US2346258A - Method for production of cellulose acetate staple - Google Patents

Description

p l s. s. HOOPER 2,346,258

METHOD FOR PRODUCTION OF GELLULOSE ACETATE STAPLES Filed June 13, 1941 INVENTOR.

Elfin-pan ETanlg H1 13 EP 1 AITORNEYE Patented Apr. i1, 1944' UNI ED-STA ES PATENT oFica METHOD FOR PRODUCTION OF CELLULOSE ACETATE STAPLE f Gilman Stanley Hooper, Waynesboro, Va

assignor to E. I. du Pont de Nemours a Company. Wilmington, Del., wrporatlon of Delaware Application June 13, 1941, Serial No. 397,990 1 Claim. (Cl. iii-41.5)

This invention relates to the production of cellulose acetate staple. More particularly, the invention is directed to the crinkllug of a very large bundleof continuous filamentsand the cutting of this crinkled bundle to produce staple of substantially uniformlength, of good strength. witha desirable crinkle andwell-opened.

Inorder to satisfactorily spin rayon staple it is highly desirable that the staple have a retentive crimp. It is also desirable that the crinkled staplefiber should havesubstantially the original strength of the filament, and that. the bundle of staple should be uniformly. open, 1.,e., it, should be fiufiyand free of stuck or coalesced fibers. v In the manufacture of cellulose acetate staple no satisfactory method has heretofore been devised which achieves all of these desiderata.

It is, therefore, an object of this invention to provide an improved process for the production of crinkled cellulose acetate staple which is eminently'suited for the production or spun yarn.

Another object of this invention is to provide optimum conditions of crinkling so that the numher of crimps per inch and the intensity or crimp can be controlled satisfacto yn-without substan tially impairing the stre Still another object of this invention is to provide optimum conditions for cutting the bundle of crinkled filaments so that substantially all the crinkle is retained in the cut fibers, so, that substantially uniform fiber lengths are produced,-

and so that the cut fibers fly apart or explode to give an exceedingly well-opened not. A still further object is to provide a novel tor: of crinkled filaments, which is admirably suited ior direct conversion into a top. Other objects will be apparent from the description that of the filaments.

6.5% based on theQweight of the dry fibers. After this, the staple fibers may be sprayed with a liquid containing an anti-static agent, blended by a mechanical blender, and packaged.

Tow, mechanically crinkled under the conditions or this invention, and comprised of cellulose acetate filaments within the range of 3 to 20 denier, and preferably within ,the range 'of 5 to 12 denier, containing from 6 to 12 crinkles per inch, the crinkles ranging in amplitude from /8 to 1: inch, is especially suited for use in cutting and drawing apparatus designed for the direct conversion of tow to top. As a practical matter, however, plants equipped for the preparation of tow are not equipped for the direct'conversion of tow to top; hence, for this purpose, the tow must be packaged and shipped to the point where it is to be cut and drawn and eventually spun into yarn. Tow containing the high percentage of solvent plus moisture required in the crinkling operation cannot'be wound into packages and stored for any length of time without seriously reducing the essential intensity and-uniformity of thecrinkle. Therefore where tow, crinkled according to my process, is to be employed in towto-top converters, it is prepared for shipment by' treating the sam in relaxed condition to remove substantially all of the solvent and to adjust the moisture content to about 6%, after which it is wound into suitable packages. Crinkledtow thus conditioned and meeting the specifications and fluffy plodabove recited, is a further feature of my invention The preferred mode of imparting crinkle to .the tow of. cellulose acetate is to mechanically These objects are accomplished my invention which, briefly stated,comprises imparting, by purely mechanical means, a crinkle of P termined frequency and amplitude to a tow or continuous filaments of cellulose acetate, the solvent plus moisture content or which is adjusted and maintained during the crinkling operation within limits hereinafter specified. Thereafter the crinkled tow is converted to'staple'by cutting yieldable clapper plate and the bite of the rolls.

the same in air with a sharp knife or other- 7 cutting device, while maintaining the tow undera slight but positive tension, and while further maintaining the solvent plus moisture content at the tow within a range tobe hereinafter specified. The resulting crinkled staple is subsequently treated to bring its solvent content to less than k 1.5% and to adjust its moisture content to about ter where the crinkled low is directly converted to staple. The moisture plus solvent content of the filamentbundle depends upon the denier of The individual. filaments of the tow-issuing, from this apparatus are uniformly crimped and the tow is substantially free of stuck or fused filamerits.

