JP2000285436A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable magnetic recording medium having low block error rate. SOLUTION: The magnetic recording medium has a magnetic layer of 0.2 μm thick or less wherein the magnetic powder contained in the magnetic layer is composed of a ferromagnetic iron based alloy powder containing Co and a rear earth element having the length of long axis L of 0.15 μm or less satisfying a relation L/λ<=1/3 (λ is shortest recording wavelength). Atomic ratio of Al/(Fe+Co) is 1.5-2.5 when the surface of the magnetic layer is measured by ESCA after being cleaned with hexane, P-V is in the range of 10-50 nm when the magnetic layer is measured arbitrarily at ten points by means of a light interference surface roughness meter, and P-V is in the range of 20-50 nm when the back coat layer is measured arbitrarily at ten points by means of the light interference surface roughness meter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable magnetic recording medium having a low block error rate.

[0002]

2. Description of the Related Art Magnetic tapes have various uses, such as audio tapes, video tapes, and computer tapes. With the increase in the capacity of the hard disk
With a storage capacity of several tens of GB per volume, a high density backup tape is indispensable in order to cope with a further increase in the capacity of a hard disk in the future.

As a magnetic tape corresponding to such a high density, means for improving the magnetic characteristics of the ferromagnetic powder, improving the dispersibility of the ferromagnetic powder, and the space between the medium and the head are used.
Means for reducing the sing loss have become necessary.

In order to improve the magnetic properties of the ferromagnetic powder, it is desirable to increase the degree of magnetization remaining in the magnetic layer in order to increase the output. Therefore, as the magnetic powder, conventional oxide magnetic powder or cobalt-containing iron oxide is used. Instead of magnetic powder, ferromagnetic iron-based alloy powder is becoming mainstream, and ferromagnetic iron-based alloy powder having a coercive force of 1,500 Oe or more has been proposed (for example, see Japanese Patent Application Laid-Open No. Hei 5-
234064, JP-A-6-25702, JP-A-6-139553).

As means for improving the dispersibility of the ferromagnetic powder, a binder having a polar functional group such as a sulfonic acid group, a phosphoric acid group or an alkali metal salt thereof, or a low-molecular-weight compound having a low molecular weight together with the binder is used. Means such as using a dispersant in combination, continuously performing a kneading and dispersing step of a magnetic paint, and post-adding a lubricant after dispersion have been proposed (for example, JP-A-62-23226, JP-A-2-1
01624, JP-A-3-216812, JP-A-3-17827, JP-A-4-47586, JP-A-8-235566, and the like.

Further, as means for reducing the spacing loss between the tape and the head, in addition to the above-mentioned means for increasing the dispersibility of the magnetic powder, a smoothing treatment of the magnetic layer under a high temperature and high pressure condition in a calendar step is carried out. Or providing a non-magnetic undercoat layer under the magnetic layer to suppress the influence of the surface properties of the non-magnetic support on the surface of the magnetic layer (for example, Japanese Patent Publication No. Sho 64). -1297, JP-B-7-60504, JP-A-4-19815, etc.).

[0007]

By the way, recently,
Digital recording systems that encode and record information data such as video, audio, and characters are becoming mainstream.
(Hereinafter, a magnetic recording medium used in such a digital recording system is referred to as a computer tape). By the way, in a digital recording system, a drive is connected to a bus line of a computer main body via a controller, and at the time of recording, when the controller receives parallel data from the bus line, it converts this into serial data. And
The data is divided into blocks of a fixed length, redundant bits for error detection / correction are added, and data conversion is performed in accordance with a certain rule for efficient recording on a magnetic recording medium. The data is sent to the drive and recorded on the magnetic recording medium as a magnetization pattern. On the other hand, at the time of reproduction, a reproduction data pulse is generated from this magnetization pattern by the peak detection method in the drive and returned to the controller. Since the magnetization pattern includes temporal fluctuations, the controller uses a window created from the reproduced data and uses the phase discrimination method to determine the original data.
It is necessary to return to the data line.

However, the position of the data pulse is
If the error exceeds the width of the window, an error occurs. If the error in the block exceeds a certain amount, correction becomes impossible. For this reason, the magnetic recording medium is also required to have a low block error rate. However, in a large-capacity recording system in which the data recording density is improved and the area per bit is reduced. Since the width of the window needs to be reduced, such an error rise cannot be avoided. Also, in the early stage of traveling, the block error
Even for magnetic recording media with low
In many cases, large-capacity backups are required in a group, and when used in a system in which recording and reproduction are performed for a long time, a problem that the block error rate increases after running has become apparent. . In particular, the above phenomenon was remarkable under high temperature and low humidity, and was frequently confirmed in a situation where the state of the head contact between the magnetic recording medium and the system deteriorated.

The present invention has been made as a result of various studies in view of the present situation, and has a small block error rate in a magnetic recording medium used in a digital system.
It is an object of the present invention to provide a highly reliable magnetic recording medium.

[0010]

According to the present invention, at least one undercoat layer and a magnetic layer are formed on one surface of a nonmagnetic support in this order, and a back coat is formed on the opposite surface. A magnetic layer, and the thickness of the magnetic layer
2 μm or less, the magnetic powder contained in the magnetic layer has a long axis length (L)
0.15 μm or less, made of a ferromagnetic iron-based alloy powder containing Co and a rare earth element that satisfies L / λ ≦ １ ／ with a relationship between the long axis length (L) and the shortest recording wavelength (λ), and is washed with hexane Later, the surface of the magnetic layer is changed to ESCA (Electron S).
pectroscopy for Chemical A
analysis (hereinafter referred to as ESCA), the atomic ratio of AL / (Fe + Co) is 1.5 to 2.5, and P at the time of measuring any 10 points of the magnetic layer with the surface roughness of the optical interferometer. -V (Peak to Valley, hereinafter referred to as PV) is in the range of 10 to 50 nm, and PV at the time of measuring any 10 points of the back coat layer with the surface roughness of the optical interferometer is 20 to 50. It has been found that by setting the thickness in the range of 50 nm, the block error rate can be reduced and a highly reliable magnetic recording medium can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, as means for improving the block error rate, it is considered to improve the S / N ratio, the resolution, reduce the dropout, and reduce the modulation failure. Can be That is, in an ideal state, the data pulse is at the center of the window, and there is a margin of ± 50% with respect to the window width. However, in an actual magnetic recording medium, a peak position of a reproduction signal shifts back and forth due to fluctuation of a magnetization pattern, and a case where the peak position jumps out of a window width is detected as a digital error. Therefore, to reduce the errors,
Although it is necessary to increase the margin, it is necessary to improve the characteristics of the magnetic recording medium as a parameter contributing to the margin.

