JP2002222515A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having enhanced thermal deformation (cupping) resistance and running durability and excellent electromagnetic transducing characteristics. SOLUTION: In the magnetic recording medium including a magnetic layer formed by an oblique vapor deposition method on a non-magnetic substrate, the head touch of the medium is made satisfactory and the electromagnetic transducing characteristics and durability are improved, since the thermal deformation (cupping) is suppressed if the non-magnetic substrate is made of a laminated film of polyethylene naphthalate and has 3.0 μm-6.0 μm thickness, >=9,000 MPa, <=12,000 MPa Young's modulus in the width direction of the film and >=6.5% and <=9.0% coefficient of shrinkage (width direction, 150 deg.C-30 min).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film, and more particularly to a deposition type magnetic recording medium having excellent electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Unlike a coating type magnetic recording medium, a vapor deposition type magnetic recording medium is suitable for high density recording because of a high packing density of a magnetic material. Therefore, it is very advantageous in terms of electromagnetic conversion characteristics, and has already been put to practical use. At present, a vapor deposition type magnetic recording medium is formed on a non-magnetic support such as a biaxially oriented polyethylene terephthalate film, a biaxially oriented polyethylene naphthalate (hereinafter sometimes abbreviated as “PEN”) film, a polyimide film, and a polyamide film. In this method, a ferromagnetic metal material such as Co or Co-Ni is formed by a vacuum deposition method.

[0003] The magnetic material of the metal thin film type magnetic layer is composed of the above-mentioned metals or alloys, but those using Co have particularly good electromagnetic conversion characteristics and are advantageous for a high recording density medium. In recent years, higher recording densities have been demanded, and with the progress of thinning of recording media, studies have been made to further reduce the thickness of nonmagnetic supports.

[0004]

However, as the non-magnetic support becomes thinner, the contact between the tape and the magnetic head (hereinafter referred to as "head touch") becomes worse and the output decreases, particularly in the short wavelength region. Not only becomes noticeable, but also causes a problem in running durability as a magnetic recording medium. Therefore, a high-strength PEN film is used for the purpose of improving the head touch even if the nonmagnetic support is thin, preventing the output from lowering, and improving the running durability.

[0005] When a PEN film is used as the non-magnetic support, the output is reduced and the running durability is improved due to insufficient strength of the non-magnetic support. It becomes susceptible to thermal deformation in the process, the head touch deteriorates due to the thermal deformation, and the output decreases due to the deterioration of the head touch,
There is a problem of running durability.

[0006]

Means for Solving the Problems The present invention has been made to solve the above problems, and in order to improve the electromagnetic conversion characteristics, the non-magnetic support has a Young's modulus in the width direction and a thermal shrinkage in the width direction. It has been found that the above problem can be solved by setting the ratio in a predetermined range.

In a magnetic recording medium including a non-magnetic support and a magnetic layer formed on the non-magnetic support by oblique deposition, the non-magnetic support is a laminated film of polyethylene naphthalate and has a thickness of 3 μm. 0.0 μm to 6.
Within the range of 0 μm, the Young's modulus in the width direction of the film is 90.
Not less than 00 MPa and not more than 12000 MPa, which means the heat shrinkage in the width direction (meaning the shrinkage of the length after heating and maintaining at 150 ° C. for 30 minutes as compared to the length before heating,
Heat shrinkage (150 ° C. for 30 minutes), or simply “heat shrinkage”. ) Is 6.5% or more and 9.0% or less, the thermal deformation (cupping) after the film forming process is suppressed, the head touch becomes good, and the electromagnetic conversion characteristics and durability are improved. I found it.

If the heat shrinkage in the width direction is larger than 9.0%, the cupping after film formation becomes excessively large on the running surface (backcoat surface) side (convex on the vapor deposition surface side), If the heat shrinkage is less than 6.5%, the cupping after film formation becomes large on the vapor deposition surface side (convex on the running surface side), and in both cases, the head touch is deteriorated and the electromagnetic conversion characteristics are reduced. Moreover, the running property is deteriorated due to the cupping, and the durability is deteriorated.
This cupping is moderately convex (−0.2 m
m) is preferred for head touch,
As described above, if the value is too large, adverse effects will occur.

As the Young's modulus in the width direction increases, the head touch improves and the electromagnetic conversion characteristics improve.
When it is larger than 000 MPa, it becomes difficult to control the heat shrinkage in the width direction, and it is difficult to reduce the heat shrinkage to 9.0% or less. On the other hand, when the pressure is less than 9000 MPa, the absolute strength is insufficient, so that the head touch is deteriorated and the output is reduced.