As previously indicated, it is essential that the moisture plus solvent content of the filarnents be maintained within certain limits to get optimum results at the crinkler, and at thecutthe filaments and the limits for satisfactory operation can best be expressed by the following.

formulae. To secure satisfactory crinkling of bundles of cellulose acetate filaments, the moisture plus solvent content should be satisfied by the following formula. wherein d=denier of the filamentz. Per cent moisture+solvent=40 log d-d+2i6 but in no case should the moisture plus solvent content, be greater than 40% or less than 8% based on the dry weight of the cellulose acetate filaments. v

At the'cutter, the moisture plus solvent content should be satisfied by the formula:

Percent moisture-tsolvent all log li-liifi but in no case should the amount of solvent plus moisture be greater than 38% or less than based on the dry weight of the filaments.

The ratio of moisture to solvent is not extremely important but, in general, the ratio is much higher for low deniers-than for heavy denier filaments. For instance, in crinkling, the solvent may comprise as little as 15 to 20% of the totalmoisture plus solvent present in 1.5 denier filaments but the solvent content may be as high as 70% or more in the case of heavy vent-moisture .content, if out when held under substantially no tension it'will not explode or fiy apart as is desired and if the tension is too great, the crinkle will, be removed and hence the desired crinkle in the cut staple will not be present. Tensions between 0.005 and 0.04 gram per denier are essential to obtain good opening of the staple and, at the same time, maintain the crinkle in the cut fibers.

l The essential operations involved in the conversion of a tow of continuous filaments'of cel-' lulose acetate to crinkled staple suitable for the production of spun yarn, according to my invention, will now be described in connection with the accompanying drawing wherein:

Fig. 1 is a diagrammatic illustration of the operations for forming a tow and crinkling the same, and a Fig. 2 illustrates diagrammatically the conver sion of the crinkled tow to staple.

Referring to Fig. 1, cellulose acetate. yarn formed by the dry or evaporatedmethod is drawn from spirming cell i by feed roll 2, and thence over guide 3 after which it is combined with yarns being simultaneously produced in similar units to form a tow which is preferably from 30,000 to 50,000 denier in size. If desired,,

any suitable finish composition may be applied,

and preferably at a. point intermediate draw roll 2 and guide 3, by any suitable means (not shown) such asapplicator rolls, fountain sprays, wicks,

and the like. Where it is necessary to reduce the moisture plus solvent content of the tow in order to bring it within the optimum conditions above defined, the tow may be subjected to. moderate drying, e. g., by passing the same through a drier 4. The combined yarns forming the tow, now properly conditioned, are fed over a guide roll 5 and into a crinkler 6 of the type disclosed in U. S. patent application Serial No. 368,925 (Hitt). Th'e crinkled tow is collected in a can i eccentrically mounted on a revolving platform 8. To form staple, the crinkled tow is passed over guide roll 9, is preferably combined with like tow from other containers and the combined tow is fed through feed rolls l0 and ll and into a centrifugal cutter i2, where it is cut in air under moderate tension. The well opened staple, thus produced, is collected in hopper it or in any other suitable container, after which it may be immediately spun or, if desired, conditioned for storage and shipment.

The following examples further illustrate the invention.

EXAMPLE I (Three denier per filament staple) 450 denier, filament cellulose acetate yarn was spunby the dry or evaporative method from an acetone solution and was drawn from the cell with a solvent content of approximately 15%. Ten per cent of an aqueous emulsion of oils, such as are commonly used in the finishing of textile fibers, was applied to the bundle of continuous filaments immediately after emersion from the spinning cell. Filament bundles from a number of cells were then collected into a very heavy denier bu'hdle or tow, for instance having a total denier of approximately 28,000 (approximately 9,300. filaments) and this tow was fed into the crinkler described in U. S. patent application-Serial No. 368,925 (Hitt) at the rate of 220 yards per minute. During the passage from the spinning cell to the crinkler, the tow was subjected to a certain amount of drying which brought the total moisture plus solvent content of the tow at the crinkler down to about 19%, consisting of approximately 7% solvent and 12% moisture. (The moisture being moisture applied as afinish emulsion .andomoisture originally contained in the spinning solution.) The crinkler was adjusted so that approximately 12 crinkles per inch of 1 6 inch amplitude were inserted in the con- .tinuous filaments comprising the bundle. The bundle of crinkled filaments leaving the crinkler was collected in a solid fiber barrel and stored without drying untilready for cutting. As spun, the yarn had a dry strength of 1.40. grams per denier and 28% elongation. After crinkling, the dry strength was 1.28 grams per denier with approximately the same elongation, whereas in the absence of'control ofmoisture plus solvent, the dry strength of crinkled filaments would frequently fall to 0.7 gram per denier which made the product unsatisfactory.

