JP5932888B2 - Magnetic tape - Google Patents

Description

  The present invention relates to a coating type magnetic tape. In particular, the present invention relates to a magnetic tape suitable for a linear serpentine magnetic recording / reproducing system.

  In general, a magnetic tape, which is a coating type magnetic recording medium, is coated with a magnetic coating material in which a magnetic powder, a binder, and optionally other additives are dispersed in a solvent, and dried on one surface of a nonmagnetic support. A magnetic layer is formed, and a backcoat layer paint in which a pigment such as carbon black, a binder, and other additives as necessary is dispersed in a solvent is applied on the other surface of the nonmagnetic support and dried. A back coat layer is formed, and the resulting wide magnetic material is cut into a predetermined width in a cutting step.

  By the way, recording / reproducing systems using a magnetic tape are roughly classified into a helical scan system using a rotating magnetic head and a linear serpentine system using a fixed magnetic head. Although each method has its advantages, the contact condition between the magnetic head and the magnetic tape is gentle, and the volume restriction of the magnetic tape cartridge is small. The linear serpentine method is widely used. For example, products such as DLT (Digital Linear Tape) and LTO (Linear Tape-Open) have been developed in the market.

  In the magnetic tape for backup as described above, since the capacity of the hard disk is increasing year by year, it is indispensable to increase the capacity of the magnetic tape in order to cope with this. In order to increase the capacity of a magnetic tape, it is necessary to increase the recording area, that is, to make the entire magnetic tape thinner and to increase the length of the magnetic tape per roll. Of these, the structure occupying the largest proportion is a non-magnetic support, and therefore it is effective to reduce the thickness to reduce the thickness. Therefore, in the above DLT and LTO, a polyethylene terephthalate (PET) film and a polyethylene naphthalate (PEN) film having a thickness of 5 to 6 μm and high strength in the longitudinal direction are used as the nonmagnetic support. From the viewpoint of increasing the capacity, it is necessary to study the use of a non-magnetic support having a thickness of 4 μm or less, and for example, a backup tape using a non-magnetic support having a thickness of 2 to 3 μm has been proposed (patent) Reference 1).

  However, in the linear serpentine magnetic recording / reproducing system as described above, a plurality of tracks are generally formed on the magnetic layer in the longitudinal direction. When recording and reproducing signals on a magnetic tape, The magnetic head moves across the track from end to end in the width direction of one track. Therefore, in order to prevent the off-track of the magnetic head, it is necessary to ensure the straight running performance of the magnetic tape that runs at high speed. Therefore, in the magnetic recording / reproducing system, there is a gap between the magnetic tape cartridge and the take-up reel. A plurality of guide rollers having flange portions are provided. For this reason, there is a case where the cut surface of the magnetic tape and the flange portion are in sliding contact with each other during traveling. However, since the bending rigidity of the magnetic tape decreases in proportion to the cube of the thickness, the magnetic force generated by making the nonmagnetic support thinner is reduced. A reduction in tape strength cannot be avoided. As a result, when the cut surface of the magnetic tape and the flange portion are in sliding contact with each other during running, the magnetic tape is easily deformed, and it is difficult to ensure straight running performance when passing through the guide roller. In addition, as the non-magnetic support is made thinner, the cutting property of the magnetic raw material deteriorates, so that there is a problem that the smoothness of the cut surface tends to be lowered. For this reason, when the magnetic tape is run in the magnetic recording / reproducing system as described above, a part of the cut surface easily comes into contact with the flange portion, the magnetic layer and the back coat layer are damaged, and the powder falls off. Is likely to occur.

  For magnetic tapes used in low-speed helical scan magnetic recording and playback systems, the magnetic material is cut with laser light, and the cut surface of the magnetic layer or backcoat layer is retracted inward from the cut surface of the nonmagnetic support. Although it has been proposed that the powder fall off from the magnetic layer and the back coat layer can be reduced (Patent Document 2), a magnetic tape using a thin non-magnetic support can be used at high speed with a linear serpentine magnetic recording / reproducing system. In the case of running, there is a problem in that powder formation on the guide roller cannot be sufficiently improved by simply forming such a cut surface, and straight running performance is not improved.

