Plastic and nonmetallic article shaping or treating: processes – With twining – plying – braiding – or textile fabric formation
Reexamination Certificate
2001-01-24
2004-03-16
Tentoni, Leo D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With twining, plying, braiding, or textile fabric formation
C264S187000, C264S203000, C264S211120, C264S211140, C264S211160
Reexamination Certificate
active
06706224
ABSTRACT:
The invention relates to a process and a device for the production of cellulosic molded bodies, in particular to the production of a spunlaid fabric containing solvent-spun fibres. Moreover, the invention relates to a spunlaid fabric obtainable by the process in accordance with the invention.
BACKGROUND OF THE INVENTION
In the last few decades intensive efforts were undertaken to produce alternative environmentally-friendly processes for the production of cellulosic fibres as a result of the environmental problems associated with the well-known viscose process. One of the most interesting possibilities to emerge in the recent past was to dissolve cellulose in an organic solvent without the formation of a derivative and to extrude moulded bodies from this solution. Fibres spun from solutions of this kind were given the generic name of Lyocell by BISFA (The International Bureau for the Standardization of Man-Made Fibres) whereby an organic solvent means a mixture of an organic chemical and water. Moreover, fibres of this kind are known as “solvent-spun fibres”.
It has turned out that a mixture of a tertiary amine oxide and water is particularly well suited as the organic solvent for the production of Lyocell fibres respectively other moulded bodies N-methyl-morpholine-N-oxide (NMMO) is thereby mainly used as the amine oxide. Other suitable amine oxides are disclosed in EP-A O 553 070. When the expression “NMMO” is used in the following this means all the amine oxides suitable to dissolve the cellulose. The process for the production of cellulosic moulded bodies from solutions of cellulose in NMMO is described as the “amine oxide process”.
Processes for the production of cellulosic molded bodies from a solution of cellulose in a mixture of NMMO and water are for example disclosed in U.S. Pat. No. 4,246,221 or PCT-WO 93/19230. In this respect the cellulose is precipitated from the solution in an aqueous precipitation bath. Fibres manufactured in this way are characterised by a high fibre tenacity in a conditioned and wet state, a high wet modulus and a high loop strength. The term “spunlaid fabrics” relates to fabrics which are made into a fabric by laying freshly spun continuous filaments. Spunlaid fabrics from cellulosic fibres are well known.
For example DE 17 60 431 describes a process in which a tow of continuous filaments freshly spun according to the viscose process with a titre of 0.1 to 10 den is transported on a slide with a 4° to 15° downhill angle and is treated on this slide using rays of water undulating vertical to the running direction. This treatment has as its object that the filaments are opened under the effect of water penetration, i.e. are arranged parallel to each other. The filaments arranged in parallel fashion are led to a screen belt the speed of which is lower than the speed of the continuous filament approaching. This leads to the formation of the spunlaid fabric.
In a talk given at the conference “Cellulosic Man-Made Fibres” in Singapore, April 1997, K. Nishiyama describes a process for the production of a spunlaid fabric according to the so-called “Bemliese” process. In the “Bemliese” process the cellulose is dissolved in a mixture of cupric sulphate and ammonia. The filaments spun from this solution are brought onto a conveyor belt vibrating diagonal to the transport direction by means of which the spunlaid fabric is formed. The formed web is strengthened with jets of water.
One disadvantage of the process described above is that moved parts are needed in each case for the formation of the fabric and/or the opening of the filaments. This means that more is required in terms of apparatus.
With regard to the amine oxide process it is known from WO 97/24476 to lay hydraulically stretched continuous cellulose filaments to a fabric and to bond this.
WO 97/01660 describes amongst other things the production of a mixture of cellulosic fibres and microfibres in accordance with the amine oxide process whereby the fibres manufactured are laid to a web. However, this relates to non continuous fibres.
WO 98/07911 describes a process for the production of Lyocell fibres whereby the freshly spun, partly continuous filaments are amongst other things stretched using an air stream and laid to a web. Stretching using an air stream is, however, complicated.
In these well known processes the formation of the spunlaid fabric takes place the first time that the spun filaments are laid. In cases like this it is difficult to deliberately influence the properties of the spunlaid fabric produced in this way via subsequent treatments.
SUMMARY OF THE INVENTION
The present invention sets itself the task of making a process and a device available for the production of spunlaid fabrics in accordance with the amine oxide process which overcomes the disadvantages of the well know processes for the production of spunlaid fabrics both according to the amine oxide process and according to the viscose or “Bemliese” processes.
This task is resolved by a process characterised in that a solution of cellulose is extruded in an aqueous tertiary amine oxide via a spinneret with orifices and the extruded filaments are stretched in an air gap and led into a precipitation bath, the filaments in the precipitation bath are intercepted by a first conveyor device whereby a curtain of threads of filaments basically oriented parallel to each other and basically of constant thickness is formed on the first conveyor device, the curtain of threads is transported out of the precipitation bath using the first conveyor device onto a second conveyor device inclined downhill and the curtain of threads is transported downwards on the second conveyor device onto a third conveyor device where the third conveyor device draws off the curtain of threads at a speed less than the speed of the curtain of threads transported downwards on the second conveyor device.
With the process in accordance with the invention it becomes possible to produce spunlaid fabrics according to the amine oxide process with a wide spectrum of properties.
In the process in accordance with the invention the solution of cellulose in NMMO is first of all extruded using a spinneret with orifices. In this respect it is important that when laying the spun continuous filaments on a first conveyor device a curtain of threads is formed of basically parallel oriented filaments and basically of constant thickness.
This can for example be achieved in that the filaments are extruded from a spinneret the orifices of which are as the case may be arranged in a staggered form one behind the other in parallel rows and basically form altogether a rectangle. Spinnerets of this kind are for example known from PCT-WO 94/28210. When filaments spun from a spinneret of this kind are placed on a conveyor device a curtain of threads occurs in which the filaments are generally arranged parallel to one another. Moreover, the thickness of this curtain of threads is basically constant across the width of the curtain of threads. This allows for more even spunlaid fabric properties.
For the expert it is easy to find other spinneret constructions in which following extrusion and lying down onto the first conveyor device a curtain of threads is formed with the desired properties.
This curtain of threads is led to a second conveyor device inclined downwards on which the curtain of threads is transported downwards to a third conveyor device. Since the curtain of threads is comprised basically of filaments lying parallel one to the other, an opening of the curtain of threads using moved parts, as is described in DE 17 60 431, is no longer necessary.
The formation of the spunlaid fabric is performed, as it is known from DE 17 60 431, when transferring the curtain of threads from the second to the third conveyor device, since the curtain of threads is led to the third conveyor device at a greater speed than the speed with which the third conveyor device removes the curtain of threads.
In the process in accordance with the invention the formation of the spunlaid fabric does not t
Firgo Heinrich
Kraft Rudolf
Rüf Harmut
Schlossnikl Christian
Baker & Botts LLP
Lenzing Aktiengesellschaft
Tentoni Leo D.
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