US2249607A - Method of dyeing cellulose acetate and dye bath compositions - Google Patents

Description

July 15, 1941. l. c. GALA-rloTo METHOD 0F DYEING` CELLULOSE CETATE AND DYELBATH COMPOSITIONS Filed Apr-11 24, 1939 QN Om Qa. QS

'da -yanlvasdwsz 15311;

Patented July 15, 1941 METHOD OF DYEING CELLULOSE ACETATE AND DYE BATH COIVIPOSITIONS Luigi C. Gala'tloto, Providence, R. I., assigner to Atlantic vRayon Corporation, Providence, R. I.. a corporation of Rhode Island Application April 24, 1939, Serial vNo.y 269,661 .24l Claims. (Cl. 859) The present invention relates to a method of dyeing cellulose acetate, in its various forms, such as yarn, woven fabrics, films, sheets or the like, and to dye bath compositions of suitable characteristics for carrying out the method.

Cellulose acetate, as originally made, was obtained by the complete acetylation of cellulose to form the tri-acetate or tri-acety cellulose. This product was utilized for a considerable period for various purposes, but it was repellant to water and to liquids generally and accordingly presented many serious difllculties in dyeing. Subsequently, it was found that by rst acetylating cellulose to the tri-acetate and then partially hydrolyzing back the acetylated compound, a product was obtained which was softer, more susceptible to wetting with liquids, including water, and which, with some dyes, could be colored. But the color was not fast.

This acetylated and partially hydrolyzed product is technically known as secondary acetate and is the product now made and used practically exclusively as cellulose acetate. Itis this product which forms the subject matter to be treated and dyed by the present process, as setforth in the following disclosure.

It is therefore an object of the present invention to provide a method of procedure and suitable reagent solutions' and dye bath compositions, which shall render it possible to dye present-day cellulose acetates-and the various products which may be made from them-such as fibers, yarns,

fabrics, films, sheet materials, granules, coatings'.

and the like-withacid dyes, to aA satisfactory range of colors and color values (such as those of the Standard Color Card of America) on'a practicable basis for commercial operations and results. It is also an object to provide a method and dye bath compositions which may be definitelyA relied upon to dye the goods under treatment effectively, and fast to washing and to light, and to a controllable degree of depthof color, including both dark andlight shades, with a pleasing quality of appearance, etc-and at the same time to retain. the desirable qualities ofthe original secondary celluloseY acetate such as tensile strength, elongation, luster, feel, lay of the fibers, smoothness of surface, etc. Other objects of the invention will appear from the following disclosure.

l It is now found that cellulose acetate as at present made and sold on the market in various formswhich is the secondary acetate as above pointed out-may be satisfactorily `and permanently'dyed with acid dyes, provided certain conditions are developed and maintained with refergenerally recognized with free cellulose bers in the form of paperthat it spontaneously takes up by adsorption and retains about 'l to 8% of moisture, by weight, even from a normally moist atmosphere. Such adsorption appears to be mechanical, rather than chemical, and the adence to the material under treatment, and to the dye bath and dyeing operations.

It is a common property of cellulose-which is sorbed moisture is retained upon the surfaces, since no swelling is observed to accompany the gain or loss of this moisture.

It is now observed that cellulose acetate, of the type under consideration, manifests a similar adsorption when immersed in water. With cellulose acetate in the form of a sheetno appreciable change in the dimensions of the sheet is observed either upon adsorption or expulsion of this amount of water, which is about 7% by weight. 4It may, therefore, be considered as a mechanical adsorption of water by the cellulose acetate surfaces. It is thought that this adsorbed Water may associate itself with the cellulose component of the cellulose acetate molecule, upon the free surfaces, analogous to the adsorption of water by free cellulose itself, above mentioned. Additional mechanical associations with water ma-y also occur, however, which are attributable to lthe porosity of the sheet and the corresponding volumes of the interstices therein as well as adsorption on free surfaces. Thisis indicated by the fact that cellulose acetate films from different sources exhibit varying degrees of preliminary adsorption.

Similar moistening of cellulose acetate yarn may in some instances be accompanied by an apparent', increase in dimensions as indicated by a slight elongation of the material, upon wetting. But such increase is slight and may be attributable to the release of surface tension of the dried surfaces or to slight slippage of the moist bers over one another, rather than due to swelling effects of moisture upon the individual fibers.

Moreover, capillary attraction between the fibers enters into the wetting of cellulose acetate yarns upon immersion in water, so that the mechanical adsorption and absorption manifested by them (under conditions mentioned hereinafter) is of the order of 42% by weight, in contrast to 7%, by weight, mentioned above with reference to sheet materials.

It is necessary to remember that cellulose acetate, in whatever form it is regarded for the puracetyl groups it is subject to further saponification and hydrolysis under alkaline conditions, with further loss of such acetyl groups, on the one hand; and on the other, it ls subject to esteriiication by combination with additional acidic groups, under sufficiently acidic conditions. But further saponication or hydrolysis tends to swell it and render it less desirable, since the physical and dyeing properties are altered. Further esteriflcation-e. g. to the tri-acetate-Would render it more resistant to wetting by water solutions.

