JPH03231931A - Aromatic polyamide film - Google Patents

Abstract

PURPOSE:To obtain the title film useful for electric wire coating material and filter membrane and having excellent electric characteristics, mechanical characteristics and long-term heat resistance by neutralizing a substantially para-oriented aromatic polyamide having a specific inherent viscosity with a trivalent metal ion containing solution. CONSTITUTION:A para-oriented aromatic polyamide (preferably poly-p-phenylene terephthalic amide) selected from units of formula I, formula II and formula III (Ar1, Ar2 and Ar3 are divalent aromatic group; formula I and formula II are substantially equimolar when they exist in a polymer) and composed thereof and having >=2.5 (preferably >=4.5) inherent viscosity etainh is dissolved in sulfuric acid, etc., to afford a dope, which is then cast on a supporting surface to convert the dope into optical isotropy and then solidified and the solidified film is preferably washed with water and then brought into contact with an aqueous solution containing 500-30000ppm trivalent metal ion (preferably Al<3+>) at <=100 deg.C for 5sec to 20min and dried to provide the aimed film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a film consisting essentially of para-oriented aromatic polyamide.

More specifically, the present invention provides excellent mechanical properties in both the longitudinal direction (hereinafter referred to as MD force direction) and the width direction (hereinafter referred to as TD force direction) due to excellent electrical properties and excellent plane orientation. The present invention relates to a para-oriented aromatic polyamide film which exhibits the following characteristics and has good long-term heat resistance.

[Conventional technology]

Poly-p-phenylene terephthalamide has particularly excellent crystallinity and high melting point, and because of its rigid molecular structure,
It is a polymeric material that has attracted particular attention in recent years as it has heat resistance and high mechanical strength. In addition, it has been reported that fibers spun from concentrated solutions exhibiting optical anisotropy exhibit high strength and modulus, and have already been implemented industrially, but there are no proposals for application to films. There are still few examples of practical use known.

Problems with para-oriented aromatic polyamides include:
The useful high molecular weight polymers are sparingly soluble in organic solvents, requiring that strong inorganic acids such as concentrated sulfuric acid be used as the solvent. To avoid this,
For example, in Japanese Patent Publication No. 5,645,421, a unit in which a halogen group is introduced into the aromatic nucleus of a linearly oriented aromatic polyamide is copolymerized with an aromatic polyamide having no substituent group in the aromatic nucleus, which is soluble in organic solvents. Attempts have been made to obtain films from it.

However, this method has the disadvantage that the cost is high because the 7-mer is expensive, and that it impairs the heat resistance and crystallinity of the para-configured aromatic polyamide.

On the other hand, Japanese Patent Publication No. 59-14567 discloses a method of extruding an aromatic polyamide solution having optical anisotropy from a slit through a short air space into a coagulation bath.
In this method, only the mechanical strength in the MD force direction was strong, but the mechanical strength in the TD force direction perpendicular to it was extremely weak, and only a product that could be easily torn was obtained.

If the optically anisotropic dope of aromatic polyamide is simply extruded and solidified as it is, it will be excessively oriented in the ejection direction, making it easy to fibrillate and weak in the TD force direction. Various methods of producing films have been studied in an attempt to improve them.

For example, in Japanese Patent Publication No. 57-35088, an aromatic polyamide solution having optical anisotropy is extruded from a circular gouie, and after being simultaneously cast in two axes in a doped state using an inflation method, wet casting is carried out. It is said that an isotropic film can be obtained by solidifying the material. However, this method has the disadvantage that it is difficult to obtain a transparent film with uniform thickness and mechanical strength, particularly tear strength, is low.

Also, Japanese Patent Publication No. 59-5407, Japanese Patent Application Publication No. 54132
No. 674 discloses that by mechanically applying a shearing force to an optically anisotropic or optically isotropic 1-p of para-oriented aromatic polyamide in a direction perpendicular to the extrusion direction,
Although it has been proposed to orient the material in two axes, one in the extrusion direction and one perpendicular to the extrusion direction during extrusion, the structure of the die is complicated and there are difficulties in industrial implementation.

