JP2005032383A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a magnetic recording medium which makes excellent C/N characteristics and traveling stability compatible. <P>SOLUTION: In the magnetic recording medium which performs recording or reproducing of signals in a recording and reproducing system which has a magnetic layer of a film thickness ≤0.25 μm on one major face of a nonmagnetic support 1 and a back layer on a major face on the opposite side and in which linear recording density is set to ≥195 kfci, the ratio α=H(s)/H(b) of the film hardness H(s) of the magnetic layer 2 and the film hardness H(b) of the back layer 3 is regulated to 1.1≤α. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-density recording type magnetic recording medium in which electromagnetic conversion characteristics are improved.

  In recent years, with the spread of digital recording and the like, there is an increasing demand for higher density and shorter wavelength recording of magnetic recording media. Along with this, in order to improve the short wavelength output and C / N characteristics, the magnetic characteristics are improved, and the magnetic layer is made thinner in order to reduce the spacing loss and modulation noise that degrade the recording / reproducing signal. Or smoothing the surface.

  For example, conventionally, magnetic recording media in which a thin and smooth magnetic layer is formed by plating a ferromagnetic metal material or vacuum thin film formation (vacuum deposition method, sputtering method, ion plating method, etc.) have been put into practical use. I came.

  In the future, it is considered that a recording / reproducing system equipped with a high-sensitivity magnetoresistive head (MR head) as a reproducing magnetic head will become mainstream. Further reduction of modulation noise and magnetic layer Although it is thought that it will be necessary to smooth the surface, the conventional design that focuses only on the surface properties of the magnetic layer is insufficient to meet the recent demand for high-density recording. It is coming.

  That is, for example, in a long-sized magnetic recording medium, it usually takes a long time to be stored in some form and stored / waiting. At this time, the surface of the magnetic layer is under a predetermined pressure with the surface on the back layer side. This is because, since the contact continues, the back surface roughness and protrusion shape are transferred to the surface of the magnetic layer, and the surface shape of the magnetic layer may be significantly deteriorated from the initial state of forming the magnetic layer surface.

  In view of such a problem, various proposals have been made on various magnetic recording media in which the surface roughness of the back layer has been studied (see, for example, Patent Documents 1 and 2).

JP 2000-331327 A JP 2001-202615 A

  However, in view of the further increase in recording density of magnetic recording media in the future, with the conventional techniques as described above, noise cannot be sufficiently reduced, and it is fatal in terms of electromagnetic conversion characteristics. It is thought that it may become a general defect, and examination about more precise surface characteristics is needed.

In general, the back layer surface is responsible for the stability of the tape running in the recording / reproducing system. In particular, in a system in which the back layer runs while contacting the guide, it is necessary to keep the back layer surface roughness moderate. is there.
On the other hand, when applying a system in which the back layer surface does not contact the guide, it is not necessary to design the surface roughness in consideration of the running stability as described above, and therefore it is possible to form an extremely smooth surface. .

  Among the recording / reproducing systems described above, in particular, in a recording / reproducing system that travels while the back layer surface is in contact with the guide, the roughness of the back layer surface of the magnetic recording medium needs to be designed so as to obtain good traveling properties. Therefore, in the future, considering application to an extremely high density recording type recording / reproducing system having a linear recording density of 195 kfci or higher, sufficient improvement in C / N characteristics and reduction in error rate have not yet been achieved. Is the current situation.

  Therefore, in the present invention, in particular, in the extremely high recording density magnetic recording medium applied to the recording / reproducing system having a linear recording density of 195 kfci or more, the surface characteristics of the back layer and the surface characteristics of the magnetic layer are studied. It is intended to provide a magnetic recording medium that suppresses the influence of transfer from the surface of the back layer to the surface to a minimum and ensures stable running performance, has high running reliability, and has excellent electromagnetic conversion characteristics. .

  In the first invention, a magnetic layer having a thickness of 0.25 μm or less is formed on one main surface of the nonmagnetic support, and a back layer is formed on the main surface opposite to the magnetic layer forming surface. A magnetic recording medium for recording and / or reproducing a signal in a recording / reproducing system in which the density is set to 195 kfci or more, and a film hardness H (s) of a magnetic layer and a film hardness H (b) of a back layer A magnetic recording medium in which the ratio α = H (s) / H (b) is 1.1 ≦ α is provided.

  In the second invention, a magnetic layer having a film thickness of 0.25 μm or less is formed on one main surface of the nonmagnetic support, and a back layer is formed on the main surface opposite to the magnetic layer forming surface. In a recording / reproducing system in which the density is set to 195 kfci or more, a magnetic recording medium that records and / or reproduces signals in a non-contact state between the back layer and the guide unit, and the surface roughness SRa (b) of the back layer Provides a magnetic recording medium in which SRa (b) ≦ 7.0 μm.