The present invention has been made in view of the above. First, in order to improve the S / N ratio, the magnetic powder to be contained in the magnetic layer is preferably made of a ferromagnetic iron-based alloy magnetic powder, (L) A ferromagnetic iron-based alloy magnetic powder containing 0.15 μm or less and containing Co and a rare earth element, in which the relationship between the major axis length (L) and the shortest recording wavelength (λ) satisfies L / λ ≦ １ ／, is used. Can be

That is, in the present invention, the thickness of the magnetic layer must be 0.2 μm or less in order to obtain a high resolution, as will be described later. Since the filling amount is reduced, the magnetic characteristics are degraded, and a high output cannot be obtained. For this reason, the present invention uses the ultrafine ferromagnetic iron-based alloy magnetic powder having a major axis length (L) of 0.15 μm or less, more preferably 0.10 μm or less and 0.05 μm or more, to reduce the magnetic properties in the magnetic layer. By improving the filling property of the powder and obtaining a high remanent magnetization, and by including Co in the magnetic powder, the magnetic properties of the magnetic powder itself, such as the saturation magnetization and coercive force, are improved, and the thickness of the magnetic layer is reduced to 0. High output can be achieved even in high-density recording with a minimum recording wavelength of 0.5 μm or less at 2 μm or less.

On the other hand, since the S / N ratio is relative, even if the output is increased using the magnetic powder, if the noise is also high at the same time, the S / N ratio will decrease, and the error will occur. -The rise cannot be avoided.

The inventors of the present invention have studied the reduction of the noise. As a result, with the ferromagnetic iron-based alloy magnetic powder of the present invention of 0.15 μm or less, the long axis length (L) and the shortest recording wavelength (λ) of It has been found that the relationship has a relationship of L / λ ≦ １ ／ and can be solved by using a magnetic powder containing a rare earth element.

That is, one of the factors of the noise generated from the medium is a particulate noise caused by magnetic powder.
This particle noise is considered to be caused by both the size of the particles of the magnetic powder and the unevenness of the particle size. Therefore, first, it is necessary to reduce the size of the particles. However, according to studies by the present inventors, the relationship between the long axis length (L) of the magnetic powder and the shortest recording wavelength (λ) is L / λ. .Ltoreq.1 / 3, the number of magnetic particles in a fixed area contributing to the head output is increased, the variation in the amount of magnetization in the fixed area due to the difference in the data recording location is prevented, and the noise based on the size of the particles is reduced. Can be reduced. In addition, by using magnetic powder of fine particles that are 1/3 or less of the shortest recording wavelength as described above, noise due to the size of the particle can be reduced, but the particle property due to unevenness of the particle size can be reduced. Noise cannot be reduced. In other words, if there is a variation in the size of each magnetic powder, even if the data is in an unrecorded state, the magnetic flux generated from the magnetic particles existing in a certain area contributing to the head output varies, and the head output is generated. Is zero, that is, the total of the magnetic flux is hard to be zero. For this reason, an output difference occurs due to a difference in data recording location, which causes an increase in noise. This is because the noise based on the output fluctuation is also superimposed in the state where the signal is recorded, so that the noise further increases and the relative S / N ratio is reduced. In particular,
When the shortest recording wavelength (.lambda.) Used in recent computer tapes is 0.5 .mu.m or less, both the track density and the linear recording density need to be increased. The effect is greater.

For this reason, the present invention provides a ferromagnetic iron-based alloy powder having the above-mentioned particle diameter, which uses a magnetic powder containing a rare earth element together with Co to make the particle size distribution of the magnetic powder uniform, Noise can be reduced, and S / N
It has been found that the ratio can be improved. In addition, the inclusion of such a rare earth element is also preferable in that the wear resistance of the magnetic powder can be improved.

In the present invention, the Co-containing ferromagnetic iron-based alloy powder is obtained by calcining a gausite powder into a magnetite powder, which is ion-exchanged with divalent iron ions and cobalt ions in a cobalt ion-containing aqueous solution. A method of heat-reducing, a method of heat-reducing a cobalt-containing acicular gausite powder obtained from an aqueous suspension of an alkali of an iron salt and a cobalt salt, and a method of obtaining from an iron salt and a cobalt salt added to an aqueous oxalic acid solution. A method of reducing coprecipitates, a method of heating and reducing iron oxide powder having cobalt deposited on the surface, a method of adding a reducing agent to a solution containing iron salts and cobalt salts, and evaporating metals in an inert gas. Can be produced by colliding with gas molecules to obtain alloy magnetic powder, reducing iron to cobalt in a mixed gas of hydrogen, nitrogen and argon while flowing vapor of iron or cobalt chloride. . Among these,
It is preferable to use a method capable of forming a solid solution with a high cobalt content and having excellent corrosion resistance.

In the Co-containing ferromagnetic iron-based alloy powder, the higher the amount of cobalt, the higher the saturation magnetization and the higher the coercive force can be achieved. However, if the amount is too large, alloying with the magnetic iron metal cannot be performed, and the excess Is an oxide, so that the above characteristics cannot be achieved. Therefore, the amount of cobalt is Co /
The range where the weight ratio of Fe is 10 to 40% is preferable, and the range where the weight ratio of Fe is 10 to 30% is more preferable.

In order to make the particle size distribution of the magnetic powder of the fine particles of the present invention uniform, the rare earth element is introduced into the Co-containing ferromagnetic iron-based alloy powder simultaneously with the rare earth element at the time of the above-mentioned goethite production. A method of co-precipitating the element, a method of suspending the raw material iron oxide powder of the alloy magnetic powder in a rare earth compound aqueous solution, and the like can be used.

Here, the rare earth elements used in the present invention include Nd, Y, La, Ce, Pr, Sm, Gd, Y
b, Tb, etc., among which Y, La, C
e is preferred.

The larger the amount of the rare earth element contained in the ferromagnetic iron alloy powder of the present invention, the more uniform the particle size distribution of the magnetic powder,
Particle noise can be reduced and a high S / N ratio can be achieved. In addition, the adhesion between the magnetic powder and the binder can be increased, and the magnetic powder can be prevented from being damaged during the coating kneading and dispersing process. Powder can be prevented from falling off, but too much Co
In order to reduce the content and decrease the saturation magnetization of the ferromagnetic iron-based alloy powder, a rare earth element / (Fe + Co) weight ratio of 0.1 is used.
The range is preferably 1 to 10%, more preferably 0.5 to 7%.

The ferromagnetic iron-based alloy powder containing Co and the rare earth element includes, as other elements, for example,
Transition metals such as Zn, Sn, Ni, Mn, Ti, Cr, and Cu can also be added. However, when an alkali metal, an alkaline earth metal, particularly Ca is present in the ferromagnetic alloy magnetic powder, it reacts with the fatty acid in the magnetic layer to form a fatty acid salt on the surface of the magnetic layer. It is preferable to avoid mixing of the above-mentioned alkali metal.

The ferromagnetic iron-based alloy powder of the present invention containing Co and a rare earth element has a particle surface made of inorganic oxide for the purpose of preventing sintering during heat reduction and improving dispersibility in a magnetic paint. It is desirable to coat. Examples of the inorganic oxide include aluminum oxide and silicon oxide. Aluminum oxide is particularly preferable because it has excellent hardness and can improve the wear resistance of the ferromagnetic iron alloy powder. In order to carry out the coating, a method is used in which water is applied to an alcohol solution of aluminum, silicon or the like in advance on the raw iron oxide powder, and these compounds are adhered and formed on the particle surface by hydrolysis. The coating amount is preferably 0.1% or more by weight to the total of Fe and Co in order to prevent sintering and improve dispersibility, and if too large, the saturation magnetization of the magnetic powder decreases. , 6% or less.
That is, when the particle surface is coated with aluminum oxide, the weight ratio of Al / (Fe + Co) is preferably in the range of 0.1 to 8%, and is preferably in the range of 0.5 to 6%. Is more preferred.

