JPH08337665A - Film made from aromatic polyamide or aromatic polyimide - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium which is excellent in slittability and wound appearance and is made from an arom. polyamide or polyimide excellent in mechanical characteristics. CONSTITUTION: This film is made from an arom. polyamide or polyimide, satisfies the relations: nz>=1.50, 0.2<=(nx-nz)<=0.55, and 0.2<=(ny-nz)<=0.55 (wherein nz, nx, and ny are the refractive indexes in the directions of thickness, length, and width, respectively), and has a moisture content of 4.0% or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aromatic polyamide film or a film made of aromatic polyimide, which has a good slitting property and is mainly useful as a support for magnetic recording media.

[0002]

2. Description of the Related Art Heretofore, as a magnetic recording medium, a magnetic recording medium having an oxide coating type magnetic layer or a metal coating type magnetic layer provided on a polymer film support has been used (for example, JP-A-61). No. 26933, JP-A-60-663.
No. 19, etc.). Polyester films are mainly used as a support for these magnetic recording media, but in recent years, due to the higher density, smaller size, longer recording time, etc. of magnetic recording media, it has become possible to reduce the thickness of the support film. The demands are becoming stronger and stronger.

A polyester film which has been conventionally used as a support for a magnetic recording medium has a limit in thinning because the thinning of the film causes a problem such as poor head touch due to a low elastic modulus and a reduction in output. . Therefore, 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 manufactured by coating or vapor-depositing a magnetic material on a support film and then slitting it into a predetermined width. The yield in this slit process is an important process because it greatly affects the productivity of the product, but when manufacturing a magnetic tape with an aromatic polyamide film or aromatic polyimide film of high elastic modulus as a support. In many cases, the life of the slitting cutter is shortened, or so-called "high edge" occurs in which the cut portion (edge) of the tape is raised. When the high edge occurs, the tape (pancake) wound by slitting may collapse, or the film may tear from the blade edge in the slit direction and the width of the film may not be constant, resulting in defective winding such as end face misalignment. However, there is a problem that the yield will deteriorate.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide an aromatic polyamide film or a film made of an aromatic polyimide, which has a good slitting property and is mainly useful as a base film of a magnetic recording medium.

[0006]

Means for Solving the Problems As a result of intensive studies by the present inventors, if a film made of aromatic polyamide or aromatic polyimide having a refractive index in a specific range is used,
The inventors have found that a good magnetic recording medium that solves the above problems can be obtained, and completed the present invention. That is, in the present invention, the refractive index nz ≧ 1.50 in the thickness direction and the refractive indices nx and ny in the longitudinal direction and the width direction are 0.2 ≦ (nx −nz) ≦.
0.55, 0.2 ≦ (ny −nz) ≦ 0.55 are both satisfied, and the moisture absorption rate is 4.0% or less, the film made of aromatic polyamide or aromatic polyimide is the skeleton. To do.

[0007]

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

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, Y is _{-O -, - CH 2 -,} - CO
_{-, - SO 2 -, -} S -, - C (CH 3) 2 - is chosen from such, but is not limited thereto. Furthermore, some of the hydrogen atoms on these aromatic rings are substituted by halogen groups (especially chlorine), nitro groups, methyl groups, ethyl groups, alkyl groups (especially methyl groups) such as propyl groups, methoxy groups, ethoxy groups, propoxy groups. 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 film tends to be oriented in the plane and the refractive index in the longitudinal direction and the width direction becomes high. If the proportion of the aromatic rings in which some of the hydrogen atoms on the aromatic ring are replaced by halogen groups (especially chlorine) is 30% or more, preferably 50% or more, more preferably 70% or more, the moisture absorption rate is small. Therefore, it is preferable.

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 Ar4 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,
It is not limited to this.

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, Y is _{-O -, - CH 2 -,} - CO
_{-, - SO 2 -, -} S -, - C (CH 3) 2 - is chosen from such, but is not limited thereto. Furthermore, some of the hydrogen atoms on these aromatic rings are substituted by halogen groups (especially chlorine), nitro groups, methyl groups, ethyl groups, alkyl groups (especially methyl groups) such as propyl groups, methoxy groups, ethoxy groups, propoxy groups. 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. .

