Magnetic tape having characterized magnetic layer, magnetic tape cartridge, and magnetic tape apparatus

Abstract

The magnetic tape includes a non-magnetic support; a non-magnetic layer including a non-magnetic powder and a binding agent on the non-magnetic support; and a magnetic layer including a ferromagnetic powder and a binding agent on the non-magnetic layer, in which a total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 μm, an isoelectric point of a surface zeta potential of the magnetic layer is equal to or greater than 5.5, the magnetic layer includes an oxide abrasive, and an average particle diameter of the oxide abrasive obtained from a secondary ion image obtained by irradiating the surface of the magnetic layer with a focused ion beam is 0.04 μm to 0.08 μm.

Claims

1. A magnetic tape comprising: a non-magnetic support; a non-magnetic layer including a non-magnetic powder and a binding agent on the non-magnetic support; and a magnetic layer including a ferromagnetic powder and a binding agent on the non-magnetic layer, wherein a total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 μm, an isoelectric point of a surface zeta potential of the magnetic layer is equal to or greater than 5.5, the magnetic layer includes an oxide abrasive, and an average particle diameter of the oxide abrasive obtained from a secondary ion image obtained by irradiating the surface of the magnetic layer with a focused ion beam is 0.04 μm to 0.08 μm.

2. The magnetic tape according to claim 1, wherein the isoelectric point is 5.5 to 7.0.

3. The magnetic tape according to claim 1, wherein the magnetic layer includes a binding agent having an acidic group.

4. The magnetic tape according to claim 3, wherein the acidic group is at least one kind of acidic group selected from the group consisting of a sulfonic acid group and a salt thereof.

5. The magnetic tape according to claim 1, wherein the oxide abrasive is an alumina powder.

6. The magnetic tape according to claim 2, wherein the oxide abrasive is an alumina powder.

7. The magnetic tape according to claim 3, wherein the oxide abrasive is an alumina powder.

8. The magnetic tape according to claim 4, wherein the oxide abrasive is an alumina powder.

9. The magnetic tape according to claim 1, wherein the total thickness of the non-magnetic layer and the magnetic layer is 0.15 μm to 0.60 μm.

10. The magnetic tape according to claim 1, further comprising: a back coating layer including a non-magnetic powder and a binding agent on a surface of the non-magnetic support opposite to a surface provided with the magnetic layer.

11. A magnetic tape cartridge comprising: the magnetic tape according to claim 1.

12. The magnetic tape cartridge according to claim 11, wherein the isoelectric point is 5.5 to 7.0.

13. The magnetic tape cartridge according to claim 11, wherein the magnetic layer includes a binding agent having an acidic group.

14. The magnetic tape cartridge according to claim 13, wherein the acidic group is at least one kind of acidic group selected from the group consisting of a sulfonic acid group and a salt thereof.

15. The magnetic tape cartridge according to claim 11, wherein the oxide abrasive is an alumina powder.

16. A magnetic tape apparatus comprising: the magnetic tape according to claim 1; and a magnetic head.

17. The magnetic tape apparatus according to claim 16, wherein the isoelectric point is 5.5 to 7.0.

18. The magnetic tape apparatus according to claim 16, wherein the magnetic layer includes a binding agent having an acidic group.

19. The magnetic tape apparatus according to claim 18, wherein the acidic group is at least one kind of acidic group selected from the group consisting of a sulfonic acid group and a salt thereof.

20. The magnetic tape apparatus according to claim 16, wherein the oxide abrasive is an alumina powder.

Description

EXAMPLES

(1) Hereinafter, the invention will be described with reference to examples. However, the invention is not limited to aspects shown in the examples. “Parts” and “%” in the following description mean “parts by mass” and “% by mass”, unless otherwise noted. In addition, steps and evaluations described below are performed in an environment of an atmosphere temperature of 23° C.±1° C., unless otherwise noted.

(2) A “binding agent A” described below is a SO.sub.3Na group-containing polyurethane resin (weight-average molecular weight: 70,000, SO.sub.3Na group: 0.20 meq/g).

(3) A “binding agent B” described below is a vinyl chloride copolymer (product name: MR110, SO.sub.3K group-containing vinyl chloride copolymer, SO.sub.3K group: 0.07 meq/g) manufactured by Kaneka Corporation.

