JP2000057560A - Magnetic tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high recording density magnetic tape capable of servo tracking with high output and high S/N keeping. SOLUTION: A magnetic recording medium obtained by forming a magnetic layer on one surface of a support 2 is the magnetic tape constituted so that a transparent back coat layer 6 is formed on another surface of the support 2, a recording layer 5 capable of optically recording a servo signal for tracking is formed between the back coat layer 6 and the support 2 and the back coat layer 6 has transparency that the reflectance of light for reading servo signal, which is made incident to a recording layer 5 from the back coat layer 6 side becomes >=40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high recording density magnetic tape capable of optically recording and reading a servo signal for tracking.

[0002]

2. Description of the Related Art As one means for improving the recording density of a magnetic recording medium, there is a method of reducing a track width. To accurately read the information recorded on the narrow track, a tracking servo is required. Tracking servos used for magnetic recording media include (1) a method for writing servo signals in tracks, (2) a method for forming dedicated servo servo tracks on the magnetic recording surface, and (3) optical methods for deep tracks. For example, a method of writing a target track signal is known.

However, in the methods (1) and (2), since the same area as the data area for magnetic recording is used as the servo tracking area, the area of the data area is reduced, and the recording capacity is limited. There are drawbacks.
In the method of (3), since a servo signal is written under the magnetic layer, it is necessary to add a function for that to the magnetic layer, so that the magnetic characteristics itself such as reproduction output and S / N are sacrificed to some extent. .

Accordingly, an object of the present invention is to provide a high recording density magnetic tape capable of performing servo tracking while maintaining high output and high S / N.

[0005]

Means for Solving the Problems The present inventors have made it possible to use a specific back coat layer and provide a layer capable of optically recording and reading a servo signal for tracking inside the back coat layer. It was found that the purpose was achieved.

The present invention has been made based on the above findings. In a magnetic recording medium having a magnetic layer formed on one surface of a support, a transparent back coat layer is formed on the other surface of the support. A recording layer capable of optically recording a servo signal for tracking is formed between the back coat layer and the support, and the back coat layer is formed on the back coat layer side. The reflectance of the servo signal reading light incident on the recording layer from
The above object has been attained by providing a magnetic tape having a transparency of at least%.

The present invention also provides a magnetic recording medium having a magnetic layer formed on one surface of a support, wherein a transparent back coat layer is formed on the other surface of the support. A recording layer on which an optical tracking servo signal is recorded is formed between the back coat layer and the support, and the back coat layer is formed on the recording layer from the back coat layer side. A magnetic tape having transparency such that the reflectance of the servo signal reading light incident on a portion other than the portion where the servo signal is recorded is 40% or more.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on preferred embodiments with reference to the drawings. FIG.
FIG. 1 is a schematic diagram of a longitudinal section showing a configuration of a first embodiment of a magnetic tape of the present invention. In this magnetic tape 1, a lower layer 3 and an upper magnetic layer 4 adjacent thereto are provided on one surface of a support 2. This surface is used as a recording surface. A back coat layer 6 is provided on the other surface of the support 2, and a recording layer (hereinafter, referred to as “recording layer”) capable of optically recording and reading a servo signal for tracking is provided between the back coat layer 6 and the support 2. , A servo signal recording layer) 5, and this surface is a non-recording surface. Servo signal recording layer 5
Is composed of a dye-containing layer 5a formed on the back coat layer 6 side and a reflective layer 5b formed on the support 2 side. This magnetic tape 1 is for a serpentine recording system, and a plurality of data tracks are formed on a recording surface in parallel with a running direction of the magnetic tape 1. In this specification, a recording surface refers to a surface used for magnetic recording, and a non-recording surface refers to a surface on which magnetic recording is not performed.

In the servo signal recording layer 5, a dye-containing layer (hereinafter referred to as a dye-containing layer) 5a is formed with a regular servo tracking pattern having optical properties different from those of most areas on the non-recording surface side. Used as a part. As the optical property, for example, a reflectance or a transmittance is used, but it is not limited to these.

As a method of forming a servo tracking pattern on the dye-containing layer 5a so that the servo tracking pattern has an optical property different from that of other areas on the non-recording surface side, for example, a magnetic track running at a predetermined speed is used. The dye-containing layer 5a of the tape is irradiated with a laser beam corresponding to the servo signal to change the color of the dye contained in the dye-containing layer 5a by decomposition or the like.
(See FIG. 2) is regularly formed in the longitudinal direction of the tape. Then, the regularly formed discolored portions 7 function as the pattern. The laser beam may be applied from any of the non-recording surface side and the recording surface side of the magnetic tape 1, but is preferably applied from the non-recording surface side in terms of efficient formation of the pattern. .

