JP3000925B2 - Film made of aromatic polyamide or aromatic polyimide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film made of an aromatic polyamide film or an aromatic polyimide film having a good slit property and mainly useful as a support for a magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, a magnetic recording medium having an oxide-coated magnetic layer or a metal-coated magnetic layer provided on a polymer film support has been used (see, for example, Japanese Patent Application Laid-Open No. Sho 61). -26933, JP-A-60-663
No. 19). As a support for these magnetic recording media, a polyester film is mainly used. In recent years, the use of a thinner film for the support film has been promoted due to a higher density, a smaller size, and a longer recording time of the magnetic recording medium. Demands are becoming stronger.

[0003] In the case of a polyester film which has been conventionally used as a support for a magnetic recording medium, the thinner the film, the lower the modulus of elasticity, the worse the head touch and the problem of reduced output. . For this purpose, it has been proposed to use aromatic polyamide or aromatic polyimide having high heat resistance and high elastic modulus (for example, JP-A-58-168655 and JP-A-62-62424).

[0004]

A magnetic recording medium (magnetic tape) is produced by applying or depositing a magnetic substance on a support film and then slitting it to a predetermined width. The yield in the slitting step is an important step because it greatly affects the productivity of the product, but when manufacturing a magnetic tape using a high elastic modulus aromatic polyamide film or aromatic polyimide film as a support, Often, the life of the slitting cutter is shortened, or a so-called "high edge" occurs in which a cut portion (edge) of the tape bulges. When a high edge occurs, the tape (pancake) wound by slitting may break, or the film may tear from the cutting edge in the slit direction, causing the film width to become inconsistent and leading to poor winding appearance such as end face deviation. The problem is that the yield is deteriorated.

An object of the present invention is to solve such a problem and to provide a film made of an aromatic polyamide film or an aromatic polyimide which has a good slit property and is mainly useful as a base film of a magnetic recording medium.

[0006]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that, if a film made of aromatic polyamide or aromatic polyimide having a specific range of refractive index is used,
The present inventors have found that it is possible to obtain a good magnetic recording medium which has solved the above-mentioned problems, and have reached the present invention. That is, according to the present invention, the refractive index nz in the thickness direction ≧ 1.50, and the refractive indexes nx and ny in the longitudinal direction and the width direction are 0.2 ≦ (nx−nz) ≦
A film made of an aromatic polyamide or an aromatic polyimide, satisfying both 0.55 and 0.2 ≦ (ny−nz) ≦ 0.55, and having a moisture absorption of 4.0% or less, I do.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The aromatic polyamide of the present invention is
Those containing 50 mol% or more of a repeating unit represented by the following general formula (I) and / or general formula (II) are preferable,
Those composed of 70 mol% or more are more preferred.

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, Y is _{-O -, - CH 2 -,} - CO
_{-, - SO 2 -, -} S -, - C (CH 3) 2 - is chosen from such, but is not limited thereto. Further, some of the hydrogen atoms on these aromatic rings may be substituted with alkyl groups (particularly methyl groups) such as halogen groups (particularly chlorine), nitro groups, methyl groups, ethyl groups, and propyl groups, methoxy groups, ethoxy groups, and propoxy groups. And the like, and those in which the hydrogen in the amide bond constituting the polymer is substituted by another substituent.

[0009] From the viewpoint of properties, those in which the above aromatic rings are bonded at the para position account for at least 50%, preferably 75%, of the total aromatic rings.
% Of the polymer is preferable because the film is easily oriented in the plane and the refractive index in the longitudinal direction and the width direction is increased. When the aromatic ring in which a part of the hydrogen atoms on the aromatic ring is substituted with a halogen group (particularly chlorine) is at least 30%, preferably at least 50%, more preferably at least 70%, the moisture absorption is low. Is preferred.

The aromatic polyamide of the present invention contains at least 50 mol% of the repeating unit represented by the general formula (I) and / or the general formula (II).
If less than, other repeating units may be copolymerized or blended.