Further, such ferromagnetic iron-based alloy powders containing Co and rare earth elements are likely to cause magnetic aggregation due to high saturation magnetization, and the particle surface becomes very active. The pH is preferably less than 10, especially less than 8, because it acts as a catalyst that causes the modification of the solvent and the modification of the isocyanate component in the crosslinking agent used as the binder. By setting the pH value of the ferromagnetic iron-based alloy powder containing Co and the rare earth element to less than 10, the formation of altered substances in the magnetic paint can be suppressed. The coating film can withstand sliding.

The average major axis length is determined by measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and averaging 100 particles. For the same reason as described above, the ferromagnetic iron-based alloy powder B
ET specific surface area is preferably at least 35m ² / g, 40m ²
/ G or more, more preferably 50 m ² / g or more.

The coercive force of the ferromagnetic iron-based alloy powder containing Co and the rare earth element is set to 1,7 in order to obtain high output and high resolution in short wavelength recording at a high linear recording density.
00-3,500 Oe, especially 2,000-2,800
Oe is preferred. The saturation magnetization is preferably from 120 to 200 emu / g, particularly from 130 to 160 emu / g, in order to obtain a good reproduction output at a high track density and to maintain the corrosion resistance of the magnetic powder. As the squareness ratio, σr / σs is 0.46 or more, especially 0.4
It is preferably 8 or more, more preferably 0.49 or more.

In the present invention, the magnetic properties of the magnetic layer using the ferromagnetic iron-based alloy powder containing Co and the rare earth element described above have a coercive force of 1,700 to 3,500O.
e, particularly preferably 2,000 to 3,000 Oe. Further, the residual magnetic flux density is preferably 1,800 G or more, particularly preferably 2,000 to 4,000 G. In addition,
The magnetic characteristics of the magnetic layer and the magnetic characteristics of the ferromagnetic iron-based alloy powder containing Co and the rare earth element both refer to values measured with an external magnetic field of 10 kOe using a sample vibrating magnetometer.

In the present invention, by using the ferromagnetic iron-based alloy powder containing Co and the rare earth element, the magnetic properties of the magnetic layer are improved, and a high output can be obtained even at the shortest recording wavelength of 0.5 μm or less. In addition, noise generated from the magnetic powder itself can be reduced, and a high S / N ratio can be obtained.
On the other hand, when the thickness of the magnetic layer is large at a high linear recording density of 0.5 μm or less in the shortest recording wavelength, the long-wavelength output increases according to the thickness, but the short-wavelength output changes little due to the thickness loss. do not do. For this reason, when the short wavelength output is relatively lower than the long wavelength output, the resolution is remarkably reduced, and the improvement by the effect of reducing the self-demagnetization loss by increasing the coercive force is not sufficient.

In order to solve such a problem of resolution,
As a result of the study, at a high recording density with a minimum recording wavelength of 0.5 μm or less, improvement in resolution could be found when the thickness of the magnetic layer was 0.2 μm or less. That is,
In the present invention, the ferromagnetic iron-based alloy powder containing Co and the rare earth element is used, and the thickness of the magnetic layer is set to 0.2.
By setting the thickness to less than μm, a high remanence of the magnetic layer and a high coercive force can be achieved, and the self-demagnetization loss can be reduced. , And can contribute to the reduction of the error rate.

From the above viewpoint, the thickness of the magnetic layer in the present invention needs to be 0.2 μm or less, but if it is too thin, the uniformity of the coating film thickness during the formation of the magnetic layer is reduced. It becomes difficult to maintain the magnetic layer, which deteriorates the PV of the surface of the magnetic layer, which will be described later. Further, the amount of magnetic powder that can be filled in the magnetic layer decreases, and the magnetic properties of the magnetic layer deteriorate. Therefore, it is desirable that the thickness of the magnetic layer is 0.03 μm or more, particularly 0.1 to 0.2 μm.

On the other hand, computer tapes need to perform high-speed data transfer in order to record / reproduce large-capacity data in a short time, and particularly to record / reproduce data on long tapes. ,
In the magnetic recording medium using the ferromagnetic iron-based alloy powder containing Co and the rare earth element, the magnetic powder during traveling in a room temperature and normal humidity environment is compared with a magnetic recording medium using a conventional ferromagnetic powder. Although the temporary error due to the drop-off has been improved, the magnetic layer is easily damaged during running under high temperature and low humidity, so that the magnetic layer is liable to drop out and the error rate tends to rise.

In order to solve the above-mentioned problems, the present inventors have proposed an abrasive such as alumina having a high hardness, which has been conventionally used for improving the strength of a coating film by sliding contact with a magnetic head or the like.
Attempts have been made to increase the polishing ability of the magnetic layer by increasing the amount of carbon black added. However, the expected improvement in durability was not observed, and the block error rate was reduced. Became clear.

For this reason, the present inventors have studied in detail the magnetic layer surface and the magnetic head after the tape running, and
The magnetic head after recording / reproducing on the computer tape has a head stain which is considered to be dust generated from the magnetic layer, and this phenomenon is particularly remarkable under high temperature and low humidity. Considering the reason, the present invention uses a ferromagnetic iron-based alloy magnetic powder of active fine particles containing Co and rare earth, so that a large amount of binder is adsorbed in order to disperse these magnetic powders when the paint is dispersed. However, it was considered that the amount of the binder for dispersing the abrasive or carbon black was insufficient, and the fixing force of these additives in the coating film was reduced.
Further, since the ferromagnetic iron-based alloy powder containing Co and the rare earth element of the present invention is considered to be poor in dispersibility due to the strong cohesive force, the binder is unevenly distributed on the surface of the magnetic layer, so that under high temperature and low humidity. It was presumed that this was softened and peeled off during sliding contact with the head, thereby increasing dropout.

For this reason, according to the present invention, AL / (Fe +
Co) The atomic ratio is set to 1.5 to 2.5.

That is, in the present invention, alumina is used as an abrasive. In the case of such an abrasive, when mixed in a large amount for improving the polishing property, the particles tend to agglomerate due to a shortage of a binder. The presence of agglomerates of abrasives on the surface of the magnetic layer allows them to directly receive the impact from the magnetic head, and the magnetic layer thinned to 0.2 μm or less according to the present invention can reduce the impact. The coating film is easily broken. For this reason, Al / (Fe
It is considered that such a problem can be avoided by setting + Co) within the above range.

The ESC of various elements such as Al of the present invention
The measurement conditions according to A are as follows. In order to eliminate an error due to the effect of the surface lubricant, a sample cut in advance to a length of 5 cm is immersed in 100 mL of hexane for 24 hours to remove the lubricant, and the dried sample is used as a measurement sample. Using an MgKα ray as an X-ray excitation source, an acceleration voltage of 12 kV, an emission current of 10 mA,
The degree of vacuum was 10-6 Pa, the path energy of the analyzer was 50 eV, and the photoelectrons of each element derived from 2p electrons were measured.

The present invention also provides at least one undercoat layer between a nonmagnetic support and a magnetic layer in order to reduce the block error rate by improving the modulation. Are 10 to 50 nm when all 10 points are measured by a light interference type surface roughness meter.
The PV was 20 to 50 nm for any 10 points of the back coat layer when measured with a light interference type surface roughness meter.

