JPH09305959A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating-type magnetic recording medium in which a very thin and uniform magnetic recording layer is formed on a nonmagnetic coating film and which is excellent in running characteristics, still characteristics and durability without decreasing the output. SOLUTION: A coating film 1 of nonmagnetic paint is applied to a nonmagnetic support 3 and a coating film 2 of magnetic paint whose main component is magnetic alloy powder is applied to the coating film 2 to obtain a magnetic recording medium. The square-root roughness of the recording layer (coating film 2) of the magnetic recording medium is so controlled as to be 2.5-6.0nm and the integrated power value in a TD direction on the recording surface 2 in a space wavelength range of 0.5-1.0μm is so controlled as to be not less than 0.3nm<2> . Or, the occupation area of polisher particles on the recording layer surface is so controlled as to be 3-10%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium widely used as a storage medium for video, audio and information equipment. Specifically, the present invention relates to a magnetic recording medium having excellent running characteristics and still life without impairing high electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art As devices become smaller and image quality becomes higher, the density of signals recorded on magnetic recording media is increasing. Looking at VTR devices already on the market, the shortest recording wavelength is becoming smaller as the format shifts to higher formats. For example, VHS format 1.3μm, 8mm
The shortest recording wavelength that was 0.7 μm in the format is S
-0.8 μm for VHS format and 0.49 μm for Hi-8 format.

It is known that the amount of signals per unit time is further increased in the currently proposed digital recording device for NTSC signals and recording device compatible with high-definition broadcasting, and the recording wavelength is further shortened in the device design. Being sought in the direction.

In addition, in digital recording, a low error rate is required as a representative of signal quality, and a high C / N characteristic is required to compensate for this.

In order to realize the recording / reproducing characteristics for such applications, an alloy magnetic powder having a large saturation magnetization is used as the magnetic powder used in the coating type magnetic recording medium, and in addition, a magnetic powder having a size smaller than the conventional size is used. Is being considered. By increasing the saturation magnetization, the saturation magnetic flux density of the recording layer is improved, and by using finer magnetic powder, the response to signals of short wavelength and the surface property are improved.

Further, an attempt to reduce the thickness of the recording layer by using a multi-layer coating film forming technique including the simultaneous two-layer coating forming technique disclosed in Japanese Patent Laid-Open No. 4-238111 has attracted attention. . This is to make the recording layer thinner as the writing depth decreases as the recording wavelength becomes shorter. As a result, it is possible to reduce the thickness loss of the magnetic signal recorded on the magnetic film and to improve the overwrite characteristic when the signal is newly overwritten.

[0007]

However, the coating type magnetic recording medium having a thin layer structure formed by using the multilayer coating film forming technique has the following problems in terms of practical characteristics.

[0008] As a first problem, when the surface finish is excellent in order to realize high electromagnetic conversion characteristics, the true contact area with the traveling system parts of the equipment increases, resulting in a large friction coefficient. Stable running cannot be obtained.

As a countermeasure, it is possible to adjust the type and amount of the lubricant added to the coating layer. However, if the magnetic coating material for the recording layer is used, the effect is sufficiently obtained because the film thickness ratio to the entire coating film is small. I can't. On the other hand, when adjusted with an undercoat layer having a large film thickness ratio, the runnability itself is improved, but the balance of the underlayer coating film is also lost, and as a result, the durability of the medium itself deteriorates.

The second problem is that the still life is short. The causes are delamination that occurs at the interface between the recording layer and the undercoat layer, damage caused by stress concentration at the interface that causes a problem of the balance of the coating strength between the upper and lower layers, and lubricants and stills contained in the upper and lower layers. It is considered that the oil film is broken due to the difference in concentration of effective components.

[0011] For such deterioration of running characteristics and still life, there has been studied a method of attempting to improve the deterioration of running characteristics and still life by the type and addition amount of abrasive particles, which has been conventionally carried out in a single layer coating film. This is to support the contact with the magnetic head and traveling system parts by appropriately adding abrasive particles having high hardness.

However, in a two-layer medium having a thin recording layer, even if the size and amount of abrasive particles are adjusted in the same manner as in a conventional single-layer medium, an appropriate effect cannot be obtained. Specifically, since the recording layer thickness is very thin, the abrasive agent protrudes greatly on the surface, which greatly impairs the surface roughness and causes a reduction in output, and the head wear amount becomes significantly large. Resulting in.

The cause is that the distribution of the abrasive in the conventional single-layer medium has a change in the thickness direction, but since the thickness is extremely thin, the degree of freedom in the thickness direction is lost. One of the reasons is that it is difficult to control the running improvement effect of the abrasive.

As described above, it is very difficult to improve the practical characteristics without deteriorating the signal quality even if measures are taken against the problems in the conventional technique. Results in worsening.

In consideration of the problems of the conventional magnetic recording medium as described above, the present invention has an object to obtain a medium excellent in running property and still characteristic while having a high electromagnetic conversion characteristic as in the conventional case. is there.

[0016]

In order to achieve the above object, the present invention provides a non-magnetic support, an undercoat layer containing a non-magnetic powder and a binder resin as a main component, and an alloy magnetic powder and a binder resin as a main component. A coating type magnetic recording medium in which two layers, a recording layer and a recording layer having a root mean square roughness of 2.5 nm or more and 6.0 nm or less, and a TD direction on the surface of the recording layer. Spatial wavelength at 0.5 to 1.0 μm
It is characterized in that the power integrated value up to is controlled to 0.3 nm ² or more.

Alternatively, in a coating type magnetic recording medium, a non-magnetic support is provided with two layers, an undercoat layer containing a non-magnetic powder and a binder resin as a main component, and a recording layer containing an alloy magnetic powder and a binder resin as a main component. In addition, the exclusive area ratio of the abrasive particles on the surface of the recording layer is controlled to be 5% or more and 10% or less.

Further, in order to make the above two characteristics more effective, the average particle diameter of the abrasive particles contained in the recording layer is 40% or more and 100% or less of the thickness of the recording layer. To do.

By having such a structure, the following effects can be obtained.

