EP0013764B1 - Hydrophilic polycarbonate fibres having a high second order transition point and process for manufacturing them - Google Patents

Description

DE-OS 2554124 describes producing hydrophilic threads and fibers from thread-forming synthetic polymers by adding 5 to 50% by weight, based on solvent and solid, of a substance which is essentially a non-solvent for the polymer to the spinning solvent which has a higher boiling point than the solvent used and which is readily miscible with the spinning solvent and a liquid suitable as a washing liquid for the threads, and then washes this non-solvent out of the threads produced. Preferred non-solvents in this process are polyhydric alcohols such as glycerin, sugar and glycols.

Such z. B. fibers spun from acrylonitrile polymers have a core / shell structure and have a water retention capacity of at least 10%.

From DE-OS 2 713 456 it is also known to produce hydrophilic polyacrylonitrile threads and fibers by bringing the threads into contact with water vapor immediately after emerging from the spinneret.

If you now transfer the principle of DE-OS 2 554 124 for the production of hydrophilic fibers from polycarbonates, for. B. the polycarbonate based on 4,4'-dihydroxydiphenyl-2,2-propane, so you get under suitable spinning conditions even hydrophilic, core / shell structure vieving polycarbonate fibers with a water retention of at least 10%, each st their freezing temperature strong lowered and is usually around 75 ° C, wa. end pure polycarbonate fibers have a freezing temperature of 148-158 ° C (cf. B. v. Falkai, Lenzinger reports, episode 32, December 1971, page 43). This means that an essential advantage of polycarbonate fibers, namely their resistance to creasing and boiling, is lost.

Apparently the added non-solvent, e.g. B. tetraethylene glycol, as an internal plasticizer, whereby the glass transition temperature decreases (see Comparative Example 6 and Table 11). It has therefore been attempted to bring the hydrophilic filaments, produced by such a spinning process, to a high glass transition temperature by removing the non-solvent by vigorous washing before the drawing process. As the comparative examples 7 to 9 (cf. Table 11) show, despite intensive washing for several hours, it is not possible to reduce the non-solvent content below 10%.

It has now surprisingly been found that hydrophilic polycarbonate fibers having a core / sheath structure with high glass transition temperatures are obtained when the spinning process is carried out in the presence of water vapor.

The invention therefore relates to dry-spun hydrophilic, core / sheath structure threads or fibers made of polycarbonate with a porosity and a water retention capacity of at least 10%, a mercury density less than 1.0 g / cm ³ , a strength of at least 1.5 cN / dtex and a freezing temperature of at least 125 ° C.

The invention further relates to a process for the production of these hydrophilic polycarbonate fibers by a dry spinning process, which is characterized in that the threads at shaft temperatures of at most 140 ° C. immediately after they emerge from the spinneret, but at the latest at a time when the thread is still solidifying is not completed, comes into contact with water vapor and then stretches the threads.

This spinning process is in principle a conventional dry spinning process, preferably from strongly polar organic solvents such as dimethylformamide, dimethylacetamide and dimethyl sulfoxide, which have a boiling point above 100 ° C. With lower boiling solvents, e.g. B. methylene chloride, there is a risk of excessive solvent depletion in the spinning shaft in the spinning conditions used, whereby the non-solvent water vapor can no longer penetrate the threads so intensely because they are already too strongly consolidated. As a result, much of the hydrophilicity is lost.

Depending on the location and intensity of the steam injection onto the polymer threads as well as the thermal conditions in the spinning shaft, the width of the outer surface and the hydrophilicity and thus also the pore volume and the density of the threads can be controlled.

It has been found that a core-shell structure, a water retention capacity greater than 10% and fiber densities less than 1.0 g / cm ³ are always obtained if the spinning is carried out at low shaft temperatures of maximum 140 ° C. In order to avoid excessive condensation of water vapor and solvent in the spinning shaft, a shaft temperature of over 100 ° C., preferably 105-125 ° C., has proven to be optimal. At higher shaft temperatures, especially above 160 ° C, significantly lower water retention values are sometimes obtained below 10% and higher fiber densities normally more than 1.0 g / cm ³ .

