JPH06290446A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium excellent in an electromagnetic conversion characteristic and a durability. CONSTITUTION:In the magnetic recording medium, an intermediate layer contg. non-magnetic fine particles in which a ratio of size of particle diameter or minor axis of a non-magnetic fine particles other than carbon black particles to a size of particles diameter of carbon black is 1.0-4.0 and carbon black is provided on a non-magnetic substrate. Then, the magnetic layer whose thickness is 0.2-1.0mum is provided on the intermediate layer.

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 having a magnetic layer having a thickness of 1.0 μm or less, and more specifically,
The present invention relates to the above magnetic recording medium having excellent electromagnetic conversion characteristics and durability, which can be suitably applied to an apparatus for recording / reproducing a digitized signal by a heli-cal scan method.

[0002]

2. Description of the Related Art A magnetic recording medium is usually prepared by coating a magnetic coating material comprising a magnetic powder, a binder component, an organic solvent and other necessary components on a non-magnetic support such as a polyester film and drying it. In response to the demand for higher density, the magnetic layer has been thinned.

Further, in recent years, with the development of signal processing and digital circuit technology, digitization and recording have also been performed in video equipment, and at the present time,
Unsaturated digital recording is performed because the magnetic layer is thick, but it is preferable to perform saturated digital recording in which digital signals are recorded and reproduced so that overwriting can be performed as in the case of a magnetic disk device for computers. When performing such saturated digital recording, it is preferable to thin the magnetic layer.

However, when the magnetic layer is made thin to improve the recording density and the overwriting characteristics, the surface property of the non-magnetic support is likely to appear.
There has been a problem that the electromagnetic conversion characteristics are deteriorated such that the reproduction output is reduced as the magnetic layer is made thinner.

Therefore, in order to prevent the influence of the surface property of the non-magnetic support and improve the surface smoothness of the magnetic layer, an intermediate layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. Although the conventional intermediate layer prevents the influence of the surface property of the non-magnetic support, it does not support the pinhole.
Durability or improvement in durability will not occur due to peeling or coating streaks.

Therefore, in recent years, after applying the intermediate layer paint,
From the rheological point of view of the intermediate layer when applying the magnetic paint, it has been attempted to improve the durability by improving the composition of the intermediate layer paint and the coating method. A method has been proposed in which a magnetic layer having a thickness of less than 1.0 μm is provided to improve electromagnetic conversion characteristics and durability. (JP-A-4-238111)

[0007]

However, in this method, although the occurrence of pinholes and coating stripes is suppressed on the surface of the magnetic layer, the surface smoothness of the magnetic layer is still sufficiently improved. However, the electromagnetic conversion characteristics may deteriorate rather than the magnetic recording medium in which the magnetic layer is directly provided on the non-magnetic support without providing the intermediate layer.

The present invention has been made as a result of various investigations in view of the above-mentioned circumstances, and the surface smoothness of a magnetic layer having a thickness of 1.0 μm or less can be sufficiently obtained without causing pinholes or coating stripes. To improve the electromagnetic conversion characteristics and durability sufficiently.

[0009]

According to the present invention, the diameter or minor axis diameter of non-magnetic fine particles (hereinafter referred to as non-magnetic fine particles) having a particle diameter ratio other than carbon black on a non-magnetic support. By providing an intermediate layer containing non-magnetic fine particles having a particle diameter of / carbon black of 1.0 to 4.0 and carbon black, and providing a magnetic layer having a thickness of 0.2 to 1.0 μm on the intermediate layer, -The surface roughness of the magnetic layer with a thickness of 1.0 μm or less can be measured in the frequency analysis of non-contact surface roughness to be 102 mm ^-1
And the strength at 205 mm ⁻¹ are 9 to 15 dB, and the electromagnetic conversion characteristics and durability are sufficiently improved.

Further, the total thickness of the magnetic recording medium including the non-magnetic support, the intermediate layer and the magnetic layer is 13 μm or less so that a sufficient recording capacity can be obtained and the electromagnetic conversion characteristics and durability are excellent. A magnetic recording medium can be obtained.

Further, by using together a vinyl chloride resin having a functional group having the same polarity and a polyurethane resin as a binder resin for the intermediate layer, the non-magnetic fine particles and carbon black in the intermediate layer can be formed. By improving the dispersibility and further improving the surface smoothness of the intermediate layer and further the surface smoothness of the magnetic layer, the electromagnetic conversion characteristics and durability of the magnetic recording medium are further improved.