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

In the present invention, in order to have a good slitting property that does not cause deterioration of the winding shape,
Refractive indices nx, ny and nz in the thickness direction are nz≥1.5
0, 0.2≤ (nx-nz) ≤0.55, 0.2≤ (n
It is necessary to satisfy y −nz) ≦ 0.55. When the refractive index is within this range, the in-plane direction and the thickness direction have a good balance of refractive indices, and a good slit property is exhibited. nz <1.5
When it is 0, not only the slit property is deteriorated, but also the hygroscopic property 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 that is caused by the unevenness of the non-magnetic surface being transferred to the magnetic surface. (Nx-nz),
When (ny-nz) is less than 0.2, not only is the film cut portion raised, 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, when it is larger than 0.55, film tearing occurs along the slit direction, which leads to deterioration of the winding shape, which is not preferable. (Nx-nz) and (ny-nz) preferably have a slit property of 0.2 or more and 0.45 or less, and more preferably 0.2 or more and 0.35 or less.

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

The moisture absorption rate of the film of the present invention is 4.0% or less,
It is preferably 3.5% or less, more preferably 2.5% or less. When the moisture absorption rate exceeds 4.0%, not only the slit property is deteriorated, but also the dimensional stability against humidity change is poor and the film is not suitable as a base film for magnetic recording media.

The elongation of the film of the present invention in the longitudinal direction is 10%.
As described above, more preferably 20% or more is desirable because the tape has appropriate flexibility.

Since the film of the present invention can have sufficient mechanical properties and dimensional stability as a support film in a magnetic recording medium, its density is 1.350 (g / cm ³ ) or more.
It is preferably 540 (g / cm ³ ) or less. When the density is less than 1.350 (g / cm ³ ), the moisture absorption becomes large, the dimensional stability against humidity change is lowered, and the excellent mechanical properties characteristic of aromatic polyamide and aromatic polyimide films are lowered. . Also, 1.5
When it is more than 40 (g / cm ³ ), the elongation becomes small and the handling becomes difficult in practical use.

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 when the magnetic tape is thinned. Good electromagnetic conversion characteristics.

The heat shrinkage rate 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 side or both sides and is useful as a magnetic recording medium.

As a method for forming the magnetic layer, there are a dry method such as a wet method in which a ferromagnetic powder is made into a magnetic coating material using various binders and applied on a support film, a vapor deposition method, a sputtering method, an ion plating method, and the like. Although not particularly limited, a wet method will be described here as an example.

The type of magnetic powder to be 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 film of the present invention to have an appropriate roughness, it is preferable that particles are present in the film. The types of particles include SiO ₂ , TiO ₂ , and 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, crosslinked copolymer particles, crosslinked polystyrene particles, Teflon particles, etc. Although there are organic polymers and the like, 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 μm.
When the thickness is in the range of 1 to 2 μm, both the electromagnetic conversion characteristics and the running property are good, which is preferable. The content of particles contained in the support film of the magnetic recording medium of the present invention is preferably 0.0
It is from 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 conversely if the content is large, the electromagnetic conversion characteristics are likely to be poor.

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

The film of the present invention can be used not only as a monolayer film but also as a laminated film. The film laminated here and the base layer portion (film constituent portion other than the laminated film of the present invention) may be the same kind 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 particles, and the content which are preferably 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 due to the appropriate waviness of the support film.

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

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.

An inorganic salt such as calcium chloride, magnesium chloride, lithium chloride or lithium nitrate may be added to the stock solution for film formation as a dissolution aid. 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 25 wt% is preferable.

The method of adding particles includes a method of sufficiently slurrying the particles in a solvent in advance and then using them as a solvent for polymerization or a solvent for dilution, or a method of directly adding 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 includes a dry-wet method, a dry method, and a wet method, and any method may be used for film formation, 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 so that the thin film has a self-supporting polymer concentration. Dry to 35-60 wt%. In this dry process, first, in the first-stage drying, a low temperature of 100 ° C. or lower is slowly dried.
Next, in the second stage drying, the remaining portion is dried at a high temperature of 150 ° C. or higher to give the film self-supporting property. At this time, at the time of extrusion, after the first-stage drying and the polymer concentrations after the second-stage drying are a, b, and cwt%, respectively,
0.2 ≦ (first-stage dry amount) = (ba) /
Drying is performed until (c−a) ≦ 0.9. The reason for carrying out in two steps is to obtain a refractive index in the target range by first drying with low temperature drying in the first step while suppressing abrupt molecular orientation in the in-plane direction, and then in the second step. This is because the in-plane orientation is promoted by drying at high temperature so that the refractive index in the thickness direction falls within the target range. As for the drying in this dry process, the drying corresponding to the first stage and the second stage may be performed in multiple stages of two or more stages. The preferable range of the first stage dry amount is 0.5 or more and 0.9 or less, and more preferably 0.7 or more and 0.9 or less.

