GB2156270A

GB2156270A - Producing cellulose diacetate fiber

Info

Publication number: GB2156270A
Application number: GB08506240A
Authority: GB
Inventors: Toshihiro Koshida
Original assignee: Mitsubishi Acetate Co Ltd; Mitsubishi Rayon Co Ltd
Current assignee: Mitsubishi Acetate Co Ltd; Mitsubishi Rayon Co Ltd
Priority date: 1984-03-12
Filing date: 1985-03-11
Publication date: 1985-10-09
Also published as: GB8506240D0; JPS60194108A; GB2156270B

Abstract

A process for producing cellulose diacetate fibers superior in yarn tenacity, which comprises preparing a spinning solution by dissolving cellulose diacetate in a mixture of methylene chloride and methanol to give a viscosity of 2200 to 4000 poises as measured at 25 DEG C by the ball fall method, and subjecting the spinning solution to dry spinning.

Description

SPECIFICATION Process for producing diacetate fiber Technical field The present invention relates to a process for producing cellulose diacetate fibers (hereinafter referred to as diacetate fibers) improved in physical properties as fibers.

Prior art Acetate fibers are generally used for linings of clothes, bedclothes, etc. However, the use of acetate fibers is restricted because they are inferior in physical properties, specially in tenacity, to synthetic fibers such as those of polyester and nylon. Accordingly, expanded use of acetate fibers for thin linings and for other materials can be expected if acetate fibers improved in fiber tenacity can be produced. But no proc ess has yet been found out for producing such acetate fibers.

A dry spinning process for acetate fibers by use of a methylene chloride-methanol solvent mixture was disclosed by the present inventors in Japanese Patent Application Laid-Open No. 163,716/83. This proc ess, though permitting efficient production of acetate fibers at low costs, has not led to the improvement thereof in physical properties, particularly in fiber tenacity.

Object of the invention In view of the above, the present inventors made intensive studies aiming at producing acetate fibers improved in fiber tenacity. As a result, it has been found that the tenacity of diacetate fibers produced by dry spinning increases with a rise in the viscosity of the spinning solution, i.e. a solution of cellulose diacetate polymer in an organic solvent. Further it has been revealed that diacetate fibers having spe cially high tenacity can be produced when the organic solvent in the spinning feed solution is a mixture of methylene chloride and methanol. Based on the finding, this invention has been accomplished.

Constitution of the invention Thus, the substance of the invention is a process for producing dicetate fibers which comprises prepar ing a spinning solution by dissolving cellulose diacetate in a mixture of methylene chloride and methanol to give a viscosity of 2200 to 4000 poises, as measured at 25"C by the ball fall method, and subjecting the spinning solution to dry spinning.

The viscosity of spinning solutions measured at 25"C by the ball fall method (hereinafter this viscosity is simply referred to as "spinning solution viscosity has great effects on physical properties of the result ing diacetate fibers. As the spinning solution viscosity is raised, the tenacity of the resulting diacetate fibers becomes higher. Whereas the tensile strength of ordinary diacetate fibers commercially available is about 1.3 glad, diacetate fibers having tensile strength as high as 1.5 g/D or more can be produced by dry spinning from a spinning solution having viscosity of 2200 poises or more. However, it is difficult to pro duce such high tenacity diacetate fibers from a spinning solution having a viscosity of less than 2200 poises.The spinning solutions of high viscosity are prepared chiefly by the method (1) of using a specific organic solvent for solving cellulose diacetate, (2) regulating the concentration of cellulose diacetate therein, or (3) using cellulose diacetate of high molecular weight. Any one of these methods or combination of two or all of these methods may be applied. The spinning solution viscosity is desired to be up to 4000 poises because exceeding 4000 poises results in high probability of filment break during spinning.

Preferably the spinning solution viscosity is from 2500 to 3500 poises from the view point of fiber strength and the probability of filament break.

Typical organic solvent suitable for the spinning solution in the present invention is a mixture of methylene chloride and methanol. For the purpose of raising the spinning solution viscosity, it is recom mended to incorporate methylene chloride in a larger proportion than that of methanol.

The solvent mixtures used in the invention are advantageous in giving high tenacity diacetate fibers over the common solvent of acetone-water mixtures used for diacetate fiber commonly.

It is desirable in carrying out the invention that the spinning solution is heated at a temperature of 55" to 70"C and then extruded through spinneret. According to the present inventors' investigation, the tem perature of the spinning solution has a significant effects on physical properties of the resulting diacetate fibers. The higher temperature tends to give fibers having higher elongation and lower tensile strength.

For the purpose of producing diacetate fibers improved in tenacity, that is, to achieve an object of the invention, the temperature of the spinning solution keeps desirably at up to 70"C, and when the temperature is below 55 C, the elongation of the fibers tends to be markedly low, so that the suitable temperatures of the spinning solution ranges from 55" to 700C.

