JP6316355B2 - Magnetic tape and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnetic tape and a manufacturing method thereof.

  There are two types of magnetic recording media, tape-shaped and disk-shaped. For storage applications such as data backup, tape-shaped magnetic recording media, ie magnetic tape, are mainly used.

  The magnetic tape is housed in a magnetic tape cartridge in a state of being wound around a reel. In order to increase the recording capacity per volume of the magnetic tape cartridge, the total length of the magnetic tape stored in one volume of the magnetic tape cartridge should be increased. For this purpose, the magnetic tape is made thinner (hereinafter referred to as “thinning”). To be described). As a means for reducing the thickness of the magnetic tape, it is possible to make one or more layers included in the magnetic tape thinner. In this regard, Patent Document 1 describes that the magnetic layer thickness is 0.1 μm or less (claim 1 of Patent Document 1).

JP 2011-48878 A

  As a means for thinning the magnetic tape, for a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on a nonmagnetic support, the total thickness of the magnetic layer and the nonmagnetic layer can be reduced. . For example, in Patent Document 1, a magnetic layer is provided on a nonmagnetic layer (paragraph 0073 of Patent Document 1) having a thickness of 1.0 μm in the embodiment. For this, it is desirable to make the nonmagnetic layer and / or the magnetic layer thinner, and to further reduce the total thickness of the magnetic layer and the nonmagnetic layer.

  However, when the present inventor examined reducing the total thickness of the magnetic layer and the nonmagnetic layer for the magnetic tape having the nonmagnetic layer and the magnetic layer in this order on the nonmagnetic support, in particular, the magnetic tape In a magnetic tape in which the total thickness of the layer and the nonmagnetic layer is reduced to 0.80 μm or less, the reproduction signal amplitude is partially reduced when a signal recorded on the tape is reproduced (hereinafter referred to as “partial output”). It has been found that the number of occurrences of "degradation" increases. Since the error rate increases and the reliability of the magnetic tape decreases as the number of occurrences of the partial output decrease increases, it is required to reduce the number of occurrences.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic tape having a total thickness of a magnetic layer and a nonmagnetic layer of 0.80 μm or less, in which the occurrence of partial output reduction during signal reproduction is suppressed. is there.

As a result of intensive studies to achieve the above object, the present inventor has obtained the following magnetic tape:
A magnetic tape having a nonmagnetic layer comprising a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer comprising a ferromagnetic powder and a binder on the nonmagnetic layer,
The total thickness of the magnetic layer and the nonmagnetic layer is 0.80 μm or less,
The logarithmic decay rate obtained by the pendulum viscoelasticity test on the surface of the magnetic layer of the magnetic tape is 0.050 or less, and the coefficient of friction measured on the base portion of the surface of the magnetic layer is 0.35 or less. tape,
I came to find. The magnetic tape can suppress the occurrence of a partial decrease in output even though the total thickness of the magnetic layer and the nonmagnetic layer is reduced to 0.80 μm or less. The inventors' inference regarding this point will be described later.

  In one aspect, the logarithmic decay rate is 0.010 or more and 0.050 or less.

  In one embodiment, the ferromagnetic powder is selected from the group consisting of ferromagnetic hexagonal ferrite powder and ferromagnetic metal powder. The ferromagnetic powder means a set of a plurality of ferromagnetic particles. Aggregation is not limited to an embodiment in which the particles constituting this are in direct contact with each other, and an embodiment in which a binder, an additive, or the like is interposed between the particles is also included. The term “particle” is sometimes used to represent powder. The same applies to the present invention and various powders in the present specification.

  In one aspect, the magnetic layer further comprises a nonmagnetic powder.

  In one aspect, the nonmagnetic powder contained in the magnetic layer is two or more kinds of nonmagnetic powders having different Mohs hardnesses.

  In one aspect, the nonmagnetic powder contained in the magnetic layer comprises an inorganic powder having a Mohs hardness of greater than 8.

  In one aspect, the nonmagnetic powder contained in the magnetic layer comprises nonmagnetic colloidal particles. In the present invention and the present specification, “colloid particles” means at least one organic solvent 100 mL of a mixed solvent containing at least methyl ethyl ketone, cyclohexanone, toluene or ethyl acetate, or two or more of the above solvents in an arbitrary mixing ratio. When 1 g per gram is added, it refers to particles that can be dispersed without settling to yield a colloidal dispersion.

A further aspect of the present invention is a method for producing the above magnetic tape,
Including a nonmagnetic layer forming step of forming a nonmagnetic layer and a magnetic layer forming step of forming a magnetic layer,
The magnetic layer formation process
A coating step of forming a coating layer by coating a magnetic layer forming composition containing a ferromagnetic powder, a binder, a curing agent and a solvent on the nonmagnetic layer;
A heat drying step of drying the coating layer by heat treatment, and
A curing process for curing the coating layer,
Including
A cooling step for cooling the coating layer is included between the coating step and the heat drying step, and a burnish processing step for burnishing the surface of the coating layer is included between the heating drying step and the curing step. Manufacturing method of magnetic tape,
About.

  In one aspect, the cooling step is performed by placing the coating layer in a cooling atmosphere of −10 ° C. to 0 ° C.

  In one aspect, the solvent contained in the composition for forming a magnetic layer includes a ketone solvent.

  In one aspect | mode, the said hardening | curing agent is a thermosetting compound, and a hardening process is performed by heat processing.

  In one aspect, the thermosetting compound is a polyisocyanate.

  In one aspect, a surface smoothing step is included between the burnishing step and the curing step.

  According to one aspect of the present invention, it is possible to provide a magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer is 0.80 μm or less, and the occurrence of partial output reduction during signal reproduction is suppressed. .

It is explanatory drawing of the measuring method of a logarithmic attenuation factor. It is explanatory drawing of the measuring method of a logarithmic attenuation factor. It is explanatory drawing of the measuring method of a logarithmic attenuation factor. An example (process schematic diagram) of the specific aspect of a magnetic tape manufacturing process is shown.

  One aspect of the present invention is a magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer. The total thickness of the magnetic layer and the nonmagnetic layer is 0.80 μm or less, and the logarithmic decay rate (hereinafter simply referred to as “logarithmic decay rate”) obtained by the pendulum viscoelasticity test on the magnetic layer side surface of the magnetic tape. ) Relates to a magnetic tape having a friction coefficient (hereinafter also referred to as “base friction”) of not more than 0.050 and a friction coefficient (hereinafter also referred to as “substrate friction”) measured in the base portion of the surface on the magnetic layer side.

