JPH08180367A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a medium excellent in durability even under repetitive running conditions by prescribing the creep of a substrate film in the longitudinal direction and the hardness while making use of the superior heat resistance and high rigidity of arom. polyamide or arom. polyimide. CONSTITUTION: A magnetic layer is formed on one side of a substrate film made of arom. polyamide or arom. polyimide to obtain the objective magnetic recording medium. The creep of the substrate film in the longitudinal direction is <=0.5% and the hardness is >=20. The height of fine protrusions on one side of the substrate film is 0.003-0.2μm and the number of coarse protrusions on the surface is <=100 per 100cm<2> . Since the substrate film made of arom. polyamide or arom. polyimide excellent in heat resistance and mechanical characteristics and having the prescribed creep and hardness is used, the resultant magnetic recording medium is excellent in electromagnetic transducing characteristics, durability and running performance under repetitive running or high frequency of stop-start.

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.

[0002]

2. Description of the Related Art Aromatic polyamide films or aromatic polyimide films have been investigated for various applications by taking advantage of their excellent heat resistance and mechanical properties. In particular, para-oriented aromatic polyamide is superior to other polymers in mechanical properties such as rigidity and strength, so it is very advantageous for thinning the film, and is expected to be used for printer ribbons, magnetic tapes, capacitors, etc. ing. For example, in the case of magnetic recording media, JP-A-58-168655 and JP-A-62-112.
No. 218, for example.

[0003]

In recent years, with the miniaturization of magnetic recording media and the rapid increase in recording capacity, there has been a demand for a thinner base film and improved surface characteristics than ever before.
In particular, magnetic tapes used for backup of computers, which have shown rapid growth in demand in recent years, are required to have very high reliability, and thus these requirements are strong.

However, in such an application, it is used in a severer environment than before, such as high temperature, repeated running, and frequent stop / start. For this reason, there are problems that the durability is poor, the drivability and electromagnetic conversion characteristics are deteriorated, and that dropout occurs during repeated running. It is considered that this is because the base film has insufficient tensile strength and heat resistance, and also has insufficient surface property and running property.

The present invention solves the above problems, makes full use of the excellent heat resistance and high rigidity of aromatic polyamide or aromatic polyimide, and defines the creep and hardness in the longitudinal direction of the base film, so that it can be repeatedly run. It is an object of the present invention to provide a magnetic recording medium excellent in durability and electromagnetic conversion characteristics even under severe conditions.

[0006]

The present invention is a magnetic recording medium comprising a base film made of an aromatic polyamide or an aromatic polyimide and a magnetic layer provided on one side of the base film. The magnetic recording medium has a hardness of 5% or less and a hardness of 20 or more.

The aromatic polyamide of the present invention preferably contains 50 mol% or more of repeating units represented by the following general formula (I) and / or general formula (II), and is composed of 70 mol% or more. Is more preferable.

General formula (I)

Embedded image General formula (II)

Embedded image Here, Ar ₁ , Ar ₂ and Ar ₃ are, for example,

Embedded image And the like, X and Y are —O—, —CH ₂ —, —CO—, —SO ₂ —, —S—,
-C (CH _{3) 2} - is chosen from such, but is not limited thereto. Further, a part of hydrogen atoms on these aromatic rings is a substituent such as a halogen group (especially chlorine), a nitro group, a C ₁ -C ₃ alkyl group (especially a methyl group), a C ₁ -C ₃ alkoxy group and the like. And those in which hydrogen in the amide bond constituting the polymer is replaced by another substituent.

From the viewpoint of characteristics, the above-mentioned aromatic ring bonded in the para position is 50% or more, preferably 75% or more of the total aromatic ring.
% Of the polymer is preferable because the creep property of the film is improved, and the rigidity and heat resistance are improved. Also, some of the hydrogen atoms on the aromatic ring are halogen groups (especially chlorine).
It is preferable that the aromatic ring substituted by 30% or more of the entire aromatic ring has improved moisture resistance and improved properties such as dimensional change due to moisture absorption and rigidity reduction.

The aromatic polyamide of the present invention contains the repeating unit represented by the general formula (I) and / or the general formula (II) in an amount of 50 mol% or more, and 50 mol% or more.
If it is less than the above, other repeating units may be copolymerized or blended.