First, as the first invention, the surface shape of the recording layer has a root mean square roughness of 2.5 nm or more and 6.0 nm or less, and the spatial wavelength of the recording layer surface in the TD direction is 0.5.
0.3 nm ^{2 in} integrated power value from μm to 1.0 μm
With the above, the following effects can be obtained.

First, the surface roughness is 2.5 nm in terms of root mean square roughness.
By setting the thickness to 6.0 nm or less, it is possible to suppress the air gap loss that can sufficiently cope with the electromagnetic conversion characteristic region required for digital recording.

However, the root-mean-square roughness of 2.5 nm or more and 6.0 nm or less causes the friction coefficient to start to increase in any region of low-speed to high-speed sliding, which may affect running characteristics and still life. Adverse effects will appear.

In the present invention, as a result of many years of research on a surface shape that achieves both electromagnetic conversion characteristics and runnability, it is possible to identify a surface shape component effective for runnability by power spectrum analysis. The purpose is to control the surface shape.

The difference from the prior art will be specifically described. Roughness control in the prior art is to improve or roughen the roughness by strengthening or weakening the calendar conditions for the same coating formation layer, and the manufacturing conditions are the same and the particle size of the magnetic powder is the same. The main method was to obtain a natural and fine surface roughness by increasing or decreasing the surface roughness.

When only the roughness is controlled without being aware of the shape of the surface in this way, when power spectrum analysis is performed on the surface, it follows the law of 1 / f which is a natural basic principle with respect to the spatial wavelength. It becomes the intensity curve. When the roughness is controlled by the conventional method, the spatial wavelength curve only fluctuates according to the magnitude of the roughness value, and the intensity of a specific spatial wavelength cannot be intentionally controlled. Therefore, if the root-mean-square roughness is set to 2.5 nm or more and 6.0 nm or less, the spectrum intensity automatically decreases at any spatial wavelength.

On the other hand, in the magnetic recording medium of the present invention, it was grasped that the surface shape corresponding to the region where the spatial wavelength in the power spectrum analysis is 0.5 μm to 1.0 μm greatly contributes to the sliding property, and the surface of the recording layer is grasped. By controlling the power integrated value in this region in the TD direction of 0.3 nm ² or more, the lubrication effect by the surface shape is consciously enhanced. By controlling the surface shape in this manner, it is possible to obtain the effect of making the sliding resistance from low speed to high speed extremely small while maintaining the void loss small.

In particular, at the time of high-speed sliding, the characteristics of the conventional chemical technique drastically deteriorated when the active ingredient was abraded. You can get an unimaginable long life.

At the same time, in order to make the solid lubrication effect the basis,
Lubricants that exhibit chemical effects only play an auxiliary role, so the amount of addition can be minimized.

Lubricants having a low molecular weight and being active inhibit the curing reaction of the coating film or are adsorbed on the surface of the inorganic powder, and have also acted as a cause of lowering of the coating film strength and powder falling. However, by suppressing the addition amount of these according to the present invention, a ripple effect of improving the durability of the entire medium can also be obtained.

The root mean square roughness is adopted as the value indicating the surface roughness for the following reason. With the maximum roughness (Rz) and centerline average roughness (Ra) adopted in the conventional technique, a special shape on the surface is calculated by handling it with the same weight as other average shapes. In recent years, the surface properties of which have become extremely good, and they have become unsuitable as criteria for judging materials and parts in the field of magnetic recording.

In discussing the delicate control of the surface shape as in the present invention, the root mean square roughness for statistically calculating the average value based on the Gaussian distribution is more consistent with the experimental result. It was adopted.

The reason why the TD (width) direction is used to control the shape of the specific spatial wavelength in the power spectrum analysis is as follows.

Particularly in a medium such as a VTR tape in which magnetic particles are aligned in a longitudinal direction by magnetic field orientation, MD (long)
The minimum unit for forming a shape differs between the direction and the TD direction. Specifically, in the MD direction, the major axis length of the acicular magnetic particles is the minimum unit, and is greatly affected by the particle size and axial ratio of the magnetic powder used. On the other hand, the TD direction is
The short axis of the magnetic powder is the minimum unit, and even if the particle size is slightly different, it is sufficiently small compared to the spatial wavelength region that requires control, so it is not affected. For the above reasons, the shape is controlled in the TD direction.

As a second invention, the following effect is brought about by controlling the exclusive area ratio of the abrasive particles on the surface of the recording layer to 3% or more and 10% or less.

Generally, a material having a high hardness is used as the abrasive particles, but when the abrasive particles are distributed so that the occupied area ratio becomes 5% or more when viewed from directly above the surface layer of the medium. , The abrasive particles effectively receive the load of the head, and the effect of point contact produces a friction reducing effect.

On the other hand, since the abrasive present in the pole surface layer does not magnetically contribute, it acts to reduce the strength of the magnetic signal during short wavelength recording, which is considered to have a shallow recording depth. However, by suppressing the occupied area to 10% or less, it is possible to suppress the output loss much smaller than the output loss caused by factors such as surface roughness and void loss at the contact interface due to seizure and uneven wear of the head.

Further, against the phenomenon that the upper layer peels off at the interface with the lower layer, which is a problem in the two-layer medium, the load on the magnetic powder itself is reduced because the plural abrasives support the head load, There is also an effect that damage to the coating film is less likely to occur.

This occupied area ratio is a very large value as compared with the conventional commercially available medium, and there is a concern about head wear. However, the alloy magnetic powder is a material having a higher abrasivity than the iron oxide magnetic powder due to its unique anti-oxidation treatment, and rather, the occupation area ratio of the abrasive is controlled to 3% or more and 10% or less to effectively receive the head load. By doing so, the amount of polishing by the alloy magnetic powder is reduced, and head wear equal to or less than that of the conventional medium can be suppressed.

The reason for controlling the amount of the polishing agent by the occupied area ratio when viewed from the surface is as follows.

In the conventional coating type magnetic recording medium having a single-layer structure, various applications have been filed as important factors for controlling various characteristics relating to the interface with the head, such as the amount, type and particle size of the abrasive. . Especially important for ensuring practical characteristics such as control of head wear amount, proposal to reduce seizure in low humidity environment peculiar to metal-based head, proposal aiming at running improvement effect by point contact similar to the present invention Many are seen.

