JP2002092852A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent running durability and satisfactory electromagnetic transducing characteristics and the most suitable for use in a magnetic recording and reproducing device with helical scanning. SOLUTION: The magnetic recording medium is provided with a non-magnetic substrate 1, a non-magnetic layer 2 formed on the non-magnetic substrate 1 and containing a non-magnetic powder and a bonding agent and a magnetic layer 3 formed on the non-magnetic layer 2 and containing a ferromagnetic powder and a bonding agent and characterized by that the magnetic layer 3 contains polyurethane resin having a tertiary amine as a polar group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium having a non-magnetic support and a magnetic layer.

[0002]

2. Description of the Related Art In today's society, audio information is distributed via networks. In the future, not only audio information but also image information may be distributed via a network. As a medium for recording various information distributed in this way, for example, a magnetic recording medium for data storage is used.

[0003]

In recent years, in the field of magnetic recording, the capacity of various data to be recorded and reproduced has been increasing. For this reason, magnetic recording media are required to have higher capacities and higher data transfer rates.

Conventionally, a single-layer coating type magnetic recording medium has been used as a magnetic recording medium for data storage.
As a magnetic recording / reproducing device, a tape streamer of a fixed head recording system is used. However, there is a limit to the improvement of the data transfer rate in the recording / reproducing by the tape streamer of the fixed head recording system.

Therefore, a helical scan type tape streamer is being developed. The helical scan type tape streamer can realize four times the recording capacity and the data transfer rate as compared with the fixed stream recording type tape streamer.

However, when a single-layer coated magnetic recording medium is run many times using a helical scan type tape streamer, the surface properties tend to deteriorate and the friction coefficient tends to increase. In other words, the single-layer coating type magnetic recording medium does not have running durability suitable for recording and reproduction by a helical scan type tape streamer, and cannot exhibit satisfactory electromagnetic conversion characteristics.

The present invention has been proposed in view of such a conventional situation, and has excellent running durability and good electromagnetic conversion characteristics. In particular, the present invention relates to a helical scan type magnetic recording / reproducing apparatus. An object is to provide a magnetic recording medium that is optimal for use.

[0008]

As a result of various studies by the present inventors to achieve the above object, a structure in which a nonmagnetic layer and a magnetic layer are sequentially formed on a nonmagnetic support. ,
With a so-called multilayer coating type structure and by including a specific binder in the magnetic layer, it has excellent running durability,
It has been found that a magnetic recording medium having good electromagnetic conversion characteristics can be obtained.

The magnetic recording medium according to the present invention has been completed on the basis of such findings, and comprises a non-magnetic support, a non-magnetic powder formed on the non-magnetic support, and a binder. A non-magnetic layer, comprising a magnetic layer formed on the non-magnetic layer and containing a ferromagnetic powder and a binder, the magnetic layer,
It is characterized by containing a polyurethane resin having a tertiary amine as a polar group.

By increasing the friction coefficient under any conditions of use by including a polyurethane resin having a tertiary amine as a polar group in the magnetic layer while having a multilayer coating type structure having a magnetic layer and a non-magnetic layer. Is done.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described in detail.

As shown in FIG. 1, a magnetic recording medium to which the present invention is applied includes a non-magnetic support 1, a non-magnetic layer 2 containing a non-magnetic powder and a binder, and a ferromagnetic powder and a binder. And a magnetic layer 3.

The magnetic layer 3 is formed by applying a magnetic paint containing a ferromagnetic powder and a polyurethane resin having a tertiary amine as a polar group on the non-magnetic layer 2.

The polyurethane resin having a tertiary amine as a polar group serves as a binder in the magnetic layer 3. A polyurethane resin having a tertiary amine as a polar group improves the dispersibility of the ferromagnetic powder in the magnetic paint, that is, can uniformly disperse and orient the ferromagnetic powder in the magnetic layer 3.

In a polyurethane resin containing a tertiary amine as a polar group, the content of the tertiary amine is 0.01%.
It is preferable that the concentration be from mmol / g to 1.0 mmol / g. The tertiary amine content is 0.01 mmol /
If it is less than g, the ferromagnetic powder may not be sufficiently dispersed in the magnetic layer 3. On the other hand, when the content of the tertiary amine exceeds 1.0 mmol / g, the solubility of the magnetic coating material in a solvent for forming the coating material is deteriorated, or the magnetic layer 3
There is a possibility that the moisture resistance of the resin may deteriorate.

