a needle shape. Also, the BET value of this granular α-Fe ₂ O ₃ is 60 to
250 (m ² / g), DBP oil absorption is 40 to 150 (m
By mixing and using 1/100 g) of carbon black, it is possible not only to reduce the electric resistance of the coating film but also to give the coating material an appropriate thixotropic property. When the BET value is less than 60, the thixotropy of the paint is insufficient and adversely affects the application, and when the BET value exceeds 250, the dispersibility is poor,
This adversely affects the filling property of the non-magnetic layer. Similarly, when the DBP oil absorption is less than 40 (ml / 100 g), the electric resistance of the coating film increases, and the DBP oil absorption becomes 150 (ml / 100 g).
If it exceeds g), the dispersibility will be poor. As such carbon black, trade names # 45B, MA8B, MA1
00B, 3150B (manufactured by Mitsubishi Chemical Corporation), Raven
760, Raven1040, Raven1060, C
ondtex SC (manufactured by Columbian Co., Ltd.) and the like. This carbon black is the same as the α-Fe ₂ O ₃ 10
It is desirable to add 20 to 80 parts by weight with respect to 0 parts by weight. If the amount is less than 20 parts by weight, the value of the electric resistance increases, and the thixotropy of the paint becomes too small. On the other hand, if it is more than 80 parts by weight, the thixotropy of the paint becomes too large, which adversely affects the applicability. The particle size of the α-Fe ₂ O ₃ is 100 n.
m or less, preferably 80 nm or less, and the average particle size is 20 to 80 nm. When the particle size exceeds 100 nm, the surface properties of the nonmagnetic layer are adversely affected. The shape is almost spherical, and the aspect ratio obtained by dividing the average major axis length by the average minor axis length is about 1 to 2. The specific surface area by the BET method is 2
0 to 80 (m ² / g), preferably 30 to 60 (m ² / g)
g). Such granular α-Fe ₂ O ₃ is commercially available, and a commercially available product can be used as it is. Such materials include Nanotight (manufactured by Showa Denko KK), FR
O (made by Sakai Chemical Co., Ltd.). Known non-magnetic pigments such as carbon graphite, Cr ₂ O ₃ and TiO ₂ may be used in combination. In particular, α-Al ₂ O ₃
By using together, the coating film strength is increased, and further improvement in durability can be expected. The addition amount is desirably 10 to 40 parts by weight based on 100 parts by weight of the total of α-Fe ₂ O ₃ and carbon black. If the amount is less than 10 parts by weight, the reinforcing effect cannot be sufficiently exhibited, and if it exceeds 40 parts by weight, the surface properties of the nonmagnetic layer deteriorate. More preferably, the particle size is 0.1 to 0.5 μm. Such products include the product name AKP2
0, AKP30, HIT50, HIT60 (manufactured by Sumitomo Chemical Co., Ltd.) and the like. As the ferromagnetic powder used for the magnetic layer of the present invention, a conventionally known material can be used, for example, γ-Fe
₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing γ-
Oxide magnetic powders such as Fe ₃ O ₄ , CrO ₂ , barium ferrite, strontium ferrite, Fe, Co, Ni
And metal magnetic powder such as an alloy thereof. These ferromagnetic powders may be selected according to the type of medium to be applied. Among them, fine powders of hexagonal oxides such as barium ferrite and strontium ferrite, metals such as Fe, Co, and Ni, and alloys thereof. Is preferred. Further, those containing a rare earth element containing Y as an additional element are also preferable. The H
c is preferably in the range of 1300 to 2800 (Oe), depending on the drive system currently existing or under development.