(4) Manufacturing of Magnetic Tape

Example 1

(5) (1) Preparation of Alumina Dispersion

(6) The amount of 2,3-dihydroxynaphthalene (manufactured by Tokyo Chemical Industry Co., Ltd.) shown in Table 1, 31.3 parts of a 32% solution (solvent is a mixed solvent of methyl ethyl ketone and toluene) of a polyester polyurethane resin including a SO.sub.3Na group as a polar group (UR-4800 (polar group amount: 80 meq/g) manufactured by Toyobo Co., Ltd.), and 570.0 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone (mass ratio of 1:1) as a solvent were mixed with 100.0 parts of oxide abrasive (alumina powder) shown in Table 1, and dispersed in the presence of zirconia beads (bead diameter: 0.1 mm) by a paint shaker for a period of time shown in Table 1 (bead dispersion time). After the dispersion, the centrifugal separation process of a dispersion liquid obtained by separating the dispersion liquid from the beads by mesh was performed. The centrifugal separation process was performed by using CS150GXL manufactured by Hitachi, Ltd. (rotor used is S100AT6 manufactured by Hitachi, Ltd.) as a centrifugal separator at a rotation per minute (rpm) shown in Table 1 for a period of time (centrifugal separation time) shown in Table 1. After that, the filtering was performed by using a filter having a hole diameter shown in Table 1, and an alumina dispersion (abrasive solution) was obtained.

(7) (2) Magnetic Layer Forming Composition List

(8) TABLE-US-00001 Magnetic Liquid Ferromagnetic powder: 100.0 parts Hexagonal barium ferrite powder having average particle size (average plate diameter) of 21 nm Binding agent A and/or binding agent B (see Table 1): see Table 1 Cyclohexanone: 150.0 parts Methyl ethyl ketone: 150.0 parts Abrasive Solution Alumina dispersion prepared in the section (1): 6.0 parts Silica Sol (projection formation agent liquid) Colloidal silica (Average particle size: 120 nm) 2.0 parts Methyl ethyl ketone: 1.4 parts Other Components Stearic acid: 2.0 parts Stearic acid amide: 0.2 parts Butyl stearate: 2.0 parts Polyisocyanate (CORONATE (registered trademark) 2.5 parts manufactured by Tosoh Corporation): Finishing Additive Solvent Cyclohexanone: 200.0 parts Methyl ethyl ketone: 200.0 parts

(9) (3) Non-Magnetic Layer Forming Composition List

(10) TABLE-US-00002 Non-magnetic inorganic powder: α-iron oxide 100.0 parts Average particle size (average long axis length): 0.15 μm Average acicular ratio: 7 BET specific surface area: 52 m.sup.2/g Carbon black 20.0 parts Average particle size: 20 nm Abrasive A: 18.0 parts Stearic acid: 2.0 parts Stearic acid amide: 0.2 parts Butyl stearate: 2.0 parts Cyclohexanone: 300.0 parts Methyl ethyl ketone: 300.0 parts

(11) (4) Back Coating Layer Forming Composition List

(12) TABLE-US-00003 Non-magnetic inorganic powder: α-iron oxide 80.0 parts Average particle size (average long axis length): 0.15 μm Average acicular ratio: 7 BET specific surface area: 52 m.sup.2/g Carbon black 20.0 parts Average particle size: 20 nm A vinyl chloride copolymer 13.0 parts A sulfonic acid salt group-containing polyurethane resin 6.0 parts Phenylphosphonic acid 3.0 parts Methyl ethyl ketone 155.0 parts Polyisocyanate 5.0 parts Cyclohexanone 355.0 parts

(13) (5) Preparation of Each Layer Forming Composition

(14) The magnetic layer forming composition was prepared by the following method.

(15) The magnetic liquid was prepared by dispersing (beads-dispersing) various components of the magnetic liquid by using a batch type vertical sand mill for 24 hours. Zirconia beads having a bead diameter of 0.5 mm were used as the dispersion beads.

(16) The prepared magnetic liquid, the abrasive solution, silica sol, the other components, and the finishing additive solvent were introduced to a dissolver stirrer, and stirred at a circumferential speed of 10 m/sec for a period of time shown in Table 1. After that, After that, a ultrasonic dispersion process was performed at a flow rate of 7.5 kg/min with a flow type ultrasonic disperser for a period of time shown in Table 1 (ultrasonic dispersion time), and filtering with a filter having a hole diameter shown in Table 1 was performed for the number of times shown in Table 1, thereby preparing the magnetic layer forming composition.

