JP3046580B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly reliable high-density digital magnetic recording medium having excellent electromagnetic characteristics and low dropout, and excellent running properties and durability.

[0002]

2. Description of the Related Art Signal recording / recording is performed by sliding a magnetic head over a medium surface.
In a digital magnetic recording medium of the type that performs reproduction, the surface properties of the medium magnetic layer are extremely important. In general, when the surface properties are improved, the electromagnetic conversion characteristics are improved and the number of dropouts is reduced, but the contact area between the head and the medium is increased, which affects running durability. If protrusions or the like made of an abrasive or the like are provided on the surface of the magnetic layer, the running durability is improved, but on the contrary, the spacing loss increases and the electromagnetic conversion characteristics deteriorate. Thus, it is difficult to achieve both high electromagnetic conversion characteristics and low dropout, and high running performance and high durability.

For the purpose of solving the above problems, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 16413 and Japanese Patent Application Laid-Open No. 6-180835 propose providing a depression on the surface of a magnetic layer. However, such a depression causes a recording defect, and causes a dropout to increase in a high-density digital magnetic recording medium having a small reproduction bit area.

[0004] Accordingly, the present invention provides a magnetic recording medium which can achieve both excellent electromagnetic conversion characteristics and low dropout, and excellent running properties and durability at a high level, and is suitable for high-density digital recording. The purpose is to:

The present inventors have found that when performing high-density digital recording, that is, when the reproduction bit area is reduced, not all of the depressions existing on the surface of the uppermost magnetic layer cause dropout. It has been found that, in relation to the reproduction bit area, a depression whose cross-sectional area at a specific depth exceeds a specific value is caused. Furthermore, the present inventors
Under the conditions of high output and low dropout in which the presence of such depressions is minimized, use is made of nonmagnetic particles having a specific particle size contained in the uppermost magnetic layer, and the surface roughness of the uppermost magnetic layer is reduced. It has been found that by setting the thickness to a specific value or less, the durability and running properties of the magnetic recording medium are also improved.

The present invention has been made on the basis of the above findings, and has a digital signal having a lower layer on one surface of a support, an uppermost magnetic layer having a thickness of 0.2 μm or less, and a back coat layer on the other surface. A magnetic recording medium, wherein the average particle size of the nonmagnetic particles contained in the uppermost magnetic layer is 0.12 μm or less;
The surface roughness Ra of the uppermost magnetic layer is 7.5 nm or less, and the cross-sectional area at a depth of 20 nm from the root mean square surface of the surface shape of the uppermost magnetic layer measured by an atomic force microscope is a reproduction bit. The above object has been attained by providing a magnetic recording medium in which the number of depressions that are 3% or more of the area is 3/100 μm ² or less.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the magnetic recording medium of the present invention will be described below with reference to the drawings. FIG.
The magnetic recording medium 1 shown in FIG. 1 is for digital recording, and a lower layer 3 and an uppermost magnetic layer (hereinafter, referred to as an upper magnetic layer) 4 are provided on one surface of a support 2 adjacent to the lower layer 3, respectively.
Further, a back coat layer 5 is provided on the other surface of the support 2. The magnetic recording medium 1 achieves both excellent electromagnetic conversion characteristics and high durability at the time of high-density recording with a reproduction bit area of 1.15 μm ² or less. The reproduction bit area is determined by the product of the track width and the recording wavelength.

The upper magnetic layer 4 is formed by dispersing ferromagnetic powder and non-magnetic particles in a binder. The upper magnetic layer 4 has a surface roughness Ra of 7.5 nm or less, preferably 7.0 to 1.5 nm. As a result, spacing loss is reduced, and good electromagnetic conversion characteristics can be obtained. As described in the above related art section, when trying to reduce the surface roughness to improve the electromagnetic conversion characteristics,
Although there is a problem that runnability and durability are reduced, in the present invention, by setting the surface shape of the upper magnetic layer 4 as described below, both excellent electromagnetic conversion characteristics and high durability are compatible.

As shown in FIG. 2, the upper magnetic layer 4 is located at a distance from the root mean square R of the surface shape of the upper magnetic layer 4 measured by an atomic force microscope (hereinafter referred to as AFM).
The number of dents D (hereinafter referred to as critical dents) whose cross-sectional area at 0 nm depth S (hereinafter referred to as slice depth) is 3% or more of the reproduction bit area is 3
Pieces / 100 μm ² or less. As a result, the occurrence of dropout is suppressed, and the electromagnetic conversion characteristics are improved, and at the same time, the durability (still durability) is improved. As a result of detailed studies by the present inventors, as shown in FIG. 3A, the number of depressions whose cross-sectional area at a depth of 20 nm from the root mean square surface is 3% or more of the reproduction bit area, It was found that there was a correlation between If the slice depth is the depth of the root mean square surface or shallow depth close to it,
Even a slight gradation on the surface of the upper magnetic layer is recognized as a depression. However, such depressions are too shallow to affect the occurrence of dropouts. Conversely, if the slice depth is set deeper from the root mean square surface, only extremely deep depressions existing in the upper magnetic layer are recognized, and the shallowest depths of the depressions that affect the occurrence of dropouts are not recognized. As a result, there is no strong correlation between the slice depth and the occurrence of dropout. As a result of the examination, it was found that the depression affecting the occurrence of the dropout was recognized when the slice was sliced at a depth of 20 nm from the root mean square surface. In addition, even if a dent is recognized when sliced at a depth of 20 nm from the root mean square, a cross-section that is too small at the depth does not affect the occurrence of dropout, It has also been found that the depression becomes a defect when viewed from the head and affects the occurrence of dropout. As a result of further investigation, it was found that the cross-sectional area at the depth was 3% or more of the reproduced bit area [FIG.
(D)]. As described above, the present invention is based on the mean square surface.
The greatest feature is that the number of dents whose cross-sectional area at a depth of 0 nm is 3% or more of the reproduced bit area is very closely related to the occurrence of dropout.

