JP2003178418A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium adaptable to an MR head wherein an error rate is low and offtrack is small. <P>SOLUTION: In the magnetic recording medium constituted of a nonmagnetic support, a lower coating layer, a magnetic layer and a backcoat layer, a thickness of the magnetic layer is set to 0.30 μm or lower and, when a center value of recessed and projected parts of the magnetic layer is P<SB>0</SB>, a maximum projecting amount of the magnetic layer is P<SB>1</SB>, and a 20th projecting amount is P<SB>20</SB>, (P<SB>1</SB>-P<SB>0</SB>) is set to 30 nm or lower, and (P<SB>1</SB>-P<SB>20</SB>) is set to 5 nm or lower, more preferably 1.8 nm or lower. Thus, a good magnetic recording medium of a small error rate is realized. Additionally, when a friction coefficient between the magnetic layer and a slider material is μ<SB>m</SB>SL, a friction coefficient between the magnetic layer and SUS is μ<SB>m</SB>SUS, and a friction coefficient between the backcoat layer and the SUS is μBSUS, [(μ<SB>m</SB>SL)/(μ<SB>m</SB>SUS)] is set to 0.7 to 1.3, and [(μ<SB>m</SB>SL)/(μBSUS)] is set to 0.7 to 1.5. Thus, a good magnetic recording medium of small offtrack is obtained. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having high recording capacity, high access speed and high transfer speed, and particularly uses a reproducing head (hereinafter, MR head) using a magnetoresistive effect element (MR element). The present invention relates to a magnetic recording medium for data backup.

[0002]

2. Description of the Related Art Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc., but especially in the field of data backup tapes, the large capacity of the hard disk to be backed up. Along with this, a storage capacity of several tens of GB or more per roll has been commercialized, and it is indispensable to increase the capacity of the backup tape in order to cope with the further increase in the capacity of the hard disk in the future. Further, in order to increase the access speed and the transfer speed, it is essential to increase the tape feeding speed and the relative speed between the tape and the head.

In order to increase the capacity per roll of backup tape, it is necessary to reduce the total thickness of the tape to increase the length of the tape per roll, and to reduce the thickness of the magnetic layer to 0.3 μm or less. It is necessary to reduce the thickness demagnetization to shorten the recording wavelength and to narrow the track width (the signal pattern width on the tape) to 15 μm or less to increase the recording density in the width direction.

If the thickness of the magnetic layer is extremely thin, 0.3 μm or less, the durability may be deteriorated. Therefore, it is necessary to provide at least one undercoat layer between the non-magnetic support and the magnetic layer. Further, when the recording wavelength is shortened, the influence of the spacing between the magnetic layer and the magnetic head becomes large. Therefore, if there is a large protrusion in the magnetic layer, the half value width (hereinafter PW50) of the output peak becomes wide due to the spacing loss. The error rate increases due to the decrease in the output and the decrease in the output.

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 becomes small. Therefore, the reproducing head uses a magnetoresistive element capable of obtaining a high output even with a minute magnetic flux. It is necessary to use a reproducing head (hereinafter, MR head).

Conventionally, in a magnetic recording medium compatible with an MR head, the magnetic flux (product of residual magnetic flux density and thickness) of the magnetic recording medium is controlled to a specific value to prevent distortion of the output of the MR head (for example, It is proposed to reduce the thermal asperity of the MR head (see, for example, Patent Document 3) by making the dent on the surface of the magnetic layer not more than a specific value.

[0007]

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-238225 (Claims, Paragraph Nos. 0007 to 0011, Examples)

[Patent Document 2] Japanese Patent Laid-Open No. 2000-40217 (Claims, Paragraph numbers 0006 to 0009, Examples)

[Patent Document 3] Japanese Unexamined Patent Publication No. 2000-40218 (claims, paragraph numbers 0005 to 0014, 0023,
Example, FIGS. 2 and 3)

As a conventional magnetic head, a chip in which a magnetic induction head for recording and a magnetic induction head for reproduction are bonded together is used as it is. 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 recording head 21 for recording. In these figures, reference numeral 20a is MR
Elements 21a and 21b are magnetic elements forming the recording head 21, 21c is a write gap, and 23 is a shield material. In addition, the MR head 20 is 2
It is embedded in a state of being retracted by about 5 nm. That is, the conventional head has a very small chip and travels in such a manner that the knife edge bites into the magnetic tape, whereas the MR head 20 as shown in FIGS. 2 and 3 retracts into the large slider 22. Since the magnetic tape 30 is embedded in the slider 22, the magnetic tape 30 travels while contacting the slider 22. Also, the magnetic tape 30 and the MR tape 20 are made to bulge toward the MR head 20.
The head 20 contacts. Since the contact form is significantly different from the conventional one, the characteristics required for the magnetic tape are completely different even if the spacing loss is reduced. Furthermore, the MR head 20 is M
Since the R element 20a is composed of a very thin thin film, it is easily worn. As shown in FIGS. 2 and 3, the MR head 20 and the recording head 21 are usually provided as a pair so that the magnetic tape 30 can be recorded / reproduced regardless of whether the magnetic tape 30 runs in the forward direction or the back direction. In addition, a plurality of tracks are provided in the left-right direction in FIG. 2 so that a plurality of tracks can be simultaneously read and written.

In addition, since the MR head has a very narrow track width, it is necessary to perform tracking servo of the MR head.
Servo signals are provided. The track servo system includes a magnetic servo system and an optical servo system. In the former, a servo band is formed on a magnetic layer by magnetic recording and magnetically read to perform servo tracking, and in the latter, a recess is formed. A servo band composed of an array is formed on the back coat layer by laser irradiation or the like, and this is optically read to perform servo tracking. In addition to these, there is a magnetic servo system in which the back coat layer is also magnetized and a magnetic servo signal is recorded on this 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.

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 travel at a high speed while tracing the servo signal, but the slider material (for example, alumina / titania / carbide) is required. If the coefficient of friction with the magnetic layer or the back coat layer for the material of the guide roller or the guide roller is insufficient, the magnetic tape meanders and tracking deviation (off-track) occurs, resulting in a PW50.
There is a problem that the error rate becomes high due to widening of the output and reduction of the output.

An object of the present invention is to improve the error rate by reducing the spacing loss of the magnetic tape corresponding to the MR head and reducing the off-track due to the meandering of the magnetic tape. Another object is to reduce wear of the MR head used in combination with the magnetic recording medium of the present invention.

