JP2001101647A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having high durability, wherein an optimum abrasive material for the magnetic recording medium having a trend toward the higher density can be selected. SOLUTION: In a magnetic recording medium wherein a magnetic layer is formed after a non-magnetic layer including a binder is applied on a non- magnetic substrate and dried and the magnetic layer has <=0.5 μm film-thickness, an abrasive material included in the magnetic layer has Mohs' hardness of 5 or more and a relative abrasive speed of 200 or more and at this time a value (A) obtained by the relational formula A=D/T (1) between the average particle size (D) of the abrasion material and the film-thickness (T) of the magnetic layer is from 0.55 to 1.20.

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, and more particularly to a magnetic recording medium having excellent running performance and running durability, and more particularly to a flexible disk-shaped magnetic recording medium and a tape-shaped magnetic recording medium.

[0002]

2. Description of the Related Art In general, a coating type magnetic recording medium has a magnetic layer in which components such as a ferromagnetic powder and an inorganic additive are dispersed in a binder on a non-magnetic support. As one of such magnetic recording media, there is a flexible disk-shaped magnetic recording medium in which a magnetic layer is provided on a disk-shaped flexible non-magnetic support.

[0003] Flexible disk-shaped magnetic recording media are:
Since the disk violently comes into contact with the magnetic head and the liner during recording and reproduction, excellent wear resistance and durability are required. Further, in recent years, the use environment of these magnetic recording media has been diversified, and a magnetic recording medium having good durability has been demanded even in an environment where temperature and humidity change drastically.

In general, as one method of improving the durability, α-Al ₂ O ₃ , Cr ₂ O ₃ , SiC
Attempts have been made to enhance the inside of the laminated coating film and to improve the abrasion resistance of the coating film surface by adding an abrasive such as.

In recent years, there has been a demand for higher density magnetic recording media, and attempts have been made to make the magnetic layer extremely thin in consideration of the thickness loss and self-demagnetization loss of the medium.

[0006] Due to the thinning of the magnetic layer, the thickness of the magnetic layer may be smaller than the particle size of the abrasive in the abrasives generally used at present. In such a case, since the particle size of the abrasive is not appropriate, an appropriate polishing ability cannot be obtained, and phenomena such as deterioration of durability and deterioration of electromagnetic conversion characteristics occur.

More specifically, by making the magnetic layer thinner,
If an abrasive that is much larger than the magnetic layer thickness is used, the surface of the head will be damaged by the abrasive that is larger than the coating, or the abrasive will fall off due to contact with the head and conversely scrape the coating Failure occurs.

[0008] On the other hand, if the abrasive is smaller than necessary, the abrasion resistance of the coating film surface is remarkably reduced, and problems such as an insufficient reinforcing effect inside the coating film occur.

Therefore, the relationship between the thickness of the magnetic layer and the particle size of the abrasive has been studied, and is disclosed in JP-A-5-282658.
In JP-A-8-263826, the thickness of the magnetic layer and the particle size of the abrasive are specified by numerical values. However, the relationship of the abrasive particle diameter to the magnetic layer thickness is not clear, and as described above, the abrasive particle diameter may be larger than the magnetic layer thickness.

Therefore, Japanese Patent Application Laid-Open No. 7-272256 discloses
JP-A-7-334835, JP-A-10-2473
In Japanese Patent Publication No. 16, the relationship between the thickness of the magnetic layer and the particle size of the abrasive is parameterized so that the range of the particle size of the abrasive with respect to the thickness of the magnetic layer can be specified more clearly.

[0011]

However, in recent years, further durability has been required for the magnetic layer, and the thickness of the magnetic layer and the particle size of the abrasive have been parameterized as disclosed in the above publications. The durability obtained by defining the above has become insufficient.

That is, according to the present invention, an optimum abrasive can be selected for a magnetic recording medium of high density, and a magnetic recording medium having high durability can be provided.

[0013]

As a result of repeated studies to solve the above problems, the magnetic layer is defined by defining the abrasive particle size within a certain range and further defining the polishing ability of the abrasive. It has been found that the optimum abrasive can always be selected even if the thickness of the magnetic recording medium is changed, and that a magnetic recording medium having high durability can be obtained.

That is, according to the present invention, a non-magnetic layer containing a binder is coated and dried on a non-magnetic support, and a magnetic layer is formed, and the thickness of the magnetic layer is 0.5 μm or less. In the above, the Mohs hardness of the abrasive contained in the magnetic layer is 5 or more, and the relative polishing rate is 200 or more. At this time, the relational expression (1) between the abrasive average particle diameter (D) and the magnetic layer thickness (T) is obtained. The above problem is solved by a magnetic recording medium in which the value (A) obtained by (1) is 0.55 to 1.20. A = D / T (1)

In a further preferred aspect of the present invention, the magnetic powder contained in the magnetic layer has a coercive force (Hc) of 1400 to 2
At 600 Oe, the binder used for the non-magnetic layer is a magnetic recording medium containing a binder which can be cross-linked by radiation, and in particular, a flexible disk-shaped magnetic recording medium in which the rotation speed of the magnetic recording medium during recording and reproduction is 700 rpm or more ( A magnetic recording medium (magnetic disk) and a tape-shaped magnetic recording medium (magnetic tape) in which the relative speed between the magnetic recording medium and the magnetic head at the time of recording / reproducing is 1.0 m / sec or more have excellent running durability and running performance and high electromagnetic conversion. With characteristics.

