JP3357921B2 - 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 magnetic recording medium such as a magnetic tape in which a back coat layer is provided on the back surface of a substrate having a magnetic layer on the front surface, and more particularly, to the friction of the back coat layer surface. The present invention relates to a magnetic recording medium having a small coefficient and excellent running stability.

[0002]

2. Description of the Related Art Audio tapes, video tapes and data tapes are known.
In a magnetic recording medium such as a tape, for the purpose of improving the recording density, an extremely smooth polyester film or the like is used as a base, and a very fine magnetic powder is used to form the magnetic layer. Smoothing the surface has been performed. However, the smoother the substrate, the greater the coefficient of friction with the guide roller of the tape cartridge and the guide roller of the deck during traveling, and the traveling becomes unstable. Therefore, for the purpose of reducing the coefficient of friction and improving running stability, it is widely used to form a back coat layer by applying a non-magnetic powder together with a binder resin on the back surface of a substrate having a magnetic layer on the surface. In order to provide a function of improving the running stability by reducing the coefficient of friction of the surface of the back coat layer, improvement of materials such as a non-magnetic powder and a binder resin has been carried out. Improvements in the surface roughness of the layers have been made. (Japanese Patent Laid-Open No. 1-232525)

[0003]

However, the surface roughness of the back coat layer is optimized by examining the shape of the non-magnetic powder, the physical properties of the binder resin, or the mixing ratio of the non-magnetic powder and the binder resin. Although it is possible to reduce the coefficient of friction of the back coat layer surface, it is not easy to secure running stability in a complex actual running system such as a magnetic tape.
The improvement of running stability in a complex actual running system is not yet sufficient.

[0004]

SUMMARY OF THE INVENTION The present invention has been made based on various studies in view of the above-mentioned situation. The present invention has a structure in which convex streaks continuous in the running direction are formed on the back surface of a substrate having a magnetic layer on the surface. By providing a back coat layer having
The friction coefficient on the surface of the back coat layer is sufficiently reduced so that sufficient running stability can be obtained in a complicated actual running system such as a magnetic tape.

In the present invention, the continuous convex streaks provided on the surface of the back coat layer cannot achieve the intended effect if the height is smaller than 10 nm, and the magnetic tape if the height is larger than 30 nm. -Roll or reel as a loop
When the magnetic layer is wound, the magnetic layer may be deformed, and the spacing loss with the magnetic head may be increased, leading to a decrease in output.

[0006] The interval between continuous convex streaks is 150
It is necessary to be within the range of ５００500 μm . This interval
When but less than 150 [mu] m, rather magnetic tape - cause running failure of meandering of flop, also as large as the desired effect is difficult to obtain than 500 [mu] m.

Further, the surface roughness between the continuous convex streaks is in the range of 0.004 to 0.015 μm in center line average roughness Ra.
Must be enclosed. This surface roughness is the center line average roughness
If the Ra is larger than 0.015 μm , the contained non-magnetic powder may fall off, which may cause dropout or guide loss.
Cause contamination.

[0008] Such a continuous convex streak is
In the case of a gravure coating method or a reverse coating method, which is conventionally known as a general indirect coating method, a non-magnetic powder is mixed with a binder resin, an organic solvent and other necessary components as a method of forming on the layer surface. The coating material for the back coat layer prepared by dispersing is applied to the back surface of the substrate having the magnetic layer on the surface by these coating methods, and the coating surface of the back coat layer formed by this application is subjected to a smoothing treatment on a curved surface. Is performed by a smoothing method using a smoothing surface of a smoother having the following.

In this case, in order to favorably form the continuous convex streaks, the smoothing-processed curved surface of the smoother is as follows:
Preferably, the radius of curvature is in the range of 1 to 10 mm,
Further, in order to maintain the surface roughness between the continuous convex streaks, it is preferable that the surface roughness of the smoothing-processed curved surface of the smoother is 0.01 μm or less in center line average roughness Ra.

In the case where such continuous convex streaks are formed on the back coat layer by an extrusion coating method which is a direct coating method, a doctor corresponding to a smoother in the case of an indirect coating method is used. A backcoat layer coating film formed by applying a coating for a backcoat layer to the back surface of the substrate with the smoothed curved surface of the edge by forming the edge portion of the edge into a curved surface; This is performed by smoothing the surface. Also in this case, the smoothed curved surface of the edge portion has a radius of curvature in the range of 1 to 10 mm, and the surface roughness of the smoothed curved surface is 0.
It is preferable that the thickness be 01 μm or less.

The non-magnetic powder used in the back coat layer includes carbon black such as acetylene black and thermal black, alumina, titania, calcium carbonate, barium sulfate, red iron oxide, zirconia, garnet, and oxidized powder. Any metal oxides such as chromium and magnesium oxide generally used for a back coat layer of a magnetic recording medium are used, and those having an average particle diameter of 0.01 to 1 μm are preferably used. The amount used is 30 to 30% with respect to the total amount of the binder resin to form a continuous convex streak well.
Preferably, it is in the range of 60% by weight.

