JP2017139043A - Magnetic tape, magnetic tape cartridge, and magnetic recording/reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic tape including a nonmagnetic layer with thickness of 0.50 μm or less, and capable of maintaining a wear property even running repeatedly under low temperature and low humidity.SOLUTION: There are provided: a magnetic tape including a nonmagnetic layer on a nonmagnetic support medium, and further including on the nonmagnetic layer ferromagnetic powder, abrasive and binding agent; a magnetic tape cartridge; and a magnetic recording/reproducing apparatus. The thickness of the nonmagnetic layer is 0.50 μm or less, the friction coefficient measured on a base material of the magnetic layer surface is 0.35 or less, and ΔSFD calculated from ΔSFD=SFD-SFDin a magnetic tape longitudinal direction is 0.50 or less. In the formula, SFDrepresents an inverted field distribution SFD that is measured at a temperature of 25°C in the magnetic tape longitudinal direction, SFDrepresents an inverted field distribution SFD that is measured at a temperature of -190°C in the magnetic tape longitudinal direction.SELECTED DRAWING: None

Description

  The present invention relates to a magnetic tape, a magnetic tape cartridge, and a magnetic signal reproducing apparatus.

There are two types of magnetic recording media, tape-shaped and disk-shaped. For storage applications such as data backup, tape-shaped magnetic recording media, ie magnetic tape, are mainly used.
For recording / reproducing signals on a magnetic tape, a magnetic tape cartridge containing a magnetic tape is usually mounted in a drive, and the magnetic tape is moved in the drive to bring the magnetic tape surface (magnetic layer surface) into contact with the magnetic head ( Sliding). Hereinafter, the magnetic tape is also simply referred to as “tape”, and the magnetic head is also simply referred to as “head”.

  In the above recording / reproducing operation, since the traveling is repeated while the surface of the magnetic layer and the head slide, a part of the surface of the magnetic layer is scraped off, and foreign matter may be generated and attached to the head. If the magnetic tape is repeatedly run with foreign matter attached to the head in this way, the distance between the magnetic tape and the head is affected by the foreign matter, and the output may fluctuate (so-called spacing). Loss). Such a spacing loss causes a decrease in electromagnetic conversion characteristics as the vehicle travels repeatedly. As countermeasures against this point, conventionally, in order to provide the magnetic layer surface with a function of removing foreign matter adhering to the head, it has been carried out to include an abrasive in the magnetic layer (see, for example, Patent Documents 1 and 2). ). In the following, the function of removing foreign matter adhering to the head on the surface of the magnetic layer is referred to as “wearability of the magnetic layer surface” or simply “wearability”.

JP 2014-179149 A JP-A-2005-243162

  By the way, with respect to the magnetic tape, in order to increase the recording capacity per volume of the magnetic tape cartridge, the tape that can be accommodated in one volume of the magnetic tape cartridge by reducing the total thickness of the magnetic tape (that is, by reducing the thickness of the magnetic tape). It is desirable to increase the overall length. Usually, in a magnetic tape having a multilayer structure having a nonmagnetic layer and a magnetic layer in this order on a nonmagnetic support, the nonmagnetic layer accounts for a large proportion of the thickness among various layers. It is effective to make the nonmagnetic layer thin.

  On the other hand, magnetic tapes used for data storage are often used in low-temperature and low-humidity environments such as data centers where temperature and humidity are controlled (for example, in an environment with a temperature of 10 to 15 ° C. and a relative humidity of about 10 to 20%). . Therefore, it is desirable for the magnetic tape to be able to maintain wearability under low temperature and low humidity.

  In view of the above, the present inventor has studied running a magnetic tape having a thin nonmagnetic layer under low temperature and low humidity. As a result, in the conventional method of incorporating an abrasive into the magnetic layer, especially in the case of a magnetic tape in which the nonmagnetic layer is thinned to a thickness of 0.50 μm or less, the wear property of the surface of the magnetic layer is low under low temperature and low humidity. It has become clear that a new problem will occur that will decrease with repeated driving.

  Accordingly, an object of the present invention is to provide a magnetic tape having a nonmagnetic layer thickness of 0.50 μm or less and capable of maintaining the wear of the surface of the magnetic layer even when it is repeatedly run at low temperature and low humidity. There is to do.

As a result of intensive studies to achieve the above object, the present inventor has obtained the following magnetic tape:
A magnetic tape having a nonmagnetic layer comprising a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer comprising a ferromagnetic powder, an abrasive and a binder on the nonmagnetic layer,
The thickness of the nonmagnetic layer is 0.50 μm or less,
A magnetic tape having a friction coefficient measured at the substrate portion on the surface of the magnetic layer of 0.35 or less and ΔSFD calculated by the following formula 1 in the longitudinal direction of the magnetic tape is 0.50 or more;
ΔSFD = SFD _{25 ° C.} −SFD _{−190 ° C.} Formula 1
(In Formula 1, SFD _{25 ° C.} is a switching field distribution (SFD) measured in the longitudinal direction of the magnetic tape in an environment at a temperature of 25 ° C., and SFD _{−190 ° C.} is an environment at a temperature of −190 ° C. The reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape.
I came to find. That is, it has been clarified that such a magnetic tape can maintain the wear property of the magnetic layer surface even when the non-magnetic layer has a thickness of 0.50 μm or less and is repeatedly run under low temperature and low humidity.

The substrate portion in the present invention refers to a portion specified by the following method on the surface of the magnetic layer.
A surface measured by an atomic force microscope (AFM) in which the volume of convex and concave components in the field of view is equal is defined as a reference surface, and a protrusion with a height of 15 nm or more from the reference surface is defined as a protrusion. It is defined as Then, a portion where the number of protrusions is zero, that is, a portion where a protrusion having a height of 15 nm or more from the reference surface is not detected on the surface of the magnetic layer is identified as a base portion.
Further, the friction coefficient measured at the substrate portion is a value measured by the following method.
In the base portion (measurement location: 10 μm length in the longitudinal direction of the magnetic tape), a diamond spherical indenter having a radius of 1 μm was loaded with a load of 100 μN and a speed of 1 μm / sec. Measure the frictional force (horizontal force) and vertical drag by reciprocating once. The friction force and the normal force measured here are arithmetic averages obtained by constantly measuring the friction force and the normal force during the one reciprocation. The above measurement can be performed with, for example, Hystron TI-950 type tribo indenter. Then, the friction coefficient μ value is calculated from the arithmetic average of the measured frictional force and the arithmetic average of the normal force. The friction coefficient is a value obtained from the following formula: F = μN from the frictional force (horizontal force) F (unit: Newton (N)) and the vertical drag N (unit: Newton (N)). The above-mentioned measurement and calculation of the friction coefficient μ value are performed at three locations of the base portion randomly determined on the surface of the magnetic layer, and the arithmetic average of the three measurement values obtained is used as the friction coefficient measured at the base portion. . Hereinafter, the friction coefficient measured in the substrate portion is also referred to as “substrate friction”.

