GB2102333A

GB2102333A - Aromatic polyimide hollow filaments

Info

Publication number: GB2102333A
Application number: GB08216083A
Authority: GB
Inventors: Hiroshi Makino; Yoshihiro Kusuki; Takashi Harada; Hiroshi Shimazaki
Original assignee: Ube Industries Ltd
Current assignee: Ube Corp
Priority date: 1981-06-11
Filing date: 1982-06-02
Publication date: 1983-02-02
Also published as: GB2102333B; JPS6135282B2; DE3221545C2; DE3221545A1; JPS57205517A

Abstract

Aromatic polyimide hollow fibers having an enhanced mechanical strength are produced by a process comprising the steps of: preparing a spinning dope solution of at least one aromatic polyimide having 90 molar % or more of a recurring unit of the formula (I). <IMAGE> wherein R is a divalent aromatic radical, in a phenolic solvent; converting the dope solution into at least one filamentary stream thereof; and solidifying the filamentary dope solution stream by drying it or by coagulating the filamentary stream with a coagulating liquid compatible with the phenolic solvent but not capable of dissolving therein 1% by weight or more of the polyimide, to provide hollow filaments.

Description

SPECIFICATION Process for producing aromatic polyimide hollow filaments Field of the invention The present invention relates to a process for producing aromatic polyimide hollow filaments.

More particularly, the present invention relates to a process for producing aromatic polyimide hollow filaments having not only an excellent heat resistance, but also, an enhanced mechanical strength.

Background of the invention Various methods for producing an aromatic polyimide fiber have been heretofore proposed.

Particularly, it is well known that the aromatic polyimide filaments can be prepared by a method such that an aromatic polyamic acid resin, which is a precursory polymer of the corresponding polyimide resin, is dissolved in an organic polar solvent, to prepare a dope solution; the dope solution is subjected to a spinning procedure; the polyamic acid in the resultant filaments is converted into the corresponding polyimide, and, then, the resultant polyimide filaments are subjected to a drawing procedure, as disclosed in Japanese Patent Application Laid-open No. 55-16925 and Japanese Patent Application Publication No. 42-2936.

However, this conventional method requires the conversion of the polyamic acid into the corresponding polyimide in the course of the filament production. The conversion procedure results in the production of water. Therefore, it is necessary to control the conversion procedure carefully. For this reason, it is difficult to stably produce the polyimide filaments with a high reliability.

Moreover, Japanese Patent Application Laid-open No. 50-64522 discloses a special method for producing an aromatic polyimide filament, which method comprises dissolving a benzophenone tetracarboxylic acid type aromatic copolyimide in an organic bipolar solvent to prepare a spinning dope solution; extruding the dope solution through a spinneret to form filamentary streams of the dope solution; introducing the filamentary streams into a specific coagulating liquid; and subjecting the coagulated filaments to a drawing procedure at an elevated temperature.

However, the copolyimide filaments produced by the above-mentioned method are unsatisfactory in heat resistance and mechanical strength thereof.

The above-mentioned prior arts disclose methods for producing only regular types of aromatic polyimide filaments or fibers and are completely silent as to a hollow type of filament or fiber produced from the aromatic polyimides.

The inventors of the present invention conducted extensive studies to develop a process for producing aromatic polyimide hollow filaments having excellent heat resistance and high mechanical strength which is free from the above-mentioned disadvantages of the conventional methods. As a result, the inventors of the present invention found that the polyimide hollow filaments having excellent heat resistance and enhanced mechanical strength can be produced by subjecting a specific dope solution, which has been prepared by dissolving a benzophenone tetracarboxylic acid type aromatic polyimide in a phenolic solvent, to a hollow spinning procedure and, then, by solidifying the resulted hollow filamentary streams of the dope solution. Thus, the inventors of the present invention accomplished this invention.

Summary of the invention An object of the present invention is to provide a process for producing aromatic polyimide hollow filaments having excellent heat resistance and enhanced mechanical strength.

Another object of the present invention is to provide a process for producing aromatic polyimide hollow filaments directly from the corresponding aromatic polyimide material.

The above-described objects can be attained by the process of the present invention which comprises the steps of: (1) preparing a spinning dope solution of a polymer material consisting of at least one aromatic polyimide having at least 90 molar % of a recurring unit of the formula (i):

wherein R represents a divalent aromatic radical, in a solvent comprising, as a main component thereof, at least one phenolic compound: (2) extruding the spinning dope solution through at least one spinning hole to form at least one hollow filamentary stream thereof: and (3) solidifying the hollow filamentary streams of the spinning dope solution, to provide solid hollow filaments of the polymer material.

The solidifying procedure may be effected by a dry method in which the phenolic solvent is evaporated from the filamentary stream of the spinning dope solution at an elevated temperature or by a wet method in which the filamentary stream of the spinning dope solution is introduced into a coagulating liquid which is compatible with the phenolic solvent but not capable of dissolving 1% by weight or more of the polymer material.

The solidified aromatic polyimide hollow filaments may be drawn at a temperature of 200C to 6000C to produce drawn hollow filaments.

Brief description of the drawings Figure 1 is an explanatory cross-sectional side view of an apparatus for producing undrawn aromatic polyimide hollow filaments in accordance with the process of the present invention; Fig. 1 is an explanatory, partially cross-sectional side view of a spinning nozzle for forming a hollow filamentary stream of a spinning dope solution; and Fig. 3 is a bottom view of the spinning nozzle indicated in Fig. 2, along line Ill-Ill.