The thickness of the recording medium has been reduced for higher recording density. In the present invention, the thickness of the nonmagnetic support is as small as 3.0 μm to 6.0 μm.
Is characterized by having a back coat layer of 0.3 μm to 0.7 μm on the surface on the side opposite to the above, but if the back coat layer is less than 0.3 μm, cupping is large on the vapor deposition surface side (convex on the running surface side). And the head touch becomes worse. On the other hand, if it is larger than 0.7 μm, the cupping becomes large on the running surface side (convex on the vapor deposition surface side), and the head touch becomes worse. Therefore, the thickness of the back coat layer is 0.3 μm to 0.7 μm, preferably 0.4 μm to 0.6 μm.
The range of m is good.

Japanese Patent Application Laid-Open Nos. 10-64036 and 11-28 disclose the publications defining the range of the heat shrinkage.
No. 3234, both of which are characterized in that the range of the heat shrinkage is 6% or less. 900 Young's modulus in width direction
Although it is not impossible to make the heat shrinkage ratio 6% or less while making it larger than 0 MPa, there are many difficulties in manufacturing, and there is a problem that the cost becomes high.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION
2,6-naphthalate is a laminated film of at least two layers, and the surface layer of the non-magnetic support on which the metal thin-film magnetic layer is provided contains fine inert particles to provide a desired surface roughness. You can get it. The type of particles to be contained is not limited, but colloidal silica and crosslinked polymer particles (crosslinked polystyrene and crosslinked divinylbenzene) are preferred. Alternatively, the desired surface roughness may be obtained by dispersing and coating the inert particles in a water-soluble polymer on a surface layer of a non-magnetic support on which a metal thin film layer is provided instead of including the inert particles. Can be obtained. The particle size of the particles is 0.01 to 0.10 μm
The desired surface roughness is obtained by using particles of m, preferably 0.02 to 0.08 μm.

A desired surface roughness can be obtained by incorporating fine inert particles into the surface layer opposite to the surface layer. The type of the particles to be contained is not limited, but colloidal silica or crosslinked polymer particles (crosslinked polystyrene or crosslinked divinylbenzene) are preferred. The particle size of the particles is 0.1 to 0.4 μm, preferably 0.1 to 0.4 μm.
The desired surface roughness is obtained by using particles of 〜0.3 μm.

Next, the polyethylene used in the present invention is
A method for producing 2,6-naphthalate is described, but is not limited thereto. Known production methods include a direct polymerization method using 2,6-naphthalenedicarboxylic acid and ethylene glycol, and a transesterification method using 2,6-naphthalenedicarboxylic acid dimethyl ester and ethylene glycol. As a method for containing the above-mentioned inert particles, it is preferable to disperse in ethylene glycol and polymerize with a dicarboxylic acid component.

The produced PEN pellets are melted, co-extruded from a two-layer die slit, cooled by a cooling drum, and sequentially and biaxially stretched to adjust the stretching ratio in the longitudinal and transverse directions so as to obtain a desired Young's modulus. After stretching in the longitudinal direction, stretching in the transverse direction, and heat setting, the film is subjected to a relaxation treatment, whereby a laminated PEN film having a desired heat shrinkage can be obtained.

Next, the magnetic material of the magnetic layer may be a pure metal such as Co or Fe or Co-Ni, Co-Fe, Co-Cu,
Co-Ni-Cr, Co-Pt, Co-Pt-Cr, C
Alloys such as o-Cr-Ta and Co-Ni-B can be used, and Co or a Co alloy is preferable. Usually, such a magnetic material is directly deposited on a non-magnetic substrate or Ni is deposited on a non-magnetic substrate, and then a magnetic layer is formed by vapor deposition. For the deposition of the magnetic layer, the inside of the deposition chamber is 10 ⁻⁶ T.
After evacuation to about orr, the magnetic material is melted by an electron gun, and when the entire magnetic material is melted, the non-magnetic substrate is caused to run along the cooled main roller to start vapor deposition at the main roller portion. At this time, in order to control the magnetic characteristics, an oxidizing gas selected from oxygen, ozone, and nitrous oxide is introduced into the magnetic layer. A plasma-polymerized hard carbon film layer may be provided on the obtained magnetic layer, if necessary.