However, in these prior art examples, the content of certain specific particles is added to the magnetic powder, and how the added abrasive is distributed in the final magnetic recording medium. I didn't see anything trying to control it.

When the actual coating type magnetic recording medium is reexamined, it is known that the abrasive particles are widely distributed in the thickness direction particularly in the conventional single layer medium and the like. Specifically, depending on the manufacturing method (addition method, coating method, drying conditions, calendar conditions, etc.), it may be raised on the surface layer of the coating film by migrating or may be distributed by sinking under the coating film. It depends a lot.

As a result, it is effective only in the unique technique possessed by the applicant, and other persons can apply these prior examples with the technique possessed by others, or the one effective in the single layer medium In most cases, even if an attempt was made to apply it to the recording layer of a thin two-layer medium, the same effect could not be obtained.

In the present invention, among the various effects expected from the addition of the polishing agent, regarding the contribution to the interface with the head, which has been previously raised, the result of accumulating the distribution state of the polishing agent and the practical characteristics is accumulated. It was concluded that controlling the area occupancy of the polar surface layer works effectively.

To specify the area of the abrasive on the extreme surface layer,
Non-deposition observation with a scanning electron microscope is the easiest and most effective. Depending on the accelerating voltage at the time of observation, the degree to which the beam reaches the depth direction changes.
Almost the same result is obtained in the range of keV to 25 keV. Also, depending on the observation field of view, the influence of the abrasive distribution on the coated surface cannot be ignored, but at an observation magnification of 5000-
If the range is 20,000 times, no large error appears. 50 on the contrary
On the low magnification side of 00 times or less, the separation of the abrasive particles becomes difficult and the error increases. As the observation conditions, the acceleration voltage is preferably 10 to 15 keV and the observation magnification is 10,000 to
It is 20,000 times.

To determine the actual area, it is fast and accurate to take a picture and analyze it. As a concrete method of separating the abrasive, trace the abrasive visually to determine the area, or capture the trace result, photograph, negative film as image data with an image scanner, and photoretouch using a commercially available personal computer. A method of analysis using software or the like can be mentioned. Alternatively, some scanning electron microscopes can directly process SEM images as data.

Using such a method, the ratio of the total area of the abrasives to the total area of the observation visual field is defined as the occupied area ratio.

In order to obtain the above two inventions more effectively, it is necessary to give sufficient consideration to the particle size of the abrasive. In particular, in the case of a thin recording layer, there is no room for abrasive particles to be widely distributed in the thickness direction, as in a medium having a single thick recording layer. Therefore, it is very important to select an abrasive with an appropriate particle size according to the thickness of the recording layer, and by doing so the point contact effect with the head can be achieved without roughening the surface more than necessary and increasing void loss. You can get it.

In general, when abrasive particles are mixed in a magnetic paint, it has been confirmed that the abrasive particles are located between the structures due to magnetic agglomeration of magnetic powder, particularly in a tape-shaped medium for magnetic field orientation. No matter how the dispersion state of the abrasive particles is increased in the paint, it is highly possible that the abrasive particles exist as an aggregate of a few particles due to the behavior of the magnetic powder.
Such aggregation behavior occurs regardless of the thickness of the coating film formed by the magnetic coating material. Therefore, an undercoat layer made of non-magnetic paint is provided between the non-magnetic support and at least 1.0 μm in thickness.
In the case of a thin recording layer having a thickness less than 40 nm, at least the recording layer thickness of 40
If the average particle size is at least%, it becomes possible to produce the point contact effect by the large-sized particles due to the dispersion of the particle size distribution and the aggregates associated with the orientation.

On the contrary, in the case of an abrasive having an average particle diameter of less than 40%, there is little possibility that the abrasive will effectively reach the head on the surface of the recording layer even if various behaviors are added, and an effect for improving practical characteristics is obtained. I can't.

If a particle having an average particle diameter exceeding 100% of the recording layer thickness is used, a very large protrusion will be produced in consideration of the variation in particle size distribution and the probability of aggregate formation, and the point contact effect can be obtained. However, the void loss is significantly increased.

In order to effectively secure the electromagnetic conversion characteristics and improve the practical characteristics, the average particle diameter of 40% or more and 100% or less works most effectively, as can be understood from the above-mentioned principle of operation.

[0053]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows an embodiment of the present invention.
Shown in In the figure, 1 is an undercoat layer containing non-magnetic powder and a binder resin as main components, and 2 is a recording layer containing alloy magnetic powder and a binder resin as main components. The alloy magnetic powder used in the magnetic paint has a metal content of 75% by weight or more and 80% by weight or more of at least one ferromagnetic metal (for example, Fe, Co, Ni, Fe-Co, Fe-N).
i), and 20% by weight or less of the metal content, preferably 0.5 to 5% by weight is Al, Si, S, Sc, T.
i, V, Cr, Mn, Cu, Zn, Y, Mo, Rh, P
d, Ag, Sn, Sb, Te, Ba, Ta, W, Re,
Au, Hy, Pb, Bi, La, Ce, Pr, Nd,
It has a composition such as B or P, and may contain a small amount of water, hydroxide, or oxide. The shape is not particularly limited, but the acicular ratio (major axis length / minor axis length) is in the range of 2 to 12,
It is particularly preferably in the range of 3-9.

As the binder resin used in the magnetic paint, a conventionally known thermoplastic resin, thermosetting resin or reactive resin, or a mixture thereof is used. As a specific example,
Contains vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl ether, vinyl acetal, etc. as constituent units. There are polymers or copolymers, polyurethane resins, and various rubber resins. Further, as the thermosetting resin or the reactive resin, phenol resin, epoxy resin, phenoxy resin, polyurethane curable resin, urea resin, melanin resin, alkyd resin, acrylic reactive resin, formaldehyde resin, silicone resin, epoxy polyamide resin, Examples thereof include a mixture of polyester resin and isocyanate prepolymer, a mixture of polyester polyol and polyisocyanate, and a mixture of polyurethane and polyisocyanate. These may be used alone or in combination of two or more. It is preferable to introduce a polar group as exemplified below into the molecule of the binder resin. For example, -COOM, -SOM, -SOM, -PO
M, -OPOM, amino group, ammonium base, -O
H, --SH, epoxy group (here, M represents a hydrogen atom, an alkali metal or ammonium, and when there are plural Ms in one group, they may be the same or different from each other).
Etc. In addition, it is preferable to use a resin containing vinyl chloride as a constituent unit in combination with a polyurethane resin. In this case, as the resin containing vinyl chloride as a constitutional unit, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, etc. are used. It In the case of a copolymer of vinyl chloride and another monomer, vinyl chloride is contained in the polymer in an amount of 10 to 90%, preferably 50 to 90%. As the polyurethane resin, polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, polycaprolactone polyurethane, etc. are used.