[0012]

Means for Solving the Problems The inventors of the present invention have made earnest studies in order to achieve the above object, and as a result, as a result, the difference between the maximum convex amount (P ₁ ) of the magnetic tape and the average value (P ₀ ) of the concave and convex portions. (P ₁ −
P ₀₎ and the following specific values, and the maximum projection height (P ₁₎ and by the following twentieth convex amount (specific value the difference (P ₁ -P ₂₀₎ of the P _20), scan Pacing loss is reduced, and the dynamic friction coefficient (hereinafter simply referred to as friction coefficient) between the magnetic layer and the slider material (for example, alumina / titania / carbide) is μ _mSL , and the magnetic layer and SUS (SUS304, hereinafter simply referred to as SUS) are the friction coefficient _μ mSUS, the friction coefficient of the back coat layer and SUS μ _{BS US} and was at the time of (μ _mSL
It was found that by controlling / _μmSUS ) and ( _μmSL / _μBSUS ) to specific values, the off-track due to the meandering of the magnetic tape is reduced and the error rate is improved.
The effect of improving the error rate by reducing the off-track is particularly large when the track width is 15 μm or less.

The present invention has been completed based on the above findings.
It was done. That is, one surface on the non-magnetic support
And at least one undercoat layer and the magnetic layer are formed in this order.
Recording medium having a back coat layer on the opposite surface
, The thickness of the non-magnetic support is 2.0 μm or more and 7.0 μm
Below, the thickness of the magnetic layer is 0.30μm or less, the unevenness of the magnetic layer
The central value of P₀ , The maximum convex amount of the magnetic layer is P₁ , Second in sequence
Th, third, fourth, fifth, ..., 19th
The 20th and 20th convex amount is P₂ , P₃ , P_Four , P _Five ・ ・
., P₁₉, P₂₀And (P₁ -P₀ ) Is less than 30 nm
Below and (P₁-P₂₀) Is less than 5 nm
Reproduction using a medium (claim 1) and a magnetoresistive effect element
Magnetic recording medium from which magnetic recording signals are reproduced by the raw head
The coercive force of the body (claim 2) and the magnetic layer is 120 to 320 k.
A / m, product of residual magnetic flux density and thickness in the longitudinal direction is 0.001
A magnetic recording medium having a thickness of 8 μTm to 0.06 μTm.
3) and the Young's modulus in the longitudinal direction of the non-magnetic support is 6.08 G
Pa (600 kg / mm² ) The above is the longitudinal direction
Ratio when MD is MD and Young's modulus is TD
(MD / TD) 0.6 to 1.80 magnetic recording medium (contract
It relates to claim 4). The friction referred to in the present invention
The coefficient means the coefficient of dynamic friction as described above, and
The physical measurement method will be described in Examples below.

[0014]

BEST MODE FOR CARRYING OUT 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 non-magnetic support, the thickness of the magnetic layer is 0.3 μm.
The magnetic recording medium having a thickness of m or less has a high recording density in the magnetic head traveling direction because the magnetic layer is extremely thin and the thickness loss is small. The thickness of the magnetic layer is preferably 0.01 to 0.3 μm,
01 to 0.25 μm is more preferable, 0.01 to 0.2 μm is further preferable, and 0.01 to 0.15 μm is further preferable. This range is more preferable because if it is less than 0.01 μm, it is difficult to obtain a uniform magnetic layer, and if it exceeds 0.3 μm, the reproducing output becomes small due to the thickness loss.

The center line average surface roughness (Ra) of the magnetic layer is 3.
2 nm or less is preferable, 0.5 to 3.2 nm is more preferable, 0.7 to 2.9 nm is further preferable, and 0.7 to 2.5 nm is preferable.
Is more preferable. This range is preferable because when the Ra of the magnetic layer is less than 0.5 nm, the running of the magnetic tape becomes unstable, and when Ra exceeds 3.2 nm, the spacing loss causes the PW50 to widen or the output to decrease. Or
This is because the error rate becomes high.

When the center value of the unevenness of the magnetic layer is P ₀ and the maximum amount of projection of the magnetic layer is P ₁ , (P ₁ -P ₀ ) is 30 nm.
The following is preferable, 5-30 nm is more preferable, and 5-2 is
5 nm is more preferable, and 5 to 20 nm is even more preferable. This range is preferable because (P ₁ -P of the magnetic layer
_{When (0} ) is less than 5 nm, the running of the magnetic tape may become unstable, and when (P ₁ -P ₀ ) exceeds 30 nm, the PW50 may be widened or the output may be decreased due to spacing loss. This is because the error rate becomes high.
Further, if (P ₁ -P ₀ ) is set to 30 nm or less, it is also effective in reducing thermal asperity due to collision with the MR head. Further, while satisfying the above condition, the maximum convex amount of the magnetic layer is P ₁ , the second, the third, and the fourth in order.
When the second, fifth, ..., 19th, and 20th convex amounts are P ₂ , P ₃ , P ₄ , P ₅ , ..., P ₁₉ , P ₂₀ (P ₁ − P ₂₀ ) is preferably 5 nm or less. (P ₁ -P ₂₀ ) is more preferably 1.8 nm or less, and 1.
It is more preferably 5 nm or less, particularly preferably 1.0 nm or less. This range is preferable because (P ₁ -P ₂₀ ) is 5n.
When it is less than m (more preferably 1.8 nm) or less, the MR head embedded by retracting about 25 nm from the slider (alumina / titania / carbide) and the magnetic tape are evenly contacted to improve the contact, reduce the PW50 and improve the output. This reduces the error rate. Further, the presence of such uniform protrusions lowers the coefficient of friction and reduces the catching on the MR slider (AlTiC; alumina / titania / carbide).
There is also a secondary effect that smooth running performance can be obtained. 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 retracted by about 25 nm from the slider surface, but there is a clear reason. Is unknown. For now, I will only describe the experimental facts.

Further, in a magnetic tape using an MR head embedded in a slider, [(P ₁ -P ₀ ) / R
a] is preferably 12 or less, more preferably 10 or less, further preferably 8 or less, and further preferably 6 or less. It is preferable that [(P ₁ −P ₀ ) / Ra] be 12 or less, because even if the MR element is worn, the MR head and the magnetic tape are evenly contacted, the PW 50 is narrow, the output is kept high, and the error rate is low. This is because Such a magnetic tape can be obtained by controlling the processing conditions of lapping / rotary / tissue processing (LRT processing) applied to the magnetic layer.

