JP7708713B2 - Solvent for dissolving aromatic polyamide, method for dissolving aromatic polyamide, and method for producing aromatic polyamide molded body - Google Patents

Description

The present invention relates to a solvent used to dissolve aromatic polyamides, and a method for producing aromatic polyamide molded articles using the solvent.

Aromatic polyamides include para-aromatic polyamides such as polyparaphenylene terephthalamide, and meta-aromatic polyamides such as polymetaphenylene isophthalamide, both of which are in practical use as fibers. Aromatic polyamides, especially para-aromatic polyamides, have excellent heat resistance and mechanical strength and have attracted attention as high-performance resins.
However, aromatic polyamides have extremely poor solubility in organic solvents, making them difficult to form into films as with ordinary plastics.

As described in Patent Document 1, a method has been proposed in which an aromatic polyamide is dissolved in an amide-based solvent containing an inorganic salt to form a film. However, this method uses a large amount of inorganic salt, and there is a risk that the inorganic salt cannot be completely removed from the film.
Also, as described in Non-Patent Document 1, a method has been proposed in which Kevlar (registered trademark) is derivatized by dissolving it in a solution of tetrabutylammonium fluoride (TBAF) and dimethyl sulfoxide. However, tetrabutylammonium fluoride is toxic and expensive, and in addition, the solubility of Kevlar (registered trademark) is only about 1%.

Meanwhile, the applicant has filed a patent application (unpublished) for a mixture of an aqueous solution of tetraalkylammonium hydroxide and dimethyl sulfoxide as a solvent for dissolving chitin.

JP 2006-241624 A

Takuo Ikeda et al., Annual Report of the Textile Industry Research Center, Graduate School of Engineering, Fukui University, Vol. 3, pp. 28-31 (2010)

The present invention provides a solvent capable of uniformly dissolving aromatic polyamides in a short time at around room temperature without requiring any special pretreatment, a method for dissolving aromatic polyamides using the solvent, and a method for producing aromatic polyamide molded articles.

As a result of extensive investigations aimed at achieving the above object, the present inventors have completed the invention described below.
[1] A solvent used for dissolving an aromatic polyamide, comprising:
The solvent comprises a tetraalkylammonium hydroxide represented by the following formula, water, and dimethyl sulfoxide:
The solvent is characterized in that the concentrations of the components in the solvent are within the ranges of 0.5 to 40 wt % for tetraalkylammonium hydroxide, 0.5 to 45 wt % for water, and 15 to 99 wt % for dimethylsulfoxide.
In the formula, R1, R2, R3 and R4 each independently represent an alkyl group having 1 to 5 carbon atoms.
[2] The solvent according to [1], wherein the tetraalkylammonium hydroxide includes at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.
[3] The solvent according to [1] or [2], wherein the aromatic polyamide dissolved therein is a para-aromatic polyamide and/or a meta-aromatic polyamide.
[4] A method for dissolving an aromatic polyamide, comprising contacting an aromatic polyamide with the solvent according to any one of [1] to [3] above to dissolve the aromatic polyamide.
[5] A method for producing an aromatic polyamide molded article, comprising producing an aromatic polyamide molded article by using an aromatic polyamide dissolved solution obtained by the method for dissolving an aromatic polyamide according to [4] above.

The solvent of the present invention is capable of dissolving aromatic polyamides uniformly in a short time without special pretreatment, regardless of the type, crystal form, and shape of the aromatic polyamide.

Compared to the solvents in Patent Document 1 and Non-Patent Document 1, the solvent of the present invention does not contain fluorine-based compounds or inorganic salts, making it safer and easier to completely remove the solvent when producing a molded body.

In addition, a solution in which aromatic polyamide is dissolved using the solvent of the present invention is highly stable and has fluidity even at room temperature, and has excellent moldability.