  In a third aspect of the invention, a magnetic layer having a thickness of 0.25 μm or less is provided on one main surface of the nonmagnetic support, a back layer is provided on the main surface opposite to the magnetic layer forming surface, and the linear recording density Is a magnetic recording medium for recording and / or reproducing a signal in a non-contact state between the back layer and the guide portion in a recording / reproducing system in which is set to 195 kfci or more, and a film hardness H (s) of the magnetic layer; Provided is a magnetic recording medium in which the ratio α = H (s) / H (b) to the film hardness H (b) of the back layer satisfies 1.1 ≦ α.

  According to the first invention, the effect of transfer from the back layer surface to the magnetic layer surface is reduced by performing a predetermined regulation on the ratio between the hardness of the magnetic layer and the hardness of the back layer.

  According to the second aspect of the present invention, the surface roughness is defined so that the back layer surface is extremely smooth, particularly in a magnetic recording medium that records and / or reproduces signals in a non-contact state between the back layer and the guide portion. This reduces the influence of the transfer from the back layer surface to the magnetic layer surface.

  According to the third aspect of the invention, particularly in a magnetic recording medium that records and / or reproduces signals in a non-contact state between the back layer and the guide portion, the film hardness H (s) of the magnetic layer and the film hardness of the back layer By controlling the ratio α = H (s) / H (b) with H (b), the influence of the transfer from the back layer surface to the magnetic layer surface is reduced.

  According to the first invention, in the high-density recording type magnetic recording medium, the prescribed ratio is set for the ratio between the hardness of the magnetic layer and the hardness of the back layer, and the effect of transfer from the back layer surface to the magnetic layer surface is affected. Due to the reduction, excellent C / N characteristics were realized while ensuring excellent running stability.

  According to the second aspect of the present invention, the surface roughness is defined so that the back layer surface is extremely smooth, particularly in a magnetic recording medium that records and / or reproduces signals in a non-contact state between the back layer and the guide portion. The C / N characteristics were improved by reducing the influence of the transfer from the back layer surface to the magnetic layer surface.

  According to the third aspect of the invention, particularly in a magnetic recording medium that records and / or reproduces signals in a non-contact state between the back layer and the guide portion, the film hardness H (s) of the magnetic layer and the film hardness of the back layer By controlling the ratio α = H (s) / H (b) with H (b) and reducing the influence of the transfer from the back layer surface to the magnetic layer surface, the C / N characteristics are improved. I was able to.

  Hereinafter, the magnetic recording medium of the present invention will be described in detail, but the present invention is not limited to the following examples.

  FIG. 1 shows a schematic configuration diagram of an example of the magnetic recording medium of the present invention. The magnetic recording medium 10 has a magnetic layer 2 with a film thickness of 0.25 μm or less on one main surface of the nonmagnetic support 1, and a back layer 3 on the main surface opposite to the magnetic layer forming surface side. Have.

As the material for forming the nonmagnetic support 1, any material that has been used as a support for a conventionally known magnetic recording medium can be applied. For example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, Examples thereof include plastics such as polycarbonate, polyimide, polyamide and polyamideimide, metals such as paper, aluminum and copper, light alloys such as aluminum alloy and titanium alloy, ceramics and single crystal silicon.
Moreover, as a form of the nonmagnetic support 1, various conventionally known shapes such as a film shape, a tape shape, a sheet shape, a disk shape, a card shape, and a drum shape can be applied.

The magnetic layer 2 is mainly composed of a ferromagnetic powder and a binder, added with various additives such as an abrasive, an antistatic agent, a rust preventive and a curing agent, and adjusted by a conventionally known method using an organic solvent or the like. It is formed by applying a magnetic paint on the nonmagnetic support 1.
In the magnetic recording medium 10 of the present invention, the magnetic layer 2 has a thickness of 0.25 μm or less, and is formed to have a thickness of 0.05 μm to 0.25 μm for practical use of a high-density recording type magnetic recording medium.

  Examples of the ferromagnetic powder for forming the magnetic layer 2 include ferromagnetic iron oxide particles, ferromagnetic chromium dioxide, ferromagnetic alloy powder, iron nitride, and the like. As a coating material for forming a magnetic layer of a so-called coating type magnetic recording medium. As long as it is applied, any conventionally known one can be applied. These may be used alone or in appropriate combination.

As the binder for forming the magnetic layer 2, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer Polymer, vinyl chloride-acrylonitrile copolymer, acrylate ester-acrylonitrile copolymer, acrylate ester-vinylidene chloride copolymer, methacrylic acid-vinylidene chloride copolymer, methacrylate ester-styrene copolymer, thermoplastic Polyurethane, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester Resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin, etc., and these may be used alone or in combination of two or more. It may be used.
In particular, a polyurethane resin, a polyester resin, an acrylonitrile-butadiene copolymer that can impart flexibility, a cellulose derivative that can impart rigidity, a phenol resin, an epoxy resin, and the like are preferable. These may use an isocyanate compound as a cross-linking agent to improve durability, or may introduce a suitable polar group to improve surface properties.

