JP6909619B2 - Magnetic recording medium for high recording density and its recording / playback mechanism - Google Patents

Description

The present invention relates to a magnetic recording medium for high recording density having excellent electromagnetic conversion characteristics and running durability, and a recording / reproduction mechanism of the magnetic recording medium for high recording density.

The coating type magnetic recording medium in which a magnetic layer containing a magnetic powder and a binder is formed on a non-magnetic support has further improved the recording density with the transition from the analog method to the digital method. Is required. In particular, this demand is increasing year by year for high-density digital video tapes, computer backup tapes, and the like.

With such an improvement in recording density, the recording wavelength has been shortened, and in order to support this short-wavelength recording, the magnetic powder has been made into fine particles year by year, and currently, ferromagnetism with an average particle diameter of about 20 nm is being attempted. Hexagonal ferrite powder has been realized, and a magnetic recording medium using this magnetic powder has been put into practical use (for example, Patent Document 1).

Then, in order to further improve the recording density of the magnetic recording medium using the ferromagnetic hexagonal ferrite powder, it is necessary to further refine the ferromagnetic hexagonal ferrite powder. However, by further miniaturizing the ferromagnetic hexagonal ferrite powder, there is a problem that the particle volume of the magnetic powder becomes smaller and it becomes more susceptible to thermal fluctuation. Therefore, it is necessary to suppress thermal fluctuation by using a magnetic material having a high coercive force and a large anisotropic energy even if the particles are made into fine particles.

_{Under these circumstances, research on ε-Fe 2} O ₃ has been conducted in recent years as a new magnetic material for magnetic recording media, and ε has ferromagnetic properties even with an average particle diameter of 15 nm or less, preferably 10 nm or less. An _{iron oxide nanomagnetic particle powder composed of a single phase of −Fe 2} O ₃ has been proposed (for example, Patent Document 2). Further, a magnetic recording medium using ε-Fe ₂ O ₃ as a magnetic powder has also been proposed (for example, Patent Documents 3 and 4).

Prior art documents related to the present invention include Patent Document 5 relating to a layer thickness measuring method, Patent Document 6 relating to a method of forming a lubricant layer on the surface of a magnetic layer, and Patent Document 7 relating to a spacing measuring method. There is.

Japanese Unexamined Patent Publication No. 2015-91747 Japanese Unexamined Patent Publication No. 2014-224027 Japanese Unexamined Patent Publication No. 2014-149886 Japanese Unexamined Patent Publication No. 2015-82329 Japanese Unexamined Patent Publication No. 2008-128672 Japanese Unexamined Patent Publication No. 2014-157644 Japanese Unexamined Patent Publication No. 2012-43495

Along with the increase in recording density for increasing the capacity of such a magnetic recording medium, the increase in track density of the magnetic layer is progressing. However, there is a problem that the track width is reduced as the track density is increased, and as a result, the output characteristics are lowered and the electromagnetic conversion characteristics are also lowered.

Further, since ε-iron oxide can be made into fine particles having an average particle diameter of 15 nm or less while maintaining a high coercive force, the electromagnetic conversion characteristics can be improved, but when the magnetic material particles become fine particles, the strength of the magnetic layer decreases. Further, since the ε-iron oxide particles are usually spherical, the magnetic layer has a dense structure, and the lubricant contained in the undercoat layer is difficult to move to the outer surface of the magnetic layer, and as a result, the magnetic layer runs. There is a problem that durability is reduced.

The present invention has been made to solve such a problem, and uses ε-iron oxide particles as magnetic particles, and has electromagnetic conversion characteristics and running durability even when the track density is increased as the recording density is increased. Provide an excellent magnetic recording medium for high recording density.

The magnetic recording medium for high recording density of the present invention is a magnetic recording medium for high recording density including a non-magnetic support and a magnetic layer containing magnetic particles, and the square ratio of the magnetic layer in the thickness direction is is 0.65 or more, when measured spacing of the surface of the magnetic layer before and after cleaning the surface of the magnetic layer in n- hexane TSA (Tape spacing Analyzer), and the spacing S _a after washing S _a -S thickness T of the surface lubricant layer obtained from _B which is the difference between the spacing S _B before washing is 3nm or more 8nm or less.

The recording / reproduction mechanism of the high recording density magnetic recording medium of the present invention includes the high recording density magnetic recording medium of the present invention and the TMR head.

According to the magnetic recording medium for high recording density of the present invention, ε-iron oxide fine particles having a high coercive force are used as magnetic particles, and the track density is increased as the recording density is increased to increase the capacity. Even if the width is reduced, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability.

FIG. 1 is a schematic cross-sectional view showing an example of a magnetic recording medium for high recording density.

(Embodiment of Magnetic Recording Medium for High Recording Density)
An embodiment of the magnetic recording medium for high recording density of the present invention will be described.

The magnetic recording medium for high recording density of the present embodiment (hereinafter, also simply referred to as a magnetic recording medium) includes a non-magnetic support and a magnetic layer containing magnetic particles, and is rectangular in the thickness direction of the magnetic layer. The ratio is 0.65 or more. Also, the when the magnetic layer surface before and after washing with n- hexane spacing of the surface of the magnetic layer was measured with TSA (Tape Spacing Analyzer), pre-cleaning the spacing S _A after washing spacing S S _a -S thickness T of the surface lubricant layer obtained from _B which is the difference between _B is 3nm or more 8nm or less.

By setting the square ratio in the thickness direction of the magnetic layer to 0.65 or more, the resolution of recording magnetization is improved. Therefore, even if the track width is 1 μm or less, the magnetism has good electromagnetic conversion characteristics (SN characteristics). A recording medium can be provided. The square ratio is more preferably 0.75 or more.

