NO303738B1 - Process for preparing cellulosic moldings - Google Patents

Description

The present invention relates to a method of the kind stated in the preamble of claim 1 for the production of a cellulose-containing molded body, where a cellulose-containing amino acid solution is pressed through a nozzle, then passed through an air gap, possibly stretched in this and finally coagulated in a precipitation bath .

It is known that fibers of high polymers with good application properties can only be obtained when a "fiber structure" can be obtained (Ullmann, 5th edition Vol. A10, 456). Among other things, it is necessary to correct micro-oriented areas in the polymer, e.g. fibrids, in the fibers. This orientation is determined by the manufacturing process and depends on physical or physiochemical processes. In many cases, this orientation is achieved by stretching.

Decisive for the fiber properties achieved is in which method step and under which conditions this stretching takes place. In melt spinning, the fibers are stretched in a hot plastic state, while the molecules are still mobile. Dissolved polymers can be spun dry or wet. During dry spinning, the stretching takes place, while the solvent escapes or evaporator; the threads extruded in a precipitation bath are stretched during coagulation. Methods of this kind are known and amply described. In all these cases, however, it is important that the transition from the liquid state (regardless of melt or solution) to the solid state takes place so that during thread formation an orientation of the polymer chains or chain packs (i.e. fibrids, fibrils) can also be achieved etc.).

In order to prevent a sudden evaporation of a solvent from a thread during dry spinning, there are several possibilities.

However, the problem of the very rapid coagulation of the polymer during wet spinning (such as, for example, in the case of cellulose-containing amine oxide solutions) could thus far only be solved by a combination of dry and wet spinning.

Thus, it is known to introduce solutions via an air gap in the coagulation medium. EP-A-295 672 describes the production of aramid fibers which are introduced via an air gap into a non-coagulating medium, stretched and then coagulated.

DD-PS 218 121 describes the spinning of cellulose in amide oxides via an air gap, as measures have been taken to prevent sticking together.

According to US-PS 4,501,886, a solution of cellulose triacetate is to be spun using an air gap.

US-PS 3 414 645 also describes the production of aromatic polyamides from solutions in a dry-wet spinning process.

With all of these methods, a certain orientation is achieved in the air gap, as the discharge of a viscous liquid solution downwards through a small opening forces the solution particles into an orientation due to the force of gravity. This orientation through gravity can be increased even more, when the extrusion speed of the polymer solution and the withdrawal speed of the thread are adjusted so that a stretch is achieved.

A method of this kind is described in AT-PS 387 792 (respectively in the corresponding US-PS 4 246 221 and 4 416 698). A solution of cellulose in NMMO (NMMO = N-methylmorpholine-N-oxide) and water is formed, stretched in the air gap and then precipitated. The stretching is carried out at a stretching ratio of at least 3.

A disadvantage of this method consists in a lack of flexibility, which can change the properties of the shaped body. In order to obtain corresponding textile data, a minimal spinning-stretching ratio is necessary. With very little extraction, only extremely modest textile fiber properties are achieved, i.e. that with e.g. fiber production produces an extremely small breaking capacity (it is the product of fiber strength and fiber elongation). A further disadvantage is that the effect of the so-called withdrawal/exit velocity resonance (cf. Navard, Haudin, "Spinning of a Cellulose N-Methylmorpholine-N-oxide solution", Polymer Process Engineering, 3(3), 291 (1985)) which leads to the irregular fiber diameters, is so much greater the greater the spin-stretch ratio. Finally, it is a disadvantage that the shaping can practically only take place in the air gap. A subsequent design is very difficult. Thus, the bandwidth of the possible products is naturally limited. The desire is a subsequent influence on the product properties, whereby this method gains significant flexibility.

The task of the present invention consists in removing these disadvantages.

This task is solved according to the invention, as stated in the claim, in that the ratio between withdrawal speed and hole exit speed is at most 1, and that the shaped body is stretched or deep drawn after coagulation.

According to the invention, the withdrawal speed is therefore less (or at most equal to) the hole exit speed in the spinning mass, so that no stretching can occur; thus, until coagulation in the precipitation bath, the cellulose remains in a relatively unoriented state. This is favorable because the less the orientation before or during the coagulation, the greater the possibility of an influence on the properties thereafter. Due to low orientation, the coagulated (precipitated) cellulose has an elasticity that is almost similar to rubber. According to the invention, this cellulose can now be stretched or deep drawn to obtain the desired properties; the desired flexibility is thus ensured.

