JP2003257011A - Magnetic recording media - Google Patents

Abstract

(57) [Problem] To provide a magnetic recording medium capable of improving output and suppressing output fluctuation and improving wear resistance and head contamination of an MR head. SOLUTION: 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, a center line average diameter of 5 mm is obtained. The magnetic recording medium was brought into contact with a cylindrical test piece having a surface roughness Ra of 10 nm ± 1 nm at a winding angle of 9 °, a relative speed of 4.0 m / sec, and a running tension of 0.9.
The dynamic friction coefficient μ with respect to the test piece in a state of sliding with 2N (0.094 kgf) (１ ／ inch tape) is 0.01 ≦ μ ≦ 0.035.

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, access speed and transfer rate, and more particularly to a magnetic recording medium for a data backup system using an inductive MR composite head.

[0002]

2. Description of the Related Art Magnetic tapes have various uses such as audio tapes, video tapes, computer tapes, etc. In particular, in the field of data backup tapes, with the increase in capacity of hard disks to be backed up, 1
A storage tape having a storage capacity of 100 GB or more per volume 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. In addition, in order to increase the access speed and the transfer speed, it is essential to increase the relative speed between the tape and the head.

In order to increase the recording density, in recent years, a current is passed through a magnetoresistive film from a magnetic recording / reproducing system using a conventional inductive head (electromagnetic induction type head) as a signal reproducing head. , A magnetoresistive head (MR which detects the resistance change as a voltage
Heads) are being replaced by magnetic recording / reproducing systems. The MR head can increase the output of the head itself by the film having a large resistance change of the element, the current density and the head structure design. In a system that employs such an MR head, since an inductive head is generally used for recording, an inductive M that integrates the recording inductive head and the reproducing MR head is used.
R composite head is adopted.

On the other hand, also in the magnetic tape itself, in order to cope with the above-mentioned improvement of the storage capacity per roll and the increase of the relative speed between the tape and the head, the magnetic layer is improved, specifically, the ferromagnetic powder. Recording density (reduction of recording wavelength and track width) by improving the magnetic characteristics and dispersibility of the tape, and high storage capacity by reducing the total thickness of the tape to lengthen the tape length per roll. The tape-head contact has been improved by optimizing the mechanical properties of the magnetic support, undercoat layer and magnetic layer.

[0005]

In the large-capacity magnetic recording / reproducing system described above, the relative speed between the tape and the head tends to be further increased because it is necessary to increase the access speed and the transfer speed. is there. However, when the relative speed between the tape and the head is increased in this way, the contact between the magnetic head and the magnetic tape becomes unstable, and as a result, output fluctuation occurs and the error characteristics are likely to deteriorate.

Therefore, in order to reduce the output fluctuation due to such contact failure, measures such as increasing the running tension to increase the contact force between the tape and the head have been taken. The protrusions on the surface of the magnetic layer frequently come into contact with the magnetoresistive element portion of the head. As a result, the magnetoresistive element portion may be worn, which may cause fatal problems such as a decrease in sensitivity, a decrease in stable operability, and a shift in initial resistance value. In addition, a large load is applied to the magnetic tape, the magnetic layer is easily damaged, and the contained material separated from the damaged magnetic layer is easily attached to the head. As a result, the reproduction output is deteriorated due to head contamination.

The present invention addresses such a problem, and an object thereof is to suppress output fluctuation (improve output characteristics), and improve wear resistance and head contamination of the MR head.

[0008]

Means for Solving the Problems The inventors of the present invention have made earnest studies to achieve the above-mentioned object, and as a result, a cylindrical test having a diameter of 5 mm and a center line average surface roughness Ra of 10 nm ± 1 nm has been conducted. The magnetic recording medium is brought into contact with a piece (material: SUS304) at a winding angle of 9 °, and the relative speed is 4.0 m.
It was found that the coefficient of kinetic friction with respect to the test piece in the state of being slid at a running tension of 0.92 N (0.094 kgf) / sec and a good correlation with the head output and the wear resistance of the head. This dynamic friction coefficient is a characteristic value that combines the surface shape, dynamic rigidity, and sliding characteristics of the magnetic layer, and the actual machine characteristics are analyzed rather than the conventionally statically measured friction coefficient, surface shape, rigidity, etc. Is excellent at

As a result of further detailed investigation of the relationship between the dynamic friction coefficient and the head output and the wear resistance of the head, the inventors set the dynamic friction coefficient within a specific range.
Alternatively, the gradient of the dynamic friction coefficient with respect to the speed change (change of the relative traveling speed of the magnetic recording medium with respect to the test piece), that is, the change amount of the dynamic friction coefficient with respect to the change amount of the relative speed when the relative speed of the magnetic recording medium is changed. It has been found that, by setting the ratio of (1) to a specific range, the output fluctuation can be reduced at high output, and at the same time, uneven wear and head contamination of the magnetoresistive element of the MR head can be reduced.