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

In the present invention and this specification, the logarithmic decay rate is a value obtained by the following method.
1 to 3 are explanatory diagrams of a method for measuring the logarithmic attenuation rate. Hereinafter, a method for measuring the logarithmic decay rate will be described with reference to these drawings. However, the illustrated embodiment is merely an example, and does not limit the present invention.
A sample for measurement is cut out from the magnetic tape to be measured. The cut measurement sample 100 is placed on the substrate 103 with the measurement surface (surface on the magnetic layer side) facing upward in the sample stage 101 in the pendulum viscoelasticity testing machine, and there is a clear wrinkle that can be visually confirmed. Fix with fixing tape 105 or the like in the absence.
A cylindrical cylinder edge 104 with a pendulum having a mass of 13 g (diameter 4 mm) is placed on the measurement surface of the measurement sample 100 so that the major axis direction of the cylinder edge is parallel to the longitudinal direction of the measurement sample 100. FIG. 1 shows an example of a state in which the pendulum-equipped cylindrical cylinder edge 104 is placed on the measurement surface of the measurement sample 100 in this manner (a state viewed from above). In the embodiment shown in FIG. 1, the holder / temperature sensor 102 is installed and the surface temperature of the substrate 103 can be monitored. However, this configuration is not essential. In the embodiment shown in FIG. 1, the longitudinal direction of the measurement sample 100 is the direction indicated by the arrow in the drawing, and refers to the longitudinal direction of the magnetic tape from which the measurement sample is cut. In addition, descriptions relating to angles such as “parallel” described in this specification include a range of errors allowed in the technical field to which the present invention belongs. For example, it means that the angle is within the range of strict angle ± 10 °, and the error from the strict angle is preferably 5 ° or less, and more preferably 3 ° or less. As the pendulum 107 (see FIG. 2), a pendulum made of a material having a property of being attracted to a magnet such as a metal or an alloy is used.
The surface temperature of the substrate 103 on which the measurement sample 100 is placed is raised to 80 ° C. by raising the surface temperature at a temperature raising rate of 5 ° C./min or less (or any temperature raising rate if it is 5 ° C./min or less). The pendulum motion is started (induced initial vibration) by releasing the adsorption between the pendulum and the magnet. FIG. 2 shows an example of the state of the pendulum 107 that is performing the pendulum motion (the state seen from the side). In the embodiment shown in FIG. 2, in the pendulum viscoelasticity tester, the pendulum motion is started by stopping energization to the magnet (electromagnet) 106 disposed below the sample stage (turning off the switch) and releasing the adsorption. Then, energization of the electromagnet is resumed (the switch is turned on), and the pendulum motion is stopped by attracting the pendulum 107 to the magnet 106. During the pendulum movement, the pendulum 107 repeats the amplitude as shown in FIG. From the result obtained by monitoring the displacement of the pendulum 107 with the displacement sensor 108 while the pendulum 107 repeats the amplitude, a displacement-time curve is obtained in which the displacement is plotted on the vertical axis and the elapsed time is plotted on the horizontal axis. An example of the displacement-time curve is shown in FIG. FIG. 3 schematically shows the correspondence between the state of the pendulum 107 and the displacement-time curve. Using a displacement-time curve obtained at a measurement interval after 10 minutes or longer (any time is acceptable if it is 10 minutes or longer) after repeating stationary (adsorption) and pendulum movement at a constant measurement interval. Thus, the logarithmic decay rate Δ (unitless) is obtained from the following formula, and this value is taken as the logarithmic decay rate on the magnetic layer side surface of the magnetic tape. The adsorption time for one adsorption is 1 second or longer (any time is acceptable if it is 1 second or longer), and the interval from the end of adsorption to the next start of adsorption is 6 seconds or longer (if 6 seconds or longer, any time is arbitrary) Time is fine.) The measurement interval is an interval from the start of adsorption to the start of the next adsorption. The humidity of the environment where the pendulum movement is performed may be any relative humidity as long as the relative humidity is in the range of 40 to 70%.

In the displacement-time curve, an interval from the minimum to the minimum again is defined as one wave period. Let n be the number of waves included in the displacement-time curve during the measurement interval, and let An be the difference between the minimum displacement and the maximum displacement in the nth wave. In Figure 3, the displacement of the n-th wave intervals up again becomes minimum of minimum, labeled Pn (e.g. P ₁ for the first _wave, for second P _2, P ₃ for _third) doing. In calculating the logarithmic decay rate, the difference between the minimum displacement and the maximum displacement that appears next to the nth wave (A _{n + 1} in the above formula, A _{4 in the} displacement-time curve shown in FIG. 3) is also used. The part where the pendulum is stationary (adsorbed) is not used for counting the number of waves. Also, the portion where the pendulum 107 is stationary (adsorbed) before the maximum displacement is not used for counting the number of waves. Therefore, in the displacement-time curve shown in FIG. 3, the number of waves is three (n = 3).

The following is not intended to limit the present invention in any way, but the magnetic tape is partially reproduced during signal reproduction even though the total thickness of the magnetic layer and the nonmagnetic layer is reduced to 0.80 μm or less. The present inventor considers the reason why the occurrence of the output decrease can be suppressed as follows.
(1) For recording / reproducing signals on a magnetic tape, a magnetic tape cartridge containing a magnetic tape is set in a drive, and the magnetic layer side surface of the magnetic tape and a magnetic head (hereinafter, also simply referred to as “head”) in the drive. .) Is brought into contact (sliding). However, in a magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer exceeds 0.80 μm, the portion that contacts the head on the magnetic layer side surface (the true contact portion) is mainly the protrusion described in the explanation of the base portion. Yes, it is considered that the base part does not touch or the contact frequency is low. On the other hand, the present inventor has intensively studied, and in the magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer is reduced to 0.80 μm or less, the strength is lowered and the flexibility is reduced as the total thickness is reduced. For this reason, the increase in the frequency with which the base portion on the magnetic layer side surface comes into contact with the head may have contributed to the partial reduction in output. Conventionally, with regard to the surface property of the magnetic layer side surface of the magnetic tape, it has been studied to adjust the height of the protrusions (for example, Patent Document 1 described above), but no consideration has been given to the base portion. On the other hand, the present inventor pays attention to a base portion that has not been considered in the past, and the friction coefficient of the base portion is set to 0.35 or less, so that the total thickness of the magnetic layer and the nonmagnetic layer is 0. It came to consider that it contributes to suppressing the generation | occurrence | production of the partial output fall at the time of signal reproduction | regeneration in the magnetic tape exceeding 80 micrometers.
(2) Further, in a magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer is reduced to 0.80 μm or less, in a magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer exceeds 0.80 μm, the head and It is considered that the area where the magnetic tape and the surface of the magnetic layer are in contact (the true contact area) is increased because the substrate portion that is considered not to contact or the contact frequency is likely to contact the head. Thus, the present inventor thought that the component derived from the magnetic tape easily adheres to the head from the surface of the magnetic tape may be a cause of the partial output decrease.
Therefore, as a result of further intensive studies to reduce the amount of the component derived from the magnetic tape adhering to the head, the present inventor thinks that the above-described logarithmic decay rate can be an indicator of the amount of the component adhering to the head. As a result, it has been newly found out that setting this value to 0.050 or less also contributes to suppressing the occurrence of partial output reduction.
Thus, in the magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer is reduced to 0.80 μm or less by setting the base friction to 0.35 or less and the logarithmic attenuation factor to 0.050 or less, It has become possible to suppress the occurrence of output drop.
In addition, about this component derived from a magnetic tape, this inventor thinks that the adhesive component released | separated from a magnetic tape during driving | running | working may adhere to a head. Although the details of such an adhesive component are not clear, the present inventors speculate that it may be derived from a resin used as a binder. Details are as follows. As the binder, various resins can be used as will be described in detail later. The resin is a polymer of two or more polymerizable compounds (including homopolymer and copolymer), and a component having a molecular weight lower than the average molecular weight (hereinafter referred to as “low molecular weight binder component”). Usually included. The present inventor believes that such a low molecular weight binder component is released from the magnetic tape while traveling and adheres to the head, resulting in a partial reduction in output. The low molecular weight binder component is considered to have adhesiveness, and the logarithmic decay rate obtained by the pendulum viscoelasticity test may be an indicator of the amount of the component adhering to the head during running. The inventor has inferred. In one embodiment, the magnetic layer is formed by applying a composition for forming a magnetic layer containing a curing agent to the nonmagnetic layer in addition to the ferromagnetic powder and the binder, and performing a curing treatment. The curing treatment here allows the binder and curing agent to undergo a curing reaction (crosslinking reaction), but the reason for the low molecular weight binder component is not clear, but the reactivity of the curing reaction is not poor. The present inventor thinks. For this reason, the low molecular weight binder component hardly stays in the magnetic layer and is easily released from the magnetic layer and easily adheres to the head, which may be one of the reasons why the low molecular weight binder component easily adheres to the head during running. The inventor speculates.
However, the above is a guess of the present inventor and does not limit the present invention.