  As the solvent for forming the magnetic layer 2, any of those conventionally used as an organic solvent for adjusting a magnetic paint can be applied. For example, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate and glycol acetate monoethyl ester, glycol ethers such as glycol monoethyl ether and dioxane Examples thereof include organic solvents, aromatic hydrocarbon solvents such as benzene, toluene and xylene, and organic chlorine compound solvents such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin and dichlorobenzene.

  The back layer 3 is prepared, for example, by using a conventionally known inorganic powder, a binder as a main component, and a dispersion containing various additives such as an antistatic agent, a rust inhibitor, and a curing agent using an organic solvent or the like. It shall be formed by apply | coating the coating material for back layers.

In addition, as a dispersion for forming the back layer 3, an equivalent product of the above magnetic dispersion may be used as it is, and carbon black, various ceramic particles, a metal oxide, or the like may be used as an inorganic powder.
Examples of the binder for the back layer include, but are not limited to, polyester-based polyurethane resin, phenoxy resin, nitrocellulose resin, and the like, and those used as the binder for the magnetic layer described above. Any of these can be applied.

  Examples of the solvent for adjusting the back layer dispersion include methyl ethyl ketone and toluene, but are not limited thereto, and any of the above-described organic solvents for adjusting the magnetic layer paint can be applied.

The configuration of the magnetic recording medium of the present invention is not limited to that shown in FIG. 1, for example, an arbitrary non-recording layer may be formed between the non-magnetic support 1 and the magnetic layer 2, or the magnetic layer 2 may have a plurality of laminated structures, or various structural additions may be added.
In addition, the nonmagnetic support 1 and the ferromagnetic powder and binder contained in the magnetic layer 2, inorganic powder mixed in the non-recording layer, binder and dispersant, other abrasives, antistatic agents, rust prevention As the agent and the solvent for adjusting the paint, any conventionally known ones can be applied and are not limited at all.

Next, a method for producing the magnetic recording medium 10 will be described.
First, a predetermined nonmagnetic support 1 is prepared. Next, the coating for the magnetic layer and, if necessary, the coating for the non-recording layer are adjusted.
The magnetic coating material and the coating material for the non-recording layer are prepared by kneading and dispersing the above-described materials together with a predetermined solvent. Any known kneading method can be applied to the kneading dispersion method, and the method is not particularly limited. Examples thereof include a method using a continuous biaxial kneader (extruder), a kneader, a pressure kneader and the like.

  The non-recording layer and the magnetic layer 2 are formed by applying the respective paints by a conventional coating method such as gravure coating, extrusion coating, air doctor coating, reverse roll coating, and the like.

  Further, when the magnetic layer 2 is formed on the non-recording layer, a so-called wet-on-dry method in which a coating is sequentially applied and dried may be used, and a non-recording layer in a wet state is formed. Alternatively, a so-called wet-on-wet method may be used in which a coating for forming the magnetic layer 2 is applied on top of the coating for coating.

  After the magnetic layer 2 was formed, a magnetic field orientation treatment and a heat drying treatment were performed, and then the back layer 3 was formed by applying the above-described coating material for the back layer. Thereafter, a calendar process and a curing process are performed. The film hardness and surface roughness were adjusted by controlling the calendar treatment conditions and the effect treatment conditions at this time.

  Next, film hardness and surface roughness will be described as surface characteristics of the magnetic layer 2 and the back layer 3 of the magnetic recording medium of the present invention.

FIG. 2 shows a schematic perspective view of an example of a hardness measuring apparatus that measures the film hardness of the magnetic layer 2 and the back layer 3. The hardness measuring apparatus 20 has a configuration in which a measuring instrument 23 including a displacement sensor 21 and a load sensor 22 and a stage 25 on which an evaluation sample 24 is arranged are installed on an apparatus base 30.
A load pedestal 26 is provided on the side of the measuring instrument 23 opposite to the evaluation sample 24. The load pedestal 26 includes a load needle 27 as shown in the enlarged schematic view of FIG. The tip of the needle 27 is provided with a spherical portion 28 having a diameter of about 0.3 μm, for example.

  On the stage 25, the magnetic recording medium manufactured as described above as the evaluation sample 24 is arranged with the magnetic layer forming surface or the back layer forming surface facing the load pedestal 26, and the load needle 27 is loaded. The stress [kgf] applied per unit depth of penetration [μm] is calculated in the vertical direction, and this is defined as the film hardness (H (s), H (b)).

  Regarding the film hardness H (s) of the magnetic layer 2 and the film hardness H (b) of the back layer 3 defined as described above, the ratio α = H (s) / H (b) is 1. By defining that 1 ≦ α, it is possible to effectively prevent transfer of the surface shape of the back layer 3 to the surface of the magnetic layer 2 even in an extremely high-density recording type magnetic recording medium, and C / N characteristics can be reduced. It has been found that deterioration can be effectively avoided.