The aromatic polyimide in the present invention is one having one or more aromatic rings and imide rings in the repeating unit of the polymer and is represented by the general formula (III) and / or the general formula (IV). The content of repeating units is preferably 50 mol% or more, more preferably 70 mol% or more.

General formula (III)

[Chemical 4] General formula (IV)

Embedded image Here, Ar ₄ and Ar ₆ include at least one aromatic ring, and two carbonyl groups forming an imide ring are bonded to adjacent carbon atoms on the aromatic ring. This Ar ₄ is derived from an aromatic tetracarboxylic acid or its anhydride.
The following are typical examples.

[0013]

[Chemical 6] Wherein Z is _{-O -, - CH 2 -,} - CO -, - SO 2 -, - S-,
-C (CH _{3) 2} - is chosen from such, but is not limited thereto.

Ar ₆ is derived from carboxylic acid anhydride or its halide. Ar ₅ and Ar ₇ are, for example,

[Chemical 7] And the like, X and Y are —O—, —CH ₂ —, —CO—, —SO ₂ —, —S—,
-C (CH _{3) 2} - is chosen from such, but is not limited thereto. Further, a part of hydrogen atoms on these aromatic rings is a substituent such as a halogen group (especially chlorine), a nitro group, a C ₁ -C ₃ alkyl group (especially a methyl group), a C ₁ -C ₃ alkoxy group and the like. And those in which hydrogen in the amide bond constituting the polymer is replaced by another substituent.

The aromatic polyimide of the present invention has the general formula (II
I) and / or the repeating unit represented by the general formula (IV) is contained in an amount of 50 mol% or more, and less than 50 mol% may be copolymerized or blended with another repeating unit. .

Further, the aromatic polyamide or aromatic polyimide of the present invention may be blended with additives such as an antioxidant, etc., to the extent that the physical properties of the film are not impaired.

The magnetic recording medium of the present invention requires that the creep of the base film in the longitudinal direction is 0.5% or less. It is more preferably 0.3% or less, still more preferably 0.15% or less. If the creep is greater than 0.5%, repeated running under tension or dimensional changes that cannot be recovered due to running / stopping will result in deterioration of electromagnetic conversion characteristics such as data damage, and wrinkles or tears in the width direction. Therefore, it becomes impossible to exhibit a good function as a magnetic recording medium.

Furthermore, in the magnetic recording medium of the present invention, the hardness of the base film must be 20 or more. It is more preferably 25 or more, still more preferably 30 or more. Hardness 2
When it is less than 0, when a roll-shaped magnetic recording medium is used,
The unevenness of the tape surface contacting the front and back surfaces is transferred to increase the spacing loss with the magnetic head, which increases the dropout. In addition, scratch resistance and abrasion resistance are insufficient, so that scratches and abrasion occur in the film processing step, which is not preferable.

In the magnetic recording medium of the present invention, the height of fine projections on at least one side of the base film is 0.003 to.
It is preferably 0.2 μm. When the height of the fine protrusions is within this range, a magnetic recording medium having a good head touch and excellent output characteristics can be obtained. Preferably 0.00
5 to 0.1 μm, more preferably 0.005 to
It is 0.07 μm.

In the magnetic recording medium of the present invention, the number of surface coarse protrusions on at least one side of the base film is 100 /
It is preferably 100 cm ² or less. When the number of coarse surface protrusions is within this range, an excellent magnetic recording medium without dropout can be obtained without impairing good running properties. The number is preferably 50/100 cm ² or less, and more preferably 30/100 cm ² or less.

The present invention is a magnetic recording medium in which a magnetic layer is provided on one surface of the base film. The method for forming the magnetic layer includes a wet method in which a ferromagnetic powder is used as a magnetic paint using various binders and applied on a base film, a vapor deposition method, a sputtering method, a dry method such as an ion plating method, and is not particularly limited. Although not limited to this, the wet method will be described here as an example.

The type of magnetic powder used as a magnetic material is not particularly limited, but ferromagnetic powder such as iron oxide, chromium oxide,
Fe, Co, Fe-Co, Fe-Co-Ni, Co-N
i and the like are preferably used.

The magnetic powder can be made into a magnetic paint by using various binders, but thermosetting resin binders and radiation curing binders are preferable, and other additives such as dispersants, lubricants and antistatic agents are used. May be.
For example, a binder composed of a vinyl chloride / vinyl acetate / vinyl alcohol copolymer, a polyurethane prepolymer and a polyisocyanate can be used.