Photographs of aromatic polyamide solutions prepared in Examples 1, 2, 3, 5, 6, 8 and 9 (the magnetic stirrer used for stirring can be seen in some photographs). Photographs of aromatic polyamide molded articles obtained in Examples 1, 5, 6 and 8 Photographs of the aromatic polyamide dispersion solutions obtained in Comparative Examples 1 and 2 Photographs of the meta-aromatic polyamide solutions prepared in Examples 11, 12, 13, and 14 (the magnetic stirrer used for stirring is visible in the photograph). Photographs of meta-aromatic polyamide films produced in Examples 10 and 12

The aromatic polyamide that dissolves in the aromatic polyamide dissolving solvent of the present invention is not particularly limited, and examples thereof include para-type aromatic polyamides such as polyparaphenylene terephthalamide, and meta-type aromatic polyamides such as polymetaphenylene isophthalamide, or derivatives thereof, regardless of the degree of crystallinity and polymerization.
Among them, para-aramids such as Kevlar (registered trademark) (PPTA) from DuPont Toray, Twaron (registered trademark) (PPTA) and Technora (registered trademark) (copolymer type aramid) from Teijin Techno Products, and meta-aramids such as Nomex (registered trademark) from DuPont and Conex (registered trademark) (meta-aramid) from Teijin are more preferred because they have excellent mechanical properties, thermal properties and chemical resistance and are used in a wide range of fields. These aramids are commercially available, and commercially available products can be used as raw materials.

The tetraalkylammonium hydroxide (TAAH) which is a component of the aromatic polyamide dissolving solvent of the present invention is not limited as long as it is a tetraalkylammonium hydroxide in which R1 to R4 in the chemical formula shown in [1] above are alkyl groups having 1 to 5 carbon atoms, and may be used alone or in combination of two or more kinds.
Specific examples of the compounds include the following compounds.
Examples of the hydroxide include tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, methyltripropylammonium hydroxide, methyltributylammonium hydroxide, ethyltripropylammonium hydroxide, ethyltributylammonium hydroxide, propyltributylammonium hydroxide, dimethyldipropylammonium hydroxide, dimethyltributylammonium hydroxide, diethyldipropylammonium hydroxide, diethyldibutylammonium hydroxide, and the like. Particularly preferred are tetraethylammonium hydroxide (TEAH), tetrapropylammonium hydroxide (TPAH), and tetrabutylammonium hydroxide (TBAH).

The tetraalkylammonium hydroxide (TAAH) used to dissolve the polyimide of the present invention is water-soluble and stable in an aqueous solution. Most of the TAAH compounds are commercially available in aqueous solution form and are easily available.
The polyimide dissolving agent of the present invention contains tetraalkylammonium hydroxide (TAAH), water and dimethylsulfoxide (DMSO), and therefore TAAH can be mixed as an aqueous solution with DMSO to form the dissolving agent.

The aromatic polyamide dissolving solvent of the present invention is composed of TAAH, water and DMSO, and the composition ratio is adjusted to be within the concentration range of 0.5 to 40 wt% TAAH, 0.5 to 45 wt% water, and 15 to 99 wt% DMSO. More preferably, the composition ratio is adjusted to be within the concentration range of 2 to 35 wt% TAAH, 2.0 to 40 wt% water, and 25 to 96 wt% DMSO, even more preferably, the composition ratio is adjusted to be within the concentration range of 2.0 to 30 wt% TAAH, 3.0 to 35 wt% water, and 35 to 95 wt% DMSO, and most preferably, the composition ratio is adjusted to be within the concentration range of 3.0 to 35 wt% TAAH, 4 to 40 wt% water, and 45 to 94 wt% DMSO.

A TAAH concentration lower than 0.5 wt% is not preferred because the solubility and dissolution rate are low. On the other hand, a concentration higher than 40 wt% is not preferred because the solubility of the aromatic polyamide decreases and the required dissolution temperature becomes high. In addition, it is not preferred because there is a risk of the aromatic polyamide precipitating when the resulting aromatic polyamide solution is stored at room temperature.

If the water concentration is lower than 0.5 wt%, it is not preferable because the solubility of the aromatic polyamide decreases and the TAAH becomes unstable and may decompose. On the other hand, if the water concentration is higher than 45 wt%, it is not preferable because the solubility of the aromatic polyamide decreases.

The solvent of the present invention may contain other organic solvents in addition to tetraalkylammonium hydroxide, water, and dimethyl sulfoxide. Examples include alcohol, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, and pyridine. Addition of these solvents can improve the dissolution of aromatic polyamides and adjust the viscosity and reactivity of the aromatic polyamide solution.