Further, the magnetic recording medium of the present embodiment is excellent in electromagnetic conversion characteristics and running durability because the thickness T of the surface lubricant layer is set to 3 nm or more and 8 nm or less. The thickness T of the surface lubricant layer is more preferably 7 nm or more and 8 nm or less. As described above, the ε-iron oxide can be made into fine particles having an average particle diameter of 15 nm or less while maintaining a high coercive force. However, when the fine particles are formed, the strength of the magnetic layer decreases, and the ε-iron oxide particles Since is usually spherical, the magnetic layer has a dense structure, and it becomes difficult for the lubricant contained in the undercoat layer to move to the outer surface of the magnetic layer. As a result, there is a problem that the running durability of the magnetic layer is lowered. .. However, by setting the thickness T of the surface lubricant layer to 3 nm or more and 8 nm or less, both the electromagnetic conversion characteristics and the running durability can be improved.

The spacing S _A, but are not limited to S measurement method and control method thereof in the thickness T _B and a surface lubricant layer is particularly carried out, for example, by the method described in JP 2012-43495 (Patent Document 7) be able to.

The magnetic recording medium of the present embodiment has a tunnel-type magnetoresistive effect when the magnetization length of the signal recorded on the magnetic layer is 1 μm or less in the width direction of the magnetic layer. It is preferably reproduced by a mold head (TMR head). Even if the magnetization length is set to 1 μm or less in order to increase the track density of the magnetic layer, a high SN ratio can be obtained by reproducing with a highly sensitive TMR head.

The length of the magnetization can be measured, for example, as follows. That is, as a magnetic force microscope, "NanoScope III" (product name) manufactured by Digital Instruments Co., Ltd. is used, and the length of magnetization in the width direction of the magnetic layer on which the signal is recorded is measured by a frequency detection method. A probe having a cobalt alloy coat (tip radius of curvature: 25 to 40 nm, coercive force: about 400 [Oe], magnetic moment: about 1 × 10 ^-13 emu) is used as the measurement probe, and the scanning range is 5 μm square. The speed is 5 μm / sec.

The magnetic particles are preferably made of ε-iron oxide having an average particle diameter of 15 nm or less. Since the magnetic particles are made of ε-iron oxide and have a track width of 1 μm or less, the coercive force of the magnetic particles does not decrease even if the average particle diameter of the magnetic particles is 15 nm or less. The average particle size of the magnetic particles made of ε-iron oxide is more preferably 12 nm or less. The lower limit of the average particle size of the magnetic particles made of ε-iron oxide is usually about 8 nm. This is because ε-iron oxide having an average particle size of less than 8 nm is not easy to produce.

The above-mentioned ε-iron oxide is usually composed of spherical particles, but is not limited to spherical particles, and may be substantially spherical or ellipsoidal.

The coercive force of the magnetic layer in the thickness direction is preferably 3000 oersted [Oe] or more. This is because by setting the coercive force to 3000 Oersted [Oe] or more, a high reproduction output with little self-demagnetization loss can be obtained even in a short wavelength recording region in a high recording density.

Further, the spacing S _A after the washing is preferably at is 5nm or 12nm or less. When the spacing S _A is below 5 nm, the surface of the magnetic layer is too smooth, the contact area between the magnetic head and the magnetic layer is increased, the friction coefficient is increased, the durability of the magnetic layer decreases Tend. On the other hand, when the spacing S _A is greater than 12 nm, the distance between the magnetic head and the magnetic layer surface becomes too large, the recording and reproducing properties tend to decrease. The spacing S _A is more preferably equal to or less than 9nm than 11 nm.

The average thickness of the magnetic layer is preferably 30 nm or more and 200 nm or less. By setting the average thickness of the magnetic layer to 200 nm or less, the short wavelength recording characteristics can be improved, and by setting the average thickness of the magnetic layer to 30 nm or more, the servo signal can be recorded. When ε-iron oxide particles are used as the magnetic particles of the present embodiment, the saturation magnetization amount of the ε-iron oxide particles is 1/2 to 1/3 of the saturation magnetization amount of the conventional ferromagnetic hexagonal ferrite particles. Since it is small, when recording a servo signal having a long recording wavelength, the average thickness of the magnetic layer needs to be 30 nm or more.

When the servo signal is not recorded on the magnetic layer, the average thickness of the magnetic layer is preferably 10 nm or more and 50 nm or less. Even if the average thickness of the magnetic layer is 10 nm or more and 50 nm or less, data signals can be recorded and reproduced by using a highly sensitive magnetic head such as a TMR head.

The method for measuring the average thickness of the magnetic layer is not particularly limited, but it can be measured, for example, by the method described in JP-A-2008-128672 (Patent Document 5).

Next, the magnetic recording medium of this embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the magnetic recording medium of the present embodiment.

In FIG. 1, the magnetic recording medium 10 of the present embodiment has a non-magnetic support 11, an undercoat layer 12 formed on one main surface (here, an upper surface) of the non-magnetic support 11, and an undercoat layer. A magnetic tape having a magnetic layer 13 formed on a main surface (here, an upper surface) opposite to the non-magnetic support 11 side of the 12 and a surface lubricant layer 14 formed on the outer surface of the magnetic layer 13. Is. Further, a back coat layer 15 is formed on the main surface (here, the lower surface) on the side where the undercoat layer 12 of the non-magnetic support 11 is not formed.

<Surface lubricant layer>
The surface lubricant layer 14 is a lubricant layer formed on the outer surface of the magnetic layer 13, and as described above, the surface spacing of the magnetic layer 13 before and after cleaning the surface of the magnetic layer 13 with n-hexane is performed. when measured at TSA (Tape spacing Analyzer), S a -S thickness T of the surface lubricant layer 14 obtained from _B which is the difference between the spacing S _a after washing the spacing S _B before cleaning, It is set to 3 nm or more and 8 nm or less.

The method of controlling the value of the thickness T of the surface lubricant layer 14 within the above range is not particularly limited, but the following method is preferably exemplified.

(A) A method of transferring and applying a lubricant to the outer surface of the magnetic layer by sliding a strip-shaped coating cloth impregnated with the lubricant on the outer surface of the magnetic layer while running.