In order for the magnetic recording medium of the present invention to have the desired roughness as described above, it is preferable that particles are present in the base film. The types of particles are Si
O ₂ , TiO ₂ , Al ₂ O ₃ , CaSO ₄ , BaS
There are inorganic particles such as O ₄ , CaCO ₃ , carbon black, zeolite, and other fine metal powders, and organic polymers such as silicon particles, polyimide particles, crosslinked copolymer particles, crosslinked polyester particles, and Teflon particles. However, it is preferable to add particles having a Mohs hardness of 5 or more from the viewpoint of improving the hardness of the film and durability. If the particles to be added are monodisperse particles or agglomerated particles, the degree of agglomeration is 100 or less, preferably 50 or less. If the aggregation degree exceeds 100, a portion where the particle concentration is extremely low is partially formed, and the hardness may not be improved, or the particles may drop out due to a decrease in the affinity of the aggregated particles with the polymer. In addition, inorganic particles are preferable in terms of durability and heat resistance. Furthermore, the average primary particle size of the particles contained in the film of the present invention is 0.005 to 5 μm, preferably 0.01 to 5 μm.
When the thickness is in the range of 2 μm, the electromagnetic conversion characteristics and the running property are good, which is desirable. The content of particles contained in the base film of the magnetic recording medium of the present invention is 0.01 to 5 wt.
%, Preferably 0.05 to 3 wt%. If the content of the particles is less than the above range, the hardness and running property of the film are likely to be poor, and conversely if the content is large, the electromagnetic conversion characteristics are likely to be poor.

The magnetic recording medium of the present invention may be used not only as a base film but also as a single layer film, but may be a laminated film. The surface on which the magnetic layer is provided is not particularly limited, but in the case of a single layer film, the fine protrusion height is 0.003 to
0.2 μm, the number of rough surface protrusions is 100/100 cm
It is desirable to provide it on the surface of ² or less because the electromagnetic conversion characteristics will be good. Also in the case of a laminated film, the surface on which the magnetic layer is provided is not particularly limited, but the height of the fine protrusions is 0.003.
~ 0.2μm, the number of rough surface protrusions is 100 / 100c
It is desirable to laminate so as to be provided on the surface of m ² or less. The base film of the magnetic recording medium of the present invention laminated here and the base layer portion (film constituting portion other than the laminated base film of the present invention) may be the same kind or different. You may also contain particles in at least one layer constituting the base layer portion, the type of particles, the average primary particle size of the particles,
It is desirable to use the content which is desirably used in the film of the present invention. When the diameter of the particles in the base layer portion is larger than the diameter of the particles in the laminated base material film of the present invention, it is possible to impart an appropriate waviness to the base material film surface and further improve tape running property. Is desirable.

The substrate film of the magnetic recording medium of the present invention preferably has a Young's modulus in at least one direction of 800 kg / mm ² or more, more preferably 900 kg / mm ² or more,
More preferably, it is 1000 kg / mm ² or more. When the Young's modulus is within this range, when a thin film magnetic recording medium is used,
It is possible to compensate for the lowering of waist strength due to thinning.

The base film of the magnetic recording medium of the present invention may be tensified in the longitudinal direction or in the width direction as long as the Young's modulus is satisfied. There is no particular limitation on the degree of tensioning, but considering the characteristics such as elongation and tear resistance, Young's modulus EMD in the longitudinal direction and Young's modulus ETD in the width direction are 0.5 ≦ E.
It is practical that MD / ETD ≦ 2.0.

The thickness of the substrate film in the magnetic recording medium of the present invention is preferably 0.5 to 50 μm, more preferably 1 to 20 μm, and further preferably 2 to 10 μm, as a thin film magnetic recording medium of the present invention. It is desirable because excellent running performance and electromagnetic conversion characteristics that are the effects are realized.

The heat shrinkage ratio of the base film in the magnetic recording medium of the present invention at 200 ° C. for 10 minutes is preferably 5% or less, and more preferably 2% or less, the dimensional change of the tape due to temperature change is small and good. It is desirable because it can maintain excellent electromagnetic conversion characteristics.

The elongation of the substrate film in the magnetic recording medium of the present invention is preferably 10% or more, more preferably 20% or more, further preferably 30% or more, since the tape has appropriate flexibility.