The following is not intended to limit the present invention, but the present inventor considers the magnetic tape as follows.
(1) The deterioration of the wear property on the surface of the magnetic layer is caused by the fact that the abrasive present in the vicinity of the surface of the magnetic layer is scraped and worn away by contact with the head while traveling under low temperature and low humidity. It is thought that. It is considered that such abrasion of the abrasive can be prevented by appropriately sinking the abrasive that receives pressure from the head toward the magnetic layer when the abrasive and the head come into contact with each other. However, a magnetic tape having a nonmagnetic layer with a thickness of 0.50 μm or less is less likely to sink an abrasive present near the surface of the magnetic layer than a magnetic tape having a thicker nonmagnetic layer. Conceivable. The present inventor believes that the so-called cushioning effect brought about by the nonmagnetic layer located below the magnetic layer is reduced by the thinning of the nonmagnetic layer, which is only an assumption.
Furthermore, the present inventor has repeatedly studied that the ferromagnetic powder supports the abrasive present in the vicinity of the surface of the magnetic layer in the magnetic layer. It was thought that the contact of the head could suppress the sinking under pressure from the head. In further investigation, the supporting effect of the abrasive by the ferromagnetic powder becomes stronger as the ferromagnetic particles constituting the ferromagnetic powder in the magnetic layer are aligned in the longitudinal direction while interacting with each other. It came to think that it might become. Based on such knowledge, if the ferromagnetic powder is present in the magnetic layer in a moderately random state in the longitudinal direction, the supporting effect of the abrasive by the ferromagnetic powder is mitigated, and the abrasive present in the vicinity of the magnetic layer surface. Is likely to sink into the magnetic layer side.
Based on the above knowledge, the present inventor compensates for the cushioning effect of the nonmagnetic layer, which has been reduced by reducing the thickness of the nonmagnetic layer to 0.50 μm or less, by relaxing the supporting effect of the magnetic layer by the ferromagnetic powder. As a result of intensive studies, it was found that ΔSFD calculated by Equation 1 in the longitudinal direction of the magnetic tape is 0.50 or more. In this regard, the present inventor believes that the ΔSFD may be an index indicating the presence state of the ferromagnetic powder in the magnetic layer. The state in which ΔSFD is 0.50 or more is a state in which the ferromagnetic powder is present in a moderately random state in the longitudinal direction in the magnetic layer. It is presumed that the supporting effect of the abrasive by the magnetic powder is alleviated. As a result, the decrease in the cushioning effect of the nonmagnetic layer, which has been reduced by reducing the thickness of the nonmagnetic layer to 0.50 μm or less, can be compensated for and the presence of the nonmagnetic layer in the vicinity of the surface of the magnetic layer while running under low temperature and low humidity. It is speculated that the abrasive can be prevented from being scraped and worn by contact with the head.
(2) Furthermore, the present inventor considers the base friction as follows. If the non-magnetic layer is thinned to 0.50 μm or less, the strength of the magnetic tape tends to decrease and the magnetic tape tends to be flexible. The present inventor thinks that it may become. As a result, the influence of the coefficient of friction of the substrate on the slidability between the surface of the magnetic layer and the head increases, and the slidability tends to decrease (becomes difficult to slide smoothly) as the coefficient of friction of the substrate increases. The present inventors speculate that there may be. As the slidability decreases, it is considered that a stronger force is applied to the abrasive at the time of contact with the head, and this is considered to be a cause of the abrasive being scraped and worn. On the other hand, the slidability can be improved by setting the coefficient of friction measured at the substrate portion of the magnetic layer surface to 0.35 or less. As a result, a nonmagnetic layer having a thickness of 0.50 μm or less can be obtained. The present inventor presumes that the magnetic tape having the above-described magnetic tape can be prevented from being scraped and worn by contact with the head during repeated running at low temperature and low humidity. doing.

  As described above, the inventor found that the friction coefficient measured at the base portion of the surface of the magnetic layer is 0.35 or less, and the ΔSFD in the longitudinal direction of the magnetic tape is 0.50 or more. It is speculated that the magnetic tape having a nonmagnetic layer of 50 μm or less is repeatedly run under low temperature and low humidity, and that it contributes to suppressing the abrasive that exists near the surface of the magnetic layer from being scraped and worn by contact with the head. ing. As a result, the present inventor believes that it is possible to maintain the wearability of the surface of the magnetic layer even if the running is repeated under low temperature and low humidity. However, the above is only an estimation and does not limit the present invention.

  In the present invention and the present specification, the powder means an aggregate of a plurality of particles. For example, the ferromagnetic powder means an aggregate of a plurality of ferromagnetic particles. The aggregate of a plurality of particles is not limited to an embodiment in which the particles constituting the assembly are in direct contact with each other, and an embodiment in which a binder, an additive, or the like described later is interposed between the particles is also included. The The term particle is sometimes used to describe powder.

  In one aspect, the abrasive comprises alumina.

  In one aspect, the coefficient of friction measured at the substrate portion of the magnetic layer surface of the magnetic tape is 0.10 or more and 0.35 or less.

  In one embodiment, the ΔSFD is 0.50 or more and 1.50 or less.

  In one aspect, the total thickness of the magnetic layer and the nonmagnetic layer is 0.60 μm or less.

  In one aspect, the magnetic tape has a backcoat layer containing a nonmagnetic powder and a binder on the side of the nonmagnetic support opposite to the side having the nonmagnetic layer and the magnetic layer.

  In one aspect, the total thickness of the magnetic tape is 6.00 μm or less.

  In one embodiment, the ferromagnetic powder is selected from the group consisting of ferromagnetic hexagonal ferrite powder and ferromagnetic metal powder.

  The further aspect of this invention is related with the magnetic tape cartridge in which the said magnetic tape was accommodated.

  In one aspect, the tape length of the magnetic tape accommodated in the magnetic tape cartridge is 10 m or more.

  A further aspect of the present invention relates to a magnetic recording / reproducing apparatus including the magnetic tape cartridge and a magnetic head.

According to one aspect of the present invention, a magnetic tape having a nonmagnetic layer with a thickness of 0.50 μm or less, and capable of maintaining the wearability of the surface of the magnetic layer even when traveling under low temperature and low humidity. Can be provided.
Furthermore, according to one aspect of the present invention, it is also possible to provide a magnetic tape cartridge in which such a magnetic tape is accommodated, and a magnetic recording / reproducing apparatus including the magnetic tape cartridge.

[Magnetic tape]
One aspect of the present invention is a magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and a magnetic layer containing a ferromagnetic powder, an abrasive and a binder on the nonmagnetic layer. The thickness of the nonmagnetic layer is 0.50 μm or less, the coefficient of friction (base friction) measured at the base portion of the magnetic layer surface is 0.35 or less, and the following formula 1 in the longitudinal direction of the magnetic tape: This relates to a magnetic tape whose ΔSFD calculated by the above is 0.50 or more.
ΔSFD = SFD _{25 ° C.} −SFD _{−190 ° C.} Formula 1
In Equation 1, SFD _{25 ° C.} is a reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape under an environment of 25 ° C., and SFD _{−190 ° C.} is in the longitudinal direction of the magnetic tape under an environment of temperature −190 ° C. It is a switching field distribution SFD to be measured. In the present invention and the present specification, unless otherwise specified, a magnetic characteristic without a specified measurement temperature is a value measured in an environment at a temperature of 25 ° C.
Hereinafter, the magnetic tape will be described in more detail.

<Base friction>
The friction coefficient (base friction) measured at the base portion of the magnetic layer surface of the magnetic tape is 0.35 or less. The method for measuring the base friction is as described above. From the viewpoint of further suppressing a decrease in electromagnetic conversion characteristics when traveling is repeated, the base friction is preferably 0.33 or less, and more preferably 0.30 or less. In addition, the base friction is, for example, 0.10 or more or 0.20 or more. However, the lower limit is particularly preferable because it is preferably as low as possible from the viewpoint of suppressing a decrease in wear when the vehicle is repeatedly driven at low temperature and low humidity. It is not limited.

Regarding the method for measuring the base friction, the reason why the protrusion having a height of 15 nm or more from the reference surface is defined as the protrusion is that the protrusion that is normally recognized as the protrusion existing on the surface of the magnetic layer is mainly 15 nm from the reference surface. This is because the protrusion has the above height. Such protrusions are formed on the surface of the magnetic layer with a nonmagnetic powder such as an abrasive. On the other hand, the present inventor believes that there are microscopic irregularities on the surface of the magnetic layer rather than the irregularities formed by such protrusions. And this inventor is guessing that a base friction can be adjusted by the shape control of this microscopic unevenness | corrugation. Based on this inference, the present inventor formed a magnetic layer using two or more kinds of ferromagnetic powders having different average particle sizes in order to control the shape of the unevenness of the substrate portion, and controlled the substrate friction to various values. It was possible to do. Accordingly, one means for adjusting the base friction is to use two or more kinds of ferromagnetic powders having different average particle sizes as the ferromagnetic powder. More specifically, since the ferromagnetic powder having a larger average particle size becomes a convex portion, the above-described microscopic unevenness can be formed on the base portion, and the mixing ratio of the ferromagnetic powder having a larger average particle size can be set. The present inventor believes that the presence ratio of the protrusions in the base portion can be increased by increasing the ratio (or the presence ratio of the protrusions in the base portion can be decreased by lowering the mixing ratio). . Details will be described later.
As another means, the present inventor has added a non-magnetic powder such as an abrasive that can form protrusions having a height of 15 nm or more from the reference surface on the surface of the magnetic layer in order to control the shape of the unevenness of the substrate portion. When the magnetic layer was formed using another nonmagnetic powder having an average particle size larger than that of the ferromagnetic powder, it was possible to control the base friction to various values. Therefore, one of the means for adjusting the base friction is to use the other non-magnetic powder described above when forming the magnetic layer. More specifically, the microscopic irregularities can be formed on the substrate portion by forming the other non-magnetic powder into a convex portion. By increasing the mixing ratio of the non-magnetic powder, the convex portion on the substrate portion can be formed. The present inventor believes that the presence rate of the portion can be increased (or the presence rate of the convex portion in the substrate portion can be reduced by lowering the mixing ratio). Details will be described later.
In addition, it is possible to adjust the base friction by combining the above two types of means.
However, the above-described adjusting means is an exemplification, and the base friction of 0.35 or less can be realized by any means capable of adjusting the base friction, and such an aspect is also included in the present invention.