The beam diameter of the laser beam is 0.25 to 3
The output is preferably 0 μm, particularly 1 to 25 μm, and the output is preferably 1 to 1000 mW, particularly preferably 10 to 100 mW. Further, the wavelength of the laser beam is selected at an appropriate value according to the type of the dye so that the dye used is sufficiently discolored. The discoloration portion 7 may be formed by using a dedicated device before using the magnetic tape 1 or by loading the magnetic tape 1 into a recording / reproducing drive having a built-in laser light generator. Is also good.

As shown in FIG. 2, the servo tracking pattern according to the present embodiment is a single dotted line along the center line in the tape width direction in plan view, that is, a dot-shaped pattern. By forming such a pattern, the read sensitivity of the servo signal is improved. The width W of the pattern is 0.25 to 3 from the viewpoint that precise servo tracking can be performed and the thermal effect on the support 2 during writing.
It is preferably 0 μm, particularly preferably 1 to 25 μm. The length L of the pattern is preferably 1 to 100 μm, particularly preferably 10 to 50 μm because it is necessary to reliably detect the servo signal. Further, the distance P between the color changing portions 7 is preferably 2 to 100 μm, particularly preferably 20 to 80 μm in order to surely separate the color changing portions 7 and increase the sensitivity at the time of reading.

An optical servo method such as a push-pull method or a three-beam method can be used as a servo tracking method for the magnetic tape 1 having a servo tracking pattern formed on the dye-containing layer 5a, that is, a method for reading a servo signal. . The principle of operation of the servo tracking method according to the present embodiment will be described with reference to FIG. 3 taking the case where the reflectance is used as the optical property as an example. In the magnetic recording / reproducing apparatus, when light of a predetermined wavelength (hereinafter referred to as “incident light”) 8 is irradiated toward the back coat layer 6 side of the magnetic tape running at a predetermined speed, the reflection layer 5b passes through the color changing portion 7 in the dye-containing layer 5a. The intensity of the reflected light [Fig.
(A)] and the intensity of light reflected by the reflective layer 5b through a region other than the discolored portion 7 in the dye-containing layer 5a [FIG.
(B). By utilizing the difference in the intensity of the reflected light, for example, the incident position of the incident light 8 is determined as shown in FIG.
In the case of a shift as shown in FIG.
As in the case of (a), tracking is performed by adjusting the position of the magnetic tape according to a command from the magnetic recording / reproducing apparatus. The incident light 8 may be emitted from any of the non-recording surface side and the recording surface side of the magnetic tape 1,
It is preferable that the light is irradiated from the non-recording surface side in order to obtain reflected light of sufficient intensity. The incident light used for the servo tracking, that is, the servo signal reading light 8
As the wavelength, an appropriate value is selected according to the color of the dye before and after the color change.

The type of the dye contained in the dye-containing layer 5a is not particularly limited as long as it is a substance that changes color when irradiated with light of a predetermined wavelength and changes the absorbance of light at a predetermined wavelength. Organic dyes and pigments (especially dye pigments) described below are used. Organic dyes include cyanine dyes, squarylium dyes, croconium dyes, azurenium dyes, triarylamine dyes, anthraquinone dyes, metal-containing azo dyes, dithiol metal complex dyes, indoaniline metal complex dyes, and phthalocyanine. Dyes, naphthalocyanine dyes,
Porphyrin dyes, intermolecular charge transfer complex dyes, and the like are preferably used. These dyes may be used alone or in combination of two or more.

Particularly, it is preferable to use a cyanine-based dye represented by the following formula (1) or (2) as the organic dye because of good compatibility with a binder described later. Such a cyanine dye has an absorption in the near infrared region.

[0016]

Embedded image

The dye-containing layer 5a can be formed using a pigment. In particular, when performing the surface smoothing treatment after the formation of the dye-containing layer 5a, it is preferable to use a dye pigment from the viewpoint of preventing elongation and bleeding of the dye. Further, when a pigment is used, there is an advantage that the film hardness is improved and the water resistance and the solvent resistance are improved due to the effect of the aggregate. In addition, there is an advantage that the phase separation of the film after the formation of the coating film and the clouding of the coating film due to the recrystallization of the pigment do not occur. As the pigment, either an organic pigment or an inorganic pigment may be used. Organic pigments include phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine green, flavanthrone yellow, chromophthal yellow, anthrapyrimidine yellow, isoindolinone yellow, benzimidazolone yellow, quinophthalone yellow, benzimidazolone yellow, perinone orange, pyran Slon Orange, Thioindigo Bordeaux, Quinacridone Magenta, Perylene Permillion, Perylene Red, Chromophtal Scarlet, Anthuanthrone Red, Gianthraquinonyl Red, Perylene Red, Perylene Maroon, Perylene Scarlet, Pyranlon Red, Quinacridone Red, Geosazine Violet , Indanthrone blue and the like. Inorganic pigments include graphite, cadmium yellow, yellow iron oxide, titanium yellow, red iron oxide, molybdate orange, lead red, silver vermilion, cadmium red, manganese violet, navy blue, cobalt blue, ultramarine, chromium oxide, viridian, pearl There are gloss pigments and the like. Both organic and inorganic pigments having good recording and reproduction characteristics at the wavelength of light used for recording and reading servo signals are selected. The particle diameter of the pigment is preferably 0.2 to 0.01 μm, particularly preferably 0.1 to 0.1 μm, in order to mainly select visible light for recording the servo signal and to keep the surface property of the back coat layer 6 smooth. 0.03 μm is preferred.

