JPS5854976B2 - Method for producing wholly aromatic polyamide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a wholly aromatic polyamide film.

Aromatic polyamides have been actively developed for use in this field because of their high heat resistance and excellent electrical properties.

Since wholly aromatic polyamides are infusible and cannot be melt-molded, they are generally molded by wet molding or dry molding from a dope obtained by dissolving in an amide solvent as described below.

However, when a film is formed by a wet molding method or a dry molding method, there are the following disadvantages in terms of economy, technology, and performance of the resulting film.

In other words, in the former case, the problem is the selection of coagulant;
Even if special consideration is given to the coagulation power, coagulation time, coagulation temperature, etc. of the coagulant, the resulting film is still opaque and has the disadvantage that it is difficult to obtain a film with excellent mechanical and electrical performance.

In addition, the latter is a method in which the solvent is removed by evaporation in a heated atmosphere or in contact with a hot plate at the edge of the blade, but the commonly used amide solvents have a high boiling point of around 200°C and have a large latent heat of vaporization, so it is difficult to dry. The drawback is that it requires a long time at a fairly high temperature.

Therefore, there are currently almost no transparent films made of wholly aromatic polyamides on the market, and only insulating paper made from fibers and fibrids partially obtained by wet spinning exists as an electrical insulating material.

However, it is difficult for insulating paper to maintain its insulation function in an electric field of several thousand volts.

The present inventors have arrived at the present invention as a result of intensive studies aimed at improving the above-mentioned drawbacks in a method for producing a film made of wholly aromatic polyamide.

That is, in the present invention, when a thin film is formed from a solution consisting of a wholly aromatic polyamide and an amide solvent, and the thin film is dried with hot air to produce a film, the amount of residual solvent is more than 30% by weight and 50% by weight downwind. (2) Forming a thin film from a solution consisting of a wholly aromatic polyamide and an amide solvent, and drying the thin film with hot air to produce a film. The gist of this method is to form a thin film thereon, then dry it until the amount of residual solvent exceeds 30 weights and becomes less than 50 weights φ, washes with water, and heat-treats and hot-stretches as necessary.

The wholly aromatic polyamide as used in the present invention refers to one whose main chain consisting of units represented by the following general formula consists essentially of aromatic groups.

In the formula, φ1 and φ2 are selected from the following group.

-HN-φ1-NH-CO-φ2-CO- and/or -HN-φ2-CO- In addition, in the wholly aromatic polyamide referred to in the present invention, 20 molar proportion or less of the polymer constituent units are other than the above-mentioned constituent units. This also includes units that are smaller than the constituent units.

The amide solvent used in the present invention refers to at least one compound selected from the following group, and is appropriately selected and used depending on the type of polymer.

N,N'-dimethylacetamide, N-methyl(2)pyrrolidone, N-methylpiperidone, N-methylcaprolactam, N,N,N',N'-tetramethylurea, N,
N,N',N',N",N"-hexamethylphosphoramide.

These amide solvents are also used as polymerization solvents for wholly aromatic polyamides in the present invention, so the polymer solution is prepared from the corresponding diamine and dicarboxylic acid halide or aminocarboxylic acid halide hydrochloride in these amide solvents. It can be obtained directly by low temperature solution polymerization method.

In the present invention, the solution produced by the low-temperature solution polymerization method as described above can also be used as it is as a dope for film production.

In this case, Ca(OH2. LiOH, Mg(OH)2゜Al(OH)3. Since hydroxides such as Zn (OH)2 can be used, CaCl2. LiC1, AlCl3゜Z n
Salts such as C12 will inevitably be included in the dope.

The presence of the above-mentioned salts contained in the dope is extremely effective in improving the stability of the solution and the solubility of the polymer.

In other words, it is useful for gelling dope and making film opaque during film production.

However, if it contains salts, which are electrolytes, the electrical insulation properties deteriorate, so in order to obtain a film with excellent electrical insulation performance, it is necessary to remove these salts by washing the film with water.