The number average molecular weight of the polyurethane resin containing a tertiary amine as a polar group is 5,000 to 100.
000 is preferred. The number average molecular weight of a polyurethane resin containing a tertiary amine as a polar group is 5000
If it is less than 3, sufficient durability may not be obtained.
On the other hand, when the number average molecular weight of the polyurethane resin containing a tertiary amine as a polar group exceeds 100,000, the solubility in a solvent for forming a magnetic paint becomes poor, and there is a possibility that the handling becomes poor.

As a binder to be contained in the magnetic layer 3, a polyurethane resin containing a tertiary amine as a polar group can be used alone, but a conventionally known material used as a binder for a coating type magnetic recording medium can be used. You may use together. As the binder to be used in combination, any of a thermoplastic resin, a thermosetting resin, and a reactive resin can be used. Specifically, vinyl chloride, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, copolymers such as acrylonitrile, and cellulose resins, polyester resins, and epoxy resins can be used. .

Examples of the ferromagnetic powder to be contained in the magnetic paint include metals such as Fe, Co, and Ni, Fe—Co, and Fe—N.
i, Fe-Al, Fe-Ni-Al, Fe-Al-P,
Fe-Ni-Si-Al, Fe-Ni-Si-Al-M
n, Fe-Mn-Zn, Fe-Ni-Zn, Co-N
i, Co-P, Fe-Co-Ni, Fe-Co-Ni-
Cr, Fe-Co-Ni-P, Fe-Co-B, Fe-
Co-Cr-B, Mn-Bi, Mn-Al, Fe-Co
Alloys such as -V can be used. Further, a ferromagnetic powder composed of iron nitride and iron carbide can be used. It is also possible to use a ferromagnetic powder obtained by adding an appropriate amount of a light metal element such as Al, Si, P, or B to these ferromagnetic powders for the purpose of preventing sintering during reduction or maintaining the shape.

Further, as a ferromagnetic powder, γ-Fe 2 O
3, Fe3O4, beltride compound of γ-Fe2O3 and Fe3O4, γ-Fe2O3 containing Co, F containing Co
e3O4, γ-Fe2O3 containing Co and Fe3O4
And oxides in which one or more metal elements such as Te, Sb, Fe, B, etc. are contained in CrO2. Further, as a ferromagnetic powder, a hexagonal plate-like ferrite can also be used.
W-type, Y-type, Z-type barium ferrite, strontium ferrite, calcium ferrite, lead ferrite,
And for the purpose of controlling the coercive force, Co-Ti,
Co-Ti-Zn, Co-Ti-Nb, Co-Ti-Z
Those to which n-Nb, Cu-Zr, Ni-Ti or the like is added can also be used.

The magnetic layer 3 preferably contains an abrasive. As an abrasive, Mohs hardness is 6 or more, 10
What is the following, specifically α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, tungsten carbide, molybdenum carbide, boron carbide,
Corundum, zinc oxide, cerium oxide, magnesium oxide, boron nitride and the like can be used.

The magnetic layer 3 preferably contains carbon black. In particular, the average particle size is 0.03
It is preferable to use carbon black having a size of not less than μm and not more than 0.3 μm.

Examples of such carbon black include # 60 (51 nm) and # 55 manufactured by Asahi Carbon Black.
(77 nm), thermal (90 nm), $ 50 (94 n
m), # 35 (115 nm), Diablack G (84 nm) manufactured by Mitsubishi Kasei, Regal SR manufactured by Cabot
FS (60 nm), Stirling NS (75 nm),
HS100 (53 nm) manufactured by Denki Kagaku or MT-CI (270 nm) manufactured by SEBA CARBON can be used.

The thickness of the magnetic layer 3 is 0.03 μm or more,
It is preferably 0.3 μm or less. When the thickness of the magnetic layer 3 is in the above range, the abrasive and the carbon black are surely exposed on the surface of the magnetic layer 3, so that the amount of the non-magnetic abrasive and the carbon black to be added can be minimized. Therefore, the degree of filling with ferromagnetic powder or the like can be increased, and excellent electromagnetic conversion characteristics can be realized.