<ΔSFD calculated by Formula 1>
ΔSFD is a value indicating the temperature dependence of the reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape. The smaller the value, the smaller the change in SFD due to temperature, and the larger the value, the greater the change in SFD due to temperature. means. The present inventors, it ΔSFD calculated by the equation 1 indicating the difference between the SFD _{25 ° C.} and _{SFD -190 ° C.} is 0.50 or higher, suppressing a decrease in abrasion resistance due to repeated running at low temperature and low humidity I think it will contribute to The inference by the present inventor regarding this point is as described above. From the viewpoint of further suppressing the deterioration of wear due to repeated running under low temperature and low humidity, the ΔSFD is preferably 0.55 or more, more preferably 0.60 or more, and 0.70 or more. More preferably, 0.80 or more, still more preferably 0.90 or more, even more preferably 1.00 or more, 1.10 or more, 1.20 or more. , 1.30 or more and 1.40 or more in order. On the other hand, ΔSFD calculated by Equation 1 means that the smaller the value as described above, the smaller the change in SFD due to temperature. A small change in SFD due to temperature is preferable from the viewpoint of stably holding a signal recorded on the magnetic tape (recording holdability). From this point, ΔSFD calculated by Equation 1 is preferably 1.60 or less, and more preferably 1.50 or less.

  The longitudinal direction SFD of the magnetic tape can be obtained by a known magnetic property measuring device such as a vibrating sample magnetometer. The same applies to the SFD measurement of the ferromagnetic powder. Moreover, the temperature at the time of SFD measurement can be adjusted with the setting of a measuring apparatus.

According to the study by the present inventor, ΔSFD calculated by Equation 1 can be controlled by the magnetic tape preparation method, and the following tendencies were mainly observed:
(A) The value decreases with increasing dispersibility of the ferromagnetic powder in the magnetic layer;
(B) The value decreases as the ferromagnetic powder having a smaller temperature dependence of SFD is used;
(C) The value decreases as the ferromagnetic powder is aligned in the longitudinal direction of the magnetic layer (as the orientation in the longitudinal direction increases), and the value increases as the orientation in the longitudinal direction decreases.

  For example, regarding (A), strengthening of dispersion conditions (longer dispersion time, smaller diameter of dispersed beads used for dispersion, higher packing, etc.), use of a dispersant, and the like can be mentioned. As the dispersant, known dispersants, commercially available dispersants and the like can be used without any limitation.

On the other hand, with regard to (B), for example, as an example, the SFD of the ferromagnetic powder calculated by the following formula 2 and measured in an environment at a temperature of 100 ° C. and SFD measured in an environment at a temperature of 25 ° C. Ferromagnetic _powder having a difference ΔSFD _powder in the range of 0.05 to 1.50 can be used. However, even if it is outside the above range, ΔSFD calculated by Equation 1 of the magnetic tape can be controlled to a range of 0.50 or more by other control.
ΔSFD _powder = SFD _{powder 100 ° C.} −SFD _{powder 25 ° C.} Equation 2
(In Formula 2, SFD _powder 100 ° _C. is a reversal magnetic field distribution SFD of a ferromagnetic powder measured in an environment at a temperature of 100 ° C., and SFD powder 25 ° _C. is a ferromagnetic powder measured in an environment at a temperature of 25 ° C. (Reversed magnetic field distribution SFD.)

  With respect to (C), a method of making the orientation treatment of the magnetic layer a vertical orientation or a method of making the orientation non-orientation without performing the orientation treatment can be employed.

  Therefore, for example, by controlling each of the above means (A) to (C) by one or arbitrarily combining two or more, it is possible to obtain a magnetic tape having ΔSFD calculated by Equation 1 of 0.50 or more. it can.

  Hereinafter, the magnetic tape will be described in more detail.

<Magnetic layer>
(Ferromagnetic powder)
As described above, one of the means for adjusting the base friction is control using ferromagnetic powder. As the ferromagnetic powder contained in the magnetic layer of the magnetic tape, various powders that are usually used as the ferromagnetic powder in the magnetic layer of the magnetic tape can be used.

  For example, as the ferromagnetic powder contained in the magnetic layer, it is preferable to use a ferromagnetic powder having the smallest average particle size from the viewpoint of improving the recording density of the magnetic tape. From this point, when two or more kinds of ferromagnetic powders having different average particle sizes are used as the ferromagnetic powders in the magnetic layer, the ferromagnetic powder having an average particle size of 50 nm or less is used as the ferromagnetic powder used in the largest proportion. Is preferably used. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder used in the largest proportion is preferably 10 nm or more. In addition, when using one kind of ferromagnetic powder without using two or more kinds of ferromagnetic powders having different average particle sizes, the average particle size of the ferromagnetic powder to be used is preferably 50 nm or less for the above reason. It is preferable that it is 10 nm or more.

  On the other hand, it is preferable that the ferromagnetic powder used together with the ferromagnetic powder used in the largest proportion has a larger average particle size than the ferromagnetic powder used in the largest proportion. This is because it is considered that the base friction can be reduced by the convex portions formed on the base portion by the ferromagnetic powder having a large average particle size. From this point, the average particle size of the ferromagnetic powder used in the largest proportion and the average particle size of the ferromagnetic powder used therewith are determined as “(the latter average particle size) − (the former average particle size)”. The difference is preferably in the range of 10 to 80 nm, more preferably in the range of 10 to 50 nm, still more preferably in the range of 10 to 40 nm, and still more preferably in the range of 12 to 35 nm. . Of course, it is possible to use two or more kinds of ferromagnetic powders having different average particle sizes as the ferromagnetic powder used together with the ferromagnetic powder used in the largest proportion. In this case, with respect to the average particle size of the ferromagnetic powder used in the largest proportion, it is preferable that the average particle size of at least one of the two or more types of ferromagnetic powder satisfies the above difference, and more It is preferable that the average particle size of the type of ferromagnetic powder satisfies the above difference, and it is further preferable that the average particle size of all the ferromagnetic powders satisfies the above difference.

  In addition, for two or more types of ferromagnetic powders having different average particle sizes, from the viewpoint of controlling the base friction, ferromagnetic powders used in the largest proportion and other ferromagnetic powders (average particles as other ferromagnetic powders) When using two or more kinds having different sizes, the mixing ratio with the total) may be in the range of the former: the latter = 90.0: 10.0 to 99.9: 0.1 on a mass basis. Preferably, the range is 95.0: 5.0 to 99.5: 0.5.

  Here, the ferromagnetic powder having a different average particle size refers to the whole or part of the ferromagnetic powder lot having a different average particle size. Thus, the number-based or volume-based particle size distribution of the ferromagnetic powder contained in the magnetic layer of the magnetic tape formed using the ferromagnetic powder having different average particle sizes can be determined by dynamic light scattering method, laser diffraction method, etc. When measured by a known measurement method, a maximum peak can be confirmed in the particle size distribution curve obtained by the measurement, usually at or near the average particle size of the ferromagnetic powder used in the largest proportion. In some cases, a peak can be confirmed at or near the average particle size of each ferromagnetic powder. Therefore, for example, when measuring the particle size distribution of the ferromagnetic powder contained in the magnetic layer of the magnetic tape formed using the largest proportion of the ferromagnetic powder having an average particle size of 10 to 50 nm, usually, in the particle size distribution curve, A maximum peak can be confirmed in a particle size range of 10 to 50 nm.

  In addition, you may replace a part of said other ferromagnetic powder with the nonmagnetic powder mentioned later.

