US2087016A - Viscose process and apparatus - Google Patents

Description

`Iuly 13,1937.` w. H. BRADSHAW ET AL 2,087,016 vIscosE rRocEss AND APPARATUS Filed July i3, 1934 EDWARD I2. MKEE A ATTOR EY.

Patented `luly 13,- 1937 UNITED STATES PATEn'r oFFicE 2,087,016 l viscosa PROCESS AND .dermatitis William Henry Bradshaw, Bualo, N. Y., and

Edward R. McKee, ,Eer-mittags, Te., signors, by mesne assients, to llont -de Nemours s llompany,

mi; it. t., en wiimingten,

Del., a corporation of Delaware E Application .miv it, naar, senat ne., essere 9 Claims..

This invention relates to a Viscose process. More particularly, the invention has to do with the treatment of substantially ripened viscose and the feeding thereof to the product-forming room.

The invention `will be described for convenience in its application to a process of making rayon, but the process is equally applicable to the manufacture of regenerated cellulose sheeting, or to any other process in which viscose is used.

In the manufacture of rayon by the viscose' process, cellulose xanthate is formed in a manner which will be understood by those skilledl in the art, is dissolved, lis ripened, is filtered, is

deaerated, and is extruded through a spinneret into a coagulating bath. The relation between the viscose solution andthe coagulatingl bath is adjusted to produce yarn of the desired properties. The maintenance of this relation is. essential in the production of a uniform product. ItA

is relatively easy to maintain thev coagulating bath at a constant value, but is diihcult to maintain the viscose a't a constant value because it changes with time and at different rates depending on the temperature. 'I'his change in the viscose is called ripening and the riper the viscose the more easily it coagulates. Viscose coagula-.

bility or its degree of ripeness is commonly measured in terms of salt index. The salt index referred to in this specification is that defined by Reinthaler and Rowe in Artificial silk, page 68, second full paragraph, published in 1929.*

In the prior art the salt index of the viscose delivered to the spinning room has been controlled to within plus or minus 0.5, but this gives rise to a non-uniform product.

In the practice of today, batches of cellulose xanthateare dissolved in an aqueous caustic solution and vthree or four such charges blended v to form a'nal viscose charge. These charges aresent to the ripening room,\are confined in tanks, filtered, confined in other tanks, and the'pro'cesses of filtering and confining repeated until the viscose has reached thel stage *The degree of ripeness of the viscose is determined by introducing small samples into common salt solutions of different concentrations. The fresher and less ripe the viscose, the stronger the solution 'of common salt of a common salt correct degree of necessary to precipitate the sodium cellulose xanthate. The salting point" of a viscose signifies the concentration solution that just suffices to coagu- ,late a drop of viscose which is allowed to fall into it. The degree of ripencss most favourable for spinning is dependent upon various factors, e. g., the nature of the preparation of the viscose, the composition and tempcrature of lthecoagulatinf.: bath, etc, In the case of a viscose prepared as already described, for example, the ripeness has -been attained when it is coagulatd by 3-4% common salt solution. Such viscose, therefore, has a salting point of 3-4.

- is further non-uniformity of the product arising process of preparing viscose.

of viscose must be left in each of these tanks to 10 prevent air from blowing through and getting in the viscose pipe lines, otherwise continuous filaments or sheets could not be formed in an orderly manner and without excessive diiiculty. When a feed tank is refilled with fresh viscose, the heel from the charge previously inthat tank has quite a diiferent salt index than the salt index of the new charge and since the two charges do not intermingle appreciably but remain substantially in distinct layers, it is impossible to deliver to the product-forming room uniform viscose or one having anywhere near a constant salt index. In addition, since the viscose musttravel diiferent distances through pipes in the relatively warm product-forming room to various machines, there from the varying amount of ripening of the viscose that takes place in this travel.

It is an object of this invention to improve the Another object of the invention is to prepare viscose having a. substantially uniform salt index. Still another Aobp ject is to deliver to the product-forming room a viscose having substantially constant salt' index and to maintain that salt index substantially con- 3f stant at all the extrusion devices or product-forming machines in that room. Other objects of the inventionwill be in part apparent and in part 4 set forth hereinafter, y p

These objects are accomplished by the improved 0 means and methodherein set forth and claimed. The drawing is a diagrammatic ow sheet rep resenting one mode of practicing the invention.

Referring to the drawing; numerals IA, IB and IC refer to dissolving tanks which perform the function of dissolving the cellulose xanthate in an aqueous caustic solution. These :dissolvers may be three in number, as shown, or more' or less. The batches ofv viscose from the several dissolvers pass through valve-controlled pipelines l0 leading from the vdissolvers to a blender 2 in whichthe batches of viscose are mixed togetherin order to improve the homogeneity of the product. The blender is of any satisfactory type known to the art. The blended viscose passes 56 from the blender ythrough valve-controlled line 20 to the first of a number of ripening tanks,3A, 3B, 3C, etc., to which the charge from the blender is transferred. These ripening tanks are located in a room kept at constant temperature. The charges of viscose are advanced from one ripening tank to another through pipelines, which may be valve-controlled as shown, as the older viscose is consumed and during this advance, they are filtered through successively finer filtering media. For instance, the relatively green viscose is passed through a filter press 3|, connected between tanks 3D and 3E by means of pipelines which may be valve-controlled. Between tanks 3K and 3L there may be another filter similarly located, having somewhat finer filter cloths, and further on, between tanks 3P and 3R, a third filter press may be similarly located, having a still finer filtering medium. After the last filtration, the viscose is stored under high vacuum, in order that the entrapped air be removed, in partly filled tanks 3R, 3S and 3T, connected to each other and to the filter press 33 by means of valvecontrolled pipelines as shown. The filtered, airfree viscose is then flowed from tank 3T by means of valve-controlled lines 330, 33| and 332 alternately to feed tanks 4A and 4B.