In carrying out the invention, it is desirable that the draw down ratio (VT/VE), i.e. the ratio between the linear speed (VT) of taking up the extruded filaments and the linear speed (VE) of extruding the spinning solution through the spinneret ranges from 0.75 to 0.90. According to the present inventors' investigation, the draw down ratio (VTNE) of lower than 0.75 makes the production of high tenacity diacetate fibers difficult and since the draw down ratio exceeding 0.90 increases the probability of filament break in spinning operation, the ratio (VTNE) is desired to be 0.90 at most.The ratio (VTNE) is expressed by the following equation (1) using the fineness (D: denier) of the filament to be spun, the number (F) of the filaments to be spun, the concentration (C wt.%) and density p/cm3) of the spinning solution, and the radius (r cm) of the spinneret nozzle hole.

VT/VE = A. C p . r2 . F/D (1) (wherein A is a constant) Thus, the ratio (VT/VE) is a value in proportion to square of the radius (r cm) of the spinneret nozzle hole. This radius (r cm) is desirably chosen so as to give a ratio (VTNE) of up to 0.90.

Moreover, the speed (VT, m/min.) of taking up filaments is desired to be less than 800 m/min. since the probability of filament break in the spinning operation increases remarkably when the speed VT exceeds 800 m/min. Further, speed VT of up to 600 m/min is more preferred since the probability of filament break is specially low at such speed.

Effect of the invention According to the invention, high tenacity diacetate fibers have become producible and utilizable for such applications as the prior art diacetate fiber has not been used because of the low tenacity thereof.

For instance, the present diacetate fibers produced by the present invention open the way to new end used such as thin lining fabrics and ornamental strings.

The invention is illustrated in more detail with reference to the following examples.

Example 1 A prescribed amount of cellulose diacetate was dissolved in the ordinary way in mixtures of methylene chloride and methanol respectively in the proportion shown in Table 1. The resultant solution was filtered then heated at 65"C and extruded through spinneret into a cabinet at a draw down ratio (VTNE) of 0.80 to 0.85. The filaments were extracted from the cabinet and taken up at a speed of 400 m/min. The resultant yarn had 100 denier per 38 filaments.Results thereof are shown in Table 1, wherein "spinning solution" concentration is the cellulose diacetate content expressed in % by weight, "methanol proportion" is the methanol content expressed in % by weight in the methylene chloride-methanol mixture, 'tensile strength is the dry tensile strength measured in accordance with the method defined in JIS-L1070, and "solution viscosity m" is the value determined by reading the time T(sec.) required for an iron ball of 0.64 cm in diameter to fall naturally by 10 cm distance in the spinning solution filled in a glass tube of 2.54 cm in inner diameter, and calculating according to the following equation:

: : Spinning solution viscosity (poise) g : Gravitational acceleration (980 cm/sec2) r : Radius of iron ball (cm) CT : Density of iron ball (g/cm3) p : Density of spinning feed solution (g/cm3) V : 10/T (cm/sec.) R : Inner radius of glass tube (cm) it can be seen from Table 1 that diacetate fibers improved in tenacity can be produced by dry spinning from a spinning solution of cellulose diacetate in a methylene chloride-methanol mixture provided that the spinning solution viscosity is 2500 poises or more.

Table 1

Run No. 1* 2 3 4 5* 6* 7 8 9 10 11* 12 Feed solution concentration 22.0 22.5 23.0 24.0 23.0 23.5 24.0 25.0 25.5 24.0 (wt. %) Methanol proportion 6 6 6 6 6 9 9 9 9 9 9 12 Feed solution viscosity 2000 2500 2900 3500 4200 1900 2200 2600 3200 4000 5000 2300 (poise) Tensile strength 1.4 1.6 1.7 1.7 1.7 1.4 1.5 1.6 1.7 1.7 1.8 1.5 (g/D) Frequency of filament break 7 10 16 19 22 8 10 14 23 25 48 13 (per 100 spindles, per day) Note (1): * Marks indicate comparative experiments.

Note (2): Frequency of filament break: frequency of filament break occuring in spinning operation per 100 spindles and per day.

Comparative Example A porescribed amount of cellulose diacetate was dissolved in the ordinary way in aceton-water mixtures the water contents of which was as shown in Table 2. The resulting solutions were filtered to make up spinning solutions, which were then heated at 65 C and extruded each through spinneret which had been chosen so as to give a draw down ratio (VTNE) of 0.80 to 0.85. The extruded filaments were dried in the usual way and then taken up at a speed of 400 m/min., with the resultant yarn of 100 denier per 26 filaments. Results thereof are shown in Table 2, wherein "water content in solvent is the water content expressed in % by weight in the acetone-water mixed solvent.

Table 2

Run No. 13 14 15 16 Water content in solvent 3.5 4.0 4.0 4.5 (s) Feed solution concent- 28.0 28.0 29.0 29.0 ration ( % ) .