The solvent used for the magnetic paint may be appropriately selected according to the kind of the binder resin, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone,
Ketones such as cyclohexanone; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol monoethyl ether acetate; glycol ethers such as ether, glycol dimethyl ether, glycol monoethyl ether, dioxane; benzene, toluene,
Examples include tars (aromatic hydrocarbons) such as xylene; chlorinated hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, and dichlorobenzene. Used as a mixture of two or more species.

The dispersion effect, lubrication effect, polishing effect, antistatic effect, rust preventive effect, plasticizing effect and friction coefficient reducing effect which have been conventionally added to magnetic paints for coating type magnetic recording media as raw materials for magnetic paints. Also, various substances known per se that impart the effect of improving the film strength can be added. In particular, in order to improve the dispersibility of the magnetic powder, it is preferable to add, for example, a surfactant such as lecithin or a purified substance thereof, a fatty acid, a phosphate ester, a silane coupling agent, or a silicone oil. Further, it is preferable to add carbon black in order to impart an antistatic effect, a friction coefficient reducing effect, and a film strength improving effect. Specific examples of carbon black include thermal black, furnace black, lamp black, channel black and the like. The carbon black may be surface-treated with a dispersant or the like, grafted with a resin, or partially surface-graphitized.

As the solvent and binder resin used for the non-magnetic paint, those used for the above-mentioned magnetic paint can be used as they are. Binder resins used in magnetic paints and non-magnetic paints both have a weight average molecular weight of 10,000 to 10
It is preferably in the range of 0000, and preferably 20,000 to 50
The range of 000 is particularly preferable. Further, the difference in solubility parameter between the binder resin and the organic solvent is preferably 5 or less. This is to dissolve the resin in the solvent without phase separation in the paint.

Examples of the non-magnetic filler used in the non-magnetic coating material include non-magnetic inorganic fine powders of metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Mention may be made of carbon black. Specific examples of the non-magnetic inorganic fine powder include titanium oxide, cerium oxide, α-alumina, β-alumina, γ-alumina, α-iron oxide, goethite, corundum, silicon nitride,
Titanium carbide, magnesium oxide, barium carbonate,
Examples thereof include strontium carbonate, barium sulfate, silicon carbide and titanium carbonate. The shape of the non-magnetic inorganic fine powder may be needle-like, spherical, or plate-like,
Particle size (long axis length in the case of needles) is 0.03 to 0.30μ
It is preferably in the range of m, particularly preferably in the range of 0.05 to 0.20 m. Specific examples of carbon black are the same as above.

The compounding ratio of various materials constituting the magnetic paint and the non-magnetic paint is determined as follows. In the magnetic paint, generally, when the alloy magnetic powder is 100 parts by weight, the compounding ratio of the binder resin is appropriately determined within the range of 10 to 30 parts by weight. When the total amount of the non-magnetic filler generally blended in the non-magnetic paint is 100 parts by weight, the blending ratio of the binder resin is appropriately determined within the range of 15 to 35 parts by weight. Other additives, dispersants, lubricants, abrasives, anti-wear agents, etc. are appropriately determined in accordance with the dispersibility of each paint and the characteristics of the coating film. The blending amount of the solvent is adjusted according to the manufacturing process of the non-magnetic paint and the magnetic paint, but at the time of final formulation, the solid content of each paint is approximately 20 to 40 wt% Is preferable for proper coating.

The magnetic coating material and the non-magnetic coating material are produced by first subjecting the coating material to a stirring treatment and then a kneading treatment. A known mixer such as a planetary mixer, a double planetary mixer, a chemical mixer, a Hensyl mixer, or a twin-screw mixer is used for the stirring process. For the kneading treatment, a kneader known per se such as a planetary mixer, a double planetary mixer, a chemical mixer, an open kneader, a pressure kneader, a continuous kneader, a twin-screw kneading extruder, and a three-roll mill is used. For diluting the kneaded product, a known device such as a planetary mixer, a double planetary mixer, a stone mill and a dissolver is used. For the dispersion treatment of the paint prepared in this way, a known apparatus such as a horizontal sand mill, a pin mill, an attritor, an ultra disc mill or the like is used. For more information TCPA
"Paint Flow and Pigment Dispersion" by TTON
For details on the coating method and optimum composition, see

The materials for the non-magnetic coating material and the non-magnetic support to which these magnetic coating materials are applied include polyesters such as polypropylene such as polyethylene terephthalate and polyethylene-2,6-naphthalate; aromatic polyamides such as aramid resin; polyethylene. , Polyolefins such as polypropylene; cellulose triacetate, cellulose diacetate, cellulose acetate butylate,
Cellulose derivatives such as cellulose acetate propionate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, polyamide-imide, etc., as well as aluminum, copper, tin, zinc, or these depending on the application. Including non-magnetic metals such as non-magnetic alloys; ceramics such as glass, pottery and porcelain; paper, baryta or polyethylene, polypropylene, ethylene pentene copolymers, etc. having 2 to 10 carbon atoms
Papers such as paper coated or laminated with the α-polyolefins can also be used. These non-magnetic supports may be transparent or opaque depending on the purpose of use. Further, the form of the non-magnetic support may be any of film, tape, sheet, disk, card, drum, etc., and various materials may be selected as necessary according to the form. The thickness of these non-magnetic supports is about 1 to 50 μm, preferably 1 to 30 μm in the case of a film, tape or sheet. In the case of a disc or a card, the length is about 0.25 to 10 mm, and in the case of a drum, the shape is cylindrical, and its type is determined according to the recorder to be used.