[0016]

FIG. 1 shows a configuration example of a magnetic disk 1 according to an embodiment of the present invention. In this preferred example,
Nonmagnetic underlayers 21 and 25 and magnetic layers 31 and 35 are sequentially laminated on both surfaces of the nonmagnetic support 10. FIG.
FIG. 9 shows a configuration example of a magnetic tape 2 according to another embodiment of the present invention. In this preferred example, the nonmagnetic underlayer 121 and the magnetic layer 131 are sequentially laminated on only one surface of the nonmagnetic support 110, and the backcoat layer 140 is applied on the back surface.

The magnetic layers 31, 3 of the magnetic recording medium of the present invention
The relative polishing rate of the abrasives contained in Nos. 5 and 131 needs to be 200 or more in order to obtain sufficient durability as a coating film, and more preferably 250 or more.

When the average particle size of the abrasive is about 55 to 120% of the thickness of the magnetic layer, high durability is obtained and the signal output is improved. When the average particle size is less than 55%, the amount of the abrasive exposed on the surface of the coating film decreases, and the effect of the addition of the abrasive decreases. When the average particle size exceeds 120%, the abrasive greatly exposed on the surface of the coating film. This causes scratches on the head, and the abrasive material falls off the coating film and damages the head and the coating film surface.

The Mohs hardness of the abrasive is 5 or more, α-alumina, β-alumina, γ-alumina, dichromium trioxide,
α-iron oxide, γ-iron oxide, goethite, SiO ₂ , Zn
There are O, TiO ₂ , ZrO ₂ , SnO _{2 and the} like, and these may be used alone or in combination.

The amount of the abrasive added is preferably 5 to 30 parts by weight, more preferably 10 to 30 parts by weight, based on 100 of the magnetic powder.
To 20 parts by weight.

If the amount is less than 5 parts by weight, the effect as an abrasive tends to decrease. If more than 30 parts by weight,
Depending on the drive, the magnetic head may be damaged due to too strong polishing ability of the coating film surface. Further, since the content of the magnetic powder is relatively small, it affects the electromagnetic conversion characteristics.

As the binder, a thermoplastic resin, a thermosetting or heat-reactive resin, a radiation-sensitive modified resin or the like is appropriately selected according to the characteristics of the medium and the process conditions, and is used in combination.

Examples of the thermoplastic resin include acrylic resin, polyester resin, polyurethane resin, polyamide resin, polyimide resin, phenol resin, polyvinyl alcohol resin, acetal resin, epoxy resin, phenoxy resin, polyether resin, and vinyl chloride resin. Copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral, nitrocellulose, styrene-butadiene copolymer, polyfunctional polyethers such as polycaprolactone, polybutadiene elastomer, chlorinated rubber,
Acrylic rubber, isoprene rubber, epoxy-modified rubber and the like can be mentioned.

Examples of the thermosetting resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, butyral resin, polymer resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, polyamide resin, Epoxy-polyamide resins, saturated polyester resins, urea-formaldehyde resins, and the like.

Of these, those having a hydroxyl group at the terminal and / or the side chain are preferred because crosslinking using a polyisocyanate as a reactive resin or radiation crosslinking modification can be easily performed.

Further, as a polar group at the terminal or side chain, -COO is used.
_{H, -SO 3 M, -OSO 3} M, -OPO 3 X, -PO
_{3 X, -PO 2 X, -N} + R 3 Cl -, -NR 2 , etc. (M is an alkali metal such as a hydrogen atom or a lithium, potassium, sodium, X is fluorine, chlorine, bromine, halogen iodine Element ions or inorganic / organic ions, R may be a hydrogen atom or a hydrocarbon group), an acidic polar group including a basic polar group, betaine, etc.
These are suitable for improving dispersibility, and may be used alone or in combination as needed.

Of these, those preferably used are a combination of a vinyl chloride resin and a urethane resin.

As an example of the resin used, a vinyl chloride resin having a vinyl chloride content of 60 to 95% by weight and an average degree of polymerization of about 100 to 500 is preferable.
A urethane-based resin used in combination with such a vinyl chloride-based resin is particularly effective in that it has good wear resistance and good adhesion to a nonmagnetic support. Note that, in addition to these resins, other resins may be further included.

Further, those resins which have been subjected to radiation-sensitive modification by introducing an acrylic double bond into these resins can also be used. The content of the radiation functional group is from 1 to 40 mol%, preferably from 10 to 30 mol% in the hydroxyl group component in view of the stability at the time of production, radiation curability, etc. When the monomers are reacted so as to have 1 to 20, preferably 2 to 10 functional groups per unit, a radiation-curable resin excellent in both dispersibility and curability can be obtained.

As the magnetic powder contained in the magnetic layer, γ-
Oxide fine powders such as Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ , hexagonal ferrite, and metals such as Fe, Co, Ni, etc. These alloy fine powder, iron carbide and the like can be mentioned.

These magnetic powders may be selected according to the type of magnetic recording medium to be applied, but barium ferrite, metal or alloy, iron carbide, etc. are preferred, and if only one kind is used, two or more kinds may be used in combination. The content is 50 to 85% by weight of the whole magnetic layer, preferably 55 to 7%.
5% by weight.

Further, in addition to these magnetic powders, binders and abrasives, carbon black, lubricants, dispersants and the like may be added to the magnetic layer, if necessary.