It is difficult to reduce the thickness of the magnetic layer 3 to less than 0.03 μm in manufacturing. On the other hand, if the thickness of the magnetic layer 3 exceeds 0.3 μm, the self-demagnetization loss may increase in a short wavelength recording region where the recording wavelength is 0.3 μm or less.

When the thickness of the magnetic layer 3 is a and the thickness of the nonmagnetic layer 2 described later is b, b / a is 8 or more,
It is preferably 8 or less. When b / a is within the above range, compatibility between electromagnetic conversion characteristics and durability can be achieved.

If b / a is less than 8, crushing due to calendar processing is poor, and sufficient reproduction output may not be obtained. On the other hand, when b / a exceeds 18, tape cupping becomes large, and there is a possibility that a good hit waveform cannot be obtained.

The non-magnetic layer 2 is formed by applying a non-magnetic paint containing a non-magnetic powder and a binder on the non-magnetic support 1.

Nonmagnetic powders include titanium oxide, boron nitride, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-Al ₂ O ₃ , α
-Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide,
Corundum, artificial diamond, garnet, garnet, quartzite, silicon nitride, silicon carbide, barium sulfate and the like can be used.

The binder contained in the non-magnetic layer 2 includes
Any conventionally known material used as a binder for a coating type magnetic recording medium can be used, and specifically, any material similar to the binder contained in the magnetic layer 3 described above is used. It is possible.

The thickness of the nonmagnetic layer 2 is 1.5 μm or more,
It is preferably not more than 2.1 μm. When the thickness of the nonmagnetic layer 2 is less than 1.5 μm, dropout may increase due to the influence of the coarse projections of the base film. On the other hand, when the thickness of the non-magnetic layer 2 exceeds 2.1 μm, the cupping of the tape becomes large, and there is a possibility that a good hit waveform cannot be obtained.

Various conventionally known additives such as a lubricant and a surfactant can be added to the magnetic layer 3 and the non-magnetic layer 2.

As the lubricant, solid lubricants such as graphite, molybdenum disulfide, and tungsten disulfide, silicone oil, fatty acids, fatty acid esters, terpene compounds, and oligomers thereof can be used. These lubricants may be added only to the magnetic layer 3 or may be added to both the magnetic layer 3 and the non-magnetic layer 2.

Examples of the nonmagnetic support 1 include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate. Etc. can be used.

In this magnetic recording medium, the running property, the antistatic property and the transfer preventing property are improved on the other main surface of the nonmagnetic support 1 opposite to the main surface on which the magnetic layer 3 is formed. It is possible to provide a back coat layer (not shown) for the purpose.

In manufacturing this magnetic recording medium, first, a non-magnetic paint prepared by dispersing a non-magnetic powder and a binder in a solvent is applied on a non-magnetic support to form a non-magnetic layer 2.
To form Next, a magnetic paint prepared by dispersing a ferromagnetic powder and a polyurethane resin having a tertiary amine as a polar group in a solvent is applied on the non-magnetic layer 2 to form the magnetic layer 3. After the magnetic layer 3 and the non-magnetic layer 2 are dried, calendering or the like for smoothing the surface of the magnetic layer 3 is performed.

In order to synthesize a polyurethane resin containing a tertiary amine as a polar group, a compound represented by the following formula (1) or (2) and a tertiary amine-containing diol are used as a chain extender. The extender is reacted with a bifunctional isocyanate. In addition, as this bifunctional isocyanate, for example, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate and the like can be used.

[0037]

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[0038]

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As the tertiary amine-containing diol, for example, the following chemical formulas 3, 4 and 5 can be used.

[0040]

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[0041]

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[0042]

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Further, diols obtained by adding 2 to 50 moles of ethylene oxide, propylene oxide and the like to the primary amine of the following chemical formula 6 (specific examples are shown in chemical formula 7) are also tertiary. It can be used as an amine-containing diol.

[0044]

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[0045]

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In preparing the magnetic paint and the non-magnetic paint,
Examples of the solvent for mixing and coating the various components described above include acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, alcohols such as methanol, ethanol, propanol and butanol, methyl acetate, and ethyl acetate. Butyl acetate, ethyl lactate, esters such as ethylene glycol monoacetate, glycol dimethyl ether, glycol monoethyl ether, dioxane, ethers such as tetrahydrofuran, benzene, toluene, aromatic hydrocarbons such as xylene, methylene chloride, ethylene chloride,
Halogenated hydrocarbons such as carbon tetrachloride, chloroform and dichlorobenzene can be used. These solvents are
They may be used alone or in combination of two or more.