The dye-containing layer 5a may be formed only of a dye, or may be formed to contain other components in addition to the dye. When the dye-containing layer 5a is made of, for example, only an organic dye, the dye-containing layer 5a can be formed, for example, by the following methods (1) to (3). Further, when formed only from a pigment, (4),
Take the method of (5). (1) Chemical vapor deposition (CVD) and physical vapor deposition (PV)
A method for forming a thin film as in D). (2) A method in which a pigment is dissolved in a solvent, and a coating material containing a surfactant, if necessary, is applied on the support 2. (3) A method in which a dye dissolved in a polymer resin or a polymer emulsion or the like is co-extruded during melt extrusion of the support 2. (4) A method in which a pigment is dispersed in a solvent, and a coating material containing a surfactant, if necessary, is applied on the support 2. (5) A method in which a pigment pigment dispersed in a polymer resin or a polymer emulsion or the like is co-extruded during melt extrusion of the support 2.

When the dye-containing layer 5a contains other components in addition to the dye, examples of the other components include a binder, inorganic particles, and a curing agent. The dye-containing layer 5a is formed by applying and drying a dye-containing paint in which these components are dispersed and dissolved in a solvent. The binder, the inorganic particles, as a curing agent,
The same components as those contained in the back coat layer 6 described below can be used. In particular, it is preferable to use non-black small-diameter inorganic particles having a particle diameter of 60 nm or less as the inorganic particles, since reflected light with sufficient intensity can be obtained and precise servo tracking can be performed.

The thickness of the dye-containing layer 5a is 0.05 to 1.0.
μm, particularly preferably 0.1 to 0.6 μm.

The servo signal recording layer 5 together with the dye-containing layer 5a
Is formed of a material having a high light reflectance, for example, a metal or an alloy, for example, Au,
Al, Ag, and alloys containing these as main components are preferably used. Further, by forming the reflective layer 5b from a conductive material such as a metal, the reflective layer 5b exhibits an antistatic function, so that the back coat layer 6 does not need to contain carbon black as described later. Thus, the transparency of the back coat layer 6 can be improved. The reflective layer 5b is preferably formed by a known thin film forming means using a vacuum film forming method. By using such a film forming method, the corrosion resistance of the formed reflective layer 5b is extremely improved, and a magnetic tape having excellent storage durability can be obtained.
Examples of such a vacuum film forming method include vacuum deposition, sputtering, and ion plating, which are appropriately selected and used according to the material for forming the reflective layer 5b. The thickness of the reflection layer 5b may be such that the incident light is sufficiently reflected, and is 0.01 to 1 μm, particularly 0.02 to 0.7 μm.
μm is preferred.

Next, the most characteristic back coat layer in the present invention will be described. The back coat layer 6 is formed from an optically transparent material. The degree of transparency is such that the reflectance of the servo signal reading light incident on the dye-containing layer 5a of the recording layer 5 from the back coat layer 6 side is 40% or more. By having such transparency, reflected light of sufficient intensity can be obtained,
Precise servo tracking can be performed. Also,
It is also preferable that the back coat layer 6 itself has transparency such that the transmittance of light having a wavelength of 300 to 900 nm is 70% or more.

In the back coat layer of the conventional magnetic tape,
Carbon black was contained for the purpose of improving running properties and antistatic properties. However, since carbon black has a high light-shielding property, it is not easy to make the above-mentioned reflectance 40% or more in a back coat layer containing carbon black. Therefore, in the present invention, it is preferable that the back coat layer 6 does not contain carbon black but instead contains non-black inorganic particles having a particle size of 60 nm or less, preferably 2 to 40 nm. In the present specification, the particle size means a major axis length when the particle shape is a needle shape or a spindle shape, and means a plate diameter when the particle shape is a plate shape. 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.

