JP2016126817A - Magnetic tape and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic tape which is made thin so that total thickness thereof is equal to or less than 4.80 μm, in which deterioration of electromagnetic conversion property in repeating travel under both of a low humidity environment and high humidity environment, is suppressed.SOLUTION: The invention relates to a magnetic tape comprising a non-magnetic layer containing a non-magnetic powder and a binder on a non-magnetic support medium, and a magnetic layer containing a ferromagnetic powder and a binder on the non-magnetic layer, in which, total thickness of the magnetic tape is equal to or less than 4.80 μm. The magnetic layer comprises one or more kinds of components selected from a group formed of fatty acid and fatty acid amide. In addition, C density derived from C-H which is calculated from a C-H peak area ratio on a C1s spectrum obtained by an X-ray photoelectron spectroscopy analysis which is performed with a photoelectron take-out angle of 10 degree on a face of the magnetic tape on the magnetic layer side, is 45 atom% or more. A production method of the magnetic tape is also provided.SELECTED DRAWING: None

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. In recording and reproducing signals on a magnetic tape, the magnetic tape is usually run in a drive, and the magnetic layer side surface of the magnetic tape is brought into contact with a magnetic head (hereinafter also simply referred to as “head”) and slid. Is done.

  In the above recording / reproducing operation, if the running is repeated with a high friction coefficient when sliding between the magnetic layer side surface and the head, the output fluctuates (spacing due to the scraping generated by scraping the magnetic layer side surface. Loss). Such a spacing loss causes a decrease in electromagnetic conversion characteristics as the vehicle travels repeatedly. Therefore, in order to prevent an increase in the coefficient of friction during repeated running as described above, conventionally, a lubricant has been added to the surface of the magnetic layer or the magnetic layer. Specifically, a lubricant is applied to the surface of the magnetic layer (so-called overcoat). And forming a magnetic layer using a magnetic layer forming composition containing a lubricant (see, for example, Patent Document 1).

JP 2008-243317 A

By the way, with respect to the magnetic tape, in order to increase the recording capacity per volume of the magnetic tape cartridge, the tape that can be accommodated in one volume of the magnetic tape cartridge by reducing the total thickness of the magnetic tape (that is, by reducing the thickness of the magnetic tape). The overall length should be longer.
Furthermore, for the magnetic tape, performance improvement should be considered on the assumption that it will be used in various environments. This is because the magnetic tape is placed in a high-humidity environment, for example, during a rainy season, but may be used in a low-humidity environment such as a data center where the humidity is controlled.
However, as a result of studies by the present inventors, the addition of a lubricant to the surface of the magnetic layer or the magnetic layer as conventionally performed, particularly in a magnetic tape having a total thickness reduced to 4.80 μm or less. It may be difficult to suppress a decrease in electromagnetic conversion characteristics in repeated driving in a low humidity environment (for example, about 15% relative humidity) and a high humidity environment (for example, about 80% relative humidity). found.

  Accordingly, an object of the present invention is a magnetic tape that is thinned to a total thickness of 4.80 μm or less, and suppresses a decrease in electromagnetic conversion characteristics in repeated running under a low humidity environment and a high humidity environment. It is to provide a magnetic tape.

As a result of intensive investigations to achieve the above object, the present inventors have 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 tape is 4.80 μm or less,
C1s obtained by X-ray photoelectron spectroscopy containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer and being performed at a photoelectron extraction angle of 10 degrees on the magnetic layer side surface of the magnetic tape A magnetic tape having a C—H-derived C concentration calculated from a C—H peak area ratio in the spectrum of 45 atomic% or more;
I came to find. Although the above magnetic tape is a thin magnetic tape having a total thickness of 4.80 μm or less, it has good electromagnetic conversion characteristics even if it is repeatedly run in both low humidity and high humidity environments. It can be demonstrated. The inference by the present inventors regarding this point will be described later.

  In one embodiment, the C—H-derived C concentration is in the range of 45-80 atomic%.

  In one embodiment, the C—H-derived C concentration is in the range of 45 to 70 atomic%.

  In one aspect | mode, the said C-H origin C density | concentration is the range of 50-65 atomic%.

  In one embodiment, the magnetic layer and the nonmagnetic layer each contain one or more components selected from the group consisting of fatty acids and fatty acid amides.

  In one embodiment, one or both of the magnetic layer and the nonmagnetic layer further includes a fatty acid ester.

  In one embodiment, the magnetic tape has a backcoat layer on a nonmagnetic support opposite to the magnetic layer and the nonmagnetic layer.

  In one embodiment, the center line average surface roughness Ra measured by a non-contact surface shaper on the surface of the magnetic tape on the magnetic layer side is 1.8 nm or less.

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

A further aspect of the present invention is a method for producing the above magnetic tape,
Including a non-magnetic layer forming step and a magnetic layer forming step,
The nonmagnetic layer forming process
A coating step of forming a coating layer by coating a nonmagnetic layer-forming composition containing one or more components selected from the group consisting of fatty acids and fatty acid amides, a nonmagnetic powder, a binder and a solvent on a nonmagnetic support. ,
A heat drying step for drying the coating layer by heat treatment;
Including, and
A method for producing a magnetic tape, further comprising a cooling step for cooling the coating layer between the coating step and the heat drying step;
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 nonmagnetic layer includes a ketone solvent.

In one aspect, the magnetic layer forming step comprises
A coating step of forming a coating layer by coating a composition for forming a magnetic layer containing a ferromagnetic powder, a binder and a solvent on the nonmagnetic layer;
A heat drying step for drying the coating layer by heat treatment;
including.

  In one embodiment, the composition for forming a magnetic layer further includes one or more components selected from the group consisting of fatty acids and fatty acid amides.

  In one embodiment, a fatty acid ester is further included in one or both of the nonmagnetic layer forming composition and the magnetic layer forming composition.

  According to one aspect of the present invention, a magnetic tape that can contribute to an improvement in recording capacity because it is thinned to a total thickness of 4.80 μm or less, and is both a low humidity environment and a high humidity environment. Below, the magnetic tape by which the fall of the electromagnetic conversion characteristic in repeated driving | running | working was suppressed can be provided.

An example (process schematic diagram) of the specific aspect of a magnetic tape manufacturing process is shown.

  The magnetic tape of the present invention is a magnetic tape having a nonmagnetic layer containing a nonmagnetic powder and a binder on a nonmagnetic support, and a magnetic layer containing a ferromagnetic powder and a binder on the nonmagnetic layer. The total thickness of the magnetic tape is 4.80 μm or less, and at least one component selected from the group consisting of fatty acids and fatty acid amides is contained in at least the magnetic layer, and the photoelectron take-off angle is 10 on the magnetic layer side surface of the magnetic tape. The C—H-derived C concentration calculated from the C—H peak area ratio in the C1s spectrum obtained by X-ray photoelectron spectroscopy performed at a temperature of 45 ° C. is 45 atomic% or more.