Further, as the magnetic powder contained in the magnetic layer, Fe powder containing 0.10 to 3.00% by weight of Al with respect to Fe is used, and the Dx value (X-ray grain size) of this Fe powder and the non-magnetic fine particles of the intermediate layer are used. The ratio of the particle diameter of Fe powder to the Dx value of Fe powder / diameter or minor axis diameter of non-magnetic fine particles in the intermediate layer is 0.2 to 1.0, or alumina particles are contained in the magnetic layer,
By setting the ratio of the alumina particles and the particle diameter of the non-magnetic fine particles in the intermediate layer to the diameter of the alumina particles / the diameter of the non-magnetic fine particles in the intermediate layer or the minor axis diameter to 3.0 to 12.0,
The durability of the magnetic recording medium is further improved.

In the present invention, the intermediate layer provided between the non-magnetic support and the magnetic layer has a particle diameter ratio of the diameter of the non-magnetic fine particles or the minor axis diameter / the particle diameter of carbon black.
It is preferable to use non-magnetic fine particles of 1.0 to 4.0 in combination with carbon black. When an intermediate layer containing such non-magnetic fine particles in combination with carbon black is formed, the surface smoothness of the intermediate layer during drying is improved. Will be good.

[0014] 102mm As a result, the surface of the intermediate layer affects the surface properties of the magnetic layer to be laminated thereon, the surface roughness of the magnetic layer, in the frequency analysis of the non-contact surface roughness ^{- A} magnetic layer having a difference between the strength at ¹ and the strength at 205 mm ^-1 of 9 to 15 dB is formed, and the thickness is 0.2 to
The surface smoothness and durability of the 1.0 μm magnetic layer are sufficiently improved. The diameter or minor axis diameter in the present invention is an average value of each particle.

Therefore, according to the present invention, the surface smoothness and durability of the intermediate layer during drying are sufficiently improved, and the surface smoothness of the magnetic layer having a thickness of 0.2 to 1.0 μm formed on the intermediate layer. A magnetic recording medium having sufficiently improved magnetic properties and sufficiently improved electromagnetic conversion characteristics and durability can be obtained.

On the other hand, the ratio of the particle diameters of the non-magnetic fine particles and the carbon black used in combination is less than 1.0 in terms of the diameter of the non-magnetic fine particles or the minor axis diameter / the particle diameter of the carbon black. Or if it exceeds 4.0, the filling property of these powders is impaired, the surface smoothness of the intermediate layer is not sufficiently good, and the surface roughness of the magnetic layer formed on this intermediate layer is non-contact surface. 102 in the frequency analysis of roughness
The difference between the strength at mm ^-1 and the strength at 205 mm ^-1 is less than 9 dB or exceeds 15 dB.

Then, the difference in intensity of this frequency analysis is 9d.
If it is less than B, the frequency of irregularities of short cycle increases in the smoothness of the magnetic layer surface, but the height difference becomes small, and the gap between the magnetic head and the magnetic recording medium becomes small, and the magnetic head and the magnetic recording medium become small. As a result of the larger sliding contact portion with and, the durability is reduced. Further, when the difference in intensity of frequency analysis exceeds 15 dB, the frequency of long-period irregularities decreases, but the difference in height increases and the gap between the magnetic head and the magnetic recording medium increases, resulting in deterioration of output. Therefore, if the difference in the intensity of frequency analysis is less than 9 dB or exceeds 15 dB, a magnetic recording medium excellent in electromagnetic conversion characteristics and durability cannot be obtained.

Further, the compounding amount of the non-magnetic fine particles and the carbon black having such a particle diameter ratio of 1.0 to 4.0 in terms of the diameter of the non-magnetic fine particles or the minor axis diameter / the particle diameter of the carbon black is: The volume ratio of non-magnetic fine particles / carbon black is preferably in the range of 70/30 to 60/40, and if the carbon black is too little or too much, the coating suitability deteriorates. Then, so-called coating stripes appear on the surface of the magnetic layer, and a magnetic recording medium having good surface smoothness cannot be obtained.

As the binder resin for the intermediate layer, a vinyl chloride resin and a polyurethane resin are used, but it is preferable to use a vinyl chloride resin having a functional group having the same polarity and a polyurethane resin together. , When both a vinyl chloride resin having a functional group having the same polarity and a polyurethane resin are used together, the dispersibility of the non-magnetic fine particles and carbon black in the intermediate layer becomes good, and the surface smoothness of the intermediate layer and thus the magnetic properties of the intermediate layer are improved. The surface smoothness of the layer is further improved, and the electromagnetic conversion characteristics and durability of the magnetic recording medium are further improved.