Furthermore, the Journal of Applied Polymer Science, Vol. 27 (No. 8), pp. 2965-2985 (1982) describes a conical mandrel coated with an optically anisotropic dope of polyparaphenylene terephthalamide through an annular die. It has been proposed to obtain a biaxially oriented film by extrusion on the
The mechanical strength is low, and when a draft is applied, the strength in the MD force direction A-wave direction is high, but the TD force direction strength is extremely low.

Japanese Patent Publication No. 57-17886 discloses that by heating an optically anisotropic dope of para-oriented aromatic polyamide until it becomes optically isotropic immediately before solidifying it, and then solidifying it, it is transparent and has equal mechanical properties. It is described to obtain a film that is oriented in the same direction. This method is an original method that goes against the concept of trying to obtain a film with higher performance than the conventional optically anisotropic dope, and it allows the relaxation of the extreme uniaxial conformation of the optically anisotropic dope. At the same time, it has been successfully avoided that the liquid crystal domain structure of the optically anisotropic dope remains even after the dope is extruded and solidifies as it is, resulting in an opaque film.

In addition, in Japanese Patent Application Laid-Open No. 115036/1982,
In JP 7-17886, the wet film after coagulation is
By neutralizing with sodium hydroxide solution, they succeeded in obtaining a film with excellent transparency.

The film obtained by this method has good long-term heat resistance, but has poor electrical properties due to the influence of residual sodium. On the other hand, when water washing was strengthened to remove sodium, it was confirmed that the mechanical properties were significantly reduced and the long-term heat resistance was inferior, similar to when the film was produced without neutralization. However, it does not specifically disclose a film that is excellent in both long-term heat resistance and electrical properties.

[Problem to be solved by the invention]

An object of the present invention is to provide a film with excellent electrical properties and long-term heat resistance using a para-oriented aromatic polyamide whose industrial production has already begun.

[Means to solve the problem]

The present inventors have made the following findings as a result of intensive research to obtain an aromatic polyamide film that meets the above objectives.

That is, by the technique disclosed in Japanese Patent Publication No. 57-17886 (in which an optically anisotropic dope of para-oriented aromatic polyamide is first prepared and the milk is coagulated by optical isostatic ratio), transparent (Technology for obtaining aromatic polyamide films with excellent mechanical performance), the solidified film is treated with a solution containing trivalent metal 6 ions, washed with water, and generally limited in shrinkage during the drying process. Furthermore, it was found that by drying at 150°C or higher, a film with excellent electrical properties and long-term heat resistance could be obtained.

Based on these findings, the present inventors conducted further research and completed the present invention.

That is, the present invention is: An aromatic polyamide film made of a substantially para-oriented aromatic polyamide having a logarithmic viscosity ηint+ of 2.5 or more and neutralized with a solution containing trivalent metal ions.

The para-oriented aromatic polyamide used in the present invention is substantially composed of units selected from the group consisting of the following structural units.

N HArt -NH---(1)Co'A
rt co --------(2) NH-Ar
3-CO---------(3) (where A r I
, A r 2 and A r 3 are each divalent aromatic groups, and (1) and (2) are substantially equimolar when present in the polymer. ) In the present invention, in order to ensure good heat resistance, A
Each of r I, A r 2, and A r 3 needs to be a so-called linearly oriented group.

Here, linear orientation means that the bonds that grow the molecular chain are located coaxially or parallel to the opposite direction of the aromatic group.

Specific examples of such divalent aromatic groups include paraphenylene, 4,4'-biphenylene, 1,4 naphthylene,
Examples include 1,5-naphthylene and 2,5-pyridylene. They may be substituted one or more with non-reactive groups such as halogen, lower alkyl, nitro, methoxy, cyano groups. In addition, as a special type of these divalent aromatic groups, a double bond conjugated to the general formula: ) is mentioned.

Specifically, as X, trans-CH=CllN1
1-C-C-Ni+ 111 0 and the like. Arl, Ar2 and Ar3 may each be two or more types, and may be the same or different.