According to the constitution of the coating film of the present invention, a non-magnetic layer is laminated on a non-magnetic support, and a magnetic layer is laminated thereon. At this time, the thickness of the non-magnetic layer is preferably from 0.5 to 3.0 μm, more preferably from 1.0 to 3.0 μm, so that it is hardly affected by the surface of the non-magnetic support and the surface property of the magnetic recording medium becomes good. Also, the electromagnetic conversion characteristics and durability are improved.

When the thickness is less than 0.5 μm, the durability is deteriorated. On the other hand, when the thickness is more than 3.0 μm, the coating property is deteriorated to increase defects and decrease the yield, which is not preferable in production.

On the other hand, the thickness of the magnetic layer can be arbitrarily selected depending on the magnetic recording system actually used. However, the thickness must be 0.5 μm or less in consideration of the thickness loss and the self-demagnetization loss of the medium.

The method of applying the non-magnetic layer and the magnetic layer is basically wet-on-dry application in which the non-magnetic layer is applied, and after drying, the magnetic layer is applied. However, from the viewpoint of production efficiency, it is more preferable to use a method in which the nonmagnetic layer is formed using a radiation-curable resin and radiation-cured before applying the magnetic layer.

As a coating means, a coating means such as a gravure coat, a reverse roll coat, and a die nozzle coat can be used.

[0038]

The present invention will be described in more detail with reference to the following examples. In the present invention, the following measuring methods were used for the relative polishing rate, running durability, and average particle size of the abrasive.

Measurement method of relative polishing rate: Mn-Zn ferrite single crystal (1
11) The surface is polished on a buff, and the polishing amount (length) per unit time is compared with the polishing amount of the standard sample. (Alumina slurry composition is 98 parts by weight of water with respect to 2 parts by weight of sample; standard sample is 98 parts by weight of water with 2 parts by weight of AKP20 manufactured by Sumitomo Chemical Co., Ltd.) Represent.

Measurement method for running durability of disk-shaped medium: 2
A disk is inserted into a ZIP drive having a rotation speed of 940 rpm, and the head is randomly randomized in the cycle environment shown in FIG.
And check visually for flaws every 100 hours.

Evaluation method for durability of tape-shaped medium Measuring method for running durability (DLT cassette): Quann
Using a DLT4000 drive from tu, reciprocate while recording / reproducing at a tape length of 5 m in an environment at normal temperature (2 pass calculation for reciprocation). . Those that cleared 1 million passes were judged to have passed. Head adhesion: After storing the tape sample in an environment of 40 ° C and 80% for 5 days,
using anntum DLT4000 drive, 1
000 passes, and the head adhesion after running was
It was confirmed with a light microscope at × 2. With head adhesion: × Without head adhesion: ○ Measuring method of running durability (8 mm cassette): Using an EV-S900 drive manufactured by Sony Corporation, 200 passes were run for 50 tape samples in an environment of 0 ° C. to check for clogging. No clogging: ○ Clogging: x

Abrasive average particle size measuring method: Using an SEM, 100 abrasive particles were measured at a magnification of 20000 times to determine the average particle size.

Example 1 <Non-magnetic layer paint> Granular α-Fe ₂ O ₃ (manufactured by Sakai Chemical Industry Co., Ltd .: FRO-
3): 55 parts by weight (average particle size = 30 nm, specific surface area (B
ET value) = 45 m ² / g) Carbon black (Mitsubishi Chemical Corporation: # 45B): 3
0 parts by weight (average particle size = 24 nm, BET value = 125)
m ² , DBP oil absorption = 47 ml / 100 g) α-Al ₂ O ₃ (AKP50, manufactured by Sumitomo Chemical Co., Ltd.):
15 parts by weight (average particle size = 0.19 μm, BET value = 8 m
² / g) Radiation-sensitive vinyl chloride resin (Toyobo Co., Ltd .: T
B0246 30% solution): 12 parts by weight (degree of polymerization = 30)
0, polar group: -OSO ₃ K = 1.5 / molecule) Radiation-sensitive urethane resin (Toyobo Co., Ltd .: TB
0242 35% solution): 4 parts by weight (molecular weight = 2500)
0, polar group: sodium hypophosphite = 1 / molecule) Trifunctional acrylic monomer (manufactured by Sanyo Chemical Industries, Ltd .: TA)
505): 2 parts by weight Isocetyl stearate: 10 parts by weight Butyl stearate: 4 parts by weight Methyl ethyl ketone (MEK): 126 parts by weight Toluene: 38 parts by weight Cyclohexanone: 38 parts by weight

After kneading the above composition, it was dispersed in a sand grinder mill to prepare a non-magnetic layer paint.

<Magnetic paint 1> Acicular Fe-based metal magnetic powder: 100 parts by weight (coercive force = 166)
0 Oe, σs = 126 emu / g, BET value = 58 m ²
/ G, average major axis length = 0.33 μm, Fe / Co / Ni /
Al = 100/5/5/4 (weight ratio)) Vinyl chloride resin (manufactured by Zeon Corporation: MR11)
0): 14 parts by weight (degree of polymerization = 300, polar group: —OSO)
₃ K = 1.5 / molecule) Phosphobetaine-containing polyurethane resin: 4 parts by weight (molecular weight = 40000, polar group concentration = 1.5 / molecule) -SO ₃ Na-containing polyurethane resin: 2 parts by weight (molecular weight = 25000, polar group concentration = 1 / molecule) Abrasive α-Al ₂ O ₃ : 10 parts by weight (average particle size = 0.23)
μm, BET value = 8 m ² / g) Carbon black (manufactured by Columbian Co., Ltd .: Sevacarb MT): 3 parts by weight (average particle size = 350 nm, BET value =
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 Methyl ethyl ketone: 250 parts by weight Toluene: 80 parts by weight Cyclohexanone: 80 parts by weight Department

After kneading the above composition, the composition was dispersed in a sand grinder mill to prepare a magnetic paint 1.