The film that has undergone the dry process is peeled from the support and introduced into the wet bath of the next wet process for 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 an organic solvent / water mixed system from the viewpoint of economy and ease of handling. Further, when the reaction is carried out in a mixed system of organic solvent / water, it is preferable that desalting and solvent removal are finally carried out with a large amount of water. If desalting and desolvation are not performed sufficiently, the aggregation state between molecules is disturbed by the presence of an inorganic salt or organic solvent that has a high affinity for water, so the refractive index in the thickness direction of the target range It is not possible to obtain a film having a tensile strength, or a film having a sufficient elongation. Although the temperature of the wet bath has a balance with other physical properties, it is desirable that the temperature is 20 ° C. or higher, preferably 30 ° C. or higher in order to enhance the effects of desalting and solvent removal. Further, it is dried and heat-treated in a tenter to form a film.

The film formed as described above is stretched to obtain a film having a desired refractive index by increasing the in-plane orientation in a tenter in a wet bath during the film forming process. The area ratio is preferably in the range of 1.0 to 5.0 (the area ratio is defined as a value obtained by dividing the film area after stretching by the area of the film before stretching), and more preferably. It is 1.1 to 3.0. When the stretching ratio is within this range, the in-plane orientation of the polymer is promoted, and a film having the improved slitting property and the excellent mechanical properties, which is the object of the present invention, is obtained, but the stretching ratio is 5.0. If it exceeds, the elongation of the film may be lowered and the film may be easily broken or the end surface of the film roll may be displaced. Further, if the draw ratio is less than 1.0, that is, if relaxation is given, insufficient plane orientation is likely to occur.

After stretching, the film is subjected to heat treatment,
The heat treatment is preferably performed at 200 to 450 ° C. If the heat treatment is carried out at a temperature below this temperature, insufficient drying and insufficient crystallization will result in a film with 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, which makes it unsuitable for practical use. Further, 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./second 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, 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.

When the film of the present invention is used for a magnetic recording medium, a magnetic layer is provided on at least one surface of the obtained film. The method of providing the magnetic layer may be either a method of dispersing and coating magnetic powder in a binder or a method of depositing a ferromagnetic metal. The magnetic layer can be applied by a known method, but a method using a gravure roll is more preferable in terms of 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.

Preferable uses of the magnetic recording medium thus obtained are, for example, 8 mm, for consumer use such as DVC, DDS-2 for broadcasting stations such as D-1, 2, 3 for professionals.
3, 4, QIC, data for 8 mm data, and the like.

[0049]

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

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

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

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

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

[0054]

[Equation 1] (5) Polymer Concentration and First Step Dry Amount The polymer concentration at each stage in the membrane forming stock solution and the drying step is
Weight W3 (g) of the collected polymer, weight W4 (g) after developing the polymer on a film on a glass plate, desalting and desolvating in a water bath for 20 minutes, and then drying in an oven at 200 ° C. for 12 hours. Was calculated from the following formula.

[0055]

[Equation 2] Also, the dry amount of the first stage is 2 after the first stage drying during extrusion.
The polymer after drying in the first stage was sampled, and the polymer concentrations were calculated as a, b, and cwt%, respectively, and calculated by the following calculation formula.

[0056]

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

(Composition of magnetic coating) 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 It was slit and rolled up to a length of 3000 m as a pancake.
The edge of the slit tape was observed by enlarging it with a microscope, and judged according to the following criteria.

There is no swelling at the edge: ○ Slight swelling is seen at the edge: △ Edge swelling can be seen at a glance: ×

(7) Winding shape The winding shape of the prepared pancake was judged according to the following criteria, and ◯ and Δ were evaluated as good characteristics.

No roll collapse or edge shift: ○ No roll collapse but slight edge shift: △ Coil roll or edge shift is clearly visible: ×

The present invention is described below based on examples, but the invention is not limited thereto.