The magnetic paint and the non-magnetic paint are prepared by kneading and dispersing with a kneading and dispersing machine. As the kneading / dispersing machine, conventionally known various kneading / dispersing machines can be used. For example, an extruder, a pressure kneader, an open kneader, a continuous kneader, a two-roll mill, a three-roll mill, or the like can be used.

As a coating method for applying the non-magnetic paint and the magnetic paint prepared as described above, any conventionally known coating method can be applied. It is preferable to apply a wet multilayer coating method in which a magnetic paint is applied repeatedly, that is, a so-called wet-on-wet coating method.

The magnetic recording medium constructed and manufactured as described above has a multilayer coating type structure in which a non-magnetic layer 2 and a magnetic layer 3 are sequentially laminated on a non-magnetic support 1. Since the magnetic layer 3 contains a polyurethane resin having a tertiary amine as a polar group, an increase in friction coefficient is suppressed under any use conditions. Therefore, this magnetic recording medium has excellent running durability and excellent electromagnetic conversion characteristics. In particular, since this magnetic recording medium is much more excellent in running durability than a conventional single-layer coating type magnetic recording medium, it is most suitable for use in a helical scan type magnetic recording / reproducing apparatus.

[0050]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a magnetic recording medium according to the present invention will be described.
This will be described in detail based on specific experimental results.

[Synthesis of Binder to be Included in Magnetic Layer] First, as a binder to be contained in the magnetic layer, 3
A polyurethane resin containing a secondary amine was synthesized to obtain binders A to G as shown in Table 1. Further, as a resin containing no tertiary amine, a binder H composed of a sulfoisophthalic acid-based polyester was synthesized.

Table 1 shows the skeleton, polar group monomer and polar group content of each of the binders A to H. In Table 1, DMH is 2-butyl-2-ethyl-
1,3-propanediol, MDI is diphenylmethane diisocyanate.

[0053]

[Table 1]

Sample 1 [Preparation of Magnetic Coating] First, each component was weighed according to the following composition, and these components were kneaded with an extruder.
Furthermore, after mixing and dispersing using a premixer and a sand mill, a 2 μm class filter was applied to prepare a magnetic paint.

<Magnetic paint composition>-Ferromagnetic powder: 100 parts by weight of Fe-Co-based metal magnetic powder-Binder: 10 parts by weight of vinyl chloride copolymer Binder C (see Table 1) 10 parts by weight-Carbon black 1 Parts by weight ・ Abrasive: 5 parts by weight of alumina ・ 1 part by weight of stearic acid ・ 1 part by weight of butyl stearate ・ 100 parts by weight of methyl ethyl ketone ・ 100 parts by weight of toluene ・ 100 parts by weight of cyclohexanone Co-containing in ferromagnetic powder The amount is 30at
%, the coercive force of the ferromagnetic powder is 188 kA / m,
Sum magnetization is 150 emu / g, SSA is 50 m ^Two/ G
there were. The degree of polymerization of the vinyl chloride copolymer was 300.
Yes, polar groups (-OSO_ThreeThe content of K) is 0.07 mm
ol / g.

[Preparation of Non-Magnetic Paint] Next, each component of the non-magnetic paint was weighed according to the following composition, these components were kneaded with an extruder, and further mixed and dispersed using a premixer and a sand mill. Thereafter, a non-magnetic paint was prepared by applying a filter of a 2 μm class.

<Nonmagnetic paint composition> Nonmagnetic powder: 100 parts by weight of acicular powder mainly composed of α-Fe ₂ O ₃ Binder: 20 parts by weight of vinyl chloride copolymer 1 part by weight of stearic acid 1 stearin 1 part by weight of butyl acid 70 parts by weight of methyl ethyl ketone 110 parts by weight of cyclohexanone The average major axis length of the nonmagnetic powder was 0.15 μm. The polymerization degree of the vinyl chloride copolymer is 280, the content of the polar group (-OSO ₃ K) is 0.07mmo
1 / g.