The present invention has been completed based on the above findings. At least one undercoat layer and a magnetic layer are formed in this order on one surface of a non-magnetic support, and a back surface is formed on the opposite surface. A magnetic recording medium having a coat layer is characterized by having the following characteristics. That is, the magnetic recording medium of the present invention has a columnar test piece (material: material having a diameter of 5 mm and a center line average surface roughness Ra of 10 nm ± 1 nm).
SUS304) and the magnetic recording medium is contacted at a winding angle of 9 °, the relative speed is 4.0 m / sec, and the running tension is 0.92 N (0.9).
094 kgf) (1/2 inch tape), the coefficient of kinetic friction μ for the test piece is 0.
It is characterized in that 01 ≦ μ ≦ 0.035.

Further, the magnetic recording medium of the present invention is
In addition to this configuration, the running tension is constant [0.92N (0.094k
gf)], the relative velocity of the magnetic recording medium is 2.5 m / sec.
(V ₁ ) To 4.0 m / sec (V₂ )
And the relative speed of the magnetic recording medium is V₁ When it is
Friction coefficient μ₁ And the relative speed of the magnetic recording medium is V₂ And
Coefficient of dynamic friction₂ When the relative speed changes
Amount (ΔV = V₂ -V ₁ ) Change in dynamic friction coefficient
(Δμ = μ₂ -Μ₁ ) Ratio (Δμ / ΔV) is -0.0
25 ≦ (Δμ / ΔV) ≦ −0.005 (Unit is (s /
(m)) is also characteristic (claim 2).

The magnetic recording medium of this structure is an LRT which will be described later.
It can be obtained by uniformly removing the protrusions on the surface of the magnetic layer by a treatment (lapping / rotary / tissue treatment) under constant conditions.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION First, a method of measuring a dynamic friction coefficient (hereinafter, also referred to as a friction coefficient) μ characterizing a magnetic recording medium of the present invention will be described, and thereafter, constituent elements of the magnetic recording medium will be described in detail.

<Friction coefficient measuring method> (A) Structure of measuring system: As shown in FIG. 1, the traveling speed is 2.
A load cell 2 [(maximum load: 0.98N (1
00gf)) and a cylindrical test piece 4 having a diameter of 5 mm and a center line average surface roughness (Ra) of 9 to 11 nm (10 nm ± 1 nm)]. At this time, magnetic tape 1
The test piece 4 is set so that the running direction of the test piece 4 and the axial direction of the test piece 4 are orthogonal to each other and the surface of the magnetic layer of the magnetic tape 1 contacts the outer peripheral surface of the test piece 4. In this state, the magnetic tape 1 is supported by the guide rollers 5 to run, and the frictional force acting on the test piece 4 at that time is measured by the load cell 2, and the frictional force is used to perform the friction using the formula (2) described later. Get the coefficient. The winding angle θ of the magnetic tape 1 around the test piece 4 at this time is 9 ° as shown in FIG. The Ra of the test piece was set in the range of 10 nm ± 1 nm because there was no difference in the dynamic friction coefficient μ in this range.

The material of the test piece 4 used is S
US 304. This test piece 4 does not come off from the groove 6a of the test piece holding portion 6 provided at the tip of the arm 3 by using the holding member 7 as shown in FIG. Attach to. Each holding member 7 is fixed to the test piece holding portion 6 with a screw 8.

(B) Calculation of friction coefficient: As shown in FIG. 4 (a), consider the simplest model in which an object M of weight W ₁ is placed on a horizontal surface H. In this model, the frictional force f ₁ generated when the external force F ₁ is horizontally applied to the object M is f ₁ = μ ₁ W ₁ (1). Applying this to the measurement system of FIG.
As shown in (b), the horizontal component T of the tape tension T
cos θ is the horizontal force F ₂ and the vertical component T sin θ is the vertical force W
It can be regarded as _2, and the measured frictional force f ₂ can be expressed as f ₂ = μT sin θ (2). From this, the dynamic friction coefficient μ at the time of measurement can be obtained.

<Non-magnetic support> The magnetic non-magnetic support has a Young's modulus in the longitudinal direction of 5.88 GPa (600 kg / mm ² ).
Above, and Young's modulus in the width direction is 3.92 GPa (400
kg / mm ² ) or more, Young's modulus in the longitudinal direction is 9.8 GPa (1000 kg / mm ² ) or more,
And the Young's modulus in the width direction is 7.84 GPa (800 kg / mm
² ) or more is more preferable. The Young's modulus in the longitudinal direction of the non-magnetic support is preferably 5.88 GPa (600 kg / mm ² ) or more because the Young's modulus in the longitudinal direction is 5.88 GPa (600 kg / mm ² ).
^If it is less than ² ), tape running may become unstable. Young's modulus in the width direction of the non-magnetic support is 3.92G
The reason why Pa (400 kg / mm ² ) or more is preferable is that when the Young's modulus in the width direction is less than 3.92 GPa (400 kg / mm ² ), edge damage of the tape may easily occur. A non-magnetic support satisfying such characteristics is
There are polyethylene terephthalate, polyethylene naphthalate, biaxially stretched aromatic polyamide base film, aromatic polyimide film and the like.

