JP3710063B2 - Magnetic recording medium - Google Patents

Description

【００７５】
【表２】

【００７６】
【表３】

【００７７】
【表４】

【００７８】
【表５】

【００７９】
【発明の効果】
表１ないし表５に示した実施例１〜１０および比較例１〜６から明らかなように、非磁性支持体、下塗層、磁性層、バックコート層からなる磁気記録媒体であって、磁性層の厚さが0.３０μｍ以下、中心線平均表面粗さＲａが3.２ｎｍ以下で、磁性層の凹凸の中心値をＰ₀ 、該磁性層の最大の凸量をＰ₁ 、第２０番目の凸量をＰ₂₀とした時の（Ｐ₁ −Ｐ₀ ）が３０ｎｍ以下で、かつ（Ｐ₁ −Ｐ₂₀）が５ｎｍ以下である磁気記録媒体は、エラーレートが小さい優れた磁気記録媒体である。このような効果は、（Ｐ₁ −Ｐ₂₀）を1.８ｎｍ以下とした磁気記録媒体において特に顕著である。また、磁性層とスライダ材料との摩擦係数をμ_mSL 、磁性層とＳＵＳとの摩擦係数をμ_mSUS、バックコート層とＳＵＳとの摩擦係数をμ_BSUSとした時の［（μ_mSL ）／（μ_mSUS）］が0.７〜1.３で、かつ［（μ_mSL ）／（μ_BSUS）］が0.８〜1.５である磁気記録媒体は、オフトラックが小さい優れた磁気記録媒体である。
【図面の簡単な説明】
【図１】本発明の磁気記録媒体を製造する場合に行うＬＲＴ（ラッピング／ロータリ／ティシュ）処理の一例を示す概略工程図である。
【図２】スライダ上に載置された、記録ヘッドと再生用のＭＲヘッドとを示す概略平面図である。
【図３】図２のＹ−Ｙ線で切断した概略断面図である。
【符号の説明】
２０ ＭＲヘッド
２２ スライダ
３０ 磁気記録媒体（磁気テープ）
３０ａ 磁性層
３０ｂ バックコート層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium having high recording capacity, access speed, and transfer speed, and more particularly to a data recording magnetic recording medium using a reproducing head (hereinafter referred to as MR head) using a magnetoresistive element (MR element). .
[0002]
[Background Art and Problems to be Solved by the Invention]
Magnetic tapes have various uses such as audio tapes, video tapes, and computer tapes. In particular, in the field of data backup tapes, storage of tens of GB or more per volume is accompanied by an increase in the capacity of a hard disk to be backed up. The capacity of the backup tape has been commercialized, and it is indispensable to increase the capacity of the backup tape in order to cope with the further increase in capacity of the hard disk in the future. Also, in order to increase the access speed and transfer speed, it is essential to increase the tape feed speed and the relative speed between the tape and the head.
[0003]
In order to increase the capacity per volume of backup tape, the total tape thickness is reduced to increase the tape length per volume, and the magnetic layer thickness is reduced to 0.3 μm or less to reduce the thickness. In addition to shortening the recording wavelength by reducing demagnetization, it is necessary to increase the recording density in the width direction by reducing the track width (signal pattern width on the tape) to 15 μm or less.
[0004]
If the thickness of the magnetic layer is as thin as 0.3 μm or less, the durability deteriorates. Therefore, it is necessary to provide at least one undercoat layer between the nonmagnetic support and the magnetic layer. Also, if the recording wavelength is shortened, the effect of spacing between the magnetic layer and the magnetic head increases, so if there are large protrusions in the magnetic layer, the half-value width (hereinafter referred to as PW50) of the output peak is wide due to spacing loss. The error rate increases because the output becomes lower or the output decreases.
[0005]
When the track width is narrowed to 15 μm or less and the recording density in the width direction is increased, the leakage magnetic flux from the magnetic recording medium is reduced. Therefore, the reproducing head uses a magnetoresistive effect element capable of obtaining a high output even with a minute magnetic flux. (Hereinafter referred to as MR head) is required.
[0006]
Conventionally, in a magnetic recording medium compatible with an MR head, the magnetic flux of the magnetic recording medium (product of residual magnetic flux density and thickness) is controlled to a specific value to prevent distortion of the output of the MR head (for example, Patent Document 1). 2), it is proposed to reduce the thermal asperity of the MR head by setting the dent on the surface of the magnetic layer to a specific value or less (see, for example, Patent Document 3).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-238225 (Claims, paragraph numbers 0007 to 0011, Examples)
[Patent Document 2]
JP 2000-40217 A (Claims, paragraph numbers 0006 to 0009, Examples)
[Patent Document 3]
JP 2000-40218 A (Claims, paragraph numbers 0005 to 0014, 0023, Examples, FIGS. 2 and 3)
[0008]
A conventional magnetic head uses a chip in which a magnetic induction head for recording and a magnetic induction head for reproduction are bonded together. On the other hand, as schematically shown in FIGS. 2 and 3, the MR head 20 is used by being embedded in a slider 22 in a form combined with a magnetic induction type recording head 21 for recording. In these drawings, reference numeral 20a denotes an MR element, 21a and 21b denote magnetic elements constituting the recording head 21, 21c denotes a write gap, and 23 denotes a shield material. The MR head 20 is embedded in a state where it is retracted by about 25 nm from the slider surface 22a. That is, the conventional head is composed of a very small chip and travels in a form in which the knife edge bites into the magnetic tape, whereas the MR head 20 as shown in FIGS. The magnetic tape 30 travels while contacting the slider 22. Further, the magnetic tape 30 and the MR head 20 come into contact so that the magnetic tape 30 swells toward the MR head 20. As described above, since the contact form is significantly different from the conventional one, the characteristics required for the magnetic tape are completely different even if it is said that the spacing loss is reduced. Further, the MR head 20 has a problem that the MR element 20a is easily worn because the MR element 20a is composed of a very thin thin film. As shown in FIGS. 2 and 3, the MR head 20 and the recording head 21 are usually provided in pairs so that the magnetic tape 30 can be recorded / reproduced even when it travels in either the forward direction or the back direction. Also, a plurality of tracks are provided in the left-right direction of FIG. 2 so that a plurality of tracks can be read and written simultaneously.
[0009]
In addition, since the track width of the MR head is very narrow, a servo signal is provided for tracking servo of the MR head. The track servo system includes a magnetic servo system and an optical servo system. The former is a servo band formed on a magnetic layer by magnetic recording, and this is magnetically read to perform servo tracking. A servo band composed of an array is formed on the backcoat layer by laser irradiation or the like, and this is optically read to perform servo tracking. In addition to these, the magnetic servo system has a system in which the back coat layer is also magnetized and records a magnetic servo signal on the back coat layer, and the optical servo system absorbs light in the back coat layer. There is also a method of recording an optical servo signal with a material or the like.
