MAGNETIC TAPE AND MAGNETIC TAPE DEVICE
20170186460 ยท 2017-06-29
Assignee
Inventors
Cpc classification
International classification
Abstract
The magnetic tape has a magnetic layer containing ferromagnetic powder and binder on a nonmagnetic support, wherein the coercive force measured in the longitudinal direction of the magnetic tape is less than or equal to 167 kA/m, a timing-based servo pattern is present on the magnetic layer, and the edge shape specified by observing the timing-based servo pattern with a magnetic force microscope is a shape in which the difference between the value of the 99.9% cumulative distribution function of the width of misalignment from the ideal shape in the longitudinal direction of the magnetic tape and the value L.sub.0.1 of the 0.1% cumulative distribution function, L.sub.99.9-L.sub.0.1, is less than or equal to 180 nm.
Claims
1. A magnetic tape, which comprises a magnetic layer comprising ferromagnetic powder and binder on a nonmagnetic support, wherein a coercive force measured in a longitudinal direction of the magnetic tape is less than or equal to 1.67 kA/m; a timing-based servo pattern is present on the magnetic layer; and an edge shape specified by observing the timing-based servo pattern with a magnetic force microscope is a shape in which a difference between a value of 99.9% cumulative distribution function of a width of misalignment from an ideal shape in the longitudinal direction of the magnetic tape and a value L.sub.0.1 of 0.1% cumulative distribution function, L.sub.99.9L.sub.0.1, is less than or equal to 180 nm.
2. The magnetic tape according to claim 1, wherein the timing-based servo pattern is a linear servo pattern continuously or discontinuously running from one side to the other in a direction of width of the magnetic tape.
3. The magnetic tape according to claim 2, wherein the timing-based servo pattern is a linear servo pattern inclined by an angle relative to the direction of width of the magnetic tape and running continuously from one side to the other side in the direction of width of the magnetic tape, and the ideal shape is a linear shape running in a direction of angle .
4. The magnetic tape according to claim 1, wherein a SFD calculated with Equation 1: Equation 1
SFD=SFD.sub.25 C.SFD.sub.190 C. in the longitudinal direction of the magnetic tape is less than or equal to 0.50, and in Equation 1, SFD.sub.25 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 25 C., and SFD.sub.190 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 190 C. 5, The magnetic tape according to claim 4, wherein the SFD is greater than or equal to 0.03 but less than or equal to 0.50.
6. The magnetic tape according to claim 2, wherein a SFD calculated with Equation 1: Equation 1
SFD=SFD.sub.25 C.SFD.sub.190 C. in the longitudinal direction of the magnetic tape is less than or equal to 0.50, and in Equation 1, SFD.sub.25 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 25 C., and SFD.sub.190 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 190 C.
7. The magnetic tape according to claim 6, wherein the SFD is greater than or equal to 0.03 but less than or equal to 0.50.
8. The magnetic tape according to claim 3, wherein a SFD calculated with Equation 1: Equation 1
SFD=SFD.sub.25 C.SFD.sub.190 C. in the longitudinal direction of the magnetic tape is less than or equal to 0.50, and in Equation 1, SFD.sub.25 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 25 C., and SFD.sub.190 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 190 C.
9. The magnetic tape according to claim 8, wherein the SFD is greater than or equal to 0.03 but less than or equal to 0.50.
10. The magnetic tape according to claim 1, wherein the coercive force is greater than or equal to 119 kA/m but less than or equal to 167 kA/m.
11. A magnetic tape device, which comprises a magnetic tape, a magnetic head, and a servo head, and wherein the magnetic tape is a magnetic tape, which comprises a magnetic layer comprising ferromagnetic powder and binder on a nonmagnetic support, wherein a coercive force measured in a longitudinal direction of the magnetic tape is less than or equal to 167 kA/m; a timing-based servo pattern, is present on the magnetic layer; and an edge shape specified by observing the timing-based servo pattern with a magnetic force microscope is a shape in which a difference between a value L.sub.99.9 of 99.9% cumulative distribution function of a width of misalignment from an ideal shape in the longitudinal direction of the magnetic tape and a value L.sub.0.1 of 0.1% cumulative distribution function, L.sub.99.9L.sub.0.1, is less than or equal to 180 nm.
12. The magnetic tape device according to claim 1, wherein the timing-based servo pattern is a linear servo pattern continuously or discontinuously running from one side to the other in a direction of width of the magnetic tape.
13. The magnetic tape device according to claim 12, wherein the timing-based servo pattern is a linear servo pattern inclined by an angle relative to the direction of width of the magnetic tape and running continuously from one side to the other side in the direction of width of the magnetic tape, and the ideal shape is a linear shape running, in a direction of angle .
14. The magnetic tape device according to claim 11, wherein a SFD calculated with Equation 1: Equation 1
SFD=SFD.sub.25 C.SFD.sub.190 C. in the longitudinal direction of the magnetic tape is less than or equal to 0.50, and in Equation 1, SFD.sub.25 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 25 C., and SFD.sub.190 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 190 C.
15. The magnetic tape device according to claim 14, wherein the SFD is greater than or equal to 0.03 hut less than or equal to 0.50.
16. The magnetic tape device according to claim 12, wherein a SFD calculated with Equation 1: Equation 1
SFD=SFD.sub.25 C.SFD.sub.190 C. in the longitudinal direction of the magnetic tape is less than or equal to 0.50, and in Equation 1, SFD.sub.25 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 25 C., and SFD.sub.190 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 190 C.
17. The magnetic tape device according to claim 16, wherein the SFD is greater than or equal to 0.03 but less than or equal to 0.50.
18. The magnetic tape device according to claim 13, wherein a SFD calculated with Equation 1: Equation 1
SFD=SFD.sub.25 C.SFD.sub.190 C. in the longitudinal direction of the magnetic tape is less than or equal to 0.50, and in Equation 1, SFD.sub.25 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 25 C., and SFD.sub.190 C. denotes a switching field distribution measured in the longitudinal direction of the magnetic tape in an environment with a temperature of 190 C.
19. The magnetic tape device according to claim 18, wherein the SFD is greater than or equal to 0.03 but less than or equal to 0.50.
20. The magnetic tape device according to claim 11, wherein the coercive force is greater than or equal to 119 kA/m but less than or equal to 167 kA/m.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The present invention will be described in the following text by the exemplary, non-limiting embodiments shown in the drawing, wherein:
[0047]
[0048]
[0049]
[0050]
[0051]
[0052]
[0053]
[0054]
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0055] Unless otherwise stated, a reference to a compound or component includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.
