JPH0778135B2 - Aromatic polyamide film and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a film made of a para-oriented aromatic polyamide and a method for producing the film, and more specifically to a longitudinal direction (referred to as MD direction) and a width direction of the film. The present invention relates to a thin para-oriented aromatic polyamide film having small thickness unevenness, which exhibits excellent opportunity characteristics (referred to as TD direction), and a method for producing the same.

[Conventional technology]

Poly (p-phenylene terephthalamide), which is a typical para-oriented aromatic polyamide (hereinafter referred to as PPTA)
Has a particularly excellent crystallinity and a high melting point, and because of its rigid molecular structure, it has high heat resistance and high opportunity strength. Fibers spun from a concentrated solution exhibiting its optical anisotropy have been reported to exhibit high strength and modulus, and it has already been industrially implemented, but few proposals for application to films have been made. , The practical application is not yet known.

The problem with PPTA is that its useful high molecular weight polymer is poorly soluble in organic solvents, and strong inorganic acids such as concentrated sulfuric acid must be used as a solvent. For example, in Japanese Patent Publication No. 56-45421, copolymerization of a linear coordination aromatic polyamide having a halogen group introduced in the aromatic nucleus and an aromatic polyamide having no substituent in the aromatic nucleus other than PPTA is to be copolymerized. Has made an attempt to make it soluble in an organic solvent and obtain a film therefrom. However, this is because the monomer is expensive,
In addition to the high cost, there is a drawback that the heat resistance and crystallinity of the straight-chain linearly coordinated aromatic polyamide are impaired.

On the other hand, JP-B-59-14567 discloses a method of extruding an aromatic polyamide solution having optical anisotropy through a slit into a coagulation bath through a short air layer. Only the mechanical strength of
The mechanical strength in the direction was extremely weak, and only those that were easy to avoid were obtained.

In this way, if the optically anisotropic dope of aromatic polyamide is simply extruded and coagulated as it is, it is likely to be fibrillated because it is excessively oriented in the discharge direction, which is weak in the TD direction. Various methods for producing films have been studied.

For example, in Japanese Examined Patent Publication No. 57-35088, an aromatic polyamide solution having optical anisotropy is extruded from a ring die, simultaneously cast in a dope state in a biaxial direction by an inflation method, and then wet-solidified. It is said that an isotropic film can be obtained. However, with this method, it is difficult to obtain a transparent film of uniform thickness, and mechanical strength,
In particular, it has the drawback of low tear strength.

Further, in JP-B-59-5407 and JP-A-54-132674, an optically anisotropic or optically isotropic dope of a linearly coordinated aromatic polyamide is introduced in a die in a direction perpendicular to the extrusion direction. It has been proposed to mechanically apply a shearing force to orient the resin in the biaxial directions of the extrusion direction and the direction perpendicular to the extrusion direction at the time of extrusion, but the structure of the die is complicated and there is a difficulty in industrial implementation. Further, it is difficult to obtain a film having high tear strength by the method of performing orientation by shearing force.

Furthermore, J.Appl.Polym.Sci.vokl.27, No.8, P.2965-29
In 85 (1982), it was proposed to obtain a biaxially oriented film by extruding an optically anisotropic dope of PPTA from a ring die onto an oil-coated conical mandrel. Although the mechanical strength is isotropic but low, when the draft is applied, the mechanical strength in the MD direction is high, but that in the TD direction is notably low, and the method using the ring die is It is difficult to reduce unevenness in film thickness.

JP-B-57-17886 discloses that an optically anisotropic dope of a linear coordinating aromatic polyamide is heated immediately before solidification until it becomes optically isotropic, and then solidified to obtain transparent and mechanical properties. It is described to obtain a film that is directional. This method is an original method that is contrary to most of the conventional concepts of achieving high performance by utilizing the optically anisotropic dope, and thereby relaxes the extreme uniaxial orientation of the optically anisotropic dope. At the same time, we succeeded in avoiding that the optically anisotropic doped liquid crystal domain structure remains even after the dope is extruded and solidifies as it is to become an opaque film. However, it does not specifically disclose a transparent film which is extremely thin and has less unevenness in thickness.