First, the non-magnetic paint was coated with a surface roughness (Ra) of 9n.
m, and applied to a PET film having a thickness of 62 μm by an extrusion die nozzle method so that the film thickness after drying becomes 1.5 μm, dried at a drying temperature of 100 ° C., and then irradiated with radiation (5 Mra
d) was performed. Next, the other surface was also formed by the same procedure, and a roll of a double-sided nonmagnetic layer was prepared.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 1, and the film thickness after drying was 0.3 μm after being extruded into the roll by a die nozzle method.
m, non-oriented by a non-oriented magnet, dried at a drying temperature of 100 ° C, and a linear pressure of 300 kg / c.
A calender treatment was performed at a temperature of 90 ° C. to complete a coating film on one side. Next, the other surface was also formed in the same procedure to prepare a raw roll of a double-sided magnetic layer.

The raw roll is punched into a disk shape,
Thermal curing was performed at 70 ° C. for 24 hours to produce a disk. The relative polishing rate of the abrasive in the magnetic layer used here was 4
50, the relation value D / T between the average particle size (D) of the abrasive and the thickness (T) of the magnetic layer was 0.77, and the produced magnetic recording medium was excellent in running durability.

Example 2 A disk was produced in the same manner as in Example 1 except that the abrasive of the magnetic paint 1 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 600. The relative polishing rate of the abrasive used here was 600, the relation value D / T between the average particle size (D) of the abrasive and the thickness (T) of the magnetic layer was 0.63, and the produced magnetic recording medium had running durability. Excellent in nature.

Comparative Example 1 A disk was produced in the same manner as in Example 1 except that the abrasive of the magnetic paint 1 was changed to an abrasive having an average particle size of 0.35 μm and a relative polishing rate of 80. The abrasive used here was manufactured because the relative value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 1.16, but the relative polishing rate was 80. The magnetic recording medium did not have sufficient running durability.

Comparative Example 2 A disk was prepared in the same manner as in Example 1 except that the abrasive of the magnetic paint 1 was changed to an abrasive having an average particle size of 0.23 μm and a relative polishing rate of 50. The abrasive used here was manufactured because the relative value D / T between the abrasive average particle diameter (D) and the magnetic layer thickness (T) was 0.77, but the relative polishing rate was 50. The magnetic recording medium did not have sufficient running durability.

Comparative Example 3 A disk was prepared in the same manner as in Example 1 except that the abrasive of the magnetic paint 1 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 170. The abrasive used here was manufactured because the relative value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 0.63, but the relative polishing rate was 170. The magnetic recording medium did not have sufficient running durability.

Comparative Example 4 A disk was prepared in the same manner as in Example 1 except that the abrasive of the magnetic paint 1 was changed to an abrasive having an average particle size of 0.14 μm and a relative polishing rate of 420. Although the relative polishing rate of the abrasive used here was 420, the average abrasive particle diameter (D)
The relational value D / T between the magnetic recording medium and the magnetic layer thickness (T) was 0.46, and thus the produced magnetic recording medium could not have sufficient running durability.

[0055]Example 3 <Magnetic paint 2> Acicular Fe-based metal magnetic powder: 100 parts by weight (coercive force = 240
0 Oe, σs = 143 emu / g, BET value = 51 m^Two
/ G, pH = 10, average major axis length = 0.1 μm, Fe / C
o / Al / Y = 100/30/5/5 (weight ratio)) Vinyl chloride resin (manufactured by Zeon Corporation: MR11)
0): 14 parts by weight (degree of polymerization = 300, polar group: —OSO)
_ThreeK = 1.5 / molecule) Phosphobetaine-containing polyurethane resin: 4 parts by weight (molecule)
(Amount = 40000, polar group concentration = 1.5 / molecule)_ThreeNa-containing polyurethane resin: 2 parts by weight (molecular weight
= 25000, polar group concentration = 1 / molecule) Abrasive α-Al_TwoO_Three: 10 parts by weight (average particle size = 0.14)
μm, BET value = 17m ^Two/ G) Carbon black (manufactured by Columbian Co., Ltd .: Sevacarb)
MT): 3 parts by weight (average particle size = 350 nm, BET value =
7m^TwoSorbitan monostearate: 3 parts by weight Isocetyl stearate: 3 parts by weight Methyl ethyl ketone: 250 parts by weight Toluene: 80 parts by weight Cyclohexanone: 80 parts by weight

After kneading the above composition, the composition was dispersed in a sand glider mill to prepare a magnetic paint 2.