[0010]
In order to cope with the increase in the tape feed speed and the relative speed between the tape and the head, it is necessary to run at high speed while tracing the servo signal. However, slider material (for example, alumina / titania / carbide) or guide roller If the friction coefficient between the magnetic layer and the back coat layer with respect to the material, etc. is not adequately optimized, the magnetic tape will meander and a tracking error (off-track) will occur, resulting in a wide PW50 or a reduced output. There is a problem that the error rate becomes high.
[0011]
  The present invention reduces the error rate by reducing the spacing loss of the magnetic tape corresponding to the MR head and reducing the off-track by meandering the magnetic tape.DeclineThe purpose is to let you. Another object of the present invention is to reduce the wear of the MR head used in combination with the magnetic recording medium of the present invention.
[0012]
[Means for Solving the Problems]
  In order to achieve the above-mentioned object, the present inventors have conducted intensive studies. As a result, the maximum convex amount (P₁ ) And the average value of the unevenness (P₀ ) (P)₁ -P₀ ) Below a specific value and the maximum convex amount (P₁ ) And the 20th convex amount (P₂₀) (P)₁ -P₂₀) Below a specific value, the spacing loss is reduced, and the dynamic friction coefficient between the magnetic layer and the slider material (eg, alumina / titania / carbide) (hereinafter simply referred to as the friction coefficient) is μ._mSL The coefficient of friction between the magnetic layer and SUS (SUS304, hereinafter simply referred to as SUS) is μ._mSUS, The coefficient of friction between the backcoat layer and SUS is μ_BSUS(Μ_mSL / Μ_mSUS) And (μ_mSL / Μ_BSUS) To a specific value, the off-track due to magnetic tape meandering is reduced and the error rate is reduced.DeclineI found out. This off-track reduction reduces the error rateReductionThe effect is particularly great when the track width is 15 μm or less.
[0013]
  The present invention has been completed based on the above findings. That is, at least one undercoat layer and a magnetic layer are formed in this order on one surface of the nonmagnetic support, and a backcoat layer is provided on the opposite surface.The magnetic recording signal is reproduced by the reproducing head using the magnetoresistive element.In the magnetic recording medium, the thickness of the nonmagnetic support is 2.0 μm or more and 7.0 μm or less, and the thickness of the magnetic layer is0. 01μm or moreThe centerline average surface roughness Ra is 0.30 μm or less.0. 5nm or more3.2 nm or less,When measured in a field of view of 350 μm × 260 μm by scanning white light interferometryThe center value of the irregularities of the magnetic layer is P₀ , The maximum convex amount of the magnetic layer is P₁ The second, third, fourth, fifth,..., Nineteenth and twentieth convex amounts are sequentially set to P.₂ , P_Three , P_Four , P_Five ... P₁₉, P₂₀(P₁ -P₀ )But5nm or more30 nm or less and (P₁ -P₂₀)But0. 4nm or moreA magnetic recording medium having a thickness of 5 nm or less (claim 1);, MagnetismA magnetic recording medium having a coercive force of 120 to 320 kA / m and a product of residual magnetic flux density and thickness in the longitudinal direction of 0.0019 μTm to 0.06 μTm.2) And a Young's modulus in the longitudinal direction of the nonmagnetic support is 6.08 GPa (600 kg / mm² )that's all1 2. 0GPa (1184 kg / mm ² )A magnetic recording medium having a ratio (MD / TD) of 0.6 to 1.80 when the Young's modulus in the longitudinal direction is MD and the Young's modulus in the width direction is TD.3). Note that the friction coefficient in the present invention means a dynamic friction coefficient as described above, and a specific measuring method thereof will be described in an example described later.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In a magnetic recording medium in which at least one undercoat layer and a magnetic layer are formed in this order on at least one surface of a nonmagnetic support, a magnetic recording medium having a magnetic layer thickness of 0.3 μm or less is magnetic Since the layer is extremely thin and the thickness loss is small, the recording density in the traveling direction of the magnetic head is high. The thickness of the magnetic layer is preferably 0.01 to 0.3 μm, more preferably 0.01 to 0.25 μm, still more preferably 0.01 to 0.2 μm, and still more preferably 0.01 to 0.15 μm. This range is more preferable because when the thickness is less than 0.01 μm, it is difficult to obtain a uniform magnetic layer, and when it exceeds 0.3 μm, the reproduction output becomes small due to the thickness loss.
[0015]
The centerline average surface roughness (Ra) of the magnetic layer is preferably 3.2 nm or less, more preferably 0.5 to 3.2 nm, further preferably 0.7 to 2.9 nm, and 0.7 to 2.5 nm. Even more preferable. This range is preferable because when the magnetic layer Ra is less than 0.5 nm, the running of the magnetic tape becomes unstable, and when Ra exceeds 3.2 nm, the PW50 becomes wide or the output decreases due to spacing loss. This is because the error rate increases.
[0016]
The center value of the irregularities of the magnetic layer is P₀ , The maximum convex amount of the magnetic layer is P₁ (P₁ -P₀ ) Is preferably 30 nm or less, more preferably 5 to 30 nm, still more preferably 5 to 25 nm, and even more preferably 5 to 20 nm. This range is preferred because the (P₁ -P₀ ) Less than 5 nm, the running of the magnetic tape may become unstable.₁ -P₀ ) Exceeds 30 nm, the PW50 is widened or the output is reduced due to spacing loss, resulting in a high error rate. Also, (P₁ -P₀ ) Of 30 nm or less is also effective in reducing thermal asperity due to collision with the MR head. Furthermore, while satisfying the above conditions, the maximum convex amount of the magnetic layer is set to P₁ The second, third, fourth, fifth,..., Nineteenth and twentieth convex amounts are sequentially set to P.₂ , P_Three , P_Four , P_Five ... P₁₉, P₂₀(P₁ -P₂₀) Is preferably 5 nm or less. (P₁ -P₂₀) Is more preferably 1.8 nm or less, further preferably 1.5 nm or less, and particularly preferably 1.0 nm or less. This range is preferred because (P₁ -P₂₀) Is 5 nm (more preferably 1.8 nm) or less, the contact is improved because the MR head embedded by about 25 nm from the slider (alumina / titania / carbide) and the magnetic tape uniformly contact each other, and the PW50 is reduced and the output is reduced. This is because the error rate is lowered by the improvement. In addition, the presence of such uniform protrusions lowers the coefficient of friction and reduces the catch with the MR slider (AlTiC; alumina / titania / carbide), thereby providing a secondary effect that smooth running performance can be obtained. There is also. The reason why the difference between the maximum convex amount and the twentieth convex amount is important is considered to be related to the fact that the MR head is embedded in a form in which about 25 nm is retracted from the slider surface. Is unknown. For now, I will only describe the experimental facts.
[0017]
Furthermore, in a magnetic tape using an MR head embedded in a slider, [(P₁ -P₀ ) / Ra] is preferably 12 or less, more preferably 10 or less, further preferably 8 or less, and even more preferably 6 or less. [(P₁ -P₀ ) / Ra] is preferably 12 or less even when the MR element is worn, because the MR head and the magnetic tape are uniformly hit, the PW50 is narrow and the output is maintained high, and the error rate is lowered. Such a magnetic tape can be obtained by controlling processing conditions of lapping / rotary / tissue processing (LRT processing) applied to the magnetic layer.