Nevertheless, partially hydrolyzed or secondary cellulose acetate is soluble in various organic solvents, and many of these solvents are, in turn, soluble in water. A series of water solutions of such solvents, containing increasing concentrations of such solvents, may be prepared and applied to the acetate, with varying effects accordingly. In very low concentrations, such solutions resemble water alone, as would be expected, and have no effect. But with increasing concentrations of the solvent, in aqueous solution, depending somewhat upon the specific solvent in question) there is a threshold point at which such solvent solutions appear to penetrate the cellulose acetate much more readily than water and ultimately to diffuse through it completely, without any tendency yto swell or disintegrate it. The first observable effect of treating cellulose acetate with solvent solutions of increasing concentrations is that with each solvent a concentration will be reached at which the cellulose acetate treated therewith loses its brilliant surface luster. This effect is referred to as "de-lustering, and

indicates that the surface of the acetate has been affected, at least sufficiently to alter its optical characteristics in respect of the uniform reflection of light. Such concentration of solvent, therefore, is a critical point in such treatment, with reference to cellulose acetates to be dyed. Upon further increasing the concentration of the solvent solution it will be found that it will later reach a point at which the absorption from the solution by the acetate treated therewith undergoes an abrupt increase in proportion, by Weight. The cellulose acetate also gives evidence of exercising a more retentive absorption of the aqueous solvent solution at this point, and swells. Increasing the concentration of solvent, therefore, leads to a solution which is capable of effecting first a very definite attack upon and finally a disintegration of the cellulose acetate, which may involve first a shrinkage, in over-al1 dimensions, followed by dispersion of the same and ultimately complete dissolution of the acetate, as is accomplished, for example, by the pure solvent itself.

While specific data, with reference to a given solvent, will vary from that for another solvent or solvents, it may nevertheless be stated that in general aqueous solutions of solvents of cellulose acetate are characterizedy in increasing concentrations, by three successive stages;

(l) A threshold concentration at and above which the solution exhibits a wetting and penetrating capacity toward the cellulose acetate which is markedly greater than that of water, but without other alterations;

(2) A critical de-lustering concentration, at which the solution causes an alteration in the optical properties of the surface of the cellulose acetate, whereby its reflection of light or lustre is noticeably affected or diminished, and the acetate issaid to be de-lustered but otherwise the material is not substantially changed; and

(3) A critical swelling concentration, at which the solution exhibits a tendency to cause the acetate to undergo marked increase of absorption and to swell, and above which disintegration and ultimately complete dispersion or dissolution of the acetate ensue. (See Table 1.)

EFFECTS 0E TIME AND TEMPERATURE It is further found that, with any given solvent solution, of fixed concentration, the percentage of absorption of the solution by the cellulose acetate (by weight) first very rapidly increases to a maximum, and then decreases, and again increases, ultimately exceeding the first maximum, as the period of time of immersion in the solution is progressively increased. (See Table 2.) Also, that Ithe percentage of absorption (by Weight) similarly first very rapidly increases and then decreases and again increases as the temperature of the solvent solution used is progressively increased. (See Table 3.) In some cases a tendency to shrink in dimensions also may be observed under these conditions. Accordingly, there is a tendency for a continuously wetted and/ or heated acetate, in contact with an aqueous solution of one or more of its solvents, to reach a point where it tends to resist further absorption or even to expel absorbed solution and to contract in its over-all dimensions.

Since the use of solvent solutions of increased concentrations tends so greatly to control the increase of absorption of the solution by the acetate,-the opposite effects of increased time and/or temperature of treatment (which in the present dyeing operation are usually standardized or fixed) are in general overcome or subordinated by the control or selection of the concentration of the solvent solution. But these tendencies of time and temperature apply to solutions of high concentrations of solvent as well as to the more dilute solvent solutions, and are extremely important, as will be pointed out below.

Results of experiments carried out upon cellulose acetates from various sources in the form of thin lms, with solvent solutions of increasing concentrations are set forth in the following table:

TABLE 1 Percentage increase in weight and length of various films3 in jormic acid Celanese l Corporation Bright acetate Time: 30min. Temp.: 125 F. l Weight changes, top figures. I Length changes, bottom iigures. l These illms were obtained by dissolving the named yan1 in acetIone and casting films upon a glass plate by the usual technique oss,

Eastman 3 dull acetate rayon (1) Viscose Du Pont Co. Bright Acele Du Pont Co.a Dull Acele (l) These results show that aqueoussolutions of formic acid of increasing concentrations cause in general a. continuously increasingl absorption of the' cellulose acetate films treatedi therewith, ac= companied by increasing dimensions-(elongation). of thefilms. Also thatsome films may take up 8-15%, by weight of solvent, without corresponding increase in dimensionsor even with a subsequent appreciable decrease in dimensions. The effects of varying the time'of immersion of the acetate in the solvent solution (ofvarious concentrations) at constant temperature-125 F.-wil1 be shown from the following table:

TABLE 2 Percentaye increase. in weight and length of celanese film in formic acid The eilects of varying the temperature of various concentrations of the solvent solution, in which the acetate is immersed for a given period of time (30 minutes), is shown by the following table:

TABLE 3 Percentage increase in weight and length of celanese film in formic acid Temperature factor Formic 30 min. 30 min. 30 min. 30 min. 30 min. 60 F. 90 F. 125 F. 150 F. 190 F.

