JP2002203308A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an MR head correspondence magnetic recording medium having a low error rate and a small off-track. SOLUTION: In the magnetic recording medium provided with a nonmagnetic support, a undercoat layer, a magnetic layer, and a backcoat layer, the thickness of the magnetic layer is set equal to/lower than 0.30 μm, a center line average surface roughness Ra is set equal to/lower than 3.2 nm, (P1-P0) is set equal to/lower than 30 nm, (P1-P20) is set equal to/lower than 5 nm, more preferably 1.8 nm when the concave and convex medium value of the magnetic layer to P0, the maximum convex amount of the magnetic layer to P1, the convex amount of the 20th to P20, Thus, the excellent magnetic recording medium having a small error rate is achieved. [(μmSL)/(μmSUS)] is set in the range of 0.7 to 1.3, and [(μmSL)/(μBSUS)] is set in the range of 0.8 to 1.5 when a friction coefficient between the magnetic layer and a slider material is set μmSL, a friction coefficient between the magnetic layer and SUS to μmSUS, and a friction coefficient between the backcoat layer and SUS to μBSUS. Thus, the excellent magnetic recording medium having a small off-track is provided.

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 a high recording capacity, high access speed and high transfer speed, and particularly to a reproducing head (hereinafter, MR head) using a magnetoresistive 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, and computer tapes. Particularly, in the field of data backup tapes, a large capacity of a hard disk to be backed up is required. With the increase in capacity, a storage capacity of several tens GB or more per roll has been commercialized, and it is indispensable to increase the capacity of a backup tape in order to cope with a further increase in the capacity of a hard disk in the future. In addition, in order to increase the access speed and the transfer speed, it is essential to increase the tape feed speed and the relative speed between the tape and the head.

In order to increase the capacity per backup tape, the total tape thickness must be reduced to increase the tape length per reel, and the thickness of the magnetic layer must be extremely thin to 0.3 μm or less. It is necessary to reduce the recording wavelength by reducing the thickness demagnetization, and to reduce the track width (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, such as 0.3 μm or less, the durability is deteriorated. Therefore, it is necessary to provide at least one undercoat layer between the nonmagnetic 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 is increased. Therefore, when the magnetic layer has a large protrusion, the half width of the output peak (hereinafter, PW50) is wide due to the spacing loss. The error rate increases due to the loss or the output being reduced.

When the track width is reduced to 15 μm or less and the recording density in the width direction is increased, the magnetic flux leaking from the magnetic recording medium is reduced. It is necessary to use a read head (hereinafter, MR head) that has been used.

[0006] Magnetic recording media compatible with MR heads include JP-A-11-238225 and JP-A-2000-4021.
7 and JP-A-2000-40218. In these prior arts, the magnetic flux (the product of the residual magnetic flux density and the thickness) of the magnetic recording medium is controlled to a specific value and the MR
The distortion of the output of the head is prevented, and the dent on the surface of the magnetic layer is reduced to a specific value or less to reduce the thermal asperity of the MR head.

A conventional magnetic head uses a chip in which a magnetic induction type head for recording and a magnetic induction type head for reproduction are bonded. 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 figures, reference numeral 20a denotes MR
The elements, 21a and 21b are magnetic elements constituting the recording head 21, 21c is a write gap, and 23 is a shield material. Also, the MR head 20 is 2
It is embedded in a recessed state by about 5 nm. That is, the conventional head is formed of 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. Since the magnetic tape 30 is embedded in the slider 22, the magnetic tape 30 runs while contacting the slider 22. Also, the magnetic tape 30 is expanded toward the MR head 20 so that the magnetic tape 30 is
The head 20 makes contact. As described above, since the contact form is significantly different from that of the related art, the characteristics required for the magnetic tape are completely different even if the spacing loss is reduced. Further, the MR head 20 has M
Since the R element 20a is formed of a very thin thin film, there is a problem that the R element 20a is easily worn. As shown in FIGS. 2 and 3, the MR head 20 and the recording head 21 are usually provided in pairs so that recording and reproduction can be performed even when the magnetic tape 30 runs 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.

In addition, since the track width of the MR head is very narrow, for the tracking servo of the MR head,
A servo signal is provided. The track servo method includes a magnetic servo method and an optical servo method.The former forms a servo band on a magnetic layer by magnetic recording and magnetically reads the servo band to perform servo tracking. 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, besides the above, there is a method in which the back coat layer is also provided with magnetism in the magnetic servo method and a magnetic servo signal is recorded in this back coat layer, and in the optical servo method, light is absorbed in the back coat layer. There is also a method of recording an optical servo signal using a material or the like.

In order to cope with an increase in the tape feeding speed or the relative speed between the tape and the head, it is necessary to run at high speed while tracing a servo signal. However, a slider material (for example, alumina / titania / carbide) is required. If the optimization of the coefficient of friction between the magnetic layer and the back coat layer with respect to the magnetic material and the guide roller material is insufficient, the magnetic tape meanders, causing a tracking shift (off-track), resulting in a PW50.
However, there is a problem that the error rate increases due to an increase in output or a decrease in output.

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

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and have found that the difference between the maximum protrusion amount (P ₁ ) of the magnetic tape and the average value (P ₀ ) of the protrusions and recesses is large. (P ₁ −
P ₀ ) is equal to or less than a specific value, and the difference (P ₁ −P ₂₀ ) between the maximum convex amount (P ₁ ) and the twentieth convex amount (P ₂₀ ) is equal to or less than a specific value. The pacing loss is reduced, 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 set to _μmSL , and the magnetic layer and SUS (SUS304, hereinafter simply referred to as SUS). 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
/ _ΜmSUS ) and ( _μmSL / _μBSUS ) are controlled to specific values, whereby off-track due to 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 significant when the track width is set to 15 μm or less.