[Problems to be solved by the invention]

It is an object of the present invention to provide an ultrathin film with less thickness unevenness, high transparency, and excellent flatness, and an industrial production method thereof, using a para-oriented aromatic polyamide.

[Means for solving problems]

The present inventors have earnestly conducted research to obtain a para-oriented aromatic polyamide film in accordance with the above purpose, and have obtained the following findings.

That is, the technology disclosed in Japanese Examined Patent Publication No. Sho 57-17886,
That is, in the method of producing an optically anisotropic dope of PPTA, and then optically isotropically solidifying it to produce a para-oriented aromatic polyamide film having excellent mechanical performance with transparency, the dope , And then adhered to the support surface at the shortest distance possible, and then optically isotropically solidified,
It was found that a novel film having extremely small thickness unevenness can be obtained with extremely high transparency and flatness by limiting the shrinkage that occurs in the drying step after washing, and as a result of further research, the present invention was found. Was completed.

The present invention is a film made of a substantially para-oriented aromatic polyamide having a logarithmic viscosity of 3.5 or more, having a thickness of 8 μm or less and having a thickness unevenness of ± 5% or less. It is an aromatic polyamide film.

Further, the production method of the aromatic polyamide of the present invention has a logarithmic viscosity of 3.
An optically anisotropic dope consisting essentially of 5 or more para-oriented aromatic polyamide and 95% by weight or more of sulfuric acid is cast onto a supporting surface moving from the die while maintaining the optical anisotropy, and absorbs moisture. Or / and in a method for producing a film in which the dope is optically isotropically converted by heating and then solidified, the dope is brought into contact with the supporting surface at a distance of 30 mm or less from a die and then optically isotropically converted. The film is then coagulated and washed, and then dried while the shrinkage of the film is limited.

PPTA as its representative polymer, which is a para-oriented aromatic polyamide used in the present invention, is substantially It is a polymer represented by the following formula, and it is convenient to produce it from a conventionally known paraphenylenediamine and terephthaloyl chloride by a low temperature solution polymerization method.

The degree of polymerization of the polymer of the present invention is not so low that a film having good mechanical properties cannot be obtained. Therefore, a logarithmic viscosity ηinh of 3.5 or more, preferably 4.5 or more (dissolving 0.3 g of the polymer in 100 ml of sulfuric acid at 30 ° C. The degree of polymerization that gives a measured value) is selected. The upper limit of the polymerization degree of the polymer is not limited as long as it can be industrially produced.

The film of the present invention can achieve the purpose only when the following two requirements are satisfied.

First of all, the film of the present invention has a thickness of 8 μm.
The following are selected: When a film having a thickness exceeding 8 μm is used as a capacitor film, for example, it is generally necessary to increase the electrode area in proportion to the square of the thickness in order to make a capacitor having the same capacity as a thin film. However, it is not possible to obtain a small and lightweight capacitor with a large electrostatic capacitance, which is a feature of film capacitors. There is no particular lower limit on the thickness of the film, but if the film is too thin, it will be difficult to handle.
When the film of the present invention is used for a capacitor, for example, a thickness of 5 μm or less is more preferable.

Secondly, the film of the present invention is required to have a thickness variation of 10% or less. This requirement is indispensable for producing capacitors having the same capacitance, for example, in the case of a capacitor film as described above, and is preferably 6% or less. If a capacitor with a film thickness unevenness of more than 10% is used, not only will the yield be high and the productivity will be poor, but also space will be generated in the capacitor, so film vibration will occur due to the application of AC power, and Since it produces a sound corresponding to, it cannot be used.

The thickness and thickness unevenness referred to in the present invention, for example, using a capacitance-type contact thickness gauge (Type CL-230 manufactured by Ono Sokki Co., Ltd.),
The average value of the thickness at 10 measurement points arbitrarily selected from the film, and (maximum value-minimum value) / average value × 100,
Is defined.