Example 1 N-methyl-2-pyrrolidone (NMP) was added with 2-chloroparaphenylenediamine corresponding to 80 mol% as an aromatic diamine component, and 4,4'-diaminodiphenylene corresponding to 20 mol%. -Dissolve the tellur and add 100
2-Chlorterephthalic acid chloride corresponding to mol% was added and stirred for 2 hours to complete the polymerization. This is 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 with a filter of 5 μm cut, cast on a belt, and first dried in hot air at 90 ° C. until the dry amount in the first step reached 70%. Then, it was heated with hot air at 180 ° C to evaporate the solvent and obtain a self-holding property. Polymer concentration 40 wt%
The film was continuously peeled from the belt. At this time, a water bath was used as the wet bath, and the film was introduced into the bath.
The residual solvent and the inorganic salt generated by neutralization were extracted for minutes. During this period, the film was stretched 1.2 times in the longitudinal direction between the rolls. Next, the film was stretched 1.3 times in the width direction at 280 ° C with a tenter and dried and heat-treated for 1 minute.
The mixture was gradually cooled at a rate of 2 seconds to obtain an aromatic polyamide film having a thickness of 6 μm.

The refractive indices nx, ny and nz of the film in the longitudinal direction, width direction and thickness direction are nx = 1.861,
ny = 1.864, nz = 1.607, and (nx -nz)
= 0.254 and (ny-nz) = 0.257.
Further, the moisture absorption rate is 1.5%, the elastic moduli in the longitudinal direction and the width direction are 1310 and 1350 kg / mm ² , respectively, and the elongation is 4
The density was 0.38% and the density was 1.5023 g / cm ³ .
Next, when the slitting property and the winding shape of the magnetic tape produced using this film were evaluated, both were good.

Examples 2 to 4, 6 and 7 In Example 1, as a result of forming a film by changing the drying conditions in the dry process and the stretching ratio to the conditions shown in Table 1, the results shown in Tables 1 and 2 were obtained. The slit property and winding shape 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, 100 mol% of 2-chloroterephthalic acid 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 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 are as shown in Tables 1 and 2, and the magnetic tape produced had good slit properties and winding appearance.

Example 8 Lithium bromide corresponding to 50% by weight of the polymer was added and dissolved in NMP as a dissolution aid. Paraphenylenediamine corresponding to 100 mol% as an aromatic diamine component was added and dissolved therein, and then terephthalic acid chloride corresponding to 50 mol% as an aromatic dicarboxylic acid component and 2-chloroterephthalic acid corresponding to 50 mol% were dissolved. 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 per polymer in an amount of 2
wt% was added.

Using this polymer solution, a film having a thickness of 4.5 μm was formed in the same manner as in Example 1 except that the first stage drying temperature was 80 ° C. and the second stage drying temperature was 200 ° C. An aromatic polyamide film was obtained.

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

Comparative Examples 1 and 2 The same polymer as in Example 1 was used to form a film in the same manner as in Example 1 except for the conditions shown in Table 1. There was no case where the produced magnetic tape had good slitting property and winding shape.

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 in this solution. % Of terephthaloyl chloride was added and the polymerization was completed by stirring for 2 hours. This is neutralized with lithium hydroxide to give a polymer concentration of 10
An aromatic polyamide solution having a weight% and a viscosity of 3000 poise 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 by the same method as in Example 1.

The physical properties of this film are as shown in Tables 1 and 2, and although the wound shape of the produced magnetic tape was good, the slit property was poor.

[0076]

[Table 1]

[Table 2]

[0077]

INDUSTRIAL APPLICABILITY According to the present invention, when a magnetic recording medium is produced using a film made of aromatic polyamide or aromatic polyimide having excellent heat resistance and mechanical properties as a support, the range of the refractive index of the film is specified. By improving the slitting property and preventing defective winding of the film and the magnetic tape, the yield of products can be significantly improved. Further, there is an effect that it is possible to prevent show-through which is caused by the unevenness of the non-magnetic surface being transferred to the magnetic surface.

Further, the present invention is not limited to the use as a magnetic recording medium, and can be suitably used for a use such as a condenser, a flexible printed circuit board, a heat-sensitive transfer ribbon, etc., which is required to have a good slitting property in the film processing step.

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Claims (6)

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