JP6852206B2 - Magnetic tape and magnetic tape device - Google Patents

Description

The present invention relates to magnetic tapes and magnetic tape devices.

There are two types of magnetic recording media, tape-shaped and disk-shaped. For data storage applications such as data backup and archiving, tape-shaped magnetic recording media, that is, magnetic tape (hereinafter, also simply referred to as "tape"). ) Is mainly used. Recording of information on a magnetic tape is usually performed by recording a magnetic signal in the data band of the magnetic tape. As a result, a data track is formed in the data band.

With the enormous increase in the amount of information in recent years, magnetic tapes are required to have a higher recording capacity (higher capacity). As a means for increasing the capacity, it is possible to increase the recording density by arranging more data tracks in the width direction of the magnetic tape by narrowing the width of the data tracks.

However, when the width of the data track is narrowed, when the magnetic tape is run in a magnetic tape device (generally called a "drive") to record and / or reproduce a magnetic signal, the position change in the width direction of the magnetic tape causes the magnetic tape to move. , It becomes difficult for the magnetic head to follow the data track accurately, and it becomes easy to cause an error during recording and / or playback. Therefore, as a means for suppressing the occurrence of such an error, a system using a head tracking servo using a servo signal (hereinafter referred to as "servo system") has been proposed and put into practical use in recent years (hereinafter, referred to as "servo system"). For example, see Patent Document 1).

U.S. Pat. No. 5,689,384

Among the servo systems, in the magnetic servo system, a servo signal (servo pattern) is formed on the magnetic layer of the magnetic tape, and this servo pattern is magnetically read to perform head tracking. More details are as follows.
First, the servo head reads the servo pattern formed on the magnetic layer (that is, reproduces the servo signal). The position of the magnetic head in the width direction of the magnetic tape is controlled according to the value obtained by reading the servo pattern (details will be described later). As a result, when the magnetic tape is run in the magnetic tape device for recording and / or reproduction of the magnetic signal (information), the magnetic head moves even if the position of the magnetic tape fluctuates in the width direction with respect to the magnetic head. The accuracy of following the data track can be improved. In this way, it is possible to accurately record the information on the magnetic tape and / or accurately reproduce the information recorded on the magnetic tape.

In recent years, the timing-based servo system has been widely used as the above-mentioned magnetic servo system. In a timing-based servo system (hereinafter referred to as "timing-based servo system"), a plurality of servo patterns having two or more different shapes are formed on a magnetic layer, and two servo heads having different shapes are formed. The position of the servo head is recognized by the time interval in which the servo pattern is read and the time interval in which two servo patterns having the same shape are read. Based on the position of the servo head recognized in this way, the position of the magnetic head in the width direction of the magnetic tape is controlled.

By the way, the magnetic tape is usually housed in a magnetic tape cartridge, distributed, and used. In order to increase the recording capacity per roll of the magnetic tape cartridge, it is desirable to increase the total length of the magnetic tape accommodated in one roll of the magnetic tape cartridge. For this purpose, it is required to reduce the total thickness of the magnetic tape (hereinafter, also referred to as “thinning”).

Further, in recent years, magnetic tapes are required to improve the surface smoothness of the magnetic layer. This is because increasing the surface smoothness of the magnetic layer leads to the improvement of the electromagnetic conversion characteristics.

In view of the above points, the present inventors have studied the application of a magnetic tape having a reduced total thickness and improved surface smoothness of a magnetic layer to a timing-based servo system. However, in this study, it has been conventionally known that if the total thickness of the magnetic tape is reduced and the surface smoothness of the magnetic layer is increased, the frequency of signal defects during servo signal reproduction increases in the timing-based servo system. It became clear that a phenomenon that had not occurred occurred. An example of such a signal defect is a signal defect called thermal asperity. Thermal asperity is caused by the fact that in a system equipped with an MR head equipped with a magnetoresistive (MR) element, the resistance value of the MR element fluctuates due to a local temperature change in the MR element. This is the fluctuation of the reproduced waveform that occurs. If a signal defect occurs during servo signal reproduction, it becomes difficult to perform head tracking servo at the location where the signal defect occurs. Therefore, in order to more accurately record information on magnetic tape and / or reproduce information recorded on magnetic tape using a timing-based servo system, signal defects during servo signal reproduction It is required to reduce the frequency of occurrence of.

Therefore, an object of the present invention is to reduce the frequency of occurrence of signal defects in a timing-based servo system in a magnetic tape having a thin total thickness and improved surface smoothness of a magnetic layer.

One aspect of the present invention is
A magnetic tape having a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support.
The total thickness of the magnetic tape is 5.30 μm or less.
The magnetic layer has a timing-based servo pattern
The center line average surface roughness Ra (hereinafter, also referred to as “magnetic layer surface Ra”) measured on the surface of the magnetic layer is 1.8 nm or less.
The ferromagnetic powder is a ferromagnetic hexagonal ferrite powder, the magnetic layer contains a polishing agent, and the ferromagnetic hexagonal ferrite powder with respect to the surface of the magnetic layer obtained by cross-sectional observation performed using a scanning transmission electron microscope. The inclination cosθ (hereinafter, also simply referred to as “cosθ”) is 0.85 or more and 1.00 or less.
Regarding.

In the present invention and the present specification, the ferromagnetic hexagonal ferrite powder means an assembly of a plurality of ferromagnetic hexagonal ferrite particles. Hereinafter, the particles constituting the ferromagnetic hexagonal ferrite powder (ferromagnetic hexagonal ferrite particles) are also referred to as "hexagonal ferrite particles" or simply "particles". The assembly is not limited to the mode in which the particles constituting the set are in direct contact with each other, and also includes a mode in which a binder, an additive, or the like is interposed between the particles. The above points also apply to various powders such as non-magnetic powders in the present invention and the present specification. Details of the calculation method of cosθ and the like will be described later.

The "timing-based servo pattern" in the present invention and the present specification refers to a servo pattern capable of head tracking in a timing-based servo system. The timing-based servo system is as described above. A servo pattern capable of head tracking in a timing-based servo system is a servo pattern recording head (also referred to as a "servo write head") as a plurality of servo patterns having two or more different shapes on a magnetic layer. It is formed. In one example, a plurality of servo patterns having two or more different shapes are continuously arranged at regular intervals for each of a plurality of servo patterns having the same shape. In another example, different types of servo patterns are arranged alternately. Note that the fact that the servo patterns have the same shape does not mean that they have exactly the same shape, and that shape errors that may occur due to devices such as servo light heads are allowed. .. The shape of the servo pattern capable of head tracking in the timing-based servo system and the arrangement in the magnetic layer are known, and the specific embodiment will be described later. Hereinafter, the timing-based servo pattern will also be simply described as a servo pattern. In the present specification, "servo light head", "servo head", and "magnetic head" are described as heads. The servo light head is a head that records a servo signal (that is, forms a servo pattern) as described above. The servo head is a head that reproduces a servo signal (that is, reads a servo pattern), and a magnetic head is a head that records and / or reproduces information.

In the present invention and the present specification, the center line average surface roughness Ra measured on the surface of the magnetic layer of the magnetic tape is measured by an atomic force microscope (AFM) in an area of 40 μm × 40 μm. Value. The following measurement conditions can be mentioned as an example of the measurement conditions. The center line average surface roughness Ra shown in the examples described later is a value obtained by measurement under the following measurement conditions. In the present invention and the present specification, the surface of the magnetic layer of the magnetic tape is synonymous with the surface of the magnetic tape on the magnetic layer side.
An area of 40 μm × 40 μm on the surface of the magnetic layer of the magnetic tape is measured by AFM (Nanoscope 4 manufactured by Veeco). The scanning speed (probe moving speed) is 40 μm / sec, and the resolution is 512pixel × 512pixel.

In one aspect, cos θ is 0.89 or more and 1.00 or less.

In one aspect, the magnetic layer further comprises a polyester chain-containing compound having a weight average molecular weight of 1,000 or more and 80,000 or less.

In one embodiment, the activation volume of the ferromagnetic hexagonal ferrite powder is 800 nm ³ or more 2500 nm ³ or less.

In one aspect, the magnetic layer surface Ra is 1.2 nm or more and 1.8 nm or less.

In one aspect, the total thickness of the magnetic tape is 3.00 μm or more and 5.30 μm or less.

In one aspect, the magnetic tape has a non-magnetic layer containing a non-magnetic powder and a binder between the non-magnetic support and the magnetic layer.

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

In one aspect, the abrasive comprises alumina powder.

A further aspect of the present invention relates to a magnetic tape device including the magnetic tape, a magnetic head, and a servo head.

According to one aspect of the present invention, the magnetic tape has a timing-based servo pattern on a magnetic layer that is thin and has high surface smoothness, and the frequency of occurrence of signal defects during servo signal reproduction in the timing-based servo system is high. A reduced magnetic tape and a magnetic tape device that records and / or reproduces a magnetic signal on the magnetic tape can be provided.

An example of arranging the data band and the servo band is shown. An example of arranging the servo pattern of the LTO (Linear-Tape-Open) Ultra format tape is shown. It is explanatory drawing of the angle θ with respect to cos θ. It is explanatory drawing of the angle θ with respect to cos θ.

[Magnetic tape]
One aspect of the present invention has a magnetic layer containing a ferromagnetic powder and a binder on a non-magnetic support, the total thickness of the magnetic tape is 5.30 μm or less, and the magnetic layer has a timing-based servo pattern. The centerline average surface roughness Ra (magnetic layer surface Ra) measured on the surface of the magnetic layer is 1.8 nm or less, the ferromagnetic powder is a ferromagnetic hexagonal ferrite powder, and the magnetic layer contains a polishing agent. The present invention relates to a magnetic tape in which the inclination cosθ of the ferromagnetic hexagonal ferrite powder with respect to the surface of the magnetic layer determined by cross-sectional observation performed using a scanning transmission type electron microscope is 0.85 or more and 1.00 or less.
Hereinafter, the magnetic tape will be described in more detail. The following description includes the inferences of the present inventors. The present invention is not limited by such speculation. Further, in the following, the description may be exemplified based on the drawings. However, the present invention is not limited to the embodiments exemplified.

<Magnetic layer surface Ra>
The center line average surface roughness Ra (magnetic layer surface Ra) measured on the magnetic layer surface of the magnetic tape is 1.8 nm or less. For magnetic tapes with a magnetic layer surface Ra of 1.8 nm or less and a total thickness of 5.30 μm or less, the frequency of signal defects during servo signal reproduction increases in timing-based servo systems unless any measures are taken. Resulting in. On the other hand, the magnetic tape containing a ferromagnetic hexagonal ferrite powder and an abrasive in the magnetic layer and having a cos θ of 0.85 or more and 1.00 or less has a magnetic layer surface Ra of 1.8 nm or less and a cos θ of 0.85 or more and 1.00 or less. Even though the total thickness is 5.30 μm or less, the occurrence of signal defects can be suppressed during the reproduction of the servo signal. The inventors of the present invention in this regard will be described later. Further, the magnetic tape having a magnetic layer surface Ra of 1.8 nm or less can exhibit excellent electromagnetic conversion characteristics. From the viewpoint of further improving the electromagnetic conversion characteristics, the magnetic layer surface Ra is preferably 1.7 nm or less, and more preferably 1.6 nm or less. Further, the surface Ra of the magnetic layer can be, for example, 1.2 nm or more or 1.3 nm or more. However, from the viewpoint of improving the electromagnetic conversion characteristics, the lower the magnetic layer surface Ra is, the more preferable it is. Therefore, the value may be lower than the above-exemplified value.

The surface Ra of the magnetic layer can be controlled by a known method. For example, the surface Ra of the magnetic layer may change depending on the size of various powders contained in the magnetic layer (for example, ferromagnetic powder, non-magnetic powder that can be arbitrarily contained, etc.), the manufacturing conditions of the magnetic tape, etc., so these should be adjusted. Therefore, a magnetic tape having a magnetic layer surface Ra of 1.8 nm or less can be obtained.

<Timing-based servo pattern>
The magnetic tape has a timing-based servo pattern on the magnetic layer. The timing-based servo pattern is the servo pattern described above. For example, in a magnetic tape applied to a linear recording method widely used as a recording method of a magnetic tape device, a region (called a "servo band") in which a servo pattern is formed on a magnetic layer is usually a magnetic tape. There are a plurality of magnets along the longitudinal direction of the magnet. The area sandwiched between the two servo bands is called the data band. The recording of the magnetic signal (information) is performed on the data band, and a plurality of data tracks are formed along the longitudinal direction in each data band.

FIG. 1 shows an example of arranging the data band and the servo band. In FIG. 1, a plurality of servo bands 10 are arranged on the magnetic layer of the magnetic tape 1 so as to be sandwiched between the guide bands 12. A plurality of regions 11 sandwiched between the two servo bands are data bands. The servo pattern is a magnetized region, which is formed by magnetizing a specific region of the magnetic layer with a servo light head. The region magnetized by the servo light head (the position where the servo pattern is formed) is defined by the standard. For example, in the LTOURtrium format tape, which is an industry standard, a plurality of servo patterns inclined with respect to the tape width direction are formed on the servo band at the time of manufacturing the magnetic tape. Specifically, in FIG. 2, the servo frame SF on the servo band 10 is composed of a servo subframe 1 (SSF1) and a servo subframe 2 (SSF2). The servo subframe 1 is composed of an A burst (reference numeral A in FIG. 2) and a B burst (reference numeral B in FIG. 2). The A burst is composed of servo patterns A1 to A5, and the B burst is composed of servo patterns B1 to B5. On the other hand, the servo subframe 2 is composed of a C burst (reference numeral C in FIG. 2) and a D burst (reference numeral D in FIG. 2). The C burst is composed of servo patterns C1 to C4, and the D burst is composed of servo patterns D1 to D4. Such 18 servo patterns are arranged in a set of 5 and 4 in subframes arranged in an array of 5, 5, 4, 4, and used to identify the servo frames. FIG. 2 shows one servo frame for the sake of explanation. However, in reality, in the magnetic layer of the magnetic tape on which the head tracking servo is performed in the timing-based servo system, a plurality of servo frames are arranged in the traveling direction in each servo band. In FIG. 2, the arrow indicates the traveling direction. The servo head sequentially reads the servo patterns in a plurality of servo frames while traveling on the magnetic layer.