The tows of crinkled continuous filaments were cut in a centrifugal type cutter having a single stationary cutting blade such as described in U. S. Patent No. 1,723,998 (Beria). "The moisture plus solvent content of the towwas allowed to decrease through storing so that as it was fed to the cutter, it contained about 14% of which about 4% was solvent. Four tows were combined and fed to the cutter at the rate of 200 yards per minute and by rotating the cutter disc at 3600 R. P. M. A tension of approximately 0.1 gram inches in length were produced. The crinkledstaple collected from the cutter was fed by suction to a feed hopper of a continuous drying apparatus wherein the solvent content was reduced to below 1.5% and the moisture adjusted to 6.5%

based on the dry weight of the fibers. On leaving the drier, the staple fibers were conveyed by air to the feed hopper of an opening device where 0.1% cetyl betaine was sprayed on the fibers to inhibit build-up of electrostatic charges thereon in subsequent operations. The fibers are then passed through a blender consisting essentially of a pin type heater and carried by'air to a receiving bin, from where the staple could be dropped into a baler.

EXAMPLE II (Twelve denier per filament staple fiber) I Cellulose acetate yarn of 12 denier per filament (816 denier, 6 8 filaments) was drawn from the dry spinning cell and approximately 8% of an aqueous emulsion of finishing agents was applied thereto to facilitate subsequent processing. The filament bundles from several cells were collected together to form a tow of about 50,000 denier and, after a mild drying action, was fed through the crinkler described in the Hitt appli cation at the rate of 123 yards per minute. The moisture plus solvent content of the tow at the crinkler was approximately 30% of which 22% was solvent (acetone) Approximately eight crinkles per inch of V8 inch amplitude were inserted in thefilaments as they passed through the crinkler. Thetow of crinkled filaments leaving the machine was collected in solid fiber barrels and stored for cutting. Tensile tests on the crinkled and uncrinkled filaments showed that about 80% of the original strength had been retained through the crinklirig operation. i

Three of the crinkled tows so produced were subsequently brought together and passed into a centrifugal type cutter such as previously referred to, at the rate of 250 yards per minute and with the centrifugal disc revolving at 1800 R. P. M., the average tension on each filament at the time of cutting was in the neighborhood of 020 gram, and the length of the staple produced was inches. The moisture plus solvent content of the tow at the cutter was 26%, of which 19% was solvent. The cut fibers fiew apart at the cutter in the same manner as'described in the previous exampleIto produce a well-opened prod uct which was passed continuously to the hopper of the drier; dried to 1.5% or less solvent content and 0.5% moisture content; sprayed with an anti-static finish consisting of 0.4% of lorolamine hydrochloride on the weight of the fibers; and then passed directly to a storage bin without any additional opening action. The fibers produced in this manner were baled and sold for use in the worsted industry.

The invention is not of course limited to the exact conditions and manipulations set out in the above examples,but is susceptible rather to wide variation and modification, observing at all times, however, the several critical factors hereinbefore recited, and the following generalities. The optimum moisture,plus solvent content of therope at the crinkler and cutter varies as a function of the denier of the material being handled. For example, fine denier filaments such as 1.5 should containrelatively little moisture and solvent when crinkled and when out. The use of higher amounts of moisture and solvent will result.

in extremely intense crinkles and very serious weakening of the filaments in the crinkling operation, and if out while they contain too high a deniers increase, however, not only can higher moisture plus solvent contents be tolerated, but

such higher moisture plus solvent contents are necessary if satisfactory crinkling and cutting are 5 to result. If the moisture plussolvent content of heavy denier filaments is maintained at too low a level, the material may be incapable of being crinkled or, at best, the crinkle will be large, nonuniform, and lacking in permanence, and of little value as an aid in subsequent processingof the to maintain the filament in a suitable pliable condition.

Not only is the moisture plus solvent content of the tow essential for the production of uniform length, well-opened, fiuffy fibers, but it is also essential that the tension on the tow at the time v of cutting be maintained within definite limits. i

To get uniform lengths of out staple, it has been found desirable to tension the tow slightly at the feed rolls before it enters the cutter disc. If the moisture plus solvent content of the tow is too great, a portion of the crinkle may be removed from the filaments at this point. control of moisture plus solvent and control of tension are both-essential to maintain the desirable amount of crimp in the staple roduct and to obtain. a well-opened and uniform length product.

The excellence of individual fiber crinkles is of outstanding importance and enables large denier fibers to be readily formed in spun yarns without necessitating special apparatus. By suitable adjustment, the frequency and intensity of crinkle may be varied through a wide range, sayfrom 5 to 30 crinkles perinch with amplitudes of from V of an inch to /4 of an inch.