X-ray photoelectron spectroscopy is an analysis method generally called ESCA (Electron Spectroscopy for Chemical Analysis) or XPS (X-ray Photoelectron Spectroscopy). Hereinafter, the X-ray photoelectron spectroscopic analysis is also referred to as ESCA. ESCA is an analysis method that utilizes the fact that photoelectrons are emitted when a sample surface to be measured is irradiated with X-rays, and is widely used as an analysis method for the surface layer portion of a sample to be measured. According to ESCA, qualitative analysis and quantitative analysis can be performed using an X-ray photoelectron spectrum obtained by analysis on the surface of a sample to be measured. Between the depth from the sample surface to the analysis position (hereinafter also referred to as “detection depth”) and the photo-electron take-off angle, the following equation is generally used: detection depth≈electron average The free stroke × 3 × sin θ is established. In the formula, the detection depth is a depth at which 95% of the photoelectrons constituting the X-ray photoelectron spectrum is generated, and θ is a photoelectron extraction angle. From the above formula, it can be seen that the smaller the photoelectron take-off angle is, the smaller the depth from the sample surface can be analyzed, and the greater the photoelectron take-out angle is, the deeper the portion can be analyzed. In the analysis by ESCA at a photoelectron take-off angle of 10 degrees, usually, a very surface layer portion having a depth of about several nm from the sample surface is an analysis position. Therefore, according to the ESCA analysis performed on the surface of the magnetic tape on the magnetic layer side with a photoelectron extraction angle of 10 degrees, it is possible to perform a composition analysis of a very surface layer portion about several nanometers deep from the surface of the magnetic layer.
On the other hand, the C—H-derived C concentration is the ratio of carbon atoms C constituting the C—H bond to the total (atomic basis) of 100 atoms% of all elements detected by qualitative analysis by ESCA. is there. The magnetic tape contains at least one component selected from the group consisting of fatty acids and fatty acid amides in at least the magnetic layer. Fatty acids and fatty acid amides are components that can each function as a lubricant in the magnetic tape. In a magnetic tape containing at least one of these components in the magnetic layer, the C—H-derived C concentration obtained by analysis by ESCA at a photoelectron take-off angle of 10 degrees is the above component (fatty acid and fatty acid amide) in the very surface layer of the magnetic layer. The present inventors consider that it is an indicator of the abundance of one or more components selected from the group consisting of: Details are as follows. In the X-ray photoelectron spectroscopy spectrum (horizontal axis: binding energy, vertical axis: intensity) obtained by ESCA analysis, the C1s spectrum includes information on the energy peak of the carbon atom C at the 1s orbital. In such a C1s spectrum, a peak located near the binding energy of 284.6 eV is a C—H peak. This C—H peak is a peak derived from the binding energy of the C—H bond of the organic compound. In the very surface layer portion of the magnetic layer containing one or more components selected from the group consisting of fatty acids and fatty acid amides, the present inventor believes that the main component of the CH peak is a component selected from the group consisting of fatty acids and fatty acid amides. Therefore, the present inventors believe that it can be used as an abundance index as described above.
In the following, the C—H-derived C concentration calculated from the C—H peak area ratio in the C1s spectrum obtained by the X-ray photoelectron spectroscopic analysis performed at the photoelectron extraction angle of 10 degrees is referred to as “surface layer C—H-derived C”. Also referred to as “concentration”.
And even if the total thickness of the magnetic tape having a surface layer portion C—H-derived C concentration of 45 atomic% or more is thinned to 4.80 μm or less, in both humidity environments of a low humidity environment and a high humidity environment, As a result of the study by the present inventors, it has been clarified that good electromagnetic conversion characteristics can be exhibited even when traveling is repeated. This is because a magnetic tape containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer and having a surface layer portion C—H-derived C concentration of 45 atomic% or more is present in the very surface layer portion of the magnetic layer. The present inventors consider that one or more components selected from the group consisting of fatty acids and fatty acid amides may be present in a larger amount than conventional magnetic tapes. On the other hand, for example, Patent Document 1 described above describes that a lubricant layer is formed on the surface of the magnetic layer by applying a lubricant to the surface of the magnetic layer (overcoat). According to these studies, the overcoated lubricant penetrates into the magnetic layer, or in the technique described in Patent Document 1, a magnetic tape having a surface layer portion C—H-derived C concentration of 45 atomic% or more is obtained. It was difficult.
Even though the above magnetic tape is a magnetic tape thinned to a total thickness of 4.80 μm or less, it is good even if the vehicle is repeatedly run in a low humidity environment and a high humidity environment. This is an inference by the present inventors about the reason why the electromagnetic conversion characteristics can be exhibited. However, the above is only an assumption and does not limit the present invention.

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

<Concentration of C derived from surface layer C—H>
The surface layer portion C—H-derived C concentration of the magnetic tape is 45 atomic% or more. From the viewpoint of further suppressing deterioration of electromagnetic conversion characteristics in repeated driving in both low humidity and high humidity environments, it is preferably 48 atomic% or more, and more preferably 50 atomic% or more. . According to the study by the present inventors, there was a tendency that the higher the surface layer portion C-H-derived C concentration, the better from the viewpoint of the deterioration of electromagnetic conversion characteristics in repeated running. Therefore, from this point, the upper limit of the surface layer portion C—H-derived C concentration is not limited. As an example, for example, the upper limit can be 95 atomic percent or less, 90 atomic percent or less, 85 atomic percent or less, 80 atomic percent or less, or 75 atomic percent or less. On the other hand, according to the study by the present inventors, the surface layer portion C—H-derived C concentration is preferably 70 atomic% or less from the viewpoint of obtaining a magnetic tape with high smoothness on the magnetic layer side surface. From this point, it is preferable that the C concentration derived from the surface layer portion C—H is 70 atomic% or less. More preferably, it is 65 atomic% or less.