The method for preparing the aromatic polyamide dissolving solvent of the present invention is not particularly limited. For example, an aromatic polyamide dissolving solvent can be obtained by preparing a commercially available TAAH aqueous solution to a desired concentration, adding DMSO thereto and stirring. If the TAAH concentration of the commercially available TAAH aqueous solution is lower than the desired concentration when the water concentration is in the optimal range, it is preferable to distill it before use and concentrate it to the desired water content before use. If the concentration is higher than the desired concentration, it is preferable to add water to dilute it before use. The weight ratio of TAAH/water is preferably 20/80 to 70/40. More preferably, it is 30/70 to 60/40, and most preferably 35/65 to 55/45.
The temperature during mixing is not particularly limited, but is preferably 10 to 120°C, more preferably 15 to 100°C, and most preferably 23 to 85°C.

There is no particular limitation on the method of dissolving aromatic polyamide in the aromatic polyamide dissolving solvent of the present invention. For example, an aromatic polyamide solution is prepared by adding aromatic polyamide to a predetermined amount of the aromatic polyamide dissolving solvent of the present invention and stirring until a transparent solution is obtained. Stirring may be performed with a commonly used mechanical stirrer. For a beaker scale, stirring with a magnetic stirrer is sufficient. The temperature during dissolution may be 10 to 150°C, and dissolution may be performed at room temperature without temperature adjustment. If the temperature is lower than 10°C, the solubility or dissolution rate of the aromatic polyamide is low, which is not preferable. If the temperature is higher than 150°C, water may evaporate or TAAH may decompose or decompose, which is not preferable. More preferably, the temperature is 15 to 140°C, even more preferably, 15 to 130°C, and most preferably, 23 to 125°C.

There are no particular limitations on the amount of aromatic polyamide dissolved. It may be adjusted appropriately depending on the type of aromatic polyamide, the degree of polymerization (molecular weight) and the application. For example, it is 1 to 50 wt %. More preferably, it is 2 to 40 wt %, and most preferably, it is 3 to 30 wt %. If the amount of solution is too low, it is not preferable because it reduces productivity and the moldability of the obtained aromatic polyamide solution is poor. On the other hand, if the amount of solution is too high, it is not preferable because the aromatic polyamide may not be completely dissolved, the uniformity of the solution may decrease, and the fluidity of the obtained aromatic polyamide solution may be lost.

The molding solution for the aromatic polyamide molded body of the present invention is obtained by dissolving aromatic polyamide in an aromatic polyamide dissolving solvent, and degassing the aromatic polyamide solution. The molding method is not particularly limited, but generally wet molding or dry molding can be applied. For example, after sucking aromatic polyamide solution into a syringe, a nozzle is attached to the syringe pump or microfeeder, and the aromatic polyamide solution is discharged from the nozzle into a coagulating liquid such as water or alcohol at room temperature while moving the syringe, and the fiber is washed and then wound up by a winder to prepare aromatic polyamide fiber.
When forming an aromatic polyamide film, for example, an aromatic polyamide solution is cast onto a glass substrate, and the resulting liquid film is washed while being coagulated in a coagulating liquid such as water or alcohol, and then dried to prepare a film.
When molding using the dry method, the aromatic polyamide solution is discharged from a mold and heated at a constant temperature to obtain fibers without DMSO and TAAH. On the other hand, when molding a film, the aromatic polyamide solution is cast on a substrate and then heated at a constant temperature to form a film. The heating temperature may be appropriately set depending on the molding method and the type of TAAH. For example, the temperature may be within the range of 50 to 300°C. It is preferable to gradually increase the temperature from 50°C, since this prevents the formation of bubbles in the molded product.

The present invention will be further explained using examples. Note that the present invention is not limited to these examples.