The coating of the present invention has a structure in which a magnetic layer is provided on a nonmagnetic support via a nonmagnetic layer. This is because the magnetic layer becomes thinner as the recording density increases, and especially when the average thickness is 1 μm or less, which is suitable for high density recording, the surface properties of the base film affect the surface properties of the coating film. In addition, because the absolute amount of the lubricant decreases and the durability deteriorates, it is preferable to provide the magnetic layer via a nonmagnetic layer containing the lubricant. The average thickness of the non-magnetic layer at this time is preferably between 1 μm and 3 μm, and if it is thinner than 1 μm, the effect as a non-magnetic layer is reduced, and if it is 3 μm or more, coatability at the time of coating is reduced, Not desirable for production. The average thickness is an average value of five thickness measurements. The above is a method of coating the non-magnetic layer and the magnetic layer. In the wet-on-wet coating in which the magnetic layer is coated while the non-magnetic layer is wet, the magnetic layer is coated after the non-magnetic layer is coated and dried. Wet-on-dry coating may be applied,
From the viewpoint of production efficiency, wet-on-wet coating, in which two coats can be simultaneously applied in one coater, is preferable.
In the wet-on-wet coating method, the magnetic layer may be applied after the non-magnetic layer is applied, or both layers may be applied simultaneously. The coater used in such a coating method is not particularly limited, but a gravure coater, a reverse roll coater, or a die nozzle coater can be used in a wet-on-dry multi-layer coating. In the wet-on-wet multi-layer coating, the lowermost layer is a gravure coater, reverse roll coater, die nozzle coater, and the other layers are
It is preferable to use a die nozzle coater. When a die nozzle coater is used, one having a plurality of application ports or one having a single application port may be used.

[0013]

Examples and Comparative Examples Example 1 <Lower layer paint 1> 65 parts by weight of granular α-Fe ₂ O ₃ (FRO-3 manufactured by Sakai Chemical Industry Co., Ltd.) (average particle size = 30 nm, BET = 45 m ²⁾ / G) Carbon black (Mitsubishi Chemical Corporation: # 45B) 35 parts by weight (Average particle size = 24 nm, BET = 125 m ² / g, DBP oil absorption = 47 ml / 100 g) Vinyl chloride-vinyl acetate copolymer 15 parts by weight (Polymerization degree: 350, polar group: carboxylic acid = 0.5% and ammonium salt N content = 300 ppm) 5 parts by weight of phosphobetaine-containing polyurethane resin (N - including Hosuhobe tines by the reaction of methyl diethanolamine and phenylphosphonic acid as a polar group) (Mw = 40000, a polar group concentration = 1.5 / 1 molecule) -SO ₃ Na-containing Polyurethane resin 3 parts by weight (Mn = 25,000, polar group concentration = 1 / molecule) Isocetyl stearate 10 parts by weight Butyl stearate 4 parts by weight Sorbitan monostearate 3 parts by weight MEK 150 parts by weight Toluene 50 parts by weight Cyclohexanone 50 Parts by weight After the above composition was kneaded, the composition was dispersed in a sand grinder mill to prepare lower layer coating material 1.

<Upper Magnetic Coating 1> Metal magnetic powder 100 parts by weight (Hc = 1660 Oe, σS = 126 emu, BET = 58 g / m ² , average major axis length = 0.33 μm, Fe / Co / Ni = 100/5) / 5, a comprises a l and Si) vinyl copolymers chloride polymer as an additive element (Nippon Zeon: MR 110) 14 parts by weight (polymerization degree = 300, polar group: -OSO ₃ K = 1.5 or / Molecule) Phosphobetaine-containing polyurethane resin 4 parts by weight (including phosphobetaine as a polar group by reaction of N-methyldiethanolamine and phenylphosphonic acid) (Mw = 40000, polar group concentration = 1.5 / molecule) − SO ₃ Na-containing polyurethane resin 2 parts by weight (Mn = 25000, polar group concentration = 1 / molecule) α-Al ₂ O ₃ (AKP30, manufactured by Sumitomo Chemical Co., Ltd.) 10 parts by weight (average particle size = 0.33 μm, BET = 8 m ² / g) Cr ₂ O ₃ (manufactured by Nippon Chemical Industry Co., Ltd .: S-1) 5 parts by weight (average particle size = 0.40 μm, BET = 3 m ² / g) Carbon black (manufactured by Columbian Co., Ltd .: Sevacarb MT) 3 parts by weight (average particle size = 350 nm, BET = 7 m ² / g, DBP oil absorption = 41 ml / 100 g) Sorbitan monostearate 3 weight Part Isocetyl stearate 3 parts by weight Butyl stearate 2 parts by weight MEK 250 parts by weight Toluene 80 parts by weight Cyclohexanone 80 parts by weight After kneading the above composition, it was dispersed by a sand grinder mill to prepare an upper layer magnetic paint 1. . Next, Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.)
And 4 parts by weight of Coronate L in the upper magnetic paint 1
The lower layer paint 1 is first extruded onto a PET film having a surface roughness (Ra) of 9 nm and a thickness of 62 μm by extrusion and applied with a die nozzle method to a thickness of 1.5 μm (dry film thickness). The upper layer paint is extruded into the state and applied with a thickness of 0.3 μm (dry film thickness) by a die nozzle method, non-oriented by a non-oriented magnet, dried at a drying temperature of 100 ° C., and then dried at a temperature of 60 ° C. A calender (working) treatment was performed at a linear pressure of 300 kg / cm to finish a coating film on one side. Next, the other side was also formed in the same procedure to prepare a raw roll of a double-sided magnetic layer. Finally, the raw roll was punched out into a disk shape, and then heat cured at 70 ° C. for 24 hours to prepare a disk.