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

[Magnetic layer]
<Logarithmic decay rate>
The logarithmic attenuation factor obtained by the pendulum viscoelasticity test on the surface of the magnetic tape on the magnetic layer side is 0.050 or less. From the viewpoint of further suppressing the occurrence of partial output reduction, the logarithmic decay rate is preferably 0.048 or less, more preferably 0.045 or less, and even more preferably 0.040 or less. . On the other hand, from the viewpoint of suppressing the occurrence of partial output decrease, the lower the logarithmic decay rate, the better. Therefore, the lower limit value is not particularly limited. As an example, the logarithmic decay rate can be, for example, 0.010 or more, or 0.015 or more, but may be less than these. A specific aspect of the means for adjusting the logarithmic decay rate will be described later.

<Base friction>
The friction coefficient (base friction) measured at the base portion of the magnetic layer surface of the magnetic tape is 0.35 or less. In addition, the measuring method of the friction coefficient of a base part is as having described previously. From the viewpoint of further suppressing the occurrence of the partial output decrease, the base friction is preferably 0.30 or less. Further, the base friction is, for example, 1.00 or more, but the lower limit is not particularly limited because it is preferably as low as possible from the viewpoint of suppressing the occurrence of a partial output decrease during signal reproduction.

The inventor believes that the substrate portion has microscopic unevenness, for example, as compared with the unevenness caused by the protrusion formed on the surface of the magnetic layer by the nonmagnetic powder described later. And this inventor is guessing that a base friction can be adjusted by the shape control of this microscopic unevenness | corrugation. Based on this inference, the present inventor formed a magnetic layer using two or more kinds of ferromagnetic powders having different average particle sizes in order to control the shape of the unevenness of the substrate portion, and controlled the substrate friction to various values. It was possible to do. Accordingly, one means for adjusting the base friction is to use two or more kinds of ferromagnetic powders having different average particle sizes as the ferromagnetic powder. More specifically, since the ferromagnetic powder having a larger average particle size becomes a convex portion, the above-described microscopic unevenness can be formed on the base portion, and the mixing ratio of the ferromagnetic powder having a larger average particle size can be set. The present inventor believes that the presence ratio of the protrusions in the base portion can be increased by increasing the ratio (or the presence ratio of the protrusions in the base portion can be decreased by lowering the mixing ratio). . Details will be described later.
As another means, the present inventor, in addition to non-magnetic powder capable of forming protrusions and protruding on the surface of the magnetic layer, controls the shape of the irregularities of the base portion. When the magnetic layer was formed using nonmagnetic powder, it was possible to control the base friction to various values. Therefore, one of the means for adjusting the base friction is to use the other non-magnetic powder described above when forming the magnetic layer. More specifically, the microscopic irregularities can be formed on the substrate portion by forming the other non-magnetic powder into a convex portion. By increasing the mixing ratio of the non-magnetic powder, the convex portion on the substrate portion can be formed. The present inventor believes that the presence rate of the portion can be increased (or the presence rate of the convex portion in the substrate portion can be reduced by lowering the mixing ratio). Details will be described later.
In addition, it is possible to adjust the base friction by combining the above two types of means.
However, the above-described adjusting means is an exemplification, and the base friction of 0.35 or less can be realized by any means capable of adjusting the base friction, and such an aspect is also included in the present invention.

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

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

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

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

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

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

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

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

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

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

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

  The magnetic tape may contain only one of ferromagnetic hexagonal ferrite powder and ferromagnetic metal powder as the ferromagnetic powder, or may contain both.

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

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

  Moreover, a hardening | curing agent can also be used with resin which can be used as the said binder. In one aspect, the curing agent can be a thermosetting compound that is a compound that undergoes a curing reaction (crosslinking reaction) by heating, and in another aspect, photocuring in which a curing reaction (crosslinking reaction) proceeds by light irradiation. It can be a sex compound. A preferred curing agent is a thermosetting compound, and polyisocyanate is suitable. JP, 2011-216149, A paragraphs 0124-0125 can be referred to for the details of polyisocyanate. The curing agent is, for example, 0 to 80.0 parts by mass with respect to 100.0 parts by mass of the binder in the composition for forming a magnetic layer, and preferably 50.0 to 80.0 masses from the viewpoint of improving coating film strength. It can be added and used in parts.

