JP2001084549A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating type magnetic recording medium for improving fatal errors leading to actual damages in the recording and reproducing system of a linear serpentine system adopting an RLL2-7 modulation system. SOLUTION: This magnetic recording medium is composed by forming a magnetic layer whose main body is ferromagnetic powder and binder on a supporting body. In this case, it is supplied for the magnetic recording and reproducing system of the linear serpentine system adopting the RLL2-7 modulation system. Recesses provided with the depth of 50 nm or more measured by a non-contact type surface roughness meter are provided at 10 pieces/46237.5 μm2 on the surface of the magnetic layer and the maximum depth Rv is 100 nm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium having a high recording density. The present invention particularly relates to a magnetic recording medium for a linear serpentine type recording / reproducing system, which has a magnetic layer and a substantially non-magnetic lower layer, and includes a ferromagnetic metal powder in an uppermost layer.

[0002]

2. Description of the Related Art In the field of use of magnetic tapes, backup tapes have been put to practical use as external storage media for computers. 2. Description of the Related Art In recent years, with the increase in the amount of information processing of a computer, a demand for a large capacity and a high density of a backup tape has been increased.

The recording systems of the backup system are roughly classified into a helical scanning system in which recording and reproduction are performed by a rotary head and a linear serpentine system in which recording and reproduction are performed by a fixed head. Each system has advantages and disadvantages. Is in a state of being overburdened.

In general, the linear serpentine system has a feature that the life of the head and the magnetic tape is longer because the contact condition between the head and the magnetic tape is less severe than the helical scanning system. On the other hand, in the helical scanning system, the tape tension is low but the head chip is small, so that the contact between the magnetic tape and the head tends to be strong. Therefore, the requirements for the backup magnetic tape are different depending on each system.

In general, various modulation methods are adopted for recording digital signals on a magnetic recording medium. The modulation method is a relation between a binary code string and a recording current waveform. When selecting a modulation method, there are problems in that the recording density can be increased, the signal reliability at that time, and the complexity of the modulation circuit. Generally, in high-density recording, it is considered that a modulation method that has a large magnetization reversal interval and avoids the influence of a peak shift is desirable.

Table 1 shows the modulation method in the recent backup tape format. In particular, Table 2 shows the code conversion rules for the RLL2-7 modulation scheme. Where RL
L is a run-length limited code, and means that RLL2-7 converts the number of consecutive 0s, that is, the run-length to 2 to 7. ing.

[0007]

[Table 1]

[Table 2]

[0008]

Conventionally, when data is written in units of blocks on a magnetic tape using the RLL2-7 modulation method, fatal errors have frequently occurred. The fatal error indicates that an uncorrectable error occurs during a read check immediately after writing and rewriting (rewriting) is performed at another location. In this case, the recording / reproducing system naturally has a storage capacity and a transfer rate. And it became a real harm.

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating type magnetic recording medium in which a critical error leading to actual harm is improved in a linear serpentine recording / reproducing system employing the RLL2-7 modulation method.

[0010]

As a result of intensive studies, the present inventors have found that the relative speed of the head and the magnetic tape is 5 m / s or less and that the linear serpentine system adopting the RLL2-7 modulation system with the shortest recording wavelength of 1 μm or less. In a magnetic recording system, as a result of intensive studies on the spacing between the head and the magnetic tape as to the cause of frequent errors in the specific data pattern after RLL2-7 modulation, the influence of the dent at the specific depth of the magnetic layer is remarkable. The present inventors have found something and have led to the present invention.

That is, the present invention relates to a magnetic recording medium in which a magnetic layer mainly composed of a ferromagnetic powder and a binder is formed on a support, and a magnetic recording medium of a linear serpentine system employing an RLL2-7 modulation system. Provided in a recording / reproducing system, wherein the number of depressions having a depth of 50 nm or more is 10 / 46237.5 μm ² or less as measured by a non-contact surface roughness meter on the surface of the magnetic layer; and A magnetic recording medium having a maximum depth Rv of 100 nm or less.

In the present invention, the following data patterns are used for error measurement. As data pattern A, R
Before LL2-7 modulation, repetition data of [000100] is input from the conversion rule table of Table 2 with repetition data of [000]. The run length in this case is 5, which is a signal pattern with a constant frequency. For the data pattern B, a random signal pattern was used. The run length in this case is a signal that changes from 2 to 7. The data pattern C was set such that the data pattern after RLL2-7 modulation was repeated [0001001001000]. In this case, the condition is such that a peak shift easily occurs.

In the present invention, by controlling the surface roughness of the magnetic layer as described above, it is possible to improve the actual harmful error particularly in the data patterns B and C which are close to the actual use conditions.

If the number of dents having a depth of 50 nm or more exceeds 10 pieces / 46237.5 μm ² , the data pattern A has a relatively good error but the data patterns B and C have a worse error. When the maximum depth Rv exceeds 100 nm, the error is deteriorated even in the data pattern A, and the deterioration in the data patterns B and C is also remarkable.