The magnetic layer and slider material (eg, alumina)
/ Titania / carbide)_mSL , Magnetic
The friction coefficient between the layer and SUS is μ_mSUS, Back coat layer and S
Friction coefficient with US μ_BSUSAnd [[μ_mSL ) /
(Μ_mSUS)] To 0.7-1.3 and [(μ_mSL )
/ (Μ_BSUS)] Is set to 0.8-1.5, the magnetic tape
The off-track due to the meandering of is reduced, and the error rate is
improves. This effect is obtained when the track width is 5 μm or less
Especially large. [(Μ_mSL ) / (Μ_mSUS)] Is 0.85-
1.15 and [(μ_mSL ) / (Μ_BSUS)] Is 1.0-1.
3 is more preferable, and [(μ_mSL ) / (Μ_mSUS)]
Is 0.9 to 1.1, and [(μ_mSL ) / (Μ _BSUS)] Is 1.
More preferably, it is 0 to 1.3. Such a magnetic tape
(1) In the magnetic layer, the oil with the ester of higher fatty acid
Contain a fatty acid amide, or adjust the amount of crosslinking agent in the magnetic layer.
(2) Back coating by applying measures such as reduction to the magnetic layer.
The carbon layer has a large particle diameter of 300 nm to 400 nm.
Rack and small carbon particles with a particle size of 5 to 200 nm
And (3) the above LRT treatment.
It is obtained by applying a theory to the magnetic layer.

The coercive force of the magnetic layer is 120 to 320 kA /
m is preferable, 140 to 320 kA / m is more preferable, and 160 to 320 kA / m is further preferable. When the coercive force of the magnetic layer is less than 120 kA / m, demagnetization of the demagnetizing field causes a reduction in output when the recording wavelength is shortened, and when it exceeds 320 kA / m, recording with a magnetic head may become difficult.

The product of the residual magnetic flux density and the thickness in the longitudinal direction is 0.0.
018 to 0.06 μTm is preferable, and 0.0036 to 0.05
0 μTm is more preferable, 0.004 to 0.045 μTm is further preferable, and 0.004 to 0.040 μTm is further preferable. The product of the residual magnetic flux density and the thickness in the longitudinal direction is 0.00
If it is less than 18 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. The magnetic recording medium including such a magnetic layer can shorten the recording wavelength and, in addition, the MR
This is preferable because the reproduction output when reproduced by the head can be increased, and further, the distortion of the reproduction output can be reduced and the output to noise ratio can be increased.

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 1.5 μm. Is more preferable.
If the thickness of the undercoat layer is less than 0.3 μm, the durability of the magnetic recording medium may deteriorate, and if it exceeds 3.0 μm, not only the durability improving effect of the magnetic recording medium is saturated, but also in the case of a magnetic tape. May increase the total thickness, shorten the tape length per roll, and reduce the storage capacity.

The thickness of the back coat layer is 0.2 to 0.8 μm.
Is preferred. When the thickness is less than 0.2 μm, the running property of the magnetic recording medium becomes poor, and when it exceeds 0.8 μm, the total thickness of the magnetic recording medium becomes thick and the tape length per roll becomes short. This is because the storage capacity becomes smaller. The center line average surface roughness (Ra) of the back coat layer is 2 to 15
nm is preferable and 3-8 nm is more preferable. When Ra of the back coat layer is less than 2 nm, the running of the magnetic tape may become unstable, and when Ra exceeds 15 nm, the surface roughness of the magnetic layer increases due to show-through and the spacing loss increases. Sometimes. In such a back coat layer, 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 are added in a total amount of the small particle size carbon black and the large particle size carbon black. 60-9 based on the weight of the inorganic powder
It is contained so as to be 8% by weight, and the particle size is 0.1 μm to 0.6
It is obtained by calendering iron oxide of μm in an amount of 2 to 40% by weight based on the weight of the inorganic powder. The addition amount of the large particle size carbon black is usually
It is 5 to 15% by weight of the small particle size carbon black.

The preferred mode for each component will be described below. <Non-magnetic support> The thickness of the non-magnetic support is preferably 7.0 μm or less, more preferably 2.0 to 7.0 μm, and 2 to 6.5.
μm is more preferable, and 2.5 to 6.0 μm is even more preferable. A non-magnetic support having a thickness in this range is preferable.
This is because if the thickness is less than 2 μm, film formation is difficult and the tape strength becomes small, and if it exceeds 7.0 μm, the total thickness of the tape becomes thick and the storage capacity per roll of tape becomes small.

The Young's modulus in the longitudinal direction of the non-magnetic support varies depending on the thickness of the non-magnetic support, but is usually 5.07 GPa.
(500 kg / mm ² ) or more is used. This Young's modulus is preferably 6.08 GPa (600 kg / mm ² ) or more, and more preferably 7.09 GPa (700 kg / mm ² ).
If the thickness of the non-magnetic support is 5.0 μm or less, 1
A Young's modulus of 0.13 GPa (1000 kg / mm ² ) or more is preferably used. If the Young's modulus in the longitudinal direction of the non-magnetic support is less than 6.08 GPa (600 kg / mm ² ), the strength of the magnetic tape may be weakened or the running of the magnetic tape may be unstable.

The Young's modulus in the longitudinal direction of the non-magnetic support is M
D, the ratio (MD / T when Young's modulus in the width direction is TD)
When a non-magnetic support having D) of 0.6 to 1.8 is used, the MR
It is preferable because it makes better contact with the head. MD / TD
The preferred range of is different between the heli-cal scan type and the linear recording type, and the preferred MD / TD range of the heli-cal scan type is 0.6 to 1.
2 is more preferably 0.6 to 1.0, still more preferably 0.60 to 0.80. This range is preferable because the mechanism is unknown at present, but the variation (flatness) of the output from the input side to the output 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 further preferable. This range is preferable because the head touch is improved. Examples of such non-magnetic support include polyethylene naphthalate film, aromatic polyamide film, aromatic polyimide film and the like.

<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, and still more preferably 0.5 to 2.0 μm. More preferably, 0.5-1.
5 μm is even more preferable. This range is preferred
If it is less than 0.3 μm, the durability of the magnetic recording medium may deteriorate, and if it exceeds 3.0 μm, not only the effect of improving the durability of the magnetic recording medium is saturated, but also in the case of a magnetic tape, the total thickness becomes thick. This is because the tape length per roll becomes shorter and the storage capacity becomes smaller.