<Additives>
(Non-magnetic powder)
The magnetic tape may include a nonmagnetic powder in the magnetic layer together with a ferromagnetic powder and a binder. Regarding the identification of the substrate portion, the reason why the portion having a height of 15 nm or more from the reference surface is defined as the protrusion is that the protrusion formed by the nonmagnetic powder contained in the magnetic layer protruding on the magnetic layer surface of the magnetic tape is This is because it is considered that the protrusions having a height of 15 nm or more from the reference surface are present on the magnetic layer side surface of the magnetic tape.
The nonmagnetic powder preferably includes at least one of a nonmagnetic powder that can function as an abrasive and a protrusion-forming agent that forms a protrusion that protrudes moderately on the surface of the magnetic layer, and both are included. Is more preferable. In general, a nonmagnetic powder having a high Mohs hardness is suitable as an abrasive, and a nonmagnetic powder having a lower Mohs hardness than a nonmagnetic powder that can function as an abrasive is suitable as a protrusion-forming agent. As the abrasive, inorganic powder having a Mohs hardness of more than 8 is preferably used, and inorganic powder having a Mohs hardness of 9 or more is more preferably used. The maximum Mohs hardness is 10 for diamond. Specific examples include alumina (Al ₂ O ₃ ), silicon carbide, boron carbide (B ₄ C), TiC, cerium oxide, zirconium oxide (ZrO ₂ ), and diamond powder. Among these, alumina is preferable. The Mohs hardness of alumina is 9. The magnetic layer containing alumina preferably contains the dispersant described in paragraphs 0012 to 0022 of JP2013-131285A for improving the dispersibility of alumina. Regarding alumina, paragraph 0021 of JP2013-229090A can also be referred to. The specific surface area can be used as an index of the size of the abrasive particles. A larger specific surface area means a smaller particle size. From the viewpoint of improving the smoothness of the magnetic layer side surface of the magnetic tape, it is preferable to use an abrasive having a specific surface area of 14 m ² / g or more. From the viewpoint of dispersibility, it is preferable to use an abrasive having a specific surface area of 40 m ² / g or less. The specific surface area is a value obtained by a nitrogen adsorption method (also called a BET (Brunauer-Emmett-Teller) one-point method), and is a value measured for primary particles. In the following, the specific surface area determined by this method is also described as the BET specific surface area. 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.

  The nonmagnetic powder that can function as a protrusion-forming agent is preferably a nonmagnetic powder having a Mohs hardness of 8 or less. From the viewpoint of enhancing the surface smoothness of the magnetic layer side surface of the magnetic tape, colloidal particles (nonmagnetic colloidal particles) ) Is preferable. The average primary particle size of the nonmagnetic colloidal particles is preferably 50 to 200 nm. In the present invention, the average primary particle size of the nonmagnetic colloidal particles is a value determined by the method described in paragraph 0015 of JP2011-48878A. As the nonmagnetic colloidal particles, inorganic colloidal particles are preferable, inorganic oxide colloidal particles are more preferable, and silica colloidal particles (colloidal silica) are particularly preferable from the viewpoint of availability of monodispersed colloidal particles. The Mohs hardness of the silica colloidal particles is about 5-7. For details of the nonmagnetic colloidal particles, reference can be made to paragraph 0023 of JP 2011-48878 A. The content of the nonmagnetic colloidal particles in the magnetic layer is preferably 0.5 to 5.0 parts by mass, more preferably 1.0 to 3.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder. is there.

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

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

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

  Furthermore, the magnetic layer may contain one or more additives as required. Specific examples of the additive include the above-described curing agent and nonmagnetic powder. The curing agent may be contained in the magnetic layer in a state of reacting (crosslinking) with other components such as a binder as the curing reaction proceeds in the magnetic layer forming step. Examples of the additive that can be contained in the magnetic layer include a lubricant, a dispersant / dispersion aid, an antifungal agent, an antistatic agent, an antioxidant, and carbon black. As the additive, commercially available products can be appropriately selected and used according to desired properties.

  The magnetic layer described above is provided on the nonmagnetic support via the nonmagnetic layer. Details of the nonmagnetic layer and the nonmagnetic support will be described later.

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

  As the binder, lubricant, dispersant, additive, solvent, dispersion method and the like of the nonmagnetic layer, known techniques relating to the nonmagnetic layer can be applied. Also, known techniques relating to the magnetic layer can be applied with respect to the amount of binder, type, additive, amount of added dispersant, type, and the like.

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

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

[Various thicknesses]
In the magnetic tape, the total thickness of the magnetic layer and the nonmagnetic layer is 0.80 μm or less, preferably 0.70 μm or less, and preferably 0.60 μm or less from the viewpoint of thinning the magnetic tape. Is more preferable. The total thickness of the magnetic layer and the nonmagnetic layer can be, for example, 0.10 μm or more, or 0.20 μm or more.
Regarding the thickness of the nonmagnetic support and each layer in the magnetic tape, the thickness of the nonmagnetic support is preferably 3.00 to 4.50 μm.
The thickness of the magnetic layer is optimized depending on the saturation magnetization of the magnetic head used, the head gap length, and the band of the recording signal, but is generally 0.01 μm to 0.15 μm. Therefore, it is preferably 0.02 μm to 0.12 μm, and more preferably 0.03 μm to 0.10 μm. There may be at least one magnetic layer, and the magnetic layer may be separated into two or more layers having different magnetic characteristics, and a configuration related to a known multilayer magnetic layer can be applied.
The thickness of the nonmagnetic layer is, for example, 0.10 to 0.65 μm, preferably 0.10 to 0.60 μm, and more preferably 0.10 to 0.50 μm.
The total thickness of the magnetic tape is preferably 6.00 μm or less from the viewpoint of improving the recording capacity. On the other hand, from the viewpoint of easy handling (handling properties) of the magnetic tape, the total thickness of the magnetic tape is preferably 1.00 μm or more.

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

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

[Manufacturing process]
<Preparation of each layer forming composition>
The composition (composition) for forming the magnetic layer, the nonmagnetic layer or the backcoat layer usually contains a solvent together with the various components described above. Examples of the solvent include various organic solvents generally used for producing a coating type magnetic recording medium. Specifically, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, etc., methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, methylcyclohexanol, etc. at an arbitrary ratio Alcohols, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, glycol acetates such as glycol acetate, glycol dimethyl ether, glycol monoethyl ether, dioxane and other glycol ethers, benzene, toluene, xylene, cresol, chlorobenzene Aromatic hydrocarbons such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin Chlorinated hydrocarbons such as dichlorobenzene, N, N- dimethylformamide, may be used hexane. Among these, from the viewpoint of solubility of a binder usually used in a coating type magnetic recording medium, the magnetic layer forming composition preferably contains one or more ketone solvents. The amount of solvent in the composition for forming a magnetic layer is not particularly limited, and can be the same as that for the composition for forming a magnetic layer of an ordinary coating type magnetic recording medium.
The above description can also be applied to solvents that can be contained in each layer forming composition such as the nonmagnetic layer forming composition.