In the present invention, when the number of the critical dents D is more than 3/100 μm ² , the occurrence of dropout increases rapidly, and the electromagnetic conversion characteristics rapidly decrease. Critical depression D
It is more preferred that the number be at one / 100 [mu] m ² or less and preferably 0.5 or / 100 [mu] m ² or less. Most preferably, it is 0.

The critical depression D easily allows a large amount of the lubricant contained in the upper magnetic layer 4 and / or the lower layer 3 to leach onto the surface of the upper magnetic layer 4. As a result, the magnetic head and the magnetic recording medium tend to stick to each other due to the lubricant that has leached in large amounts, and the running property is reduced. Further, since the lubricant easily oozes out, the replenishment of the lubricant from the inside of the medium to the surface of the upper magnetic layer is interrupted in a short time, and the running property and the durability also decrease. The method of measuring the number of depressions on the surface of the upper magnetic layer will be described in detail in Examples described later.

The closer the number of the critical dents D is to zero, the more the durability becomes sufficient, the occurrence of dropout is suppressed, and the electromagnetic conversion characteristics are improved. In the present invention, a depression having a cross-sectional area at a depth of 20 nm from the root mean square surface is less than 3% of the reproduction bit area on the surface of the upper magnetic layer 4 (hereinafter, this depression is referred to as a minute depression). ) Is preferably present. As a result, the contact area between the medium surface and the magnetic head is reduced, and the lubricant is constantly supplied to the medium surface through the minute recess, so that the friction between the medium surface and the magnetic head is suppressed, and the running property and durability are improved. Is maintained. Since the micro pit has a small cross-sectional area, a space loss from the magnetic head due to the presence of the micro pit and a reduction in output due to a recording defect are negligibly small.

The number of the micro recesses is set to 800 to 10/100 μm in order to make the ease of seepage of the lubricant within an appropriate range.
m ² , particularly preferably 400 to 20 particles / 100 μm ² .

The upper magnetic layer 4 has a surface roughness Ra of 7.5 μm or less while having the above-described stipulation of the depression. As described above, the durability is usually deteriorated when the surface roughness Ra is small. However, in the magnetic recording medium of the present invention, the durability is good because the leaching property of the lubricant is appropriate.

The upper magnetic layer 4 contains non-magnetic particles as described above.
It is blended. By reducing the particle size of these non-magnetic particles,
Loss of non-magnetic particles by reducing the amount
Can reduce the number of critical depressions caused by the above.
Further, a head using a magnetoresistive element (hereinafter referred to as MR)
When playback is performed using a
-Mal asperity problem (contact between media and magnetic head)
Temperature of MR head rises due to sliding heat generated by
Problem that the resistance value fluctuates and noise occurs)
You can also. Specifically, the average particle size of the non-magnetic particles
0.12 μm or less, preferably 0.1 μm or less, more preferably
More preferably, it is 0.080 μm or less. Average of non-magnetic particles
When the particle size exceeds 0.12 μm, critical cavities D are 3/1 /
00 μm ^TwoIt is difficult to
Packing performance is disturbed, resulting in low playback output during high-density recording.
The film of the upper magnetic layer 4 as thin as 0.2 μm or less
Problems such as an increase in dropouts that affect strength
Occur. The lower limit of the average particle size of the non-magnetic particles is 0.01 μm.
m. When compounding two or more types of non-magnetic particles
Means that the average particle size of each non-magnetic particle is as described above. Non-magnetic
The amount of the conductive particles is determined by the amount of the ferromagnetic powder mixed in the upper magnetic layer 4.
0.1 to 16 parts by weight based on 100 parts by weight of powder
Parts, more preferably 0.1 to 15 parts by weight, more preferably
Is 0.1 to 14 parts by weight. Number of critical depressions as described above
From the viewpoint of reducing the amount of non-magnetic particles, the smaller the amount of non-magnetic particles, the better.
However, if the amount is less than the above lower limit,
The aggregate effect of the conductive particles is not effectively exhibited. 2 or more
When the non-magnetic particles are blended, the sum of all non-magnetic particles
It is preferable that the compounding amount be within the above range.