In the present invention, a measuring method for evaluating the depth and the number of recesses on the surface of the magnetic layer will be described. In the present invention, the depth of the dent means the distance from the average surface roughness of the magnetic layer to the deepest part of the dent after measuring three-dimensional surface roughness using NT-2000 manufactured by WYKO. Here, the average surface is a surface in which the volume of unevenness in the measurement surface is equal.
The measurement is 246.6 μm × 187.5 μm (46237.
It is performed within a range of 5 μm ² ). The number of dents is 5 in the above measurement range.
The number of depressions having a depth of 0 nm or more is obtained. Rv is the depth [nm] of the maximum dent among the dents in the above measurement range.

The relative speed between the head and the magnetic tape is 5 m
In a magnetic recording system employing a linear serpentine system employing an RLL2-7 modulation system having a shortest recording wavelength of 1 μm or less, the depth of the recess on the surface of the magnetic layer may cause actual harm as a factor of the linear serpentine system. It is presumed that this is due to a combination of the characteristic reduction in the contact condition between the head and the magnetic tape and the RLL2-7 modulation method. Due to the decrease in the contact condition between the head and the magnetic tape, a spacing loss greater than a certain depth causes an increase in spacing loss and an instantaneous decrease in output. In a general magnetic tape, foreign matters and projections are removed to some extent on the surface of the magnetic layer by surface treatment such as cleaning and polishing, but dents cannot be removed. Further, since a remarkable difference is observed in the data pattern to be recorded, the influence of RLL2-7 modulation is presumed. In the RLL2-7 modulation method, the transition of the run length becomes large as compared with the 8-10 conversion or the like, and the influence of the peak shift becomes large depending on the data pattern. If the number of dents exceeds a certain number, errors due to dropout cannot be corrected, and it is expected that actual harmful errors will occur.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail. The magnetic recording medium of the present invention has at least two coating films on a non-magnetic support, that is, a lower non-magnetic layer and an upper magnetic layer having a thickness of 0.3 μm or less are provided in this order. On the lower surface side of the support, a back coat layer is provided as necessary. In the present invention, a lubricant coating or various coatings for protecting the magnetic layer may be provided on the upper magnetic layer as necessary. On the surface of the non-magnetic support on which the magnetic layer is provided, an undercoat layer (easily adhesive layer) can be provided for the purpose of improving the adhesion between the coating film and the non-magnetic support.

[Lower Non-Magnetic Layer] The lower non-magnetic layer contains at least carbon black and a radiation-curable binder resin. By including carbon black in the lower non-magnetic layer, the lubricant can be retained, so that the amount of the lubricant on the surface of the upper magnetic layer can be easily adjusted to a desired range. When the thickness of the upper magnetic layer is as thin as 0.3 μm or less, it is difficult to contain a sufficient amount of lubricant only with the upper magnetic layer, and the lower carbon black is an important component. The carbon black in the lower non-magnetic layer also has the effect of lowering the surface electric resistance of the upper magnetic layer and has the effect of reducing the light transmittance.

As the carbon black contained in the nonmagnetic layer, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 600 m ² / g, DB
P oil absorption is 30-400ml / 100g, particle size is 10
~ 100 nm is preferred. The carbon black that can be used can be specifically referred to “Carbon Black Handbook” edited by Carbon Black Association.

For the non-magnetic layer, various inorganic powders other than carbon black can be used. For example, acicular non-magnetic iron oxide (α-Fe ₂ O ₃ ) can be used.
However, high dispersibility can be obtained by using spherical ultrafine iron oxide particles, and the packing ratio of particles in the nonmagnetic layer can be increased. Therefore, the surface properties of the non-magnetic layer itself are improved, and the surface properties of the magnetic layer are improved, and the electromagnetic conversion characteristics are improved. Besides, various non-magnetic powders such as CaCO ₃ , titanium oxide, barium sulfate, α-Al ₂ O _{3 and the} like may be used.

The mixing ratio of carbon black and inorganic powder is preferably 100/0 to 75/25 by weight. If the mixing ratio of the inorganic powder exceeds 25 parts by weight, a problem occurs in the surface electric resistance.

The compounding amount of carbon black in the lower non-magnetic layer is 35 to 90% by weight, preferably 40 to 85% by weight. If it is less than 35% by weight, the desired amount of lubricant cannot be held. On the other hand, if 90% by weight is used, a sufficient amount of the lubricant can be held. If the amount exceeds 90% by weight, the ratio of the binder resin in the lower non-magnetic layer decreases, and sufficient coating film strength cannot be obtained.

The binder resin usable for the nonmagnetic layer is preferably a radiation-curable binder resin. With a conventionally used thermoplastic resin or thermosetting resin, in order to obtain sufficient coating film properties, a non-magnetic layer coated raw roll is placed in an oven for a long time (for example, 70 ° C., 2 to 48 hours). It needs to be put in and cured. This poses a problem in that the coating of the non-magnetic layer is deformed due to the tightening of the winding and the smoothness of the surface of the non-magnetic layer is reduced, while the manufacturing process is troublesome.

