JP2002001805A - Method for manufacturing aromatic polyamide film and aromatic polyamide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an aromatic polyamide film which shows high productivity by enabling high ratio stretch and gives an aromatic polyamide film of a high quality by preventing neck down during high ratio stretch. SOLUTION: An aromatic polyamide film is manufactured by stretching a solvent-containing polymer sheet of an aromatic polyamide having a width of not less than 50 cm in a lengthwise direction in a stretching region of 5 to 300 cm at a stretch rate of 50 to 3,000 %/sec while the polymer sheet is soaked in a solvent mixture of a good solvent and a poor solvent during stretch, the ratio of the good solvent to the poor solvent being 80/20 to 30/70 wt.%.

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 having high productivity and process stability, capable of suppressing neck-down even during high-magnification stretching, and capable of obtaining a high-quality film. And a method for producing the same.

[0002]

2. Description of the Related Art Aromatic polyamide films are widely used as industrial materials. In particular, PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) has been conventionally used as a base film for a magnetic recording medium. However, a highly rigid aromatic polyamide film having more excellent heat resistance has been used. It is being developed rapidly as a base film for use. Furthermore, higher productivity and higher mechanical properties have been demanded with the increase in the amount. Generally, an aromatic polyamide is formed into a film by a solution casting method. In the solution casting method, a polymer cast from a die onto a support such as a belt or a drum is provided with a self-holding property and then separated from the support. Since the speed at which the polymer solution is cast is limited and a certain amount of time is required to remove the solvent, it is necessary to stretch the polymer with self-holding properties at a high magnification in the stretching process. Is considered one of the most effective means of raising However, aromatic polyamides, especially para-based aromatic polyamides, have been considered to be difficult to achieve high stretching because of their rigidity and poor stretchability.

Further, when the film is stretched in the longitudinal direction, the width direction is reduced based on the Poisson's ratio (hereinafter, this phenomenon is referred to as neck-down). In particular, as the stretching ratio increases, the neck down increases. If the neck-down is large, not only the productivity is lowered, but also the flatness and physical properties in the width direction of the film are significantly deteriorated, and thickness unevenness occurs.

In Japanese Patent Application Laid-Open No. 62-62424, the tensile Young's modulus in the width direction is 700 kg / mm ² or more, and the tensile Young's modulus in the length direction is equal to the tensile Young's modulus in the width direction of 1.
A three or more times magnetic recording medium is described. Further, Japanese Patent Application Laid-Open No. 62-70022 discloses that the sum of the tensile modulus in the longitudinal direction and the tensile modulus in the transverse direction is 350 in the stretched film state.
An aromatic polymer film of 0 to 11,000 kg / mm ² is described.

[0005]

However, Japanese Patent Application Laid-Open No. 62-62424 only vaguely describes that an aromatic polyamide film is cast on a mirror-polished Hastelloy belt and stretched. Nothing is disclosed about the stretching method and conditions, it is difficult to produce with high productivity (higher film forming speed and stretching sustainability), and the quality of the base film, especially in the longitudinal direction There was a problem of uneven thickness.

Japanese Unexamined Patent Publication (Kokai) No. 62-70022 discloses that the sum of the tensile elastic modulus in the longitudinal direction and the tensile modulus in the transverse direction of a film obtained by stretching is 3,500. １11000 kg / mm ² , and in this case, it is described that multi-stage stretching is performed at 300 ° C. to 600 ° C., but the method and conditions for longitudinal stretching are not particularly described.

Further, Japanese Patent Application Laid-Open No. H11-48334 describes a method for longitudinally stretching an aromatic polyamide film, but the stretching ratio is at most 1.6 times, and it can be said that productivity is still high. Absent.

[0008] The present invention provides high productivity in the process of producing an aromatic polyamide film because high draw ratio is possible, and also suppresses neck-down during high draw ratio. The aim is to provide a method that can be obtained.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have achieved these objects by immersing a polymer sheet having self-holding properties in a specific solvent liquid and performing plasticization. They have found that this can be achieved, and have accomplished the present invention.