Carbon black is added to the undercoat layer for the purpose of improving conductivity, and non-magnetic particles are added for the purpose of controlling the viscosity of the paint and the rigidity of the tape. The non-magnetic particles used in the undercoat layer include titanium oxide, iron oxide, alumina and the like, but iron oxide alone or a mixed system of iron oxide and alumina is used. For the undercoat layer, based on the weight of all the inorganic powder in the undercoat layer, 15 to 35% by weight of carbon black having a particle size of 10 to 100 nm, major axis length of 0.05 to 0.20 μm, minor axis length. 5-200n
When non-magnetic iron oxide of m is contained in an amount of 35 to 83% by weight and, if necessary, 0 to 20% by weight of alumina having a particle size of 10 to 100 nm, it is wet-on-wet to form a magnetic layer formed thereon. It is preferable because it reduces the surface roughness. The non-magnetic iron oxide is usually acicular, but when using granular or amorphous non-magnetic iron oxide, the particle size is 5 to 200 n.
m iron oxide is preferred. It should be noted that addition of carbon black having a large particle size of 100 nm or more is not excluded so long as the surface smoothness is not impaired. In this case, the amount of carbon black is preferably the sum of the amount of small particle size carbon black and the amount of large particle size carbon black within the above range. The amount of large particle size carbon black is usually 20% by weight or less of the total amount of carbon black.

As carbon black (hereinafter, also referred to as CB) added to the undercoat layer, acetylene black, furnace black, thermal black or the like can be used.
Usually, 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 CB has a structure, so that if the particle size is less than 10 nm, it is difficult to disperse CB, and if it exceeds 100 nm, the smoothness deteriorates. The amount of CB added varies depending on the particle size of CB.
5 to 35% by weight is preferable. This range is preferred
This is because if it is less than 15% by weight, the effect of improving conductivity is poor, and if it exceeds 35% by weight, the effect is saturated. Particle size 15nm
It is more preferable to use 15 to 35% by weight of CB having a particle size of -80 nm, and CB having a particle size of 20 nm to 50 nm is 20 to 30%.
It is more preferable to use the weight percent. By adding carbon black having such a particle size and amount, electric resistance is reduced and running unevenness is reduced.

In the case of needles, the non-magnetic iron oxide 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. The amorphous particles preferably have a particle size of 5 to 200 nm. The particle size is more preferably 0.05 to 150 nm, and the particle size is 0.05 to 1
00 nm is more preferable. A needle-like material is more preferable because the orientation of the magnetic layer is improved. Addition amount is 35
83% by weight is preferable, 40 to 80% by weight is more preferable, and 50 to 75% by weight is further preferable. A particle size in this range (short axis length in the case of needles) is preferred to be 5 nm.
If it is less than 200 nm, uniform dispersion is difficult, and if it exceeds 200 nm, unevenness at the interface between the undercoat layer and the magnetic layer increases. The amount added in this range is preferable because if it 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 be rather lowered.

Alumina may be added to the undercoat layer in addition to iron oxide. The particle size of alumina is preferably 10 to 100 nm, more preferably 20 to 100 nm, and 30 to 10 nm.
0 nm is more preferable. 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
It is usually 0 to 20% by weight, more preferably 2 to 10% by weight, still more preferably 4 to 8% by weight.

<Lubricant> Lubricants having different roles are used in the coating layer composed of the undercoat layer and the magnetic layer. The subbing layer contains 0.5 to 4.0% by weight of higher fatty acid based on the total powder,
It is preferable to contain an ester of a higher fatty acid in an amount of 2 to 3.0% by weight, because the coefficient of friction between the magnetic tape and the running 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 undercoat layer may be plasticized and the toughness may be lost. It is preferable to add an ester of a higher fatty acid in this range because the effect of reducing the friction coefficient is small when the amount is less than 0.5% by weight and the amount of transfer to the magnetic layer is too large when the amount exceeds 3.0% by weight. This is because there is a side effect such that the tape is stuck to the traveling system head and the guide roller.

0.2 to 3.0 with respect to the ferromagnetic powder in the magnetic layer
If the fatty acid amide is contained in an amount of 0.2% by weight and the higher fatty acid ester is included in an amount of 0.2 to 3.0% by weight, the friction coefficient between the magnetic tape and the capstan of the traveling system or the slider of the MR head is reduced. preferable. If the content of the fatty acid amide is less than 0.2% by weight, the friction coefficient of the head slider / magnetic layer tends to be large, and if it exceeds 3.0% by weight, bleeding out may occur 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. Examples of the fatty acid ester include butyl stearate, octyl stearate, amyl stearate, isooctyl stearate, octyl myristate, butoxyethyl stearate, mono-stearic anhydride sorbitan, di-stearic anhydride sorbitan, and tri-stearic anhydride sorbitan. Etc. are used. As the fatty acid amide, amides of the above higher fatty acids such as palmitic acid and stearic acid can be used. Further, it is preferable to add an ester of higher fatty acid in the above range, if the amount is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it 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. The mutual movement of the lubricant of the magnetic layer and the lubricant of the undercoat layer is not excluded. The coefficient of friction of the MR head with the slider is preferably 0.30 or less,
It is more preferably 25 or less. This range is preferably 0.
This is because if the number exceeds 30, the spacing loss easily occurs due to the dirt on the slider. In addition, it is difficult to achieve less than 0.10. The friction coefficient with SUS is preferably from 0.10 to 0.25, more preferably from 0.12 to 0.20. This range is preferable because when it is less than 0.10, the head and the guide roller are easily slippery and the traveling becomes unstable, and when it is more than 0.25, the head and the guide roller are easily soiled. Also, [(μ _mSL ) / (μ _mSUS )] is 0.7 to 1.3.
Is preferred, and 0.8 to 1.2 is more preferred. This range is preferable because tracking deviation (off-track) due to meandering of the magnetic tape is reduced.