In order to eliminate such drawbacks, a radiation curable binder resin is used as a binder resin for the lower non-magnetic layer, a lower non-magnetic layer paint is applied, dried, smoothed, and then irradiated with radiation. Suitable results could be obtained by causing three-dimensional crosslinking by radiation and then applying the upper magnetic layer coating thereon. According to this method, the lower nonmagnetic layer is not swelled by the organic solvent because the three-dimensional crosslink has already been formed at the time when the upper magnetic layer is provided. Therefore, the magnetic paint can be applied onto the lower non-magnetic layer immediately after the formation of the lower non-magnetic layer, so that the process can be continued and simplified.

The radiation-curable binder resin used in the present invention is a resin containing one or more unsaturated double bonds in a molecular chain, which generates a radical by radiation and is cured by crosslinking or polymerization. Say.

Examples of the radiation-curable binder resin include a large number of resins such as vinyl chloride resins, polyurethane resins, polyester resins, epoxy resins, phenoxy resins, fiber resins, polyether resins, and polyvinyl alcohol resins. Can be Among them, vinyl chloride resin,
Polyurethane resins are typical, and it is preferable to use a mixture of both.

The content of the radiation-curable binder in the lower non-magnetic layer is a total of 10% of carbon black and inorganic powder.
10 to 100 parts by weight, preferably 1 to 100 parts by weight,
2.5 to 70 parts by weight is more preferred. If the content of the binder is too small, the ratio of the binder resin in the lower non-magnetic layer decreases, and sufficient coating film strength cannot be obtained. If the content of the binder is too large, poor dispersion occurs during the preparation of the coating material for the lower non-magnetic layer, making it impossible to form a smooth lower non-magnetic layer surface.

The radiation used in the present invention is an electron beam, γ-ray, β-ray, ultraviolet ray, etc., preferably an electron beam. The dose is preferably 1 to 10 Mrad.
~ 7 Mrad is more preferred. The irradiation energy (acceleration voltage) is preferably 100 Kv or more. Irradiation with radiation is preferably performed before winding after coating and drying, but may be performed after winding.

The lower non-magnetic layer of the present invention preferably contains a lubricant as required. Lubricant is saturated,
Regardless of unsaturation, known fatty acids, esters, and saccharides may be used alone or as a mixture of two or more, and it is preferable to use a mixture of two or more fatty acids and esters having different melting points. This is because it is necessary to continuously supply a lubricant corresponding to any temperature environment used for the magnetic recording medium to the medium surface.

Specific examples of the fatty acid include saturated linear fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid and erucic acid; saturated fatty acids such as isosetyl acid and isostearic acid; and oleic acid. ,
Unsaturated fatty acids such as linoleic acid and linolenic acid can be used as appropriate. As esters, butyl stearate, linear saturated fatty acid esters such as butyl palmitate, isocetyl stearate, saturated fatty acid esters having side chains such as isostearyl stearate, unsaturated fatty acid esters such as isostearyl oleate,
Fatty acid esters of unsaturated alcohols such as oleyl stearate, esters of unsaturated fatty acids and unsaturated alcohols such as oleyl oleate, esters of dihydric alcohols such as ethylene glycol distearate, ethylene glycol monooleate, ethylene glycol dioleate Ester, esters of dihydric alcohols such as neopentyl glycol dioleate and unsaturated fatty acids, and saccharides such as sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate with saturated or unsaturated fatty acids Esters and the like. The content of the lubricant in the lower non-magnetic layer may be appropriately adjusted according to the purpose, but is preferably 1 to 20% by weight based on the total weight of the carbon black and the inorganic powder.

The coating for forming the lower non-magnetic layer is prepared by adding an organic solvent to the above components. The organic solvent used is not particularly limited, and one or two or more of various solvents such as ketone solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone and cyclohexanone, and aromatic solvents such as toluene are appropriately selected. It may be used. The amount of the organic solvent to be added may be about 100 to 900 parts by weight based on 100 parts by weight of the total of the solid content (carbon black, various inorganic particles, etc.) and the binder.

The thickness of the lower non-magnetic layer is usually from 0.1 to
It is 2.5 μm, preferably 0.3 to 2.3 μm. When the non-magnetic layer is too thin, the surface properties of the non-magnetic support are easily affected, and as a result, the surface properties of the non-magnetic layer are deteriorated, and the surface properties of the magnetic layer are also likely to deteriorate. It tends to decrease. In addition, since the light transmittance increases, there is a problem in detecting the tape end based on a change in the light transmittance. On the other hand, even if the nonmagnetic layer is made thicker than a certain degree, the performance is not improved.