That is, according to the present invention, when a polymer sheet made of an aromatic polyamide containing a solvent and having a sheet width of 50 cm or more is stretched in the longitudinal direction, the polymer sheet has a good solvent / poor solvent composition ratio. Solvent / poor solvent = 80 / 20-3
This is a method for producing an aromatic polyamide film, wherein the film is stretched at a stretching section of 5 to 300 cm and a stretching speed of 50 to 3000% / sec while being immersed in a mixed solvent solution of 0/70% by weight.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The aromatic polyamide used in the present invention has a repeating unit represented by the following formula (1) and / or formula (2).

Equation (1):

Embedded image

Equation (2):

Embedded image

Here, the groups Ar ₁ , Ar ₂ and Ar ₃ include, for example,

Embedded image Etc. can be mentioned, X, group Y _{is, -O -, - CH 2 -} , -
_{CO -, - CO 2 -,} - S -, - SO 2 -, - C (C
H ₃ ) ₂ − and the like.

Further, some of the hydrogen atoms on these aromatic rings may be substituted with halogen groups (particularly chlorine) such as fluorine, bromine and chlorine;
Those substituted with substituents such as nitro groups, alkyl groups (especially methyl groups) such as methyl, ethyl and propyl, and alkoxy groups such as methoxy, ethoxy and propoxy, have dimensions due to changes in humidity in order to reduce the moisture absorption. This is preferable because the change is small. Further, hydrogen in the amide bond constituting the polymer may be substituted by another substituent. In the aromatic polyamide used in the present invention, those in which the above-mentioned aromatic ring has para-orientation are 80% of the total aromatic ring.
%, More preferably 90% or more. The term "para-orientation" as used herein refers to a state in which the divalent bonds constituting the main chain on the aromatic nucleus are coaxial or parallel to each other. If the para-orientation is less than 80%, the rigidity and heat resistance of the film may be insufficient. Further, it is preferable that the aromatic polyamide contains the repeating unit represented by the formula (3) in an amount of 60 mol% or more, since the stretchability and the physical properties of the film are particularly excellent.

Equation (3):

Embedded image

The film of the present invention preferably has a tensile modulus in at least one direction of 7 GPa or more. When the tensile elastic modulus is 7 GPa or more, it is easy to handle even when the magnetic recording medium is made thin, the head touch is good, and the electromagnetic conversion characteristics are good. In addition, the tensile modulus is 7
If it is less than GPa, the runnability as a magnetic tape may deteriorate. It is more preferably at least 8 GPa in all directions of the film, more preferably at least 10 GPa. Further, in the film of the present invention, it is preferable that the ratio E _TD / E _MD of the tensile elastic modulus in the longitudinal direction and the width direction is 0.8 ≦ E _TD / E _MD ≦ 3, because better recording / reproducing characteristics can be obtained. , E _TD / E _MD is more preferably 1 <E _TD / E _MD <2.

The film of the present invention may contain particles for imparting lubricity to the film. The particle size and content of the contained particles should be appropriately selected depending on the application, but the average primary particle size is preferably 0.001 to 2 μm. Further, the content of the particles contained in the film is preferably 0.001 to 5% by weight, and more preferably 0.05 to 3% by weight. If the particle diameter and the content of the particles are larger or larger than the above ranges, the magnetic tape is not preferable because the adhesion between the tape and the magnetic head is poor and the electromagnetic conversion characteristics are deteriorated.
If the particle diameter and the content of the particles are smaller or smaller than the above ranges, the running property of the film deteriorates, which is not preferable from the viewpoint of durability. The types of particles include SiO ₂ , TiO ₂ , Al
Inorganic particles such as ₂ 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 (registered trademark) Organic polymers such as particles are exemplified. As a method of imparting slipperiness to the film, in addition to the method of adding particles,
It is also possible to use a method in which a different polymer is blended with the base polymer, and the different polymer is formed into a projection in the film forming step.