Detailed description of the invention The term "degree of imidization" used herein refers to a proportion in percent of the real amount of imide bonds existing in a polymeric chain of an aromatic polyimide to the theoretical amount of the imide bonds that are theoretically possible to exist in she polymeric chain. The amount of the imide bonds can be determined by means of an infrared absorption spectrum analysis. That is, the amount of the imide bonds is determined from the height of the absorption peaks at 1780 cm-l and 720 cm1.

The aromatic polyimide usable for the process of the present invention should have a degree of imidization of at least 90% as defined above.

If the degree of imidization of the aromatic polyimide to be used for the present invention is less than 90%, the resultant filaments will exhibit unsatisfactory mechanical strength and heat-resistance.

In the process of the present invention, the polymer material to be converted into a hollow filament or filaments, consists of at least one aromatic polyimide having at least 90 molar %, preferably, at least 95 molar %, of a recurring unit of the formula (I):

wherein R represents a divalent aromatic radical, and is soluble in the solvent comprising, as a main component thereof, at least one phenolic compound. The divalent aromatic radical represented by R may be a residue of an aromatic diamine of the formula (ill): H2N-R-NH2, from which two amino groups are excluded. If the content of the recurring unit of the formula (I) is less than 90%, the resultant hollow filaments will exhibit an unsatisfactory mechanical strength and heat resistance.

The aromatic polyimide preferably has a high molecular weight and, therefore, exhibits a logarithmic viscosity of from 0.3 to 7.0, more preferably from 0.4 to 5.0, still more preferably from 0.5 to 4.0, determined at a concentration of 0.5 g per 100 ml of a mixture solvent of 4 parts by volume of P-chlorophenol and 1 part by volume of O-chlorophenol at a temperature of 300C.

The aromatic polyimide can be produced by the poIymrization and imidization (imide ring cyclization) of a tetracarboxylic acid component containing at least 90 molar % at least one benzophenone tetracarboxylic acid or its anhydride, salt, or ester, for example, 3,3',4,4'-benzophenone tetracarboxylic dianhydride or 2,3,31,4'-benzophenone tetracarboxylic dianhydride, with a diamine component comprising at least one aromatic diamins of the formula (II). The polymerization and imidization operations can be carried out by any conventional process.

The aromatic polyimide usable for the process of the present invention can be prepared in the following manner. That is, a benzophenone tetracarboxylic acid component and an aromatic diamine component, which are in approximately equal molar amounts to each other, are dissolved in an organic polar solvent, for example, N-methylpyrrolidone, pyridine, N,N-dimethylacetamide, N,N dimethylformamide, dimethyl sulfoxide, tetramethyl urea, phenol or cresol; the solution is heated at a temperature of about 800C or less, preferably from OOC to 600C, so as to allow the benzophenone tetracarboxylic acid component and the aromatic die mine component to be polymerized with each other to provide a polyamic acid having a logarithmic viscosity of 0.3 or more, preferably, 0.5 to 7, determined at a concentration of 0.5 g per 100 ml of N-methyl pyrrolidone at a temperature of 300 C;; a solution of the resultant polyamic acid in the organic polar solvent, which solution can be the above mentioned polymerization reaction mixture itself, is subjected to an imidization reaction at a temperature of from 50C to 1 500C by using an imidization accelerator consisting of at least one member selected from tertiary amine compounds, such as trimethyl amine, triethyl amine and pyridine, acetic anhydride, sulfonyl chloride, and carbodiimide. The imidization procedure is carried out to an extent that the resultant imide polymer has a degree of imidization of 90% or more. The imidization procedure may be carried out at a temperature of from 1 000C to 3000 C, preferably, from 1 200C to 2500C, without using the imidization accelerator.The resultant imide polymer is isolated in the form of fine particles from the reaction mixture by means of precipitation.

In another process for producing the aromatic polyimide, the solution of the corresponding polyamic acid in the organic polar solvent, which solution has been prepared by the above-mentioned process and which has a logarithmic viscosity of 0.5 or more, determined at a concentration of 0.5 g per 100 ml of N-methylpyrrolidone at a temperature of 300C, is mixed with a large amount of a precipitating agent consisting of acetone or an alcohol, so as to allow the polyamic acid to precipitate from the solution. In another method, the solution of the polyamic acid is mixed with the precipitating agent while evaporating the organic polar solvent from the solution, so as to allow the polyamic acid to precipitate from the reaction mixture. The polyamic acid precipitate is isolated in the form of fine particles from the reaction mixture.The isolated polyamic acid is heated at a temperature of from 1 500C to 3000C until the degree of imidization of the resultant imide polymer reaches 90% or more.

In still another process for producing the aromatic polyimide, a tetracarboxylic acid component consisting of 2,3,3',4'- anchor 3,3',4,4'-benzophenone tetracarboxylic acid and an aromatic diamine component are polymerized and imidized in a single step in a phenolic compound in the state of a liquid or melt, at a temperature of from 1 200C to 4000C, preferably from 1 500C to 3000C. This single step process is most preferable for the process of the present invention, because the polyimide composition of the polyimide and the phenolic compound can be directly obtained and the resultant reaction mixture can be directly utilized as a spinning dope solution for the hollow spinning operation of the present invention.

