Claims
- 1. Non-flammable, high temperature resistant polyimide fibers comprising units of the general formula ##STR4## wherein R is present partly as a group of the formula ##STR5## and partly as a group of the formula ##STR6## produced by dry spinning in a spinning column a 20 to 40% solution of said polyimide in aprotic organic solvents from spinnerets having circular orifices, orifice numbers ranging from 20 to 800 and orifice diameters of from 100 to 300 .mu.m, applying an extrusion speed of between 20 and 100 m/min, a take-up speed of between 100 and 800 m/min, an amount of spin gas between 40 and 100 m.sup.3 /h at standard conditions, and a spin gas temperature between 200.degree. and 350.degree. C., to obtain a tow leaving the spinning column having a residual solvent content of 5 to 25% by weight - based on the dry polymer - and a single filament titer of between 3.5 and 35 dtex, washing said tow in hot water, drying said tow to a moisture content of less than 5%, and drawing said tow at high temperature,
- said fibers having a wide variety of irregularly lobed or serrated cross-sections resembling the letters W, U, C, Y, E, V, T and X, a wool-like smooth hand and a high-brightness.
- 2. The polyimide fibers produced as set forth in claim 1 wherein said tow is washed in water at take-in speeds of from 2 to 20 m/min, at temperatures of between 80.degree. and 100.degree. C., pre-finished, dried at temperatures of between 120.degree. and 300.degree. C. to a moisture content of less than 5%, drawn in at least one step at a ratio of from 1:2 to 1:10 at temperatures of between 315.degree. and 450.degree. C., post-finished with a conventional preparation, crimped at room temperature, and cut into fibers.
- 3. The polyimide fibers produced as set forth in claim 1 wherein said solvent is selected from the group consisting of dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone and dimethylformamide.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 820/83 |
Mar 1983 |
ATX |
|
BACKGROUND OF THE INVENTION
This application is a continuation of application Ser. No. 818,989, filed Jan. 10, 1986, now abandoned, which is a continuation of application Ser. No. 584,477, filed Feb. 28, 1984, now abandoned.
The invention relates to a method of producing non-flammable, high-temperature-resistant polyimide fibers according to the dry-spinning technique from a solution in aprotic organic solvents.
Heat-resistant polymers have been known for a long time. They contain aromatic groups in their molecule chains so as to form highly conjugated bond systems, which are essential for high-temperature resistance. Examples for that are aromatic polyamides and polyimides, where the temperature resistance was substantially increased by substitution of aliphatic groups by aromatic groups.
A disadvantage for their technological application is the fact that they are normally neither soluble in solvents nor meltable. Therefore, they cannot be processed by extrusion, melt-spinning, dry-spinning, wet-spinning or similar procedures, like other synthetic materials.
In order to avoid these difficulties it was proposed to prepare as a prepolymer a polyamide acid by condensation of tetracarboxylic acid dianhydride with a diamine under relatively mild conditions in a first step. Thus any amine group primarily reacts with one of the two respective available carboxyl groups of the anhydride. This polyamide acid is soluble, and sheets, films or fibers may be formed from its solutions. Subsequently, the solvent is evaporated from these products and upon further heating polyimide is formed.
However, this method has some serious disadvantages: the intermediate compound is very sensitive to hydrolytic degradation and water is formed during the final condensation step to polyimide. Water can escape from the interior of the shaped products (sheets, films, fibers) by diffusion only. If this reaction is carried out too fast, the evaporating water forms bubbles which cause voids within the final product. These are detrimental to the end-use properties.
Another proposal to obtain non-flammable, high-temperature-resistant polymers is disclosed in DE-PS No. 2 143 080. The copolyimides described in that patent are soluble in polar aprotic organic solvents, such as dimethylformamide, dimethylacetamide,N-methylpyrrolidone or dimethylsulfoxide. The polymers are produced by solution condensation of benzophenone tetracarboxylic acid dianhydride with a mixture of toluylene diisocyanate and diphenyl methane diisocyanate in one of the above mentioned solvents. The polymer can be further processed directly from these solutions. According to DE-OS No. 2 442 203 fibers can be produced from the solutions, particularly by wet-spinning. The fiber cross-section varies depending on the spin bath chosen. When using water with varying amounts of a polar aprotic solvent (e.g. dimethylformamide, dimethylacetamide, N-methylpyrrolidone or the like), the fiber cross-section will be round or elliptical. When using glycerin in the spin bath, pseudo hollow fibers with a narrow longitudinal slot and a serrated outer side will form. As to dry spinning, only general remarks without any indication as to the fiber properties attainable are found in DE-OS No. 24 42 203.