(17) The non-magnetic layer forming composition was prepared by the following method.

(18) Each component excluding the lubricant (stearic acid, stearic acid amide, and butyl stearate), cyclohexanone, and methyl ethyl ketone was dispersed by using batch type vertical sand mill for 24 hours to obtain a dispersion liquid. As the dispersion beads, zirconia beads having a bead diameter of 0.5 mm were used. After that, the remaining components were added into the obtained dispersion liquid and stirred with a dissolver stirrer. The dispersion liquid obtained as described above was filtered with a filter having a hole diameter of 0.5 μm and a non-magnetic layer forming composition was prepared.

(19) The back coating layer forming composition was prepared by the following method.

(20) Each component excluding polyisocyanate and cyclohexanone was kneaded by an open kneader and diluted, and was subjected to a dispersion process of 12 passes, with a transverse beads mill disperser and zirconia beads having a bead diameter of 1 mm, by setting a bead filling percentage as 80 volume %, a circumferential speed of rotor distal end as 10 m/sec, and a retention time for 1 pass as 2 minutes. After that, the remaining components were added into the obtained dispersion liquid and stirred with a dissolver stirrer. The dispersion liquid obtained as described above was filtered with a filter having a hole diameter of 1 μm and a back coating layer forming composition was prepared.

(21) (6) Manufacturing Method of Magnetic Tape

(22) The non-magnetic layer forming composition prepared in the section (5) was applied to a surface of a support made of polyethylene naphthalate having a thickness of 5.00 μm so that the thickness after the drying becomes a thickness shown in Table 1 and was dried to form a non-magnetic layer.

(23) Then, in a coating device disposed with a magnet for applying an alternating magnetic field, the magnetic layer forming composition prepared in the section (5) was applied onto the surface of the non-magnetic layer so that the thickness after the drying becomes a thickness shown in Table 1, while applying an alternating magnetic field (magnetic field strength: 0.15 T), to form a coating layer. The applying of the alternating magnetic field was performed so that the alternating magnetic field was applied vertically to the surface of the coating layer. After that, a homeotropic alignment process was performed by applying a magnetic field having a magnetic field strength of 0.30 T in a vertical direction with respect to a surface of a coating layer, while the coating layer of the magnetic layer forming composition is wet (not dried). After that, the coating layer was dried to form a magnetic layer.

(24) After that, the back coating layer forming composition prepared in the section (5) was applied to the surface of the support made of polyethylene naphthalate on a side opposite to the surface where the non-magnetic layer and the magnetic layer were formed, so that the thickness after the drying becomes 0.50 μm, and was dried to form a back coating layer.

(25) The magnetic tape obtained as described above was slit to have a width of ½ inches (0.0127 meters), and the burnishing process and the wiping process of the surface of the coating layer were performed. The burnishing process and the wiping process were performed in a process device having a configuration shown in FIG. 1 of JP-H06-52544A, by using a commercially available abrasive tape (product name: MA22000 manufactured by Fujifilm Holdings Corporation, abrasive: diamond/Cr.sub.2O.sub.3/red oxide) as an abrasive tape, by using a commercially available sapphire diamond (manufactured by Kyocera Corporation, width of 5 mm, length of 35 mm, an angle of a distal end of 60 degrees) as a blade for grinding, and by using a commercially available wiping material (product name: WRP736 manufactured by Kuraray Co., Ltd.) as a wiping material. For the process conditions, process conditions of Example 12 of JP-H06-52544A were used.

(26) After the burnishing process and the wiping process, a calender process (surface smoothing treatment) was performed by using a calender roll configured of only a metal roll, at a speed of 80 m/min, linear pressure of 300 kg/cm (294 kN/m), and a calender temperature (surface temperature of a calender roll) of 100° C.

(27) Then, the heat treatment (curing process) was performed in the environment of the atmosphere temperature of 70° C. for 36 hours. After that, a servo pattern was formed on the magnetic layer by a commercially available servo writer.

(28) By doing so, a magnetic tape of Example 1 was manufactured.

Examples 2 to 6, Comparative Examples 1 to 7, and Reference Examples 1 and 2

(29) A magnetic tape was manufactured by the same method as in Example, except that various conditions were changed as shown in Table 1.