The surface roughness of the film should be appropriately designed depending on the application.
p is 2 to 500 nm, more preferably 3 to 300 nm,
Ra is 0.1 to 100 nm, more preferably 0.2 to 5
0 nm, 2 to 500 nm in Rz, more preferably 3 to 4
00 nm.

The film of the present invention has a moisture absorption of 3.5.
% Or less, and more preferably 2.5% or less. When the moisture absorption exceeds 3.5%, the dimensional stability with respect to a change in humidity tends to be deteriorated, and curl and wrinkles may be caused to deteriorate the flatness, or the electromagnetic conversion characteristics of the magnetic tape may be deteriorated.

The elongation of the film obtained by the present invention is 1
0% or more, more preferably 20%
Above is desirable because the tape has appropriate flexibility and excellent workability.

The film of the present invention can be used not only as a base film for a magnetic recording medium but also for applications such as a flexible printed board, a thermal transfer ribbon, and a capacitor.

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

When the aromatic polyamide is obtained from, for example, acid chloride and diamine, N-methylpyrrolidone (N
MP), dimethylacetamide (DMAc), dimethylformamide (DMF) and other aprotic organic polar solvents, and is synthesized by solution polymerization or interfacial polymerization using an aqueous medium. When acid chloride and diamine are used as monomers, hydrogen chloride is by-produced in the polymer solution.When neutralizing this, an inorganic neutralizing agent such as calcium hydroxide, calcium carbonate, lithium carbonate, or ethylene is used. Organic neutralizing agents such as oxides, propylene oxide, ammonia, triethylamine, triethanolamine, diethanolamine and the like are used. When an aromatic polyamide is obtained from the reaction between an isocyanate and a carboxylic acid, the reaction is performed in an aprotic organic polar solvent in the presence of a catalyst.

In order to obtain the aromatic polyamide film of the present invention, the intrinsic viscosity η _{inh of the} polymer (0.5 g of
(A value measured at 30 ° C. as a 100 ml solution in 8% sulfuric acid) is preferably 0.5 (dl / g) or more, since the elongation of the film becomes high.

The method of adding the particles is as follows:
There are a method in which particles are sufficiently slurried in a solvent in advance to form a slurry liquid, and the slurry liquid is used as a solvent for polymerization or a solvent for dilution, or a method in which particles are directly added after preparing a stock solution for film formation.

An inorganic salt such as calcium chloride, magnesium chloride, lithium chloride,
In some cases, lithium nitrate or the like is added. Further, as a film forming stock solution, a polymer solution after neutralization may be used as it is, or a solution obtained by once isolating a polymer and then re-dissolving it in a solvent may be used. As the solvent, organic polar solvents such as N-methyl-2-pyrrolidone, dimethylacetamide and dimethylformamide are preferable because they are easy to handle, but strong acidic solvents such as concentrated sulfuric acid, concentrated nitric acid and polyphosphoric acid may be used. The polymer concentration in the stock solution is preferably about 2 to 40% by weight.

The membrane-forming stock solution prepared as described above is
The film is formed by a so-called solution casting method. The solution film forming method includes a dry-wet method and a wet method, and any method may be used. However, the dry-wet method is more preferable because the surface property of the film is improved.

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 form a polymer having a self-supporting property. Dry until concentration (20-70% by weight). If the solvent content exceeds 70% by weight, the self-supporting property of the polymer sheet is insufficient, and the stretchability tends to be uneven. If the solvent content is less than 20% by weight, the polymer is partially precipitated and the stretchability tends to be uneven. Or the elongation of the film may be reduced. Such unevenness in stretchability is not preferred because unevenness is likely to occur in the thickness and physical properties of the film. Because the thickness and physical properties of the film become more uniform,
The solvent content of the polymer sheet is more preferably from 30 to 70% by weight, even more preferably from 30 to 60% by weight. The solvent contained in the polymer sheet is the organic polar solvent described above and / or
Alternatively, a composition containing a strongly acidic solvent in an amount of 10% by weight or more is preferable because the film is hardly broken even when stretched at a high magnification. Here, the polymer sheet refers to a self-supporting film or sheet containing a solvent and a dissolution aid in addition to the polymer.