That is, it is considered that the increase in the error due to the modulation defect is caused by the undulation of the magnetic layer. However, in the present invention, as described above, in order to improve the resolution, the thickness of the magnetic layer is made as extremely thin as 0.2 μm or less, so when a single magnetic layer is provided, a uniform magnetic layer may be provided. It will be difficult. Therefore, in the present invention,
The modulation is improved by providing at least one undercoat layer between the magnetic layer and the non-magnetic support. Further, even if the magnetic layer is simply made uniform, the shape of the magnetic layer surface is not uniform at the time of short-wavelength recording.
It has been clarified that the modulation is thereby deteriorated. In particular, in the case of a tape having a large capacity such as a computer tape, it is necessary to make the surface roughness extremely smooth in order to improve the S / N ratio. Since the set-off phenomenon on the surface of the back coat layer becomes remarkable, the modulation is further deteriorated. In order to solve such a problem, the present invention provides a method in which, at any 10 points of the magnetic layer, the PV measured with an optical interference type surface roughness meter is 10 to 50 nm,
It has been found that excellent modulation can be achieved by adjusting the PV with the optical interferometer three-dimensional surface roughness to 20 to 50 nm at any of the arbitrary 10 points on the layer. .

That is, it has been conventionally attempted to improve the average surface roughness Ra which is an index of the smoothness of the magnetic layer surface. The present inventors also considered that by extremely smoothing Ra from this viewpoint, the output could be improved and the modulation could be improved.
Another sufficient characteristic could not be obtained. Considering the reason, the average surface roughness Ra is obtained by averaging the irregularities on the surface of the magnetic layer along the center line. On the other hand, the cause of the poor modulation is the protruding portion or the surface of the magnetic layer. It was considered that the undulation of the depression affected the influence. The conventional surface roughness is measured only at a specific point, whereas the modulation is affected by a certain length of surface roughness, and in the case of a tape for a computer. Has a fixed block error over the entire length.
Due to the necessity of a rate, there is a problem that even if the surface roughness of only a specific point is excellent but the surface roughness is not uniform as a whole, the error rate differs.
In particular, in the case of a long tape for a computer, the so-called tightening phenomenon at high temperatures becomes large, so that the surface property of the back coat layer is easily transferred to the magnetic layer. As a result, the surface properties of the surface of the magnetic layer are apt to deteriorate, and the block error rate is likely to be non-uniform. For this reason, the present invention has an average surface roughness PV that reflects the unevenness of the magnetic layer and is 1
0 to 50 nm, preferably 15 to 45 nm, and the average surface roughness PV of the back coat layer is 20 to 50 nm, preferably 25 to 45 nm. Is an improvement. That is, when the surface roughness PV of the magnetic layer is larger than 50 nm, the unevenness on the surface of the magnetic layer becomes remarkable, and the modulation is deteriorated. On the other hand, P of the magnetic layer
When -V is less than 10 nm, the modulation as measured by the magnetic layer alone is improved, but the surface property is too smooth, so that the transfer from the back coat layer becomes remarkable, and the surface property of the back coat layer becomes poor. The modulation is similarly deteriorated because it is easily affected. Also, as described above, the modulability is also affected by the surface properties of the back coat layer.
In this case, the PV of the back coat layer is 50
When the diameter is larger than 10 nm, the transfer to the magnetic layer is increased. On the other hand, when the diameter is smaller than 20 nm, powder contact is liable to occur due to sliding contact with a guide pin, which is transferred to the surface of the magnetic layer to increase dropout. Becomes In addition,
Non-contact surface roughness measuring device TOPO
-3D (manufactured by WYKO) with an objective head (40x) set, measurement wavelength 648.9 nm, measurement area 250 μm ×
At 250 μm, the surface roughness of each measurement point (P−
V) was measured.

The PV of the magnetic layer and the back coat layer is preferably designed to be larger in the back coat layer. By designing in this way, air is generated when the magnetic layer and the back coat layer overlap at the time of high-speed winding. Can be reduced, and so-called turbulent winding can be prevented. And since the irregular winding can be prevented, the rise of the error rate due to the tape deformation at the time of winding can be reduced.

Next, the composition and manufacturing method of the magnetic recording medium of the present invention will be described in the order of the magnetic layer and the undercoat layer.

The binder used in the magnetic layer includes vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, nitrocellulose. -There is a combination of at least one kind selected from polyurethane and a polyurethane resin. Among them, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Polyurethane resins include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and the like.

The binder preferably has a functional group in order to improve the dispersibility of the ferromagnetic iron-based alloy powder containing Co and the rare earth element and to enhance the filling property. Functional groups include COOM, SO ₃ M, OSO ₃ M, and P = O (OM)
_{3, O-P = O (} OM) 2, (M is a hydrogen atom, an alkali metal base or amine _{salt), OH, NR 2, N} + R 3 (R is a hydrogen or a hydrocarbon group), and the like epoxy group . When two or more resins are used in combination, it is preferable that the functional groups are the same, and among them, a -SO3M group is preferable.

These binders are used in an amount of 5 to 50 parts by weight based on 100 parts by weight of the ferromagnetic iron alloy powder containing Co and the rare earth.
It is used in an amount of 10 parts by weight, preferably 10 to 35 parts by weight. In particular, when a vinyl chloride resin is used as the binder, the range is 5 to 30 parts by weight, and when a polyurethane resin is used, the range is 2 to 20 parts by weight. preferable.

It is desirable to use together with these binders a thermosetting crosslinking agent that forms a crosslink by binding to a functional group or the like contained in the binder. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate
, Isophorone diisocyanate and the like, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and various polyisocyanates such as condensation products of the above isocyanates. Is preferred. These crosslinking agents are generally used in a proportion of 15 to 70 parts by weight based on 100 parts by weight of the binder.

As the alumina used in the present invention, α-Al ₂ O ₃ , β having a grain-form, angular, or acicular α-formation ratio of 90% or more are used.
-Al ₂ O ₃ and γ-Al ₂ O ₃ are mentioned.
0.05 μm to 1 μm is preferable, and 0.1 μm to 0.4 μm
μm is more preferred. When the thickness is 0.05 μm or more, the polishing ability of alumina can be sufficiently obtained, and the dispersibility can be ensured. When the thickness is 1 μm or less, the spacing between the medium and the head is reduced, and the Conversion characteristics can be ensured. Specific examples of such alumina include AKP-10 manufactured by Sumitomo Chemical Co., Ltd.
AKP-12, AKP-15, AKP-30, AKP-
50, HIT-82, HIT-60, Uemura Kogyo UB
40B and the like.

The amount of alumina added is preferably 6 to 20 parts by weight, more preferably 8 to 15 parts by weight, based on 100 parts by weight of the magnetic powder, from the viewpoints of electromagnetic conversion characteristics and head contamination.

As a method for adding alumina, a method in which alumina powder is directly added in a kneading step of a kneader or the like or a preliminary stirring step together with a magnetic powder and a binder, or an alumina dispersion liquid is prepared in advance separately from a magnetic paint. There is a method of separately adding this to the magnetic paint, but from the viewpoint of productivity, the former which does not require a separate step is preferable.