(30) In Table 1, in Examples 2 to 6 and Comparative Examples 3 and 5 in which “performed” is shown in the column of the alternating magnetic field application during coating and the column of the burnishing process, the step subsequent to the coating step of the magnetic layer forming composition was performed by the same method as in Example 1. That is, the application of the alternating magnetic field was performed during coating of the magnetic layer forming composition in the same manner as in Example 1, and the burnishing process and the wiping process were performed with respect to the magnetic layer.

(31) With respect to this, in Comparative Example 7 in which “not performed” is shown in the column of the burnishing process, the step subsequent to the coating step of the magnetic layer forming composition was performed by the same method as in Example 1, except that the burnishing process and the wiping process were not performed with respect to the magnetic layer.

(32) In Comparative Example 6 in which “not performed” is shown in the column of the alternating magnetic field application during coating, the step subsequent to the coating step of the magnetic layer forming composition was performed by the same method as in Example 1, except that the application of the alternating magnetic field was not performed.

(33) In Comparative Examples 1, 2, and 4 and Reference Examples 1 and 2 in which “not performed” is shown in the column of the alternating magnetic field application during coating and the column of the burnishing process, the step subsequent to the coating step of the magnetic layer forming composition was performed by the same method as in Example 1, except that application of the alternating magnetic field is not performed and the burnishing process and the wiping process were not performed with respect to the magnetic layer.

(34) The thickness of each layer and the thickness of the non-magnetic support of each magnetic tape of the examples, the comparative examples, and the reference examples were acquired by the following method, and it was confirmed that the thicknesses of the non-magnetic layer and the thickness of the magnetic layer were the thicknesses shown in Table 1 and the thickness of the back coating layer and the non-magnetic support is the thickness described above.

(35) A cross section of the magnetic tape in a thickness direction was exposed to ion beams and the exposed cross section was observed with a scanning electron microscope.

(36) Various thicknesses were obtained as an arithmetical mean of thicknesses obtained at two portions, randomly extracted from the cross section observation.

(37) Evaluation of Physical Properties of Magnetic Tape

(38) (1) Isoelectric Point of Surface Zeta Potential of Magnetic Layer

(39) Six samples for isoelectric point measurement were cut out from each magnetic tape of the examples, the comparative examples, and the reference examples and disposed in the measurement cell of two samples in one measurement. In the measurement cell, a sample installing surface and a surface of the back coating layer of the sample were bonded to each other by using a double-sided tape in upper and lower sample table (size of each sample installing surface is 1 cm×2 cm) of the measurement cell. Accordingly, in a case where an electrolyte flows in the measurement cell, the surface of the magnetic layer of the sample comes into contact with the electrolyte, and thus, the surface zeta potential of the magnetic layer can be measured. The measurement was performed three times in total by using two samples in each measurement, and the isoelectric points of the surface zeta potential of the magnetic layer were obtained. An arithmetical mean of the obtained three values was shown in Table 1, as the isoelectric point of the surface zeta potential of the magnetic layer of each magnetic tape. As a surface zeta potential measurement device, SurPASS manufactured by Anton Paar was used. The measurement conditions were set as follows. Other details of the method of obtaining the isoelectric point are as described above.

(40) Measurement cell: variable gap cell (20 mm×10 mm)

(41) Measurement mode: Streaming Current

(42) Gap: approximately 200 μm

(43) Measurement temperature: room temperature

(44) Ramp Target Pressure/Time: 400,000 Pa (400 mbar)/60 seconds

(45) Electrolyte: KCl aqueous solution having concentration of 1 mmol/L (adjusted pH to 9)

(46) pH adjusting solution: HCl aqueous solution having concentration of 0.1 mol/L or KOH aqueous solution having concentration of 0.1 mol/L

(47) Measurement pH: pH 9.fwdarw.pH 3 (measured at 13 measurement points in total at interval of approximately 0.5)

(48) (2) FIB Abrasive Diameter

(49) The FIB abrasive diameter of each magnetic tape of the examples, the comparative examples, and the reference examples was obtained by the following method. As a focused ion beam device, MI4050 manufactured by Hitachi High-Technologies Corporation was used, and the image analysis software, Image J which is free software was used.