The plasma-polymerized hard carbon film layer includes a feed roller, a take-up roller, a main roller having plasma-polymerized partial cylindrical surface-shaped (partially circular in section) electrode plates facing each other at intervals, and the like. Accordingly, in a chamber (vacuum chamber) having a pass roller, a raw material (a substrate on which a ferromagnetic metal is vapor-deposited and wound into a roll) is set on a feeding roller, evacuated to 10 ^-5 Torr or more, and then hydrocarbons. 1 to 10 ^-2 Torr, with gas and additive gas as reaction pressures
It is obtained by plasma polymerization while introducing a predetermined amount so that The amount to be introduced depends on the size of the chamber, and is appropriately determined as needed. The hydrocarbon gas is selected from methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, ethylene, propylene, acetylene, methylacetylene, and toluene, and is used alone or in combination of two or more. Examples of the added gas include hydrogen, neon, helium, argon, oxygen, nitrogen, and the like. The added ratio is about 1 to 0.01 in terms of the added gas / hydrocarbon ratio with respect to the amount of hydrocarbon. In particular, 0.1 to 0.05 is preferable. If the amount of the added gas is too large with respect to the hydrocarbon, the film formation rate is reduced. If the amount is too small, the film does not become dense. Discharge power supply is 10kHz ~
A frequency of 450 kHz is desirable, especially from 50 kHz to 20 kHz.
0 kHz is desirable. If the frequency is longer than 10 kHz, long-time operation becomes difficult. If the wavelength is shorter than 450 kHz, the film does not become dense. Such a plasma-polymerized hard carbon film has a refractive index of 1.9 or more and further 2.
It is desirable to control the discharge frequency, the reaction pressure, and the flow rate of the reaction gas so as to be about 0 to 2.25.

As the lubricant, a conventionally used lubricant may be used, but a lubricant containing fluorine is preferable. The lubricant base structure comprising the fluorine, which is represented by R1-A-R2, R1: CF 3 (CF 2) n -, CF 3 (CF 2) n (CH 2) m
—, CH ₃ (CH ₂ ) ₁ —, HA: COO, O, COOCH (C ₁ H _{21 + 1} ) CH _{2
COO R2: CF 3 (CF 2} ) n -, CF 3 (CF 2) n (CH 2)
_m −, CH ₃ (CH ₂ ) _l −, where R1 ≠ R2, n = 7 to 17, m = 1 to 3, l = 7
Those satisfying ３０30 are desirable. Further, when R1 and R2 are linear, the lubricating effect is large. When n is less than 7, the water repellency is low, and when n is more than 17, a blocking phenomenon occurs between the lubricant and the nonmagnetic substrate or the back coat layer, and the friction does not decrease. The same applies to 1 for n. Further, two or more kinds of such lubricants may be mixed.

[0019]

Example 1 Ethylene glycol having colloidal silica having an average particle size of 30 nm and dimethyl 2,6-naphthalenedicarboxylate were subjected to transesterification and polycondensation to obtain PEN.
Pellets were made (PEN-A). Average particle size 300n
Then, ethylene glycol having m crosslinked vinylbenzene particles and dimethyl 2,6-naphthalenedicarboxylate were subjected to transesterification and polycondensation to prepare PEN pellets (PEN-B). The PEN pellets A and B were each melted, co-extruded from a two-layer die slit, cooled by a cooling drum, sequentially stretched in a longitudinal direction by a biaxial stretching method, stretched in a lateral direction, and heat-fixed. The film was relaxed to obtain a 4.7 μm-thick laminated PEN film having a heat shrinkage ratio as shown in Table 1.

On the obtained PEN film having a thickness of 4.7 μm, while introducing Co and oxygen, two layers each having a thickness of 1000 ° were formed to form a magnetic layer. Ethylene and Ar (flow ratio 2: 1) were introduced onto the magnetic layer, and a predetermined discharge frequency (50 kHz) was applied to form a plasma-polymerized hard carbon film. A predetermined discharge frequency was applied to the surface of the hard carbon film, and plasma treatment was performed with carbon dioxide containing oxygen. Lubricants (succinic acid derivative COOHCH (C
_{14 H 29) CH 2 COOCH 2} CH 2 (CF 2) 7 C
F ₃ ) was applied by a reverse coating method, and a back coat layer having a dry thickness of 0.5 μm was provided on the side where the magnetic layer was not provided, and then slit into 8 mm width to obtain a sample. Table 1 shows the properties of the obtained magnetic recording medium. The plasma polymerized hard carbon film was also formed on a Si wafer under the same conditions as in the table, and the film thickness and the like were determined. The composition of the back coat layer is as follows (the numbers indicate parts by weight).

Carbon black (particle size 80 nm) 10 Same as above (particle size 20 nm) 40 Calcium carbonate (particle size 70 nm) 50 Nc (nitrocellulose) 40 (Asahi Kasei Kogyo Co., Ltd. (BTH1 / 2S) Polyurethane resin (Toyobo Co., Ltd.) : UR-8300) 60 methyl ethyl ketone 800 toluene 640 cyclohexanone 160 polyisocyanate (solid content 50%) 40 (Nippon Polyurethane Industry Co., Ltd .: Coronate L)

[0022]

EXAMPLE 2 to COMPARATIVE EXAMPLE 4 The film of Example 1 was co-extruded from a two-layer die slit, cooled by a cooling drum, stretched in the longitudinal direction by a successive biaxial stretching method, and then stretched in the transverse direction. After adjusting the stretching ratio so that the Young's modulus in the width direction becomes the numerical value shown in Table 1, further heat-setting, and then, when performing the relaxation treatment of the film, the film is wound up by changing the relaxation conditions, and is shown in Table 1. A 4.7 μm-thick laminated PEN film having such a thermal shrinkage was obtained.