Example 2 <Lower layer paint 2> 55 parts by weight of granular α-Fe ₂ O ₃ (FRO-3 manufactured by Sakai Chemical Industry Co., Ltd.) (average particle size = 30 nm, BET = 45 m ² / g) carbon black (Mitsubishi Chemical Corp .: # 45B) 30 parts by weight (Average particle size = 24 nm, BET = 125 m ² / g, DBP oil absorption = 47 ml / 100 g) α-Al ₂ O ₃ (Sumitomo Chemical Industries, Ltd.) 15 parts by weight (average particle size = 0.33 μm, BET = 8 m ² / g) Vinyl chloride-vinyl acetate copolymer (manufactured by Nissin Chemical Industry Co., Ltd .: Solvain MK6) 12 parts by weight (degree of polymerization) : 350, polar group: carboxylic acid = 0.5% and ammonium salt N content = 300 ppm) 4 parts by weight of a phosphobetaine-containing polyurethane resin (by reaction between N-methyldiethanolamine and phenylphosphonic acid) (Includes phosphobetaine as a polar group) (Mw = 40000, polar group concentration = 1.5 / molecule) —SO ₃ Na-containing polyurethane resin 2 parts by weight (Mn = 25000, polar group concentration = 1 / molecule) Isocetyl stearate 10 parts by weight Butyl stearate 4 parts by weight Sorbitan monostearate 3 parts by weight MEK 150 parts by weight Toluene 50 parts by weight Cyclohexanone 50 parts by weight After kneading the above composition, it is dispersed by a sand grinder mill and the lower layer is formed. Paint 2 was prepared. Next, the upper layer magnetic paint 1 and the lower layer paint 2 are applied by the method described in Example 1,
Created a disc.

Example 3 <Lower layer paint 3> 55 parts by weight of granular α-Fe ₂ O ₃ (FRO-3 manufactured by Sakai Chemical Industry Co., Ltd.) (average particle size = 30 nm, BET = 45 m ² / g) carbon black (Mitsubishi Chemical Corp .: # 45B) 30 parts by weight (Average particle size = 24 nm, BET = 125 m ² / g, DBP oil absorption = 47 ml / 100 g) α-Al2O3 (Sumitomo Chemical Co., Ltd .: AKP30) 15 parts by weight (average particle size = 0.33 μm, BET = 8 m ² / g) Vinyl chloride-vinyl acetate copolymer (manufactured by Nissin Chemical Industry Co., Ltd .: Solvain MK6) 12 parts by weight (degree of polymerization: 350; Polar group: carboxylic acid = 0.5% and ammonium salt N content = 300 ppm) Phosphobetaine-containing polyurethane resin 6 parts by weight (by reaction between N-methyldiethanolamine and phenylphosphonic acid) (Includes phosphobetaine as a polar group) (Mw = 40000, polar group concentration = 1.5 / molecule) Isocetyl stearate 10 parts by weight Butyl stearate 4 parts by weight Sorbitan monostearate 3 parts by weight MEK 150 parts by weight Toluene 50 parts by weight cyclohexanone 50 parts by weight After the above composition was kneaded, it was dispersed by a sand grinder mill to prepare lower layer coating material 3. Next, the upper layer magnetic paint 1 and the lower layer paint 3 are applied by the method described in Example 1,
Created a disc.