The thickness of the non-magnetic support varies depending on the application, but is usually 2 to 7 μm. More preferably, it is 2.5 to 4.5 μm. When the thickness of the non-magnetic support is within this range, it is difficult to form a film with a thickness of less than 2 μm, and the tape strength becomes small. Is smaller. The surface roughness (Ra) of the undercoat layer / magnetic layer formation surface of the non-magnetic support is more preferably 2.5 nm or more and 20 nm or less. The thickness of 2.5 nm or more and 20 nm or less is more preferable, if it is 2.5 nm or more, the coating characteristics (running characteristics of the non-magnetic support during coating) are excellent, and if it is 20 nm or less, the undercoat layer is made thin. This is also because the irregularities on the surface of the undercoat layer and the surface of the magnetic layer are reduced. The structures of the undercoat layer and the magnetic layer will be described later.

<Magnetic layer> The coercive force in the tape longitudinal direction is 13
5 kA / m to 280 kA / m (1700 to 3500O
e), the residual magnetic flux density in the longitudinal direction of the tape is 0.18T (18
00G) or higher is preferable. This range is preferable because when the coercive force is less than 135 kA / m, the output decreases due to the demagnetizing field, and when it exceeds 280 kA / m, writing by the head becomes difficult. The residual magnetic flux density is preferably 0.18T or more because the output is reduced when the residual magnetic flux density is less than 0.18T. Coercive force of 160 kA / m to 240 kA / m
(2000-3000 Oe), residual magnetic flux density is 0.2-0.
It is more preferably 4T (2000 to 4000G).
The magnetic properties of this magnetic layer and the magnetic properties of the ferromagnetic iron-based metal powder are both measured by a sample vibrating magnetometer and an external magnetic field of 1.28.
It is a value measured at MA / m (16 kOe).

As the magnetic powder added to the magnetic layer, a ferromagnetic powder, specifically, a ferromagnetic iron-based metal powder is used. The coercive force of the magnetic powder is 135 kA / m to 280 kA / m (1700
~ 3500 Oe) is preferred, and the saturation magnetization is 120 ~
200 A · m ² / kg (120 to 200 emu / g) is preferable, and 130 to 180 A · m ² / kg (130 to 180)
emu / g) is more preferable. The average major axis length of the ferromagnetic iron-based metal powder is preferably 80 nm or less as described above, and 2
0-60 nm is more preferable. This range is preferable because if it is larger than 80 nm, particle noise based on the size of particles becomes large, and if the average major axis length is less than 10 nm, the coercive force decreases and the cohesive force of the magnetic powder increases. This is because it becomes difficult to disperse it in the inside. The average major axis length is obtained by actually measuring the particle size of a photograph taken with a scanning electron microscope (SEM) and averaging 100 particles. In addition, B of this ferromagnetic iron-based metal powder
The ET specific surface area is preferably 35 to 85 m ² / g, 40
-80 m < ² > / g is more preferable, 50-70 m < ² > / g is the most preferable.

The magnetic layer contains 0.
Containing 5 to 3.0% by weight of fatty acid amide, 0.2 to 3.0
It is preferred to include weight percent esters of higher fatty acids. This is because the coefficient of friction between the tape and the head is reduced in this way. Fatty acid amides in this range are preferable, if less than 0.2% by weight, direct contact is likely to occur at the head / magnetic layer interface, and the seizure prevention effect is small, and if more than 3.0% by weight, bleed-out occurs and drops occur. Defects such as out occur. As the fatty acid amide, amides such as palmitic acid and stearic acid can be used. Further, it is preferable to add an ester of a 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 3.
This is because when it exceeds 0% by weight, there are side effects such as sticking of the tape and the head. The mutual movement of the lubricant of the magnetic layer and the lubricant of the undercoat layer is not excluded.

Magnetic layer (same for the undercoat layer described later)
A binder is used for. Examples of the binder include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic anhydride. A combination of a polyurethane resin and at least one selected from a copolymer, a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer, nitrocellulose and the like 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 in these formulas is a hydrogen atom, an alkali metal base or an amine salt], OH, NR ₁ R ₂ , N ⁺ R ₃ R
₄ R ₅ [R ₁ , R ₂ , R ₃ , R ₄ , R _{5 in} these formulas
Is hydrogen or a hydrocarbon group], and it is preferable to use a binder such as a urethane resin made of a polymer having an epoxy group. The use of such a binder is preferable 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 iron-based metal powder. In particular, it is most preferable to use 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin as a binder 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 15 to 35 parts by weight.