[0018]
  The friction coefficient between the magnetic layer and the slider material (for example, alumina / titania / carbide) is μ_mSL , The coefficient of friction between the magnetic layer and SUS is μ_mSUS, The coefficient of friction between the backcoat layer and SUS is μ_BSUS[(Μ_mSL ) / (Μ_mSUS)] Between 0.7 and 1.3 and [(μ_mSL ) / (Μ_BSUS)] Between 0.8 and 1.5 reduces off-track caused by magnetic tape meandering and reduces the error rate.DeclineTo do. This effect is particularly great when the track width is 5 μm or less. [(Μ_mSL ) / (Μ_mSUS)] Between 0.85 and 1.15, and [(μ_mSL ) / (Μ_BSUS)] Is more preferably 1.0 to 1.3, and [(μ_mSL ) / (Μ_mSUS)] Is 0.9 to 1.1, and [(μ_mSL ) / (Μ_BSUS)] Is more preferably 1.0 to 1.3. In such a magnetic tape, (1) the magnetic layer contains a fatty acid amide together with an ester of higher fatty acid, or the magnetic layer is devised to reduce the amount of the crosslinking agent in the magnetic layer, and (2) the backcoat layer. Is obtained by adding a large particle size carbon black having a particle size of 300 nm to 400 nm and a small particle size carbon black having a particle size of 5 nm to 200 nm, and (3) applying the above LRT treatment to the magnetic layer.
[0019]
The coercive force of the magnetic layer is preferably 120 to 320 kA / m, more preferably 140 to 320 kA / m, and still more preferably 160 to 320 kA / m. If the coercive force of the magnetic layer is less than 120 kA / m, if the recording wavelength is shortened, the output is reduced due to demagnetization, and if it exceeds 320 kA / m, recording by the magnetic head may be difficult.
[0020]
The product of the residual magnetic flux density in the longitudinal direction and the thickness is preferably 0.0019 to 0.06 μTm, more preferably 0.0030 to 0.050 μTm, still more preferably 0.004 to 0.045 μTm, and 0.004 to 0.005. 040 μTm is even more preferred. If the product of the residual magnetic flux density in the longitudinal direction and the thickness is less than 0.0019 μTm, the reproduction output by the MR head is small, and if it exceeds 0.06 μTm, the reproduction output by the MR head may be easily distorted. A magnetic recording medium comprising such a magnetic layer can shorten the recording wavelength, increase the reproduction output when reproduced by an MR head, and further reduce the distortion of the reproduction output, thereby reducing the output to noise ratio. Can be increased.
[0021]
The thickness of the undercoat layer is preferably 0.3 to 3.0 μm, more preferably 0.5 to 2.5 μm, still more preferably 0.5 to 2.0 μm, and even more preferably 0.5 to 1.5 μm. . If the thickness of the undercoat layer is less than 0.3 μm, the durability of the magnetic recording medium may be deteriorated. If the thickness exceeds 3.0 μm, not only the durability improvement effect of the magnetic recording medium is saturated but also in the case of magnetic tape. May increase the overall thickness, shorten the tape length per roll, and reduce the storage capacity.
[0022]
The thickness of the back coat layer is preferably 0.2 to 0.8 μm. This range is preferable when the magnetic recording medium is run less than 0.2 μm, and when it exceeds 0.8 μm, the total thickness of the magnetic recording medium is increased, and the tape length per roll is shortened. This is because the storage capacity is reduced. The center line average surface roughness (Ra) of the backcoat layer is preferably 2 to 15 nm, and more preferably 3 to 8 nm. When the backcoat layer Ra is less than 2 nm, the running of the magnetic tape may become unstable. When the Ra exceeds 15 nm, the surface roughness of the magnetic layer increases due to the back copy and the spacing loss increases. Sometimes. Such a backcoat layer comprises a small particle size carbon black having a particle size of 5 nm to 100 nm and a large particle size carbon black having a particle size of 300 to 400 nm. Iron oxide containing 60 to 98% by weight based on the weight of the inorganic powder and having a particle size of 0.1 μm to 0.6 μm is contained in an amount of 2 to 40% by weight based on the weight of the inorganic powder. It is obtained by performing calendar processing. The addition amount of the large particle size carbon black is usually 5 to 15% by weight of the small particle size carbon black.
[0023]
Below, the preferable form for every component is described.
<Non-magnetic support>
The thickness of the nonmagnetic support is preferably 7.0 μm or less, more preferably 2.0 to 7.0 μm, further preferably 2 to 6.5 μm, and even more preferably 2.5 to 6.0 μm. Nonmagnetic supports with a thickness in this range are preferred because film formation is difficult if the thickness is less than 2 μm, and the strength of the tape decreases, and if it exceeds 7.0 μm, the total thickness of the tape increases, and the storage capacity per tape roll This is because becomes smaller.
[0024]
The Young's modulus in the longitudinal direction of the nonmagnetic support varies depending on the thickness of the nonmagnetic support, but is usually 5.07 GPa (500 kg / mm² ) The above is used. This Young's modulus is 6.08 GPa (600 kg / mm² ) Or more, preferably 7.09 GPa (700 kg / mm² The above is preferable. Further, when the thickness of the nonmagnetic support is 5.0 μm or less, it is 10.13 GPa (1000 kg / mm² ) The above Young's modulus is preferably used. The Young's modulus in the longitudinal direction of the nonmagnetic support is 6.08 GPa (600 kg / mm² If it is less than), the strength of the magnetic tape may be weakened or the running of the magnetic tape may become unstable.
[0025]
When a nonmagnetic support having a ratio (MD / TD) of 0.6 to 1.8 when the Young's modulus in the longitudinal direction of the nonmagnetic support is MD and the Young's modulus in the width direction is TD is used, the MR head This is preferable because the contact with the surface is improved. The preferable range of MD / TD is different between the helical scan type and the linear recording type. The preferable MD / TD range is 0.6 to 1.2 for the helical scan type, and 0.6 to 1. 0 is more preferable, and 0.60 to 0.80 is even more preferable. This range is preferable because the mechanism is unknown at present, but the output variation (flatness) between the entrance side and the exit side of the track of the magnetic head becomes large. In the linear recording type, 1.0 to 1.8 is preferable, 1.1 to 1.7 is more preferable, and 1.2 to 1.6 is more preferable. This range is preferable because the head touch is improved. Such nonmagnetic supports include polyethylene naphthalate films, aromatic polyamide films, aromatic polyimide films and the like.