4 parts by weight of a polyisocyanate (manufactured by Nippon Polyurethane Industry Co., Ltd .: Coronate L) was added as a curing agent to the magnetic paint and the non-magnetic paint prepared as described above. Then, the magnetic paint and the non-magnetic paint are applied to a thickness of 8
A wet multilayer coating was performed on a non-magnetic support made of polyethylene terephthalate having a thickness of μm. The thickness of the magnetic layer was 0.1 μm, and the thickness of the non-magnetic layer was 1.8 μm.

Then, while the non-magnetic layer and the magnetic layer are not dried, a magnetic field orientation treatment is performed. After the magnetic layer and the non-magnetic layer are dried, a calendering treatment is performed to smooth the surface of the magnetic layer. Got anti. In addition, 60 ℃
The curing treatment was performed for 20 hours under the environment. And
This material was cut into a width of 12.65 mm to obtain a magnetic tape.

Sample 2 A magnetic tape was prepared in the same manner as in Sample 1, except that Binder A was used as the binder contained in the magnetic layer and the thickness of the magnetic layer was set to 0.2 μm.

Samples 3 to 8 Magnetic tapes were prepared in the same manner as in Sample 2, except that the binders shown in Table 2 below were used as binders to be contained in the magnetic layer.

Sample 9 The magnetic paint prepared in Sample 1 was applied on a non-magnetic support to prepare a magnetic tape having only a 3 μm-thick magnetic layer.

Samples 10 to 17 Magnetic tapes were prepared in the same manner as in Sample 1 except that the thickness of the magnetic layer and the thickness of the nonmagnetic layer were as shown in Table 3 below.

Tables 2 and 3 show the types of binders contained in the magnetic layers of these magnetic tapes. Further, the thickness of the magnetic layer is denoted by a, the thickness of the nonmagnetic layer is denoted by b, and a, b, and b / a, which is the ratio of the thickness of the nonmagnetic layer to the thickness of the magnetic layer, are also shown in Tables 2 and 3. It is shown in Table 3.

[0065]

[Table 2]

[0066]

[Table 3]

The following measurements were performed on the magnetic tapes of Samples 1 to 17 produced as described above, and the electromagnetic conversion characteristics, running durability and friction of each magnetic tape were evaluated.

[Evaluation of Electromagnetic Conversion Characteristics] Using a magnetic tape recording / reproducing apparatus (GY-8240, manufactured by Sony Corporation) having a rotating drum on which 19 magnetic heads are mounted, a recording wavelength of 0. Record a 3 μm signal,
The reproduction output was measured to evaluate the electromagnetic conversion characteristics. The value of the reproduction output is 0 dB for the reproduction output of sample 14.
And the relative value when

The magnetic tape of each sample, on which a signal having a recording wavelength of 0.3 μm was recorded as described above, was run for 100 hours, and the reproduction output after running for 100 hours was measured. Then, the amount of decrease in the reproduction output after running for 100 hours with respect to the initial reproduction output was measured, and the electromagnetic conversion characteristics were evaluated.

[Evaluation of Running Durability] After running the magnetic tape of each sample for 100 hours, the amount of powder falling on the magnetic head or the like was visually observed. Then, a sample having a very small amount of powder falling was rated at 1 point, and a sample having a very large amount of powder falling was rated at 5 points, and evaluated on a 5-point scale.

Also, a magnetic tape recording / reproducing apparatus (manufactured by Sony Corporation) having a rotating drum on which 14 magnetic heads are mounted.
DVW-500P) under a 5 ° C environment.
A signal having a recording wavelength of 0.69 μm was recorded on the magnetic tape of each sample. Next, a cycle of performing still reproduction for 10 minutes, performing normal reproduction for 20 seconds, rewinding, cueing up, and then performing still reproduction again for 10 minutes was repeated. The running durability was evaluated by measuring the time until the RF output attenuated by 50% from the initial RF output.

[Evaluation of Friction] In a 23 ° C., 50% RH environment, the magnetic tape of each sample was shuttle-run 1000 times on a stainless steel guide pin under a load of 40 g. The shuttle speed is 20 mm / sec and the shuttle length is 200 mm
And The stainless steel guide pin used was SU
In step S303, the diameter was 7 mm, and _Rmax was 0.1 μm. Then, the friction coefficient was calculated, and the change was evaluated.