The formation of the upper magnetic layer 4 as described above is based on (1) to
This is achieved by using one or more of the methods in (6).

(1) At the time of preparing the upper coating composition for forming the upper magnetic layer 4, the ferromagnetic powder mixed with the upper coating composition is preliminarily dispersed so that no aggregate of the ferromagnetic powder is generated in the upper magnetic layer. To As a result, it is possible to suppress the occurrence of depressions due to the loss of aggregates. As a method of preliminary dispersion,
For example, there is a method in which a ferromagnetic powder is put into a planetary mixer, an open kneader or the like together with a binder and a part of a solvent to perform preliminary dispersion.

(2) At the time of preparing the upper layer coating material, non-magnetic particles are pre-dispersed so that no aggregates of the non-magnetic particles are generated in the upper magnetic layer. This method has the same effect as the above (1).

(3) Solid content concentration of upper layer paint and upper layer paint
Adjust the drying temperature and the amount of dry air after coating to make the upper layer paint
Adjust the drying speed of the contained solvent to control the size of the depression.
I will. If the drying rate is too fast, rapid solvent evaporation
The amount of critical depressions generated on the surface increases. Conversely, drying speed is too slow
When the solvent evaporates slowly, there are almost all dents
No surface. Number of critical pits due to moderate drying rate
Is smaller than or equal to the above value and a table in which a predetermined number of micro-dents exist.
It becomes a plane state. The preferred drying rate of the solvent is 1.0 × 1
0^-3~ 8.0 × 10^-3kg / (m^Twosec), especially 1.5 × 10
^-3~ 6.0 × 10 ^-3kg / (m^Twosec), especially 1.8 × 1
0^-3~ 4.0 × 10^-3kg / (m^Twosec).

(4) The calender conditions (roll surface properties, number of steps, temperature, linear pressure) of the upper magnetic layer 4 are appropriately selected to control the formation of the depression. That is, under appropriate calendering conditions, the critical pits are effectively removed, resulting in a surface having fine pits. If the calendering conditions are too strong, even small depressions are removed, while if too weak, the critical depressions are not effectively removed. Preferred calendar conditions are as follows.・ Roll surface property: 0.1S or more ・ Number of steps: 3 to 7 steps ・ Temperature: 80 to 120 ° C. ・ Line pressure: 2.5 to 3.4 kN / cm Note that “S” in the roll surface property indicates surface property. This is a symbol that is known to those skilled in the art as indicating the maximum height.

(5) The surface shape of the back coat layer 5 is controlled to suppress the formation of depressions due to the transfer of the surface shape of the back coat layer 5 to the upper magnetic layer 4 during winding and storage of the magnetic recording medium. As the surface shape of the back coat layer 5,
The surface roughness Ra is preferably 20 nm or less, particularly preferably 2 to 12 nm, and the ten-point average roughness Rz is 200 nm or less,
In particular, it is preferably from 18 to 124 nm. Furthermore, A
The number of protrusions whose cross-sectional area at a height of 60 nm from the root mean square surface in the surface shape of the back coat layer 5 measured by FM is 3% or more of the reproduction bit area is 5 /
It is preferably 100 μm ² or less, particularly preferably 3/100 μm ² or less.

(6) In connection with the above (5), the support 2
The surface shape on the back coat layer side of the support 2 and the surface shape of the back coat layer 5 reflecting the surface shape on the back coat layer side when the magnetic recording medium is wound and stored are changed to the upper layer. The formation of depressions due to the transfer to the magnetic layer 4 is suppressed. The surface shape of the support 2 on the back coat layer side is such that the surface roughness Ra is 10 nm or less, particularly 2 to 8 nm.
And the ten-point average roughness Rz is 160 nm.
Hereinafter, it is particularly preferable to be 18 to 140 nm. Furthermore, the number of protrusions whose cross-sectional area at a height of 40 nm from the root mean square surface of the surface shape of the support 2 on the back coat layer side measured by AFM is 3% or more of the reproduction bit area is 23/100 μm. ² or less, especially 18 pieces / 1
It is preferably not more than 00 μm ² .

In order to make the magnetic recording medium 1 more suitable for high-density recording, the product of the residual magnetic flux density Br of the upper magnetic layer 4 and the thickness δ of the upper magnetic layer 4 (hereinafter, this product is referred to as Brδ) ) Is set to 0.005 to 0.045 Tm, particularly 0.005 to 0.042 Tm, and it is preferable to perform reproduction with an MR head, particularly a fixed MR head. Brδ is a measure of the amount of magnetic flux of the upper magnetic layer 4. If this value exceeds 0.045 Tμm, the MR head magnetic field may be saturated and high density recording may not be performed.
Further, the amount of magnetic flux becomes too large, and the influence of the demagnetizing field is so large that high-density recording may not be performed. On the other hand, if the value of Brδ is less than 0.005 T μm, the amount of magnetic flux is too small to obtain a sufficient reproduction output. Since the value of Brδ depends on the value of the thickness δ of the upper magnetic layer 4, the value of Brδ can be set within the above range by adjusting the value of δ, but the value of δ is 0.2 μm or less. It is necessary to If the value of δ is 0.2 μm or more, the influence of the demagnetizing field during high-frequency recording increases, and sufficient input / output characteristics cannot be obtained. The value of δ is 0.01 to 0.2 μm,
In particular, it is preferably from 0.01 to 0.1 μm. Further, the value of Brδ also depends on the value of the residual magnetic flux density Br of the upper magnetic layer 4. If the value of Br is too high, the output may decrease due to self-demagnetization. If the value is too low, the leakage flux may decrease and the output may also decrease. , Especially 0.1-0.4T
It is preferred that