[Upper Magnetic Layer] The upper magnetic layer contains at least a ferromagnetic powder, a binder resin and an abrasive. In the present invention, it is preferable to use a metal alloy fine powder or a hexagonal plate-like fine powder as the ferromagnetic powder. As the metal alloy fine powder, the holding force Hc is 1500 to 3000 Oe,
Saturation magnetization σs is 120 to 160 emu / g, average major axis diameter is 0.05 to 0.2 μm, average minor axis diameter is 10 to 20 n
m and the aspect ratio are preferably 1.2 to 20. The Hc of the prepared medium is 1500 to 3000O.
e is preferred. As an additive element, N
i, Zn, Co, Al, Si, Y, and other rare earth elements may be added. The hexagonal plate-like fine powder has a coercive force Hc of 1000 to 2000 Oe and a saturation magnetization s of 50 to
It is preferable that 70 emu / g, average plate particle diameter is 30 to 80 nm, and plate ratio is 3 to 7. In addition, the H
c is preferably from 1200 to 2200 Oe. As the additional element, Ni, Co, Ti, Zn, Sn,
In addition, a rare earth or the like may be added. In addition, known materials can be used according to the purpose without any particular limitation.

Such a ferromagnetic powder may be contained in an amount of about 70 to 90 parts by weight in the composition of the magnetic layer. If the content of the ferromagnetic powder is too large, the content of the binder is reduced, so that the surface smoothness due to calendar processing is liable to deteriorate. On the other hand, if the content is too small, a high reproduction output cannot be obtained.

The binder resin is not particularly limited as long as it is generally used, and any of a thermoplastic resin, a thermosetting or reactive resin, and a radiation-curable binder resin can be used.

For example, polyester polyurethane resin,
Vinyl chloride copolymer, vinyl chloride-acrylate copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate -Acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride-vinylidene chloride-acrylonitrile copolymer Polymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate,
Cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin-chlorovinyl ether acrylate copolymer, amino resin, and synthetic rubber thermoplastic resin.

The content of these binders used in the magnetic layer is preferably 5 to 40 parts by weight, particularly preferably 10 to 30 parts by weight, per 100 parts by weight of the ferromagnetic powder. If the content of the binder is too small, the strength of the magnetic layer decreases, so that the running durability tends to deteriorate. On the other hand, if the content is too large, the content of the ferromagnetic powder decreases, so that the electromagnetic conversion characteristics decrease.

As a crosslinking agent for curing these binders, various polyisocyanates, particularly diisocyanates, can be used. In particular, tolylene diisocyanate,
It is preferable to use at least one of hexamethylene diisocyanate and methylene diisocyanate. These crosslinking agents include a crosslinking agent modified to one having a plurality of hydroxyl groups such as trimethylolpropane or a diisocyanate compound 3
It is particularly preferable to use the compound as an isocyanurate-type cross-linking agent to which molecules are bonded. The content of the crosslinking agent is preferably 10 to 30 parts by weight based on 100 parts by weight of the binder. In order to cure such a thermosetting resin, it may be generally heated in a heating oven at 50 to 70 ° C. for 12 to 48 hours.

Furthermore, in order to increase the mechanical strength of the magnetic layer and to prevent clogging of the magnetic head,
Contains abrasives. Examples of the abrasive include α-alumina (Mohs hardness 9), chromium oxide (Mohs hardness 9),
Polishing of silicon carbide (Mohs hardness 9.5), silicon oxide (Mohs hardness 7), aluminum nitride (Mohs hardness 9), boron nitride (Mohs hardness 9.5), etc., with a Mohs hardness of 6 or more, preferably a Mohs hardness of 9 or more. It is preferable to include at least one material. These are usually indeterminate shapes, prevent clogging of the magnetic head, and improve the strength of the coating.

The average particle size of the abrasive is, for example, 0.01 to
0.2 μm, preferably 0.05 to 0.2 μm. If the average particle size is too large, the amount of protrusion from the surface of the magnetic layer increases, which causes a decrease in electromagnetic conversion characteristics, an increase in dropout, an increase in head wear, and the like. If the average particle size is too small, the amount of protrusion from the surface of the magnetic layer becomes small, and the effect of preventing head clogging becomes insufficient. The average particle size is usually measured by a transmission electron microscope. The content of the abrasive is 3 to 25 parts per 100 parts by weight of the ferromagnetic powder.
It may be contained by weight, preferably 5 to 20 parts by weight.

Further, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, and silicone oil, and other various additives may be added to the magnetic layer, if necessary.

The coating material for forming the magnetic layer is prepared by adding an organic solvent to each of the above components. The organic solvent used is not particularly limited, and the same organic solvents as those used for the lower non-magnetic layer can be used.

The thickness of the upper magnetic layer is 0.30 μm or less,
Preferably it is 0.05 to 0.30 μm, more preferably 0.10 to 0.25 μm. A thickness of less than 0.20 μm, such as 0.15 μm, is also suitable. If the magnetic layer is too thick, self-demagnetization loss and thickness loss increase.

