JPS6363124A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the generation of property deterioration in spite of exposing a substrate to a high temp. during production or use by using a specific PPTA film to the substrate of a perpendicular magnetic recording medium. CONSTITUTION:The film which consists substantially of the poly-P-phenylene terephthalic amide (PPTA) having >=1,000kg/mm<2> Young's modulus in the arbitrary direction parallel with the film plane, >=10% elongation and >=3X10<-5>mm/ mm/%RH coefft. of hygroscopic expansion is formed thereon with a ferromagnetic layer having the axis of easy magnetization in the direction perpendicular to said film plane and consisting of cobalt or iron compd. This film has preferably <=2.5X10<-5>mm/mm/%RH coefft. of hygroscopic expansion in the arbitrary direction parallel with the film plane and has >=35kg/mm<2>, more preferably >=45kg/mm<2> strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film magnetic recording medium, and particularly to a perpendicular magnetic recording medium using a high performance aramid film as a substrate.

[Conventional technology]

Conventional perpendicular magnetic recording media include those in which a cobalt-based or iron-based alloy thin film layer is formed by sputtering or electron beam evaporation on an organic polymer film such as polyethylene terephthalate (PET) or an inorganic substrate. It is used.

Conventionally, polyethylene terephthalate films have been mainly used as substrates for such magnetic recording media. However, since the glass transition point is as low as around 70° C., the film must be sufficiently cooled when forming a magnetic layer by vapor deposition or the like, resulting in deterioration of magnetic properties and low adhesion strength. Therefore, a material with good heat resistance is desired for this type of base film for perpendicular magnetic recording media.

Aromatic polyamides and aromatic polyimides can withstand high temperatures of 200°C or higher, so they can form metal thin films at higher temperatures than polyethylene terephthalate films, improving coercive force, which is a static magnetic property, and improving the squareness ratio of hysteresis loops. , is a very promising material for this type of base film for recording media.

However, aromatic polyamides and aromatic polyimide films generally have a high moisture absorption rate, and due to this, a large dimensional change rate due to moisture absorption, and are therefore unsatisfactory as substrates for abrasive media. especially.

Unlike paint-on magnetic recording media, no binder is used.
In the case of perpendicular magnetic recording media in which a ferromagnetic layer is deposited on a substrate, the difference in dimensional stability between the ferromagnetic layer and the substrate becomes a fatal defect. Furthermore, in the case of recording media made of ultra-thin substrates (for example, 5 m or less), using conventional films for the substrate does not have enough resistance to mechanical external forces, resulting in cracks in one ferromagnetic layer. Sometimes I even went inside.

[Problem that the invention seeks to solve]

The present invention has excellent dimensional stability against external forces and temperature and humidity,
The purpose is to provide a high-quality perpendicular magnetic recording medium using a tough aromatic polyamide film as a substrate.

[Means for solving the problems] The present invention provides a method in which the Young's modulus in any direction parallel to the film surface is t.
oook&/& or more, and the elongation is 10% or more.

The coefficient of hygroscopic expansion is 3X10-''B/1111I/%R
H or less, a ferromagnetic layer having an axis of easy magnetization perpendicular to the film surface and consisting of a cobalt-based or iron-based compound is formed on a film consisting essentially of I+ruboly P-phenylene terephthalamide. This is a perpendicular magnetic recording medium characterized by the following.

Poly-P-phenylene terephthalamide (PPTA) used in the present invention is a type of aromatic polyamide and has a substantial K
(-Cotsu-COkitsuichitenichi).

It is a polymer expressed by the conventionally known paraphenylene diamine and terephthaloyl chloride.

Conveniently, they are produced by low temperature solution polymerization methods.

If the degree of polymerization of the polymer of the present invention is too low, a film with good mechanical properties cannot be obtained.

Logarithmic viscosity Winh preferably 3.5 or more, more preferably 4.5 or more (sulfuric acid 10 o!ILt and polymer 0.
A polymer having a degree of polymerization that gives a value measured at 30° C. after dissolving 59 is selected.

The film used in the present invention has an elongation of at least 10% in any direction parallel to the film plane. Preferably 15%
That's all. Films with an elongation of less than 10% are brittle and difficult to handle. The magnitude of elongation.

It is also related to tear strength, and it is important to have an elongation of 10% or more in any direction in order to improve the workability of film slitting and other processing.

The film used in the present invention has a Young's modulus of at least 100 okq/xyl in any direction parallel to the film surface.

Preferably 1200kl? /II'' or higher.This requirement is.