The film of the present invention preferably has extremely high transparency and smooth flatness. High transparency is, for example, 600n
The transmittance of visible light having a wavelength of m is preferably 55% or more, more preferably 70% or more.

Also, the film of the present invention is preferably substantially free of voids.

Further, the films of the present invention typically have a density of 1.370.
It is in the range of ~ 1.420 g / cm ³ . This density value is measured at 30 ° C. by a density gradient tube method using carbon tetrachloride-toluene. Scope of this density is considerably smaller compared to that of known PPTA fibers is from 1.43 g / cm ³ in the range of 1.46 g / cm ^3. If the density is less than 1.370 g / cm ³ , the mechanical properties will be deteriorated, and if it exceeds 1.420 g / cm ³ , the film will be inferior in the plane orientation and hence the isotropy of the mechanical properties. In any case, because of such low density, a light and high-strength film can be obtained.

The film of the present invention preferably has a plane orientation defined by a crystal orientation angle by X-ray diffraction described below.
That is, 2θ due to X-rays that are incident at right angles to the film surface
The crystal orientation angle with respect to the peak of ≈23 ° is 30 ° or more,
It is preferable that the crystal orientation angle with respect to the peak of 2θ≈18 ° by X-rays incident on the film surface in parallel is 60 ° or less.

The incidence of X-rays is divided into a case where the X-rays are incident on the film surface at right angles (hereinafter, referred to as TV direction) and a case that the X-rays are incident on the surface in parallel (hereinafter referred to as SV direction). There is a large diffraction peak at 2θ≈23 ° due to X-rays from the direction, but the crystal orientation angle at 2θ≈23 ° is
It is preferably 30 ° or more. More preferably, it is 50 ° C. or higher. Furthermore, 2θ ≒ due to incidence from the SV direction
A large 18 ° diffraction peak appears on the equator line.
The crystal orientation angle at θ≈18 ° is preferably 60 ° or less. It can be said that the film of the present invention has a structure of so-called plane orientation when both of these crystal orientation angles are satisfied, and it has high mechanical properties (eg, strength, Elongation, Young's modulus) and high tear strength are very preferable. And in this respect, Japanese Patent Publication No. 55-14170
It can be clearly distinguished from the film disclosed in the publication.

A known method can be adopted as a method for measuring the crystal orientation angle,
For example, the following method is used. Predetermined 2θ
The diffraction intensity curve is obtained by placing the counter at an angle of and rotating the film 180 °. In addition, in the TV, the maximum strength is the center of rotation and the front and rear are rotated 90 °. The arc length in the diffractogram, expressed in degrees, corresponding to the point at which the highest intensity of this curve is half the intensity of the baseline drawn between the lowest intensity points (ie, 50% of the highest intensity baseline). The angle with respect to the point) is measured and used as the crystal orientation angle of the sample. At the time of measurement, the diffraction intensity can be measured by stacking several films as necessary.

Such a thin film with less unevenness in thickness can be manufactured according to the following method. It should be noted that the fact that the film has less unevenness is also related to the fact that the shrinkage during drying is limited as described later.

In the method of the present invention, it is first necessary to adjust the optically anisotropic doping of PPTA.

A suitable solvent for adjusting the dope used for molding the PPTA film of the present invention is sulfuric acid at a concentration of 95% by weight or more.
If the sulfuric acid content is less than 95%, it will be difficult to dissolve or the dope after dissolution will have an abnormally high viscosity. The dope of the present invention may contain a small amount of chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid or the like. 100% by weight of sulfuric acid
Although the above are possible, 98 to 100% by weight concentration is preferably used from the viewpoint of stability and solubility of the polymer.

The polymer concentration in the dope used in the present invention is preferably at least a concentration exhibiting optical anisotropy at room temperature (about 20 to 30 ° C.) or higher, specifically about 10% by weight or more. . At a polymer concentration that does not exhibit optical anisotropy at room temperature or higher, the molded PPTA film often loses desirable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited,
Usually less than 20% by weight, especially 1 for PPTA with high ηinh
8 wt% or less is preferably used, more preferably 16
It is less than or equal to wt.