Example 4 A disk was prepared in the same manner as in Example 2 except that the polar group of the phosphobetaine-containing polyurethane resin was changed to phosphamine. Example 5 One molecule of the phosphobetaine-containing polyurethane resin of Example 2 contains one phosphobetaine by the reaction of N-methyldiethanolamine and phenylphosphonic acid and one phosphamine by the reaction of diethanolamine and phenylphosphonic acid in one molecule. A disk changed to polyurethane resin was created.

Example 6 <Upper layer magnetic paint 2> Barium ferrite magnetic powder 100 parts by weight (Hc = 2000 Oe, σS = 56 emu, BET = 43 g / m ² , average particle diameter = 36 nm, average thickness = 11 nm) Copolymer (manufactured by Zeon Corporation: MR110) 14 parts by weight (degree of polymerization = 300, polar group: —OSO ₃ K = 1.5 / molecule) Phosphobetaine-containing polyurethane resin 4 parts by weight (N-methyldiethanolamine) (Mw = 40,000, polar group concentration = 1.5 / molecule) -SO ₃ Na-containing polyurethane resin 2 parts by weight (Mn = 25,000, polar group) concentration = 1/1 molecule) α-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd.: AKP30) 10 parts by weight (average particle size = 0.33 ^{, BET = 8m 2 / g)} Cr 2 O 3 ( Nippon Chemical Industrial Co., Ltd.: S-1) 5 parts by weight (average particle size ^{= 0.40μm, BET = 3m 2 /} g) Carbon black (Columbian ( Co., Ltd .: Sevacarb MT) 3 parts by weight (average particle size = 350 nm, BET = 7 m ² / g, DBP oil absorption = 41 ml / 100 g) Sorbitan monostearate 3 parts by weight Isocetyl stearate 3 parts by weight butyl stearate 2 parts by weight MEK 250 parts by weight Toluene 80 parts by weight Cyclohexanone 80 parts by weight After the above composition was kneaded, it was dispersed by a sand grinder mill to prepare an upper layer magnetic paint 2. Next, the upper layer magnetic paint 2 and the lower layer paint 2 were applied in the same manner as in Example 1 to prepare a disk.

Example 7 A disk was prepared in the same manner as in Example 3 except that the blending weight ratio of the vinyl chloride resin and the polyurethane resin as the lower layer coating material was changed from 7/3 to 9/1. Example 8 A disk was prepared in the same manner as in Example 3, except that the blending weight ratio of the vinyl chloride resin and the polyurethane resin as the lower layer coating material was changed from 7/3 to 6/4. Example 9 A disc was prepared in the same manner as in Example 3 except that the blending weight ratio of the vinyl chloride resin and the polyurethane resin as the lower layer paint was changed from 7/3 to 5/5.

Comparative Example 1 A disc was prepared in the same manner as in Example 2 except that the polar group of the vinyl chloride resin of the lower layer coating material was changed to only an ammonium salt. Comparative Example 2 A disc was prepared in the same manner as in Example 2 except that the polar group of the vinyl chloride resin of the lower layer paint was changed to carboxylic acid only. Comparative Example 3 A disc was prepared in the same manner as in Example 2 except that the polar group of the vinyl chloride resin in the lower layer coating material was changed to potassium sulfate. Comparative Example 4 A disk was prepared in the same manner as in Example 2 except that a vinyl chloride resin having no polar group was used as the vinyl chloride resin of the lower layer paint. Comparative Example 5 A disk was prepared in the same manner as in Example 2 except that the polar group of the phosphobetaine-containing polyurethane resin of the lower layer paint was changed to sodium phosphate. Comparative Example 6 A disk was prepared in the same manner as in Example 2 except that the polar group of the phosphobetaine-containing polyurethane resin of the lower layer paint was changed to sodium sulfamate. Comparative Example 7 A disk was prepared in the same manner as in Example 2 except that the polar group of the phosphobetaine-containing polyurethane resin of the lower layer paint was changed to sodium sulfonate. Comparative Example 8 A disk was prepared in the same manner as in Example 2 except that the polar group of the phosphobetaine-containing polyurethane resin in the lower layer paint was changed to an ammonium salt. Comparative Example 9 A disk was prepared in the same manner as in Example 2 except that the polar group of the phosphobetaine-containing polyurethane resin in the lower layer paint was removed. Comparative Example 10 A disk was prepared in the same manner as in Example 6 except that the polar group of the phosphobetaine-containing polyurethane resin of the lower layer coating was changed to sodium phosphate. Comparative Example 11 A disc was prepared in the same manner as in Example 6 except that the polar group of the phosphobetaine-containing polyurethane resin in the lower layer paint was changed to sodium sulfonate.