Next, the surface roughness of the back layer 3 will be described.
The surface roughness SRa (b) of the back layer 3 should be measured in an arbitrary area range using a conventionally known surface roughness measuring device, for example, Nano Scope IIIa / D-3000 (manufactured by Digital Instruments). It can ask for. By defining the surface roughness SRa (b) of the back layer 3 as 7.0 μm ≦ SRa (b) ≦ 18.0 μm, in the recording / reproducing system, signal recording and / or Or even when performing regeneration, stable running performance can be ensured.

On the other hand, in the magnetic recording medium in which the back layer 3 and the guide portion of the recording / reproducing system perform signal recording and / or reproduction in a non-contact state, the back layer 3 can be formed extremely smoothly. Therefore, in this case, by selecting the surface roughness SRa (b) as SRa (b) ≦ 7.0 μm, the influence of the transfer from the back layer surface to the magnetic layer surface can be effectively reduced. / N characteristics can be improved.
Further, in a magnetic recording medium in which signals are recorded and / or reproduced in a non-contact state between the back layer 3 and the guide portion of the recording / reproducing system, the film hardness H (s) of the magnetic layer 2 and the film of the back layer 3 By defining the ratio of hardness H (b) α = H (s) / H (b) to 1.1 ≦ α, transfer of the surface shape of the back layer 3 to the surface of the magnetic layer 2 can be reliably prevented. Degradation of C / N characteristics can be effectively avoided.

  Hereinafter, the magnetic recording medium of the present invention will be described with specific examples and comparative examples.

[Examples A1 to A8], [Comparative Examples A1 to A11]
A magnetic layer dispersion having the following composition was prepared.
[Dispersion composition for magnetic layer]
Ferromagnetic powder: Iron-cobalt alloy metal magnetic powder: 100 parts by weight Binder: Polyester polyurethane resin: 8 parts by weight (amount-average molecular weight 41200)
Binder: Vinyl chloride copolymer (average polymerization degree 350): 10 parts by weight Inorganic powder (abrasive): α-alumina: 5 parts by weight
(Particle size 200 nm, specific surface area / BET method 11.1 m ² / g)
Lubricant: Stearic acid: 1 part by weight Butyl stearate: 2 parts by weight Solvent: Methyl ethyl ketone: 20 parts by weight Toluene: 20 parts by weight Cyclohexanone: 10 parts by weight

  The above materials were kneaded with a kneader, further diluted with methyl ethyl ketone, toluene, and cyclohexanone, and then dispersed in a sand mill. 4 parts by weight of polyisocyanate (Japanese polyurethane curing agent “Coronate L”) was added to the dispersion after the sand mill dispersion, and after stirring, this was coated on the nonmagnetic support to a predetermined film thickness. Then, the magnetic field orientation process was performed, and it dried and wound up at predetermined temperature.

Next, a back layer dispersion was prepared.
As the backcoat layer dispersion, two kinds of inorganic powders a1, a2, and a3 having different blending ratios were prepared as shown below using two kinds of inorganic powders. Then, 10 parts by weight of polyisocyanate (Nippon polyurethane curing agent “Coronate L”) was added to each, and applied to the surface opposite to the magnetic layer to form a back layer 3 having a thickness of 0.5 μm.

[Back layer dispersion composition a1]
Inorganic powder: Carbon black: 50 parts by weight (particle size 40 nm, DBP oil absorption 112.0 ml / 100 g)
Inorganic powder: Carbon black: 50 parts by weight (particle size 80 nm, DBP oil absorption 55.0 ml / 100 g)
Binder: Polyester polyurethane resin: 13 parts by weight (weight average molecular weight 71200)
Binder: Phenoxy resin (average polymerization degree 100): 43 parts by weight Binder: Nitrocellulose resin (average polymerization degree 90): 10 parts by weight Solvent: Methyl ethyl ketone: 500 parts by weight Toluene: 500 parts by weight

[Back layer dispersion composition a2]
Inorganic powder: Carbon black: 30 parts by weight (particle size 40 nm, DBP oil absorption 112.0 ml / 100 g)
Inorganic powder: Carbon black: 70 parts by weight (particle size 80 nm, DBP oil absorption 55.0 ml / 100 g)
Binder: Polyester polyurethane resin: 13 parts by weight (weight average molecular weight 71200)
Binder: Phenoxy resin (average polymerization degree 100): 43 parts by weight Binder: Nitrocellulose resin (average polymerization degree 90): 10 parts by weight Solvent: Methyl ethyl ketone: 500 parts by weight Toluene: 500 parts by weight