On the other hand, when a vinyl chloride resin containing functional groups having different polarities and a polyurethane resin are used in combination,
Since these functional groups are attracted to each other and their dispersion improving effects are offset, the surface smoothness is not sufficiently improved.

Further, the mixing ratio of the non-magnetic fine particles and the carbon black to these binder resins is 80/20 to 60 in terms of the weight ratio of powder / binder resin.
It is preferably used within the range of / 40. If the amount of these powders is too large, the stability of the intermediate layer coating upon standing is poor, and it is difficult to obtain a homogeneous magnetic recording medium in a long magnetic recording medium. If it is too small, the curl of a so-called magnetic tape becomes large, the running property of the magnetic recording medium is deteriorated at the time of recording / reproducing information, and data error occurs at the time of reproducing at the time of recording.

The non-magnetic fine particles used for such an intermediate layer may be spherical, needle-shaped or dice-shaped, and have a particle size of 20 to 100 nm.
The ones used are preferred.

Specific examples include, for example, alumina and α
-Hematite, titanium oxide, chromium oxide, zinc oxide, barium sulfate, calcium carbonate and the like can be mentioned. Specific examples of commercial products include, for example, Showa Denko KK; Nanotite 6
0, manufactured by Toda Kogyo Co., Ltd .; TF-100, TF-120, TF
-140, DPN-245, manufactured by Ishihara Sangyo Kaisha; Type-
KU, TT055, CR-50, Sumitomo Chemical Co., Ltd .; AK
P-50, AOS-50, HIT-50, etc. are mentioned.

As carbon black,
Any of Nesblack, thermal black, acetylene black and the like may be used, and the particle size is 10 to 50 n.
m is preferably used. A so-called neutral one is preferable, and one having a pH of 6 to 8.5 is preferably used.

Specific examples of commercial products include, for example, Cabonet; Monarch 800, Monarch 880, Monarch 900, Monarch 460, Monarch 280, Monarch.
Ra 230, Monarch 120, Regal 330R, Regal 415R, Regal 250R, Regal 99R, Columbia Carbon Co .; Raven 1250 and the like.

Further, as the binder resin used in the intermediate layer, --SO ₃ M (where M is H or alcal metal), --PO (OH) ₂ , --PO (OH) (ON ₁ R
₂ R ₃ H) (where, R ₁ to R ₃ is H or OH or an alkyl group), - CO ₂ M (where, M is H or Arukaru metal) anionic functional groups, such as, -NR ₁ R ₂ R ₃ A vinyl chloride resin and a polyurethane resin having a cationic functional group such as X (wherein R _{1 to} R ₃ are alkyl groups, X is a halogen atom) are preferably used in combination, and both have functional groups having the same polarity. Vinyl chloride resin and polyurethane resin are used together.

As such a vinyl chloride resin, for example, manufactured by Nippon Zeon Co .; MR110, MR113, M
R116, Sekisui Chemical Co., Ltd .; S-REC E C1
30, Eslec E C110, manufactured by Nissin Chemical Industry Co., Ltd .; M
PR-TAO, U.S.S. C. Company C; VMCH, MXR-5
27, MXR-536, MXR-535 and the like.

As the polyurethane resin, for example, Toyobo Co .; UR8300, UR8700, UR8
200 etc. can be given.

As the binder resin for the intermediate layer, in addition to these vinyl chloride resin and polyurethane resin,
A polyisocyanate compound may be used in combination, and a binder resin used in a magnetic recording medium may also be used, if necessary.

Further, a lubricant may be added to the intermediate layer paint, and in particular, a fatty acid ester type lubricant such as stearic acid-n-butyl is wet with the magnetic layer formed thereon. In order to improve the sex, it is preferable to use them by mixing,
Furthermore, fatty acids such as stearic acid, myristic acid and palmitic acid may be added.

In this case, the amount of the fatty acid ester lubricant used is based on the total amount of the non-magnetic fine particles and carbon black.
If less than 0.5% by weight, the desired effect cannot be obtained, and 5.0% by weight
If it exceeds this range, the durability of the intermediate layer will decrease, so it is preferably in the range of 0.5 to 5.0% by weight.

The amount of the fatty acid used is preferably 4.0% by weight or less because the durability of the intermediate layer is lowered when the amount exceeds 4.0% by weight based on the total amount of the non-magnetic fine particles and carbon black.

