US2297260A - Manufacture of artificial silk - Google Patents

Description

Patented se i. 29,1942

um 'rso f ST TE VEFPAIE .OFFICE. f

. Manor-across or aarmcmnsna I JohannJosephStoeckly, Teltow, and Wolfgang Linnhofl, Berlin-M171 Alien Proper y (3!" Noni-swin assu es-my, 1939, semi No.

the

tRGcrmany;vestedin 272,834. In Germany Mayll, 1938 V 4, Claims. It is already Well known to spin viscose solutions into a conventional, primary, acid spin bath containing various salts, and to stretchthe threads, thus obtained, in a hot secondary bath. British Patent #467,500, for example, discloses the beneficial eil'ect of the primary -spinfbath upon the ultimate physical characteristics of i. e., bathscontaining 4% of zinc sulphate spun viscose threads, and it recommends the -use-- of primary spin baths with a high zinc content,

(about 50 g. of ZnSOrper' liter of bath); Ac- 1 cording to-this process, it is possible to produce a 120 den. thread with 60 filaments in a warm spin bath containing about 9.5% of sulphuric acid, 20% of sodium'sulphate and 4% of zincsulphate and to stretch the thread 87% after a bath travel of about 20 'cm. in said primary bath acid contentof the. primary bath'cause's a reduction of its coagulating and/or precipitating flciency by adding other suitable ingredients thereto. Thus, we have found that the zinc sulphate and sulphuric acid content of the priin a secondary bath maintained at a temperature or at least 60 C. and preferably of about 95 0., this secondary bath containing only small quantities of the bath ingredients present inthe' primary bath. The high zinc content of the primary bath is evidently responsible for the good physical properties of viscosethreads pro:

duced therein. However, it has .been found in actual practice that spin baths having a high zinc content cause rapid clogging of spinneret' orifices through which the viscose solution is extruded into such baths.

It is, therefore, a-primary object of our invention to provide a zinc-bearing spin bath..

which substantially prevents the clogging of spinneret orifices without reducing the physical characteristics of viscose threads formed therein in comparison in the art.

with spin baths heretofore known Other objects of our invention will become apparent to those skilled in the art from of the following specification.

Many theories have been advanced to explain therole'which zinc sulphate and other soluble zinc. salts play in.the aforementioned spinning astudy processes. It has been saidthat the favorable lesultsobtained with zinc sulphate-are due to its retarding eifect upon the decomposition of 5' the thread at the beginning of the stretching step. However, our experiments have shown that this retarding eitect of zinc sulphatecannot fully explain the beneficial results obtained therewith sinceammonium sulphate baths, as is well known, neither cause the formation of a. de-

thread nor a favorable result. 2 For thisreasomitis 'topresumethatzinc sulphate causes very specific eirects besides retarding the and/or decomposition of.

viscose threads. It is very likely that the zinc viscose (xanthate) formed in the primary spin bath causes a retardation of the final decomposition of the thread and that the thread and/or this compound ought not be completely decomposed upon entering the fixing and/or stretching bath.- The ;rate of decomposition ofjthis intermediate. compound is however, as our experiments showed, only retarded when the sulphuric acid concentration of the primary spin bathis reduced and preferably. brought to a minimum. Sinceareductioh of the sulphuric power, it is necessary tocompensate for this demary bath my be reduced provided larger amountsof magnesium sulphate'are added thereto. Additions of 150 g.,' 200 g., 250 g. and

more of magnesium sulphate per liter of spin bath have given excellent results.' Instead of using a primary'bath containing 125 g. of sulphuric acid, 260 g. of sodium sulphate and 52 g.

of zinc sulphate per liter,'it'is possible to use spin bath's having the'following compositions:

Sulphuric Sodium fl Zinc a id, sulphate Bath um Gram P,"

m an. m0

' 'Ihesenovel spin baths substantially inhibit clogging of spinneret orifices. This is especially true when the zinc sulphate content is reduced to about 30 grams .per liter of bath,- or below this value. The stretchability of threads is at least equalto that main -baths having a higher zinc content while the physical characteristics of'the finished threads are maintained. This reical which reduces the stretchability of viscose threads spun in its presence. Indeed, further experiments have proven that magnesium sulphate is not capable of completely replacing zinc sulphate in primary'spin baths. For this reason *1 w sulphate makes it and tocause indirectly a-retardation of.the decomposition of viscose. For this reason it issulpbate suit is-entirely unexpected since magnesium sulphate has heretofore been regarded as a .chemalso possible to reduce the zincsulphate concentratlons of the primary spin baths.

We claim:

1. The process of producing threads of regenerated cellulose which comprises first spinning a viscose solution through the orifices of a spinneret into a primary, zinc-bearing, aqueous spin bath to form an incompletely decomposed viscose thread therein and subsequently stretching and decomposing said thread in a hot, secondary, aqueous spin bath to form a threadof regenerated cellulose, said primary spin bath containing about 16 to 30 grams of zinc sulphate, about 110 to 115 grams of sulphuric acid, about 150 to 250 grams of magnesium sulphate and about 200 to 260 grams of sodium sulphate per liter of bath, and said secondary spin bath having a temperature of at least 60 C. and containing less sodium sulphate, zinc sulphate, sulphuric acid and magnesium sulphate per liter of bath than said priand decomposing said thread in a hot, secondary,

aqueous spin bath to form a thread of regenerated cellulose, said primary spin bath containing about 200 grams of sodium sulphate, about 20 Y grams of zinc sulphate, about 115 grams of sulmary bath, whereby incrustation of said spinneret is substantially prevented. a

2. The process of producing threads of regenerated cellulose which comprises first spinning a viscose solution through the orifices of a spinneret into-a primary, zinc-bearing, aqueous spin bath to form an incompletely decomposed viscose thread therein and subsequently stretching and decomposing said thread in a hot, secondary, aqueous spin bath to form a thread of regenerated cellulose, said primary spin bath containing about 260 grams of sodium sulphate, about 30 grams of zinc sulphate, about 115 grams of sulphuric acid and about 200 grams of magnesium sulphate per liter of spin bath, and said secondary spin bath having a temperature of at least 60 C. and containing less sodium sulphate, zinc sulphate, sulphuric acid and magnesium sulphate per liter of bath than said primary bath, whereby incrustation of said spinneret is substantially prevented.

phuric acid and about 250 grams of magnesium sulphate per liter of spin bath, and said secondary spin bath having a temperature of at least 60 C. and-containing less sodium sulphate, zinc sulphate, sulphuric acid and magnesium sulphate per liter of bath than said primary bath, whereby incrustation of said spinneret is substantially prevented.

4. The process of producing threads of regenerated cellulose which comprises first spinning a viscose solution through the orifices of a spinneret into a-primary, zinc-bearing, aqueous spin bath to form an incompletely decomposed viscose thread therein and subsequently stretching and decomposing said thread in a hot, secondary,-

p by incrustation of said spinneret is substantially