11. 7 9. 9 8. 1 5. 0 5. 1 l l.. 2 1. l 0 0 l 1. 2 15.7 8.1 8.4 7.8 7.7 2. 2 1. 2 0 0 5.9 20. 7 V14.8 12.9 10. 5 9.9 2. 4 1.1 1. 3 o 1.1 25. 3 y18. 5 15.1 13.8 15. 5 2%.?. i 3'? i 22' 1 1 -3 1.6 25% 13.0 8.9 6.2 1.1 o

l Weight changes, .top figures.-

I Length changes, bottom figures.' Tiinfaetor' 25 'm5- f Analogous data forxcellulose acetate yarn is 5 nin. l 1o rgiin, 3o 12in. conningiven in the following table, with increasing con- 125 F' 1.25 F.' '125 F". 125. F centrations of the aqueous solutions of 4various .i lcellulose acetate solvents-with indications of Water alone-f (7)2 30 Vwhether or not thesolvent solution of any par- .'For'mieacid (cally-umana .l 9 tcular concentration lin question has delustered 5% 8W?? TTT. 'I 9.7 6.8 9.1' 9,0 the yarn and h ence equals or exceeds the criticali 21.1 point with respect to cle-lustering. All of these 1H 1,12 0 ,12 samples of acetate yarn were liberated from ex- 15.0 lill) 112. 35 cess of the solventsolution by uniform treatment 1618 15j, 141-, in the centrifuge to give comparable results. It 123.1) 1% should be noted that the yarn manifested an 2,5% ,jg 61.1 6;'2 516 initial mechanical absorption of water of 41.9%

40 by weight (under the conditions hereafter described) and that all of the solvent solutions lWiht ha es,t fi res. 2 Leggo; ghaesbgtolgmes. used upon the acetate had the effect of increasing the absorptivity iigure.

TABLE 4 Absorption' of dye bath by cellulose acetate yam in percent of bone-dry weight of yarn Pfacgff 80% acetic 85%iormic ,Ascetic 85%10ti0 100%igllll- 100%a. C mi (by. y y ,/z tornje y ene c orf one on ons volume) weight) weight)V weight) hydrm 5 `44.901; 5230K 4910K. 47.5vsL. 53.30K. 4570K. a/ioo/s Bright- 1o 4910K; 55.0SL.. 45.esL. 41.5SL. .56.51355 4590K. A5515 (skein 2 15 v53.9sL. 54.2Bad 41.513191 46.9 sL. 50.91395 49.9SL. on.) ao min. .29 y 52.51355 41.913511 455.915511 56.8 sL. 83.21555 49.215 125 EL (A) 52.91355 53.313551 51.21355 59.9 SL. v101.0131111 49.311511 sona)` 1 92.6135@ 57.31355 y 51.51555 59.5 sL. 1122.013115 50.71355 1oV Y. 79.915511 resoa'd Smead .59.1 sL. (2)v .94.91355 `5o y 1137.115911 4223.313541 1157.313115 91.9M0d. (I) l 96.913541 Commentsv referto effect on luster: OK.-luster` unaffected. vSL.- luster very slightly aected. SL.-luster slightly aected. v Mod-.luster moderatelyaected.

Bad-luster badly allected. l-skeln barliy-y attacked.

i-sken too badly attacked to extract in centrifuge.

(A). No dye used' in dye beth solution.

(B) Bone-dry weight determined on seperate skeins from those used in the dye baths.

It will be noted from these results that an aqueous solution of solvent, having a concentration of 5% or more has the effect of enhancing the absorptivity of the acetate above that of water alone (41.9%). Also, that this increase of absorptivity continues with solutions oi' increasing concentration of solvent, but that it generally ceases to increase or even declines at the higher concentrations and then resumes its effect of increasing absorptivity up to the point of disintegration or dissolution of the acetate by the highly concentrated solutions oi solvent.

`In respect of increasing concentration of the various solvent solutionsl used, therefore, the threshold concentration of aqueous solutions of solvents of cellulose acetate may be taken as approximately 5%.

It is to be observedhowever, that the critical lpoin with respect to de-lustering of the yarn,

varies greatly depending upon the solvent in question. And with respect to the critical point of adsorption-characterized by a resumed or sharp increase' of absorption with increasing concentrations of the solvent-it will be noted that this also varies greatly depending upon the solvent used, and also follows the de-lulstering critical point by varying differences in concentration.

At such latter concentrations of solvent solutions-with due consideration o! the times and temperatures and other conditions and purposes of treatment-the yarn is usually so profoundly altered in its physical structure and composition that it can hardly be regarded as useful as a customary textile or'flbrous material.

Accordingly, in general, the safest criterion for textile dyeing purposes is to employ aqueous solutions of the acetate solvents which-at the times and temperatures of the dyeing or other process to be employed-willl effect an increase of absorption not exceeding the initial critical point-i. e., that with respect to concentration at which a de-lustering of the acetate occurs.