In the magnetic recording medium 1, the coercive force Hc of the upper magnetic layer 4 is increased in order to prevent the generation of a demagnetizing field in the magnetization reversal region which hinders the improvement of the linear recording density and to improve the recording density. 170 to 280 kA / m, preferably 170 to 260 kA / m, more preferably 170 to 280 kA / m
240 kA / m. The improvement in linear recording density is particularly advantageous when reproducing magnetically recorded information with an MR head capable of reducing the track width (that is, reducing the reproduction bit area). In order to keep the coercive force of the upper magnetic layer 4 within the above range, for example, a method of using a ferromagnetic powder having a particle diameter described later, or controlling the magnetic field orientation conditions when forming the upper magnetic layer is used. Can be

As the ferromagnetic powder contained in the upper magnetic layer 4, for example, a needle-shaped or spindle-shaped ferromagnetic powder and a plate-shaped ferromagnetic powder can be used. Examples of the acicular or spindle-shaped ferromagnetic powder include a ferromagnetic metal powder mainly composed of iron and a ferromagnetic iron oxide-based powder. Examples of the plate-like ferromagnetic powder include a ferromagnetic hexagonal ferrite powder. When any of the ferromagnetic powders is used, the average particle size is 0.01 to 0.12 μm, particularly 0.02 to 0.
It is preferable to use one having a size of 12 μm from the viewpoint of increasing the value of Br by increasing the number of ferromagnetic powders present in the minimum recording bit volume. In the present specification, the particle size of the powder, regardless of whether the powder is magnetic or non-magnetic, means the major axis length when the powder shape is needle-like or spindle-like, and is plate-like The case means the plate diameter. In the case of a spherical shape, it means a diameter, and in the case of an amorphous shape, it means the length of the longest part.

Examples of the ferromagnetic metal powder include a ferromagnetic metal powder in which the metal content is 40% by weight or more and the metal content is 40% or more of iron. Specific examples of the ferromagnetic metal powder include columns 3 to 42 of JP-A-9-35246.
And the like described in the column. The coercive force Hc of this ferromagnetic metal powder is 125 to 200 kA / m, the saturation magnetization s is 110 to 170 Am ² / kg, and the BET specific surface area is 40 to 200 kA / m.
It is preferably 70 m ² / g. As the ferromagnetic hexagonal ferrite powder, for example, fine flat barium ferrite powder described in column 4, lines 1 to 5 of JP-A-9-35246 can be mentioned. This ferromagnetic hexagonal ferrite powder has a coercive force Hc of 135 to 260 kA / m, a saturation magnetization s of 27 to 72 Am ² / kg, and a BET specific surface area of 3
It is preferably from 0 to 70 m ² / g.

Examples of the binder contained in the upper magnetic layer together with the ferromagnetic powder include those described in JP-A-9-35246, column 4, lines 25-32.
Among these, a polyurethane resin having a polar group such as a sulfate group, a sulfonate group, an epoxy group, a hydroxyl group or a carboxyl group in a molecule, a vinyl chloride copolymer, and a nitrocellulose resin are preferably used. The amount of the binder is 5 to 3 parts per 100 parts by weight of the ferromagnetic powder.
It is preferably 0 parts by weight. In particular, it is preferable to use a polyurethane resin and a vinyl chloride-based copolymer in combination and to set the ratio of the two (the former / the latter) to 20/80 to 70/30.

In addition to the above-mentioned components, abrasives made of powder of a substance having a Mohs hardness of 7 or more such as α-alumina and chromium oxide, non-magnetic particles such as carbon black as an antistatic agent, fatty acids and fatty acid esters, etc. The performance of the magnetic recording medium can be further improved by including the above-mentioned lubricant, a curing agent such as an isocyanate compound in the upper magnetic layer. In particular, those having the above average particle diameter are used as the non-magnetic particles. Preferred amounts of these components are as follows with respect to 100 parts by weight of the ferromagnetic metal powder. The preferable range of the total amount of the abrasive and the non-magnetic particles such as carbon black is as described above. Abrasive material: 1 to 16 parts by weight, particularly 2 to 14 parts by weightCarbon black: 0.01 to 1.0 part by weight, particularly 0.05 to 0.8 part by weightLubricant: 1 to 10 parts by weight Curing agent: 5 parts by weight or less, especially 2 parts by weight or less

