WO2005080661A1 - Method for the production of non-wovens, non-wovens, and use thereof - Google Patents

Abstract

The invention relates to a method for producing non-wovens, according to which a lyotropic solution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) is spun to several continuous threads into a precipitation bath via an air gap by extruding the same through a nozzle beam comprising several openings, whereupon said continuous threads are intermingled with the aid of gaseous medium and/or fluid that flows thereagainst. The invention further relates to such non-wovens and the use thereof.

Description

 Process for the production of nonwovens, nonwovens and their use

The invention relates to a process for the production of nonwovens, in which a lyotropic solution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) by means of extrusion through a nozzle bar containing several openings via an air gap into a coagulation bath to form a plurality of continuous threads which are spun in Connection can be swirled by inflowing with gaseous medium and / or fluid. The invention also relates to such nonwovens and their use.

Nonwovens are textile fabrics in which the cohesion of the fibers is ensured not by weaving or knitting, but by interlocking and sometimes also gluing after the fibers have been swirled. Because of the wide range of uses and the low production costs, the Nonwovens production continues to show high annual growth rates. The advantages of these nonwoven materials lie in particular in the high moisture absorption, the high variability of density and thickness as well as the extensive surface anisotropy, which results in the numerous possible uses, e.g. in medicine (surgical drapes, bed sheets, wound coverings, gauze, cotton baths, etc.) for hygiene products , as wipes in household and industry, as decorative nonwovens (tablecloths, serviettes, curtains), inlay nonwovens in the clothing industry and for numerous technical applications (eg insulating mats in the construction industry).

In principle, the formation of fleece from short fibers, staple fibers or continuous filaments is possible. The processes known as “spunbonding” or “spunlacing” of forming nonwovens from continuous fibers have the advantage that the fibers are spun and laid to form nonwovens in one process

Subject of this invention. A large number of fiber-forming polymers can be used as the starting material for the nonwovens. Nonwovens made from continuous filaments are preferably made from synthetic fibers such as polyester, polyacrylonitrile or polypropylene.

Viscose fibers are preferably used as short or staple fibers for the manufacture of nonwovens.

Since the viscose process, which is still used to produce the majority of regenerated cellulose fibers, is associated with considerable environmental pollution and high investment costs, extensive efforts have been made for several years to replace the viscose process with alternative processes. This also applies to the production of

Cellulose nonwovens. For example, the so-called “Bern developed "liese" process in which cotton backs are spun according to the Cuproam onium process and processed into nonwovens (US Pat. No. 3,833,438). Both processes also have the advantage that the nonwovens products can be produced from continuous filaments in a direct process.

Another method, according to which the known “Lyocell” fiber is made by precipitating a solution of cellulose in a system composed of N-methylmorpholine-N-oxide (NMMNO) and water (US Pat. No. 3,767,756, DE 28 30 685), the solution using a The process is also used for the production of nonwovens products (WO 00/18991, WO 98/07911).

Another known process for the production of fibers and other molded articles from regenerated cellulose consists in the precipitation of a solution of cellulose carbamate (EP-A 57 105, EP-A 178 292), which is obtained by reacting cellulose with urea with thermal splitting of the urea into isocyanic acid and ammonia and reaction of the isocyanic acid with the OH groups of the cellulose is formed. Cellulose carbamate is soluble in cold, dilute sodium hydroxide solution and can be regenerated back to cellulose in heated sodium hydroxide solution.

Proceeding from this, it was an object of the present invention to provide a process for the production of nonwovens from cellulose carbamate or regenerated cellulose which is independent of the viscose process and which, with good product properties, meets the requirements in terms of low investment and production costs and low environmental impact.

It was also an object of the invention to use nonwovens to provide superior product properties.

This object is achieved by the method with the features of claim 1 and the nonwovens with the features of claims 20 and 23. The further dependent claims show advantageous developments. Claims 28 to 33 specify uses of the nonwoven fabric according to the invention.

According to the invention, this object is achieved in that a lyotropic solution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) by means of extrusion through at least 20 openings, i.e. Nozzles containing the nozzle block through an air gap in one

Precipitation bath is spun into a plurality of continuous filaments, which are then swirled by flowing with gaseous medium and / or fluid to form the nonwoven.

