WO2015198514A1 - 磁気記録媒体 - Google Patents
磁気記録媒体 Download PDFInfo
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- WO2015198514A1 WO2015198514A1 PCT/JP2015/002029 JP2015002029W WO2015198514A1 WO 2015198514 A1 WO2015198514 A1 WO 2015198514A1 JP 2015002029 W JP2015002029 W JP 2015002029W WO 2015198514 A1 WO2015198514 A1 WO 2015198514A1
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- magnetic
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- recording medium
- cubic
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
- G11B5/70626—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances
- G11B5/70642—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
- G11B5/70605—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material metals or alloys
- G11B5/70621—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material metals or alloys containing Co metal or alloys
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
- G11B5/70626—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances
- G11B5/70642—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides
- G11B5/70678—Ferrites
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/714—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the dimension of the magnetic particles
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/74—Record carriers characterised by the form, e.g. sheet shaped to wrap around a drum
- G11B5/78—Tape carriers
Definitions
- This technology relates to a magnetic recording medium.
- the present invention relates to a magnetic recording medium including a support and a magnetic layer containing magnetic powder.
- Magnetic recording media are widely used to store electronic data.
- magnetic tape is widely used.
- As a magnetic tape one having a configuration in which a nonmagnetic layer and a magnetic layer containing magnetic powder are laminated on a flexible support is known.
- magnetic layers in which magnetic powders such as ferromagnetic iron oxide, Co-modified ferromagnetic iron oxide, CrO 2 , and ferromagnetic alloys are dispersed in a binder are widely used. It is done. These magnetic powders are generally acicular and magnetized in the longitudinal direction.
- ultrashort wavelength recording reducing the recording wavelength to an ultrashort wavelength
- the coercive force is lowered. This is because the expression of the coercive force of the acicular particles is caused by the shape of the acicular particles. Further, if short wavelength recording is performed, the self-demagnetization becomes large and sufficient output cannot be obtained.
- hexagonal barium ferrite magnetic powder is used in recent magnetic tapes compatible with LTO6 (abbreviation of LTO: Linear Tape Open).
- LTO6 abbreviation of LTO: Linear Tape Open
- a technique using a cubic CoMn spinel ferrite magnetic powder see, for example, Patent Document 1
- a technique using ⁇ -Fe 2 O 3 magnetic powder see, for example, Patent Document 2 Etc.
- an object of the present technology is to provide a magnetic recording medium capable of recording at a short wavelength and having a high signal-noise ratio.
- the present technology A support; A magnetic layer containing magnetic powder,
- the magnetic powder includes at least one of magnetic powder made of magnetic particles containing cubic ferrite and magnetic powder made of magnetic particles containing ⁇ -phase iron oxide,
- the average particle size of the magnetic powder is 14 nm or less,
- the average aspect ratio of the magnetic powder is 0.75 or more and 1.25 or less,
- the ten-point average roughness Rz is a magnetic recording medium having a thickness of 35 nm or less.
- FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the magnetic recording medium according to the first embodiment of the present technology.
- FIG. 2A is a schematic diagram illustrating an example of the shape of a magnetic particle.
- FIG. 2B is a cross-sectional view showing an example of a cross section of the magnetic layer.
- FIG. 2C is a plan view showing an example of the surface of the magnetic layer.
- FIG. 3A is a schematic diagram illustrating an example of the shape of a magnetic particle.
- FIG. 3B is a cross-sectional view showing an example of a cross section of the magnetic layer.
- FIG. 3C is a plan view showing an example of the surface of the magnetic layer.
- 4A is a cross-sectional TEM image of the magnetic tape of Example 1.
- FIG. 4B is an enlarged view of a part of the magnetic layer of FIG. 4A.
- 5A is a cross-sectional TEM image of the magnetic tape of Comparative Example 13.
- FIG. 5B is an enlarged view of a part of the magnetic layer in FIG. 5A.
- 6A is a cross-sectional TEM image of the magnetic tape of Comparative Example 17.
- FIG. 6B is an enlarged view of a part of the magnetic layer in FIG. 6A.
- Magnetic recording media using barium ferrite magnetic powder are currently in practical use as magnetic recording media compatible with LTO6.
- the magnetic powder of next-generation magnetic recording media is barium ferrite magnetic powder. It is considered.
- the barium ferrite magnetic powder has the following problems.
- barium ferrite particles have a hexagonal plate shape (a hexagonal column shape with a low height), when barium ferrite particles are made ultrafine, hexagons of adjacent barium ferrite particles There is a possibility that the shape surfaces are in close contact with each other and the magnetic powder is aggregated. That is, even if the barium ferrite particles are made ultrafine, the dispersion of individual barium ferrite particles may not proceed.
- the barium ferrite particles are subjected to a vertical alignment treatment by a vertical magnetic field, the surface of the nonmagnetic support and the hexagonal surface of the barium ferrite particles are naturally parallel.
- the easy magnetization axis direction of the barium ferrite particles is a direction perpendicular to the hexagonal surface, and the hexagonal surface is arranged on the medium surface.
- the contact area of the barium ferrite particles in the thickness direction of the medium increases, the possibility that the particles aggregate will increase. Therefore, in order to improve the dispersibility of magnetic powder composed of ultrafine particles and realize high-density recording, which is an advantage of making fine particles, the contact area between adjacent supermagnetic particles is reduced to suppress aggregation as much as possible. It seems to be effective.
- Unit lattice size The crystal structure of barium ferrite particles is a magnetoplumbite type, and the unit cell has a relatively large C-axis of 2.3 nm. Although barium ferrite is currently in practical use, cubic iron oxide with the smallest unit cell size is considered suitable for future ultrafine particle formation.
- the short wavelength magnetic recording is performed from the three viewpoints of (1) the contact area between adjacent particles, (2) the exposed area of the particle on the medium surface, and (3) the unit cell size.
- the following are used as the magnetic powder. That is, the unit crystallite has a crystal structure such as a small cubic crystal, has a cubic shape with a small aspect ratio, a spherical shape, or a shape close to them, and the magnetic particle exposed on the recording surface of the magnetic recording medium has a small area. Use powder.
- At least one of cubic ferrite magnetic powder having a cubic shape or a substantially cubic shape and ⁇ -Fe 2 O 3 magnetic powder ( ⁇ -phase iron oxide magnetic powder) having a spherical shape or a substantially spherical shape is used.
- the particle size and aspect ratio of cubic or nearly cubic magnetic particles are referred to as plate diameter and plate ratio, respectively, and the particle size and aspect ratio of spherical or nearly spherical magnetic particles are referred to as particle size and spherical shape, respectively.
- ratio usually called ratio.
- the particle size and aspect ratio of hexagonal plate-like or almost hexagonal plate-like magnetic particles are referred to as plate diameter and plate-like ratio.
- the particle size and aspect ratio of needle-like or almost needle-like magnetic particles are referred to as major axis diameter and needle-like ratio. There is.
- the magnetic recording medium according to the first embodiment of the present technology is a so-called perpendicular magnetic recording medium, and is provided on a nonmagnetic support 1 and one main surface of the nonmagnetic support 1. And a magnetic layer 3 provided on the underlayer 2.