The dope of the present invention contains the usual additives such as extenders, delusterants, UV stabilizers, heat stabilizers, antioxidants, pigments,
A dissolution aid or the like may be mixed.

Whether the dope is optically anisotropic or optically isotropic can be examined by a known method, for example, the method described in JP-B-508474. The critical point is the kind of solvent, temperature, and polymer concentration. , It depends on the degree of polymerization of the polymer, the content of non-solvent, etc., so by investigating these relations in advance, an optically anisotropic dope is created, and by changing the conditions to become an optically isotropic dope, an optical anisotropy is obtained. The property can be changed from optical to isotropic.

In the dope used in the present invention, insoluble dust, foreign matters, etc. are removed by filtration etc. as much as possible prior to molding and solidification, and the base such as air generated or caught during melting is removed. It is preferable. The deaeration can be performed after the dope is once adjusted, or can be achieved by consistently performing the vacuum (reduced pressure) from the raw material charging step for the adjustment. The dope can be adjusted continuously or batchwise.

The dope thus prepared is cast on a supporting surface moving from a die, for example, a slit die, which retains optical anisotropy. The distance until the dope contacts the supporting surface is important and must be 30 mm or less. This distance is 30
If the thickness is more than mm, although the reason is not clear, not only the particulate matter is generated and the thickness is uneven, but also the tear is generated. This phenomenon is particularly noticeable when the film is thinned, and is an essential requirement for obtaining a thin film with a thickness variation of ± 5% or less. The distance until the film-like dope coming out of the die contacts the supporting surface should be as short as possible.

In the present invention, the steps of casting and subsequent conversion to optical isotropy, coagulation, washing, stretching, drying and the like are preferably carried out continuously, but if necessary, all or part of them may be intermittently carried out. In other words, it may be carried out batchwise.

To obtain a transparent film having excellent mechanical properties of the present invention,
After casting the dope on the support surface, it is necessary to convert the dope from optical anisotropy to optically isotropic prior to solidification.

In order to make the optical anisotropy from the optical anisotropy, specifically, the optically anisotropic dope cast on the support surface is solidified prior to coagulation to reduce the concentration of the solvent that forms a dope to reduce the concentration of the solvent. The dope is transferred to the optically isotropic region by changing the solubility and the polymer concentration, or the temperature of the dope is raised by heating, and the phase of the dope is optically isotropic, or moisture absorption and heating are performed simultaneously or sequentially. Can be achieved by using Of these, the method that utilizes moisture absorption is
It is useful, including the method of using heating in combination, because optical anisotropy of optical anisotropy is efficiently performed without causing decomposition of PPTA.

Air having a normal temperature and humidity may be used for absorbing the dope, but humidified or warmed air is preferably used. The humidified air may contain mist-like water in excess of the saturated vapor pressure, or may be so-called steam. However, supersaturated steam having a temperature of about 45 ° C. or lower often contains large amounts of condensed water, which is not preferable. Moisture absorption is usually performed with humidified air at room temperature to about 180 ° C, preferably 50-150 ° C.

In the case of a method by heating, the heating means is not particularly limited,
Examples include the method of applying the humidified air to the casting dope, the method of irradiating an infrared lamp, the method of dielectric heating and the like.

The cast dope that is optically isotropic on the support surface then contacts the coagulation station and undergoes coagulation. In the present invention, usable as the coagulating liquid of the dope are, for example, dilute sulfuric acid containing about 70% by weight or less of water, aqueous sodium hydroxide solution containing about 20% by weight or less and ammonia water, sodium sulfate containing about 10% by weight or less, sodium chloride. For example, an aqueous solution and an aqueous calcium chloride solution.

In the present invention, the temperature of the coagulating liquid is preferably 15 ° C or lower, more preferably 5 ° C or lower. It was generally found that the lower the temperature of the coagulating liquid, the less voids were contained in the film.