The achievable hydrophilicity and fiber density are - in addition to the shaft temperature - also dependent on the amount of water vapor used. In general, an increase in the hydrophilicity and a decrease in the fiber density is observed with increasing amount of steam (cf. Examples 2-5).

Depending on the other spinning conditions, the amount of water vapor required to achieve a desired hydrophilicity can therefore be easily determined. In general, the minimum amount of water vapor injected is that of a spinning process in a vapor / air atmosphere sphere with 30 m ³ / h is required to produce hydrophilic core sheath fibers with water retention greater than 10%, at about 2 kg per 1 kg of spun material.

In the method according to the invention, the steam is preferably blown in above the spinneret in the direction of the air flow and the thread take-off. However, it is also possible to blow crosswise to the threads below the nozzle if the blowing takes place in such a way that excessive turbulence does not occur.

When dry spinning polycarbonate solutions made from dimethylformamide, solution temperatures above 120 ° C. are desirable in order to keep the solutions flowable and spinnable. Likewise, high air temperatures greater than 300 ° C and air volumes greater than 30 m ³ / hour have proven themselves to solidify the threads. In the method according to the invention, a spinning process in a steam / air atmosphere is therefore preferred.

Another important property of the hydrophilic polycarbonate threads is a sufficient strength of at least 1.5, preferably at least 2.2 centinewtons / dtex, in order to achieve good processability and usability. The usual stretching of approx. 1: 5-1: 6 over heating godets at temperatures above the freezing temperature at 180-220 ° C. is not possible with the hydrophilic core sheath fibers made of polycarbonate according to the invention because the porosity is lost at the high temperatures. On the other hand, boiling water only reaches a maximum stretch of 1: 2, which corresponds to a fiber strength of less than 1.5 centinewtons / dtex. With higher stretching, capillary cracks appear more. It has now been found that the degree of stretching can be increased to approximately 1: 3.5-1: 3.8 if the hydrophilic polycarbonate threads in water containing approximately 30% by weight of DMF at 95-100 ° C. and residence times stretched by a maximum of 2 seconds. With longer dwell times, the individual capillaries stick together. If the composition of the stretching bath liquid is changed, the maximum degree of stretching decreases again. For example, the hydrophilic polycarbonate threads can only be stretched a maximum of 1: 2.7 times in 50% by weight DMF-containing water. With 40% by weight of DMF-containing water, the maximum degree of stretching increases to 1: 3.6 and in 30% by weight of DMF-containing water a stretching by 1: 3.8 can also be achieved. It has proven to be advantageous to carry out the drawing in the drawing bath as soon as possible after the spinning process, since the maximum drawing conditions can be significantly lower after an intermediate storage of a few days. Double stretching is likewise advantageous in that first stretching in air is carried out immediately after leaving the threads of the shaft and then the described bath stretching. In this way, total stretching ratios above the maximum stretching ratio mentioned in the stretching bath, for example those of 1: 6, can be achieved.

Hydrophilic polycarbonate fibers produced in this way have a strength of at least 1.5 centinewtons / dtex.

Threads or fibers according to the method according to the invention have a matt, wadded appearance. They are particularly suitable as self-absorbent fleeces and tampons. Because of their resistance to cooking, they are preferred for hygiene articles.

The determination of the physical quantities mentioned above was carried out as described below. These methods relate to dyed or blind-dyed, preparation-free fibers, yarns or textile fabrics. The cross-sectional structure of the core-sheath fibers was determined on the basis of electron micrographs.