As described above, the surface layer C—H-derived C concentration is a value determined by analysis by ESCA. The region to be analyzed is a 300 μm × 700 μm region at an arbitrary position on the magnetic layer side surface of the magnetic tape. Qualitative analysis is performed by wide scan measurement by ESCA (path energy: 160 eV, scan range: 0 to 1200 eV, energy resolution: 1 eV / step). Next, the spectra of all elements detected by qualitative analysis are obtained by narrow scan measurement (path energy: 10 eV, energy resolution: 0.1 eV, scan range: set for each element so that the whole spectrum to be measured is included). From the peak area in each spectrum thus obtained, the atomic concentration (unit: atomic%) of each element is calculated. Here, the atomic concentration of carbon atoms (C concentration) is also calculated from the peak area of the C1s spectrum.
Furthermore, a C1s spectrum is acquired (path energy: 10 eV, scan range: 276 to 296 eV, energy resolution: 0.1 eV / step). The obtained C1s spectrum is subjected to fitting processing by a nonlinear least square method using a Gauss-Lorentz composite function (Gauss component 70%, Lorentz component 30%), and the C—H bond peak in the C1s spectrum is separated into peaks. The ratio (peak area ratio) in the C1s spectrum of the -H peak is calculated. The C—H-derived C concentration is calculated by multiplying the calculated C—H peak area ratio by the above C concentration.
The arithmetic average of the values obtained by performing the above treatment three times at different positions on the magnetic layer side surface of the magnetic tape is defined as the surface layer C—H-derived C concentration. Moreover, the specific aspect of the above process is shown in the below-mentioned Example.

  As a preferable means for adjusting the surface layer portion C—H-derived C concentration described above to 45 atomic% or more, a cooling step can be performed in the nonmagnetic layer forming step as will be described in detail later. However, the magnetic tape of the present invention is not limited to one manufactured through such a cooling step.

<Fatty acid, fatty acid amide>
The magnetic tape contains at least one component selected from the group consisting of fatty acids and fatty acid amides in at least the magnetic layer. The magnetic layer may contain only one of fatty acid and fatty acid amide, or may contain both. As described above, the presence of a large amount of these components in the very surface layer of the magnetic layer means that the magnetic tape thinned to a total thickness of 4.80 μm or less in both low and high humidity environments. The present inventors consider that it contributes to suppressing the electromagnetic conversion characteristic fall in the repeated driving | running | working below. One or more components selected from the group consisting of fatty acids and fatty acid amides may be contained in the nonmagnetic layer.

Examples of fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenic acid, erucic acid, elaidic acid, and the like. Stearic acid, myristic acid, palmitic acid Is preferred, and stearic acid is more preferred. The fatty acid may be contained in the magnetic layer in the form of a salt such as a metal salt.
Examples of fatty acid amides include amides of various fatty acids such as lauric acid amide, myristic acid amide, palmitic acid amide, and stearic acid amide.
For fatty acids and fatty acid derivatives (amides and esters described below), the fatty acid-derived site of the fatty acid derivative preferably has the same or similar structure as the fatty acid used in combination. For example, as an example, when stearic acid is used as the fatty acid, it is preferable to use stearic acid amide or stearic acid ester.

  The amount of fatty acid is, for example, 0.1 to 10.0 parts by weight, preferably 1.0 to 7.0 parts by weight, per 100.0 parts by weight of ferromagnetic powder, as the content in the composition for forming a magnetic layer. is there. In addition, when adding 2 or more types of different fatty acid to the composition for magnetic layer formation, content shall mean those total content. In this specification, the same applies to the contents of other components unless otherwise specified.

  The fatty acid amide content in the composition for forming a magnetic layer is, for example, 0.1 to 3.0 parts by weight, preferably 0.1 to 1.0 parts by weight, per 100.0 parts by weight of the ferromagnetic powder. .

  On the other hand, the fatty acid content in the composition for forming a nonmagnetic layer is, for example, 1.0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. It is. The fatty acid amide content in the composition for forming a nonmagnetic layer is, for example, 0.1 to 3.0 parts by weight, preferably 0.1 to 1.0 parts by weight, per 100.0 parts by weight of the nonmagnetic powder. Part.

<Fatty acid ester>
One or both of the magnetic layer and the nonmagnetic layer whose details will be described later may or may not contain a fatty acid ester.
One cause of the deterioration of the electromagnetic conversion characteristics in repeated running is the above-described spacing loss caused by shavings on the magnetic layer side surface. The present inventors speculate that this is the main factor of the deterioration of the electromagnetic conversion characteristics in repeated running under a high humidity environment. On the other hand, the main cause of the deterioration of the electromagnetic conversion characteristics in repeated driving in a low-humidity environment is a decrease in the performance (head cleaning ability) of removing head deposits on the surface of the magnetic layer, although the reason is not clear in a low-humidity environment. The present inventors believe that this is to be done.
The present inventors speculate that a component selected from the group consisting of fatty acids and fatty acid amides contributes to suppressing the deterioration of electromagnetic conversion characteristics due to the above factors. On the other hand, although the fatty acid ester is a component that can function as a lubricant, the present inventors speculate that the deterioration of the electromagnetic conversion characteristics due to the above factors does not affect (or even slightly). Yes. Lubricants are generally roughly classified into fluid lubricants and boundary lubricants. Fatty acid esters are said to be components that can function as fluid lubricants, whereas fatty acid amides and fatty acids are said to be components that can function as boundary lubricants. The boundary lubricant is considered to be a lubricant that can reduce the contact friction by adsorbing to the surface of a powder (for example, ferromagnetic powder) to form a strong lubricant film. On the other hand, the fluid lubricant is considered to be a lubricant that itself forms a liquid film on the surface of the magnetic layer and can reduce friction by the flow of the liquid film. Thus, it is considered that the action as a lubricant is different from that of fatty acid and fatty acid amide, the reason why fatty acid ester is different from fatty acid and fatty acid amide on the influence on the deterioration of electromagnetic conversion characteristics due to the above factors, The present inventors are thinking. Since the fatty acid ester is generally said to be a lubricant that contributes to improving the running durability of the magnetic tape, the fatty acid ester is added to one or both of the magnetic layer and the non-magnetic layer, which will be described in detail later, for example to improve scratch resistance. Esters may be included.
Examples of fatty acid esters include esters of the above-mentioned various fatty acids, such as butyl myristate, butyl palmitate, butyl stearate (butyl stearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitan distearate, sorbitan tris. Examples include stearate, oleyl oleate, isocetyl stearate, isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate, butoxyethyl stearate, and the like.

The amount of the fatty acid ester is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the ferromagnetic powder, as the content in the composition for forming a magnetic layer. .
The fatty acid ester content in the composition for forming a nonmagnetic layer is, for example, 0 to 10.0 parts by mass, preferably 1.0 to 7.0 parts by mass, per 100.0 parts by mass of the nonmagnetic powder. is there.

  Next, the magnetic layer and nonmagnetic layer of the magnetic tape will be described in more detail.

<Magnetic layer>
(Ferromagnetic powder)
As the ferromagnetic powder, various powders that are usually used as a ferromagnetic powder in a magnetic layer of a magnetic tape can be used. It is preferable to use a ferromagnetic powder having a small average particle size from the viewpoint of improving the recording density of the magnetic tape. From this point, it is preferable to use a ferromagnetic powder having an average particle size of 50 nm or less as the ferromagnetic powder. On the other hand, from the viewpoint of magnetization stability, the average particle size of the ferromagnetic powder is preferably 10 nm or more.