Graphs of the Vinitial or de-lustering Vcritical points for several solvent solutionsv are plotted against times and temperatures of treatment on the accompanying chart. From this it will be evident thatany one of the solutions of the concentrations indicated may be safely employed, with respect to cellulose acetate yarn, without danger of de-lustering the same, under conditions falling below the corresponding `lilies on the chart. l

Of course, as is well known, de-lustering of cellulose acetate yarn (or other acetate textile products) may not be undesirable but actually "desirable, from the 'commercial standpoint. In

such cases, the critical point with respect to delustering may purposely be reached or exceeded, so that de-lusteing is in fact effected upon the surfaces of the cellulose acetate under treat ment. But when this.is to be done, as will be obvious from the tables above and from the graph just referred to, precautions must be observed in order not to develop conditions of excessive absorption, by applying excessive concentrations, toolong periods of time or too high temperatures, with reference to the speciiic solvent or solvents whichl are being used.

But, within the limitations of concentration, of fthe aqueous solutions of cellulose acetate solvents, and of the times and temperatures of treat ment as above described, it is found that cellulose acetate products in general and more specifi- With products other than textiles it may well,

be practicable to ignore the critical points with respect to delustering or withA respect to increased absorption and thus to apply mild or drastic actions of the solvent solutions at will and dye with acid dyes-and still get eilective and fast dyeing, without detriment to the resulting product. But this is not the case with cellulose acetate yarn, iibers or textile materials generally.

It is now further discovered as a part of the present invention that within these limitations of treating cellulose acetate with aqueous solutions containing one or more solvents of cellulose acetate the latter may not only be dyed with acid. dyes, vbut more effectively and uniformly dyed, if further conditions in the dye bath are observed. i

In this connection it is thought that the preliminary absorption of solvent solution by the cellulose acetate,\ in moderate proportions, as above described, is attributable to the summation of three factors: (l) 'Ihe natural adsorptivity by the cellulose molecule of 7-8% by weight'ot'water or'aqueous solution; (2) the inclusion of the solvent solution in the interstitial and pore spaces of the cellulose acetate fibers or the like; and (3) the permeation and diusion of the aqueous solution of solvent throughout the cellulose acetate structure, perse, which remains in solid form tion; in such a system is increased to a suf-- flcient degree in any given case, (orvits action is enhanced by increased time or temperature of treatment), this solid-liquid phase tends to merge -into a liquid-liquid phase in which the cellulose acetate is liquefied. Thereupon the solid acetate tends to swell, because it partially goes into liquid solution, with'intermediate dispersion and hydrolysis by the water present, which induces swelling of the structure as a whole. This latter stage, of marked swelling and subsequent liquei'action of the cellulose acetate by the solvent solution, is definitely to be avoided in the conduct of the present invention, especially for the dyeing of textiles-for in such condition the cellulose acetate is unmanageable and loses its intrinsically desirable properties, as already mentioned. In such condition of limited increase ofweight by absorption and limited dimensional expansion or shrinkage, h owever, it would appear that the'cellulose acetate is uniformly and completely penetrated by the aqueous solution of its potential solvent, butv that dissolution of the acetate thereby is not appreciably effected.

'Ihe potential solvents of cellulose acetate are now found to be effective solvents for the dye acids of the acid dyes-even though used in the form of relatively dilute aqueous solutions. Such 2,249,607 solutions are therefore capable both of dissolv-V im man .dye acidsJand also of penetratincand diiluslng through thecellulose acetate as above described. Consequently, when in sumcient co n'` point of de-lusteringor swelling the cellulose l'litate. j

However, using most solvent organic acids alone (i. e., without. inorganic acids such as sul- -phuric) .it 'is impossible tol lower 'the pH lbelow 1.0-that is, below the limiting pH value required for satisfactory washing fastnes's-withoutv iniuring, the yarn. Nevertheless, it is possible to acetate, followed by washing and drying,`etc., the

distribution ratio ofthe dissolveddye between the'aqueous solution within the acetateand -in the exterior wash watelWillbe variously. altered, generally in the direction' lof removing the .dii-r fused dye solution from'the cellulose acetate, thus generally leaving a low color value in the material treated. Likewise, the residual ldye actually retained by the cellulose'acetate vwill notl be fast against subsequent washing. It is now further found, however. that an acid dye solution may be diilused uniformly into and through the cellulose acetate `as'thus treated andV simultaneously rendered eii'ective 'to dye -and become f ast' therein, if vthev dyebath'is impressed with a certain degree of acidity-namely, of sufficient concentration to have a pH value between 0.4 and 1.4, and preferably 'below 1.0 since' the depress the pH value below 1.4 with certain solvent organic acids alone, suchas for'mc acid, and thus 'to obtain-satisfactory dyeings where `great fastness to washingis not necessary. Such acidity may likewise be provided partly by the aoidf ity of the acetate solvent (such as formic and/or acetic acid) and partly by the addition of a stronger, inorganicacid-suchas sulphuric, hydrochloric and phosphoric acids-which vapparwashing' fastness is decidedly improved by operating below pH 1.0.