In the timing-based servo system, the position of the servo head is determined by the time interval in which the servo head reads two servo patterns of different shapes (reproduces the servo signal) and the time interval in which two servo patterns of the same shape are read. Recognize. The time interval is usually obtained as the time interval of the peak of the reproduced waveform of the servo signal. For example, in the embodiment shown in FIG. 2, the A-burst servo pattern and the C-burst servo pattern have the same shape, and the B-burst servo pattern and the D-burst servo pattern have the same shape. .. The A-burst servo pattern and the C-burst servo pattern are servo patterns having different shapes from the B-burst servo pattern and the D-burst servo pattern. The time interval in which the servo head reads two servo patterns having different shapes is, for example, the interval between the time in which one of the A burst servo patterns is read and the time in which one of the B burst servo patterns is read. .. The time interval at which the servo head reads two servo patterns of the same shape is, for example, the interval between the time when one of the A burst servo patterns is read and the time when one of the C burst servo patterns is read. is there. The timing-based servo system is a system on the premise that when the above time interval deviates from the set value, the time interval deviation occurs due to the position change in the width direction of the magnetic tape. The set value is a time interval when the magnetic tape travels in the width direction without causing a position change. In the timing-based servo system, the magnetic head is moved in the width direction according to the degree of deviation from the set value of the obtained time interval. Specifically, the larger the deviation from the set value of the time interval, the larger the movement of the magnetic head in the width direction. This point is not limited to the embodiments shown in FIGS. 1 and 2, and applies to the timing-based servo system in general. In a magnetic tape device using such a timing-based servo system, if a signal defect occurs during servo signal reproduction, it becomes difficult to obtain a measurement result of a time interval at a location (servo frame) where the defect occurs. As a result, it becomes partially difficult to position the head by moving the magnetic head in the width direction when the magnetic tape is run and the magnetic signal (information) is recorded or reproduced by the magnetic head. Regarding this point, in the study by the present inventors, in the magnetic tape having a total thickness of 5.30 μm or less and a magnetic layer surface Ra of 1.8 nm or less, signal defects are remarkably generated during servo signal reproduction. It turned out to be. The present inventors impede smooth sliding between the servo head and the surface of the magnetic layer as a cause of signal defects during servo signal reproduction (hereinafter, referred to as "decrease in slidability"). I think that can be mentioned. The magnetic tape having a total thickness of 5.30 μm or less and a magnetic layer surface Ra of 1.8 nm or less slides because the contact state between the servo head and the magnetic layer surface is different from that of the conventional magnetic tape. The present inventors speculate that it may be the cause of the decrease in sex. However, it is just a guess.
On the other hand, as a result of diligent studies by the present inventors, it has been clarified that the occurrence of signal defects during servo signal reproduction can be suppressed by setting cos θ to 0.85 or more and 1.00 or less. The inventors of the present invention in this regard will be described later.

<Cosθ>
In the above magnetic tape, the inclination cosθ of the ferromagnetic hexagonal ferrite powder with respect to the surface of the magnetic layer determined by cross-sectional observation performed using a scanning transmission electron microscope is 0.85 or more and 1.00 or less. cosθ is more preferably 0.89 or more, still more preferably 0.90 or more, still more preferably 0.92 or more, and even more preferably 0.95 or more. On the other hand, cosθ has a maximum value of 1.00 when hexagonal ferrite particles having an aspect ratio and a length in the major axis direction, which will be described later, are all present in parallel with the surface of the magnetic layer. According to the study by the present inventors, the larger the value of cosθ, the less frequently signal defects occur during servo signal reproduction in the timing-based servo system. That is, from the viewpoint of further reducing the frequency of signal defects during servo signal reproduction in the timing-based servo system in a magnetic tape having a total thickness of 5.30 μm or less and a magnetic layer surface Ra of 1.8 nm or less. , The larger the value of cosθ, the more preferable. Therefore, in the above magnetic tape, the upper limit of cosθ is 1.00 or less. Note that cosθ may be, for example, 0.99 or less. However, as described above, the larger the value of cosθ, the more preferable it tends to be. Therefore, cosθ may exceed 0.99.

(Calculation method of cosθ)
cosθ is determined by cross-sectional observation performed using a scanning transmission electron microscope (hereinafter, also referred to as “STEM”). The cos θ in the present invention and the present specification is a value measured and calculated by the following method.

(1) A sample for cross-section observation is prepared by cutting out from a randomly determined position of the magnetic tape for which cosθ is to be obtained. The cross-section observation sample is prepared by FIB (Focused Ion Beam) processing using ^{a gallium ion (Ga +) beam.} Specific examples of such a production method will be described later with reference to Examples.
(2) STEM observation of the prepared cross-section observation sample and imaging of the STEM image. The STEM images are taken at randomly selected positions in the same cross-section observation sample except for the points where the imaging ranges are selected so as not to overlap, and a total of 10 images are obtained. The STEM image is a STEM-HAADF (High-Angle Anal Dark Field) image imaged at an acceleration voltage of 300 kV and an imaging magnification of 450,000 times, and is imaged so that one image includes the entire region in the thickness direction of the magnetic layer. To do. The entire region in the thickness direction of the magnetic layer is a region from the surface of the magnetic layer observed in the cross-section observation sample to the interface between the magnetic layer and the adjacent layer or the non-magnetic support. The adjacent layer is a non-magnetic layer when the magnetic tape for which cos θ is to be obtained has a non-magnetic layer described later between the magnetic layer and the non-magnetic support. On the other hand, when the magnetic tape for which cosθ is to be obtained has a magnetic layer directly on the non-magnetic support, the interface is the interface between the magnetic layer and the non-magnetic support.
(3) In each STEM image thus obtained, a straight line connecting both ends of the line segment representing the surface of the magnetic layer is defined as a reference line. Both ends of the above line segment are, for example, an image of the STEM image when the STEM image is imaged so that the magnetic layer side of the cross-section observation sample is located above the image and the non-magnetic support side is located below. It is a straight line connecting the intersection of the left side of (usually a rectangle or a square) and the line segment and the intersection of the right side of the STEM image and the line segment.
(4) Among the hexagonal ferrite particles observed in the STEM image, the aspect ratio is. The angle θ formed by the major axis direction of hexagonal ferrite particles (primary particles) having a length in the range of 1.5 to 6.0 and a length in the major axis direction of 10 nm or more and the reference line is measured. For the measured angle θ, cos θ is calculated as cos θ based on the unit circle. Such calculation of cosθ is performed for 30 particles randomly selected from hexagonal ferrite particles having the above aspect ratio and length in the major axis direction in each STEM image.
(5) The above measurement and calculation are performed for each of the 10 images, and the value of cos θ obtained for the 30 hexagonal ferrite particles in each image, that is, for a total of 300 hexagonal ferrite particles in the 10 images, is calculated. Average. The arithmetic mean thus obtained is defined as the inclination cosθ of the ferromagnetic hexagonal ferrite powder with respect to the surface of the magnetic layer obtained by cross-sectional observation performed using a scanning transmission electron microscope.

Here, the "aspect ratio" observed in the STEM image means the ratio of "length in the major axis direction / length in the minor axis direction" of the hexagonal ferrite particles.
The "semi-major direction" is defined as the farthest end of the image of one hexagonal ferrite particle observed in the STEM image, from the end closest to the reference line. It means the direction when the far end is tied. When the line segment connecting one end and the other end is parallel to the reference line, the direction parallel to the reference line is the major axis direction.
The "length in the major axis direction" is the length of a line segment created by connecting the farthest ends in the image of one hexagonal ferrite particle observed in the STEM image. means. On the other hand, the "length in the semi-minor axis direction" means the length of the longest line segment among the line segments connecting the two intersections of the outer edge of the image of the particle and the perpendicular line in the semi-minor axis direction. ..
Further, the angle θ formed by the reference line and the inclination of the particles in the long axis direction is defined in a range of 0 ° or more and 90 ° or less, with the angle in which the long axis direction is parallel to the reference line being 0 °. To do. The angle θ will be further described below with reference to the drawings.

3 and 4 are explanatory views of the angle θ. In FIGS. 3 and 4, reference numeral 101 indicates a line segment (length in the long axis direction) created by connecting the most distant ends, reference numeral 102 indicates a reference line, and reference numeral 103. Indicates an extension line of the line segment (reference numeral 101). In this case, the angles formed by the reference line 102 and the extension line 103 may be θ1 and θ2 as shown in FIGS. 3 and 4. Here, a smaller angle is adopted among θ1 and θ2, and this is assumed to be the angle θ. Therefore, in the embodiment shown in FIG. 3, θ1 is defined as the angle θ, and in the embodiment shown in FIG. 4, θ2 is defined as the angle θ. It should be noted that the case of θ1 = θ2, that is, the case of the angle θ = 90 °. The cos θ based on the unit circle is 1.00 when θ = 0 ° and 0 when θ = 90 °.

The magnetic tape contains an abrasive and a ferromagnetic hexagonal ferrite powder in a magnetic layer, and has a cos θ of 0.85 or more and 1.00 or less. Among the hexagonal ferrite particles constituting the ferromagnetic hexagonal ferrite powder contained in the magnetic layer, the present inventors use a polishing agent for the hexagonal ferrite particles satisfying the above aspect ratio and the length in the major axis direction. I think we can support it. The present inventors consider that this contributes to suppressing the occurrence of signal defects during servo signal reproduction in the timing-based servo system in the magnetic tape. This point will be further described below.
The abrasive can provide the surface of the magnetic layer with a function (hereinafter referred to as "wearability") of removing foreign substances (hereinafter referred to as "adhesions") adhering to the servo head. Since the surface of the magnetic layer exhibits wearability, it is possible to remove the deposits attached to the servo head caused by scraping a part of the surface of the magnetic layer when the servo head travels on the magnetic layer. .. However, if the surface of the magnetic layer cannot sufficiently exhibit wearability, the servo head runs on the magnetic layer with deposits attached to the servo head, and signal defects occur due to the influence of the deposits. The present inventors speculate. The present inventors consider that this decrease in wear resistance of the magnetic layer surface is caused by the abrasive existing near the surface of the magnetic layer being pushed into the magnetic layer by contact with the servo head. ..
On the other hand, when the abrasive present near the surface of the magnetic layer is pushed into the magnetic layer by contact with the servo head, hexagonal ferrite particles satisfying the above aspect ratio and the length in the major axis direction are the abrasive. It is thought that it can be suppressed by supporting. As a result, it is possible to suppress a decrease in the wear resistance of the surface of the magnetic layer, and as a result, it may be possible to suppress the occurrence of signal defects due to the influence of deposits adhering to the servo head during servo signal reproduction. The inventors speculate. However, it is just a guess.
The square ratio is known as an index of the existence state (orientation state) of the ferromagnetic hexagonal ferrite powder in the magnetic layer. However, according to the study by the present inventors, a good correlation was not found between the control of the square ratio and the frequency of occurrence of signal defects during servo signal reproduction. The square ratio is a value representing the ratio of the residual magnetization to the saturation magnetization, and is measured for all particles regardless of the shape and size of the particles contained in the ferromagnetic hexagonal ferrite powder. On the other hand, cosθ is a value measured by selecting hexagonal ferrite particles having an aspect ratio in the above range and a length in the major axis direction. The present inventors consider that such a difference may cause a good correlation with the frequency of occurrence of signal defects during servo signal reproduction according to cosθ. However, the above is only speculation and does not limit the present invention in any way.

(Adjustment method of cosθ)
The magnetic tape can be produced through a step of applying a composition for forming a magnetic layer on a non-magnetic support. Then, as a method for adjusting cosθ, control of the dispersed state of the ferromagnetic hexagonal ferrite powder in the composition for forming a magnetic layer can be mentioned. In this regard, the present inventors have the dispersibility of the ferromagnetic hexagonal ferrite powder in the composition for forming a magnetic layer (hereinafter, also simply referred to as "dispersity of the ferromagnetic hexagonal ferrite powder" or "dispersity"). In the magnetic layer formed by using this magnetic layer forming composition, hexagonal ferrite particles having an aspect ratio in the above range and a length in the major axis direction are more parallel to the surface of the magnetic layer. It is thought that it will be easier to orient in a state close to. As a means for increasing the dispersibility, one or both of the following methods (1) and (2) can be mentioned.
(1) Adjustment of dispersion conditions (2) Use of dispersant As a means for improving dispersibility, it is also possible to separately disperse the ferromagnetic hexagonal ferrite powder and the abrasive. More specifically, the separate dispersion is a magnetic liquid containing a ferromagnetic hexagonal ferrite powder, a binder, and a solvent (however, substantially free of an abrasive), and an abrasive containing an abrasive and a solvent. This is a method of preparing a composition for forming a magnetic layer through a step of mixing with a liquid. By separately dispersing the abrasive and the ferromagnetic hexagonal ferrite powder and then mixing them in this way, the dispersibility of the ferromagnetic hexagonal ferrite powder in the composition for forming a magnetic layer can be enhanced. The above-mentioned "substantially free of abrasive" means that it is not added as a constituent component of the magnetic liquid, and it is permissible that a small amount of abrasive is present as an impurity mixed unintentionally. It shall be done. It is also preferable to combine either or both of the above methods (1) and (2) with the above separate dispersion. In this case, by controlling the dispersion state of the ferromagnetic hexagonal ferrite powder in the magnetic liquid, the dispersion of the ferromagnetic hexagonal ferrite powder in the composition for forming a magnetic layer obtained through the step of mixing the magnetic liquid with the abrasive liquid. The state can be controlled.

