AU648618B2 - A method for producing a cellulose shaped article - Google Patents

Description

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: A METHOD FOR PRODUCING A CELLULOSE SHAPED ARTICLE.

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5 .of a shaped cellulose article, in which a cellulose amine oxide solution is forced through a nozzle or a gap, is then conducted It is known that fibres with good performance characteristics can only be obtained from high polymers, when a "fibre-structure" is achieved (Ullmann, 5th edi ootion Vol 456). To this end, it is inter alia necessary to align in the fibre microoriented regions in the polymer, for instance fibrids. This Sorientation is defined by the production method and is based upon physical or physicochemical processes. In many cases, this orientation is effected by stretching.

Both the prota step in which this stretching occurs and the conditions under which it is carried out determine the fibre characteristics obtained. In melt spinning, the fibres are stretched when in a warm plastic state, while the molecules are still mobile. Dissolved polymers may be dry spun or wet spun. In dry spinning, stretching occurs as the solvent escapes or evaporates; the filaments extruded into a coagulating bath are stretched during the filaments extruded into a coagulating bath are stretched during the 18 coagulation. Methods of this type are known and are amply described. However, in all of these cases, it is important for the transition from the 7iquid state (regardless of whether it is a melt or a solution) to the solid state to occur in such a manner that an orientation of the polymer chains or polymer chain packets (in other words fibrids, fibrils etc.) may also be achieved during the formation of the filaments.

There are several possibilities available for preventing the sudden evaporation of a solvent from a filament during dry spinning.

The problem of extremely rapid coagulation of the polymers during wet spinning (as for instance in the case of cellulose amine oxide solutions) until now could only be resolved by a combination of dry spinning and wet spinning.

It is therefore known to introduce polymer solutions into the coagulant through an air gap. In EP-A-295 672, there is described the production of aramid fibres, which are introduced into a non-coagulating medium through an air gap, are stretched, and are subsequently coagulated.

East German Patent 218 121 is directed to the spinning of cellulose in amine oxides by way of an air gap, arrangements being provided for preventing adhering.

According to US-ipatent 4 501 886, a cellulose triacetate solution is spun by means of an air gap.

In US-Ipatent 3 415 645, the production of aromatic polyamides from solutions in a dry-wet spinning method is also described.

A degree of orientation is achieved in the air gap in all of these methods, because even the mere fact of a viscous sol i..t being allowed to flow downwards out through a small opening causes an orientation to occur, due to gravitational force on'the particles of the solution. This orientation by means of gravitational force can even be increased, if the speed of extrusion of the polymer solution -2- 3 and the rmarching-off velocity of the filament are adjusted so that stretching occurs.

A method of this type is described in Australian patent 387792 (or its equivalents US 4,246,221 and US 4,416,698). A solution of cellulose in NMMO (NMMO N- Methylmorpholine-N-Oxide) and water is formed, is stretched in the air gap and is subsequently precipitated. The stretching takes place at a stretching ratio of at least 3.

A disadvantage of this method is the lack of flexibility in regard to the ability to change the characteristics of the shaped article. A minimum spin to stretch ratio is required in order to obtain corresponding textile properties. Only extremely modest textile fibre characteristics are achievable in the case of very low draw ratio, which means that extremely poor average toughness the product .f fibre tenacity and fibre elongation) is achieved for example in fibre production. A further disadvantage is that the effect of the so-called marchingoff/exit speed resonance (see Navard, Haudin "Spinning of a Cellulose N-Methylmorpholine-lN-Oxide Solution", Polymer Process Engineering 291 (1985)), which leads to irregular fibre diameters, is greater, the greater the spin to stretch ratio. Finally, it is also disadvantageous that formation occurs for all practical purposes only in the air S" 25 gap. Later formation is only possible with extreme difficulty. The bandwidth of possible products is obviously restricted by this. Subsequent influencing of the product characteristics would be desirable, by virtue of which this method would gain considerable flexibility.

30 It is an object of the present invention to overcome these disadvantages.

According to the present invention there is provided a method for producing a cellulose shaped article, in which a solution of cellulose in an amine oxide and 35 water is forced through a nozzle or a gap, is subsequently conducted through an air gap and is finally coagulated in a coagulating bath, characterised in that the ratio of 3A marching-off speed to hole exit velocity is at most 1 and that the shaped article is stretched or deep drawn after coagulation.

According to an embodiment of the invention, the marching-off speed is therefore less than (or at most equal to) the hole exit velocity (spinning speed) of the *S* g

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0 0 spinning mass, so that no stretching can occur. The cellulose thus remains in a relatively unoriented condition until coagulation in the coagulating bath. This is advantageous, because the less the orientation before or at coagulation, the greater the possibility of influencing the characteristics afterwards. Because of the low orientation, the coagulated (precipitated) cellulose has an elasticity, which is almost like rubber. In accordance with the invention, this cellulose may then be stretched or deep drawn in order to obtain the desired characteristics; the flexibility sought is thus assured.

A further advantage exists in that as a result of the stretching no longer being present, the air gap may be made almost as short as wished, so that even if the spinning nozzles have a very high hole density, there is nonetheless no danger of adjacent fibres adhering. As productivity can be considerably increased in large-scale production by raising the hole density, this is also a considerable advantage of the present invention.