The polymer used in the present invention can be produced from diamines, dicarboxylic acids, and aminocarboxylic acids corresponding to each unit by a method known so far. Specifically, a method is used in which carboxylic acid groups are first induced into acid halides, acid imidazolides, esters, etc., and then reacted with amino groups. A method such as a solid phase polymerization method can be used.

The aromatic polyamide used in the present invention may be copolymerized with groups other than those mentioned above in an amount of about 10 mol % or less, or may be blended with other polymers.

The most typical aromatic polyamide of the present invention is
Poly-p-phenylene terephthalamide (hereinafter referred to as PPTA)
) and poly-p-benzamide. When a homopolymer in which these aromatic rings are not substituted has much better heat resistance than a copolymer in which the aromatic ring is substituted, a film with high heat resistance and mechanical properties can be obtained.

The degree of polymerization of the aromatic polyamide used in the present invention is usually 2.5 or more, preferably 3.
．． Logarithmic viscosity ηin of 5 or more, more preferably 4.5 or more
h (98.5% concentrated sulfuric acid 100% polymer 0.2
A degree of polymerization is selected that gives a value measured at 30'C after dissolving g.

The film of the present invention is produced from a dope in which a polymer consisting essentially of para-oriented aromatic polyamide is dissolved in a strong acid such as sulfuric acid, which is neutralized with a solution containing trivalent metal 1 〇- ions. It is. Further, metals other than trivalent metals may be included at the same time. Here, the trivalent metal ion concentration is preferably 0.01 to 0.2% by weight. The trivalent metal ion may be present in an undissolved state or in the form of an acid ion.

Here, the trivalent metal ions are A Q ”, I n”
Ga", Y", and AI! ,” are preferably used.

The film of the present invention usually contains 500 to 500 trivalent metal ions.
It contains about 3000 ppm, and this is thought to be mainly bonded to the carboxyl group at the end of the polymer and the sulfone group in the polymer, but there is also Affz (5O
-)+l, AjICh, Ir+z (SO-
)3.

It can also exist as a free salt, such as YCl3.

Conventionally obtained films contain a relatively large amount of sodium, but the sodium content in the film of the present invention is as low as 1100 pp or less.

The film of the present invention is mainly excellent in volume resistivity and dielectric breakdown voltage among electrical properties.

For example, in terms of volume resistivity, the film of the present invention has a volume resistivity of about 7X101 SΩ·(,,Ill), which is more than 100 times higher than that of the conventional film of 4×10”Ω·cm.

Volume resistivity is a very important property for use as an electrical insulating material, and low volume resistivity not only causes insulation failure under high voltage, but also causes migration after long-term use. It may also cause. Although it has long been known that impurities are a cause of a decrease in volume resistivity, it is completely unexpected that such a large effect could be obtained by changing the metal used for neutralization as in the present invention. Was that.

The film of the present invention also has extremely high mechanical properties, such as strength, elongation, and Young's modulus of 15 kg/M2.
The films of the present invention are also preferably substantially void-free.

Furthermore, the film of the present invention typically has a density in the range of 12 to 1.370 g/aa to 405 g/aa. This density value was determined at 30'C by density gradient tube method using carbon tetrachloride-toluene. This density range is 1.5% of that of known PPTA fibers. ．． 43g/
This is a much smaller value than the cffl color range of 1.46 g/cIIl.

When the density becomes 1.370 g/cnl without grooves, mechanical properties are added, and when it exceeds 1.405 g/cJ, the film becomes a film with excessive planar orientation and isotropic mechanical properties. Become. In any case, this low density results in a light and high-strength film.

The film of the present invention preferably has plane orientation defined by the crystal orientation angle determined by X-ray diffraction as described below.

There are two types of incident X-rays: when they are incident at right angles to the film surface (hereinafter referred to as the TV direction), and when they are incident parallel to the surface (hereinafter referred to as the TV direction).
(hereinafter referred to as SV force direction).