[Back layer dispersion composition a3]
Inorganic powder: Carbon black: 100 parts by weight
(Particle size 80nm, DBP oil absorption 55.0ml / 100g)
Binder: Polyester polyurethane resin: 13 parts by weight (weight average molecular weight 71200)
Binder: Phenoxy resin (average polymerization degree 100): 43 parts by weight Binder: Nitrocellulose resin (average polymerization degree 90): 10 parts by weight Solvent: Methyl ethyl ketone: 500 parts by weight Toluene: 500 parts by weight

  After forming a back layer using the above-mentioned coating material, a drying process was performed at 90 ° C., and a calendar process was further performed. The linear pressure during the calendar process was set to 5 conditions of 50, 100, 150, 200, and 250 [kgf / cm], the temperature was set to 2 conditions of 100 and 130 ° C., and the calendar process was performed by appropriately combining them. Then, the hardening process was performed and the obtained wide tape was slit to 12 mm width, and it was set as the sample magnetic tape.

  [Examples A1 to A8] and [Comparative Examples A1 to A11] Sample magnetic tape back layer formation dispersion type, magnetic layer thickness, drying treatment temperature, calendering linear pressure, and calendering temperature These are shown in Table 1 below.

  For the sample magnetic tape manufactured as described above, the back layer surface roughness SRa (b), the magnetic layer surface roughness SRa (m), the magnetic layer surface hardness H (s), and the back layer surface hardness H (B), C / N characteristics, and dropout were measured. Each measuring method is shown below.

(Surface roughness measurement)
A product name: Nano Scope IIIa / D-3000 (manufactured by Digital Instruments) was used to measure a range of 50 × 50 [μm ² ]. In the measurement, a commonly used frequency filter (cut-off frequency) or the like was not used.

[Surface hardness measurement]
The coating film hardness was measured using a push-type hardness measuring apparatus 20 having a configuration as shown in FIG. 2 having a spherical diamond needle having a diameter of 0.3 μm.
The magnetic layer and back layer of the magnetic tape of arbitrary shape are each weighted with a needle in the vertical direction, and the stress [kgf] applied to the needle per unit indentation depth [μm] is calculated (unit: [kgf / μm]) Then, the hardness was measured. The measurement results are shown in Tables 2 and 3 below.

[C / N characteristics measurement]
The sample magnetic tape used was a drum tester equipped with a recording magnetic head (MIG, gap 0.15 μm). After recording a signal of 195 kfci or 250 kfci, the reproduction output and noise were measured using a spectrum analyzer. Note that a laminated amorphous head and an MR head were used as magnetic heads for reproduction. The magnitude of the frequency component of ± 2 MHz from the reproduction signal is defined as the noise level, and the reproduction signal output ratio of the noise output is defined as the C / N characteristic.
Table 2 shows the measurement results when using the laminated amorphous head, and Table 3 shows the measurement results when selecting an arbitrary sample magnetic tape from Table 2 and reproducing the signal using the MR head. Indicated.
In any case, relative values were shown when the C / N value was defined as 0.0 dB with the magnetic tape of Comparative Example A1 as a reference.

[Dropout measurement]
Dropout evaluation was performed using a media tester for LTO (a modified machine manufactured by D & TT). Table 2 and Table 3 show the number of dropouts within the full width of the tape between the magnetic tape lengths of 20m and the ratio to the reference tape count (the ratio when the reference magnetic tape is 100%). It was. Note that the dropout was measured by using the above-described measurement apparatus and measuring the case where deterioration of the signal output larger than −9 dB continued for 1 μm or more as one.
However, although the MR head is mounted on the measuring apparatus, dropout can be evaluated by the same system regardless of whether the head type is an induction type or an MR type. Therefore, even if the apparatus used in this measurement is only the MR head mounted type, this evaluation result also reflects the evaluation result in the case where the actual system has the induction head mounted.

[Running stability]
Running stability was evaluated at room temperature (25 ° C., 50%) using an LTO1 Ultrium drive (Viper200 modified machine manufactured by Seagate) and a VS-160 drive (VS-160 modified machine manufactured by Quantum). This Ultrium drive is a system in which the back layer surface of the magnetic recording medium runs in a non-contact state with the guide, and the VS-160 drive is a system in which the back layer surface of the magnetic recording medium is in contact with the guide.
Each magnetic tape was subjected to a shuttle test using the above drive.
In the shuttle test, the evaluation was performed by reciprocating 25000 times between the 20 GB and the 60 GB among the arbitrary 80 GB recording sites. The state of the running magnetic tape was observed, and the evaluation results are shown in Tables 2 and 3 below.
If the magnetic tape sticks to the guide or head during the specified number of runs, if the magnetic tape is damaged due to deviation from the guide, or if the magnetic tape breaks during running, it is regarded as running unstable. Those that showed practically sufficient running stability were marked with ◯.
However, although a drive equipped with an MR head was applied as the measurement drive, the running stability noted here can be evaluated with the same system regardless of whether the head type is induction type or MR type. .