[Backcoat layer] The backcoat layer is provided for improving running stability and preventing the magnetic layer from being charged. The back coat layer preferably contains 30 to 80% by weight of carbon black. If the content of carbon black is too small, the antistatic effect tends to decrease, and the running stability tends to decrease. Also, since the light transmittance is likely to be high, there is a problem in a method of detecting the end of the tape by a change in the light transmittance. On the other hand, if the content of carbon black is too large, the strength of the back coat layer is reduced, and running durability is likely to be deteriorated. Any carbon black may be used as long as it is commonly used, and the average particle size is preferably about 5 to 500 nm. The average particle size is usually measured by a transmission electron microscope.

The back coat layer may contain, in addition to the carbon black, non-magnetic inorganic powders such as various abrasives mentioned in the description of the magnetic layer in order to increase the mechanical strength. The content of the nonmagnetic inorganic powder is preferably 0.1 to 5 parts by weight, based on 100 parts by weight of carbon black,
More preferably, it is 0.5 to 2 parts by weight. The average particle size of the non-magnetic inorganic powder is preferably 0.1 to 0.5 μm. If the content of such a nonmagnetic inorganic powder is too small, the mechanical strength of the back coat layer tends to be insufficient, and if it is too large, the amount of abrasion of the guide in the tape sliding path tends to increase.

In addition, if necessary, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, and silicone oil, and other various additives may be added.

A binder, a crosslinking agent,
The solvent and the like may be the same as those used in the above-mentioned coating for the magnetic layer. The content of the binder is preferably 15 to 200 parts by weight, more preferably 50 to 180 parts by weight, based on 100 parts by weight of the total of the solid content. If the content of the binder is too large, the friction with the medium sliding contact path becomes too large, the running stability is reduced, and a running accident is likely to occur.
In addition, problems such as blocking with the magnetic layer occur. When the content of the binder is too small, the strength of the back coat layer is reduced, and the running durability is easily reduced.

The thickness (after calendering) of the back coat layer is 1.0 μm or less, preferably 0.1 to 1.0 μm.
m, more preferably 0.2 to 0.8 μm. If the back coat layer is too thick, the friction between the back coat layer and the medium sliding contact path becomes too large, and the running stability tends to decrease. On the other hand, if it is too thin, the surface properties of the backcoat layer will decrease due to the influence of the surface properties of the nonmagnetic support. For this reason, when the back coat is thermally cured, the roughness of the back coat layer surface is transferred to the magnetic layer surface, resulting in a decrease in high-frequency output, S / N, and C / N. On the other hand, if the back coat layer is too thin, the back coat layer will be shaved during running of the medium.

[Non-Magnetic Support] The material used as the non-magnetic support is not particularly limited, and may be selected from various flexible materials and various rigid materials according to the purpose, and may be tape-shaped or the like according to various standards. The shape and the size may be set. For example, as a flexible material, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyolefins such as polypropylene, polyamide, polyimide,
Various resins such as polycarbonate are exemplified. The thickness of these nonmagnetic supports is preferably from 3.0 to 20.0 μm.

The surface roughness of the nonmagnetic support used in the present invention is not more than 20 nm, preferably not more than 15 nm, as a center line average surface roughness Ra. The surface roughness of the non-magnetic support is
It can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include, in addition to oxides and carbonates such as Ca, Si, Ti, and Al, organic resin fine powders such as an acrylic resin. Preferably, a combination of Al ₂ O ₃ and an organic resin fine powder is used. It is.

[Production Method] In the magnetic recording medium of the present invention, a coating material for the lower non-magnetic layer and a coating material for the upper magnetic layer are respectively prepared using the above-mentioned materials, and are applied on the non-magnetic support in this order. Can be manufactured.

Each of the coating materials for the lower non-magnetic layer and the upper magnetic layer may be subjected to at least a kneading step, a dispersing step and, if necessary, a mixing step, a viscosity adjusting step and a filtering step before and after these steps. It is manufactured by Each step may be divided into two or more steps. All materials used in the present invention, such as ferromagnetic powder, non-magnetic inorganic powder, binder, abrasive, carbon black, lubricant, solvent, etc., may be used at the beginning or during any process or at least two individual materials. May be added separately in the above step, but the dents change depending on the timing of addition of the abrasive, carbon black, etc., and therefore, it is preferable to use them so as to control them.

For kneading and dispersing the paint, it is a matter of course that a conventionally known manufacturing technique can be used for a part or all of the steps. However, in the kneading step, a material having a strong kneading force such as a continuous kneader or a pressure kneader is used. It is preferred to use
In the case of using a continuous kneader or a pressure kneader, kneading treatment is performed with all or a part of the ferromagnetic powder or nonmagnetic inorganic powder and the binder (however, preferably 10% by weight or more of the total binder). The slurry temperature during kneading is 50 ° C to 110 ° C.
C is preferred.