Conventionally known abrasives can be added to the magnetic layer. Examples of these abrasives include α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide and α-iron oxide. , Corundum, artificial diamond, silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, boron nitride, etc. are mainly used with a Mohs hardness of 6 or more alone or in combination, and among them, alumina has a high hardness. In particular, a small addition amount is excellent in head cleaning effect, and is particularly preferable. The average particle size of the abrasive is usually 2 depending on the thickness of the magnetic layer.
The particle size is preferably 30 to 30 and preferably 0 to 400 nm.
0 nm is more preferable. The addition amount is preferably 5 to 20% by weight with respect to the ferromagnetic iron-based metal powder. More preferably 8 to 1
8% by weight.

Conventionally known carbon black (CB) may be added to the magnetic layer for the purpose of improving conductivity and surface lubricity. As this type of CB, acetylene black, furnace black, thermal black or the like can be used. In that case, particles having a particle diameter of 5 nm to 200 nm can be used, but particles having a particle diameter of 10 nm to 100 nm are preferably used. This is 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, and in any case, the surface becomes rough, which causes a reduction in output. The amount of CB added is preferably 0.2 to 5% by weight with respect to the ferromagnetic iron-based metal powder. It is more preferably 0.5 to 4% by weight.

<Undercoat layer> An undercoat layer is provided between the non-magnetic support and the magnetic layer for the purpose of improving durability. A binder similar to the binder used in the previous magnetic layer is added to the undercoat layer, but alumina is also added. The particle size of alumina added to the undercoat layer is preferably 100 nm or less, and the addition amount is 2-3 based on the weight of all inorganic powders.
0% by weight is preferred. Alumina of 100 nm or less is preferable because the surface roughness (Ra) of the undercoat layer / magnetic layer formation surface is 2.5.
When a non-magnetic support having a low smoothness of not less than nm is used and the undercoat layer is as thin as 1.5 μm or less, the particle size of alumina is 100
This is because if the thickness exceeds nm, the smoothing effect on the surface of the undercoat layer becomes insufficient. 10-100 nm is more preferable, and 30-
90 nm alumina addition is more preferred, 50-90
nm is more preferred. The amount of alumina added in this range is preferable because if it is less than 2% by weight, the fluidity of the coating is insufficient.
This is because if it exceeds 0% by weight, irregularities on the surface of the undercoat layer / magnetic layer become large. The amount of alumina added is 6 to 25.
% Is more preferable, 8 to 20% is more preferable, and 11 to 20% is even more preferable. The alumina added to the undercoat layer is preferably alumina having a corundum phase as a main component. Alumina mainly composed of corundum phase (alpha conversion rate:
30% or more) is preferable because the Young's modulus of the undercoat layer is increased and the tape strength is increased with a small amount as compared with the case where σ, θ, γ alumina or the like is used. It should be noted that, together with alumina having the above particle diameter, α of 100 to 800 nm of less than 3 wt%
The addition of alumina is not excluded.

As described above, when the above-mentioned alumina is contained in the above-mentioned amount in the above-mentioned amount, the unevenness at the interface between the undercoat layer and the magnetic layer becomes small, and the variation in the output due to the waviness of the tape edge (edge weave) is also improved. . In particular, the addition of alumina mainly composed of the corundum phase has a great effect. Also, the tape strength is increased. In addition to alumina having the above particle size and amount, carbon black is added for the purpose of improving conductivity, and non-magnetic iron oxide is added for the purpose of increasing strength.

Carbon black is added to the undercoat layer for the purpose of preventing charging. As carbon black (CB) to be added, acetylene black, furnace black, thermal black or the like can be used. Particle size is 5
nm to 200 nm is used, but the particle size is 10 to 1
It is preferably 00 nm. This range is preferred
Because carbon black has a structure,
When the particle size is 10 nm or less, it is difficult to disperse CB.
This is because if the thickness is 0 nm or more, the smoothness becomes poor. The amount of CB added varies depending on the particle size of CB, but is preferably 15 to 40% by weight. This range is preferable because if it is less than 15% by weight, the effect of improving conductivity is poor, and if it exceeds 40% by weight, the effect is saturated. It is more preferable to use 15 to 35% by weight of CB having a particle size of 15 nm to 80 nm, and further preferable to use 20 to 30% by weight of CB having a particle size of 20 nm to 50 nm. By adding carbon black having such a particle size and amount, the electrical resistance is reduced, and the occurrence of electrostatic noise and tape running unevenness are reduced.

