US2997365A - Production of regenerated cellulose filaments - Google Patents

Description

United States Fate-mt ()flice Patented Aug. 22, 1961 2,997,365 PRODUCTIGN F REGENERATED CELLULOSE FILAMENTS John Oliver Smith, Coventry, and David Nicholson Tyler, Codsall, near Woverhampton, England, assignors to Courtaulds Limited, London, England, a British comp y No Drawing. Filed July 30, 1959, Ser. No. 830,477 Claims priority, application Great Britain Aug. 12, 1958 6 (Ilaims. (Cl. 18-54) This invention relates to the production of regenerated cellulose filaments from viscose and in particular to a process for the production of filaments having a high ratio of wet to dry tenacity, low extensibility, no skincore differentiation and low water-imbibition.

We have found that by modifying or eliminating certain features of the basic viscose rayon process, highly oriented viscose rayon textile filaments having low extensibility can be produced.

The present process differs from the basic viscose rayon process in the following respects (1) The use of a cellulose having a higher degree of polymerisation (D.P.). In practice this may lead to the elimination or shortening of mercerising or the ageing of the alkali cellulose.

(2) The use of a higher viscosity viscose. This is, to an extent, associated with the use of high D.P. cellulose, for only low cellulose concentrations of about 3 percent in the viscose could be used if normal ball-fall viscosities of, say, about 40 were to be used. However the increased viscosity assists in the rapid coagulation of the viscose during spinning and this is advantageous. The maximum increase in the viscosity is determined practically by the ability of the spinning equipment to handle the viscose. Thus a cellulose concentration of from 4 percent to 6 percent in the viscose and a viscose ball fall viscosity of over 50 and preferably from 100 to 200 may be used in practice.

(3) The use of a lower caustic soda concentration in the viscose which enables a low acid coagulation bath to be used. Such a bath can co-operate in the rapid coagulation of the filaments, but only slowly regenerates the cellulose. In practice the cellulose xanthate crumbs may be mixed with water rather than with the caustic soda solutions of normal viscose manufacture.

(4) The spinning of viscoses having higher salt figures so that an unusually large concentration of cellulose xanthate is present in the freshly extruded filaments and is preserved to a large extent in the filaments during the stretching operation, the more plastic cellulose xanthate molecules allowing more applied stretch than the relatively rigid regenerated cellulose molecules.

(5) The use of a coagulating bath containing much less acid, a lower sodium sulphate concentration and no zinc sulphate or only such zinc sulphate as is inevitably present as an impurity and in any case not more than 0.02 percent. The temperature of the bath should be between 20 C. and 30 C., that is to say lower than usual. All of these modifications are calculated to reduce the rate of regeneration of the cellulose.

(6) The use of a greatly reduced immersion path of the filaments in the bath, only sufiicient to cause the filaments to coagulate so that they may be drawn from the bath without damage whilst preserving, as much as possible, the original xanthate groups of the viscose. The filaments are then in the very plastic condition required for the stretch which is applied outside the bath.

The necessary length of the immersion path varies with the denier of the filaments being spun.

(7) The stretch of at least percent is applied to the filaments immediately they emerge from the bath. The plastic condition of the filaments makes the application of such a large stretch relatively easy and the filaments are fully regenerated only after the stretch has been applied.

The invention accordingly consists in a process for the production of viscose rayon filaments comprising extruding viscose having a cellulose content between 4 and 6 percent and a caustic soda content approximately half that of the cellulose, the cellulose having an average degree of polymerisation of at least 300 and the viscose having a salt figure of at least 10 and a ball fall viscosity of at least 50, preferably between and 200, into a coagulating bath containing from 2.0 percent to 3.5 percent of sulphuric acid, less than 15 percent and preferably between 1 percent and 10 percent sodium sulphate, and not more than 0.02 percent of zinc sulphate as an impurity, maintaining the bath temperature between 20 C. and 30 C., limiting the length of the immersion path so that the filaments may be stretched by at least 80 percent of their original length on emerging from the bath, stretching the filaments immediately after they have emerged from the bath by at least 80 percent and subsequently completing the regeneration of the fila ments.

The required inmiersion path of the filaments in the bath varies with the denier of the filaments. Thus for filaments having deniers up to 4.5 the immersion path should not exceed 6 inches and it is preferred for fila: ments having deniers of 3 or less that the immersion path should not exceed 3 inches.