A laminated PEN film having a thickness of 4.7 μm was obtained in the same manner as in Example 1 except that the Young's modulus and the heat shrinkage were adjusted.
On the 4.7 μm-thick PEN film, two layers were formed with a thickness of 1000 ° each while introducing Co and oxygen to form a magnetic layer.

Table 1 shows the results obtained in the above embodiments using the following criteria. (About cupping) Cupping strength was expressed by the maximum height of the tape from a line connecting the tape end faces. The case of convex on the vapor deposition surface side is indicated by-, and the case of convex on the running surface side is indicated by +.
In terms of the relationship with the head touch, it is preferable that the head touch is about -0.2, that is, the head is slightly convex on the vapor deposition surface side.

(Regarding the head touch) The waveform at the time of reproducing the tape was observed with a digital oscilloscope manufactured by LeCroy Japan Co., Ltd., when the output signal was normal, 若干; when the output signal was slightly distorted, 、; The case where the output was significantly reduced was represented by x.

(Electromagnetic Conversion Characteristics) A 10 MHz signal was recorded and reproduced by a Sony VCR EV-S900 for measurement. The numerical values are based on Comparative Example 2 (0d
As B), the reproduced output was displayed.

(Durability) With a VCR EV-S900 manufactured by Sony Corporation, a reciprocating running test was performed 100 times with 50 samples in a 20 ° C.-60% RH environment. Observation of the occurrence status of the running trouble was indicated by ◎ for the trouble occurrence volume 0, ○ for the trouble occurrence volume 1, and × for the trouble occurrence volume 2 or more.

(Regarding Young's Modulus) PE before forming magnetic layer
The N film was cut into a size of 150 mm in length × 10 mm in width to obtain a test piece. The cutting direction was such that the longitudinal direction at the time of producing the PEN film was 10 mm. Using this constant-stretch type tensile tester, the tensile interval of the test piece was 1
A tensile test was performed at 00 mm and a tensile speed of 5 mm / min, a tangent line was drawn at the rising portion of the stress curve, and the load on the tangent line where the elongation of the test piece was 1% was determined. Young's modulus is
Young's modulus obtained from the following equation = [load / (width x thickness)] x 100

(Regarding the heat shrinkage) Three test pieces having the same Young's modulus (only the length was changed from 150 mm to 100 mm) were prepared. The mark line for the measurement interval is put on the test piece, and the length before heating is measured by a micrometer (VM-250) manufactured by Nikon Corporation. Thereafter, the test piece is heated in a hot-air circulation type high temperature bath for a certain period of time and taken out. After allowing the taken-out test piece to cool for 10 minutes, the length is measured again with a micrometer. The heat shrinkage was calculated by the following equation, and the average value was calculated. Heat shrinkage = [(length before heating−length after heating) / length before heating] × 100 The heating conditions are 150 ± 1 ° C. and 30 ± 1 minute.

[0030]

[Table 1]

It is apparent from Table 1 that the Young's modulus in the width direction of the nonmagnetic support is from 9000 MPa to 12000 MPa.
And the heat shrinkage in the width direction is 6.5% to 9.0%.
In the case of (1), the electromagnetic conversion characteristics are evaluated by the reproduction output, and when the output is generated to some extent, the waveform at the time of reproduction is normal, and there is no running trouble.

[0032]

According to the present invention, when a non-magnetic support of the present invention is applied to a magnetic recording medium in which a metal thin film type magnetic layer, a plasma-polymerized hard carbon film and a lubricant are laminated on a non-magnetic support, thermal deformation (cupping) occurs. Further, a magnetic recording medium having significantly improved running durability and excellent electromagnetic conversion characteristics can be obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masao Nakayama 1-13-1, Nihonbashi, Chuo-ku, Tokyo FTD term (reference) 5D006 BB07 CB01 CB07 CB08 CC03 EA03

Claims (3)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer formed on the support by an oblique evaporation method.
The nonmagnetic support is a laminated film of polyethylene naphthalate, and the Young's modulus in the width direction of the film is 9000.
A magnetic recording medium having a thermal shrinkage in the width direction of 6.5% or more and 9.0% or less. 2. The magnetic recording medium according to claim 1, wherein the thickness of the nonmagnetic support is 3.0 μm or more and 6.0 μm or less. 3. The magnetic recording medium according to claim 1, further comprising a backcoat layer having a thickness of 0.3 μm or more and 0.7 μm or less on a surface opposite to the magnetic layer.