The concentration of the polymer in the molding dope used in the present invention varies depending on the type of polymer and the type of solvent used, but it is generally preferably 10 to 35 weight φ, particularly 10 to 20 weight φ.

To produce a film by the method of the present invention, first, the obtained dope is cast into a thin film, and the film surface is blown with hot air to evaporate the solvent, so that the remaining solvent amount is 30% by weight.
When the weight reaches 0 weight or less, the drying with hot air is completed, and the residual solvent, salts, monomers, etc. are removed and purified by subsequent washing with water.

In addition, the amount of residual solvent referred to in the present invention is defined by the following formula.

When a semi-dry film with a residual solvent amount exceeding 50% by weight is immersed in water, it becomes opaque.
The electrical performance of the film is greatly reduced.

A semi-dry film with a residual solvent amount of 50% by weight or less will no longer become opaque even when immersed in water or other coagulating liquids.

In other words, a film in a semi-dry state with a residual solvent amount of 50% by weight or less can be dried by simply removing the residual solvent and residual salts by water washing and scouring, and the mechanical strength can be improved without any particular heat treatment. is low, but 120 kV/
It is possible to obtain a film having a dielectric breakdown voltage as high as mm.

In addition, as mentioned above, in the present invention, it is necessary to reduce the amount of residual solvent in the film before washing with water to 50% by weight or less, but in order to obtain a film with even better mechanical and electrical properties, washing with water is necessary. It is desirable that the amount of residual solvent in the previous film is 40% by weight or less.

As described above, a transparent film with excellent electrical insulation performance can be produced by switching from hot air drying to water scouring, which has a high extraction rate for solvents, salts, etc., at any point when the amount of residual solvent becomes 50 weight φ or less. It becomes possible to manufacture in a short time.

On the other hand, hot air drying of a highly viscous liquid in the form of a thin film of several hundred poise or more is lapse rate drying, and the diffusion rate of the solvent inside the thin film determines the drying rate, so the drying progresses and the concentration of the thin film increases. As the viscosity increases, the drying rate becomes extremely slow.

In fact, reducing the amount of residual solvent to 30% by weight or less is industrially disadvantageous because it requires a very long time to dry at a drying temperature that does not cause excessive coloring of the film.

If the drying temperature is increased to a high temperature in order to reduce the amount of residual solvent to 30% by weight or less in a short time, productivity will increase, but the film will be markedly colored and only a product of inferior quality will be obtained.

Therefore, it is recommended to switch from hot air drying to washing with water when the amount of residual solvent reaches 50% by weight or less and exceeds 30% by weight, more preferably 40% by weight or less and exceeds 30% by weight. It is industrially advantageous in terms of film productivity and performance.

In terms of the removal rate of solvents and salts, the higher the water washing temperature, the better, and water washing is usually carried out at room temperature or under heating.
Transparency of the film can be improved by immersing the semi-dry film containing the residual solvent in water or an aqueous solution of an amide solvent at a temperature of 20° C. or below, preferably 10° C. or below.

In order to manufacture films continuously, a thin film of molding dope is cast onto the surface of a running roller or an endless steel belt to match the thickness of the desired film, and hot air is blown onto the film surface. When the solvent is evaporated and the amount of remaining solvent is more than 30% by weight and less than 50% by weight, preferably less than 40% by weight, the thin film thus obtained is peeled off from the surface of the roller or endless steel belt and washed with water, and then removed as required. By drying according to the conditions, a continuous film that is transparent and has excellent electrical insulation properties can be easily obtained.

The film obtained as described above from which the solvent has been removed can be put to practical use as it is, but if necessary, it may be subjected to heat treatment and hot stretching.

For example, by heat-treating the obtained film at 150°C or higher under tension, a film having the desired strength and elongation can be produced.

Since the film shrinks several times when heated, it is preferable to carry out the heat treatment by heating the film under tension or by stretching the film in the vertical direction, in the horizontal direction, or in both the vertical and horizontal directions.

Heating may be done by any method such as hot plate heating, atmospheric heating, infrared heating, or microwave heating, but especially when processing at high temperatures of 2500G or higher, it should be done in an inert gas such as nitrogen gas to prevent thermal deterioration. is desirable.