As the above-mentioned inorganic particles, nonmagnetic particles having a small cohesive force between particles and easy to disperse are preferably used.
Such materials include barium sulfate, tin oxide (SnO
_x ), titanium oxide (TiO _x ), zinc oxide (Zn)
O _x ), non-magnetic iron oxide (α-Fe ₂ O ₃ ), barium carbonate, aluminum oxide (Al ₂ O _x ), antimony-doped tin oxide (ATO), indium-doped tin oxide (IT
O) and silicon oxide (SiO _x ), in particular, barium sulfate, tin oxide (SnO _x ), titanium oxide (TiO _x )
Alternatively, zinc oxide (ZnO _x ) is preferable. For the same reason, the shape is preferably acicular, granular or spherical.

The back coat layer 6 is preferably formed by dispersing the inorganic particles in a binder. The inorganic particles are used to maintain the strength of the back coat layer 6 and maintain the running stability of the magnetic tape 1.
200 to 2000 parts by weight, especially 21
It is preferably contained in an amount of 0 to 1900 parts by weight.
The binder may be a vinyl chloride copolymer or a modified product thereof, a polyurethane resin, or a magnetic tape such as a cellulose resin (nitrocellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, etc.). The same ones as those usually used can be used. These binders contain a polarizable functional group (a so-called polar group) such as a sulfonate group, a sulfate group, a carboxyl group, a hydroxyl group, and an epoxy group from the viewpoint that the dispersibility of the inorganic particles can be further enhanced. Is also good.

The back coat layer 6 further contains a lubricant such as a phosphoric acid ester, a fatty acid, a fatty acid ester, a curing agent, and the like in addition to the inorganic particles and the binder, thereby further improving the function of the back coat layer. be able to. The content of these components in the back coat layer 6 is preferably as follows with respect to 100 parts by weight of the binder.・ Lubricant: 0 to 20 parts by weight, especially 0 to 10 parts by weight ・ Curing agent: 0 to 40 parts by weight, especially 5 to 30 parts by weight

The back coat layer 6 is formed by applying and drying a back coat paint in which the above components are dispersed and dissolved in a solvent. In particular, when the above-mentioned pigment-containing layer 5a is formed from a pigment-containing paint, both layers are formed by a simultaneous multilayer coating method of a wet-on-wet method to improve productivity and improve pigment-containing properties. It is preferable from the viewpoint of preventing the dissolution of the dye from the layer 5a.

In preparing the backcoat paint, it is preferable to sufficiently disperse the inorganic particles in advance so as to prevent their aggregation. As a method of the preliminary dispersion, for example, there is a method in which the inorganic particles are put into a planetary mixer, an open kneader, or the like together with a binder and a part of a solvent and dispersed.

The thickness of the back coat layer 6 formed in this manner is set at 0 in consideration of the transmittance of incident light and the balance with the thicknesses of the upper magnetic layer 4 and the lower layer 3 provided on the recording surface side. 0.1 to 2.0 μm, particularly preferably 0.2 to 1.5 μm.

Next, a second embodiment of the magnetic tape of the present invention will be described with reference to FIG. Here, FIG.
FIG. 2 is a schematic diagram illustrating a configuration of a second embodiment of the magnetic tape of the present invention, and is a diagram corresponding to FIG. 1 in the first embodiment. In the second embodiment, only different points from the first embodiment will be described, and the same points will not be particularly described. However, the detailed description of the first embodiment is appropriately applied. In FIG. 4, the same members as those in FIG. 1 are denoted by the same reference numerals.

The magnetic tape of the present embodiment is different from the magnetic tape of the first embodiment in that the servo signal recording layer 5 of the magnetic tape of the first embodiment is composed of a dye-containing layer 5a and a reflective layer 5b. On the other hand, in the magnetic tape of the present embodiment, the servo signal recording layer 5 is formed of a low melting point metal or alloy layer (hereinafter, referred to as a metal layer).
Then, a servo tracking pattern is formed on this metal layer so that the servo tracking pattern has an optical property different from that of other areas on the non-recording surface side. As a method of forming a servo tracking pattern, for example, irradiating a laser beam corresponding to a servo signal toward a metal layer of a magnetic tape running at a predetermined speed, melting a metal or alloy constituting the metal layer, There is a method of forming a concave portion 9 (see FIG. 4) having a predetermined depth in the metal layer regularly in the longitudinal direction of the tape. The regularly formed depressions 9 function as servo tracking patterns, similarly to the color changing portions 7 in the first embodiment. As a method of reading the servo tracking signal, it is preferable to use reflected light with respect to incident light as in the first embodiment, but it is also possible to use transmitted light in some cases.