In the above-mentioned processes for producing the aromatic polyimide, 3,3',4,4'-benzophenone tetracarboxylic dianhydride (hereinafter referred to as S-BTDA, for brevity) and 2,3,3',4'-benzophenone tetracarboxylic dianhydride can be preferably used as a main tetracarboxylic acid component. 2,3,3',4'and 3,3',4,4'-benzophenone tetracarboxylic acids, and salts and ester derivatives thereof, may also be used as the main tetracarboxylic acid component. The above-mentioned benzophenone tetracarboxylic acids may be used in mixtures thereof.

The tetracarboxylic acid component may contain, in addition to the above-mentioned benzophenone tetracarboxylic acids, 10 molar % or less, preferably, 5 molar % or less, of one or more other tetracarboxylic acids, for example, pyromellitic acid, 3,3',4,4'-biphenyl tetracarboxylic acid, 2,3,3',4'-biphenyl tetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl) propane, bis(3,4dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)ether, bis(3,4-dicarboxyphenyl)thioether, butane tetracarboxylic acid, and anhydrides, salts and ester derivatives thereof.

The aromatic diamine of the formula: H2N-R-NH2, which is used in the above-mentioned process for producing the aromatic polyimide, is preferably selected from the group consisting of those of the formulae (Ill) and (IV):

wherein R1 and R2, respectively and independently from each other, represent a member selected from the group consisting of hydrogen atoms, lower alkyl radicals having 1 to 3 carbon atoms and lower alkoxy radicals having 1 to 3 carbon atoms, A represents a divalent radical selected from the group consisting of -0-, -S-, -CO-, SO2, -SO-, -CH2- and -C(CH3)2-, and m represents an integer of from 1 to 4.

The aromatic diamines of the formula (Ill) may involve diphenyl ether compounds, for example, 4,4'-diaminodiphenyl ether (hereinafter referred to as DADE, for brevity), 3,3'-dimethyl-4,4'diaminodiphenyl ether, 3,3'-dimethoxy-4,4'-diamlnodiphenyl ether, 3,3'-diaminodiphenyl ether and 3,4'diaminodiphenyl ether: diphenyl thioether compounds, for example, 4,4'-diaminodiphenyl thioether, 3,3'-dimethyl-4,4'-diaminodiphenyl thioether, 3,3'-dimethoxy-4,4'-diaminodiphenyl thioether, and 3,3'-diaminodiphenyl thioether; benzophenone compounds, for example, 4,4'diaminobenzophenone and 3,3'-dimethyl-4,4'-diaminobenzophenone; diphenyl methane compounds, for example, 3,3'-diaminodiphenyl methane, 4,4'-diaminodiphenyl methane (hereinafter referred to as DADM, for brevity), 3.3'-dimethoxy-4,4'-diaminodiphenyl methane, and 3,3'-dimethyl-4,4'diaminodiphenyl methane; bisphenyi propane compounds, for example, 2,2-bis(4aminophenyl)propane and 2,2-bis(3-aminophenyl)propene; 4,4'-diaminophenyl suífoxide; 4,4'diaminodiphenyl sulfone; and 3,3'-diaminodiphenyl sulfone.

The aromatic diamines of the formula (IV) may involve 3,3'-dimethyl benzidine, 3,3'dimethoxybenzidine (orthodianisidine) and 3,3'-diaminobiphenyl.

The diamine component may contain at least one member selected from those of the formula (V):

The aromatic diamines of the formula (V) may be selected from 2,6-diaminopyridine, 3,6diaminopyridine, 2,5-diaminopyridine and 3,4-diaminopyridine.

It is preferable that the aromatic diamine component consist of at least one member selected from the group consisting of 4,4'-diaminodiphenyl ether (DADE), 4,4'-diaminodiphenyl thioether, 4,4' diaminodiphenyl methan (DADM), 3,3'-dimethoybsnidine (ortho-dianisidine, which will be hereinafter referred to as l:)-DAN, for brevity), and 3,3'-dimethyl benzidine.

In the process of the present invention, a solvent, into which the aromatic polyimide is dissolved, comprises, as a main component, at least one phenolic compound. It is preferable that the solvent consist of a phenolic compound alone. The solvent usable for the process of the present invention may contain, in addition to the phenolic compound, at least one additional solvent compatible with the phenolic compound which is selected from the group consisting of carbon disulfide, dichloromethane, trichloromethane, nitrobenzene, and orthodichlorobenzens, in an amount of 50% by weight or less, preferable, 30% by weight or less.

It is preferable that the phenolic compound usable for the process of the present invention has a melting point of about 9 600C or less, more preferably, C000 or less, and a boiling point under atmospheric pressure of about 30000 or less, more preferably, 280 C or less. Examples of the preferred phenolic compounds are monohydric phenols, such as phenol, ortho-, metal end paracresols, 3,5-xylenol, carvecrol and thymol, and halogenated monohydric phenols in which a hydrogen atom in the benzene nucleus of the phenol is replaced with a halogen.

The most preferable halogenated phenols for the process of the present invention are those having a melting point of about 1 000C or less and a boiling point under atmospheric pressure of about 3000C or less and which are represented by the formula (fl):

wherein R3, represents a member selected from the group consisting of hydrogen atoms and alkyl radicals having 1 to 3 carbon atoms and X represents a halogen atom. In the formula (VI), it is preferable that the substituent X is located in the pare- or mete-position to the hydroxyl group.These halogenated phenols have a high ability to dissolve the aromatic polyimide of the benzophenone tetracarboxylic acid type.