Further, in order to further reduce the dropout and improve the block error rate, the present invention is to measure the amount of Ti and / or P with respect to Fe by ESCA measurement after washing the magnetic layer surface with hexane. Is preferably contained in a specific amount. Although it is not clear why the block error rate can be further improved by allowing such an element to be present on the surface of the magnetic layer, direct sliding between the magnetic powder and the head can be mitigated at the atomic level. In particular, it is considered that the generation of dust from the magnetic layer can be reduced even when the vehicle is driven under high temperature and low humidity, thereby contributing to a reduction in dropout. The amount of Ti / Fe is 0.02 to 0.06.
Is preferably set to 0.02 to 0.05, and the P / Fe amount is preferably set to 0.15 to 0.75, and set to the range of 0.20 to 0.60. Is more preferred. Note that the element amounts are based on the same measurement conditions as those for AL on the surface of the magnetic layer. Such Ti or P is preferably added not as a form in which these elements are added alone but as a compound such as a dispersant. In particular, when the amount of Ti or P of the present invention is adjusted by using a dispersant containing the above element, it is difficult to control the abundance by a method of adding these dispersants in a kneading step for dispersing magnetic powder. Therefore, it is preferable to mix after the initial dispersion step. That is, in order to improve the dispersibility of the magnetic powder, it has conventionally been customary to add these dispersants during the dispersing step of a kneader or the like. In the alloy powder, since the surface of the magnetic powder is extremely active and the pH is also in an alkaline range, when the dispersant is added from the beginning of kneading, the dispersibility can be improved at the time of initial dispersion, but the dispersant is added to the magnetic powder surface. Since the binder is preferentially adsorbed, the adsorption of the binder is hindered, and a large amount of the binder component is present on the surface of the magnetic layer. When the dispersant is adsorbed on the surface of the magnetic powder, an active site remains on the surface of the magnetic powder. As a result, when the isocyanate-based crosslinking agent is used at the time of coating, the isocyanate group loses its activity, and It is considered that curing does not proceed sufficiently. For this reason, it is preferable to add the above-mentioned dispersant at least after an initial dispersion step such as kneading.

Examples of the dispersant include Ti-based dispersants such as commercially available Ajinomoto Prenact KR-38S, KR
-TTS, KR-46B, KR-55, KR-41B,
KR-138S, KR-238S, KR-44, KR-
Examples of titanate coupling agents such as 9SA include P-type dispersants such as alkyl phosphates such as monomethyl phosphate, dimethyl phosphate, monoethyl phosphate and diethyl phosphate, and phenylphosphonic acid. Examples thereof include aromatic phosphoric acids, and commercially available products include GARFAC RS410 manufactured by Toho Chemical Co., Ltd., JP-502, JP-508 manufactured by Johoku Chemical Co., Ltd.

The amount of the dispersant added is preferably at least 0.5 part by weight, more preferably at most 5 parts by weight, based on 100 parts by weight of the ferromagnetic iron alloy powder.

In the present invention, conventionally known fatty acids, fatty acid esters, fatty acid amides, fatty acid metal salts, hydrocarbons and the like can be used alone or as a mixture of two or more kinds. It is preferable to add 10 or more, preferably 12 or more and 24 or less fatty acids. Some of these fatty acids are adsorbed on the ferromagnetic iron alloy magnetic powder, helping the dispersibility of the magnetic powder, and at the same time, reduce the contact between the medium and the head in the initial wear, reduce the friction coefficient, and reduce the contamination of the head. Contribute to reduction.

Such fatty acids include straight-chain, branched,
Either an unsaturated structure or a saturated structure may be used, but a linear type having excellent lubricating performance is preferable. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, oleic acid, isostearic acid and the like.
The amount of the fatty acid to be added is preferably 0.2 to 10 parts by weight, more preferably 0.5 to 10 parts by weight based on 100 parts by weight of the ferromagnetic iron alloy powder.
-5 parts by weight is more preferred.

In the present invention, it is preferable to add carbon black having a particle size of 75 nm or less as an additive to the magnetic layer, and to combine carbon black having a large particle size to reduce the friction coefficient. It is preferred to add. The particle size of such carbon black is 10
0 nm to 500 nm is preferable, and 200 to 400 nm is more preferable. Specific examples of the carbon black include SEVACARB® manufactured by Columbian Carbon Co., Ltd.
MTCI, ThermaxPowde manufactured by Kancab
r · N-991 and the like. These particles have a particle size of 100 to
It is preferable that carbon black of 500 nm is blended in an amount of 3.0 wt% or less with respect to the ferromagnetic iron alloy powder.

In the formation of the magnetic layer, any of the conventionally used solvents can be used as a solvent for preparing a magnetic paint, a lubricant solution and the like. For example, aromatic solvents such as benzene, toluene, and xylene; ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone; acetate solvents such as ethyl acetate and butyl acetate; and carbonate esters such as dimethyl carbonate and diethyl carbonate. Solvent,
In addition to alcohol solvents such as ethanol and isopropanol, hexane, tetrahydrofuran, dimethylformamide and the like can be mentioned.

As the method for producing the magnetic layer of the present invention, a conventionally known coating production step can be used in forming the magnetic layer, and it is particularly preferable to use a kneading step using a kneader or the like and a primary dispersion step together. . In the primary dispersion step, the use of a sand mill is preferable because the dispersibility of the magnetic powder can be improved and the surface properties can be controlled.

Next, in the present invention, at least one undercoat layer is provided between the nonmagnetic support and the magnetic layer. The components of the undercoat layer include inorganic powder, binder, lubricant, carbon black, and the like. and so on. Both non-magnetic powder and magnetic powder can be used as the inorganic powder. Non-magnetic powders include α-alumina, β-alumina, γ-alumina, α-iron oxide, TiO ₂ (rutile, anatase) and T
iO _X, cerium oxide, tin oxide, tungsten oxide,
ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , gatetite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO
₃ , CaCO ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like are used alone or in combination. As the magnetic powder, γ-Fe ₂ O ₃ , Co-γ-
Magnetic powder having a low coercive force of 300 Oe or less, such as Fe ₂ O ₃ or Ba ferrite, is used.

These inorganic powders may be in any of spherical, needle-like, and plate-like shapes. If the particle size of the inorganic powder is too large, the surface property of the undercoat layer is reduced, which affects the PV value of the magnetic layer. Therefore, the particle size is preferably 0.5 μm or less. On the other hand, if it is too small, the filling property of the inorganic powder in the undercoat layer increases, the number of pores capable of holding the lubricant decreases, and the cushioning effect decreases.
It is preferably at least 0.05 μm. For the same reason as the above particle size, the amount of the inorganic powder used is 60% of the entire undercoat layer.
It is preferably from 90 to 90% by weight, particularly preferably from 70 to 80% by weight.

As the binder used for the undercoat layer, the same resin as the above-mentioned binder constituting the magnetic layer is used, and preferably, the same resin as the binder of the magnetic layer is used. In particular, if they are matched in the combined use of vinyl chloride resin and polyurethane resin, the elasticity of the undercoat layer and the magnetic layer becomes closer,
The load from the magnetic head can be satisfactorily dispersed. The binder of the undercoat layer preferably has the same type of functional group as the binder of the magnetic layer. In particular, when the functional groups of the undercoat layer and the magnetic layer are matched to each other in a combined system of a vinyl chloride resin and a polyurethane resin, the adhesion between both layers is improved, and the leaching of the lubricant from the undercoat layer to the magnetic layer is smooth. Is preferable.