Cellulose carbamate is soluble in NMMNO and can be deformed in a similar way to cellulose. The following advantageous differences can be seen compared to the conventional NMMNO process:

1. The viscosity of the solution increases sharply with an increasing content of cellulose or cellulose carbamate. However, too high a viscosity affects the spinnability of the solution. The limit of spinnability is therefore a maximum of 15% in the conventional cellulose solution. In contrast, this limit is around 30% for cellulose carbamate. Solutions with a cellulose carbamate content of 25% can still be easily spun. The higher concentration of the solution means less use of solvent and thus less effort in the reprocessing of the precipitation bath for the recovery of the NMMNO and thus leads to a significant cost reduction.

2. Solutions with a cellulose carbamate content of over 20% surprisingly show a lyotropic behavior, i.e. the cellulose carbamate is in a liquid-crystalline state, as can be seen from polarization microscopic images (Figures 1 and 2). This results in the extremely advantageous application that the molecules are almost perfectly aligned in the fiber direction during spinning due to the shear in the nozzle channel, and the fibers therefore have an extraordinarily high orientation and therefore a very high strength. Strengths of 60 cN / tex and above can be achieved.

3. Cellulose carbamate has a significantly higher water absorption capacity and better dyeability than cellulose.

A nozzle bar with at least 10,000 openings is preferably used for the extrusion. The ratio of length to diameter (L / D ratio) of the nozzles is preferably between 1 and 20.

The width of the air gap between the nozzle and the precipitation bath is preferably 5 to 250 mm, particularly preferably 10 to 150 mm.

In a preferred embodiment variant of the method, the continuous filaments are guided downward into a slit-shaped funnel after spinning, the intermingling with the gaseous medium and / or fluid taking place at the outlet of the funnel. to To improve the intermingling of the continuous filaments, it is further preferred to realize this by shaking the funnel.

Air and / or water are preferably used as the gaseous medium and / or fluid.

It is further preferred that the continuous threads are deposited on a conveyor belt after the intermingling. A further intermingling of the continuous threads is preferably realized by shaking the conveyor belt.

The lyotropic solution is preferred by swelling the cellulose carbamate in a 50% solution of

NMMNO in water and subsequent withdrawal of the water to a ratio of NMMNO to water between 80:20 and 90:10, particularly preferably 87:13.

The cellulose carbamate content of the lyotropic solution is preferably at least 20% by weight, particularly preferably 22 to 27% by weight. The percentages relate to the entire lyotropic solution.

The precipitation bath preferably consists of a solution of NMMNO in water with an NMMNO content of 0.5 to 25% by weight, particularly preferably 5 to 15% by weight, based on the solution of NMMNO in water.

The extrusion or spinning is preferably carried out at a temperature of 80 to 110 ° C, particularly preferably of 85 to 95 ° C.

In a further advantageous embodiment variant of the method, the nonwoven is subsequently attached the previously described steps are washed, pressed and dried. The washing can preferably be carried out by a high pressure water jet.

It is further preferred that the cellulose carbamate is regenerated to cellulose in a regeneration bath of 0.3 to 1% by weight sodium hydroxide in water at a temperature of 60 to 95 ° C. This enables nonwovens from regenerated

To produce cellulose. In a first advantageous variant, it is possible to carry out the regeneration between extrusion and swirling. Another preferred variant provides that the regeneration is carried out after the swirling.

According to the invention, a nonwoven fabric is also provided from a random scrim made of cellulose carbamate filaments. It is preferred that the continuous filaments have a strength of at least 60 cN / tex. Furthermore, such a nonwoven fabric can preferably be produced by the method according to one of claims 1 to 19.

According to the invention, a nonwoven fabric is also made from a

Tangled scrim made of continuous filaments made of regenerated cellulose. With regard to the regeneration of the cellulose carbamate to cellulose, reference is made to claims 16 to 19. The fibers made from regenerated cellulose preferably have a residual nitrogen content (residual N content) of 0.3 to 0.5, particularly preferably 0.1 to 1.2.

The nonwoven fabric has a pore structure with a preferred porosity of 1 to 10%. It is further preferred that the nonwoven fabric has a specific inner surface between 20 and 50 m / cm ³ , measured by means of small-angle X-ray scattering (SAXS).

The nonwoven fabric according to the invention can particularly preferably be produced from regenerated cellulose by the process according to one of Claims 16 to 19.