The halogenated phenols usable for the process of the present invention include 3-chlorophenol, 4-chiorophenol (P-chlorophenol, hereinafter referred to as PCP. for brevity), 3-bromophenol, 4bromophenol, 2-chloro-4-hydroxytoluene, 2-chlorn--hyo'ro:; , huene, 3-chloro-6-hydroxytoluene, 4chloro-2-hydroxytoluene, 2-bromo-4-hydroxytoluene, 2-bromo-5-hydroxytoluene, 3-bromo-5 hydroxytoluene, 3-brnmo--hydrnxytoluene, and 4-bromo-2-hydroxytoluene.

In the process of the present invention, in the case where the aromatic polyimide is prepared by subjecting the benzophenone tetracarboxylic acid component and the aromatic diamine component to the single-step polymerization-imidization procedure in a phenolic compound in the state of a liquid or melt at a temperature of from 12000 to 40000, as is described for the production of the aromatic polyimide, the resultant polymerization reaction mixture can be directly utilized as a dope solution for the spinning operation. if necessary, the polyimido concentration or viscosity of the reaction mixture is adjusted to a desired value before being subjected to the spinning operation.

On the other hand, in the case where the aromatic polyimide is prepared as an isolated product in the form of fine particles, l the polymide composition usable for the process of the present invention can be prepared by dispersing the polyimide particles in a solvent consisting mainly of the phenolic compound while stirring the mixture and heating the dispersion to a temperature high enough to dissolve the polyimide particles in the solvent thoroughly.

In the process of the present invention, the polymer material to be dissolved in the solvent may comprise at least two types of imide polymers, each having at least 90 molar % of a recurring unit of the formula (I). Also, the polymer material may contain, in addition to a major portion consisting of one or more imide polymers having at least 90 molar % of a recurring unit of the formula (I), a minor portion consisting of one or more other types of aromatic imide polymers.

In the process of the present invention, it is preferable that the spinning dope solution contains the polymer material in a total content of from 5 to 30% by weight, more preferably, from 7 to 20% by weight, based on the entire weight of the spinning dope solution. Also, it is preferable that the spinning dope solution is a homogeneous solution and exhibits a rotation viscosity of at least 500 centipoises, more preferably, from 10 to 100,000 poises, at a temperature of from OOC to 1 500C, particularly, from 200C to 1 200C, at which the spinning dope solution is extruded.

In the process of the present invention, the spinning dope solution is extruded through at least one hollow spinning hole, and the resultant hollow filamentary stream of the dope solution is introduced into a drying procedure in which the phenolic solvent is evaporated from the filamentary stream of the spinning dope solution at an elevated temperature of from 200C to 4000C, or into a coagulating procedure in which the hollow filamentary stream is coagulated in a coagulating liquid which is compatible with the phenolic solvent, but not capable of dissolving therein 1% by weight or more of the polymer material.

In the process of the present invention, the spinning dope solution can be shaped into at least one hollow filament by any conventional hollow spinning method. The formation of the hollow filament can be effected by using any type of spinning nozzle for forming the hollow filament, for example, a tube-inorifice type hollow nozzle or a segmented arc type hollow nozzle. A preferable spinning nozzle for the process of the present invention is of the tube-in-orifice type.

The hollow spinning procedure in the process of the present invention can be carried out, for example, by using an apparatus as shown in Figs. 1 , 2 and 3.

Referring to these drawings, a spinning dope solution 1 is supplied into a spinning head 2 having a spinning nozzle (spinneret) 3. The temperature of the spinning dope solution 1 in the spinning head 2 is maintained at a predetermined level of from 200C to 1 500C. When the spinning nozzle 3 is of a tube-in-orifice type, as indicated in Figs. 2 and 3, a hole 4 is formed in the bottom of the spinning head 2. The diameter of the hole 4 is variable, depending on the desired denier of the hollow filament to be produced. Usually, the diameter of the hole 4 is in the range of from 0.2 to 2 mm. Into the hole 4, a tube 5 is concentrically inserted, in the manner indicated in Figs. 1, 2 and 3, to form an annular spinning orifice 4a around the tube 5. The size of the tube 5 depends on the size of the hole 4 and the desired width of the annular slit 4a.Usually, the lower end of the tube 5 has an outside diameter of from 0.1 5 to 1.6 mm and an inside diameter of from 0.05 to 1.4 mm.

The spinning dope solution 1 is extruded through the annular slit 4a at the predetermined spinning temperature, while a back pressure usually of from 0.1 to 20 kg/cm2 is applied to the spinning dope solution 1 in the spinning head 2 by blowing an inert gas, for example, nitrogen gas, into the spinning head 2 through a conduit line 6, while a stream of a gas or liquid, for example, hot water, flows through the tube 5. The resultant hollow filamentary stream 7 of the spinning dope solution is introduced under tension into a first coagulating liquid 8 contained in a first coagulating vessel 9, while the hollow filamentary stream 7 of the spinning dope solution 1 is stretched at a predetermined extent.