<Magnetic Layer> The thickness of the magnetic layer is as described above.
Usually 0.3 μm or less, preferably 0.01 to 0.3 μm, and
01 to 0.25 μm is more preferable, 0.01 to 0.2 μm is further preferable, and 0.01 to 0.15 μm is further preferable. This range is more preferable if it is less than 0.01 μm, it is difficult to obtain a uniform magnetic layer, and if it exceeds 0.3 μm, the reproduction output becomes small due to thickness loss, and the residual magnetic flux density (Br) in the magnetic layer is reduced. Product with thickness (δ) (Brδ)
Is too large and distortion of the reproduction output due to saturation of the MR head is likely 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 160
-320 kA / m is more preferable. When the coercive force of the magnetic layer is less than 120 kA / m, the output decreases due to demagnetization when the recording wavelength is shortened, and when it exceeds 320 kA / m, recording with a magnetic head may become difficult. The product of residual magnetic flux density and thickness in the longitudinal direction is 0.0018 to 0.06 μT.
m is preferable, 0.0036 to 0.050 μTm is more preferable, 0.004 to 0.045 μTm is further preferable, and 0.004 to 0.045 μTm is more preferable.
More preferably, it is 004 to 0.040 μTm. This range is preferable when the reproduction output by the MR head is small when it is less than 0.0018 μTm, and when it exceeds 0.06 μTm.
This is because the reproduction output by the R head is easily distorted.

Ferromagnetic iron-based metal powder and hexagonal barium ferrite powder are used as the magnetic powder added to the magnetic layer. The coercive force of the ferromagnetic iron-based metal powder and the hexagonal barium ferrite powder is preferably 120 to 320 kA / m, and the saturation magnetization is 120 to 200 in the ferromagnetic iron-based metal powder.
A · m ² / kg (120 to 200 emu / g) is preferable, and 130 to 180 A · m ² / kg (130 to 180 em)
u / g) is more preferred. In the hexagonal barium ferrite powder, 50 to 70 A · m ² / kg (50 to 70 emu /
g) is preferred. The magnetic properties of the magnetic layer and the magnetic properties of the ferromagnetic powder are both measured values with an external magnetic field of 1.28 MA / m (16 kOe) with a sample vibrating magnetometer.

The average major axis length of the ferromagnetic iron-based metal powder used in the magnetic recording medium of the present invention is 0.03 to 0.2.
μm is preferable, 0.03 to 0.18 μm is more preferable,
More preferably, it is 0.04 to 0.15 μm. 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 and it becomes difficult to disperse it in the paint, and when it exceeds 0.2 μm, the coercive force decreases. This is also because particle noise based on the size of particles becomes large.
In the case of hexagonal barium ferrite powder, the plate diameter is preferably 5 to 200 nm for the same reason. The above-mentioned average major axis length and particle diameter are obtained by actually measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and averaging 100 particles. Further, the BET specific surface area of this ferromagnetic iron-based metal powder is preferably 35 m ² / g or more,
It is more preferably 40 m ² / g or more, most preferably 50 m ² / g or more. BET of hexagonal barium ferrite powder
The specific surface area is preferably 1 to 100 m ² / g or more.

As the binder contained 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. A combination of at least one selected from vinyl chloride-vinyl acetate-maleic anhydride copolymer, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer, nitrocellulose, and the like and a polyurethane resin can be used. Above all, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer in combination with a polyurethane resin. Polyurethane resins include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane and the like.

COOH, SO ₃ M, OSO as functional groups
₂ M, P = O (OM) ₃ , O-P = O (OM) ₂ [M is hydrogen atom, alkali metal base or amine salt], OH, N
R'R '', N ⁺ R '''R''''R''''' [R ', R'',
R ''',R''''andR''''' are hydrogen or a hydrocarbon group],
A binder such as a urethane resin made of a polymer having an epoxy group is used. The use of such a binder is
This is because the dispersibility of the magnetic powder and the like is improved as described above.
When two or more kinds of resins are used in combination, it is preferable that the polarities of the functional groups are the same, and in particular, the combination of —SO ₃ M groups is preferable.

These binders are used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of the ferromagnetic powder. Particularly, as a binder, 5 to 30 parts by weight of vinyl chloride resin and 2 to 2 of polyurethane resin are used.
Most preferably, 0 part by weight is used in combination.

It is desirable to use together with these binders, a thermosetting cross-linking agent which bonds with functional groups contained in the binder and cross-links. As the cross-linking agent, tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, condensation products of the above isocyanates, etc. 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. It is more preferably 10 to 35 parts by weight. It is preferable that the amount of the cross-linking agent used in the magnetic layer is 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 preferable when the content is less than 30%, the coating strength of the magnetic layer tends to be weak, and when it exceeds 60%, the LRT treatment condition needs to be strengthened in order to reduce the friction coefficient with respect to the slider, resulting in an increase in cost. This is because it leads to.

Conventionally known CB can be added for the purpose of improving conductivity and surface lubricity. As these CB, acetylene black, furnace black, thermal black or the like can be used. Particle size is 5nm-100n
Although m of m is used, a particle size of 10 nm to 100 nm is preferable. This range is preferable because the particle size is 5n.
This is because when it is less than m, it is difficult to disperse CB, and when it is 100 nm or more, it is necessary to add a large amount of CB, and in any case, the surface becomes rough, which causes a decrease in output.
The addition amount is preferably 0.2 to 5% by weight, more preferably 0.5 to 4% by weight, and 0.5 to 3.5% by weight based on the ferromagnetic powder.
Is more preferable, and 0.5 to 3% by weight is even more preferable. This range is preferable because if it is less than 0.2% by weight, the effect is small, and if more than 5% by weight CB is added, the surface of the magnetic layer tends to be rough.

<Backcoat layer> For the purpose of improving the running property,
A conventionally known back coat layer having a thickness of 0.2 to 0.8 μm can be used. The reason why this range is good is that if it is less than 0.2 μm, the effect of improving the running property 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 0.1
0 to 0.30 is preferable, and 0.10 to 0.25 is more preferable. This range is preferable because if it is less than 0.10, the guide rollers will slip easily and the running will become unstable.
This is because the guide roller is easily soiled if the value exceeds the range.
Further, [(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 small.

Carbon black (C
As B), acetylene black, furnace black, thermal black or the like can be used. Usually, small particle size carbon and large particle size carbon are used. As the small particle size carbon, particles having a particle size of 5 nm to 100 nm can be used, but particles having a particle size of 10 nm to 100 nm are more preferable. This range is more preferable because it is difficult to disperse CB when the particle size is 10 nm or less, and it is necessary to add a large amount of CB when the particle size is 100 nm or more. This is because it can cause set-off to (emboss). As large particle size carbon, particle size is 30
When carbon of 0 to 400 nm is added in a proportion of 5 to 15% by weight with respect to the addition amount of the small particle size carbon, the surface does not become rough and the running performance improving effect becomes large. 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. Centerline average surface roughness R of backcoat layer
a is preferably 2 to 15 nm, more preferably 3 to 8 nm.