The film of the present invention has a large diffraction peak at 32θ8; 23° due to X-rays from the TV direction;
The crystal orientation angle at -23° is preferably 30° or more, and more preferably 50° or more. Further, a large diffraction peak of 2θ-18° appears on the equator line due to the incidence in the S force direction, and it is preferable that the crystal orientation angle at 2θ':186 is 60a or less. When both of these crystal orientation angles are satisfied, the film has high mechanical properties both in the drawing direction and in a direction perpendicular thereto, and is preferably very high in tear strength.

A known method can be used to measure the crystal orientation angle.
For example, the following method is used.

Place the counter at the predetermined angle of 20, and rotate the film at 180°.
By rotating, a diffraction intensity curve is obtained.

In addition, for TV, the maximum intensity is centered around 90
Rotate between °. The value expressed in degrees is the arc length of 14 to 50 degrees in the diffraction photograph for the point showing half the intensity of the highest intensity of this curve with respect to the baseline drawn between the lowest intensity points (i.e., 50 degrees with respect to the baseline of maximum intensity) % point) and use it as the crystal orientation angle of the sample. During the measurement, the diffraction intensity can be measured by stacking several films if necessary.

Next, a method for obtaining such an aromatic polyamide film will be described, taking as an example the case where PPTA is used as the para-coordinating aromatic polyamide.

In producing the film of the present invention, it is first necessary to prepare an optically anisotropic tope of PPTA.

A suitable solvent for preparing the gutter used in forming 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%, dissolution may be difficult or the dope will have an abnormally high viscosity after dissolution.

The dobu of the present invention may contain a small amount of chlorosulfuric acid, fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, and the like. Although it is possible to use sulfuric acid with a concentration of 100% by weight or more, from the viewpoint of stability and solubility of the polymer, the concentration should be 98 to 100% by weight.
Heavy weight % concentration weight is used properly.

The polymer concentration in the dope used in the present invention is at room temperature (
A concentration that exhibits optical anisotropy at a temperature of about 20°C to 30"C or higher is preferably used, and specifically, it is used at a concentration of about 10% by weight or more, preferably about 12% by weight or more. At polymer concentrations below this, i.e., polymer concentrations that do not exhibit optical anisotropy at room temperature or higher temperatures, the formed PPTA film often does not have favorable mechanical properties.The upper limit of the polymer concentration in the dope is Although not particularly limited, usually 20% by weight
Hereinafter, for PPTA with particularly high ηinh, 18% by weight or less is preferably used, and more preferably 16 weight% or less.

The dope of the present invention may contain conventional additives, such as fillers, light removers, UV stabilizers, heat stabilizers, antioxidants, pigments, solubilizing agents, and the like.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, for example, the method described in Japanese Patent Publication No. 50-8474, but the critical point = 16 depends on the type of solvent and temperature. , depends on the polymer concentration, polymerization degree of the polymer, content of additives, etc., so by investigating these relationships in advance, creating an optically anisotropic dope and changing the conditions to an optically isotropic dope, It is possible to change from optical anisotropy to optical isotropy.

Before the dope used in the present invention is molded and solidified,
It is preferable to remove as much insoluble dust, foreign matter, etc. as possible by filtration, etc., and to remove gases such as air generated or entrained during melting. Deaeration can be performed after the dope is prepared, or can be achieved by performing it under vacuum (reduced pressure) from the stage of charging raw materials for preparation. Preparation of the dope can be carried out continuously or batchwise.

The dope thus prepared is cast from a die, for example a slit die, onto a moving support surface while maintaining its optical anisotropy. In the present invention, steps such as casting and subsequent conversion to optical isotropy, coagulation, washing, stretching, and drying are preferably carried out continuously, but if necessary, all or part of these steps are performed. may be carried out intermittently, that is, batchwise.

The method of obtaining a transparent film with excellent mechanical properties according to the present invention is to cast a dope onto a supporting surface and then convert the dope from optically anisotropic to optically isotropic prior to solidification.