Methods Mercury density determination ( _Q Hg)

After heating the sample at 50 ° C under vacuum (10 ^-2 mbar ₎ , the Hg density (mean, apparent density) is determined by volume measurements in mercury at an overpressure of 10 bar

Helium density determination (He)

After heating the sample at 50 ° C under vacuum (10- ² bar), the helium density ("true density" is determined by measuring the volume in helium with a gas comparison pycnometer.

Definition of porosity (P)

The water retention capacity is determined on the basis of DIN specification 53814 (cf. Melliand Textile Reports 4 [1973], page 350).

• m_f = Gewicht des feuchten Fasergutes
• m_tr = Gewicht des trockenen Fasergutes.

The fiber samples are immersed in water containing 0.1% wetting agent for 2 hours. The fibers are then centrifuged for 10 minutes at an acceleration of 10000 m / sec ² and the amount of water, which is retained in and between the fibers, is determined gravimetrically. To determine the dry weight, the fibers are dried to constant moisture at 105 ° C. The water retention capacity (WR) in percent by weight is:

• m _f = weight of the moist fiber material
• m _tr = weight of the dry fiber material.

Determination of the freezing temperature (E _T )

The fiber sample is placed in an oven under a pre-tension of 15 mN / tex and a heating rate before 5 ° C / min. heated and examined with the thermomechanical analyzer TMS-1 from Perkin-Elme. Upon reaching the glass transition temperature of a strong plastic flow set of the fibers, the corresponding glass transition temperature _(T E) is obtained by an extrapolation in the temperature-strain diagram (abscissa = heating temperature) to the temperature axis.

The following examples serve to further explain the invention. Unless otherwise noted, partial and percentage figures relate to weight.

Examples 1-5

1 a) 74 kg of dimethylformamide are mixed with a polycarbonate of 4,4'-dihydroxydiphenyl-2,2-propane (MW approx. 80,000; η _rei = 2.2 in 0.5% methylene chloride solution) in a kettle at room temperature. The mixture is then heated to 130 ° C. for 3-4 hours with stirring and the spinning solution is fed to a heating device via a gear pump and kept at 130 ° C. The residence time in the heating device was 3 minutes. The spinning solution was then filtered and fed directly to a 240-hole nozzle. 40 kg of saturated steam per hour were blown into the spinning chess above the nozzle. The shaft temperature was 125 ° C. and the temperature of the spinning solution, also measured at the nozzle entry point, was 125 ° C. 40 m ^{3 of} air / hour at 420 ° C. were also blown in. About 9 kg of steam were consumed per kg of spinning material. The threads with a total denier of 2400 dtex were collected from bobbins and brought together to form a cable of 240,000 dtex. The cable was then stretched 3.8 times at 100 ° C. in 30% dimethylformamide-containing water. The dwell time in the stretching tub was approximately 2 seconds. It was then washed, provided with an antistatic preparation, dried at 120 ° C., crimped and cut into staple fibers 60 mm in length. The individual fibers with a final titer of 3.3 dtex have a strength of 2. centinewton / dtex and a water retention capacity according to DIN 53 814 of 93%. The fibers have a pronounced core-shell structure with a round cross-sectional shape. The proportion of the outer surface of the total cross-sectional area is approximately 18%. The freezing temperature of the fibers was 129 ° C.

The individual fibers had a helium density of 1.225 g / cm ³ and a mercury density of 0.572 g / cm ³ ; the porosity was 53.3%.

1 b) A part of the fiber cable with a total denier of 240,000 dtex was stretched in boiling water. The maximum degree of stretch was approx. 200-220%, then there are increased capillary cracks in the stretching tub. The strength of such post-treated fibers was 1.3 centinewtons / dtex with a single final titer of 4.6 dtex.

Further examples are given in Table I below. The spinning solutions were spun as described in Example 1 a) to give core sheath fibers with a final titer of 3.3 dtex and aftertreated. The amount of steam and the shaft temperature were varied during the spinning process. Constant were the air volume with 40 cbm / hour, the air temperature with 420 ° C and the spinning solution temper; with 125 ° C. With air volumes <20 cbm / hour, air temperatures <300 ° C and solution temperatures <110 ° C, spinning was no longer possible (missing thread consolidation). The polymer described above was used as a solid in the weight ratios specified therein.