(Materials and solvents used)
Polyparaphenylene terephthalamide: Tiara (registered trademark) (microfibrous aromatic polyamide) manufactured by Daicel Corporation was used after drying in a blower dryer at 105° C. Alternatively, commercially available Kevlar (registered trademark) fiber was used as it was.
Meta-aramid: Commercially available Conex® staple fibers were used.
35% tetraethylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd.
45% tetraethylammonium hydroxide aqueous solution: Obtained by concentrating a 35% Tokyo Chemical Industry Co., Ltd. product.
48% tetraethylammonium hydroxide aqueous solution: Obtained by concentrating a 35% Tokyo Chemical Industry Co., Ltd. product.
40% tetrapropylammonium hydroxide aqueous solution: manufactured by Tokyo Chemical Industry Co., Ltd.
48% tetrapropylammonium hydroxide aqueous solution: Obtained by concentrating a 40% Tokyo Chemical Industry Co., Ltd. product.
40% aqueous tetrabutylammonium hydroxide solution: manufactured by Tokyo Chemical Industry Co., Ltd.
Other reagents were purchased from Nacalai Tesque.

(Dissolution method)
For dissolving the aromatic polyamide, a 10 ml or 20 ml sample bottle and a magnetic stirrer or a magnetic hot stirrer were used.

[Example 1]
0.7 g of 40% tetrapropylammonium hydroxide (TPAH) aqueous solution and 4.3 g of dimethyl sulfoxide (DMSO) were added to a 10 ml vial, and 0.2 g of commercially available Kevlar (registered trademark) fiber was added while stirring with a magnetic hot stirrer set at 80° C., and the appearance of the solution was observed while stirring. It was confirmed that the appearance of the solution tended to change from yellow to brown as Kevlar (registered trademark) dissolved. After 40 minutes, a brown transparent solution was obtained. A photograph of the appearance of the aromatic polyamide solution is shown in FIG. 1. The stirring time until a transparent solution was obtained was 40 minutes.
The obtained aromatic polyamide solution was cast onto a glass substrate using a glass rod, and the glass substrate was placed into the ethanol solution. After about 10 minutes, the aromatic polyamide solidified and became hard. The ethanol was exchanged four times to remove the DMSO and TPAH. The film was then spread onto a glass substrate and air-dried. The appearance of the obtained film is shown in Figure 2.

[Example 2]
The dissolution was carried out in the same manner as in Example 1, except that 0.2 g of Tiara was added instead of 0.2 g of commercially available Kevlar (registered trademark) fiber. The stirring time until a brown transparent solution was obtained was 90 minutes. The appearance of the obtained solution is shown in Figure 1.

[Example 3]
The same procedure as in Example 2 was carried out except that 4.6 g of DMSO and 0.4 g of 40% tetrapropylammonium hydroxide aqueous solution were used instead of 4.3 g of DMSO and 0.7 g of 40% tetrapropylammonium hydroxide aqueous solution, and 0.1 g of Tiara (registered trademark) was dissolved. The stirring time until a brown transparent solution was obtained was 120 minutes. The appearance of the obtained solution is shown in Figure 1.

[Example 4]
0.25 g of Tiara (registered trademark) was dissolved in the same manner as in Example 2, except that 4.0 g of DMSO and 1.0 g of 40% tetrapropylammonium hydroxide aqueous solution were used instead of 4.3 g of DMSO and 0.7 g of 40% tetrapropylammonium hydroxide aqueous solution. The stirring time until a brown transparent solution was obtained was 180 minutes.

[Example 5]
Dissolution of 0.2 g of dried Tiara (registered trademark) was carried out in the same manner as in Example 3, except that a 45% aqueous solution of tetraethylammonium hydroxide was used instead of a 40% aqueous solution of tetrapropylammonium hydroxide. The stirring time until a brown transparent solution was obtained was 60 minutes. The appearance of the obtained solution is shown in Figure 1. A film was produced using the obtained aromatic polyamide solution in the same manner as in Example 1. The appearance of the obtained film is shown in Figure 2.

[Example 6]
The dried Tiara (registered trademark) was dissolved in the same manner as in Example 2, except that a 40% aqueous solution of tetrabutylammonium hydroxide was used instead of a 40% aqueous solution of tetrapropylammonium hydroxide. The stirring time until a brown transparent solution was obtained was 120 minutes. The appearance of the obtained solution is shown in Figure 1. A film was produced in the same manner as in Example 1 using the obtained aromatic polyamide solution. The appearance of the obtained film is shown in Figure 2.