The average particle size of the ferromagnetic powder 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. Measurement of the average particle size shown in Examples described later was performed 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. The average particle size (average plate diameter) of the ferromagnetic hexagonal ferrite powder is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 50 nm or less, from the viewpoint of high density recording and magnetization stability. . Details of the ferromagnetic hexagonal ferrite powder include, for example, paragraphs 0012 to 0030 of JP2011-225417A, paragraphs 0134 to 0136 of JP2011-216149A, paragraphs 0013 to 0030 of JP2012-204726A. You can refer to it.

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

(Binder, curing agent)
The magnetic tape of the present invention is a coating type magnetic tape, and a magnetic layer contains a binder together with a ferromagnetic powder. As binders, polyurethane resins, polyester resins, polyamide resins, vinyl chloride resins, acrylic resins copolymerized with styrene, acrylonitrile, methyl methacrylate, cellulose resins such as nitrocellulose, epoxy resins, phenoxy resins, A single resin or a mixture of a plurality of resins can be used from polyvinyl alkylal resins such as polyvinyl acetal and polyvinyl butyral. Among these, preferred are polyurethane resins, acrylic resins, cellulose resins, and vinyl chloride resins. These resins can also be used as a binder in the nonmagnetic layer described later. JP, 2010-24113, A paragraphs 0028-0031 can be referred to for the above binder. Moreover, a hardening | curing agent can also be used with resin which can be used as the said binder. A polyisocyanate is suitable as the curing agent. 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 the coating film strength. It can be added and used in parts.

(Additive)
Additives can be added to the magnetic layer as necessary. Examples of the additive include an abrasive, 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.

  By the way, it is desired to increase the smoothness of the magnetic layer side surface of a magnetic tape for high density recording such as a data backup tape. This is because the spacing loss can be reduced by increasing the smoothness of the surface on the magnetic layer side, and as a result, good electromagnetic conversion characteristics can be obtained during reproduction of signals recorded at high density. From the above viewpoint, the magnetic tape of the present invention also preferably has a high surface smoothness of the magnetic layer.

As an indicator of the surface smoothness of the magnetic layer side surface of the magnetic tape, in one aspect, the centerline average surface roughness Ra measured by a non-contact surface shape measuring device on the magnetic layer side surface of the magnetic tape can be used. . The centerline average surface roughness Ra measured by a non-contact surface shape measuring instrument is a centerline average surface measured in an area of 350 μm × 260 μm in area on the magnetic layer side of the magnetic tape using a 20 × objective lens. Roughness Ra shall be said. As the non-contact surface shape measuring instrument, for example, an optical three-dimensional roughness meter can be used. As an example of the measuring apparatus, a NEWVIEW (registered trademark) 5022 manufactured by Zygo, a non-contact optical roughness measuring machine can be used.
The centerline average surface roughness Ra measured on the surface of the magnetic layer of the magnetic tape by a non-contact surface shape measuring instrument is preferably 1.8 nm or less from the viewpoint of reducing the spacing loss, and is 1.7 nm or less. Is more preferably 1.6 nm or less, and further preferably 1.5 nm or less. From the viewpoint of running stability, the Ra is preferably 0.2 nm or more.

  As described above, the surface layer portion C—H-derived C concentration is preferably 70 atomic% or less, more preferably 65 atomic% or less, because the surface smoothness of the magnetic layer side surface of the magnetic tape From the viewpoint of increasing

  One means for improving the surface smoothness of the magnetic layer side surface of the magnetic tape is to increase the dispersibility of the abrasive in the magnetic layer. For this purpose, in the preparation of the composition for forming a magnetic layer, it is preferable to disperse the abrasive separately from the ferromagnetic powder, and to disperse separately from various granular or powdery components including the ferromagnetic powder. preferable.

  In addition, as one means for improving the surface smoothness of the magnetic layer side surface of the magnetic tape, use of a component (abrasive dispersant) for increasing the dispersibility of the abrasive is also mentioned. Examples of such components include aromatic hydrocarbon compounds having a phenolic hydroxyl group. A phenolic hydroxyl group refers to a hydroxyl group bonded directly to an aromatic ring.

  The aromatic ring contained in the aromatic hydrocarbon compound having a phenolic hydroxyl group may be a single ring, a polycyclic structure, or a condensed ring. From the viewpoint of improving the dispersibility of the abrasive, an aromatic hydrocarbon compound containing a benzene ring or a naphthalene ring is preferred. The aromatic hydrocarbon compound may have a substituent other than the phenolic hydroxyl group. Examples of the substituent other than the phenolic hydroxyl group include a halogen atom, an alkyl group, an alkoxy group, an amino group, an acyl group, a nitro group, a nitroso group, and a hydroxyalkyl group from the viewpoint of availability of the compound. be able to. As for compounds having substituents other than phenolic hydroxyl groups, compounds having substituents having electron donating properties with Hammett's substituent constant of 0.4 or less tend to be advantageous for the dispersibility of the abrasive. . In this respect, preferable substituents include those showing an electron donating property higher than that of a halogen atom, and more specifically, halogen atoms, alkyl groups, alkoxy groups, amino groups, and hydroxyalkyl groups.

The aromatic hydrocarbon compound may include one phenolic hydroxyl group, two, three, or more phenolic hydroxyl groups. When the aromatic ring which an aromatic hydrocarbon compound has is a naphthalene ring, it is preferable that two or more phenolic hydroxyl groups are included, and it is more preferable that two are included. As such a compound, a naphthalene ring-containing compound represented by the general formula (1) of JP2013-229090A can be exemplified. The details of the naphthalene ring-containing compound represented by the general formula (1) of JP2013-229090A can be referred to paragraphs 0028 to 0030 of the same publication. On the other hand, the aromatic hydrocarbon compound containing a benzene ring as an aromatic ring preferably contains one or more phenolic hydroxyl groups, and more preferably contains one or two. As such a compound, the benzene ring containing compound represented by General formula (2) of Unexamined-Japanese-Patent No. 2013-229090 can be mentioned. The details of the benzene ring-containing compound represented by the general formula (2) in JP2013-229090A can be referred to paragraphs 0032 to 0034 of the same publication.
The aromatic hydrocarbon compound which has a phenolic hydroxyl group can use 1 type (s) or 2 or more types. The amount used is preferably about 2.0 to 20.0 parts by mass with respect to 100.0 parts by mass of the abrasive.