- the magnetic recording medium may further include a backcoat layer 4 provided on the other main surface of the nonmagnetic support 1 as necessary. Further, a protective layer and a lubricant layer may be further provided on the magnetic layer 3.
- the nonmagnetic support 1 is, for example, a long film having flexibility.
- the material of the nonmagnetic support 1 include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose butyrate, polyvinyl chloride, and polyvinylidene chloride. Vinyl resins, polycarbonates, polyimides, polyamideimides and other plastics, light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass. Furthermore, in order to increase the mechanical strength, a thin film containing an oxide of Al or Cu formed on at least one of the main surfaces of the nonmagnetic support 1 containing a vinyl resin may be used. .
- the magnetic layer 3 is a perpendicular recording layer capable of short wavelength recording or ultrashort wave super recording.
- the magnetic layer 3 has magnetic anisotropy in the thickness direction of the magnetic layer 3. That is, the easy axis of magnetization of the magnetic layer 3 is oriented in the thickness direction of the magnetic layer 3.
- the average thickness of the magnetic layer 3 is preferably 30 nm to 100 nm, more preferably 50 nm to 70 nm.
- the coercive force Hc of the magnetic layer 3 is preferably 230 kA / m or more and 400 kA / m or less. If the coercive force Hc is less than 230 kA / m, the output in a short wavelength region necessary for a high-density magnetic recording medium may be reduced, and a good S / N ratio may not be obtained. On the other hand, if the coercive force Hc exceeds 400 kA / m, saturation recording becomes difficult during signal writing, and as a result, a good S / N ratio may not be obtained.
- the sum “d + a” of the spacing d and the transition width a is preferably 30 nm or less. Spacing d strongly depends on the surface roughness of the magnetic recording medium, and is the distance between the magnetic head and the magnetic recording medium.
- the transition width a is the width of the region where the magnetization is reversed, and also depends on the spacing d, and a steep magnetization transition is formed as the spacing d is smaller. This is because the recording magnetic field shape of the magnetic head changes depending on the spacing d.
- “d + a” is described in H. Neal Bertram, Theory of Magnetic Recording.
- the ten-point average roughness Rz of the recording surface (outermost surface) of the magnetic recording medium is preferably 35 nm or less.
- Rz exceeds 35 nm, the spacing d increases and “d + a” may exceed 30 nm. That is, there is a possibility that good electromagnetic conversion characteristics cannot be obtained.
- the 10-point average roughness Rz of the surface of the thin film is 10-point average roughness of the recording surface of the magnetic recording medium.
- the squareness ratio Rs (residual magnetization Mr / saturation magnetization Ms) measured in the perpendicular direction of the magnetic layer 3 is preferably 0.6 or more, specifically 0.6 or more and 1.0 or less. When the squareness ratio in the vertical direction is less than 0.6, the S / N ratio can be further improved.
- the upper limit value of the squareness ratio Rs is 1.0 in principle.
- the magnetic layer 3 includes, for example, magnetic powder, a binder, and conductive particles.
- the magnetic layer 3 may further contain additives such as a lubricant, an abrasive, and a rust preventive as necessary.
- Magnetic powder is cubic ferrite magnetic powder.
- magnetic powder composed of cubic ferrite magnetic particles is referred to as cubic ferrite magnetic powder.
- the magnetic recording medium has a high S / N ratio.
- a higher output tends to be obtained when the coercive force Hc is higher due to the influence of the demagnetizing field.
- the higher coercive force is excellent in thermal stability when microparticulated.
- the next generation magnetic recording medium preferably has a high coercive force Hc.
- cubic ferrite magnetic powder having a high possibility of developing a coercive force Hc higher than that of hexagonal barium ferrite magnetic powder is used.
- the cubic ferrite magnetic powder 21 has a cubic shape or a substantially cubic shape.
- “cubic ferrite magnetic powder 21 is substantially cubic” means that the average plate ratio (average aspect ratio (average plate diameter L AM / average plate thickness L BM )) of cubic ferrite magnetic powder 21 is 0.
- a rectangular parallelepiped shape that is 75 or more and 1.25 or less. Since the cubic ferrite magnetic powder 21 has a small unit cell size, it is advantageous from the viewpoint of ultrafine particles in the future.
- the cubic ferrite magnetic powder 21 is dispersed in the magnetic layer 3.
- the easy magnetization axis of the cubic ferrite magnetic powder 21 is oriented in the thickness direction of the magnetic layer 3 or substantially in the thickness direction of the magnetic layer 3. That is, a cubic ferrite magnetic powder 21, the square-shaped surface S A is such that the thickness direction perpendicular or nearly perpendicular magnetic layer 3, is dispersed in the magnetic layer 3.
- the contact area between the particles in the thickness direction of the medium can be reduced and aggregation of the particles can be suppressed as compared with the hexagonal plate-shaped barium ferrite magnetic powder 21. That is, the dispersibility of the magnetic powder can be enhanced.
- the square surface S A is exposed from the surface of the magnetic layer 3. Performing the short wavelength recording by the magnetic head to the square plane S A, as compared with the case where the hexagonal surface of the hexagonal plate-like barium ferrite magnetic powder having the same volume performing short wavelength recording, in view of high density recording Is advantageous. As shown in the plan view of FIG. 2C, on the surface of the magnetic layer 3, from the viewpoint of high density recording, it is preferable that a square surface S A cubic ferrite magnetic powder 21 is spread.
- the cubic ferrite magnetic particles are so-called spinel ferrimagnetic particles.
- the cubic ferrite magnetic particles are iron oxide particles having cubic ferrite as a main phase.
- the cubic ferrite contains one or more selected from the group consisting of Co, Ni, Mn, Al, Cu and Zn.
- the cubic ferrite contains at least Co, and further contains at least one selected from the group consisting of Ni, Mn, Al, Cu and Zn in addition to Co. More specifically, for example, cubic ferrite has an average composition represented by the general formula MFe 2 O 4 .
- M is one or more metals selected from the group consisting of Co, Ni, Mn, Al, Cu and Zn.
- M is a combination of Co and one or more metals selected from the group consisting of Ni, Mn, Al, Cu and Zn.
- the average plate diameter (average particle size) of the cubic ferrite magnetic powder 21 is preferably 14 nm or less, more preferably 10 nm or more and 14 nm or less.
- the average plate diameter exceeds 14 nm, the exposed area of particles on the medium surface increases, and the S / N ratio may decrease.
- the average plate diameter is less than 10 nm, it may be difficult to produce the cubic ferrite magnetic powder 21.
- the average plate diameter of the cubic ferrite magnetic powder 21 is obtained as follows. First, the surface of the magnetic layer is observed with an atomic force microscope (AFM), and the length L A of one side of the square surface S A of several hundred cubic ferrite magnetic powders 21 included in the AFM image is observed. Is obtained as a plate diameter (see FIGS. 2A and 2C). Then, simply mean a plate diameter of several hundred cubic ferrite magnetic powders 21 to (arithmetic mean) to obtain an average plate diameter L AM.