To change optical anisotropy to optical isotropy, specifically, before solidifying an optically anisotropic dope cast on a support surface, the concentration of the solvent forming the dope is lowered by absorbing moisture. Changes in solubility and polymer concentration lead to a transition to an optically isotropic region, but the temperature of the dope is increased by heating to transform the phase of the dope to an optically isotropic region, or moisture absorption and heating are used simultaneously or sequentially. This can be achieved by

In particular, methods using moisture absorption, including methods that use heating in combination, can efficiently improve the optical isopower ratio of optical anisotropy and
This is useful because it can be done without causing decomposition of A.

To make the dope absorb moisture, air at normal temperature and humidity may be used, but preferably humidified or heated and humidified air is used. The humidified air may contain atomized moisture exceeding the saturated vapor pressure, and may be so-called water vapor. However, supersaturated steam at a temperature of about 45° C. or lower is not preferable because it often contains large particles of condensed water. Moisture absorption is usually between room temperature and about 180°C, preferably between 50'C and 15°C.
This is done with humidified air at 0'C.

In the case of a heating method, the heating means is not particularly limited;
A method of applying heated air to the casting dope as described above,
Methods include irradiation with an infrared lamp and dielectric heating.

The cast tube, optically balanced on the support surface, then undergoes solidification. In the present invention, the dope coagulating liquid that can be used is, for example, dilute sulfuric acid containing about 70% water or less, about 20% water by weight or less,
These include sulfur hydroxide aqueous solution and aqueous ammonia of less than about 10% by weight, sodium sulfate, sodium chloride aqueous solution and calcium chloride aqueous solution of about 10% by weight or less.

In the present invention, the temperature of the coagulating liquid is preferably equal to or less than 1915°C, more preferably equal to or less than 5°C. This is because, in general, it has been found that the lower the temperature of the coagulating liquid, the less voids are included in the film.

Since the coagulated film contains acid as it is, the acid content is preferably removed by water, and then,
Neutralize with an aqueous solution containing trivalent metal ions. Although the temperature of the neutralizing liquid is not limited, it is preferably 100°C or less. The concentration of the neutralizing solution is approximately 0. (N~0.20 weight is preferred. The contact time with the neutralizing liquid is usually about 5 seconds to 20 minutes.

As the cleaning liquid after neutralization, water is usually used, but warm water may be used if necessary. Cleaning is performed, for example, by running the film in a cleaning liquid or by spraying the cleaning liquid. The washed film may be stretched in a wet state before being subjected to drying, with wet stretching being a preferred embodiment to obtain high mechanical properties.

Drying must be carried out under tension, at a constant length, or with slight stretching to limit shrinkage of the film. 0 If a film that has a tendency to shrink with the removal of a cleaning solution (e.g. water) is dried without any restriction on shrinkage, the film may lose its flatness or curl. . To dry while limiting shrinkage, it is possible to use, for example, a Tenku dryer or drying between metal frames.

The drying method is not particularly limited and can be freely selected from methods such as heating or using room temperature gas (air, nitrogen, argon, etc.), radiant heating methods such as electric heaters and infrared lamps, dielectric heating methods, etc. can.

In one embodiment of the method of the present invention, it is preferable to manufacture the film while continuously running it throughout the entire process.
However, if desired, it may be done partially batchwise. Further, an oil agent, an identification dye, etc. may be added to the film in any step.

〔Example〕

Examples are shown below, but these examples are intended to explain the present invention and do not limit the present invention.

In the examples, parts by weight or weight % are shown unless otherwise specified.

■ Logarithmic viscosity ηinh: 98% sulfuric acid 100mβ with 0 polymer
．． 2g was dissolved and measured at 30°C in a conventional manner.

(2) Viscosity of dope: Measured using a B-type viscometer at a rotational speed of 1 rpm.

■Film thickness: Measured using a dial gauge with a measuring surface of 21W+ in diameter.

■Strength and elongation and modulus: Cut the film sample into a rectangle of 10,100 mm x 10 using a constant speed extension type strength and elongation measuring machine, initial grip length is 30 mm, and tensile speed is 30 m.
The load-extension curve was drawn five times at m/min, and the calculation was made from this.

■Volume resistivity: (a) Cut the film into a square with approximately 100 cylinders on each side.

