JP6005500B2 - Method for measuring magnetic recording medium and method for manufacturing magnetic recording medium - Google Patents

Description

  The present application relates to a measurement method and a manufacturing method of a magnetic recording medium, and in particular, an interface between a lower nonmagnetic layer and an upper magnetic layer of a magnetic recording medium in which a lower nonmagnetic layer and an upper magnetic layer are stacked on a support. The present invention relates to a measurement method capable of grasping the state of the magnetic recording medium, and a method for manufacturing a magnetic recording medium for determining pass / fail based on a measurement result obtained by the measurement method.

  Magnetic tape as one of magnetic recording media has various uses such as audio tape, video tape, and computer tape. In recent years, a magnetic tape is often used as a recording medium for backing up hard disk data as a data backup tape.

  In the field of data backup tape, as the capacity of a hard disk to be backed up increases, the capacity of magnetic tape is increasing, such as a product with a storage capacity of 800 GB or more per volume of magnetic tape is commercialized. . As a method for increasing the capacity of a magnetic tape, a perpendicular recording method in which the magnetization direction is the thickness direction of the magnetic tape has been proposed.

  Conventionally, a so-called coating type magnetic tape in which a magnetic layer is manufactured by applying a magnetic coating material in which magnetic powder is dispersed in a binder onto a flexible support is used as a computer tape. . In order to increase the capacity and density of coated magnetic tapes, it is necessary to reduce the thickness of the magnetic layer more than before. Currently, magnetic tapes with a magnetic layer thickness of 300 nm or less are also available. Are known. Such a thin magnetic layer is formed by coating a flexible support with a nonmagnetic lower nonmagnetic layer containing nonmagnetic powder and a binder and an upper magnetic layer containing magnetic powder and a binder. In this case, it is also called a so-called simultaneous multi-layer coating method (“wet-on-wet method”) in which the coating material for the upper magnetic layer is applied onto the lower non-magnetic layer coating material while it is in a wet state. ) Can be realized (see Patent Document 1).

  By the way, in order to realize a magnetic recording medium having high electromagnetic conversion characteristics, it is necessary to make the upper magnetic layer thin and at the same time uniform the thickness of the upper magnetic layer. For that purpose, the lower non-magnetic layer and the upper magnetic layer are required. The interface should be as smooth as possible. In the manufacturing process of the coating type magnetic recording medium, the upper magnetic layer coating material and the lower nonmagnetic layer coating material are usually applied in a fluid state, and vortex and turbulence are generated in the coating layer. This unavoidably results in a decrease in smoothness at the interface between the lower nonmagnetic layer and the upper magnetic layer. In order to prevent such a decrease in the smoothness of the interface, a technique for controlling the fluidity of the upper magnetic layer paint and the lower nonmagnetic layer paint has been introduced.

  As a method of measuring the thickness of the upper magnetic layer and the interface state between the lower nonmagnetic layer and the upper magnetic layer formed by the simultaneous multi-layer coating method, the cross section of each layer is created by a focused ion beam (FIB). A method has been proposed in which a cross-sectional photographic image taken with a scanning electron microscope is processed and judged by its luminance distribution (see Patent Document 2).

  Further, when a signal having a sufficiently long wavelength, for example, 10 times or more than the film thickness of the upper magnetic layer is recorded on the upper magnetic layer in saturation, the signal output is proportional to the coating film thickness, and the signal output is A method for measuring the thickness of the upper magnetic layer by measurement is known (see Patent Document 3).

Japanese Patent Laid-Open No. 5-73833 JP 2008-128672 A JP 2004-5891 A

  In the method described in Patent Document 2, which is a conventional method for measuring the interface state between the lower non-magnetic layer and the upper magnetic layer, one sample such as cross-section preparation, cross-section photography, and luminance gradation value averaging is used. It takes a very long time to analyze. Further, since the cross section is photographed with a scanning electron microscope, there is a problem that the measurement range is limited to a narrow range of several μm square.

  Further, in the method of measuring the thickness of the upper magnetic layer described in Patent Document 3 based on the magnitude of the signal output, since the signal output is detected by the reproducing head, the influence of the roughness of the upper magnetic layer surface appears in the measurement result. As a result, there is a problem that it is impossible to accurately measure the thickness distribution of the upper magnetic layer.

  The present application solves the problems in the above conventional magnetic recording medium measurement method, and is a simple method, but can measure the state of the interface between the lower non-magnetic layer and the upper magnetic layer accurately. It aims to provide a method. It is another object of the present invention to provide a method of manufacturing a magnetic recording medium that can realize cost reduction by performing quality determination of the manufactured magnetic recording medium by a simple method.

  In order to solve the above-described problems, a magnetic recording medium measuring method disclosed in the present application is formed by laminating a lower nonmagnetic layer and an upper magnetic layer on a nonmagnetic support, and the easy magnetic axis direction of the upper magnetic layer Is a method for measuring a magnetic recording medium having a coercive force in the range of 2000 to 3000 Oe, wherein the magnetic properties of the upper magnetic layer with respect to an external magnetic field are measured, and the hysteresis is normalized with the amount of magnetization in the external magnetic field of 10000 Oe as 100% In the hysteresis loop, by comparing the value of the normalized magnetization amount in a region where an external magnetic field having an absolute value larger than the coercive force is applied so that the absolute value increases. The interface state between the lower nonmagnetic layer and the upper magnetic layer is measured.

  Further, the method for manufacturing a magnetic recording medium disclosed in the present application is formed by laminating a lower nonmagnetic layer and an upper magnetic layer on a nonmagnetic support, and the method for measuring a magnetic recording medium according to the present invention is used. The state of the interface between the lower non-magnetic layer and the upper magnetic layer is measured, and the quality of the manufactured magnetic recording medium is determined based on the measurement result.

  The measurement method of the magnetic recording medium disclosed in the present application represents the magnetic characteristics of the upper magnetic layer as a normalized hysteresis loop, and the normalized magnetization value in a region to which an external magnetic field of a predetermined magnitude is applied. By comparing, the state of the interface between the lower nonmagnetic layer and the upper magnetic layer can be measured. Therefore, it is possible to provide a method for measuring a magnetic recording medium, which is a simple method but can accurately grasp the thickness uniformity of the upper magnetic layer.

  In addition, the method for manufacturing a magnetic recording medium disclosed in the present application measures the state of the interface between the lower non-magnetic layer and the upper magnetic layer of the magnetic recording medium manufactured using the magnetic recording medium measuring method according to the present application. The pass / fail judgment is performed. Therefore, it is possible to easily determine whether the thickness distribution of the upper magnetic layer of the manufactured magnetic recording medium is good, and to obtain desired output characteristics, and to manufacture a magnetic recording medium capable of reducing the cost A method can be realized.

  The magnetic recording medium measurement method and the magnetic recording medium manufacturing method disclosed in this application are not limited to simultaneous multilayer coating, but are also effective for sequential multilayer coating in which the upper magnetic layer is coated after the lower nonmagnetic layer is dried. It is a thing.

It is sectional drawing which shows the structure of the magnetic tape explaining the measuring method by this embodiment. It is a figure for demonstrating the condition of mixing in the interface of the lower nonmagnetic layer and upper magnetic layer of a magnetic tape. FIG. 2 (a) shows a state where the lower nonmagnetic layer and the upper magnetic layer are not mixed, and FIG. 2 (b) shows a state where the lower nonmagnetic layer and the upper magnetic layer are mixed. Show. It is a figure explaining the structure of the vibration sample type magnetometer for measuring a hysteresis loop. It is a figure which shows the normalized hysteresis loop showing the magnetic characteristic of the upper magnetic layer of the magnetic tape demonstrated in this embodiment. It is a figure which shows the value of the normalized magnetization amount in each measurement area | region of the magnetic tape which has a different interface state. It is a figure which shows the magnitude | size of the difference of the value of the normalized magnetization amount in each measurement area | region of the magnetic tape which has a different interface state. It is a figure which expands and shows the hysteresis loop of the comparison area part of the magnetic tape which has a different interface state. It is a figure for comparing the mixing degree in the interface of a lower nonmagnetic layer and an upper magnetic layer of the magnetic tape which has a different interface state. It is a figure which shows the relationship between the degree of mixing in the interface of a lower nonmagnetic layer and an upper magnetic layer, and a signal output of the magnetic tape which has a different interface state.