It appears to be lpractically immaterial lhowv this acidity or pH valueis obtained. It may be afforded by using a suiilcient concentration of an acidic cellulose acetate solvent, per.se,if this does not atthe same' time exceed'the critical entlyin the concentrations .necessary for .this purpose are without deleterious effect upon they absorption', structural formation vor otherphysical properties, of. the cellulose acetate iibers or fllms, butv whichdo, by enhancing the acidity vof thefdye solution, render .it eiiective. to form and to dissolvethe dye acid and to diiluseinto-and dye the -cellulose acetate structure uniformly Vthroughout to a fasaccmr, thedepth off 'cjolqr dependingdirectly upon theconcentration of the dyein the solution. Again, the cellulose .acetate solvent may be non-acidic, 'suchI as ethylene` chlore'.

hydrin. in .whence ne inorganic' acid* ense. may be reliedupon to provide the reguiredpH value.' v Using solvent compositions containing an ap. propriate :oncentrationI ot kcellulose acetate solv ent and o f mineral acid, in accordance with the foregoing, numerous. .skeins of cellulose acetate yarn were treated and results obtainedfin accordance with the following'table:

. Tam.: 5 v

v Efect ojvcuzousl bath conditions on absorption and Zuster of. yarn (Nota-.A11 acids by volume) Y l, .f

Concentratidraagld makeup l J Weight Treatment Weight Condi- Runn before bone alter .Mtisgp tion oi colniiiJ-l,g Acetic Formio H4804 mnd "um: yam 1.01.13 (8.5%) (20 BBJ f Percent Percent Percent Pmtmt Mn; F 8.3 f 8.31 8.13- j 70.91 65.80 101.07 53.60 OK.. 30-125 8.3 -.8.3 8.3 70.01 64.96 99.27 52.95 OK. '60-125 as 6.3 as 69.60 64.16 91.36 .60.40 0K.. 12o-125 8.3. 8.3 8.3 70.41 65.34 98.53 50.80 OK. 180125 8. 3 8. 3 8. 3 69. 64. 93- WJ 71 50. 50 OK. 240-125 8.3 .8,3 8.3 73.19 67.93. 107.56 v 58.34 Sl.` -360-125 8 3 3 3 8,;3 37.1) 35.39 54.36 53.60 0K. 30-80 8.3 8.3 8.3 42.80 40.05 62.49 56:10 0K. 30120 8.3. 8.3 8.3 62.12 58.81 89.04 51.42 Bad ,30- 8,3 8.3 8.3 i 69.62 66.00 92.34 39.190 Bad 30-160 8.3 8.3 8.3 64.70 60.04 87.72 46.00 Bad 30-180 2.5 2.5 as m41 69.36 91.55 40.80 .,.oK. 30-125 5 5 8.3 60.21 57.19 82.38 44.10 OK. 30-125 7.5 7.5 vas 6.9.83 66.19 95.16 -v 43.80 0K. 30.125 10 10 8.3 43.2) v 41.10 60.46', y 47.10 Bad f 3 0-125 2.5 2.5` .2.5 70.48 66.82 99.96 49.60 0K. 30-125 ,5 .5 f 5v 71.32'r .67.61- .101.04 :49.50 OK." 30-125 `7.`5` 7.5 7.5 69.37 65.76 98.5.0 49.82 E OK.l .3D-125 10 10 10%'A 70.63 66.96 100.17` 49. 62 Sl. 30.-'125 5 2..5. 68.98 64.03 i 94.15 47.06' OK. a 304125 10 15"" 70.45 65.38 94.69 44N OK.. 30-125 ,.15 7.5 69.67` v64.64* 95.90 '48.36 OK. 30"-125 20 10' 70.65.,v 65.46 101.68. 55.33 Sl.' 30-125 '.5 8.3 66.29 61.51 .51 47.15 OK. 30-125 k10 8.3 41% 45.58 67.40 47:70 OK. 30-'125 15 8.3 49.49, 47.04 68.61 45. 824 OK. 30-125 mm f' aan 41.88 4 39.90 i-saas 49.20. rs1. .3o-125 `5 2.5 43. 56. 41.44 l 60.61 45.78 0K. 30-125 ..10 5 ...51.26 48.70 'l1-.41,v v46.68 0K. 30-125 15 7.5 48.37 46.00 68.81 49.58 Sl. 30-125 m '10 69. 49 64. 47 97. 45 51. 19 Bad 30-125 5 8.3 '71.60 66.44 94.84 42. 75 OK.' 30-125 10 8. 3, 71. 81 66. 64 102. 54 53. 87 0K. 30-125 15 8. 3 71. 90 66. 72 103. 01 54. 18 0K. 30-125 al 8.3 71.29* 66.15 101.35 53.14 OK. 30-

In each case the yarn was conditioned-to 80%A humidity and calculated to bone dry weight, by analysis of representative skeins treated, and then freed from surplus `moisture after treat- Vment and weighed. These several weighings were all recorded and show that (with one exception) all of the treatments resulted in increased ab assaeor to the flanged top, which was t wide. TheI perforations in the side walls were diameter. 'I'he basket was first loaded, with three skeinsas used in these experiments, and then brought up to full speed in nve seconds, held at full speed of 4300 R.. P. M. for twenty seconds, and nnally allowed to coast to rest, usually taking about thirty seconds.