Further, for the purpose of improving strength, iron oxide having a particle diameter of 0.1 μm to 0.6 μm is preferably added to the backcoat layer, 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.

The same resin as that used in the magnetic layer or the undercoat layer described above can be used as the binder in the back coat layer. Among them, a cellulose-based resin is used in order to reduce the friction coefficient and improve the running property. It is preferable to use a resin and a polyurethane resin in combination. The content of the binder is usually 40 to 150 parts by weight and 50 to 1 part by weight based on 100 parts by weight of the total amount of carbon black and the inorganic non-magnetic powder.
20 parts by weight is preferable, 60 to 110 parts by weight is more preferable, and 70 to 110 parts by weight is further preferable. This range is preferable because if it is less than 50 parts by weight, the strength of the back coat layer is insufficient, and if it exceeds 120 parts by weight, the friction coefficient tends to be high. Cellulosic resin 30 ~
It is preferable to use 70 parts by weight and 20 to 50 parts by weight of polyurethane resin. Further, in order to further cure the binder, it is preferable to use a crosslinking agent such as a polyisocyanate compound.

As the cross-linking agent for the back coat layer, the cross-linking agent used for the magnetic layer or the undercoat layer is used. The amount of the crosslinking agent is usually 10 to 50 parts by weight based on 100 parts by weight of the binder. It is preferably 10 to 35 parts by weight, more preferably 10 to 30 parts by weight. If the amount is less than 10 parts by weight, the coating strength of the back coat layer tends to be weak, and if it exceeds 35 parts by weight, the S content is preferably 20% by weight.
This is because the dynamic friction coefficient with respect to US becomes large.

For the special purpose back coat layer for recording magnetic servo signals, 30 to 60 parts by weight of the above-mentioned ferromagnetic powder used for the magnetic layer and 40 to 70 parts of the above-mentioned carbon black used for the back coat layer are used. Parts by weight, if necessary,
The above-mentioned iron oxide and alumina used for the back coat layer are 2
Add ~ 15 parts by weight. Further, as the binder, a total amount of ferromagnetic powder, carbon black, and inorganic non-magnetic powder is 10
The resin used for the back coat layer is usually used in an amount of 40 to 150 parts by weight, preferably 50 to 120 parts by weight, based on 0 parts by weight. As the cross-linking agent, the above-mentioned cross-linking agent can be used usually in a ratio of 10 to 50 parts by weight with respect to 100 parts by weight of the binder. For the same reason as described above for the 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.

<LRT (Wrapping / Rotary / Tissue) Processing> The outline of the LRT processing will be described with reference to FIG.
Reference numeral 1 in FIG. 1 is a delivery roll for the magnetic tape 30,
2 is a feed roll, 3 is a polishing tape (lapping tape), 4 is a guide block for the polishing tape, 5 is a rotating roll for the polishing tape, 6 is a rotary wheel made of aluminum, and 7 is a back coat layer 30b of the magnetic tape 30. Rotating rod for non-woven fabric contact with the magnetic layer 30a side, 8 non-woven fabric rotating rod for magnetic layer 30a side, 9 non-woven fabric (tissue), 10 non-woven rotary roll, 11 feed roller, 12 take-up roll Indicates.

(1) Lapping treatment: As shown in FIG. 1, the polishing tape (lapping tape) 3 is a rotating roll 5
The magnetic tape 30 is moved at a constant speed (standard: 14.4 cm / min) in the opposite direction to the magnetic tape 30 (standard: 400 m / min), and is guided by the guide block 4 from the lower side in the figure. By being pressed, the magnetic tape 30 comes into contact with the magnetic layer 30a side, and the polishing treatment is performed with the tension of the magnetic tape unwinding and the tension of the polishing tape 3 being constant (standard: 100 g and 250 g, respectively). The polishing tape (wrapping tape) 3 used in this step is, for example, M20000, WA100.
A lapping tape with fine abrasive grains such as No. 00 or No. K10000. In addition, the polishing wheel (lapping wheel) is replaced with the polishing tape (lapping tape) 3
Although it is not excluded that it is used instead of or in combination, the polishing tape (lapping tape) 3 is only used when frequent replacement is required.

(2) Rotary treatment: A rotary wheel with a groove for air bleeding shown in FIG. 1 [standard: width 1 inch (25.4
mm), diameter 60 mmφ, air vent groove 2 mm width, groove angle 4
5 degrees, manufactured by Kyowa Seiko Co., Ltd.] 6 in a direction opposite to the running direction of the magnetic tape 30 (indicated by an arrow in the figure) at a constant rotation speed (normal: 200 to 3000 rpm, standard: 1100 rpm).
The surface treatment of the magnetic layer 30a is performed by contacting the magnetic layer 30a of the magnetic tape 30 at a constant contact angle (standard: 90 degrees) while rotating at.

(3) Tissue treatment: Tissue (nonwoven fabric, such as Toraysee manufactured by Toray Industries, Inc.)
Constant speed (standard: 14.0 mm /
min)), and the magnetic tape 30 with each of the rotating rods 7 and 8.
A cleaning process is performed by pressing the surfaces of the back coat layer 30b and the magnetic layer 30a.

The cassette tape incorporating the tape of the present invention has a large capacity per roll, a small PW50 when an MR reproducing head is used, and a high reproduction output.
It has a low error rate, is highly reliable, and is particularly excellent as a backup tape for hard disk drives.

[0052]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In addition, the part of an Example and a comparative example shows a weight part.