Examples of the binder resin include cellulose resins such as nitrocellulose, acetylcellulose, methylcellulose, and ethylcellulose; vinyl chloride-vinyl acetate-vinyl alcohol copolymer; Generally, a magnetic material such as vinyl chloride-based resin such as vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, polyester-based resin, polyurethane-based resin, phenol-based resin, epoxy-based resin, or a mixture thereof. Any of those used for the back coat layer of the recording medium is used.

Examples of the organic solvent include ketone solvents such as cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene and xylene, and isopropyl alcohol. Solvents suitable for dissolving the binder resin to be used, such as alcohol solvents such as alcohol, acetate amide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran and dioxane, are particularly limited. They can be used alone or as a mixture of two or more.

In the coating for the back coat layer, various other commonly used additives such as a lubricant may be optionally added.

The magnetic layer formed on the surface of the substrate has a γ-F
e ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing γ-Fe ₂ O
Conventionally used magnetic powder such as ₃ powder, Co-containing Fe ₃ O ₄ powder, hexagonal ferrite powder such as barium ferrite, strontium ferrite, CrO ₂ powder, Fe powder, Co powder, Fe-Ni powder, etc. The magnetic paint is prepared by mixing and dispersing with the binder resin, the organic solvent and other necessary components to be prepared, and the magnetic paint is applied to the surface of the substrate and dried. In addition, Co, Ni, Fe, Co-Ni alloy, Co
-Vacuum deposition of ferromagnetic material such as Cr alloy, ion pre-
It is also formed by a method such as attaching to the surface of the substrate by means such as plating, sputtering, plating and the like.

[0016]

Next, an embodiment of the present invention will be described. Example 1 Co-containing γ-Fe ₂ O ₃ magnetic powder 500 parts by weight Nitrocellulose (manufactured by Asahi Kasei Corporation; Nitrocellulose L1 / 2) 65〃 Polyurethane resin (manufactured by Nippon Polyurethane Industry Co., Ltd .; Nipporan 38〃N-2301) isocyanate -Compound (manufactured by Nippon Polyurethane Industry Co., Ltd .; Corone 25〃-toL) Alumina (manufactured by Sumitomo Chemical Co., Ltd .; AKP-28) 40〃carbon black 3〃-n-butyl stearate 6〃stearic acid 5〃cyclohexanone 600 組成 toluene 600 〃 The above composition was mixed and dispersed in a ball mill for 72 hours to prepare a magnetic paint, and the magnetic paint was dried on the surface of a 14 μm-thick polyester film to a thickness of 3.5 μm after drying. , Dried and calendered to form a magnetic layer.

Next, the following backcoat layer composition was mixed and dispersed in a ball mill for 72 hours to prepare a backcoat layer coating composition. The backcoat layer coating composition was used to form the magnetic layer. The surface of the polyester film is coated by a gravure coating method at a coating speed of 70 m / min. A smoothing treatment is performed using a smoother having a curvature radius of a curved surface of 2 mm and a surface roughness of 0.008 μm in center line average roughness Ra. Then, a back coat layer having a thickness of 1 μm after drying was formed. Thereafter, the tape was cut into a width of 8 mm to produce a magnetic tape. Backcoat layer composition Carbon black (manufactured by Cabot Corporation in the United States; black par 840 parts by weight 00) Alumina (manufactured by Sumitomo Chemical Co., Ltd .; AKP-28) 2〃Nitrocellulose (manufactured by Asahi Kasei Corporation; nitrocellulose) L1 / 2) 50 （polyurethane resin (manufactured by Nippon Polyurethane Industry Co., Ltd .; Nipporan 30〃 N-2301) isocyanate compound (manufactured by Nippon Polyurethane Industry Co., Ltd .; corone 20〃-to-L) myristate 2 ２cyclohexanone 285〃toluene 285 〃

Example 2 In forming the back coat layer in Example 1, the coating speed of the coating for the back coat layer was increased from 70 m / min to 100 m / min.
A magnetic tape was produced in the same manner as in Example 1 except that the tape was changed to m / min.

Example 3 In forming the back coat layer in Example 1, the coating speed of the coating material for the back coat layer was increased from 70 m / min to 150 m / min.
A magnetic tape was produced in the same manner as in Example 1 except that the tape was changed to m / min.

Example 4 In the formation of the back coat layer in Example 1, instead of the smoother having a curvature radius of the smoothing-processed curved surface of 2 mm and a surface roughness of 0.008 μm in center line average roughness Ra, Smoothing was performed in the same manner as in Example 1 except that a smoother having a curvature radius of the curved surface of 5 mm and a surface roughness of 0.005 μm in center line average roughness Ra was used. Was prepared.

Example 5 In forming the back coat layer in Example 4, the coating speed of the coating material for the back coat layer was increased from 70 m / min to 100 m / min.
A magnetic tape was produced in the same manner as in Example 4 except that the tape was changed to m / min.

Example 6 In forming the back coat layer in Example 4, the application speed of the coating material for the back coat layer was increased from 70 m / min to 150 m / min.
A magnetic tape was produced in the same manner as in Example 4 except that the tape was changed to m / min.