The filaments can then be washed, dried and collected in a continuous form, or cut to produce a staple fibre, and subsequently washed and dried. Regeneration can be accelerated by treating the fibres at a suitable stage with warm dilute acid for example 2 percent of sulphuric acid at a temperature of 60 C.

The amount of sulphuric acid in the regenerating bath is kept within the stated range of 2.0 to 3.5 percent and it is preferably just sufiicient to secure adequate coagulation. The actual amount varies with the number of filaments, the filament denier, spinning speed and the sodium sulphate concentration in the bath.

The highly oriented filaments of low extensibility can be made into fabrics having good dimensional stability and this is mainly due to the low imbibition of the filaments and their high initial wet modulus, that is the markedresistance of the wet fibres to stretch under low loads. The fabrics show reduced relaxation shrinkages and greatly reduced or eliminated progressive shrinkages.

These properties of the fabrics are similar to or better than cotton cloths of the same construction and are markedly superior to similar fabrics made from commercially available viscose rayon filaments.

The invention is illustrated by the following examples in which percentages are by weight.

Example 1 A high quality wood pulp such as that sold under the trade name Cordenier J. was steeped in an 18.6 percent aqueous solution of caustic soda for 1 /2 hours at 19 C. The surplus solution was removed by squeezing the pulp to a press ratio of 2.8 and the pulp was then disintegrated into'crumbs for 2 /2 hours at 19 C. after which the crumbs were allowed to age for -17 hours at the same temperature. The alkali cellulose was then xanthated for 3 hours with 42 percent of carbon disulphide (calculated on the original alpha-cellulose content of the wood pulp) at 24 C. and the resulting xanthate was mixed in a water-cooled vessel at 15 C. The mixing time was 3 hours during which the temperature rose to :17 C. A further 10 percent of carbon disulphide (also based on the alpha-cellulose) was then added in the mixer and the viscose was then filtered, deaerated by a flash deaeration process andleft to age for 12 hours in vacuum.

The viscose, containing percent of cellulose, 2.4 percent of caustic soda and 2.1 percent of sulphur and at a salt figure of 15, was then extruded at a ball fall viscosity of 100 seconds at 18 C. into a regenerating bath containing 2.7 percent of sulphuric acid and 1 percent of sodium sulphate at a temperature of 20 C. The viscose was extruded vertically upwards into the bath through a jet the face of which was about 1 /2 inches below the surface.

The filament bundle travelled vertically upwards through the bath and then a distance of inches through the air onto two skewed sets of concentric discs of diameters 5, 6, 7, 8 and 9 inches respectively, giving 80 percent stretch for four stages. From the last disc the bundle was taken up on a roller and was stretched a further 17 percent between the last'disc and the roller. It was then passed through a hot fixing bath containing 2 percent of sulphuric acid at a temperature of 90 C. in which it was stretched a further 3 percent. After washing and drying, the filaments had the following properties:

Filament denier 1.5 Conditioned tenacity grams per denier 3.6 Wet tenacity, do 2.6 Extensibility conditioned percent 6.0 Extensibility wet do 8.0 Water imbibitinn d0 65.0

The crosssection of the filaments was circular and no differentiation between skin and core could be detected upon staining.

Example 2 Viscose prepared as inExample l was spun through 3 mil diameter holes into a bath containing 2.5 percent of snlphuric acid and 5.3 percent of sodium sulphate at a temperature of 23 C., the immersion being two inches. The thread wasstretched a total of 100 percent in two stages and was then fully regenerated, washed, dried and collected. The final spinning speed was 50 metres per minute. The filaments produced had the following properties:

Denier 1.84 Conditioned tenacity grams per denier 3.62 MM tenacity m--- 2.46 Extensibility conditioned percent 8.3 Extensibility wet do 10.6

Water imbibitinn dn 75.0

The cross-section was circular and showed no skincore differentiation on staining.