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. Alumina is a preferred abrasive in that it can achieve particularly good dispersibility improvement in combination with the above aromatic hydrocarbon compound having a phenolic hydroxyl group. 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 surface, it is preferable to use an abrasive having a specific surface area (BET specific surface area) measured by the BET method of 14 m ² / g or more. From the viewpoint of dispersibility, it is preferable to use an abrasive having a BET specific surface area of 40 m ² / g or less. The content of the abrasive in the magnetic layer is preferably 1.0 to 20.0 parts by mass with respect to 100.0 parts by mass of the ferromagnetic powder.

  The magnetic layer can also contain a granular nonmagnetic substance (nonmagnetic particles). From the viewpoint of enhancing the surface smoothness of the magnetic layer side surface of the magnetic tape, the nonmagnetic particles are preferably colloidal particles (nonmagnetic colloidal particles). 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. JP, 2011-48878, A paragraph 0023 can be referred to for the details of nonmagnetic colloid particles. 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.

  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 of the present invention 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. The details can be referred to paragraphs 0146 to 0150 of JP2011-216149A. JP, 2010-24113, A paragraphs 0040-0041 can also be referred to about carbon black which can be used for a nonmagnetic layer.

  The fatty acid, fatty acid amide, and fatty acid ester that can be contained in the nonmagnetic layer are as described above. Further, the binder, additive, dispersion method, etc. of the nonmagnetic layer can be applied to those of the magnetic layer. In particular, with regard to the amount and type of the binder and the amount and type of the additive, known techniques relating to the magnetic layer can be applied.

The nonmagnetic layer can be formed by applying and drying a composition for forming a nonmagnetic layer on the nonmagnetic layer, as will be described in detail later. The composition for forming a nonmagnetic layer usually contains one or more solvents. 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 for a coating type magnetic recording medium, the composition for forming a nonmagnetic layer preferably contains one or more ketone solvents. The amount of solvent in the composition for forming a nonmagnetic layer is not particularly limited, and can be the same as that for the composition for forming a nonmagnetic layer of a normal 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 magnetic layer forming composition.

<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.

<Layer structure>
Regarding the thickness of the nonmagnetic support and each layer in the magnetic tape of the present invention, 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 amount of the magnetic head to be used, the head gap length, and the band of the recording signal, but is generally 0.01 μm to 0.15 μm (10 nm to 150 nm). From the viewpoint of recording density, it is preferably 0.02 μm to 0.12 μm (20 nm to 120 nm), more preferably 0.03 μm to 0.10 μm (30 nm to 100 nm). 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 1.50 μm, and preferably 0.10 to 1.00 μm. In addition, the nonmagnetic layer of the magnetic tape in the present invention 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.

<Back coat layer>
The magnetic tape of the present invention 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.

<Total thickness of magnetic tape>
Regarding magnetic tape, from the viewpoint of improving the recording capacity, it is desired to make the magnetic tape thinner in order to increase the recording capacity per magnetic tape cartridge. Since the total thickness of the magnetic tape of the present invention is 4.80 μm or less, it can be said to be a preferable magnetic tape from the viewpoint of improving the recording capacity. However, as described above, in a magnetic tape having a total thickness of 4.80 μm or less, a phenomenon was observed in which electromagnetic conversion characteristics deteriorated during repeated running in both low humidity and high humidity environments. The reason for this is that, as a result of the total thickness of the magnetic tape being reduced, the strength of the magnetic tape is reduced and the magnetic tape becomes flexible, so that the magnetic tape having a total thickness of more than 4.80 μm Although it is considered that the contact state between the tape surface and the head changes, it is only a guess and the reason is not clear. And according to the present invention, in this magnetic tape containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer, the surface layer portion C—H-derived C concentration is 45 atomic% or more. Can be solved. The total thickness of the magnetic tape can be, for example, 4.50 μm or less or 4.30 μm or less, but if it is 4.80 μm or less, the recording capacity can be sufficiently improved, so that it exceeds 4.50 μm. May be greater than 4.30 μm. On the other hand, the total thickness of the magnetic tape is preferably 1.0 μm or more from the viewpoint of easy handling (handling properties) of the magnetic tape.
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.

<Manufacturing process>
(Preparation of each layer forming composition)
The composition (coating liquid) for forming the magnetic layer, the nonmagnetic layer, or the backcoat layer usually contains a solvent together with the various components described above. As the solvent, various organic solvents generally used for producing a coating type magnetic tape can be used. The step of preparing 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, non-magnetic powder, fatty acid, fatty acid amide, binder, and various additives and solvents used in the present invention may be added at the beginning or middle of any step. Absent. In addition, individual raw materials may be added in two or more steps. In preparing the composition for forming a magnetic layer, it is preferable to separately disperse the abrasive and the ferromagnetic powder as described above. 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 and packing rate of these dispersed beads can be optimized and used. A well-known thing can be used for a disperser.

(Coating process, cooling process, heat drying process)
The magnetic layer can be formed by applying the magnetic layer forming composition in layers or sequentially with the nonmagnetic layer forming composition. JP, 2010-231843, A paragraph 0066 can be referred to for the details of application for formation of each layer.

  In a preferred embodiment, the magnetic tape of the present invention 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.

  In such a production method by sequential multilayer coating, the nonmagnetic layer forming step is performed using a nonmagnetic layer forming composition containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the coating step, and the coating step. Performing a cooling step for cooling the coating layer between the heating and drying step in the magnetic tape containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer at the surface layer portion CH This is preferable for adjusting the derived C concentration to 45 atomic% or more. The reason for this is not clear, but by cooling the coating layer of the composition for forming a nonmagnetic layer before the heat drying step, the above components (fatty acid, fatty acid amide) are nonmagnetic layer during solvent evaporation in the heat drying step. The present inventors speculate that it may be easy to migrate to the surface. However, this is merely a guess and does not limit the present invention.

That is, one aspect of the present invention is a method for producing a magnetic tape of the present invention,
Including a non-magnetic layer forming step and a magnetic layer forming step,
The nonmagnetic layer forming process
A coating step of forming a coating layer by coating a nonmagnetic layer-forming composition containing one or more components selected from the group consisting of fatty acids and fatty acid amides, a nonmagnetic powder, a binder and a solvent on a nonmagnetic support. ,
A heat drying process for drying the coating layer by heat treatment;
Including, and
A method for producing a magnetic tape, further comprising a cooling step for cooling the coating layer between the coating step and the heat drying step;
About.

  In the magnetic layer forming step, a coating layer is formed by applying a magnetic layer forming composition containing a ferromagnetic powder, a binder, and a solvent on the nonmagnetic layer. A heat drying step of drying by heat treatment can be performed. The magnetic tape of the present invention contains at least one component selected from the group consisting of fatty acids and fatty acid amides in at least the magnetic layer. In order to produce such a magnetic tape, the composition for forming a magnetic layer preferably contains one or more components selected from the group consisting of fatty acids and fatty acid amides. However, it is not essential that the magnetic layer forming composition contains one or more components selected from the group consisting of fatty acids and fatty acid amides. After these components contained in the composition for forming a nonmagnetic layer have migrated to the surface of the nonmagnetic layer, the composition for forming a magnetic layer is applied onto the nonmagnetic layer to form a magnetic layer. This is because it is considered that a magnetic layer containing at least one component selected from the group consisting of fatty acid amides can be formed.