Example 1: << Coating Components for Undercoat Layer >> (1) Iron Oxide Powder (Average Particle Size: 0.11 × 0.02 μm) 68 Parts α-Alumina (Average Particle Size: 0.07 μm) 8 Parts carbon black (average particle diameter: 25 nm, oil absorption: 55g / cc) 2.0 parts vinyl chloride 24 parts of stearic acid - hydroxypropyl acrylate copolymer 0.8 parts (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalents / g) Polyester polyurethane resin 4.4 parts (Tg: 40 ° C, content -SO ₃ Na group: 1 x 10 ^-4 equivalents / g) cyclohexanone 25 parts methyl ethyl ketone 40 parts toluene 10 parts (2) butyl stearate 1 part Cyclohexanone 70 parts Methyl ethyl ketone 50 parts Toluene 20 parts (3) Polyisocyanate (Coronate L manufactured by Nippon Polyurethane Company) 4.4 parts Cyclohexanone 10 parts Methyl ether Ketone 15 parts 10 parts of toluene

<< Paint component for magnetic layer >> (1) Ferromagnetic iron-based metal powder 100 parts (Co / Fe: 20 at%, Y / (Fe + Co): 3 at%, Al / (Fe + Co): 5 wt%, Ca / Fe : 0 wt%, σs: 155 A · m ² / kg, Hc: 149.6 kA / m, pH: 9.4, major axis length: 0.10 μm) Vinyl chloride-hydroxypropyl acrylate copolymer 12.3 parts (contained) -SO ₃ Na group: 0.7 × 10 ^-4 eq / g) 5.5 parts polyester polyurethane resin (containing -SO ₃ Na group: 1.0 × 10 ^-4 eq / g) alpha-alumina (average particle size : 0.12 μm) 8 parts α-alumina (average particle size: 0.07 μm) 2 parts Carbon black 1.0 part (average particle size: 75 nm, DBP oil absorption: 72 cc / 100 g) Metal acid phosphate 2 parts Palmitic acid amide 1.5 parts stearic acid n-butyrate 1.0 parts Tetrahydrofuran 65 parts Methyl ethyl ketone 245 parts Toluene 85 parts (2) Polyisocyanate 2.0 parts Cyclohexanone 167 parts

After kneading (1) with the kneader in the above-mentioned coating composition for the undercoat layer, adding (2) and stirring, a dispersion treatment was carried out with a sand mill for a residence time of 60 minutes, and (3) was added to this. After adding and stirring and filtering, it was used as a paint for the undercoat layer.
Separately from this, after kneading the above-mentioned magnetic layer coating component (1) with a kneader, dispersing with a sand mill with a residence time of 45 minutes, adding the magnetic layer coating component (2) thereto, stirring and filtering, It was magnetic paint. A polyethylene naphthalate film (thickness 6.2 μm, MD = 6.
08 GPa, MD / TD = 1.3, manufactured by Teijin Ltd.) so that the thickness after drying and calendering would be 1.8 μm. The coating is applied wet-on-wet so that the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendering is 0.15 μm, and after magnetic field orientation treatment it is dried using a drier to obtain a magnetic sheet. It was For the magnetic field orientation treatment, an N-N anti-magnet (5 kG) was installed in front of the dryer, and the N-N anti-magnet (5
kG) was installed in two units at 50 cm intervals. The coating speed was 100 m / min.

<< Backcoat Layer Coating Components >> Carbon black (average particle size: 25 nm) 80 parts Carbon black (average particle size: 370 nm) 10 parts Iron oxide (major axis length: 0.4 μm, axial ratio: about 10) 10 parts Nitrocellulose 45 parts Polyurethane resin (containing SO ₃ Na group) 30 parts Cyclohexanone 260 parts Toluene 260 parts Methyl ethyl ketone 525 parts

After dispersing the above coating composition for the back coat layer in a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate was added to prepare the coating composition for the back coat layer, which was filtered, and then the magnetic layer of the magnetic sheet prepared above. Was coated on the surface opposite to the above so that the thickness after drying and calendering would be 0.5 μm, and dried. The magnetic sheet thus obtained was mirror-finished in a 7-stage calender consisting of metal rolls at a temperature of 100 ° C. and a linear pressure of 150 kg / cm, and the magnetic sheet was wound around 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 prepare a computer tape. Ra of the back coat layer was 8 nm.

<LRT (Wrapping / Rotary / Tissue) Processing> (1) Wrapping processing: As shown in FIG. 1, the polishing tape (lapping tape) 3 is fed by the rotating roll 5 to the magnetic tape 30 in the feeding direction (magnetic tape feeding speed). : 4 as standard
00m / min) at a speed of 14.4 cm / min, and is pressed by the guide block 4 from the lower part in the figure to make contact with the surface of the magnetic layer 30a of the magnetic tape 30. Tape unwinding tension is 1
The polishing treatment was carried out with the tension of the polishing tape 3 set to 00 g and the tension of the polishing tape 3 set to 250 g.

(2) Rotary wheel treatment: 1 inch (25.4 mm) wide, 60 mm in diameter, 2 mm groove width aluminum rotary wheel with air vent groove shown in FIG. 1 (groove angle 45
Surface treatment of the magnetic layer 30a by rotating the magnetic tape 30 in a direction opposite to the feeding direction of the magnetic tape 30 (rotation speed 1100 rpm) and contacting the magnetic layer 30a at a contact angle of 90 degrees. I went.

(3) Tissue treatment: A non-woven fabric (here, non-woven fabric Toraysee manufactured by Toray Industries Inc.) 9 is attached to a magnetic tape 30.
Feed at the speed of 14.0mm / min in the direction opposite to the feed direction of
The surfaces of the back coat layer 30b and the magnetic layer 30a were pressed by the rotating rods 7 and 8 to perform cleaning treatment on these surfaces.

Examples 2 to 10: Magnetic tapes for computers of Examples 2 to 10 were prepared in the same manner as in Example 1 except that the conditions were partially changed to those shown in Tables 1 to 3.

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.

Comparative Example 2: The following LB was used instead of the LRT treatment.
A computer tape of Comparative Example 2 was produced in the same manner as in Example 1 except that the T treatment was performed.

<LBT processing> Magnetic tape 400 m / mi
While running at n, the magnetic layer surface is lapped tape polished, blade polished and surface wiped aftertreatment,
A magnetic tape was produced. At this time, K10000 was used for the wrapping tape (polishing tape), a super-hard blade was used for the blade, and Toraysee manufactured by Toray Industries, Inc. was used for wiping the surface, and processing was performed at a running tension of 30 g. The magnetic tape obtained as described above was incorporated into a cartridge to produce a magnetic tape for computer.

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.

Comparative Examples 4 and 5, Example 11 Comparative Example 2 except that some conditions were changed to those shown in Table 5.
Magnetic tapes for computers of Comparative Examples 4 and 5 and Example 11 were produced in the same manner as in.