  As shown in Tables 2 and 3, the ratio α = H (s) / H (b) between the film hardness H (s) of the magnetic layer and the film hardness H (b) of the back layer is 1.1 ≦ In the magnetic tapes of Examples A1 to A8 with α, good C / N characteristics were obtained in any system in which the linear recording density was set to 195 kfci or more, and a drastic improvement in dropout was confirmed. .

  In the system (VS-160 drive) in which the back layer is in contact with the guide by setting the surface roughness SRa (b) of the back layer to 7.0 μm ≦ SRa (b) ≦ 18.0 μm. In addition, high running reliability was obtained.

  On the other hand, in the comparative examples A1 to A8 in which the ratio α = H (s) / H (b) of the film hardness H (s) of the magnetic layer and the film hardness H (b) of the back layer is less than 1.1. In the sample magnetic tape, the shape on the back layer side was transferred to the magnetic layer side, and C / N characteristics, dropout characteristics, etc. could not be sufficiently improved.

In Comparative Example A9, since the back surface was too smooth, traveling reliability deteriorated in a system (VS-160 drive) that travels with the back layer in contact with the guide.
In Comparative Example A10, since the back surface was rough, a slight increase in noise was confirmed.

  In Comparative Example A11, since the magnetic layer was thicker than 0.25 μm, it was confirmed that the C / N characteristics were deteriorated in the high frequency region.

Further, as shown in Table 3, the sample magnetic tapes of Examples 4 to 7 according to the magnetic recording medium of the present invention are good at the recording densities of 195 kfci and 250 kfci, as in the case of using the induction head. C / N characteristics were obtained.
That is, according to the magnetic recording medium of the present invention, it has been confirmed that both good C / N characteristics and good dropout can be realized regardless of the type of head, and further, high running reliability independent of the type of drive can be realized. It was.

On the other hand, in Comparative Examples A1, A2, A4, and A6 to A8, the deterioration of the C / N characteristics was confirmed as in the test using the induction head.
In Comparative Example A11, since the magnetic layer was thicker than 0.25 μm, it was confirmed that the C / N characteristics were deteriorated in the high frequency region.

[Examples B1 to B9], [Comparative Examples B1 and B2]
First, a dispersion for a magnetic layer for forming a magnetic layer having the following composition was prepared.
[Dispersion composition for magnetic layer]
Fine ferromagnetic powder: Iron-cobalt alloy metal magnetic powder: 100 parts by weight Binder: Polyester polyurethane resin (quantity average molecular weight 41200): 8 parts by weight Binder: vinyl chloride copolymer (average degree of polymerization 350): 10 parts by weight inorganic powder (abrasive): α-alumina: 5 parts by weight (particle size 200 nm, specific surface area / BET method 11.1 m ² / g)
Lubricant: Stearic acid: 1 part by weight
Butyl stearate: 2 parts by weight Solvent: methyl ethyl ketone: 20 parts by weight Toluene: 20 parts by weight Cyclohexanone: 10 parts by weight

  The above materials were kneaded with a kneader, further diluted with methyl ethyl ketone, toluene, and cyclohexanone, and then dispersed in a sand mill. 4 parts by weight of polyisocyanate (Japanese polyurethane curing agent “Coronate L”) was added to the dispersion after the sand mill dispersion and stirred to obtain a coating for forming a magnetic layer.

Next, a coating material for forming a back layer was prepared.
Two kinds of inorganic powders b1 to b3 having different blending ratios were prepared by using two kinds of inorganic powders for the back layer dispersion. To these, 10 parts by weight of polyisocyanate (Japanese polyurethane curing agent “Coronate L”) was added to obtain a coating material for forming a back layer.

[Back layer forming dispersion b1]
Inorganic powder: Carbon black: 50 parts by weight
(Particle size 40 nm, DBP oil absorption 112.0 ml / 100 g)
Carbon black: 50 parts by weight
(Particle size 80nm, DBP oil absorption 55.0ml / 100g)
Binder: Polyester polyurethane resin: 13 parts by weight
(Weight average molecular weight 71200)
Binder: Phenoxy resin (average polymerization degree 100): 43 parts by weight Binder: Nitrocellulose resin (average polymerization degree 90): 10 parts by weight Solvent: Methyl ethyl ketone: 500 parts by weight Solvent: Toluene: 500 parts by weight

[Back layer dispersion composition b2]
Inorganic powder: Carbon black: 30 parts by weight (particle size 40 nm, DBP oil absorption 112.0 ml / 100 g)
Inorganic powder: Carbon black: 70 parts by weight (particle size 80 nm, DBP oil absorption 55.0 ml / 100 g)
Binder: Polyester polyurethane resin: 13 parts by weight
(Weight average molecular weight 71200)
Binder: Phenoxy resin: 43 parts by weight
(Average polymerization degree 100)
Binder: Nitrocellulose resin: 10 parts by weight
(Average polymerization degree 90)
Solvent: Methyl ethyl ketone: 500 parts by weight Toluene: 500 parts by weight