[Example 7]
Dissolution of Kevlar (registered trademark) fiber was carried out in the same manner as in Example 1, except that the dissolution temperature was room temperature. The stirring time until a brown transparent solution was obtained was 150 minutes.

[Example 8]
The procedure of Example 2 was repeated except that 3.0 g of DMSO and 2.0 g of 40% aqueous tetrapropylammonium hydroxide solution were used and the temperature was set to 120° C., and 0.2 g of Tiara was dissolved. The stirring time until a brown transparent solution was obtained was 40 minutes. The appearance of the obtained solution is shown in FIG.
The cellulose solution obtained was then drawn into a syringe and discharged into a distilled water bath at room temperature using a nozzle having a pore diameter of 0.5 mm, while the fibrous gel was stretched. The fibrous gel was then washed with distilled water to remove tetrapropylammonium hydroxide and dimethylsulfoxide, and air-dried at room temperature to obtain fibers. A photograph of the obtained fibers is shown in Figure 2.

[Example 9]
The same procedure as in Example 8 was carried out except that 4.75 g of DMSO and 0.25 g of 40% aqueous tetrapropylammonium hydroxide solution were used, and 0.1 g of Tiara was dissolved. The stirring time until a brown transparent solution was obtained was 150 minutes. The appearance of the obtained solution is shown in Figure 1.

[Comparative Example 1]
In the same manner as in Example 1, 0.2 g of Tiara was added using 5 g of DMSO without adding 40% tetrapropylammonium hydroxide aqueous solution, and the mixture was stirred for 5 hours, but no dissolution or color change occurred. The appearance was a pale yellow paste-like dispersion liquid as shown in Figure 3.

[Comparative Example 2]
0.25 g of calcium chloride and 4.75 g of N-methyl-2-pyrrolidone (NMP) were mixed, and 0.2 g of Tiara was stirred for 5 hours in the same manner as in Example 1, but no dissolution or color change occurred. The appearance was a pale yellow paste-like dispersion liquid as shown in Figure 3.

[Example 10]
0.3 g of Kevlar fiber was dissolved in the same manner as in Example 1, except that 0.7 g of 40% tetrapropylammonium hydroxide aqueous solution was replaced with 48% tetrapropylammonium hydroxide aqueous solution. The stirring time until a brown transparent solution was obtained was 70 minutes. The obtained solution was cast on a glass substrate with a glass rod, and the glass substrate was placed in distilled water. After about 5 minutes, the solution solidified and became hard. The distilled water was exchanged four times to remove DMSO and TPAH. The film was then spread on a glass substrate and air-dried. The appearance of the obtained film is shown in FIG. 5.

[Example 11]
3.0 g of DMSO and 2.0 g of 48% tetraethylammonium hydroxide aqueous solution were added to a 20 ml vial, and 1.2 g of meta-aramid short fibers were added while stirring with a non-heating magnetic hot stirrer, and the appearance of the solution was observed while stirring. It was confirmed that the appearance of the solution tended to change from colorless to yellow as the meta-aramid short fibers dissolved. After 120 minutes, a yellow transparent solution was obtained. As shown in a photograph of the appearance of the obtained solution in Figure 4, it had fluidity at room temperature.

[Example 12]
0.75 g of meta-aramid short fibers were dissolved in the same manner as in Example 11, except that 4.2 g of DMSO and 0.8 g of 48% aqueous tetraethylammonium hydroxide solution were used. The stirring time until a yellow transparent solution was obtained was 110 minutes. The obtained solution has fluidity at room temperature as shown in Figure 4. The obtained solution was cast on a glass substrate with a glass rod, and the glass substrate was placed in distilled water. After about 5 minutes, the solution solidified and became hard. The distilled water was exchanged four times to remove DMSO and TEAH. The film was then spread on a glass substrate and air-dried. The appearance of the obtained film is shown in Figure 5.

[Example 13]
0.3 g of meta-aramid short fibers was dissolved in the same manner as in Example 11, except that 4.6 g of DMSO and 0.4 g of 48% aqueous tetraethylammonium hydroxide solution were used. The stirring time until a yellow transparent solution was obtained was 60 minutes. The obtained solution had fluidity at room temperature as shown in FIG.