The amount of the binder used in the undercoat layer is determined based on the amount of the inorganic powder 1
20 to 45 parts by weight, especially 25 to
Preferably it is 40 parts by weight. In addition, in order to increase the strength of the undercoat layer, similarly to the case of the magnetic layer, together with the binder, a thermosetting crosslinking agent that is combined with a functional group contained in the binder and crosslinked is used in combination. Is also desirable. The amount of the crosslinking agent used is preferably 15 to 70 parts by weight based on 100 parts by weight of the binder.

As the lubricant used for the undercoat layer, the same lubricant as that for the magnetic layer can be used. However, since fatty acids are inferior to the upper layer more than fatty acid esters, fatty acid esters are used alone or when fatty acid esters are added. It is desirable to use a larger ratio. The amount of lubricant added to the undercoat layer is
The amount is usually 4 to 18 parts by weight, preferably 5 to 16 parts by weight, more preferably 6 to 14 parts by weight based on 100 parts by weight of the inorganic powder. The weight ratio of the fatty acid and the fatty acid ester to the undercoat layer is preferably 0/100 to 40/60, particularly preferably 0/100 to 30/70. The lubricant may be included in the undercoat layer by adding it at the time of mixing the undercoat layer paint with a kneader or the like, before or after the mixing, or by adding the surface of the undercoat layer formed beforehand. , A lubricant solution or the like may be applied or sprayed.

As the carbon black used in the undercoat layer, it is preferable to use a carbon black having a particle size of 0.01 to 0.03 μm and a carbon black having a particle size of 0.05 to 0.3 μm. The former carbon black is used to secure holes for holding the lubricant, as in the case of the magnetic layer. The latter carbon black improves the coating strength of the undercoat layer and improves the cushioning effect. It is to balance the two. The amount of carbon black added to the undercoat layer is 5 to 70 parts by weight, especially 15 to 50 parts by weight, based on 100 parts by weight of the inorganic powder, inclusive of both carbon blacks.
Preferably it is 40 parts by weight. In addition, particle size 0.01 ~
For the 0.03 μm carbon black, “BLACK PEARLS 800” and “Mogu” manufactured by Cabot
1-L "," VULCAN XC-72 "," Rega
l660R "and" Ra "manufactured by Columbian Carbon Co., Ltd.
ven 1255 "and" Conductex SC ". For carbon black having a particle size of 0.05 to 0.3 μm, “BLACK PEARLS” manufactured by Cabot Corporation is used.
130 "," Monarch 120 "," Raven 450 "," Rav 450 "manufactured by Columbian Carbon Co., Ltd.
en 410 "and" TermaxPo "manufactured by Kancarb.
wr. N-991 ".

In forming the undercoat layer, the same aromatic solvents, ketone solvents, ester solvents, alcohol solvents, and the like as those for the magnetic layer may be used as solvents for preparing the undercoat layer paint and the lubricant solution. Solvents such as hexane and tetrahydrofuran are used.

Next, as the non-magnetic support, any conventionally used non-magnetic support for a magnetic recording medium can be used. Specifically, polyethylene terephthalate
Polyesters such as polyethylene naphthalate,
A film having a thickness of usually 3 to 100 μm, which is composed of polyolefins, cellulostriacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide and the like is used. As the surface roughness of the non-magnetic support, it is preferable to use different surface properties for the magnetic layer and the back coat layer. Due to such a difference in surface properties, the PV of the magnetic layer and the back coat layer can be easily controlled.

When the anisotropy of shrinkage of the non-magnetic support, which is generated in a test in a use environment, particularly in a high temperature environment, is large, the followability is reduced, and tracking errors are likely to occur. For this reason, the non-magnetic support has a heat shrinkage of 105 ° C. for 30 minutes, that is, a heat shrinkage of 1.5% or less in the vertical direction and 1% in the horizontal direction after heat treatment at 105 ° C. for 30 minutes and cooling. .0
% Is preferred. The above heat shrinkage ratio was determined by measuring six test pieces having a width of 10 mm and a length of 300 mm of the nonmagnetic support.
Each sample was taken from D / TD, heat-treated in hot air at 105 ° C. for 30 minutes, cooled, and the length was measured. [(Original length−length after shrinkage) / original length] × 100 ( %).

In the coating step, gravure coating and roasting are performed.
Conventional coating methods such as metal coating, blade coating, and extrusion coating can be used. At that time, the method of applying the undercoat layer and the magnetic layer is to apply the magnetic layer after coating and drying the undercoat layer on the non-magnetic support, or to sequentially coat the undercoat layer and the magnetic layer, Any of the simultaneous multilayer coating methods may be employed.

In the magnetic recording medium of the present invention, a back coat layer is provided on the surface opposite to the magnetic layer. Such a back coat layer is formed by using a filler together with conductive carbon black and friction. In order to reduce the coefficient and increase the mechanical strength, α-Fe ₂ O ₃ , which is generally used as an abrasive,
Fe ₃ 0 _4, TiO _2, graphite, CaO, SiO _2,
Cr ₂ O ₃ , α-Al ₂ O ₃ , SiC, CaCO ₃ , BaS
O ₄ , ZnO, MgO, boron nitride, TiC, ZnS,
It may contain an inorganic non-magnetic powder such as MgCO ₃ or SnO ₂ .

In the back coat layer, lubricants such as higher fatty acids, fatty acid esters and silicone oils, dispersants such as surfactants, and other various additives may be added and used as necessary. Can be.

As the binder for the back coat layer, any of the above-mentioned binders used for the magnetic layer can be preferably used. Among them, a cellulose resin is used in order to reduce the friction coefficient and improve the running property. And a polyurethane resin are preferably used in combination. Usually, the content of the binder is preferably about 15 to 200 parts by weight based on 100 parts by weight of carbon black or the inorganic nonmagnetic powder. Also,
Further, in order to cure the binder, it is preferable to use a crosslinking agent such as a polyisocyanate compound.

The thickness of the back coat layer is preferably about 0.3 to 1.0 μm after calendering. If the backcoat layer is too thick, the total thickness of the magnetic recording medium will be too thick, while if too thin, the surface properties of the backcoat layer will be reduced due to the surface properties of the nonmagnetic support, and the backcoat
When the surface of the magnetic layer is transferred to the magnetic layer, the electromagnetic conversion characteristics and the like are likely to deteriorate.

In manufacturing the magnetic recording medium of the present invention,
After coating and drying, it is desirable to perform a surface treatment with a calendar using a plastic roll or a metal roll. By performing the calendar treatment, the PV of the surface of the magnetic layer and the surface of the back coat layer can be adjusted, the filling degree of the ferromagnetic iron-based alloy powder can be improved, and the residual magnetic flux density can be improved.

In the present invention, aging is preferably performed after the calendar processing. That is, the coating film hardens due to aging, and the coating film strength can be improved. If the aging temperature is too high, the tightness of winding of the magnetic sheet becomes remarkable, the surface roughness of the back coat layer is transferred, and the surface property of the magnetic layer is deteriorated. It is preferable to carry out in 5
It is preferable to carry out in an environment of 60% RH.