- AFM atomic force microscope
- the average plate ratio (average aspect ratio (average plate diameter L AM / average plate thickness L BM )) of the cubic ferrite magnetic powder 21 is preferably 0.75 or more and 1.25 or less. If the average plate ratio is out of this numerical range, the shape of the cubic ferrite magnetic powder 21 is not a cubic shape or a substantially cubic shape, so that aggregation occurs and short wavelength recording may be difficult.
- the average plate ratio of the cubic ferrite magnetic powder 21 is obtained as follows. First, as described above, obtaining an average plate diameter L AM cubic ferrite magnetic powders 21. Next, the cross section of the magnetic layer is observed with a transmission electron microscope (TEM), and the side face width L B of the hundreds of cubic ferrite magnetic powders 21 included in the TEM image, that is, the side face is formed. determining the side of the square-shaped surface S B of length L B as the plate thickness (Fig. 2A, see FIG. 2B). Next, the plate thickness L B of several hundreds of cubic ferrite magnetic powders 21 is simply averaged (arithmetic average) to obtain the average plate thickness L BM . Next, an average plate ratio (average plate diameter L AM / average plate thickness L BM ) is determined using the average plate diameter L AM and the average plate thickness L BM determined as described above.
- TEM transmission electron microscope
- the binder a resin having a structure in which a crosslinking reaction is imparted to a polyurethane resin, a vinyl chloride resin, or the like is preferable.
- the binder is not limited to these, and other resins may be appropriately blended depending on the physical properties required for the magnetic recording medium.
- the resin to be blended is not particularly limited as long as it is a resin generally used in a coating type magnetic recording medium.
- thermosetting resins or reactive resins examples include phenol resins, epoxy resins, urea resins, melamine resins, alkyd resins, silicone resins, polyamine resins, urea formaldehyde resins, and the like.
- Each binder described above is introduced with a polar functional group such as —SO 3 M, —OSO 3 M, —COOM, P ⁇ O (OM) 2 for the purpose of improving the dispersibility of the magnetic powder. It may be.
- M in the formula is a hydrogen atom or an alkali metal such as lithium, potassium, or sodium.
- examples of the polar functional group include a side chain type having terminal groups of —NR1R2 and —NR1R2R3 + X—, and a main chain type of> NR1R2 + X—.
- R1, R2, and R3 in the formula are hydrogen atoms or hydrocarbon groups
- X- is a halogen element ion such as fluorine, chlorine, bromine, or iodine, or an inorganic or organic ion.
- examples of the polar functional group include —OH, —SH, —CN, and an epoxy group.
- the conductive particles fine particles containing carbon as a main component, for example, carbon black can be used.
- carbon black for example, Asahi # 15, # 15HS manufactured by Asahi Carbon Co., Ltd. can be used.
- the magnetic layer 3 is made of aluminum oxide ( ⁇ , ⁇ , or ⁇ alumina), chromium oxide, silicon oxide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide (non-magnetic reinforcing particles). Rutile type or anatase type titanium oxide) may be further contained.
- the underlayer 2 is a nonmagnetic layer containing nonmagnetic powder and a binder as main components.
- the underlayer 2 may further contain various additives such as conductive particles and a lubricant as necessary.
- the nonmagnetic powder may be an inorganic substance or an organic substance. Carbon black can also be used.
- the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides.
- the shape of the nonmagnetic powder include various shapes such as a needle shape, a spherical shape, and a plate shape, but are not limited thereto.
- polyisocyanate may be used in combination with the resin, and this may be crosslinked and cured.
- the polyisocyanate include toluene diisocyanate and adducts thereof, alkylene diisocyanate, and adducts thereof.
- conductive particles of the underlayer 2 as with the conductive particles of the magnetic layer 3 described above, for example, carbon black, hybrid carbon in which carbon is attached to the surface of silica particles, or the like can be used.
- Examples of the lubricant contained in the magnetic layer 3 and the underlayer 2 include esters of monobasic fatty acids having 10 to 24 carbon atoms and monohydric to hexahydric alcohols having 2 to 12 carbon atoms, and mixtures thereof. Esters, difatty acid esters, and trifatty acid esters can be used as appropriate.
- lubricants include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate , Isooctyl stearate, octyl myristate, and the like.
- a coating for forming an underlayer is prepared by kneading and dispersing nonmagnetic powder, conductive particles, a binder and the like in a solvent.
- a magnetic layer forming coating material is prepared by kneading and dispersing magnetic powder, conductive particles, a binder, and the like in a solvent. The same solvent, dispersing apparatus and kneading apparatus can be applied to the preparation of the magnetic layer forming paint and the underlayer forming paint.
- Examples of the solvent used for the above-mentioned coating preparation include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, alcohol solvents such as methanol, ethanol, and propanol, methyl acetate, ethyl acetate, butyl acetate, and propyl acetate.
- ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone
- alcohol solvents such as methanol, ethanol, and propanol, methyl acetate, ethyl acetate, butyl acetate, and propyl acetate.
- Ester solvents such as ethyl lactate and ethylene glycol acetate, ether solvents such as diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, methylene chloride, ethylene chloride, Halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform, chlorobenzene and the like. These may be used singly or may be mixed as appropriate.
- Examples of the kneading apparatus used for the coating preparation described above include a continuous biaxial kneader, a continuous biaxial kneader capable of diluting in multiple stages, a kneader, a pressure kneader, and a roll kneader.
- the present invention is not particularly limited to these devices.
- a dispersing device such as a sonic disperser can be used, but is not particularly limited to these devices.
- the base layer 2 is formed by applying the base layer-forming coating material to one main surface of the nonmagnetic support 1 and drying it.
- the magnetic layer 3 is formed on the underlayer 2 by applying a coating for forming the magnetic layer on the underlayer 2 and drying it.
- the cubic ferrite magnetic powder contained in the magnetic powder is magnetically oriented so that the easy axis of magnetization of the cubic ferrite magnetic powder is oriented in the thickness direction of the magnetic layer 3 or substantially the magnetic layer 3. It is preferable to direct in the thickness direction.
- the backcoat layer 4 is formed by applying the coating material for forming the backcoat layer to the other main surface of the nonmagnetic support 1 and drying it.
- the nonmagnetic support 1 on which the underlayer 2, the magnetic layer 3, and the backcoat layer 4 are formed is rewound around a large-diameter core and subjected to a curing treatment.
- the nonmagnetic support 1 on which the underlayer 2, the magnetic layer 3, and the backcoat layer 4 are formed is calendered and then cut into a predetermined width. In this way, a pancake cut to a predetermined width can be obtained.
- the step of forming the back coat layer 4 may be after the calendar process.
- the formation process of the underlayer 2 and the magnetic layer 3 is not limited to the above example.
- an undercoat layer-forming coating material is applied to one main surface of the nonmagnetic support 1 to form a coating film, and the magnetic layer-forming coating material is applied on the coating film in a wet state.
- both the coating films may be dried to form the underlayer 2 and the magnetic layer 3 on one main surface of the nonmagnetic support 1.