The characteristic evaluation was carried out as follows.
<Measurement of PW50, playback output and error rate, etc.> P
The W50, reproduction output and error rate (ERT) were measured by recording (recording wavelength 0.55 μm) / reproduction using an LTO drive modified to measure thin tape. PW50 is PW of Comparative Example 1 tape
The value when 50 is 1, the reproduction output is the value when the tape of Comparative Example 1 is 0 dB, and the output deterioration is the value after recording and reproducing 100 times with the initial value of each magnetic tape being 0 dB. .

<Surface Roughness of Magnetic Layer, Center Value of Roughness and
Evaluation of convex amount> General-purpose three-dimensional surface structure analyzer manufactured by ZYGO
By scanning white light interferometry by NewView5000
Scan Length was measured at 5 μm. Measurement field of view
Is 350 μm × 260 μm. Center line flat of magnetic layer
The uniform surface roughness is Ra and the center value of the unevenness is P₀ , Maximum convex
The amount (first convex amount) is P₁ , 2nd, 3rd in sequence
Eyes, 4th, 5th, ..., 19th, 20th
The convexity of the th, P₂ , P ₃ , P_Four , P_Five ...
P₁₉, P₂₀And (P₁ -P₀ ) And (P₁ -P₂₀)
And [(P₁ -P₀ ) / Ra] was calculated.

<Measurement of MR Head Protrusion and Wear>
Scanning probe microscope manufactured by DI (Digital Instrument)
(Nano Scopea / Dimension-3100 Tapping mode AFM)
After measuring the field of view of 80 μm × 80 μm and correcting the tilt, noise, etc., the cross-sectional profile is analyzed and the MR
The amount of protrusion of the head and the amount of wear before and after running were measured.

<Measurement of Coefficient of Friction between Magnetic Layer and Slider Material and SUS> [SUS] A magnetic tape was applied to a SUS pin (SUS304) having an outer diameter of 5 mm at an angle of 90 ° and a load of 0.64 N, and the magnetic tape was placed at the same location. The friction coefficient was measured when the sample was repeatedly slid 10 times at a feed rate of 20 mm / sec.

[Slider Material] A magnetic tape is applied to an ALTIC pin having an outer diameter of 7 mm at an angle of 90 ° and a load of 0.64 N.
The friction coefficient was measured when the same portion of the magnetic tape was repeatedly slid 10 times at a feed rate of 20 mm / sec.

<Young's modulus of non-magnetic support (MD, TD)
Measurement> Using a small tensile tester (manufactured by Yokohama System Co., Ltd.), strain / tensile strength was measured in an environment of 23 ° C. and 50% RH. Measured length of sample is 10mm, pulling speed is 1
Tensile strain at 0% strain / minute was used to evaluate the 0.3% elongation elastic modulus 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.

The above measurement results are shown in Tables 1-5. The abbreviations in the table have the following meanings. _-ΜmSL : Coefficient of friction between magnetic layer and slider material- _μmSUS : Coefficient of friction between magnetic layer and SUS- _μBSUS : Coefficient of friction between backcoat layer and SUS-Brδ: Residual magnetic flux density (Br) of magnetic layer And thickness (δ)
Product, Hc: coercive force of magnetic layer, BC: back coat layer, CB: carbon black, MD / TD: Young's modulus of the non-magnetic support in the longitudinal direction (M
D) and Young's modulus (TD) in the width direction / Roughness of magnetic surface Ra: Center line average surface roughness R of magnetic layer
a

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

[Table 3]

[0077]

[Table 4]

[0078]

[Table 5]

[0079]

Effects of the Invention Examples 1 to 11 shown in Tables 1 to 5
As is clear from Comparative Examples 1 to 5, according to the present invention, an excellent magnetic recording medium having a small error rate can be obtained. Such an effect is particularly remarkable in a magnetic recording medium having (P ₁ -P ₂₀ ) of 1.8 nm or less. _Further , the coefficient of friction between the magnetic layer and the slider material is μ _mSL , and the magnetic layer and S
When the friction coefficient with US is μ _mSUS and the friction coefficient _between the back coat layer and SUS is μ _BSUS , [(μ _mSL ) /
(Μ _mSUS )] is 0.7 to 1.3, and [(μ _mSL ) / (μ
_{BS US} )] of 0.8 to 1.5 is an excellent magnetic recording medium with a small off-track.

[Brief description of drawings]

FIG. 1 is an L performed when manufacturing a magnetic recording medium of the present invention.
It is a schematic process drawing which shows an example of RT (lapping / rotary / tissue) processing.

FIG. 2 is a schematic plan view showing a recording head and an MR head for reproduction mounted on a slider.

FIG. 3 is a schematic cross-sectional view taken along line YY of FIG.

[Explanation of symbols]

20 MR head 22 Slider 30 Magnetic recording medium (magnetic tape) 30a magnetic layer 30b back coat layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Noriju Yoshimoto             Hitachi Ma, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. (72) Inventor Kenichiro Yoshida             Hitachi Ma, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F-term (reference) 5D006 BA19 CB07 EA01 FA00 FA09

Claims (4)

[Claims] 1. A magnetic recording medium having at least one undercoat layer and a magnetic layer formed in this order on one surface of a non-magnetic support, and having a back coat layer on the opposite surface, the thickness of the non-magnetic support. Of 2.0 μm or more and 7.0 μm or less, the thickness of the magnetic layer is 0.30 μm or less, and the center value of the irregularities of the magnetic layer is P ₀ ,
The maximum convex amount of the magnetic layer is P ₁ , the second, the third,
The fourth, fifth, ..., Nineteenth, and twentieth convex amounts are P ₂ , P ₃ , P ₄ , P ₅ , ..., P ₁₉ , P _20.
And (P ₁ −P ₀ ) is 30 nm or less, and (P ₁ −P ₀ ) is
_1- P ₂₀ ) is 5 nm or less, a magnetic recording medium. 2. A magnetic recording medium according to claim 1, wherein a magnetic recording signal is reproduced by a reproducing head using a magnetoresistive effect element. 3. The magnetic layer has a coercive force of 120 to 320.
kA / m, product of residual magnetic flux density in the longitudinal direction and thickness is 0.0
It is 018 μTm to 0.06 μTm.
The magnetic recording medium described. 4. The non-magnetic support has a Young's modulus in the longitudinal direction.
A ratio (MD / TD) when the Young's modulus in the longitudinal direction is MD and the Young's modulus in the width direction is TD is 6.0 to 1.80, which is 6.08 GPa (600 kg / mm ² ) or more. Item 4. The magnetic recording medium according to any one of Items 1 to 3.