Feed solution viscosity 2800 2500 3200 2900 (poise) Tensile strength 1.4 1.3 1.4 1.4 (g/D) As evident from comparing results of Table 1 with those of Table 2, tensile strengths of diacetate fibers obtained from acetone-water mixed solvents are lower than those from methylene chloride-methanol mixed solvents whereas the spinning solution viscosity in the former case is high, and accordingly it is better to use a methylene chloride-methanol mixed solvent for the purpose of producing high tenacity diacetate fibers, which is an object of the invention.

Example 2 A prescribed amount of cellulose diacetate was dissolved in the ordinary way in a methylene chloridemethanol mixture in which the methanol content was 9% by weight to prepare a spinning solution of concentration of 24%. Portions of this solution were heated at different temperatures, respectively, shown in Table 3, and extruded each through spinneret which had been chosen so as to give a draw down ratio (VTNE) of 0.80. The extruded filaments were dried in the usual way, and taken up at a speed of 400 m/ min., giving a yarn of 100 denier per 76 filaments. Results thereof are shown in Table 3, wherein "elongation is the dry elongation of the obtained fiber measured in accordance with the method defined in JIS-L-1070. The spinning solution viscosity was 2600 poises.

Table 3

Run No. 17* 18 19 | 20 21* Temperature 50 55 65 70 75 (0c) Tensile strength 1.7 1.7 1.6 1.5 1.4 (gID) Elongation 17 20 25 27 30 (%) Table 3 reveals that in the production of diacetate fibers by dry spinning from a spinning solution of high viscosity, high-strength fibers are difficult to obtain when the feed solution is heated at a temperature of 75"C and extruded through spinnerets, and diacetate fibers produced by heating the feed solution at a temperature of 50"C to extrude it through spinnerets exhibit low elongation. Therefore, favorable temoetatures of the feed solution for spinning are from 55" to 70"C.

Example 3 The same spinning solution as used in Example 2 was heated at 65"C and extruded through different spinneret which had been chosen so as to give the respective ratios (VT/VE) shown in Table 4. The extruded filaments were dried in the usual way, and taken up at a speed of 400 m/min., giving a yarn of 100 denier per 26 filaments. Results thereof are shown in Table 4, wherein "frequency of filament break" means the frequency of filament break occuring in spinning operation per 100 spindles and per day. Table 4

Run No. 22* 23 24 25 26 27* 28* Inner diameter 35 36 37 38 39 40 41 of nozzles (p) 35 36 37 38 39 40 41 Ratio (VT/VR) 0.70 0.75 0.80 0.85 0.90 0.95 1.00 Tensile strength 1.5 1.6 1.6 1.7 1.6 1.6 1.5 (g/D) Frequency of filament break 12 10 14 16 19 28 40 (per 100 spindles, per day) From Table 4, it proves that in the production of diacetate fibers by dry spinning from a spinning solution with the viscosity of 2200 poises or more, diacetate fibers of low tensile strength are obtained when the draw down ratio (VT/VE) is less than 0.75, and filament break in spinning operation occurs frequently when the draw down ratio (VT/VE) exceeds 0.90. Therefore the spinneret has to be chosen adequately so as to give a draw down ratio (VT/VE) of 0.75 to 0.90.

Example 4 The same spinning solution as used in Example 2 was heated to 65"C and extruded through spinnerets which had been chosen so as to give a ratio (VT/VE) of 0.80. The extruded filaments were dried in the usual way, and taken up at different speeds shown in Table 5, giving a yarn of 100 denier per 26 filaments. Results thereof are shown in Table 5.

Table 5

Run No. 29 30 31 32 33 34* Take-up speed 400 500 600 700 800 900 (m/min.) Tensile strength 1.6 1.7 1.6 1.5 1.5 1.4 (g/D) Frequency of filament break 14 14 18 24 25 36 (per 100 spindles, per day) It can be seen from Table 5 that for producing high- strength diacetate fibers by dry spinning from a spinning solution with the viscosity of 2200 poises or more, the speed of taking up filaments is desirably up to 800 m/min., preferably up to 600 m/min.

Claims

1. A process for producing cellulose diacetate fibers which comprises preparing a spinning solution by dissolving cellulose diacetate in a mixture of methylene chloride and methanol to give a viscosity of 2200 to 4000 poises, as measured at 25C by the ball fall method, and subjecting the spinning solution to dry spinning.

2. The process for producing cellulose diacetate fibers according to Claim 1, wherein the extrusion temperature of the spinning solution is in the range of 55" to 70"C.

3. A process for producing cellulose diacetate fibers which comprises preparing a spinning solution by dissolving cellulose diacetate in a mixture of methylene chloride and methanol to give a viscosity of 2200 to 4000 poises, as measured at 25"C by the ball fall method, and subjecting the spinning solution to dry spinning in such a manner that drawn down ratio of the linear speed, VT, of takine up the extruded filaments to the linear speed, VE, of extruding the spinning solution will be in the range of 0.75 to 0.90.

4. The process for producing cellulose diacetate fibers according to Claim 3, wherein the speed, VT, of taking up the extruded filaments is up to 800 m/min., preferably up to 600 m/min.