Hereinafter, specific embodiments of the above (1) and (2) will be described.

(1) Adjustment of Dispersion Conditions The dispersion treatment of the composition for forming a magnetic layer, preferably the magnetic liquid, can be performed by adjusting the dispersion conditions using a known dispersion method. Examples of the dispersion condition in the dispersion processing include the type of the disperser, the type of the distributed media used in the disperser, the residence time in the disperser (hereinafter, also referred to as “dispersion residence time”) and the like.
As the disperser, various known dispersers using shearing force such as a ball mill, a sand mill, and a homomixer can be used. Two or more dispersers may be connected to perform two or more stages of dispersion processing, or different dispersers may be used in combination. The peripheral speed at the tip of the disperser is preferably 5 to 20 m / sec, more preferably 7 to 15 m / sec.
Examples of the dispersed medium include ceramic beads, glass beads and the like, and zirconia beads are preferable. Two or more kinds of beads may be used in combination. The particle size of the dispersed media is, for example, 0.03 to 1 mm, preferably 0.05 to 0.5 mm. When the dispersers are connected to perform the dispersion treatment in two or more stages as described above, dispersion media having different particle sizes may be used in each stage. It is preferable to use a dispersed medium having a smaller particle size for each step. The filling rate of the dispersed media can be, for example, 30 to 80%, preferably 50 to 80% on a volume basis.
The dispersion residence time may be appropriately set in consideration of the peripheral speed at the tip of the disperser, the filling rate of the dispersion media, and the like, and may be, for example, 15 to 45 hours, preferably 20 to 40 hours. When two or more stages of dispersion processing are performed by connecting the dispersers as described above, it is preferable that the total dispersion residence time of each stage is within the above range. By performing such a dispersion treatment, the dispersibility of the ferromagnetic hexagonal ferrite powder can be enhanced, and cosθ can be adjusted to 0.85 or more and 1.00 or less.

(2) Use of Dispersant By using a dispersant when preparing a composition for forming a magnetic layer, preferably when preparing a magnetic liquid, the dispersibility of the ferromagnetic hexagonal ferrite powder can be enhanced. Here, the dispersant refers to a component capable of enhancing the dispersibility of the ferromagnetic hexagonal ferrite powder in the composition for forming a magnetic layer and / or the magnetic liquid as compared with the state in which this agent does not exist. The dispersion state of the ferromagnetic hexagonal ferrite powder can also be controlled by changing the type and amount of the dispersant contained in the composition for forming the magnetic layer and / or the magnetic liquid. As the dispersant, from the viewpoint of enhancing the durability of the magnetic layer, it is also possible to use a dispersant that prevents aggregation of hexagonal ferrite particles constituting the ferromagnetic hexagonal ferrite powder and imparts appropriate plasticity to the magnetic layer. preferable.

As one aspect of the dispersant preferable for improving the dispersibility of the ferromagnetic hexagonal ferrite powder, a polyester chain-containing compound can be mentioned. The polyester chain-containing compound is also preferable for imparting appropriate plasticity to the magnetic layer. Here, the polyester chain is represented by E in the general formula A described later. Specific embodiments thereof include a polyester chain contained in the general formula 1 described later, a polyester chain represented by the formula 2-A, and a polyester chain represented by the formula 2-B. By mixing the polyester chain-containing compound together with the ferromagnetic hexagonal ferrite powder into the composition for forming a magnetic layer and / or the magnetic liquid, the polyester chains are interposed between the hexagonal ferrite particles to suppress the aggregation of the particles. The present inventors speculate that this is possible. However, this is merely speculation and does not limit the present invention in any way. The weight average molecular weight of the polyester chain-containing compound is preferably 1,000 or more from the viewpoint of improving the dispersibility of the ferromagnetic hexagonal ferrite powder. The weight average molecular weight of the polyester chain-containing compound is preferably 80,000 or less. The present inventors consider that a polyester chain-containing compound having a weight average molecular weight of 80,000 or less may be able to enhance the durability of the magnetic layer by acting like a plasticizer. The weight average molecular weight in the present invention and the present specification refers to a value obtained by converting a value measured by gel permeation chromatography (GPC) into standard polystyrene. Specific examples of measurement conditions will be described later. Further, a preferable range of the weight average molecular weight will be described later.

A preferred embodiment of such a polyester chain-containing compound is a compound having a partial structure represented by the following general formula A. Unless otherwise specified, the groups described in the present invention and the present specification may have substituents or may be unsubstituted. When a group has a substituent, the substituents include an alkyl group (for example, an alkyl group having 1 to 6 carbon atoms), a hydroxy group, an alkoxy group (for example, an alkoxy group having 1 to 6 carbon atoms), and a halogen atom (for example, fluorine). Atomic, chlorine atom, bromine atom), cyano group, amino group, nitro group, acyl group, carboxy (salt) group and the like can be mentioned. Further, with respect to a group having a substituent, the "carbon number" shall mean the carbon number of the portion not containing the substituent.

In the general formula A, Q represents -O-, -CO-, -S-, -NR ^a- or a single bond, T and R ^a independently represent a hydrogen atom or a monovalent substituent, and E is ^{- (O-L a -CO)} a- or ^{- (CO-L a -O)} a- a represents, L ^a represents a divalent linking group, a is integer of 2 or more, b is 1 or more Represents an integer of, and * represents the bonding position with other partial structures constituting the polyester chain-containing compound.

In formula A, L ^A is included × b number a. Further, b are included in each of T and Q. If L ^A is contained more in the general formula A, the plurality of L ^A may be different may be the same. This point is the same for T and Q.

It is considered that the above compound can suppress the aggregation of hexagonal ferrite particles in the magnetic liquid and the composition for forming the magnetic layer due to the steric hindrance caused by the partial structure.

A preferred embodiment of the polyester chain-containing compound is a compound having a group or a partial structure (hereinafter, referred to as “adsorption portion”) that can be adsorbed on the surface of hexagonal ferrite particles together with the polyester chain in the molecule. Further, the polyester chain is preferably included in the partial structure represented by the general formula A. Further, it is more preferable that the partial structure represented by the general formula A and the adsorption portion form a bond via * in the general formula A.
In one aspect, the adsorption portion can be a polar functional group (polar group) that serves as an adsorption point on the surface of hexagonal ferrite particles. Specific examples include a carboxy group (-COOH) and a salt thereof (-COO ^- M ⁺ ), a sulfonic acid group (-SO ₃ H) and a salt thereof (-SO ₃ ^- M ⁺ ), and a sulfate group (-OSO ₃ H). ) and its salts (-OSO ₃ ^- M ^+), phosphoric acid group _{(-P = O (OH) 2} ) and its salts ^{(-P = O (O - M} +) 2), amino group (-NR ₂₎ , -N ⁺ R ₃ , epoxy group, thiol group (-SH), and cyano group (-CN) (where M ⁺ represents a cation such as an alkali metal ion, R represents a hydrogen atom or a hydrocarbon group), etc. At least one polar group selected from can be mentioned. The "carboxy (salt) group" shall mean one or both of the carboxy group and its salt (carboxy salt). As described above, the carboxy salt is in the form of a salt having a carboxy group (−COOH).
Moreover, as one aspect of the adsorption part, a polyalkyleneimine chain can also be mentioned.
The type of bond formed by the partial structure represented by the general formula A and the adsorption portion is not particularly limited. Such bonds are preferably selected from the group consisting of covalent bonds, coordination bonds and ionic bonds, and may have different types of bonds within the same molecule. By efficiently adsorbing the hexagonal ferrite particles via the adsorption portion, the effect of suppressing aggregation of the hexagonal ferrite particles based on the steric hindrance caused by the partial structure represented by the general formula A can be further enhanced. It is thought that it can be done.

In one aspect, the polyester chain-containing compound can have at least one polyalkyleneimine chain. Such a polyester chain-containing compound can preferably contain the polyester chain in the partial structure represented by the general formula A. Preferred examples of such a polyester chain-containing compound include, as a general formula A, a polyester chain selected from the group consisting of a polyester chain represented by the following formula 2-A and a polyester chain represented by the following formula 2-B. Examples include polyalkyleneimine derivatives. Details of these examples will be described later.

^{L 1} in formula 2-A ^{and L 2} in formula 2-B each independently represent a divalent linking group, and b11 in formula 2-A and b21 in formula 2-B are independent of each other. Representing an integer of 2 or more, b12 in Equation 2-A and b22 in Equation 2-B independently represent 0 or 1, respectively, X ^{1 in Equation 2-A and X 2 in} Equation 2-B. Represent each independently a hydrogen atom or a monovalent substituent.

In the general formula A, Q represents -O-, -CO-, -S-, -NR ^a- or a single bond, preferably X in the general formula 1 described later, and (-CO) in the above formula 2-A. -) The portion represented by b12 or (-CO-) b22 in the formula 2-B can be mentioned.

In the general formula A, T and R ^a independently represent a hydrogen atom or a monovalent substituent, preferably R in the general formula 1 described later, X ¹ in the formula 2-A or the formula 2-B. The part represented by ^{X 2 is mentioned.}

In Formula A, E is ^{- (O-L A -CO)} a- or ^{- (CO-L A -O)} a- a represents, L ^A represents a divalent linking group, a is an integer of 2 or more Represents.
Examples of the divalent linking group L ^A represents, with preference given to L ¹ or moiety represented by L ² in Formula 2-B in L, the formula 2-A in the general formula 1 described below.

Also, in one aspect, the polyester chain-containing compound can have at least one group selected from the group consisting of carboxy groups and carboxy salts. Such a polyester chain-containing compound can preferably contain the polyester chain in the partial structure represented by the general formula A. Preferred examples of such a polyester chain-containing compound include a compound represented by the following general formula 1.

<Compound represented by general formula 1>
General formula 1 is as follows.

（一般式１中、Ｘは−Ｏ−、−Ｓ−または−ＮＲ¹−を表し、ＲおよびＲ¹は、それぞれ独立に水素原子または一価の置換基を表し、Ｌは二価の連結基を表し、Ｚはカルボキシ基およびカルボキシ塩からなる群から選ばれる基（カルボキシ（塩）基）を少なくとも１つ有するｎ価の部分構造を表し、ｍは２以上の整数を表し、ｎは１以上の整数を表す。）

(In General Formula 1, X represents -O-, -S- or -NR ^1- , R and R ¹ independently represent a hydrogen atom or a monovalent substituent, and L is a divalent linking group. , Z represents an n-valent partial structure having at least one group (carboxy (salt) group) selected from the group consisting of a carboxy group and a carboxy salt, m represents an integer of 2 or more, and n represents 1 or more. Represents an integer of.)

In the general formula 1, m × n L is included. Further, n R and X are included, respectively. When a plurality of L's are included in the general formula 1, the plurality of L's may be the same or different. This point is the same for R and X.

The compound represented by the general formula 1 has a structure (polyester chain) represented by-((C = O) -LO) m-, and has a carboxy (salt) group as the above-mentioned adsorption portion in the Z portion. Included in. The carboxy (salt) group contained in the Z portion serves as an adsorption portion on the surface of the hexagonal ferrite particles, so that the compound represented by the general formula 1 is efficiently adsorbed on the hexagonal ferrite particles and then on the polyester chain. It is considered that the agglomeration of hexagonal ferrite particles can be prevented by causing steric hindrance.

In the general formula 1, X represents −O−, −S− or −NR ¹⁻ , and R ¹ represents a hydrogen atom or a monovalent substituent. Examples of the monovalent substituent represented by R ¹ include the above-mentioned substituents such as an alkyl group, a hydroxy group, an alkoxy group, a halogen atom, a cyano group, an amino group, a nitro group, an acyl group and a carboxy (salt) group. It can be preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably a methyl group or an ethyl group. More preferably, R ¹ is a hydrogen atom. X preferably represents −O−.

R represents a hydrogen atom or a monovalent substituent. R preferably represents a monovalent substituent. Examples of the monovalent substituent represented by R include a monovalent group such as an alkyl group, an aryl group, a heteroaryl group, an alicyclic group and a non-aromatic heterocyclic group, and the above monovalent group. A monovalent substitution in which a valent linking group is linked (ie, R has a structure in which a divalent linking group is linked to the monovalent group, and is bonded to X via the divalent linking group. It is a group.) Etc. can be mentioned. As the divalent linking group, for example, -C (= O) -O-, -O-, -C (= O) -NR ^10- (R ¹⁰ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Represented), -OC (= O) -NH-, a phenylene group, and one or more selected from the group consisting of an alkylene group having 1 to 30 carbon atoms and an alkenylene group having 2 to 30 carbon atoms. A divalent linking group composed of a combination can be mentioned. Specific examples of the monovalent substituent represented by R include the following structures. In the following structure, * represents the bonding position with X. However, R is not limited to the following specific examples.