The width of the polymer sheet is required to be 50 cm or more from the viewpoint of film productivity, and the width of the sheet is determined when the stock solution is extruded from the die, that is, cast on a support. It is adjusted according to the casting width.

The polymer sheet having undergone the dry process is cooled, peeled from the support, and further cooled to room temperature in order to have sufficient self-supporting properties, and then introduced into a wet bath in the next wet process. Then, desalting and desolvation are performed. This wet bath may contain an inorganic salt, but it is preferable to finally extract a solvent or an inorganic salt contained in the polymer sheet with a large amount of water. The polymer sheet that has passed through the wet process is subsequently dried and heat-treated in a tenter to form a film.

The film formed as described above is
During the film forming process, stretching is performed to improve mechanical properties and productivity. The stretching method in the case of a film obtained by solution casting as in the present invention is different from the stretching method in melt casting performed in the formation of a film of polyethylene, polypropylene, polyester, etc., and a solvent or a wet bath component is contained in the film. Is contained and includes a process for moving those components out of the film,
Special techniques are required to obtain the desired film. That is, as the stretching method, an aromatic polyamide, particularly a para-based aromatic polyamide is rigid and poor in stretchability, so that the polymer sheet peeled off from the support through the dry process is a mixed solvent of a good solvent and a poor solvent. It is necessary to stretch the film in the longitudinal direction while immersing it in a bath of liquid to make the film plastic and easily stretchable.

The good solvent used herein is a solvent capable of dissolving a polymer, and N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMC) used as a solvent for polymer polymerization are used.
Organic polar solvents such as F) or strong acids such as concentrated sulfuric acid are preferred. The poor solvent is a solvent in which the polymer is insoluble,
Water or organic non-polar solvents are preferred. As a composition ratio of this mixed bath, the ratio of a good solvent to a poor solvent is 8 parts by weight.
It needs to be 0/20 to 30/70. If the proportion of the good solvent exceeds 80% by weight, the polymer may be dissolved, and if the proportion of the good solvent is less than 30% by weight, the stretching ratio of the film is undesirably lowered. If the weight fraction is more preferably 75/25 to 35/65, and still more preferably 70/30 to 60/40, it is easy to stably obtain a desired stretching ratio. Further, in order to further improve the plasticization of the film, the mixed solvent liquid may contain an inorganic salt such as calcium chloride, magnesium chloride, lithium chloride, lithium nitrate and the like.

The stretching ratio at this time is preferably 1.5 to 5 times. If the ratio is less than 1.5 times, the productivity may be low or the flatness of the film may not be sufficient. If the ratio exceeds 5 times, the molecular chains are too oriented and the film is apt to be torn. The stretching ratio is more preferably 1.5 to 4 times, and still more preferably 1.5 to 3 times, because the film has a better balance between Young's modulus and elongation.

The stretching section needs to be 5 to 300 cm. It is difficult to reduce the stretching section to less than 5 cm in terms of equipment or the stretching property may be reduced. 3
If it exceeds 00 cm, the neck-down becomes large, and the physical properties may be uneven or the flatness may be deteriorated. Since the flatness and the physical properties in the width direction are improved, the stretching section is more preferably 5 to 250 cm, and more preferably 5 to 250 cm.
More preferably, it is 200 cm. The stretching section referred to here refers to a section in which the polymer sheet to be stretched is stretched in a state of being immersed in the mixed solvent solution, and when stretching with a roll, the stretching from the contact point of the roll and the polymer sheet to the contact point is performed. The distance indicates the distance between the centers of the chucks when they are stretched while being held by the chucks.

Further, the stretching speed needs to be 50 to 3000% / sec. If the stretching speed is less than 50% / sec, the orientation of the polymer sheet may be excessively advanced, and the stretching ratio may be reduced. If it is higher than 3000% / sec, the film surface may be damaged or the film may be broken. The stretching speed is more preferably 50 to 2800% / sec, and still more preferably 100 to 2800% / sec, since the stretchability becomes better.
~ 2500% / sec.