When the moisture absorption rate of the substrate film in the magnetic recording medium of the present invention is 5% or less, more preferably 3% or less, even more preferably 2% or less, the dimensional change of the tape due to humidity change is small and good electromagnetic properties are obtained. It is desirable because the conversion characteristics can be maintained.

It is preferable that these characteristics are also satisfied in the laminated film when laminated.

Next, the manufacturing method of the present invention will be explained, but the present invention is not limited to this.

First, an aromatic polyamide, but when it is obtained from an acid chloride and a diamine, it is used in an aprotic organic polar solvent such as N-methylpyrrolidone (NMP), dimethylacetamide (DMAc) or dimethylformamide (DMF). , Solution polymerization or interfacial polymerization using an aqueous medium. When acid chloride and diamine are used as monomers in the polymer solution, hydrogen chloride is by-produced.When neutralizing this, inorganic neutralizing agents such as calcium hydroxide, calcium carbonate and lithium carbonate, and ethylene Oxide, propylene oxide, ammonia,
Organic neutralizing agents such as triethylamine, triethanolamine, diethanolamine are used. The reaction between isocyanate and carboxylic acid is carried out in the presence of a catalyst in an aprotic organic polar solvent.

These polymer solutions may be directly used as a film forming stock solution, or the polymer may be isolated once and then redissolved in the above organic solvent or an inorganic solvent such as sulfuric acid to prepare a film forming stock solution. Good.

In order to obtain the aromatic polyamide film of the present invention, the intrinsic viscosity of the polymer (value measured at 30 ° C. in a solution of 0.5 g of polymer in 100 ml of sulfuric acid) is 0.
It is preferably 5 or more.

Inorganic salts such as calcium chloride, magnesium chloride, lithium chloride and lithium nitrate may be added as a dissolution aid to the stock solution for film formation. The polymer concentration in the stock solution for film formation is preferably about 2 to 40 wt%.

On the other hand, a solution of aromatic polyimide or polyamic acid is obtained as follows. That is, polyamic acid is N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DM).
It can be prepared by reacting a tetracarboxylic acid dihydrate with an aromatic diamine in an aprotic organic polar solvent such as F). The aromatic polyimide can be prepared by heating a solution containing the above polyamic acid or adding an imidizing agent such as pyridine to obtain a polyimide powder, which is dissolved again in a solvent. Polymer concentration in the film forming solution is 5
About 40 wt% is preferable.

The method for adding particles includes a method in which the particles are sufficiently slurried in a solvent in advance and then used as a solvent for polymerization or a solvent for dilution, and a method in which they are directly added after preparing a film-forming stock solution.

The stock solution for film formation prepared as described above is formed into a film by a so-called solution film forming method. The solution film-forming method may be a dry-wet method, a dry method, a wet method, or the like, and the film may be formed by any method, but here, the dry-wet method will be described as an example.

When a film is formed by a dry-wet method, the stock solution is extruded from a spinneret onto a support such as a drum or an endless belt to form a thin film, and then the solvent is scattered from the thin film layer until the thin film has a self-holding property. To do. Drying conditions are room temperature to the boiling point of the solvent + 20 ° C., within a range of 60 minutes, and preferably room temperature to the boiling point of the solvent. When the drying temperature exceeds the boiling point of the solvent + 20 ° C., the film surface may be roughened due to the rapid evaporation of the solvent to increase rough surface protrusions, or the surface layer may become brittle, resulting in a large decrease in hardness.

After the dry process, the film is peeled from the support and introduced into the wet process, desalting, desolventizing, etc. are carried out in the same manner as the above-mentioned wet process, and further stretching, drying and heat treatment are carried out. Becomes

The heat treatment is performed at 240 to 450 ° C. for 1 minute or more and 60 minutes.
Hardness, creep characteristics, mechanical characteristics,
It is preferable in terms of compatibility with other physical properties such as moisture absorption characteristics. If the heat treatment is below this range, the hardness, creep properties and moisture absorption properties will be reduced, and sufficient mechanical properties will not be obtained. On the other hand, if it is in this range or more, the film becomes brittle and is not suitable for practical use even if hardness, creep properties and moisture absorption properties are satisfied.
More preferably, it is 1 minute or more and 30 minutes or less at 260 ° C to 400 ° C.