Examples 6-9 (Comparative examples)

6a) 74 kg of dimethylformamide are mixed with 26 kg of polycarbonate from Example 1 as described in Example 1, dissolved, sent through a heating device and filtered. A 26% solution of polycarbonate in DMF is obtained. Via a three-way tap, 130 ° C warm tetraethylene glycol is metered in using a gear pump so that the weight ratio of polycarbonate solid to tetraethylene glycol = 3.65: 1. After mixing, the 130 ° C hot solutions are homogenized using mixing combs and spun directly from a 240-hole nozzle. The shaft temperature is 180 ° C, the air temperature is 300 ° C and the air volume used was 40 cbm / hour. The threads with a total titer of 2400 dtex were collected on spools and brought together to form a cable of 240,000 dtex. The cable was then stretched 1: 2 times in boiling water, washed, provided with antistatic preparation, dried at 120 ° C., crimped and cut into staple fibers of 60 mm. The individual fibers with a final titre of 6.3 dtex had a water retention capacity of 12%. The fibers. again had a core-shell structure with a dumbbell-shaped cross-sectional shape. The proportion of the outer surface of the total cross-sectional area is approximately 80%. The fiber's freezing temperature is 97 ° C. According to gas chromatographic analysis, the fibers still contain 6.9% tetraethylene glycol.

6b) A part of the fiber cable was treated several times with boiling water before the stretching process in order to remove the non-solvent tetraethylene glycol. The cable was then post-treated into fibers as described above. The freezing temperature of the fibers is 99 ° C and the content. non-solvent tetraethylene glycol was 6.4%. The water retention capacity remained unchanged at 12%. Despite intensive washing, it is apparently not possible to completely wash out the non-detergent.

Further examples are given in Table 11 below. The spinning solutions were spun as described in Example 6 to give core sheath fibers with a final titer of 6.7 dtex and aftertreated by the method of Examples 6a) and 6b). The weight ratio of polymer solid to non-solvent was varied. Tetraethylene glycol was used as the non-solvent. In all cases core mantet fibers with dumbbell-shaped to oval cross-sectional shape are obtained.

Claims (9)

1. Dry spun, hydrophilic filaments or fibres of a corejacket structure produced from a polycarbonate having a porosity and a water retention capacity of at least 10%, a mercury density of less than 1.0 g/cc, a strength of at least 1.5 cN/dtex and a second order transition temperature of at least 125⁰ C.

2. Filaments or fibres according to Claim 1, characterised in that the polycarbonate used is a polycarbonic acid ester of 4,4'-dihydroxydiphenyl-2,2-propane.

3. A process for producing the filaments or fibres according to Claim 1 by a dry spinning process, characterised in that, immediately on leaving the spinning jet, but at the latest at a time when they have not completely solidified, the filaments are brought into contact with steam at duct temperatures of at most 140° C, and the filaments are thereafter drawn.

4. A process according to Claim 3, characterised in that the polycarbonate used is a polycarbonic acid ester of4,4'-dihydroxydipheny)-2,2-propane.

5. A process according to Claims 3 and 4, characterised in that the steam is blown into the spinning duct above the jet in the spinning direction.

6. A process according to Claims 3 to 5, characterised in that the filaments are drawn in an aqueous solution containing spinning solvent.

7. A process according to Claim 6, characterised in that the aqueous solution contains approximately 30% by weight of the spinning solvent.

8. A process according to Claims 6 and 7, characterised in that drawing is carried out in a ratio of from 1 : 3.5 to 1 : 3.8.

9. A process according to Claims 3 to 8, characterised in that the spinning solvent is dimethyl formamide.