  The step of preparing the composition for forming each layer usually comprises at least a kneading step, a dispersing step, and a mixing step provided as necessary before and after these steps. Each process may be divided into two or more stages. All raw materials such as ferromagnetic powder, binder, nonmagnetic powder, and various additives and solvents added in the present invention may be added at the beginning or middle of any step. In addition, individual raw materials may be added in two or more steps. For example, in the preparation of the magnetic layer forming composition, it is preferable to separately disperse the abrasive and the ferromagnetic powder. In the kneading step, it is preferable to use a kneading force such as an open kneader, a continuous kneader, a pressure kneader, or an extruder. Details of these kneading treatments are described in JP-A-1-106338 and JP-A-1-79274. Further, in order to disperse each layer forming composition, glass beads or other beads can be used. As such dispersed beads, zirconia beads, titania beads, and steel beads, which are dispersed beads having a high specific gravity, are suitable. The particle diameter (bead diameter) and filling rate of these dispersed beads can be optimized and used. A well-known thing can be used for a disperser.

<Application process, cooling process, heat drying process, burnish process, curing process>
The magnetic layer can be formed by coating the composition for forming a magnetic layer on a nonmagnetic support successively or simultaneously with the composition for forming a nonmagnetic layer. For details of coating for forming each layer, reference can be made to paragraph 0066 of JP2010-231843A.

In a preferred embodiment, the magnetic tape has a magnetic layer forming step.
A coating step of forming a coating layer by coating a magnetic layer forming composition containing a ferromagnetic powder, a binder, a curing agent and a solvent on the nonmagnetic layer;
A heat drying step of drying the coating layer by heat treatment, and
A curing process for curing the coating layer,
Including
A manufacturing method including a cooling step for cooling the coating layer between the coating step and the heating drying step, and a burnishing step for burnishing the surface of the coating layer between the heating drying step and the curing step. Can be manufactured.

  The present inventor considers that the cooling step and the burnishing step in the magnetic layer forming step of the above manufacturing method are preferable means for setting the logarithmic decay rate described above to 0.050 or less. . Details are as follows. Performing a cooling process that cools the coating layer between the coating process and the heat-drying process localizes the adhesive component released from the magnetic tape during running on the surface of the coating layer or the surface layer near the surface. The present inventor speculates that this may contribute to this. The reason for this is not clear, but by cooling the coating layer of the magnetic layer forming composition before the heat drying step, the adhesive component moves to the surface of the coating layer or the surface layer when the solvent volatilizes in the heat drying step. The present inventor speculates that this may be easier. And this inventor thinks that an adhesive component can be removed by burnishing the surface of the coating layer in which the adhesive component localized on the surface or surface layer part. The present inventor has inferred that performing the curing step after removing the adhesive component in this way leads to the logarithmic decay rate of 0.050 or less. However, the above is only an assumption and does not limit the present invention.

That is, one aspect of the present invention is a method of manufacturing the magnetic tape,
Including a nonmagnetic layer forming step of forming a nonmagnetic layer and a magnetic layer forming step of forming a magnetic layer,
The magnetic layer formation process
A coating step of forming a coating layer by coating a magnetic layer forming composition containing a ferromagnetic powder, a binder, a curing agent and a solvent on the nonmagnetic layer;
A heat drying step of drying the coating layer by heat treatment, and
A curing process for curing the coating layer,
Including
A magnetic tape comprising a cooling step for cooling the coating layer between the coating step and the heat drying step, and a burnishing step for burnishing the surface of the coating layer between the heat drying step and the curing step. Production method,
About.

  As described above, the composition for forming a magnetic layer can be applied successively or simultaneously with the composition for forming a nonmagnetic layer. In a preferred embodiment, the magnetic tape can be produced by sequential multilayer coating. The manufacturing process by sequential multilayer coating can be preferably performed as follows. The nonmagnetic layer is formed through a coating process for forming a coating layer by coating a composition for forming a nonmagnetic layer on a nonmagnetic support, and a heat drying process for drying the formed coating layer by heat treatment. Then, the magnetic layer is formed through an application step of forming a coating layer by applying a composition for forming a magnetic layer on the formed nonmagnetic layer, and a heating and drying step of drying the formed coating layer by heat treatment.

  Hereinafter, a specific aspect of the manufacturing method will be described with reference to FIG. However, the present invention is not limited to the following specific embodiments.

  FIG. 4 is a process schematic diagram showing a specific embodiment of a process for producing a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one side of a nonmagnetic support and a backcoat layer on the other side. It is. In the embodiment shown in FIG. 4, the operation of continuously winding the nonmagnetic support (long film) from the sending-out part by the sending-out winding part is performed, and coating is performed in each part or each zone shown in FIG. 4. By performing various treatments such as drying and orientation, a nonmagnetic layer and a magnetic layer can be successively formed on one surface of a traveling nonmagnetic support by multilayer coating, and a backcoat layer can be formed on the other surface. it can. Except for including a cooling zone in the magnetic layer forming step and a varnishing step before the curing process, it can be the same as the manufacturing process normally performed for manufacturing a coating type magnetic recording medium.

  On the nonmagnetic support sent out from the delivery part, the nonmagnetic layer forming composition is applied in the first application part (application process of the nonmagnetic layer forming composition).

  After the coating step, in the first heat treatment zone, the coating layer of the composition for forming a nonmagnetic layer formed in the coating step is heated to dry the coating layer (heat drying step). The heat drying treatment can be performed by passing a nonmagnetic support having a coating layer of the composition for forming a nonmagnetic layer through a heated atmosphere. Although the atmospheric temperature of a heating atmosphere here is about 60-140 degreeC, for example, what is necessary is just to set it as the temperature which can volatilize a solvent and can dry an application layer, and is not limited to the said range. Moreover, you may spray the heated gas on the coating layer surface arbitrarily. The same applies to the heat drying step in the second heat treatment zone and the heat drying step in the third heat treatment zone, which will be described later.

  Next, in the second application part, the magnetic layer forming composition is applied onto the nonmagnetic layer formed by performing the heat drying step in the first heat treatment zone (of the magnetic layer forming composition). Application process).

  After the coating step, the coating layer of the magnetic layer forming composition formed in the coating step is cooled in the cooling zone (cooling step). For example, the cooling step can be performed by passing a nonmagnetic support having the coating layer formed on the nonmagnetic layer through a cooling atmosphere. The atmospheric temperature of the cooling atmosphere can be preferably in the range of −10 ° C. to 0 ° C., more preferably in the range of −5 ° C. to 0 ° C. The time for performing the cooling step (for example, the time from when an arbitrary part of the coating layer is carried into the cooling zone until it is carried out (hereinafter also referred to as “stay time”) is not particularly limited, Since the value of the logarithmic decay rate tends to decrease as the length increases, it is preferable to adjust the logarithmic decay rate by performing preliminary experiments as necessary so that a logarithmic decay rate of 0.050 or less can be realized. The cooled gas may be sprayed on the surface of the coating layer.