For dispersion of the paint, it is desirable to use a dispersion medium having a high specific gravity, and ceramic media such as zirconia and titania are suitable. Conventionally used glass beads, metal beads, alumina beads and the like can be selectively used depending on the composition.

In manufacturing the magnetic recording medium, the lower layer non-magnetic layer coating material is coated on a non-magnetic support, dried, smoothed, irradiated with radiation, and cured, and then the upper layer is coated on the lower non-magnetic layer. It is preferable to apply a paint for a magnetic layer. The backcoat layer may be applied before or after the lower nonmagnetic layer and the upper magnetic layer are applied, or may be applied simultaneously.

The coating means may be any of, for example, gravure coat, reverse coat, extrusion nozzle, etc., but from the viewpoint of operability and productivity, a method using a die nozzle coater is preferable.

In the present invention, after the magnetic layer is provided, it is preferable to apply a magnetic field to orient the magnetic particles in the layer. The orientation direction may be parallel, perpendicular, or oblique to the running direction of the medium, depending on the purpose. In order to direct in a predetermined direction, it is preferable to apply a magnetic field of 1000 G or more with a permanent magnet such as a ferrite magnet or a rare earth magnet, an electromagnet, a solenoid, or the like, or to use a plurality of these magnetic field generating means. Furthermore, an orientation may be performed by providing an appropriate drying step before the orientation or performing drying at the same time as the orientation so that the orientation after the drying is the highest.

After the application of the magnetic layer in this manner, the coating film subjected to the orientation treatment is usually dried and evaporated by a known method such as hot air, far infrared rays, an electric heater, or a vacuum device provided inside a drying oven. It is dried and fixed by means. The drying temperature is
The temperature may be selected from room temperature to about 300 ° C. depending on the heat resistance, solvent type, concentration, etc. of the nonmagnetic support, and a temperature gradient may be provided in the drying furnace. Further, as the gas atmosphere in the drying furnace, general air or an inert gas may be used.

After the magnetic layer is dried as described above, a calendar process is performed as a surface smoothing process as needed.
As the calendering roll, a heat-resistant plastic roll such as epoxy, polyester, nylon, polyimide, polyamide, or polyimide amide (carbon,
It is preferable to use a combination of metal and other inorganic compounds) and a metal roll (combination of three to seven steps). Further, the treatment can be performed between metal rolls. The treatment temperature is preferably 90 ° C. or higher, more preferably 100 ° C. or higher. The line pressure is
Preferably at least 200 kg / cm, more preferably 2 kg / cm
50 kg / cm or more, processing speed is 20 m / min to 900
m / min. In the present invention, the effect can be further enhanced at a temperature of 100 ° C. or more and a linear pressure of 250 kg / cm or more.

The dents on the surface of the magnetic layer of the magnetic tape can be formed by controlling the type and amount of coarse particles added to the back coat layer. This is because the magnetic tape becomes a product in a wound state, so that the surfaces of the magnetic layer and the backcoat layer come into contact with each other, and the shape of the rough backcoat surface is transferred to a smooth magnetic layer surface and becomes concave.

As another method of forming the depression of the present invention on the surface of the magnetic layer, for example, in the step of preparing the coating material for the magnetic layer, the abrasive is separately dispersed, the degree of dispersion is adjusted, and then the coating material is applied in addition to the magnetic coating material. There is a method of adjusting the degree of hardening of the non-magnetic lower layer, a method of adjusting the degree of hardening of the non-magnetic lower layer, and a method of appropriately burying the abrasive or the aggregate in the upper magnetic layer in the non-magnetic lower layer by calendering.

[0062]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. [Preparation of paint for upper magnetic layer] (Preparation of binder solution) 10 parts by weight of vinyl chloride resin (manufactured by Zeon Corporation: MR-110) 7 parts by weight of polyester polyurethane resin (UR-8300 manufactured by Toyobo Co., Ltd.) 21 parts by weight of MEK Part Toluene 21 parts by weight Cyclohexanone 21 parts by weight The above composition was charged into a hypermixer, mixed and stirred to obtain a binder solution.

(Kneading) The following composition was charged into a pressure kneader and kneaded for 2 hours. α-Fe magnetic powder 100 parts by weight (Hc = 1850 Oe, σs = 130 emu / g, BET = 57 m ² / g, major axis length = 0.10 μm) 2 parts by weight of α-Al ₂ O ₃ (Sumitomo Chemical Co., Ltd .: HIT -60A, average particle size = 0.20 μm) α-Al ₂ O ₃ 10 parts by weight (HIT-82, manufactured by Sumitomo Chemical Co., Ltd., average particle size = 0.13 μm) Binder solution 40 parts by weight The following composition was added to the slurry after kneading. To adjust the viscosity to the optimum for the dispersion treatment. Binder solution 40 parts by weight MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 15 parts by weight

(Dispersion) The above slurry was subjected to dispersion treatment in a sand mill.