Further, in order to adjust the amounts of Al, Ti and P on the surface of the magnetic layer, to remove dust components on the surface of the magnetic layer which may cause dropout, and to remove in advance the fragile parts of the surface of the magnetic layer. Further, P on the surface of the magnetic layer
In order to adjust the value of -V, it is preferable to polish the magnetic layer after coating and drying. Examples of the polishing treatment include a blade treatment and a treatment with a polishing wheel.
In terms of productivity, the latter treatment with a grinding wheel is preferred. Such polishing wheels are disclosed in JP-A-62-150519, JP-A-62-172532,
It is described in JP-A-2-23521. Examples of the material used for the polished portion of the wheel include ceramic, super steel, sapphire, diamond and the like. When the grinding wheel is used, the peripheral speed of the wheel and the winding angle around the wheel are such that the peripheral speed is within ± 200% of the tape traveling speed (50 to 300 m / min). Preferably, the winding angle around the wheel is:
10-80 ° is preferred.

Hereinafter, the present invention will be described specifically with reference to examples. In each example, “parts” means “parts by weight”.

[0076]

EXAMPLES (Example 1) << Coating component for undercoat layer >> 70 parts of titanium oxide powder (particle diameter: 0.035 μm) 10 parts of titanium oxide powder (particle diameter: 0.1 μm) 10 parts of carbon black (particle diameter) : 0.075 μm) 20 parts Vinyl chloride copolymer 10 parts (Contains -SO ₃ Na group: 0.7 × 10 −4 equivalents / g) Polyester polyurethane resin 5 parts (Contains -SO ₃ Na group: 1 × 10 −) (4 equivalents / g) methyl ethyl ketone 130 parts toluene 80 parts myristic acid 1.0 part butyl stearate 1.5 parts cyclohexanone 65 parts << Coating composition for magnetic layer >> (1) Ferromagnetic alloy powder (Co / Fe: 20 wt%) , Y / (Fe + Co): 3 wt%, Al / (Fe + Co): 5 wt%, Ca / Fe: 0, σs: 140 emu / g, Hc: 1840 Oe, pH: 8, particle size: 0.10 μm) 100 parts Vinyl chloride Le - hydroxypropyl acrylate copolymer 8 parts (containing -SO ₃ Na group: 0.7 × 10-4 eq / g) Polyester polyurethane resin 4 parts (containing -SO ₃ Na group: 1.0 × 10-4 eq / G) α-alumina (average particle size: 0.4 μm) 10 parts Carbon black (average particle size: 100 nm) 1.5 parts Myristic acid 1.5 parts Methyl ethyl ketone 133 parts Toluene 100 parts (2) titanate Coupling agent (Ajinomoto Prenact KR38S) 1.5 parts Stearic acid 1.5 parts Polyisocyanate 4 parts Cyclohexanone 133 parts Toluene 33 parts Dispersion treatment was performed for 60 minutes, 6 parts of polyisocyanate was added thereto, and the mixture was stirred and filtered to obtain a coating for an undercoat layer. Separately, the above-mentioned magnetic layer coating component (1) is kneaded with a kneader, dispersed by a sand mill with a residence time of 45 minutes, and the magnetic layer coating component (2) is added thereto. , Magnetic paint.
The above undercoat paint is dried and calendered on a support made of polyethylene terephthalate film (105 ° C., heat shrinkage for 30 minutes at 0.8% in the vertical direction and 0.6% in the horizontal direction). Is applied to a thickness of 2 μm, and the above magnetic paint is further dried and calendered on the undercoat layer.
The magnetic layer after the treatment was coated so as to have a thickness of 0.2 μm and dried to obtain a magnetic sheet.

<< Coating composition for back coat layer >> Carbon black (particle size: 25 nm) 40.50 parts Carbon black (particle size: 370 nm) 0.50 parts Barium sulfate 4.05 parts Nitrocellulose 28.00 parts Polyurethane resin ( SO ₃ Na group-containing) 20.00 parts cyclohexanone 100.00 parts toluene 100.00 parts Methyl ethyl ketone 100.00 parts the above back coating - after a coat layer for coating components were dispersed with a residence time of 45 minutes in a sand mill, Poriishishiane - DOO 8.5 parts by adding back coating - DOO After the coating for the layer was prepared and filtered, it was applied to the opposite side of the magnetic layer of the magnetic sheet prepared as described above so that the thickness after drying and calendering became 0.7 μm and dried.

The magnetic sheet thus obtained is mirror-finished with a five-stage calender (temperature: 70 ° C., linear pressure: 150 kg / cm), and the magnetic sheet is wound around a sheet core at 60 ° C.
After aging for 48 hours under 40% RH, 3.8 mm
The magnetic layer surface was polished with a ceramic wheel (rotational speed + 150%, winding angle of 30 °) while running at 100 m / min to a tape length of 125 m. A tape was prepared. The magnetic tape obtained as described above was incorporated into a cartridge to prepare a tape for a computer.

(Example 2) In the preparation of the magnetic tape of Example 1, in the magnetic layer coating component (1), the ferromagnetic alloy powder was changed to a ferromagnetic alloy powder (Co / Fe: 10 wt%, La /
(Fe + Co): 2 wt%, Al / (Fe + Co): 5
wt%, Ca / Fe: 0 wt%, σs: 135 emu /
g, Hc: 1740 Oe, pH: 8, particle size: 0.07
μm), the α-alumina (0.2 μm) was changed to 15 parts, the residence time of the magnetic layer coating component (1) in the sand mill was changed to 60 minutes, and the magnetic layer coating component (2) In place of 1.5 parts of the titanate-based coupling agent, 1.5 parts of a phosphoric ester (JP502 manufactured by Johoku Chemical Co., Ltd.) was used,
The thickness of the magnetic layer is 0.1 μm, the temperature is 80 ° C, and the linear pressure is 200k
A tape for a computer was prepared in the same manner as in Example 1 except that the calendar was performed at g / cm.

Example 3 In the preparation of the magnetic tape of Example 1, 7 parts of α-alumina and 7 parts of titanate of the magnetic layer coating component (2) in the magnetic layer coating component (1) were used. The system-based coupling agent was changed to 4 parts of Ajinomoto Prenact KR-TTS, the retention time of the magnetic layer coating component (1) was 30 minutes, and carbon black having a particle size of 370 nm in the back coating layer coating component was used. Was changed to 4 parts, the residence time was changed to 30 minutes, calendering was performed at a temperature of 60 ° C. and a linear pressure of 100 kg / cm, aging was performed at 50 ° C. and 40% RH for 30 hours, and the rotation speed of the polishing wheel was +125. %, Winding angle 10
° and aged for 35 hours at a temperature of 50 ° C and a relative humidity of 40% in the same manner as in Example 1, except that the tape was used for a computer.
Was prepared.

(Example 4) In the preparation of the magnetic tape of Example 1, the ferromagnetic alloy powder (Co / Fe: 20 wt%, Ce /
(Fe + Co): 4 wt%, Al / (Fe + Co): 3
wt%, Ca / Fe: 0.001 wt%, σs: 145
emu / g, Hc: 1880 Oe, pH: 9, particle diameter:
0.1 μm,) in the magnetic layer coating component (2),
2.0 parts of a phosphate ester was used instead of 1.5 parts of a titanate-based coupling agent, the thickness of the magnetic layer was 0.1 μm, and the heat shrinkage at 105 ° C. for 30 minutes as a nonmagnetic support was in the longitudinal direction. Using polyethylene naphthalate of 0.3% in the transverse direction and 0.1% in the transverse direction, and increasing the rotation speed of the polishing wheel by +125.
%, Example 1 except that the winding angle was changed to 10 °
A tape for a computer was produced in the same manner as described above.