Further, it is preferable that the stress at the time of 5% stretching of the polymer sheet immersed in the mixed solvent liquid is 0.1 to 20 MPa. If it is less than 0.1 MPa, the film is too soft, and thickness unevenness is likely to occur. On the other hand, 20MP
If it is larger than a, the load on the device increases, which is not practical. Since the film thickness unevenness becomes better, 5
% At the time of stretching, more preferably 0.5 to 15MP
a, more preferably 1 to 10 MPa.

After being stretched only in the longitudinal direction by the stretching method described above, the polymer sheet is introduced into a wet process,
Desolvation and the like are performed. If the heat treatment is performed without passing through the wet process, the surface may be greatly roughened or curl may be generated, which is not preferable.

The film after the wet process is subjected to drying of water, stretching in the width direction, and heat treatment. Heat treatment temperature is 200
It is preferably in the range of -400 ° C. More preferably, it is 240 to 320 ° C. If the heat treatment temperature is less than 200 ° C., the Young's modulus of the film may be reduced,
If the temperature exceeds 400 ° C., the crystallization of the film proceeds excessively, and the film may be hard and brittle, which is not preferable.

In the heat treatment, the film may be stretched in the longitudinal or width direction again. Stretching temperature is 200
To 400 ° C, more preferably 240 to 320 ° C. If the stretching temperature is lower than this range, the film is easily broken at the time of stretching, and if it is too high, the molecules are less likely to be oriented and the Young's modulus may be insufficient, which is not preferable.

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.

Next, the wet method will be described.

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 introduced into a coagulation bath to remove additives such as a solvent and a dissolution aid. At this time, the coagulation bath is
It is preferable to use a mixed solvent of a good solvent such as a polymerization solvent and a poor solvent such as water. Further, a bath prepared by adding an inorganic salt such as calcium chloride, magnesium chloride, lithium chloride, lithium bromide, and lithium nitrate to a poor solvent may be used.
The polymer sheet from which the solvent has been extracted is peeled off from the support, and is then formed into a film by a method similar to the dry-wet method.

The film of the present invention may be a laminated film. For example, in the case of two layers, a method of dividing the polymerized aromatic polyamide solution into two, adding different particles to each other, and then laminating the solution is mentioned as one example. The same applies to the case of three or more layers. Examples of these lamination methods include lamination in a die, lamination in a composite tube,
There is a method in which one layer is formed once, and another layer is formed thereon.

As described above, the film of the present invention can be obtained, but is not limited thereto.

[0046]

[Example] [Method for measuring physical properties and method for evaluating effects]
The method for measuring physical properties and the method for evaluating effects in the present invention were performed according to the following methods. (1) Solvent content of polymer sheet The polymer content is calculated from the weight of the peeled polymer sheet and the weight of the final film. The value obtained by subtracting the weight of the product was taken as the content of the solvent, and the ratio of the solvent to the weight of the polymer sheet was calculated. (2) Measurement of Stretching Speed of Polymer Sheet The polymer sheet before stretching was marked, the time required to pass through the stretching section was measured, and the stretching speed was calculated from the stretching ratio during this time. (3) Measurement of stress at 5% elongation of polymer sheet Measurement was performed at a temperature of 20 ° C. and a relative humidity of 60% using Robot Tensilon RTA (manufactured by Orientec). After peeling the polymer sheet from the support, wrapped with polypropylene film on both sides, sampled to a width of 10 mm and a length of 50 mm without absorbing moisture, peeled off the polypropylene film, immersed in a predetermined mixed solvent for 10 seconds, and then immersed in Tensilon After setting, the stretching speed was set to each stretching condition, and the stress at the time of 5% stretching in the longitudinal direction was measured. As the film thickness, the thickness of the polymer sheet was used.

(4) Neck Down Ratio After stretching the polymer sheet peeled from the support, the length in the width direction of the film was measured, and the shrinkage ratio calculated by the following equation was defined as the neck down ratio (%). .