In general formula 1, L represents a divalent linking group. The divalent linking group includes an alkylene group which may be a linear, branched or ring structure, an alkenylene group which may be a linear, branched or ring structure, -C (= O)-, -O- and A divalent linking group composed of one or a combination of two or more selected from the group consisting of arylene groups, which may have a halogen atom as a substituent or an anion in the divalent linking group. A divalent linking group can be mentioned. More specifically, an alkylene group having 1 to 12 carbon atoms which may be a linear, branched or ring structure, an alkenylene group having 1 to 6 carbon atoms which may be a linear, branched or ring structure, -C (=). O) Divalent linking groups composed of one or a combination of two or more selected from-, -O- and phenylene groups can be mentioned. The divalent linking group described above preferably comprises 1 to 10 carbon atoms, 0 to 10 oxygen atoms, 0 to 10 halogen atoms, and 1 to 30 hydrogen atoms. It is a divalent linking group. Specific examples include an alkylene group and the following structure. In the following structures, * indicates the bonding position with other structures in the general formula 1. However, the above divalent linking group is not limited to the following specific examples.

L is preferably an alkylene group, more preferably an alkylene group having 1 to 12 carbon atoms, more preferably an alkylene group having 1 to 5 carbon atoms, and further preferably an unsubstituted alkylene group having 1 to 5 carbon atoms. It is a group.

Z represents an n-valent partial structure having at least one group (carboxy (salt) group) selected from the group consisting of a carboxy group and a carboxy salt.

The number of carboxy (salt) groups contained in Z is at least one per Z, preferably two or more, and more preferably 2 to 4.

Z can include one or more structures selected from the group consisting of linear, branched and cyclic structures. From the viewpoint of ease of synthesis and the like, Z is preferably a reaction residue of a carboxylic acid anhydride. For example, the following structure can be mentioned as a specific example. In the following structures, * indicates the bonding position with other structures in the general formula 1. However, Z is not limited to the following specific examples.

The carboxylic acid anhydride is a compound having a partial structure represented by − (C = O) −O− (C = O) −. In the carboxylic acid anhydride, the above partial structure serves as a reaction site, and the oxygen atom of − ((C = O) −LO) m− in the general formula 1 and Z form a carbonyl bond (− (C =). O)-) is attached and a carboxy (salt) group is provided. The partial structure thus produced is the reaction residue of the carboxylic acid anhydride. A carboxylic acid anhydride is obtained by synthesizing a compound represented by the general formula 1 using a carboxylic acid anhydride having one partial structure-(C = O) -O- (C = O)-. A compound represented by the general formula 1 having a monovalent reaction residue can be obtained, and by using a compound having two compounds, the compound represented by the general formula 1 having a divalent reaction residue of a carboxylic acid anhydride can be obtained. Compounds can be obtained. The same applies to the compound represented by the general formula 1 having a reaction residue of trivalent or higher carboxylic acid anhydride. As described above, n is an integer of 1 or more, for example, an integer in the range of 1 to 4, preferably an integer in the range of 2 to 4.

As the carboxylic acid anhydride, for example, by using a tetracarboxylic dianhydride, a compound represented by the general formula 1 of n = 2 can be obtained. The tetracarboxylic acid anhydride is a compound having four carboxy groups in one molecule, and is a carboxylic acid anhydride having two of the above partial structures in one molecule by dehydration condensation of each two carboxy groups. In the general formula 1, the compound in which Z represents the reaction residue of the tetracarboxylic dianhydride is preferable from the viewpoint of further improving the dispersibility of the ferromagnetic hexagonal ferrite powder and the durability of the magnetic layer. Examples of the tetracarboxylic dianhydride include various tetracarboxylic dianhydrides such as an aliphatic tetracarboxylic dianhydride, an aromatic tetracarboxylic dianhydride, and a polycyclic tetracarboxylic dianhydride.

As the aliphatic tetracarboxylic dianhydride, for example, various aliphatic tetracarboxylic dianhydrides described in paragraph 0040 of JP-A-2016-071926 can be used. Further, as the aromatic tetracarboxylic dianhydride, for example, various aromatic tetracarboxylic dianhydrides described in paragraph 0041 of JP-A-2016-071926 can be used. As the polycyclic tetracarboxylic dianhydride, various polycyclic tetracarboxylic dianhydrides described in paragraph 0042 of JP-A-2016-071926 can be used.

In general formula 1, m represents an integer of 2 or more. As described above, in the compound represented by the general formula 1, the structure (polyester chain) represented by-((C = O) -LO) m- contributes to the improvement of dispersibility and durability. It is thought that. From these viewpoints, m is preferably an integer in the range of 5 to 200, more preferably an integer in the range of 5 to 100, and even more preferably an integer in the range of 5 to 60.

<< Weight Average Molecular Weight >>
As described above, the weight average molecular weight of the compound represented by the general formula 1 is preferably 1,000 or more and 80,000 or less, and more preferably 1,000 or more and 20,000 or less. The weight average molecular weight of the compound represented by the general formula 1 is more preferably less than 20,000, further preferably 12,000 or less, and even more preferably 10,000 or less. The weight average molecular weight of the compound represented by the general formula 1 is preferably 1,500 or more, more preferably 2,000 or more. The weight average molecular weight of the compound represented by the general formula 1 shown in Examples described later is a value obtained by converting a value measured under the following measurement conditions using GPC into standard polystyrene. Further, the weight average molecular weight of a mixture of two or more structural isomers means the weight average molecular weight of two or more structural isomers contained in this mixture.
GPC device: HLC-8220 (manufactured by Tosoh)
Guard column: TSKguardvolume Super HZM-H
Columns: TSKgel Super HZ 2000, TSKgel Super HZ 4000, TSKgel Super HZ-M (manufactured by Tosoh, 4.6 mm (inner diameter) x 15.0 cm, three types of columns are connected in series)
Eluent: Tetrahydrofuran (THF), stabilizer (2,6-di-t-butyl-4-methylphenol) included Eluent flow velocity: 0.35 mL / min Column temperature: 40 ° C.
Inlet temperature: 40 ° C
Refractive index (RI) measurement temperature: 40 ° C
Sample concentration: 0.3% by mass
Sample injection volume: 10 μL

<< Synthesis method >>
The compound represented by the general formula 1 described above can be synthesized by a known method. As an example of the synthesis method, for example, a method of subjecting a carboxylic acid anhydride and a compound represented by the following general formula 2 to a reaction such as a cycloaddition reaction can be mentioned. In the general formula 2, R, X, L and m are synonymous with the general formula 1. A represents a hydrogen atom, an alkali metal atom or a quaternary ammonium base, and is preferably a hydrogen atom.

The reaction between the carboxylic acid anhydride and the compound represented by the general formula 2 is carried out at a ratio of 0.4 to 0.5 mol with respect to 1 equivalent of the hydroxy group, for example, when butanetetracarboxylic acid anhydride is used. Butanetetracarboxylic acid anhydride is mixed and heated and stirred for about 3 to 12 hours in the presence of no solvent, an organic solvent having a boiling point of 50 ° C. or higher as necessary, and a reaction catalyst such as a tertiary amine or an inorganic base. It is carried out by. Even when other carboxylic acid anhydrides are used, the reaction between the carboxylic acid anhydride and the compound represented by the general formula 2 can be carried out according to the above reaction conditions or according to known reaction conditions. it can.

After the above reaction, a post-step such as purification may be performed if necessary.

Further, the compound represented by the general formula 2 may be a commercially available product, or can be obtained by a known polyester synthesis method. For example, as a polyester synthesis method, ring-opening polymerization of lactone can be mentioned. For ring-opening polymerization of lactone, paragraphs 0050 to 0051 of JP-A-2016-071926 can be referred to. However, the compound represented by the general formula 2 is not limited to the compound obtained by ring-opening polymerization of the lactone, and a known polyester synthesis method, for example, polycondensation of a polyvalent carboxylic acid and a polyhydric alcohol, is used. It can also be a compound obtained by polycondensation of hydroxycarboxylic acid or the like.

The synthesis method described above is an example, and does not limit the synthesis method of the compound represented by the general formula 1. As long as the compound represented by the general formula 1 can be synthesized, a known synthesis method can be used without any limitation. The reaction product after synthesis can be used as it is or, if necessary, purified by a known method and used for forming a magnetic layer. The compound represented by the general formula 1 may be used alone for the formation of the magnetic layer, or two or more compounds having different structures may be used in combination. Further, the compound represented by the general formula 1 may be used as a mixture of two or more structural isomers. For example, when two or more structural isomers can be obtained by a synthetic reaction of a compound represented by the general formula 1, such a mixture can also be used for forming a magnetic layer.

Examples of the compound represented by the general formula 1 include various compounds contained in the reaction products shown in the synthetic examples in the examples of JP-A-2016-071926. For example, as a specific example, the compounds shown in Table 1 below can be exemplified. The weight average molecular weight shown in Table 1 is the weight average molecular weight of the compound represented by the structural formula shown in Table 1 or the weight average molecular weight of the compound represented by the structural formula shown in Table 1 and a mixture of structural isomers thereof. is there.

As a preferred example of the compound having a partial structure and an adsorption portion represented by the general formula A, a polyalkyleneimine derivative containing a polyester chain represented by the following formula 2-A or 2-B as the general formula A is used. Can be mentioned. Hereinafter, such a polyalkyleneimine derivative will be described.

<Polyalkyleneimine derivative>
The polyalkyleneimine derivative comprises at least one polyester chain selected from the group consisting of a polyester chain represented by the following formula 2-A and a polyester chain represented by the following formula 2-B, and a number average molecular weight of 300 to 3, It is a compound containing a polyalkyleneimine chain in the range of 000. In this compound, the proportion of the polyalkyleneimine chain is preferably less than 5.0% by mass.

The polyalkyleneimine derivative has a polyalkyleneimine chain, which is one aspect of the adsorption portion described above. Furthermore, it is considered that the aggregation of hexagonal ferrite particles can be suppressed by causing the steric hindrance caused by the polyester chain of the polyalkyleneimine derivative in the composition for forming a magnetic layer and / or the magnetic liquid. Be done.

Hereinafter, the polyester chain and the polyalkyleneimine chain contained in the polyalkyleneimine derivative will be described.

<< Polyester chain >>
Structure of Polyester Chain The polyalkyleneimine derivative is selected from the group consisting of the polyester chain represented by the following formula 2-A and the polyester chain represented by the following formula 2-B together with the polyalkyleneimine chain described later. Contains one polyester chain. In one aspect, the polyester chain is bonded to the alkyleneimine chain represented by the formula A described later by the nitrogen atom N contained in the formula A and the carbonyl bond − (C = O) − ^{in * 1 in the formula A.} , -N- (C = O)-can be formed. In another aspect, the alkyleneimine chain and the polyester chain represented by the formula B described later ^{may form a salt-crosslinked group by the nitrogen cation N +} in the formula B and the anionic group of the polyester chain. it can. Examples of the salt-crosslinking group include those formed by the ^{oxygen anion O − contained in the polyester chain and N +} in the formula B.

Examples of the polyester chain represented by the formula A and the polyester chain bonded by the nitrogen atom N contained in the formula A and the carbonyl bond-(C = O)-include the polyester chain represented by the above formula 2-A. be able to. In the polyester chain represented by the above formula 2-A, the nitrogen atom contained in the alkyleneimine chain and the carbonyl group − (C = O) − contained in the polyester chain are −N at the bond position represented by ^{* 1.} By forming − (C = O) −, it can be bonded to the alkyleneimine chain represented by the formula A.

Further, the polyester chain in which the alkyleneimine chain represented by the formula B and the ^{anionic group contained in the N +} and the polyester chain in the formula B are bonded by forming a salt-crosslinked group is represented by the above formula 2-B. The polyester chain represented can be mentioned. The polyester chain represented by the above formula 2-B can form a salt-crosslinking group with ^{N +} in the formula B by the ^{oxygen anion O −.}

L ¹ in Formula 2-A, L ² in Formula 2-B each independently represent a divalent linking group. As the divalent linking group, preferably, an alkylene group having 3 to 30 carbon atoms can be mentioned. When the alkylene group has a substituent, the carbon number of the alkylene group means the carbon number of the portion (main chain portion) excluding the substituent, as described above.

B11 in Formula 2-A and b21 in Formula 2-B each independently represent an integer of 2 or more, and are, for example, an integer of 200 or less. The number of lactone repeating units shown in Table 3 below corresponds to b11 in Formula 2-A or b21 in Formula 2-B.

B12 in formula 2-A and b22 in formula 2-B independently represent 0 or 1, respectively.

^{X 1} in Formula 2-A ^{and X 2} in Formula 2-B each independently represent a hydrogen atom or a monovalent substituent. Examples of the monovalent substituent include a monovalent substituent selected from the group consisting of an alkyl group, a haloalkyl group (for example, a fluoroalkyl group, etc.), an alkoxy group, a polyalkyleneoxyalkyl group and an aryl group.

The alkyl group may have a substituent or may be unsubstituted. As the alkyl group having a substituent, an alkyl group substituted with a hydroxy group (hydroxyalkyl group) and an alkyl group substituted with one or more halogen atoms are preferable. Further, an alkyl group (haloalkyl group) in which the total hydrogen atom bonded to the carbon atom is replaced with a halogen atom is also preferable. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and the like. The alkyl group is more preferably an alkyl group having 1 to 30 carbon atoms, and further preferably an alkyl group having 1 to 10 carbon atoms. The alkyl group may be linear, branched or cyclic. The same applies to the haloalkyl group.