Japanese Patent Laid-Open No. 10-134337

Japanese Patent Publication No.7-114012

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to record / reproduce a magnetic tape having a thinner nonmagnetic support than conventional ones using a linear serpentine magnetic recording / reproducing system. Another object of the present invention is to provide a magnetic tape that is excellent in straight running performance during high-speed running with a guide roller having a flange portion and that has less powder falling.

The present invention is a magnetic tape having a magnetic layer containing a magnetic powder and a binder on one surface of a nonmagnetic support having a thickness of 4 μm or less and used in a linear serpentine magnetic recording / reproducing system. And
The Young's modulus in the width direction of the nonmagnetic support is 8 to 20 GPa, and the Young's modulus in the longitudinal direction is 9 to 22 GPa.
The center line average roughness (Ra) in the roughness curve of the cut surface of the magnetic tape is 0.08 to 0.25 μm.

  According to the magnetic tape, even when this magnetic tape is recorded / reproduced with a linear serpentine magnetic recording / reproducing system, the friction coefficient between the flange portion of the guide roller and the magnetic tape cut surface is small during high-speed running, and Since the one-piece contact is suppressed, powder falling can be reduced while ensuring straight running performance.

Preferably, the centerline average roughness (Ra) in the roughness curve of the cut surface of the magnetic tape is 0.09 to 0.12 μm.

An undercoat layer containing an inorganic powder and a binder may be provided between the nonmagnetic support and the magnetic layer.

  As described above, according to the present invention, even when a magnetic tape using a thin non-magnetic support for large capacity is applied to a linear serpentine magnetic recording / reproducing system, the straight running performance of the guide roller is improved. In addition, it is possible to reduce powder falling due to sliding contact with the guide roller.

It is the schematic which shows an example of the tape running system in the magnetic recording / reproducing system of the linear serpentine system in which the magnetic tape of this Embodiment is used. It is the elements on larger scale which show the sliding contact state of the guide roller and magnetic tape in the tape running system of FIG. It is the schematic which shows the cutting device for manufacturing the magnetic tape of this Embodiment. It is the schematic of the cutting means of FIG. 3, and the principal part expanded sectional view.

  FIG. 1 is a schematic diagram showing an example of a tape running system in a linear serpentine magnetic recording / reproducing system in which the magnetic tape of this embodiment is used. As shown in FIG. 1, the magnetic tape cartridge 1 is a single reel type cartridge in which a magnetic tape 3 is wound around a single tape reel 2. In this magnetic recording / reproducing system, when the magnetic tape cartridge 1 is inserted into the cassette compartment 5 of the magnetic recording / reproducing system, the opening / closing door 4 provided on the front side of the magnetic tape cartridge 1 is opened, and the opened opening / closing door is opened. 4, the magnetic tape 3 is pulled out by a tape pulling means in the system. The drawn magnetic tape 3 is guided by a plurality of guide rollers 6 having flange portions on the upper and lower sides and wound around a take-up reel 7.

  FIG. 2 is a schematic sectional view showing a sliding contact state between the magnetic tape 3 and the guide roller 6 in the tape running system of FIG. 1, and in this magnetic recording / reproducing system, a magnetic layer 3a of a nonmagnetic support 3b is provided. The back coat layer 3 c on the opposite side of the surface is in contact with the hub surface of the guide roller 6. When the magnetic tape 3 is run at a high speed in such a magnetic recording / reproducing system, the cut surface S of the magnetic tape 3 may come into sliding contact with the upper and lower flange portions 6a due to the vertical movement of the magnetic tape 3. For this reason, the magnetic tape 3 using the thin non-magnetic support 3b is liable to fall off from the magnetic tape 3 during sliding contact, and is liable to be deformed, so that the straight running performance is likely to be reduced. In the linear serpentine magnetic recording / reproducing system, such a problem becomes serious because a large number of guide rollers 6 are used in order to ensure straight running of the magnetic tape 3.