[0026]
<Undercoat layer>
As described above, the thickness of the undercoat layer is preferably 0.3 to 3.0 μm, more preferably 0.5 to 2.5 μm, still more preferably 0.5 to 2.0 μm, and 0.5 to 1 More preferred is .5 μm. This range is preferable when the magnetic recording medium has a durability of less than 0.3 μm, and when it exceeds 3.0 μm, not only the durability improvement effect of the magnetic recording medium is saturated but also in the case of a magnetic tape. This is because the total thickness is increased, the tape length per roll is shortened, and the storage capacity is reduced.
[0027]
Carbon black and nonmagnetic particles are added to the undercoat layer for the purpose of controlling the viscosity of the paint and the tape rigidity for the purpose of improving conductivity. Nonmagnetic particles used for the undercoat layer include titanium oxide, iron oxide, alumina, and the like, and iron oxide alone or a mixed system of iron oxide and alumina is used. In the undercoat layer, 15 to 35% by weight of carbon black having a particle diameter of 10 to 100 nm, a major axis length of 0.05 to 0.20 μm, and a minor axis length based on the weight of the total inorganic powder in the undercoat layer When 35 to 83% by weight of non-magnetic iron oxide of 5 to 200 nm is contained, and 0 to 20% by weight of alumina having a particle size of 10 to 100 nm is contained as necessary, the magnetic material formed thereon is wet-on-wet. This is preferable because the surface roughness of the layer becomes small. In addition, although nonmagnetic iron oxide is usually acicular, when granular or amorphous nonmagnetic iron oxide is used, iron oxide having a particle size of 5 to 200 nm is preferable. The addition of carbon black having a large particle diameter of 100 nm or more is not excluded as long as the smoothness of the surface is not impaired. In this case, the amount of carbon black is preferably within the above range, with the sum of the small particle size carbon black amount and the large particle size carbon black amount. The amount of large particle carbon black is usually 20% by weight or less of the total carbon black amount.
[0028]
As carbon black (hereinafter also referred to as CB) to be added to the undercoat layer, acetylene black, furnace black, thermal black and the like can be used. Usually, those having a particle size of 5 nm to 100 nm are used, but those having a particle size of 10 nm to 100 nm are preferred. This range is preferable because CB has a structure, so that dispersion of CB is difficult when the particle diameter is less than 10 nm, and smoothness is deteriorated when it exceeds 100 nm. The amount of CB added varies depending on the particle size of CB, but is preferably 15 to 35% by weight. This range is preferable because if the amount is less than 15% by weight, the effect of improving conductivity is poor, and if it exceeds 35% by weight, the effect is saturated. It is more preferable to use 15 to 35% by weight of CB having a particle size of 15 to 80 nm, and it is even more preferable to use 20 to 30% by weight of CB having a particle size of 20 to 50 nm. By adding carbon black having such a particle size and amount, electric resistance is reduced and running unevenness is reduced.
[0029]
The nonmagnetic iron oxide to be added to the undercoat layer preferably has a major axis length of 0.05 to 0.20 μm and a minor axis length (particle diameter) of 5 to 200 nm in the case of needles, and is granular or amorphous. In the thing, a particle size of 5-200 nm is preferable. A particle size of 0.05 to 150 nm is more preferable, and a particle size of 0.05 to 100 nm is more preferable. Needle-shaped ones are more preferable because the orientation of the magnetic layer is improved. The added amount is preferably 35 to 83% by weight, more preferably 40 to 80% by weight, and still more preferably 50 to 75% by weight. The particle size within this range (short axis length in the case of needles) is preferred because uniform dispersion is difficult when the particle size is less than 5 nm, and unevenness at the interface between the undercoat layer and the magnetic layer increases when the particle size exceeds 200 nm. . The addition amount within this range is preferable because if the amount is less than 35% by weight, the effect of improving the coating film strength is small, and if it exceeds 83% by weight, the coating film strength may decrease.
[0030]
In addition to iron oxide, alumina may be added to the undercoat layer. The particle diameter of alumina is preferably 10 to 100 nm, more preferably 20 to 100 nm, and further preferably 30 to 100 nm. If the particle size is less than 10 nm, uniform dispersion is difficult, and if it exceeds 100 nm, irregularities at the interface between the undercoat layer and the magnetic layer may increase. The amount of alumina added is usually 0 to 20% by weight, more preferably 2 to 10% by weight, and still more preferably 4 to 8% by weight.
[0031]
<lubricant>
Lubricants with different roles are used in the coating layer composed of the undercoat layer and the magnetic layer. When the subbing layer contains 0.5 to 4.0% by weight of higher fatty acid and 0.2 to 3.0% by weight of higher fatty acid ester based on the total powder, it will run with magnetic tape. This is preferable because the friction coefficient with the system head, guide roller, and the like becomes small. If the amount of the higher fatty acid added is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 4.0% by weight, the primer layer may be plasticized and the toughness may be lost. The addition of higher fatty acid esters within this range is preferable because if the amount is less than 0.5% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3.0% by weight, the amount transferred into the magnetic layer is too large. This is because there are side effects such as sticking of the tape and the running system head, guide rollers, and the like.
[0032]
When the magnetic layer contains 0.2 to 3.0% by weight of fatty acid amide and 0.2 to 3.0% by weight of higher fatty acid ester with respect to the ferromagnetic powder, the magnetic tape and the running system This is preferable because the coefficient of friction with the capstan or the slider of the MR head becomes small. If the fatty acid amide content is less than 0.2% by weight, the friction coefficient of the head slider / magnetic layer tends to increase, and if it exceeds 3.0% by weight, bleed out and defects such as dropout may occur. is there. As the fatty acid, higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid and linoleic acid are used. Fatty acid esters include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, mono-stearic anhydride sorbitan, di-stearic anhydride sorbitan, tri-stearic anhydride sorbitan Etc. are used. As the fatty acid amide, amides of higher fatty acids such as palmitic acid and stearic acid can be used. The addition of higher fatty acid esters in the above range is preferable when the content is less than 0.2% by weight, and the effect of reducing the friction coefficient is small. When the content exceeds 3.0% by weight, the magnetic tape and the head and guide roller of the running system are stuck. This is because there are side effects such as sticking. Note that the mutual movement of the lubricant in the magnetic layer and the lubricant in the undercoat layer is not excluded. The friction coefficient with the slider of the MR head is preferably 0.30 or less, and more preferably 0.25 or less. This range is preferable because if it exceeds 0.30, spacing loss due to slider contamination is likely to occur. In addition, if less than 0.10, it is difficult to realize. The coefficient of friction with SUS is preferably 0.10 to 0.25, more preferably 0.12 to 0.20. This range is preferable because when it is less than 0.10, the head and the guide roller are slippery and the running becomes unstable, and the head and the guide roller exceeding 0.25 are easily soiled. Also, [(μ_mSL ) / (Μ_mSUS)] Is preferably 0.7 to 1.3, more preferably 0.8 to 1.2. This range is preferable because tracking deviation (off-track) due to meandering of the magnetic tape is reduced.