  Thereafter, while the coating layer of the magnetic layer forming composition is in a wet state, the orientation treatment of the ferromagnetic powder in the coating layer is performed in the orientation zone. Regarding the alignment treatment, reference can be made to paragraph 0067 of JP2010-231843A.

  The coating layer after the orientation treatment is subjected to a heat drying step in the second heat treatment zone.

  Next, in the third application part, the composition for forming the backcoat layer is applied to the surface of the nonmagnetic support opposite to the surface on which the nonmagnetic layer and the magnetic layer are formed to form a coating layer. (Application | coating process of the composition for backcoat layer formation). Thereafter, in the third heat treatment zone, the coating layer is heat treated and dried.

  In this way, it is possible to obtain a magnetic tape having a coating layer of the composition for forming a magnetic layer heated and dried on the nonmagnetic layer on one surface of the nonmagnetic support and a backcoat layer on the other surface. . The magnetic tape obtained here becomes a product magnetic tape after performing various processes to be described later.

  The obtained magnetic tape is wound around the winding portion and then cut (slit) into the size of the product magnetic tape. The slit can be performed using a known cutting machine.

  Before the slitting magnetic tape is subjected to a curing treatment (heating, light irradiation, etc.) according to the type of curing agent contained in the magnetic layer forming composition, the magnetic tape forming composition is heated and dried. The surface of the coating layer is burnished (burnishing step between the heat drying step and the curing step). By this burnishing treatment, the adhesive component that has been cooled in the cooling zone and transferred to the surface of the coating layer or the surface layer portion can be removed, which leads to the logarithmic attenuation factor of 0.050 or less. I guess. However, as described above, this is merely a guess and does not limit the present invention.

  The burnishing process is a process of rubbing the surface to be processed with a member (for example, a grinding tool such as a polishing tape, a grinding blade, or a grinding wheel), and is a known burnishing process for manufacturing a coating type magnetic recording medium. The same can be done. However, after the cooling step and the heat drying step, the burnish treatment has not been performed in the stage before the curing step. On the other hand, the logarithmic decay rate can be reduced to 0.050 or less by performing the burnish process in the above stage. This point was newly found by the present inventors.

  The burnish treatment is preferably carried out by performing one or both of rubbing (polishing) the surface of the coating layer to be treated with an abrasive tape and rubbing (grinding) the surface of the coating layer to be treated with a grinding tool. can do. When the magnetic layer forming composition contains an abrasive, it is preferable to use an abrasive tape containing at least one abrasive having a higher Mohs hardness than the abrasive. As a polishing tape, a commercial item may be used and the polishing tape produced by the well-known method may be used. As the grinding tool, a known grinding blade such as a fixed blade, a diamond wheel, or a rotary blade, a grinding wheel, or the like can be used. Moreover, you may perform the wiping process which wipes off the coating layer surface rubbed with the polishing tape or the grinding tool with the wiping material. For details of the preferred polishing tape, grinding tool, burnishing and wiping, reference can be made to paragraphs 0034 to 0048 of JP-A-6-52544, FIG. As the burnishing process is strengthened, the value of the logarithmic decay rate tends to decrease. The burnish treatment can be strengthened as a hard abrasive is used as the abrasive contained in the abrasive tape, and can be enhanced as the amount of the abrasive in the abrasive tape is increased. Moreover, it can strengthen, so that a high-hardness grinding tool is used as a grinding tool. Regarding the burnish treatment conditions, the burnish treatment can be strengthened as the sliding speed between the surface of the coating layer to be treated and the member (for example, polishing tape or grinding tool) is increased. The sliding speed can be increased by increasing one or both of the speed of moving the member and the speed of moving the magnetic tape to be processed.

  After the above burnish treatment (burnish treatment step), the coating layer of the magnetic layer forming composition is cured. In the embodiment shown in FIG. 4, the coating layer of the magnetic layer forming composition is subjected to a surface smoothing treatment after the burnishing treatment and before the curing treatment. The surface smoothing process is preferably performed by a calendar process. For details of the calendar process, reference can be made to, for example, paragraph 0026 of Japanese Patent Application Laid-Open No. 2010-231843.

  Thereafter, the coating layer of the composition for forming a magnetic layer is subjected to a curing treatment according to the type of curing agent contained in the coating layer (curing step). The curing process can be performed by a process according to the type of curing agent contained in the coating layer, such as heat treatment or light irradiation. The curing treatment conditions are not particularly limited, and may be appropriately set according to the formulation of the magnetic layer forming composition used for forming the coating layer, the type of curing agent, the thickness of the coating layer, and the like. For example, when the coating layer is formed using a magnetic layer forming composition containing polyisocyanate as a curing agent, the curing treatment is preferably a heat treatment. In addition, when a hardening | curing agent is contained in layers other than a magnetic layer layer, the hardening reaction of the layer can also be advanced by the hardening process here. Or you may provide a hardening process separately. In addition, you may perform a burnishing process after a hardening process.

  As described above, a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one surface of a nonmagnetic support and a backcoat layer on the other surface can be produced. The above production method is suitable for adjusting the logarithmic decay rate obtained by the pendulum viscoelasticity test to 0.050 or less on the surface of the magnetic tape on the magnetic layer side. However, the above manufacturing method is an exemplification, and a logarithmic attenuation factor of 0.050 or less can be realized by any means capable of adjusting the logarithmic attenuation factor, and such an aspect is also included in the present invention.

  As for the base friction, as described above, the use of two or more kinds of ferromagnetic powders having different average particle sizes can be cited as a means for adjusting the base friction. More specifically, the magnetic layer can be formed as a ferromagnetic powder using a first ferromagnetic powder and one or more ferromagnetic powders having an average particle size larger than that of the first ferromagnetic powder.

The following aspects can be mentioned as a preferable aspect of the said adjustment means. A combination of two or more of the following aspects is a more preferable aspect of the adjusting means. The first ferromagnetic powder refers to one kind of ferromagnetic powder used among two or more kinds of ferromagnetic powder, and is preferably the ferromagnetic powder used in the largest proportion described above. The other details of the adjusting means are as described above.
The average particle size of the first ferromagnetic powder is in the range of 10 to 80 nm.
The difference between the average particle size of the ferromagnetic powder having an average particle size larger than that of the first ferromagnetic powder and the average particle size of the first ferromagnetic powder is in the range of 10 to 50 nm.
The mixing ratio between the first ferromagnetic powder and the ferromagnetic powder having an average particle size larger than that of the first ferromagnetic powder is, on the mass basis, the former: the latter = 90.0: 10.0 to 99.9: 0. .1 range.

  Further, as other means for adjusting the base friction, it is also possible to use other nonmagnetic powders together with nonmagnetic powders having a Mohs hardness of more than 8 and nonmagnetic colloidal particles as the nonmagnetic powders of the magnetic layer.