The amount of the lubricant added is determined not only from the viewpoint of the durability of the intermediate layer, but also from the viewpoint of the durability of the magnetic recording medium. When the addition amount is regulated by the extraction amount described in JP-A 5-128495, when n-hexane is used as a solvent and left at room temperature for 16 hours, in the case of a fatty acid ester, it is in the range of ^{20 to} 50 mg / m ² . Is preferable, and in the case of fatty acid, it is preferably 10 mg / m ² or less.

In such an intermediate layer, the above-mentioned non-magnetic fine particles and carbon black are mixed and dispersed with the above-mentioned vinyl chloride resin and polyurethane resin having a functional group having the same polarity and an organic solvent. It is formed by preparing an intermediate layer paint, applying the intermediate layer paint on a non-magnetic support, and drying.

Here, as the organic solvent used in the intermediate layer coating, any of those used in conventionally known magnetic recording media can be used. For example, a ketone solvent such as methyl ethyl ketone, cyclohexanone or methyl isobutyl ketone, Tetrahydrofuran, dioxane, etc.
Tellurium solvents, acetic acid ester solvents such as ethyl acetate and butyl acetate, etc. may be used alone or in combination, and further mixed with toluene or the like.

The magnetic layer formed on such an intermediate layer comprises Fe powder, Co powder, Fe-Ni powder and various conventionally known magnetic powders such as barium ferrite and strontium ferrite, a binder resin, an organic solvent and the like. A magnetic paint is prepared by mixing and dispersing with this magnetic paint.
It is formed by coating and drying on the intermediate layer formed on the non-magnetic support.

The binder resin for the intermediate layer is a resin having a cationic functional group, and the binder resin for the magnetic layer is a resin having an anionic functional group. When a resin containing functional groups with different polarities is used, the adhesiveness between the magnetic layer and the intermediate layer is improved by the amount of the slightly attracting force of the polarities, and the durability is further improved. It is more preferred to use in combination.

As the magnetic powder, in order to sufficiently improve durability, it is preferable to use a magnetic powder containing alumina. In the case of Fe powder containing alumina, alumina contained in Fe is 0.10 as Al. If it is less than wt%, there is no effect in improving durability, and if it is more than 3.00 wt%, the electromagnetic conversion characteristics deteriorate. Therefore, those containing 0.10 to 3.00 wt% are preferably used. Those containing 0.5 to 2.00% by weight are preferably used.

As described above, the particle diameter of the magnetic powder containing alumina is such that the ratio of the Dx value (X-ray particle diameter) of the magnetic powder to the particle diameter of the non-magnetic fine particles in the intermediate layer is Dx value of the magnetic powder /
The diameter or minor axis diameter of the non-magnetic particles in the intermediate layer is 0.2.
If it is smaller, the durability cannot be improved sufficiently,
If it is larger than 1.0, it will be difficult to secure the playback output.
Those within the range of 2 to 1.0 are preferably used, especially 0.4
Those within the range of to 1.0 are preferably used.

As the abrasive contained in the magnetic layer, alumina is preferably used in order to sufficiently improve durability. In this case, the particle size of the alumina particles is the same as the alumina particles and the non-magnetic particles in the intermediate layer. If the ratio of the particle size to the particle size of the alumina particles is the diameter of the alumina particles / the diameter of the non-magnetic particles in the intermediate layer or the minor axis diameter is less than 3.0, the durability cannot be sufficiently improved, and if it is more than 12.0. Since the magnetic head is scratched, those in the range of 3.0 to 12.0 are preferably used, and those in the range of 3.3 to 10.0 are particularly preferably used.

As described above, the amount of alumina contained in the magnetic layer is 6.5 to 15.0% by weight as Al with respect to Fe.
It is preferably contained, and if less than 6.5 wt% as Al relative to Fe, the durability is not sufficiently improved,
If it exceeds 15.0% by weight, the amount of non-magnetic components increases, and the reproduction output decreases.

Alumina may be added to the magnetic layer as described above, or may be contained in the magnetic powder as described above. In either case, the inclusion of alumina improves the polishing power and improves the durability. Be improved.

The magnetic recording medium of the present invention is formed by laminating the intermediate layer and the magnetic layer on the non-magnetic support as described above. The sufficient recording capacity is obtained and the electromagnetic conversion characteristics of the magnetic recording medium are obtained. In order to further improve the durability, the total thickness of the non-magnetic support, the intermediate layer and the magnetic layer is 13 μm or less, the squareness ratio of the magnetic layer is 0.78 or more, and the residual magnetic flux density is 3000. It is preferable that it is not less than Gauss.