[0033]
<Magnetic layer>
As described above, the thickness of the magnetic layer is usually 0.3 μm or less, preferably 0.01 to 0.3 μm, more preferably 0.01 to 0.25 μm, still more preferably 0.01 to 0.2 μm, 0.01 to 0.15 μm is even more preferable. It is more preferable that this range is less than 0.01 μm, and it is difficult to obtain a uniform magnetic layer, and if it exceeds 0.3 μm, the reproduction output is reduced due to thickness loss, or the residual magnetic flux density (Br) in the magnetic layer. This is because the product (Brδ) with the thickness (δ) becomes too large, and distortion of the reproduction output due to saturation of the MR head tends to occur. Further, as described above, the coercive force of the magnetic layer is preferably 120 to 320 kA / m, more preferably 140 to 320 kA / m, and further preferably 160 to 320 kA / m. When the coercive force of the magnetic layer is less than 120 kA / m, the output is reduced due to demagnetization when the recording wavelength is shortened, and when it exceeds 320 kA / m, recording by the magnetic head may be difficult. The product of the residual magnetic flux density in the longitudinal direction and the thickness is preferably 0.0019 to 0.06 μTm, more preferably 0.0030 to 0.050 μTm, still more preferably 0.004 to 0.045 μTm, and 0.004 to 0.005. 040 μTm is even more preferred. This range is preferable because the reproduction output by the MR head is small if it is less than 0.0019 μTm, and the reproduction output by the MR head tends to be distorted if it exceeds 0.06 μTm.
[0034]
Ferromagnetic iron metal powder and hexagonal barium ferrite powder are used for the magnetic powder added to the magnetic layer. The coercive force of the ferromagnetic iron metal powder and the hexagonal barium ferrite powder is preferably 120 to 320 kA / m, and the saturation magnetization is 120 to 200 A · m for the ferromagnetic iron metal powder.² / Kg (120 to 200 emu / g) is preferred, 130 to 180 A · m² / Kg (130 to 180 emu / g) is more preferable. For hexagonal barium ferrite powder, 50-70A ・ m² / Kg (50-70 emu / g) is preferred. The magnetic characteristics of the magnetic layer and the magnetic characteristics of the ferromagnetic powder are both measured values with a sample vibration type magnetometer at an external magnetic field of 1.28 MA / m (16 kOe).
[0035]
The average major axis length of the ferromagnetic iron-based metal powder used in the magnetic recording medium of the present invention is preferably 0.03 to 0.2 μm, more preferably 0.03 to 0.18 μm, and 0.04 to 0.00. 15 μm is more preferable. This range is preferable because when the average major axis length is less than 0.03 μm, the cohesive force of the magnetic powder increases, making it difficult to disperse in the paint. When the average major axis length is greater than 0.2 μm, the coercive force decreases. This is because the particle noise based on the size of the particles becomes large. Moreover, in the hexagonal barium ferrite powder, a plate diameter of 5 to 200 nm is preferable for the same reason. The average major axis length and particle size are obtained by measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and calculating the average value of 100 pieces. The ferromagnetic iron-based metal powder has a BET specific surface area of 35 m.² / G or more is preferable, 40 m² / G or more is more preferable, 50 m² / G or more is most preferable. The BET specific surface area of hexagonal barium ferrite powder is 1-100m² / G or more is preferable.
[0036]
As binders to be included in the undercoat layer and the magnetic layer, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride A combination of at least one selected from vinyl acetate-maleic anhydride copolymer, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer, nitrocellulose and the like and a polyurethane resin can be used. Among these, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer and a polyurethane resin in combination. Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.
[0037]
COOH, SO as functional groups_Three M, OSO₂ M, P = O (OM)_Three , O-P = O (OM)₂ [M is a hydrogen atom, an alkali metal base or an amine salt], OH, NR′R ″, N⁺ R '' 'R' '' 'R' '' '' [R ′, R ″, R ′ ″, R ″ ″, R ′ ″ ″ are hydrogen or hydrocarbon groups], epoxy groups A binder such as a urethane resin made of a polymer having the following is used. The reason why such a binder is used is that the dispersibility of magnetic powder and the like is improved as described above. When two or more kinds of resins are used in combination, it is preferable to match the polarities of the functional groups._Three A combination of M groups is preferred.
[0038]
These binders are used in the range of 7 to 50 parts by weight, preferably 10 to 35 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. In particular, it is most preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin as a binder.
[0039]
In addition to these binders, it is desirable to use a thermosetting crosslinking agent that is bonded to a functional group contained in the binder and crosslinked. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are usually used in a proportion of 10 to 50 parts by weight with respect to 100 parts by weight of the binder. More preferably, it is 10-35 weight part. Note that it is preferable that the amount of the crosslinking agent used in the magnetic layer be about ½ (30% to 60%) of the amount used in the undercoat layer because the friction coefficient of the MR head with respect to the slider becomes small. This range is preferred if the coating strength is less than 30%, the coating strength of the magnetic layer tends to be weak, and if it exceeds 60%, it is necessary to increase the LRT processing conditions in order to reduce the friction coefficient against the slider, resulting in an increase in cost. Because it leads to.
[0040]
Conventionally known CB can be added for the purpose of improving conductivity and improving surface lubricity. As these CB, acetylene black, furnace black, thermal black, etc. can be used. A particle size of 5 nm to 100 nm is used, but a particle size of 10 nm to 100 nm is preferable. This range is preferable because when the particle size is 5 nm or less, it is difficult to disperse CB. When the particle size is 100 nm or more, it is necessary to add a large amount of CB. In any case, the surface becomes rough and the output decreases. Because. The addition amount is preferably 0.2 to 5% by weight, more preferably 0.5 to 4% by weight, still more preferably 0.5 to 3.5% by weight, and more preferably 0.5 to 3% by weight based on the ferromagnetic powder. Is more preferable. This range is preferable because the effect is small if it is less than 0.2% by weight, and the surface of the magnetic layer tends to become rough if CB exceeding 5% by weight is added.
[0041]
<Back coat layer>
For the purpose of improving running performance, a conventionally known back coat layer having a thickness of 0.2 to 0.8 μm can be used. This range is good because if it is less than 0.2 μm, the effect of improving the running performance is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape becomes thick and the storage capacity per roll becomes small. The coefficient of friction between the backcoat layer and SUS is preferably from 0.10 to 0.30, and more preferably from 0.10 to 0.25. This range is preferable because if it is less than 0.10, the guide roller portion is slippery and traveling becomes unstable, and if it exceeds 0.30, the guide roller is likely to become dirty. Also, [(μ_mSL ) / (Μ_BSUS)] Is preferably 0.8 to 1.5, more preferably 0.9 to 1.4. This range is preferable because tracking deviation (off-track) due to meandering of the magnetic tape may be reduced.