  One of the reasons that powder falling easily occurs with a magnetic tape using a thin non-magnetic support is considered to be because the smoothness of the cut surface is lowered during cutting. That is, when cutting the magnetic material, the rigidity of the magnetic material decreases as the non-magnetic support becomes thinner, so that the magnetic material tends to fluctuate and the cut surface is likely to be rough. For this reason, it is considered that the protruding portion of the cut surface of the magnetic tape comes into contact with the flange portion, and stress concentrates on the protruding portion, so that powder falling easily occurs. On the other hand, by smoothing the cut surface, stress concentration at the protruding portion as described above can be avoided, but as a result of increasing the contact area between the cut surface and the flange portion, the friction increases. As a result, when a thin non-magnetic support that is easily deformed by sliding contact is used, it is difficult to ensure straight traveling performance during high-speed traveling.

  Under the circumstances as described above, the present inventors have examined a cut surface that can achieve both powder falling when the magnetic tape is in sliding contact with the flange portion and straight running performance at the flange portion. If the center line average roughness (Ra) on the curve is in the range of 0.08 to 0.25 μm, the cut surface of the magnetic tape can be obtained even when a magnetic tape using a thin nonmagnetic support of 4 μm or less is run at high speed. It was found that the sliding contact with the flange portion is good, powder falling can be reduced, and straight running performance can be secured. According to the study by the present inventors, when the center line average roughness (Ra) is less than 0.08 μm, the smoothness of the cut surface is excellent, but the coefficient of friction between the cut surface and the flange portion is increased, and is easily deformed. With a magnetic tape having a thin nonmagnetic support, it is difficult to ensure straight running performance. On the other hand, if the center line average roughness (Ra) is larger than 0.25 μm, the friction coefficient between the cut surface and the flange portion decreases, but local stress concentration occurs at the protruding portion, and powder fall tends to increase. . By restricting the roughness of the cut surface of such a magnetic tape, when a magnetic tape having a thin non-magnetic support is run in a linear serpentine magnetic recording / reproducing system, the straight running performance and powder fall are reduced. There has been no example of studying compatibility. The centerline average roughness (Ra) in the roughness curve of the cut surface is a value obtained when the cut surface of the magnetic tape is measured with a laser microscope.

  Next, a preferred method for producing a magnetic tape having the above-described cut surface will be specifically described.

  FIG. 3 is a schematic view showing an example of a cutting apparatus for manufacturing the magnetic tape of the present embodiment. FIG. 4 is a front view showing the structure of the cutting means in FIG. It is.

  As shown in FIG. 3, this cutting apparatus includes a cutting means 10 for cutting the magnetic raw fabric M into a predetermined width, an unwinding roll 21 around which the magnetic original fabric M is wound, and a cutting means from the unwinding roll 21. The unwinding part 20 which consists of many conveyance rollers 22 which convey the magnetic raw material M to 10, the winding roll 31 which winds up the magnetic tape 3, and the magnetic tape 3 cut | judged from the cutting means 10 to the winding roll 31 And a winding unit 30 including a large number of conveying rollers 32 to be conveyed. The winding unit 30 can be installed corresponding to the number of magnetic tapes 3 cut from the magnetic material M.

  As shown in FIG. 4, in the cutting means 10, the thin blade 11 that is the upper rotary blade and the thick blade 12 that is the lower rotary blade are arranged to face each other with a predetermined meshing dimension (L). When cutting the magnetic material M, the thin blade 11 and the thick blade 12 are synchronized with each other by a rotating mechanism including a motor (not shown) in a state where the side surface 11a of the thin blade 11 is pressed against the side surface 12a of the thick blade 12. To rotate. Note that the speeds of the blade edges of the thin blade 11 and the thick blade 12 are set to be substantially equal to the feed speed of the magnetic material M conveyed from the unwinding unit 20 to the cutting means 10.

  As a cutting condition for cutting the magnetic material M with the above-described cutting device, the shear force from the double-edged blades 11 and 12 is efficiently applied to the magnetic material M with the magnetic material M not changing as much as possible. There is a need. That is, at the time of cutting, it is necessary to adjust the web tension with the unwinding roll 21, the winding roll 31, and the conveying rollers 22, 32 so that the shearing force from the both blades 11 and 12 is efficiently applied to the magnetic material. When a thin nonmagnetic support is used, the waist of the nonmagnetic support becomes weak due to insufficient mechanical strength, and the nonmagnetic support tends to extend in the longitudinal direction rather than in the width direction, and has a roughness in the above range. It becomes difficult to form a cut surface. According to the study by the present inventors, it has been found that a magnetic tape having a cut surface within the range of the center line average roughness (Ra) can be obtained if the following four conditions are satisfied.