The nonwovens according to the invention are preferably used in medicine, in particular as surgical drapes, bed sheets, wound coverings, gauze or cotton pads. The nonwovens can also be used as hygiene materials or as wipes in the household. Another field of application of the nonwovens according to the invention are decorative nonwovens, in particular tablecloths, napkins or curtains, and insert nonwovens in the clothing industry. Furthermore, the nonwovens according to the invention are used as insulating mats or reinforcing nonwovens, e.g. as replacement for

Glass fiber fleece, used in the construction industry. Because of the high strength, the nonwovens according to the invention can be used in a similar way to glass fiber nonwovens for reinforcing plastics.

The subject according to the invention is to be explained in more detail with reference to the following figures and the following example, without restricting it to the embodiment variants described herein.

Fig. 1 shows a schematic representation of the process flow according to the invention.

2 shows a slot-shaped funnel according to the invention, at the exit of which the swirling takes place. The basic sequence of the method is shown in FIG. 1. Here, the spinning solution 1 is extruded into a precipitation bath 4 by means of a spinning pump 2 by means of a nozzle bar 3, which contains a large number of nozzles. Spinning is carried out vertically from top to bottom through the air gap into the precipitation bath. The fibers are drawn off in a horizontal direction via deflection rollers 5. A first wash bath and a stretching section can optionally be located on this route.

Another deflection roller 6 then leads the fiber bundle down into a slit-shaped funnel 7, at the exit of which the fiber bundle is flown by air or water on both sides. The fibers swirled in this way are placed on the one underneath

Transport belt 8 deposited, with further swirling by shaking the depositing device or the conveyor belt transversely to the direction of travel. The strip passes through a washing bath with a washing nozzle 9, which can also be realized by a water jet under high pressure, and thus leads to a further solidification of the material in the sense of spun lacing. The conveyor belt consists of a wide-meshed network, preferably made of metal, which ensures that the washing liquid runs off quickly. The material can then be dried in appropriate drying devices. However, the water can also be squeezed out by a pair of rollers, which at the same time enables the nonwoven to be compressed.

Figure 2 shows the structure of a slot-shaped funnel according to the invention. The fiber can be introduced into said funnel via the fiber inlet 1. The transport of the fiber through the funnel is made possible by a Venturi nozzle implements the water jet principle. Through the opening 3 there is the supply of water, air or a mixture thereof which, due to the Venturi profile, flows past the channel 4 in such a way that a negative pressure is created which transports the fiber through the channel 4. At the lower end 5 of the funnel is the fiber exit, from where the filaments can then be transported on.

example

800 g of pulp with a DP ( _Cu oχam) of 520 are in a kneader with 3200 g of a solution consisting of 12 wt .-% NaOH, 30 wt .-% urea and 58 wt .-% water for 1 h at 25 ° C. mixed intensively and then pre-matured at 23 ° C for 48 h on a DP _(Cu oχaπι) of 300. The moist alkali cellulose is kneaded at room temperature in a 5 l kneader with 1200 g of solid crystalline urea for 30 minutes. The temperature of the kneader is then raised to 140 ° C. and the water present is drawn off. After reaching a product temperature of 140 ° C increased and the existing water removed. After reaching a product temperature of 140 ° C, the mass is kneaded for a further 120 min and then discharged from the kneader. To obtain the pure CC, the dry crumbly mass is washed 3 times with deionized water at a liquor ratio of 1:16, suctioned off over a frit and then dried at room temperature. This loosened and crumbly product had a nitrogen content of 3.0% and a DP _(Cuoxam ) of 290.

The cellulose carbamate was mixed in a kneader with a 50% aqueous NMMO solution, this solution by removing the excess water with a Concentrated in a vacuum of 80 mbar to the NNMO monohydrate and thereby the cellulose carbamate dissolved. The spinning solution had a cellulose content of 25% by mass. The solution was spun on a laboratory system with 10,000 capillaries, led to the swirling nozzle via a roller system, swirled there in a water stream and continuously deposited on a conveyor belt to form a fleece, washed and dried. The basis weight of the fleece was 75.7 g / m, the dry strength 8.5 kN / m.