The laser beam has a beam diameter of 0.1 to 30.
μm, particularly 1 to 10 μm, is preferable because a servo track pattern capable of performing precise servo tracking is formed. The output is appropriately selected from a range in which the layers constituting the magnetic tape 1 and the support 2 are not damaged and the metal or alloy constituting the metal layer can be sufficiently melted, and is generally 1 to 50 mW per incident beam. Especially 3 ~
Although 25 mW is preferable, a high-output laser beam of about 1 to 100 W may be used after shortening the pulse. The wavelength is preferably from 0.3 to 1.3 [mu] m, particularly preferably from 0.4 to 0.9 [mu] m, from the viewpoint of light absorption of the metal or alloy.

The width of the pattern formed in the same manner as the servo tracking pattern in the first embodiment is 0.1 to 0.1 from the viewpoint that precise servo tracking can be performed and the thermal influence on the support 2 during writing. 30 μm, especially 1
It is preferably from 20 to 20 μm. The length of the pattern,
That is, the length of the concave portion 9 is preferably 1 to 100 μm, particularly preferably 10 to 50 μm because it is necessary to reliably detect the servo signal. Further, the distance between the concave portions 9 is preferably 2 to 100 μm, particularly preferably 20 to 80 μm in order to surely separate the concave portions 9 and increase the sensitivity at the time of reading. Furthermore, the depth of the servo tracking pattern is
From the viewpoint that the optical properties of the pattern and the other part on the non-recording surface side are sufficiently different, the thickness of the metal layer 5 is set to 1/3 to 1 times, particularly 2/3 to 1 times. preferable. In the present embodiment, as shown in FIG. 4, the servo tracking pattern, that is, the depth of the concave portion 9 is the same as the thickness of the metal layer. In addition, in FIG.
Is drawn as a cavity for the sake of convenience, but the support 2 and / or the back coat layer 6 actually penetrates the recess 9. Since the thickness of the metal layer in the present embodiment is significantly smaller than the thickness of the back coat layer 6, even when the back coat layer 6 penetrates into the recessed portion 9,
The depression due to the penetration does not occur on the surface of the back coat layer 6, or even if it occurs, the decrease in surface properties due to the depression is negligible.

The servo signal recording layer 5 made of a metal layer can be formed by the same method as the reflection layer 5b in the first embodiment. As the metal or alloy constituting the metal layer, a material which can be melted by the above-mentioned laser beam irradiation with a heat quantity that does not damage the layers constituting the magnetic tape 1 and the support 2 is used. Preferably, a low melting point metal or alloy having a melting point of 500 ° C. or less is used. Such metals and alloys include, for example, indium, tin, lead, zinc, gallium, selenium, rubidium, cadmium, tellurium, cesium, thallium, bismuth, polonium, astatine, lithium, sodium,
Potassium, silver-indium alloy (containing about 25% or more indium), silver-bismuth alloy (containing several% or more bismuth)
And the like, and in particular, indium, tin, lead, and zinc are preferred in view of optical characteristics such as light absorption and chemical stability.
The thickness of the metal layer is 5 to 500 nm, particularly 10 to 30 nm.
It is preferably 0 nm.

Next, items common to the above embodiments will be described. The upper magnetic layer 4 formed on the recording surface side of the magnetic tape 1 is formed by dispersing ferromagnetic powder in a binder. As the binder, the same binder as that used for forming the back coat layer 6 can be used. In particular, it is preferable to include a polar group such as a sulfonate group or a sulfate group in the binder from the viewpoint of improving the dispersibility of the ferromagnetic powder. As the ferromagnetic powder, for example, a needle-shaped or spindle-shaped ferromagnetic powder and a plate-shaped ferromagnetic powder can be used. Examples of the needle-shaped 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.

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 of this ferromagnetic metal powder is 125 to 200 kA / m, and the saturation magnetization is 110 to
170 Am ² / kg, BET specific surface area is 40 to 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. The ferromagnetic hexagonal ferrite powder has a coercive force of 135 to 260 kA / m and a saturation magnetization of 27 to 7
2Am ² / kg, BET specific surface area of 30 to 70 m ² / g
It is preferred that Both the major axis length of the ferromagnetic metal powder and the plate diameter of the ferromagnetic hexagonal ferrite powder are 0.01 to
The thickness is preferably 0.12 μm, particularly preferably 0.02 to 0.1 μm from the viewpoint of improving the output of the magnetic tape.