More specifically, as described in Japanese Patent Application Laid-Open No. 2014-157644 (Patent Document 6), a strip-shaped coating cloth impregnated with a lubricant is slidably contacted with the outer surface of the magnetic layer while running. When the lubricant is transferred to the outer surface of the magnetic layer and applied, the amount of the lubricant on the outer surface of the magnetic layer increases and T becomes large. By transferring and applying the lubricant to the outer surface of the magnetic layer (lubrication treatment) in this way, the size of T can be finely controlled. Further, the amount of lubricant on the outer surface of the magnetic layer can be controlled by increasing or decreasing the number of times of the lubrication treatment. As the lubricant used in this method, for example, a fatty acid ester of a polyol, a silicone oil, or the like can be used. On the other hand, in the conventional method of applying a lubricant, the size of T cannot be finely controlled because the lubricant is directly applied (top coat) to the outer surface of the magnetic layer.

Further, in the magnetic recording medium of the present embodiment, when spherical iron oxide particles having an average particle diameter of 15 nm or less are used as the magnetic material particles, the magnetic layer has a dense structure and is included in the magnetic layer and the undercoat layer. Although it is difficult to move the existing lubricant to the outer surface of the magnetic layer, by transferring and applying the lubricant to the outer surface of the magnetic layer as described above, the lubricant can be reliably supplied to the outer surface of the magnetic layer. The size can be easily controlled.

(B) A method of forming a magnetic layer and then polishing the surface thereof with a rotor, a blade, a lapping tape, a polishing wheel, or the like.

After forming the magnetic layer, the lubricant existing on the surface of the magnetic layer can be removed by polishing with a rotor, a blade, a lapping tape, a polishing wheel, or the like, so that T becomes small. Specifically, the size of T can be controlled by appropriately changing the pressure, contact angle, relative speed, etc. when the rotor, blade, lapping tape, polishing wheel, etc. come into contact with the magnetic layer.

(C) Calendar conditions of the magnetic layer, such as a method of controlling pressure and temperature.

More specifically, the magnitude of T can be controlled by changing the calendar conditions in the range of linear pressure 196 to 294 kN / m and temperature 70 to 120 ° C. When the linear pressure and temperature under the calendar conditions are increased, the lubricant contained in the magnetic layer and the undercoat layer is removed by the pressure of the calendar even when the magnetic particles contained in the magnetic layer are densely packed. T increases because it moves toward the surface layer.

In the present embodiment, the magnetic recording medium in which the value of T is controlled within the above range can be produced by using the above methods alone and preferably by using some of these methods in combination. In particular, it is preferable to combine all of the transfer coating of the lubricant (a), the polishing treatment of the magnetic layer (b), and the calendar conditions of (c).

As the lubricant used for the surface lubricant layer 14, the same lubricant as the lubricant used for the magnetic layer 13 described later can be used.

<Magnetic layer>
The magnetic layer 13 contains magnetic particles and a binder. As the magnetic particles, it is preferable to use ε-iron oxide particles having an average particle diameter of 15 nm or less.

The ε-iron oxide particles are preferably formed in a single phase represented by the general composition formula ε-Fe ₂ O _3. This is because the coercive force of the magnetic layer decreases when α-iron oxide or γ-iron oxide is mixed. However, α-iron oxide and γ-iron oxide may be contained as impurities as long as the coercive force of the magnetic layer does not decrease.

Further, in the present embodiment, ε-iron oxide and other γ-iron oxide and α-iron oxide can be distinguished by analyzing their crystal structures by X-ray diffraction.

The coercive force of the ε-iron oxide particles is preferably 3000 oersted [Oe] or more. As a result, the coercive force in the thickness direction of the magnetic layer can be set to 3000 oersted [Oe] or more. Further, if impurities are contained in the ε-iron oxide particles represented by the general composition formula ε-Fe ₂ O ₃ , the coercive force of the ε-iron oxide particles is lowered, so that it is preferable that the ε-iron oxide particles do not contain impurities. However, in the above-mentioned ε-iron oxide particles, a part of Fe sites in the crystal is replaced with a trivalent metal element such as aluminum (Al), gallium (Ga), rhodium (Rh), and indium (In). , Coercive force can be controlled. Therefore, the ε-iron oxide particles may contain a metal element other than iron as an impurity as long as the coercive force can be maintained at 3000 oersted [Oe] or more.

As described above, the average particle size of the ε-iron oxide particles contained in the magnetic layer is preferably set to 8 nm or more and 15 nm or less. When the average particle size of the ε-iron oxide particles exceeds 15 nm, the noise of the magnetic recording medium increases, especially in short wavelength recording, so that high electromagnetic conversion characteristics tend not to be obtained.

In the present embodiment, the average particle size of the magnetic particles contained in the magnetic layer is determined by using a scanning electron microscope (SEM) “S-4800” manufactured by Hitachi, Ltd. on the surface of the magnetic layer, accelerating voltage: 2 kV, magnification: Observation conditions: 10000 times (10 k times), observation conditions: From a photograph taken with a U-LA100, 100 magnetic particles in one visual field are used, and the determination is made as follows.

When the particles are needle-shaped, the average major axis diameter of 100 particles is used. When the particles are plate-shaped, the average maximum plate diameter of 100 particles is used. The ratio of the major axis length to the minor axis length of the particles. In the case of a spherical or elliptical shape having a value of 1 to 3.5, the average maximum transfer diameter of 100 particles is calculated and determined.

As the binder contained in the magnetic layer 13, conventionally known thermoplastic resins, thermosetting resins and the like can be used. Specific examples of the thermoplastic resin include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, and vinyl chloride. Examples thereof include a vinyl chloride-maleic anhydride copolymer resin, a vinyl chloride-hydroxyl chloride-containing alkyl acrylate copolymer resin, and a polyester polyurethane resin. Specific examples of the thermosetting resin include phenol-based resins, epoxy-based resins, polyurethane-based resins, urea-based resins, melamine-based resins, and alkyd-based resins.