  In the method for measuring a magnetic recording medium disclosed in the present application, a lower nonmagnetic layer and an upper magnetic layer are laminated on a nonmagnetic support, and the coercive force in the easy axis direction of the upper magnetic layer is 2000 to 3000 Oe. A method of measuring a magnetic recording medium in a range, wherein the magnetic characteristics of the upper magnetic layer with respect to an external magnetic field are measured and expressed in a hysteresis loop normalized with an amount of magnetization in an external magnetic field of 10000 Oe as 100%. By comparing the value of the normalized magnetization amount in a region where an external magnetic field having an absolute value larger than the coercive force is applied so that the absolute value increases, the lower nonmagnetic layer and the lower magnetic layer The state of the interface with the upper magnetic layer is measured.

  The measurement method of the magnetic recording medium disclosed in the present application described above shows a normalized hysteresis loop by measuring the magnetization characteristics of the upper magnetic layer laminated on the lower nonmagnetic layer with respect to the external magnetic field, and has an absolute value larger than the coercive force. The value of the magnetization amount normalized in the region where the external magnetic field is applied so that its absolute value increases is obtained. As a result, the magnetic energy of the upper magnetic layer that varies depending on the degree of mixing at the interface between the lower nonmagnetic layer and the upper magnetic layer can be measured. By comparing the magnitude of this magnetic energy, the lower nonmagnetic layer and the upper magnetic layer can be measured. The state of the interface with the magnetic layer can be grasped. Therefore, it is possible to realize a measurement method that can grasp the interface state between the lower non-magnetic layer and the upper magnetic layer of the magnetic recording medium by a simple method using a general magnetic property measurement method for obtaining a hysteresis loop. it can.

  In the method for measuring a magnetic recording medium disclosed in the above application, a comparison region that is a region in which the value of the normalized magnetization amount greatly differs depending on a state of an interface between the lower nonmagnetic layer and the upper magnetic layer, It is desirable to measure the interface state based on the normalized magnetization value in the comparison region. By doing in this way, the difference of the interface state of a lower nonmagnetic layer and an upper magnetic layer can be grasped more reliably from the normalized value of magnetization.

  In addition, the comparison region is set to a width in which the difference between the maximum value and the minimum value of the applied external magnetic field is 600 to 1000 Oe, and the comparison region includes a plurality of at least the maximum value and the minimum value. It is preferable to measure the state of the interface using an average value of the normalized magnetization amount with respect to an external magnetic field. By doing so, it is possible to obtain a suitable magnetization amount value that directly represents the state of the interface between the lower nonmagnetic layer and the upper magnetic layer.

  Further, the squareness ratio of the upper magnetic layer is preferably 0.5 to 0.65. In a magnetic material having a squareness ratio of 0.5 to 0.65, the degree of mixing of the lower non-magnetic layer and the upper magnetic layer can be grasped most remarkably.

  Further, the magnetic recording medium measuring method of the present invention can be effectively applied to a magnetic tape as a magnetic recording medium.

  The method for manufacturing a magnetic recording medium disclosed in the present application is formed by laminating a lower nonmagnetic layer and an upper magnetic layer on a nonmagnetic support, and the method for measuring a magnetic recording medium according to any one of the present invention. The state of the interface between the lower nonmagnetic layer and the upper magnetic layer is measured, and the quality of the magnetic recording medium manufactured is determined based on the measurement result.

  The method for manufacturing a magnetic recording medium disclosed in the present application measures the state of the interface between the lower non-magnetic layer and the upper magnetic layer formed on the support using the magnetic recording medium measuring method disclosed in the present application. Then, the quality of the magnetic recording medium manufactured is determined based on the result. This makes it possible to grasp the state of the interface between the lower non-magnetic layer and the upper magnetic layer by a simple method, taking advantage of the measurement method of the magnetic recording medium of the present invention, and manufacturing from the state of the upper magnetic layer. Therefore, it is possible to determine the quality of the magnetic recording medium thus manufactured, and to realize a method for manufacturing the magnetic recording medium at a reduced cost.

  In the method for manufacturing a magnetic recording medium disclosed in the present application, it is preferable that the lower nonmagnetic layer and the upper magnetic layer are formed by a simultaneous multilayer coating method. Since the smoothness of the interface between the lower non-magnetic layer and the upper magnetic layer can be grasped by a simple method, the magnetic characteristics of the magnetic recording medium manufactured using the simultaneous multi-layer coating method in which the interface state is likely to change Quality can be secured above a certain level.

  Further, the magnetic recording medium manufacturing method disclosed in the present application can be effectively applied to a magnetic tape as a magnetic recording medium.

  Hereinafter, a method for measuring a magnetic recording medium and a method for manufacturing a magnetic recording medium disclosed in the present application will be described with reference to the drawings, illustrating a magnetic tape used for backup of a hard disk of a computer as a magnetic recording medium. To do.

  For convenience of explanation, the drawings referred to below show only a portion necessary for explaining a magnetic recording medium measuring method and a magnetic recording medium manufacturing method disclosed in the present application. Moreover, the dimension of the member in each figure does not necessarily represent the dimension of an actual structural member, and the dimension ratio of each member faithfully.

(Embodiment)
FIG. 1 is a cross-sectional view showing a configuration of a magnetic tape as a magnetic recording medium exemplified in this embodiment.

  The magnetic tape exemplified in this embodiment is formed by laminating a lower nonmagnetic layer 2 and an upper magnetic layer 1 on a nonmagnetic support 3 as shown in FIG. The upper magnetic layer 1 is a so-called perpendicular magnetization type magnetic layer in which the direction of the easy magnetization axis is the thickness direction of the magnetic tape.

  By disposing the lower nonmagnetic layer 2 on the support 3, it is possible to improve the head contact with the magnetic head as the underlayer of the upper magnetic layer 1 and to reduce the thickness of the upper magnetic layer 1. And a magnetic tape suitable for short wavelength recording.

  In addition, the magnetic tape exemplified in the present embodiment improves the tape running performance on the back side of the support 3, that is, on the surface opposite to the side where the lower nonmagnetic layer 2 and the upper magnetic layer 1 are laminated. The back layer 4 is provided. The back layer 4 may be appropriately formed as necessary, and is not an essential component in the magnetic tape that is the magnetic recording medium exemplified in this embodiment.

  Hereinafter, materials and manufacturing methods of each layer constituting the magnetic tape will be described.

[Upper magnetic layer]
The upper magnetic layer 1 may be composed of at least one layer, and may have a multilayer structure of two or more layers as necessary.

  The upper magnetic layer 1 may contain a fatty acid amide as a lubricant. As the fatty acid amide, amides such as lauric acid, palmitic acid, stearic acid, and oleic acid are used. The magnetic powder added to the upper magnetic layer 1 is preferably iron nitride magnetic powder, ferromagnetic iron metal powder, plate-shaped hexagonal Ba-ferrite magnetic powder, or the like.

  Known iron nitride magnetic powders can be used. As for the shape of the iron nitride magnetic powder, an indeterminate shape such as a spherical shape or a cubic shape can be used in addition to the needle shape. In order to clear the required characteristics for magnetic recording, the particle diameter and specific surface area are restricted to appropriate ranges described later. The iron nitride magnetic powder satisfying such conditions can be realized by selecting known appropriate manufacturing conditions.

  The ferromagnetic iron-based metal powder may contain a transition metal such as Mn, Zn, Ni, Cu, and Co as an alloy. Among these, Co and Ni are preferable, and Co is particularly preferable because saturation magnetization can be most improved. The amount of the transition metal element is preferably 5 to 50 atomic% and more preferably 10 to 30 atomic% with respect to iron.

  Further, at least one rare earth element selected from yttrium, cerium, ytterbium, cesium, praseodymium, samarium, lanthanum, europium, neodymium, terbium and the like may be included. Among these, cerium, neodymium, samarium, terbium, and yttrium are preferable because high coercive force can be obtained. The amount of rare earth element is preferably 0.2 to 20 atomic%, more preferably 0.3 to 15 atomic%, and still more preferably 0.5 to 10 atomic% with respect to iron. .

The iron nitride magnetic powder and the ferromagnetic iron-based metal powder preferably have a coercive force of 80 to 320 kA / m (1005 to 4021 Oe). Further, it is preferable saturation magnetization amount is ^{80~200A · m 2 / kg (80~200emu} / g), more preferably from ^{100~180A · m 2 / kg (100~180emu} / g).