First, the same non-magnetic paint as in Example 1 was extruded onto a PET film having a surface roughness (Ra) of 9 nm and a thickness of 62 μm, and the film thickness after drying by a die nozzle method was 1.5 μm.
After drying at 100 ° C., radiation irradiation (5 Mrad) was performed. Similarly, the other side was also formed to produce a roll of a double-sided nonmagnetic layer.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 2, and the film thickness after drying was 0.2 μm after being extruded into the roll by a die nozzle method.
m, non-oriented by a non-oriented magnet, dried at 100 ° C, and calendered at a linear pressure of 300 kg / cm and a temperature of 90 ° C to finish a coating film on one side. Similarly, the other side was formed, and a raw roll of a double-sided magnetic layer was produced.

This raw roll is punched into a disk shape,
Thermal curing was performed at 70 ° C. for 24 hours to produce a disk. Here, the relative polishing rate of the abrasive used for the magnetic layer was 42.
0, the relation value D / T between the abrasive average particle diameter (D) and the magnetic layer thickness (T) was 0.70, and the manufactured magnetic recording medium was excellent in running durability.

Example 4 A disk was produced in the same manner as in Example 3 except that the abrasive of the magnetic paint 2 was changed to an abrasive having an average particle size of 0.12 μm and a relative polishing rate of 270. The relative polishing rate of the abrasive used here was 270, the relation value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 0.60, and the produced magnetic recording medium had running durability. The character was excellent.

Example 5 A disk was produced in the same manner as in Example 3 except that the abrasive of the magnetic paint 2 was changed to an abrasive having an average particle size of 0.23 μm and a relative polishing rate of 450. The relative polishing rate of the abrasive used here was 450, and the relational value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 1.15. Was excellent.

Comparative Example 5 A disk was produced in the same manner as in Example 3 except that the abrasive of the magnetic paint 2 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 170. The abrasive used here was produced because the relative value D / T between the abrasive average particle diameter (D) and the magnetic layer thickness (T) was 0.95, but the relative polishing rate was 170. The magnetic recording medium did not have sufficient running durability.

Comparative Example 6 A disk was prepared in the same manner as in Example 3 except that the abrasive of the magnetic paint 2 was changed to an abrasive having an average particle size of 0.04 μm and a relative polishing rate of 70. The relative polishing rate of the abrasive used here was 70, the average abrasive particle diameter (D) and the thickness of the magnetic layer (T).
Was 0.20, and the produced magnetic recording medium did not have sufficient running durability.

Example 6 <Magnetic paint 3> Barium ferrite magnetic powder: 100 parts by weight (coercive force = 2
200 Oe, σs = 57 emu / g, BET value 50 m ²
/ G, particle size = 3.5 nm, plate ratio = 3) Vinyl chloride resin (manufactured by Zeon Corporation: MR11)
0): 14 parts by weight (degree of polymerization = 300, polar group: —OSO)
₃ K = 1.5 / molecule) Phosphobetaine-containing polyurethane resin: 4 parts by weight (molecular weight = 40000, polar group concentration = 1.5 / molecule) -SO ₃ Na-containing polyurethane resin: 2 parts by weight (molecular weight = 25,000) , Polar group concentration = 1 / molecule) Abrasive α-Al ₂ O ₃ : 10 parts by weight (average particle size = 0.23)
μm, BET value = 8 m ² / g) Carbon black (manufactured by Columbian Co., Ltd .: Sevacarb MT): 3 parts by weight (average particle size = 350 nm, BET value =
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 Methyl ethyl ketone: 250 parts by weight Toluene: 80 parts by weight Cyclohexanone: 80 parts by weight Department

After kneading the above composition, the composition was dispersed in a sand grinder mill to prepare a magnetic coating material 3.

First, the same non-magnetic paint as in Example 1 was extruded onto a PET film having a surface roughness (Ra) of 9 nm and a thickness of 62 μm, and the film thickness after drying was 1.5 μm by a die nozzle method.
After drying at 100 ° C., radiation irradiation (5 Mrad) was performed. Similarly, the other surface was formed, and a roll of a double-sided nonmagnetic layer was prepared.

Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic coating material 3, and the roll was extruded into this roll with a thickness of 0.3 μm after drying by a die nozzle method.
m and de-oriented by a non-oriented magnet,
After drying at 100 ° C, linear pressure 300kg / cm, temperature 90 ° C
To form a coating film on one side. Similarly, the other side was formed, and a raw roll of a double-sided magnetic layer was produced.

This raw roll is punched into a disk shape,
Thermal curing was performed at 70 ° C. for 24 hours to produce a disk. Here, the relative polishing rate of the abrasive used for the magnetic layer is 45.
0, the relation value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 0.77, and the produced magnetic recording medium was excellent in running durability.

Example 7 A disk was prepared in the same manner as in Example 6, except that the abrasive of the magnetic paint 3 was an abrasive having an average particle size of 0.12 μm and a relative polishing rate of 270, and the thickness of the magnetic layer was changed to 0.2 μm. Was prepared.
The relative polishing rate of the abrasive used here was 270, the relation value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 0.60, and the produced magnetic recording medium had running durability. The character was excellent.

Comparative Example 7 A disk was prepared in the same manner as in Example 6, except that the abrasive of the magnetic paint 3 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 170. The abrasive used here was manufactured because the relative value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 0.63, but the relative polishing rate was 170. The magnetic recording medium did not have sufficient running durability.

Comparative Example 8 A disk was produced in the same manner as in Example 6 except that the abrasive of the magnetic paint 3 was changed to an abrasive having an average particle diameter of 0.14 μm and a relative polishing rate of 420. The relative polishing rate of the abrasive used here was 420, but the relative value D / T between the average particle size (D) of the abrasive and the thickness (T) of the magnetic layer was 0.46. The magnetic recording medium did not have sufficient running durability.

