EP1896635B1 - Method for the production of nonwoven fabrics - Google Patents

Abstract

The method involves pressing a dope at increased temperature by a nozzle block, where fabrics leaving the block are inflow with temperature airflow having specified temperature. Filaments are coagulated by spraying water and fabrics are deposited on a transport device. Solvent is removed by washing, where a solution of cellulose carbamate in n-methyl-morpholine-n-oxide is used as the dope. An independent claim is also included for a non-woven fabric.

Description

The invention relates to a process for producing nonwovens, in which a solution of cellulose carbamate in N-methylmorpholine-N-oxide is forced through the holes of a nozzle beam and is stretched many times by an air flow. The formed fiber curtain is placed on a perforated conveyor belt, washed and dried.

Nonwovens are textile fabrics in which the surface formation does not take place by weaving or knitting, but by entanglement of the fibers with subsequent fixation. Nonwovens still have high annual growth rates due to their versatility and comparatively low production costs compared to knitted and woven fabrics.

The advantages of these nonwoven materials are a high moisture absorption, the manufacturing processes allow a high variability in density and thickness and lead to a broad surface isotropy. From these advantageous properties, numerous uses in medicine for hygiene products, e.g. Surgical drapes, sheets, gauze, etc., household wipes and decorative non-wovens, e.g. Tablecloths, napkins, in the garment industry as interlining nonwovens as well as for technical applications, e.g. Insulating mats, cover mats.

In principle, web formation is possible from short fibers, staple fibers or continuous filaments. The pile formation for cut fibers is carried out by the dry or wet nonwoven method. In the former, the staple fibers delivered in bale form are combed by means of carding or carding to fleece and stored on a tape. In the wet-laid process, the pile formation takes place by applying a suspension of fiber and water to a perforated screen belt with subsequent squeezing of the water. The webs formed can then be further consolidated by needling, thermal and / or chemical treatment or by means of water jet.

In the production of spunbonded nonwovens, the direct linking of the spinning and web forming process takes place. Both melt and dry spinning processes and wet spinning processes are suitable for nonwoven on the basis of continuous fibers. As the starting material for the nonwoven fabrics, a variety of fiber-forming polymers are known. Nonwovens of continuous materials are preferably made of polyester and polypropylene (meltblown - meltblown nonwovens) and polyacrylonitrile (Wet spiders - spunlaid nonwovens).

Viscose fibers, i. Celluloseregeneratfasern, are preferably used as short or staple fibers for Nonwovenher-position. Nonwovens based on cellulose regenerated fiber have a significant market share due to their potential properties with expected continuous growth.

Since the viscose process, which still produces most of the regenerated cellulose fibers, is associated with significant environmental stresses, e.g. Carbon disulfide, hydrogen sulfide, heavy metals, and high investment costs, efforts have been made for years to replace the viscose process by alternative methods. Methods based on the direct dissolution of pulp in a suitable solvent or alternative derivatization variants without carbon disulfide have been developed. These activities also cover the production of nonwovens from cellulose.

The so-called "Bemliese" process, in which cotton inters is deformed into nonwoven by the cuproammonium process, is one of the first proposed spunbonding processes for the production of cellulosic nonwovens from continuous filaments (US Pat. US 3,833,438 ).

Deformation of melts of synthetic polymers by extrusion of the melt through fine nozzle holes into a fiber-flow gas stream through which the fiber is cooled and drawn and drawn to a multiple of its length is a well-known nonwoven production method. This process, also known as meltblown, is suitable for the production of microfibers. In the European patent specification EP 0 920 548 B1 the use of meltblowing is also claimed for solutions of cellulose in amine oxides, preferably N-methylmorpholine-N-oxide (NMMO). The process is strongly influenced by the viscosity of the cellulose / NMMO solution, which in turn is determined by the polymer (cellulose), the molecular weight (DP of the cellulose) and the concentration.

Another known, environmentally friendly process for the production of cellulosic fibers and moldings is based on the precipitation of cellulose carbamate from a solution of this cellulose derivative in sodium hydroxide ( EP 57 105 . EP 178 292 ). Cellulose carbamate is formed in the reaction of cellulose with urea at elevated temperature and can be dissolved in cold dilute sodium hydroxide solution.

The WO 88/05090 relates to a nonwoven fabric whose fibers are capable of bonding to other fibers, the fibers being formed of cellulose carbamate.

From the WO 2005/080661 is a process for the production of nonwovens is known in which a lyotropic solution of cellulose carbamate in N-methylmorpholine-N-oxide (NMMNO) is spun by extrusion through a multi-orifice-containing nozzle bar via an air gap in a precipitation bath to form several endless filaments, which be swirled by flowing with gaseous medium and / or fluid. Likewise, the concerns WO 2005/080661 Such nonwovens and their use.

A disadvantage for the productivity of all cellulose wet-spinning processes, in particular also the NMMO and the carbamate process, is the low solids concentration of the cellulose in the spinning solution, which is generally 8 to 12%.

Based on this, it was an object of the present invention to provide a process for the production of nonwovens from cellulose carbamate, which meets the requirements for low investment and production costs and low environmental impact with good product properties.