  Moreover, 10-200 nm is preferable and, as for the average particle diameter of these magnetic powder, 10-150 nm is more preferable. If the average particle size is less than 10 nm, the coercive force is lowered, and the surface energy of the particles is increased, making it difficult to disperse in the paint. When the average particle diameter is larger than 200 nm, the particle noise based on the particle size increases.

Furthermore, the BET specific surface area of these magnetic powders is preferably 35 m ² / g or more, more preferably 40 m ² / g or more, and most preferably 50 m ² / g or more. Usually, it is 100 m ² / g or less.

The hexagonal Ba-ferrite magnetic powder preferably has a coercive force of 120 to 320 kA / m (1508 to 4021 Oe) and a saturation magnetization of 40 to 70 A · m ² / kg (40 to 70 emu / g). Is preferred.

Further, the particle size (size in the plate surface direction) of the magnetic powder is preferably 10 to 50 nm, more preferably 10 to 30 nm, and further preferably 10 to 20 nm. When the particle size is less than 10 nm, the surface energy of the particles increases, so that dispersion in the paint becomes difficult. When the particle size exceeds 50 nm, particle noise based on the particle size increases. Further, the plate ratio (plate diameter / plate thickness) of the magnetic powder is preferably 2 to 10, more preferably 2 to 5, and further preferably 2 to 4. Moreover, as a BET specific surface area of this magnetic powder, 1-100 m < ² > / g is preferable.

  The binder is used in the same polymer compound as in the case of the lower nonmagnetic layer 2 described later, that is, a combination of at least one selected from a vinyl chloride resin and a cellulose resin and a polyurethane resin. Among these, those having a functional group are particularly preferably used. The addition amount is 7 to 50% by weight, preferably 10 to 35% by weight, based on the total solid content mainly composed of magnetic powder, especially 5 to 30% by weight of vinyl chloride resin, 2 to 2% of polyurethane resin. It is preferable to use 20% by weight in combination. Further, together with these binders, thermosetting cross-linking agents that are cross-linked by bonding with functional groups contained in the binder, particularly polyisocyanates are preferably used.

  A conventionally known abrasive can be added to the upper magnetic layer 1. Such abrasives 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, silicon dioxide. Boron nitride and the like having a Mohs hardness of 6 or more are mainly used alone or in combination of two or more. Among these, alumina is particularly preferably used because it has a high hardness and an excellent head cleaning effect with a small addition amount.

  The particle size of these abrasives depends on the thickness of the upper magnetic layer 1, but is preferably 0.02 to 0.4 μm, more preferably 0.03 to 0.3 μm in average particle size. . Moreover, the addition amount of these abrasive | polishing agents becomes like this. Preferably it is 5 to 13 weight% with respect to magnetic powder, More preferably, it is 5 to 10 weight%. If the addition amount is less than 5% by weight, the head cleaning effect of the upper magnetic layer 1 is insufficient, and if it exceeds 13% by weight, the filling property of the ferromagnetic powder in the upper magnetic layer 1 is lowered and the output is lowered. End up.

These abrasives are preferably made into a slurry previously dispersed in a binder solution, and this slurry is preferably added to the magnetic paint. This is because it is easy to achieve both polishing ability and coating film surface properties. The addition method includes the following method (1) or (2).
(1) After the kneading step, a part of the slurry is added and stirred to perform a primary dispersion step for a predetermined time, and then the remaining slurry is added in a secondary dispersion step to perform dispersion for a predetermined time.
(2) After the kneading step, the whole amount of the slurry is added and stirred, and a primary dispersion step is performed for a predetermined time, followed by dispersion for a predetermined time in the secondary dispersion step.

  On the other hand, when the total amount of the slurry is added in the kneading step, the abrasive is strongly adsorbed by the binder and is less likely to be present on the surface of the coating film, and the head cleaning effect of the upper magnetic layer 1 is reduced. Moreover, when the whole amount of the slurry is added after the secondary dispersion step, the dispersibility of the abrasive is lowered, the surface property of the upper magnetic layer 1 is excessively deteriorated, and the output is lowered.

  For the purpose of improving conductivity and improving surface lubricity, conventionally known carbon black can be added to the upper magnetic layer 1. For example, acetylene black, furnace black, thermal black, etc. can be used. An average particle size of 5 to 200 nm is used, but 10 to 100 nm is preferable. If the particle size is too small, it is difficult to disperse, and if it is too large, it is necessary to add a large amount of carbon black. In either case, the surface becomes rough, causing a decrease in output. The amount of carbon black added is preferably 0.2 to 5% by weight, more preferably 0.5 to 4% by weight, based on the magnetic powder.

  The thickness of the upper magnetic layer 1 is preferably 0.02 μm or more and 0.3 μm or less, and more preferably 0.02 μm or more and 0.25 μm or less. If the thickness is less than 0.02 μm, the head output becomes small because the leakage magnetic field from the upper magnetic layer 1 is small.

  As the magnetic characteristics of the upper magnetic layer 1, the coercive force in the vertical direction is preferably 160 to 240 kA / m (2000 to 3000 Oe), and more preferably 176 to 224 kA / m (2200 to 2800 Oe). If the coercive force is less than 160 kA / m, the output decreases due to the demagnetizing field, and if it exceeds 240 kA / m, writing by the head becomes difficult.

  The magnetic characteristics of the upper magnetic layer 1 and the magnetic characteristics of the magnetic powder refer to values measured with an external magnetic field of 0.796 kA / m (10 kOe) using a sample vibration magnetometer. In addition, the average particle diameter of the magnetic powder added to the upper magnetic layer 1 is the maximum diameter of each particle from the photograph taken with a transmission electron microscope (TEM). (Plate diameter) was actually measured, and the average value of 100 pieces was obtained.

[Lower nonmagnetic layer]
As a base layer of the upper magnetic layer 1 provided on one surface of the nonmagnetic support 3, a nonmagnetic powder and a binder are included for buffering the head contact between the magnetic tape and the magnetic head and controlling the head touch. A lower nonmagnetic layer 2 is provided.

  The lower nonmagnetic layer 2 may be composed of at least one layer, and may have a multilayer structure of two or more layers as necessary. The thickness of the lower nonmagnetic layer 2 is usually 0.3 to 2.0 μm, preferably 0.5 to 1.5 μm, considering the total thickness of the tape.

  As the nonmagnetic powder added to the lower nonmagnetic layer 2, conventionally known powders can be used. Examples include α-alumina, β-alumina, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride, and the like.

  Usually, nonmagnetic iron oxide is mainly used, and if necessary, carbon black or aluminum oxide having an average particle diameter of 0.1 to 0.5 μm is supplementarily used.

  The nonmagnetic iron oxide preferably has a major axis length of 0.05 to 0.4 μm (particularly 0.05 to 0.2 μm, a minor axis length of 5 to 200 nm), and the addition amount is 35 to 83% by weight. preferable. The particle size in the above range is preferred because uniform dispersion is difficult when the major axis length is less than 0.05 μm, and unevenness at the interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1 increases when the major axis length exceeds 0.4 μm. is there. The addition amount in the above range is preferable because the effect of improving the coating film strength is small if it is less than 35% by weight, and the coating film strength is lowered if it exceeds 83% by weight.

  As the carbon black, acetylene black, furnace black, thermal black, or the like is used. An average particle size of 5 to 200 nm is used, but an average particle size of 10 to 100 nm is preferable. This range is preferable because carbon black has a structure, so that it is difficult to disperse carbon black when the average particle diameter is less than 10 nm, and smoothness is deteriorated when it exceeds 100 nm.

  The amount of carbon black added varies depending on the particle size of the carbon black, but is usually preferably 15 to 40% by weight. This range is preferable because if the amount is less than 15% by weight, the effect of improving conductivity is poor, and if it exceeds 40% by weight, the effect is saturated. It is more preferable to use 15 to 35% by weight of carbon black having an average particle diameter of 15 to 80 nm, and it is further preferable to use 20 to 30% by weight of carbon black having an average particle diameter of 20 to 50 nm. By adding carbon black having such a particle size and amount, electrical resistance is reduced, and generation of electrostatic noise and tape running unevenness are reduced.

  As the binder used for the lower nonmagnetic layer 2, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, Polyurethane resins and at least one selected from vinyl chloride resins such as vinyl chloride-vinyl acetate-maleic anhydride copolymer resins, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resins, and cellulose resins such as nitrocellulose And a combination of these.

  Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

As a functional group, —COOH, —SO ₃ M, —OSO ₃ M, —P═O (OM) ₃ , —O—P═O (OM) ₂ (M is a hydrogen atom, an alkali metal base or an amine salt. ), —OH, —NR ¹ R ² , —N ⁺ R ³ R ⁴ R ⁵ (where R ¹ , R ² , R ³ , R ⁴ , R ⁵ are hydrogen or hydrocarbon groups), high having an epoxy group A binder made of a molecular compound is preferably used. This is because the use of such a binder improves the dispersibility of the nonmagnetic powder. When two or more resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

  These binders are used in the range of 7 to 50% by weight, preferably 10 to 35% by weight, based on the total solid content. If it is less than 7% by weight, the dispersibility of the nonmagnetic powder to be contained in the undercoat layer becomes poor. If it exceeds 50% by weight, the relative amount of the binder to the nonmagnetic powder becomes excessive, the amount of the binder that is not adsorbed by the nonmagnetic powder increases, the voids in the coating film decrease, and the buffer of the lower nonmagnetic layer 2 The effect is reduced. As the binder, it is most preferable to use a composite of 5 to 30% by weight of vinyl chloride resin and 2 to 20% by weight of polyurethane resin. This is because the strength of the vinyl chloride resin and the dispersibility of the nonmagnetic powder can be compatible with the flexibility of the polyurethane resin.

  In addition to these binders, it is desirable to use a thermosetting crosslinking agent that is bonded to a functional group contained in the binder and crosslinked. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are usually used at a ratio of 1 to 30 parts by weight with respect to 100 parts by weight of the binder. Particularly preferred is 5 to 20 parts by weight. This range is preferred when the content is less than 1 part by weight, the crosslinkability is lowered, and when it exceeds 30 parts by weight, the amount of uncrosslinked low-molecular components in the coating film increases, and in any case, the rigidity of the lower nonmagnetic layer 2 This is because there is a shortage.

  The Young's modulus of the lower nonmagnetic layer 2 is preferably 80 to 99% of the Young's modulus of the upper magnetic layer 1. The lower Young's modulus of the lower nonmagnetic layer 2 should be lower than that of the upper magnetic layer 1 because the lower nonmagnetic layer 2 acts as a kind of cushion.

  As a method for controlling the Young's modulus of the coating layer composed of the lower nonmagnetic layer 2 and the upper magnetic layer 1, for example, a control method based on calendar conditions can be used.

  For the lower nonmagnetic layer 2, a lubricant having a role different from that of the upper magnetic layer 1 is used. When the lower nonmagnetic layer 2 contains 0.5 to 4.0% by weight of higher fatty acid and 0.2 to 3.0% by weight of higher fatty acid ester with respect to the total powder, And the coefficient of friction between the rotating cylinder and the rotating cylinder are reduced. If the higher fatty acid is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 4.0% by weight, the lower nonmagnetic layer 2 is plasticized and the toughness is lost. If the higher fatty acid ester is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, the amount of transfer to the upper magnetic layer 1 is too large. is there. If necessary, the same fatty acid amide as that used for the upper magnetic layer 1 may be used.

[Support]
The nonmagnetic support 3 preferably has a Young's modulus in the longitudinal direction of 9.80 GPa (1000 kg / mm ² ) or more and a Young's modulus in the longitudinal direction / Young's modulus in the width direction of 0.5 to 0.9. More preferably, the Young's modulus in the longitudinal direction is 10.78 GPa (1100 kg / mm ² ) or more, and the Young's modulus in the longitudinal direction / Young's modulus in the width direction is in the range of 0.67 to 0.73.

  The reason why the Young's modulus in the longitudinal direction is preferably 9.80 GPa or more is that the tape running becomes unstable if it is less than 9.80 GPa. The range of Young's modulus in the longitudinal direction / Young's modulus in the width direction is preferably in the range of 0.5 to 0.9. This is because output variation (flatness) increases. This variation is minimized when the Young's modulus in the longitudinal direction / Young's modulus in the width direction is around 0.70.

  Examples of the non-magnetic support 3 material satisfying such characteristics include biaxially stretched aromatic polyamide film, aromatic polyimide film, and the like. It is not limited.

  The thickness of the nonmagnetic support 3 varies depending on the use of the magnetic tape, but is usually 2 to 5 μm, preferably 2.5 to 3.8 μm. This range is preferable because if less than 2 μm, film formation is difficult, and the tape strength decreases, and if it exceeds 5 μm, the total thickness of the tape increases and the storage capacity per tape roll decreases.

[Back layer]
A back layer 4 is provided on the other surface of the nonmagnetic support 3 on which the lower nonmagnetic layer 2 and the upper magnetic layer 1 are formed in order to improve running performance. The thickness of the back layer 4 is preferably 0.2 to 0.8 μm. If it is less than 0.2 μm, the effect of improving running performance is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape is increased and the storage capacity per roll is reduced. The back layer 4 is usually a coat layer containing a nonmagnetic powder and a binder, but may be another form of the back layer 4 as long as it has an effect of improving running performance.

  It is preferable to add iron oxide or alumina having an average particle size of 0.1 to 0.6 μm to the back layer 4 for the purpose of improving the strength. In addition, a thing with an average particle diameter of 0.2-0.5 micrometer is more preferable. The amount added is preferably 2 to 40% by weight, more preferably 5 to 30% by weight, based on the weight of the inorganic powder.

  Examples of carbon black used for the back layer 4 include acetylene black, furnace black, and thermal black. Usually, small particle size carbon and large particle size carbon are used.

  The small particle size carbon is preferably one having an average particle size of 5 to 200 nm, and more preferably 10 to 100 nm. If the particle size is too small, it is difficult to disperse the carbon black, and if it is too large, it is necessary to add a large amount of carbon black. In either case, the surface becomes rough and the back to the upper magnetic layer 1 (emboss) Cause.

  If carbon having an average particle size of 200 to 400 nm is used as a large particle size carbon at a ratio of 5 to 15% by weight of the small particle size carbon, the surface is not roughened and the effect of improving running performance is increased. The total addition amount of the small particle size carbon and the large particle size carbon is preferably 60 to 98% by weight, more preferably 70 to 95% by weight, based on the weight of the inorganic powder. The surface roughness Ra is preferably 3 to 8 nm, and more preferably 4 to 7 nm.

  Hereinafter, specific manufacturing conditions for the magnetic tape will be described as an example of the magnetic tape described in the present embodiment.

[Preparation of magnetic paint]
The magnetic coating component (1) shown below was put into a surface treatment tank, and a rotary shear type stirrer (Cleamix manufactured by M Technique Co., Ltd., rotor blade diameter: 50 mm, gap: 2 mm, rotation speed: 2000 rpm, shear rate: 2. 6 × 10 ⁴ / sec) for 60 minutes, and surface treatment of the magnetic powder and alumina powder was performed to obtain a first composition.

  The obtained first composition was put into a vertical vibration dryer (VFD-01 manufactured by Chuo Kako Co., Ltd.), the inside of the tank was vibrated (frequency: 1800 cpm, amplitude: 2.2 mm), and the pressure was reduced to 20 KPa. The mixture was heated to 60 ° C. and concentrated to obtain a second composition having a solid content concentration of 90% by mass.

  The following magnetic coating component (2) was added to the obtained second composition and kneaded with a pressure-type batch kneader.

  Next, the following magnetic coating component (3) was added to the pressure type batch kneader in two stages to dilute the kneaded material to prepare a slurry. This slurry was dispersed in a sand mill (residence time: 45 minutes) filled with zirconia beads (specific gravity: 6, particle size: 0.1 mm), and then the obtained dispersion and the following magnetic coating component (4) were mixed. The mixture was stirred with a dispaper and filtered through a filter to prepare a magnetic paint.

[Preparation of resin solution]
Resins shown in the following resin liquid components were stirred using a dispaper to prepare a resin liquid.

[Preparation of paint for back layer]
A mixed solution in which the following coating components for the back layer were mixed was dispersed with a sand mill (residence time: 45 minutes). 15 parts of polyisocyanate was added to the obtained dispersion and stirred, and this was filtered through a filter to prepare a coating material for the back layer.

[Preparation of paint for topcoat layer]
The top coat layer coating components shown below were mixed and dissolved with a stirrer to prepare a top coat layer coating.