Thus the production of polyimide fibers by dry-spinning from solutions containing polymers formed of benzophenone tetracarboxylic acid dianhydride and a mixture of toluylene diisocyanate and diphenylmethane diisocyanate has not been satisfactorily achieved till today. Due to avoiding coagulation baths and being able to recover spinning solvents more easily in case of dry-spinning, fiber production by dry-spinning is more favorable than by wet spinning even from an economical point of view.
Fibers with lobed or serrated cross-sections have proved to show better end-use characteristics in textile applications. It is known in the art to obtain such fibers by dry or melt spinning by means of spinneret orifices with appropriate cross-sections, for instance cross-like or asterisk-like. Thus it is described e.g. in DE-OS No. 30 40 970 that acrylic fibers with a modified cross-section can be obtained by dry-spinning by means of said spinneret orifices. In addition to the difficult and expensive production of spinneret plates having complicated orifices, they also corrode substantially faster than those having circular orifices. Despite of these disadvantages this method has been used to produce fibers with better end-use properties, in particular improved soiling behavior, increased dye brightness, a good hand and improved overall textile characteristics.
Round fiber cross-sections are obtained by melt spinning when using circular orifices whereas a dog-bone shaped fiber cross-section is obtained by dry-spinning of solutions. Thus, the same result was to be expected when using polyimide solutions in a conventional dry-spinning method.
It is the object of this invention to manufacture fibers of non-flammable, high-temperature-resistent polyimide polymers by a dry-spinning method. Those fibers should show improved end-use properties, having in particular an irregular fiber cross-section. Thereby is guaranteed a good hand and high brightness as well as an improved area coverage at an equal area mass as compared to fibers having a circular cross-section.
According to the invention, this object is achieved with a method of the initially defined kind by departing from a polyimide polymer comprising units of the general formula ##STR1## wherein R is present partly as a group of the formula ##STR2## and partly as a group of the formula ##STR3## in that, in order to obtain fibers having irregularly lobed or serrated cross-sections, a wool-like, smooth hand and high brightness, the dry-spinning process is carried out in a spinning column, wherein a solution containing 20 to 40% by weight of the polyimide is spun from spinnerets having circular orifices, the number of orifices ranges from 20 to 800 and their diameter from 100 to 300 .mu.m, an extrusion speed of between 20 and 100 m/min and take-up speeds of between 100 and 800 m/min are applied, and spin gas in an amount of between 40 and 100 m.sup.3 /h, under standard conditions of temperature and pressure, i.e., a temperature of 0.degree. C. and a pressure of 760 mm Hg (hereinafter standard conditions) and at a temperature of between 200.degree. C. and 350.degree. C. is used, the fiber bundle or tow leaving the column has a residual solvent content of from 5 to 25% by weight - based on dry polymer - and a single filament titer of between 3.5 and 35 dtex, is washed in hot water, then dried to a moisture content of less than 5%, subsequently drawn at high temperature and, if desired, is crimped and cut into staple fibers.
US Referenced Citations (3)
| Number |
Name |
Date |
Kind |
| 3717696 |
Rochina et al. |
Feb 1973 |
|
| 3985934 |
Farrissey, Jr. et al. |
Oct 1976 |
|
| 4370290 |
Makino et al. |
Jan 1983 |
|
Foreign Referenced Citations (2)
| Number |
Date |
Country |
| 0040042 |
Jan 1981 |
EPX |
| 2102333 |
Feb 1983 |
GBX |
Continuations (2)
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Number |
Date |
Country |
| Parent |
818989 |
Jan 1986 |
|
| Parent |
584477 |
Feb 1984 |
|
Patent Grant
4801502