This object is achieved by the method having the features of claim 1. The other dependent claims show advantageous developments.

According to the invention, this object is achieved by a melt-blowing process in which a spinning solution is pressed at elevated temperature through a nozzle block, the fibers emerging from the nozzle holes are drawn through a tempered air stream and thereby stretched and cooled and coagulated by spraying with water. Subsequently, the fibers are deposited on a transport device to form a random fabric, wherein the individual fibers are self-binding. The solvent is then removed by washing.

A special feature of the process is that a solution of cellulose carbamate in N-methylmorpholine-N-oxide is used as the spinning solution.

Solutions of cellulose carbamate in NMMO can be deformed comparable to corresponding cellulose solutions become. The advantages of the cellulose carbamate compared to the cellulose are improved solubility in NMMO, so that it is possible to work at higher concentrations. This results in higher throughput and lower solvent recovery costs.

Surprisingly, it has now been found that from solutions of cellulose carbamate in NMMO after the meltblown process nonwovens can be produced with higher strength and higher water absorption compared to cellulose, which make these nonwovens particularly suitable for use in sanitary articles for medicine, for household articles but also as decorative nonwovens.

The nozzle block used preferably has at least 20, preferably 150 to 1500 and particularly preferably 500 to 1000 nozzle holes per meter of nozzle width. With regard to the diameter of the nozzle holes, diameters of 0.05 to 1 mm and especially of 0.3 to 0.5 mm are preferred.

The spinning solution temperature in the extrusion is preferably in the range between 80 and 130 ° C, particularly preferably in the range of 90 to 110 ° C. In this case, the spinning solution delivery rate is between 0.25 to 2.5, more preferably 0.75 to 1.5 g per nozzle hole and minute.

The air stream used for the removal of the fibers from the nozzle is preferably heated to 100 to 190 ° C, particularly preferably an air temperature of 120 to 160 ° C is set in the nozzle interior. The pressure generated by the air flow inside the nozzle is preferably from 3 to 150 MPa (0.03 to 1.5 bar), especially preferably between 15 and 80 MPa (0.15 and 0.8 bar).

The nozzle exit velocity is preferably 1 to 20 m / min, but more preferably 3 to 10 m / min. Due to the adjacent stream of hot air, the extruded filaments are preferably drawn to 50 to 800 times their length after the nozzle exit, resulting in spinning speeds of up to 10,000 m / min.

Single fiber diameter significantly smaller than 10 μm and single fiber titer smaller than 1 dtex can be achieved by the appropriate adjustment of the stretching conditions.

At least 10 cm below the nozzle, the fibrous web which forms is sprayed with water or with a NMMO / water mixture having an NMMO content of preferably at most 20%, preferably 5 to 15%, and thus coagulated.

The batt is laid down on a perforated belt at high speed, which causes the fiber to become entangled and forms a batt having such good mechanical properties that subsequent operations such as washing with a high pressure water jet, squeezing and drying can be performed without additional solidification of the web.

In a preferred embodiment of the process, the spinning solution contains from 5 to 20% by weight of cellulose carbamate. A further preferred variant provides that the spinning solution contains 20 to 30 wt .-% cellulose carbamate. In the latter case, this gives a solution of cellulose carbamate in NMMO, which surprisingly has a lyotropic behavior, ie the cellulose carbamate is in a liquid crystalline state. This results in the particularly advantageous application that the molecules are aligned almost perfectly in the fiber direction during spinning due to the shear in the nozzle channel, whereby the fibers have an extremely high orientation and thus a very high strength.

By the method according to the invention, a cellulose carbamate nonwoven fabric can thus be provided from a random knitted fabric or from a finite length of fibers resulting from the breakage of single capillaries.

The nonwoven fabrics produced by the claimed process preferably have basis weights between 20 and 500 g / m ² preferably have a water retention capacity of at least 180% and after conditioning longitudinal strengths of at least 350 N / m and in the transverse direction of at least 120 N / m at a Basis weight of 33 g / m ² .

The nonwoven fabrics according to the invention are preferably used in medicine, in particular as surgical drapes, bed sheets, wound coverings, gauze or cotton wool pads. Likewise, the nonwovens are also used as hygiene substances or as wipes in the home. Another field of application of the nonwovens according to the invention are decorative nonwovens, in particular tablecloths, napkins or curtains, as well as interlayer nonwovens in the clothing industry.

If the cellulose carbamate is used in an amount that allows a lyotropic solution as described above, it is also possible to use the nonwoven fabrics according to the invention as a reinforcing material.

The subject according to the invention is intended to be explained in more detail with reference to the following examples without restricting it to the embodiments described herein.

example 1

180 g of cellulose carbamate (DP-Cuen 453) are mixed in a kneader with 2430 g of a 50% aqueous NMMO solution, this solution is concentrated by distilling off water at a vacuum of 8 MPa (80 mbar) to the NMMO monohydrate and the Cellulose carbamate dissolved. The formed spinning solution has a cellulose carbamate content of 12%. The spinning solution at a temperature of 90 ° C is filtered through a 50 micron filter and pressed by spin pump through a 15 cm wide nozzle with 60 nozzle holes diameter 0.48 mm with a flow rate of 0.9 g / hole / min. The fibers emerging from the nozzle holes at a speed of 4 m / min are drawn by passing air heated to 125 ° C to 459 times their length, with a mixture of 7.5% NMMO / 92.5% water about 20 cm below sprayed the nozzle and deposited on a conveyor belt at a speed of 1 m / min, the formed web is washed with a sharp jet of water, squeezed off and dried under tension with the admission of a shrinkage of 12%.