The aromatic polyimide in the present invention is a polymer containing one or more aromatic rings and imide rings in the repeating unit of the polymer and represented by the general formula (III) and / or the general formula (IV). Those containing a repeating unit in an amount of 50 mol% or more are preferable, and more preferably 70 mol% or more.

General formula (III)

Embedded image General formula (IV)

Embedded image Here, Ar ₄ and Ar _{6 each} 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 Ar4 is derived from an aromatic tetracarboxylic acid or its anhydride.
The following are typical examples.

[0013]

Embedded image Wherein Z is _{-O -, - CH 2 -,} - CO -, - SO
_{2 -, - S -, -} C (CH 3) 2 - is chosen from such,
It is not limited to this.

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

Embedded image And the like, X, Y is _{-O -, - CH 2 -,} - CO
_{-, - SO 2 -, -} S -, - C (CH 3) 2 - is chosen from such, but is not limited thereto. Further, some of the hydrogen atoms on these aromatic rings may be substituted with alkyl groups (particularly methyl groups) such as halogen groups (particularly chlorine), nitro groups, methyl groups, ethyl groups, and propyl groups, methoxy groups, ethoxy groups, and propoxy groups. And the like, and those in which the hydrogen in the amide bond constituting the polymer is substituted by another substituent.

The aromatic polyimide of the present invention has the general formula (II)
It contains at least 50 mol% of the repeating unit represented by I) and / or general formula (IV), and less than 50 mol% may be copolymerized or blended with another repeating unit. .

The aromatic polyamide and the aromatic polyimide of the present invention may be blended with a lubricant, an antioxidant and other additives to such an extent that the physical properties of the film are not impaired.

In the present invention, in order to have a good slit property which does not cause deterioration of the winding shape, it is necessary to use a longitudinal direction, a width direction,
The refractive index nx, ny, nz in the thickness direction is such that nz ≧ 1.5
0, 0.2 ≦ (nx−nz) ≦ 0.55, 0.2 ≦ (n
y−nz) ≦ 0.55. When the refractive index is within this range, a good balance between the in-plane direction and the refractive index in the thickness direction is obtained, and good slit properties are exhibited. nz <1.5
When it is 0, not only the slitting property is deteriorated, but also the moisture absorption of the film is increased and the dimensional stability is deteriorated, so that the film is not suitable as a support film for a magnetic recording medium. Also, n
When z ≧ 1.50, there is also an effect of preventing show-through in which unevenness of the nonmagnetic surface is transferred to the magnetic surface. (Nx-nz),
If (ny-nz) is less than 0.2, not only the rise of the cut portion of the film occurs, but also the in-plane orientation of the film is insufficient and the elastic modulus becomes small, which is not preferable. On the other hand, if it is larger than 0.55, it is not preferable because the film is torn along the slit direction and the wound appearance is deteriorated. (Nx-nz) and (ny-nz) preferably have a good slit property when they are 0.2 or more and 0.45 or less, more preferably 0.2 or more and 0.35 or less.

Further, nx and ny are both 1.80 or more and 2.
When it is 20 or less, the slit property becomes better, and
It is preferable because both a sufficient elastic modulus and elongation can be achieved as a magnetic tape.

The film of the present invention has a moisture absorption of 4.0% or less,
It is preferably at most 3.5%, more preferably at most 2.5%. When the moisture absorption exceeds 4.0%, not only does the slitting property deteriorate, but also the dimensional stability against a change in humidity is poor, so that it is not suitable as a base film for a magnetic recording medium.

The elongation in the longitudinal direction of the film of the present invention is 10%
Above, more preferably at least 20%, since the tape has appropriate flexibility.