The average particle size of the ferromagnetic powder in the present invention and the present specification is a value measured by the following method using a transmission electron microscope.
The ferromagnetic powder is photographed at a photographing magnification of 100,000 using a transmission electron microscope and printed on a photographic paper so that the total magnification is 500,000 times to obtain a photograph of particles constituting the ferromagnetic powder. The target particle is selected from the photograph of the obtained particle, the outline of the particle is traced with a digitizer, and the size of the particle (primary particle) is measured. Primary particles refer to independent particles without agglomeration.
The above measurements are performed on 500 randomly extracted particles. The arithmetic average of the particle sizes of the 500 particles thus obtained is defined as the average particle size of the ferromagnetic powder. As the transmission electron microscope, for example, Hitachi transmission electron microscope H-9000 type can be used. The particle size can be measured using known image analysis software, for example, image analysis software KS-400 manufactured by Carl Zeiss.
In the present invention and the present specification, the average particle size of the ferromagnetic powder and other powders means the average particle size determined by the above method unless otherwise specified. The average particle size shown in the below-mentioned Examples is a value measured using a Hitachi transmission electron microscope H-9000 type as a transmission electron microscope and Carl Zeiss image analysis software KS-400 as image analysis software.

  As a method for collecting sample powder such as ferromagnetic powder from the magnetic layer for particle size measurement, for example, the method described in paragraph 0015 of JP2011-048878A can be employed.

In the present invention and the present specification, the size of the particles constituting the powder such as ferromagnetic powder (hereinafter referred to as “particle size”) is the shape of the particles observed in the above particle photograph,
(1) In the case of needle shape, spindle shape, columnar shape (however, the height is larger than the maximum major axis of the bottom surface), it is represented by the length of the major axis constituting the particle, that is, the major axis length,
(2) In the case of a plate or column (however, the thickness or height is smaller than the maximum major axis of the plate surface or bottom surface), it is represented by the maximum major axis of the plate surface or bottom surface,
(3) In the case of a spherical shape, a polyhedral shape, an unspecified shape, etc., and the major axis constituting the particle cannot be specified from the shape, it is represented by an equivalent circle diameter. The equivalent circle diameter is a value obtained by a circle projection method.

The average acicular ratio of the powder is determined by measuring the length of the minor axis of the particle, that is, the minor axis length in the above measurement, and obtaining the value of (major axis length / minor axis length) of each particle. Refers to the arithmetic average of the values obtained for the particles. Here, the short axis length refers to the length of the short axis constituting the particle in the case of (1) in the definition of the particle size, and the thickness or the height in the case of (2), In the case of (3), since there is no distinction between the major axis and the minor axis, (major axis length / minor axis length) is regarded as 1 for convenience.
And when the shape of the particle is specific, for example, in the case of definition (1) of the above particle size, the average particle size is the average major axis length, and in the case of definition (2), the average particle size is the average plate diameter. The average plate ratio is an arithmetic average of (maximum major axis / thickness or height). In the case of the same definition (3), the average particle size is an average diameter (also referred to as an average particle diameter or an average particle diameter).

  Preferable specific examples of the ferromagnetic powder include ferromagnetic hexagonal ferrite powder. When the ferromagnetic powder used in the largest proportion is a ferromagnetic hexagonal ferrite powder, the average particle size (average plate diameter) is 10 nm or more and 50 nm or less from the viewpoint of high density recording and magnetization stability. It is preferably 20 nm or more and 50 nm or less. For details of the ferromagnetic hexagonal ferrite powder, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to JP2012-204726A 0030 can be referred to.

  Preferable specific examples of the ferromagnetic powder include a ferromagnetic metal powder. When the ferromagnetic powder used in the largest proportion is a ferromagnetic metal powder, the average particle size (average major axis length) is 10 nm or more and 50 nm or less from the viewpoint of high density recording and magnetization stability. Is preferable, and it is more preferable that it is 20 nm or more and 50 nm or less. For details of the ferromagnetic metal powder, reference can be made to, for example, paragraphs 0137 to 0141 of JP2011-216149A and paragraphs 0009 to 0023 of JP2005-251351A.

  The magnetic tape may contain only one of a ferromagnetic hexagonal ferrite powder and a ferromagnetic metal powder as a ferromagnetic powder, or both of them, and one or both of them may contain another type of ferromagnetic powder. May be included.

In one aspect, the difference ΔSFD _powder between the SFD measured in the environment of 100 ° C. and the SFD measured in the environment of 25 ° C. calculated by the above formula 2 is in the range described above. Preference is given to using powder.

  The content (filling rate) of the ferromagnetic powder in the magnetic layer is preferably in the range of 50 to 90% by mass, more preferably in the range of 60 to 90% by mass. A high filling factor is preferable from the viewpoint of improving the recording density.

(Abrasive)
The magnetic tape contains an abrasive in the magnetic layer. The abrasive is preferably a nonmagnetic powder having a Mohs hardness of more than 8, and more preferably a nonmagnetic powder having a Mohs hardness of 9 or more. The maximum Mohs hardness is 10 for diamond. Specific examples include alumina (Al ₂ O ₃ ), silicon carbide, boron carbide (B ₄ C), TiC, cerium oxide, zirconium oxide (ZrO ₂ ), and diamond powder. Among these, alumina is preferable. Alumina can achieve particularly good dispersibility improvement in combination with a dispersant (aromatic hydrocarbon compound having a phenolic hydroxyl group) described in paragraphs 0012 to 0022 of JP2013-131285A. Abrasives that are also preferable in this respect. Regarding alumina, paragraph 0021 of JP2013-229090A can also be referred to. The specific surface area can be used as an index of the size of the abrasive particles. A larger specific surface area means a smaller particle size. The specific surface area is a value obtained by a nitrogen adsorption method (also called a BET (Brunauer-Emmett-Teller) one-point method), and is a value measured for primary particles. Below, the specific surface area calculated | required by this method is described also as a BET specific surface area. From the viewpoint of improving the smoothness of the magnetic layer surface, it is preferable to use an abrasive having a BET specific surface area of 14 m ² / g or more. From the viewpoint of dispersibility, it is preferable to use an abrasive having a BET specific surface area of 40 m ² / g or less. The content of the abrasive in the magnetic layer is preferably 1.0 to 20.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

(Binder, curing agent)
The magnetic tape is a coating type magnetic tape, and a magnetic layer contains a binder together with a ferromagnetic powder and an abrasive. As the binder, various resins usually used as a binder for a coating type magnetic recording medium can be used. For example, as a binder, polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin copolymerized with methyl methacrylate, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, A single resin or a mixture of a plurality of resins can be used from polyvinyl alkylal resins such as polyvinyl butyral. Among these, preferred are polyurethane resin, acrylic resin, cellulose resin, and vinyl chloride resin. These resins can also be used as a binder in nonmagnetic layers and backcoat layers described later. As for the above binder, paragraphs 0028 to 0031 of JP 2010-24113 A can be referred to. The average molecular weight of the resin used as the binder can be, for example, 10,000 or more and 200,000 or less as the weight average molecular weight. In addition, the weight average molecular weight in this invention and this specification is the value by polystyrene conversion measured by gel permeation chromatography (GPC). The following conditions can be mentioned as measurement conditions. The weight average molecular weight shown in the Examples described later is a value obtained by converting a value measured under the following measurement conditions into polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh Corporation):
Column: TSK gel Multipore HXL-M (Tosoh, 7.8 mm ID (inner diameter) × 30.0 cm)
Eluent: Tetrahydrofuran (THF)

  Moreover, a hardening | curing agent can also be used with resin which can be used as the said binder. In one aspect, the curing agent can be a thermosetting compound that is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another aspect, photocuring in which a curing reaction (crosslinking reaction) proceeds by light irradiation. It can be a sex compound. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The content of the hardener in the composition for forming a magnetic layer can be, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder. It is preferable to be in the range of ˜80.0 parts by mass.

(Additive)
The magnetic layer contains a ferromagnetic powder, an abrasive and a binder, and may contain one or more additives as necessary. Examples of the additive include the above-described curing agent. The curing agent may be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as a binder as the curing reaction proceeds in the magnetic layer forming step. Additives that can be included in the magnetic layer include nonmagnetic powders (nonmagnetic particles) other than abrasives, lubricants, dispersants, dispersion aids, antifungal agents, antistatic agents, antioxidants, carbon black And so on. As the additive, commercially available products can be appropriately selected and used according to desired properties.