From these resinas it is demonstrated that mcreased concentration of the solvent, and accompanying increased absorptivity of the yarn. progress together.

Likewise, increased depth of shade in the yarn is effected by the dye bath, as thus induced by the presence of solvent, and full shades may be obtained in the yarn thereby. When the time, temperature or concentration of the'solution exceeds the critical point the yarn is de-lusteredmr even partially hydrated. For some purposes, as already noted, such de-lustering may be dirable, butif these conditions are carried too far the yarn or textile may be partially or completely decomposed so that the product is ruined. In such case the decomposed yarn may and usually does retain the acid dye therein, but the procedure is not one which can be 'successfully applied to cellulose acetate yarns, fabrics, `or other textiles.

It is believed that the free dye acid, which is liberated at the low pH values hereinabove recommended, is also thereby maintained in free acid condition and dissolved in the dye bath solution in this form. Also that these pH values, in the presence of the acetate solvent solution. condition the cellulose acetate throughout its structure, to a similar acidity and that under these acidic conditions the cellulose acetate and dissolved free dye acid react to form an insoluble, colored reaction product. Subsequent dilution' and washing with water will dissolve out and remove both the acetate solvent and the acid; but not the dye acid which has thus become associated with and within the solid cellulose acetate structure. That this is the case is demonstrated by the fact that while the acetate solvent which has also dissolved the dye and carried it into and throughout the cellulose acetate structure is still present both outside of and throughout the acetate ber it does not appear to be able to dissolve the dye and remove it from within the fiber structure'. At least the partition ratio of the dye in the solution and within the acid-dyed cellulose acetate ilber is diiferent from the partition ratio of the dye between the solution and the undyed cellulose acetate ber. In this respect, the results are quite different from those which obtain when cellulose 4etate is treated with a solvent solution of like con'centration and containing an acid dye in solution, but having ahigh pH value. Under such conditions, while the dye will dissolve and permeate the structure of thecellulose acetate fiber it will also migrate outwardly into the surrounding solution, upon dilution, washing. and the like.V

Another advantageous feature of the present procedure is that the yarn may be dyed in package form, by pressure dyeing-i. e., by pumping the dye solution through the wound yarn-much more readily than by previously known methods of dyeing acetate. In the present process, it is believed that the liberated dye acid is completely dissolved to form a true or molecular solution in the dye bath which consequently passes both between and into the cellulose acetate fibers and structure without segregation until within 'the cellulose acetate structure of the yarn and that here itbecomes permanently and uniformly iixed and insoluble.

By thus permitting the dyeing operation to be effected with dye acids and by the pressure method, it is also madepossible to use short liquor ratios, with consequent reduction in the amounts of dye bath compositions required and the residual amounts of solution left over after each given dyeing operation has been completed. For example, liquor ratios asxlow as 3 to 1 may be used as compared to formerly required ratios of 20-40 to l.

The application of the invention will be exempliiled by the following specinc procedures which are representative of its fundamental aspects of utility in the art of dyeing cellulose acetate with acid dyes.

The following uniform dyeing procedure was followed in each case shown in Tables B to l0:

Skeins of acetate yarn were wet out and secured in the ordinary way. They werethen entered into the dye bath. Up to this point all skeins were treated alike. In all cases the weight of the dye bath was 15 times that of the yarn.

and the dye concentration was 0.15% on the temperature can be 'increased to as high as 180 I". depending on fastness requirements.

Examples of the dyes which have been thus employed may be numbered as follows:

TAaLl 8 #1. Wool Fast Blue BLA Extra New Color Index No. 833.

#2. Am Rubinol 3 GP. (Patented) .Chemical Works Inc.

#3. mizarme cyanine Green ons nxm color Index No. 1078.

#4. Fast Silk Yellow G (Geigy Company). '#5. Milling Red BWG Color Index No. 430.

Sandoz TABLE 7 pH determinations of solutions having dierent amounts of acids corresponding to those of dye bath SOllLtiOnS l The code letters are those appearing in the specification below. Parts nre by volume.

Inasmuch as the acidity here involved is so high, colorimetric methods would not be satisfactory. Accordingly the values given in the table were determined electrometrically, using a Coleman Electrometer No. 3. Similar commerical apparatus could be used instead.

The pH readings at '72 F.' were taken with both the room temperature and the solution temperature at '72 F., in the conventional manner, the apparatus being standardized against a pH value of 1.00 for 0.1 N HC1 at 72. The standard against which the set was calibrated was 0.1 N HC1, which was taken to have a pH Value of 1.00 at 125 F. This was then further checked against 1.0 N HC1. at 125 F. Whose theoretical pH is and the actual pH value was found to be less than 0.001.