Specific examples of the substituted or unsubstituted alkyl group or haloalkyl group include, for example, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, and the like. Dodecyl group, tridecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, eicosyl group, isopropyl group, isobutyl group, isopentyl group, 2-ethylhexyl group, tert-octyl group, 2-hexyldecyl group, cyclohexyl group, Cyclopentyl group, cyclohexylmethyl group, octylcyclohexyl group, 2-norbornyl group, 2,2,4-trimethylpentyl group, acetylmethyl group, acetylethyl group, hydroxymethyl group, hydroxyethyl group, hydroxypropyl group, hydroxybutyl group, Hydroxypentyl group, hydroxyhexyl group, hydroxyheptyl group, hydroxyoctyl group, hydroxynonyl group, hydroxydecyl group, chloromethyl group, dichloromethyl group, trichloromethyl group, bromomethyl group, 1,1,1,3,3,3 -Hexafluoroisopropyl group, heptafluoropropyl group, pentadecafluoroheptyl group, nonadecafluorononyl group, hydroxyundecyl group, hydroxydodecyl group, hydroxypentadecyl group, hydroxyheptadecyl group, and hydroxyoctadecyl group.

Examples of the alkoxy group include a methoxy group, an ethoxy group, a propyloxy group, a hexyloxy group, a methoxyethoxy group, a methoxyethoxyethoxy group, a methoxyethoxyethoxymethyl group and the like.

The polyalkyleneoxyalkyl group is ^{a monovalent substituent represented by R 10} (OR ¹¹ ) n1 (O) m1-. R ¹⁰ represents an alkyl group, R ¹¹ represents an alkylene group, n1 represents an integer of 2 or more, and m1 represents 0 or 1.
The ^{alkyl group represented by R 10} is as described for the alkyl group represented by X ¹ or X ² . For details of the alkylene group represented by R ^{11 , the above description regarding the alkyl group represented by X 1} or X ² should be read as an alkylene group obtained by removing one hydrogen atom from these alkylene groups (for example, methyl). The group can be applied (replaced with a methylene group). n1 is an integer of 2 or more, for example, an integer of 10 or less, preferably 5 or less.

The aryl group may have a substituent or a fused ring, and more preferably an aryl group having 6 to 24 carbon atoms, for example, a phenyl group, a 4-methylphenyl group, a 4-phenylbenzoic acid, 3 -Cyanophenyl group, 2-chlorophenyl group, 2-naphthyl group and the like can be mentioned.

The polyester chain represented by the formula 2-A and the polyester chain represented by the formula 2-B described above can have a polyester-derived structure obtained by a known polyester synthesis method. Examples of the polyester synthesis method include ring-opening polymerization of the lactone described in paragraphs 0056 to 0057 of JP-A-2015-28830. However, the polyester chain is not limited to the polyester-derived structure obtained by ring-opening polymerization of the lactone, and is not limited to a known polyester synthesis method, for example, polycondensation of a polyvalent carboxylic acid and a polyhydric alcohol, hydroxy. It can also be a polyester-derived structure obtained by polycondensation of a carboxylic acid or the like.

Number average molecular weight of polyester chains The number average molecular weight of polyester chains is preferably 200 or more, more preferably 400 or more, and more preferably 500 or more, from the viewpoint of improving the dispersibility of the ferromagnetic hexagonal ferrite powder. Is even more preferable. From the same viewpoint, the number average molecular weight of the polyester chain is preferably 100,000 or less, and more preferably 50,000 or less. As described above, it is considered that the polyester chain can exert a steric hindrance in the composition for forming a magnetic layer and / or a magnetic liquid and suppress the aggregation of hexagonal ferrite particles. It is presumed that the polyester chain having the above number average molecular weight can satisfactorily exert such an effect. The number average molecular weight of the polyester chain refers to a value obtained by converting a value measured by GPC for a polyester obtained by hydrolyzing a polyalkyleneimine derivative into standard polystyrene. The value thus obtained is the same as the value obtained by converting the value measured by GPC for the polyester used for synthesizing the polyalkyleneimine derivative into standard polystyrene. Therefore, the number average molecular weight obtained for the polyester used for synthesizing the polyalkyleneimine derivative can be adopted as the number average molecular weight of the polyester chain contained in the polyalkyleneimine derivative. For the measurement conditions of the number average molecular weight of the polyester chain, the measurement conditions of the number average molecular weight of the polyester in the specific examples described later can be referred to.

<< Polyalkyleneimine chain >>
Number average molecular weight The number average molecular weight of the polyalkyleneimine chain contained in the above polyalkyleneimine derivative is the value measured by GPC for the polyalkyleneimine obtained by hydrolyzing the polyalkyleneimine derivative, converted into standard polystyrene. The value obtained by The value thus obtained is the same as the value obtained by converting the value measured by GPC for the polyalkyleneimine used for synthesizing the polyalkyleneimine derivative into standard polystyrene. Therefore, the number average molecular weight of the polyalkyleneimine used for synthesizing the polyalkyleneimine derivative can be adopted as the number average molecular weight of the polyalkyleneimine chain contained in the polyalkyleneimine derivative. For the measurement conditions of the number average molecular weight of the polyalkyleneimine chain, a specific example described later can be referred to. The polyalkyleneimine is a polymer that can be obtained by ring-opening polymerization of the alkyleneimine. In the polyalkyleneimine derivative, the polymer includes a homopolymer containing repeating units having the same structure and a copolymer containing repeating units having two or more different structures. It shall be used.
Further, the hydrolysis of the polyalkyleneimine derivative can be carried out by various methods usually used as a method for hydrolyzing an ester. For details of such a method, for example, "Experimental Chemistry Lecture 14 Synthesis of Organic Compounds II-Alcohol Amin (5th Edition)" (edited by the Chemical Society of Japan, Maruzen Publishing, published in August 2005), pp. 95-98. "Experimental Chemistry Lecture 16 Synthesis of Organic Compounds IV-Carboxylic Acids / Amino Acids / Peptides (5th Edition)" (edited by the Chemical Society of Japan, Maruzen Publishing Co., Ltd., published in March 2005), pp. 10-15. The description regarding the hydrolysis method can be referred to.
Polyalkyleneimine can be separated from the obtained hydrolyzate by a known separation means such as liquid chromatography, and the number average molecular weight can be determined.

The number average molecular weight of the polyalkyleneimine chain contained in the polyalkyleneimine derivative is in the range of 300 to 3,000. The present inventors speculate that the polyalkyleneimine derivative can be effectively adsorbed on the surface of hexagonal ferrite particles when the number average molecular weight of the polyalkyleneimine chain is in the above range. From the viewpoint of adsorptivity to the surface of hexagonal ferrite particles, the number average molecular weight of the polyalkyleneimine chain is preferably 500 or more. From the same viewpoint, it is preferably 2,000 or less.

Percentage of Polyalkyleneimine Chain in Polyalkyleneimine Derivative As described above, the present inventors have stated that the polyalkyleneimine chain contained in the polyalkyleneimine derivative can function as an adsorption part on the surface of hexagonal ferrite particles. thinking. The proportion of the polyalkyleneimine chain in the polyalkyleneimine derivative (hereinafter, also referred to as “polyalkyleneimine chain ratio”) is preferably 5.0% by mass from the viewpoint of enhancing the dispersibility of the ferromagnetic hexagonal ferrite powder. Is less than. From the viewpoint of improving the dispersibility of the ferromagnetic hexagonal ferrite powder, the polyalkyleneimine chain ratio is more preferably 4.9% by mass or less, further preferably 4.8% by mass or less, and 4.5% by mass. % Or less, more preferably 4.0% by mass or less, and even more preferably 3.0% by mass or less. Further, from the viewpoint of improving the dispersibility of the ferromagnetic hexagonal ferrite powder, the polyalkyleneimine chain ratio is preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and 0. It is more preferably 5% by mass or more.
The proportion of the polyalkyleneimine chain described above can be controlled by, for example, the mixing ratio of the polyalkyleneimine used in the synthesis and the polyester.

The proportion of the polyalkyleneimine chain in the polyalkyleneimine derivative ^{can be obtained by nuclear magnetic resonance (NMR), more specifically, 1} H-NMR and ¹³ C-NMR, and elemental analysis of a known method. It can be calculated from the analysis result. Since the value calculated in this way is the same as the theoretical value obtained from the compounding ratio of the synthetic raw material of the polyalkyleneimine derivative, the theoretical value obtained from the compounding ratio is used as the ratio of the polyalkyleneimine chain in the polyalkyleneimine derivative. Can be adopted.

Structure of Polyalkyleneimine Chain A polyalkyleneimine chain is a polymerization structure containing two or more of the same or different alkyleneimine chains. Examples of the alkyleneimine chain contained include an alkyleneimine chain represented by the following formula A and an alkyleneimine chain represented by the formula B. Among the alkyleneimine chains represented by the following formulas, the alkyleneimine chain represented by the formula A may include a bonding position with the polyester chain. Further, the alkyleneimine chain represented by the formula B can be bonded to the polyester chain by the salt cross-linking group as described above. The polyalkyleneimine derivative can have a structure in which one or more polyester chains are bonded to the polyalkyleneimine chain by containing one or more such alkyleneimine chains. Further, the polyalkyleneimine chain may have only a linear structure or may have a branched tertiary amine structure. From the viewpoint of further improving dispersibility, a polyalkyleneimine chain containing a branched structure is preferable. Examples of those containing a branched structure include those that bind to an adjacent alkyleneimine chain in ^{* 1} in the following formula A and those that bind to an adjacent alkyleneimine chain in ^{* 2 in the following formula B.}

In formula A, R ¹ and R ² independently represent a hydrogen atom or an alkyl group, a1 represents an integer of 2 or more, and * ¹ is a polyester chain, an adjacent alkyleneimine chain, or a hydrogen atom or a substituent. Represents the connection position of.

In formula B, R ³ and R ⁴ independently represent a hydrogen atom or an alkyl group, and a2 represents an integer of 2 or more. The alkyleneimine chain represented by the formula B is bonded to the polyester chain having an anionic group by forming a salt-crosslinked group with ^{N + in the formula B and the anionic group contained in the polyester chain.}

* In formulas A and B, and * ^{2 in} formula B, respectively, represent positions that independently bond with adjacent alkyleneimine chains or hydrogen atoms or substituents.

Hereinafter, the above formulas A and B will be described in more detail.

^{R 1} and R ² in formula A and R ^{3 and R 4 in} formula B each independently represent a hydrogen atom or an alkyl group. Examples of the alkyl group include an alkyl group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group, and further preferably a methyl group. Is. The combination of R ¹ and R ^{2 in} the formula A is an embodiment in which one is a hydrogen atom and the other is an alkyl group, both are hydrogen atoms, and both are alkyl groups (same or different alkyl groups). There is an embodiment, preferably both of which are hydrogen atoms. The above points are the same for R ³ and R ^{4 in the formula B.}

The structure having the smallest number of carbon atoms constituting the ring as alkyleneimine is ethyleneimine, and the main chain of the alkyleneimine chain (ethyleneimine chain) obtained by ring-opening of ethyleneimine has 2 carbon atoms. Therefore, the lower limit of a1 in the formula A and a2 in the formula B is 2. That is, a1 in the formula A and a2 in the formula B are independently integers of 2 or more. From the viewpoint of the adsorptivity of the ferromagnetic powder to the particle surface, a1 in the formula A and a2 in the formula B are independently preferably 10 or less, more preferably 6 or less, respectively. The following is more preferable, 2 or 3 is more preferable, and 2 is even more preferable.

The details of the bond between the alkyleneimine chain represented by the formula A or the alkyleneimine chain represented by the formula B and the polyester chain are as described above.

Each of the above alkyleneimine chains is bonded to an adjacent alkyleneimine chain or a hydrogen atom or a substituent at a position represented by * in each formula. Examples of the substituent include, but are not limited to, a monovalent substituent such as an alkyl group (for example, an alkyl group having 1 to 6 carbon atoms). Further, a polyester chain may be bonded as a substituent.

Weight Average Molecular Weight of Polyalkyleneimine Derivatives As described above, the molecular weight of the polyalkyleneimine derivative is preferably 1,000 or more and 80,000 or less as the weight average molecular weight. The weight average molecular weight of the polyalkyleneimine derivative is more preferably 1,500 or more, further preferably 2,000 or more, and further preferably 3,000 or more. The weight average molecular weight of the polyalkyleneimine derivative is more preferably 60,000 or less, further preferably 40,000 or less, further preferably 35,000 or less, and 34,000 or less. It is even more preferable to have. For the measurement conditions of the weight average molecular weight of the polyalkyleneimine derivative, a specific example described later can be referred to.

Synthesis method The synthesis method is not particularly limited as long as the polyalkyleneimine derivative contains a polyalkyleneimine chain having a number average molecular weight in the range of 300 to 3,000 in the above ratio together with the polyester chain. .. For a preferred embodiment of the synthesis method, paragraphs 0061 to 0069 of JP-A-2015-28830 can be referred to.

Specific examples of the polyalkyleneimine derivative include various polyalkyleneimine derivatives shown in Table 2 synthesized using polyethyleneimine and polyester shown in Table 2. For details of the synthetic reaction, the description of Examples described later and / or Examples of JP-A-2015-28830 can be referred to.

(* Note) The polyethyleneimines shown in Table 2 are as shown below.
SP-003 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) Number average molecular weight 300)
SP-006 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) Number average molecular weight 600)
SP-012 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) Number average molecular weight 1,200)
SP-018 (Polyethyleneimine (manufactured by Nippon Shokubai Co., Ltd.) Number average molecular weight 1,800)

The polyester shown in Table 2 above is a polyester synthesized by ring-opening polymerization of the lactone using the lactone and the nucleophile (carboxylic acid) shown in Table 3. For details of the synthetic reaction, the description of Examples described later and / or Examples of JP-A-2015-28830 can be referred to.