[0056] As used herein, the singular forms a, an, and the include the plural reference unless the context clearly dictates otherwise.
[0057] Except where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term about. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not to be considered as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding conventions.
[0058] Additionally, the recitation of numerical ranges within this specification is considered to be a disclosure of all numerical values and ranges within that range. For example, if a range is from about 1 to about 50, it is deemed to include, for example, 1, 7, 34, 46.1, 23.7, or any other value or range within the range.
[0059] The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and non-limiting to the remainder of the disclosure in any way whatsoever. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for fundamental understanding of the present invention; the description taken with the drawings making apparent to those skilled in the art how several forms of the present invention may be embodied in practice.
Magnetic Tape
[0060] The magnetic tape according to an aspect of the present invention is a magnetic tape having a magnetic layer containing ferromagnetic powder and binder on a nonmagnetic support, wherein the coercive force measured in the longitudinal direction of the magnetic tape is less than or equal to 167 kA/m (less than or equal to 2,100 Oe), a timing-based servo pattern is present on the magnetic layer, and the edge shape specified by observing the timing-based servo pattern with a magnetic force microscope is a shape in which the difference between the value L.sub.99.9 of the 99.9% cumulative distribution function of the width of misalignment from the ideal shape in the longitudinal direction of the magnetic tape and the value L.sub.0.1 of the 0.1% cumulative distribution function, L.sub.99.9L.sub.0.1, is less than or equal to 180 nm.
[0061] The above magnetic tape will be described in greater detail below. The description in the present specification contains presumptions by the present inventors. The present invention is not to be construed as being limited by these presumptions.
[0062] <Coercive Force>
[0063] The coercive force measured in the longitudinal direction of the above magnetic tape is less than or equal to 167 kA/m. Research by the present inventors has revealed that the phenomenon of a drop in positioning precision that is not seen in magnetic tapes in which the coercive force exceeds 167 kA/m occurs in magnetic tapes in which the coercive force is less than or equal to 167 kA/m. The presumptions of the present inventors in this regard are as set forth above. This drop in positioning precision can be inhibited by controlling the difference L.sub.99.9L.sub.0.1 so that it remains within the range set forth above. This point will be described in greater detail further below. The coercive force Hc can be, for example., less than or equal to 160 kA/m, less than or equal to 155 kA/m, or less than or equal to 150 kA/m. However, so long as it is less than or equal to 167 kA/m, it can exceed these upper limits given by way of example. From the perspective of retaining the information recorded on the magnetic tape, the coercive force is, for example, greater than or equal to 119 kA/m, greater than or equal to 120 kA/m, or greater than or equal to 130 kA/m. The coercive force measured in the longitudinal direction of the magnetic tape can generally be controlled by means of the coercive force of the ferromagnetic powder contained in the magnetic layer.
[0064] <Difference L.sub.99.9L.sub.0.1>
[0065] The methods of measuring and calculating the difference L.sub.99.9L.sub.0.1 of a timing-based servo pattern present on a magnetic tape are as set forth above. The fact that in a magnetic tape with a coercive force of less than or equal to 167 kA/m, keeping the difference L.sub.99.9L.sub.0.1 to less than or equal to 180 nm can enhance the head positioning precision in a timing-based servo system was discovered by the present inventors based on extensive research.
[0066] Difference L.sub.99.9L.sub.0.1 is less than or equal to 180 nm. Difference L.sub.99.9L.sub.0.1 can be, for example, less than or equal to 170 nm, less than or equal to 160 nm, less than or equal to 150 nm, less than or equal to 140 nm, less than or equal to 130 nm, less than or equal to 120 nm, less than or equal to 110 nm, or less than or equal to 100 nm. However, so long as the difference L.sub.99.9L.sub.0.1 is less than or equal to 180 nm, the head positioning precision of a timing-based servo system can be enhanced in a magnetic tape with a coercive force of less than or equal to 167 kA. Accordingly, so long as the difference L.sub.99.9L.sub.0.1 is less than or equal to 180 nm, the above limits given by way of example can be exceeded. The difference L.sub.99.9L.sub.0.1 can be, for example, greater than or equal to 50 nm, greater than or equal to 60 nm, or greater than or equal to 70 nm. However, in the same manner as above, so long as the difference L.sub.99.9L.sub.0.1 is less than or equal to 180 nm, a value falling below these lower limits given by way of example is possible. The difference L.sub.99.9L.sub.0.1 can be controlled, for example, by means of the SFD of the magnetic tape and by the type of servo write head (specifically, the leakage magnetic field) employed to form the servo pattern. It is difficult to achieve a difference L.sub.99.9L.sub.0.1 that is less than or equal to 180 nm just by increasing the capacity of the servo write head (specifically, employing a servo write head with a large leakage magnetic field). By contrast, keeping the SFD to less than or equal to 0.50, for example makes it possible to achieve a difference L.sub.99.9L.sub.0.1 that is less than or equal to 180 nm.
[0067] <SFD>
[0068] In the above magnetic tape, the SFD is desirably less than or equal to 0.50. By way of example, the SFD can be less than or equal to 0.45, less than or equal to 0.40, less than or equal to 0.35, less than or equal to 0.30, less than or equal to 0.25, or less than or equal to 0.20. By way of example, the SFD can he greater than or equal to 0.03 or greater than or equal to 0.05.
[0069] However, so long as the SFD is less than or equal to 0.50, a difference L.sub.99.9L.sub.0.1 of less than or equal to 180 nm can be readily achieved. Thus, it becomes possible to increase the head positioning precision in a timing-based servo system in a magnetic tape with a coercive force of fess than or equal to 167 kA/m. This fact was discovered by the present inventors.
[0070] Based on research by the present inventors, the SFD could be controlled by the method used to prepare the magnetic tape and the tendencies (A) to (C) described above were observed.
[0071] For example, as regards (A), examples are intensifying the dispersion conditions (lengthening the dispersion period, reducing the diameter and increasing packing of the dispersion beads used in dispersion, and the like) and using a dispersing agent. Known dispersing agents, commercial dispersing agents, and the like can be used without limitation as the dispersing agent.
[0072] Additionally, as an example of (B), the ferromagnetic powderin which the difference SFD.sub.powder between the SFD as measured in an environment with a temperature of 100 C. and the SFD as measured in an environment with a temperature of 25 C. as calculated with Equation 2 below falls within a range of 0.05 to 1.50 can be employed. However, even outside the above range, SFD can be kept within the range of greater than or equal to 0.50.