The lower layer 3 may be a magnetic layer containing ferromagnetic powder or a non-magnetic layer containing no ferromagnetic powder. The lower layer 3 contains a binder, a non-magnetic particle such as carbon black as an antistatic agent, a lubricant, a hardener, and the like, regardless of whether it is magnetic or not. The details of these components are the same as those in the upper magnetic layer 4. Further, the lower layer 3 is made of non-magnetic iron oxide (α-iron oxide),
Contains non-magnetic fillers such as titanium oxide and calcium carbonate. The preferable compounding amount of these components contained in the lower layer 3 is 100 parts by weight of the total amount of the ferromagnetic powder and the nonmagnetic filler (when the lower layer 3 is a magnetic layer) or 100 parts by weight of the nonmagnetic filler. On the other hand (when the lower layer 3 is a non-magnetic layer), each is as follows. Binder: 5 to 50 parts by weight, especially 10 to 30 parts by weight Abrasive: 1 to 30 parts by weight, especially 2 to 18 parts by weight Carbon black: 0.3 to 30 parts by weight, especially 1-2
0 parts by weight Lubricant: 1 to 20 parts by weight, especially 3 to 10 parts by weight Hardener: 12 parts by weight or less, especially 8 parts by weight or less

When the lower layer 3 is a magnetic layer, the coercive force of the lower layer 3 is 135 to 260 kA / m, particularly 160 to 260 kA / m, from the viewpoint of controlling the magnetic properties of the upper magnetic layer 4.
m, and the saturation magnetic flux density is 0.05 to
It is preferably 0.1T, particularly preferably 0.05 to 0.08T.

The thickness of the lower layer 3 is preferably 2.0 μm or less, more preferably 0.2 μm to 1 μm, from the viewpoint of the relationship with the thickness of the upper magnetic layer 4 and the improvement of durability of the magnetic recording medium and prevention of cupping. 0.5 μm, more preferably 0.5
１．５1.5 μm.

The lower layer 3 and the upper magnetic layer 4 are formed by applying a lower paint for forming the lower layer and an upper paint for forming the upper magnetic layer. The lower layer paint and the upper layer paint are obtained by dispersing the above-mentioned various components in a predetermined amount of a solvent. As the solvent, ketone solvents, aromatic solvents, hydrocarbon solvents and the like are preferably used. When preparing these paints, especially when preparing the upper coating,
By adopting the methods (1) and / or (2), the surface shape of the upper magnetic layer 4 can be made as described above.

As the back coat layer 5 formed on the other side of the support 2, a layer in which carbon black is dispersed in a binder can be used. Specifically, for example, those described in JP-A-9-35246, column 5, line 41 to column 9, line 4 can be used. Its thickness is 0.05 to 0.8 μm from the viewpoint of improving durability and preventing cupping.
m, particularly preferably 0.1 to 0.7 μm. Also, carbon black having a predetermined particle size is blended in the back coat layer 5 and the surface shape is as described in the above (5), so that the surface shape of the upper magnetic layer 4 is as described above. Can be.

As the support, if it is for a magnetic recording medium, a known support can be used, and specifically, those described in JP-A-9-35246, column 2, lines 30 to 42 can be used. Among these, polyethylene terephthalate (PE
Non-magnetic materials such as T), polyethylene naphthalate and polyamide are preferred. The thickness of the support is preferably 8 μm or less, particularly preferably 6 μm or less in order to increase the capacity of the magnetic recording medium. Further, an easy-adhesion layer may be provided on the surface of the support to enhance the adhesiveness with the lower layer 3 and the back coat layer 5. Further, by making the surface shape of the support 2 on the back coat layer side as described in (6) above, the surface shape of the upper magnetic layer 4 can be made as described above. The support 2 having such a surface shape can be obtained, for example, by adjusting the size and content of the filler contained in the support.

The total thickness of the magnetic recording medium 1 is preferably 7 μm or less, particularly 4 to 7 μm, from the viewpoint of increasing the capacity of the magnetic recording medium and ensuring durability.