The following aspects can be mentioned as a preferable aspect of the said adjustment means. A combination of two or more of the following aspects is a more preferable aspect of the adjusting means. Details of the adjusting means are as described above.
The average particle size of the other non-magnetic powder is larger than the average particle size of the ferromagnetic powder.
The difference between the average particle size of the ferromagnetic powder and the average particle size of the other non-magnetic powder is in the range of 10 to 80 nm.
The mixing ratio of the ferromagnetic powder and the other nonmagnetic powder is in the range of the former: the latter = 90.0: 10.0 to 99.9: 0.1 on a mass basis.

  However, the adjusting means is an exemplification, and the base friction of 0.35 or less can be realized by any means capable of adjusting the base friction, and such an aspect is also included in the present invention.

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

[Examples 1-12, Comparative Examples 1-15]
1. Preparation of Alumina Dispersion 3.0 parts of 2,3-dihydroxynaphthalene (100.0 parts of alumina powder (HIT-70, manufactured by Sumitomo Chemical Co., Ltd.) having an alpha conversion rate of about 65% and a BET specific surface area of 30 m ² / g ( Manufactured by Tokyo Chemical Industry Co., Ltd.), a 32% solution of a polyester polyurethane resin having a SO ₃ Na group as a polar group (UR-4800 manufactured by Toyobo (registered trademark) (polar group amount: 80 meq / kg)) (solvent is a mixed solvent of methyl ethyl ketone and toluene) 31.3 parts, and 570.0 parts of a mixed solution of methyl ethyl ketone and cyclohexanone 1: 1 (mass ratio) as a solvent were mixed and dispersed in a paint shaker for 5 hours in the presence of zirconia beads. After dispersion, the dispersion and beads were separated with a mesh to obtain an alumina dispersion.

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

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

4). Composition for forming backcoat layer Nonmagnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average major axis length): 0.15 μm
Average needle ratio: 7
BET specific surface area: 52 m ² / g
Carbon black 20.0 parts Average particle size 20nm
Vinyl chloride copolymer 13.0 parts Polysulfonate resin containing sulfonate group 6.0 parts Phenylphosphonic acid 3.0 parts Cyclohexanone 155.0 parts Methyl ethyl ketone 155.0 parts Stearic acid 3.0 parts Butyl stearate 3.0 parts Poly Isocyanate 5.0 parts Cyclohexanone 200.0 parts

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

6). Production of Magnetic Tape A magnetic tape was produced according to the specific embodiment shown in FIG. The details are as follows.
The polyethylene naphthalate support having the thickness shown in Table 1 is sent out from the feed-out part, and on one surface, the thickness after drying in the first coating part becomes the thickness shown in Table 1 above. The composition for forming a nonmagnetic layer prepared in (1) was applied and dried in the first heat treatment zone (atmosphere temperature 100 ° C.) to form a coating layer.
Then, said 5. so that the thickness after drying may become the thickness shown in Table 1 in a 2nd application part. The composition for forming a magnetic layer prepared in (1) was applied on the nonmagnetic layer to form a coating layer. While the formed coating layer is in a wet state, it is passed through a cooling zone adjusted to an atmospheric temperature of 0 ° C. with the residence time shown in Table 1, and a cooling process is performed. In the orientation zone, a magnetic field having a magnetic field strength of 0.3 T is applied in the vertical direction. After performing vertical alignment treatment, the film was dried in a second heat treatment zone (atmospheric temperature 100 ° C.) having an atmospheric temperature of 100 ° C.
Thereafter, in the third coating portion, the thickness after drying is the thickness shown in Table 1 on the surface opposite to the surface on which the nonmagnetic layer and magnetic layer of the polyethylene naphthalate support are formed. . The composition for forming a backcoat layer prepared in (1) was applied to form a coating layer, and the formed coating layer was dried in a third heat treatment zone (atmosphere temperature 100 ° C.).
After slitting the magnetic tape thus obtained to a width of ½ inch (0.0127 meter), burnishing and wiping treatments were performed on the surface of the coating layer of the magnetic layer forming composition. The burnishing and wiping treatments were performed using a commercially available polishing tape (trade name MA22000, manufactured by Fuji Film Co., Ltd., abrasive: diamond / Cr ₂₎ as the polishing tape in the processing apparatus having the configuration shown in FIG. 1 of JP-A-6-52544. O ₃ / Bengara), a commercially available sapphire blade (made by Kyocera, width 5 mm, length 35 mm, tip angle 60 degrees) as a grinding blade, and a commercially available wiping material (Kuraray product) The name WRP736) was used. As the processing conditions, the processing conditions in Example 12 of JP-A-6-52544 were adopted.
After the above burnishing and wiping treatment, the calender is composed of only a metal roll, and the calender treatment (surface smoothing treatment) at a speed of 80 m / min, a linear pressure of 300 kg / cm, and a calender temperature (calendar roll surface temperature) of 100 ° C. Went.
Thereafter, a curing treatment (heating treatment) was performed for 36 hours in an environment with an atmospheric temperature of 70 ° C. to obtain a magnetic tape.
In Table 1, in the comparative example in which “0 seconds” is described in the column of the cooling zone residence time, a magnetic tape was manufactured by a manufacturing process not including the cooling zone.
In Table 1, in the comparative example described as “not yet implemented” in the column of the burnishing process before the curing process, a magnetic tape was manufactured by a manufacturing process in which the burnishing process was not performed in the process before the curing process was performed. . However, in Comparative Example 15, the burnishing and wiping processes described above were performed after the curing process.
Through the above steps, magnetic tapes of Examples and Comparative Examples were produced.

Each layer of the magnetic tape, the nonmagnetic support, and the total thickness were determined by the following method.
After the cross section in the thickness direction of the magnetic tape is exposed with an ion beam, the exposed cross section is observed with a scanning electron microscope. Various thicknesses were obtained as an arithmetic average of thicknesses obtained at two locations in the thickness direction in cross-sectional observation.

7). Evaluation method (1) Friction coefficient (base friction) measured at the base portion of the magnetic layer side surface of the magnetic tape
First, the measurement surface was marked with a laser marker in advance, and an atomic force microscope (AFM) image of a part away from the measurement surface by a certain distance (about 100 μm) was measured. The visual field area was 7 μm × 7 μm. At this time, as will be described later, the cantilever was changed to a hard one (single crystal silicon) so as to easily take a scanning electron microscope (SEM) image of the same location, and a ruled line was put on the AFM. All protrusions at a height of 15 nm or more from the reference plane were extracted from the AFM image thus measured. And the location determined that there was no protrusion was specified as the substrate portion, and the substrate friction was measured by the method described above using a Hystron TI-950 type tribo indenter.
In addition, the component map is obtained by measuring the SEM image at the same location where the AFM was measured, and it was confirmed that the protrusion with a height of 15 nm or more from the extracted reference plane was formed by alumina or colloidal silica. did. Moreover, in Examples 1-12, the alumina and colloidal silica were not confirmed by the base part in the component map by the said SEM. In addition, although component analysis was performed by SEM here, component analysis is not limited to SEM, but energy dispersive X-ray spectroscopy (EDS), Auger Electron Spectroscopy (AES) It can carry out by well-known methods, such as.
The measurement results are shown in Table 1.