• Flächengewicht: 36 g/m²
• Festigkeit längs (konditioniert): 356 N/m
• Festigkeit quer (konditioniert): 120 N/m
• Wasserrückhaltevermögen (DIN 53814): 192%

Fleece parameters:

• Basis weight: 36 g / m ²
• Strength along (conditioned): 356 N / m
• Strength transverse (conditioned): 120 N / m
• Water retention capacity (DIN 53814): 192%

Example 2 (comparative example)

150 g of PHK pulp (DP-Cuen 840) are mixed in a kneader with 1945 g of a 50% aqueous NMMO solution, this solution by distilling off water at a vacuum of 8 MPa (80 mbar) to the NMMO mono- hydrate concentrated while the pulp dissolved. The spinning solution formed has a cellulose content of 8%. The spinning solution at a temperature of 90 ° C is filtered through a 50 micron filter and pressed by spin pump through a 15 cm wide nozzle with 60 nozzle holes diameter 0.48 mm with a flow rate of 0.9 g / hole / min. The fibers emerging from the nozzle holes at a speed of 4 m / min are drawn by passing air heated to 125 ° C to 459 times their length, with a mixture of 7.5% NMMO / 92.5% water about 20 cm below the nozzle sprayed and deposited on a conveyor belt at a speed of 1 m / min. The formed web is washed with a sharp jet of water, squeezed off and dried under tension with the admission of a shrinkage of 12%.

• Flächengewicht: 37 g/m²
• Festigkeit längs (konditioniert): 133 N/m
• Festigkeit quer (konditioniert): 45 N/m
• Wasserrückhaltevermögen (DIN 53814): 145 %

The formed nonwoven made of regenerated cellulose had the following parameters:

• Basis weight: 37 g / m ²
• Strength along (conditioned): 133 N / m
• Strength transverse (conditioned): 45 N / m
• Water retention capacity (DIN 53814): 145%

Claims (19)

1. A process for the production of nonwoven fabrics by the melt blowing process, in which

   - a spinning solution is forced through a die block at elevated temperature,

   - the fibres emerging from the die block are subjected to a flow of temperature-controlled airflow, resulting in stretching of the fibres with subsequent cooling,

   - the threads are coagulated by spraying with water,

   - the fibres are laid on a conveying device, forming a random network, and

   - the solvent is removed by washing,
   characterised in that
   a solution of cellulose carbamate in N-methylmorpholine-N-oxide is used as spinning solution.
2. The process according to claim 1,
   characterised in that the die block has at least 20, in particular from 150 to 1500, die holes per metre.
3. The process according to one of the preceding claims,
   characterised in that the diameter of the die holes is from 0.05 to 1 mm.
4. The process according to one of the preceding claims,
   characterised in that the spinning solution temperature in the die is 80 to 130°C.
5. The process according to one of the preceding claims,
   characterised in that the spinning solution flow rate is from 0.25 to 1.5 g per die hole per minute.
6. The process according to one of the preceding claims,
   characterised in that the airflow has a temperature of 100 to 190°C.
7. The process according to one of the preceding claims,
   characterised in that a pressure of 3 to 150 MPa (0.03 to 1.5 bar) is established by the airflow in the die.
8. The process according to one of the preceding claims,
   characterised in that the die exit speed of the fibres is from 1 to 20 m/min.
9. The process according to one of the preceding claims,
   characterised in that the threads are stretched by a factor of 50 to 800 by the airflow.
10. The process according to one of the preceding claims,
    characterised in that the spinning speed is in the range of 150 to 10000 m/min.
11. The process according to one of the preceding claims,
    characterised in that the fibres have a diameter of no more than 20 µm.
12. The process according to one of the preceding claims,
    characterised in that the fibres have a fineness of no more than 2.5 dtex.
13. The process according to one of the preceding claims,
    characterised in that the fibres are sprayed at least 10 cm below the die with water or with a mixture of N-methylmorpholine-N-oxide and water.
14. The process according to one of the preceding claims,
    characterised in that the mixture contains from 0.5 to 20 wt.% of N-methylmorpholine-N-oxide.
15. The process according to one of the preceding claims,
    characterised in that the fibres are laid on a perforated conveyer belt.
16. The process according to one of the preceding claims,
    characterised in that the washing is carried out by a water jet at high pressure.
17. The process according to one of the preceding claims,
    characterised in that the nonwoven fabric is squeezed out and/or dried after washing.
18. The process according to one of the preceding claims,
    characterised in that the spinning solution contains from 5 to 20 wt.% of cellulose carbamate.
19. The process according to one of the preceding claims,
    characterised in that the spinning solution contains 20 to 30 wt.% of cellulose carbamate.