[Back layer dispersion composition b3]
Inorganic powder: Carbon black: 100 parts by weight (particle size 80 nm, DBP oil absorption 55.0 ml / 100 g)
Binder: Polyester polyurethane resin: 13 parts by weight (weight average molecular weight 71200)
Binder: Phenoxy resin: 43 parts by weight (average degree of polymerization 100)
Binder: Nitrocellulose resin: 10 parts by weight (average degree of polymerization 90)
Solvent: Methyl ethyl ketone: 500 parts by weight Toluene: 500 parts by weight

  On the non-magnetic support, the magnetic layer-forming coating material was applied, followed by magnetic field orientation treatment, dried at a predetermined temperature and wound up. And the coating material for back layers was apply | coated to the surface on the opposite side to a magnetic layer, and the 0.5 micrometer-thick back layer was formed.

  After forming the back layer, it was dried at 90 ° C. and further subjected to a calendar treatment. The calendering was performed by selecting and combining the linear pressure during the calendering process from five conditions of 50, 100, 150, 200, and 250 [kgf / cm] and the temperature of two conditions of 100 and 130 ° C. Thereafter, curing treatment was performed, and the obtained wide tape was slit into a width of 12 mm to obtain a sample magnetic tape.

  [Examples B1 to B9] and [Comparative Examples B1 and B2] Sample magnetic tape back layer forming dispersion type, magnetic layer thickness, calendering linear pressure, and calendering temperature are as follows. Table 4 shows.

  For the sample magnetic tape manufactured as described above, the back layer surface roughness SRa (b), the magnetic layer surface roughness SRa (m), the magnetic layer surface hardness H (s), and the back layer surface hardness H (B) C / N characteristics and dropout were measured. Each measuring method is shown below.

(Surface roughness measurement)
A product name: Nano Scope IIIa / D-3000 (manufactured by Digital Instruments) was used to measure a range of 50 × 50 [μm ² ].

[Surface hardness measurement]
The coating film hardness was measured using an indentation hardness measuring apparatus 20 having a configuration as shown in FIG. 2 having a spherical diamond needle having a diameter of 0.3 μm.
The magnetic layer and back layer of the magnetic tape of arbitrary shape are each weighted with a needle in the vertical direction, and the stress [kgf] applied to the needle per unit indentation depth [μm] is calculated (unit: [kgf / μm]) Then, the hardness was measured. The measurement results are shown in Tables 5 and 6 below.

[C / N characteristics measurement]
The sample magnetic tape used was a drum tester equipped with a recording magnetic head (MIG, gap 0.15 μm). After recording a signal of 195 kfci or 250 kfci, the reproduction output and noise were measured using a spectrum analyzer. As a reproducing magnetic head, a laminated amorphous head and a magnetoresistive head (AMR head) were used.
The magnitude of the frequency component of ± 2 MHz from the reproduction signal is defined as the noise level, and the reproduction signal output ratio of the noise output is defined as the C / N characteristic.
Table 5 shows the measurement results when using the laminated amorphous head, and Table 6 shows the measurement results when selecting an arbitrary sample magnetic tape from Table 5 and reproducing the signal using the MR head. Indicated.
In any case, relative values were shown when the C / N value was defined as 0.0 dB with reference to the magnetic tape of Comparative Example B1.

[Dropout measurement]
Dropout evaluation was performed using a media tester for LTO (a modified machine manufactured by D & TT). Table 5 and Table 6 show the number of dropouts within the full width of the tape between the magnetic tape lengths of 20m and the ratio to the reference tape count (the ratio when the reference magnetic tape is 100%). It was. Note that the dropout was measured by using the above-described measurement apparatus and measuring the case where deterioration of the signal output larger than −9 dB continued for 1 μm or more as one.
However, although the MR head is mounted on the measuring apparatus, dropout can be evaluated by the same system regardless of whether the head type is an induction type or an MR type. Therefore, even if the apparatus used in this measurement is only the MR head mounted type, this evaluation result also reflects the evaluation result when the actual system is mounted with the induction type head.

[Running stability]
Running stability was evaluated at room temperature (25 ° C. 50%) using an LTO1 Ultrium drive (Viper200 modified machine manufactured by Seagate). This evaluation apparatus is a system in which the back layer surface of a magnetic recording medium travels in a non-contact state with a guide.
A shuttle test was performed using each magnetic tape.
In the shuttle test, evaluation was performed by reciprocating 25000 times between 20 GB and 50 GB among arbitrary 100 GB recording sites. The state of the running magnetic tape was observed, and the evaluation results are shown in Tables 5 and 6 below.
If the magnetic tape sticks to the guide or head during the specified number of runs, if the magnetic tape is damaged due to deviation from the guide, or if the magnetic tape breaks during running, it is regarded as running unstable. The case where a practically sufficient running stability was obtained was rated as ◯.
However, although a drive equipped with an MR head was applied as the measurement drive, the running stability noted here can be evaluated with the same system regardless of whether the head type is induction type or MR type. .