(I?) Film thickness 0.001m using a micrometer
Accurately measure up to m, and evaporate the diagonally shaded areas in Figure 1-(a) and -(b) to a thickness of approximately 2,000 mm.

(c) The evaporated sample was heated at 23°C, 560% I? I
The measurement was carried out after the sample was left for 48 hours in an atmosphere of 1.

(d) The measurement method was performed by connecting the battery as shown in FIG. 2 and charging it for 1 minute.

■Dielectric breakdown voltage: (a) Cut the film into a square with each side approximately 100 mm.

(11) Measuring the thickness of the film using a micrometer is 0.001m.
Accurately measure up to m.

(c) This sample was left in an atmosphere of 160% R1+ at 23° C. for 48 hours and then measured.

(d) The measurement method is to use a 6-cylinder φ cylindrical electrode with a withstand voltage meter, and apply the voltage manually to approximately 1 to ν(AC)/approximately 15
The voltage was applied at a rate of seconds and measurements were taken.

Example 1 A PPTA polymer with 1 inh of 5.7 was dissolved in 99.7% 3 sulfuric acid at a polymer concentration of 12.0% to obtain a dope with optical anisotropy at 60°C. The viscosity of this dope was measured at room temperature and was found to be 10,200 voids.

To facilitate film formation, the dope was degassed under vacuum while being maintained at about 70°C.

This case also has optical anisotropy as above, and the viscosity is 4,
It was 800 voices. The 1.5 m long curved pipe from the tank, through the filter, through the gear pump, to the die is heated to approximately 70°C.
The cast dope was cast onto a mirror-polished tantalum belt through a gouie with a slit of 0.2 mm x 300 mm, and air at about 70°C with a relative humidity of about 85% was blown to make the dope optically isotropic. temperature, along with the belt, at 5°C.
It was introduced into water and coagulated. The coagulated film was then peeled off the belt and left in water.

The still wet film was immersed in a bath of 0.1% aluminum hydroxide in a 1% aqueous sodium hydroxide solution and then washed with running water.

Place the washed film between 10cm square metal frames to prevent shrinkage, and dry in a hot air dryer at 390"C for about 4 hours.
- Dry for 5 minutes. Table 1 shows the aluminum hydroxide aqueous solution concentration and film results at that time.

Example 2 A film was formed in the same manner as in Example 1, and the wet film left in water was diluted with 0.1% of a 1% aqueous sodium hydroxide solution.
% of indium hydroxide and then washed with running water.

The washed film was dried in the same manner as in Example 1.

The results of the obtained film are shown in Table 1.

Comparative Example 1 A film was formed in the same manner as in Example 2, washed with running water for one day and night without being neutralized, and dried in the same manner as in Example 1. The results of the obtained film are shown in Table 1.

Comparative Example 2 A film was formed in the same manner as in Example I, and immersed in a 0°1% NaOH bath for 3
The film was soaked for 0 minutes, then washed with running water, and dried in the same manner as in Example 1. The results of the films obtained at that time are shown in Table 1.

(The following is a blank space) 5 [Effects of the Invention] The film of the present invention has excellent electrical properties and good mechanical properties expressed by high strength and high modulus that are not found in commercially available films. Moreover, it exhibits extremely balanced physical properties in the MD force direction and the TD force direction.

In addition to these properties, it also has excellent heat resistance, oil resistance, pressure resistance, resistance to chemicals other than strong acids, and dense structure.

Therefore, the film of the present invention can be suitably used for insulating materials, magnetic tapes, flexible printed wiring boards, wire covering materials, filtration membranes, etc. of electrical equipment that rotates at high speed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a sample for measuring volume resistivity, and the shaded area in the diagram is A! It is a vapor deposition electrode. Figure 2 is a cross-sectional view of Figure 1, and the black area in the figure is A.
This is a j2 vapor deposition electrode.

Claims (1)

[Claims] An aromatic polyamide film comprising a substantially para-oriented aromatic polyamide having a logarithmic viscosity ηinh of 2.5 or more, and characterized in that the film is neutralized with a solution containing trivalent metal ions.