Example 3 spinning speed being. m./rninute. The filament denier was 1.5 and the average properties of randomly chosen filaments were:

Conditioned tenacity "grams per denier 4.31 Conditioned extensibility percent 8.0 Wet tenacity grams per denier 3.05 Wet extensibility percent 10.4 Water imbibition do 74.0

Example 4 and the denier 1.5. The filaments were cut to a staple length of 1 inches, Washed and dried. The average properties of the fibres were:

Conditioned tenacity 2.90 Conditioned extensibility percent 12.5 Wet tenacity 1.80 Wet extensibility percent 14.8

The staple fibres were spun into a yarn of 1/l8s cotton count which was woven into a cloth of construction 64 ends/54 picks. 10 pounds of this cloth was washed in soap at 60 C. in a rotary washing machine for 30 minutes, rinsed for 5 minutes at 40 C., rinsed again for 10 minutes at 40 C., hydroextracted and dried in a tumbler drier. The laundering cycle was repeated at number of times and the dimensions of the cloth measured at intervals. The results are shown in the following table.

Percent shrinkage Water imbibi- Wash tion (percent on weight Warp Weft of fabric) 1 loose dried 1. 4 4. 0 +1. 2 l. 4 4. 2 1. 8 0. 6 1.0 4. G 5.0 1. 0 1. 8

It will be noted that the properties of the fabric are equivalent to or better than cotton in a cloth of the same construction and are much improved compared with normal viscose rayon textile fibres in a cloth of the same construction.

What we claim is:

1. A process for the production of viscose rayonfilaments comprising extruding viscose having a cellulose content between 4 and 6 percent and a caustic soda content approximately half that of the cellulose, the cellulose having an average degree of polymerization of at least 300 and the viscose having a salt figure of at least 10 and a ball fall viscosity between about 50 and about 200 seconds at 18 G, into a coagulating bath containing from 2.0 percent to 3.5 percent of sulphuric acid, less than 15 percent sodium sulphate, and not more than 0.02 percent of zinc sulphate as an impurity, to form filaments, maintaining the bath temperature between 20 C. and 30 C., removing the filaments from the bath while they are still capable of being stretched in air at least 80% of their original length, stretching the filaments in air immediately after they have been removed from the bath by at least 80% and completing the regeneration of the filaments after they have been stretched.

2. Aprocess for the production of viscose rayon filaments having deniers of up to 4.5 according to claim 1, in which the length of the immersion path of the filaments in the bath is not more than 6 inches.

2,997,365 5 6 3 A process for the production of viscose rayon fila- 6. A process as claimed in claim 1 in which the salt ments having deniers of up to 3 according to claim 1, in figure of the viscose is at least 12. which the maximum length of the immersion path of the filaments in the bath is 3 inches References Cited in the file of this patent 4. A process as claimed in claim 1 in which the bath 5 UNITED STATES PA ENTS contains from 1 percent to 10 percent of sodium sulphate. 2,611,923 Marion Sept 30, 1952 5. A process as claimed in claim 1 in which the ball 2,732,279 Tachikawa Ian. 24, 1956 fall viscosity of the viscose is between 100 and 200. 2,775,505 Pedlow Dec. 25, 1956

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF VISCOSE RAYON FILAMENTS COMPRISING EXTRUDING VISCOSE HAVING A CELLULOSE CONTENT BETWEEN 4 AND 6 PERCENT AND A CAUSTIC SODA CONTENT APPROXIMATELY HALF THAT OF THE CELLULOSE, THE CELLULOSE HAVING AN AVERAGE DEGREE OF POLYMERIZATION OF AT LEAST 300 AND THE VISCOSE HAVING A SALT FIGURE OF AT LEAST 10 AND A BALL FALL VISCOSITY BETWEEN ABOUT 50 AND ABOUT 200 SECONDS AT 18* C., INTO A COAGULATING BATH CONTAINING FROM 2.0 PERCENT TO 3.5 PERCENT OF SULPHURIC ACID, LESS THAN 15 PERCENT SODIUM SULPHATE, AND NOT MORE THAN 0.02 PERCENT OF ZINC SULPHATE AS AN IMPURITY, TO FORM FILAMENTS, MAINTAINING THE BATH TEMPERATURE BETWEEN 20* C. AND 30* C., REMOVING THE FILAMENTS FROM THE BATH WHILE THEY ARE STILL CAPABLE OF BEING STRETCHED IN AIR AT LEAST 80% OF THEIR ORIGINAL LENGTH, STRETCHING THE FILAMENTS IN AIR IMMEDIATELY AFTER THEY HAVE BEEN REMOVED FROM THE BATH BY AT LEAST 80% AND COMPLETING THE REGENERATION OF THE FILAMENTS AFTER THEY HAVE BEEN STRETCHED.