- the magnetic layer 3 includes cubic ferrite magnetic powder 21 that is cubic iron oxide magnetic powder. Moreover, the average plate diameter of the cubic ferrite magnetic powder 21 is 14 nm or less, the average plate ratio of the cubic ferrite magnetic powder 21 is 0.75 or more and 1.25 or less, and the ten-point average roughness of the magnetic layer 3. Rz is 35 nm or less. Therefore, it is possible to provide a magnetic recording medium capable of short wavelength recording suitable for the perpendicular magnetic recording system and having a high S / N ratio.
- the magnetic recording medium according to the second embodiment differs from the magnetic recording medium according to the first embodiment in that the magnetic layer 3 includes ⁇ -Fe 2 O 3 magnetic powder instead of the cubic ferrite magnetic powder 21. Is different.
- magnetic powder composed of ⁇ -Fe 2 O 3 magnetic particles is referred to as ⁇ -Fe 2 O 3 magnetic powder.
- next-generation magnetic recording medium one having a high coercive force Hc is preferable as described in the first embodiment.
- ⁇ -Fe 2 O 3 magnetic powder having a higher possibility of developing a coercive force Hc higher than that of hexagonal barium ferrite magnetic powder is used.
- the ⁇ -Fe 2 O 3 magnetic powder 22 is spherical or almost spherical. Since ⁇ -Fe 2 O 3 magnetic powder 22 has a small unit cell size, it is advantageous from the viewpoint of ultrafine particles in the future. As shown in the sectional view of FIG. 3B, the ⁇ -Fe 2 O 3 magnetic powder 22 is dispersed in the magnetic layer 3. The easy magnetization axis of the ⁇ -Fe 2 O 3 magnetic powder 22 is oriented in the thickness direction of the magnetic layer 3 or substantially in the thickness direction of the magnetic layer 3.
- the spherical or nearly spherical ⁇ -Fe 2 O 3 magnetic powder 22 can reduce the contact area between the particles in the thickness direction of the medium and suppress the aggregation of the particles compared to the hexagonal plate-shaped barium ferrite magnetic powder. . That is, the dispersibility of the magnetic powder can be enhanced.
- a part SA of the spherical surface is exposed from the surface of the magnetic layer 3.
- This portion S A spherical surface to perform a short wavelength recording by the magnetic head as compared with the case where the hexagonal surface of the hexagonal plate-like barium ferrite magnetic powder having the same volume performing short wavelength recording, high density recording It is advantageous from the viewpoint.
- a portion S A spherical surface of the ⁇ -Fe 2 O 3 magnetic powder 22 is spread .
- the average particle size (average particle size) of the ⁇ -Fe 2 O 3 magnetic powder 22 is preferably 14 nm or less, more preferably 10 nm or more and 14 nm or less.
- the average particle diameter of the ⁇ -Fe 2 O 3 magnetic powder 22 is determined by observing a cross section of the magnetic layer with a TEM, and the particle diameter D of several hundreds of ⁇ -Fe 2 O 3 magnetic powder 22 included in the TEM image. , that determine the particle size D of a portion S B of the spherical surface (Fig. 3A, see Fig. 3B).
- the average particle diameter D M is obtained by simply averaging (arithmetic average) the particle diameters D of several hundred ⁇ -Fe 2 O 3 magnetic powders 22.
- ⁇ -Fe 2 O 3 magnetic powder 22 Since ⁇ -Fe 2 O 3 magnetic powder 22 because it has a spherical or substantially spherical, it is ⁇ -Fe 2 O 3 particle size of the magnetic powder 22 regardless of the measurement direction constant or nearly constant, ⁇ -Fe 2 O 3
- the average spherical ratio (average aspect ratio) of the magnetic powder 22 is defined as 1 or about 1.
- the ⁇ -Fe 2 O 3 magnetic powder 22 is an iron oxide particle powder whose main phase is ⁇ -Fe 2 O 3 crystals (including those in which part of the Fe site is replaced with the metal element M).
- the ⁇ -Fe 2 O 3 crystal includes a pure ⁇ -Fe 2 O 3 crystal in which the Fe site is not substituted with another element, and a part of the Fe site is trivalent. And a crystal having the same space group as that of a pure ⁇ -Fe 2 O 3 crystal (that is, the space group is Pna2 1 ).
- the configuration of the magnetic recording medium other than the above is the same as that of the magnetic recording medium according to the first embodiment described above.
- the configuration in which the magnetic layer 3 includes the ⁇ -Fe 2 O 3 magnetic powder 22 instead of the cubic ferrite magnetic powder 21 has been described.
- the configuration of the magnetic recording medium is not limited to this. Absent.
- the magnetic layer 3 may include both the cubic ferrite magnetic powder 21 and the ⁇ -Fe 2 O 3 magnetic powder 22.
- the average particle size (average plate diameter, average particle diameter, average major axis diameter) and average aspect ratio (average plate ratio, average spherical ratio, average needle ratio) of the magnetic powder are as follows: I asked for it.
- the average plate diameter of the cubic magnetic powder (Co-based ferrite magnetic powder) contained in the magnetic layer was determined as follows. Using a Nanoscope IV of Veeco, a 200 nm ⁇ 200 nm area was observed in Phase mode, and using one of the grain sizes in the analysis process, the mean grain size was determined, and this was taken as the average plate diameter.
- the average plate ratio of the cubic magnetic powder (Co-based ferrite magnetic powder) contained in the magnetic layer was determined as follows. First, a cross section of the magnetic layer was taken with a TEM at a magnification of 400,000 times. Next, from the cross-sectional TEM image, hundreds of particles with visible side surfaces were randomly selected. Next, the average plate thickness of several hundred particles selected was simply averaged (arithmetic average) to obtain the average plate thickness. Next, the average plate ratio (average plate diameter / average plate thickness) was determined using the average plate diameter and average plate thickness determined as described above.
- the average spherical ratio of the spherical magnetic powder ( ⁇ -Fe 2 O 3 crystalline magnetic powder) contained in the magnetic layer was determined as follows. First, a cross section of the magnetic layer was taken with a TEM at a magnification of 400,000 times. Next, from the cross-sectional TEM image, hundreds of particles with visible side surfaces were randomly selected. Next, the particle size (diameter) of several hundred particles selected was measured, and they were simply averaged (arithmetic average) to obtain the average particle size.
- the average plate diameter of hexagonal plate-like magnetic powder (hexagonal barium ferrite magnetic powder) contained in the magnetic layer was determined in the same manner as the above-mentioned “average plate diameter of cubic magnetic powder”.
- the average plate ratio of hexagonal plate-like magnetic powder (hexagonal barium ferrite magnetic powder) contained in the magnetic layer was determined as follows. First, a cross section of the magnetic layer was taken with a TEM at a magnification of 400,000 times. Next, from the cross-sectional TEM image, hundreds of particles with visible side surfaces were randomly selected. Next, the average plate thickness of several hundred particles selected was simply averaged (arithmetic average) to obtain the average plate thickness. Next, the average plate ratio (average plate diameter / average plate thickness) was determined using the average plate diameter and average plate thickness determined as described above.
- the average major axis diameter of the acicular magnetic powder (metal magnetic powder) contained in the magnetic layer was determined in the same manner as the “average plate diameter of the cubic magnetic powder” described above.