The content of the binder in the magnetic layer 13 is preferably 7 to 50 parts by mass, and more preferably 10 to 35 parts by mass with respect to 100 parts by mass of the magnetic particles.

Further, it is preferable to use a thermosetting cross-linking agent that binds to a functional group or the like contained in the binder to form a cross-linked structure together with the above-mentioned binder. Specific examples of the cross-linking agent include isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate; reaction products of isocyanate compounds and compounds having a plurality of hydroxyl groups such as trimethylolpropane; isocyanate compounds. Various polyisocyanates such as the condensation product of. The content of the cross-linking agent is preferably 10 to 50 parts by mass with respect to 100 parts by mass of the binder.

The magnetic layer 13 may further contain additives such as an abrasive, a lubricant, and a dispersant as long as it contains the above-mentioned magnetic particles and a binder. In particular, from the viewpoint of durability, abrasives and lubricants are preferably used.

Specific examples of the abrasive include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, and the like. Examples thereof include silicon dioxide and boron nitride, and among these, an abrasive having a Mohs hardness of 6 or more is more preferable. These may be used alone or in plurality. The average particle size of the above-mentioned abrasive is preferably 10 to 200 nm, although it depends on the type of the abrasive used. The content of the abrasive is preferably 5 to 20 parts by mass, and more preferably 8 to 18 parts by mass with respect to 100 parts by mass of the magnetic particles.

Examples of the lubricant include fatty acids, fatty acid esters, and fatty acid amides. The fatty acid may be a linear type, a branched type, or a cis-trans isomer, but a linear type having excellent lubrication performance is preferable. Specific examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid and the like. Specific examples of the fatty acid ester include n-butyl oleate, hexyl oleate, n-octyl oleate, 2-ethylhexyl oleate, oleyl oleate, n-butyl laurate, heptyl laurate, and myristin. Examples thereof include n-butyl acid, n-butoxyethyl oleate, trimethylolpropane trioleate, n-butyl stearate, s-butyl stearate, isoamyl stearate, and butyl cellosolve stearate. Specific examples of the fatty acid amide include palmitate amide and stearic acid amide. These lubricants may be used alone or in combination of two or more.

Among these, it is preferable to use a fatty acid ester and a fatty acid amide in combination. In particular, 0.2 to 3 parts by mass of fatty acid ester and 0.5 to 5 parts by mass of fatty acid amide should be used with respect to 100 parts by mass of the total amount of solids such as magnetic particles and abrasives in the magnetic layer 13. Is preferable. If the content of the fatty acid ester is less than 0.2 parts by mass, the effect of reducing the friction coefficient is small, and if it exceeds 3.0 parts by mass, side effects such as the magnetic layer 13 sticking to the head may occur. Is. Further, if the content of the fatty acid amide is less than 0.5 parts by mass, the effect of preventing seizure caused by the mutual contact between the magnetic head and the magnetic layer 13 becomes small, and it exceeds 5 parts by mass. This is because there is a risk that the fatty acid amide will bleed out.

Further, the magnetic layer 13 may contain carbon black for the purpose of improving conductivity and surface lubricity. Specific examples of such carbon black include acetylene black, furnace black, and thermal black. The average particle size of carbon black is preferably 0.01 to 0.1 μm. When the average particle size is 0.01 μm or more, the magnetic layer 13 in which carbon black is well dispersed can be formed. On the other hand, when the average particle size is 0.1 μm or less, the magnetic layer 13 having excellent surface smoothness can be formed. Further, if necessary, two or more types of carbon black having different average particle diameters may be used. The content of the carbon black is preferably 0.2 to 5 parts by mass, and more preferably 0.5 to 4 parts by mass with respect to 100 parts by mass of the magnetic particles.

The surface roughness of the magnetic layer 13 is preferably less than 2.0 nm as the center line average roughness Ra defined in Japanese Industrial Standards (JIS) B0601. The higher the surface smoothness of the magnetic layer 13, the higher the output can be obtained. However, if the surface of the magnetic layer 13 is too smooth, the friction coefficient becomes high and the running stability is lowered. Therefore, Ra is preferably 1.0 nm or more.

<Undercoat layer>
Under the magnetic layer 13, it is preferable to provide an undercoat layer 12 having a function of holding a lubricant and a function of buffering external stress (for example, pressing by a magnetic head). Further, since the strength of the magnetic recording medium 10 is increased by providing the undercoat layer 12, the calendar treatment can be performed when the magnetic recording medium 10 is formed, and the filling property of the magnetic layer 13 can be improved. The undercoat layer 12 contains a non-magnetic powder, a binder, and a lubricant.

Examples of the non-magnetic powder contained in the undercoat layer 12 include carbon black, titanium oxide, iron oxide, aluminum oxide and the like. Usually, carbon black is used alone, or carbon black and titanium oxide, iron oxide and the like are used. , Aluminum oxide and other non-magnetic powders are mixed and used. In order to form a coating film having less uneven thickness and to form a smooth undercoat layer 12, it is preferable to use a non-magnetic powder having a sharp particle size distribution. The average particle size of the non-magnetic powder is, for example, preferably 10 to 1000 nm, preferably 10 to 500 nm, from the viewpoint of ensuring the uniformity, surface smoothness, rigidity, and conductivity of the undercoat layer 12. Is more preferable.

The particle shape of the non-magnetic powder contained in the undercoat layer 12 may be spherical, plate-shaped, needle-shaped, or spindle-shaped. The average particle size of the needle-shaped or spindle-shaped non-magnetic powder is preferably 10 to 300 nm in terms of average major axis diameter, and preferably 5 to 200 nm in terms of average minor axis diameter. The average particle size of the spherical non-magnetic powder is preferably 5 to 200 nm, more preferably 5 to 100 nm. The average particle size of the plate-shaped non-magnetic powder is preferably 10 to 200 nm, which is the largest plate diameter.