The resultant first coagulated hollow filament 10 is withdrawn from the first coagulating vessel 9 through guide rolls 1 1 and 12 and, then, introduced into a second coagulating liquid 13 contained in a second coagulating vessel 14, and recycled one or more times along the path passing through the guide rolls 15, 16 and 17 in the manner indicated in Table 1. In the second coagulating vessel 14, the coagulation of the hollow filaments is substantially completed. The resultant second coagulated hollow filament 18 is introduced through a guide roll 21 into an inert medium 19 contained in a storing tank 20 and stored therein. All or some of guide rolls 1 1, 12, 1 5, 17 and 21 may be driven separately from each other each by a driving motor (not shown in the drawings, each at a predetermined speed, so as to stretch the hollow filaments to a predetermined extent.Usually, the second coagulated hollow filament is delivered from the second coagulating vessel 14 at a speed of from 1 to 100 m/min, preferably, from 2 to 80 m/min.

Before being subjected to the hollow spinning procedure, the spinning dope solution is usually filtered and, then, degassed at a temperature of from 200C to 2000C, preferably, from 300C to 1 500 C.

Subsequently, the degassed dope solution is subjected to the extruding procedure through the hollow spinning nozzle, at an extruding temperature of from 200C to 1 500C, preferably, from 300C to 1 200C, at a back pressure of from about 0.1 to 20 kg/cm2G, preferably, from 0.2 to 10 kg/cm2G, more preferably, from 0.3 to 5 kg/cm2G, so as to continuously form a hollow filamentary stream from the dope solution.

In the case where the tube-in-orifice type hollow spinning nozzle is used, the extruding procedure of the dope solution is carried out while a gas or liquid, preferably, a liquid, flows through the tube 5, as indicated in Figs. 1 through 3, into the hollow space in the resultant hollow filamentary stream of the dope solution, so as to form a core of the hollow filamentary stream. The liquid flow is effective for preventing an undesirable deformation of the extruded hollow filamentary stream of the dope solution during the coagulating procedure.

The core liquid preferably consists of at least one polar liquid compound which is not capable of coagulating the dope solution and of dissolving the polymer material in the dope solution. Usually, water is used as the core liquid.

Then, the hollow filamentary stream of the dope solution is introduced into a coagulating liquid, which is usually maintained at a temperature of from about -1 00C to 600C. A solidified filament is obtained.

The coagulating liquid usable for the present invention should be compatible with the phenolic solvent, but not capable of dissolving therein 9 1% by weight or more of the polymer material. The coagulating liquid comprises at least one member selected from the group consisting of water; lower aliphatic alcohols having 1 to 5 carbon atoms, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol and iso-propyl alcohol: lower aliphatic ketones having 3 to 5 carbon atoms, for example, acetone, methyl ethyl ketone, diethyl ketone and methyl propyl ketone; tetrahydrofuran; dioxane; aliphatic ethers, such as ethyleneglycol monomethylether; aliphatic amides, such as dimethyl acetamide and dimethyl formamide; dimethylsulfoxide; diethylsulfoxide, lower alkylene glycols, for example, ethylene glycol and propylene glycol; lower aliphatic carboxylic acid having 1 to 4 carbon atoms, for example, formic acid, acetic acid, propionic acid and butyric acid, and mixtures of at least one of the above-mentioned compounds with water, preferably, in a weight ratio of at least 3:7.

The coagulating liquid preferably contains at least 30% by weight of at least one aliphatic alcohol having 9 to 5 carbon atoms. Also, it is preferable that the coagulating liquid consist essentially of one part by weight of at least one aliphatic alcohol having 1 to 5 carbon atoms with 0.1 to 1.5 parts by weight of water.

Just after the spinning dope solution is extruded through the spinning nozzle, the non-coagulated hollow filamentary stream of the dope solution is preferably stretched, under tension, to a small extent.

Also, it is preferable that the hollow filamentary stream be introduced into the coagulating liquid under tension, so as to be slightly stretched.

After the hollow filament stream of the dope solution is coagulated to such an extent that the hollow filament is not easily deformed, the coagulated hollow filament is brought into contact with a desired guide roll or stretching roll.

As indicated in Fig. i, the hollow filamentary stream of the dope solution may be coagulated in a single step coagulating procedure or in a two or more step coagulating procedure. The two or more step coagulating procedure is effective for completely eliminating the phenolic solvent from the body of the coagulated hollow filament.

The resultant hollow filament is optionally washed with an inert washing medium, for example, water, to eliminate the phenolic solvent and then, stored in an inert medium, for example, water.

Otherwise, the washed hollow filament may be dried in an adequate manner before storage.

The hollow filament produced in accordance with the process of the present invention may be drawn in a dry or wet condition, at a temperature of from 20 G to 6000C, preferably, from 300C to 500 C, at a draw ratio of from 1.1 to 5.0, preferably, from 1.2 to 4.0. The drawing procedure is effective for increasing the mechanical strength of the hollow filament. For example, undrawn hollow filament produced in accordance with the process of the present invention usually exhibits a tensile strength approximately of 1.0 g/d or more. By applying the drawing procedure to the undrawn hollow filament, the tensile strength of the hollow filament can be increased to 4.0 g/d or more, preferably, 7.0 g/d or more.

The drawing operation is preferably carried out by using either a hot plate contact method, in which the filament is drawn in contact with a hot plate heated to an elevated temperature, or an infrared heating method, in which the filament is drawn while being heated by infrared rays. The drawing operation may be carried out in any type of atmospher"., such as air or an inert gas. However, high temperature drawing is preferably carried out in an inert as atmosphere.