The measurement results were evaluated for two types of magnetic tape of each sample, and the maximum value was obtained up to 1000 times.

Table 4 shows the measurement results of the magnetic tapes of Samples 1 to 9 among the above measurement results. In Table 4, * indicates that measurement was not possible due to sticking after running 100 times.

[0075]

[Table 4]

From Table 4, it can be seen that Samples 1 to 4 having a multilayer coating structure having a magnetic layer and a nonmagnetic layer and having a magnetic layer containing a tertiary amine as a polar group, ie, binders A to G, were used. It can be said that the magnetic tape of Sample 7 has a large reproduction output, has a small powder drop, achieves a practically sufficient still durability time, and has a small friction coefficient.

On the other hand, the magnetic tape of Sample 8 provided with a resin not containing a tertiary amine as a polar group, ie, a magnetic layer containing a binder H, has a large output drop, a large amount of powder drop, and a still life time. Is short, and the coefficient of friction increases.

Further, it can be seen that Sample 9 which is a single-layer coating type magnetic tape has a very large coefficient of friction and a small reproduction output.

Therefore, a multilayer coating type structure having a magnetic layer and a non-magnetic layer, and having a magnetic layer containing a polyurethane resin containing a tertiary amine as a polar group, has excellent electromagnetic conversion characteristics and is practically sufficient. It is possible to obtain a magnetic recording medium having excellent running durability and suppressing an increase in friction coefficient.

Next, the results of measurements on the magnetic tapes of Samples 10 to 17 are shown in Table 5.

[0081]

[Table 5]

Comparison between Sample 13 and Sample 16 shows that Sample 13 having b / a of 8 has a higher reproduction output, less dusting, and still endurance time than Sample 16 having b / a of less than 8. Is long. In addition, comparing Sample 17 with Sample 1 in Table 4, it was found that b / a
It can be seen that Sample 1 having a value of 18 has a higher reproduction output and less powder loss than Sample 17 having a b / a of more than 18.

Accordingly, when b / a is 8 or more and 18 or less, a magnetic tape having more excellent running durability and battery conversion characteristics can be obtained.

[0084]

As is apparent from the above description, the magnetic recording medium according to the present invention comprises a non-magnetic support and a non-magnetic layer formed on the non-magnetic support and containing a non-magnetic powder and a binder. And a magnetic layer formed on the non-magnetic layer and containing a ferromagnetic powder and a binder. Since the magnetic layer contains a polyurethane resin having a tertiary amine as a polar group, good running durability is provided. It has excellent electromagnetic conversion characteristics. In particular, this magnetic recording medium has excellent running durability and is optimal for use in a helical scan type magnetic recording / reproducing apparatus.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing one configuration of a magnetic recording medium.

[Explanation of symbols]

 1 Non-magnetic support, 2 Non-magnetic layer, 3 Magnetic layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G11B 5/70 G11B 5/70 5/738 5/738 F term (reference) 4J002 CK021 DA016 DA086 DC006 DE096 DE116 DE136 DE146 DG046 DJ006 DJ016 DK006 FD170 FD200 FD206 GF00 GS01 4J038 DG001 GA09 HA216 KA20 NA22 5D006 BA15 BA19 CA05 FA02 FA05 FA09

Claims (5)

[Claims] 1. A non-magnetic support, a non-magnetic layer formed on the non-magnetic support and containing a non-magnetic powder and a binder, and a ferromagnetic powder and a binder formed on the non-magnetic layer And a magnetic layer containing: a polyurethane resin having a tertiary amine as a polar group. 2. The magnetic recording medium according to claim 1, wherein the thickness of the magnetic layer is 0.03 μm or more and 0.3 μm or less. 3. The magnetic recording medium according to claim 1, wherein the thickness of the nonmagnetic layer is 1.5 μm or more and 2.1 μm or less. 4. When the thickness of the magnetic layer is a and the thickness of the non-magnetic layer is b, the ratio of the thickness of the non-magnetic layer to the thickness of the magnetic layer represented by b / a is: 2. The magnetic recording medium according to claim 1, wherein the number is not less than 8 and not more than 18. 5. The content of the tertiary amine is 0.01 mmol / g or more to the polyurethane resin.
2. The magnetic recording medium according to claim 1, wherein the amount is not more than mmol / g.