- the average acicular ratio of the acicular magnetic powder (metal magnetic powder) contained in the magnetic layer was determined as follows. First, a cross section of the magnetic layer was taken with a TEM at a magnification of 400,000 times. Next, from the cross-sectional TEM image, hundreds of particles with visible side surfaces were randomly selected. Next, the short axis diameter of several hundred particles selected was simply averaged (arithmetic average) to obtain the average short axis diameter. Next, the average needle diameter ratio (average major axis diameter / average minor axis diameter) was determined using the average plate diameter and average plate thickness determined as described above.
- Examples 1 to 6, Comparative Examples 1 to 6) The first composition having the following composition was kneaded with an extruder. Then, the 1st composition and the 2nd composition of the following mixing
- Vinyl chloride resin 27.8 parts by mass (resin solution: resin content 30% by mass, cyclohexanone 70% by mass)
- n-butyl stearate 2 parts by mass
- Methyl ethyl ketone 121.3 parts by mass
- Toluene 121.3 parts by mass
- Cyclohexanone 60.7 parts by mass
- a third composition having the following composition was kneaded with an extruder. Then, the 3rd composition and the 4th composition of the following mixing
- an underlayer and a magnetic layer were formed as follows on a polyethylene naphthalate film (PEN film) as a nonmagnetic support.
- PEN film polyethylene naphthalate film
- the underlayer was formed on the PEN film by applying and drying the underlayer-forming paint on the 6.2 ⁇ m-thick PEN film as a nonmagnetic support.
- the magnetic layer was formed on the underlayer by applying and drying the magnetic layer-forming paint on the underlayer. Note that the magnetic powder was magnetically oriented during drying.
- the PEN film on which the underlayer and the magnetic layer were formed was calendered with a metal roll to smooth the surface of the magnetic layer. The ten-point average roughness Rz was adjusted as shown in Tables 1 and 2 by adjusting the conditions of the calendar process.
- a coating material having the following composition was applied to a thickness of 0.6 ⁇ m on the surface opposite to the magnetic layer and dried.
- Carbon black (Asahi Co., Ltd., trade name: # 80): 100 parts by mass Polyester polyurethane: 100 parts by mass (Nippon Polyurethanes, trade name: N-2304) Methyl ethyl ketone: 500 parts by mass Toluene: 400 parts by mass Cyclohexanone: 100 parts by mass
- the PEN film on which the underlayer, the magnetic layer, and the backcoat layer were formed as described above was cut into a 1 ⁇ 2 inch (12.65 mm) width to obtain a magnetic tape.
- Example 7 In the preparation process of the first composition, CoNiMn ferrite magnetic powder having an average particle size (average plate diameter) and an average aspect ratio (average plate ratio) shown in Table 1 was used instead of the CoNi ferrite magnetic powder.
- the ten-point average roughness Rz was adjusted as shown in Table 1 by adjusting the calendar processing conditions. Except for this, a magnetic tape was obtained in the same manner as in Example 1.
- Example 9 In the preparation process of the first composition, CoNiMnZn ferrite magnetic powder having an average particle size (average plate diameter) and an average aspect ratio (average plate ratio) shown in Table 1 was used instead of the CoNi ferrite magnetic powder.
- the ten-point average roughness Rz was adjusted as shown in Table 1 by adjusting the calendar processing conditions. Except for this, a magnetic tape was obtained in the same manner as in Example 1.
- Examples 10 to 15, Comparative Examples 7 to 12 In the preparation process of the first composition, in place of the CoNi ferrite magnetic powder, ⁇ -Fe 2 O 3 crystals having the average particle size (average particle size) and the average aspect ratio (average spherical ratio) shown in Tables 1 and 2 Magnetic powder was used. The ten-point average roughness Rz was adjusted as shown in Tables 1 and 2 by adjusting the conditions of the calendar process. Except for this, a magnetic tape was obtained in the same manner as in Example 1.
- Magnetic properties Magnetic properties (coercive force Hc, squareness ratio Rs) were measured using an oscillating sample magnetometer (manufactured by Lakeshore) at 23 to 25 ° C. and an applied magnetic field of 15 kOe.
- Hc, Rs magnetic properties in the direction perpendicular to the magnetic layer surface (the thickness direction of the magnetic layer) were measured.
- Comparative Examples 17 and 18 Magnetic properties (Hc, Rs) in the horizontal direction (longitudinal direction of the magnetic layer surface) with respect to the magnetic layer surface were measured.
- S / N ratio (S / N ratio) First, the tape was run with a commercially available LFF manufactured by Magnetic Mountain Engineering, and recording / reproduction was performed using a head for a linear tape drive to obtain the S / N ratio. The recording wavelength was 270 kFCI (kilo Flux Changes per Inch). Next, the obtained S / N ratio was evaluated according to the following criteria. A: S / N ratio is 17 dB or more. A: The S / N ratio is 15 dB or more and less than 17 dB. X: S / N ratio is less than 15 dB. The S / N ratio required to establish the recording / reproducing system is generally about 15 dB, so 15 dB was used as a criterion for determining the S / N ratio.
- Table 1 shows the configurations and evaluation results of the magnetic tapes of Examples 1 to 15.
- Table 2 shows the structures and evaluation results of the magnetic tapes of Comparative Examples 1 to 18.
- a CoNi ferrite magnetic powder having a cubic shape or a substantially cubic shape that is, a rectangular parallelepiped shape having an average plate ratio of 0.75 or more and 1.25 or less
- the average plate diameter is 10 nm or more and 14 nm or less.
- CoNiMn ferrite magnetic powder obtained by adding Mn to CoNi ferrite and CoNiMnZn ferrite magnetic powder obtained by adding MnZn to CoNi ferrite are used. Also in this case, recording and reproduction at a short wavelength is possible by making the shape (average plate ratio), average plate diameter, coercive force, and ten-point average roughness Rz of the magnetic powder as described above, and A high S / N ratio is obtained.
- the shape of the CoNi ferrite magnetic powder is not a cubic shape or a substantially cubic shape (that is, a rectangular parallelepiped shape having an average plate ratio of 0.75 to 1.25). Also, the ten-point average roughness Rz exceeds 35 nm.
- Examples 10 to 15 spherical ⁇ -Fe 2 O 3 magnetic powder was used, the average particle size was 10 nm to 14 nm, the coercive force was 230 kA / m to 400 kA / m, and the ten-point average roughness Rz was 35 nm or less. It is said. For this reason, recording / reproduction of a short wavelength is possible and a high S / N ratio is obtained. In Comparative Example 7, the ten-point average roughness Rz exceeds 35 nm. For this reason, a high S / N ratio is not obtained. In Comparative Example 8, the average plate diameter of the magnetic powder exceeds 14 nm. Also, the ten-point average roughness Rz exceeds 35 nm.
- the present technology can also employ the following configurations.
- the magnetic recording medium according to (1), wherein the coercive force in the vertical direction is 230 kA / m or more and 400 kA / m or less.