In addition to the above-mentioned components, an abrasive made of a powder of a substance having a Mohs hardness of 7 or more such as alumina and chromium oxide, carbon black as an antistatic agent, a lubricant such as a fatty acid or a fatty acid ester, an isocyanate compound The performance of the magnetic tape 1 can be further improved by including a hardener such as Preferred amounts of these components are as follows with respect to 100 parts by weight of the ferromagnetic powder. Abrasive: 1 to 20 parts by weight, especially 3 to 15 parts by weight Carbon black: 0.5 to 10 parts by weight Lubricant: 1 to 10 parts by weight Hardener: 5 parts by weight or less, especially 2 parts by weight or less

The thickness of the upper magnetic layer 4 is 0.01 to 1 μm, particularly 0.05 to improve the S / N and prevent self-demagnetization.
It is preferably about 0.8 μm.

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 may contain a binder, an abrasive, a nonmagnetic powder such as carbon black as an antistatic agent, a lubricant, a hardener, or 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 a non-magnetic iron oxide (α
-Fe ₂ O ₃ ), 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

The thickness of the lower layer 3 is from 0.2 to 3.0 μm from the viewpoint of improving the durability of the magnetic recording medium and preventing occurrence of cupping.
m, particularly preferably 0.5 to 2.5 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, methyl ethyl ketone (M
Ketone solvents such as EK), aromatic solvents, hydrocarbon solvents and the like are preferably used.

As the support 2, a known support can be used as long as it is for a magnetic tape. Specifically, those described in column 2, lines 30 to 42 of JP-A-9-35246 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 2 is 6 μm or less,
In particular, the thickness is preferably 5 μm or less for increasing the capacity of the magnetic tape. Further, an easy-adhesion layer may be provided on the surface of the support 2 to enhance the adhesion with the servo signal recording layer 5 and the lower layer 3.

The total thickness of the magnetic tape 1 is 7 μm or less, preferably 4.5 to 6.8 μm, from the viewpoint of increasing the recording capacity. That is, the magnetic tape of the present embodiment is an extremely thin magnetic tape. Generally, when the thickness of a magnetic tape is reduced, the rigidity of the magnetic tape is reduced, so that the contact with a magnetic head is reduced and the output tends to be reduced. However, in the present invention, a highly rigid reflective layer or a metal layer is formed. Because
Despite being a thin tape, it has high rigidity. Therefore, the magnetic tape 1 of the present invention has an advantage that it is easy to increase the recording capacity by reducing the total thickness.

Although the present invention has been described based on the preferred embodiment, the present invention is not limited to the above embodiment.
Various changes can be made without departing from the spirit of the present invention. For example, the servo tracking pattern is not limited to the above-described embodiment, and may include other patterns, for example, one or more continuous linear, band-like or dot-like (circular, rectangular, triangular, cross-shaped) patterns along the tape longitudinal direction, or A combination of these patterns can be used. In particular, a continuous linear pattern is useful in that it is easy to manufacture. In the above-described embodiment, the coating type magnetic tape is used. However, the same effect can be obtained by using a metal deposition type magnetic tape instead. Further, the magnetic recording medium of the present invention includes a tape for recording audio and video such as a DVC tape, an 8 mm video tape, a DAT tape, and the like.
It is suitable as a magnetic tape such as a data recording tape such as a T, DDS tape, a 1/4 inch data cartridge tape, and a data 8 mm tape.

[0045]

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

Example 1 The following ingredients (excluding the curing agent) were kneaded with a kneader, dispersed by a stirrer, and finely dispersed by a sand mill to obtain 1 μm
After filtering through a filter, a curing agent was added last to prepare a pigment-containing paint, a backcoat paint, an upper paint and a lower paint having the following compositions. In particular, in the preparation of the back coat paint and the pigment-containing paint, the inorganic particles (barium sulfate) were pre-dispersed with a binder and a part of a solvent by a planetary mixer, and then mixed with other components and further dispersed.

<Blending of pigment-containing paint> 100 parts of barium sulfate (granular shape having a particle diameter of 35 nm) 6 parts of 3,3'-dipropylthiadicarbocyanine iodide (colorant) 28 parts of polyurethane resin (binder) [number average molecular weight 25000] Sulfonic acid group content: 1.2 × 10 ⁻⁴ mol / g, glass transition point 45 ° C.) 4 parts of polyisocyanate (curing agent) [“Coronate L” (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.) ), Solid content 75%]-MEK (solvent) 120 parts-Toluene (solvent) 80 parts-Cyclohexanone (solvent) 40 parts

<Blending of back coat paint> 100 parts of barium sulfate (granular shape having a particle diameter of 35 nm) 3 parts of phosphoric ester (lubricant) [Phosphanol RE610 (trade name) manufactured by Toho Chemical Co., Ltd.] Resin (binder) 28 parts [Number average molecular weight 25,000, sulfonic acid group content: 1.2 × 10 ^-4 mol / g, glass transition point 45 ° C] Stearic acid (lubricant) 0.5 part Poly 4 parts of isocyanate (curing agent) [“Coronate L” (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd., trade name: 75%)] ・ MEK (solvent) 120 parts ・ Toluene (solvent) 80 parts ・ Cyclohexanone (solvent) 40 Department