Equation 2
[0073] SFD.sub.powder=SFD.sub.powder 100 C.SFD.sub.powder 25 C.
(In Equation 2, SFD.sub.powder 100 C. denotes the switching field distribution SFD of the ferromagnetic powder as measured in an environment with a temperature of 100 C. and SFD.sub.powder 25 C. denotes the switching field distribution SFD of the ferromagnetic powder as measured in an environment with a temperature of 25 C.)
[0074] As regards (C), there is a tendency that the SFD becomes small when the orientation processing of the magnetic tape is conducted by longitudinal orientation. There is a tendency that the SFD becomes large when the orientation processing of the magnetic tape is conducted by vertical orientation processing or no orientation processing is conducted.
[0075] Accordingly; for example, by employing one of means (A) to (C) above, or any combination of two or more thereof, to control these factors, it is possible to obtain a magnetic tape in which the SFD calculated with Equation 1 is less than or equal to 0.50.
[0076] Keeping the SFD to less than or equal to 0.50 is an example of a desirable way to keep difference L.sub.99.9L.sub.0.1 to less than or equal to 180 nm. Any tape having a magnetic layer containing ferromagnetic powder and binder on a nonmagnetic support, in which the magnetic layer has one or more timing-based servo patterns, for example, the magnetic layer has one or more data bands and one or more servo bands running in the longitudinal direction of the magnetic tape, having one or more timing-based servo patterns on the servo bands, in which the coercive force is less than or equal to 167 kA/m, and in which difference L.sub.99.9L.sub.0.1 is less than or equal to 180 nm, as well as a magnetic tape in which the SFD exceeds 0.50, is included in the magnetic tape according to one aspect of the present invention.
[0077] The above magnetic tape will be described in greater detail below.
[0078] <Magnetic Layer>
(Ferromagnetic Powder)
[0079] The magnetic layer contains ferromagnetic powder and binder. Various powders that are commonly employed as ferromagnetic powder in the magnetic layers of magnetic recording media such as magnetic tapes can be employed as the ferromagnetic powder. The use of ferromagnetic powder of small average particle size is desirable from the perspective of enhancing the recording density of the magnetic tape. To that end, the ferromagnetic powder with an average particle size of less than or equal to 50 nm is desirably employed. From the perspective of the stability of magnetization, the ferromagnetic powder with an average particle size of greater than or equal to 10 nm is desirably employed.
[0080] The average particle size of the ferromagnetic powder is a value measured with a transmission electron microscope by the following method.
[0081] Ferromagnetic powder is photographed at a magnification of 100,000-fold with a transmission electron microscope, and the photograph is printed on print paper at a total magnification of 500,000-fold to obtain a photograph of the particles constituting the ferromagnetic powder. A target particle is selected from the photograph of particles that has been obtained, the contour of the particle is traced with a digitizer, and the size of the (primary) particle is measured. The term primary particle refers to an unaggregated independent particle.
[0082] The above measurement is conducted on 500 randomly extracted particles. The arithmetic average of the particle size of the 500 particles obtained in this manner is adopted as the average particle size of the ferromagnetic powder. A Model 1-1-9000 transmission electron microscope made by Hitachi can be employed as the above transmission electron microscope, for example. The particle size can be measured with known image analysis software, such as KS-400 image analysis software from Carl Zeiss.
[0083] In the present invention and the present specification, the average particle size of the powder, such as ferromagnetic powder and various kinds of powder, is the average particle size as obtained by the above method. The average particle size indicated in Examples further below was obtained using a Model H-9000 transmission electron microscope made by Hitachi and KS-400 image analysis software made by Carl Zeiss.
[0084] The method described in paragraph 0015 of Japanese Unexamined Patent Publication (KOKAI) No. 2011-048878, which is expressly incorporated herein by reference in its entirety, far example, can be employed as the method of collecting sample powder such as ferromagnetic powder from a magnetic layer for particle size measurement.
[0085] In the present invention and the present specification, the size of the particles constituting, powder such as ferromagnetic powder (referred to as the particle size, hereinafter) is denoted as follows based on the shape of the particles observed in the above particle photograph:
(1) When acicular, spindle-shaped, or columnar (with the height being greater than the maximum diameter of the bottom surface) in shape, the particle size is denoted as the length of the major axis constituting the particle, that is, the major axis length.
(2) When platelike or columnar (with the thickness or height being smaller than the maximum diameter of the plate surface or bottom surface) in shape, the particle size is denoted as the maximum diameter of the plate surface or bottom surface.
(3) When spherical, polyhedral, of unspecific shape, or the like, and the major axis constituting the particle cannot be specified from the shape, the particle size is denoted as the diameter of an equivalent circle. The term diameter of an equivalent circle means that obtained by the circle projection method.
[0086] The average acicular ratio of a powder refers to the arithmetic average of values obtained for the above 500 particles by measuring the length of the minor axis, that is the minor axis length, of the particles measured above, and calculating the value of the (major axis length/minor axis length) of each particle. The term minor axis length refers to, in the case of the particle size definition of (1), the length of the minor axis constituting the particle; in the case of (2), the thickness or height, and in the case of (3), since the major axis and minor axis cannot he distinguished, (major axis length/minor axis length) is deemed to be 1 for the sake of convenience.
[0087] When the particle has a specific shape, such as in the particle size definition of (1) above, the average particle size is the average major axis length. In the case of (2), the average particle size is the average plate diameter, with the average plate ratio being the arithmetic average of diameter/thickness or height). For the definition of (3), the average particle size is the average diameter (also called the average particle diameter).