In taking the pH readings of the solutions at 125 F. precautions were observed to correct for the temperature dierence between the solutions and the room. In making these pH measurements and those of the solutions, the tem-f perature compensator of the set was placed in the Abath kept at 125 F. and the 0.1 N HC1 was kept by a temperature bath arrangement at 125 F. in the sample cup. The assymetry potential knob was adjusted until the set balanced at pH=1.00 Nhen testing the 0.1 N HC1. The calomel electrode Was at room temperature during all of the measurements. The solutions being tested at 125 F. were introduced at that temperature and maintained at that temperature by means .of a Water bath. Readings were taken at once and again after various intervals from 1 to 5 minutes. The pH variation between the different times of readings lwas generally less 'than 0.01 and never over 0.02.

TABLE 8 Quantitative comparison of color depth obtained with dyes of Table 6 used in dye baths having amounts of acids and pH values corresponding to those of Table 7 [An arbitrary scale is taken for cach color, from 0 to 20, the darkest shsd their; designated by 20 and absence of any dyeing deslgnate y l #2 v #4 #5 Run No. gg? Az o lxllrilgg Fast Silk Milling Rubinol Green Yellow Red It may be remarked, with reference to the data in the above table, that those dye bath compositions containing sulphuric acid and no organic acid solvent, are not to be considered as Within. the present invention. Sulphuric acid is not, per se, a solvent of cellulose acetate, an-d the dyeing results obtained are manifestly too low for consideration as being satisfactory. likewise solutions containing 5% of formic acid alone (and Without sulphuric acid) demonstrate that this concentration is at the threshold value with respect to its action toward cellulose acetate, and also of insuflicient acidity (pH 1.8) per se, to provide Ithe required pH (1.4) for imparting a fast dyeing eiect to the cellulose acetate yarn.

It is also found that results similar to those given above may be obtained by using comparable amounts of other inorganic acids, instead of sulphuric acid-such as hydrochloric acid and phosphoric acid-Which are actually equivalent in the ratio 1:2:5 by weight, of 100% hydro.

chloric, sulphuric and phosphoric acids respectively. Thus, using Azo Rubinol (#2) under conditions corresponding to A, B, G and H, the following comparative color values were obtained in dyeing:

Again, using lactic acid in place of the formic or acetic acids of the above tables yields effective results, the lactic acid being a decidedly less active solvent:

In the` commercial application of the process of the invention, especially for the dyeing of cellulose acetate yarns, it is particularly desirable to carry it out by the pressure method of forcing the dyeing solution through the yarn while it is in wound or package form. For this purpose, the apparatus described in U. S. Patent No. 2,125,937 is entirely suitable and convenient to use.

The yarn is wound in packages of about a pound and these are loaded upon hollow, perforated spindles, with a separator plate between the end of each package and the end of the one next to it. The full spindles (holding eight packages on each) are loaded onto the removable machine carrier.

In a given case, using acetate yarn of 200 denier, 64 filaments, 3 turns per inch, the full load may amount to approximately 1000l pounds. This is lowered into the dye machine and scoured with soap for 15 minutes at 160 F. to remove the softening oils on the natural yarn. The charge is then rinsed free of soap, extracted in a centrifuge, and dried at 150 F. for 20 hours.

The dye bath is prepared in the following manner.

4000 lbs. total weight of bath, are made up as follows:

1000 lbs. water 333.3 lbs. of 85% formic acid 333.3 lbs. of 84% acetic acid 333.3 lbs. of 20 Be. sulphuric acid solution (or 85 lbs 66 B. sulphuric acid and 248.3 lbs. water) 2000 lbs. water (180 F.) to dissolve the following dyes.

44.0 lbs. '(44% of weight of yarn) Alizarine Cyanine Green GHA extra 12.0 lbs.(1.2% of weight of yarn) Fast Silk Yellow G 2.5 lbs. (0.25% of weight of yarn) Wool Fast Blue BLA The dyes are dissolved in the 2000 lbs. of hot water and the resulting solution is put into the dyeing machine which already contains the 2000 lbs. of solvent solution, made up of the constituents, as listed above, and the two solutions are intimately mixed.

The yarn is then entered into the dye bath, and the bath is pumped through the packages for 30 minutes, at about 80 F. The temperature is then gradually increased to 125 F. and the dye bath circulated for 90 minutes. The dye bath is then dropped and the yarn is rinsed with three successive water baths to remove the acids. The yarn is then soaped twice at 170 F., rinsed, and softened in an oil emulsion rinse. The packages are then extracted by centrifuging and dried. The yarn is inspected for defects, and may be wrapped, and shipped in the package form.

I claim:

1. Method of dyeing cellulose acetate with an acid dye, comprising the step of treating the acetate with an acid dye and with an aqueous solution of an organic solvent thereof having a concentration between its threshold value and its critical point, with .reference to the absorption of the material treated, and an inorganic acid.

2. Method of dyeing cellulose acetate with an acid dye, comprising tho step of treating the acetate with an acid dye and with an aqueous solution of an organic acid solvent thereof having a concentration between its threshold value and its critical point, with reference to the absorption of the material treated.

3. Method of dyeing cellulose acetate with an acid dye, comprising the step of treating the acetate with an acid dye and with an aqueous solution of an organic solvent thereof having a concentration between its threshold value and its critical point, with reference to the de-lustering of the material treated, andan inorganic acid.