The film of the present invention has a density of 1.350 (g / cm ³ ) or more so that it can have sufficient mechanical properties and dimensional stability as a support film in a magnetic recording medium.
It is preferably 540 (g / cm ³ ) or less. When the density is less than 1.350 (g / cm ³ ), the moisture absorption increases, the dimensional stability with respect to a change in humidity decreases, and the excellent mechanical properties characteristic of aromatic polyamide and aromatic polyimide films decrease. . Also, 1.5
If it exceeds 40 (g / cm ³ ), the elongation becomes small and handling becomes difficult in practice.

When the elastic modulus of the support film in the present invention is 800 kg / mm ² or more, preferably 1000 kg / mm ² or more in both the longitudinal direction and the width direction, the head touch does not deteriorate even if the magnetic tape is thinned. Electromagnetic conversion characteristics are improved.

The thermal shrinkage of the film of the present invention at 200 ° C. for 10 minutes is preferably 5% or less, and more preferably 2% or less, because the thermal method stability is good and the electromagnetic conversion characteristics are good.

The film of the present invention is provided with a magnetic layer on one or both sides thereof and is useful as a magnetic recording medium.

The magnetic layer may be formed by a dry method such as a wet method, a vapor deposition method, a sputtering method, or an ion plating method, in which a ferromagnetic powder is formed into a magnetic paint using various binders and coated on a support film. Although not particularly limited, a wet method will be described here as an example.

The type of the magnetic powder to be a magnetic material is not particularly limited, but ferromagnetic powders 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 a thermosetting resin-based binder and a radiation-curable binder are preferable, and a dispersant, a lubricant, an antistatic agent and the like are used as other additives. You may.
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 film of the present invention to have an appropriate roughness, it is preferable that particles are present in the film. As the type of the particles, SiO ₂ , TiO ₂ , Al ₂
Inorganic particles such as O ₃ , CaSO ₄ , BaSO ₄ , CaCO ₃ , carbon black, zeolite, and other fine metal powders, silicon particles, polyimide particles, cross-linked copolymer particles, cross-linked polystyrene particles, Teflon particles, etc. There are organic polymers and the like, but inorganic particles are more preferable from the viewpoint of heat resistance. Further, the average primary particle diameter of the particles contained in the film of the present invention is 0.005 to 5 μm, preferably 0.05 to 5 μm.
When the thickness is in the range of 1 to 2 μm, both the electromagnetic conversion characteristics and the running properties are good, which is preferable. The content of the particles contained in the support film of the magnetic recording medium of the present invention is preferably 0.0
The content is from 0.01 to 5 wt%, more preferably from 0.01 to 3 wt%. If the content of the particles is less than the above range, the running property of the film tends to be poor, and if it is too large, the electromagnetic conversion characteristics tend to be poor.

The surface roughness of the film thus obtained is preferably 0.1 to 100 nm in Ra, more preferably 0.2 to 50 nm.

The film of the present invention may of course be used as a single-layer film, but may be a laminated film. Here, the laminated film and the base layer (film components other than the laminated film of the present invention) may be of the same type or different. Particles may be contained in at least one layer constituting the base layer portion, and it is desirable to use the kind of particles, the average primary particle diameter of the particles, and the content that are desirably used in the film of the present invention. The diameter of the particles in the base layer is not particularly limited, but may be larger than the diameter of the particles in the film of the present invention laminated for the purpose of improving the tape running property by moderate undulation of the support film.

The thickness of the film of the present invention is preferably 0.5
Especially when the thickness is from 20 to 20 μm, and more preferably from 1 to 10 μm, the improvement of the slit property which is the effect of the present invention is remarkable.

Next, the manufacturing method of the present invention will be described, but the present invention is not limited thereto.

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

These polymer solutions may be used directly as a film-forming stock solution. Alternatively, 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. Is also good.

In order to obtain the aromatic polyamide film of the present invention, the intrinsic viscosity of the polymer (measured at 30 ° C. as a 100 ml solution of 0.5 g of the polymer in sulfuric acid) is 0.1.
It is preferably 5 or more.