(Viscosity Adjusting Liquid) The following composition was charged into a hypermixer and mixed and stirred for 1 hour to obtain a viscosity adjusting liquid. 95% cut filtration accuracy of the viscosity adjusting liquid = 1.2μ
Circulation filtration was performed using a depth filter of m. Stearic acid 0.5 parts by weight Myristic acid 0.5 parts by weight Butyl stearate 0.5 parts by weight MEK 65 parts by weight Toluene 65 parts by weight Cyclohexanone 65 parts by weight

(Viscosity adjustment) The above solution was mixed and stirred with the dispersed slurry, and then subjected to a dispersion treatment again with a sand mill to obtain a coating material. 95% cut filtration accuracy of the above paint =
Circulation filtration was performed using a 1.2 μm depth filter.

(Final paint) 0.8 parts by weight of an isocyanate compound (manufactured by Nippon Polyurethane, Coronate L) was added to 100 parts by weight of the filtered paint, and the mixture was stirred and mixed, and a 95% cut filtration filter having a filtration accuracy of 1.2 μm was used. And the resulting mixture was subjected to circulation filtration to obtain a final coating material for the magnetic layer.

[Preparation of Lower Non-Magnetic Layer Coating Material] (Preparation of Binder Solution) Electron beam-curable vinyl chloride resin 10 parts by weight (vinyl chloride-epoxy containing monomer copolymer, average degree of polymerization = 310, epoxy content = 3 wt%, S content = 0.6 wt%, acrylic content = 6 / molecule, Tg = 60 ° C.) Electron beam-curable polyester polyurethane resin 7 parts by weight (phosphorus compound-hydroxy-containing polyester polyurethane, number average molecular weight = 13000) , Acrylic content = 6 per molecule, Tg = 10 ° C) MEK 21 parts by weight Toluene 21 parts by weight Cyclohexanone 21 parts by weight The above composition was charged into a hypermixer and stirred to obtain a binder solution.

(Kneading) The following composition was charged into a pressure kneader and kneaded for 2 hours. 75 parts by weight of needle-shaped α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: DPN-250BW, major axis length = 0.15 μm, specific surface area = 53 m ² / g) 25 parts by weight of carbon black (manufactured by Columbia Carbon Corporation: Raven760B, average) Particle size = 30 nm, specific surface area = 70 m ² / g, DPB oil absorption = 48 ml / 100 g) Binder solution 40 parts by weight The following composition was added to the slurry after kneading to adjust the viscosity to be optimal for dispersion treatment. Binder solution 40 parts by weight MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 15 parts by weight

(Dispersion) The above slurry was subjected to dispersion treatment in a sand mill.

(Viscosity Adjusting Liquid) The following composition was charged into a hypermixer and stirred to obtain a viscosity adjusting liquid. Stearic acid 0.5 parts by weight Myristic acid 0.5 parts by weight Butyl stearate 0.5 parts by weight MEK 65 parts by weight Toluene 65 parts by weight Cyclohexanone 65 parts by weight

(Viscosity Adjustment and Final Coating) The above solution was mixed and stirred with the dispersed slurry, and then subjected to a dispersion treatment again with a sand mill to obtain a coating. The paint was circulated and filtered using a depth filter having a 95% cut filtration accuracy of 1.2 μm to obtain a final paint for the lower nonmagnetic layer.

[Preparation of Backcoat Layer Paint] (Preparation of Binder Solution) 65 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (monomer weight ratio = 92: 3: 5, average polymerization degree = 420) Polyester polyurethane Resin (manufactured by Toyobo Co., Ltd .: UR-8300) 35 parts by weight MEK 260 parts by weight Toluene 260 parts by weight Cyclohexanone 260 parts by weight The above composition was charged into a hyper mixer and stirred to obtain a binder solution. The binder solution was circulated and filtered using a depth filter having a 95% cut filtration accuracy of 5.0 μm.

(Dispersion) The following composition was charged into a ball mill and dispersed for 24 hours. 80 parts by weight of carbon black (Columbia Carbon: Conductex SC, average particle size = 20 nm, BET = 220 m ² / g) X parts by weight of carbon black (shown in Table 3) (Columbia Carbon: Sevacarb MT, average particle size) = 350 nm, BET = 8 m ² / g) Carbon black (shown in Table 3) Y part by weight (manufactured by Cabot: Black Pearls 130, average particle size = 75 nm, BET = 25 m ² / g) α-Fe ₂ O ₃ ( Toda Kogyo Co., Ltd .: TF100, average particle size = 0.1 μm) 1 part by weight Binder solution 880 parts by weight

(Viscosity Adjusting Liquid) The following composition was charged into a hypermixer and stirred to obtain a viscosity adjusting liquid. The viscosity adjusting liquid was subjected to circulating filtration using a depth filter having a 95% cut filtration accuracy of 1.2 μm. 1 part by weight of stearic acid 1 part by weight of myristic acid 2 parts by weight of butyl stearate 210 parts by weight of MEK 210 parts by weight of toluene 210 parts by weight of cyclohexanone

(Viscosity Adjustment) After mixing and stirring the above solution with the slurry after dispersion, dispersion treatment was performed again for 3 hours by a ball mill. 95% cut filtration accuracy of the above paint = 1.2μ
Circulation filtration was performed using a depth filter of m.