  As shown in Table 5 above, in the magnetic tapes of Examples B1 to B9 in which the surface roughness SRa (b) of the back layer was selected as SRa (b) ≦ 7.0 μm, the linear recording density was set to 195 kfci or more. In all the systems, good C / N characteristics were obtained, and a drastic improvement in dropout was confirmed.

  Magnetic tapes of Examples B5 to B8 in which the ratio α = H (s) / H (b) between the film hardness H (s) of the magnetic layer and the film hardness H (b) of the back layer is 1.1 ≦ α In any system in which the linear recording density was set to 195 kfci or more, the C / N characteristics were more reliably improved, and the dropout was further improved.

  On the other hand, the surface roughness SRa (b) of the back layer is SRa (b)> 7.0 μm, and the ratio α = H between the film hardness H (s) of the magnetic layer and the film hardness H (b) of the back layer. In the sample magnetic tape of Comparative Example B1 in which (s) / H (b) is less than 1.1, the shape on the back layer side is transferred to the magnetic layer side, and C / N characteristics, dropout characteristics, etc. Could not be improved sufficiently.

  In Comparative Example B2, since the thickness of the magnetic layer was thicker than 0.25 μm, it was confirmed that the C / N characteristics deteriorated in the high frequency region.

Further, as shown in Table 6, in the sample magnetic tapes of Examples 1 to 4, 8, and 9 relating to the magnetic recording medium of the present invention, the induction type head was used at any recording density of 195 kfci and 250 kfci. In the same manner, good C / N characteristics were obtained.
In particular, the ratio α = H (s) / H (b) to the film hardness H (b) of the back layer is 1.1 ≦ α, and the surface roughness SRa (b) of the back layer is SRa (b) ≦ In the magnetic tape of Example 8 which is 7.0 μm, extremely excellent C / N characteristics and good dropout characteristics were realized.

On the other hand, in Comparative Example B1, the C / N characteristics deteriorated as in the test using the induction head.
In Comparative Example B2, since the thickness of the magnetic layer was thicker than 0.25 μm, it was confirmed that the C / N characteristics deteriorated in the high frequency region.

1 is a schematic cross-sectional view of an example of a magnetic recording medium of the present invention. The schematic perspective view of a hardness measuring apparatus is shown. The schematic of the principal part of a hardness measuring apparatus is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 2 ... Magnetic layer, 3 ... Back layer, 10 ... Magnetic recording medium, 20 ... Hardness measuring device, 21 ... Displacement sensor, 22 ... Load sensor, 23 ... Measurement 24 ... Evaluation sample 25 ... Stage 26 ... Load base 27 ... Load needle 28 ... Spherical part 30 ... Device base

Claims (7)

One main surface of the nonmagnetic support has a magnetic layer with a film thickness of 0.25 μm or less, and has a back layer on the main surface opposite to the magnetic layer forming surface,
A magnetic recording medium for recording and / or reproducing a signal in a recording / reproducing system having a linear recording density set to 195 kfci or higher,
The ratio of the film hardness H (s) of the magnetic layer to the film hardness H (b) of the back layer;
α = H (s) / H (b) satisfies 1.1 ≦ α. The surface roughness SRa (b) of the back layer is
The magnetic recording medium according to claim 1, wherein 7.0 μm ≦ SRa (b) ≦ 18.0 μm. 2. The magnetic recording medium according to claim 1, wherein a signal is reproduced using a magnetoresistive head. One main surface of the nonmagnetic support has a magnetic layer with a film thickness of 0.25 μm or less, and has a back layer on the main surface opposite to the magnetic layer forming surface,
In a recording / reproducing system in which the linear recording density is set to 195 kfci or more, a magnetic recording medium for recording and / or reproducing a signal in a non-contact state between the back layer and the guide unit of the recording / reproducing system,
A magnetic recording medium, wherein the surface roughness SRa (b) of the back layer is SRa (b) ≦ 7.0 μm. One main surface of the nonmagnetic support has a magnetic layer with a film thickness of 0.25 μm or less, and has a back layer on the main surface opposite to the magnetic layer forming surface,
In a recording / reproducing system in which the linear recording density is set to 195 kfci or more, a magnetic recording medium for recording and / or reproducing a signal in a non-contact state between the back layer and the guide unit of the recording / reproducing system,
The ratio of the film hardness H (s) of the magnetic layer to the film hardness H (b) of the back layer;
α = H (s) / H (b) satisfies 1.1 ≦ α. The ratio of the film hardness H (s) of the magnetic layer to the film hardness H (b) of the back layer, α = H (s) / H (b) satisfies 1.1 ≦ α. The magnetic recording medium according to claim 4. 5. The magnetic recording medium according to claim 4, wherein a signal is reproduced using a magnetoresistive head.

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