  The first condition is that the ratio (Ew / Et) of the Young's modulus (Ew) in the width direction of the magnetic material M to the Young's modulus (Et) in the longitudinal direction is in the range of 0.85 to 1.15. It is to use a magnetic material having a certain elasticity. If the ratio of the Young's modulus in the longitudinal direction to the width direction (Ew / Et) of the magnetic original is outside the above range, the elasticity of the magnetic original will show anisotropy, so that the unidirectional stretching will increase and the magnetic The material becomes easy to fluctuate.

  The second condition is to adjust the meshing dimension (L) of the thin blade 11 and the thick blade 12 to a range of 0.05 to 0.1 mm. When the meshing dimension (L) is out of the above range, the magnetic tape 3 tends to be stretched easily, and the smoothness of the cut surface is likely to be impaired.

  The third condition is to use a thin blade and a thick blade in which the maximum surface roughness (P-V) of the side surfaces 11a and 12a where the thin blade 11 and the thick blade 12 are engaged with each other is 0.05 μm or less. When the maximum surface roughness (P-V) of the side surfaces 11a and 12a of the double-edged blades 11 and 12 is outside the above range, cracks are generated in the cut surface, and the smoothness tends to be impaired. In addition, the said maximum surface roughness (PV) represents the distance of the largest peak and valley in the measurement length of the roughness curve obtained when optically evaluating the side surface of each blade.

  The fourth condition is to control the web tension of the magnetic original fabric M so as to always maintain the fluctuation in the width direction of the magnetic original fabric M in the vicinity of the cutting means 10 at 100 μm or less. When a large web tension is applied to the magnetic material during cutting, the magnetic material becomes easy to meander, and the magnetic material is cut in a state of being stretched in the longitudinal direction. For this reason, the cutting property differs between the large stretched portion and the small stretched portion, and when manufacturing a long magnetic tape, the centerline average roughness (Ra) should be regulated within the above range over the entire tape length. Becomes difficult. The fluctuation can be detected by disposing a detecting means 40 such as an edge position control (EPC) in the vicinity of the cutting means 10.

Next, each configuration of a nonmagnetic support, a magnetic layer, and the like that are preferably used for manufacturing the magnetic tape of the present embodiment will be specifically described.
As the non-magnetic support, a thin polymer resin film having a thickness of 4 μm or less is used for increasing the capacity. The thickness of the nonmagnetic support is preferably as thin as possible. However, if the thickness is too thin, it is difficult to obtain a nonmagnetic support with a uniform thickness. Specific examples of such a nonmagnetic support include a polyamide film and a polyimide film. Further, in order to produce a magnetic material having an isotropic Young's modulus in the longitudinal direction and the width direction, the non-magnetic material having a Young's modulus in the width direction of 8 to 20 GPa and a Young's modulus in the longitudinal direction of 9 to 22 GPa. A support is preferred.

  The magnetic layer contains magnetic powder and a binder. Specific examples of the magnetic powder include ferromagnetic iron oxide magnetic powder, cobalt-containing ferromagnetic iron oxide magnetic powder, hexagonal ferrite magnetic powder, ferromagnetic metal iron magnetic powder, and iron nitride magnetic powder. Etc. Among these, hexagonal ferrite magnetic powder and iron nitride magnetic powder that can form a magnetic layer with small Young's modulus anisotropy are preferable, and iron nitride magnetic powder is most preferable. The iron nitride magnetic powder is described in detail in, for example, Japanese Patent Application Laid-Open No. 2004-273094.