(Equation 1) ○, when the neck down rate is 20% or less, 20% to 30%
% Was evaluated as Δ, and 30% or more as X. (5) Young's modulus and elongation Measured at 20 ° C. and 60% relative humidity using a robot Tensilon RTA (manufactured by Orientec). The test piece is 10mm wide, 50mm long and the pulling speed is 300m
m / min. (6) Thickness unevenness The film thickness was measured at an interval of 10 cm in the width direction using an Anritsu electronic micro thickness gauge, and a value obtained by subtracting the minimum value from the maximum value of the thickness was obtained. This was measured 10 times continuously at 1 m intervals in the longitudinal direction, and the average value was determined.

Hereinafter, the present invention will be described in more detail with reference to Examples, but it goes without saying that the present invention is not limited to these.

Example 1 Dissolved in N-methyl-2-pyrrolidone dehydrated was 80 mol% of 2-chloroparaphenylenediamine and 20 mol% of 4,4'-diaminodiphenyl ether. Then, 2-chloroterephthalic chloride corresponding to 98.5 mol% was added thereto, and the mixture was stirred for 2 hours, polymerized by stirring, and neutralized with lithium carbonate to obtain an aromatic polyamide solution having a polymer concentration of 11% by weight. Was.

The aromatic polyamide solution was supplied to a die with an extruder, and was cast on a mirror-like stainless steel belt at a casting speed of 25.2 m / min. The cast polymer solution was first heated with hot air at 160 ° C. and then at 180 ° C. for 1 minute each to evaporate the solvent and peel off. The width of the peeled polymer sheet is 80 cm, and the solvent content is 40.
%, And the stress at 5% elongation after immersion in the mixed solvent solution was 9.6 MPa. This polymer sheet was introduced into a bath of a mixed solvent liquid having a weight ratio of NMP and water of 60/40, and stretched in the longitudinal direction by changing the rotation speed between rolls. The stretching was performed in a stretching section of 50 m at a stretching speed of 100% / sec in the longitudinal direction of the film by 1.7 times. Next, the film was passed through a water tank for 2 minutes to perform water extraction of the residual solvent and the inorganic salt generated by the neutralization. After this,
The length in the width direction was measured, and the neck-down ratio was calculated. Thereafter, in a tenter, a temperature of 280
1. ° C., in the width direction of the film under hot air at a wind speed of 5 m / sec.
One-time stretching and heat treatment were performed. Thus, an aromatic polyamide film having a thickness of 4.4 μm was obtained. Table 1 shows the physical properties of the final film.

[Example 2] In Example 1, the weight ratio of NMP and water in the mixed solvent liquid was set to 70/30, and the stretching section was set to 1
A film was formed in the same manner as in Example 1 except that the stretching rate was changed to 0%, the stretching rate was set to 600% / sec, the stretching ratio in the longitudinal direction was changed to 1.8 times, and the stretching ratio in the width direction was changed to 2.2 times. The film was excellent in both neck-down ratio and thickness unevenness. Table 1 shows the physical properties of the final film.

Example 3 The aromatic polyamide solution of Example 1 was introduced into a mixer together with pure water to precipitate and pulverize the polymer. After washing this polymer with pure water and drying,
The polymer was dissolved in N-methyl-2-pyrrolidone so that the polymer concentration was 15% by weight and lithium chloride was 35% by weight based on the polymer. This solution was supplied to a die with an extruder, and a casting speed of 2 was placed on a mirror-like stainless steel belt.
It was cast at 5.2 m / min. The cast polymer solution was heated with hot air at 130 ° C. for 2 minutes to evaporate the solvent and peel off. The width of the peeled polymer sheet was 80 cm, the solvent content was 73% by weight, and the stress at the time of 5% stretching after dipping in the mixed solvent liquid was 15.1 MPa. This polymer sheet was introduced into a bath of a solvent liquid in which the weight ratio of NMP and water was 50/50, and stretched 1.6 times in the longitudinal direction at a stretching section of 50 cm and a stretching speed of 80% / sec. Next, the film was passed through a water tank for 2 minutes to extract the remaining solvent with water. After this,
The film was stretched 2.0 times in the width direction and heat-treated in a tenter under hot air at a temperature of 280 ° C. and a wind speed of 5 m / sec. Thus, an aromatic polyamide film having a total thickness of 4.4 μm was obtained. Table 1 shows the physical properties of the final film.