(2) Measurement of logarithmic attenuation rate As a measuring device, a rigid pendulum type physical property tester RPT-3000W (pendulum: made of brass, substrate: glass substrate, substrate heating rate 5 ° C./min) manufactured by A & D Co., Ltd. Using the method described above, the logarithmic decay rate of the magnetic layer side surface (magnetic layer surface) of each of the magnetic tapes of Examples and Comparative Examples was determined. As shown in FIG. 1, the measurement samples cut out from the magnetic tapes of the examples and comparative examples were fixed on a glass substrate having a size of about 3 cm × about 5 cm with a fixing tape (Toray DuPont Kapton tape) as shown in FIG. Was fixed and placed. The adsorption time was 1 second and the measurement interval was 7 to 10 seconds. A displacement-time curve was created for the 86th measurement interval, and the logarithmic decay rate was determined using this curve. The measurement was performed in an environment with a relative humidity of about 50%.

(3) Measurement of the number of partial reproduction output reductions The magnetic tape cartridges containing the magnetic tapes of the examples and comparative examples (total length of magnetic tape 500 m) were placed in an IBM LTO-G6 (Linear Tape-Open Generation 6) drive. The magnetic tape was set to run 100 reciprocations at a tension of 0.6 N and a running speed of 5 m / sec.
When the reproduction signal during driving is taken into an external AD (Analog / Digital) converter, the reproduction signal amplitude is reduced by 60% or more with respect to the average (average of measured values in all tracks) over a time of 1 second or more. It was determined that a decrease in output was generated, and the number of times that a decrease in output occurred during the 100 reciprocating travels was determined. If the number of partial output drops is 3 or less, it can be determined that the magnetic tape is practically reliable.

  Table 1 shows details of the magnetic tapes of Examples and Comparative Examples, and the evaluation results. In Table 1, BF is a ferromagnetic hexagonal barium ferrite powder, and MP is a ferromagnetic metal powder. The prescription ratio of the ferromagnetic powders (1) and (2) is the content of each ferromagnetic powder with respect to the total amount of the ferromagnetic powder of 100.0% by mass. In Table 1, the average particle size of the ferromagnetic powder is the average plate diameter for the ferromagnetic hexagonal barium ferrite powder and the average major axis length for the ferromagnetic metal powder. The average particle size of the ferromagnetic powder is a value obtained by collecting a necessary amount from the ferromagnetic powder lot used for manufacturing the magnetic tape and measuring the average particle size by the method described above. The ferromagnetic powder after the measurement was used to prepare a magnetic liquid for producing a magnetic tape.

From the results shown in Table 1, the following points can be confirmed.
(1) In the magnetic tapes of Comparative Examples 1 to 6 in which the total thickness of the magnetic layer and the nonmagnetic layer exceeds 0.80 μm, the logarithmic attenuation factor on the magnetic layer side surface exceeds 0.050, and the base friction is 0. Even when 35 was exceeded, the number of partial power reductions was 3 or less. That is, in the magnetic tape in which the total thickness of the magnetic layer and the nonmagnetic layer exceeds 0.80 μm, there is no correlation between the number of partial output reductions, the logarithmic decay rate, and the base friction.
(2) On the other hand, from the comparison between Examples 1 to 12 and Comparative Examples 7 to 15, the magnetic tape having a total thickness of the magnetic layer and the nonmagnetic layer of 0.80 μm or less is logarithmic attenuation of the magnetic layer side surface. When the rate is 0.050 or less and the base friction is 0.35 or less, it can be confirmed that the occurrence of partial output reduction can be suppressed.

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

100 Sample for Measurement 101 Sample Stage 102 Holder / Temperature Sensor 103 Substrate 104 Cylindrical Cylinder Edge with Pendulum 105 Fixing Tape 106 Magnet (for Inducing Initial Vibration)
107 Pendulum 108 Displacement sensor

Claims (13)

A magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and having a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer,
The total thickness of the magnetic layer and the nonmagnetic layer is 0.80 μm or less,
The logarithmic attenuation factor obtained by the pendulum viscoelasticity test on the surface of the magnetic layer of the magnetic tape is 0.050 or less, and the coefficient of friction measured on the surface portion of the surface of the magnetic layer is 0.35 or less. A magnetic tape. The magnetic tape according to claim 1, wherein the logarithmic decay rate is 0.010 or more and 0.050 or less. The magnetic tape according to claim 1, wherein the ferromagnetic powder is selected from the group consisting of a ferromagnetic hexagonal ferrite powder and a ferromagnetic metal powder. The magnetic tape according to claim 1, wherein the magnetic layer further includes a nonmagnetic powder. The magnetic tape according to claim 4, wherein the nonmagnetic powder contained in the magnetic layer is two or more kinds of nonmagnetic powders having different Mohs hardnesses. The magnetic tape according to claim 4 or 5, wherein the nonmagnetic powder contained in the magnetic layer comprises an inorganic powder having a Mohs hardness of more than 8. The magnetic tape according to claim 4, wherein the nonmagnetic powder contained in the magnetic layer contains nonmagnetic colloidal particles. It is a manufacturing method of the magnetic tape of any one of Claims 1-7,
Including a nonmagnetic layer forming step of forming a nonmagnetic layer and a magnetic layer forming step of forming a magnetic layer,
The magnetic layer forming step includes
A coating step of forming a coating layer by coating a magnetic layer forming composition containing a ferromagnetic powder, a binder, a curing agent and a solvent on the nonmagnetic layer;
A heat drying step of drying the coating layer by heat treatment; and
A curing step of performing a curing treatment on the coating layer,
Including
A varnish treatment step including a cooling step for cooling the coating layer between the coating step and the heating drying step, and a burnishing treatment on the surface of the coating layer between the heating drying step and the curing step; A method for producing the magnetic tape. The method for producing a magnetic tape according to claim 8, wherein the cooling step is performed by placing the coating layer in a cooling atmosphere of −10 ° C. to 0 ° C. The method for producing a magnetic tape according to claim 8, wherein the solvent contained in the composition for forming a magnetic layer contains a ketone solvent. The said hardening | curing agent is a thermosetting compound, and the manufacturing method of the magnetic tape of any one of Claims 8-10 which performs the said hardening process by heat processing. The method for producing a magnetic tape according to claim 11, wherein the thermosetting compound is polyisocyanate. The manufacturing method of the magnetic tape of any one of Claims 8-12 including a surface smoothing process between the said burnishing process and a hardening process.