The hollow polyimide filaments produced by the proses eE the present invention exhibit a high mechanical strength, excellent resistance to heat and chemicew and an excellent electrical insulating property. Therefore, the hollow polyimide filament of the prevent invention can be used in the applications of high temperature electrical insulating meterials, cable coverings, protective clothing, curtains, packing and linings.

Since the hollow polyimide filaments exhibit a semi-permeable property with various gas mixtures and/or liquid mixtures, the hollow polyimide filaments of the present invention are useful as a separating module.

Examples of the present invention and comperative examples will be described hereunder.

Example 1 (Preparation of spinning dope solution 1) A mixture of 4 100 millimoles of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (S-BTDA), 100 millimoles of 4,4'-diaminodiphenyl ether (BASE), and 470 ml of N-methyl-2-pyrrolidone was placed in a separable flask with a stirrer and a conduit for introducing thereinto nitrogen gas. The mixture was subjected to a polymerization reaction at a temperature of 200C for 7 hours while flowing nitrogen gas through the flask, to prepare polyamic acid.

The resultant polymerization mixture was cooled to a temperature of 100C or less and, then, admixed with 600 millimoles of acetic anhydride and 600 millimoles of pyridine. The admixture was homogenized by thoroughly stirring it, and, then, gradually heated to and maintained at a temperature of approximately 300C for about 20 minutes so as to allow the resultant aromatic imide polymer to precipitate in the form of fine particles from the polymerization mixture. Thereafter, the polymerization mixture was heated to a temperature of from 700C to 800C and maintained at this temperature for 30 minutes or more to complete the imidization reaction and the precipitation of the aromatic imide polymer.

The polymerization mixture containing the aromatic imide polymer powder was added to a large amount of methyl alcohol, and the admixture was filtered to separate the imide polymer powder. The imide polymer powder was thoroughly washed with methyl alcohol and, then, dried under a reduced pressure at room temperature.

The resultant aromatic polyimide powder was subjected to a determination of degree of imidization. The result is indicated in Table 1. Also, the powder was subjected to a determination of logarithmic viscosity in the following manner. A viscosity of the polyimide powder was measured at a concentration of 0.5 g per 100 ml of a mixture of 4 parts by volume of parachlorophenol and 1 part by volume of orthochlorophenol at a temperature of 300 C. The logarithmic viscosity of the polyimide was calculated from the following equation.

wherein L represents a logarithmic viscosity of the polyimide, Vr represents the above-mentioned viscosity of the polyimide solution, V2 represents a viscosity of the parachlorophenol-orthochlorophenol mixture solvent and C represents the concentration of the polyimide in the polyimide solution.

The result is indicated in Table 1.

A mixture of 20 g of the above-mentioned polyimide powder and 80 g of parachlorophenol was placed in a separable flask with a stirrer and heated at a temperature of from 80 to 900C, so as to dissolve the polyimide powder in the fused parachlorophenol. The resultant solution was filtered under pressure by using a press-filtering apparatus equipped with a filter comprising two pieces of filtering paper, which does not allow particles having a size of 3 microns or more to pass therethrough, a piece of 100 mesh metal net (ASTM Standard) and a piece of 400 mesh metal net (ASTM Standard). The filtered solution was used as spinning dope solution 1. The rotation viscosity of the dope solution 1 at a temperature 1 000C is indicated in Table 1.

Table 1 Monomeric component Resultant polyimide Spinning dope solution Degree of Logarithmic Concentration Rotation Example Type of tetra- Type of Polymerization imidization viscosity of polyimide viscosity No. carboxylic acid diamine time (hr) (%) (30 C) (%) (polse, 100 C) 1 BTDA DADE 7 > 95 1.5 20 2,300 Examples 2 through 4 (Preparation of hollow filaments) In each of the Examples 2 through 4, aromatic polyimide hollow filaments were produced from the spinning dope solution prepared in Example 1 by using the hollow spinning apparatus indicated in Figs. 1 through 3.

Referring to Figs. 1, 2 and 3, the spinning dope solution 1 was fed into the spinning head 2. The hollow spinning nozzle 3 was of a tube-in-orifice type and had a circular hole 4 having a diameter of 1.6 mm and a tube 5 inserted concentrically into the hole 4. The lower end of the tube 5 had an outside diameter of 1.0 mm and an inside diameter of 0.5 mm. The resultant annular spinning orifice 4a had an outside diameter of 1.6 mm, and inside diameter of 1.0 mm and a width of 0.3 mm.

The back pressure indicated in Table 2 was applied to the dope solution 1 in the spinning head 2 by blowing nitrogen gas into the spinning head 2 through the conduit 6, so as to extrude the dope solution 1 through the annular spinning orifice 4a at the temperature indicated in Table 2, and to form a hollow filamentary stream of the dope solution, while a core gas or liquid, indicated in Table 2, flowed into the hollow space of the resultant hollow filamentary stream 7 through the tube 5.

The hollow filamentary stream 7 of the dope solution was introduced into a first coagulating liquid 8, which was of the type indicated in Table 2, and was contained at a depth of 40 cm in a first coagulating vessel 9.

The first coagulated hollow filament 10 was removed from the first coagulating vessel 9 through guide rolls 1 1 and 12 and, then, introduced into the second coagulating liquid 13, which was of the type indicated in Table 2, and was contained in a second coagulating vessel 14. In the second vessel 14, the hollow filament 10 was recycled 8 times along the path passing through guide rolls 15, 16 and 17, in the manner indicated in Fig. 1. The distance between the centers of the guide rolls 1 5 and 17 was 80 cm.