  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. 1 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. 1, the operation of continuously winding the nonmagnetic support (long film) from the sending-out part at the sending-out winding part is performed, and coating is performed in each part or each zone shown in FIG. 1. 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 the point including the cooling zone, it can be the same as the manufacturing process normally performed for manufacturing the 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, the coating layer of the nonmagnetic 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 on which the coating layer is formed in 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 surface layer portion C—H-derived C concentration tends to increase as the length increases, adjustment is performed by performing preliminary experiments as necessary so that a surface layer portion C—H-derived C concentration of 45 atomic% or more can be realized. In the cooling step, the cooled gas may be sprayed onto the surface of the coating layer.

  After the cooling zone, in the first heat treatment zone, the coating layer after the cooling 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 after the cooling step into 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).

  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. JP, 2010-231843, A paragraph 0067 can be referred to for orientation processing.

  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.

  As described above, a magnetic tape having a nonmagnetic layer and a magnetic layer in this order on one surface of the nonmagnetic support and a backcoat layer on the other surface can be obtained. The obtained magnetic tape may be optionally subjected to various post-treatments (various surface treatments such as calendar treatment) after being wound on the take-up portion. For these post-treatments, known techniques relating to the production of coating-type magnetic recording media can be applied without any limitation. In addition, for a cutting step that is usually performed after arbitrarily performing various post-treatments, reference can be made to, for example, paragraph 0069 of JP2010-231843A.

  The magnetic tape of the present invention described above is suitable as a magnetic tape used in both low humidity and high humidity environments.

  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%".

The weight average molecular weight described below is a value in terms of polystyrene measured by gel permeation chromatography (GPC) under the following measurement conditions.
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)

[Examples 1-14, Comparative Examples 1-13]
1. Preparation of Alumina Dispersion 3.0 parts of 2,3-dihydroxynaphthalene (100.0 parts of alumina powder (HIT-80 manufactured by Sumitomo Chemical Co., Ltd.)) having an alpha conversion rate of about 65% and a BET specific surface area of 20 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 100.0 parts Ferromagnetic hexagonal barium ferrite powder or ferromagnetic metal powder (see Table 5)
SO ₃ Na group-containing polyurethane resin 14.0 parts Weight average molecular weight: 70,000, SO ₃ Na group: 0.2 meq / g
Cyclohexanone 150.0 parts Methyl ethyl ketone 150.0 parts (Abrasive liquid)
Above 1. 6.0 parts (silica sol) of alumina dispersion prepared in
Colloidal silica (average particle size 120 nm) 2.0 parts methyl ethyl ketone 1.4 parts (other ingredients)
Stearic acid See Table 5 Stearic acid amide See Table 5 Butyl stearate See Table 5 Polyisocyanate (Coronate (registered trademark) manufactured by Nippon Polyurethane) 2.5 parts (finishing addition solvent)
Cyclohexanone 200.0 parts Methyl ethyl ketone 200.0 parts

  In Table 5, BaFe is a ferromagnetic hexagonal barium ferrite powder having an average particle size (average plate diameter) of 21 nm, and MP is a ferromagnetic metal powder having an average particle size (average major axis length) of 30 nm.

3. Nonmagnetic layer forming composition formulation Nonmagnetic inorganic powder: α-iron oxide 100.0 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: 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 See Table 5 Stearate amide See Table 5 Butyl stearate See Table 5 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 Polyisocyanate 5.0 parts Cyclohexanone 200.0 parts

5). Preparation of Composition for Forming Each Layer A composition for forming a magnetic layer 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 dispersion beads, 0.5 mmφ zirconia beads 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 prepared the composition for magnetic layer formation.
A composition for forming a nonmagnetic layer was prepared 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 dispersion beads, 0.5 mmφ zirconia beads 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 prepared by the following method. After kneading and diluting each component except polyisocyanate and cyclohexanone with an open kneader, using a horizontal bead mill disperser, using 1 mmΦ zirconia beads, beads filling rate 80%, rotor tip peripheral speed 10 m / sec. The time was 2 minutes and 12-pass distributed processing was performed. Thereafter, the remaining components were added to the obtained dispersion and stirred with a dissolver. The dispersion thus obtained was filtered using a filter having an average pore size of 1 μm to prepare a composition for forming a backcoat layer.

6). 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 5 is fed out from the feed-out part, and on the one surface, the thickness after drying in the first application part becomes the thickness shown in Table 5 above. The coating layer was formed by applying the nonmagnetic layer-forming composition prepared in (1). 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. for the residence time shown in Table 5 to perform a cooling step, and then a first heat treatment zone having an atmospheric temperature of 100 ° C. A non-magnetic layer was formed by passing through a heat drying process.
Then, said 5. so that the thickness after drying may become the thickness shown in Table 5 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 coating layer was in a wet state (undried state), a magnetic field having a magnetic field strength of 0.3 T was applied in the orientation zone in a direction perpendicular to the surface of the coating layer of the composition for forming a magnetic layer to perform a vertical orientation treatment. Then, it was dried in the second heat treatment zone (atmosphere temperature 100 ° C.).
Thereafter, in the third coating part, the above-mentioned 5. so that the thickness after drying on the surface opposite to the surface on which the nonmagnetic layer and magnetic layer of the support made of polyethylene naphthalate are formed becomes the thickness shown in Table 5. The composition for backcoat layer formation prepared in (1) was applied to the surface of the nonmagnetic support to form a coating layer, and the formed coating layer was dried in a third heat treatment zone (atmospheric temperature 100 ° C.).
Thereafter, a calendar composed only of a metal roll was subjected to a calendar process (surface smoothing process) at a speed of 80 m / min, a linear pressure of 300 kg / cm, and a temperature of 100 ° C., followed by a heat treatment for 36 hours in an environment at an ambient temperature of 70 ° C. Went. After the heat treatment, it was slit to a width of 1/2 inch (0.0127 meter) to obtain a magnetic tape.
In Table 5, in Comparative Examples 1 and 4 to 13 where “not implemented” is described in the column of the cooling zone residence time, a magnetic tape was manufactured by a manufacturing process not including a cooling zone.
Furthermore, in Comparative Example 13, after the calendar treatment, the magnetic layer surface was subjected to corona treatment by the following method, and then stearic acid was overcoated.
The magnetic layer surface was subjected to corona treatment by the method described in paragraph 0138 of JP-A-2008-243317 (Patent Document 1). Next, a 10% methyl ethyl ketone solution of stearic acid was applied to the surface of the magnetic layer subjected to corona treatment with a wire bar and dried, and then the above heat treatment and slitting were performed.