For the recording medium, first, a coating film of a non-magnetic paint is formed on a support, and while the coating film is in a wet state, a coating film of a magnetic paint is continuously formed, the magnetic field is oriented, and the coating film is dried. Manufactured by sequentially performing calendaring. A known coating method can be used for forming the coating film. For example,
Examples thereof include air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, die coat, transfer roll coat, gravure coat, kiss coat and spin coat. For a detailed explanation of these, see "Coating Engineering", pages 253 to 277, published by Asakura Shoten (Showa 46.0).
3.20 issue) etc.

Further, the calendering process is carried out by a super calendering method in which two rolls of a combination of metal roll and cotton roll or synthetic resin roll, metal roll and metal roll, synthetic resin roll and synthetic resin roll are passed. Is preferred. As the resin of the synthetic resin roll, heat resistant resin such as epoxy, polyimide, nylon is used. The condition of the super calendar depends on the size of the equipment and the combination of rolls, but it is about 350
70 to 100 ° C. at pressure between rolls of up to 600 kg / cm
It is preferable to carry out the treatment at a temperature of 50 to 150 m / min. If the temperature and pressure exceed these upper limits, the magnetic layer, the nonmagnetic layer, and the nonmagnetic support are adversely affected.
If the processing speed is lower than the lower limit, the processing takes too long, and if it is higher than the upper limit, it becomes difficult to obtain the surface smoothing effect.

In the present invention, the surface roughness and the area occupied by the polishing agent are analyzed in the following manner with respect to the coating type two-layer medium having the recording layer extremely thin and uniform and smooth thus produced.

The square root roughness of the recording medium surface was measured with a three-dimensional non-contact surface roughness meter. Specifically, it was used by using TOPO-3D manufactured by WYKO with a 200 × objective lens. The minimum lateral resolution at this time is 0.2
μm. The three-dimensional surface roughness analyzer is used here because the information on one shape on the surface can be obtained spatially, and the subtle unevenness of the surface can be grasped more accurately than the result of the two-dimensional analysis. Is. Due to the measurement principle, it is different from the value obtained by two-dimensional analysis.

For the integrated power value in the region of spatial wavelength 0.5 μm to 1.0 μm, software for TOPO-3D power spectrum analysis was used.

In the analysis, the Fourier transform of the measurement data in the TD direction is performed without applying the Hanning window.
Further, of the 256 two-dimensional data in the measurement field of view, the analysis data after Fourier transform is averaged for every four data of four, and the S / N is improved for the power intensity of the spatial wavelength corresponding to the characteristic shape. Are treated like. Based on the analyzed and averaged data, the power integrated value in the region of the spatial wavelength of 0.5 μm to 1.0 μm can be obtained.

FIG. 1 shows the actual data of the power spectrum analyzed using TOPO-3D manufactured by WYKO. The horizontal axis in FIG. 1 represents the spatial frequency, which corresponds to the number of waves per mm when the roughness component is regarded as a wave. 0.5 at spatial wavelength
Spatial frequency 2000 (1 / mm) corresponds to μm,
A spatial frequency of 1000 corresponds to a spatial wavelength of 1.0 μm.
(1 / mm). The vertical axis in FIG. 1 represents the intensity of each frequency component, and is represented by a relative index value with reference to the amplitude of 1 nm, and the dimension is (nm ² ). FIG. 1 shows (Example 1-a) and (Example 1-b).
And the power spectrum curves of (Comparative Example 1) are shown, each of which is cut by an auxiliary line drawn vertically from points 1000 (1 / mm) and 2000 (1 / mm) on the horizontal axis. The area of each trapezoidal figure corresponds to the power integrated value of each region having a spatial wavelength of 0.5 μm to 1.0 μm. Those having a high power integrated value in this region have a large area of this trapezoidal figure and have excellent running characteristics. On the contrary, when the power integrated value is low, the intercept between the power spectrum curve and the horizontal axis gradually becomes 1
It falls within the range of 000 (1 / mm) to 2000 (1 / mm), and changes from a trapezoidal shape to a triangular shape on the graph. In this case, the roughness component that effectively contributes to the running property becomes too small, which leads to an increase in the friction coefficient and a marked decrease in the still life.

As a non-contact type surface roughness meter having the same ability as this measuring instrument, a phase difference interference method roughness meter made by WYKO, ZYGO or Tokyo Seimitsu, or Kosaka Laboratory The optical stylus type roughness meter can be used. Each measuring device is designed to calculate data with a personal computer, and can perform the same analysis as the power spectrum analysis of TOPO-3D.

Not limited to the equipment introduced above, any other equipment may be used as long as it has the same measuring ability and analysis method.

Further, in the analysis of the area occupied by the abrasive in the present invention, CL-130 made of a filament of a lanthanoid hexaborite single crystal manufactured by Topcon Co., Ltd. was used.
The analysis was performed based on the SEM photograph taken using the. As described above, it is necessary to set a relatively low acceleration voltage in order to perform non-deposition observation without damaging the surface of the recording medium. At that time, in order to obtain image quality and resolution required for analysis, it is preferable to use a filament having a high electron density, and it is preferable to use a scanning electron microscope having a lanthanoid hexabolite or field emission type electron gun.

The SEM photograph thus obtained was loaded into a personal computer as gray scale image information of 256 gradations using an image scanner and processed as follows with commercially available photo retouching software.

FIG. 2 shows an image processed according to an example of the present invention. 2a is a printer output of an actual SEM photograph captured as 256-gradation image data, and b) is a polishing agent (for example, white) with the critical point adjusted for this image. After processing to divide into two gradations of a part (for example, black),
The black / white is reversed so that the abrasive particles become black dots. Here, the portion at the bottom of the SEM photograph image containing the character information is trimmed. As can be seen from FIG. 2-b), at the time of adjusting the critical point, the parts other than the abrasive remain in the same color as the abrasive, but
With respect to these, the processing is added so as to obtain a highly accurate analysis image by painting in white with photo retouching software while referring to the SEM photograph image. By reading the ratio of the black portion from the histogram distribution of the image information for the black-and-white image processed in this way, it is possible to accurately analyze the exclusive area of the abrasive particles in the entire visual field of the SEM image.