Next, the preferred embodiment of the magnetic recording medium 1 of the above embodiment will be described.
An outline of a preferred manufacturing method will be described. First, on the support 2
The upper layer paint and the lower layer paint are mixed so that each layer has a predetermined thickness.
Simultaneous multi-layer coating by wet-on-wet method
Then, an upper magnetic layer and a lower coating film are formed. Then
After performing a magnetic field alignment treatment on these coating films, a drying treatment is performed.
And wind it up. Thereafter, a calendar process is performed. This
(3) above as the conditions for drying and calendering
By adopting the conditions of (4) and (4), the surface of the upper magnetic layer 4 is
The shape can be as described above. Further, the support 2
Apply the back coat paint on the opposite side of the
The back coat layer 5 is formed by drying. This drying condition
The drying speed of the solvent is 1.0 × 10^-3~ 8.0 × 1
0^-3kg / (m ^Twosec), especially 2.0 × 10^-3~ 6.5 × 10
^-3kg / (m^Twosec), especially 2.2 × 10^-3~ 4.3 ×
10^-3kg / (m^Twosec).
The surface shape of the back coat layer 5 can be easily adjusted as described in (5) above.
You can do it. Then, 6 to 10 at 40 to 80 ° C.
Aging treatment for 0 hours to obtain wide magnetic recording medium
You. For example, when manufacturing a magnetic tape,
Is cut into a predetermined width along its longitudinal direction.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to the above embodiments.
Various changes can be made without departing from the spirit of the present invention. For example, the magnetic recording medium of the above-described embodiment is a multilayer magnetic recording medium having an upper magnetic layer and a lower layer, but instead of this, a single-layer magnetic recording medium having only one magnetic layer is different from that of the above-described embodiment. Similar effects are achieved.
In the above embodiment, a primer layer or a layer capable of recording a servo signal for tracking may be formed between the support 2 and the lower layer 3 or the back coat layer 5. Also,
The magnetic recording medium of the present invention includes a video / audio recording tape such as a DVC tape, an 8 mm video tape, and a DAT tape;
It is suitable as a magnetic tape such as a data recording tape such as an LT, a DDS tape, a 1/4 inch data cartridge tape, and a data 8 mm tape, but is also applicable as another magnetic recording medium such as a magnetic disk such as a flexible disk. You can also.

[0038]

EXAMPLES In the following examples, parts and% mean parts by weight and% by weight, respectively, unless otherwise specified.

Example 1 In the following upper layer coating composition, a ferromagnetic powder was put into a planetary mixer together with a binder and a part of a solvent and preliminarily dispersed. Separately, the abrasive was predispersed in a similar manner. The two predispersions were mixed and subjected to a dispersion treatment using a sand mill. afterwards,
The solvent was added to adjust the thixotropic index, and the mixture was filtered using a filter having an absolute filtration accuracy of 1 μm. Finally, a curing agent was added to obtain an upper layer paint. Further, a lower layer paint and a back coat paint were obtained in the same manner.

<Blending of upper layer paint> 100 parts of acicular ferromagnetic metal magnetic powder (Fe: Co = 80/20) (coercive force: 175 kA / m, saturation magnetization: 147 Am ² / kg, average particle size: 65 nm)・ Α-alumina (abrasive, average particle size: 70 nm) 3.2 parts ・ Carbon black (average particle size: 20 nm) 0.4 parts ・ Sulfate group-containing vinyl chloride copolymer [binder, manufactured by Zeon Corporation MR104 (trade name)] 10 parts ・ Sulfonate group-containing polyurethane resin [Binder, UR-8300 (trade name) manufactured by Toyobo] 7 parts ・ Stearic acid 2 parts ・ 2-ethylhexyl oleate 1.5 parts ・ Polyisocyanate [Curing agent, Coronate L (trade name) manufactured by Nippon Polyurethane Industry, solid content 75%] 4.5 parts-132 parts of methyl ethyl ketone-88 parts of toluene-cyclohexa Down 210 parts

<Blending of lower layer paint> Hexagonal plate hexagonal ferromagnetic barium ferrite powder 60 parts (coercive force: 152 kA / m, saturation magnetization: 52 Am ² / kg, average particle size: 30 nm) -Fe ₂ O ₃ 40 parts (non-magnetic filler, average particle size: 100 nm), alpha-alumina (abrasive, average particle diameter: 70 nm) 6 parts carbon black (average particle diameter: 20 nm) 10 parts sulfuric acid base-containing Vinyl chloride copolymer [Binder, MR104 (trade name) manufactured by Zeon Corporation] 14 parts ・ Sulfonate group-containing polyurethane resin [Binder, UR-8300 (trade name) manufactured by Toyobo] 12 parts ・ Stearic acid 4 Parts-2-ethylhexyl oleate 1.5 parts-Polyisocyanate [curing agent, Coronate L (trade name) manufactured by Nippon Polyurethane Industry, solid content 75%] 4 parts-Methyl Ethyl ketone 84 parts Toluene 56 parts Cyclohexanone 60 parts

<Blending of back coat paint>-38 parts of carbon black (average particle size: 28 nm)-2 parts of carbon black (average particle size: 52 nm)-50 parts of "Nipporan 2301" [trade name, Nippon Polyurethane Industry Co., Ltd. ) Polyurethane, solid content 40%] Nitrocellulose 20 parts (Viscosity display 1/2 second manufactured by Hercules Powder Co.) Polyisocyanate (solid content 75%) 4 parts Copper phthalocyanine 5 parts Stearic acid 2 parts ・ Methyl ethyl ketone 120 parts ・ Toluene 120 parts ・ Cyclohexanone 120 parts

A lower layer paint and an upper layer paint are coated on a support made of a PET film having a thickness of 4.5 μm by a die coater so that the dry thicknesses of the lower layer and the upper magnetic layer become 1.2 μm and 0.1 μm, respectively. , A simultaneous multilayer coating was performed by a wet-on-wet method to form respective coating films. Then, while these coatings are wet,
T is passed through the solenoid of the T to perform a magnetic field orientation treatment in the longitudinal direction, and further, the coating film is dried by adjusting the temperature and air volume of the drying furnace so that the drying speed of the solvent becomes a value shown in Table 1.
Wound up. Next, under the conditions shown in Table 1, the line speed 15
Calendar processing was performed at 0 m / min. The surface property of the calender roll used at this time was 0.1S. Further, a back coat paint is applied on the back surface of the support so as to have a dry thickness of 0.5 μm.
After being dried under the condition of 0 × 10 ⁻³ kg / (m ² sec), the film was wound up. Thereafter, an aging treatment was performed at 50 ° C. for 16 hours, and the resultant was cut into a half-inch width to obtain a magnetic tape.