<Mixing 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) 3.2 parts of α-alumina (abrasive, average particle size: 70 nm) 0.4 parts of carbon black (average particle size: 20 nm) 10 parts of vinyl chloride copolymer [binder, manufactured by Zeon Corporation MR104 (trade name)]-7 parts of polyurethane resin [Binder, UR-8300 (trade name) manufactured by Toyobo]-2 parts of stearic acid-1.5 parts of 2-ethylhexyl oleate-polyisocyanate (curing agent) 4.5 Parts [Coronate L (trade name) manufactured by Nippon Polyurethane Industry, solid content 75%]-132 parts of MEK-88 parts of toluene-210 parts of cyclohexanone

<Blending of lower layer coating composition> 60 parts of hexagonal plate-like hexagonal ferromagnetic barium ferrite powder (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 vinyl chloride Copolymer 14 parts [Binder, MR104 (trade name) manufactured by Zeon Corporation]-Polyurethane resin 12 parts [Binder, UR-8300 (trade name) manufactured by Toyobo]-Stearic acid 4 parts-2-ethylhexyl oleate 1 .5 parts ・ Polyisocyanate (curing agent) 4 parts [Coronate L (trade name) manufactured by Nippon Polyurethane Industry, solid content 75%] ・ MEK 84 parts ・ Toluene 56 parts ・ Si Rohekisanon 60 parts

A reflective layer made of aluminum and having a thickness of 30 nm was formed on one surface of a support made of a PET film having a thickness of 4.5 μm by vapor deposition. On top of this, a pigment-containing paint and a backcoat paint are applied simultaneously in this order by wet-on-wet method to form a pigment-containing layer (0.15 μm thick).
m) and a back coat layer as the outermost layer (film thickness 0.35
μm). Next, on the other surface of the support, a lower layer paint and an upper layer paint are simultaneously coated with a die coater so that the dry thicknesses of the lower layer and the upper magnetic layer become 1.5 μm and 0.2 μm, respectively. Then, each coating film was formed. Then, while these coatings were wet,
Magnetic field orientation treatment was performed with a 00 kA / m solenoid. Furthermore, the coating film was dried by blowing hot air at 80 ° C. at a speed of 10 m / min in a drying furnace. After drying, the coating film was calendered to form a lower magnetic layer and an upper magnetic layer. The raw material of the magnetic tape thus obtained was slit to a width of 12.7 mm to obtain a magnetic tape having a structure shown in FIG. A wavelength of 680 nm and an output of 2 were applied to the dye-containing layer of this magnetic tape.
A servo tracking pattern shown in FIG. 2 is irradiated with a laser beam having a beam diameter of 0 mW and a beam diameter of 1 μm (width 1 μm, length 2 μm, distance 2 μm between adjacent patterns in the longitudinal direction).
Was formed.

Example 2 Instead of barium sulfate blended in the back coat paint, ZnO (spherical, particle size 50n) was used.
A magnetic tape was obtained in the same manner as in Example 1 except that m) was added. Then, a servo tracking pattern was formed on this magnetic tape in the same manner as in Example 1.

Example 3 A magnetic tape was obtained in the same manner as in Example 1 except that barium ferrite was not added to the lower layer coating material and 100 parts of needle-like α-Fe ₂ O ₃ was added.
Then, a servo tracking pattern was formed on this magnetic tape in the same manner as in Example 1.

Example 4 A magnetic tape was obtained in the same manner as in Example 1 except that the dye-containing layer was not formed and the reflection layer was formed of indium having a thickness of 20 nm. 780 nm wavelength and 4 m output from the back coat layer side of this magnetic tape
W, a laser beam having a beam diameter of 1 μm was intermittently irradiated to melt the indium and form the same servo tracking pattern as in Example 1. The servo tracking pattern had a depth of 20 nm.

[Evaluation of Performance] In order to evaluate the performance of the magnetic tape obtained in the examples, the light reflectance of the magnetic tape was measured by the following method, and a servo tracking test was further performed. Table 1 shows the results.

<Light Reflectance> Monochromatic light having the wavelength of the light used for reading the servo signal is irradiated from the back coat layer side of the magnetic tape, and the ratio (%) of the reflected light to the incident light is obtained. Value. The values shown in Table 1 are values before the servo tracking pattern is formed on the recording layer.