Non-magnetic iron oxide can be added to the undercoat layer for the purpose of improving the strength of the coating film. The non-magnetic iron oxide to be added preferably has a particle size of 50 to 400 nm, and the addition amount is preferably 35 to 83% by weight.
The particle size in this range is preferable because if the particle size is less than 50 nm, uniform dispersion is difficult, and if it exceeds 400 nm, irregularities at the interface between the undercoat layer and the magnetic layer increase. 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 is reduced and the coating film strength is lowered.

The Young's modulus of the undercoat layer is preferably 80 to 99% of the Young's modulus of the magnetic layer. The Young's modulus of the undercoat layer is preferably lower than that of the magnetic layer because the undercoat layer acts as a kind of cushion.

<Backcoat layer> A backcoat layer is provided on the opposite surface of the non-magnetic support, that is, the surface opposite to the surface on which the undercoat layer and the magnetic layer are formed, for the purpose of improving running properties. Can be provided. The thickness of the back coat layer is 0.2
The thickness is preferably 0.8 μm. This is because if the thickness is less than 0.2 μm, the running property improving effect is insufficient, and if it exceeds 0.8 μm, the total thickness of the tape increases and the storage capacity per roll decreases.

It is preferable to add carbon black (CB) to the back coat layer for the purpose of preventing static charge. As CB in this case, acetylene black, furnace black, thermal black or the like can be used. Further, usually, small particle size carbon and large particle size carbon are used as CB. The small particle size carbon has a particle size of 5 nm to 200 n
m having a particle diameter of 10 nm to 100 nm is more preferable. 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, and in any case, the surface becomes rough and the cause of settling (embossing) to the magnetic layer is caused. This is because If 5 to 15% by weight of the small particle size carbon and the large particle size carbon having the particle size of 300 to 400 nm are used as the large particle size carbon, the surface is not roughened and the running property 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. The surface roughness Ra is preferably 3 to 8 nm, more preferably 4 to 7 nm.

Further, it is preferable to add iron oxide having a particle diameter of 100 nm to 600 nm to the back coat layer for the purpose of improving strength. The particle size of the added iron oxide is 200
nm to 500 nm is more preferable. 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. A cassette tape incorporating the above-mentioned tape has a large capacity per roll and is highly reliable and particularly excellent as a backup tape for a hard disk drive.

The same resin as that used for the magnetic layer or the undercoat layer can be used as the binder in the back coat layer. Among them, a cellulose-based resin is used 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.

<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 friction coefficient (μ _mSL ) of the MR head with the slider is preferably 0.30 or less, more preferably 0.25 or less. This range is preferable because if it exceeds 0.30, spacing loss due to slider dirt easily occurs. In addition, it is difficult to achieve less than 0.10. Friction coefficient with SUS (μ _mSUS )
Is preferably 0.10 to 0.25, more preferably 0.12 to 0.20. This range is preferable because when it is less than 0.10, the head and the guide roller are easily slippery and the traveling becomes unstable, and when it is more than 0.25, the head and the guide roller are easily soiled. In addition, [(μ _mSL ) / (μ
_mSUS )] is preferably 0.7 to 1.3, and more preferably 0.8 to 1.2. This range is preferable because tracking deviation (off-track) due to meandering of the magnetic tape becomes small.

<LRT processing (wrapping / rotary /
Tissue treatment> As for the magnetic layer, the protrusions on the surface of the magnetic tape are removed by the LRT treatment including the lapping, rotary and tissue treatments described below, and the magnetic tape floats evenly. The dynamic friction coefficient can be reduced.

(1) Lapping treatment: The polishing tape (lapping tape) was moved at a constant speed (standard: 14.4 cm / min) in the direction opposite to tape feeding (standard: 400 m / min) by a rotating roll, The tape is brought into contact with the surface of the tape magnetic layer by pressing it from above with a guide block. At this time, the tension for unwinding the magnetic tape and the tension for the wrapping tape are constant (standard: 10 for each).
0 g, 250 g (1/2 inch width)) and the magnetic tape is polished. The polishing tape (wrapping tape) used in this process is, for example, M20000,
It is a polishing tape (lapping tape) with fine abrasive grains such as WA10000 or K10000.
It should be noted that the use of polishing wheels (lapping wheels) instead of or in combination with polishing tapes (lapping tapes) is not excluded, but if frequent replacement is required, use only polishing tapes (lapping tapes). To do.

(2) Rotary treatment: Air bleeding wheel [standard: width 1 inch (25.4 mm), diameter 60 m
m, air vent groove 2 mm width, groove angle 45 degrees, manufactured by Kyowa Seiko Co., Ltd.] and the magnetic layer at a constant winding angle (standard: 90
Constant rotation speed in the opposite direction of tape feed (normal:
The magnetic tape is treated by contacting it at 200-3000 rpm, standard: 1100 rpm).