[0042]
As the carbon black (CB) of the back coat layer, acetylene black, furnace black, thermal black, and the like can be used. Usually, small particle size carbon and large particle size carbon are used. As the small particle size carbon, those having a particle size of 5 nm to 100 nm can be used, but those having a particle size of 10 nm to 100 nm are more preferable. This range is more preferable because when the particle size is 10 nm or less, it is difficult to disperse CB, and when the particle size is 100 nm or more, it is necessary to add a large amount of CB. This is because it causes a setback (embossing). When carbon having a particle size of 300 to 400 nm is added as a large particle size carbon at a ratio of 5 to 15% by weight with respect to the addition amount of the small particle size carbon, the surface is not roughened and the effect of improving running performance is increased. The total addition amount of the small particle size carbon and the large particle size carbon is preferably 60 to 98% by weight, more preferably 70 to 95% by weight based on the weight of the inorganic powder. The center line average surface roughness Ra of the backcoat layer is preferably 2 to 15 nm, and more preferably 3 to 8 nm.
[0043]
Further, for the purpose of improving the strength, it is preferable to add iron oxide having a particle diameter of 0.1 μm to 0.6 μm, and more preferably 0.2 μm to 0.5 μm. The addition amount is preferably 2 to 40% by weight, more preferably 5 to 30% by weight based on the weight of the inorganic powder.
[0044]
As the binder, the same resin as that used in the magnetic layer and the undercoat layer can be used for the back coat layer. Among these, the cellulose resin and polyurethane are used for reducing the friction coefficient and improving the running property. It is preferable to use a combination of resins. The binder content is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight, more preferably 60 to 110 parts by weight, based on 100 parts by weight of the total amount of carbon black and the inorganic nonmagnetic powder. More preferred is 70 to 110 parts by weight. This range is preferable because if the amount is less than 50 parts by weight, the strength of the backcoat layer is insufficient, and if it exceeds 120 parts by weight, the friction coefficient tends to increase. It is preferable to use 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin. In order to further cure the binder, it is preferable to use a crosslinking agent such as a polyisocyanate compound.
[0045]
As the crosslinking agent, the crosslinking agent used in the magnetic layer and the undercoat layer described above is used for the backcoat layer. The amount of the crosslinking agent is usually 10 to 50 parts by weight with respect to 100 parts by weight of the binder. Preferably it is 10-35 weight part, More preferably, it is 10-30 weight part. This range is preferred because if less than 10 parts by weight, the coating strength of the backcoat layer tends to be weak, and if it exceeds 35 parts by weight, the dynamic friction coefficient against SUS increases.
[0046]
The special-purpose backcoat layer on which the magnetic servo signal is recorded includes 30 to 60 parts by weight of the above-described ferromagnetic powder used for the magnetic layer, 40 to 70 parts by weight of the above-described carbon black used for the backcoat layer, If necessary, 2 to 15 parts by weight of the above-described iron oxide and alumina used for the back coat layer are added. The binder is usually 40 to 150 parts by weight, preferably 50 to 120 parts by weight of the resin used for the back coat layer with respect to 100 parts by weight of the total amount of the ferromagnetic powder, carbon black, and inorganic nonmagnetic powder. Use parts by weight. Moreover, the above-mentioned crosslinking agent can be normally used for a crosslinking agent in the ratio of 10-50 weight part with respect to 100 weight part of binders. For the same reason as described in the above magnetic layer, the coercive force is preferably 120 to 320 kA / m, and the product of the residual magnetic flux density Br and the film thickness is preferably 0.018 to 0.06 μTm.
[0047]
<LRT (wrapping / rotary / tissue) processing>
An outline of the LRT process will be described with reference to FIG. In FIG. 1, reference numeral 1 is a feeding roll for the magnetic tape 30, 2 is a feeding roll, 3 is an abrasive tape (wrapping tape), 4 is a guide block for the abrasive tape, 5 is a rotating roll for the abrasive tape, and 6 is aluminum. 7 is a rotating rod for contact with the nonwoven fabric against the back coat layer 30b side of the magnetic tape 30, 8 is a rotating rod for contact with the nonwoven fabric against the magnetic layer 30a side, 9 is a nonwoven fabric (tissue), and 10 is a nonwoven fabric. Rotating roll 11, 11 is a feed roller, and 12 is a winding roll.
[0048]
(1) Wrapping treatment: As shown in FIG. 1, the polishing tape (wrapping tape) 3 has a constant speed in the direction opposite to the feeding direction of the magnetic tape 30 (tape feeding speed is standard: 400 m / min) by the rotating roll 5. (Standard: 14.4 cm / min), and is pressed by the guide block 4 from the lower side in the figure to come into contact with the magnetic layer 30a side of the magnetic tape 30, and the magnetic tape unwinding tension and polishing at this time Polishing is performed with the tension of the tape 3 being constant (standard: 100 g and 250 g, respectively). The polishing tape (wrapping tape) 3 used in this step is a wrapping tape with fine abrasive grains such as M20000, WA10000 or K10000. Although it is not excluded to use a polishing wheel (wrapping wheel) instead of or in combination with the polishing tape (wrapping tape) 3, only the polishing tape (wrapping tape) 3 is required when frequent replacement is required. Is used.
[0049]
(2) Rotary treatment: Rotary wheel with groove for air venting shown in FIG. 1 [Standard: width 1 inch (25.4 mm), diameter 60 mmφ, width 2 mm for air venting, groove angle 45 degrees, manufactured by Kyowa Seiko Co., Ltd.] The magnetic tape 30 is rotated relative to the magnetic layer 30a of the magnetic tape 30 while rotating at a constant rotational speed (normally: 200 to 3000 rpm, standard: 1100 rpm) in a direction opposite to the traveling direction of the magnetic tape 30 (indicated by an arrow in the drawing). The magnetic layer 30a is subjected to a surface treatment by contacting at a contact angle of (standard: 90 degrees).
[0050]
(3) Tissue treatment: Tissue (non-woven fabric, for example, Toraysee, manufactured by Toray Industries, Inc.) is fed at a constant speed (standard: 14.0 mm / min) in the direction opposite to the feeding direction of the magnetic tape 30 and rotating rods 7 and 8 Then, they are pressed against the surfaces of the back coat layer 30b and the magnetic layer 30a of the magnetic tape 30 to perform the cleaning process.
[0051]
The cassette tape incorporating the tape of the present invention has a large capacity per volume, a small PW50 when the MR reproducing head is used, and a high reproduction output. It is highly reliable and particularly excellent.
[0052]
【Example】
EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In addition, the part of an Example and a comparative example shows a weight part.