[0088] Ferromagnetic hexagonal ferrite powder is a specific example of desirable ferromagnetic powder. From the perspectives of achieving higher density recording and magnetization stability, the average particle size (for example, average plate diameter) of ferromagnetic hexagonal ferrite powder desirably ranges from 10 nm to 50 nm, preferably 20 nm to 50 nm, Reference can be made to Japanese Unexamined Patent Publication (KOKAI) No. 2011-225417, paragraphs 0012 to 0030, Japanese Unexamined Patent Publication (KOKAI) No. 2011-216149, paragraphs 0134 to 0136, and Japanese Unexamined Patent Publication (KOKAI) No. 2012-204726, paragraphs 0013 to 0030, for details on ferromagnetic hexagonal ferrite powder. The contents of the above publications are expressly incorporated herein by reference in their entirety
[0089] Ferromagnetic metal powder is also a specific example of desirable ferromagnetic powder, From the perspectives of achieving higher density recording and magnetization stability, the average particle size for example, average major axis length) of ferromagnetic metal powder desirably ranges from 10 nm to 50 nm, preferably 20 nm to 50 nm. Reference can be made to Japanese Unexamined Patent Publication (KOKAI) No. 2011-216149, paragraphs 0137 to 0141, and Japanese Unexamined Patent Publication (KOKAI) No. 2005-251351, paragraphs 0009 to 0023, for details on ferromagnetic metal powder. The contents of the above publications are expressly incorporated herein by reference in their entirety,
[0090] The content (fill rate) of ferromagnetic powder in the magnetic layer desirably falls within a range of 50 weight % to 90 weight %, preferably within a range of 60 weight % to 90 weight %. A high fill rate is desirable from the perspective of increasing recording density,
[0091] <Binder, Curing Agent>
[0092] The above magnetic tape is a particulate magnetic tape. The magnetic layer contains ferromagnetic powder and binder. The various resins that are commonly employed as binders in particulate magnetic recording media can be employed as the binder. Examples of binders are: polyurethane resin, polyester resin, polyamide resin, vinylchloride resin, styrene, copolymerized acrylic resin of acrylonitrile, methyl methacrylate, and the like; nitrocellulose and other cellulose resin; epoxy resin; phenoxy resin; and polyvinyl acetal, polyvinyl butyral, and other polyvinyl alkyral resin. These can be employed singly, or multiple resins can be mixed for use, Of these, polyurethane resin, acrylic resin, cellulose resin, and vinylchloride resin are desirable. These resins can also be employed as binders in the nonmagnetic layer and backcoat layer described further below. Reference can be made to Japanese Unexamined Patent Publication (KOKAI) No. 2010-24113, paragraphs 0028 to 0031, with regard to these resins. The content of the above publication is expressly incorporated herein by reference in its entirety. The average molecular weight of resins that are employed as binders is, by way of example, greater than or equal to 10,000 and less than or equal to 200,000 as a weight average molecular weight. The weight average molecular weight in the present invention and present specification is a value that is obtained by measurement by gel permeation chromatography (GPC) and converted to a polystyrene equivalent. Examples of measurement conditions are given below. The weight average molecular weights given in Examples further below are values obtained by measurement under the following measurement conditions and converted to polystyrene equivalents.
GPC device: HLC-8120 (made by Tosoh Corp.)
Column: TSK gel Multipore HXL-M (7.8 mm inner diameter (ID)30.0 cm, made by Tosoh Corp.)
Fluent: Tetrahydrofuran (THF)
[0093] A curing agent can be employed along with the above resins employed as binders. The curing agent can be a thermosetting compounda compound in which a curing reaction (crosslinking reaction) progresses when heatedin one embodiment. In another embodiment, the curing agent can be a photo-curable compounda compound in which a curing reaction (crosslinking reaction) progresses when irradiated with light. Thermosetting compounds are desirable as curing agents; polyisocyanate is suitable. Reference can be made to Japanese Unexamined Patent Publication 2011-216149, paragraphs 0124 and 0125, far details regarding polyisocyanate. In the magnetic layer-forming composition, the curing agent can be employed, for example, in a quantity of 0 to 80.0 weight parts per 100.0 weight parts of binder. From the perspective of enhancing coating strength, a curing agent can be added in a quantity of 50.0 to 80.0 weight parts for use.
[0094] (Additives)
[0095] Ferromagnetic powder and binder are contained in the magnetic layer The magnetic layer can also contain one or more additives as needed. An example of an additive is the above curing agent. By having the curing agent undergo a curing reaction in the process of forming the magnetic layer, at least a portion of the curing agent can be contained in the magnetic layer in a form where it has reacted (crosslinked) with another component, such as the binder. Examples of additives that can be incorporated into the magnetic layer are nonmagnetic fillers, lubricants, dispersing agents, dispersion adjuvants, antifungal agents, antistatic agents, oxidation inhibitors, and carbon black. Nonmagnetic filler is synonymous with nonmagnetic powder. In the present invention and the present specification, the term nonmagnetic powder means an aggregation of multiple nonmagnetic particles. The term aggregation is not limited to forms in which the particles are in direct contact, but includes forms in which binder, an additive, or the like is present between the particles. The term particle is sometimes used to denote powder. These points also apply to various powders in the present invention and the present specification. Examples of nonmagnetic fillers are nonmagnetic fillers capable of functioning as protrusion-forming agents forming protrusions that suitably protrude from the surface of the magnetic layer (referred to as protrusion-forming agents hereinafter) and nonmagnetic fillers capable of functioning as abrasives (referred to as abrasives hereinafter). The protrusion-forming agents are components that can contribute to controlling the frictional characteristics of the surface of the magnetic layer. Either a protrusion-forming agent or an abrasive is desirably contained in the magnetic layer of the above magnetic tape. It is also desirable for both to be contained, Additives can be employed in the form of suitable quantities of commercial products or additives manufactured by known methods.
[0096] [Nonmagnetic Layer]
[0097] The nonmagnetic layer will be described next. In the above magnetic tape, a magnetic layer can he present directly on the nonmagnetic support, or a nonmagnetic layer containing nonmagnetic powder and binder can be present between the nonmagnetic support and the magnetic layer. The nonmagnetic powder that is employed in the nonmagnetic layer can be an organic or an inorganic substance. Carbon black or the like can also be employed. Examples of inorganic materials are metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are available as commercial products and can be manufactured by known methods. Reference can be made to Japanese Unexamined Patent Publication (KOKAI) No. 2011-216149, paragraphs 0146 to 0150, for details. Reference can he made to Japanese Unexamined Patent Publication (KOKAI) No. 2010-24113, paragraphs 0040 and 0041, for details on carbon black that can be used in the nonmagnetic layer. The content (fill rate) of nonmagnetic powder in the nonmagnetic layer desirably fails within a range of 50 weight % to 90 weight %, preferably within a range of 60 weight % to 90 weight %.
[0098] Known techniques can be applied to the nonmagnetic layer with regard to the binder, additives, and other details relating to the nonmagnetic layer. For example, known techniques relating to the magnetic layer can be applied to the quantity and type of binder and the quantity and type of additives.
[0099] The nonmagnetic layer in the present invention and the present specification may be in the form of an essentially nonmagnetic layer containing small quantities of ferromagnetic powder, either in the form of impurities or by intention, for example, along with nonmagnetic powder. The term essentially nonmagnetic layer refers to a layer with a residual magnetic flux density of less than or equal to 10 mT, a coercive force of less than or equal to 7.96 kA/m (100 Oe), or a layer with a residual magnetic flux density of less than or equal to 10 mT and a coercive force of less than or equal to 7.96 kA/m (100 Oe). The nonmagnetic layer desirably has neither residual magnetic flux density nor coercive force.