The back coating in Comparative Example 1 Example 1 - In the formation of the coat layer, Sum - instead of The, - curvature radius 2mm GIN processing curved, surface roughness is the center line average roughness Ra Sum of 0.008μm Using a smoother having a radius of curvature of the smoothing treated surface of 0.5 mm and a surface roughness of 0.008 μm in center line average roughness Ra, the coating speed of the coating for the back coat layer is increased from 70 m / min to 10 m / min.
Smoothing was performed in the same manner as in Example 1 except that the speed was changed to 0 m / min, to produce a magnetic tape.

COMPARATIVE EXAMPLE 2 In the formation of the back coat layer in Example 1, instead of the smoother having a curvature radius of a smoothing-processed curved surface of 2 mm and a surface roughness of 0.008 μm in center line average roughness Ra, Using a smoother having a curvature radius of 20 mm and a surface roughness of 0.005 .mu.m in center line average roughness Ra, the coating speed of the back coat layer coating was increased from 70 m / min to 10 m / min.
Smoothing was performed in the same manner as in Example 1 except that the speed was changed to 0 m / min, to produce a magnetic tape.

COMPARATIVE EXAMPLE 3 In forming the back coat layer in Example 1, instead of the smoother having a curvature radius of the smoothing-processed curved surface of 2 mm and a surface roughness of 0.008 μm in center line average roughness Ra, Using a smoother having a radius of curvature of the smoothing-processed curved surface of 5 mm and a surface roughness of 0.02 μm in center line average roughness Ra, the coating speed of the coating for the back coat layer is from 70 m / min to 100 m.
/ Min in the same manner as in Example 1 except that the
Zing was performed to produce a magnetic tape.

The magnetic tapes obtained in each of the examples and comparative examples
The continuous coating formed on the surface of the back coat layer
The height and interval of the convex streaks are made by WYKO; TOPO-
Measured with 3D and light microscope. Also, the convex interstitial part
Surface roughness of Tokyo Seimitsu Co., Ltd .;
(Stylus tip radius of curvature 1 μm, needle pressure 10 mg, cut-off
0.08 μm). Table 1 below shows the results.

[0027]

[Table 1]

The magnetic properties obtained in each of the examples and the comparative examples are as follows.
The coefficient of friction of the back coat layer surface
Tester and guide rollers are measured for dirt by the following method.
Specified .

<Friction Coefficient> A stainless steel (SUS304) cylinder having a diameter of 4 mm (surface
The surface of the back coat layer is contacted with a magnetic tape with a roughness of 0.2S).
And apply a load of 20 g to one end
Apply and pull the other end 100 times back and forth at a speed of 1.4 cm / sec
It was determined by the load at the time.

<Jitter> A magnetic tape is loaded into a VCR and a video signal is recorded.
Recording and playback, 15.75 KHz horizontal sync signal of the playback signal
Of the horizontal synchronization signal for one second at that time
The maximum value is measured with a jitter meter, and the
-.

<Dirt of Guide Roller> A magnetic tape is loaded on a VCR and continuously operated for 100 hours.
Observe the guide rollers after running with an optical microscope and check for dirt.
(○) when there is no, (△) when it is slightly recognized,
The case where the dirt was severe was defined as (x). Table 2 below shows the results
It is.

[0032]

[Table 2]

[0033]

As is clear from the above Tables 1 and 2,
The magnetic tape (Examples 1 to 6 ) obtained by the present invention was actually used.
The backcoating between the embodiment 6 and the comparative example 1
Except that the friction coefficient of the surface of the back coat layer was the same, the friction coefficient of the surface of the back coat layer was small, the jitter was small, and the guide roller was smaller than the magnetic tapes obtained in Comparative Examples 1 to 3. This indicates that the magnetic recording medium obtained by the present invention has a sufficiently small coefficient of friction on the surface of the back coat layer and excellent running stability. Note that the magnetic tape obtained in Comparative Example 1
The number is the same as that of the magnetic tape according to Example 6
Of the present invention because the interval between the convex streaks is as small as 85 μm.
Jitter is larger than that of the magnetic tape (Examples 1 to 6)
Also, some dirt was found on the guide rollers. Also,
The tape obtained in Comparative Example 2 did not stain the guide rollers.
However, since the interval between the convex streaks is as large as 520 μm,
Friction coefficient compared to the magnetic tape of the present invention (Examples 1 to 6)
And large jitter. Further, the magnet according to Comparative Example 3
The tape has a center line average roughness Ra of the surface between the convex streaks.
Is as large as 0.017 μm, so the guide rollers are very dirty.
New

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-292613 (JP, A) JP-A-62-226419 (JP, A) JP-A-59-201219 (JP, A) JP-A-61-219 192025 (JP, A) JP-A-62-219318 (JP, A)

Claims (1)

(57) [Claims] 1. A back coat layer having, on the surface thereof, convex streaks continuous in the running direction on the back surface of a substrate having a magnetic layer on the surface, wherein the surface roughness between the convex streaks is a center line. 0.00 in average roughness Ra
4 to 0.015 μm, and the interval between continuous convex streaks in the running direction is 150 to 500 μm.
m .