  Examples of the binder for the magnetic layer include conventionally known thermoplastic resins and thermosetting resins. Specific examples of the thermoplastic resin include vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic ester, styrene, butadiene, ethylene, Examples thereof include a polymer or copolymer containing vinyl butyral, vinyl acetal, vinyl ether or the like as a structural unit. Specific examples of the thermosetting resin include phenolic resins, epoxy resins, polyurethane resins, urea resins, melamine resins, alkyd resins, and the like. The content of these binders used in the magnetic layer is preferably 5 to 50 parts by mass with respect to 100 parts by mass of the magnetic powder.

  In addition to the above binder, a thermosetting crosslinking agent that binds to a functional group contained in the binder and forms a crosslinked structure may be used in combination. Specific examples of such a crosslinking agent include isocyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate; reaction products of isocyanate compounds and compounds having a plurality of hydroxyl groups such as trimethylolpropane; Examples include various polyisocyanates such as condensation products of isocyanate compounds. A crosslinking agent is normally used in 10-50 mass parts with respect to 100 mass parts of binders.

  The magnetic layer may contain additives such as carbon black, a lubricant, and a non-magnetic powder for the purpose of improving characteristics such as conductivity, surface lubricity, and durability. Specifically, carbon black such as acetylene black, furnace black, and thermal black can be used as the carbon black. The content of carbon black is preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the magnetic powder. Specific examples of the lubricant that can be used include fatty acids, fatty acid esters, and fatty acid amides having 10 to 30 carbon atoms. The content of the lubricant is preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the magnetic powder. Specifically, for example, nonmagnetic powders such as alumina and silica can be used as the nonmagnetic powder. The content of the nonmagnetic powder is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the magnetic powder.

  The thickness of the magnetic layer is preferably 300 nm or less, more preferably 10 to 300 nm, further preferably 10 to 250 nm, and most preferably 10 to 200 nm for increasing the recording density. When the thickness of the magnetic layer exceeds 300 nm, the reproduction output tends to be small due to the thickness loss. If the thickness of the magnetic layer is less than 10 nm, it is difficult to obtain a uniform magnetic layer. The Young's modulus in the width direction of the magnetic layer is preferably 4 to 10 GPa, and the Young's modulus in the longitudinal direction is preferably 4 to 9 GPa.

  When manufacturing a magnetic material, a magnetic paint is prepared by mixing the above magnetic powder, binder and, if necessary, other additives with a solvent, and this is applied to a nonmagnetic support and applied. It can manufacture by orienting and drying the made magnetic coating film. As a solvent, the organic solvent conventionally used for preparation of a magnetic coating material can be used. Specific examples include cyclohexanone, toluene, methyl ethyl ketone, and tetrahydrofuran. In preparing the magnetic coating material, conventionally known coating manufacturing methods used in the manufacture of magnetic recording media can be used. In particular, the combined use of a kneading step with a kneader or the like and a primary dispersion step is preferable. In the primary dispersion step, it is desirable to use a sand mill because the dispersibility is improved and the surface properties can be controlled.

  The magnetic tape of the present embodiment may have at least one undercoat layer containing an inorganic powder and a binder between the nonmagnetic support and the magnetic layer. The thickness of the undercoat layer is preferably from 0.1 to 3.0 μm, more preferably from 0.15 to 2.5 μm. In particular, it is preferable to form an undercoat layer containing an acicular inorganic powder having an average major axis length of 30 to 100 nm and an average axis ratio of 2 to 4. By forming such an undercoat layer containing an acicular inorganic powder, a waist can be imparted to the magnetic raw material, and the cutting property can be improved. Examples of such inorganic powder include non-magnetic powders such as iron oxide and aluminum oxide; γ-iron oxide, Co-γ-iron oxide, magnetite, chromium oxide, Fe—Ni alloy, Fe—Co alloy, Fe—Ni—. Examples thereof include magnetic powder such as Co alloy. These may be used alone or in combination.