<Servo Tracking Test> With respect to the magnetic tape obtained in the example, signals were recorded on the magnetic layer while performing push-pull servo tracking using reflected light, and the controllability was evaluated. The light used for detecting the servo signal has the same wavelength as the light used for measuring the reflectance of the magnetic tape shown in Table 1. In addition to this evaluation, the reproduced output of the recorded signal was measured by the head tester method, and the envelope characteristics were measured. The reproduction output was based on the value of Comparative Example 1. The envelope characteristics were evaluated according to the following criteria.・ ・ ・: The output level was constant over one track, and the envelope shape was uniform. Δ: One track had a distorted envelope shape with a low output portion in the front half or the rear half. ×: One track had a distorted envelope shape as a whole.

[0058]

[Table 1]

As is clear from the results shown in Table 1, it is understood that the magnetic tape of the embodiment (the product of the present invention) can obtain a high reproduction output and perform the servo tracking reliably.
Further, after the magnetic tape of each example was wound around a reel and stored for 3 months, the surface condition of the upper magnetic layer was observed. The results are as shown in Table 1, and the surface condition at the same level as before storage was obtained. It was found that the surface shape of the back coat layer was not transferred to the upper magnetic layer due to the formation of the servo tracking pattern. Further, although not shown in the table, it was found that the magnetic tapes of the respective examples maintain the same level of reproduction output and dropout as those of ordinary magnetic tapes.

[0060]

According to the present invention, it is possible to obtain a magnetic tape having a high recording density capable of performing servo tracking while maintaining high output and high S / N. Further, according to the present invention, since the servo tracking pattern is formed on the non-recording surface side of the magnetic tape, a magnetic tape capable of performing servo tracking without reducing the area of the data area on the recording surface can be obtained. In addition, since no servo tracking pattern is provided deep in the magnetic layer, sufficient electromagnetic conversion characteristics can be obtained. Also, noise can be reduced. Further, according to the present invention, a magnetic tape having an improved track density and a high recording capacity can be obtained. Further, by providing a back coat layer on the recording layer, while the recording layer is protected,
The unevenness of the recording layer is reduced. As a result, reliable track control can be performed, and the surface shape of the back coat layer is prevented from being transferred to the magnetic layer, so that output characteristics and dropout characteristics are improved. Further, since the back coat layer is transparent, a non-contact optical system can be used for writing / reading the servo tracking signal, and no dust is generated. In particular, by providing a metal layer (reflection layer) between the support and the back coat layer, the rigidity can be increased even for a thin magnetic tape having a total thickness of 7 μm or less, and the running property and durability can be improved. Is prevented, and the recording capacity can be easily increased.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing a configuration of a magnetic tape according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a main part of a servo tracking pattern.

FIG. 3 is a schematic diagram illustrating a method of servo tracking of a magnetic tape according to the present invention.

FIG. 4 is a schematic diagram (corresponding to FIG. 1) of a longitudinal section showing a configuration of a magnetic tape according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic tape 2 Support 3 Lower layer 4 Upper magnetic layer 5 Recording layer (metal layer) 5a Dye containing layer 5b Reflective layer 6 Back coat layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kunio Ando 2606 Kabane-cho, Akaga-bane, Haga-gun, Tochigi Prefecture, Japan (72) Inventor Manabu Hosoya 2606, Kabashi-cho, Akaga-bane, Haga-gun, Tochigi Prefecture, Kao Corporation F Terms (reference) 5D006 CC01 CC02 CC03 CC04 DA05 DA06 DA07 FA00 FA02 FA05 FA09

Claims (5)

[Claims] 1. A magnetic recording medium comprising a support and a magnetic layer formed on one surface of the support, wherein a transparent back coat layer is formed on the other surface of the support and the back coat layer A recording layer capable of optically recording a tracking servo signal is formed between the back coat layer and the support; and the back coat layer includes the servo signal incident on the recording layer from the back coat layer side. A magnetic tape having transparency such that the reflectance of reading light is 40% or more. 2. The magnetic tape according to claim 1, wherein the back coat layer is made of non-black small-diameter inorganic particles having a particle diameter of 60 nm or less without containing carbon black. 3. The magnetic tape according to claim 1, wherein the recording layer comprises a dye-containing layer formed on the back coat layer side and a reflective layer formed on the support side. . 4. The magnetic tape according to claim 1, wherein the recording layer comprises a low melting point metal or alloy layer. 5. A magnetic recording medium in which a magnetic layer is formed on one surface of a support, wherein a transparent back coat layer is formed on the other surface of the support, and the back coat layer A recording layer on which an optical tracking servo signal is recorded is formed between the substrate and the support, and the backcoat layer has the tracking servo signal in the recording layer from the backcoat layer side. A magnetic tape having transparency such that the reflectance of the servo signal reading light incident on a portion other than the recorded portion is 40% or more.