CN1180142C - Process for producing cellulose fibers - Google Patents

Abstract

The present invention relates to a process for producing cellulose fibres. According to said method, a solution of cellulose in a tertiary amine oxide is extruded through the spinning orifices of a spinning nozzle, the extruded strand is introduced into a coagulation bath under traction through an air gap, and the strand is exposed to a gas stream in the air gap. The invention is characterized in that the temperature of the gas before contact with the filament bundle is such that T is greater than 60 ℃ and less than 90 ℃.

Description

Production method of cellulose fiber

The invention relates to a method as outlined in claim 1 .

This method of producing cellulose fibers is called "amine oxide method" or "Lyocell method".

"Lyocell" is a designation granted by BISFA (International Man-made Fiber Standards Bureau) to a class of cellulose fibers produced by dissolving cellulose in an organic solvent without generating derivatives, and extruding fibers from the solution. Genus name. The so-called "organic solvent" should be understood to include the mixture of organic compounds and water. Such fibers are also called "solvent spun fibers". As an organic solvent, N-methylmorpholine-N-oxide is currently used on an industrial scale.

It is known that the properties of Lyocell fibers and the stability of the spinning process are largely influenced by the conditions in the so-called air gap between the spinneret and the level of the coagulation bath.

For example, from PCT-WO 93/19230 is known a method for cooling the extruded tow with an air stream immediately after forming. In the following, this air flow is referred to as "cooling air". In the embodiment of PCT-WO 93/19230, the temperature of cooling air is -6 ℃～24 ℃.

PCT-WO 94/28218 describes a method similar to that in PCT-WO 93/19230. According to this document, the temperature of the cooling air is kept below 50°C.

Know a kind of method from PCT-WO 95/02082, according to this method, spinneret hole diameter, per hole spinning quality output, monofilament fineness, air gap width and the humidity of the air in the air gap, according to a certain mathematical expression should be kept within a certain range. In the examples of PCT-WO 95/02082 no information is given on the temperature of the cooling air. In the descriptive part it is only indicated generally that the temperature is between 10°C and 60°C, preferably between 20°C and 40°C.

PCT-WO 96/17118 deals with the moisture content of cooling air. The maximum cooling air temperature given in this document is about 40°C.

According to PCT-WO 96/21758, the temperature of the cooling air can be between 0°C and 40°C. In PCT-WO 97/38153, the temperature of the cooling air is said to be -10°C to 50°C.

PCT-WO 98/58103 describes that in the case of a large number of extruded filaments, i.e. when using a spinneret with a large number of spinneret holes, a very humid atmosphere will be created in the air gap. To ensure that the spinning process remains stable also under such conditions, PCT-WO 98/58103 proposes that the spinning solution should contain a specific proportion of cellulose and/or another cellulose with a higher molecular weight immediately before spinning. polymer.

One problem with spinning cellulose solutions in NMMO is that the spinning solutions have to be spun at elevated temperatures in case the solutions have a high viscosity. A high viscosity of the spinning solution occurs, for example, when the concentration of cellulose in the solution is high, which is of course desirable from an economic point of view. High viscosity also occurs when the pulp used has a high proportion of high molecular weight cellulose.

However, the temperature of the spinning solution must also be maintained at a high level when spinning fibers with small deniers, eg less than 1 dtex. In the case of such fibers, the tow in the air gap must be drafted to a particularly high degree. Without increasing the temperature of the spinning solution, the viscosity of the spinning solution at this time would also be too high to achieve such a draw.

Generally speaking, during spinning, the temperature of the spinning solution should be between 80°C and 120°C, especially between 100°C and 120°C. However, increasing the temperature of the cellulose solution is not desirable since solutions of cellulose in NMMO are thermally unstable and tend to undergo exothermic decomposition reactions.

It is also an object of the present invention to provide a method belonging to this generic name, by which highly viscous cellulose solutions can be spun better and fibers of finer denier can be produced better.

This object is achieved in that the temperature (T) of the cooling air before contact with the tow is 60°C<T<90°C.

Surprisingly, it has been found that when using higher temperature cooling air in the range of claim 1, higher viscosity cellulose solutions can also be spun very well, without necessarily raising the spinning solution. temperature. Small denier fibers such as 0.9 dtex can also be spun well without raising the temperature of the spinning solution.

In addition, fibers produced with higher temperature cooling air had higher strength values than fibers produced with lower temperature cooling air at the same spinning solution temperature.

Preferably, the moisture content of the cooling air is between 4g water/kg air and 15g water/kg air.

In particular, the method according to the invention is suitable for producing fibers having a denier of less than 1 dtex.

Example 1:

A spinning solution having 15 wt% cellulose (pulp: Cellunier F, manufacturer: Rayonnier), 10 wt% water, and 75 wt% NMMO was spun into fibers using cooling air with different temperatures.

Determination of the minimum fiber titer that can be produced in each case: For this purpose, the maximum draw-off speed (m/min) of the fibers is determined by increasing the draw-off speed until the fiber breaks. Record this speed and use it to calculate titer according to the calculation method described in PCT-WO 98/58103.

Furthermore, the strength of the spun fibers under the condition of temperature regulation and humidity regulation are respectively determined. Spinning solution temperature (°C) Cooling air temperature (℃) Minimum fineness (dtex) State intensity of temperature and humidity adjustment (cN/dtex) 100 20 2.01 38.1 100 50 1.70 38.7 100 60 1.59 40.1 100 70 1.36 39.8 100 80 1.32 40.6

From the table it is clear that at cooling air temperatures above 60°C the minimum achievable titer decreases considerably. Furthermore, the fiber strength is significantly improved.

Example 2:

A spinning solution with 14.6 wt% cellulose (pulp: Borregaard LVU), 9.5 wt% water and 75.9 wt% NMMO was spun into fibers with a denier of 1.3 dtex in a continuous experimental setup. Using different cooling air temperatures, determine what temperature of the spinning mass is required to produce fibers of this denier without interfering with the production process. Cooling air temperature (℃) Required spinning material temperature (°C) twenty two 116 65 109

It is clear from the table that it is possible to produce fibers at much lower spinning solution temperatures when cooling air at a temperature of 65°C is used.

Example 3:

A spinning solution having 15 wt% cellulose (pulp: Alicell VLV, manufacturer: Western Pulp), 10 wt% water and 75 wt% NMMO was spun into fibers using cooling air with different temperatures. As described in Example 1, determine the minimum obtainable fiber denier and the strength of the spun fiber under the condition of temperature and humidity adjustment:

Spinning solution temperature (°C) Cooling air temperature (℃) Minimum fineness (dtex) Strength of temperature and humidity control state (cN/dtex) 100 20 1.34 37.4 100 50 1.05 39.2 100 70 0.98 40.4 100 80 0.92 39.1

It is clear from the table that when higher temperature cooling air is used, it is possible to produce fibers having a denier of less than 1 dtex well.

Claims (4)

1. A method for producing cellulose fibers, comprising: the solution of cellulose in the tertiary amine oxide is extruded through the spinneret holes of the spinneret, and the extruded filament bundle is introduced into the coagulation bath through the air gap under traction In the method, the tow is exposed to a stream of air in the air gap, and it is characterized in that the temperature T of the gas before contacting the tow satisfies 60°C<T<90°C. 2. The method of claim 1, wherein the gas is air. 3. The method of claim 2, characterized in that the moisture content of the flowing air is between 4 g water/kg air and 15 g water/kg air. 4. A method as claimed in any one of claims 1 to 3, characterized in that yarns having a titer of less than 1 dtex are produced.