  As the binder for the undercoat layer, the same thermoplastic resin or thermosetting resin as the binder for the magnetic layer may be used. However, radicals are generated by electron beams and are not contained in the molecule that is cured by crosslinking or polymerization. It is more preferable to use an electron beam curable resin containing one or more saturated double bonds. In general, in a high-density magnetic tape, the undercoat layer is thicker than the magnetic layer. Therefore, the rigidity of the undercoat layer is dominant in the rigidity of the magnetic film. Therefore, if an electron beam curable resin, which is more rigid than a thermoplastic resin or a thermosetting resin, is included as a binder for the undercoat layer, the strength of the magnetic fabric can be improved, thereby further cutting. Can be improved. Examples of electron beam curable resins include vinyl chloride resins and polyurethane resins, (meth) acrylic resins, polyester resins, acrylonitrile-butadiene copolymers, polyamide resins, polyvinyl butyral, nitrocellulose, styrene-butadiene copolymers. Polyfunctional polyethers such as coalescence, polyvinyl alcohol resin, acetal resin, epoxy resin, phenoxy resin, polyether resin, polycaprolactone, polyimide resin, phenol resin, polybutadiene elastomer, chlorinated rubber, acrylic rubber, isoprene rubber, It is possible to use a resin such as an epoxy-modified rubber that has been subjected to electron beam sensitive modification by introducing a (meth) acrylic double bond by a known method. Among these, a vinyl chloride resin or a polyurethane resin is used as a raw material, and this is sensitive to an electron beam under a specific water content using a compound having an isocyanate group and a radical polymerizable unsaturated double bond in one molecule. An electron beam curable resin obtained by modification is preferred. 7-50 mass parts is preferable with respect to 100 mass parts of inorganic powder, and, as for content of the binder in undercoat, 10-35 mass parts is more preferable.

  The undercoat layer preferably contains carbon black and a lubricant in order to impart conductivity and surface lubricity to the magnetic layer. As such carbon black and lubricant, those similar to the magnetic layer can be used. As a method for preparing the undercoat layer paint, the same method as that for the magnetic paint can be used. When forming the undercoat layer, either the sequential multi-layer coating method or the simultaneous multi-layer coating method (wet-on-wet method) may be used for applying the magnetic paint and the undercoat layer paint. When the undercoat layer is formed, the Young's modulus in the width direction of the combined magnetic layer and undercoat layer is preferably 4 to 10 GPa, and the Young's modulus in the longitudinal direction is preferably 4 to 9 GPa.

  The magnetic tape of the present embodiment may have a backcoat layer on the surface opposite to the surface on which the magnetic layer of the nonmagnetic support is provided. The thickness of the back coat layer is preferably 0.2 to 0.8 μm, and more preferably 0.3 to 0.8 μm. The back coat layer preferably contains carbon black such as acetylene black, furnace black, or thermal black. As the binder for the backcoat layer, the same resin as that used for the magnetic layer can be used. Among these, in order to reduce the coefficient of friction and improve the runnability, the combined use of a cellulose-based resin and a polyurethane-based resin is preferable. When the backcoat layer is formed, the Young's modulus in the width direction of the backcoat layer is preferably 4 to 10 GPa, and the Young's modulus in the longitudinal direction is preferably 4 to 9 GPa.

  The Young's modulus in the width direction and longitudinal direction of the entire magnetic raw material obtained as described above varies depending on the type and thickness of the nonmagnetic support, the composition and thickness of the magnetic layer, and the presence or absence of the undercoat layer and the backcoat layer. Therefore, the ratio of the Young's modulus in the width direction and the longitudinal direction is not particularly limited as long as it is within the above range, but the Young's modulus in the width direction is preferably 4 to 10 GPa and the Young's modulus in the longitudinal direction is preferably 4 to 10 GPa.

  The magnetic tape of the present embodiment can be manufactured by cutting the magnetic material obtained as described above under the above cutting conditions. The magnetic tape manufactured in this way is excellent in straight running performance at high speed running and even with a thin non-magnetic support, and it is possible to lengthen the magnetic tape because there is little powder falling off. A high-capacity magnetic tape can be obtained. The thinner the total thickness of the magnetic tape is, the higher the capacity can be achieved, so 2-8 μm is preferable, and 3-6 μm is more preferable.

  Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. In the following, “part” means “part by mass”.