[Example 14]
0.6 g of meta-aramid short fibers was dissolved in the same manner as in Example 13, except that 4.3 g of DMSO and 0.7 g of 48% aqueous tetrapropylammonium hydroxide solution were used. The stirring time until a yellow transparent solution was obtained was 120 minutes. The obtained solution has fluidity at room temperature as shown in FIG.

[Example 15]
0.25 g of meta-aramid short fibers was dissolved in the same manner as in Example 13, except that 4.4 g of DMSO and 0.6 g of 40% aqueous tetrapropylammonium hydroxide solution were used. The stirring time until a yellow transparent solution was obtained was 105 minutes. The obtained solution has fluidity at room temperature.

[Example 16]
The meta-aramid solution prepared in Example 12 was cast onto a PET film, and then left on a 60°C hot plate for 1 hour to remove the water contained therein. The temperature of the hot plate was then raised to 150°C and heated for another 1 hour to form a film-like solid. This film-like solid was dried in a 250°C air drier for 1 hour, and then subjected to FT-IR analysis, which showed that neither TEAH nor DMSO was detected.

[Comparative Example 3]
Except for using 4.95 g of DMSO and 0.05 g of a 48% aqueous solution of tetraethylammonium hydroxide, an attempt was made to dissolve 0.25 g of meta-aramid short fibers in the same manner as in Example 15. As a result of stirring for 180 minutes at room temperature, the meta-aramid short fibers swelled, but a transparent solution was not obtained.

The dissolution conditions and evaluation results for Examples 1 to 15 and Comparative Examples 1 to 3 are summarized in Tables 1 and 2, and the solvent composition ratios are shown in Table 3.

As shown in Tables 1 to 3, in Examples 1 to 15, the aromatic polyamide was not pretreated, and it was possible to dissolve the aromatic polyamide uniformly in a short time at room temperature to 120°C. Tiara, Kevlar (registered trademark) fiber, and meta-aramid short fiber were polyphenylene terephthalamides with different shapes, but all of them were able to dissolve. From these results, it can be seen that the aromatic polyamide dissolving solvent of the present invention can be used to dissolve aromatic polyamides regardless of their shape. On the other hand, in Comparative Examples 1, 2, and 3, it was not possible to dissolve the aromatic polyamide.

As mentioned above, the aromatic polyamide dissolving solvent of the present invention can dissolve aromatic polyamide uniformly in a short time, regardless of the degree of polymerization and crystalline form of aromatic polyamide, and does not require highly toxic solvents as in the past.Furthermore, the aromatic polyamide-containing solution dissolved in the solvent of the present invention has excellent fluidity and moldability, and can be widely applied to the technical field of producing aromatic polyamide, especially aromatic polyamide molded body, by wet molding.Furthermore, the aromatic polyamide-containing solution dissolved in the solvent of the present invention can also be applied to the synthesis of aromatic polyamide derivatives.

Claims (5)

A solvent used for dissolving an aromatic polyamide,
The solvent comprises a tetraalkylammonium hydroxide represented by the following formula, water, and dimethyl sulfoxide:
The solvent is characterized in that the concentrations of the components in the solvent are in the ranges of 2.0 to 30 wt % for tetraalkylammonium hydroxide, 3.0 to 35 wt % for water, and 35 to 95 wt % for dimethyl sulfoxide.
In the formula, R1, R2, R3 and R4 each independently represent an alkyl group having 1 to 5 carbon atoms. The solvent according to claim 1, characterized in that the tetraalkylammonium hydroxide includes at least one of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide. 2. The solvent according to claim 1 , wherein the aromatic polyamide to be dissolved is a para-aromatic polyamide and/or a meta-aromatic polyamide. A method for dissolving an aromatic polyamide, comprising contacting the aromatic polyamide with a solvent according to any one of claims 1 to 3 to dissolve the aromatic polyamide. A method for producing an aromatic polyamide molded body, comprising the steps of: producing an aromatic polyamide molded body using an aromatic polyamide dissolution solution obtained by the method for dissolving an aromatic polyamide according to claim 4;