Comparative Example 9 A disk was produced in the same manner as in Example 6, except that the abrasive of the magnetic paint 3 was changed to an abrasive having an average particle diameter of 0.04 μm and a relative polishing rate of 70 to a magnetic layer thickness of 0.2 μm. did. The relative polishing rate of the abrasive used here was 70, and the relation value D / T between the average particle diameter (D) of the abrasive and the thickness (T) of the magnetic layer was 0.20.
Thus, the produced magnetic recording medium did not have good running durability.

Example 8 <Non-magnetic layer coating material 2> α-Fe ₂ O ₃ (manufactured by Toda Kogyo KK: DPN-250B)
W): 80 parts by weight (average minor axis diameter = 23 nm, BET = 5)
5 m ² / g) Carbon black (manufactured by Mitsubishi Chemical Corporation: # 850B):
20 parts by weight (average particle size = 16 nm, BET = 200 m ²⁾
/ G, DBP oil absorption = 70 ml / 100 g) α-Al ₂ O ₃ (manufactured by Sumitomo Chemical Co., Ltd .: HIT60)
A): 5 parts by weight (average particle size = 0.18 μm, BET = 1)
2m ² / g) Radiation-sensitive vinyl chloride resin (Toyobo Co., Ltd .: T
B0246 30% solution): 16 parts by weight (degree of polymerization = 30)
0, polar group: -OSO ₃ K = 1.5 / molecule) Radiation-sensitive urethane resin (Toyobo Co., Ltd .: TB
0242 35% solution): 8 parts by weight (molecular weight = 2500)
0, polar group: sodium hypophosphite = 1 / molecule) Trifunctional acrylic monomer (manufactured by Sanyo Chemical Industries, Ltd .: TA)
505): 4 parts by weight MEK: 120 parts by weight Toluene: 120 parts by weight Cyclohexanone: 60 parts by weight

After kneading the above composition, it was dispersed in a sand grinder mill. Next, the following additives and solvents were added to adjust the viscosity, and a non-magnetic coating material 2 was prepared. Butyl stearate: 1 part by weight Stearic acid: 1 part by weight MEK: 40 parts by weight Toluene: 40 parts by weight Cyclohexanone: 40 parts by weight

<Magnetic paint 4> Fe-based metal magnetic powder: 100 parts by weight (Hc = 1830O)
e, σs = 130 emu / g, BET value = 57 m ² /
g, average major axis length = 0.10 μm, Fe / Co / Al / Y
= 100/10/5/2 (weight ratio)) Vinyl chloride copolymer (manufactured by Zeon Corporation: MR11)
0): 10 parts by weight (degree of polymerization = 300, polar group: —OSO)
₃ K = 1.5 / molecule) -SO ₃ Na-containing polyurethane resin: 7 parts by weight (Mn =
Α-Al ₂ O ₃ : 12 parts by weight (average particle diameter = 0.12 μm, 25000, polar group concentration = 1 / molecule)
BET = 20 m ² / g) Myristic acid: 2 parts by weight MEK: 90 parts by weight Toluene: 90 parts by weight Cyclohexanone: 120 parts by weight

After the above composition was kneaded, it was dispersed in a sand glider mill. Next, the following additives and solvents were added to adjust the viscosity to prepare a magnetic paint 4. Butyl stearate: 1 part by weight Stearic acid: 1 part by weight MEK: 110 parts by weight Toluene: 110 parts by weight Cyclohexanone: 160 parts by weight

<Coating for Back Coat Layer> Carbon black: 80 parts by weight (Conductex SC, manufactured by Columbian Carbon Co., Ltd.)
m, BET = 220 m ² / g) Carbon black: 1 part by weight (manufactured by Columbian Carbon Co., Ltd .: SevacarbMT) Average particle size = 350 nm, B
ET = 8 m ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: TF100, average particle size = 0.1 μm): 1 part by weight vinyl chloride-vinyl acetate-vinyl alcohol copolymer:
65 parts by weight (weight ratio of monomer = 92: 3: 5, average degree of polymerization = 420) Polyester polyurethane resin (manufactured by Toyobo Co., Ltd .: U
R-8300): 35 parts by weight MEK: 260 parts by weight Toluene: 260 parts by weight Cyclohexanone: 260 parts by weight

After the above composition was kneaded, it was dispersed in a sand glider mill. Next, the following additives and solvents were added to adjust the viscosity. Stearic acid: 1 part by weight Myristic acid: 1 part by weight Butyl stearate: 2 parts by weight MEK: 210 parts by weight Toluene: 210 parts by weight Cyclohexanone: 210 parts by weight

First, a non-magnetic coating material 2 is first extruded onto a 6.1 μm-thick PET film by a die nozzle method so as to have a dry film thickness of 2.0 μm, dried at a drying temperature of 100 ° C., and then dried at a temperature of 100 ° C. A calender treatment was performed at a pressure of 300 kg / cm, and finally an electron beam irradiation (5 Mrad) was performed to prepare a nonmagnetic layer raw material. Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 4, 1 part by weight was added to 100 parts by weight of the back coat paint, and the magnetic paint 4 was extruded on the non-magnetic layer raw material. Coating was performed by a die nozzle method so that the dry film thickness became 0.20 μm, orientation was performed, and the coating film was dried at a drying temperature of 100 ° C., and then calendered at a temperature of 100 ° C. and a linear pressure of 300 kg / cm. . Next, the back coat paint was extruded onto the base surface opposite to the magnetic layer, and the dry film thickness was reduced to 0.
It was applied so as to have a thickness of 5 μm to prepare a raw roll.