[Preparation of non-magnetic paint]
A kneaded product was prepared by kneading the following nonmagnetic coating component (1) with a batch kneader. The obtained kneaded product and the nonmagnetic coating component (2) shown below were stirred using a dispaper to prepare a mixed solution. After the obtained mixed liquid was dispersed by a sand mill (retention time: 60 minutes) to prepare a dispersion, the dispersion and the nonmagnetic coating component (3) shown below were stirred using a dispaper. The non-magnetic paint was prepared by filtering with a filter.

[Detailed components of each component]
Magnetic paint component (1)
Iron nitride magnetic powder (YN—Fe) 100 parts (Y / Fe: 5.5 at%, N / Fe: 11.9 at%)
σs: 103 A · m ² / kg (103 emu / g)
Hc: 211 kA / m (2650 Oe)
Average particle diameter: 17 nm, axial ratio: 1.1
Polyester polyurethane resin 2 parts (containing -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Granular alumina powder (average particle size: 80 nm) 5 parts Methyl acid phosphate 4 parts Tetrahydrofuran 271 parts

Magnetic paint component (2)
17 parts of vinyl chloride-hydroxypropyl acrylate copolymer (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)
Polyester polyurethane resin 4 parts (Glass transition temperature: 40 ° C., contained—SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Methyl ethyl ketone 5 parts Cyclohexanone 7 parts Toluene 5 parts

Magnetic paint component (3)
Palmitic acid amide 4 parts Cyclohexanone 175 parts Methyl ethyl ketone 175 parts

Magnetic paint component (4)
Polyisocyanate 1.5 parts Cyclohexanone 14.5 parts Methyl ethyl ketone 14.5 parts

Resin liquid component Vinyl chloride-hydroxypropyl acrylate copolymer 1 part Cyclohexanone 5 parts Methyl ethyl ketone 5 parts

Carbon black (average particle size: 25 nm) 87 parts Carbon black (average particle size: 300 nm) 10 parts Granular alumina powder (average particle size: 80 nm) 3 parts Nitrocellulose 45 parts Polyurethane resin (containing -SO ₃₎ Na group) 30 parts cyclohexanone 260 parts toluene 260 parts methyl ethyl ketone 525 parts

Paint component for topcoat layer Stearic acid 1 part Butyl stearate 1 part Isopropyl alcohol 100 parts

Non-magnetic paint component (1)
Acicular iron oxide (average particle diameter: 110 nm) 68 parts Carbon black (average particle diameter: 17 nm) 20 parts Granular alumina powder (average particle diameter: 120 nm) 12 parts Methyl acid phosphate 1 part Vinyl chloride-hydroxypropyl acrylate copolymer coalescing 9 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 eq / g)
Polyester polyurethane resin 5 parts (Glass transition temperature: 40 ° C., contained -SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / g)
Tetrahydrofuran 13 parts Cyclohexanone 63 parts Methyl ethyl ketone 137 parts

Non-magnetic paint component (2)
Stearic acid 1 part Butyl stearate 1.5 parts Cyclohexanone 50 parts Methyl ethyl ketone 50 parts

Non-magnetic paint component (3)
Polyisocyanate 2.5 parts Cyclohexanone 9 parts Toluene 9 parts.

[Preparation method of coating material and coating method]
In preparing the coating for the upper magnetic layer, a coating production method conventionally used in the production of magnetic recording media can be used. Specifically, a combined use of a kneading step with a kneader or the like and a primary dispersion step with a sand mill, a pin mill or the like is preferable. In addition, when applying a coating for the upper magnetic layer on a non-magnetic support, coating that has been conventionally used as a method for producing a magnetic recording medium, such as gravure coating, roll coating, blade coating, and extrusion coating You can use the method.

  In the magnetic tape as the magnetic recording medium described in the present embodiment, the lower nonmagnetic layer 2 and the upper magnetic layer 1 laminated on the nonmagnetic support 3 are applied, and the lower nonmagnetic layer 2 is applied. After that, the lower nonmagnetic layer 2 is applied by a simultaneous multilayer coating method in which the upper magnetic layer 1 is laminated and applied in a wet state without being completely dried.

  FIG. 2 shows a magnetic tape manufactured by coating and forming the lower nonmagnetic layer 2 and the upper magnetic layer 1 on the support 3 by the simultaneous multi-layer coating method using materials having specific components as the above-described embodiment. FIG. 3 is an enlarged cross-sectional view of a main part for explaining a state in the vicinity of an interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1.

  FIG. 2A shows the interface state of the magnetic tape in which the mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 hardly occurs because the manufacturing conditions can be controlled satisfactorily. In this case, as schematically shown in FIG. 2 (a), in the upper magnetic layer 1, magnetic powder 12 is dispersed in the binder resin 11.

  On the other hand, FIG. 2B shows the interface state of the magnetic tape in which the lower nonmagnetic layer 2 and the upper magnetic layer 1 are mixed. In this case, as shown in FIG. 2B, the hematite 13 of the lower nonmagnetic layer 2 is mixed in the binder resin 11 of the upper magnetic layer 1 in addition to the magnetic powder 12.

  As can be seen by comparing FIG. 2A and FIG. 2B, when mixing of the lower non-magnetic layer 2 and the upper magnetic layer 1 occurs, the lower non-magnetic layer is incorporated into the binder resin 11 of the upper magnetic layer 1. As the hematite 13 is mixed, the interval between the particles of the magnetic powder 12 in the binder resin 11 is increased. As a result, the density of the magnetic powder 12 in the upper magnetic layer 1 is reduced. When the inter-particle distance of the magnetic powder 12 increases and the density decreases, the magnetic energy as the upper magnetic layer 1 decreases. In other words, the upper magnetic layer 1 having a small interparticle distance as shown in FIG. 2A in which no mixing with the lower nonmagnetic layer 2 occurs is not mixed with the lower nonmagnetic layer 2. Compared with the upper magnetic layer 1 having a large interparticle distance as shown in FIG. 2B, it can be said that the magnetic energy is large.

  In the method for measuring a magnetic recording medium described in the present embodiment, the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 with respect to the state of the interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1 is described above. This is understood as the difference in energy size. When the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 is small, the upper magnetic layer 1 is laminated on the lower nonmagnetic layer 2 in a state close to a desired state. In this case, it can be said that the interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1 is relatively flat, and the thickness of the upper magnetic layer 1 is nearly uniform in the magnetic tape. On the other hand, the case where the degree of mixing between the lower nonmagnetic layer 2 and the upper magnetic layer 1 is a state where the interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1 is not formed in a desired state. In this case, it can be said that the interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1 is not flat, and the thickness of the upper magnetic layer 1 as a magnetic tape is not uniform.

  In the method for measuring a magnetic recording medium of this embodiment, the magnitude of the magnetic energy of the upper magnetic layer 1 is grasped by measuring a hysteresis loop. Hereinafter, specific measurement contents of the magnetic recording medium measurement method of the present embodiment will be described.

  FIG. 3 is a block diagram showing a configuration of a vibrating sample magnetometer (VSM) used in the method for measuring a magnetic recording medium according to the present embodiment.

  As shown in FIG. 3, the vibration sample type magnetometer has a sample 21 attached to the tip of a support rod 22 and a vibration generator 24 using a magnet 23 or the like, and vibrations of a predetermined frequency controlled by a vibration control device 24. Vibrate at 80 Hz as an example. In addition, the vibration width of a sample can be 0.1-0.2 mm as an example. An external magnetic field is applied by a pair of electromagnets 26 arranged so as to sandwich the sample 21, and a current flowing in a search coil 27 arranged near the sample 21 is measured by the principle of electromagnetic induction. The current flowing through the search coil 27 is amplified by the amplifier 28 and input to the phase detector 29, and the phase detector 29 extracts only the signal component having the same frequency as the vibration frequency of the sample 21 (80 Hz in this case). Then, noise components such as components due to minute fluctuations in the external magnetic field flowing through the search coil 27 are removed, and the magnetization amount of the sample 21 can be measured electrically and accurately.

  Note that the measurement of the hysteresis loop as the magnetic characteristics is very general, and in measuring the magnetic characteristics of the upper magnetic layer 1 in the measuring method of the magnetic recording medium of the present embodiment, a special measuring device or measuring method is used. Is not what you need.

  FIG. 3 shows an example of a measured hysteresis loop.