In some cases, an inorganic salt such as calcium chloride, magnesium chloride, lithium chloride, lithium nitrate, or the like is added as a dissolution aid to the stock solution for film formation. The polymer concentration in the stock solution is preferably about 2 to 40% by weight.

On the other hand, a solution of an aromatic polyimide or a polyamic acid is obtained as follows. That is, polyamic acid is N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DM
It can be prepared by reacting tetracarboxylic 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-mentioned polyamic acid or adding an imidizing agent such as pyridine to obtain a polyimide powder, which is dissolved in a solvent again. The polymer concentration in the film forming solution is 5
About 25 wt% is preferable.

As a method for adding the particles, there is 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, or a method in which a stock solution is directly added after preparing a stock solution.

The film-forming stock solution prepared as described above is formed into a film by a so-called solution casting method. The solution film forming method includes a dry-wet method, a dry method, a wet method and the like, and any method may be used for forming the film. 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 die 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 to make the thin film have a self-holding polymer concentration. Dry to 35-60 wt%. In this dry process, first, in the first-stage drying, drying is performed slowly at a low temperature of 100 ° C. or less.
Next, in the second-stage drying, the remaining portion is dried at a high temperature of 150 ° C. or more to give the film a self-supporting property. At this time, at the time of extrusion, when the polymer concentrations after the first-stage drying and after the second-stage drying are a, b, and cwt%, respectively,
0.2 ≦ (first stage dry amount) = (ba) /
Drying is performed until (ca) ≦ 0.9. The reason for performing the two steps is to first obtain a refractive index in the target range by drying at a low temperature in the first stage while suppressing rapid molecular orientation in the in-plane direction, and then in the second stage. This is because the in-plane orientation is promoted by high-temperature drying so that the refractive index in the thickness direction falls within a desired range. The drying in this dry process may be performed in two or more stages, each of which corresponds to the first stage and the second stage. The preferable range of the first-stage dry amount is 0.5 or more and 0.9 or less, more preferably 0.7 or more and 0.9 or less.

After the dry process, the film is peeled off from the support, introduced into a wet bath in the next wet process, and subjected to desalting and solvent removal. The wet bath composition is not particularly limited as long as it is a poor solvent for the polymer, but it is preferable to use water or a mixed system of organic solvent / water in terms of economy and easy handling. Further, when the reaction is carried out in an organic solvent / water mixed system, it is preferable that the desalting and desolvation are finally carried out with a large amount of water. If the desalting and desolvation are not performed sufficiently, the aggregation state between the molecules is disturbed by the presence of an inorganic salt or an organic solvent having a high affinity for water, so that the refractive index in the thickness direction in a target range is disturbed. Cannot be obtained, or a film having sufficient elongation cannot be obtained. The temperature of the wet bath may be in balance with other physical properties, but is preferably 20 ° C. or higher, preferably 30 ° C. or higher in order to enhance the effects of desalting and desolvation. Further, drying and heat treatment are performed in a tenter to form a film.

The film formed as described above is stretched in a wet bath during the film forming process to increase the in-plane orientation in the tenter to obtain a film having a desired refractive index. The magnification is preferably in the range of 1.0 to 5.0 (area magnification is defined as a value obtained by dividing the area of the film after stretching by the area of the film before stretching), and more preferably. 1.1 to 3.0. When the stretching ratio is within this range, the in-plane orientation of the polymer is advanced, and a film having improved slit properties, which is the object of the present invention, and having excellent mechanical properties can be obtained, but the stretching ratio is 5.0. If the ratio exceeds the above range, the elongation of the film is lowered and the film is easily broken, and the end face of the film roll is easily shifted. In addition, when the stretching ratio is smaller than 1.0, that is, when relaxation is given, insufficient plane orientation is likely to occur.