The second coagulated hollow filament 18 was withdrawn from the second vessel 14 through a guide roll 21 and introduced into an inert storing liquid 19, which was of the same type as that of the second coagulating liquid, and was contained in a storing tank 20.

The temperatures of the first and second coagulating liquid are indicated in Table 2.

The delivery speed of the second coagulated hollow filament 1 8 was as indicated in Table 2.

The resultant hollow filament was subjected to an observation of its cross-sectional profile and measurement of the inside diameter and the width of the annular body thereof. The results are indicated in Table 2.

Also, the resultant hollow filament was subjected to a determination of the separating properties thereof, in the following manner.

A liquid-separating module was made by bonding a bundle composed of a plurality of the hollow filaments to a stainless steel tube with an epoxy resin bonding agent.

The module was placed in an apparatus for measuring the liquid-separating property.

An aqueous saline solution of 0.5% by weight of sodium chloride was supplied to the outside of the hollow filament bundle under a pressure of 40 kg/cm2G. The permeating rate of the saline solution through the hollow filaments was measured. Also, the concentration of sodium chloride in the saline solution, that permeated through the hollow filaments into the hollow spaces thereof, was measured by using an electro-conductivity tester.

The percent of salt exclusion of the hollow filament was calculated in accordance with the following equation.

wherein C0 represents the concentration of salt in the original saline solution and C1 represents the concentration of salt in the saline solution that permeated through the hollow filaments. The results are indicated in Table 2.

Table 2 Dellvery Hollow filament Formation of hollow filamentary Coagulation of hollow filament speed of Separating stream of dope solution First coagulating Second coagulating coagu- Configuration property Extruding liquid liquid lated Width of Permeat Type of Back temper- Core Temper- Temper- hollow Cross- Outside anullar ing rate Percent Example dope pressure ature ges or ature ature filament sectional diameter body m /m. of salt No. solution (kg/cmG) ( C) liquid Type ( C) Type ( C) (m/min) profile ( ) ( ) day exclusion 2 1 1.4 110 Phenol- Methanol- 4 Methanol- 2 5.8 Accurate 400 120 0.41 52 formamide water water circular mixture mixture mixture annulus (1:1) (1:1) (1::1) 3 1 " " " " " " " 12.9 " 200 50 0.08 81 4 1 2.2 2 N2gas " " " " 11.6 " 300 80 0.11 74 In Example 4, the hollow filaments were drawn at a temperature of 3000C at a draw ratio of 2.0.

Separately, other hollow filaments of Example 4 were drawn at a temperature of 3700C at a draw ratio of 2.0. The properties of the resultant drawn hollow filaments are indicated in Table 3.

Table 3 Undrawn Drawn at 300 C Drawn at 370 C Cross-sectionai profile Approximately Approximately Approximately accurate circle accurate circle accurate circle Outside diameter (fez) 300 210 200 Inside diameter (u) 80 60 50 Tensile strength (g/d) 1.9 7.0 10.0 Ultimate elongation (%) 10 1.2 1.0 Young's modulus (g/d) 70 350 400 Example 5 The same hollow filaments as those described in Example 3 were immersed in methyl alcohol for 24 hours and, then, in decahydronaphthalene for 24 hours, each at a temperature of 250C. The immersed hollow filaments were air-dried to provide dried hollow filaments.

The dried hollow filaments were subjected to a gas-separating test in the following manner.

A bundle consisting of a plurality of the dried hollow filaments was bonded to a glass tube with an epoxy resin bonding agent to provide a gas-separating module. The permeating rates of hydrogen gas and carbon monoxide gas through the hollow filaments were.measured separately under a pressure of 2 kg/cm2G.

The hydrogen gas-permeating rate was 1.5 xl 0cm3/cm2. sec. cmHg, and the carbon monoxide gas-permeating rate was 1 .0x 10-' cm3/cm2 . see . cmHg. That is, the ratio (PHPco) of the hydrogen gas-permeating rate to the carbon monoxide gas-permeating rate was approximately 15:1. It was evident that the hollow filament had an excellent gas separating property of hydrogen gas from carbon monoxide gas.

The gas permeating rate was calculated from the following equation:

wherein P represents the permeating rate of a gas; W represents an amount by volume (cm3) of a gas permeated through a membrane (tubular membrane of the hollow filament); A represents an area (cm2) of the membrane; T represents a permeating time (seconds) of the gas through the membrane; and Dp represents a differential pressure of the gas between one side and the other side of the membrane.

Example 6 The same procedures as those described in Example 5 were carried out, except that the same hollow filaments as those described in Example 4 were used.

The dried hollow filaments exhibited a hydrogen gas-permeating rate of 5 x 10-8 cm3/cm2 . sec. cmHg and a ratio (PHPco) of approximately 7:1.

Claims

1. A process for producing aromatic polyimide hollow filaments comprising the steps of: (1) preparing a spinning dope solution of a polymer material consisting of at least one aromatic polyimide having at least 90 molar % of a recurring unit of the formula (I):

wherein R represents a divalent aromatic radical, in a solvent comprising, as a main component thereof, at least one phenolic compound; (2) extruding said spinning dope solution through at least one spinning hole to form at least one hollow filamentary stream thereof: and (3) solidifying said hollow filamentary stream or streams of said spinning dope solution to form at least one hollow filament.