Examples 2, 3 and 7 and Comparative Example 1 In Example 1, the drying conditions and the calendering conditions for coating the upper magnetic layer were changed to the conditions shown in Table 1, and as a support, the results are shown in Table 2. A magnetic tape was obtained in the same manner as in Example 1 except that a magnetic tape having a surface shape was used.

Example 4 In Example 3, the coercive force of 167 kA /
m, a saturation magnetization of 124 Am ² / kg, an acicular ferromagnetic metal powder having an average particle size of 80 nm, an upper magnetic layer having a thickness of 0.04 μm, and a support having a surface shape shown in Table 2 is used. A magnetic tape was obtained in the same manner as in Example 3 except for the above.

Example 5 A magnetic tape was prepared in the same manner as in Example 3 except that the thickness of the upper magnetic layer was 0.14 μm and that the support had the surface shape shown in Table 2. I got

Example 6 In Example 3, no hexagonal barium ferrite powder was blended in the lower layer, and instead, the blending amount of acicular α-Fe ₂ O ₃ was changed to 100 parts, and further, as a support, A magnetic tape was obtained in the same manner as in Example 3, except that a tape having the surface shape shown in Table 2 was used.

[Embodiment 8]
The drying speed of the paint solvent is 7.0 × 10^-3kg / (m ^Twosec)
Having a surface shape shown in Table 2 as a support.
A magnetic tape was obtained in the same manner as in Example 3 except that
Was.

Example 9 A magnetic tape was obtained in the same manner as in Example 3 except that a support having the surface shape shown in Table 2 was used.

Comparative Example 2 Comparative Example 1 was repeated except that alumina having an average particle diameter of 200 nm was used as an abrasive compounded in the upper magnetic layer, and a support having a surface shape shown in Table 2 was used as a support. A magnetic tape was obtained in the same manner as in Example 1.

Comparative Example 3 In Comparative Example 1, the coercive force of 143 kA /
m, saturation magnetization 120 Am ² / kg, average particle size 160 nm
, And the thickness of the upper magnetic layer was set to 0.1.
Carbon black 2 having an average particle size of 28 nm as the carbon black to be blended in the back coat layer.
A magnetic tape was obtained in the same manner as in Comparative Example 1, except that 38 parts of carbon black having an average particle diameter of 52 nm and 38 parts of a support were used.

Comparative Example 4 A magnetic tape was obtained in the same manner as in Comparative Example 1, except that a PET film having a thickness of 10 μm and a surface shape shown in Table 2 was used as the support.

[Evaluation of Performance] For the magnetic tapes obtained in the examples and comparative examples, the surface roughness Ra, the number of depressions, and the magnetic characteristics (coercive force Hc, saturation magnetic flux density Br) of the upper magnetic layer were determined by the following methods. The surface roughness Ra and the ten-point average roughness R of the back coat layer and the back coat layer side of the support were determined.
z and the number of protrusions are obtained, and further, the reproduction output of the magnetic tape,
Dropout, still durability and coefficient of friction were determined.
Table 2 shows the results.

<Surface Roughness of Upper Magnetic Layer> Optical Surface Roughness Tester (Model Maxim 3D570, manufactured by Zygo)
0), a 40 × Fizeau lens was used, and Cyln was used.
The der correction was performed, and five points were measured.
a.

<Number of Depressions in Upper Magnetic Layer> Using a Nanoscope manufactured by Digital Instruments, 10 μm × 10
A μm square AFM image is measured. The measured AFM image
Perform smoothing processing by the flatten command of off-line modify. At this time, the flatten order is set to 2. The image subjected to the smoothing process is inverted by the inversion process of off-line modify, and the dent is displayed as a protrusion. Then, off-line a
The height of 20 nm from the reference plane (root mean square surface) by the grain size command of nalyze (ie, 20
(depth of nm), and the particle size and the number on the slice plane of the mountain existing in the sliced cross section are calculated. From the calculation result, the number of peaks having a cross-sectional area of 3% or more of the reproduced bit area and the number of peaks having a cross-sectional area of less than 3% are counted. The former is a dent having a cross-sectional area of 3% or more (critical dent) in the real image, and the latter is a dent (micro-dent) having a cross-sectional area of less than 3%. At least 50 points are measured for at least one sample, and the arithmetic average of the number of dents having a cross-sectional area of 3% or more and the arithmetic average of the number of dents having a cross-sectional area of less than 3% in a real image are obtained.