Since the coagulated film contains acid as it is, it is necessary to wash and remove the acid component as much as possible in order to produce a film in which mechanical properties are not significantly deteriorated by heating. Specifically, it is desirable to remove the acid component up to about 500 ppm or less. Water is usually used as the cleaning liquid, but if necessary, it may be carried out with warm water, or may be neutralized with an alkaline aqueous solution and then washed with water or the like. The cleaning is performed, for example, by running the film in the cleaning liquid or spraying the cleaning liquid.

The washed film may be stretched in the wet before it is subsequently dried. Stretching must be performed in a wet state before drying, and stretching that is effective for improving mechanical properties cannot be performed in a state where a large amount of sulfuric acid remains or after drying.

Drying should be performed under tension, under constant length or while slightly stretching while limiting the shrinkage of the film. If the film, which has a tendency to shrink with the removal of the washing liquid (for example, water), is dried without any restriction of shrinkage, it may be because micro-uniform structure formation (crystallization etc.) occurs. The light transmittance of the applied film becomes small. Further, in the case of the thin film of the present invention, not only a film having inferior mechanical properties is often obtained, but also uneven thickness due to partial shrinkage or the like, further impairing the flatness of the film, It may curl. To limit the shrinkage while drying, for example, a tenter dryer or a sandwiching method with a metal frame can be used. Other conditions relating to drying are not particularly limited, and heated gas (air, nitrogen, argon, etc.)
Or a method using a room temperature gas, a method of utilizing radiant heat such as an electric heater or an infrared lamp, a method of dielectric heating, etc., and the drying temperature is not particularly limited, but if the temperature is room temperature or higher. Good. However, in order to increase the mechanical strength of the film, the drying temperature is preferably high, for example, 100 ° C or higher, more preferably 200 ° C or higher. The maximum drying temperature is not particularly limited, but is preferably 500 ° C. or lower in consideration of drying energy and polymer degradability.

In the method of the present invention, it is preferable to produce the film while continuously running the film through all steps.
However, if desired, it may be partially batchwise. Further, an oil agent, a dye for identification, or the like may be applied to the film in any process.

Incidentally, in the present invention, excellent transparency, that is, extremely large light transmittance, in order to obtain a film, the dope is, of course, a hygroscopic gas, a heating gas, a support surface, a coagulating liquid, a cleaning liquid, a dry It is preferable to reduce the content of dust such as gas and dust as much as possible. In this respect, it is also one of the preferred embodiments to produce the film of the present invention in a so-called clean room or clean water.

〔Example〕

Examples of production of Examples and Reference Examples (PPTA) are shown below,
These Reference Examples and Examples illustrate the invention but do not limit the invention. In the examples, unless otherwise specified, parts by weight or% by weight is shown. Logarithmic viscosity η inh is 0.2% polymer dissolved in 100% 98% sulfuric acid,
It was measured at 30 ° C. by a conventional method. The viscosity of the dope was measured with a B type viscometer at a rotation speed of 1 rpm. The thickness of the film was arbitrarily selected from the film using a capacitance-type non-contact thickness gauge (Type CL-230, manufactured by Ono Sokki Co., Ltd.) 1
The average value of the thickness at 0 measurement points was obtained, and the thickness unevenness was calculated from (maximum value-minimum value) / average value × 100. For strength and elongation, a constant-speed elongation type strength and elongation measuring machine cuts a film sample into a rectangle of 100 mm × 10 mm, and draws the load-stretch curve 5 times at an initial grip length of 30 mm and a pulling speed of 30 mm / min. , Calculated from this.