(50) (i) Acquiring of Secondary Ion Image

(51) The surface of the back coating layer of the sample for measurement cut out from each magnetic tape was bonded to an adhesive layer of a commercially available carbon double-sided tape for SEM measurement (double-sided tape in which a carbon film is formed on a base material formed of aluminum). An adhesive layer of this double-sided tape on a surface opposite to the surface bonded to the surface of the back coating layer was bonded to a sample table of the focused ion beam device. By doing so, the sample for measurement was disposed on the sample table of the focused ion beam device so that the surface of the magnetic layer faces upwards.

(52) Without performing the coating process before the imaging, the beam setting of the focused ion beam device was set so that an acceleration voltage is 30 kV, a current value is 133 pA, a beam size is 30 nm, and brightness is 50%, and an SI signal was detected by a secondary ion detector. In three portions of non-imaging region of the surface of the magnetic layer, a tint of the image was stabilized by performing the ACB, and a contrast reference value and a brightness reference value were determined. A contrast value obtained by decreasing 1% from the contrast reference value determined by the ACB and the brightness reference value were determined as the imaging conditions. A non-imaged region of the surface of the magnetic layer was selected, and the imaging was performed under the imaging conditions determined as described above at pixel distance=25.0 (nm/pixel). As an image capturing method, PhotoScan Dot×4_Dwell Time 15 μsec (capturing time: 1 min), and a capturing size was set as 25 μm×25 μm. By doing so, a secondary ion image of a region of the surface of the magnetic layer having a size of 25 μm×25 μm was obtained. After the scanning, the obtained secondary ion image was stored as a file format, JPEG, by ExportImage, by clicking mouse right button on the captured screen. The pixel number of the image which was 2,000 pixel×2,100 pixel was confirmed, the cross mark and the micron bar on the captured image were deleted, and an image of 2,000 pixel×2,000 pixel was obtained.

(53) (ii) Calculation of FIB Abrasive Diameter

(54) The image data of the secondary ion image obtained in (i) was dragged and dropped in Image J which is the image analysis software.

(55) A tone of the image data was changed to 8 bit by using the image analysis software. Specifically, Image of the operation menu of the image analysis software was clicked and 8 bit of Type was selected.

(56) For the binarization process, 250 gradations was selected as a lower limit value, 255 gradations was selected as an upper limit value, and the binarization process was executed by these two threshold values. Specifically, on the operation menu of the image analysis software, Image was clicked, Threshold of Adjust was selected, the lower limit value was selected as 250, the upper limit value was selected as 255, and then, apply was selected. Regarding the obtained image, Process of the operation menu of the image analysis software was clicked, and Despeckle of Noise was selected, and Size 4.0-Infinity was set by Analyze Particle, to perform the removal of noise components.

(57) Regarding the binarization process image obtained as described above, Analyze particle was selected from the operation menu of the image analysis software, and the number and Area (unit: Pixel) of white-shining portions on the image were obtained. The area of each white-shining portion on the image was obtained by converting Area (unit: Pixel) into the area by the image analysis software. Specifically, 1 pixel of the image obtained under the imaging conditions corresponded to 0.0125 μm, and accordingly, the area A [μm.sup.2] was calculated by an expression, area A=Area pixel×0.0125{circumflex over ( )}2. By using the area calculated as described above, an equivalent circle diameter L of each white-shining portion was obtained by an expression, equivalent circle diameter L=(A/π){circumflex over ( )}(½)×2=L.

(58) The above step was performed four times at different portions (25 μm×25 μm) of the surface of the magnetic layer of the sample for measurement, and the FIB abrasive diameter was calculated from the obtained result by an expression, FIB abrasive diameter=Σ(Li)/Σi.

(59) Change of Electromagnetic Conversion Characteristics (Signal-to-Noise-Ratio (SNR)) after Repeated Reproducing in Low Temperature and High Humidity Environment (SNR Decrease Amount)

(60) The electromagnetic conversion characteristics (SNR) were measured with a reel tester having a width of ½ inches (0.0127 meters) to which a head was fixed, by the following method.

(61) The recording was performed by setting a head/tape relative speed as 5.5 m/sec, using a metal-in-gap (MIG) head (gap length of 0.15 μm, track width of 1.0 μm), and setting a recording current as an optimal recording current of each magnetic tape.