[Preparation of magnetic paint (I)]
After the magnetic paint (I) component having the composition shown in Table 1 below is kneaded with a kneader, the kneaded product is subjected to dispersion treatment using a sand mill (retention time: 60 minutes), and polyisocyanate 6 is added to the obtained dispersion. Part was added, stirred, and filtered to prepare a magnetic paint (I).

[Preparation of undercoat layer paint (i)]
The undercoat layer paint (i) component shown in Table 2 below was kneaded with a kneader, and then the kneaded product was dispersed with a sand mill (retention time: 60 minutes). To the obtained dispersion, 6 parts of dipentaerythritol hexaacrylate, which is an electron beam curable resin, was added, stirred, and filtered to prepare an undercoat layer paint (i).

[Preparation of undercoat layer paint (ii)]
Undercoat layer paint (ii) was prepared in the same manner as undercoat layer paint (i) except that no electron beam curable resin was added.

[Preparation of back coat layer paint]
The backcoat layer paint components shown in Table 3 below are dispersed by a sand mill (retention time: 45 minutes), and 8.5 parts of polyisocyanate is added to the resulting dispersion, followed by stirring and filtration. A paint was prepared.

[Preparation of magnetic material]
Using each of the nonmagnetic supports shown in Table 4 below, the above-mentioned undercoat layer paint (i) or (ii) is first dried and calendered on the nonmagnetic support in the combination of paints shown in Table 5. An undercoating film is formed by coating so that the subsequent thickness is 2 μm, and the magnetic coating (I) is further formed on the undercoating film so that the thickness after drying and calendering is 100 nm. Were simultaneously coated and dried to form an undercoat layer and a magnetic layer while performing an orientation treatment in the longitudinal direction. In addition, about the thing using the undercoat layer coating material (i) containing an electron beam curable resin as a binder, the electron beam of 4MRad was irradiated after drying.

  Next, the back coat layer paint is applied to the surface opposite to the surface of the nonmagnetic support on which the magnetic layer is formed so that the thickness after drying and calendering is 700 nm, dried, and then back coated. A layer was formed.

  As described above, a magnetic sheet having an undercoat layer and a magnetic layer formed on one side of a non-magnetic support and a back coat layer formed on the other side is mirror-finished with a five-stage calendar (temperature: 70 ° C., linear pressure: 150 kg / cm). In a state where it was wound around a sheet core, it was aged at 60 ° C. and 40% RH for 48 hours to produce a magnetic original fabric.

  The Young's modulus in the longitudinal direction and the width direction of each magnetic raw material produced as described above was measured under the following conditions.

〔Young's modulus〕
Using a tensile tester equipped with a precision displacement measuring instrument, a measurement sample having a square shape of 1/2 inch square was pulled, and the Young's modulus was calculated from the amount of elongation when the strain was 0.3%.

  Next, each magnetic raw material was cut into ½ inch widths under the cutting conditions shown in Table 5 using the cutting apparatus shown in FIG. 3 to produce each magnetic tape. In order to adjust the fluctuation in the width direction of the magnetic material, EPC was arranged in the vicinity of the cutting means, and the web tension was changed by the unwinding roll, the winding roll, and the adjusting roller to adjust the fluctuation in the width direction. .

  About the obtained magnetic tape, the centerline average roughness (Ra) of the following cut surfaces, a friction coefficient, the straight running property of a magnetic tape, and powder fall were evaluated. Table 5 shows these results.

[Center line average roughness (Ra)]
The cut surface of the magnetic tape is fixed with a jig, and the roughness curve of the cut surface is a laser microscope (Realtime scanning laser microscope 1LM21D, He-Ne laser, CW type manufactured by Lasertec Co., Ltd., wavelength: 632.8 mm, maximum) (Output: 0.1 mW). The measurement conditions were a microscope magnification of 1000 times, a resolution of 0.3 μm, a slow scan of 8, and a scan time of 40 seconds. A roughness curve was obtained from 10 locations on the cut surface of each sample, data processing of the obtained roughness curve was performed, and a center line average roughness (Ra) was obtained.

〔Coefficient of friction〕
Using an evaluation device with an LTO guide roller (made of SUS) and tension gauges installed at both ends, wind the magnetic tape around the upper flange at an angle of 0.5 ° and run the tape at 1.2 m / min. The friction coefficient was calculated from the tension difference between the tension gauges at both ends.