Reference Example (Production of PPTA) PPTA was obtained by the low temperature solution polymerization method as follows. Tokusho
In a polymerization apparatus disclosed in Japanese Patent Laid-Open No. 53-43986, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine was dissolved. After cooling to 8 ° C., 91.4 parts of terephthalic acid dichloride was added all at once in powder form. After a few minutes, the polymerization reaction product solidified into a cheese, so the polymerization reaction product was discharged from the polymerization apparatus according to the method described in JP-B-53-43986, immediately transferred to a biaxial closed type kneader, and polymerization was carried out in the kneader. The reaction was finely ground. Next, the finely pulverized product was transferred into a Hexiel mixer, added with approximately the same amount of water, further pulverized, filtered, washed several times in warm water, and dried in hot air at 110 ° C. 95 parts of a pale yellow PPTA polymer having an ηinh of 5.5 was obtained. Note that different η
The polymer of inh can be easily obtained by changing the ratio of N-methylpyrrolidone and the monomers (paraphenylenediamine and terephthalic acid dichloride), and / or the ratio between the monomers.

Examples 1-2 and Comparative Example 1 A PPTA polymer having an ηinh of 5.3 was dissolved in 99.6% sulfuric acid at a polymer concentration of 12.0% to obtain a dope having optical anisotropy at 60 ° C. When the viscosity of this dope was measured at room temperature, it was 10,200
It was a poise. In order to facilitate film formation, the dope was degassed under vacuum while keeping the dope at about 60 ° C. Also in this case, the optical anisotropy was the same as above, and the viscosity was 4000 poise. A 1.5 mm bent tube that reaches the die through the filter from the tank and the gear pump is kept at about 60 ° C, and a mirror made tantalum belt (3 to 8 m / min) is used from the die with a 0.2 mm x 250 mm slit. Cast on the belt at the distance between the die and the supporting surface shown in Table 1, and the relative humidity is about 15% at about 90 ° C.
The air was blown into the casting dope to make the casting dope optically isotropic, and the belt was introduced into water at 5 ° C. to be solidified. Next, the coagulated film was peeled off from the belt and run in water at about 20 ° C. for washing.

The washed film was sandwiched between gold frames and dried at 320 ° C. under a fixed length. Table 1 summarizes the results of sampling films having different thicknesses obtained by changing the belt speed. The film of Comparative Example 1 had granular irregularities on one surface.

Comparative Example 2 When the same apparatus and method as in Example 1 were used and the film-like dope discharged from the die was brought into contact with the belt at a distance of 40 mm at a belt speed of 4 m / min and the belt was cast, the dope was cut and could not be cast. .

[Effects of the Invention] The film of the present invention, as shown in the examples, is extremely thin and has few thickness irregularities, which are not found in commercially available films, and has good mechanical properties represented by high strength and high Young's modulus. is doing. In addition to these mechanical properties, they also have excellent electrical insulation, heat resistance, oil resistance, pressure resistance, chemical resistance other than strong acid, and structural tightness. Therefore, the film of the present invention can be suitably used for an insulating material of a high-speed rotating electric device, a porcelain tape, a flexible printed wiring board, an electric wire coating material, a filtration membrane, and the like. Due to its excellent properties, it is also useful as a packaging material, a plate-making material, a photographic film and the like.

Further, since the film of the present invention is extremely thin, has less thickness unevenness, and is excellent in heat resistance, it is lightweight and ultra-small when used as a capacitor film, but can be directly put in a molten solder bath for soldering. Since it can be used as a capacitor, it is useful as a film for capacitors, which is unprecedented in organic films.

Claims (2)

[Claims] 1. A film made of a substantially para-oriented aromatic polyamide having an inherent viscosity of 3.5 or more, having a thickness of 8 μm or less and having a thickness unevenness of 10% or less. Aromatic polyamide film. 2. An optical anisotropic dope consisting essentially of a para-oriented aromatic polyamide having a logarithmic viscosity of 3.5 or more and sulfuric acid of 95% by weight or more, which is moved from a die while maintaining the optical anisotropy. In the method for producing a film, which is cast on a surface and is converted into an optically isotropic mixture by moisture absorption and / or heating and then solidified, the dope is contacted with the supporting surface at a distance of 30 mm or less from a die. A method for producing an aromatic polyamide film, which comprises converting to an optically isotropic state, then coagulating and washing, and then drying the film while limiting shrinkage of the film.