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Abstract
Description
支持体と、
磁性粉を含む磁性層と
を備え、
磁性粉は、立方晶フェライトを含む磁性粒子からなる磁性粉、およびε相酸化鉄を含む磁性粒子からなる磁性粉の少なくとも一方を含み、
磁性粉の平均粒子サイズは、14nm以下であり、
磁性粉の平均アスペクト比は、0.75以上1.25以下であり、
十点平均粗さRzは、35nm以下である磁気記録媒体である。
バリウムフェライト粒子は六角板状(高さが低い六角柱状)を有しているため、バリウムフェライト粒子を超微粒子化した場合には、隣接するバリウムフェライト粒子の六角形状面同士が密着し、磁性粉が凝集してしまう可能性がある。すなわち、バリウムフェライト粒子を超微粒子化したとしても、バリウムフェライト粒子個々の分散が進行しない可能性がある。また、バリウムフェライト粒子に垂直磁界による垂直配向処理を施した場合、おのずと非磁性支持体表面とバリウムフェライト粒子の六角形状面が並行になる。これは、バリウムフェライト粒子の磁化容易軸方向は六角形状面に垂直な方向であるため、六角形状面が媒体表面に配列することになるためである。このような粒子配列では、媒体の厚さ方向におけるバリウムフェライト粒子の接触面積が増えるため、粒子同士が凝集する可能性が増大する。したがって、超微粒子からなる磁性粉の分散性を高めて、微粒子化の利点である高密度記録を実現するためには、隣接する超磁性粒子同士の接触面積を小さくして、できる限り凝集を抑制することが有効になると考えられる。
垂直配向方式では、六角板状のバリウムフェライト粒子では、最も面積が大きい六角形状面が磁気記録媒体の表面に露出することになる。この六角形状面に磁気ヘッドにより短波長記録を行うことは、同一体積の立方体状磁性粒子の正方形状面、あるいは球状磁性粉の球面に短波長記録を行う場合に比べて、高密度記録の観点で明らかに不利である。
バリウムフェライト粒子の結晶構造は、マグネトプラムバイト型であり単位格子のC軸が2.3nmと比較的大きい。バリウムフェライトが現在実用化されているとはいえ、将来の超微粒子化に対しては、単位格子サイズができる限り小さい立方晶酸化鉄の方が好適であると考えられる。
1 第1の実施形態
1.1 磁気記録媒体の構成
1.2 磁気記録媒体の製造方法
1.3 効果
2 第2の実施形態
2.1 磁気記録媒体の構成
2.2 効果
2.3 変形例
[1.1 磁気記録媒体の構成]
図1に示すように、本技術の第1の実施形態に係る磁気記録媒体は、いわゆる垂直磁気記録媒体であり、非磁性支持体1と、非磁性支持体1の一方の主面上に設けられた下地層2と、下地層2上に設けられた磁性層3とを備える。磁気記録媒体が、必要に応じて、非磁性支持体1の他方の主面に設けられたバックコート層4をさらに備えるようにしてもよい。また、磁性層3上に保護層および潤滑剤層などをさらに設けるようにしてもよい。
非磁性支持体1は、例えば、可撓性を有する長尺状のフィルムである。非磁性支持体1の材料としては、例えば、ポリエチレンテレフタレートなどのポリエステル類、ポリエチレン、ポリプロピレンなどのポリオレフィン類、セルローストリアセテート、セルロースダイアセテート、セルロースブチレートなどのセルロース誘導体、ポリ塩化ビニル、ポリ塩化ビニリデンなどのビニル系樹脂、ポリカーボネート、ポリイミド、ポリアミドイミドなどのプラスチック、アルミニウム合金、チタン合金などの軽金属、アルミナガラスなどのセラミックなどを用いることができる。さらには、機械的強度を高めるために、AlまたはCuの酸化物を含む薄膜を、ビニル系樹脂などを含む非磁性支持体1の主面のうち少なくとも一方に成膜したものを用いてもよい。
磁性層3は、短波長記録または超短波超記録が可能な垂直記録層である。磁性層3は、磁性層3の厚さ方向に磁気異方性を有する。すなわち、磁性層3の磁化容易軸は、磁性層3の厚さ方向に向いている。磁性層3の平均厚さは、好ましくは30nm以上100nm以下、より好ましくは50nm以上70nm以下である。
下地層2は、非磁性粉および結着剤を主成分として含む非磁性層である。下地層2が、必要に応じて、導電性粒子、潤滑剤などの各種添加剤をさらに含んでいてもよい。
次に、上述の構成を有する磁気記録媒体の製造方法の一例について説明する。
まず、非磁性粉、導電性粒子および結着剤などを溶剤に混練、分散させることにより、下地層形成用塗料を調製する。次に、磁性粉、導電性粒子および結着剤などを溶剤に混練、分散させることにより、磁性層形成用塗料を調製する。磁性層形成用塗料および下地層形成用塗料の調製には、同様の溶剤、分散装置および混練装置を適用することができる。
本技術の第1の実施形態に係る磁気記録媒体では、磁性層3は、立方晶酸化鉄磁性粉である立方晶フェライト磁性粉21を含んでいる。また、立方晶フェライト磁性粉21の平均板径が14nm以下であり、立方晶フェライト磁性粉21の平均板状比が0.75以上1.25以下であり、磁性層3の十点平均粗さRzが35nm以下である。したがって、垂直磁気記録方式に好適な短波長記録が可能で、かつ高いS/N比を有する磁気記録媒体を提供できる。
[2.1 磁気記録媒体の構成]
第2の実施形態に係る磁気記録媒体は、磁性層3が立方晶フェライト磁性粉21に代えてε-Fe2O3磁性粉を含む点において、第1の実施形態に係る磁気記録媒体とは異なっている。本明細書では、ε-Fe2O3磁性粒子からなる磁性粉をε-Fe2O3磁性粉という。
本技術の第2の実施形態では、第1の実施形態と同様に、垂直磁気記録方式に好適な短波長記録が可能で、かつ高いS/N比を有する磁気記録媒体を提供できる。
第2の実施形態では、磁性層3が立方晶フェライト磁性粉21に代えてε-Fe2O3磁性粉22を含む構成について説明したが、磁気記録媒体の構成はこれに限定されるものではない。例えば、磁性層3が立方晶フェライト磁性粉21とε-Fe2O3磁性粉22の両方を含んでいてもよい。
磁性層に含まれる立方体状磁性粉(Co系フェライト磁性粉)の平均板径を以下のようにして求めた。Veeco社のNanoscopeIVを用いて200nm×200nmのエリアをPhaseモードで粒子観察を行い、解析処理の一つのGrain Sizeを用いて、Mean Grain sizeを求め、これを平均板径とした。
磁性層に含まれる立方体状磁性粉(Co系フェライト磁性粉)の平均板状比を以下のようにして求めた。まず、TEMで磁性層断面を40万倍で撮影した。次に、断面TEM像から、側面が見える粒子を無作為に数百個選び出した。次に、選び出した数百個の粒子の平均板厚を単純に平均(算術平均)して、平均板厚を求めた。次に、上述のようにして求められた平均板径および平均板厚を用いて、平均板状比(平均板径/平均板厚)を求めた。