It is closely related to the film's deformation resistance to external forces. And 1. Perpendicular magnetic recording medium (magnetic tape) of the present invention
Since the Young's modulus in the longitudinal direction is large, the tape has good running properties even if it is made thinner.

This means that the jitter characteristics are excellent. When the Young's modulus in the width direction is large, wrinkles and folds are less likely to occur in the tape, resulting in improved workability during tape manufacture and ease of handling during use. The Young's modulus of the film used in the present invention is at a high level due to the unique process of first making the optically anisotropic dope optically isotropic and then solidifying it, but it also depends on the stretching ratio and heat treatment temperature during production. ing.

The film used in the present invention further has a hygroscopic expansion coefficient of 3 x 10-'H/home/in any direction parallel to the film surface.
%RH or less. Preferably, it is 2.5 x 10-1S h/j11/%RH or less. Hygroscopic expansion coefficient is 3X1
A film with a RH of more than 0 m/m/% means that the film lacks dimensional stability against changes in humidity,
Since the length of the perpendicular magnetic recording medium changes depending on the humidity, there are disadvantages such as so-called skew in reproduced images, peeling of ferromagnetic layer 1 from the substrate, and cracking of ferromagnetic layer 9.

In addition to the above requirements, the film used in the present invention meets the above requirements.

It is preferable that the following aspects are provided.

The film used in the present invention is preferably 35 to 97a!
has a strength of 2 or more, more preferably 45 kg
It has a strength of /- or more. Such high strength in PPTA films is inherent to the unique process of optically isotropically making a relatively highly concentrated optically anisotropic dope and then solidifying it into a film.

Further, the film used in the present invention preferably has excellent surface properties such that the center line average roughness (Ra) of at least one surface thereof is not more than O,OS μm.

More preferably, Ra is 0.02 μm or less. By using a film with a small Ra as the substrate, when the perpendicular magnetic recording medium of the present invention is used, for example, as a tape for a video recorder, the running properties of the magnetic head are improved and dropouts are eliminated. The center line average roughness (Ra) is based on JIS B-0601 and JIS B
-0651. for example.

The all-purpose surface profile measuring device Surfcom 3B manufactured by Tokyo Seimitsu Co., Ltd. can be used.

The film used in the present invention is preferably 25"C,6
The moisture absorption rate at 5% RH is 2% or less.

More preferably, it is 1.5% or less. In order to reduce the moisture absorption rate of the film, it is effective to increase the heat treatment temperature, but it also depends a little on the stretching ratio of the swollen gel after washing with water. as a special method.

PPTA with hydrophobic comonomers and end-capping agents
It is also preferable to further reduce the moisture absorption rate by using
This is an embodiment. By reducing the moisture absorption rate of the film, workability during vapor deposition and sputtering of the two ferromagnetic layers is improved.

Furthermore, the film used in the present invention is preferably.

The heat shrinkage rate at 250°C is 0.2% or less, more preferably 0.15% or less. Such favorable features are disclosed in Japanese Patent Publication No. 55-51248 and Japanese Patent Publication No. 53-4.
This is something that the copolyamide hydrazide film disclosed in JP-A No. 4957 and the aramid copolymer film disclosed in JP-A-58-168655 do not have. For example, a film with a low heat shrinkage rate is 1.

This is useful because the substrate does not deform during the deposition of the ferromagnetic layer.

The thickness of the film used in the present invention should be appropriately designed according to each application and is not particularly limited, but the thickness that can fully bring out the film's characteristic of high Young's modulus is about 10 μm or less. This applies to thin films of 2 to 7 μm, preferably 2 to 7 μm.

The PPTA film used in the present invention is produced by casting an optically anisotropic dope consisting essentially of PPTA and 95% by weight or more of sulfuric acid onto a supporting surface while maintaining its optical anisotropy, and then absorbing moisture or heating the film. After converting to the optically isotropic state using
It can be obtained by a unique method of biaxially stretching the film to more than double its original size, followed by drying and heat treatment at about 400°C while limiting shrinkage of the film.
This is completely different from the manufacturing method of TA film.

9. Prior to forming the magnetic recording layer described in the next section, the substrate used in the present invention has the following properties:
Various surface treatments and pre-treatments may be performed for the purpose of imparting wear resistance and the like.

In the present invention, a ferromagnetic layer having an axis of easy magnetization perpendicular to the substrate surface is defined as first-order.

The magnetic properties of the ferromagnetic layer can be measured by the vibrating magnetometer method specified in JIS C-2561 or the self-recording magnetometer method.