(3) Tissue treatment: A tissue [for example, woven cloth Toraysee manufactured by Toray Industries, Inc.] is rotated by a rotating rod on the backcoat layer and the magnetic layer surface in a direction opposite to the tape feeding at a constant speed (standard: 14.0 mm / min). ) To perform cleaning processing on the magnetic tape.

[0043]

EXAMPLES Examples of the present invention will be described below together with comparative examples, but the present invention is not limited to the following examples. 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 x 0.02 µm) 68 parts Alumina (alpha conversion rate: 50%, particle size: 0) .05 μm) 8 parts Carbon black (average particle size: 20 nm) 24 parts Stearic acid 2.0 parts Vinyl chloride copolymer 10 parts (Contained-SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g) Polyester polyurethane Resin 4.5 parts (Tg: 40 ° C., contained —SO ₃ Na group: 1 × 10 ⁻⁴ equivalent / 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 4.5 parts Cyclohexanone 10 parts Methyl ethyl ketone 15 parts Toluene 10 parts

<< Coating Components for Magnetic Layer >> (1) Ferromagnetic iron-based metal powder 100 parts (Co / Fe: 30 at%, Y / (Fe + Co): 3 at%, Al / (Fe + Co): 5 wt%, Ca / Fe : 0 wt%, σs: 155 A · m ² / kg, Hc: 188.2 kA / m, pH: 9.4, major axis length: 0.10 μm) Vinyl chloride-hydroxypropyl acrylate copolymer 11 parts (containing-SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g) Polyester polyurethane resin 5 parts (containing —SO ₃ Na group: 1.0 × 10 ⁻⁴ equivalent / g) α-alumina (average particle diameter: 0.15 μm) ) 15 parts carbon black 2.0 parts (average particle diameter: 75 nm, DBP oil absorption: 72 cc / 100 g) methyl acid phosphate 2 parts palmitic acid amide 1.5 parts n-butyl stearate 1.0 part tetrahydrofuran 65 parts methyl ester Ethyl ketone 245 parts 85 parts of toluene (2) Polyisocyanate 4 parts Cyclohexanone 167 parts

After kneading (1) with a kneader in the above coating composition for the undercoat layer, (2) is added and stirred, and a dispersion treatment is carried out with a sand mill for a residence time of 60 minutes, and (3) is added to this. After adding and stirring and filtering, it was used as a paint for the undercoat layer.
Separately, after kneading a predetermined amount of the above-mentioned magnetic layer coating composition (1) with a kneader, the remaining solvent was added, and the mixture was dispersed in a sand mill with a residence time of 45 minutes, and the magnetic layer coating composition ( 2) was added, and the mixture was stirred and filtered to give a magnetic paint. Aromatic polyamide film (thickness
3.9 μm, Young's modulus in longitudinal direction = 9.5 GPa, MD / TD
= 0.70, trade name: Miktron, manufactured by Toray Industries, Inc., on a non-magnetic support (hereinafter, also simply referred to as a support),
It is coated so that the thickness after drying and calendering will be 0.8 μm, and the magnetic coating above will be further applied onto this undercoat layer to give a magnetic layer thickness of 0.08 after magnetic field orientation treatment, drying and calendering treatment.
It was applied so as to have a thickness of .mu.m, subjected to magnetic field orientation treatment, and dried to obtain a magnetic sheet. 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.

<< Paint component for back coat layer >> Carbon black (average particle size: 20 nm) 80 parts Carbon black (average particle size: 350 nm) 10 parts Iron oxide (particle size: 0.3 μm) 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, and after filtration, the magnetic layer of the magnetic sheet prepared above was prepared. Apply to the opposite surface so that the thickness after drying and calendering will be 0.2 μm.
Dried.

The magnetic sheet thus obtained was placed in a 7-stage calender consisting of metal rolls at a temperature of 100 ° C. and a linear pressure of 2
It was mirror-finished under the condition of 00 kg / cm.

After aging the magnetic sheet around the core at 70 ° C. for 72 hours, the magnetic sheet was cut into ½ inch widths and the magnetic layer surface was subjected to the following LRT treatment while running at 200 m / min. A magnetic tape was produced.

LBT treatment (lapping / rotary /
Tissue treatment >> (1) Lapping treatment: Abrasive tape (wrapping tape) is fed by a rotating roll (standard: 400)
m / min) and a constant speed (standard: 14.4 cm /)
Minute) and press the guide block from above to bring it into contact with the tape magnetic layer surface. At this time, the magnetic tape unwinding tension and the wrapping tape tension are constant (standard: 100 g each, 250
As g), the magnetic tape is polished. The polishing tape (wrapping tape) used in this step is, for example, M20000, WA10000 or K10.
It is a polishing tape (lapping tape) with fine abrasive grains such as No. 000. It should be noted that the use of polishing wheels (lapping wheels) instead of or in combination with polishing tapes (lapping tapes) is not excluded, but if frequent replacement is required, use only polishing tapes (lapping tapes). To do.