After leaving this roll at room temperature for 24 hours,
After curing for 24 hours in a heating oven at 0 ° C.,
It was cut into inch width and assembled into a DLT cassette to obtain a magnetic tape sample.

Here, the relative polishing rate of the abrasive used for the magnetic layer was 270, the average abrasive particle diameter (D) and the thickness of the magnetic layer (T).
Was 0.60, and the produced magnetic recording medium was excellent in running durability and head adhesion properties.

Example 9 A tape sample was produced in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle diameter of 0.14 μm and a relative polishing rate of 420. The relative polishing rate of the abrasive used here was 420, the relation value D / T between the abrasive average particle diameter (D) and the thickness of the magnetic layer (T) was 0.70, and the produced magnetic recording medium had running durability. Properties and head adhesion properties were excellent.

Example 10 A tape sample was prepared in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 600. The relative polishing rate of the abrasive used here was 600, the relation value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 0.95, and the produced magnetic recording medium had running durability. Properties and head adhesion properties were excellent.

Example 11 A tape sample was prepared in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle size of 0.23 μm and a relative polishing rate of 450. The relative polishing rate of the abrasive used here was 450, the relation value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 1.15, and the produced magnetic recording medium had running durability. Properties and head adhesion properties were excellent.

Comparative Example 10 A tape sample was prepared in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 170. The abrasive used here is a relational value D between the abrasive average particle diameter (D) and the magnetic layer thickness (T).
/ T was 0.95, but since the relative polishing rate was 170, the produced magnetic recording medium had sufficient running durability,
No head adhesion characteristics were obtained.

Comparative Example 11 A tape sample was produced in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle size of 0.04 μm and a relative polishing rate of 70. The relative polishing rate of the abrasive used here was 70, and the relation value D / T between the average particle diameter (D) of the abrasive and the thickness (T) of the magnetic layer was 0.20. Running durability and head adhesion characteristics could not be obtained.

Comparative Example 12 A tape sample was prepared in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle size of 0.23 μm and a relative polishing rate of 50. The abrasive used here is a relational value D / between the abrasive average particle diameter (D) and the magnetic layer thickness (T).
Although T was 1.15, since the relative polishing rate was 50, the produced magnetic recording medium could not obtain sufficient running durability and head adhesion characteristics.

Comparative Example 13 A tape sample was prepared in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle diameter of 0.35 μm and a relative polishing rate of 80. The relative polishing rate of the abrasive used here was 80, and the relationship value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 1.75. Running durability and head adhesion characteristics could not be obtained.

Comparative Example 14 A tape sample was produced in the same manner as in Example 8, except that the abrasive of the magnetic paint 4 was changed to an abrasive having an average particle diameter of 0.36 μm and a relative polishing rate of 220. The relative polishing rate of the abrasive used here was 220, and the relation value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) was 1.80. Running durability and head adhesion characteristics could not be obtained.

Example 12 <Magnetic paint 5> Fe-based metal magnetic powder: 100 parts by weight (Hc = 1680O)
e, σs = 125 emu / g, BET value = 58 m ² /
g, average major axis length = 0.15 μm, Fe / Co / Ni / A
1 / Si = 100/5/3/4/1 (weight ratio)) Vinyl chloride copolymer (manufactured by Zeon Corporation: MR11)
0): 10 parts by weight (degree of polymerization = 300, polar group: —OSO)
₃ K = 1.5 / molecule) -SO ₃ Na-containing polyurethane resin: 7 parts by weight (Mn =
Α-Al ₂ O ₃ : 12 parts by weight (average particle diameter = 0.23 μm, 25000, polar group concentration = 1 / molecule)
Relative polishing rate = 450, BET = 8 m ² / g) Myristic acid: 2 parts by weight MEK: 90 parts by weight Toluene: 90 parts by weight Cyclohexanone: 120 parts by weight

After kneading the above composition, it was dispersed in a sand grinder mill. Next, the following additives and solvents were added to adjust the viscosity, and magnetic paint 5 was prepared. Butyl stearate: 1 part by weight Stearic acid: 1 part by weight MEK: 110 parts by weight Toluene: 110 parts by weight Cyclohexanone: 160 parts by weight

First, a non-magnetic coating material 2 was first extruded onto an 8.0 μm-thick PET film by a die nozzle method so as to have a dry film thickness of 2.0 μm, dried at a drying temperature of 100 ° C., and then dried at a temperature of 100 ° C. A calendering process was performed at a pressure of 300 kg / cm, and finally, electron beam irradiation (5 Mrad) was performed to prepare a nonmagnetic layer raw material. Next, 4 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic paint 5, 1 part by weight was added to 100 parts by weight of the back coat paint, and the magnetic paint was extruded onto the non-magnetic layer raw material. Apply so that the dry film thickness becomes 0.30 μm by the method,
After performing orientation and drying the coating film at a drying temperature of 100 ° C.,
A calendar treatment was performed at a temperature of 100 ° C. and a linear pressure of 300 kg / cm. Next, the back coat paint was extruded on the base surface opposite to the magnetic layer, and the dry film thickness was 0.5 μm by a die nozzle method.
m to give a raw roll.