The present invention has been completed based on the above findings. That is, in 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 magnetic layer is 0.30 μm. Hereinafter, the center line average surface roughness Ra is 3.2 nm or less, the center value of the unevenness of the magnetic layer is P ₀ , the maximum amount of protrusion of the magnetic layer is P ₁ , and the second, third, and fourth successively. , The fifth,..., The nineteenth, and the twentieth are represented by P ₂ , P ₃ , P ₄ , P ₅ ,
A magnetic recording medium wherein (P ₁ −P ₀ ) when P ₁₉ and P ₂₀ are 30 nm or less and (P ₁ −P ₂₀ ) is 5 nm or less, a magnetic layer, a slider material and _mSL the coefficient of friction mu, _MSUS friction coefficient between the magnetic layer and the SUS μ, _BSUS friction coefficient between the backcoat layer and SUS mu, and the time _{[(μ mSL) / (μ} mSUS)] is zero. A magnetic recording medium (Claim 2) with a value of 7 to _1.3 and [( _μmSL ) / ( _μBSUS )] of 0.8 to 1.5, and a reproducing head using a magnetoresistive element. A magnetic recording medium from which a magnetic recording signal is reproduced (claim 3); and a coercive force of the magnetic layer of 120 to 320.
kA / m, the product of the residual magnetic flux density and the thickness in the longitudinal direction is 0.00
A magnetic recording medium having a particle size of 18 μTm to 0.06 μTm (claim 4); a back coat layer comprising a small particle size carbon black having a particle size of 5 nm to 100 nm and a particle size of 200 nm to 400 nm;
The addition amount of the small particle size carbon black and the large particle size carbon black is based on the weight of the inorganic powder (total weight of carbon black and other inorganic powders; the same applies hereinafter). Containing iron oxide having a particle diameter of 0.1 μm to 0.6 μm, based on the weight of the inorganic powder, 2 to 40% by weight.
A magnetic recording medium having a surface roughness Ra of 2 to 15 nm (claim 5); a nonmagnetic support having a thickness of 7.0 μm or less; and a non-magnetic support having a Young's modulus in the longitudinal direction of 6.08 GPa.
(600 kg / mm ² ) or more, and the ratio (MD) when the Young's modulus in the longitudinal direction is MD and the Young's modulus in the width direction is TD.
/ TD) is 0.6 to 1.80 (claim 6). The coefficient of friction in the present invention means the coefficient of kinetic friction as described above, and a specific measuring method thereof will be described in Examples described later.

[0013]

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 nonmagnetic support, the thickness of the magnetic layer is 0.3 μm.
m or less, the magnetic layer is extremely thin and has a small thickness loss, and therefore has a high recording density in the direction in which the magnetic head runs. The thickness of the magnetic layer is preferably 0.01 to 0.3 μm, more preferably 0.01 to 0.3 μm.
The thickness is more preferably from 0.01 to 0.25 μm, still more preferably from 0.01 to 0.2 μm, and still more preferably from 0.01 to 0.15 μm. 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 reproduction output becomes small due to 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 still more preferable, and 0.7 to 2.5 nm is used.
Is even more preferred. 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 the Ra exceeds 3.2 nm, the PW50 becomes wider or the output decreases due to spacing loss. Or
This is because the error rate increases.

(P ₁ −P ₀ ) when the center value of the unevenness of the magnetic layer is P ₀ and the maximum amount of protrusion of the magnetic layer is P ₁ is 30 nm.
The following is preferable, 5 to 30 nm is more preferable, and 5-2
5 nm is more preferred, and 5-20 nm is even more preferred. This range is preferable because (P ₁ -P
_{If (0} ) is less than 5 nm, the running of the magnetic tape may become unstable, and if (P ₁ −P ₀ ) exceeds 30 nm, the PW50 becomes wider or the output decreases due to spacing loss. This is because the error rate increases.
Setting (P ₁ −P ₀ ) to 30 nm or less is also effective in reducing thermal asperity due to collision with the MR head. Further, while satisfying the above conditions, the maximum protrusion amount of the magnetic layer is represented by P ₁ , and the second, third, fourth
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} - P ₂₀ ) is preferably 5 nm or less. (P ₁ -P ₂₀ ) is more preferably 1.8 nm or less.
It is more preferably at most 5 nm, particularly preferably at most 1.0 nm. This range is preferable because (P ₁ -P ₂₀ ) is 5n
m (preferably 1.8 nm) or less, the MR tape embedded with the magnetic tape retracted by about 25 nm from the slider (alumina / titania / carbide) uniformly contacts the magnetic tape, so that the contact is improved and the PW50 is reduced and the output is improved. This reduces the error rate. In addition, when such uniform projections are provided, the friction coefficient is reduced, and the engagement with the MR slider (AlTiC; alumina / titania / carbide) is reduced,
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 recessed by about 25 nm from the slider surface. Is unknown. For now, we will only mention 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 still more preferably 6 or less. [(P ₁ −P ₀ ) / Ra] is preferably 12 or less because even when the MR element is worn, the MR head and the magnetic tape are evenly contacted, the PW50 is narrow, the output is kept high, and the error rate is low. It is because it becomes. Such a magnetic tape can be obtained by controlling the processing conditions of the wrapping / rotary / tissue processing (LRT processing) applied to the magnetic layer.