  As an example of the additive, the magnetic layer may include nonmagnetic powder (hereinafter referred to as “protrusion forming agent”) for controlling friction characteristics (reducing friction coefficient). The protrusion forming agent may be an inorganic substance or an organic substance. In one embodiment, from the viewpoint of uniform frictional characteristics, the particle size distribution of the protrusion-forming agent is preferably not monodisperse having a plurality of peaks in the distribution but monodisperse showing a single peak. From the viewpoint of easy availability of the monodisperse particles, the nonmagnetic powder is preferably an inorganic powder. Examples of the inorganic substance powder include metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfide powders, with inorganic oxide powders being preferred. The protrusion-forming agent is more preferably colloidal particles, and further preferably inorganic oxide colloidal particles. Further, from the viewpoint of easy availability of monodisperse particles, the inorganic oxide constituting the inorganic oxide colloidal particles is preferably silicon dioxide (silica), and the inorganic oxide colloidal particles are colloidal silica (silica colloidal particles). ) Is more preferable. In the present invention and the present specification, “colloid particles” means at least one organic solvent 100 mL of a mixed solvent containing at least methyl ethyl ketone, cyclohexanone, toluene or ethyl acetate, or two or more of the above solvents in an arbitrary mixing ratio. When 1 g per gram is added, it refers to particles that can be dispersed without settling to yield a colloidal dispersion. For colloidal particles, the average particle size is a value determined by the method described in paragraph 0015 of JP2011-048878A as a method for measuring the average particle size. In another embodiment, the protrusion forming agent is preferably carbon black.

  The average particle size of the protrusion forming agent is, for example, 30 to 300 nm, and preferably 40 to 200 nm. The content of the protrusion forming agent in the magnetic layer is preferably 1.0 to 4.0 parts by mass, more preferably 1.5 to 3.5 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. is there.

  Further, as described above, in order to control the base friction to 0.35 or less, other nonmagnetic powders can be used in addition to the nonmagnetic powder described above. Such non-magnetic powder preferably has a Mohs hardness of 8 or less, and various non-magnetic powders commonly used for non-magnetic layers can be used. The details are as described later for the nonmagnetic layer. A more preferred nonmagnetic powder is Bengala. Bengala has a Mohs hardness of about 6.

  The other nonmagnetic powders described above preferably have an average particle size larger than that of the ferromagnetic powder, similar to the ferromagnetic powder used together with the ferromagnetic powder used in the largest proportion described above. This is because it is considered that the base friction can be reduced by the convex portions formed on the base portion by the other nonmagnetic powder. From this point, the average particle size of the ferromagnetic powder and the average particle size of the other non-magnetic powder used together therewith are obtained as “(the latter average particle size) − (the former average particle size)”. However, it is preferable that it is the range of 10-80 nm, and it is more preferable that it is the range of 10-50 nm. When two or more types of ferromagnetic powders having different average particle sizes are used as the ferromagnetic powder, the ferromagnetic powder for calculating the difference from the average particle size of the other non-magnetic powders is two or more types of strong powders. The ferromagnetic powder used in the largest proportion of the magnetic powder. It is of course possible to use two or more kinds of nonmagnetic powders having different average particle sizes as the other nonmagnetic powders. In this case, with respect to the average particle size of the ferromagnetic powder, it is preferable that at least one of the other non-magnetic powders satisfies the above difference, and more types of non-magnetic powders. It is preferable that the average particle size of the magnetic powder satisfies the above difference, and it is further preferable that all the average particle sizes of the other nonmagnetic powders satisfy the above difference.

  Further, from the viewpoint of controlling the base friction, the ferromagnetic powder and the other nonmagnetic powder (the total when two or more different average particle sizes are used as the other nonmagnetic powder) The mixing ratio is preferably in the range of the former: the latter = 90.0: 10.0 to 99.9: 0.1 on a mass basis, and 95.0: 5.0 to 99.5: 0.5. It is more preferable to set the range.

<Nonmagnetic layer>
Next, the nonmagnetic layer will be described. The magnetic tape has a nonmagnetic layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer. The nonmagnetic powder used for the nonmagnetic layer may be an inorganic substance or an organic substance. Carbon black or the like can also be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. These nonmagnetic powders are available as commercial products, and can also be produced by a known method. Details thereof can be referred to paragraphs 0146 to 0150 of JP2011-216149A. Regarding the carbon black that can be used in the nonmagnetic layer, paragraphs 0040 to 0041 of JP2010-24113A can also be referred to. The content (filling rate) of the nonmagnetic powder in the nonmagnetic layer is preferably in the range of 50 to 90 mass%, more preferably in the range of 60 to 90 mass%.

  For other details such as binders and additives for the nonmagnetic layer, known techniques relating to the nonmagnetic layer can be applied. For example, with respect to the amount and type of the binder and the amount and type of the additive, known techniques relating to the magnetic layer can also be applied.

  The nonmagnetic layer of the magnetic tape includes a substantially nonmagnetic layer containing a small amount of ferromagnetic powder together with the nonmagnetic powder, for example, as impurities or intentionally. Here, the substantially non-magnetic layer means that the residual magnetic flux density of this layer is 10 mT or less, the coercive force is 7.96 kA / m (100 Oe) or less, or the residual magnetic flux density is 10 mT or less. And a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The nonmagnetic layer preferably has no residual magnetic flux density and coercive force.

<Non-magnetic support>
Next, the nonmagnetic support will be described. Examples of the nonmagnetic support include known ones such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyamideimide, and aromatic polyamide. Among these, polyethylene terephthalate, polyethylene naphthalate, and polyamide are preferable. These supports may be subjected in advance to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like.

<Various thicknesses>
The magnetic tape has a nonmagnetic layer thickness of 0.50 μm or less. The thickness of the nonmagnetic layer is, for example, 0.10 μm or more. From the viewpoint of thinning the magnetic tape, the thickness is preferably 0.40 μm or less, and preferably 0.30 μm or less.
The thickness of the nonmagnetic support is preferably 3.00 to 4.50 μm.
The thickness of the magnetic layer is optimized depending on the saturation magnetization of the magnetic head used, the head gap length, and the band of the recording signal, but is generally 0.01 μm to 0.15 μm. Therefore, it is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.10 μm. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.
From the viewpoint of reducing the thickness of the magnetic tape, the total thickness of the magnetic layer and the nonmagnetic layer is preferably 0.60 μm or less, and more preferably 0.50 μm or less. The total thickness of the magnetic layer and the nonmagnetic layer can be, for example, 0.10 μm or more, or 0.20 μm or more.
Further, the total thickness of the magnetic tape is preferably 6.00 μm or less, more preferably 5.70 μm or less, and more preferably 5.50 μm or less, from the viewpoint of improving the recording capacity per magnetic tape cartridge. More preferably. On the other hand, from the viewpoint of easy handling (handling properties) of the magnetic tape, the total thickness of the magnetic tape is preferably 1.00 μm or more.

<Back coat layer>
The magnetic tape may have a backcoat layer on the surface opposite to the surface having the magnetic layer of the nonmagnetic support. The backcoat layer is a layer containing a nonmagnetic powder and a binder, and the nonmagnetic powder can contain at least one of carbon black and inorganic powder, preferably both. For the binder and various additives for forming the backcoat layer, the formulation of the magnetic layer and the nonmagnetic layer can be applied. The thickness of the back coat layer is preferably 0.90 μm or less, and more preferably 0.10 to 0.70 μm.

  The thickness of each layer of the magnetic tape and the nonmagnetic support can be determined by a known film thickness measurement method. As an example, for example, after a cross section in the thickness direction of the magnetic tape is exposed by a known method such as an ion beam or a microtome, the exposed cross section is observed with a scanning electron microscope. Various thicknesses can be obtained as an arithmetic average of thicknesses obtained at one location in the thickness direction in cross-sectional observation, or at two or more locations randomly extracted, for example, at two locations. Alternatively, the thickness of each layer may be obtained as a design thickness calculated from manufacturing conditions.

<Magnetic surface roughness of magnetic layer>
Incidentally, high-density recording magnetic tapes such as data backup tapes are desired to improve the smoothness of the magnetic layer surface. This is because the spacing loss can be reduced by increasing the smoothness of the surface of the magnetic layer, and as a result, good electromagnetic conversion characteristics can be obtained when reproducing a signal recorded at high density. From the above viewpoint, it is preferable that the magnetic tape also has high surface smoothness of the magnetic layer. As an index of the surface smoothness of the magnetic layer, a center line average surface roughness Ra measured by an atomic force microscope (AFM) on the surface of the magnetic layer can be used. The centerline average surface roughness Ra measured by an atomic force microscope refers to the centerline average surface roughness Ra measured in a region having an area of 40 μm × 40 μm on the surface of the magnetic layer. As an atomic force microscope, for example, NANO SCOPE (registered trademark) III manufactured by DIGITAL INSTRUMENT can be used in contact mode. The centerline average surface roughness Ra measured by the atomic force microscope on the magnetic layer surface of the magnetic tape is preferably 2.8 nm or less, and preferably 2.5 nm or less from the viewpoint of reducing the spacing loss. It is more preferable that the thickness is 2.2 nm or less. Further, from the viewpoint of running stability, it is preferably 0.5 nm or more, more preferably 1.0 nm or more, and further preferably 1.5 nm or more.