(Straight running)
The magnetic tape was incorporated into an LTO cartridge, and this was run in the shuttle mode of the LTO drive device (simple running, no recording / playback, tape speed: 6 m / s). The traveling property of the magnetic tape in sliding contact with the guide roller in the drive was visually observed, and the straight traveling property was evaluated according to the following criteria.
○: No tape edge deflection △: Vibration is observed at the tape edge ×: Bending is observed at the tape edge

[Food fall]
The magnetic tape was incorporated into an LTO cartridge, and this was run for 2000 passes in the shuttle mode (tape speed: 6 m / s) of the LTO drive device. After running, the dirt on the flange portion of the guide roller was visually observed, and powder falling was evaluated according to the following criteria.
○: Clear powder fall is not seen. △: Flange is discolored to black. ×: Black powdery dirt is seen on the flange.

  As shown in the table above, a thin blade is used using a magnetic material having a ratio (Ew / Et) of Young's modulus (Ew) in the width direction to Young's modulus (Et) in the longitudinal direction in the range of 0.85 to 1.15. Cutting depth (L) between 0.05 mm and 0.1 mm between the blade and the thick blade, and the maximum surface roughness (PV) of the side surface where the thin blade and the thick blade mesh with each other are both 0.05 μm or less The magnetic tape having a cut surface having a center line average roughness (Ra) of 0.08 to 0.25 μm can be manufactured by cutting the magnetic material while maintaining the fluctuation in the width direction at 100 μm or less. I understand. And it turns out that the magnetic tape which has the centerline average roughness (Ra) of this range has a low friction coefficient with a cut surface and a flange part. For this reason, these magnetic tapes are excellent in straight running performance. Further, it can be seen that the magnetic tape having the center line average roughness (Ra) has less powder fall off at the flange portion even when it is run at a high speed. Furthermore, a magnetic tape having an undercoat layer containing an electron beam curable resin has a further reduced coefficient of friction and powder fall compared to a magnetic tape having an undercoat layer containing only a thermoplastic resin and a thermosetting resin. I understand. This is presumably because the cutting property was improved by using an electron beam curable resin as a binder for the undercoat layer.

  On the other hand, the magnetic tape having a center line average roughness (Ra) of less than 0.08 μm has improved powder falling, but has a high coefficient of friction between the cut surface and the flange portion, resulting in a decrease in straight running performance. . This is thought to be because the cut surface was too smooth and the contact area with the flange portion of the cut surface increased. Further, the magnetic tape having a center line average roughness (Ra) larger than 0.25 μm has a reduced friction coefficient but increased powder fall. This is presumably because the cut surface is too rough and local contact occurs at the protruding portion.

DESCRIPTION OF SYMBOLS 3 Magnetic tape 3a Magnetic layer 3b Nonmagnetic support body 3c Backcoat layer 6 Guide roller 6a Flange part 10 Cutting means 11 Thin blade 11a Thin blade side surface 12 Thick blade 12a Thick blade side surface 20 Unwinding part 30 Winding part M Magnetic raw material L Engagement depth S Cut surface

Claims (4)

A magnetic tape having a magnetic layer containing a magnetic powder and a binder on one surface of a nonmagnetic support having a thickness of 4 μm or less, and used in a linear serpentine magnetic recording / reproducing system,
The Young's modulus in the width direction of the nonmagnetic support is 8 to 20 GPa, and the Young's modulus in the longitudinal direction is 9 to 22 GPa.
The magnetic tape whose centerline average roughness (Ra) in the roughness curve of the cut surface of the said magnetic tape is 0.08-0.25 micrometer. The magnetic tape according to claim 1, wherein a center line average roughness (Ra) in a roughness curve of the cut surface of the magnetic tape is 0.09 to 0.12 μm. The magnetic tape according to claim 1, further comprising an undercoat layer containing an inorganic powder and a binder between the nonmagnetic support and the magnetic layer. The magnetic tape according to claim 1, wherein a roughness curve of the cut surface of the magnetic tape is a thickness direction of the magnetic tape.

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