The magnetic layer and the slider material (for example, alumina
/ Titania / carbide)_mSL , Magnetic
The coefficient of friction between the layer and SUS is μ_mSUS, Back coat layer and S
Coefficient of friction with US_BSUS[(Μ_mSL ) /
(Μ_mSUS)] Is set to 0.7 to 1.3, and [(μ_mSL )
/ (Μ_BSUS)] Is set to 0.8 to 1.5, magnetic tape
Off-track due to meandering is reduced and error rate is reduced
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 to 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) The fatty acid is added to the magnetic layer together with the higher fatty acid ester.
Fatty acid amide or the amount of cross-linking agent in the magnetic layer
The magnetic layer is devised to reduce it, and (2)
Layer with a large particle size of 300 to 400 nm
Rack and a small particle size carbon nanotube having a particle size of 5 nm to 200 nm.
And (3) the LRT treatment described above.
It is obtained by applying a treatment to the magnetic layer.

The coercive force of the magnetic layer is 120 to 320 kA /
m is preferable, 140-320 kA / m is more preferable, and 160-320 kA / m is still more preferable. If the coercive force of the magnetic layer is less than 120 kA / m, if the recording wavelength is shortened, the output will decrease due to demagnetization, and if it exceeds 320 kA / m, it may be difficult to perform recording with a magnetic head.

The product of the residual magnetic flux density in the longitudinal direction and the thickness is 0.0
018 to 0.06 μTm, preferably 0.0036 to 0.05.
0 μTm is more preferable, 0.004 to 0.045 μTm is more preferable, and 0.004 to 0.040 μTm is more preferable. The product of the residual magnetic flux density and 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. A magnetic recording medium comprising such a magnetic layer can shorten the recording wavelength, and furthermore, the MR
This is preferable because the reproduction output at the time of reproduction by the head can be increased, 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 from 0.3 to 3.0 μm, more preferably from 0.5 to 2.5 μm, further preferably from 0.5 to 2.0 μm, and more preferably from 0.5 to 1.5 μm. Is even more preferred.
When the thickness of the undercoat layer is less than 0.3 μm, the durability of the magnetic recording medium may be deteriorated. When the thickness exceeds 3.0 μm, the effect of improving the durability of the magnetic recording medium is not only saturated, but also in the case of a magnetic tape. In some cases, the total thickness is increased, the tape length per roll is reduced, and the storage capacity may be reduced.

The thickness of the back coat layer is 0.2 to 0.8 μm
Is preferred. This range is preferable because when the thickness is less than 0.2 μm, the running property of the magnetic recording medium deteriorates, and when the thickness 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 is reduced. The center line average surface roughness (Ra) of the back coat layer is 2 to 15
nm is preferable, and 3 to 8 nm is more preferable. If the Ra of the back coat layer is less than 2 nm, the running of the magnetic tape may become unstable. If the Ra exceeds 15 nm, the surface roughness of the magnetic layer increases due to show-through, and the spacing loss increases. Sometimes. Such a back coat layer has 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, and a small particle size carbon black and a large particle size carbon black. 60 to 9 based on the weight of the inorganic powder
8% by weight, and the particle size is 0.1 μm to 0.6.
It is obtained by adding 2 to 40% by weight of iron oxide of μm based on the weight of the inorganic powder and performing a calendar treatment. 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.

Preferred embodiments for each component will be described below. <Nonmagnetic Support> The thickness of the nonmagnetic support is preferably 7.0 μm or less, more preferably 2.0 to 7.0 μm, and 2 to 6.5 μm.
μm is more preferred, and 2.5-6.0 μm is even more preferred. Nonmagnetic supports having a thickness in this range are preferred
If the thickness is less than 2 μm, it is difficult to form a film, and the strength of the tape is reduced. If the thickness exceeds 7.0 μm, the total thickness of the tape is increased, and the storage capacity per tape roll is reduced.

The longitudinal Young's modulus 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. The Young's modulus is preferably 6.08 GPa (600 kg / mm ² ) or more, and more preferably 7.09 GPa (700 kg / mm ² ) or more.
When the thickness of the nonmagnetic support is 5.0 μm or less, 1
Those having a Young's modulus of 0.13 GPa (1000 kg / mm ² ) or more are preferably used. If the Young's modulus of the non-magnetic support in the longitudinal direction is less than 6.08 GPa (600 kg / mm ² ), the strength of the magnetic tape may become weak or the running of the magnetic tape may become unstable.

The Young's modulus of the non-magnetic support in the longitudinal direction is M
D, the ratio when the Young's modulus in the width direction is TD (MD / T
When a nonmagnetic support having D) of 0.6 to 1.8 is used, MR
This is preferable because the contact with the head is improved. MD / TD
Is different between the helical scan type and the linear recording type, and the preferred MD / TD range for the helical scan type is 0.6 to 1.
In 0.6, 0.6 to 1.0 is more preferable, and 0.60 to 0.80 is further preferable. This range is preferable because the mechanism is unknown at present, but the variation (flatness) of the output from the entry side to 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 still more preferable. This range is preferable because the head touch is improved. Such a nonmagnetic support includes a polyethylene naphthalate film, an aromatic polyamide film, an aromatic polyimide film, and the like.

<Undercoat layer> As described above, the thickness of the undercoat layer is preferably from 0.3 to 3.0 µm, more preferably from 0.5 to 2.5 µm, and more preferably from 0.5 to 2.0 µm. More preferably, 0.5 to 1.
5 μm is more preferred. This range is preferred because
If the thickness 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 effect of improving the durability of the magnetic recording medium is saturated, but also in the case of a magnetic tape, the overall thickness is increased. This is because the tape length per roll becomes shorter, and the storage capacity becomes smaller.