[0053]
Example 1:
《Coating component for undercoat layer》
(1)
68 parts of iron oxide powder (average particle size: 0.11 × 0.02 μm)
α-alumina (average particle size: 0.07 μm) 8 parts
Carbon black (average particle size: 25 nm, oil absorption: 55 g / cc) 24 parts
Stearic acid 2.0 parts
0.8 parts of vinyl chloride-hydroxypropyl acrylate copolymer
(Contains-SO_Three Na group: 0.7 × 10^-FourEquivalent / g)
Polyester polyurethane resin 4.4 parts
(Tg: 40 ° C, contained -SO_Three Na group: 1 × 10^-FourEquivalent / g)
25 parts of cyclohexanone
40 parts of methyl ethyl ketone
Toluene 10 parts
(2)
1 part butyl stearate
70 parts of cyclohexanone
50 parts of methyl ethyl ketone
20 parts of toluene
(3)
Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) 4.4 parts
10 parts of cyclohexanone
15 parts of methyl ethyl ketone
Toluene 10 parts
[0054]
<Coating component for magnetic layer>
(1)
100 parts of ferromagnetic iron metal powder
(Co / Fe: 20 at%, Y / (Fe + Co): 3 at%,
Al / (Fe + Co): 5 wt%, Ca / Fe: 0 wt%,
σs: 155 A · m² / Kg, Hc: 149.6 kA / m,
(pH: 9.4, long axis length: 0.10 μm)
12.3 parts of vinyl chloride-hydroxypropyl acrylate copolymer
(Contains-SO_Three Na group: 0.7 × 10^-FourEquivalent / g)
Polyester polyurethane resin 5.5 parts
(Contains-SO_Three Na group: 1.0 × 10^-FourEquivalent / g)
α-alumina (average particle size: 0.12 μm) 8 parts
α-alumina (average particle size: 0.07 μm) 2 parts
Carbon black 1.0 parts
(Average particle size: 75 nm, DBP oil absorption: 72 cc / 100 g)
Metal acid phosphate 2 parts
Palmitic acid amide 1.5 parts
N-Butyl stearate 1.0 part
65 parts of tetrahydrofuran
245 parts of methyl ethyl ketone
Toluene 85 parts
(2)
Polyisocyanate 2.0 parts
167 parts of cyclohexanone
[0055]
After kneading (1) with the kneader in the paint component for the undercoat layer, add (2) and stir, and then disperse with a sand mill for a residence time of 60 minutes. After filtering, it was set as the coating material for undercoat layers. Separately, after kneading the above-mentioned magnetic layer coating component (1) with a kneader, it was dispersed with a sand mill with a residence time of 45 minutes, and after adding and stirring and filtering the magnetic layer coating component (2), A magnetic paint was used. The undercoat paint is dried on a support made of polyethylene naphthalate film (thickness 6.2 μm, MD = 6.08 GPa, MD / TD = 1.3, manufactured by Teijin Ltd.), and after calendering. The thickness of the magnetic layer is applied to the undercoat layer, and the above magnetic coating is further wetted so that the thickness of the magnetic layer after the magnetic field orientation treatment, drying, and calendering treatment is 0.15 μm. -On-wet coating, magnetic field orientation treatment, and drying using a drier to obtain a magnetic sheet. In the magnetic field orientation treatment, an NN counter magnet (5 kG) is installed in front of the dryer, and two NN counter magnets (5 kG) are spaced from each other at a distance of 50 cm from the front side 75 cm of the position where the coating film is dry. It was installed at. The coating speed was 100 m / min.
[0056]
《Paint component for back coat layer》
80 parts of carbon black (average particle size: 25 nm)
Carbon black (average particle size: 370 nm) 10 parts
10 parts of iron oxide (major axis length: 0.4 μm, axial ratio: approx. 10)
45 parts of nitrocellulose
Polyurethane resin (SO_Three (Containing Na group) 30 parts
260 parts of cyclohexanone
260 parts of toluene
525 parts of methyl ethyl ketone
[0057]
After the coating component for the backcoat layer is dispersed with a sand mill for a residence time of 45 minutes, 15 parts of polyisocyanate is added to adjust and filter the coating for the backcoat layer, and then the opposite side of the magnetic layer of the magnetic sheet prepared above Then, it was applied so that the thickness after drying and calendering was 0.5 μm and dried. The magnetic sheet thus obtained was mirror-finished at a temperature of 100 ° C. and a linear pressure of 150 kg / cm with a seven-stage calendar made of a metal roll, and the magnetic sheet was wound on a core at 70 ° C. for 72 hours. After aging, it was cut into a 1/2 inch width and subjected to LRT treatment under the following conditions. The magnetic tape thus obtained was incorporated into a cartridge to produce a computer tape. Ra of the backcoat layer was 8 nm.
[0058]
<LRT (wrapping / rotary / tissue) processing>
(1) Lapping process: As shown in FIG. 1, the polishing tape (lapping tape) 3 is 14.4 cm in the direction opposite to the feeding direction of the magnetic tape 30 (magnetic tape feeding speed: 400 m / min as a standard) by the rotating roll 5. Of the magnetic tape 30 is brought into contact with the surface of the magnetic layer 30a of the magnetic tape 30 by being pushed by the guide block 4 from the lower part in the figure. Polishing was performed with a tension of 250 g.
[0059]
(2) Rotary wheel processing: A grooved aluminum rotary wheel (groove angle 45 degrees, manufactured by Kyowa Seiko Co., Ltd.) 6 having a width of 1 inch (25.4 mm), a diameter of 60 mm, and a groove width of 2 mm shown in FIG. The surface treatment of the magnetic layer 30a was performed by rotating it in the direction opposite to the feeding direction of 30 (rotation speed 1100 rpm) and bringing it into contact with the magnetic layer 30a at a contact angle of 90 degrees.
[0060]
(3) Tissue treatment: Non-woven fabric (here, Toray's non-woven Toraysee) 9 is fed at a speed of 14.0 mm / min in the direction opposite to the feeding direction of the magnetic tape 30, and each of the rotating rods 7 and 8 is backcoated. The surface of the layer 30b and the magnetic layer 30a was pressed to perform a cleaning process on these surfaces.
[0061]
Examples 2-10:
Magnetic tapes for computers of Examples 2 to 10 were produced in the same manner as in Example 1 except that the partial conditions were changed to those in Tables 1 to 3.
[0062]
Comparative Example 1:
A computer tape of Comparative Example 1 was produced in the same manner as in Example 1 except that the LRT treatment was not performed.
[0063]
Comparative Example 2:
A computer tape of Comparative Example 2 was produced in the same manner as in Example 1 except that the following LBT process was performed instead of the LRT process.
[0064]
<LBT processing>
While the magnetic tape was run at 400 m / min, the surface of the magnetic layer was subjected to post-processing such as lapping tape polishing, blade polishing, and surface wiping to prepare a magnetic tape. At this time, K10000 was used for the wrapping tape (polishing tape), a carbide blade was used for the blade, and Toray Toray manufactured by Toray was used for wiping the surface, and processing was performed with a running tension of 30 g. The magnetic tape obtained as described above was incorporated into a cartridge to produce a magnetic tape for computers.
[0065]
Comparative Example 3:
A computer tape of Comparative Example 3 was produced in the same manner as Comparative Example 2 except that the LBT treatment was performed 10 times.
[0066]
Comparative Examples 4-6:
Magnetic tapes for computers of Comparative Examples 4 to 6 were produced in the same manner as Comparative Example 2 except that the partial conditions were changed to those shown in Table 5.
[0067]
The characteristics were evaluated as follows.