2. The process as claimed in claim 1, wherein said solidifying procedure is carried out by evaporating said solvent from said filamentary stream or streams of said spinning dope solution at an elevated temperature of from 200C to 4000C.

3. The process as claimed in claim 1, wherein said solidifying procedure is effected by introducing said filamentary stream or streams of said spinning dope solution into a coagulating liquid which is compatible with said solvent, but not capable of dissolving 1% by weight or more of said polymer material.

4. The process as claimed in claim 1, wherein the divalent aromatic group represented by R in the formula (I) is a residue of an aromatic diamine from which two amino groups are excluded.

5. The process as claimed in claim 1, wherein said aromatic polyimide has a logarithmic viscosity of from 0.3 to 7.0, determined at a concentration of 0.5 g per 100 ml of a mixture solvent of 4 parts by volume of parachlorophenol and 1 part by volume of orthochlorophenol at a temperature of 300C.

6. The process as claimed in claim 1, wherein said aromatic polyimide is a polymerization-andimidization product of a tetracarboxylic acid component comprising at least 90 molar % of at least one benzophenone tetracarboxylic acid or its anhydride, salt or ester with a diamine component comprising at least one aromatic diamine of the formula (ill): H2N-R-NH (Il) wherein R is as defined above.

7. The process as claimed in claim 6, wherein said tetracarboxylic acid component comprises at least 90 molar % of at least one member selected from the group consisting of 3,3',4,4'-benzophenone tetracarboxylic dianhydride and 2,3,3',4'-benzophenone tetracarboxylic dianhydride.

8. The process as claimed in claim 6, wherein said tetracarboxylic acid component contains 10 molar % or less of at least one member selected from the group consisting of pyromellitic acid, 3,3',4,4'-biphenyl tetracarboxylic acid, 2,3,3',4'-biphenyl tetracarboxylic acid 2,2-bis(3,4 dicarboxyphenyl)propane, bis(3,4-dicarboxyphenyl)sulfone, bis(3,4-dicarboxyphenyl)ether, bis(3,4dicarboxyphenyl)thioether, butane tetracarboxylic acid, and anhydrides, salts and esters of the abovementioned compounds.

9. The process as claimed in claim 6, wherein said aromatic diamine of the formula (II) is selected from the group consisting of those of the formulae (I II) and (IV):

wherein R1 and R2 respectively represent, independently from each other, a member selected from the group consisting of a hydrogen atom, lower alkyl radicals having 1 to 3 carbon atoms and lower alkoxyl radicals having 1 to 3 carbon atoms; A represents a divalent linking member selected from the class consisting of -, -S-, -CO-, SO2, -SO- -CH- and C(CHa)2. and m represents an integer of from 1 to 4.

10. The process as claimed in claim 1 , wherein said pheriolic compound has a melting point of 1 000C or less and a boiling point of about 3000C or less under atrnospheric pressure.

11. The process as claimed in claim 1, wherein said phenolic compound is selected from the group consisting of phenol, alkyl-substituted monohydric phenol compounds and halogenated monohydric phenol compounds.

12. The process as claimed in claim 1 wherein said alkyl-substituted monohydric phenol compound is selected from the group consisting of O-, m- and P-cresols, 3,5-xylenol, carvacrol, and thymol.

13. The process as claimed in claim 11, wherein said monohydric halogenated phenol compound is selected from the group consisting of those of the formula (VI):

wherein R3 represents a member selected from the group consisting of a hydrogen atom and alkyl radicals having 1 to 3 carbon atoms, and X represents halogen atoms.

14. The process as claimed in claim 1 , wherein said spinning dope solution contains 5% to 30% by weight of said polymer material.

15. The process as claimed in claim 1, wherein said spinning dope solution has a rotation viscosity of at least 500 centipoises at a temperature of from OOC to 1 500C.

16. The process as claimed in claim 3, wherein said coagulating liquid comprises at least one member selected from the groups consisting of lower aliphatic alcohols having 1 to 5 carbon atoms, lower aliphatic ketones having 3 to 5 carbon atoms, tetrahydrofuran, dioxane, ethyleneglycol monomethylether, lower alkylene glycols, dimethylacetamide, dimethylformamide, dimethylsulfoxide, diethylsulfoxide, lower aliphatic carboxylic acids having 1 to 4 carbon atoms, and mixtures of at least one of the above-mentioned compounds with water.

17. The process as claimed in claim 3, wherein said coagulation is carried out in two or more stages.

18. The process as claimed in claim 1, wherein the resultant hollow filaments are drawn at a temperature of from 200C to 6000C.

19. The process as claimed in claim 1, wherein the resultant hollow filaments are drawn at a draw ratio of from 1.1 to 5.0.

20. The process as claimed in claim 18, wherein said drawing procedure is carried out in a dry atmosphere.

21. The process as claimed in claim 18, wherein said drawing procedure is carried out in a wet medium.

22. The process as claimed in claim 3, wherein said coagulating liquid contains at least 30% by weight of at least one aliphatic alcohol having 1 to 5 carbon atoms.

23. The process as claimed in claim 3, wherein said coagulating liquid consists essentially of a mixture of one part of at least one aliphatic alcohol having 1 to 5 carbon atoms with 0.1 to 1.5 parts by weight of water.

24. The process as claimed in claim 3, wherein said coagulating liquid has a temperature of from -1 00C to 600C.

25. An aromatic polyimide hollow filament produced in accordance with the process as claimed in claim 1.