In the undercoat layer, carbon black is added for the purpose of improving conductivity, and non-magnetic particles are added for the purpose of controlling paint viscosity and tape rigidity. Non-magnetic particles used for the undercoat layer include titanium oxide, iron oxide, and alumina, 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 size of 10 to 100 nm, based on the weight of the entire inorganic powder in the undercoat layer, 0.05 to 0.20 μm in major axis length, and minor axis length 5-200n
m of non-magnetic iron oxide 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. This is preferable because the surface roughness is reduced. The non-magnetic iron oxide is usually acicular, but when granular or amorphous non-magnetic iron oxide is used, the particle size is 5 to 200 n.
m of iron oxide is preferred. The addition of carbon black having a large particle diameter of 100 nm or more is not excluded as long as the surface smoothness is not impaired. In this case, the amount of carbon black is preferably such that the sum of the amount of the small particle size carbon black and the amount of the large particle size carbon black is 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) to be added to the undercoat layer, acetylene black, furnace black, thermal black and the like can be used.
Usually, particles having a particle size of 5 nm to 100 nm are used, but particles having a particle size of 10 nm to 100 nm are preferable. This range is preferable because the CB has a structure, so that when the particle size is less than 10 nm, the CB is difficult to disperse, and when it exceeds 100 nm, the smoothness deteriorates. The amount of CB to be added depends on the particle size of CB.
5-35% by weight is preferred. This range is preferred 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
More preferably, CB having a particle size of 20 to 50 nm is used in an amount of 20 to 30%.
More preferably, it is used by weight. By adding carbon black having such a particle size and amount, electric resistance is reduced and running unevenness is reduced.

The non-magnetic 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 size) of 5 to 200 nm in the case of a needle shape. In the case of an amorphous material, the particle size is preferably 5 to 200 nm. The particle size is more preferably 0.05 to 150 nm, and the particle size is 0.05 to 1 nm.
00 nm is more preferred. Needle-like ones are more preferable because the orientation of the magnetic layer is improved. The addition amount is 35-
83% by weight is preferable, 40-80% by weight is more preferable, and 50-75% by weight is further preferable. It is preferable that the particle diameter in this range (short axis length in the case of a needle) is 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 addition amount 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.

The undercoat layer may contain alumina 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 preferred. If the particle size is less than 10 nm, uniform dispersion is difficult, and if it exceeds 100 nm, unevenness at the interface between the undercoat layer and the magnetic layer may increase. The amount of alumina added is
Usually, it is 0 to 20% by weight, preferably 2 to 10% by weight, 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 undercoat layer contains 0.5 to 4.0% by weight of higher fatty acid based on the whole powder,
It is preferable to contain 2 to 3.0% by weight of an ester of higher fatty acid because the coefficient of friction between the magnetic tape and the head and guide rollers of the traveling system becomes small. If the amount of the higher fatty acid is less than 0.5% by weight, the effect of reducing the coefficient of friction is small, and if it exceeds 4.0% by weight, the undercoat layer may be plasticized and the toughness may be lost. Also, the addition of esters of higher fatty acids in this range is preferable if the amount is less than 0.5% by weight, the effect of reducing the coefficient of friction is small, and if it exceeds 3.0% by weight, the amount of transfer to the magnetic layer is too large. This is because there are side effects such as sticking of the tape to the traveling system head and guide rollers.

In the magnetic layer, 0.2 to 3.0 with respect to the ferromagnetic powder
When the fatty acid amide is contained in an amount of 0.2% by weight and the fatty acid ester is contained in an amount of 0.2 to 3.0% by weight, the coefficient of friction between the magnetic tape and the capstan of the traveling system or the slider of the MR head becomes small. preferable. When 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 increase, and when it exceeds 3.0% by weight, bleed out and defects such as dropout may occur. is there. As fatty acids, 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, sorbitan mono-stearate anhydride, sorbitan di-stearate anhydride, sorbitan tri-stearate anhydride Are used. As the fatty acid amide, amides of the above higher fatty acids such as palmitic acid and stearic acid can be used. Also, the addition of esters of higher fatty acids in the above range is preferable if the content is less than 0.2% by weight, the effect of reducing the coefficient of friction is small. This is because there are side effects such as sticking. Note that this does not exclude mutual movement between the lubricant of the magnetic layer and the lubricant of the undercoat layer. The coefficient of friction between the MR head and the slider is preferably 0.30 or less, and 0.3.
It is more preferably at most 25. This range is preferably 0.
If it exceeds 30, spacing loss due to slider contamination is likely to occur. It should be noted that it is difficult to realize a value of less than 0.10. The coefficient of friction with SUS is preferably 0.10 to 0.25, more preferably 0.12 to 0.20. The reason why this range is preferable is that when the value is less than 0.10, the head and the guide roller are slippery and the traveling becomes unstable, and the head and the guide roller exceeding 0.25 are easily stained. [( _ΜmSL ) / ( _μmSUS )] is 0.7 to 1.3.
Is preferable, and 0.8 to 1.2 is more preferable. 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.
It is usually 0.3 μm or less, preferably 0.01 to 0.3 μm, more preferably 0.3 μm.
The thickness is more preferably from 0.01 to 0.25 μm, still more preferably from 0.01 to 0.2 μm, and still more preferably from 0.01 to 0.15 μm. 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 reproduction output is reduced due to the thickness loss, and the residual magnetic flux density (Br) in the magnetic layer is reduced. Product with thickness (δ) (Brδ)
Is too large, and the distortion of the reproduction output due to the saturation of the MR head is likely to occur. Further, as described above, the coercive force of the magnetic layer is preferably from 120 to 320 kA / m, more preferably from 140 to 320 kA / m, and 160
~ 320 kA / m is more preferred. If the coercive force of the magnetic layer is less than 120 kA / m, the output will decrease due to demagnetization when the recording wavelength is shortened, and if it exceeds 320 kA / m, it may be difficult to perform recording with a magnetic head. The product of the residual magnetic flux density in the longitudinal direction and the thickness is 0.0018 to 0.06 µT
m is preferable, 0.0036 to 0.050 Tm is more preferable, 0.004 to 0.045 Tm is more preferable, and 0.004 to 0.045 Tm is more preferable.
004 to 0.040 µTm is more preferred. This range is preferable because the reproduction output by the MR head is small below 0.0018 μTm, and the reproduction output exceeds 0.06 μTm.
This is because the reproduction output by the R head is easily distorted.