[0074]

EXAMPLES Examples of the present invention will be described below. The examples and comparative examples were prepared as coating type metal tapes for DVC-Pro, and their characteristics were compared.

The material compositions of these examples and comparative examples were prepared based on (Table 1) and (Table 2) of the magnetic coating material for the recording layer and the non-magnetic coating material for the undercoat layer, respectively.

[0076]

[Table 1]

[0077]

[Table 2]

In forming a coating material, these materials were subjected to respective treatments of mixing, kneading, dispersing and blending as follows.

First, regarding the magnetic coating material for the recording layer, alloy magnetic powder and carbon black (Tokai Carbon # 3800) were used.
And a mixed solvent of methyl ethyl ketone: toluene: cyclohexanone = 3: 3: 1 were mixed and stirred for about 4 hours while being added to a mixer (Chemical mixer manufactured by Aikosha Seisakusho). This is for the purpose of sufficiently performing the wetting operation for replacing the gas phase on the powder surface with the liquid phase.

Then, vinyl chloride resin (manufactured by Zeon Corporation)
MR-110), a polyurethane resin (UR-8197, manufactured by Toyobo), an appropriate amount of a mixed solvent and an abrasive were added to the mixer and further stirred for 1 hour, and these materials were mixed so as to be in a state suitable for kneading treatment. The amount of binder should be 13
It was decided to the department. Further, the ratio of the vinyl chloride resin and the polyurethane resin was set to 1: 1 which is a mixing ratio used in general magnetic recording media. At the time of this stirring and blending, various α-alumina particles having a particle size ranging from 0.12 μm to 0.30 μm were examined as abrasive particles, and the addition amount was changed from 6 parts by weight to 15 parts by weight for each magnetic material. Paints were made and the subsequent processing continued for each.

The materials thus prepared were kneaded by a kneading machine (Inoue Seisakusho 10ι pressure kneader) for about 2 hours.

This magnetic kneaded product was diluted with a double planetary mixer (Inoue Seisakusho Co., Ltd. 50ιPLM) to a solid content ratio such that the viscosity was 50 to 70 poises, and then it was used in a horizontal sand mill (Sinmaru Enterprise Co., Ltd. 15ι Dynomill). Dispersion processing was performed. In the dispersion treatment, this composition is performed up to the saturation point of the sand mill dispersion. The saturation point of dispersion was measured until the change disappeared by measuring the gloss of the magnetic coating film prepared for each pass with a gloss meter (Tokyo Seiki).

The magnetic coating material thus dispersed was filtered and purified with a deposition filter, and then a predetermined amount of a lubricant, a curing agent and a diluent solvent for viscosity adjustment were added to complete the preparation.

The non-magnetic coating material for the undercoat layer was also produced through the same process. Specifically, the needle-shaped non-magnetic iron oxide powder and carbon were kneaded and diluted in the same manner as the magnetic paint, and then the dispersion treatment was carried out by a horizontal sand mill to carry out filtration, purification and preparation.

In this way, 2 which was sufficiently dispersed
The two paints were first formed on the base film by the non-magnetic paint, and the magnetic paint was applied before the drying of the paint film progressed. Specifically, a non-magnetic coating material was applied and formed by a gravure coater head, and this coating film was smoothed by a smoother. Immediately after that, a thin nozzle coating material was sequentially formed by a magnetic coating material by a die nozzle coater head. When sequentially forming two layers in this way, due consideration should be given to the viscosity characteristics and solid content of the non-magnetic paint and magnetic paint, the amount of magnetic paint supplied, the coating speed, etc. Was applied. For all prototype media, the coating conditions were examined so that the recording layer thickness on the final tape was 0.3 μm and the undercoat layer thickness was 1.7 μm.
It was formed on a thick ultra-smooth PET film.

After sequentially forming two layers by coating as described above,
A calendar process and a hardening process were applied. In the calendar processing, the processing temperature for each sample is 60-
Samples having different finish roughness were prepared while changing the temperature up to 100 ° C. in steps of 10 ° C. After that, apply a back coat layer on the back surface and cut it to a quarter inch width.
It was wound into a cassette as a tape for C-Pro.

With respect to the prototype medium manufactured in this manner, the root mean square roughness (Rrms: nm) and the power integrated value in a specific spatial wavelength range (Σpower: nm ² ), and the polishing agent exclusive area ratio (Sab.:%) were inspected, and prototype media corresponding to each invention were selected.

(Example 1) (Example 1-a) Prototype having a square root mean square roughness of 4.0 nm and a power integrated value of 0.61 nm ^{2 in} a region of a spatial wavelength of 0.5 μm to 1.0 μm. Let the medium be (Example 1-a).

(Example 1-b) The root mean square roughness was 4.0 nm, which was the same as in Example 1-a, and the spatial wavelength was 0.5.
Power integrated value in the range of μm to 1.0 μm is 1.16 nm
² is designated as (Example 1-b).

(Example 1-c) The square root roughness was 6.0.
(Example 1-c) is a prototype medium having a power integrated value of 0.30 nm ^{2 in} the region having a spatial wavelength of 0.5 μm to 1.0 μm.

(Example 1-d) The square root roughness is 2.5.
(Example 1-d) is a prototype medium having a power integrated value of 0.31 nm ^{2 in} the region of 0.5 nm to 1.0 μm in spatial wavelength of 0.5 μm to 1.0 μm.

(Example 1-e) The square root roughness is 2.5.
(Example 1-e) is a prototype medium having a power integrated value of 0.63 nm ^{2 in} the region of 0.5 nm to 1.0 μm in spatial wavelength of 0.5 μm to 1.0 μm.

(Embodiment 2) The root mean square roughness is 4.0 nm.
From the finished prototype media, the following a to d were selected as those in which the exclusive area ratio of the abrasive exceeds 3%.

(Example 2-a) The area occupied by the abrasive is 3.1.
What was% was set as (Example 2-a).

(Example 2-b) The area occupied by the abrasive is 5.2.
What was% was set as (Example 2-b).

(Example 2-c) Area occupied by abrasive is 7.4.
What was% was set as (Example 2-c).