(2) Rotary treatment: Grooved wheel for air venting [Standard: 1 inch (25.4 mm) width, 60 m diameter
m, air vent groove 2 mm width, groove angle 45 degrees, manufactured by Kyowa Seiko Co., Ltd.] and the magnetic layer at a constant contact angle (standard: 90
Constant rotation speed in the opposite direction of tape feed (normal:
The magnetic tape is treated by contacting it at 200-3000 rpm, standard: 1100 rpm).

(3) Tissue treatment: A tissue [for example, woven cloth Toraysee manufactured by Toray Industries, Inc.] was rotated by a rotating rod on the backcoat layer and the magnetic layer surface in a direction opposite to the tape feeding at a constant speed (standard: 14.0 mm / min). ) To perform cleaning processing on the magnetic tape.

The magnetic tape obtained as described above is
It was incorporated into a cartridge to produce a computer tape.

(Comparative Example 1) The calender temperature was changed to 75 ° C., and the LBT treatment (conditions described below) consisting of conventional lapping, blade and tissue treatments was carried out instead of the LRT treatment. Other than that,
A magnetic tape of Comparative Example 1 was produced in the same manner as in Example 1.

<< LBT (Wrapping / Blade / Tissue) Treatment >> (1) Wrapping treatment: Abrasive tape (lapping tape) is fed by a rotating roll (400 m /
Min.) At a speed of 14.4 cm / min and contact with the tape magnetic layer surface by pressing from above with a guide block. At this time, the magnetic tape unwinding tension was 100 g and the lapping tape tension was 250 g, and the magnetic tape was polished.

(2) Blade treatment: Following the polishing treatment,
A blade made of cemented carbide was pressed against the magnetic tape (feed rate: 400 m / min), and the blade treatment for the magnetic tape was performed instead of the rotary treatment.

(3) Tissue treatment: A woven cloth Toraysee manufactured by Toray Industries, Inc. was fed with a rotating rod to the backcoat layer and the magnetic layer surface in the opposite direction to the tape feeding at a rate of 14.0 mm / min to clean the magnetic tape. I went.

(Comparative Example 2) The nonmagnetic support was changed to PET (polyethylene terephthalate), and the magnetic layer, undercoat layer,
A magnetic tape of Comparative Example 2 was produced in the same manner as Comparative Example 1 except that the thickness of the back coat layer was changed to the values shown in Table 1. <Evaluation> The evaluation was performed on the following items in addition to the dynamic friction coefficient obtained by the above method.

Center line average surface roughness of the support (support R
a): Measured using a surface roughness meter SE-3FA (manufactured by Kosaka Laboratory). After sticking the support surface on the side where the back coat layer is formed on a smooth semi-cylindrical glass, the center line average surface roughness of the support surface on the side where the undercoat layer and the magnetic layer are formed, The measurement was carried out under the conditions of a stylus of 5 μm, a vertical magnification of 100,000 times and a cutoff of 0.08 mm.

Center line average surface roughness Ra of the magnetic layer surface:
The measurement was carried out in the same manner as in the case of the above support.

Young's modulus of support: A piece of support having a width of 10 mm and a length of 150 mm was cut out from the support used in Examples and Comparative Examples to prepare a sample, and the load of the sample was measured by an Instron type universal tensile tester. The elongation curve was measured to determine the Young's modulus in the longitudinal direction (MD) and the Young's modulus in the width direction (TD). In that case, chuck spacing is 100 mm and pulling speed is 2
The sample was pulled at 0 mm / sec and the recorded chart was 0.
Young's modulus was calculated from the load of 3% elongation.

Young's modulus of coating layer: A tape piece having a width of 12.7 mm and a length of 150 mm was cut out from each of the magnetic tapes prepared in Examples and Comparative Examples to prepare a sample, and a load-elongation curve was obtained in the same manner as in the case of the support. Was measured and Young's modulus was calculated.

Reproduction output and output fluctuation: A sample tape was wound on a DLT1 standard cartridge and recorded / reproduced by a DLT1 drive. The reproduction signal is measured from the output terminal of the MR head of the DLT1 drive using a digital oscilloscope, and the average value AVR, the maximum value Max, and the minimum value Min of the reproduction output for 0.1 seconds are calculated as [(Max-Min) /
AVR] × 100 (%) was taken as the output fluctuation.

Head life: A sample tape was wound on a DLT1 standard cartridge and continuously recorded / reproduced by the DLT1 drive, and the reproduction output value was 75% of the initial value.
The time until it became less than or equal to% was measured.