磁性層に含まれる球状磁性粉(ε-Fe2O3結晶磁性粉)の平均球状比を以下のようにして求めた。まず、TEMで磁性層断面を40万倍で撮影した。次に、断面TEM像から、側面が見える粒子を無作為に数百個選び出した。次に、選び出した数百個の粒子の粒径(直径)を測定し、それらを単純に平均(算術平均)して、平均粒径を求めた。
磁性粉が球状である場合には、粒径は測定方向に依らず一定であることから、平均球状比を実測値から求めずに、“1”と定義した。
上述の“立方体状磁性粉の平均板径”と同様にして、磁性層に含まれる六角板状磁性粉(六方晶バリウムフェライト磁性粉)の平均板径を求めた。
磁性層に含まれる六角板状磁性粉(六方晶バリウムフェライト磁性粉)の平均板状比を以下のようにして求めた。まず、TEMで磁性層断面を40万倍で撮影した。次に、断面TEM像から、側面が見える粒子を無作為に数百個選び出した。次に、選び出した数百個の粒子の平均板厚を単純に平均(算術平均)して、平均板厚を求めた。次に、上述のようにして求められた平均板径および平均板厚を用いて、平均板状比(平均板径/平均板厚)を求めた。
上述の“立方体状磁性粉の平均板径”と同様にして、磁性層に含まれる針状磁性粉(メタル磁性粉)の平均長軸径を求めた。
磁性層に含まれる針状磁性粉(メタル磁性粉)の平均針状比を以下のようにして求めた。まず、TEMで磁性層断面を40万倍で撮影した。次に、断面TEM像から、側面が見える粒子を無作為に数百個選び出した。次に、選び出した数百個の粒子の短軸径を単純に平均(算術平均)して、平均短軸径を求めた。次に、上述のようにして求められた平均板径および平均板厚を用いて、平均針状比(平均長軸径/平均短軸径)を求めた。
下記配合の第一組成物をエクストルーダで混練した。その後、ディスパーを備えた攪拌タンクに、第一組成物と、下記配合の第二組成物を加えて予備混合を行った。その後、さらにサンドミル混合を行い、フィルター処理を行い、磁性層形成用塗料を調製した。
CoNiフェライト結晶磁性粉:100質量部
(但し、CoNiフェライト結晶磁性粉としては、表1、表2に示す平均粒子サイズ(平均板径)および平均アスペクト比(平均板状比)を有するものを用いた。)
塩化ビニル系樹脂(シクロヘキサノン溶液30質量%):55.6質量部
(重合度300、Mn=10000、極性基としてOSO3K=0.07mmol/g、2級OH=0.3mmol/gを含有する。)
酸化アルミニウム粉末:5質量部
(α-Al2O3、平均粒径0.2μm)
カーボンブラック:2質量部
(東海カーボン社製、商品名:シーストTA)
塩化ビニル系樹脂:27.8質量部
(樹脂溶液:樹脂分30質量%、シクロヘキサノン70質量%)
n-ブチルステアレート:2質量部
メチルエチルケトン:121.3質量部
トルエン:121.3質量部
シクロヘキサノン:60.7質量部
針状酸化鉄粉末:100質量部
(α-Fe2O3、平均長軸長0.15μm)
塩化ビニル系樹脂:55.6質量部
(樹脂溶液:樹脂分30質量%、シクロヘキサノン70質量%)
カーボンブラック:10質量部
(平均粒径20nm)
ポリウレタン系樹脂UR8200(東洋紡績製):18.5質量部
n-ブチルステアレート:2質量部
メチルエチルケトン:108.2質量部
トルエン:108.2質量部
シクロヘキサノン:18.5質量部
カーボンブラック(旭社製、商品名:#80):100質量部
ポリエステルポリウレタン:100質量部
(日本ポリウレタン社製、商品名:N-2304)
メチルエチルケトン:500質量部
トルエン:400質量部
シクロヘキサノン:100質量部
第一組成物の調製工程において、CoNiフェライト磁性粉に代えて、表1に示す平均粒子サイズ(平均板径)および平均アスペクト比(平均板状比)を有するCoNiMnフェライト磁性粉を用いた。カレンダー処理の条件を調整することで、十点平均粗さRzを表1に示すように調整した。これ以外のことは、実施例1と同様にして磁気テープを得た。
第一組成物の調製工程において、CoNiフェライト磁性粉に代えて、表1に示す平均粒子サイズ(平均板径)および平均アスペクト比(平均板状比)を有するCoNiMnZnフェライト磁性粉を用いた。カレンダー処理の条件を調整することで、十点平均粗さRzを表1に示すように調整した。これ以外のことは、実施例1と同様にして磁気テープを得た。
第一組成物の調製工程において、CoNiフェライト磁性粉に代えて、表1、表2に示す平均粒子サイズ(平均粒径)および平均アスペクト比(平均球状比)を有するε-Fe2O3結晶磁性粉を用いた。カレンダー処理の条件を調整することで、十点平均粗さRzを表1、表2に示すように調整した。これ以外のことは、実施例1と同様にして磁気テープを得た。
第一組成物の調製工程において、CoNiフェライト磁性粉に代えて、表2に示す平均粒子サイズ(平均板径)および平均アスペクト比(平均板状比)を有する六方晶バリウムフェライト磁性粉を用いた。カレンダー処理の条件を調整することで、十点平均粗さRzを表2に示すように調整した。これ以外のことは、実施例1と同様にして磁気テープを得た。
第一組成物の調製工程において、CoNiフェライト磁性粉に代えて、表2に示す平均粒子サイズ(平均長軸径)および平均アスペクト比(平均針状比)を有する針状メタル磁性粉を用いた。カレンダー処理の条件を調整することで、十点平均粗さRzを表2に示すように調整した。これ以外のことは、実施例1と同様にして磁気テープを得た。
磁気特性(保磁力Hc、角型比Rs)は、振動試料型磁束計(Lakeshore社製)を用い、23~25℃で印加磁界15kOeで測定した。なお、実施例1~15、比較例1~16では、磁性層表面に対して垂直方向(磁性層の厚さ方向)の磁気特性(Hc、Rs)を測定し、比較例17、18では、磁性層表面に対して水平方向(磁性層表面の長手方向)の磁気特性(Hc、Rs)を測定した。
Veeco社のNanoscopeIVを用いてタッピングAFM(Atomic Force Microscope)のモードで40μmμm×40μmのエリアの測定行い、解析処理の一つRoughnessを用いて十点平均粗さRzを導出した。
まず、磁気テープの周波数特性から求められるスペーシングdと遷移幅aの和(d+a)を求めた(H. Neal Bertram著、Theory of Magnetic Recording参照)。次に、この和(d+a)を評価指標とし、以下のように評価した。なお、スペーシングdに影響を与える十点平均粗さRzは、テープ作製後の金属ロールによるプレス処理(カレンダー処理)により変化させた。
○:d+aが30nm以下である
×:d+aが30nmを超える
まず、市販の磁気Mountain Engineering社製のLFFでテープを走行させ、リニアテープドライブ用のヘッドを用いて記録再生を行うことにより、S/N比を求めた。なお、記録波長を270kFCI(kilo Flux Changes per Inch)とした。次に、求めたS/N比を以下の基準で評価した。
◎:S/N比が17dB以上である。
○:S/N比が15dB以上17dB未満である。
×:S/N比が15dB未満である。