  The surface smoothness of the magnetic layer can be improved (that is, Ra is reduced) by increasing the dispersibility of various powders in the composition for forming the magnetic layer. From this point, when preparing the composition for forming the magnetic layer, it is preferable to disperse the abrasive separately from the ferromagnetic powder, and to disperse separately from various powders including the ferromagnetic powder. More preferred.

<Manufacturing process>
The composition (coating liquid) for forming the magnetic layer, the nonmagnetic layer, or the backcoat layer usually contains a solvent together with the various components described above. As the solvent, various organic solvents generally used for producing a coating type magnetic tape can be used. The step of preparing a composition for forming each layer usually includes at least a kneading step, a dispersing step, and a mixing step provided as necessary before and after these steps. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, non-magnetic powder, abrasive, binder, and various additives and solvents used in the present invention may be added at the beginning or middle of any step. In addition, individual raw materials may be added in two or more steps. In one aspect, it is preferable to separately disperse the abrasive and the ferromagnetic powder in the preparation of the magnetic layer forming composition. In order to manufacture the magnetic tape, known manufacturing techniques can be used. In the kneading step, it is preferable to use a material having a strong kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Moreover, in order to disperse each layer forming composition, glass beads or other dispersed beads can be used. As such dispersed beads, zirconia beads, titania beads, and steel beads, which are dispersed beads having a high specific gravity, are suitable. The particle diameter and packing rate of these dispersed beads can be optimized and used. A well-known thing can be used for a disperser. In addition, as described above, as one of means for obtaining a magnetic tape having ΔSFD of 0.50 or more calculated by Equation 1, dispersion conditions are strengthened (dispersion time is increased, dispersion beads used for dispersion) It is also preferable to reduce the diameter and increase the filling. For details of the method of manufacturing the magnetic tape, for example, paragraphs 0051 to 0057 of JP2010-24113A can also be referred to. As for the orientation treatment, paragraph 0052 of JP2010-24113 can be referred to, but as described above, means for obtaining a magnetic tape having ΔSFD calculated by Equation 1 of 0.50 or more. As one of the above, it is preferable to perform vertical alignment. It is also preferable not to perform the alignment treatment (non-alignment).

Regarding the control of the base friction, as described above, in one aspect, a magnetic tape can be manufactured using two or more kinds of ferromagnetic powders having different average particle sizes. That is, the magnetic layer can be formed as a ferromagnetic powder using the first ferromagnetic powder and one or more ferromagnetic powders having an average particle size larger than that of the first ferromagnetic powder. Preferred embodiments of the method for forming such a magnetic layer include the following embodiments. A combination of two or more of the following embodiments is a more preferable embodiment of the method for forming the magnetic layer. The first ferromagnetic powder refers to one kind of ferromagnetic powder used among two or more kinds of ferromagnetic powder, and is preferably the ferromagnetic powder used in the largest proportion described above. The other details of the method for forming the magnetic layer are as described above.
The average particle size of the first ferromagnetic powder is in the range of 10 to 80 nm.
The difference between the average particle size of the ferromagnetic powder having an average particle size larger than that of the first ferromagnetic powder and the average particle size of the first ferromagnetic powder is in the range of 10 to 50 nm.
The mixing ratio between the first ferromagnetic powder and the ferromagnetic powder having an average particle size larger than that of the first ferromagnetic powder is, on the mass basis, the former: the latter = 90.0: 10.0 to 99.9: 0. .1 range.

In another embodiment, a magnetic tape can also be produced by using other nonmagnetic powder together with an abrasive and a protrusion forming agent as the nonmagnetic powder of the magnetic layer. That is, the magnetic layer can be formed as the nonmagnetic powder using another nonmagnetic powder together with the abrasive and the protrusion forming agent. Preferred embodiments of the method for forming such a magnetic layer include the following embodiments. A combination of two or more of the following embodiments is a more preferable embodiment of the method for forming the magnetic layer. The other details of the method for forming the magnetic layer are as described above.
The average particle size of the other non-magnetic powder is larger than the average particle size of the ferromagnetic powder.
The difference between the average particle size of the ferromagnetic powder and the average particle size of the other non-magnetic powder is in the range of 10 to 80 nm.
The mixing ratio of the ferromagnetic powder and the other nonmagnetic powder is in the range of the former: the latter = 90.0: 10.0 to 99.9: 0.1 on a mass basis.

[Magnetic tape cartridge, magnetic recording / reproducing device]
One embodiment of the present invention relates to a magnetic tape cartridge in which a magnetic tape cartridge in which the magnetic tape is stored is stored.
Another aspect of the present invention relates to a magnetic recording / reproducing apparatus including the magnetic tape cartridge and a magnetic head.

  In a magnetic tape cartridge, generally, a magnetic tape is accommodated inside a cartridge body in a state of being wound around a reel. The reel is rotatably provided inside the cartridge body. As the magnetic tape cartridge, a single reel type magnetic tape cartridge having one reel inside the cartridge body and a dual reel type magnetic tape cartridge having two reels inside the cartridge body are widely used. When a single reel type magnetic tape cartridge is mounted on a magnetic recording / reproducing apparatus (drive) for recording and / or reproducing magnetic signals on the magnetic tape, the magnetic tape is pulled out of the magnetic tape cartridge and the drive side It is wound on a reel. A magnetic head is disposed on the tape conveyance path from the magnetic tape cartridge to the take-up reel. The magnetic tape is fed and taken up between the reel (supply reel) on the magnetic tape cartridge side and the reel (winding reel) on the drive side. During this time, the magnetic head and the magnetic layer surface of the magnetic tape are in contact (sliding), so that magnetic signals are recorded and reproduced. On the other hand, in the dual reel type magnetic tape cartridge, both the supply reel and the take-up reel are provided inside the magnetic tape cartridge. The magnetic tape cartridge according to one embodiment of the present invention may be either a single reel type or a dual reel type magnetic tape cartridge. The configuration of the magnetic tape cartridge is known, and the known configuration can be applied to the magnetic tape cartridge according to one embodiment of the present invention without any limitation. For example, the magnetic tape cartridge according to one aspect of the present invention can be an LTO (Linear-Tape-Open) format magnetic tape cartridge. Alternatively, the magnetic tape cartridge according to one embodiment of the present invention can be a magnetic tape cartridge other than the LTO format.

  The recording capacity per roll can be improved as the total length of the magnetic tape accommodated per roll of the magnetic tape cartridge is increased. From this point, the total length of the magnetic tape accommodated in the magnetic tape cartridge is preferably 10 m or more, for example, about 10 to 1500 m. However, as the total length of the tape increases, the time required for recording / reproducing increases if the running speed (hereinafter also referred to as “conveying speed”) during recording and / or reproducing of magnetic signals on the magnetic tape does not change. Increasing the speed is preferable for shortening the recording / reproducing time when the total length of the tape is increased in order to improve the recording capacity. Further, it is preferable to increase the transport speed regardless of the total length of the tape in order to shorten the recording / reproducing time. On the other hand, a thin magnetic tape having a nonmagnetic layer thickness of 0.50 μm or less exhibited a phenomenon in which the wear resistance deteriorates when the magnetic tape is repeatedly run under low temperature and low humidity. This phenomenon also tended to become more pronounced as the transport speed was increased (high-speed transport). On the other hand, in the magnetic tape according to one embodiment of the present invention, the nonmagnetic layer has a thickness of 0.50 μm or less, but by setting the base friction and ΔSFD calculated by Equation 1 within the above range, Thus, even if the running is repeated, it is possible to suppress a decrease in wear, and further, it is possible to suppress a decrease in wear even if high-speed conveyance is repeated under low temperature and low humidity. Therefore, the magnetic tape according to one aspect of the present invention is used for a magnetic recording / reproducing apparatus having a high conveyance speed for shortening recording / reproducing time, and a magnetic tape cartridge having a long tape for increasing recording capacity. It is suitable as a magnetic tape. High-speed conveyance means, for example, that the conveyance speed is 7 m / sec. As the relative speed between the magnetic tape and the magnetic head during recording / reproduction of magnetic signals. Or 8 m / sec. That's it. The conveyance speed in the high-speed conveyance is, for example, 8 to 15 m / sec. Can be about.