The film formed as described above may be stretched for the purpose of improving creep properties and mechanical properties during the film forming process. The draw ratio is 0.8-5.0 in terms of area ratio (the area ratio is defined as a value obtained by dividing the film area after drawing by the area of the film before drawing. 1 or less means relaxing). Is preferable from the viewpoint of creep characteristics and mechanical characteristics, and more preferably 1.1 to 3.5. Mechanical properties of less than 0.8,
The flatness of the film may be deteriorated and the creep characteristics may be deteriorated. If it exceeds 5.0, the film becomes brittle and may not be suitable for practical use as a magnetic material. Further, slow cooling of the film after heat treatment is effective in forming a smooth surface, and cooling at a rate of 50 ° C./sec or less is effective.

Further, during slow cooling, 0.9 to 0.9 in the longitudinal direction.
By applying a relaxation of 9, preferably 0.93 to 0.97 times, the residual stress of the heat-treated film is relaxed, which is effective for improving the creep characteristics.

The film of the present invention may be a laminated film. For example, in the case of two layers, the polymerized aromatic polyamide solution is divided into two, and different particles are added, respectively, and then laminated. The same applies to the case of three or more layers.
As a method of stacking these, there are known methods such as stacking in a die, stacking in a composite tube, and a method in which one layer is once formed and then another layer is formed thereon.

Next, a magnetic layer is formed on this film. The magnetic layer forming method may be either a coating method or a vapor deposition method, but the coating method will be described here as an example. The method for applying the magnetic layer can be performed by a known method, but a method using a gravure roll is more preferable in terms of the uniformity of the coating film. The drying temperature after coating is preferably 90 ° C to 150 ° C. The calendering step is preferably performed in the range of 25 ° C to 150 ° C.

Thereafter, a back coat layer may be provided on the surface opposite to the magnetic layer by a known method in order to further improve the running property.

Further, the film coated with the magnetic layer is cured and then slit to obtain the magnetic recording medium of the present invention.

As the magnetic recording medium, particularly for consumer use of 8 mm or the like, for professional use, for broadcasting of D-1, 2, 3, etc., DDS
-2, 3, 4, QIC, data of 8 mm, etc. are particularly preferably used.

[0051]

EXAMPLES The methods of measuring physical properties and evaluating effects of the present invention are as follows.

(1) Creep property A film is sampled in a strip shape and the elongation under a load of 2.9 kg / mm ² is measured by TMA. The measurement is 25 ℃,
Creep (%) was obtained by multiplying by 100 under the condition of 60% RH, elongation after 30 minutes from the start of measurement divided by sample length, and multiplying by 100.

(2) Hardness The hardness was measured by a Vickers hardness meter according to JIS B-7734. However, the measurement load was 35 g, and the film thinner than 20 μm was stacked and measured so as to have a thickness exceeding 20 μm. In order to make the surface of the film easy to see, 100-150 nm of aluminum was vapor-deposited and measured.

(3) Number of coarse surface projections Foreign matter is observed and marked in a range of 100 cm ² of the film surface under polarized light with a stereoscopic microscope. The height of the marked foreign matter was observed using a multiple interferometer at a wavelength of 546 nm, and the number of interference fringes having a single ring or more was defined as the number of surface coarse protrusions.

(4) Fine protrusion height Using a thin film level difference measuring instrument (ET-10) manufactured by Kosaka Laboratory, stylus radius 0.5 μm, load 4 mg, cutoff value 0.0
Under the condition of 8 mm, the surface roughness direction is enlarged by 500,000 times and the chart is stretched to find the highest peak height for the portion corresponding to the film length of 25 μm of the cross-section curve, and similarly, it corresponds to any film length of 25 μm The height of the highest mountain in the part to be filled is shown as an average value of 10 points obtained in total.

(5) Young's modulus The Young's modulus was measured using an Instron type tensile tester. The test piece is 10 mm wide and 50 mm long, and the pulling speed is 300 mm / min.

(6) Moisture Absorption Rate The film was dried at 200 ° C. for 1 hour, and the weight in an absolutely dry state was taken as W 0. The film was dried at 20 ° C. and a relative humidity of 75% for 4 hours.
Weight after moisture absorption for 8 hours is W1 (W1-W0) / W0
The moisture absorption rate (%) was expressed by a value obtained by multiplying by 100.

(7) Electromagnetic conversion characteristics The film coated with the magnetic layer was slit into a 1/2 inch width and incorporated into a VTR cassette to obtain a VTR tape. Record on this tape using a home VTR, 40 ° C 80R
The number of white spots (dropouts) appearing on the TV screen when reproduced under the condition of H% was evaluated according to the following criteria. ○
The above is good.