For a magnetic layer having a squareness ratio of 0.78 or more and a residual magnetic flux density of 3000 gauss or more, after applying the intermediate layer coating material on the non-magnetic support, the magnetic coating material is applied and dried. It is formed by sometimes performing magnetic field orientation processing. The magnetic layer becomes denser and more durable as the orientation of the magnetic powder is improved by such magnetic field orientation treatment.
When the squareness ratio is 0.78 or more and the residual magnetic flux density is 3000 gauss or more, the orientation of the magnetic powder becomes sufficiently good, the magnetic layer becomes dense, and the durability is further improved.

Further, the higher the packing density of the magnetic powder, the denser the magnetic layer and the better the durability. Therefore, it is preferable to improve the orientation as well as the packing property of the magnetic powder. The property is adjusted by performing a surface smoothing treatment with a calendar after forming the magnetic layer. Although this surface smoothing treatment depends on the composition, for example, 80
150kg / for the magnetic layer between the metal rolls heated to ℃
It is performed by running while applying a linear pressure of cm.

When the intermediate layer and the magnetic layer of the present invention are provided on the non-magnetic support, the total thickness of the non-magnetic support, the intermediate layer and the magnetic layer is 7.5 to 20.0 μm. Sufficient durability is obtained within the range, and when the total thickness of the non-magnetic support, the intermediate layer and the magnetic layer is 13 μm or less, sufficient recording capacity and sufficient durability can be obtained.

Therefore, if the total thickness of the nonmagnetic support, the intermediate layer and the magnetic layer is 13 μm or less, the squareness ratio of the magnetic layer is 0.78 or more, and the residual magnetic flux density is 3000 gauss or more. A sufficient recording capacity can be obtained, and the electromagnetic conversion characteristics and durability of the magnetic recording medium can be further improved.

As a method for applying the magnetic coating material and the intermediate layer coating material, a conventionally known method, for example, JP-B-5-5949.
There is a method described in No. 1, for example, a roll coat, a gravure coat, an extrusion die coat, a carten coat, etc. are used for applying the intermediate layer paint. An extrusion die coat is used for coating.

[0049]

EXAMPLES Next, examples of the present invention will be described. Example 1 Titanium oxide (manufactured by Ishihara Sangyo Co., Ltd .; TTO55, particle size 35 nm) 60 parts by weight Carbon black (manufactured by Cabot; Monarch 800, particles 15 〃 size 17 nm) MR110 (manufactured by Nippon Zeon Co., Ltd .; -SO _3). K-containing vinyl chloride type 12.5〃 resin UR8300 (manufactured by Toyobo Co., Ltd.-SO ₃ Na-containing polyurethane 7.5〃 resin) -n-butyl stearate 1.5〃 cyclohexanone 110〃 toluene 110〃 The above composition is mixed and mixed with sand grind mill. After the dispersion treatment, 5 parts by weight of polyisocyanate compound (Nippon Polyurethane Industry Co., Ltd .; Coroneto L) was added and mixed, and the mixture was filtered through a filter having an average pore size of 0.5 μm to obtain an intermediate layer paint. .

On the other hand Fe magnetic powder (Dx value 15nm, Al / Fe = 0.5% by weight) 80 parts by weight of MR 110 (manufactured by Nippon Zeon Co., Ltd.; -SO ₃ K-containing vinyl 8 〃 chloride resin) UR8300 (manufactured by Toyobo Co., Ltd.; -SO ₃ Na-containing polyurethane 8 〃 Resin) Alumina (particle size 200 nm) 8 〃 Carbon black 4 〃 Stearic acid-n-butyl 1.2 〃 Myristic acid 1.2 〃 Cyclohexanone 72.5 〃 Methyl ethyl ketone 72.5 〃 Toluene 72.5 〃 After dispersing with a sand grind mill, 4 parts by weight of a polyisocyanate compound (Nippon Polyurethane Industry Co., Ltd .; Coroneto L) was added and mixed, and the mixture was filtered with a filter having an average pore size of 0.5 μm to obtain a magnetic paint. Got

Then, the obtained intermediate layer paint is applied to a thickness of 8 μm.
Gravure coater was applied to the polyester film of m to a thickness of 2.0 μm after drying, and while the intermediate layer paint was wet with the solvent, the magnetic paint obtained was applied to the die coater. It was applied so that the thickness after drying would be 0.5 μm using a magnetic tape, and was subjected to magnetic field orientation treatment and dried.