なお、記録再生システムを成立させるのに最低必要となるS/N比は、一般に15dB程度といわれているため、15dBをS/N比の判断基準とした。
実施例1、比較例13、17の磁気テープの断面TEM像を取得した。その結果を図4A、図4B、図5A、図5B、図6A、図6Bに示す。
実施例1~15では、十点平均粗さRzは35nm以下であるため、d+aが30nm以下になっている。
比較例1、2、5~8、11~18では、十点平均粗さRzは35nmを超えているため、d+aが30nmを超えている。
実施例7~9では、CoNiフェライトにMnを添加したCoNiMnフェライト磁性粉、およびCoNiフェライトにMnZnを添加したCoNiMnZnフェライト磁性粉を用いている。この場合にも、磁性粉の形状(平均板状比)、平均板径、保磁力、および十点平均粗さRzを、上述のようにすることで、短波長の記録再生が可能で、かつ高いS/N比が得られる。
比較例1では、CoNiフェライト磁性粉の形状が、立方体状またはほぼ立方体状(すなわち平均板状比0.75以上1.25以下の範囲の直方体状)でない。また、十点平均粗さRzも35nmを超えている。このため、高いS/N比が得られていない。
比較例2では、CoNiフェライト磁性粉の形状が、立方体状またはほぼ立方体状ではない。また、磁性粉の平均板径が、14nmを超えている。さらに、十点平均粗さRzが35nmを超えている。このため、高いS/N比が得られていない。
比較例3では、保磁力が230kA/m未満であるため、高いS/N比が得られていない。
比較例4では、CoNiフェライト磁性粉の磁性粉の平均板径が14nmを超えている。また、保磁力が400kA/mを超えている。このため、高いS/N比が得られていない。
比較例5、6では、十点平均粗さRzが35nmを超えている。このため、高いS/N比が得られていない。
比較例7では、十点平均粗さRzが35nmを超えている。このため、高いS/N比が得られていない。
比較例8では、磁性粉の平均板径が14nmを超えている。また、十点平均粗さRzも35nmを超えている。このため、高いS/N比が得られていない。
比較例9では、保磁力が230kA/m未満である。このため、高いS/N比が得られていない。
比較例10では、磁性粉の平均板径が14nmを超えている。また、保磁力が400kA/mを超えている。このため、高いS/N比が得られていない。
比較例11、12では、十点平均粗さRzが35nmを超えている。このため、高いS/N比が得られていない。
(1)
支持体と、
磁性粉を含む磁性層と
を備え、
上記磁性粉は、立方晶フェライトを含む磁性粒子からなる磁性粉、およびε相酸化鉄を含む磁性粒子からなる磁性粉の少なくとも一方を含み、
上記磁性粉の平均粒子サイズは、14nm以下であり、
上記磁性粉の平均アスペクト比は、0.75以上1.25以下であり、
十点平均粗さRzは、35nm以下である磁気記録媒体。
(2)
垂直方向の保磁力は、230kA/m以上400kA/m以下である(1)に記載の磁気記録媒体。
(3)
垂直方向の角型比は、0.6以上である(1)または(2)に記載の磁気記録媒体。
(4)
上記立方晶フェライトは、Coを含んでいる(1)から(3)のいずれかに記載の磁気記録媒体。
(5)
上記立方晶フェライトは、Ni、MnおよびZnのうちの1種以上をさらに含んでいる(4)に記載の磁気記録媒体。
(6)
上記立方晶フェライトを含む磁性粒子からなる磁性粉は、立方体状またはほぼ立方体状を有し、
上記ε相酸化鉄を含む磁性粒子からなる磁性粉は、球状またはほぼ球状を有している(1)から(5)のいずれかに記載の磁気記録媒体。
(7)
上記磁性層は、垂直記録層である(1)から(6)のいずれかに記載の磁気記録媒体。
(8)
上記磁性粉は、立方晶フェライトを含む磁性粒子からなる磁性粉を含んでいる(1)から(7)のいずれかに記載の磁気記録媒体。
(9)
上記磁性粉は、ε相酸化鉄を含む磁性粒子からなる磁性粉を含んでいる(1)から(7)のいずれかに記載の磁気記録媒体。
(10)
上記磁性粉の平均アスペクト比は、1または約1である(9)に記載の磁気記録媒体。
2 下地層
3 磁性層
4 バックコート層
21 立方晶フェライト磁性粉
22 ε-Fe2O3磁性粉
LAM 平均板径
LBM 平均板厚
SA、SB 正方形状面
Claims (10)
- 支持体と、
磁性粉を含む磁性層と
を備え、
上記磁性粉は、立方晶フェライトを含む磁性粒子からなる磁性粉、およびε相酸化鉄を含む磁性粒子からなる磁性粉の少なくとも一方を含み、
上記磁性粉の平均粒子サイズは、14nm以下であり、
上記磁性粉の平均アスペクト比は、0.75以上1.25以下であり、
十点平均粗さRzは、35nm以下である磁気記録媒体。 - 垂直方向の保磁力は、230kA/m以上400kA/m以下である請求項1に記載の磁気記録媒体。
- 垂直方向の角型比は、0.6以上である請求項1に記載の磁気記録媒体。
- 上記立方晶フェライトは、Coを含んでいる請求項1に記載の磁気記録媒体。
- 上記立方晶フェライトは、Ni、MnおよびZnのうちの1種以上をさらに含んでいる請求項4に記載の磁気記録媒体。
- 上記立方晶フェライトを含む磁性粒子からなる磁性粉は、立方体状またはほぼ立方体状を有し、
上記ε相酸化鉄を含む磁性粒子からなる磁性粉は、球状またはほぼ球状を有している請求項1に記載の磁気記録媒体。 - 上記磁性層は、垂直記録層である請求項1に記載の磁気記録媒体。
- 上記磁性粉は、立方晶フェライトを含む磁性粒子からなる磁性粉を含んでいる請求項1に記載の磁気記録媒体。
- 上記磁性粉は、ε相酸化鉄を含む磁性粒子からなる磁性粉を含んでいる請求項1に記載の磁気記録媒体。
- 上記磁性粉の平均アスペクト比は、1または約1である請求項9に記載の磁気記録媒体。
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JP2019021372A (ja) | 2019-02-07 |
JP6565908B2 (ja) | 2019-08-28 |
US20190066723A1 (en) | 2019-02-28 |
JP6604412B2 (ja) | 2019-11-13 |
CN106471581A (zh) | 2017-03-01 |
JP2020009526A (ja) | 2020-01-16 |
JPWO2015198514A1 (ja) | 2017-04-20 |
US20170162220A1 (en) | 2017-06-08 |
US10839848B2 (en) | 2020-11-17 |
US10204651B2 (en) | 2019-02-12 |
JP6766938B2 (ja) | 2020-10-14 |
CN106471581B (zh) | 2019-11-08 |
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