0.5 or less ◎ 0.5 or more and 1.0 or less ○ 1.0 or more and 2.0 or less △ over 2.0 × (8) Runnability A film having a width of 1/2 inch Using a tape running tester SFT-700 type (manufactured by Yokohama System Laboratory Co., Ltd.), the slits were run in an atmosphere of 40 ° C and 80% RH, and the friction coefficient was calculated from the following formula. .

ΜK = 0,733 log (T2 / T1) where T1 is the inlet tension and T2 is the outlet tension. The guide diameter is 6 mmφ, the guide material is polyoxymethylene (with a surface roughness of about 20-40 nm), and the winding angle is 9
0 °, the running speed is 3.3 cm / sec, and the repeating stroke is 15 cm. The difference ΔμK between the friction coefficient of the first pass and the friction coefficient of the 50th pass obtained by this measurement was obtained and evaluated according to the following criteria. ○ The above is good.

Not more than 0.05 ◎ Not less than 0.05 and not more than 0.15 ○ Not less than 0.15 and not more than 0.25 △ Not more than 0.25 × (9) Durability A VTR cassette similar to (7) was prepared. , 40 ° C 80R
The number of white spots (dropouts) on the screen after 100 times of repeated running at H% was evaluated according to the following criteria.

0.2 or less ◎ 0.2 or more and 0.5 or less ○ 0.5 or more and 1.0 or less △ ≥ 1.0 or more × The present invention will be described based on examples below. It is not limited.

Example 1 N-methylpyrrolidone (NMP) was mixed with 80 mol% of 2-chloroparaphenylenediamine as an aromatic diamine component and 20 mol% of 4,4-diaminodiphenyl ether. Dissolve and add 100 mol% of 2-chloroterephthalic acid chloride to this,
The polymerization was completed by stirring for a period of time. This was neutralized with lithium hydroxide to obtain an aromatic polyamide solution having a polymer concentration of 10% by weight and a viscosity of 3000 poise. To this solution, dry silica having a primary particle size of 16 nm was dispersed in NMP, and 2 wt% was added to the polymer.

This polymer solution was passed through a 5 μm-cut filter and then cast on an endless belt at 180 ° C.
The film was heated for 2 minutes with hot air to evaporate the solvent, and the self-supporting film was continuously peeled from the belt. Next is NM
The film was introduced into a water tank having a P concentration gradient, and the residual solvent and the inorganic salt generated by neutralization were extracted with water.
Then, water was dried and heat treatment was performed to obtain an aromatic polyamide film having a thickness of 6 μm. In the meantime, the film was stretched 1.2 times and 1.3 times in the longitudinal direction and the width direction, respectively, to obtain 280
After drying and heat treatment at 1.5 ° C. for 1.5 minutes, the film was gradually cooled at a rate of 20 ° C./sec while relaxing 0.97 times in the longitudinal direction due to the difference in speed between the tenter and winding.

The creep of this film was 0.06%, the hardness was 34, the height of fine projections on the surface opposite to the belt (hereinafter A surface) was 60 nm, and the number of coarse surface projections was 15 pieces / 100 cm.
^{Was 2} .

Next, the runnability, electromagnetic conversion characteristics, and durability of the magnetic tape using this film were measured and found to be good.

Example 2 A polymer having the same composition as in Example 1 except that silica was contained in an amount of 1 wt% was formed in the same manner as in Example 1 to obtain a 6 μm film.

The creep of this film was 0.06%, the hardness was 30, the height of fine protrusions on the A-side was 10 nm, and the number of coarse surface protrusions was 9/100 cm ² .

Next, the runnability, electromagnetic conversion characteristics, and durability of the magnetic tape using this film were measured and found to be good.

Example 3 Using the polymer used in Example 1, the drying temperature was 220 ° C.
A film having a thickness of 6 μm was obtained in the same manner as in Example 1 except that the above was used.

The creep of this film was 0.06%, the hardness was 28, the height of fine projections on the A-side was 70 nm, and the number of coarse surface projections was 55/100 cm ² .

Next, the runnability, electromagnetic conversion characteristics, and durability of the magnetic tape using this film were measured and found to be good.

Example 4 Using the polymer used in Example 2, the stretching ratio is 1.0 times in the longitudinal direction, 1.1 times in the width direction, and the heat treatment temperature is 250 ° C.
The film was formed in the same manner as in Example 1 except that the time was 1 minute, and the thickness was 6 μm.
Was obtained.