After the stretching, the film is subjected to a heat treatment.
The heat treatment is preferably performed at 200 to 450 ° C. If the heat treatment is at or below this temperature, insufficient drying and crystallization will result, resulting in a film having a low density, and sufficient mechanical properties cannot be obtained. On the other hand, if it is more than this range, the film becomes brittle and the elongation is lowered. It is effective to gradually cool the film after stretching or heat treatment, and it is effective to cool the film at a rate of 50 ° C./sec or less.

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 parts, different particles are added, and then the layers are laminated. The same applies to the case of three or more layers.
These laminating methods include well-known methods such as lamination in a die, lamination in a composite tube, and a method in which one layer is formed once and another layer is formed thereon.

When the film of the present invention is used for a magnetic recording medium, a magnetic layer is provided on at least one side of the obtained film. The method for providing the magnetic layer may be any of a method of dispersing and applying a magnetic powder in a binder and a method of depositing a ferromagnetic metal. When a magnetic layer is applied, it can be performed by a known method, but a method using a gravure roll is more preferable in terms of uniformity of a coating film. The drying temperature after application is preferably from 90C to 150C. The calendering step is preferably performed in a 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 running properties.

Further, after the film coated with the magnetic layer is cured, slitting is performed to obtain the magnetic recording medium of the present invention.

Preferred uses of the magnetic recording medium obtained in this way include, for example, 8 mm, DDS-2 for broadcast stations such as D-1, 2, 3 for consumer use such as DVC, etc.
3, 4, QIC, and data for 8 mm data.

[0049]

EXAMPLES The method for measuring physical properties and the method for evaluating effects according to the present invention are as follows.

(1) Refractive Index A phase difference measuring device NPDM-1000 manufactured by Nikon Corporation was used for measuring the refractive index in the longitudinal direction and the width direction. Using a xenon lamp as a light source and a measurement wavelength of 590 nm, a refractive index was measured from reflected light when a light beam was applied to the sample at an incident angle of 70 °. The refractive index in the thickness direction was measured using an Abbe refractometer type 4 manufactured by Atago Co., Ltd., and using a methylene sulfur iodide solution having a refractive index of 1.79 as an intermediate liquid using sodium D line (589 nm) as a light source.

(2) Density The density was measured at 25.0 ° C. by a density gradient tube method using an aqueous solution of lithium bromide as a specific gravity liquid.

(3) Elastic Modulus and Elongation Using an Instron type tensile tester, the width of the test piece was 10 mm, the length was 50 mm, and the tensile speed was 300 mm /
The elastic modulus and elongation of the film were measured in minutes.

(4) Moisture absorption The film weight (W1) after drying at 150 ° C. for 60 minutes and 7
The film weight (W2) after being left in 5% RH for 48 hours was measured and calculated by the following formula.

[0054]

(Equation 1) (5) Polymer concentration and first-stage dry amount The polymer concentration at each stage in the film forming stock solution and the drying process is as follows:
Weight W3 (g) of the collected polymer, weight W4 (g) after developing the polymer on a glass plate on a film, desalting and desolvating in a water bath for 20 minutes, and drying in an oven at 200 ° C. for 12 hours. From the following formula.

[0055]

(Equation 2) The amount of drying in the first stage is 2 hours after extrusion, after drying in the first stage.
The polymer after the drying in the stage was sampled, and the polymer concentration was defined as a, b, and cwt%, respectively, and was calculated by the following formula.

[0056]

(Equation 3) (6) Slit property A magnetic paint having the following composition is applied to the film with a gravure roll, magnetically oriented, and dried. Further, after calendering at a temperature of 75 ° C. and a linear pressure of 220 kg / cm using a calender, curing is performed at 70 ° C. for 48 hours.

(Composition of magnetic paint) Co-containing iron oxide: 100 parts by weight Vinyl chloride / vinyl acetate copolymer: 10 parts by weight Polyurethane elastomer: 10 parts by weight Polyisocyanate: 5 parts by weight Lecithin: 1 part by weight Parts-Methyl ethyl ketone: 75 parts by weight-Methyl isobutyl ketone: 75 parts by weight-Toluene: 75 parts by weight-Carbon black: 2 parts by weight-Lauric acid: 1.5 parts by weight The prepared magnetic tape raw material is 1/2 inch wide. And 3,000 m in length was rolled up as a pancake.
The end of the slit tape was observed under magnification with a microscope, and evaluated by the following criteria.