[0100] <Nonmagnetic Support>
[0101] The nonmagnetic support will be described next. Known nonmagnetic supports in the form of biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamide-imide, aromatic polyamide, and the like are examples. Of these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are desirable. These supports can be subjected in advance to treatments such as corona discharge, plasma treatments, adhesion-enhancing treatments, and heat treatments.
[0102] <Various Thicknesses>
[0103] The thicknesses of the various layers and nonmagnetic support in the above magnetic tape are as follows. The thickness of the nonmagnetic support is desirably 3.0 m to 80.0 m. The thickness of the magnetic layer can be normally optimized based on the bandwidth of the recording signal, the length of the head gap, and the degree of saturation magnetization of the magnetic head employed in recording. The thickness of the magnetic layer can be generally 10 nm to 150 nm, desirably 20 nm to 120 nm, and preferably, 30 nm to 100 nm. It suffices for the magnetic layer to be comprised of a single layer. It can also be divided into two or more layers having different magnetic characteristics, and a known magnetic multilayer configuration can be applied.
[0104] The thickness of the nonmagnetic layer is, for example, 0.1 m to 3.0 m, desirably 0.1 m to 2.0 m, and preferably, 0.1 m to 1.5 m.
[0105] The thickness of the various layers and nonmagnetic support of the magnetic tape can be determined by known film thickness measurement methods. As an example, the cross section of the magnetic tape in the direction of thickness can be exposed by a known method such as an ion beam or microtome, and the exposed cross section can be observed by a scanning electron microscope. The various thicknesses can be determined as the thickness determined at one spot in the direction of thickness, or as the arithmetic average of the thicknesses obtained at multiple spots, such as two or more randomly extracted spots. The thickness of the various layers can also be determined as the design thickness calculated from the manufacturing conditions.
[0106] <Backcoat Layer>
[0107] The magnetic tape can contain a backcoat layer on the opposite surface of the nonmagnetic support from that on which the magnetic layer is present. The backcoat layer desirably contains carbon black and/or an inorganic powder. The formula. of the magnetic layer and/or the nonmagnetic layer can be applied for the binder and various additives used to form the backcoat layer. The thickness of the backcoat layer is desirably less than or equal to 0.9 m, preferably 0.1 m to 0.7 m.
[0108] <Manufacturing Process>
(Fabrication of a Magnetic Tape in which a Servo Pattern is Formed)
[0109] The compositions for forming the magnetic layer, nonmagnetic layer, and backcoat layer (generally referred to as coating liquids) generally contain solvent in addition to the various components set forth above. The various organic solvents generally employed to manufacture particulate magnetic tapes can be employed as the solvent. The process of preparing the compositions for forming the various layers normally includes at least a kneading step, a dispersing step, and mixing steps conducted as needed before and after these steps. Each of the various steps can be divided into two or more stages. All of the starting materials employed in the present invention, such as the ferromagnetic powder, nonmagnetic powder, binder, various optionally added additives, and solvent can he added at the start of, or part way through, any step. The various starting materials can be divided up and added in two or more steps. For example, when preparing the magnetic layer-forming composition, the abrasive and the ferromagnetic powder are desirably separately dispersed. To manufacture a magnetic tape, known manufacturing techniques can be employed. In the kneading step, it is desirable to employ a device with a strong kneading force, such as an open kneader, continuous kneader, pressurizing kneader, or extruder. Details regarding these kneading processes are described in Japanese Unexamined Patent Publication (KOKAI) Heisei Nos. 1-106338 and 1-79274, which are expressly incorporated herein by reference in their entirety. Glass beads or some other dispersion bead can be employed to disperse the various layer-forming compositions. Dispersion beads of high specific gravity such as zirconia beads, titania beads, and steel beads, are suitable as the dispersion beads. A known dispersing device can be employed as the disperser. As set forth above, one desirable way to obtain a magnetic tape with a SFD of less than or equal to 0.50 as calculated with Equation 1 is to intensify the dispersion conditions (for example, increase the period of dispersion, reduce the diameter and/or increase the fill ratio of the dispersion beads employed in dispersion). Reference can be made, for example, to Japanese Unexamined Patent Publication (KOKAI) No. 2010-24113, paragraphs 0051 to 0057, for details regarding methods of manufacturing magnetic tapes. Reference can be made to Japanese Unexamined Patent Publication (KOKAI) No. 2010-24113, paragraph 0052, in regard to orientation processing.
[0110] (Forming the Servo Pattern)
[0111] The above magnetic tape can have one or more data bands and one or more servo bands running in the longitudinal direction of the magnetic tape in the magnetic layer, and has one or more timing-based servo pattern on the servo band. An example of the configuration of the data band and servo band is given in Table 1. However, these are merely examples, and it suffices to dispose a data hand and a servo band in any configuration corresponding to the system of a magnetic tape device (generally referred to as a drive). Each data band has multiple data tracks. A timing-based servo pattern is formed on the servo band.
[0112] The servo pattern care be formed by magnetizing specific regions on the servo hand with a servo write head mounted on a servo writer. For example, a servo write head with a leakage magnetic field of 150 kA/m to 400 kA/m, desirably falling within a range of 200 kA/m to 400 kA/m, can be employed as the servo write head. The regions that are magnetized by the servo write head (positions where the servo pattern is formed) are determined by a standard, A commercial servo writer or a servo writer of known configuration can be employed as the servo writer. A known technique such as that described in Japanese Unexamined Patent Publication (KOKAI) 2011-175687 or U.S. Pat. Nos. 5,689,384 or 6,542,325, can be adopted without limitation for the configuration of the servo writer. The contents of the above publications are expressly incorporated herein by reference in their entirety.
Magnetic Tape Device
[0113] An aspect of the present invention relates to a magnetic tape device including the above magnetic tape, a magnetic head, and a servo head.