<Measurement of PW50, playback output, error rate, etc.>
The PW50, reproduction output and error rate (ERT) were measured by recording (recording wavelength 0.55 μm) and reproducing using an LTO drive modified so that thin tape could be measured. PW50 is the value when the PW50 of the comparative example 1 tape is 1, the reproduction output is the value when the comparative example 1 tape is 0 dB, and the output deterioration is 100 dB when the initial value of each magnetic tape is 0 dB. It is the value after having performed it once.
[0068]
<Evaluation of surface roughness of magnetic layer, center value of unevenness and convexity>
Scan Length was measured at 5 μm by scanning white light interferometry using a general-purpose three-dimensional surface structure analyzer NewView 5000 manufactured by ZYGO. The measurement visual field is 350 μm × 260 μm. Ra is the centerline average surface roughness of the magnetic layer, and P is the center value of the irregularities.₀ , P is the maximum convex amount (first convex amount)₁ , The second, third, fourth, fifth,..., 19th and 20th convex amounts in order, P₂ , P_Three , P_Four , P_Five ... P₁₉, P₂₀(P₁ -P₀ ) And (P₁ -P₂₀) And [(P₁ -P₀ ) / Ra].
[0069]
<Measurement of MR head protrusion and wear>
DI (Digital Instrument) scanning probe microscope (Nano Scopea / Dimension-3100 Tapping mode AFM) measures 80 μm × 80 μm field of view, corrects tilt, noise, etc., and analyzes cross-sectional profile The amount of protrusion of the MR head and the amount of wear before and after running were measured.
[0070]
<Measurement of friction coefficient between magnetic layer and slider material and SUS>
[SUS]
The friction coefficient was measured when a magnetic tape was applied to a SUS pin (SUS304) with an outer diameter of 5 mm at an angle of 90 ° and a load of 0.64 N, and the same part of the magnetic tape was repeatedly slid 10 times at a feed rate of 20 mm / sec. .
[0071]
[Slider material]
The friction coefficient was measured when the magnetic tape was applied to an ALTIC pin with an outer diameter of 7 mm at an angle of 90 ° and a load of 0.64 N, and the same part of the magnetic tape was repeatedly slid 10 times at a feed rate of 20 mm / sec.
[0072]
<Measurement of Young's modulus (MD, TD) of non-magnetic support>
Using a small tensile tester (manufactured by Yokohama System Co., Ltd.), the strain and tensile strength in an environment of 23 ° C. and 50% RH were measured. The measured length of the sample was 10 mm, the sample was pulled at a tensile rate of 10% strain / minute, and the 0.3% elongation elastic modulus was evaluated based on the value of 0.3% strain of the obtained strength. This evaluation was performed in the longitudinal direction and the width direction of the sample.
[0073]
The above measurement results are shown in Tables 1 to 5. The meanings of the abbreviations in the table are as follows.
・ Μ_mSL : Friction coefficient between magnetic layer and slider material
・ Μ_mSUS: Friction coefficient between magnetic layer and SUS
・ Μ_BSUS: Friction coefficient between backcoat layer and SUS
Brδ: product of residual magnetic flux density (Br) and thickness (δ) of the magnetic layer
Hc: coercivity of the magnetic layer
・ BC: Backcoat layer
・ CB: Carbon black
MD / TD: Ratio of Young's modulus (MD) in the longitudinal direction and Young's modulus (TD) in the width direction of the non-magnetic support
Magnetic surface roughness Ra: center line average surface roughness Ra of the magnetic layer
[0074]
[Table 1]

[0075]
[Table 2]

[0076]
[Table 3]

[0077]
[Table 4]

[0078]
[Table 5]

[0079]
【The invention's effect】
As apparent from Examples 1 to 10 and Comparative Examples 1 to 6 shown in Tables 1 to 5, a magnetic recording medium comprising a nonmagnetic support, an undercoat layer, a magnetic layer, and a backcoat layer, When the layer thickness is 0.30 μm or less, the center line average surface roughness Ra is 3.2 nm or less, and the center value of the unevenness of the magnetic layer is P₀ , The maximum convex amount of the magnetic layer is P₁ , The 20th convex amount is P₂₀(P₁ -P₀ ) Is 30 nm or less and (P₁ -P₂₀) Of 5 nm or less is an excellent magnetic recording medium having a small error rate. Such an effect is (P₁ -P₂₀) Is particularly remarkable in a magnetic recording medium having a thickness of 1.8 nm or less. Also, the coefficient of friction between the magnetic layer and the slider material is μ_mSL , The coefficient of friction between the magnetic layer and SUS is μ_mSUS, The coefficient of friction between the backcoat layer and SUS is μ_BSUS[(Μ_mSL ) / (Μ_mSUS)] Is 0.7 to 1.3, and [(μ_mSL ) / (Μ_BSUS)] Is 0.8 to 1.5, which is an excellent magnetic recording medium with small off-track.
[Brief description of the drawings]
FIG. 1 is a schematic process diagram showing an example of LRT (wrapping / rotary / tissue) processing performed when manufacturing a magnetic recording medium of the present invention.
FIG. 2 is a schematic plan view showing a recording head and a reproducing MR head placed on a slider.
3 is a schematic cross-sectional view taken along line YY in FIG.
[Explanation of symbols]
20 MR head
22 Slider
30 Magnetic recording media (magnetic tape)
30a Magnetic layer
30b Backcoat layer

Claims (3)

At least one undercoat layer and magnetic layer are formed in this order on one surface of a nonmagnetic support, and a backcoat layer is formed on the opposite surface, and reproduction is performed using a magnetoresistive element retracted from the slider surface. In a magnetic recording medium in which a magnetic recording signal is reproduced by a head,
The thickness of the non-magnetic support is 2.0 μm or more and 7.0 μm or less,
The thickness of the magnetic layer is 0.01 μm or more and 0.30 μm or less,
The center line average surface roughness Ra is 0.5 nm or more and 3.2 nm or less,
The center value of the unevenness of the magnetic layer when measured in a field of view of 350 μm × 260 μm by scanning white light interferometry is P ₀ , the maximum convex amount of the magnetic layer is P ₁ , and the second, third, and fourth in order. th, fifth, ..., th first 19, P ₂ the twentieth projection height, P _3, P _4, P _5, ..., at the time of the _{P 19, P 20 (P 1} - the magnetic recording medium comprising a P ₀₎ is in 5nm or 30nm or less, and (P ₁ -P ₂₀₎ are under 5nm or less than 0.4 nm.   The magnetic recording medium according to claim 1, wherein the magnetic layer has a coercive force of 120 to 320 kA / m and a product of a residual magnetic flux density and a thickness in the longitudinal direction of 0.0019 μTm to 0.06 μTm. Non-magnetic support, the longitudinal Young's modulus is 6.08GPa (600kg / mm ²⁾ or more 12.0GPa (1184kg / mm ²⁾ or less, the longitudinal Young's modulus MD, the Young's modulus in the width direction TD The magnetic recording medium according to claim 1, wherein the ratio (MD / TD) is 0.6 to 1.80.

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