<Magnetic Properties> Only the upper magnetic layer was peeled off from the magnetic tape, punched to a predetermined size, and measured with an external magnetic field of 1194 kA / m using VSM manufactured by Toei Kogyo. However, only in Example 8, the magnetic tape itself was punched out and measured.

<Surface Roughness, Ten-Point Average Roughness Rz on Back Coat Layer Side of Back Coat Layer and Support> Measured in the same manner as the surface roughness Ra of the upper magnetic layer. However, for the support, the measurement was performed using a 50 × Mirau lens.

<Number of protrusions on the back coat layer side of the back coat layer and the support> The number of depressions on the upper magnetic layer was measured in the same manner as the number of depressions. However, in order to measure protrusions instead of depressions, no image inversion processing was performed.

<Electromagnetic Conversion Characteristics and Dropout of Magnetic Tape> A DLT-7000 drive equipped with a fixed head was modified, and an output signal at a reproduction bit area of 0.2 μm × 5 μm was measured. Here, the output was a relative evaluation using the magnetic tape of Comparative Example 1 as a reference (0 dB). Dropout is performed by converting a signal having a reproduction bit area of 0.2 μm × 5 μm to 1 M
Bit recording was performed, and the number of bits at which the output was reduced by 50% during reproduction was counted and measured.

<Still Durability> Using the above-mentioned DLT-7000 drive, the time until the reproduced output decreased by 3 dB from the initial value was measured while repeatedly reproducing a 1 Mbit recording signal.

<Coefficient of friction> Measured in accordance with the SMC certified test method. The upper magnetic layer side of the magnetic tape is wound around a SUS round bar having a diameter of 20 mm and a surface roughness of 0.2 S at an angle of 90 degrees, and the friction is performed by running 100 passes at a speed of 18.8 mm / sec and a tension of 0.1 N. The coefficient was measured, and the maximum value was defined as the value of the coefficient of friction.

[0062]

[Table 1]

[0063]

[Table 2]

As is clear from Table 2, the magnetic tape of the example (product of the present invention) has less occurrence of dropout and higher electromagnetic conversion characteristics than the magnetic tape of the comparative example. I understand. Further, it can be seen that the magnetic tapes of the examples have a small coefficient of friction, good running properties, and high still durability.

[0065]

As described above, according to the present invention,
Excellent electromagnetic conversion characteristics and low dropout and excellent running performance and durability can be compatible at a high level,
In addition, a magnetic recording medium suitable for high-density digital recording can be obtained. The magnetic recording medium of the present invention has a particularly high effect of high-density recording when magnetically recorded information is reproduced by a reproducing head using a magnetoresistive element.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a structure of an embodiment of a magnetic recording medium according to the present invention.

FIG. 2 is a schematic diagram showing a surface shape of an upper magnetic layer.

FIG. 3 is a graph showing the relationship between the number of depressions and the occurrence of dropouts.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Support 3 Lower layer 4 Upper magnetic layer 5 Back coat layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-230617 (JP, A) JP-A-4-69812 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/70 G11B 5/735

Claims (5)

(57) [Claims] 1. A support having a lower layer on one surface and a thickness of 0.2 μm
m or less, and a backcoat layer on the other surface, wherein the nonmagnetic particles contained in the uppermost magnetic layer have an average particle size of 0.12 μm or less. The surface roughness Ra of the uppermost magnetic layer is 7.5 nm or less, and the cross-sectional area at a depth of 20 nm from the root mean square surface of the surface shape of the uppermost magnetic layer measured by an atomic force microscope is A magnetic recording medium in which the number of depressions that are 3% or more of the reproduction bit area is 3/100 μm ² or less. 2. The product of the residual magnetic flux density of the uppermost magnetic layer and the thickness of the uppermost magnetic layer is 0.005 to 0.045 Tμ.
m, the coercive force of the uppermost magnetic layer is 170 to 280 kA / m
The magnetic recording medium according to claim 1, wherein the magnetic recording information is reproduced by a reproducing head using a magnetoresistive element. 3. The magnetic recording medium according to claim 2, wherein the reproduction bit area is 1.15 μm ² or less, the reproduction head is a fixed head, and the total thickness is 7 μm or less. 4. The surface roughness Ra of the back coat layer is 2
0 nm or less and the ten-point average roughness Rz is 200 nm or less, and the cross-sectional area at a height of 60 nm from the root mean square surface in the surface shape of the back coat layer measured by an atomic force microscope is the above-mentioned reproduction bit area. 4. The magnetic recording medium according to claim 1, wherein the number of protrusions of 3% or more is 5/100 μm ² or less. 5. The support has a surface roughness Ra on the back coat layer side of 10 nm or less and a ten-point average roughness Rz of 1
60 nm or less, and 40 n from the root mean square surface shape of the support on the back coat layer side measured by an atomic force microscope.
The magnetic recording medium according to any one of claims 1 to 4, wherein the number of protrusions whose cross-sectional area at a height of m is 3% or more of the reproduced bit area is 23/100 µm ² or less.