Example 4 The aromatic polyamide solution of Example 1 was introduced into a mixer together with pure water to precipitate and pulverize the polymer. After washing this polymer with pure water and drying,
The polymer was dissolved in N-methyl-2-pyrrolidone so that the polymer concentration became 15% by weight.

This solution was supplied to a die with an extruder, and the casting speed was 29 m / m on a stainless steel belt having a mirror-like surface.
Cast in minutes. The cast polymer solution is heated to 110 ° C.
Was heated for 104 seconds with hot air to evaporate the solvent and peel off.
The width of the peeled polymer sheet is 80 cm, and the solvent content is 1
5% by weight, and the stretching stress after immersion in the mixed solvent liquid is 2%.
It was 3.8 MPa. This polymer sheet is introduced into a bath of a solvent liquid in which the weight ratio of NMP and water is 60/40, and is stretched 1.6 cm in a stretching section of 160 cm at a stretching speed of 60% / sec.
Double stretching was performed. Next, the film was passed through a water tank for 2 minutes to extract the remaining solvent with water. Thereafter, the film was stretched 2.0 times in the width direction of the film and heat-treated in a tenter under hot air at a temperature of 280 ° C. and a wind speed of 5 m / sec. Thus, an aromatic polyamide film having a total thickness of 4.4 μm was obtained. Table 1 shows the physical properties of the final film.
Both thickness unevenness became slightly larger.

Example 5 To dehydrated N-methyl-2-pyrrolidone, 40 mol% of 2-chloroparaphenylenediamine and 60 mol% of 3,4'-diaminodiphenyl ether were added. Dissolve and add 98.5
2-Chloroterephthalic acid chloride was added in an amount of 2 mol%, and the mixture was polymerized by stirring for 2 hours and neutralized with lithium carbonate to obtain an aromatic polyamide solution having a polymer concentration of 11% by weight.

The above aromatic polyamide solution was supplied to a die with an extruder, and was cast on a mirror-like stainless steel belt at a casting speed of 29 m / min. The cast polymer solution was first heated with hot air at 170 ° C. and then at 180 ° C. for 52 seconds each to evaporate the solvent and peel off. The width of the peeled polymer sheet was 80 cm, the solvent content was 35% by weight, and the stress at the time of 5% stretching after dipping in the mixed solvent solution was 0.04 MPa. This polymer sheet was introduced into a bath of a solvent solution in which the weight ratio of NMP and water was 80/20, and was stretched 5.2 times in the longitudinal direction of the film at a stretching section of 40 cm and a stretching speed of 2640% / sec. Next, the film was passed through a water tank for 2 minutes to perform water extraction of the residual solvent and the inorganic salt generated by the neutralization. Thereafter, in a tenter, at a temperature of 280 ° C.
The film was stretched 2.6 times in the width direction of the film and heat-treated under hot air at a wind speed of 5 m / sec. Thus, an aromatic polyamide film having a total thickness of 4.4 μm was obtained. Table 1 shows the physical properties of the final film. The elongation was lower than that of Example 1.

[Comparative Example 1] In Example 1, the weight ratio of NMP and water in the solvent liquid was set to 60/40, and the stretching section was set to 250.
cm, and the stretching speed was changed to 20% / sec. Table 1 shows the physical properties of the final film. Compared with Example 1, the elongation was significantly reduced.

Comparative Example 2 In Example 5, the weight ratio of NMP and water in the solvent liquid was set to 70/30, and the stretching section was set to 350
cm, the stretching speed was changed to 30% / sec, the longitudinal stretching magnification was changed to 2.1 times, and the width stretching ratio was changed to 2.5 times. Table 1 shows the physical properties of the final film. Compared with Example 4, thickness unevenness was increased, and elongation was significantly reduced.