(Final paint) One part by weight of an isocyanate compound (manufactured by Nippon Polyurethane Co., Coronate-L) was added to 100 parts by weight of the filtered paint, and the mixture was stirred and mixed to obtain a back coat paint.

[Preparation of Magnetic Tape] (Examples 1 to 4, Comparative Examples 1 to 3) In Examples 1 to 4 and Comparative Examples 1 to 3, the back coat paints containing the carbon black shown in Table 3 were used. . Non-magnetic support (thickness 6.
A coating for a lower non-magnetic layer was applied to the surface of a 2 μm-thick polyethylene terephthalate film), dried, calendered, and cured by irradiation with an electron beam in a nitrogen gas atmosphere. On the lower non-magnetic layer, a coating material for an upper magnetic layer was applied, oriented, dried, and calendered. The thickness of the upper magnetic layer / lower non-magnetic layer after calendering is 0.25 μm for all samples.
/2.0 μm. Further, a paint for a back coat layer was applied to the back surface of the nonmagnetic support. After drying, calendering was performed. The thickness of the back coat layer after calendering was 0.5 μm for all samples. This roll is 2
After leaving it at room temperature for 4 hours, 2
After curing for 4 hours, the roll was cut into 1/2 inch widths and assembled into a DLT cartridge to make a magnetic tape sample.

[0079]

[Table 3]

<Method of Measuring Depression on Surface of Magnetic Layer> A method of measuring the depth and the number of dents on the surface of the magnetic layer will be described. In the present invention, the depth of the recess is defined as NT made by WYKO.
The three-dimensional surface roughness is measured using -2000, and refers to the distance from the average surface roughness of the magnetic layer to the deepest part of the recess. Here, the average surface is a surface in which the volume of unevenness in the measurement surface is equal. The measurement is 246.6 μm × 187.5 μm
(46237.5 μm ² ). As the number of dents, the number of dents having a depth of 50 nm or more in the above measurement range was determined. Rv was defined as the maximum dent depth [nm] among the dents in the above measurement range. The measurement conditions are as follows:
50 times, interferometer type: Mirau.

<Error Measurement Method> The number of times that signals of various data patterns were written on a magnetic tape sample over the entire length of the tape, an uncorrectable error occurred during a read check immediately after writing, and rewriting (rewriting) was performed at another location. Was measured. Measure the total write capacity, 1MB
It was calculated as an error value per hit. Drive used: Quantum DLT-7000
(DLT5 mode) A signal whose data pattern after RLL2-7 modulation is as follows is recorded. Input data pattern A: Repetition of 000100 Input data pattern B: Random signal Input data pattern C: Repetition of 0001001001000 Table 4 shows the evaluation results of each magnetic tape sample.

[0082]

[Table 4]

As shown in Table 4, in each of the magnetic tape samples of Examples 1 to 4 in which the surface roughness of the magnetic layer was within the range of the present invention, the number of errors was very small in any of the data patterns A, B and C. On the other hand, in Comparative Example 3, Rv is 1
It is smaller than 00 nm, and the data pattern A has a relatively small number of errors, but the data patterns B and C which are close to actual use conditions have a large number of errors. In Comparative Examples 1 and 2, Rv exceeded 100 nm, the number of errors increased even in the data pattern A, and the deterioration in the data patterns B and C was remarkable.

[0084]

According to the present invention, there is provided a magnetic recording medium having an extremely small number of errors, which is suitable for a linear serpentine type recording / reproducing system.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 23:00 101: 00 F term (Reference) 4F006 AA12 AA35 AA36 AA38 AA39 AB03 AB16 AB17 AB18 AB19 AB24 AB33 AB37 AB72 BA06 BA07 BA09 CA02 DA04 EA03 EA05 4J038 CA021 CD031 CD061 CD071 CD081 CD091 CG141 CG161 DG111 DH001 HA066 HA216 HA316 HA436 HA446 HA476 KA07 KA20 NA22 PB11 5D006 BA04 BA05 BA06 BA19 CA01 CA04 FA09

Claims (1)

[Claims] A magnetic recording medium comprising a support and a magnetic layer mainly composed of a ferromagnetic powder and a binder formed on a support,
A magnetic recording / reproducing system of a linear serpentine system employing an RLL2-7 modulation system, wherein the magnetic layer surface has a dent having a depth of 50 nm or more measured by a non-contact type surface roughness meter. Is 10 pieces / 462
37.5 μm ² or less and the maximum depth Rv is 100
nm or less.