As the magnetic powder added to the magnetic layer, ferromagnetic iron-based metal powder and hexagonal barium ferrite powder are used. The coercive force of the ferromagnetic iron-based metal powder and hexagonal barium ferrite powder is preferably 120 to 320 kA / m, and the saturation magnetization is 120 to 200 kA for the ferromagnetic iron-based metal powder.
^{A · m 2 / kg (120~200emu} / g) are ^{preferable, 130~180A · m 2 / kg (} 130~180em
u / g) is more preferred. In the case of hexagonal barium ferrite powder, 50 to 70 A · m ² / kg (50 to 70 emu /
g) is preferred. Note that the magnetic properties of the magnetic layer and the magnetic properties of the ferromagnetic powder are measured values of an external magnetic field of 1.28 MA / m (16 kOe) using 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 from 0.03 to 0.2.
μm is preferable, and 0.03 to 0.18 μm is more preferable.
0.04 to 0.15 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, so that it is difficult to disperse the magnetic powder in the coating material. This is because the particle noise based on the particle size increases.
In the case of hexagonal barium ferrite powder, the plate diameter is preferably 5 to 200 nm for the same reason. The average major axis length and the particle diameter are determined by measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and averaging 100 particles. The BET specific surface area of the ferromagnetic iron-based metal powder is preferably 35 m ² / g or more,
It is more preferably at least 40 m ² / g, most preferably at least 50 m ² / g. BET of hexagonal barium ferrite powder
The specific surface area is preferably from 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 And 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. Among them, it is preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer and a polyurethane resin in combination. Polyurethane resins include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and the like.

COOH, SO ₃ M, OSO
₂ M, P = O (OM) ₃ , OP = O (OM) ₂ [M is a hydrogen atom, an alkali metal base or an amine salt], OH, N
R′R ″, N ⁺ R ″ ′ R ″ ″ R ′ ″ ″ [R ′, R ″,
R ′ ″, R ″ ″, R ′ ″ ″ represent a hydrogen or 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 used in combination of two or more resins are preferably match the polarity of the functional groups, among them the combination of each other -SO ₃ M group.

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 a vinyl chloride resin and 2-2 to a polyurethane resin
It is most preferable to use 0 parts by weight in combination.

It is desirable to use together with these binders a thermosetting crosslinking agent that bonds to a functional group or the like contained in the binder to crosslink. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and the like, reaction products of these isocyanates with those having a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferred. These crosslinking agents are generally used in a proportion of 10 to 50 parts by weight based on 100 parts by weight of the binder. More preferably, it is 10 to 35 parts by weight. It is preferable that the amount of the cross-linking agent used for the magnetic layer is set to about half (30% to 60%) of the amount used for the undercoat layer, because the coefficient of friction of the MR head with respect to the slider is reduced. This range is preferable because if it 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 coefficient of friction with respect to the slider. Because it leads to.

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

<Backcoat layer> For the purpose of improving running properties,
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 when the thickness is less than 0.2 μm, the effect of improving the running property is insufficient, and when the thickness 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 back coat 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, it becomes slippery at the guide roller portion and running becomes unstable, and
This is because the guide roller becomes liable to be contaminated when the ratio exceeds.
[( _ΜmSL ) / ( _μBSUS )] is preferably 0.8 to 1.5, and 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.

The carbon black (C
As B), 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-diameter carbon, those having a particle size of 5 nm to 100 nm can be used, and 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 set-off (embossing). As large-diameter carbon, particle size 30
When carbon of 0 to 400 nm is added at a ratio of 5 to 15% by weight based on the amount of the small-diameter carbon added, the surface is not roughened, and the effect of improving running properties is increased. The 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. Center line average surface roughness R of the back coat layer
a is preferably 2 to 15 nm, more preferably 3 to 8 nm.

It is preferable to add iron oxide having a particle size of 0.1 μm to 0.6 μm to the back coat layer, and more preferably 0.2 μm to 0.5 μm, for the purpose of improving the strength. 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.

As the binder, the same resin as that used for the magnetic layer and the undercoat layer described above can be used for 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 based on 100 parts by weight of the total of carbon black and the inorganic nonmagnetic powder, and 50 to 1 part by weight.
It is preferably 20 parts by weight, more preferably 60 to 110 parts by weight, and even more preferably 70 to 110 parts by weight. This range is preferable because the strength of the back coat layer is insufficient when the amount is less than 50 parts by weight, and the friction coefficient tends to increase when the amount exceeds 120 parts by weight. 30-cellulosic resin
It is preferable to use 70 parts by weight and 20 to 50 parts by weight of a polyurethane resin. Further, in order to further cure the binder, it is preferable to use a crosslinking agent such as a polyisocyanate compound.

The crosslinking agent used for the magnetic layer and the undercoat layer described above is used as the crosslinking agent in the back coat layer. The amount of the crosslinking agent is usually used in a ratio of 10 to 50 parts by weight based on 100 parts by weight of the binder. Preferably it is 10 to 35 parts by weight, more preferably 10 to 30 parts by weight. This range is preferable because when the amount is less than 10 parts by weight, the coating strength of the back coat layer tends to be weak, and when the amount exceeds 35 parts by weight, S
This is because the dynamic friction coefficient with respect to US increases.