(62) As a reproducing head, a giant-magnetoresistive (GMR) 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. A signal was recorded at linear recording density (270 kfci) and a reproducing signal was measured with a spectrum analyzer manufactured by Shibasoku Co., Ltd. The unit kfci is a unit of linear recording density (not convertible into the unit SI). As the signal, a sufficiently stabilized portion of the signal after starting the running of the magnetic tape was used. A ratio of an output value of a carrier signal and integral noise over whole spectral range was set as an SNR.

(63) Under the conditions described above, the reproduction (head/tape relative speed: 8.0 m/sec) was performed by reciprocating 8,000 passes in an environment of an atmosphere temperature of 13° C. and relative humidity of 80%, by setting a tape length per 1 pass as 1,000 m, and the SNR was measured. A distance between the SNR of the first pass and the SNR of the 8,000th pass (SNR of the 8,000th pass—SNR of the first pass) was obtained. In a case where the distance is less than −2.0 dB, it can be determined that it is a magnetic tape showing excellent electromagnetic conversion characteristics desired for the data back-up tape.

(64) The results described above are shown in Table 1 (Table 1-1 to Table 1-2).

(65) TABLE-US-00004 TABLE 1 Example Example Example Example Example Example 1 2 3 4 5 6 Magnetic layer thickness 0.10 μm 0.10 μm 0.10 μm 0.10 μm 0.10 μm 0.10 μm Non-magnetic layer thickness 0.50 μm 0.50 μm 0.50 μm 0.30 μm 0.10 μm 0.10 μm Total thickness of non-magnetic layer and 0.60 μm 0.60 μm 0.60 μm 0.40 μm 0.20 μm 0.20 μm magnetic layer Preparation of Oxide abrasive product name Hit70 Hit70 Hit70 Hit80 Hit80 Hit70 magnetic layer (manufactured by Sumitomo Chemical Co., Ltd.) Oxide abrasive BET specific 20 20 20 30 30 20 surface area (m.sup.2/g) Content of abrasive solution 3.0 parts 3.0 parts 3.0 parts 3.0 parts 3.0 parts 3.0 parts dispersing agent (2,3-dihydroxynaphthalene) Beads dispersion time 60 60 60 180 180 60 minutes minutes minutes minutes minutes minutes Centrifugal Rotation rate 5500 rpm 5500 rpm 5500 rpm 3500 rpm 3500 rpm 5500 rpm separation Centrifugal 3.8 3.8 3.8 3.8 3.8 3.8 separation time minutes minutes minutes minutes minutes minutes Filter hole diameter 0.3 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm Preparation Stirring time 180 180 180 360 360 180 of magnetic minutes minutes minutes minutes minutes minutes layer forming Ultrasonic dispersion time 60 60 60 60 60 60 composition minutes minutes minutes minutes minutes minutes Filter hole diameter 0.3 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm Number of times of filter 2 times 2 times 2 times 3 times 3 times 2 times process Content of binding agent A in magnetic liquid 10.0 20.0 10.0 10.0 10.0 10.0 parts parts parts parts parts parts Content of binding agent B in magnetic liquid 0 part 0 part 10.0 0 part 0 part 0 part parts Alternating magnetic field application during Performed Performed Performed Performed Performed Performed coating Burnishing process Performed Performed Performed Performed Performed Performed Result Isoelectric point of surface zeta 6.0 6.5 6.4 6.2 6.0 6.0 potential of magnetic layer FIB abrasive diameter (μm) 0.08 0.08 0.08 0.04 0.04 0.08 SNR decrease amount (dB) −1.0 −0.7 −0.8 −1.3 −1.5 −1.5 Reference Reference Comparative Comparative Comparative Comparative Example 1 Example 2 Example 1 Example 2 Example 3 Example 4 Magnetic layer thickness 0.10 μm 0.10 μm 0.10 μm 0.10 μm 0.10 μm 0.10 μm Non-magnetic layer thickness 1.00 μm 0.70 μm 0.50 μm 0.10 μm 0.50 μm 0.50 μm Total thickness of non-magnetic layer and 1.10 μm 0.80 μm 0.60 μm 0.20 μm 0.60 μm 0.60 μm magnetic layer Preparation Oxide abrasive product name Hit80 Hit80 Hit80 Hit80 Hit80 Hit80 of magnetic (manufactured by Sumitomo layer Chemical Co., Ltd.) Oxide abrasive BET specific 30 30 30 30 30 30 surface area (m.sup.2/g) Content of abrasive solution 3.0 parts 3.0 parts 0 part 0 part 0 part 