  The data shown in FIG. 3 was measured using a vibrating sample magnetometer “TSM-P7 type (product name)” manufactured by Toei Industry Co., Ltd. As a sample, 20 magnetic tapes cut to 8 mmφ are stacked in the direction of external magnetic field application. That is, the application direction of the external magnetization is the same as the direction of the easy axis of the magnetic tape described in this embodiment. The plot mode for data from the vibrating sample magnetometer is a time constant TC of 0.03 sec, the drawing step is 6 bits for the expansion condition of the external magnetic field in the range of -5000 Oe to 5000 Oe, and 40 bits for the other parts. The time was set to 0.3 sec under the above enlargement condition and 0.1 sec for the other portions. The size of the sample, the number of stacked layers, the type of vibration sample type magnetometer to be used, and the setting conditions thereof are merely examples, and are appropriately selected based on the magnetic characteristics of the upper magnetic layer 1 of the magnetic recording medium to be measured. It goes without saying that the appropriate conditions should be selected.

  As shown in FIG. 3, in the magnetic recording medium measuring method of the present embodiment, the measured magnetic characteristics of the upper magnetic layer 1 are the hysteresis loop 31 indicating the relationship between the external magnetic field (Hc) and the magnetization (M). Represent as At this time, the value of the magnetization amount on the vertical axis is expressed by using [M / Ms (%)], a numerical value normalized by setting the value of the magnetization amount when the applied external magnetic field is 10,000 Oe (10 kOe) as 100%. Yes.

  Note that the magnetic recording medium to be measured in the present embodiment is a perpendicular magnetization type magnetic recording medium capable of high-density recording and reproduction, and therefore the coercive force is in the range of 2000 to 3000 Oe. In the hysteresis loop, the value of the magnetization amount 0 represents the coercive force. In the magnetic tape described in this embodiment whose hysteresis loop 31 is illustrated in FIG. 3, the coercive force is a portion indicated by reference numeral 32 in FIG. 3, and the size thereof is about 2900 Oe.

  In the measurement method of the magnetic recording medium shown in the present embodiment, the magnitude of the magnetic energy in the upper magnetic layer 1 of the magnetic tape is calculated by the numerical value [M / Ms (%)] of the magnetization amount normalized by the magnetization amount in the external magnetic field 10000 Oe. The degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 is determined by grasping this. At this time, in the measured hysteresis loop, the value of the magnetization amount normalized in the region where the external magnetic field having an absolute value larger than the coercive force is applied so that the absolute value increases is used.

  In the magnetic recording medium in which the upper magnetic layer 1 is laminated on the lower nonmagnetic layer 2, the magnetic energy of the upper magnetic layer 1 depends on the degree of mixing of the two layers at the interface between the lower nonmagnetic layer 2 and the upper magnetic layer 1. Change. For this reason, the upper magnetic layer 1 having a different degree of mixing of the two layers has different magnetization characteristics and different saturation magnetic field magnitudes. As described above, the upper magnetic layer 1 of the magnetic recording medium, which is the measurement target of the measurement method of the present embodiment, has a coercive force of 2000 to 3000 Oe, so that it is saturated when an external magnetic field of 10000 Oe (10 kOe) is applied. State or almost saturated. Therefore, in the method for measuring a magnetic recording medium of the present embodiment, the upper magnetic layer 1 to be measured is used by using the numerical value [M / Ms (%)] of the magnetization amount normalized by the magnetization amount in the external magnetic field 10000 Oe. It is possible to grasp the “easy to be magnetized”. Further, in the hysteresis loop, the portion where the magnitude of the external magnetic field exceeds the coercive force is a portion representing a state in which the upper magnetic layer 1 is magnetized by the external magnetic field, and thus the amount of magnetization in this state By comparing the values [M / Ms (%)], the difference in magnetic energy of the upper magnetic layer 1 can be most remarkably grasped.

  As shown in FIG. 3, the hysteresis loop 31 has a normalized magnetization amount from the point 32 where the external magnetic field indicating the coercive force is 2900 Oe to the state 33 where the external magnetic field where the upper magnetic layer 1 is almost saturated is 10000 Oe. Although the numerical value [M / Ms (%)] increases, the magnitude of the slope of the hysteresis loop indicating the degree of increase is not constant. In comparing the easiness of magnetization of the upper magnetic layer 1, it is effective to use a portion where the numerical value of the magnetization amount greatly changes with respect to a change in the external magnetic field, that is, a portion having a larger slope in the hysteresis loop. Is. For this reason, in the measuring method of the magnetic recording medium of the present embodiment, in order to measure the degree of mixing of the two layers of the lower nonmagnetic layer 2 and the upper magnetic layer 1, the hysteresis loop A portion having a large inclination, that is, a portion where the value of the magnetization amount greatly changes with respect to the magnitude of the external magnetic field is selected, and the normalized value of the magnetization amount in this portion is used.

  From this point of view, in the case of the magnetic tape showing the hysteresis loop in FIG. 3, the upper magnetic layer is used by using a range in which the normalized magnetization value [M / Ms (%)] is 0 to 90. It is preferable to compare the magnetic energy of unity. In addition, it is more preferable to use a range in which the normalized magnetization amount value [M / Ms (%)] shown as region A in FIG.

  As is well known, since the hysteresis loop has symmetry with respect to the origin 0, instead of the first quadrant region A, the third quadrant range shown as region B in FIG. When the external magnetic field is a negative value, the value of the amount of magnetization in the range where the absolute value of the external magnetic field increases from the coercive force (the external magnetic field becomes a small value) can also be used.

  In the method for measuring a magnetic recording medium according to the present embodiment, in order to grasp the magnetic energy of the upper magnetic layer 1 to be measured, the normalized magnetization value [M / Ms ( %)]. Here, when the magnetic energy of the upper magnetic layer 1 is compared, one numerical value of a predetermined external magnetic field is determined, and the normalized magnetization value in this external magnetic field is compared, that is, pinpoint comparison is performed. It is possible. However, based on the idea of the magnetic recording medium measurement method of the present embodiment, which represents a hysteresis loop and grasps the magnetic energy of the upper magnetic layer 1 to be measured using the value of the magnetization amount magnetized by the increasing external magnetic field. Furthermore, in consideration of measurement errors, it is possible to determine the region of the external magnetic field in a certain range and use the value of the amount of magnetization in the range of the magnitude of the external magnetic field, so to compare the amount of magnetization as a zone, This is considered to be a more preferable method for accurately measuring the magnitude of the magnetic energy of the upper magnetic layer 1 to be measured.

  Therefore, in the measurement method of the present embodiment, in order to study a more preferable comparison region (zone), the 600 Oe width obtained by shifting the minimum value by 100 Oe in the range from 3000 Oe to 5000 Oe as the magnitude of the applied external magnetic field. Were divided into 15 areas. Then, as the normalized magnetization value in each region, the magnetization value for the three external magnetic fields that are the minimum value, median value, and maximum value of each region is obtained, and this is simply averaged. did.

  FIG. 5 is a diagram illustrating a measuring method according to the present embodiment. An external magnetic field is 10000 Oe for three types of magnetic tapes having different manufacturing methods and the interface state between the formed lower nonmagnetic layer 2 and the upper magnetic layer 1. This is expressed in a hysteresis loop using the amount of magnetization normalized by the value of, and the values obtained by averaging the amounts of magnetization for three external magnetic fields in a predetermined measurement region are compared and shown.

  There are three types of magnetic tapes to be measured: “simultaneous multilayer A”, “simultaneous multilayer B”, and “sequential multilayer”. Here, “simultaneous multi-layer A” is a relatively non-magnetic layer 2 and upper magnetic layer among magnetic tapes in which a lower non-magnetic layer 2 and an upper magnetic layer 1 are formed on a support 3 by a simultaneous multi-layer coating method. The interface with the layer 1 is not uniform. The “simultaneous multilayer B” is a relatively lower magnetic layer 2 and upper magnetic layer among magnetic tapes in which the lower nonmagnetic layer 2 and the upper magnetic layer 1 are formed on the support 3 by the simultaneous multilayer coating method. 1 is uniform. Further, the “sequential multilayer” is a magnetic tape in which a lower nonmagnetic layer 2 and an upper magnetic layer 1 are formed on a support 3 by a sequential multilayer coating method.