The special-purpose back coat layer on which the magnetic servo signal is recorded contains 30 to 60 parts by weight of the above-mentioned ferromagnetic powder used for the magnetic layer and 40 to 70 parts by weight of the above-mentioned carbon black used for the back coat layer. Parts by weight, if necessary
The above iron oxide and alumina used for the back coat layer
Add ~ 15 parts by weight. The binder contains a total amount of 10 parts of ferromagnetic powder, carbon black and inorganic non-magnetic powder.
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. Further, as the cross-linking agent, the above-mentioned cross-linking agent can be used usually in a proportion 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 (Lapping / Rotary / Tissue) Processing> The outline of the LRT processing will be described with reference to FIG.
The reference numeral 1 in FIG.
2 is a feed roll, 3 is a polishing tape (lapping tape), 4 is a block for a polishing tape, 5 is a rotating roll for a polishing tape, 6 is a rotary wheel made of aluminum, and 7 is a magnetic tape 30 on the back coat layer 30b side. , A rotating rod for applying the nonwoven fabric to the magnetic layer 30a side, a nonwoven fabric (tissue) 9, a rotating roll for the nonwoven fabric, a feed roller 11, and a winding roll 12. Show.

(1) Lapping treatment: As shown in FIG. 1, a polishing tape (lapping tape) 3 is
The tape moves at a constant speed (standard: 14.4 cm / min) in a direction opposite to the feed direction of the magnetic tape 30 (the tape feed speed is standard: 400 m / min), and is moved 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 process is performed with the magnetic tape unwinding tension and the tension of the polishing tape 3 being constant (standard: 100 g and 250 g, respectively). The polishing tape (lapping tape) 3 used in this step is, for example, M20000, WA100
It is a fine lapping tape of abrasive grains such as No. 00 or K10000. In addition, the polishing wheel (lapping wheel) 3
Although it is not excluded to use instead of or in combination with, the polishing tape (lapping tape) 3 alone is used when frequent replacement is required.

(2) Rotary treatment: Rotary wheel with groove for air release shown in FIG. 1 [Standard: 1 inch wide (25.4)
mm), diameter 60mmφ, air vent groove 2mm width, groove angle 4
5 degrees, manufactured by Kyowa Seiko Co., Ltd.] at a constant rotational speed (normal: 200 to 3000 rpm, standard: 1100 rpm) in the direction opposite to the running direction of the magnetic tape 30 (indicated by an arrow in the figure).
The magnetic layer 30a is brought into contact with the magnetic layer 30a of the magnetic tape 30 at a constant contact angle (standard: 90 degrees) while being rotated at a time, thereby performing the surface treatment of the magnetic layer 30a.

(3) Tissue treatment: Tissue (non-woven fabric, for example, Toraysee manufactured by Toray Co., Ltd.)
Constant speed (standard: 14.0 mm /
min) and the rotary tapes 7 and 8 respectively
The surface of the back coat layer 30b and the surface of the magnetic layer 30a are pressed to perform a cleaning process.

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 reproducing output.
It has a low error rate and is highly reliable and particularly excellent as a backup tape for hard disk drives.

[0051]

The present invention will be described in detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. In addition, the part of an Example and a comparative example shows a weight part.

Example 1 << Coating Component 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 size: 25 nm, oil absorption: 55 g / cc) 24 parts Stearic acid 2.0 parts Vinyl chloride-hydroxypropyl acrylate copolymer 0.8 parts (contained -SO ₃ Na group: 0.7 × 10) ^-4 equivalents / g) Polyester polyurethane resin 4.4 parts (Tg: 40 ° C., containing-SO ₃ Na group: 1 × 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 (Nippon Polyurethane Co., Ltd. Coronate L) 4.4 parts cyclohexanone 10 parts methyl Ethyl ketone 15 parts 10 parts of toluene

<< Coating Component for Magnetic Layer >> (1) 100 parts of ferromagnetic iron-based metal powder (Co / Fe: 20 at%, Y / (Fe + Co): 3 at%, Al / (Fe + Co): 5 wt%, Ca / Fe : 0 wt%, σs: 155 Am ² / kg, Hc: 149.6 kA / m, pH: 9.4, major axis length: 0.10 µm) 12.3 parts of vinyl chloride-hydroxypropyl acrylate copolymer (contained —SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalents / g) Polyester polyurethane resin 5.5 parts (contained —SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalents / g) α-alumina (average particle size) 8 parts α-alumina (average particle diameter: 0.07 μm) 2 parts Carbon black 1.0 part (average particle diameter: 75 nm, DBP oil absorption: 72 cc / 100 g) Metal acid phosphate 2 parts Palmitic acid amide 1.5 parts n-butyric stearate 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) in the above undercoat layer coating composition with a kneader, adding (2), stirring and performing a dispersion treatment with a sand mill with a residence time of 60 minutes, and adding (3) to this. After stirring and filtration, the mixture was used as a coating for an undercoat layer.
Separately, the above-mentioned magnetic layer coating component (1) is kneaded with a kneader, dispersed by a sand mill with a residence time of 45 minutes, and the magnetic layer coating component (2) is added thereto, followed by stirring and filtration. It was a magnetic paint. The above-mentioned undercoat layer paint was prepared using a polyethylene naphthalate film (thickness 6.2 μm, MD = 6.
08 GPa, MD / TD = 1.3, manufactured by Teijin Co., Ltd.) so as to have a thickness of 1.8 μm after drying and calendering. The thickness of the magnetic layer after magnetic field orientation, drying and calendering
It was applied wet-on-wet so as to have a thickness of 0.15 μm, subjected to a magnetic field orientation treatment, and dried using a dryer to obtain a magnetic sheet. The magnetic field orientation treatment is performed before the dryer.
-N counter magnet (5kG) is installed, and NN counter magnet (5k
G) were installed at 50 cm intervals. Coating speed is 1
00 m / min.