After leaving this roll at room temperature for 24 hours,
After curing for 24 hours in a heating oven at 0 ° C., 8 mm
It was cut into a width, assembled into an 8 mm cassette, and used as a magnetic tape sample.

Here, the relative polishing rate of the abrasive used for the magnetic layer was 450, the average abrasive particle diameter (D) and the thickness of the magnetic layer (T).
Was 0.76, and the produced magnetic recording medium was excellent in running durability.

Example 13 A tape sample was prepared in the same manner as in Example 11, except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 600. The relative polishing rate of the abrasive used here was 600, the relation value D / T between the average particle size (D) of the abrasive and the thickness (T) of the magnetic layer was 0.63, and the produced magnetic recording medium had running durability. The character was excellent.

Example 14 A tape sample was produced in the same manner as in Example 11, except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle diameter of 0.36 μm and a relative polishing rate of 220. The relative polishing rate of the abrasive used here was 220, the relation value D / T between the average particle diameter (D) of the abrasive and the thickness (T) of the magnetic layer was 1.20, and the produced magnetic recording medium had running durability. The character was excellent.

Comparative Example 15 A tape sample was produced in the same manner as in Example 11 except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle diameter of 0.14 μm and a relative polishing rate of 420. Although the relative polishing rate of the abrasive used here was 420, the relationship value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 0.1.
As a result, the produced magnetic recording medium did not have sufficient running durability.

Comparative Example 16 A tape sample was prepared in the same manner as in Example 11, except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle size of 0.19 μm and a relative polishing rate of 170. The abrasive used here had a relation value D / T between the average abrasive particle diameter (D) and the magnetic layer film thickness (T) of 0.63, but had a relative polishing rate of 170.
Therefore, the produced magnetic recording medium did not have sufficient running durability.

Comparative Example 17 A tape sample was produced in the same manner as in Example 11, except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle size of 0.23 μm and a relative polishing rate of 50. The abrasive used here was produced because the relative value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 0.76, but the relative polishing rate was 50. The magnetic recording medium did not have sufficient running durability.

Comparative Example 18 A tape sample was prepared in the same manner as in Example 11, except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle diameter of 0.46 μm and a relative polishing rate of 380. Although the relative polishing rate of the abrasive used here was 380, the relationship value D / T between the average abrasive particle diameter (D) and the magnetic layer thickness (T) was 1.
As a result, the produced magnetic recording medium did not have sufficient running durability.

Comparative Example 19 A tape sample was prepared in the same manner as in Example 11, except that the abrasive of the magnetic paint 5 was changed to an abrasive having an average particle size of 0.57 μm and a relative polishing rate of 150. The abrasive used here had a relation value D / T between the average abrasive particle diameter (D) and the thickness of the magnetic layer (T) of 1.90 and a relative polishing rate of 150. The medium did not have sufficient running durability. The above results are shown in Tables 1 to 4 below.

[0102]

[Table 1]

[0103]

[Table 2]

[0104]

[Table 3]

[0105]

[Table 4]

[0106]

According to the present invention, there is provided a magnetic recording system wherein a non-magnetic layer containing a binder is formed on a non-magnetic support after coating and drying, and the thickness of the magnetic layer is 0.5 μm or less. In the medium, when the Mohs hardness of the abrasive contained in the magnetic layer is 5 or more and the relative polishing rate is 200 or more, the relational expression (1) between the average particle diameter (D) of the abrasive and the thickness (T) of the magnetic layer. = D / T (1) By using an abrasive whose value (A) is 0.55 to 1.20, a flexible disk having a magnetic recording medium rotation speed of 700 rpm or more during recording and reproduction is used. Running durability in a tape-shaped magnetic recording medium and a tape-shaped magnetic recording medium in which the relative speed between the magnetic recording medium and the magnetic head during recording and reproduction is 1.0 m / sec or more.
A magnetic recording medium having excellent running performance and high electromagnetic conversion characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a preferred configuration example of a magnetic disk of the present invention.

FIG. 2 is a sectional view of a preferred configuration example of the tape-shaped magnetic recording medium of the present invention.

FIG. 3 is a graph showing environmental cycle conditions when a durability test is performed in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic disk 2 Tape-shaped magnetic recording medium 10,110 Non-magnetic support 21,25,121 Non-magnetic underlayer 31,35,131 Magnetic layer 140 Back coat layer

Claims (5)

[Claims] 1. A magnetic recording medium wherein a non-magnetic layer containing a binder is coated and dried on a non-magnetic support, and the magnetic layer has a thickness of 0.5 μm or less. The contained abrasive has a Mohs hardness of 5 or more and a relative polishing rate of 200 or more. At this time, a value obtained by the relational expression (1) between the average particle diameter (D) of the abrasive and the thickness (T) of the magnetic layer. (A) 0.55 to 1.20, a magnetic recording medium. A = D / T (1) 2. The coercive force (Hc) of the magnetic powder contained in the magnetic layer is from 1400 to 2600 Oe.
The magnetic recording medium according to the above. 3. The magnetic recording medium according to claim 1, wherein the binder used for the non-magnetic layer contains a binder that can be crosslinked by radiation. 4. The rotation speed during recording and reproduction is 700 rpm
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a flexible disk-shaped magnetic recording medium having a length of at least m. 5. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is a tape-shaped magnetic recording medium having a relative speed of 1.0 m / sec or more during recording and reproduction. .