The above acid value and amine value are determined by the potentiometric method (solvent: tetrahydrofuran / water = 100/10 (volume ratio), titration solution: 0.01 N (0.01 mol / l) aqueous sodium hydroxide solution (acid value), 0. It is determined by 01N (0.01 mol / l) hydrochloric acid (amine value)).

The above average molecular weights (number average molecular weight and weight average molecular weight) are obtained by converting the values measured by GPC into standard polystyrene.
Specific examples of measurement conditions for the average molecular weight of polyester, polyalkyleneimine, and polyalkyleneimine derivatives are as follows.

(Measurement conditions for average molecular weight of polyester)
Measuring instrument: HLC-8220GPC (manufactured by Tosoh Corporation)
Column: TSKgel Super HZ 2000 / TSKgel Super HZ 4000 / TSKgel Super HZ-H (manufactured by Tosoh)
Eluent: tetrahydrofuran (THF),
Flow velocity: 0.35 mL / min,
Column temperature: 40 ° C
Detector: Differential Refractometer (RI) Detector

(Measurement conditions for average molecular weight of polyalkyleneimine and average molecular weight of polyalkyleneimine derivative)
Measuring instrument: HLC-8320GPC (manufactured by Tosoh Corporation)
Column: TSKgel Super AWM-H (manufactured by Tosoh Corporation) 3 Eluent: N-methyl-2-pyrrolidone (10 mmol / l lithium bromide added as an additive)
Flow velocity: 0.35 mL / min
Column temperature: 40 ° C
Detector: Differential Refractometer (RI) Detector

A composition for forming a magnetic layer can be prepared by mixing the dispersant described above with a ferromagnetic hexagonal ferrite powder, a binder, an abrasive and a solvent. Further, the magnetic layer of the magnetic tape may contain the dispersant together with the ferromagnetic hexagonal ferrite powder, the binder and the abrasive. The above dispersant may be used alone or in combination of two or more having different structures. When two or more kinds are used in combination, the content means the total content of the compounds used in combination. The above points are the same for the contents of various components described in the present specification.
The content of the dispersant is preferably 0.5 to 25.0 parts by mass per 100.0 parts by mass of the ferromagnetic hexagonal ferrite powder. The content of the dispersant is preferably 0.5 parts by mass or more per 100.0 parts by mass of the ferromagnetic hexagonal ferrite powder from the viewpoint of improving the dispersibility of the ferromagnetic hexagonal ferrite powder and the durability of the magnetic layer. , 1.0 part by mass or more, more preferably 5.0 parts by mass or more, and even more preferably 10.0 parts by mass or more. On the other hand, in order to improve the recording density, it is preferable to increase the filling rate of the ferromagnetic hexagonal ferrite powder in the magnetic layer. From this point, it is preferable that the content of components other than the ferromagnetic hexagonal ferrite powder is relatively low. From the above viewpoint, the content of the dispersant is preferably 25.0 parts by mass or less with respect to 100.0 parts by mass of the ferromagnetic hexagonal ferrite powder, and more preferably 20.0 parts by mass or less. It is more preferably 18.0 parts by mass or less, and even more preferably 15.0 parts by mass or less.

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

<Magnetic layer>
(Ferromagnetic powder)
The magnetic layer contains a ferromagnetic hexagonal ferrite powder as the ferromagnetic powder. The activated volume can be used as an index of the particle size of the ferromagnetic hexagonal ferrite powder. The "activated volume" is a unit of magnetization reversal. The activated volume described in the present invention and the present specification is measured using a vibrating sample magnetometer at magnetic field sweep speeds of 3 minutes and 30 minutes in the coercive force Hc measuring unit, and the following Hc and activated volume V are used. It is a value obtained from the relational expression of.
Hc = 2Ku / Ms {1-[(kT / KuV) ln (At / 0.693)] ^1/2 }
[In the above formula, Ku: anisotropic constant, Ms: saturation magnetization, k: Boltzmann constant, T: absolute temperature, V: activation volume, A: spin aging frequency, t: magnetic field inversion time]
With the enormous increase in the amount of information in recent years, magnetic tapes are desired to have an increased recording density (high-density recording). Examples of the method for achieving high-density recording include a method of reducing the particle size of the ferromagnetic powder contained in the magnetic layer and increasing the filling rate of the ferromagnetic powder in the magnetic layer. In this respect, the activation volume of the ferromagnetic hexagonal ferrite powder is preferably at 2500 nm ³ or less, more preferably 2300 nm ³ or less, and further preferably 2000 nm ³ or less. On the other hand, from the viewpoint of the stability of magnetization, the activated volume is ^{preferably, for example, 800 nm 3} or more, more preferably 1000 nm ³ or more, and ^{further preferably 1200 nm 3} or more. Among all hexagonal ferrite particles observed in the STEM image, the proportion of hexagonal ferrite particles having the above-mentioned aspect ratio and length in the major axis direction is the ratio of all hexagonal ferrite particles observed in the STEM image. The ratio based on the number of particles can be, for example, 50% or more. Further, the above ratio can be, for example, 95% or less, and can be more than 95%. For details of other ferromagnetic hexagonal ferrite powders, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, and paragraphs of JP2012-204726A. You can refer to 0013 to 0030.

The content (filling rate) of the ferromagnetic hexagonal ferrite powder in the magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass. The components of the magnetic layer other than the ferromagnetic hexagonal ferrite powder are at least a binder and an abrasive, and may optionally include one or more other additives. A high filling rate of the ferromagnetic hexagonal ferrite powder in the magnetic layer is preferable from the viewpoint of improving the recording density.

(Binder)
The magnetic tape contains a binder in a magnetic layer together with a ferromagnetic hexagonal ferrite powder. A binder is one or more resins. Examples of the binder include polyurethane resin, polyester resin, polyamide resin, vinyl chloride resin, styrene, acrylonitrile, acrylic resin obtained by copolymerizing methyl methacrylate and the like, cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal and polyvinyl butyral. It can be used alone or in combination of a plurality of resins from the polyvinyl archillal resin and the like. Of these, polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins are preferred. These resins may be homopolymers or copolymers. These resins can also be used as a binder in the non-magnetic layer and / or the backcoat layer described later. For the above binder, paragraphs 0028 to 0031 of JP-A-2010-24113 can be referred to. Further, the binder may be a radiation curable resin such as an electron beam curable resin. For the radiation-curable resin, paragraphs 0044 to 0045 of JP2011-48878A can be referred to.
Further, a curing agent can be used together with the resin that can be used as the binder. The curing agent is a compound having at least one, preferably two or more crosslinkable functional groups in one molecule. 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 process of forming the magnetic layer. As the curing agent, polyisocyanate is suitable. For details of the polyisocyanate, refer to paragraphs 0124 to 0125 of JP2011-216149A. The curing agent is preferably used in an amount of 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder, and preferably 50.0 to 80.0 parts by mass from the viewpoint of improving the strength of each layer such as a magnetic layer. can do.

(Abrasive)
The magnetic tape contains an abrasive in a magnetic layer. The abrasive means a non-magnetic powder having a Mohs hardness of more than 8, and is preferably a non-magnetic powder having a Mohs hardness of 9 or more. The polishing agent may be an inorganic substance powder (inorganic powder) or an organic substance powder (organic powder), and is preferably an inorganic powder. The abrasive is more preferably an inorganic powder having a Mohs hardness of more than 8, and further preferably an inorganic powder having a Mohs hardness of 9 or more. The maximum value of Mohs hardness is 10 for diamond. Specifically, examples of the abrasive include powders of alumina (Al ₂ O ₃ ), silicon carbide, boron carbide (B ₄ C), TiC, cerium oxide, zirconium oxide (ZrO ₂ ), diamond and the like. Of these, alumina powder is preferable. Regarding the alumina powder, paragraph 0021 of JP2013-229090A can also be referred to. Further, the specific surface area can be used as an index of the particle size of the abrasive. The larger the specific surface area, the smaller the particle size. From the viewpoint of reducing the surface area of the magnetic layer, an abrasive having a ^{specific surface area of 14 m 2} / g or more measured by the BET (Brunauer-Emmett-Teller) method (hereinafter referred to as "BET specific surface area") is used. It is preferable to use it. 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.

(Additive)
The magnetic layer contains a ferromagnetic hexagonal ferrite powder, a binder and an abrasive, and may further contain one or more additives, if desired. Examples of the additive include the above-mentioned dispersant and curing agent. Examples of additives that can be contained in the magnetic layer include non-magnetic fillers, lubricants, dispersants, dispersion aids, fungicides, antistatic agents, antioxidants, carbon black and the like. Non-magnetic filler is synonymous with non-magnetic powder. Examples of the non-magnetic filler include non-magnetic fillers (hereinafter, referred to as “protrusion forming agents”) that can function as protrusion forming agents that form protrusions that appropriately protrude on the surface of the magnetic layer. The protrusion forming agent is a component that can contribute to controlling the frictional characteristics of the surface of the magnetic layer. As the protrusion forming agent, various non-magnetic powders generally used as the protrusion forming agent can be used. These may be inorganic substances or organic substances. In one aspect, from the viewpoint of uniform friction characteristics, the particle size distribution of the protrusion forming agent is preferably a monodisperse showing a single peak rather than a polydisperse having a plurality of peaks in the distribution. From the viewpoint of availability of the monodisperse particles, the protrusion forming agent is preferably a powder of an inorganic substance (inorganic powder). Examples of the inorganic powder include powders of metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides and the like, and powders of inorganic oxides are preferable. The protrusion forming agent is more preferably colloidal particles, and even more preferably inorganic oxide colloidal particles. Further, from the viewpoint of availability of monodisperse particles, it is preferable that the inorganic oxide constituting the inorganic oxide colloidal particles is silicon dioxide (silica). The inorganic oxide colloidal particles are more preferably colloidal silica (silica colloidal particles). In the present invention and the present specification, "colloidal particles" are defined as at least one organic solvent per 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 is added, it means particles that can disperse without settling and give a colloidal dispersion. In another aspect, the protrusion forming agent is also preferably carbon black. The average particle size of the protrusion forming agent is, for example, 30 to 300 nm, preferably 40 to 200 nm. Further, from the viewpoint that the protrusion forming agent can exert its function better, the content of the protrusion forming agent in the magnetic layer is preferably 1.0 with respect to 100.0 parts by mass of the ferromagnetic powder. It is ~ 4.0 parts by mass, more preferably 1.5 to 3.5 parts by mass.

As an example of an additive that can be used for a magnetic layer containing an abrasive, the dispersant described in paragraphs 0012 to 0022 of JP2013-131285 can be used to improve the dispersibility of the abrasive in the composition for forming a magnetic layer. It can be mentioned as a dispersant for making it. Improving the dispersibility of the abrasive in the composition for forming a magnetic layer is preferable in order to reduce the surface Ra of the magnetic layer.

As the additive, a commercially available product or a product manufactured by a known method can be appropriately selected and used depending on the desired properties.

<Non-magnetic layer>
Next, the non-magnetic layer will be described. The magnetic tape may have a magnetic layer directly on the non-magnetic support, and has a non-magnetic layer containing a non-magnetic powder and a binder between the non-magnetic support and the magnetic layer. May be good. The non-magnetic powder used for the non-magnetic layer may be an inorganic substance or an organic substance. In addition, 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, metal sulfides and the like. These non-magnetic powders are commercially available and can also be produced by known methods. For details thereof, refer to paragraphs 0146 to 0150 of JP2011-216149A. For carbon black that can be used for the non-magnetic layer, paragraphs 0040 to 0041 of JP2010-24113A can also be referred to. The content (filling rate) of the non-magnetic powder in the non-magnetic layer is preferably in the range of 50 to 90% by mass, and more preferably in the range of 60 to 90% by mass.

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

The non-magnetic layers in the present invention and the present specification include not only non-magnetic powders but also substantially non-magnetic layers containing a small amount of ferromagnetic 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. It refers to a layer having a coercive force of 7.96 kA / m (100 Oe) or less. The non-magnetic layer preferably has no residual magnetic flux density and coercive force.

<Back coat layer>
The magnetic tape may also have a backcoat layer containing a non-magnetic powder and a binder on the side opposite to the side of the non-magnetic support having the magnetic layer. The backcoat layer preferably contains one or both of carbon black and inorganic powder. Known techniques for formulating magnetic and / or non-magnetic layers can be applied to the binders and optionally the various additives contained in the backcoat layer.

<Non-magnetic support>
Next, a non-magnetic support (hereinafter, also simply referred to as a “support”) will be described. Examples of the non-magnetic 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 to corona discharge, plasma treatment, easy adhesion treatment, heat treatment and the like in advance.

<Total thickness of magnetic tape>
The total thickness of the magnetic tape is 5.30 μm or less. A thin total thickness (thinning) is preferable in order to increase the recording capacity per winding of the magnetic tape cartridge. The total thickness of the magnetic tape may be, for example, 5.20 μm or less, 5.10 μm or less, or 5.00 μm or less. Further, the total thickness of the magnetic tape is preferably 1.00 μm or more, more preferably 2.00 μm or more, for example, from the viewpoint of ease of handling (handleability) of the magnetic tape. It is more preferably 3.00 μm or more.