<< Coating composition for back coat layer >> 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, axis 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 the above-mentioned coating composition for a backcoat layer was dispersed in a sand mill with a residence time of 45 minutes, 15 parts of polyisocyanate was added to prepare a coating for the backcoat layer, followed by filtration, and then the magnetic layer of the magnetic sheet prepared above. Was dried and applied so that the thickness after calendering would be 0.5 μm, and then dried. The magnetic sheet thus obtained was subjected to mirror finishing at a temperature of 100 ° C. and a linear pressure of 150 kg / cm using a seven-stage calender made of metal rolls, and the magnetic sheet was wound around a core at 70 ° C. for 72 hours. After aging, it was cut into half-inch widths and subjected to LRT processing under the following conditions. The magnetic tape thus obtained was assembled in a cartridge to produce a computer tape. Ra of the back coat layer was 8 nm.

<LRT (Lapping / Rotary / Tissue) Processing> (1) Lapping Processing: As shown in FIG. 1, a polishing tape (lapping tape) 3 is fed by a rotating roll 5 to a magnetic tape 30 in a feeding direction (magnetic tape feeding speed). : Standard 4
00m / min) at a speed of 14.4 cm / min, and is pressed from below by a guide block 4 to come into contact with the surface of the magnetic layer 30a of the magnetic tape 30. Tape unwind tension 1
The polishing treatment was performed by setting the tension of the polishing tape 3 to 00 g and 250 g.

(2) Rotary wheel processing: An aluminum rotary wheel with a groove for air bleeding having a width of 1 inch (25.4 mm), a diameter of 60 mmφ and a groove width of 2 mm shown in FIG.
(Manufactured by Kyowa Seiko Co., Ltd.) 6 is rotated in a direction opposite to the feeding direction of the magnetic tape 30 (rotational speed 1100 rpm), and is brought into contact with the magnetic layer 30a at a contact angle of 90 degrees, whereby the surface treatment of the magnetic layer 30a is performed. Was done.

(3) Tissue treatment: A non-woven fabric (here, non-woven fabric Toraysee manufactured by Toray Industries, Ltd.) 9 is applied to a magnetic tape 30.
Feed at a speed of 14.0 mm / 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 against the surfaces of the back coat layer 30b and the magnetic layer 30a by the rotating rods 7 and 8, respectively, to perform a cleaning process on these surfaces.

Examples 2 to 10: Computer magnetic tapes of Examples 2 to 10 were produced in the same manner as in Example 1 except that some of the conditions were changed to those of Tables 1 to 3.

Comparative Example 1 A computer tape of Comparative Example 1 was prepared in the same manner as in Example 1 except that the LRT treatment was not performed.

Comparative Example 2: Instead of LRT processing, the following LB
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> The magnetic tape is 400 m / mi.
While running with n, the surface of the magnetic layer is subjected to post-processing such as lapping tape polishing, blade polishing and surface wiping,
A magnetic tape was prepared. At this time, K10000 was used for the wrapping tape (polishing tape), a carbide blade was used for the blade, and Toraysee manufactured by Toray was used for wiping the surface, and the treatment was performed with a running tension of 30 g. The magnetic tape obtained as described above was assembled in a cartridge to produce a magnetic tape for a computer.

Comparative Example 3 A computer tape of Comparative Example 3 was produced in the same manner as in Comparative Example 2, except that the LBT treatment was performed 10 times.

Comparative Examples 4 to 6: Comparative Examples 4 to 6 were performed in the same manner as in Comparative Example 2, except that some of the conditions were changed to the conditions in Table 5.
Was manufactured.

The evaluation of the characteristics was performed as follows.
<Measurement of PW50, playback output, error rate, etc.> P
W50, reproduction output, and error rate (ERT) were determined by recording (recording wavelength: 0.55 μm) and reproducing using an LTO drive modified so that thin tapes can also be measured. PW50 is the PW of Comparative Example 1 tape.
The reproduction output is a value when 50 is set to 1 and the reproduction output is a value when the tape of Comparative Example 1 is set to 0 dB, and the output deterioration is a value after recording and reproducing 100 times with the initial value of each magnetic tape set to 0 dB. .

<Surface roughness of magnetic layer, median value of unevenness and
Evaluation of convexity> ZYGO general-purpose three-dimensional surface structure analyzer
Scanning white light interferometry with NewView 5000
Scan Length was measured at 5 μm. Measurement field of view
Is 350 μm × 260 μm. Center line flat of magnetic layer
The average surface roughness is Ra, and the central value of the irregularities is P₀ The largest convex
Amount (first convex amount) is P₁ , Second and third in turn
Eyes, 4th, 5th, ..., 19th, 20th
The convexity of the_Two , P _Three , P_Four , P_Five , ...,
P₁₉, P₂₀(P₁ −P₀ ) And (P₁ −P₂₀)
And [(P₁ −P₀ ) / Ra] was determined.

<Measurement of the amount of protrusion and wear of the MR head>
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 inclination, noise, etc., the cross-sectional profile is analyzed and MR
The amount of head protrusion and the amount of wear before and after running were measured.

<Measurement of Coefficient of Friction between Magnetic Layer, 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 same portion of the magnetic tape was applied. Was repeatedly slid 10 times at a feed rate of 20 mm / sec, and the friction coefficient was measured.

[Slider material] A magnetic tape was hung on 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 when the same portion of the magnetic tape was repeatedly slid 10 times at a feed speed of 20 mm / sec was measured.