(Example 5) In the preparation of the magnetic tape of Example 1, in the magnetic layer coating component (1), the ferromagnetic alloy powder was replaced with a ferromagnetic alloy powder (Co / Fe: 30 wt%, Y / ( Fe
+ Co): 5 wt%, Al / (Fe + Co): 5 wt%
%, Ca / Fe: 0.001 wt%, σs: 145 em
u / g, Hc: 2340 Oe, pH: 8, particle diameter: 0.1.
1 μm), and 2 parts of a titanate-based coupling agent and 1.5 parts of a phosphoric acid ester are used in the coating component (2) for the magnetic layer, the thickness of the magnetic layer is set to 0.1 μm, and the non-magnetic support is used. As the body, polyethylene naphthalate having a heat shrinkage of 0.3% in the vertical direction and 0.1% in the horizontal direction at 105 ° C. for 30 minutes, the rotation speed of the polishing wheel is + 125%, and the winding angle is 1
A tape for a computer was produced in the same manner as in Example 1 except that the angle was changed to 0 °.

Comparative Example 1 In the preparation of the magnetic tape of Example 1, the ferromagnetic alloy magnetic powder in the magnetic layer coating component (1) was changed to Fe—Ni—Z containing no Co or rare earth element.
n-based ferromagnetic alloy powder (Al / (Fe + Co): 0.0
3, Ca / Fe: 0.05 wt%, pH: 11, major axis length: 0.20 μm, Hc: 1,650 Oe, σs: 12
0 emu / g) A tape for a computer was prepared in the same manner as in Example 1 except that the residence time was changed to 100 parts, the residence time was changed to 15 minutes, and the undercoat layer was not provided and the magnetic layer thickness was set to 2.3 μm. .

Comparative Example 2 In the preparation of the magnetic tape of Example 1, α-alumina was used in 3 parts in the coating component (1) for the magnetic layer, and titanium oxide was used in the coating component (2) for the magnetic layer. Except that no magnetic coupling agent was added, the thickness of the magnetic layer was 0.3 μm, and the residence time of the back coat layer was 90 minutes.
In the same manner as in Example 1, a tape for a computer was produced.

Comparative Example 3 In the preparation of the magnetic tape of Example 1, 1.5 parts of a titanate coupling agent (KR-TTS) was added to the magnetic layer coating component (1). , A vinyl chloride-vinyl alcohol copolymer resin and a polyurethane resin were changed from those having -SO ₃ Na groups as functional groups to those having only -OH groups, and 10 parts of α-alumina having a particle size of 0.7 µm. The magnetic paint component (2) was calendered at a temperature of 60 ° C. and a linear pressure of 100 kg / cm without adding a titanate coupling agent to the magnetic paint component (2). A tape for a computer was manufactured in the same manner as in Example 1 except that the angle was changed to 5 °.

(Comparative Example 4) In the preparation of the magnetic tape of Example 1, 20 parts of α-alumina were used in the coating component (1) for the magnetic layer, and titanium oxide was used in the coating component (2) for the magnetic layer. Phosphate ester 1.
Using 5 parts, a particle size of 37 in the coating composition for the back coat layer
10 parts of 0 nm carbon black are calendered at a temperature of 60 ° C. and a linear pressure of 100 kg / cm.
A tape for a computer was prepared in the same manner as in Example 1 except that aging was performed with H for 60 hours.

With respect to the tapes for the computers of Examples 1-4 and Comparative Examples 1-4, the major axis length of the magnetic powder, Al
The amount, the amount of Ti or P, the fluctuation width of PV of the magnetic layer, and the PV of the back coat layer were measured by the methods described in the text. For reference, Ra by an optical interference type surface roughness meter is also shown. The major axis length of the magnetic powder is shown in relation to the shortest recording wavelength described later. The fluctuation range of the PV of the magnetic layer was measured at any 10 points including the outermost and innermost points of the reel of the cassette. In addition, ESCA LAB M
ARK2 was used. These results were as shown in Table 1.

[0088]

[Table 1]

<< Measurement of Al, Ti and P >> Using an ESCA analyzer, ESCA-Lab. Mark2 manufactured by VG, the abundance of each element under the above-mentioned measurement conditions, the photoelectron intensity of each emitted element Was measured in units of 0.1 eV, the background was corrected with a straight line, and the obtained area intensity was corrected with a sensitivity coefficient such as an apparatus function to obtain a relative amount of an element.

<< Measurement of PV >> Ten points of PV were measured at intervals of 10 m including the two points of the tape start and end points of each tape under the above measurement conditions.

<< Measurement of Ra >> Of the 10 points where PV was measured, Ra at one point at the end was determined under the same measurement conditions as for PV.

<< Measurement of Block Error Rate >> Using a DDS drive (C1554A) manufactured by Hewlett-Packard Co., Ltd., traveled 5 times under the conditions of 40 ° C. and 5% RH, and the shortest recording wavelength was 0.44 μm. The random data signal was recorded, and the block error rate of each computer tape was measured by a block error rate measuring device.

[0093]

As can be seen from Table 1, the configuration of the magnetic recording medium of the present invention can provide a highly reliable magnetic recording medium with a small block error rate.

Claims (5)

[Claims] 1. A magnetic recording medium having at least one undercoat layer and a magnetic layer formed on one surface of a non-magnetic support in this order, and having a back coat layer on the opposite surface, wherein the thickness of the magnetic layer is Is 0.2 μm or less, the magnetic powder contained in the magnetic layer has a major axis length (L) of 0.15 μm or less, and the relationship between the major axis length (L) and the shortest recording wavelength (λ) is L / λ ≦ 1/3. Al / (Fe + Co) atomic ratio when the magnetic layer surface is measured by ESCA after washing with hexane and comprising a ferromagnetic iron-based alloy powder containing Co and a rare earth element to be filled, and When any 10 points of the magnetic layer were measured with a light interference surface roughness meter, the PV was in the range of 10 to 50 nm, and any 10 points of the back coat layer were measured with the light interference surface roughness. PV is 20 to 50 n when measured with a meter
m. A magnetic recording medium having a range of m. 2. The ferromagnetic iron-based alloy powder containing Co and a rare earth element has a Co / Fe weight ratio of 10 to 40% and a rare earth element / (Fe + Co) weight ratio of 0.1 to 10%. Item 2. The magnetic recording medium according to Item 1. 3. The magnetic recording medium according to claim 1, wherein the shortest recording wavelength (λ) is 0.5 μm or less. 4. After cleaning with hexane, the surface of the magnetic layer is subjected to ESC.
A, the Ti / Fe atomic ratio is 0.02 to 0.
06 and / or an atomic ratio of P / Fe of 0.15 to 0.7
The magnetic recording medium according to any one of claims 1 to 3, wherein 5. The non-magnetic support has a heat shrinkage of not more than 1.5% in the longitudinal direction and not more than 1.0% in the transverse direction after being heat-treated at 105 ° C. for 30 minutes and allowed to cool. 4. The magnetic recording medium according to any one of claims 1 to 3.