When used in a magnetic recording medium, the larger the area (S) surrounded by the hysteresis loose obtained by these measurements is, the larger the recording capacity is, and it is suitable for high-density recording.

The area surrounded by hysteresis looseness measured while applying an external magnetic field perpendicularly to the surface of the ferromagnetic layer used as a sample is 81
Let S be the area of the hysteresis loop when an external magnetic field is applied in a direction parallel to the surface of the first ferromagnetic layer. When S is larger than S, it can be said that the magnetic recording medium is suitable for magnetic recording in the perpendicular +1 direction.

In the present invention, a ferromagnetic layer having a magnetization axis in a direction perpendicular to the substrate surface is defined as a ferromagnetic layer having a hysteresis loose area S in response to an external magnetic field perpendicular to the substrate surface, and a hysteresis loose area S in response to an external magnetic field parallel to the substrate surface. The magnetic anisotropy coefficient (S/5II) calculated from the loop area Sll is greater than 160, preferably 1.2 or more, and more preferably 1.4 or more.

In addition, another index that indicates the magnetic anisotropy of a perpendicular magnetic recording medium in the perpendicular direction is the perpendicular anisotropy magnetic field (Hk). I can say that.

The ferromagnetic layer in the present invention is made of a cobalt-based or iron-based compound, and the thickness of the ferromagnetic layer is not particularly limited, but is practically in the range of 0.02 μm to 5 μm,
In consideration of flexibility, head touch, and film formation speed of the ferromagnetic layer, a range of 0.05 μm to 2.0 μm is desirable.

Furthermore, the ferromagnetic layer in the present invention has an axis of easy magnetization in a direction perpendicular to the substrate surface, and is suitable for perpendicular magnetic recording. Even if the materials and compositions are the same, they are not included in the present invention.

Furthermore, the adhesive force between the ferromagnetic layer and the substrate of the present invention is improved.

There is no problem in laminating one or more underlayers for the purpose of improving recording/reproducing characteristics or for other purposes.

The cobalt-based compound in the present invention is Co.

Co-Cr alloy, Co-Ni alloy, Co-Ni
-Fe alloy, Co -Fe alloy, Co oxide (
000 etc.).

and these and trace amounts of P*SieB, Mn
*Refers to alloys with Zn, etc.

In addition, iron-based compounds in the present invention include iron, iron oxides, iron nitrides, iron hydroxides, iron sulfides, iron carbonates, etc. Specifically, iron oxides include FeO, Fetus, etc.
a Fe3O4 etc., and iron nitride is F et
N, Fe, N, etc., and iron hydroxides include Fe(OH)z, Fe(OH)a -Fe0O
Examples of iron ferrous compounds include Fe5sFetSs, and iron carbonate compounds include FeCO5# FeC.
05aH*O, etc. Also.

Also included are non-stoichiometric iron compounds with intermediate compositions other than those described herein.

Also, the atomic percent ratio between iron and other elements is 90 for iron.
% to 30%, and other elements preferably in a range of 10% to 70% in order to improve magnetic properties in the vertical direction.

Also, among iron-based compounds, containing iron oxide improves magnetic properties in the vertical direction.

It is very interesting that it contains iron oxide.

In this case, the atomic percentage ratio of iron and oxygen contained in the ferromagnetic layer is preferably in the range of 90% to 30% iron, 10% to 70% oxygen, furthermore, 80% to 50% iron and 20% oxygen.
A range of % to 50% is more desirable.

Furthermore, in addition to cobalt-based or iron-based compounds, trace amounts of other elements or compounds may not be included in the ferromagnetic layer for the purpose of improving corrosion resistance, abrasion resistance, flexibility, surface roughness, head touch, etc. It may be used as long as it does not impede the effects of the present invention.

The method for forming the perpendicular magnetic recording medium of the present invention is as follows.

Ion blating, sputtering, etc.
It is not necessarily limited to these. An example of a method for manufacturing a perpendicular magnetic recording medium by vapor deposition is shown below.

The equipment used is an unwinding roll in a vacuum chamber.

A long film running system consisting of a cooling drum and a take-up roll is provided, and is located directly below the cooling drum.

This is a semi-continuous electron beam evaporator equipped with an electron beam evaporator with a recessed portion. Inside the device, there is a shielding plate having an opening only in the portion directly below the drum to prevent the evaporated vapor flow having an angle between the evaporated vapor flow and the normal line of the cooling drum, that is, an incident angle exceeding 30 degrees, from entering the substrate. was placed close to the cooling drum.