<Young's modulus of non-magnetic support (MD, TD)
Measurement> Strain and tensile strength in an environment of 23 ° C. and 50% RH were measured using a small tensile tester (manufactured by Yokohama System Co., Ltd.). The measurement length of the sample is 10mm and the pulling speed is 1
The film was pulled at 0% strain / minute, and the 0.3% elongation modulus was evaluated based on the obtained value of 0.3% strain. This evaluation was performed in the longitudinal direction and the width direction of the sample.

Tables 1 to 5 show the above measurement results. The meanings of the abbreviations in the table are as follows.・ Μ _mSL : Coefficient of friction between magnetic layer and slider material ・ μ _mSUS : Coefficient of friction between magnetic layer and SUS ・ μ _BSUS : Coefficient of friction between back coat layer and SUS ・ Brδ: Residual magnetic flux density (Br) of magnetic layer And thickness (δ)
Hc: coercive force of magnetic layer BC: backcoat layer CB: carbon black MD / TD: Young's modulus (M
Ratio of D) to Young's modulus (TD) in width direction Magnetic surface roughness Ra: center line average surface roughness R of the magnetic layer
a

[0073]

[Table 1]

[0074]

[Table 2]

[0075]

[Table 3]

[0076]

[Table 4]

[0077]

[Table 5]

[0078]

Examples 1 to 10 shown in Tables 1 to 5
And as is apparent from Comparative Examples 1 to 6,
Magnetic recording consisting of body, undercoat layer, magnetic layer and back coat layer
A medium having a thickness of 0.30 μm or less and a center line
With an average surface roughness Ra of 3.2 nm or less,
Heart value is P₀ , The maximum amount of protrusion of the magnetic layer is P₁ , 20th
Is the convex amount of₂₀(P₁ −P₀ ) Is 30 nm or less
And (P₁ −P₂₀) Is 5 nm or less
The body is an excellent magnetic recording medium with a low error rate.
You. Such an effect is (P₁ −P₂₀) Is 1.8 nm or less
This is particularly remarkable in the magnetic recording media described above. Also, magnetic
Coefficient of friction between the conductive layer and the slider material_mSL , Magnetic layer and S
Coefficient of friction with US_mSUS, Back coat layer and SUS
Coefficient of friction μ _BSUS[(Μ_mSL ) /
(Μ_mSUS)] Is 0.7 to 1.3 and [(μ_mSL ) / (Μ
_BSUS)] Is 0.8 to 1.5.
It is an excellent magnetic recording medium with a small magnetic shock.

[Brief description of the drawings]

FIG. 1 illustrates a method of manufacturing a magnetic recording medium according to the present invention.
It is a schematic process drawing showing an example of RT (lapping / rotary / tissue) processing.

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

FIG. 3 is a schematic sectional view taken along line YY of FIG. 2;

[Explanation of symbols]

 Reference Signs List 20 MR head 22 Slider 30 Magnetic recording medium (magnetic tape) 30a Magnetic layer 30b Back coat layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihisa Yoshimoto 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture Inside Hitachi Maxell Co., Ltd. (72) Inventor Kenichiro Yoshida 1-1-88 Ushitora, Ibaraki City, Osaka Prefecture F-term (reference) in Hitachi Maxell, Ltd. 5D006 BA04 BA06 BA19 CB01 CB02 CB03 CB07 CC01 CC03

Claims (6)

[Claims] At least one undercoat layer and a magnetic layer are formed in this order on one surface of a nonmagnetic support, and in a magnetic recording medium having a back coat layer on the opposite surface, the thickness of the magnetic layer is reduced. 0.30 μm or less, center line average surface roughness Ra is 3.
At 2 nm or less, the central value of the unevenness of the magnetic layer is P ₀ , the maximum amount of protrusion of the magnetic layer is P ₁ , and the second, third, fourth, fifth,. the twentieth projection height _{P 2, P 3, P 4} , P 5, ···, at the time of the _{P 19, P 20 (P 1} -P 0) is 30nm or less, and (P ₁ - P
₂₀ ) the magnetic recording medium characterized in that the thickness is 5 nm or less. 2. 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 (SUS304) is _μmSUS , and the coefficient of friction between the backcoat layer and SUS (SUS304) is _μBSUS [( _μmSL ) /
( _ΜmSUS )] is 0.7 to 1.3, and [( _μmSL ) / ( _μmSUS )
_BSUS )] is 0.8 to 1.5. 3. A magnetic recording signal is reproduced by a reproducing head using a magnetoresistive element.
The magnetic recording medium according to the above. 4. The magnetic layer has a coercive force of 120 to 320.
kA / m, the product of the residual magnetic flux density in the longitudinal direction and the thickness is 0.0
4. The method according to claim 1, wherein the temperature is from 018 μTm to 0.06 μTm.
The magnetic recording medium according to any one of the above. 5. The backcoat layer has a particle size of 5 nm to 100 nm.
nm small particle size carbon black and particle size 200 nm-40
0 nm large particle size carbon black is contained such that the total amount of the small particle size carbon black and the large particle size carbon black is 60 to 98% by weight based on the weight of the inorganic powder, and the particle size is 0%. 5. The method according to claim 1, wherein the content of iron oxide of 0.1 μm to 0.6 μm is 2 to 40% by weight based on the weight of the inorganic powder, and the center line average surface roughness Ra is 2 to 15 nm. The magnetic recording medium according to the above. 6. The non-magnetic support has a thickness of 7.0 μm or less and a Young's modulus in the longitudinal direction of 6.08 GPa (600 kg / mm).
² ) The 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 0.6 to
6. The magnetic recording medium according to claim 1, wherein the ratio is 1.80.