<Thickness of non-magnetic support and each layer>
The thickness of the non-magnetic support is preferably 3.00 to 4.50 μm. The thickness of the magnetic layer is preferably 0.15 μm or less, and more preferably 0.10 μm or less, from the viewpoint of high-density recording that has been demanded in recent years. The thickness of the magnetic layer is more preferably in the range of 0.01 to 0.10 μm. The magnetic layer may be at least one layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multi-layer magnetic layer can be applied. The thickness of the magnetic layer when separated into two or more layers is the total thickness of these layers.

The thickness of the non-magnetic layer is, for example, 0.0 to 1.50 μm, preferably 0.10 to 1.00 μm.

The thickness of the backcoat layer is preferably 0.90 μm or less, more preferably 0.10 to 0.70 μm.

The thickness of each layer of the magnetic tape and the non-magnetic support can be determined by a known film thickness measuring method. As an example, for example, a cross section in the thickness direction of a magnetic tape is exposed by a known method such as an ion beam or a microtome, and then the cross section is observed using a scanning electron microscope in the exposed cross section. Various thicknesses can be obtained as the arithmetic mean of the thicknesses obtained at one place in the thickness direction in the cross-sectional observation, or at two or more randomly selected places, for example, two places. Alternatively, the thickness of each layer may be obtained as a design thickness calculated from the manufacturing conditions.

<Manufacturing method>
<< Manufacturing of magnetic tape on which servo patterns are formed >>
The composition for forming the magnetic layer, the non-magnetic 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 the composition for forming each layer usually includes at least a kneading step, a dispersion step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. All raw materials used in the present invention may be added at the beginning or in the middle of any step. Further, each raw material may be added separately in two or more steps. In the preparation of the composition for forming a magnetic layer, as described above, it is preferable to separately disperse the abrasive and the ferromagnetic hexagonal ferrite powder. A known manufacturing technique can be used to manufacture the magnetic tape. In the kneading step, it is preferable to use a kneader having a strong kneading force such as an open kneader, a continuous kneader, a pressurized kneader, and an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, in order to disperse each layer-forming composition, one or more of glass beads and other dispersed beads can be used as the dispersion medium. As such dispersed beads, zirconia beads, titania beads, and steel beads, which are dispersed beads having a high specific gravity, are suitable. The particle size (bead diameter) and filling rate of these dispersed beads can be optimized and used. A known disperser can be used. Further, as one of the means for obtaining a magnetic tape having a cos θ of 0.85 or more and 1.00 or less, the dispersion conditions are strengthened (for example, the dispersion time is lengthened, the diameter of the dispersion beads used for dispersion is reduced, and / Alternatively, high filling, use of a dispersant, etc.) are also preferable. The preferred embodiment regarding the strengthening of the dispersion conditions is as described above. For details of other methods for producing a magnetic tape, for example, paragraphs 0051 to 0057 of JP-A-2010-24113 can be referred to. For the orientation treatment, paragraph 0052 of JP-A-2010-24113 can be referred to. It is preferable to perform a vertical alignment treatment as one of the means for obtaining a magnetic tape having a cos θ of 0.85 or more and 1.00 or less.

<< Formation of servo pattern >>
The magnetic tape has a timing-based servo pattern on the magnetic layer. FIG. 1 shows an arrangement example of a region (servo band) in which a timing-based servo pattern is formed and a region (data band) sandwiched between two servo bands. An arrangement example of the timing-based servo pattern is shown in FIG. However, the arrangement example shown in each drawing is an example, and the servo pattern, the servo band, and the data band may be arranged in an arrangement according to the method of the magnetic tape device (drive). Regarding the shape and arrangement of the timing-based servo pattern, for example, FIG. 4, FIG. 5, FIG. 6. FIG. 9, FIG. 17, FIG. Known techniques such as the arrangement examples exemplified in 20 and the like can be applied without any limitation.

The servo pattern can be formed by magnetizing a specific region of the magnetic layer with a servo light head mounted on a servo lighter. The region magnetized by the servo light head (the position where the servo pattern is formed) is defined by the standard. As the servo writer, a commercially available servo writer or a servo writer having a known configuration can be used. As for the configuration of the servo lighter, known techniques such as those described in Japanese Patent Application Laid-Open No. 2011-175678, US Pat. No. 5,689,384, US Pat. No. 6,542,325 and the like can be adopted without any limitation.

The magnetic tape according to one aspect of the present invention described above is a magnetic tape having a total thickness of 5.30 μm or less, having a high surface smoothness with a magnetic layer surface Ra of 1.8 nm or less, and having a magnetic layer surface Ra of 1.8 nm or less. In a timing-based servo system, it is possible to suppress the occurrence of signal defects during servo signal reproduction.

[Magnetic tape device]
One aspect of the present invention relates to a magnetic tape device including the magnetic tape, a magnetic head, and a servo head.

The details of the magnetic tape mounted on the magnetic tape device are as described above. Such magnetic tapes have a timing-based servo pattern. Therefore, when the magnetic head records a magnetic signal on the data band to form a data track and / or reproduces the recorded signal, the timing is based on the servo pattern read while reading the servo pattern by the servo head. By performing the head tracking of the base servo method, the magnetic head can be made to follow the data track with high accuracy.

As the magnetic head mounted on the magnetic tape device, a known magnetic head capable of recording and / or reproducing a magnetic signal on the magnetic tape can be used. The recording head and the playback head may be one magnetic head or separate magnetic heads. As the servo head, a known servo head capable of reading the timing-based servo pattern of the magnetic tape can be used. For example, a known MR head equipped with an MR element can be used as the servo head. At least one servo head is included in the magnetic tape device, and two or more servo heads may be included.

For more information on head tracking in timing-based servo systems, known techniques such as those described in US Pat. No. 5,689,384, US Pat. No. 6,542,325, and US Pat. No. 7,876,521 may be applied without limitation. it can.

A commercially available magnetic tape device is usually provided with a magnetic head and a servo head according to the standard. Further, a commercially available magnetic tape device is usually provided with a servo control mechanism for enabling head tracking in a timing-based servo system according to a standard. The magnetic tape device according to one aspect of the present invention can be configured, for example, by incorporating the magnetic tape according to one aspect of the present invention into a commercially available magnetic tape device.

Hereinafter, the present invention will be described based on examples. However, the present invention is not limited to the embodiments shown in the examples. The indications of "part" and "%" described below indicate "parts by mass" and "% by mass" unless otherwise specified.

The average particle size in the present invention and the present specification is a value measured by the method described in paragraphs 0058 to 0061 of JP-A-2016-071926. The average particle size described below was measured using a transmission electron microscope H-9000 manufactured by Hitachi as a transmission electron microscope and an image analysis software KS-400 manufactured by Carl Zeiss as image analysis software.

[Examples 1 to 9, Comparative Examples 1 to 9]
1. 1. Preparation of alumina dispersion (polishing agent solution) 3.0 with respect to 100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd .; Morse hardness 9) having an pregelatinization rate of about 65% and a BET specific surface area of 20 m ^{2 / g.} A 32% solution (solvent) of 2,3-dihydroxynaphthalene (manufactured by Tokyo Kasei Co., Ltd.) and a polyester polyurethane resin (UR-4800 manufactured by Toyo Boseki Co., Ltd. (polar group amount: 80 meq / kg)) having an _{SO 3 Na group as a polar group.} 31.3 parts of a mixed solvent of methyl ethyl ketone and toluene) 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 for 5 hours with a paint shaker in the presence of zirconia beads. It was. After the dispersion, the dispersion liquid and the beads were separated by a mesh to obtain an alumina dispersion (abrasive liquid).

2. Composition formulation for forming a magnetic layer (magnetic liquid)
Ferromagnetic hexagonal barium ferrite powder (activated volume: see Table 4) 100.0 parts SO ₃ Na group-containing polyurethane resin 14.0 parts (weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g )
Dispersant See Table 4 Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (abrasive solution)
Above 1. 6.0 parts of alumina dispersion prepared in (Silica sol (projection forming agent solution))
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 (registered trademark) manufactured by Nippon Polyurethane Industry Co., Ltd.) 2.5 parts (finishing additive solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

Details of the method for synthesizing the dispersant shown in Table 4 will be described later.

3. 3. Composition for forming a non-magnetic layer Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average major axis length): 0.15 μm
Average needle-like ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size: 20 nm
18.0 parts of SO ₃ Na group-containing polyurethane resin (weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g)
Stearic acid 1.0 part Cyclohexanone 300.0 part Methyl ethyl ketone 300.0 part

4. Composition for backcoat layer formation Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average needle-like ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size 20 nm
Vinyl chloride copolymer 13.0 parts Sulfonic acid base-containing polyurethane resin 6.0 parts Phosphonate 3.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Polyisocyanate 5.0 parts Cyclohexanone 355.0 parts

5. Preparation of each layer forming composition (1) Preparation of magnetic layer forming composition A magnetic layer forming composition was prepared by the following method.
A magnetic liquid was prepared by dispersing the above magnetic liquid components in a batch type vertical sand mill using beads as a dispersion medium. Specifically, as the bead dispersion of each stage (1st stage and 2nd stage, or 1st to 3rd stages), zirconia beads having the bead diameters shown in Table 4 are used and the dispersion residence time shown in Table 4 is used. Distributed processing was performed. In the bead dispersion, the obtained dispersion was filtered using a filter (average pore size 5 μm) after each step was completed. In the bead dispersion at each stage, the filling rate of the dispersed media was about 50 to 80% by volume.
The magnetic liquid thus obtained is mixed with the above-mentioned abrasive liquid, silica sol, other components and a finishing addition solvent, bead-dispersed for 5 minutes using the above-mentioned sand mill, and then further subjected to a batch type ultrasonic device (20 kHz, 300 W). Ultrasonic dispersion was performed for 0.5 minutes. Next, the obtained mixed solution was filtered using a filter (average pore size 0.5 μm) to prepare a composition for forming a magnetic layer.
The peripheral speed at the tip of the sand mill when the beads were dispersed was in the range of 7 to 15 m / sec.
(2) Preparation of composition for forming a non-magnetic layer A composition for forming a non-magnetic layer was prepared by the following method.
Each component excluding stearic acid, cyclohexane and methyl ethyl ketone was bead-dispersed (dispersion medium: zirconia beads (bead diameter: 0.1 mm), dispersion residence time: 24 hours) using a batch vertical sand mill to prepare a dispersion. Obtained. Then, the remaining components were added to the obtained dispersion, and the mixture was stirred with a dissolver. Next, the obtained dispersion was filtered using a filter (average pore size 0.5 μm) to prepare a composition for forming a non-magnetic layer.
(3) Preparation of backcoat layer forming composition A backcoat layer forming composition was prepared by the following method.
Each component except stearic acid, butyl stearate, polyisocyanate and cyclohexanone was kneaded and diluted with an open kneader. Then, with respect to the obtained mixed solution, zirconia beads having a bead diameter of 1 mm were used with a horizontal bead mill, the bead filling rate was 80% by volume, the rotor tip peripheral speed was 10 m / sec, and the residence time per pass was set to 2 minutes. A 12-pass distributed process was performed. Then, the remaining components were added to the obtained dispersion, and the mixture was stirred with a dissolver. Next, the obtained dispersion was filtered using a filter (average pore size 1 μm) to prepare a composition for forming a backcoat layer.

6. Fabrication of magnetic tape and formation of timing-based servo pattern 5. On the surface of the polyethylene naphthalate support having the thickness shown in Table 4, the thickness after drying is the thickness shown in Table 4. The composition for forming a non-magnetic layer prepared in (2) was applied and dried to form a non-magnetic layer. Next, the thickness of the non-magnetic layer after drying is set to the thickness shown in Table 4. The composition for forming a magnetic layer prepared in (1) was applied. In the examples and comparative examples described as "Yes" in the vertical alignment treatment in Table 4, a magnetic field having a magnetic field strength of 0.3 T was applied perpendicularly to the coated surface while the applied magnetic layer forming composition was in an undried state. A magnetic layer was formed by applying in the direction to perform vertical alignment treatment and then drying. For the comparative example described as “None” in the vertical alignment treatment in Table 4, the applied composition for forming a magnetic layer was dried without performing the vertical alignment treatment to form a magnetic layer.
After that, on the surface of the polyethylene naphthalate support opposite to the surface on which the non-magnetic layer and the magnetic layer were formed, the thickness after drying was set to the thickness shown in Table 4. The composition for forming a back coat layer prepared in (3) was applied and dried to obtain a laminate.
Then, for the obtained laminate, a calendar roll composed of only metal rolls was used to obtain a calendar processing speed of 100 m / min, a linear pressure of 294 kN / m (300 kg / cm), and a calendar roll shown in Table 4. A surface smoothing treatment (calendar treatment) was performed at the surface temperature. The stronger the calendar treatment conditions (for example, the higher the surface temperature of the calendar roll), the smaller the magnetic layer surface Ra tends to be.
Then, the heat treatment was performed for 36 hours in an environment having an ambient temperature of 70 ° C. The heat-treated laminate was cut to a width of 1/2 inch (0.0127 m) using a slitter to prepare a magnetic tape.
With the magnetic layer of the produced magnetic tape demagnetized, a servo pattern having an arrangement and shape according to the LTO Ultra format was formed on the magnetic layer by a servo light head mounted on a servo tester. As a result, a magnetic tape having a data band, a servo band, and a guide band in an arrangement according to the LTO Ultra format on the magnetic layer and a servo pattern having an arrangement and a shape according to the LTO Ultra format on the servo band was produced. ..
In this way, the magnetic tapes of Examples and Comparative Examples were obtained. The servo tester includes a servo light head and a servo head. This servo tester was also used in the evaluation described later.