(Example 2-d) Abrasive exclusive area is 9.8.
What was% was set as (Example 2-d).

(Example 2-e) The square root roughness is 2.5.
Among the trial media finished to nm, the one having an abrasives exclusive area ratio of 3.4% was set as (Example 2-e).

(Comparative Example 1) 6 parts by weight, which is a commonly used addition amount as a magnetic paint, of 0.17 μm in diameter, which is widely used as a general abrasive, was used as a standard calendar condition. The prototype medium manufactured at 80 ° C. and 400 kg / cm was used as (Comparative Example 1). The root mean square roughness of this tape is 4.0 nm, and the spatial wavelength is 0.5 μm.
The power integrated value in the 1.0 μm region was 0.28 nm ² , and the abrasive occupancy area was 1.2%. (Comparative Example 2) 0.17 μm, which is smaller than that of (Comparative Example 1), among those widely used as general abrasives
(Comparative Example 2) was used as a prototype medium prepared by adding 400 parts by weight of the above and operating under standard calendar conditions at 80 ° C. and 400 kg / cm. The square root roughness of this tape is 2.5 nm, and the spatial wavelength is 0.5 μm to 1.0 μm.
The integrated power value in the region was 0.16 nm ² , and the area occupied by the abrasive was 0.8%.

Representative analysis results of these examples and comparative examples are shown in FIGS. FIG. 1 shows W for two examples (Example 1) having different power integrated values and (Comparative Example 1).
The result analyzed by TOPO-3D of YKO is shown.
In addition, FIG. 2 is a diagram showing (Example 2-a) and FIG. 3 (Comparative Example 2) showing SEM images and image processing results in the process of analyzing the polishing agent exclusive area ratio.

The following characteristics were compared for the prototype media of Examples 1 and 2 and Comparative Examples 1 and 2, which were selected based on the analysis results.

First, the friction coefficient related to running characteristics was measured by the drawing method. This method is φ3
Approximately 30c for mm SUS303 pin (JIS standard)
Apply m-length tape, move the other end up and down with a stroke of 10 cm with a load of 20 g applied to one corner,
It is calculated from the running resistance generated by the contact of the focus at this time. The output of the running resistance is obtained from a strain gauge attached to a movable support that moves the tape up and down. The coefficient of friction (μk50) when this vertical movement is repeated 50 times and the coefficient of friction (μk50) when it is repeated 200 times
200) was compared.

As a test on a real deck, DVC-P
Using a stationary deck for ro (AJ-D750 manufactured by Matsushita Electric Industrial Co., Ltd.), recording wavelength 0.5 μm, relative speed 1
The output at 0.2 m / sec and the still life under the environment were measured. Regarding the output, after recording a single rectangular wave by the internal oscillator, the output of the reproducing head was drawn from the test pin on the circuit board and measured with a spectroanalyzer.
Here, the result is shown as a relative output in which (Comparative Example 1) is Ref.

The still life was measured using a dedicated test deck in which the control system ROM was rewritten for the continuous life test. Specifically, a signal was recorded on the prototype medium in each environment of low temperature and low humidity (3 ° C 5%), normal temperature and low humidity (25 ° C 20%), and high temperature and low humidity (40 ° C 5%), and continuously reproduced in still mode. Then, the elapsed time (Hour) required for the reproduction output to decrease to −6 dB was measured.

The results of Examples and Comparative Examples in the above test items are shown in (Table 3).

As a reference for Example 1 as well, the polishing agent exclusive area ratio is shown, and similarly for Example 2, the square root roughness and power integrated value are shown.

[0107]

[Table 3]

As is clear from this result, the trial media of Examples 1 and 2 have the following effects when compared with Comparative Examples 1 and 2 having the same square root roughness. To be

First, regarding the coefficient of friction in the repeated running test by drawing, Examples 1 and 2 have the same level of 2
Μk50 and μk more than Comparative Examples 1 and 2 having square root roughness
Both have achieved a low level of 200. Especially in Comparative Example 1,
In No. 2, μk200 is remarkably increased as compared with μk50, whereas in Examples 1 and 2, such an increase in friction coefficient is not observed. This is because the control of the surface shape and the control of the load on the medium surface by the abrasive particles according to the present invention are effective.

Looking at the practical characteristics of the actual deck, it can be seen that the still lives of Examples 1 and 2 according to the present invention are significantly longer than those of Comparative Examples 1 and 2 according to the prior art. With respect to the still life under a room temperature and low humidity environment, Comparative Examples 1 and 2 are 1 hour to several hours, while Example is excellent in 40 to 80 hours and the square root roughness (Example 2-e). ) Also shows a long life of 28 hours. In a high temperature low humidity environment and a low temperature low humidity environment, which are more severe environments for the still life, Comparative Examples 1 and 2 do not have 1 hour, whereas the Examples show a life of 2 hours or more even if it is short. ing.

As described above, in the examples, although the running characteristics and the still life are greatly improved, the electromagnetic conversion characteristics are hardly deteriorated.

For example, when the reproduction output at the recording wavelength of 0.5 μm and the root mean square roughness of 4 nm are compared, 0 dB of the comparative example 1 is +0 for the 4 nm prototype media of the first and second embodiments. It is within the range of 0.3 to -0.3 dB. Looking at the breakdown, the reproduction output was increased when the occupation area ratio of the abrasive particles was moderately earned (Example 2a) and (Example 2b) as compared with the case where the surface shape was strongly controlled. You can see that This indicates that the abrasive particles appear more on the surface to enhance the load control effect and improve the head cleaning property, and as a result, the recording / reproducing is performed in a better state than (Comparative Example 2). ing. Also, in the other examples in which the output was measured to be lower than that of (Comparative example 2), the extent of the decrease was not fatal and was suppressed to a negligible level when considering the effect of improving practical / reliability characteristics. There is. The same comparison result is obtained for the square root surface roughness of 2.5 nm.

Here, in (Example 1), only (1-d) had an abrasive-proprietary area ratio below 3%, and other prototype media according to (Example 1) had this (Example 1-d). The still life is slightly longer than that. In other (Example 1), both the control of the surface specific spatial wavelength component according to the present invention and the load control by the abrasive particles act effectively, so that it is more synergistic than the effect brought by each invention. It shows that it is increasing. The same can be seen from the five prototype media of (Example 2).