The thickness and total thickness of each layer and nonmagnetic support of the produced magnetic tape were determined by the following method. It was confirmed that each thickness is the thickness shown in Table 5.
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.

[Evaluation method]
1. Surface layer part C-H origin C density | concentration By the following method, X-ray photoelectron spectroscopy analysis was performed using the ESCA apparatus in the magnetic layer side surface (measurement area: 300 micrometers x 700 micrometers) of the magnetic tape of an Example and a comparative example, and an analysis result From the surface area, the C-H-derived C concentration was calculated. Table 5 shows the calculated values.

(Analysis and calculation method)
The following measurements (1) to (3) were performed under the measurement conditions shown in Table 1.

(1) Wide scan measurement Wide scan measurement (measurement conditions: see Table 2) was performed on the magnetic layer side surface of the magnetic tape by using an ESCA apparatus, and the types of detected elements were examined (qualitative analysis).

(2) Narrow scan measurement Narrow scan measurement (measurement conditions: see Table 3) was performed for all the elements detected in (1) above. The atomic concentration (unit: atomic%) of each element detected from the peak area of each element was calculated using data processing software (Vision 2.2.6) attached to the apparatus. Here, the C concentration was also calculated.

(3) Acquisition of C1s spectrum A C1s spectrum was acquired under the measurement conditions described in Table 4. The acquired C1s spectrum is corrected for shift (physical shift) due to sample charging using the data processing software (Vision 2.2.6) attached to the apparatus, and then the C1s spectrum is fitted using the software. (Peak separation) was performed. For the peak separation, a Gauss-Lorentz compound function (Gauss component 70%, Lorentz component 30%) is used, C1s spectrum fitting is performed by nonlinear least square method, and the proportion of C—H peaks in the C1s spectrum (peak area ratio) Was calculated. The C—H-derived C concentration was calculated by multiplying the calculated C—H peak area ratio by the C concentration obtained in (2) above.

  The arithmetic average of the values obtained by performing the above treatment three times at different positions on the magnetic layer side surface of the magnetic tape was defined as the surface layer portion CH-derived C concentration. Table 5 shows the calculated values.

2. Confirmation of contribution of fatty acid and fatty acid amide to C concentration derived from surface layer C—H (1) Two magnetic tapes (sample tapes) were produced in the same manner as in Example 1. One sample tape was subjected to solvent extraction after measurement by the ESCA apparatus, and the other sample tape was subjected to solvent extraction in an unmeasured state (solvent: methanol).
When the amount of fatty acid, fatty acid amide and fatty acid ester in the solution obtained by extraction was quantified by gas chromatographic analysis, the difference in the quantitative value between fatty acid (stearic acid) and fatty acid amide (stearic acid amide) between the two sample tapes It was hardly seen. On the other hand, the fatty acid ester (butyl stearate) had a significantly lower quantitative value on the sample tape after measurement than on the unmeasured sample tape. This is presumably because the fatty acid ester volatilizes in the vacuum chamber in which the sample to be measured is placed during measurement in the ESCA apparatus.
From the above results, it can be determined that the fatty acid ester has no effect on the surface layer C—H-derived C concentration obtained by analysis by ESCA.
(2) Among the components contained in the magnetic layer forming composition and the components contained in the nonmagnetic layer forming composition that may be transferred from the nonmagnetic layer to the magnetic layer in the magnetic tape, Organic compounds excluding polyisocyanate (cross-linking with other components by treatment with heating) are stearic acid, stearamide, butyl stearate, 2,3-dihydroxynaphthalene, and polyurethane resin. Among these components, it can be determined that butyl stearate does not affect the surface layer portion C—H-derived C concentration from the result of (1) as described above.
Next, the influence of 2,3-dihydroxynaphthalene and polyurethane resin on the surface layer portion C—H-derived C concentration was confirmed by the following method.
For the 2,3-dihydroxynaphthalene and polyurethane resin used in Example 1, a C1s spectrum was obtained by the same method as described above, and a peak located near the binding energy of 286 eV by the treatment described above for the obtained spectrum and C- Each H peak was separated. The ratio of each separated peak to the C1s spectrum (peak area ratio) was calculated, and the peak area ratio between the peak located near the binding energy of 286 eV and the C—H peak was calculated.
Next, in the C1s spectrum obtained in Example 1, a peak located near the binding energy of 286 eV was separated by the above-described treatment. In the C1s spectrum, 2,3-dihydroxynaphthalene and polyurethane resin have a peak located near the binding energy of 286 eV, whereas fatty acid (stearic acid) and fatty acid amide (stearic amide) have a peak at the above position. No. Therefore, it can be determined that the peak located near the binding energy of 286 eV in the C1s spectrum obtained in Example 1 is derived from 2,3-dihydroxynaphthalene and polyurethane resin. Therefore, using this peak, the contribution of 2,3-dihydroxynaphthalene and polyurethane resin in the C—H peak of the C1s spectrum obtained in Example 1 was calculated from the peak area ratio calculated above, and only 10% was calculated. It was about. From this result, it can be judged that many (about 90%) of C—H peaks in the C1s spectrum obtained in Example 1 are derived from fatty acid (stearic acid) and fatty acid amide (stearic acid amide).
From the above results, it was demonstrated that the C concentration derived from the surface layer C—H can be an indicator of the abundance of fatty acids and fatty acid amides.

3. Calculation of decrease in S / N ratio due to repeated driving in low and high humidity environment Under low humidity environment (temperature and humidity controlled to 15% relative humidity 15%) and high humidity environment ((temperature In an atmosphere in which the temperature and humidity are controlled at 32 ° C. and a relative humidity of 80%, respectively, using a 1/2 inch (0.0127 meter) reel tester with a head fixed by the following method, before and after running Recording and reproduction were performed for each of the above, and electromagnetic conversion characteristics (S / N ratio (Signal-to-Noise-Ratio)) were measured.
The measurement of electromagnetic conversion characteristics was performed by the method described below. The conveyance speed (head / tape relative speed) is set to 5.5 m / sec, recording uses a MIG (Metal-In-Gap) head (gap length 0.15 μm, track width 1.0 μm), and the recording current of each tape The optimum recording current was set. A GMR (Giant-Magnetoresistive) head having an element thickness of 15 nm, a shield interval of 0.1 μm, and a lead width of 0.5 μm was used as the reproducing head. A signal having a linear recording density of 270 KFci was recorded, and the reproduced signal was measured with a spectrum analyzer manufactured by Shiba-Sok Co., Ltd., and the ratio of the carrier signal output to the integrated noise of the entire spectrum band was defined as the S / N ratio. For the signal, a portion where the signal was sufficiently stable after the start of running of the magnetic tape was used.
Traveling was performed by using the reel tester with a conveyance speed (head / tape relative speed) of 6.0 m / sec and reciprocating the magnetic tape at 5,000 passes at 1,000 m per pass.
Before and after traveling, the electromagnetic conversion characteristics are measured by the above method to determine the S / N ratio, and the S / N ratio before traveling and the S / N ratio after traveling (after 5000 round trips) are respectively determined. Table 5 shows the difference “(S / N ratio before traveling) − (S / N ratio after traveling)” obtained as the S / N ratio decrease. If the S / N ratio decrease is 2.0 dB or less, it can be determined that the magnetic tape can exhibit excellent electromagnetic conversion characteristics over a long period of time with little decrease in electromagnetic conversion characteristics due to repeated running in the above environment. it can.