3.0 parts dispersing agent (2,3-dihydroxynaphthalene) Beads dispersion time 5 minutes 5 minutes  60 minutes  60 minutes  60 minutes  60 minutes Centrifugal Rotation rate None None 3500 rpm 3500 rpm 3500 rpm 3500 rpm separation Centrifugal None None 3.8 minutes 3.8 minutes 3.8 minutes 3.8 minutes separation time Filter hole diameter 0.5 μm 0.5 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm Preparation Stirring time  30 minutes  30 minutes 60 minutes 60 minutes 60 minutes 360 minutes of magnetic Ultrasonic dispersion time 0.5 minutes 0.5 minutes 60 minutes 60 minutes 60 minutes  60 minutes layer forming Filter hole diameter 0.5 μm 0.5 μm 0.3 μm 0.3 μm 0.3 μm 0.3 μm composition Number of times of filter 1 time 1 time 2 times 2 times 2 times 3 times process Content of binding agent A in magnetic liquid 10.0 parts 10.0 parts 10.0 parts 10.0 parts 10.0 parts 10.0 parts Content of binding agent B in magnetic liquid 0 part 0 part 0 part 0 part 0 part 0 part Altemating magnetic field application during Not Not Not Not Performed Not coating performed performed performed performed performed Burnishing process Not Not Not Not Performed Not performed performed performed performed performed Result Isoelectric point of surface zeta 5.0 4.6 4.6 4.6 5.8 4.6 potential of magnetic layer FIB abrasive diameter (μm) 0.16 0.16 0.11 0.11 0.11 0.06 SNR decrease amount (dB) −1.0 −1.0 −2.5 −3.8 −2.5 −2.5 Comparative Comparative Comparative Example 5 Example 6 Example 7 Magnetic layer thickness 0.10 μm 0.10 μm 0.10 μm Non-magnetic layer thickness 0.50 μm 0.50 μm 0.50 μm Total thickness of non-magnetic layer and 0.60 μm 0.60 μm 0.60 μm magnetic layer Preparation Oxide abrasive product name Hit100 Hit80 Hit80 of magnetic (manufactured by Sumitomo layer Chemical Co., Ltd.) Oxide abrasive BET specific 40 30 30 surface area (m.sup.2/g) Content of abrasive solution 3.0 parts 3.0 parts 3.0 parts dispersing agent (2,3-dihydroxynaphthalene) Beads dispersion time 180 minutes  60 minutes  60 minutes Centrifugal Rotation rate 3500 rpm 3500 rpm 3500 rpm separation Centrifugal  3.8 minutes 3.8 minutes 3.8 minutes separation time Filter hole diameter 0.3 μm 0.3 μm 0.3 μm Preparation Stirring time 360 minutes 360 minutes 360 minutes of magnetic Ultrasonic dispersion time  60 minutes  60 minutes  60 minutes layer forming Filter hole diameter 0.3 μm 0.3 μm 0.3 μm composition Number of times of filter 3 times 3 times 3 times process Content of binding agent A in magnetic liquid 10.0 parts 10.0 parts 10.0 parts Content of binding agent B in magnetic liquid 0 part 0 part 0 part Altemating magnetic field application during Performed Not Performed coating performed Burnishing process Performed Performed Not performed Result Isoelectric point of surface zeta 6.1 4.6 4.3 potential of magnetic layer FIB abrasive diameter (μm) 0.03 0.06 0.06 SNR decrease amount (dB) −3.5 −2.5 −2.3

(66) By comparing the reference examples and the comparative examples, in a case where the total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 μm (Examples 1 to 7), it was confirmed that a deterioration in electromagnetic conversion characteristics during the repeated reproducing in a low temperature and high humidity environment was significant, compared to a case where the total thickness of the non-magnetic layer and the magnetic layer is greater than 0.60 μm (Reference Examples 1 and 2).

(67) On the other hand, from the results shown in Table 1, according to the magnetic tapes of Examples 1 to 6, it can be confirmed that it is possible to prevent a deterioration in electromagnetic conversion characteristics during the repeated reproducing in a low temperature and high humidity environment, compared to the magnetic tapes in Comparative Examples 1 to 7, although the total thickness of the non-magnetic layer and the magnetic layer is equal to or smaller than 0.60 μm.

(68) One aspect of the invention is effective in a technical field of various magnetic recording media such as magnetic tapes for data storage.