In the selection of these Examples 1 and 2, the two invention elements in the present invention were not selected by consciously associating with each other, but the results were obtained by focusing on only one of them, and at least By implementing one of the invention elements, it is possible to realize better running performance and still life than those of the prior art. Further, if the two elements of the present invention can be realized at the same time, more excellent characteristics can be obtained by the synergistic effect as shown in the above embodiment.

Although not mentioned here as a comparative example, a trial medium was prepared under the same conditions for abrasive particles having a particle size of more than 0.3 μm. There is a problem that the stability is affected and the streak tends to occur. In addition, when the medium for which the trial manufacture was completed successfully was tested in the same manner as in the example, the root mean square roughness was remarkably poor and the reproduction output was remarkably reduced in all of the abrasives having an area ratio of more than 3%. Was there. Similarly, spatial wavelength 0.5 μm to 1.0
Even in the case where the integrated power value in the μm region exceeds 0.3 nm ² , the square root roughness does not fall within the range of 2.5 to 6.0 nm, resulting in a decrease in output. this is,
Since the particle diameter is larger than the coating thickness of the recording layer, it is easy to control the specific spatial frequency and the area ratio of the polishing agent, but the height at which the polishing agent protrudes from the recording layer surface is also large. This is because the roughness also increases. In the above embodiments, the coated metal tape for DVC-Pro has been described, but the effect of the present invention can be obtained with any standard as long as it is a device that can obtain the necessary electromagnetic conversion characteristics even with a thin recording layer. Can be confirmed. 1 if tape
1/2 inch wide D-3, D-5, W-VHS, Betacam tapes, 3/4 inch wide commercial VTR tape,
8mm tape for Hi-8, tape for audio in 3.8mm width, tape for DDS-I-III, 3.5 inch 2DD-2HD for disk, Zip driver advocated by Iomega Corporation in the United States For example, a 3.7-inch disc for use.

Further, the tape structure is not limited to the base thickness, non-magnetic layer thickness, magnetic layer thickness and back coat layer thickness shown in the examples, but the mixing ratio of each coating layer, the manufacturing method, the manufacturing conditions, etc. Is not a factor that regulates the effects of the present invention.

It is important that the present invention is composed of two layers, that is, a very thin recording layer made of an alloy magnetic powder and an undercoat layer mainly made of a non-magnetic material. Not limited.

[0118]

As is apparent from the above description,
In the magnetic recording medium according to the present invention, it is possible to leave a roughness component that effectively contributes to the sliding characteristics with the traveling system components and the head that are in contact with each other while keeping the air gap loss with the head small.

As a result, it is possible to obtain a medium having excellent running characteristics and still characteristics while having the conventional high electromagnetic conversion characteristics.

This is particularly effective when the relative velocity of the head slides at a high speed of a dozen m / sec like a digital VTR, and it can exhibit a long life in the still mode which cannot be obtained by the conventional technique.

Alternatively, it shows the effect of supporting the load applied from the head and the traveling parts by the point contact of the abrasive present in the extreme surface layer without deteriorating the magnetic characteristics so as to affect the electromagnetic conversion characteristics.

As a result, the running characteristics and the sliding resistance are improved, and the self-cleaning characteristics of the medium, which is the original purpose of adding the abrasive, is stabilized, and the signal reliability under each environment is also improved.

These inventions can be more effectively added from the head and running parts by using the abrasive particles having an average particle diameter of 40% or more and 100% or less with respect to the thickness of the thin recording layer. Supports the load. Further, in that case, only the roughness component effective for improving the running property can be imparted without causing the deterioration of the surface that causes a large void that deteriorates the electromagnetic conversion characteristics.

Furthermore, since the moderately present abrasive particle structure supports much of the head load, the load applied to other parts is reduced, and the phenomenon that the thin recording layer peels off or between the two layers is reduced. Damage caused by improper strength balance is greatly reduced.

As can be seen from the above, according to the present invention, the sliding resistance can be enhanced without impairing the electromagnetic conversion characteristics, and a highly reliable digital-compatible coating type magnetic recording medium can be supplied. .

[Brief description of drawings]

FIG. 1 shows the results of power spectrum analysis of the surface of a magnetic recording medium according to an embodiment of the present invention and a conventional magnetic recording medium using a non-contact three-dimensional surface roughness meter of the optical interference type. It is the figure shown.

FIG. 2 is a surface S of a magnetic recording medium according to an embodiment of the present invention.
An EM image and a halftone image obtained by performing image processing on the EM image and displayed on a display are output from a printer, and are photographs instead of drawings.

FIG. 3 is a surface S of a magnetic recording foreign medium that is a comparative example of the present invention.
An EM image and a halftone image obtained by performing image processing on the EM image and displayed on a display are output from a printer, and are photographs instead of drawings.

FIG. 4 is a schematic cross-sectional view of an embodiment of the present invention.

[Explanation of symbols]

 1 Undercoat layer 2 Recording layer 3 Non-magnetic support

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirofumi Ito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Kazunori Kubota, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A coating type magnetic comprising two layers of a non-magnetic support, an undercoat layer containing a non-magnetic powder and a binder resin as a main component, and a recording layer containing an alloy magnetic powder and a binder resin as a main component. A recording medium, wherein the recording layer has a root mean square roughness of 2.5 nm or more and 6.0 nm or less, and a spatial wavelength of 0.5 μm to 1.0 in the TD direction on the surface of the recording layer.
A magnetic recording medium having a power integrated value up to μm of 0.3 nm ² or more. 2. A coating type magnetic comprising two layers of a non-magnetic support, an undercoat layer containing a non-magnetic powder and a binder resin as a main component, and a recording layer containing an alloy magnetic powder and a binder resin as a main component. A recording medium, wherein the exclusive area ratio of the abrasive particles on the surface of the recording layer is 3% or more and 10% or less. 3. The magnetic recording medium according to claim 1, wherein the abrasive particles contained in the recording layer have an average particle diameter of 40% or more and 100% or less of the thickness of the recording layer.