Viscose is pumped or otherwise flowed alternately from the tanks 4A and 4B, through valvecontrolled pipelines 43|, 432 and 433 to a pump 5 which may be of any suitable type but preferably is a constant delivery pump driven by an electric motor. 'I'he pump discharges the viscose into a homogenizer 6, which may be any suitable blending means. The homogenizer is so constructed that the two viscoses (the second of which will be described hereinafter) fed thereinto will be thoroughly blended together to form a homogeneous mixture. The viscose passes on from the homogenizer tank 6 through valve-controlled pipe and into the agitated line tank 1. This agitated line tank contains agitating means which preferably is a relatively slowly revolving paddle which will not violently disturb the surface of the viscose and permit air to be entrapped therein. It should be understood, however, that thorough mixing of the viscose leaving the homogenizer with that in the agitated line tank must be provided to prevent pocketing or by-passing of unblended viscose. The volume of the agitated line tank should be sufiiciently large to suppress fluctuations in index but not so large as to cause an excessive salt index drop from the feed tank to it. In general, the capacity of this tank should be about that of one of the feed tanks. This agitated line tank is jacketed preferably to about two-thirds the height of the tank or to about the normal viscose level. This jacketed space is connected with warm and cold l waterlines or with other temperature control media such as brine. The homogenizer may also be jacketed for temperature control.

The viscose flowing into tank 1 should preferably enter below the viscose level therein. A porc tion of the viscose is drawn from the bottom of this tank through valve-controlled line II-'I2 by means of pump 8, which is set to deliver viscose throughA line 8| in excess of the require-v ments of the spinning machines or to other machines for forming shaped articles. A pressure control Valve 83 maintains the pressure in the feed line 82 constant by permitting a certain quantity vof viscose to return by means of lines 84 and 14 through pump 5 and homogenizer 6 to blend with the viscose coming from one of the iced tanks 4A or 4B. If it is found desirable, a filter press may be located between pump 8 and the extrusion devices in order to insure the cleanliness of the viscose.

In the practice of our invention, viscose is fed continuously into the homogenizer and blending system from one of the two feed tanks alternately. This viscose is passed through pump 5 to homogenizer 6 along with approximately 10 times its volume of viscose taken from line tank Afterpassing through homogenizer 6, it is i'ed into the line tank immediately below the surface of the viscose therein. In passing down through line tank 1, it is blended with the Viscose in the tank and emerges from the bottom of the tank, being then fed in part to the feed line 82. By this system of operation, even though the small heel of the previous charge in the feed tank may have an index so far below the balance of the charge that it would not produce a good product, it becomes so thoroughly and completely blended with the large volume of thevmaterial in line tank 1 that the index of the viscose leaving line tank and going to feed line 82 is changed but very slightly. y

In addition to correcting the Variations that arise from the periodic passage of these small heels and other small amounts of viscose having similar, greatly different indices, the volume of viscose in this systemand the close control of it permit to a very great degree the neutralizing of other types of index variation of comparatively short duration and is therefore a useful means of insuring a constant supply, to the extrusion room, of uniform viscose. 4

For example, if the index of the charge of viscose being drawn from the feed tank is abnormally high, viscose of the standard salt index can be delivered to the spinning room by temporarily reducing the volume of Viscose fed into this system from the feed tanks and if necessary by increasing the temperature of the' viscose in the homogenizer and in the line tanks. l

Thus the operation of the plant is considerably facilitated and it is possible to produce a product far superior to that produced heretofore.

By the process just previously described, we are able to deliver viscose having a substantially constant salt index to the spinning room. However, since the viscose must be conducted various distances or for various lengths of time through pipes in the relatively warm spinning room, in order to reach all the machines and spinning positions therein, it becomes further and non-uniformly ripened. This variation in ripening as measured by salt index of Viscose taken from various machines and various spinning positions may be as much as 0.3 or even more.

In order to diminish this variation and improve the uniformity of the products formed, we incorporate in the viscose an agent that inhibits or retards further ripening of the Viscose. For instance, we may add a small amount of sodium sulfite, such as 0.1% to 5% or more and preferably about 1%, based on the cellulose content of the viscose. The addition may be made either as a solution or as a solid. When we add to the viscose 1% of sodium sulte based on the cellulose content of the viscose, we find the uniformity of the viscose as measured by salt index is improved throughout the spinning room about three-fold. The addition of the inhibitor is preferably made to the thoroughly blended viscose described above as it leaves the system in line 82. It is to be understood that suitable precaution will be taken to

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