It is desirable to remove nearly all the solvent remaining in the fibers after cutting and to adjust the moisture content to that at which cellulose acetate staple 'is normally sold. Any one of a A number of anti-static agents may be applied at this point (after drying) and preferably this is done by spraying a solution or an aqueous emulsion of the desired anti-static agent onto the stapie. Any of the following well known anti-static materials may be used for this purpose: diethyl cyclohexylamine salt of along chain sulfate, cetyl betaine, lorolamine hydrochloride, salts of triethanolamine, reaction products of long chain amides and dimethyl sulfate, and sodium potassium ethyl phosphate. v

I have found that only when the filament bundles are crinkled directlyfrom the spinning machine or when the solvent content is appreciable (as well as an appreciable moisture content) that a satisfactory tow for direct conversion can be produced. However, other factors are also essential to produce a satisfactory tow for this purpose. As indicated above, a relatively deep coarse crinkle should be impressed in the filaments in order that the fibers formed therefrom will have adequate fiber adhesion in the spinning operation, for without sufiic'ient and proper crinkle 5, 8 and i2 denier fibers cannot be handled in drawing operations.

When the tow of continuous crinkled filaments is to be shipped to a distant plant for conversion.

into top, it is desirable to wind the samein some sort of package from which it may be e unwound. However, the winding of the crin tow while itcOntalns in the neighborhood o or 30% moisture plus solvent and storing such Accordingly,

making the tow unsatisfactory for subsequent processing. On the other hand, when the tow of crinkled filaments isf'collected in loose coils,

for instance in a perforated basket, and uniformly dried to reduce the moisture content to 6.0%' or less and to substantially completely eliminate the solvent, it may be wound at relatively low tension and fibers are maintained in an essentially dry onto tubes to form. relatively large cylindrical packagess 12 pounds or more)- and even though stored for several months the crimp will be sumciently retained'for satisfactory processing. It

is best to apply a finish at the spinning machine 15 free from any anti-static agent; for in subsequent, cutting operations, the electrostatic'charges on the filaments cause the cut fibers to strongly repel each other with the tendency for bundles of in'size, for example, from 20,000 denier or less to theiilaments without losing-their parallelism and directly form therefrom a top, it is to be noted that during cutting a smallbut positive pull is needed to efiectively separate the filaments and 3e prevent bundles. Because the tow of crinkled filaments after being subjected to tension is comprised largely of individual and separated fila-' merits, when subjected to cutting, there is much by scissors or other coacting bladecutters, This improved resistance to fusing greatly widens. the field of utility of this tow as compared with prior art tows of dry cellulose acetate filaments, for

heretofore it has been considered essential to cutv 40 dry cellulose acetate filaments with a single non-' coacting blade to prevent fusing and sticking together of the cut fiber ends.

By following this invention an exremely wellopened, essentially untangled, controlled crinkled 45 cellulose acetate staple fiber of good strength that is eminently suited for handling on the cotton. woolen or worsted system to produce spun yarn of excellent quality may be produced. The tow filaments to separate. The tow may vary widely greater resistance to fusing even'th'ough severed aseaasa of crinkled filaments made and handled inaccordance with this invention is extremely well suited for use in continuous processes for conversion of continuous filaments into staple and maintainingtheir substantial parallelism throughout the processing to produce a top or sliver. The very large bundle of filaments which can be crinkled or cut at one time and at a reasonably high rate of speed makes this process extremely economical to operate and because the filaments moisture), no expensive drying steps are needed as in thecase where cellulose acetate fibers are crinkled by means oi hot water or steam. More important than all the aforementioned advantages is the production of a uniformly high quality product which is easily and readily controlled according to the demands of the trade.

I claim:

The process which comprises forming a; tow comprised of a plurality of cellulose acetate filaments oi uniform denier within the range of 1.5 to 20 deniers, adjusting the moisture plus solvent content of said tow to within limits determined by the following formula, wherein at is .the denier of the filaments:

Per cent moisture+solvent= log dd+2:6

the moisture plus solvent content in no case to be less than 8% or more than 40% by weight based on the weight of the dry cellulose acetate filaments, imparting to said tow 'by mechanical means a uniform crinkle, said crinkle being substantially transverse to the longitudinal axis of the filaments, cutting the crinkled tow into staple of uniform length while maintaining said tow under a tension within the range of from 0.005 to 0.04.- gram per denier,'and at a moisture plus solvent content within the limits determined by the following formula, wherein d is the denier of the filaments:

Per cent moisture+solvent=40 log d-difi the moisture plus solvent content of the tow during cutting in no case to be less than 5% or more than 38% by weight based on the weight of the dry cellulose acetate filaments.

Gm s'ramnr Ho'ornn.

Images