  As the magnetic head of the magnetic recording / reproducing apparatus according to one embodiment of the present invention, a known magnetic head can be used as a recording head or reproducing head such as a magnetoresistive head (MR (magnetically effective) head). The configuration of the magnetic recording / reproducing apparatus is known, and the known configuration can be applied to the configuration of the magnetic recording / reproducing apparatus according to one embodiment of the present invention without any limitation.

  Hereinafter, the present invention will be described based on examples. However, this invention is not limited to the aspect shown in the Example. In addition, unless otherwise indicated, the display of "part" described below and "%" shows "mass part" and "mass%".

[Example 1]
1. Preparation of Alumina Dispersion 3.0 parts of 2,3-dihydroxynaphthalene (100.0 parts of alumina powder (HIT-70, manufactured by Sumitomo Chemical Co., Ltd.) having an alpha conversion rate of about 65% and a BET specific surface area of 30 m ² / g ( Manufactured by Tokyo Chemical Industry Co., Ltd.), a 32% solution of a polyester polyurethane resin having a SO ₃ Na group as a polar group (UR-4800 manufactured by Toyobo (registered trademark) (polar group amount: 80 meq / kg)) (solvent is a mixed solvent of methyl ethyl ketone and toluene) 31.3 parts, and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) as a solvent were mixed and dispersed in a paint shaker for 5 hours in the presence of zirconia beads. After dispersion, the dispersion and beads were separated with a mesh to obtain an alumina dispersion.

2. Composition formulation for magnetic layer (magnetic liquid)
Ferromagnetic powder (1) (see Table 1) Table 1 see Ferromagnetic powder (2) (see Table 1) See Table 1 SO ₃ Na group-containing polyurethane resin 14.0 parts (weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g)
Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (Abrasive liquid)
Above 1. 6.0 parts (silica sol) of alumina dispersion prepared in
Colloidal silica (average particle size 100 nm) 2.0 parts methyl ethyl ketone 1.4 parts (other ingredients)
Stearic acid 2.0 parts Butyl stearate 6.0 parts Polyisocyanate (Coronate (registered trademark) manufactured by Nippon Polyurethane) 2.5 parts (finishing additive solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

3. Nonmagnetic layer forming composition formulation Nonmagnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 10 nm
Average needle ratio: 1.9
BET specific surface area: 75 m ² / g
Carbon black 20.0 parts Average particle size 20nm
SO ₃ Na group-containing polyurethane resin 18.0 parts (weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g)
Stearic acid 1.0 part Cyclohexanone 300.0 parts Methyl ethyl ketone 300.0 parts

4). Composition for forming backcoat layer Nonmagnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average needle ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size 20nm
Vinyl chloride copolymer 13.0 parts Polysulfonate resin containing sulfonate group 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 Poly Isocyanate 5.0 parts Cyclohexanone 200.0 parts

5. Preparation of each layer forming composition A magnetic layer forming composition was prepared by the following method. The magnetic liquid was prepared by dispersing (bead dispersion) each component for the time shown in Table 1 using a batch type vertical sand mill. As the dispersion beads, zirconia beads having a bead diameter of 0.5 mmΦ were used. Using the sand mill, the prepared magnetic liquid and the abrasive liquid are mixed with other components (silica sol, other components and finishing additive solvent) and dispersed for 5 minutes with a batch type ultrasonic apparatus (20 kHz, 300 W). Treatment (ultrasonic dispersion) was performed for 0.5 minutes. Then, it filtered using the filter which has an average hole diameter of 0.5 micrometer, and produced the composition for magnetic layer formation. A part of the produced magnetic layer forming composition was sampled, and the dispersed particle size, which is an index of the dispersibility of the ferromagnetic powder, was measured by the method described later. The measured values are shown in Table 1.
A composition for forming a nonmagnetic layer was produced by the following method. Each component except stearic acid, cyclohexanone and methyl ethyl ketone was dispersed for 24 hours using a batch type vertical sand mill to obtain a dispersion. As the dispersion beads, zirconia beads having a bead diameter of 0.1 mmΦ were used. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver. The dispersion thus obtained was filtered using a filter having an average pore size of 0.5 μm to prepare a composition for forming a nonmagnetic layer.
A composition for forming a backcoat layer was produced by the following method. After kneading and diluting each component except lubricant (stearic acid and butyl stearate), polyisocyanate, and cyclohexanone with an open kneader, using a zirconia bead of 1 mmΦ with a horizontal bead mill disperser, a bead filling rate of 80% by volume, The rotor tip peripheral speed was 10 m / sec, the 1-pass residence time was 2 minutes, and 12-pass dispersion treatment was performed. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver. The dispersion thus obtained was filtered using a filter having an average pore size of 1 μm to prepare a composition for forming a backcoat layer.

6). 5. Preparation of magnetic tape 5. On the surface of a polyethylene naphthalate support having the thickness shown in Table 1, the thickness after drying is the thickness shown in Table 1. After applying and drying the nonmagnetic layer forming composition prepared in (5) above, the thickness after drying becomes the thickness shown in Table 1 above. The composition for forming a magnetic layer prepared in (1) was applied and dried without performing an orientation treatment. Thereafter, the surface of the support made of polyethylene naphthalate is opposite to the surface on which the nonmagnetic layer and the magnetic layer are formed, so that the thickness after drying becomes the thickness shown in Table 1 above. The composition for forming a backcoat layer prepared in (1) was applied and dried.
Thereafter, a surface roll treatment (calendar treatment) is performed at a speed of 100 m / min, a linear pressure of 300 kg / cm, and a calender temperature (calendar roll surface temperature) of 100 ° C. The heat treatment was performed for 36 hours in an environment of ° C. After the heat treatment, it was slit to a width of 1/2 inch (0.0127 meter) to obtain a magnetic tape.

[Examples 2-7, Comparative Examples 1-10]
Ferromagnetic powder used for magnetic tape preparation of Examples 2 to 7 and Comparative Examples 1 to 10, bead dispersion time when preparing composition for magnetic layer formation, presence or absence of orientation treatment, thickness of each layer and nonmagnetic support Is shown in Table 1. The method shown in Table 1 and the method using ferromagnetic metal powder as the ferromagnetic powder were the same as in Example 1 except that each component of the magnetic liquid was kneaded and diluted with an open kneader before dispersing the beads. The magnetic tapes of Examples and Comparative Examples were produced.
In Table 1, those using ferromagnetic hexagonal barium ferrite powder as ferromagnetic powder are shown as BF, and those using ferromagnetic metal powder as MP. The prescription rate described in Table 1 is the content rate of each ferromagnetic powder based on the mass of 100.0 parts by mass of the total amount of ferromagnetic powder. In Table 1, the average particle size of the ferromagnetic powder is the average plate diameter for the ferromagnetic hexagonal barium ferrite powder and the average major axis length for the ferromagnetic metal powder. The average particle size of the ferromagnetic powder is a value obtained by collecting a necessary amount from the ferromagnetic powder lot used for manufacturing the magnetic tape and measuring the average particle size by the method described above. The ferromagnetic powder after the measurement was used to prepare a magnetic liquid for producing a magnetic tape.
In addition, in the orientation column, “None” indicates that the alignment treatment is not performed, and “Vertical” indicates that the applied magnetic layer forming composition is in an undried state. In the meantime, a magnetic field having a magnetic field strength of 0.3 T is applied in a direction perpendicular to the coating surface to perform a vertical alignment treatment and then dried.

The thickness and total thickness of each layer and nonmagnetic support of the produced magnetic tape were determined by the following method. It was confirmed that the thicknesses of the formed layers and the nonmagnetic support were those shown in Table 1.
After the cross section in the thickness direction of the magnetic tape is exposed with an ion beam, the exposed cross section is observed with a scanning electron microscope. Various thicknesses were obtained as an arithmetic average of thicknesses obtained at two locations in the thickness direction in cross-sectional observation.