[0114] Details regarding the magnetic tape that is mounted in the above magnetic tape device are as set forth above. Since the magnetic tape has a timing-based servo pattern, when recording a magnetic signal and/or reproducing a signal that has been recorded on the data band by means of the magnetic head, while reading the pattern with the servo head, head tracking can be conducted by the timing-based servo method based on the servo pattern that is read to cause the magnetic head to follow the data track with high precision. An example of an indicator of head positioning precision is the position error signal (PES) based on the method set forth in Examples further below. PES is an indicator of the fact that the head is not running where it should be running even when head tracking is being conducted by a servo system in the course of a magnetic tape running in a magnetic tape device. The higher the value, the lower the head positioning precision by the servo system that is indicated. In the magnetic tape according to an aspect of the present invention, by achieving a difference L.sub.99.9L.sub.0.1 by keeping the SFD to less than or equal to 0.50, it is possible to achieve a PES of, for example, less than or equal to 9.0 m (for example, falling within a range of 7.0 to 9.0).
[0115] A known magnetic head that is capable of recording and/or reproducing a magnetic signal on a magnetic tape can be employed as the magnetic head mounted on the above magnetic tape device. The recording head and the reproduction head can be a single head, or can be separate magnetic heads. A known servo head that is capable of reading a servo pattern formed on the servo band of the above magnetic tape can be employed as the servo head.
[0116] For details regarding head tracking by a timing-based servo system, a known technique such as that described in U.S. Pat. Nos. 5,689,384, 6,542,325, or 7,876,421, can be applied without limitation. The contents of the above publications are expressly incorporated herein by reference in their entirety.
[0117] A commercial magnetic tape device will normally be equipped with a magnetic head and a servo head in accordance with the standard. A commercial magnetic tape device will normally be equipped with a servo control mechanism to permit head tracking by the timing-based servo system in accordance with the standard. The magnetic tape device according to an aspect of the present invention can be constituted, for example, by incorporating, the magnetic tape according to an aspect of the present invention into a commercial magnetic tape device.
EXAMPLES
[0118] The present invention will be described in greater detail below through Examples. However, the present invention is not limited to the embodiments shown in Examples. The parts and percent (%) indicated below denote weight parts and weight percent (%).
Example 1
1. Preparation of Alumina Dispersion (Abrasive Liquid)
[0119] To 100.0 parts of alumina powder (HIT-70 made by Sumitomo Chemical Co., Ltd.) with an alpha conversion rate of about 65% and a Brunauer-Emmett-Teller (BET) specific surface area of 30 m.sup.2/g were admixed 3.0 parts of 2,3-dihydroxynaphthalene (made by Tokyo Chemical Industry Co., Ltd.), 31.3 parts of a 32% solution (the solvent being a mixed solvent of methyl ethyl ketone and toluene) of polyester polyurethane resin (UR-4800 (polar group content: 80 meq/kg) made by Toyobo (Japanese registered trademark) having polar groups in the form of SO.sub.3Na groups, and 570.0 parts of a mixed solution with a 1:1 (weight) ratio of methyl ethyl ketone and cyclohexanone as solvent and the mixture was dispersed for 5 hours in a paint shaker in the presence of zirconia beads. Following dispersion, the dispersion and the beads were separated with a mesh to obtain an alumina dispersion.
[0120] 2. Formula of the Magnetic Layer-Forming Composition
TABLE-US-00001 (Magnetic liquid) Ferromagnetic hexagonal barium ferrite powder 100.0 parts (see Table 1) Polyurethane resin containing SO.sub.3Na 14.0 parts (weight average molecular weight: 70,000; SO.sub.3Na groups: 0.2 meq/g) Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (Abrasive liquid) Alumina dispersion prepared in 1. above 6.0 parts (Silica sol) Colloidal silica (average particle size: 100 nm) 2.0 parts Methyl ethyl ketone 1.4 parts (Other components) Stearic acid 2.0 parts Butyl stearate 6.0 parts Polyisocyanate (Coronate (Japanese registered trademark) 2.5 parts made by Nippon Polyurethane Industry Co., Ltd.) (Solvent added to finish) Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts
[0121] 3. Formula of Nonmagnetic Layer-Forming Composition
TABLE-US-00002 Nonmagnetic inorganic powder: -iron oxide 100.0 parts Average particle size (average major axis length): 10 nm Average acicular ratio: 1.9 BET specific surface area: 75 m.sup.2/g Carbon black 20.0 parts Average particle size: 20 nm Polyurethane resin containing SO.sub.3Na 18.0 parts (weight average molecular weight: 70,000; SO.sub.3Na groups: 0.2 meq/g) Stearic acid .sup.1.0 part Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts
[0122] 4. Formula of Backcoat Layer-Forming Composition
TABLE-US-00003 Nonmagnetic inorganic powder: -iron oxide 80.0 parts Average particle size (average major axis length): 0.15 m Average acicular ratio: 7 BET specific surface area: 52 m.sup.2/g Carbon black 20.0 parts Average particle size: 20 nm Vinyl chloride copolymer 13.0 parts Polyurethane resin containing sulfonate groups 6.0 parts Phenylphosphonic acid 3.0 parts Cyclohexanone 155.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Polyisocyanate 5.0 parts Cyclohexanone 200.0 parts
[0123] 5. Preparation of Various Layer-Forming Compositions
[0124] A magnetic layer-forming composition was prepared by the following method. The above magnetic liquid was prepared by dispersing the various components for 24 hours (bead dispersion) using a batch-type vertical sand mill. Zirconia beads having a bead diameter of 0.5 mm were employed as the dispersion beads. The above sand mill was used to mix the above abrasive liquid and magnetic liquid that had been prepared with the other components (silica sol, other components, and solvents added to finish) and the mixture was bead dispersed for 5 minutes. The mixture was then processed. for 0.5 minutes (ultrasonically processed) in a batch-type ultrasonic device (20 kHz, 300 W). Subsequently, filtering was conducted with a filter having an average pore diameter of 0.5 m to prepare a magnetic layer-forming composition. A portion of the magnetic layer-forming composition that had been prepared was collected and the dispersed particle diameter, an indicator of dispersion of ferromagnetic powder, was measured by the method set thrill further below. The measured values are given in Table 1.
[0125] A nonmagnetic layer-forming composition was prepared by the following method. The various components excluding the stearic acid, cyclohexanone, and methyl ethyl ketone were dispersed for 24 hours in a batch-type vertical sand mill to obtain a dispersion. Zirconia beads having a bead diameter of 0.1 mm were employed as the dispersion beads, Subsequently, the remaining components were added to the dispersion obtained and the mixture was stirred in a dissolver. The dispersion thus obtained was filtered using a filter having an average pore diameter of 0.5 m to obtain a nonmagnetic layer-forming composition.