As the binder and lubricant contained in the undercoat layer 12, the same binder and lubricant as those used in the magnetic layer 13 described above can be used. The content of the binder is preferably 7 to 50 parts by mass, and more preferably 10 to 35 parts by mass with respect to 100 parts by mass of the non-magnetic powder. The content of the lubricant is preferably 2 to 6 parts by mass, and more preferably 2.5 to 4 parts by mass with respect to 100 parts by mass of the non-magnetic powder.

When ε-iron oxide particles are used as the magnetic particles of the magnetic layer 13 described above, the saturation magnetization amount of the ε-iron oxide particles is 1/2 to 1/1 of the saturation magnetization amount of the conventional ferromagnetic hexagonal ferrite particles. Since it is as small as 3, when recording a servo signal having a long recording wavelength, the undercoat layer 12 contains magnetic particles. As the magnetic material particles contained in the undercoat layer 12, for example, needle-shaped metallic iron-based magnetic particles, plate-shaped hexagonal ferrite magnetic particles, granular iron nitride-based magnetic particles, and the like can be used.

The thickness of the undercoat layer 12 is preferably 0.1 to 3 μm, more preferably 0.3 to 2 μm. Within this thickness range, the lubricant holding function and the external stress buffering function can be maintained without unnecessarily increasing the total thickness of the magnetic recording medium 10.

<Non-magnetic support>
As the non-magnetic support 11, a conventional non-magnetic support for a magnetic recording medium can be used. Specific examples thereof include films made of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulphon, and aramid.

The thickness of the non-magnetic support 11 varies depending on the application, but is preferably 1.5 to 11 μm, more preferably 2 to 7 μm. When the thickness of the non-magnetic support 11 is 1.5 μm or more, the film forming property is improved and high strength can be obtained. On the other hand, if the thickness of the non-magnetic support 11 is 11 μm or less, the total thickness does not become unnecessarily thick, and for example, in the case of magnetic tape, the recording capacity per roll can be increased.

The Young's modulus in the longitudinal direction of the non-magnetic support 11 is preferably 5.8 GPa or more, and more preferably 7.1 GPa or more. When the Young's modulus in the longitudinal direction of the non-magnetic support 11 is 5.8 GPa or more, the runnability can be improved. Further, in the magnetic recording medium used in the helical scan method, the ratio (MD / TD) of the Young's modulus (MD) in the longitudinal direction to the Young's modulus (TD) in the width direction is preferably 0.6 to 0.8. It is more preferably 0.65 to 0.75, and even more preferably 0.7. Within the range of the above ratio, it is possible to suppress the variation (flatness) of the output between the entry side and the exit side of the track of the magnetic head. In the magnetic recording medium used in the linear recording method, the ratio (MD / TD) of the Young's modulus (MD) in the longitudinal direction to the Young's modulus (TD) in the width direction is preferably 0.7 to 1.3.

<Back coat layer>
It is preferable to provide a back coat layer 15 on the main surface (here, the lower surface) on the side opposite to the main surface on which the undercoat layer 12 of the non-magnetic support 11 is formed, for the purpose of improving runnability and the like. .. The thickness of the backcoat layer 15 is preferably 0.2 to 0.8 μm, more preferably 0.3 to 0.8 μm. If the thickness of the back coat layer 15 is too thin, the effect of improving the running performance becomes insufficient, and if it is too thick, the total thickness of the magnetic recording medium 10 becomes thick, and for example, the recording capacity per winding of the magnetic tape becomes small.

The backcoat layer 15 preferably contains carbon black such as acetylene black, furnace black, and thermal black. Usually, small particle size carbon black and large particle size carbon black, which have relatively different particle sizes, are used in combination. The reason for using them together is that the effect of improving the running performance is increased.

Further, the backcoat layer 15 contains a binder, and as the binder, the same binder as that used for the magnetic layer 13 and the undercoat layer 12 can be used. Among these, in order to reduce the friction coefficient and improve the running performance of the magnetic head, it is preferable to use a cellulosic resin and a polyurethane resin in combination.

The backcoat layer 15 preferably further contains iron oxide, alumina, and the like for the purpose of improving the strength.

Next, a method of manufacturing the magnetic recording medium of the present embodiment will be described. In the method for producing a magnetic recording medium of the present embodiment, for example, each layer-forming component and a solvent are mixed to prepare a magnetic layer-forming paint, an undercoat layer-forming paint, and a backcoat layer-forming paint, respectively. An undercoat layer-forming paint is applied to one side of a magnetic support and dried to form an undercoat layer, and then a magnetic layer-forming paint is applied onto the undercoat layer and dried. A layer is formed, and a backcoat layer-forming paint is applied to the other side of the non-magnetic support and dried to form a backcoat layer. After that, the whole is calendered, and finally, a lubricant is applied to the outer surface of the magnetic layer to obtain a magnetic recording medium.

Further, instead of the above-mentioned sequential layer coating method, after the undercoat layer forming paint is applied to one side of the non-magnetic support, before the undercoat layer forming paint dries, it is placed on the undercoat layer forming paint. It is also possible to adopt a simultaneous multi-layer coating method in which a paint for forming a magnetic layer is applied and dried.

The coating method of each of the above paints is not particularly limited, and for example, gravure coating, roll coating, blade coating, extrusion coating and the like can be used.

In the above-mentioned magnetic layer, as a method of setting the thickness T of the surface lubricant layer to 3 nm or more and 8 nm or less, the above-mentioned transfer coating of the lubricant of (a) and polishing treatment of the magnetic layer of (b) are performed. There is a setting of the calendar condition of (c), and these methods can be carried out independently, or a plurality of these methods can be carried out in combination. It is preferable to combine all the methods of c).

(Recording / playback mechanism of magnetic recording medium for high recording density)
Next, an embodiment of the recording / reproducing mechanism of the magnetic recording medium for high recording density of the present invention will be described.