After drying, the surface was smoothed and stored at 60 ° C. for 24 hours to form an intermediate layer and a magnetic layer. Then, a back coat layer coating composition having the following composition had a thickness of 0.7 after drying.
It was applied so as to have a thickness of μm and dried to form a backcoat layer. After that, it was cut into a width of 8 mm to obtain an 8 mm video tape.

Coating for back coat layer Carbon black (particle size: 17 nm) 40.50 parts by weight Carbon black (particle size: 370 nm) 0.45 〃 Barium sulfate 4.05 〃 Nitrocellulose 27.50 〃 Polyurethane resin 19.25 〃 Cross-linking agent 8.25 〃 Cyclohexanone 78.25〃 Methyl ethyl ketone 223.13〃 Toluene 223.13〃

The titanium oxide particle diameter / carbon black particle diameter in the intermediate layer of the thus obtained video tape was 2.06. The particle size of alumina particles in the magnetic layer / the particle size of titanium oxide in the intermediate layer was 5.71.

Example 2 As in Example 1, except that the same amount of α-hematite (manufactured by Showa Denko KK; Nanotite 60, particle diameter 60 nm) was used in place of titanium oxide in the composition of the intermediate layer coating composition in Example 1. Similarly, an 8 mm video tape was obtained.

The particle size of α-hematite / carbon black particle size in the intermediate layer of the video tape thus obtained was 3.53. The particle size of the alumina particles in the magnetic layer / the particle size of α-hematite in the intermediate layer is 3.
It was 33.

Example 3 In the composition of the intermediate layer coating composition in Example 1, α-hematite (manufactured by Toda Kogyo KK; DPN-2) was used instead of titanium oxide.
An 8 mm video tape was obtained in the same manner as in Example 1 except that the same amount of 45 and particle size 185 nm × 31 nm) was used.

The particle size of α-hematite in the intermediate layer of the video tape thus obtained / the minor axis size of carbon black was 1.82. The particle size of the alumina particles in the magnetic layer / the particle size of α-hematite in the intermediate layer is 6.
It was 45.

Example 4 In the composition of the intermediate layer coating composition of Example 1, carbon black was changed from Monarch 800 to Regal 250 (manufactured by Cabot Co., particle size 35 nm), and the same amount was used. An 8 mm video tape was obtained in the same manner as in Example 1.

The particle diameter of titanium oxide / the minor axis diameter of carbon black in the intermediate layer of the thus obtained video tape was 1.00. The particle size of the alumina particles in the magnetic layer / the particle size of α-hematite in the intermediate layer was 5.71.

Example 5 In the composition of the intermediate layer coating composition of Example 2, carbon black was changed from Monarch 800 to Regal 250 (manufactured by Cabot Co., particle size 35 nm), and the same amount was used. An 8 mm video tape was obtained in the same manner as in Example 2.

The particle size of α-hematite in the intermediate layer of the video tape thus obtained / the minor axis size of carbon black was 1.71. The particle size of the alumina particles in the magnetic layer / the particle size of α-hematite in the intermediate layer is 3.
It was 33.

Example 6 An 8 mm video tape was obtained in the same manner as in Example 1 except that the thickness of the magnetic layer was changed from 0.5 μm to 0.2 μm in the formation of the magnetic layer in Example 1.

Example 7 An 8 mm video tape was obtained in the same manner as in Example 1 except that in the formation of the magnetic layer in Example 1, the thickness of the magnetic layer was changed from 0.5 μm to 1.0 μm.

Example 8 In the composition of the intermediate layer paint in Example 1, MR11
0 instead LEC E C130; ^- (manufactured by Sekisui Chemical Co., -N ⁺ (CH _{3) 3} Cl-containing vinyl chloride resin) using the same amount in place of the UR8300 -N ⁺ (CH
₃ ) ₃ Cl ^- containing polyurethane resin (basic skeleton: butylene-adipate / 4,4-diphenylmethane diisocyanate, molecular weight: 23000, functional group amount: 0.2 meq / g)
An 8 mm video tape was obtained in the same manner as in Example 1 except that the same amount was used.

Example 9 In the composition of the magnetic coating material of Example 1, the Dx value was 1
A large number of 8 mm video tapes were prepared in the same manner as in Example 1 except that the same amount of Fe magnetic powder containing 5 nm of Fe magnetic powder and different alumina contents was used.
I got a pu

FIG. 1 shows the video tape thus obtained.
Content of Fe magnetic powder (Al
/ Fe) and durability and electromagnetic conversion characteristics. In the figure, graph A shows the relationship between Al content (Al / Fe) and durability, and graph B shows Al content (Al / F).
The relationship between e) and electromagnetic conversion characteristics is shown.