A PPTA film is placed in the running system of the device, and a ferromagnetic material is placed in the recess of the electron beam evaporator.

First, the inside of the vacuum chamber of the electron beam evaporation equipment was
First, the pressure in the vacuum chamber is reduced by evacuation to Torr, and then a single gas or a mixture of two or more gases such as oxygen gas, nitrogen gas, water vapor, hydrogen sulfide gas, carbon dioxide gas, etc. The perpendicular magnetic recording medium of the present invention is formed by running a PPTA film in air and evaporating iron by electron beam evaporation.

〔Example〕

(Measurement method) Logarithmic viscosity ηinh is determined by adding polymer o to 100 mJ of 98% sulfuric acid.
, sy was dissolved and measured at 30°C in a conventional manner. The viscosity of the dope was measured using a B-type viscometer at a rotation speed of 1 rpm.

The strength and elongation and Young's modulus of the film were measured using a constant speed extension type strength and elongation measuring machine.
Cut a rectangle of ax, draw a load-extension curve 5 times with an initial grip length of 30 mm and a pulling speed of 301 + m/min,
It was calculated from this.

The coefficient of hygroscopic expansion was determined by holding a film sample with a width of 2111 in a thermomechanical analyzer, using a grip length of 8, and a load of 0.1 s kg/xs.
tX, and the ratio of the increment to the initial length of the sample was determined with respect to the change in relative humidity when the humidity was changed from 0% to 90% at 25°C.

Ra was measured by the method described above.

Moisture absorption rate is measured at 25°C from the absolute dry state of the sample.

The ratio of the increase to the initial weight of sample ' when left in an atmosphere of 65% RH is expressed as a percentage.

The heat shrinkage rate is determined by taking a sample to a length of approximately 10 cIrL.

After precisely measuring the length at 25°C and 65% RH.

Put it in the open at 250℃ for 2 hours, take it out and leave it at 25℃
, measured the length after being left in an atmosphere of 65% RH for 2 hours,
The ratio of the decrement to the initial length of the sample is expressed as a percentage.

Measurement of coercive force, saturation magnetization, and magnetic anisotropy coefficient: Using a vibrating sample magnetometer, record the hysteresis looseness when an external magnetic field is applied in the direction perpendicular and parallel to the substrate surface, respectively, and measure the coercive force, Obtain saturation magnetization. In addition, the area surrounded by the hysteresis loose is measured with a plan meter, and the ratio (s, /511) of the area of the loop in the vertical direction (S) and the area of the loop in the parallel direction (SR) is calculated by the magnetic anisotropy. It is taken as the gender coefficient.

Measurement of perpendicular anisotropy magnetic field: Use a vibrating sample magnetometer to obtain the hysteresis looseness when an external magnetic field is applied in a direction parallel to the substrate surface. The strength of the external magnetic field at the intersection of a tangent line drawn from the origin to this hysteresis loop and a straight line drawn parallel to the external magnetic field axis passing through the positive saturation magnetization point is the perpendicular anisotropic magnetic field.

(Manufacturing of PPTA film Inh: 5.50 PPTA polymer was dissolved in 99.7% sulfuric acid at a polymer concentration of 11.5% to obtain a dope with optical anisotropy at 60°C. The viscosity of this dope was determined at room temperature. When measured, it was 10,600 voids.In order to facilitate film formation, this dope was degassed under vacuum while being kept at about 70°C.In this case, it also has optical anisotropy as above, The viscosity was 4400 boids. Passed through a filter from the tank.

The bent tubes of I and SM that go through the gear pump and reach the die are heated to about 70℃.
At a linear velocity of 3.5 m/min from a die with a slit of 0.15 m x 300 H, cast a tantalum bell with a polished surface (moving in 12 m 7 min) at a relative temperature of about 85 The cast dope is made optically isotropic by blowing air at about 90°C, and then heated to -5°C along with the belt.
It was introduced into a 5% by weight aqueous sulfuric acid solution and coagulated. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C, first in a 1% aqueous solution of soda carbonate, and then in water at 25°C.

First, the washed film with a moisture content of 280% is rolled in the longitudinal direction (MD) at room temperature by 1.
Uniaxially stretched to 2 times, then placed in a tenter, stretched to 1.2 times in the width direction (TD) near the entrance, heated to 150'C for a fixed length near the center of the tenter, dried, and then placed in a tenter. Infrared lamps are installed near the exit 4
After heat treatment at 00'C, the long film was rolled up.

The obtained PPTA film has excellent transparency.