The recording / reproduction mechanism of the high recording density magnetic recording medium of the present embodiment includes the high recording density magnetic recording medium of the above embodiment of the present invention and a TMR head. As described above, the magnetic recording medium for high recording density can improve the electromagnetic conversion characteristics, but by combining with a more sensitive TMR head, better electromagnetic conversion characteristics (SN characteristics) can be obtained.

Further, the TMR head has high sensitivity, and a high SN ratio can be obtained by combining it with fine particles of ε-iron oxide. However, since the TMR head has high sensitivity, when the spacing with the magnetic layer becomes small, the TMR Due to heat dissipation due to contact between the head and the magnetic layer protrusions, thermal asperity noise (cooling noise) generated due to the momentary cooling of the TMR element is likely to occur. As described above, the magnetic layer of the magnetic recording medium is likely to be generated. Since the thickness T of the surface lubricant layer is set to 3 nm or more and 8 nm or less, thermal asperity noise can be reduced. In particular, by setting the thickness T of the surface lubricant layer to 7 nm or more and 8 nm or less, thermal asperity noise can be further reduced.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to the following Examples. Further, in the following description, the term "part" means "part by mass".

(Example 1)
[Preparation of magnetic paint]
The magnetic paint component (1) shown in Table 1 was mixed at high speed with a high-speed stirring mixer to prepare a mixture. Next, the obtained mixture was dispersed in a sand mill for 20 minutes, then the magnetic coating component (2) shown in Table 2 was added and dispersed for 230 minutes, and then the magnetic coating component (3) shown in Table 3 was added. Prepared the dispersion. Next, the obtained dispersion liquid and the magnetic paint component (4) shown in Table 4 were stirred using a dispa, and this was filtered through a filter to prepare a magnetic paint.

[Preparation of undercoat paint]
A kneaded product was prepared by kneading the undercoat paint component (1) shown in Table 5 with a batch kneader. Next, the obtained kneaded product and the undercoat coating component (2) shown in Table 6 were stirred using a dispa to prepare a mixed solution. Next, the obtained mixed liquid was dispersed in a sand mill for 100 minutes to prepare a dispersion liquid, and then this dispersion liquid and the undercoat paint component (3) shown in Table 7 were stirred using a dispa, and this was filtered. The undercoat paint was prepared by filtering with.

[Preparation of paint for back coat layer]
A mixed solution containing the coating components for the back coat layer shown in Table 8 was dispersed in a sand mill for 50 minutes to prepare a dispersion. Fifteen parts of polyisocyanate was added to the obtained dispersion, and the mixture was stirred and filtered through a filter to prepare a coating material for a backcoat layer.

[Preparation of magnetic tape for evaluation]
The above-mentioned undercoat paint is applied onto a non-magnetic support (polyethylene naphthalate film, thickness: 5 μm) so that the thickness of the undercoat layer after the calendar treatment is 1.1 μm, and dried at 100 ° C. An undercoat layer was formed. Next, the magnetic paint is applied onto the undercoat layer at a coater tension of 4.5 N / inch using a die coater so that the thickness of the magnetic layer after the calendar treatment is 55 nm, and at 100 ° C. It was dried to form a magnetic layer. Then, a vertical alignment process was performed while applying an alignment magnetic field having a strength of 450 kA / m in the vertical direction using an NS counter magnet.

Next, the paint for the back coat layer is applied to the surface of the non-magnetic support opposite to the surface on which the undercoat layer and the magnetic layer are formed, and the thickness after the calendar treatment is 0.5 μm. And dried at 100 ° C. to form a backcoat layer.

After that, the raw fabric roll having the undercoat layer and the magnetic layer formed on the upper surface side of the non-magnetic support and the backcoat layer formed on the lower surface side was subjected to a temperature of 100 ° C. in a calendar device having a seven-stage metal roll. Calendar treatment was performed at a linear pressure of 300 kg / cm.

Next, the obtained raw fabric roll was cured at 60 ° C. for 48 hours to prepare a magnetic sheet. This magnetic sheet was cut to a width of 1/2 inch to produce a magnetic tape.

Next, the prepared magnetic tape was surface-treated. In this surface treatment, a super steel rotor having a spiral groove is rotated and slid on a magnetic tape to treat the surface of the magnetic layer of the magnetic tape.

Specifically, using a super steel rotor with a diameter of 30 mm and a groove width of 2 mm, the rotation speed of the super steel rotor is 3000 rpm, the traveling speed of the magnetic tape is 5 m / sec, the winding tension of the magnetic tape is 120 g, and the unwinding tension is set. The surface of the magnetic tape was treated with 80 g and the winding angle of the magnetic tape around the super steel rotor set to 120 °.

Further, the magnetic tape subjected to the above surface treatment was lubricated. In this lubrication treatment, as described above, the lubricant is transferred to the outer surface of the magnetic layer and applied by sliding the strip-shaped coating cloth impregnated with the lubricant on the outer surface of the magnetic layer while running. It is a process.

Specifically, the coating cloth "TECHNO WIPER CRN500" (product name) manufactured by Technos Co., Ltd. is used as the coating cloth, and the lubricant "Unistar H-" manufactured by Nichiyu Co., Ltd. is used as the lubricant. Using a mixed solution of 10 parts by mass of 208BRS "and 90 parts by mass of hexane as a solvent for adjusting the viscosity, the coating cloth was impregnated with the mixed solution and lubricated as follows.

The traveling speed of the magnetic tape during the lubrication treatment was 5 m / sec, the traveling tension was 1 N, the traveling speed of the coated cloth was 100 mm / min, and the coated cloth was moved in the direction opposite to the traveling direction of the magnetic tape. The winding angle of the magnetic tape around the sliding contact guide pin around which the coating cloth was wound was 30 °, and the diameter of the sliding contact guide pin was 25 mm. In this example, the above lubrication treatment was performed twice to prepare a magnetic tape for evaluation of Example 1.