Example 10 A large number were prepared in the same manner as in Example 1 except that the same amount of Fe magnetic powder having the same alumina content and different Dx values was used in the composition of the magnetic coating material in Example 1. 8 mm video tape was obtained.

FIG. 2 shows the video tape thus obtained.
FIG. 4 is a graph showing the relationship between the Dx value of the Fe magnetic powder in the magnetic layer / the particle size of titanium oxide in the intermediate layer and the durability and the electromagnetic conversion characteristics, where graph A is the Dx value of the Fe magnetic powder / intermediate value. The relationship between the particle size of titanium oxide in the layer and the durability is shown. Graph B shows the relationship between the Dx value of the Fe magnetic powder / the particle size of titanium oxide in the intermediate layer and the electromagnetic conversion characteristics.

As is clear from FIGS. 1 and 2, the content of alumina (Al / Fe) in the Fe magnetic powder is
When 0.10 to 3.00% by weight, when the Dx value (X-ray particle size) of this Fe powder / the particle size of titanium oxide in the intermediate layer is 0.2 to 1.0, good electromagnetic conversion characteristics are obtained and durability is also good. I understand.

Example 11 In the composition of the magnetic coating material of Example 1, the particle size was 2
8 in the same manner as in Example 1 except that the same amount of alumina having a particle diameter of 400 nm was used instead of 00 nm of alumina.
mm video tape was obtained. The particle diameter of the alumina particles in the magnetic layer of the video tape thus obtained / the particle diameter of titanium oxide in the intermediate layer was 11.4.

Example 12 In the composition of the magnetic coating material of Example 1, the particle size was 2
8 was carried out in the same manner as in Example 1 except that the same amount of alumina having a particle diameter of 170 nm was used instead of the alumina of 00 nm.
mm video tape was obtained. The particle size of the alumina particles in the magnetic layer of the video tape thus obtained / the particle size of titanium oxide in the intermediate layer was 4.86.

Comparative Example 1 In the composition of the intermediate layer coating composition of Example 1, α-hematite (manufactured by Toda Kogyo Co., Ltd .; TF-10) was used in place of titanium oxide.
An 8 mm video tape was obtained in the same manner as in Example 1 except that the same amount was used.

The particle diameter of α-hematite in the intermediate layer of the thus obtained video tape / the minor axis diameter of carbon black was 5.88. The particle size of the alumina particles in the magnetic layer / the particle size of α-hematite in the intermediate layer is 2.
It was 00.

Comparative Example 2 In the composition of the magnetic coating material of Comparative Example 1, the particle size was 2
Instead of 00 nm alumina, the same amount of alumina having a particle size of 170 nm was used, and in the composition of the intermediate layer coating, carbon black was changed from Monarch 800 to Sevacarb MT-CI (manufactured by Colombian Chemistry, Inc., Particle size 3
An 8 mm video tape was obtained in the same manner as in Comparative Example 1 except that the same amount was used after changing to 70 nm).

The particle diameter of α-hematite in the intermediate layer of the thus obtained video tape / the minor axis diameter of carbon black was 0.27. The particle size of the alumina particles in the magnetic layer / the particle size of α-hematite in the intermediate layer is 0.
It was 59.

Comparative Example 3 An 8 mm video tape was obtained in the same manner as in Example 1 except that the thickness of the magnetic layer was changed from 0.5 μm to 0.18 μm in the formation of the magnetic layer in Example 1.

Comparative Example 4 An 8 mm video tape was obtained in the same manner as in Example 1 except that in the formation of the magnetic layer in Example 1, the thickness of the magnetic layer was changed from 0.5 μm to 1.1 μm.

Comparative Example 5 In the composition of the intermediate layer paint in Example 1, MR11
0 instead LEC E C130; ^- except that (manufactured by Sekisui Chemical Co., -N ⁺ (CH _{3) 3} Cl-containing vinyl chloride resin) was used the same amount, in the same manner as in Example 1 8m
m video tape was obtained.

Comparative Example 6 In the composition of the magnetic coating material of Example 1, the Dx value was 1
At 5 nm, the alumina content is Al / Fe 0.5% by weight
Instead of the Fe magnetic powder of, Al / F with Dx value of 15 nm
The same amount of Fe magnetic powder with e = 0 was used, and carbon black was changed from Monarch 800 to Sebacarb MT-CI (Colombian Chemistry, particle size 370 nm) in the composition of the intermediate layer paint. Then, an 8 mm video tape was obtained in the same manner as in Example 1 except that the same amount was used.