The thickness and total thickness of each layer of the produced magnetic tape and the non-magnetic support were determined by the following method. It was confirmed that the thickness of each formed layer was the thickness shown in Table 4.
After exposing the cross section of the magnetic tape in the thickness direction with an ion beam, the cross section of the exposed cross section is observed with a scanning electron microscope. Various thicknesses were obtained as the arithmetic mean of the thicknesses obtained at two points in the thickness direction in the cross-sectional observation.

7. Preparation of Dispersants Dispersants 1 to 4 shown in Table 4 were prepared by the following methods. The temperature described below for the synthetic reaction is the temperature of the reaction solution.
In Comparative Example 9, 2,3-dihydroxynaphthalene was used instead of the dispersants 1 to 4. 2,3-Dihydroxynaphthalene is a compound used as an additive for adjusting the square ratio in Japanese Patent Application Laid-Open No. 2012-203955.

(1) Preparation of Dispersant 1 <Synthesis of Precursor 1>
197.2 g of ε-caprolactone and 15.0 g of 2-ethyl-1-hexanol were introduced into a 500 mL three-necked flask, and the mixture was stirred and dissolved while blowing nitrogen. 0.1 g of monobutyltin oxide was added and heated to 100 ° C. After 8 hours, after confirming that the raw material had disappeared by gas chromatography, the mixture was cooled to room temperature to obtain 200 g of solid precursor 1 (structure below).

<Synthesis of Dispersant 1>
40.0 g of the obtained precursor 1 was introduced into a 200 mL three-necked flask, and the mixture was stirred and dissolved at 80 ° C. while blowing nitrogen. 2.2 g of meso-butane-1,2,3,4-tetracarboxylic dianhydride was added and heated to 110 ° C. After 5 hours, ¹ H-NMR confirmed that the peak derived from precursor 1 had disappeared, and then the mixture was cooled to room temperature to obtain 38 g of solid reaction product 1 (mixture of the following structural isomers). .. The reaction product 1 thus obtained is a mixture of the compound 1 shown in Table 1 and its structural isomer. The reaction product 1 is referred to as "dispersant 1".

(2) Preparation of Dispersant 2 <Synthesis of Dispersant 2>
The synthesis was carried out in the same manner as the dispersant 1 except that 2.2 g of butanetetracarboxylic dianhydride was changed to 2.4 g of pyromellitic dianhydride, and the solid reaction product 2 (the following structural isomerism) was synthesized. A mixture of bodies) was obtained in an amount of 38 g. The reaction product 2 thus obtained is a mixture of the compound 2 shown in Table 1 and its structural isomer. The reaction product 2 is referred to as "dispersant 2".

(3) Preparation of Dispersant 3 <Synthesis of Polyester (i-1)>
In a 500 mL three-necked flask, 12.6 g of n-octanoic acid (manufactured by Wako Pure Chemical Industries, Ltd.) as a carboxylic acid, 100 g of ε-caprolactone (Plaxel M manufactured by Daicel Industrial Chemistry Co., Ltd.) as a lactone, and monobutyl tin oxide (manufactured by Wako Pure Chemical Industries, Ltd.) as a catalyst. ) (C ₄ H ₉ Sn (O) OH) 2.2 g was mixed and heated at 160 ° C. for 1 hour. 100 g of ε-caprolactone was added dropwise over 5 hours, and the mixture was further stirred for 2 hours. Then, it cooled to room temperature to obtain polyester (i-1).
The synthesis scheme is shown below.

<Synthesis of Dispersant 3 (Polyethyleneimine Derivative (J-1))>
5.0 g of polyethyleneimine (SP-018 manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 1800) and 100 g of the obtained polyester (i-1) were mixed and heated at 110 ° C. for 3 hours to obtain a polyethyleneimine derivative (J-1). ) Was obtained. The polyethyleneimine derivative (J-1) is referred to as "dispersant 3".
The synthesis scheme is shown below. In the following synthesis scheme, a, b and c each indicate the polymerization molar ratio of the repeating unit, which is 0 to 50, and a + b + c = 100. l, m, n1 and n2 each indicate the polymerization molar ratio of the repeating unit, l is 10 to 90, m is 0 to 80, n1 and n2 are 0 to 70, and l + m + n1 + n2 = 100.

(4) Preparation of Dispersant 4 <Synthesis of Polyester (i-2)>
Polyester (i-2) was obtained in the same manner as in the synthesis of polyester (i-1) except that the amount of carboxylic acid charged shown in Table 3 was changed.

<Synthesis of Dispersant 4 (Polyethyleneimine Derivative (J-2))>
Synthesis was carried out in the same manner as in compound J-1 except that the polyethyleneimine shown in Table 2 and the obtained polyester (i-2) were used to obtain a polyethyleneimine derivative (J-2). The polyethyleneimine derivative (J-2) is referred to as "dispersant 4".

The weight average molecular weights of the dispersants 1 and 2 were measured by the method described above as a method for measuring the weight average molecular weight of the compound represented by the general formula 1. As a result of the measurement, the weight average molecular weight of the dispersant 1 was 9200, and the weight average molecular weight of the dispersant 2 was 6300.

The weight average molecular weights of the dispersant 3 (polyethyleneimine derivative (J-1)) and the dispersant 4 (polyethyleneimine derivative (J-2)) are measured by GPC under the measurement conditions of the specific examples described above. Was calculated by converting to standard polystyrene, and the values shown in Table 3 were obtained.

The other weight average molecular weight described above is a value obtained by converting a value measured by GPC under the following measurement conditions into standard polystyrene.
GPC device: HLC-8120 (manufactured by Tosoh)
Column: TSK gel Multipore HXL-M (manufactured by Tosoh, 7.8 mm (inner diameter) x 30.0 cm)
Eluent: tetrahydrofuran (THF)

8. Measurement of activated volume As a sample for measuring the activated volume, a powder in the same powder lot as the ferromagnetic hexagonal barium ferrite powder used for preparing the composition for forming a magnetic layer was used. The measurement was performed using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) at magnetic field sweep speeds of 3 minutes and 30 minutes in the Hc measuring unit, and the activated volume was calculated from the relational expression described above. The measurement was performed in an environment of 23 ° C. ± 1 ° C. The calculated activation volume is shown in Table 4.

9. Measurement of cosθ A sample for cross-section observation was cut out from each magnetic tape of Examples and Comparative Examples, and cosθ was determined by the method described above using this sample. Table 4 shows the cos θ obtained for each magnetic tape of Examples and Comparative Examples. In each of the magnetic tapes of Examples and Comparative Examples, the total hexagonal ferrite particles observed in the STEM image have an aspect ratio and a length in the major axis direction in the above-mentioned range for which cosθ is to be measured. The proportion of hexagonal ferrite particles was about 80 to 95% based on the number of particles.

The cross-section observation sample used for the measurement of cosθ was prepared by the following method.

(I) Preparation of sample with protective film A sample with protective film (laminated film of carbon film and platinum film) was prepared by the following method.
A sample having a size of 10 mm in the width direction × 10 mm in the longitudinal direction of the magnetic tape was cut out from the target magnetic tape for which cosθ was to be obtained using a razor. The width direction described below for the sample means the direction that was the width direction of the magnetic tape before cutting. The same applies to the longitudinal direction.
A protective film was formed on the surface of the magnetic layer of the cut sample to obtain a sample with a protective film. The protective film was formed by the following method.
A carbon film (thickness 80 nm) was formed on the surface of the magnetic layer of the sample by vacuum deposition, and a platinum (Pt) film (thickness 30 nm) was formed on the surface of the formed carbon film by sputtering. Vacuum vapor deposition of the carbon film and sputtering of the platinum film were carried out under the following conditions, respectively.
<Vacuum deposition conditions for carbon film>
Deposition source: Carbon (mechanical pencil lead with a diameter of 0.5 mm)
Vacuum degree in the chamber of vacuum vapor deposition equipment: 2 x 10 ^-3 Pa or less Current value: 16A
<Sputtering conditions for platinum film>
Target: Pt
Vacuum degree in the chamber of the sputtering equipment: 7 Pa or less Current value: 15 mA

(Ii) Preparation of sample for cross-sectional observation A thin film sample was cut out from the sample with a protective film prepared in (i) above ^{by FIB processing using a gallium ion (Ga +) beam.} The cutting was performed by the following two FIB processes. The acceleration voltage in FIB processing was set to 30 kV.
In the first FIB processing, one end in the longitudinal direction of the sample with the protective film (that is, the portion including one side surface in the width direction of the sample with the protective film) including the region from the surface of the protective film to a depth of about 5 μm is covered. I cut it out. The cut-out sample includes a protective film to a part of the non-magnetic support.
Next, a microprobe was attached to the cut-out surface side of the cut-out sample (that is, the cross-sectional side of the sample exposed by cutting out), and the second FIB processing was performed. In the second FIB processing, a gallium ion beam was applied to a surface opposite to the cut surface side (that is, one side surface in the width direction) to cut out the sample. The cutout surface in the second FIB processing was attached to the end surface of the mesh for STEM observation to fix the sample. After fixation, the microprobe was removed.
Further, a gallium ion beam was applied to the surface from which the microprobe was removed from the sample fixed to the mesh at the same acceleration voltage as described above to perform FIB processing, and the sample fixed to the mesh was further thinned.
The cross-section observation sample fixed to the mesh thus produced was observed with a scanning transmission electron microscope, and cos θ was determined by the method described above. The cos θ thus obtained is shown in Table 4.

10. Magnetic layer surface Ra
Using an atomic force microscope (AFM, Nanoscope4 manufactured by Veeco), a measurement area of 40 μm × 40 μm was measured, and the center line average surface roughness Ra was determined on the surface of the magnetic layer of the magnetic tape. The scanning speed (probe moving speed) was 40 μm / sec, and the resolution was 512pixel × 512pixel. The measurement results are shown in Table 4.

11. Evaluation of Square Ratio (SQuarenes Ratio; SQ) The square ratio was measured for each magnetic tape produced at a magnetic field strength of 1194 kA / m (15 kOe) using a vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.). The measurement results are shown in Table 4.

12. Frequency of signal defects (thermal asperity) during servo signal reproduction A magnetic tape on which the above timing-based servo pattern was formed was attached to the servo tester. In this servo tester, the magnetic tape is run, and the surface of the magnetic layer of the running magnetic tape and the servo head on which the MR element is mounted are brought into contact with each other and slid, so that the servo head reads the servo pattern (servo). (Signal reproduction) was performed. In the playback waveform of the servo signal obtained by playback, the part that is not a normal burst signal and shows an output of 200% or more with the average value of the noise level output as 100% is judged as thermal asperity. , The number of occurrences of thermal asperity was counted. The value obtained by dividing the counted number of occurrences of thermal asperity by the total length of the magnetic tape (number of times / m) was defined as the frequency of occurrence of thermal asperity. The measurement results are shown in Table 4.

The above results are shown in Table 4.

By comparison between Comparative Examples 1 to 4 and Comparative Examples 5 to 9, the total thickness of the magnetic tape is more than 5.30 μm (Comparative Examples 1 and 2), and the magnetic layer surface Ra is more than 1.8 nm (Comparative Example). Compared with 3 and 4), when the total thickness of the magnetic tape is 5.30 μm or less and the surface Ra of the magnetic layer is 1.8 nm or less, the frequency of signal defects may increase remarkably during servo signal reproduction. confirmed.
On the other hand, the magnetic tapes of Examples 1 to 9 have a total thickness of 5.30 μm or less and a magnetic layer surface Ra of 1.8 nm or less, but have a servo signal as compared with the magnetic tapes of Comparative Examples 5 to 9. The frequency of signal defects during playback has been greatly reduced.
In addition, from the results shown in Table 4, there is a good correlation between cosθ and the frequency of signal defects during servo signal reproduction, that the larger the cosθ, the less frequently the signal defects occur during servo signal reproduction. It can be confirmed that there is. On the other hand, such a correlation was not found between the square ratio (SQ) and the frequency of signal defects during servo signal reproduction, as shown in Table 4.

The present invention is useful in the technical field of high-density recording magnetic tapes.

Claims (7)

A magnetic tape having a magnetic layer containing ferromagnetic powder on a non-magnetic support.
The thickness of the non-magnetic support is 3.00 μm or more and 4.50 μm or less.
The magnetic layer has a timing-based servo pattern.
The center line average surface roughness Ra measured on the surface of the magnetic layer is 1.8 nm or less, and is 1.
The ferromagnetic powder is a ferromagnetic hexagonal ferrite powder, and the inclination cosθ of the ferromagnetic hexagonal ferrite powder with respect to the surface of the magnetic layer determined by cross-sectional observation performed using a scanning transmission electron microscope is 0. A magnetic tape that is 85 or more and 1.00 or less. The magnetic tape according to claim 1, wherein the cos θ is 0.89 or more and 1.00 or less. The magnetic tape according to claim 1 or 2, wherein the magnetic layer further contains a polyester chain-containing compound having a weight average molecular weight of 1,000 or more and 80,000 or less. The activation volume of the ferromagnetic hexagonal ferrite powder is 800 nm ³ or more 2500 nm ³ or less, the magnetic tape according to any one of claims 1 to 3. The magnetic tape according to any one of claims 1 to 4, wherein the center line average surface roughness Ra measured on the surface of the magnetic layer is 1.2 nm or more and 1.8 nm or less. The magnetic tape according to any one of claims 1 to 5, further comprising a non-magnetic layer containing non-magnetic powder between the non-magnetic support and the magnetic layer. A magnetic tape device including the magnetic tape according to any one of claims 1 to 6, a magnetic head, and a servo head.

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