  As shown in FIG. 5, for each magnetic tape, the normalized magnetization amount value [M / Ms (%) with respect to the three external magnetic fields that are the minimum value, median value, and maximum value in each measurement region. )] Is averaged in the order of simultaneous multi-layer A, simultaneous multi-layer B and sequential multi-layer in all 15 regions with a width of 600 Oe ranging from 3000 Oe to 5000 Oe. From this, it can be seen that the larger the mixing ratio of the lower non-magnetic layer 2 and the upper magnetic layer 1 is, the easier the magnetism is with respect to an external magnetic field of the same strength as the magnetic energy of the upper magnetic layer 1 is small.

  FIG. 6 shows the numerical value of the simultaneous multi-layer A having the largest value [M / Ms (%)] of the magnetization amount and the numerical value of the sequential multi-layer having the smallest value in each measurement range of the width 600 Oe width shown in FIG. Difference, that is, Δ [M / Ms (%)] is shown in comparison. From FIG. 6, the magnitude of Δ [M / Ms (%)] is a relatively large value in the measurement range of the external magnetic field from 3300 Oe to 3900 Oe to 3900 to 4500 Oe. Thus, when external magnetic fields of the same magnitude are applied, the measurement range of 3900 to 4500 Oe having a large difference in normalized magnetization value (Δ [M / Ms (%)]) It can be said that the difference in the degree of mixing between the magnetic layer 2 and the upper magnetic layer 1 is a range that can be easily grasped as a difference in the amount of magnetization. Therefore, in measuring the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 in the magnetic tape shown as the measurement method of the present embodiment, the difference in the magnetization amount value (Δ [M / Ms (%)]) and an external magnetic field in the range of 3500-4100 Oe are defined as a comparison region for comparing magnetic energy, and a normalized magnetization value in this range is used, so that the lower layer can be obtained with higher accuracy. The degree of mixing of the nonmagnetic layer 2 and the upper magnetic layer 1 can be measured. In addition, as shown in FIG. 6, the difference (Δ [M / Ms (%)]) of the normalized magnetization amount in the measurement range from 3300 Oe to 3900 Oe to the measurement range of 3900 to 4500 Oe is the external magnetic field. Even if any one of these measurement ranges is determined as a comparison region instead of the range of 3500 to 4100 Oe and used for measurement, the lower nonmagnetic layer 2 and the upper magnetic layer 1 are mixed. Can be measured with relatively good accuracy. Further, as shown in FIGS. 5 and 6, in all 15 regions having a width of 600 Oe ranging from 3000 Oe to 5000 Oe, the normalized magnetization amount value [M / Ms (%)] Since A, simultaneous multi-layer B, and sequential multi-layer are used, even if any of 15 regions with a width of 600 Oe in a range from 3000 Oe to 5000 Oe is defined as a comparison region and used for measurement, the lower non-magnetic layer 2 and the upper layer Needless to say, the degree of mixing with the magnetic layer 1 can be measured.

  FIG. 7 shows an enlarged hysteresis loop for the three magnetic tapes of “simultaneous multilayer A”, “simultaneous multilayer B”, and “sequential multilayer” having different interface states in the comparison region where the external magnetic field is 3500-4100 Oe. It is shown. As shown in FIG. 7, the normalized magnetization value [M / Ms () shown in the hysteresis loop of the magnetic tape having different interface states of “simultaneous multilayer A”, “simultaneous multilayer B”, and “sequential multilayer”. %)] Always maintains the relationship of “simultaneous multilayer A”> “simultaneous multilayer B”> “sequential multilayer” in the range of the comparison region where the external magnetic field is 3500-4100 Oe.

  From the enlarged view of the hysteresis loop shown in FIG. 7, the hysteresis loop of “simultaneous multilayer B” and “sequential multilayer” gradually changes, whereas the hysteresis loop of “simultaneous multilayer A” is more wavy. I understand that. This is considered to be because in the “simultaneous multilayer A” in which the magnetic energy of the upper magnetic layer 1 is relatively small, the rate of change in the amount of magnetization varies with the change in the external magnetic field. Also from this, a predetermined comparison region is determined and its minimum value (3500 Oe) and median value (3800 Oe) are compared with the case of comparing the normalized magnetization amount with respect to an external magnetic field of a predetermined one point, for example, 3800 Oe. It can be seen that it is possible to compare the magnetization amounts more accurately by averaging the magnetization amounts in the external magnetic field at the three points of the maximum value (4100 Oe). In the present embodiment, as described above, in the measurement region having a width of 600 Oe, the normalized magnetization amounts for the three external magnetic fields of the minimum value, the median value, and the maximum value are obtained, and the average of these three points is obtained. The value of the amount of magnetization in each measurement region was taken. However, for example, the values of normalized magnetization amounts with respect to seven external magnetic fields of 3500 Oe, 3600 Oe, 3700 Oe, 3800 Oe, 3900 Oe, 4000 Oe, and 4100 Oe are obtained, and the average value of the magnetization amounts of 7 points is used. Needless to say, there is no restriction on the average value of points when obtaining the amount of magnetization as a zone in the width measurement region. Considering the relationship between the effect of averaging using a plurality of magnetization amounts and the complexity due to the increase in data amount, the numerical value of the external magnetic field to be averaged is preferably about 2 to 7 points. In addition, it is preferable that the intervals between the values of the plurality of external magnetic fields be as uniform as possible, but there is no restriction that all must be selected at equal intervals.

  FIG. 8 shows the amount of magnetization normalized by the value when the external magnetic field is 10,000 Oe as the mixing degree of the lower nonmagnetic layer 2 and the upper magnetic layer 1 as it is. As described above, in the measurement method of the present embodiment, the amount of magnetic energy reflecting the degree of mixing in the upper magnetic layer 1 of the magnetic recording medium is used by using the normalized magnetization amount with respect to the external magnetic field in the predetermined comparison region. Since the magnitude can be expressed, the value of the magnetization can be used as an index of the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 as it is. In this index, as shown in FIGS. 5 to 7, the larger the amount of magnetization, the greater the degree of mixing between the lower nonmagnetic layer 2 and the upper magnetic layer 1.

  As shown in FIG. 8, the lower non-magnetic layer 2 and the upper magnetic layer 1 obtained from the amount of magnetization in three types of magnetic tapes of “simultaneous multilayer A”, “simultaneous multilayer B”, and “sequential multilayer” having different interface states. Of the lower nonmagnetic layer 2 and the upper magnetic layer 1 can be relatively grasped on the basis of a magnetic tape by “sequential multi-layer” which can be judged to be small. It has been confirmed that the measurement error in the vibrating sample magnetometer is about plus / minus 1 in the normalized value of magnetization used in the measurement method of the present embodiment. In FIG. 8, the measurement error in the vibrating sample magnetometer is shown as a variation width as an index of the mixing degree in each tape. As can be seen from FIG. 8, according to the method for measuring a magnetic recording medium according to the present embodiment, the value of the normalized magnetization amount is taken into account even when the measurement error of the vibrating sample magnetometer for obtaining the hysteresis loop is taken into account. Can be used to accurately represent the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1.

  FIG. 9 shows the relationship between the value of the normalized magnetization amount, which is the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 of each magnetic tape having different interface states, and the output of the magnetic tape. FIG.

  The magnetic tape output indicates 2T output for one cycle, and is measured under the conditions of a tape running speed of 1.5 m / s, a tape tension of 0.65 N, and a recording wavelength of 270 nm in an LTO drive device. The value of the tape output is normalized by assuming that the 2T output in the sequentially laminated magnetic tape is 100%, which can be considered that the lower nonmagnetic layer 2 and the upper magnetic layer 1 are well separated. .

  In FIG. 9, the output of the “sequential multi-layer” magnetic tape is denoted by reference numeral 41, the output of the “simultaneous multi-layer B” magnetic tape is denoted by reference numeral 42, and the output of the “simultaneous multi-layer A” magnetic tape is denoted by reference numeral 43. ing.

  As shown in FIG. 9, a very strong correlation is recognized between the index of the degree of mixing of the lower nonmagnetic layer 2 and the upper magnetic layer 1 shown in FIG. 8 and the 2T output obtained from the tape. . From this result, it can be confirmed that the output characteristics of the magnetic tape can be indirectly grasped by the magnetic recording medium measuring method described in the present embodiment.