The 8 mm video tapes obtained in the respective examples and comparative examples were measured by frequency analysis with a non-contact surface roughness meter by the following method, and electromagnetic conversion characteristics and durability were examined.

<Frequency analysis by non-contact surface roughness meter> Non-contact surface roughness measuring device TOPO-3D (manufactured by WYCO)
The objective head PX-40 was set on and the surface roughness of the video tape was measured. Next, using the same device, frequency analysis of surface roughness was performed with Hanning Window: OFF, Sample Interval: 3.
, ReferenceLevel: 1.000nm, Maximum Y Value: Automa
tic, Integration Limit: 0.00 / mm-1000.00 / mm, Integr
ation Area: Absolute FFT parameter condition,
The difference between the measured intensity at a frequency of 102 mm ^{-1 and} the measured intensity at a frequency of 205 mm ^-1 was obtained.

<Electromagnetic conversion characteristics> 8 mmV manufactured by Sony Corporation
A CR was used to record a 100% white signal, and the output when this signal was reproduced was measured with an oscilloscope.

<Durability> Using a reciprocating sliding test device using a bearing copper ball having a diameter of 6.35 mm as a slider,
At a sliding speed of 30 mm / sec and an applied load of 20 g, the surface of an 8 mm video tape was rubbed with a steel ball, and the number of times of reciprocal sliding until the friction coefficient sharply increased was measured. Table 1 below shows the results.

[0085]

[0086]

As is apparent from Table 1 above, the 8 mm video tape (Examples 1 to 8 and 1) obtained by the present invention was used.
1, 12) have better electromagnetic conversion characteristics and better durability than the 8 mm video tapes obtained in Comparative Examples 1 to 6. Further, as is apparent from FIGS. 1 and 2, the 8 mm video tape obtained by the present invention has good electromagnetic conversion characteristics and good durability, and therefore the magnetic recording medium obtained by the present invention is It can be seen that the electromagnetic conversion characteristics and durability are improved.

[Brief description of drawings]

FIG. 1 is a relational diagram of Al content (Al / Fe) of Fe magnetic powder in a magnetic layer of a video tape obtained by the present invention and durability and electromagnetic conversion characteristics.

FIG. 2 is a relationship diagram of Dx value of Fe magnetic powder in the magnetic layer of the video tape obtained by the present invention / particle diameter of titanium oxide in the intermediate layer and durability and electromagnetic conversion characteristics.

Claims (5)

[Claims] 1. A non-magnetic support having a particle diameter ratio of non-magnetic fine particles other than carbon black or a minor axis diameter /
An intermediate layer containing non-magnetic fine particles having a particle size of carbon black of 1.0 to 4.0 and carbon black is provided, and a magnetic layer having a thickness of 0.2 to 1.0 μm is provided on the intermediate layer. Magnetic recording media 2. The total thickness of the non-magnetic support, the intermediate layer and the magnetic layer is 13 μm or less, and the surface roughness of the magnetic layer is 102 mm ⁻¹ in the frequency analysis of the non-contact surface roughness. 2. The magnetic recording medium according to claim 1, wherein the difference in strength at 205 mm ⁻¹ is 9 to 15 dB. 3. The magnetic recording medium according to claim 1, wherein the intermediate layer is an intermediate layer containing, as a binder resin, a vinyl chloride resin having a functional group having the same polarity together and a polyurethane resin. 4. The magnetic powder contained in the magnetic layer is an Fe powder containing 0.10 to 3.00% by weight of Al with respect to Fe, and the Dx value (X-ray grain size) of this Fe powder and carbon black of the intermediate layer are excluded. The ratio with the particle size of the non-magnetic fine particles of is the Dx value of the Fe powder /
4. The magnetic recording medium according to claim 1, wherein the diameter or minor axis diameter of the non-magnetic fine particles other than carbon black in the intermediate layer is 0.2 to 1.0. 5. A magnetic layer containing alumina particles, wherein the ratio of the alumina particles to the particle size of non-magnetic fine particles other than carbon black of the intermediate layer is the diameter of alumina particles / other than carbon black of the intermediate layer. The magnetic recording medium according to claim 1, 2, 3, or 4, wherein the diameter or the minor axis diameter of the non-magnetic fine particles is 3.0 to 12.0.