Claims

claims 1. A process for the production of nonwovens, in which a lyotropic solution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) by means of extrusion through a nozzle block containing at least 20 openings is spun through an air gap into a precipitation bath to form a plurality of continuous filaments, which are subsequently can be swirled by inflowing with gaseous medium and / or fluid. 2. The method according to claim 1, characterized in that a nozzle block with at least 10,000 openings is used. 3. The method according to any one of claims 1 or 2, characterized in that the ratio of length to diameter of the nozzles is from 1 to 20. 4. The method according to any one of the preceding claims, characterized in that the width of the air gap between the nozzle and the precipitation bath is 5 to 150 mm, in particular 10 to 50 mm. Method according to one of the preceding claims, characterized in that the continuous filaments are guided downward into a slit-shaped funnel after spinning, the intermingling with the gaseous medium and / or fluid taking place at the outlet of the funnel. 6. The method according to the preceding claim, characterized in that a further swirling of the continuous threads is achieved by shaking the funnel. 7. The method according to any one of the preceding claims, characterized in that air and / or water are used as the gaseous medium and / or fluid. 8. The method according to any one of the preceding claims, characterized in that the continuous filaments are deposited on a conveyor belt after the intermingling. 9. The method according to the preceding claim, characterized in that a further swirling of the continuous threads is achieved by shaking the conveyor belt. 10. The method according to any one of the preceding claims, characterized in that the cellulose carbamate content of the lyotropic solution is at least 20% by weight, in particular 22 to 27% by weight, based on the solution. 11. The method according to any one of the preceding claims, characterized in that the lyotropic solution by swelling the cellulose carbamate in a 40 to 70%, in particular a 50% solution of NMMNO in water and then removing the water to a ratio of NMMNO is produced in water between 80:20 and 90:10. 12. The method according to any one of the preceding claims, characterized in that the precipitation bath from a solution of NMMNO in water with an NMMNO content of 0.5 to 25 wt .-%, in particular 5 to 15 wt .-%, based on the Solution exists. 13. The method according to any one of the preceding claims, characterized in that the extrusion is carried out at a temperature between 80 to 110 ° C, in particular 85 to 95 ° C. 14. The method according to any one of the preceding claims, characterized in that the nonwoven fabric is then washed, pressed and dried. 15. The method according to the preceding claim, characterized in that the washing is carried out by a high pressure water jet. 16. The method according to any one of the preceding claims, characterized in that the cellulose carbamate is regenerated to cellulose in a regeneration bath. 17. The method according to the preceding claim, characterized in that the regeneration bath consists of 0.3 to 1 wt .-% sodium hydroxide in water and the regeneration takes place at a temperature of 60 to 95 ° C. 18. The method according to any one of claims 16 or 17, characterized in that the regeneration is carried out between extrusion and fluidization. 19. The method according to any one of claims 16 or 17, characterized in that the regeneration is carried out after the swirling. 20. Nonwoven fabric made of a random scrim made of cellulose carbamate filaments. 21. Nonwoven fabric according to claim 20, characterized in that the continuous filaments have a strength of at least 60 cN / tex. 22. Nonwoven fabric according to claim 20 or 21, characterized in that the nonwoven fabric can be produced by the method according to one of claims 1 to 15. 23. Nonwoven fabric made of a random scrim made of continuous filaments made of regenerated cellulose. 24. Nonwoven fabric according to claim 23, characterized in that the residual N content is from 0.3 to 0.5%, in particular 0.1 to 0.2%. 25. Nonwoven fabric according to one of claims 23 or 24, characterized in that the nonwoven fabric is a Pore structure with a porosity of 1 to 10%. 26. Nonwoven fabric according to one of claims 23 to 25, characterized in that the nonwoven fabric has a specific inner surface between 20 and 50 m ² / cm ³ , measured by means of X-ray small-angle separation (SAXS). , having. 27. Nonwoven fabric according to one of claims 23 to 26, characterized in that the nonwoven fabric can be produced by the method according to one of claims 16 to 19. 28. Use of the nonwovens according to one of claims 20 to 27 in medicine, in particular as surgical drapes, bed sheets, wound coverings, gauze or cotton pads. 29. Use of the nonwovens according to one of claims 20 to 27 as hygiene materials or as wipes in the household. 30. Use of the nonwovens according to one of claims 20 to 27 as decorative nonwovens, in particular tablecloths, napkins or curtains. 31. Use of the nonwovens according to one of claims 20 to 27 as insert nonwovens in the clothing industry. 32. Use of the nonwovens according to one of claims 20 to 27 as reinforcing nonwovens or insulating mats in the construction industry. 33. Use of the nonwovens according to one of claims 20 to 27 as a reinforcing material for fiber-reinforced thermoplastic and thermoset plastics.