Comparative Example 3 In Example 5, the weight ratio of NMP and water in the solvent liquid was set to 85/15, and the casting speed was set to 7 m / m.
Minutes, and the cast polymer solution is first heated to 140 ° C.
Subsequently, the solvent was evaporated by heating each with hot air of 150 ° C. for 3 minutes to elongate the stretching section to 4 cm and the stretching speed to 205 cm.
The film was formed in the same manner as in Example 5, except that the stretching ratio in the longitudinal direction was changed to 3.2 times and the stretching ratio in the width direction was changed to 2.5 times. Table 1 shows the physical properties of the final film. The neck down rate has deteriorated significantly.

[Comparative Example 4] In Example 3, the weight ratio of NMP and water in the solvent liquid was 85/15, and the stretching section was 30 c.
m, the stretching speed was changed to 3900% / sec, the stretching ratio in the longitudinal direction was changed to 5.8, and the stretching ratio in the width direction was changed to 2.7 times. Other than that, the film was formed in the same manner as in Example 3. Table 1 shows the physical properties of the final film. A film with a large neck down and large thickness unevenness was obtained.

[Comparative Example 5] In Example 3, the weight ratio of NMP and water in the solvent liquid was set to 0/100, and the stretching section was set to 10c.
m, the stretching speed was changed to 160% / sec, and the stretching ratio in the longitudinal direction was changed to 2 times or more, and the stretching was attempted, but the film was broken and the film could not be formed. Therefore, the stretching ratio is set to 1.3 in the longitudinal direction.
A film was formed in the same manner as in Example 3 except that the film was 1.8 times in the width direction. Table 1 shows the physical properties of the final film.

[0062]

[Table 1]

[0063]

According to the method of the present invention, it is possible to stretch at a high magnification during the production of an aromatic polyamide film, and it is possible to suppress neck down even when stretching at a high magnification, thereby reducing thickness unevenness and increasing the thickness. Since the high draw ratio of the aromatic polyamide can be exhibited by the draw ratio, the productivity of the aromatic polyamide film can be improved, the cost can be reduced, and the aromatic polyamide particularly useful as a base film of a magnetic recording medium can be obtained. A film is obtained.

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Claims (9)

[Claims] When a polymer sheet made of an aromatic polyamide containing a solvent and having a sheet width of 50 cm or more is stretched in the longitudinal direction, the polymer sheet has a good solvent / poor solvent composition ratio of good solvent / poor solvent. A method for producing an aromatic polyamide film, characterized in that the film is stretched at a stretching section of 5 to 300 cm and a stretching speed of 50 to 3000% / sec while being immersed in a mixed solvent liquid of 80/20 to 30/70% by weight. 2. The method for producing an aromatic polyamide film according to claim 1, wherein the good solvent is an organic polar solvent and / or a strongly acidic solvent, and the poor solvent is an organic non-polar solvent and / or water. 3. The method for producing an aromatic polyamide film according to claim 1, wherein the stretching ratio in the longitudinal direction is 1.5 to 5 times. 4. 5% of a polymer sheet immersed in a mixed solvent liquid
The method for producing an aromatic polyamide film according to any one of claims 1 to 3, wherein a stress at the time of stretching is 0.1 MPa to 20 MPa. 5. The method for producing an aromatic polyamide film according to claim 1, wherein the solvent content of the polymer sheet before immersion in the mixed solvent liquid is 20 to 70% by weight. 6. The method for producing an aromatic polyamide film according to claim 1, wherein the mixed solvent liquid contains an inorganic compound. 7. The aromatic ring 8 constituting the aromatic polyamide
The method for producing an aromatic polyamide film according to any one of claims 1 to 6, wherein 0 mol% or more is an aromatic ring having para-orientation. 8. The method for producing an aromatic polyamide film according to claim 7, wherein the aromatic polyamide contains at least 60 mol% of the repeating unit represented by the formula (3). Formula (3): 9. An aromatic polyamide film obtained by forming a film by the production method according to claim 1.