[0126] A backcoat layer-forming composition was prepared by the following method. The various components excluding the lubricants (stearic acid and butyl stearate), polyisocyanate, and cyclohexanone were kneaded in an open kneader and diluted. Subsequently, the mixture was subjected to 12 passes of dispersion processing, each pass comprising a retention time of 2 minutes with a rotor tip peripheral speed of 10 m/s and a bead till rate of 80 volume % using zirconia beads with a bead diameter of 1 mm in a horizontal-type bead mill disperser. The remaining components were then added to the dispersion obtained and the mixture was stirred in a dissolver. The dispersion thus obtained was filtered with a filter having an average pore diameter of 1 m to prepare a backcoat layer-forming composition.
[0127] 6. Fabrication of Magnetic Tapes
[0128] The nonmagnetic layer-forming composition prepared in 5, above was coated and dried on the surface of a polyethylene naphthalate support 5.0 m in thickness to a dry thickness of 0.1 m, after which the magnetic layer-forming composition prepared in 5, above was coated in a quantity calculated to yield a thickness upon drying of 70 nm. The magnetic layer-forming composition was dried without being orientation processed. Subsequently, the backcoat layer-forming composition prepared in 5, above was coated and dried to a dry thickness of 0.4 m on the opposite surface of the polyethylene naphthalate support from that on which the nonmagnetic, layer and magnetic layer had been formed.
[0129] Subsequently, a surface smoothing treatment (calendering treatment) was conducted with calender rolls comprised solely of metal rolls at a rate of 100 m/min, a linear pressure of 300 kg/cm, and a calender roil surface temperature of 100 C., after which the product was heat treated for 36 hours in an environment with an ambient temperature of 70 C. After the heat treatment, the product was cut to inch (0.0127 meter) width to obtain a magnetic tape.
[0130] The thicknesses of the various layers set forth above were design thicknesses calculated from the manufacturing conditions.
[0131] 7. Forming the Timing-Based Servo Pattern
[0132] A servo band was formed in a demagnetized state magnetic layer of the magnetic tape that had been fabricated and a servo pattern with a configuration and shape in accordance with the LTO Ultrium format was formed using a servo writer on the servo band that had been formed. The leakage magnetic field of the servo head mounted on the servo writer was the value given in Table 1.
[0133] A magnetic tape having a servo pattern with a configuration and shape in accordance with the LTO lithium format on the servo band and having a data band, servo band, and guide band with a configuration in accordance with the LTO Ultrium format on the magnetic layer was obtained.
[0134] 7. Evaluation Methods
(1) Measurement of the Dispersed Particle Diameter of the Ferromagnetic Powder in the Magnetic Layer-Forming Composition
[0135] A portion of the magnetic layer-forming composition fabricated in 5, above was collected and a sample solution was prepared by dilution to 1/50 based on weight with the organic solvents employed to prepare the magnetic layer-forming composition. The sample solution was measured with a light-scattering particle size distribution meter (LB500 made by Horiba) and the arithmetic average particle diameter was adopted as the dispersion particle diameter.
(2) Measurement of the Average Particle Size of the Ferromagnetic Powder
[0136] The average particle size of the ferromagnetic particles was determined by the method set forth above.
(3) Measurement of the Coercive Force Hc and the SFD.SUB.powder .of the Ferromagnetic Powder
[0137] The SFD.sub.powder of the ferromagnetic powder specified by Equation 2 above and the coercive force Hc were measured at an applied magnetic filed of 796 kA/m (10 kOe) with a vibrating sample magnetometer (made by Toei-Kogyo Co., Ltd.).
(4) Measurement of the SFD and Coercive Force in the Longitudinal Direction of the Magnetic Tape
[0138] The SFD specified by Equation 1 above and the coercive force in the longitudinal direction of the magnetic tape were measured at an applied magnetic field of 796 kA/m (10 kOe) with a vibrating sample magnetometer (made by Toei-Kogyo Co., Ltd.).
(5) Measurement and Calculation of Difference L.sub.99.9L.sub.0.1
[0139] A magnetic force microscope in the form of a Dimension 3100 made by Bruker was employed in frequency modulation mode and an SSS-MFMR (with a nominal curvature radius of 15 nm) as employed as probe to conduct coarse measurement at a pitch of 100 nm over a measurement range of 90 m90 m on the surface of the magnetic layer of the magnetic tape on which the servo pattern had been formed and a servo pattern (magnetized region) was extracted. The distance between the tip of the probe and the surface of the magnetic layer during magnetic force microscopic observation was 20 nm. Since live A burst servo patterns farmed according to the LTO Ultrium format was contained within the measurement range, the five servo patterns were extracted.
[0140] Using the above magnetic force microscope and probe, the area near the boundary of the magnetized region and unrnagnetized region was measured at a pitch of 5 nm and a magnetic profile was obtained for an edge downstream in the running direction for each servo pattern. Since the magnetic profile obtained was inclined by =12, a rotational correction was made with analytic software to render =0.
[0141] Measurements were made in three different spots on the surface of the magnetic layer. Each measurement range contained five A burst servo patterns.
[0142] Subsequently, difference L.sub.99.9L.sub.0.1 was determined by the method set forth above using analytic software. MATLAB prepared by MathWorks was employed as the analytic software.
(5) Measurement of PES
[0143] For each of the magnetic tapes on which the above timing-based servo pattern was formed, the servo pattern was read with the verify head on the servo writer used to form the servo pattern. The verify head was a reading magnetic head for verifying the quality of the servo pattern formed on the magnetic tape. in the same manner as for the magnetic heads of known magnetic tape devices (drives), an element reading the position relative to the position of the servo pattern (pattern in the direction of width of the magnetic tape) was disposed. A known PES calculating circuit calculating the head position precision based on a servo system from the electric signal obtained by reading the servo pattern was connected to the verify head. The PES calculation circuit calculated as needed the displacement in the direction of width of the magnetic tape from the electric signal (pulse signal) that was inputted, and calculated the PES as a value obtained by applying a high-pass filter (cutoff: 500 cycles/m) to the temporal change information (signal) of this displacement. Applying this high-pass filter reduced the effect of physical vibration on the PES obtained, making it possible to more precisely evaluate the effect of location shifting of the edge shape of the servo pattern on head positioning precision.
Examples 2 to 7, Comparative Examples 1 to 9
[0144] Table 1 gives the ferromagnetic powders, bead dispersion times during preparation of the magnetic layer-forming composition, whether orientation processing was conducted, and the leakage magnetic field of the servo write head used to prepare the magnetic tapes of Examples 2 to 7 and Comparative Examples 1 to 9. For the servo write head, the stronger the leakage magnetic field, the greater the capacity to record the servo pattern. Three servo write heads with different leakage magnetic fields were employed in the Examples and Comparative Examples. Table 1 records the servo write head recording capacity in the order of lowest to highest leakage magnetic field as low, medium, or high.