-Head dirt: After continuously recording and reproducing for 16 hours under the conditions of tape speed of 3.3 m / sec and tape tension of 1.1 N with DLT1 drive, the tape sliding surface of the head was changed to 2
It was observed under a measuring microscope with a magnification of 00. The judgment is "◎" ...
Almost no dirt on the tape sliding surface, "○" ... There is dirt on a part of the tape sliding surface except near the head gap,
“△” ・ ・ ・ Dirt near the head gap, “×”
・ ・ ・ The head gap part was covered with dirt and clogged.

Table 1 shows the above measurement results.

[0068]

[Table 1]

Dependence of friction coefficient on tape speed and tape tension: In addition to the above, when the tape tension is set to 0.92 N (0.094 kg) in the above-described measurement system, the tape speed (relative Speed) to 2.54
Dynamic friction coefficient (μ ₁ ) when m / sec (V ₁ ) and 4.
The dynamic friction coefficient (μ ₂ ) was measured at 0 m / sec (V ₂ ). The measurement result is shown in FIG. The comparative example shown in FIG. 5 is that of Comparative Example 1 in Table 1, and the graph of Comparative Example 2 in Table 1 is omitted for clarity.

From the above measured values, the tape speed change amount under each tape tension (ΔV = V ₂ −V
Change of dynamic friction coefficient with respect to ₁ ) (Δμ = μ ₂ −μ ₁ )
The ratio (Δμ / ΔV) was calculated and used as the value of “change in dynamic friction coefficient with respect to tape speed” in Table 1.

Looking at Table 1, under the conditions described above,
0.01 ≦ μ ≦ 0.035 and −0.025 ≦ (Δμ / Δ
V) ≦ −0.005, the magnetic tape of the example of the present invention is less likely to cause head contamination than the magnetic tape of each comparative example in which the range of μ and (Δμ / ΔV) deviates from the above range. It can be seen that the head life has been extended.
Further, the output fluctuation was 5% for each of the comparative tapes 1 and 2, whereas it was 4% for the magnetic tapes of the examples of the present invention. Therefore, it is also understood that the tapes of the examples of the present invention have smaller output fluctuations and less output deterioration (good output characteristics) than the comparative example tapes.

[0072]

As described above, according to the magnetic recording medium of the present invention, the diameter is 5 mm and the center line average surface roughness Ra is 1.
The magnetic recording medium was brought into contact with a cylindrical test piece of 0 nm ± 1 nm at a winding angle of 9 °, and a relative speed was 4 m /
By setting the dynamic friction coefficient with respect to the test piece in a state of being slid at a traveling tension of 0.92 N (0.094 kgf) for a second within a specific range, it is possible to suppress output fluctuation (improve output characteristics), Moreover, it is possible to improve wear resistance and head contamination of the MR head.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a measurement system used to measure a dynamic friction coefficient of a magnetic recording medium.

FIG. 2 is an enlarged view showing a peripheral portion of the tate piece in FIG. 1 in an enlarged manner.

FIG. 3 is a diagram showing a state viewed from a direction of an arrow P in FIG.

FIG. 4 is an explanatory diagram used for explaining a principle of measuring a dynamic friction coefficient.

FIG. 5 is a graph showing the measurement result of the tape velocity dependence of the dynamic friction coefficient, where the tape tension is 0.92 N (0.0
94 kgf).

[Explanation of symbols]

1 Magnetic tape (magnetic recording medium) 4 test pieces θ winding angle

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Motoya Miura             Hitachi Ma, 1-88, Torora, Ibaraki City, Osaka Prefecture             Within Kucsel Co., Ltd. F-term (reference) 3C049 AA05 AA07 AA12 CA01                 5D006 BA04 BA19

Claims (2)

[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 backcoat layer on the opposite surface, the diameter of which is 5 mm. The magnetic recording medium is brought into contact with a cylindrical test piece (material: SUS304) having a center line average surface roughness Ra of 10 nm ± 1 nm at a winding angle of 9 °, and a relative speed is 4.
0 m / sec, traveling tension 0.92 N (0.094 kgf) (1 /
A magnetic recording medium having a coefficient of dynamic friction μ with respect to the test piece in a state of being slid with a 2 inch tape) is 0.01 ≦ μ ≦ 0.035. 2. A constant traveling tension [0.92N (0.094k
gf)], the relative velocity of the magnetic recording medium is V _{1 when} the relative velocity of the magnetic recording medium is changed from 2.5 m / sec (V ₁ ) to 4.0 m / sec (V ₂ ). the dynamic friction coefficient is mu ₁ when the relative speed of the magnetic recording medium when the dynamic friction coefficient mu ₂ when a V _2, the variation of the relative velocity (ΔV = V ₂ -V ₁₎ for the dynamic friction coefficient The rate (Δμ / ΔV) of the amount of change (Δμ = μ ₂ −μ ₁ ) is -0.0
25 ≦ (Δμ / ΔV) ≦ −0.005 (Unit is (s /
m)), the magnetic recording medium according to claim 1.