These heat treatment conditions are determined depending on the use of the film, the type of polymer, etc.

According to the method of the present invention, a film with excellent transparency, toughness, heat resistance, electrical properties, especially electrical insulation properties can be produced continuously and economically.

Electrical insulation performance can be evaluated by dielectric breakdown voltage, J
A voltage of 150 kV/volt or higher measured according to IS C2518 can be easily obtained by the method of the present invention.

Furthermore, by selecting the polymer, molding conditions, and heat treatment conditions within suitable ranges, the dielectric breakdown voltage can be increased to 250 kV/m.
You can roam through more than i films.

The film obtained by the method of the present invention, which has such a high dielectric breakdown voltage, is particularly suitable as an insulating material for rotors and stators of large electric motors that are exposed to high electric fields of several thousand volts or more, and as a high-voltage wire coating material. ing.

In general, the higher the voltage used, the higher the heat generation, and sometimes the temperature of the material used can exceed 200°C, so if normal thermoplastic polymers are used in such applications, thermal decomposition or melting may occur. Therefore, for such purposes, polymer materials with a ladder structure such as polyimide and polyamideimide have been developed, but such polymers are generally expensive and the manufacturing process is difficult. This is economically disadvantageous because it also becomes complicated.

In contrast, the wholly aromatic polyamide film obtained by the method of the present invention is economically advantageous because it can be obtained from relatively inexpensive monomers and raw materials.

EXAMPLES The present invention will be explained in more detail by showing Examples and Comparative Examples below, but the present invention is not limited to the Examples.

Note that "parts" in the examples indicate "parts by weight."

Comparative Example 1 m-phenylenediamine 64. distilled and purified according to the method described in Japanese Patent Publication No. 35-14399.
8 parts and anhydrous N,N'- distilled in the presence of barium oxide
567.6 parts of dimethylacetamide was placed in a cylindrical glass container with an inner diameter of 580 m1 and a height of 150 mm, and the clearance with the inner wall of the container was 31 n1 r in an N2 gas flow.
Stir vigorously with an L helical stirring rod to uniformly dissolve, cool the container on ice, and add powdered isophthaloyl chloride 121.8
1 part was added while being careful not to allow the internal temperature to exceed 30°C.

Addition took approximately 2 minutes. After adding isophthaloyl chloride, stirring was continued at room temperature for 30 minutes, and the reaction product became a pale yellow viscous liquid.

The reaction product thus obtained contained 18% by weight of poly, m-phenylene isophthalamide.

A portion of the reactant taken out was added dropwise to a mixer containing a large amount of cold water with vigorous stirring, and the resulting precipitate was collected and dried to obtain a 259C1 concentration of 0 in N,N'-dimethylacetamide.
．． ηinh determined from the value measured using an Ubbelohde viscometer at 5 g/100 ml was 1.54.

22.2 parts of powdered calcium hydroxide was added to the remaining reaction product under cooling to neutralize it to obtain a film-forming dope.

This dope was uniformly applied to a thickness of 300 μm on a 200 square hard glass plate using an applicator.

After putting the glass plate coated with the dope in a hot air circulation dryer at 100°C and drying it for 20 minutes, a part of the film was cut off to measure the amount of remaining solvent, and most of the remaining part was put in water at room temperature to determine the remaining solvent and salt content. and monomers were removed by washing with water.

After washing with water for 60 minutes, the film became completely white and opaque.

After drying the film after washing with water, fix it on the frame for 320'
Although heat treatment was performed at C for 5 minutes, the appearance did not change.

Note that the amount of residual solvent before washing with water was 52% by weight.

The obtained film had a strength of 8.8 kg/rraN, an elongation of 87, and a dielectric breakdown voltage of 67 kV/rrLrIL.

Example 1 The same dope used in Comparative Example 1 was applied to a glass plate to a thickness of 200μ in exactly the same manner as in Comparative Example 1, and then placed in a hot air circulation dryer at 125°C and dried for 20 minutes. After that, in the same manner as in Comparative Example 1, the amount of remaining solvent was measured and scouring by washing with water was performed.