The creep of this film was 0.25%, the hardness was 24, the height of fine projections on the A-side was 20 nm, and the number of coarse surface projections was 12/100 cm ² .

Next, the runnability, electromagnetic conversion characteristics, and durability of the magnetic tape using this film were measured and found to be good.

Example 5 100 mol% of 2-chloroparaphenylenediamine corresponding to 100 mol% was dissolved in NMP as an aromatic diamine component, and 100 mol% of 3,3 ', 4,4'-biphenyltetracarboxylic acid corresponding thereto was dissolved. An acid dianhydride was added and polymerized to obtain a polyamic acid solution. To this solution, 2 wt% per polymer was added after dispersion in dry silica NMP having a temporary particle size of 16 μm.

This polymer solution was passed through a 5 μm-cut filter and then cast on an endless belt at 150 ° C.
It was dried with hot air until it was self-retaining and continuously peeled from the belt. Next, after heat treatment was performed with a tenter at 420 ° C., it was gradually cooled at a rate of 20 ° C./sec while relaxing in the longitudinal direction as in Example 1. Stretch ratio is MD, TD
Both were 1.1 times and the thickness was 6 μm.

The creep of this film was 0.08%, the hardness was 27, the height of the fine projections on the A-side was 60 nm, and the number of coarse surface projections was 27/100 cm ² .

Next, the runnability, electromagnetic conversion characteristics, and durability of the magnetic tape using this film were measured and found to be good.

Comparative Example 1 Using the polymer used in Example 2, the heat treatment temperature was set to 230.
A film having a thickness of 6 μm was obtained in the same manner as in Example 1 except that the temperature was adjusted to 0 ° C. and the temperature was not relaxed during slow cooling.

The creep of this film was 0.15%, the hardness was 18, the height of fine projections on the A surface was 15 nm, and the number of coarse surface projections was 15/100 cm ² .

Next, the running property, electromagnetic conversion property, and durability of the magnetic tape using this film were measured and found to be poor.

Comparative Example 2 A polymer was prepared in the same manner as in Example 2 except that the same silica as in Example 1 was used without dispersion, and a film was formed in the same manner as in Example 2 to obtain a 6 μm film. .

The creep of this film was 0.17%, the hardness was 16, the height of fine projections on the A surface was 130 nm, and the number of coarse surface projections was 140/100 cm ² .

Next, the running properties, electromagnetic conversion characteristics, and durability of magnetic tapes using this film were measured and found to be poor.

Comparative Example 3 4,4-diaminodiphenylmethane corresponding to 100 mol% as an aromatic diamine component was dissolved in N-methylpyrrolidone (NMP), and 100 mol% of isophthalic chloride was added thereto. Polymerization was completed by stirring for 2 hours. This was neutralized with lithium hydroxide to obtain an aromatic polyamide solution having a polymer concentration of 10% by weight and a viscosity of 3000 poise. To this solution, dry silica having a primary particle size of 16 nm was dispersed in NMP, and 1 wt% was added to the polymer.

Using this polymer solution, an aromatic polyamide film having a thickness of 6 μm was obtained in the same manner as in Example 1.

The creep of this film was 0.65%, the hardness was 20, the height of fine projections on the A-side was 20 nm, and the number of coarse surface projections was 14/100 cm ² .

Next, the running property, electromagnetic conversion property, and durability of the magnetic tape using this film were measured and found to be poor.

[0090]

[Table 1]

[0091]

INDUSTRIAL APPLICABILITY The present invention uses a base film made of aromatic polyamide or aromatic polyimide having excellent heat resistance and mechanical properties, and by defining creep and hardness in the longitudinal direction of the base film, The magnetic recording medium is excellent in electromagnetic conversion characteristics, durability, and running property under high frequency of repeated running and stop / start. Further, by defining the surface property of the base film, a more excellent magnetic recording medium can be obtained.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a base film made of aromatic polyamide or aromatic polyimide and a magnetic layer provided on one side thereof, wherein the base film has a longitudinal creep of 0.5% or less and a hardness. Is 20 or more. 2. The substrate according to claim 1, wherein the height of fine projections on at least one side of the base film is 0.003 to 0.2 μm, and the number of coarse surface projections is 100 pieces / 100 cm ² or less. Magnetic recording medium.