[Experimental data] The following items were measured for the disks prepared in the examples and comparative examples. (1) Dispersion gloss of the lower layer (2) Surface roughness of the medium (Ra) • Unprocessed upper layer single layer (only the upper layer magnetic paint is applied on a PET film so as to have a dry film thickness of 0.3 μm, and then dried. The surface roughness of the processed magnetic layer was measured.)-Unprocessed lower single layer (only the lower nonmagnetic paint was applied on a PET film to a dry film thickness of 1.5 µm and dried.
The surface roughness of the unprocessed nonmagnetic layer was measured. -Unprocessed multilayer (measured by measuring the surface roughness of the surface of the multilayer coating film before processing in the method for producing a magnetic disk described in Example 1)-Layer processing (magnetism described in Example 1) The surface roughness of the magnetic disk obtained by the disk forming method was measured.) The above-mentioned "processed" and "unprocessed" relate to calendering. (3) Electromagnetic conversion characteristics (4) Durability

[0022]

[Table 1]

[0023]

[Table 2]

<Measurement method> Electromagnetic conversion characteristics Using a GUZIK electromagnetic conversion characteristic measuring instrument, 2940 rpm
Measured at m disk rotation speed. The measured value was 100% of the output of the drive maker reference disk.・ Durability Insert a disk into a zip drive with a rotation speed of 3000 rpm, randomly seek the head in the following cycle environment of FIG. 1, and visually check for scratches. It ends when the scratch enters. <Measuring method of surface roughness> Measuring device: Taly step system manufactured by Taylor Hobson Co., Ltd. Measuring condition: Filter condition 0.18 to 9 Hz Stylus 0.1 × 2.5 μm Special stylus Stylus pressure 2 mg Measuring speed 0.03 mm / sec Measurement length 500 μm <Gloss measurement method> Measuring instrument: GLASS METER GM-3D manufactured by MURAKAMI COLOR RESEARCH LABORATORY (incident angle-reflective angle: 60 ° -60 °)

[0025]

According to the present invention, a magnetic recording medium having an excellent lower layer dispersibility and a small surface roughness (Ra) after layering, that is, excellent surface properties, good electromagnetic conversion characteristics, and excellent durability. Is obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing durability cycle conditions in durability measurement.

 ──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Kaoru Miyamori 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation

Claims (6)

[Claims] 1. A magnetic recording medium having a magnetic layer on a nonmagnetic support via a nonmagnetic layer, wherein the nonmagnetic layer is a vinyl chloride resin containing a carboxylic acid and an amine polar group as a binder in one molecule, and A magnetic recording medium using a polyurethane resin containing phosphobetaine and / or phosphamine as a polar group. 2. The method according to claim 1, wherein the non-magnetic layer comprises a particulate α-Fe as a pigment.
_2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium contains carbon black having ₂ O ₃ , BET = 60 to 250 (m ² / g), and DBP oil absorption = 40 to 150 (ml / 100 g). 3. The method according to claim 1, wherein the non-magnetic layer is a particulate α-Fe as a pigment.
₂ O ₃ , α-Al ₂ O ₃ , and BET = 60 to 250 (m ²
/ G), DBP oil absorption = 40-150 (ml / 100
2. The magnetic recording medium according to claim 1, comprising g) carbon black. 4. The magnetic recording medium according to claim 1, wherein the magnetic powder contained in the magnetic layer is a metal magnetic powder or a hexagonal ferromagnetic powder. 5. The magnetic recording medium according to claim 1, wherein the average thickness of the magnetic layer is 1.0 μm or less, and the average thickness of the nonmagnetic layer is 1 to 3 μm. 6. The magnetic recording medium according to claim 1, wherein the magnetic layer has a non-magnetic layer applied thereto, which is applied simultaneously or successively in a still wet state. TECHNICAL FIELD OF THE INVENTION