(Example 2)
An evaluation magnetic tape of Example 2 was produced in the same manner as in Example 1 except that the magnetic tape after cutting was lubricated four times.

(Example 3)
_{Example 1 and Example 1 except that the average particle size of the ε-Fe 2} O ₃ magnetic powder of the magnetic coating component (1) shown in Table 1 was changed to 12 nm, and the magnetic tape after cutting was further lubricated three times. Similarly, the evaluation magnetic tape of Example 3 was produced.

(Example 4)
Example 4 in the same manner as in Example 1 except that the strength of the alignment magnetic field of the vertical alignment treatment after the formation of the magnetic layer was increased to 550 A / m and the magnetic tape after cutting was further lubricated three times. A magnetic tape for evaluation was prepared.

(Example 5)
The evaluation magnetic tape of Example 5 was used in the same manner as in Example 1 except that the coercive force _{of the ε-Fe 2} O ₃ magnetic powder of the magnetic paint component (1) shown in Table 1 was changed to 2800 [Oe]. Made.

(Example 6)
Example 1 except that the produced raw fabric roll was calendar-treated at a temperature of 90 ° C. and a linear pressure of 300 kg / cm in a calendar device having a 7-stage metal roll, and the magnetic tape after cutting was lubricated three times. In the same manner as in the above, the evaluation magnetic tape of Example 6 was produced.

(Example 7)
_{Example 1 and Example 1 except that the average particle size of the ε-Fe 2} O ₃ magnetic powder of the magnetic coating component (1) shown in Table 1 was changed to 16 nm, and the magnetic tape after cutting was further lubricated three times. Similarly, the evaluation magnetic tape of Example 7 was produced.

(Example 8)
The evaluation magnetic tape of Example 8 was produced in the same manner as in Example 1 except that the surface treatment was not performed on the cut magnetic tape and the lubrication treatment was performed four times.

(Comparative Example 1)
Comparative Example 1 in the same manner as in Example 1 except that the strength of the alignment magnetic field of the vertical alignment treatment after the formation of the magnetic layer was reduced to 350 A / m and the magnetic tape after cutting was further lubricated three times. A magnetic tape for evaluation was prepared.

(Comparative Example 2)
The produced raw fabric roll is calendar-treated at a temperature of 110 ° C. and a linear pressure of 300 kg / cm in a calendar device having a 7-stage metal roll, and the magnetic tape after cutting is not surface-treated and lubricated once. A magnetic tape for evaluation of Comparative Example 2 was produced in the same manner as in Example 1 except for the above.

(Comparative Example 3)
The produced raw fabric roll is calendar-treated at a temperature of 90 ° C. and a linear pressure of 300 kg / cm in a calendar device having a 7-stage metal roll, and the magnetic tape after cutting is not surface-treated and lubricated 5 times. A magnetic tape for evaluation of Comparative Example 3 was produced in the same manner as in Example 1 except for the above.

(Comparative Example 4)
The evaluation magnetic tape of Comparative Example 4 was produced in the same manner as in Example 1 except that the surface treatment was not performed on the cut magnetic tape and the lubrication treatment was performed once.

Next, the following characteristics were measured using the prepared magnetic tape for evaluation.

<Square ratio and coercive force of magnetic layer>
The hysteresis curve of the evaluation magnetic tape was obtained using a vibrating sample magnetometer "VSM-P7 type" (product name) manufactured by Toei Kogyo Co., Ltd. From the hysteresis curve, the square ratio and coercive force in the thickness direction of the magnetic layer were obtained. Specifically, the evaluation magnetic tape is cut into a circle with a diameter of 8 mm to obtain a cut sample, and 20 pieces of the cut sample are laminated with the thickness direction of the magnetic tape aligned with the application direction of the external magnetic field to form a measurement sample. did. As the plot mode of the data from the vibrating sample magnetometer, the applied magnetic field was set to -16 kOe to 16 kOe, the time constant TC was set to 0.03 sec, the drawing step was set to 6 bits, and the weight time was set to 0.3 sec.

<Thickness of spacing and surface lubricant layer>
Using Micro Physics Co. TSA (Tape Spacing Analyzer), and the spacing S _A after cleaning the surface of the magnetic layer in n- hexane, and a spacing S _B before cleaning was measured, S _A -S _B The thickness T of the surface lubricant layer was obtained from the above.

Specifically, the pressure for pressing the magnetic layer on a glass plate with urethane hemisphere was ^{0.5atm (5.05 × 10 4 N /} m). In this state, white light is emitted from the stroboscope through a glass plate onto a certain region (2400,000 to 280000 μm ² ) of the surface of the evaluation magnetic tape on the magnetic layer side, and the reflected light from the region is reflected by the IF filter (633 nm) and the IF filter. By receiving light with a CCD through (546 nm), an interference fringe image generated by the unevenness of this region was obtained.

Next, this image is divided into 66000 points, the distance from the glass plate at each point to the surface of the magnetic layer is obtained, and this is used as a histogram (frequency distribution curve), which is further processed into a smooth curve by low-pass filter (LPF) processing. The distance from the glass plate at the peak position to the surface of the magnetic layer was defined as the spacing.

The optical constants (phase, reflectance) of the magnetic layer surface used in the above spacing calculation were measured using a reflection spectroscopic film thickness meter "FE-3000" (product name) manufactured by Otsuka Electronics Co., Ltd., and the wavelength was measured. A value near 546 nm was used.

Cleaning with n-hexane was performed by immersing the evaluation magnetic tape in n-hexane and ultrasonically cleaning at room temperature for 30 minutes.

<Output characteristics>
Using a linear tape electromagnetic conversion characteristic measuring device manufactured by modifying the LTO drive, an inductive / GMR composite magnetic head with a write track width of 5 μm and a read track width of 2.3 μm was attached to the tape speed of 1.5 m /. In sec, a signal having a recording wavelength of 200 nm (line recording density of G7 × 1.05 times) was recorded on an evaluation magnetic tape and evaluated.