  In the magnetic tape manufacturing process, it is managed whether the manufactured magnetic tape is a non-defective product that satisfies a predetermined specification or a defective product that does not satisfy the predetermined specification. From the practical viewpoint, the 2T output magnitude of the magnetic tape may be used as an index for determining the quality of such manufactured products. For example, when manufacturing a magnetic tape by a simultaneous multi-layer method that can form the upper magnetic layer 1 that is simpler and thinner, the output of the manufactured magnetic tape is the 2T output of the magnetic tape manufactured by the sequential multi-layer method. If the magnetic tape is 85% or more, the mixing ratio of the lower non-magnetic layer 2 and the upper magnetic layer 1 is relatively small even by the simultaneous multi-layer method, and the magnetic tape is sufficiently practical. In this case, as shown in FIG. 9, the “simultaneous multilayer B” magnetic tape indicated by reference numeral 42 can be determined to be a non-defective product because the 2T output is 85% or more. On the other hand, in the “simultaneous multi-layer A” tape indicated by reference numeral 43, the 2T output is 68% of the “sequential multi-layer” magnetic tape, which is less than 85% of the non-defective product standard, and thus is judged as a defective product.

  By using the magnetic tape measurement method described in the present embodiment, the magnetic tape manufactured by measuring the hysteresis loop without actually operating the magnetic tape on the magnetic tape drive satisfies the desired output characteristics. It can be judged whether it is a non-defective level. For this reason, the magnetic tape manufacturing method disclosed in the present application can make an accurate quality judgment by a simple method, and provides a low-cost magnetic tape manufacturing method.

  As described above, the measurement method of the magnetic recording medium according to the present embodiment measures the hysteresis loop and normalizes the amount of magnetization in a predetermined external magnetic field, thereby expressing on the nonmagnetic support in the magnetic recording medium. It is possible to grasp the state of the interface between the nonmagnetic lower nonmagnetic layer and the upper magnetic layer formed in (1). In addition, as described in the above embodiment, the mixing of the lower nonmagnetic layer and the upper magnetic layer basically does not occur, and the interface state between the lower nonmagnetic layer and the upper magnetic layer is considered good. By using the data of the magnetic recording medium manufactured by the sequential multi-layer method as a reference, the state of the interface between the lower non-magnetic layer and the upper magnetic layer formed by the simultaneous multi-layer method can be determined as good or bad. It can be judged whether it is a non-defective product level.

  In particular, since the measurement method of the magnetic recording medium of the present embodiment is a general measurement method of magnetic characteristics, hysteresis that can be measured easily and inexpensively due to the widespread use of measurement devices and the like. Loop measurement is used, and it is very practical when compared with measurement methods that require expensive electron microscopes for measurement because it takes time to prepare samples and process data, as in the prior art. It can be said that it is a simple method. For this reason, by using the magnetic recording medium measurement method shown in the present embodiment, the magnetic recording medium is determined by pass / fail determination of the magnetic recording medium in which the lower nonmagnetic layer and the upper magnetic layer are stacked. Both the process itself and the pass / fail judgment process can be reduced in cost, and a practical magnetic recording medium manufacturing method can be obtained.

  In the measurement method of the magnetic recording medium of the present embodiment, an example in which the width of the external magnetic field is 600 Oe as a comparison region when obtaining the magnetization amount with respect to the external magnetic field within a predetermined range from the hysteresis loop is shown. The external magnetic field width value 600 Oe that defines the region is merely an example, and is not limited in any way by the measurement method of the present embodiment. However, if the width of the comparison region is too narrow, the effect of using the amount of magnetization for an external magnetic field having a predetermined width as the comparison region becomes poor. If the width of the comparison region is made too large, a region having a large slope in the hysteresis loop as described with reference to FIG. 3 is selected, and the flatness of the interface between the lower nonmagnetic layer and the upper magnetic layer is set to the magnetization amount. There is a risk that it will be difficult to obtain an effect that is effectively reflected in the image. Considering these things, it is preferable that the width of the magnitude of the external magnetic field as the comparison region is about 600 Oe to 1000 Oe.

  In the method for measuring a magnetic recording medium according to the present embodiment, the hysteresis loop preferably has a squareness ratio of 0.5 to 0.65. The upper magnetic layer used in the perpendicular recording type magnetic tape described in the present embodiment has a squareness ratio of 0.5 to 0.65, and the upper magnetic layer in this range is effectively in the state of its interface. Can be measured.

  In the above embodiment, the magnetic tape is exemplified as the magnetic recording medium. However, the magnetic recording medium measuring method and the manufacturing method according to the present invention can be applied to non-magnetic supports in addition to the magnetic tape. The present invention can also be applied to other magnetic recording media having a nonmagnetic lower nonmagnetic layer and an upper magnetic layer stacked thereon, for example, a magnetic disk.

  In particular, when the present invention is applied to a magnetic disk as a magnetic recording medium, it is not limited to a structure in which a lower nonmagnetic layer and an upper magnetic layer are laminated on only one surface of a support as illustrated in FIG. Alternatively, it may include a laminate in which a lower nonmagnetic layer and an upper magnetic layer are formed on both surfaces of a support. In this case, the magnitude of the external magnetic field obtained by using the hysteresis loop in the case where the upper magnetic layer is formed on both surfaces of the support via the lower nonmagnetic layer is normalized by the magnetization amount of 10000 Oe. The correlation between the normalized magnetization value and the degree of mixing between the lower non-magnetic layer and the upper magnetic layer is obtained again, and the normalized magnetization value that appears as the degree of mixing indicates the lower non-magnetic layer and the upper magnetic layer. It is preferable to grasp the situation of the boundary with the layer.

  The magnetic recording medium measuring method and the magnetic recording medium manufacturing method disclosed in the present application can grasp the interface state between the lower non-magnetic layer and the upper magnetic layer by a simple method. By determining the quality of the magnetic tape manufactured based on the measurement result, it is possible to realize a method for manufacturing a magnetic recording medium at a reduced cost. Therefore, it can be used for various magnetic recording media such as magnetic tapes and magnetic disks for various purposes including data backup in a hard disk of a computer.

DESCRIPTION OF SYMBOLS 1 Upper magnetic layer 2 Lower nonmagnetic layer 3 Support body 4 Back layer

Claims (8)

A method for measuring a magnetic recording medium in which a lower nonmagnetic layer and an upper magnetic layer are laminated on a nonmagnetic support, and the coercivity in the easy axis direction of the upper magnetic layer is in the range of 2000 to 3000 Oe. ,
The magnetic characteristics of the upper magnetic layer with respect to an external magnetic field are measured, and expressed in a hysteresis loop normalized with the amount of magnetization in an external magnetic field of 10000 Oe as 100%,
In the hysteresis loop, by comparing the value of the normalized magnetization amount in a region where an external magnetic field having an absolute value larger than the coercive force is applied so that the absolute value increases, A method of measuring a magnetic recording medium, comprising measuring an interface state between a magnetic layer and the upper magnetic layer.   A comparison region that is a region in which the normalized magnetization value differs greatly depending on the state of the interface between the lower non-magnetic layer and the upper magnetic layer is specified, and the normalized magnetization value in the comparison region The method of measuring a magnetic recording medium according to claim 1, wherein the state of the interface is measured based on the method.   The comparison region is set to a width where the difference between the maximum value and the minimum value of the applied external magnetic field is 600 to 1000 Oe, and a plurality of external magnetic fields including at least the maximum value and the minimum value in the comparison region The method of measuring a magnetic recording medium according to claim 2, wherein the state of the interface is measured using an average value of the normalized magnetization amount with respect to.   The method for measuring a magnetic recording medium according to claim 1, wherein a squareness ratio of the upper magnetic layer is 0.5 to 0.65.   The method for measuring a magnetic recording medium according to claim 1, wherein the magnetic recording medium is a magnetic tape. A nonmagnetic support is formed by laminating a lower nonmagnetic layer and an upper magnetic layer,
6. A magnetic recording medium manufactured by measuring a state of an interface between the lower nonmagnetic layer and the upper magnetic layer by the method for measuring a magnetic recording medium according to claim 1, and manufacturing the magnetic recording medium based on the measurement result A method of manufacturing a magnetic recording medium, wherein the quality is determined.   The method for manufacturing a magnetic recording medium according to claim 6, wherein the lower nonmagnetic layer and the upper magnetic layer are formed by a simultaneous multilayer coating method.   The method of manufacturing a magnetic recording medium according to claim 6, wherein the magnetic recording medium is a magnetic tape.

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