There is no swell at the end: ○ Slight swell is seen at the end: △ The swell at the end can be seen at a glance: ×

(7) Roll Form The roll form of the prepared pancake was judged according to the following criteria, and ○ and △ were evaluated as having good characteristics.

No roll collapse or edge displacement: ○ No roll collapse, but slight edge displacement: Δ Roll collapse or edge displacement clearly seen: ×

Hereinafter, the present invention will be described with reference to Examples, but it should not be construed that the invention is limited thereto.

Example 1 N-methyl-2-pyrrolidone (NMP) was used as an aromatic diamine component in 2-chloroparaphenylenediamine corresponding to 80 mol%, and 4,4'-diaminodiphenyleamine corresponding to 20 mol%. -Dissolve tel and add 100
The mole% 2-chloroterephthalic acid chloride was added and stirred for 2 hours to complete the polymerization. This was neutralized with lithium hydroxide to give a polymer concentration of 11% by weight and a viscosity of 300%.
A 0 poise aromatic polyamide solution was obtained. In this solution,
2 wt% of dry silica with a primary particle size of 16 nm per polymer
Was added.

This polymer solution was filtered through a 5 μm-cut filter, then cast on a belt, and first dried at 90 ° C. with hot air at 90 ° C. until the first-stage dry amount became 70%. After that, the polymer was heated with hot air at 180 ° C. to evaporate the solvent and obtain a self-holding polymer concentration of 40 wt%.
Was continuously peeled from the belt. At this time, a water bath was used as a wet bath, and the film was introduced into the bath.
Extraction of the residual solvent and the inorganic salt generated by the neutralization was performed for minutes. During this time, the film was stretched 1.2 times in the longitudinal direction between the rolls. Next, drying and heat treatment were performed for 1 minute while stretching 1.3 times in the width direction at 280 ° C. with a tenter, and then 20 ° C. /
Slow cooling was performed at a speed of 2 seconds to obtain an aromatic polyamide film having a thickness of 6 μm.

The refractive indices nx, ny and nz in the longitudinal direction, width direction and thickness direction of this film are as follows: nx = 1.861,
ny = 1.864, nz = 1.607, and (nx-nz)
= 0.254, (ny-nz) = 0.257.
The moisture absorption was 1.5%, the elastic modulus in the longitudinal direction and the elastic modulus in the width direction were 1310 and 1350 kg / mm ² , and the elongation was 4
0, 38% and density was 1.5023 g / cm ³ .
Next, when the slit property and the winding appearance of the magnetic tape produced by using this film were evaluated, both were evaluated as ○.

Examples 2 to 4, 6, 7 In Example 1, the film was formed by changing the drying conditions in the dry process and the stretching ratio to the conditions shown in Table 1, and the results were as shown in Tables 1 and 2. The slit properties and winding appearance of the produced magnetic tape were evaluated, and all were good.

Example 5 Paraphenylenediamine corresponding to 60 mol% as an aromatic diamine component and 4,4′-diaminodiphenyl ether corresponding to 40 mol% were dissolved in NMP.
To this, 2-chloroterephthalic acid chloride corresponding to 100 mol% was added and stirred for 2 hours to complete the polymerization. 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, 2 wt% of dry silica having a primary particle size of 16 nm was added per polymer.

This polymer was formed into a film in the same manner as in Example 1 to obtain a polyamide film having a thickness of 5 μm.

The physical properties of this film were as shown in Tables 1 and 2. Both the slit properties and the winding appearance of the produced magnetic tape were good.