It has a thickness of 4.5μm, and 7inh=4.9. Moisture absorption rate: 1.3%2 Strength: 5o±3y/xrx” (variations refer to variations in each direction within the film plane. The same applies hereinafter), elongation: 17±1%, Young's modulus: 1300±+5
0 to 9/d, hygroscopic expansion coefficient (2,3±0.2)
10-'g/depression/%RH, Ra = O, O1μm
, with a heat shrinkage rate of 0.12%.

No curling occurred either after manufacture or during the deposition of the ferromagnetic layer described below.

(Manufacture of perpendicular magnetic recording medium) The inside of the vacuum chamber of a semi-continuous electron beam evaporation apparatus is evacuated by an exhaust system until the pressure reaches I.times.10-s Torr or less.

Next, as an introduced gas, a mixed gas balanced with 20% by volume of oxygen and the balance of nitrogen was introduced through the parisur leak pulp until the pressure in the vacuum chamber reached 2 x 10-' Torr, and the PPTA film described above was heated to about 2 m1. A ferromagnetic layer made of iron and an iron compound and having a thickness of 200 OA was continuously formed by electron beam evaporation. The vacuum chamber of the device is equipped with a film running system consisting of two unwinding rolls, a cooling drum, and a take-up roll, and an electron beam evaporator with a recess directly below the cooling drum is installed to control the flow of evaporated vapor. The angle of incidence on the cooling drum is 16
A shielding plate with an opening such that the temperature is less than 30°C was placed adjacent to the cooling drum. The obtained magnetic recording medium had a perpendicular coercive force of 99006. The perpendicular anisotropy field is 3. 'yxo
These properties hardly changed even if the sample was left open for 8 hours at 160°C.

Further, it was confirmed that the magnetic anisotropy coefficient of the magnetic recording medium before being put into the open state was 2.0, that is, it was larger than 1.0 and had an axis of easy magnetization perpendicular to the substrate surface.

Further, as a result of compositional analysis of the monoferromagnetic layer, it was found that the main component of the ferromagnetic layer was composed of Fe # Fe1031 Fe504*pe (containing OH).

Next, using the same semi-continuous electron beam evaporation apparatus, the above-mentioned PPTA was attached to a running system equipped with a shielding plate having an opening such that the incident angle of the evaporated vapor flow to the cooling drum was 16 degrees or less. Place the film.

With cobalt placed in the recess of the electron beam evaporator,
The vacuum chamber of the vacuum evaporation apparatus is heated to IX 10-' by the exhaust system.
The pressure inside the vacuum chamber is 3.
In the atmosphere introduced until it reached X 10” Torr,
While the PPTA film was running at a speed of about 3 m/min, a ferromagnetic layer made of cobalt and cobalt oxide with a thickness of about 180 OA was deposited on the PP by electron beam evaporation.
It was formed on a TA film. Its perpendicular coercive force was 10,100e, perpendicular anisotropy magnetic field was 4.7 KOe, magnetic anisotropy coefficient was 1.7, and it was a perpendicular magnetic recording medium with an axis of easy magnetization perpendicular to the substrate surface. .

Moreover, it was confirmed as a result of analysis that the first ferromagnetic layer mainly contains CO and CoO.

〔Effect of the invention〕

The perpendicular magnetic recording medium of the present invention has excellent substrate pressure, light weight, and heat resistance, and has a high Young's modulus and a small coefficient of hygroscopic expansion.
In addition, since a PPTA film with the necessary elongation is used, there is no deterioration even in high-temperature KIIB during production or use, and there is little dimensional change due to humidity or external force, resulting in high quality. In particular, when using a thin substrate film, these characteristics are exhibited, and a high-quality, high-performance perpendicular magnetic recording medium can be provided.

Because of these characteristics, the perpendicular magnetic recording medium of the present invention has the following advantages:
In particular, perpendicular magnetic recording type video tapes are particularly useful, as well as perpendicular magnetic recording type fluoro, tubi disks, and recordable/erasable digital audio disks.
Suitable for digital audio tape isobaric.

Patented wheat flour Asahi Kasei Industries Co., Ltd.

Claims (1)

[Claims] Young's modulus in any direction parallel to the film surface is 1000k
g/mm^2 or more, an elongation of 10% or more, and a hygroscopic expansion coefficient of 3 x 10^-^5 mm/mm/%RH or less, on a film consisting essentially of poly-P-phenylene terephthalamide. A perpendicular magnetic recording medium comprising a ferromagnetic layer having an axis of easy magnetization perpendicular to the film surface and comprising a cobalt-based or iron-based compound.