This device is a traveling system in which two magnetic heads can be attached, and two of the above magnetic heads are attached. The magnetic head is mounted on a precision piezo stage (movement resolution 10 nm) that can move in the track width direction. The magnetic head on the upstream side records signals, and the magnetic head on the downstream side performs AC erasure in one run, upstream. A signal having a magnetization width of 0.8 μm was recorded on the evaluation magnetic tape by offsetting the magnetic head on the side and the magnetic head on the downstream side by 0.8 μm in the track width direction.

Next, the evaluation magnetic tape was run again to reproduce the signal, and after amplifying the reproduced signal with a commercially available Read amplifier for MR head, a spectrum analyzer "N9020A" manufactured by Keysight Technology (former Agilent Technologies) was used. Using (product name), the fundamental wave component output (S) of the signal and the integrated noise (N) up to twice the frequency were measured.

<Coefficient of friction>
In order to evaluate the repeated running durability in an actual drive, the friction coefficient of the magnetic layer of the evaluation magnetic tape was repeatedly measured up to 800 passes using a stainless steel round bar. When this friction coefficient becomes large, running defects are likely to occur due to tape sliding, and repeated running durability deteriorates.

Specifically, a stainless steel round bar having a diameter of 6 mm is wrapped with the magnetic layer side of the evaluation magnetic tape at 90 °, and a load of 63.36 g is applied to the tip of the evaluation magnetic tape at 1200 mm / min. After sliding 70 mm at a speed, the load during sliding on the 11th and 800th passes was detected by the load cell and used as the measured load, and the friction coefficient was calculated by the following formula.
Friction coefficient = In [Measured load (g) /63.36 (g)] /0.5π

<Thermal asperity noise>
Using the linear tape electromagnetic conversion characteristic measuring device produced in the above-mentioned measurement of output characteristics, a TMR head with a track width of 0.2 μm is attached, the tape speed is 1.5 m / sec, and the recording wavelength is 200 nm (G7 × 1.05). A signal of double line recording density) was recorded on an evaluation magnetic tape, and the number of thermal asperity noises at a tape length of 500 m was measured.

The above evaluation results are shown in Tables 9 and 10.

From Table 10, in Examples 1 to 8 according to the present invention, the output characteristics are good, the change in the friction coefficient after 800 passes is small, the durability is good, the thermal asperity noise is small, and good error characteristics are obtained. You can see that it has been obtained. That is, it can be seen that the present invention can provide a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability.

In particular, in Examples 2 and 8 in which the thickness of the surface lubricant layer of the magnetic layer is 7 nm or more and 8 nm or less, the thermal asperity noise can be set to an extremely small level of 5 or less.

On the other hand, in Comparative Example 1 in which the square ratio was less than 0.65, the magnetization transition width became large and the output characteristics deteriorated probably because interference between waveforms occurred. Raising the temperature of the calendering, in Comparative Example 2 was not performed only once lubrication process, the thickness of the surface lubricant layer of the magnetic layer below the 3 nm, the spacing S _A becomes small as 9 nm, the magnetic layer Probably because the surface became extremely smooth, the change in friction coefficient after 800 passes was large and the durability was inferior, and the thermal asperity noise was also large, and the error characteristics were also inferior. In Comparative Example 3 the thickness of the surface lubricant layer of the magnetic layer by performing lubricated five times exceeds the 8 nm, or for the spacing S _A is increased, the output characteristic is lowered. In Comparative Example 4, in which the temperature of the calendar treatment was lower than that of Comparative Example 2 and the lubrication treatment was performed only once as in Comparative Example 2, the thickness of the surface lubricant layer of the magnetic layer was less than 3 nm, so 800. Although the increase in the friction coefficient after the pass was slightly lower than that in Comparative Example 2, there was a lot of thermal asperity noise and the error characteristics were inferior.

The magnetic recording medium for high recording density of the present invention can be used as a magnetic recording medium having excellent electromagnetic conversion characteristics and running durability.

10 Magnetic recording medium (magnetic tape)
11 Non-magnetic support 12 Undercoat layer 13 Magnetic layer 14 Surface lubricant layer 15 Backcoat layer

Claims (8)

A magnetic recording medium for high recording density including a non-magnetic support and a magnetic layer containing magnetic particles.
The square ratio of the magnetic layer in the thickness direction is 0.65 or more.
When the spacing on the surface of the magnetic layer before and after washing the surface of the magnetic layer with n-hexane was measured by TSA (Tape Spacing Analyzer), the spacing S _A after washing and the spacing S _{B before washing} S _a -S thickness T of the surface lubricant layer obtained from _B, high recording density magnetic recording medium, characterized in that at 7 nm or more 8nm or less a difference. The high recording density according to claim 1, which is reproduced by the TMR head when the magnetization length of the signal recorded on the magnetic layer is 1 μm or less in the width direction of the magnetic layer. Magnetic recording medium for. The magnetic recording medium for high recording density according to claim 1 or 2 , wherein the magnetic particles are made of ε-iron oxide having an average particle diameter of 15 nm or less. The magnetic recording medium for high recording density according to claim 3 , wherein the ε-iron oxide is composed of spherical particles. The magnetic recording medium for high recording density according to any one of claims 1 to 4 , wherein the coercive force in the thickness direction of the magnetic layer is 3000 oersted [Oe] or more. It said spacing S _A after cleaning, high recording density magnetic recording medium according to any one of claims 1 to 5, in 5nm or 12nm or less. The magnetic recording medium for high recording density according to any one of claims 1 to 6 , wherein the average thickness of the magnetic layer is 30 nm or more and 200 nm or less. A recording / reproduction mechanism for a magnetic recording medium for high recording density, which comprises the magnetic recording medium for high recording density according to any one of claims 1 to 7 and a TMR head.

Images