[0145] For the items shown in Table 1 and where ferromagnetic metal powders were employed as the ferromagnetic powder, with the exception that kneading and dilution were conducted prior to dispersion by kneading the various components of the magnetic liquid in an open kneader, the magnetic tapes of the various Examples and Comparative Examples were fabricated and evaluated by the same methods as in Example 1.
[0146] In Table 1, BF is recorded when ferromagnetic hexagonal barium ferrite powder as employed as the ferromagnetic powder and MP is recorded when ferromagnetic metal powder was employed.
[0147] None is recorded in the orientation column when no orientation processing was conducted. Perpendicular is recorded when a magnetic field with a magnetic field intensity of 0.3 T was applied in a direction perpendicular to the coating surface to conduct a perpendicular orientation processing followed by drying while the magnetic layer-forming composition that had been coated was still wet. Longitudinal is recorded when a magnetic field with a magnetic field intensity of 0.3 T was applied in the longitudinal direction relative to the coating surface to conduct a longitudinal orientation processing while the magnetic layer-forming composition that had been coated was still wet.
[0148] The results of the above are given in Table 1.
TABLE-US-00004 TABLE 1 Unit Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ferromagnetic Type BF BF BF BF BF BF MP powder SFD.sub.powder 0.20 0.30 0.10 0.10 0.80 0.10 0.10 Hc kA/m 160 157 146 146 147 146 224 Oe 2011 1978 1840 1840 1850 1840 2820 Average particle size nm 25 25 23 23 23.5 23 38 Dispersion Dispersion time hours 48 48 35 48 48 48 48 condition Diameter of nm 20 20 50 20 20 20 20 dispersion beads Orientation None Longitudinal Longitudinal Longitudinal Longitudinal Perpendicular Perpendicular Tape Hc kA/m 165 165 158 158 160 138 156 Oe 2072 2072 1982 1982 2011 1734 1960
SFD 0.48 0.21 0.16 0.05 0.33 0.48 0.45 Servo write head Servo write head Medium Medium Medium Medium Medium Medium Medium recording capacity Leakage magnetic kA/m 247 247 247 247 247 247 247 field Oe 3100 3100 3100 3100 3100 3100 3100 Servo pattern L.sub.99.9-L.sub.0.1 nm 172 111 92 80 138 163 159 Evaluation result PES nm 8.4 8.6 8.3 8.2 8.4 8.1 8.7 Unit Comp. Ex. 1 Comp. Ex. 2 Comp. Ex. 3 Comp. Ex. 4 Comp. Ex. 5 Ferromagnetic Type BF MP MP BF BF powder
SFD.sub.powder 0.30 0.80 0.80 0.30 0.30 Hc kA/m 188 224 224 170 166 Oe 2360 2810 2810 2130 2085 Average particle size nm 27 35 35 27 26.5 Dispersion Dispersion time hours 35 40 40 35 35 condition Diameter of nm 50 35 35 50 50 dispersion beads Orientation None None None None None Tape Hc kA/m 194 235 235 176 170 Oe 2440 2950 2950 2210 2130
SFD 0.82 0.79 0.79 0.84 0.84 Servo write head Servo write head Medium Medium High Medium Medium recording capacity Leakage magnetic field kA/m 247 247 366 247 247 Oe 3100 3100 4600 3100 3100 Servo pattern L.sub.99.9-L.sub.0.1 nm 169 158 121 176 178 Evaluation result PES nm 8.6 8.7 8.4 8.6 8.9 Unit Comp. Ex. 6 Comp. Ex. 7 Comp. Ex. 8 Comp. Ex. 9 Ferromagnetic Type BF BF BF BF powder
SFD.sub.powder 0.30 0.30 0.30 0.20 Hc kA/m 157 157 157 160 Oe 1978 1978 1978 2011 Average particle size nm 25 25 25 25 Dispersion Dispersion time hours 35 35 48 48 condition Diameter of nm 50 50 20 20 dispersion beads Orientation None None None None Tape Hc kA/m 163 163 164 165 Oe 2052 2052 2063 2072
SFD 0.84 0.84 0.63 0.48 Servo write head Servo write head Medium High High Low recording capacity Leakage magnetic field kA/m 247 366 366 191 Oe 3100 4600 4600 2400 Servo pattern L.sub.99.9-L.sub.0.1 nm 272 263 198 228 Evaluation result PES nm 13.8 13.4 10.2 11.9
[0149] The fact that the PES determined by the above method was less than or equal to 9 nm meant that highly precise positioning of the recording head was possible by head tracking in a timing-based servo system.
[0150] A comparison of Comparative Examples 1 to 5 and Comparative Examples 6 to 9 reveals that in magnetic tapes in which the coercive force measured in the longitudinal direction was less than or equal to 167 kA/m, the phenomenon of the PES greatly exceeding 9 nm (a drop in head positioning precision) occurred. This drop in head positioning precision. was determined to be difficult. to inhibit by enhancing the recording capacity of the servo write head.
[0151] By contrast, in the magnetic tapes of Examples 1 to 7, the coercive force measured in the longitudinal direction was less than or equal to 167 kA/m, but the difference L.sub.99.9L.sub.0.1 was kept to less than or equal to 180 nm. It was thus possible to achieve a PES of less than or equal to 9 nm, that is, enhance the head positioning precision in a timing-based servo system, by keeping the difference L.sub.99.9L.sub.0.1 to less than or equal to 180 nm.
[0152] An aspect of the present invention is useful in the technical field of magnetic tapes for high-density recording.
[0153] Although the present invention has been described in considerable detail with regard to certain. versions thereof, other versions are possible, and alterations, permutations and equivalents of the version shown will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. Also, the various features of the versions herein can be combined in various ways to provide additional versions of the present invention. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention. Therefore, any appended claims should not be limited to the description of the preferred versions contained herein and should include all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.
[0154] Having now fully described this invention, it will be understood to those of ordinary skill in the art that the methods of the present invention can be carried out with a wide and equivalent range of conditions, formulations, and other parameters without departing from the scope of the invention or any Examples thereof.
[0155] All patents and publications cited herein are hereby fully incorporated by reference in their entirety. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that such publication is prior art or that the present invention is not entitled to antedate such publication by virtue of prior invention.