A further advantage is that the air gap can be made almost as short as desired, because there is no longer any stretching, so that there is no danger of neighboring threads sticking together, even if the spin-down nozzles have a high hole density. Because productivity in large-scale production can be increased considerably by increasing the hole density, this also constitutes a significant advantage of the present invention.

The invention shall be explained in more detail by means of the following examples.

EXAMPLE 1: Fabrication of fibers at a ratio between pull-off speed and hole exit speed of less than 1 (comparison test).

A 13% cellulose-containing NMMO solution (cellulose of type Viskokraft from the company ICP, 10% water, 77% NMMO, 0.1% oxalic acid as stabilizer) was pressed through a nozzle with 100 holes (hole diameter 130 µm). Ejection was 16.5 g/min; the resulting ejection velocity was 10.35 m/min. The 100 threads were passed through an 8 mm long air gap and then at a speed of 6 m/min through a 15 cm long spinning bath (temperature: 2°C, NMMO concentration: 5%). The ratio between extraction and output speed was thus 0.58.

The resulting fibers had a tenacity of 11.8 cN/tex at an elongation of 77.5%. The value of the extension is extremely high; this proves that the cellulose exists in a relatively disordered state.

EXAMPLE 2: Stretching of the fibers after coagulation in air.

In this experiment, the procedure was the same as in example 1. In this case, however, after the spin bath, i.e. after coagulation, the fibers were wound on a galette at 6 m/min, and the thread bundle was passed over a second galette at a speed at 13 m/min. The stretch thus amounted to 117%.

(With stretching of a fiber in % is meant within the scope of the present application (final length-beginning length) - /beginningIeslengde . 100). The resulting fibers had a tenacity of 22.4 cN/tex at an elongation of 15.3

EXAMPLE 3: Stretching of fibers after coagulation in water.

Here, the fibers were again, as in example 1, passed through a spinning bath at 6 m/min (withdrawal/exit speed: 0.58), and then passed through an 80 cm long stretching bath with water (temperature: 77°C) . The second galette was driven at different speeds v. The fibers obtained had the following properties:

EXAMPLE 4: Production of fibers at a ratio between withdrawal speed and hole exit speed greater than 1 (comparison test).

A 13% cellulose-containing NMMO solution (Visokraft type cellulose from the company ICP, 10% water, 77% NMMO, 0.1% oxalic acid as stabilizer) was pressed through a die with 100 holes (hole diameter 70 ptm). The transport amount was 5.1 g/min, this corresponds to an output speed of 11.1 m/min. The extraction speed of the first galette was 33.3 m/min, i.e. the ratio between extraction and output speed was 3.0. At the speed of galette 1, the threads were passed through a spinning bath whose temperature was 33 °C and NMMO concentration 10%. The subsequent stretching bath had a temperature of 79°C and an NMMO concentration of 9%. The second galette had, after the stretching bath, a withdrawal speed of 46.9 m/min, i.e. the stretching was 41%.

The fibers obtained had the following textile properties: Titer: 3.5 dtex

Strength conditioned: 25 cN/tex

Elongation conditioned: 8.8%

At a ratio between withdrawal speed and hole exit speed of greater than 1, the fibers are in principle also still stretchable, but not as much as documented in examples 2 to 4.

EXAMPLE 5: Production of a foil.

A 9% cellulose-containing NMMO solution (Buckeye V5 cellulose from the company Procter&Gamble, 12% water, 79% NMMO, 0.1% oxalic acid as a stabilizer) was pressed through a slit nozzle (gap: 50/im; length: 30 etc.). The ejection was 21.3 g/min, which corresponds to an output speed of

11.7 m/min. The extruded solution was drawn off by means of a first galette at a speed of 6 m/min. The ratio between extraction speed and output speed was thus 0.51. During the same work process, the foil was passed through an 80 cm long stretching bath (temperature: 90°C; concentration: 20%), and stretched with a second galette (speed: 11 m/min). This stretch thus accounted for 83%. The properties of the washed and dried film were: thickness: 10 µm; strength: 200 N/mm<2>; elongation: 6.5%.

EXAMPLE 6: Production of a molded body.

A foil was produced as in example 5, but without being stretched, i.e. the foil was taken out after the first galette. In the unstretched state, it was deep-drawn 3 mm with a glass rod, washed and dried, whereby a stable molded body was formed.

Claims (1)

Process for the production of a cellulose-containing shaped body, in which a cellulose-containing amine oxide solution is pressed through a nozzle or a slot, then passed through an air gap and finally coagulated in a precipitation bath, characterized in that the ratio between draw-off speed and hole exit speed is at most 1 and that the shaped body coagulation is stretched or deeply drawn.