7). Evaluation Method (1) Measurement of Dispersion Particle Diameter of Magnetic Layer Forming Composition A part of the magnetic layer forming composition prepared in 1 was collected, and a sample solution diluted to 1/50 on a mass basis with the organic solvent used for the preparation of the composition was prepared. About the prepared sample solution, the arithmetic average particle diameter measured using the light-scattering type particle size distribution analyzer (LB500 by HORIBA) was made into the dispersion particle diameter.
(2) Measurement of average particle size of ferromagnetic powder The average particle size of the ferromagnetic powder was determined by the method described above.
(3) Measurement of ΔSFD _powder and coercive force Hc of ferromagnetic powder Using ferromagnetic sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) in an environment of temperatures of 100 ° C. and 25 ° C., an applied magnetic field of 796 kA / m SFD and coercive force Hc were measured at (10 kOe). From the SFD measurement results, ΔSFD _powder (in Table 1, ΔSFD (100 ° C.) − (25 ° C.)) was calculated by the above equation 2.
(4) Substrate Friction First, the measurement surface was marked with a laser marker in advance, and an atomic force microscope (AFM) image of a part away from the surface was measured. The visual field area was measured at 7 μm × 7 μm. At this time, as will be described later, the cantilever was changed to a hard one (single crystal silicon) so that a scanning electron microscope (SEM (Scanning Electron Microscope)) image of the same location was easily taken, and a ruled line was put on the AFM. . All protrusions at a height of 15 nm or more from the reference plane were extracted from the AFM image thus measured. And the location determined that there was no protrusion was specified as the substrate portion, and the substrate friction was measured by the method described above using a Hystron TI-950 type tribo indenter.
In addition, the component map is obtained by measuring the SEM image at the same location where the AFM was measured, and it was confirmed that the protrusion with a height of 15 nm or more from the extracted reference plane was formed by alumina or colloidal silica. did. Further, in Examples 1 to 7, alumina and colloidal silica were not confirmed in the substrate portion in the component map by the SEM. In addition, although component analysis was performed by SEM here, component analysis is not limited to SEM, but energy dispersive X-ray spectroscopy (EDS), Auger Electron Spectroscopy (AES) It can carry out by well-known methods, such as.
(5) Measurement of ΔSFD in the longitudinal direction of the magnetic tape Using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) in an environment at temperatures of 25 ° C. and −190 ° C., the longitudinal direction of the magnetic tape with an applied magnetic field of 796 kA / m (10 kOe) SFD was measured in the direction. From the measurement results, ΔSFD in the longitudinal direction of the magnetic tape (in Table 1, longitudinal ΔSFD (25 ° C.) − (− 190 ° C.)) was calculated according to the above formula 1.
(6) Centerline average surface roughness Ra of the magnetic layer surface
The center line average surface roughness Ra of the surface of the magnetic layer was measured by the method described above using NANOSCOPE III manufactured by DIGITAL INSTRUMENT in contact mode as an atomic force microscope. As a result of the measurement, it was confirmed that the center line average surface roughness Ra of the magnetic layer surface of the magnetic tape of the example was in the range of 2.0 to 2.2 nm.
(7) Change in wear of magnetic layer before and after repeated running under low temperature and low humidity (wear test)
About each Example and the comparative example, the magnetic tape for measuring the following wear width A and the magnetic tape for measuring the following wear width B were prepared, respectively.
In an atmosphere in which the temperature and humidity were controlled at a temperature of 13 ° C. ± 1 ° C. and a relative humidity of 15%, the magnetic layer surfaces of the magnetic tapes of the examples and comparative examples were placed on an AlFeSil prism (ECMA (European Computer Manufacturers Association) -288 / Annex H). In this state, a magnetic tape having a total length of 20 m is applied with a tension of 1.0 N so as to be brought into contact with one ridge side (edge) of the AlFeSil prism so that it is perpendicular to the longitudinal direction of the prism / H2). 3 m / sec. 50 reciprocations at a speed of The AlFeSil prism is a prism made of AlFeSil, which is a Sendust alloy.
The edge of the prism was observed from above using an optical microscope, and the wear width (AlFeSil wear width) described in paragraph 0015 of Japanese Patent Application Laid-Open No. 2007-026564 was explained based on FIG.
The wear width obtained for the magnetic tape in the non-running state is the wear width A, and the wear width obtained for the magnetic tape after the repeated running described below is the wear width B, and the difference in wear width after the repeated running with respect to the non-running state (wear) (Width change amount) was calculated by the following equation.
(Wear width change amount) = AB
The calculated results are shown in Table 1. If the amount of change in the wear width thus obtained is 5 μm or less, it can be determined that the wear property of the magnetic layer surface is maintained even after repeated running under low temperature and low humidity.
(Repeated driving conditions)
The magnetic layer surface and the magnetic head were brought into contact (sliding) in the tape running system under the following conditions in an atmosphere in which the temperature and humidity were controlled at a temperature of 13 ° C. ± 1 ° C. and a relative humidity of 15%. ) Repeatedly running.
In a tape running system to which a magnetic head removed from an IBM LTO-G6 (Linear Tape-Open Generation 6) drive is attached, a 20 m long magnetic tape is fed between the feeding roll and the take-up roll of the tape running system. And a winding speed of 0.6 m and a conveyance speed of 12 m / sec. For 10,000 cycles.

  The results are shown in Table 1.

From the results shown in Table 1, the following points can be confirmed.
(1) In the magnetic tapes of Comparative Examples 1 to 3 in which the thickness of the nonmagnetic layer exceeds 0.50 μm, even when the base friction is more than 0.35 and ΔSFD calculated by Equation 1 is less than 0.50, under low temperature and low humidity There was little decrease in wear of the magnetic layer due to repeated running. That is, for a magnetic tape having a non-magnetic layer thickness exceeding 0.50 μm, there is a correlation between the decrease in wear of the magnetic layer due to repeated running under low temperature and low humidity, the base friction, and ΔSFD calculated by Equation 1. I couldn't see it.
(2) On the other hand, from the comparison between Examples 1 to 7 and Comparative Examples 4 to 10, a magnetic tape having a nonmagnetic layer thickness of 0.50 μm or less has a base friction of 0.35 or less and is calculated by Equation 1. When ΔSFD is 0.50 or more, it can be confirmed that the wearability of the magnetic layer is maintained even when the vehicle is repeatedly driven at low temperature and low humidity.

  The present invention is useful in the technical field of magnetic tapes such as backup tapes.

Claims (11)

A magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer containing a ferromagnetic powder, an abrasive and a binder on the nonmagnetic layer,
The nonmagnetic layer has a thickness of 0.50 μm or less,
A magnetic tape having a friction coefficient measured at the substrate portion on the surface of the magnetic layer of 0.35 or less and ΔSFD calculated by the following formula 1 in the longitudinal direction of the magnetic tape is 0.50 or more;
ΔSFD = SFD _{25 ° C.} −SFD _{−190 ° C.} Formula 1
In Equation 1, SFD _{25 ° C.} is a reversal magnetic field distribution SFD measured in the longitudinal direction of the magnetic tape under an environment of 25 ° C., and SFD _{−190 ° C.} is in the longitudinal direction of the magnetic tape under an environment of temperature −190 ° C. It is a switching field distribution SFD to be measured. The magnetic tape according to claim 1, wherein the abrasive contains alumina. 3. The magnetic tape according to claim 1, wherein a friction coefficient measured at a base portion of the surface of the magnetic layer is 0.10 or more and 0.35 or less. The magnetic tape according to claim 1, wherein the ΔSFD is 0.50 or more and 1.50 or less. The magnetic tape according to claim 1, wherein the total thickness of the magnetic layer and the nonmagnetic layer is 0.60 μm or less. The magnetic tape according to any one of claims 1 to 5, further comprising a backcoat layer containing a nonmagnetic powder and a binder on a side opposite to the side having the nonmagnetic layer and the magnetic layer of the nonmagnetic support. . The magnetic tape according to claim 1, wherein the total thickness of the magnetic tape is 6.00 μm or less. The magnetic tape according to claim 1, wherein the ferromagnetic powder is selected from the group consisting of a ferromagnetic hexagonal ferrite powder and a ferromagnetic metal powder. A magnetic tape cartridge containing the magnetic tape according to claim 1. The magnetic tape cartridge according to claim 9, wherein the tape length of the magnetic tape accommodated is 10 m or more. A magnetic recording / reproducing apparatus comprising the magnetic tape cartridge according to claim 9 and a magnetic head.