4). AlFeSil wear width 3. AlFeSil so that the surface of the magnetic layer of the magnetic tape is orthogonal to the longitudinal direction of the AlFeSil prism (a prism defined in ECMA-288 / AnnexH / H2) in a low and high humidity environment similar to One ridge side (edge) of the prism was brought into contact at a wrap angle of 12 degrees, and in this state, the magnetic tape having a length of 580 m was reciprocated 50 times at a speed of 3 m / sec under a tension of 1.0 N.
The edge of the prism was observed from above using an optical microscope, and the wear width (AlFeSil wear width) described in JP-A-2007-026564, paragraph 0015, based on FIG. 1 was measured. Table 5 shows the measurement results. If the wear width thus obtained is 15 μm or more, it can be determined that the head cleaning ability of the magnetic layer side surface of the magnetic tape is good, and if it is 53 μm or less, the surface of the magnetic layer side surface that causes spacing loss. It can be determined that there is little generation of shavings.
From the results shown in Table 5, the magnetic tapes of Examples 1 to 14 have good head cleaning performance and generation of scraped material on the surface of the magnetic layer in both low humidity and high humidity environments. It can be judged that there are few.
Further, for the magnetic tapes of Examples 1 to 14, when the AlFeSil wear width was measured in the same manner even in an atmosphere in which the temperature and humidity were controlled at a temperature of 32 ° C. and a relative humidity of 50%, it was in the range of 32 to 37 μm.
From the above results, it is determined that the magnetic tapes of Examples 1 to 14 have a good head cleaning performance and a small amount of scraped material on the magnetic layer side surface under a wide range of humidity from low humidity to high humidity. Can do.

5). Centerline average surface roughness Ra measured by a non-contact surface shape measuring device on the magnetic layer side surface
The center line average surface roughness Ra of the magnetic layer side surface was measured by the method described above using a non-contact optical roughness measuring machine Zygo NewView 5022. Table 5 shows the measurement results.

From the results shown in Table 5, the following points can be confirmed.
(1) In the magnetic tapes of Comparative Examples 1 to 6 having a total thickness of more than 4.80 μm, the surface layer portion C—H-derived C concentration may be 45 atomic% or more or less than 45 atomic% in a low humidity environment. In any of the high humidity environments, the S / N ratio decrease due to repeated running is small. That is, there is no correlation between the C concentration derived from the surface layer C—H and the S / N ratio decrease due to repeated running in the above environment.
(2) On the other hand, from the comparison between Examples 1 to 14 and Comparative Examples 7 to 13, in the magnetic tape having a total thickness of 4.80 μm or less, the surface layer portion C—H-derived C concentration is 45 atomic% or more. It can be confirmed that it is possible to suppress a decrease in the S / N ratio due to repeated running in a low-humidity environment and a high-humidity environment.

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

Claims (15)

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 tape is 4.80 μm or less,
Obtained by X-ray photoelectron spectroscopic analysis containing at least one component selected from the group consisting of fatty acids and fatty acid amides in the magnetic layer and performed at a photoelectron extraction angle of 10 degrees on the surface of the magnetic tape on the magnetic layer side. A magnetic tape having a C—H-derived C concentration calculated from a C—H peak area ratio in a C1s spectrum of 45 atomic% or more. The magnetic tape according to claim 1, wherein the C—H-derived C concentration is in the range of 45 to 80 atomic%. The magnetic tape according to claim 1, wherein the C—H-derived C concentration is in the range of 45 to 70 atomic%. The magnetic tape according to claim 1, wherein the C—H-derived C concentration is in the range of 50 to 65 atomic%. The magnetic tape according to any one of claims 1 to 4, wherein the magnetic layer and the nonmagnetic layer each contain one or more components selected from the group consisting of fatty acids and fatty acid amides. The magnetic tape according to claim 1, further comprising a fatty acid ester in one or both of the magnetic layer and the nonmagnetic layer. The magnetic tape according to claim 1, further comprising a backcoat layer on a nonmagnetic support opposite to the magnetic layer and the nonmagnetic layer. The magnetic tape according to any one of claims 1 to 7, wherein a centerline average surface roughness Ra measured by a non-contact surface shaper on the surface of the magnetic layer on the magnetic layer side is 1.8 nm or less. . The magnetic tape according to any one of claims 1 to 8, wherein the ferromagnetic powder is a ferromagnetic powder selected from the group consisting of a ferromagnetic hexagonal ferrite powder and a ferromagnetic metal powder. A method for producing a magnetic tape according to any one of claims 1 to 9,
Including a non-magnetic layer forming step and a magnetic layer forming step,
The nonmagnetic layer forming step includes:
A coating step of forming a coating layer by coating a nonmagnetic layer-forming composition containing one or more components selected from the group consisting of fatty acids and fatty acid amides, a nonmagnetic powder, a binder and a solvent on a nonmagnetic support. ,
A heat drying step of drying the coating layer by heat treatment;
Including, and
The method for manufacturing the magnetic tape, further comprising a cooling step for cooling the coating layer between the coating step and the heat drying step. The method for producing a magnetic tape according to claim 10, 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 10 or 11, wherein the solvent contained in the composition for forming a nonmagnetic layer contains a ketone solvent. The magnetic layer forming step includes
A coating step of forming a coating layer by coating a composition for forming a magnetic layer containing a ferromagnetic powder, a binder and a solvent on the nonmagnetic layer;
A heat drying step of drying the coating layer by heat treatment;
The manufacturing method of the magnetic tape of any one of Claims 10-12 containing this. The method for producing a magnetic tape according to claim 13, wherein the composition for forming a magnetic layer further comprises one or more components selected from the group consisting of fatty acids and fatty acid amides. The method for producing a magnetic tape according to claim 13 or 14, further comprising a fatty acid ester in one or both of the composition for forming a nonmagnetic layer and the composition for forming a magnetic layer.