The amount of residual solvent was 37 weight φ.

The resulting film had very high transparency and an excellent appearance.

When the film thus obtained was further heat treated at 300°C for 2 minutes in a N2 stream, the strength was 16.2k.
g/mA, elongation 88.6%, breakdown voltage 181 kV
/TrL11L film was obtained.

Examples 2 to 5 and Comparative Examples 2 to 9 Each side shown in Tables 1 and 2 shows the manufacturing conditions of the film and the mechanical performance and dielectric breakdown voltage of the resulting film.

In addition, after drying with hot air, each side was washed with warm water of 30 to 50° C. and refined.

The meanings of the abbreviations in the table are as follows (the same applies below).

[A] Nidiamine [C] Nidicarboxylic acid chloride MPD: m-phenylenediamine PPD: P-phenylenediamine DDPM: 4,4'-diaminodiphenylmethane PABC: P-aminobenzoyl chloride hydrochloride IPC: Isophthaloyl chloride TPC: Terephthalo Il chloride DMAC: N,N-dimethylacetamide NMP
: N-Methyl-2-pyrrolidone TMU : Tetramethylurea (a) Measured in 96% sulfuric acid at C=0.5.25°C (
b) Polymer concentration (related) versus total solution Example 6 The dope used in Comparative Example 1 was
．． It was discharged from a slit with a length of 12 mm and 500 mrIL at a discharge rate of 30 CC/min, and was uniformly cast to a thickness of 125 μ on an endless steel belt running at 50 CrrL/min. It was dried by blowing hot air from the countercurrent direction for 15 minutes.

At the end of drying, the film was peeled off from the endless steel belt, a portion of it was sampled, and the amount of residual solvent was measured and found to be 37.0% by weight.

Immediately introduce most of the other parts into the washing tank and rinse with warm water at 40°C.
Washed for 0 minutes, then dried, and then heat treated continuously for 2 minutes in a heat treatment machine at 350°C to ensure no coloration.
A film with a thickness of 26 μm and excellent transparency was obtained.

The strength of the obtained film was 14.7 kg/xi, the elongation was 90%, and the dielectric breakdown voltage was 220 kV 7 mm.

Example 7 A film treated under the same conditions as Example 4 until washing and drying was heat-stretched at 320°C by 1.2 times in each of the vertical, horizontal, and biaxial directions at the same time to obtain a film with a thickness of 1811 mm. Hetate snow white strong hemp has 22.3kG/-1 elongation of 4
3%, horizontal strength is 21.0 kg/ma, elongation is 5
The film was 1oIo, had a dielectric breakdown voltage of 260 kV/mrN, had no coloration, and had very good transparency.

Example 8 The dope used in Example 2 had a diameter of 100 cm and a length of 50 cm.
Thickness 30mm with serrations on the surface of the rIL casting drum
The film was cast to a thickness of 0 μm, and hot air at 120° C. was blown onto the surface of the cast film in parallel for 10 minutes to dry it, and the film was continuously peeled off.

The amount of residual solvent in this film was 45.0% by weight.

Subsequently, it was washed in warm water at 50°C for 30 minutes, then dried and heat-treated at 320°C for 5 minutes.

The strength of the obtained film was 13.0 kg/mr7t,
Elongation is 12s, x%, breakdown voltage is 127■/mm
It was a film with a thickness of 55 μm and no coloration and good transparency.

Examples 9 and 10 Comparative Examples 10 to 13 Each side shown in Table 3 shows the manufacturing conditions of the film and the mechanical performance and dielectric breakdown voltage of the obtained film.

After drying with hot air, each side was washed with running water at 5°C and scoured.

Claims (1)

[Claims] 1 Form a thin film from a solution consisting of a wholly aromatic polyamide and an amide solvent, dry the thin film with hot air to produce a film, and dry until the amount of remaining solvent exceeds 30 weight φ and becomes 50 weight φ. A method for producing a wholly aromatic polyamide film, which comprises washing the film with water.