Example 8 Lithium bromide equivalent to 50% by weight based on the polymer was added to NMP and dissolved therein. After adding and dissolving para-phenylenediamine corresponding to 100 mol% as an aromatic diamine component, terephthalic acid chloride corresponding to 50 mol% as an aromatic dicarboxylic acid component and 2-chloroterephthalic acid corresponding to 50 mol% are used. Chloride was added and stirred for 2 hours to complete the polymerization. This was neutralized with lithium hydroxide to obtain an aromatic polyamide solution having a polymer concentration of 6% by weight and a viscosity of 3600 poise. To this solution, dry silica having a primary particle size of 16 nm was added at a rate of
wt% was added.

Using this polymer solution, a film was formed in the same manner as in Example 1 except that the first-stage drying temperature was set to 80 ° C. and the second-stage drying temperature was set to 200 ° C. An aromatic polyamide film was obtained.

The film properties of this film were as shown in Tables 1 and 2. Both the slit property and the winding appearance of the produced magnetic tape were good.

Comparative Examples 1 and 2 Using the same polymer as in Example 1, a film was formed in the same manner as in Example 1 except for the conditions shown in Table 1. There was no example in which the produced magnetic tape had good slit properties and good winding appearance.

Comparative Example 3 4,4'-Diaminodiphenylmethane corresponding to 100 mol% as an aromatic diamine component was dissolved in N-methylpyrrolidone (NMP), and 50 mol% of isophthalic acid chloride and 50 mol% were dissolved therein. % Terephthalic acid chloride was added and stirred for 2 hours to complete the polymerization. This is neutralized with lithium hydroxide to give a polymer concentration of 10
An aromatic polyamide solution having a weight percentage of 3000 poise and viscosity was obtained. To this solution, 2 wt% of dry silica having a primary particle size of 16 nm was added per 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 physical properties of this film were as shown in Tables 1 and 2. The winding appearance of the produced magnetic tape was good, but the slit property was poor.

[0076]

[Table 1]

[Table 2]

[0077]

According to the present invention, in producing a magnetic recording medium using a film made of an aromatic polyamide or aromatic polyimide having excellent heat resistance and mechanical properties as a support, the refractive index range of the film is defined. By improving the slitting property and preventing the winding of the film and the magnetic tape from being defective, the yield of products can be greatly improved. Also, there is an effect that show-through in which irregularities of the non-magnetic surface are transferred to the magnetic surface can be prevented.

Further, the present invention is not limited to applications for magnetic recording media, but is also suitably used for applications such as capacitors, flexible printed boards, and thermal transfer ribbons that require good slitting properties during the film processing process.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // C08L 77:10 79:08 (56) References JP-A-6-16836 (JP, A) JP-A-5-73876 (JP, A) JP-A-2-107635 (JP, A) JP-A-63-183613 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 5/18 G11B 5/62-5 / 72

Claims (6)

(57) [Claims] 1. A refractive index nz ≧ 1.50 in a thickness direction, and a refractive index nx and ny in a longitudinal direction and a width direction are 0.2 ≦ (nx−nz) ≦ 0.55 0.2 ≦ (ny−nz). A film made of an aromatic polyamide or an aromatic polyimide, both satisfying ≦ 0.55 and having a moisture absorption of 4.0% or less. 2. nx and ny are both 1.80 or more;
The film comprising the aromatic polyamide or the aromatic polyimide according to claim 1, which has a molecular weight of 20 or less. 3. The film comprising the aromatic polyamide or the aromatic polyimide according to claim 1, wherein the elongation in the longitudinal direction is 10% or more. 4. The film comprising the aromatic polyamide or the aromatic polyimide according to claim 1, wherein the film has a thickness of 0.5 to 20 μm. 5. A density of 1.350 (g / cm ³ ) or more and 1.5
40 (g / cm ³ ) or less.
5. A film comprising the aromatic polyamide or the aromatic polyimide according to any one of 4. 6. A magnetic recording medium comprising a film according to claim 1 and a magnetic layer provided on at least one side of the film.