The invention is described in more detail with reference to the following examples: Example 1 Production of a fibre with a marching-off speed to hole exit velocity ratio less than 1 (comparative test) A 13% cellulose NMMO solution (cellulose of the Viskokraft type made by ICP, 10% water, 77% NMMO, 0.1% oxalic acid as stabiliser) was forced through a nozzle having 100 holes (hole diameter in each case 130 The rate of ejection was 16.5 g/min; the resulting speed of ejection was thus 10.35 m/min. The 100 filaments were conducted through an 8 mm long air gap and then through a 15 cm long spinning bath (temperature 2 0 C, NMMO concentration at a rate of 6 m/min. The ratio of marching-off speed to exit velocity was thus 0.58.

The resulting fibre had a tenacity of 11.8 cN/tex at an elongation of 77.5%. The value for elongation is extremely high; this proves that the cellulose is present in a relatively unordered 4 state.

Example 2 Stretch of the fibre after coagulation in air The same procedure was employed in this test as in Example 1. In this case however, after the spinning bath, i.e. after coagulation, the fibre was wound onto a godet roll at 6 m/min and the filament bundle was conducted over a second godet roll at a rate of 13 m/min. The stretch thus amounted to 117%. (Stretch of a fibre in percentage terms in the sense of this application means (final length less initial length) divided by initial length, all multiplied by 100). The fibres thereby obtained had atenacity of 22.4 cN/tex at an elongation of 15.3%.

Example 3 Stretch of the fibre after.coagulation in water Here, again as in Example 1, the fibre was conducted through I a spinning bath at 6 m/min (marching-off speed to exit velocity 0.58) and subsequently conducted through an 80 cm long stretching bath with water (temperature 770C). The second godet roll different speeds v. The fibres obtained had the following properties v Stretch Titre Conditioned Conditioned tenacity elongation m/min dtex cN/tex S14 133 32.4 19.7 17.5 21 250 10.3 22.3 9.2 Off** Example 4 Production of a fibre with a marching-off speed to hole exit velocity ratio greater than 1 (comparative test) A 13% cellulose NMMO solution (cellulose of the Visokraft type made by ICP, 10% water, 77% NMMO, 0.1% oxalic acid as stabiliser) was forced through a nozzle having 100 holes (hole diameter in each case 70 pm). The delivery was 5.1 g/min, which corresponds to an exit velocity of 11.1 m/min. Themarching-off velocity of the first godet roll was 33.3 m/min, which means that the ratio of marching-off speed to exit velocity was 3.0. At the speed of the godet roll 1, the filaments were conducted through a spinning bath, the temperature of which was 33 0 C and the NMMO concentration of which was 10%. The subsequent stretching bath had a temperature of 79 0 C and an NMMO concentration of The second godet roll after the stretching bath had a draw-off velocity of 46.9 m/min, which means that the stretching amounted to 41%.

The textile characteristics of the fibre obtained were Titre 3.5 dtex Conditioned tenacity 25 cN/tex Conditioned elongation 8.8% At a ratio of marching-off speed to hole exit velocity greater than 1, the fibres are still capable in principle of being stretched, but not however to the extent recorded for Examples 2 to 4.

Example 5 Manufacture of a foil A 9% cellulose NMMO solution (cellulose of the Buckeye type made by Procter Gamble, 12% water, 79% NMMO, 0.1% oxalic acid as stabiliser) was forced through a slit nozzle (gap 50 pm, length 30 mm). The ejection rate was 21.3 g/min which corresponds to an exit velocity of 11.7 m/min. The extruded solution was then drawn through a 7 mm long air gap and subsequently through a 15 cm long spinning bath (temperature 24°C, NMMO cort.entration 20%) by means of a first godet roll at a rate of 6 m/min. The ratio of V. marching-qff speed to exit velocity was thus 0.51. In the same S operation, the foil was conducted through an 80 cm long stretching bath (temperature 90 0 C; concentration 20%) and was stretched by a second godet roll (speed 11 m/min). The stretch thus amounted to 83%. The characteristics of the washed and d'ied foil were Thickness 10 pm; Strength 200 N/mm 2 Elongation -6- Example 6 Manufacture of a shaped article A foil similar to that of Example 5 was manufactured, but nnt stretched, i.e. the foil was removed after the first godet roll, It was deep drawn 3 mm in an unstretched state with a glass rod, and washed and dried, whereby a dimensionally stable shaped article resulted.

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Claims (2)

1. A method for producing a collulose shaped article, in which a solution cf cellulose in an amine oxide and water is forced through a nozzle or a gap, is subsequently conducted through an air gap and is finally coagulated in a coagulating bath, characterised in that the ratio of marching-off speed~ to hole exit velocity is at most 1 and that the shaped article is stretched or deep drawn after coagulation.

2. A method for producing a cellulose shaped article according to claim 1 substantially as herein described. DATZD THIS 23RD DAY OF FEBRUARY 1994 LENZING ATIENGESELLSCHAFT By Its Patent Att~orneys: GRIFFITH HACK CO., Fellows institute of Patent Attorneys of Australia o *:t 060 *t 0 6 ABSTRACT In order to produce a cellulose shaped article, a cellulose amine oxide solution is forced through a nozzle or through a gap, is subsequently conducted through an air gap and is finally coagulated in a coagulating bath. In accordance with the irvention, stretching does not occur in the air gap, i.e. the ratio of marching-off velocity to hole exit velocity is at most 1; only after coagulation is the cellulose stretched or deep drawn. 01 *s I4 04 .J r a 0 S