4. Method of dyeing cellulose acetate with an acid dye, comprising the step of treating the acetate with an acid dye and with an aqueous solution of an organic acid solvent thereof having a concentration between its threshold value and its critical point, with reference `to the delustering of the material treated.

5. Method of dyeing cellulose acetate, cornprising treating the same with an aqueous solution of one of its organic solvents having a concentration between its threshold kvalue and its critical point, with reference to the absorption of the material treated, and containing an acid dye or dye acid, at a pH valuebelow 1.4.

6. Methodof dyeing cellulose acetate, comprising treating the same with an aqueous solution of one of its organic acid solvents having a concentration between its threshold value and its critical point, with reference to the absorption of the material treated, and containing an acid dye or dye-acid, at a pH value belowr 1.4.

'7. Method of dyeing cellulose acetate, comprising treating the same with an aqueous solution of one of its organic solvents having a concentration between its threshold value and its critical point, with reference to the de-lustering of the material treated, and containing an acid dye or dye acid, at a pH value below 1.4.

8. Method of dyeing cellulose acetate, comprising treating the same with an aqueous solution of one of its organic acid solvents having a concentration between its threshold value Vand its critical point, with reference to the de-,lustering of the material treated, and containing an acid dye or dye acid, at a pH value below 1.4.

9. Method of ldyeing cellulose acetate, comprising the step of circulating through a mass of the same, under pressure, a dye bath composition containing an aqueous solution Aof an organic solvent of the acetate having aconcentration between its threshold value and its critical point with reference to absorption, and a dye acid in solution therein, and characterized by a pH value below 1.4.

10. Method of dyeing cellulose acetate, comprising the step of circulating through a mass of the same, under pressure, a dye bath composition containing an aqueous solution, of an organic solvent of the vacetate having a concentration between its threshold value and its critical point with reference to delustering, and fa'. dye acid in solution therein, and characterized by a pH value below 1.4.

11, Method of dyeing cellulose acetate, comprising the steps of treating successive charges of the same in a dye bath composition containing an aqueous solution of an organic solvent of the acetate, having a concentration betweenfits 2,24aeov threshold value and its critical point with reference to absorption, and a dye acid in solution therein, and characterized by a pH value below 1.4, and maintaining said dye bath composition by additions of the dye acid thereto.

12. Method of dyeing cellulose acetate, comprising the steps of treating successive charges of the same in a dye bath composition containing an aqueous solution of an organic solvent of the acetate, having a concentration between its threshold value and its critical point with reference to de-lustering, and a dye acid in solution therein, and characterized by a pH value below 1.4, and maintaining said dye bath composition by additions of the dye acid thereto.

13. A composition for use in dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of a dye acid and of an organic solvent of cellulose acetate, having a concentration between its threshold value and its critical point with reference to absorption at the temperatures and for the period of dyeing in question, and an inorganic acid.

14. A composition for use in dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of -a dye acid and of an organic acid solvent of cellulose acetate, having a concentration between its threshold value and its critical point with reference to absorption at the temperatures and for the period of dyeing in question. I

15. A composition for use in dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of a dye acid and of an organic solvent of cellulose acetate, having a concentration between its threshold value and its critical point with reference to de-lustering. at the temperatures and for the period of dyeing in question, and an inorganic acid.

16. A composition for use in dyeing cellulose acetate with acid dyes, characterized by containing an aqueous. solution of a dye acid and of an organic acid solvent of .cellulose acetate, having a concentration between its threshold value and its critical point with reference to delustering at the temperatures and for the period of dyeing in question.

17. A dye bath composition for dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of an organic solvent of cellulose acetate, having a concentration between its threshold value and its critical point, with reference to absorption, a dye acid, and a pH value below 1.4.

18. A dye bath composition for dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of an organic acid solvent of cellulose acetate, having a concentration between its threshold value and its critical point, with reference to absorption, a dye acid, and a pH value below 1.4. I

19. A dye bath composition for dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of an organic solvent of cellulose acetate, having a concentration between its threshold value and its critical point, with reference to de-lustering, a dye acid, and a pH value below 1.4.

20. A dye bath composition for dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution of an organic acid solvent of cellulose acetate, having a concentration between its threshold value and its critical point, with reference to de-lustering, a dye acid, and a pH value below 1.4.

21. Method of dyeing cellulose acetate with an acid dye, comprising treating the acetate with an acid dye and with an aqueous solution of an inorganic acid and an organic acid solvent for said cellulose acetate, said solution having a concentration between its threshold value and its critical point with reference to the absorption of the material treated.

22. Method of dyeing cellulose acetate with anA acid dye, comprising treating the acetate with an acid dye and with an aqueous solution of an inorganic acidl and an organic acid solventtor said cellulose acetate, said solution having o. concentration between its threshold value and its critical point with reference to the de-lustering of the material treated.

23. A composition for use in dyeing cellulose acetate withlacid dyes, characterized by containing an aqueous solution of a dye acid, an inorganic acid and an organic acid solvent of cellulose acetate, said solution having a concentration between its threshold value and its criti- 'cal point with reference to absorption, at the temperatures and for the period of dyeing in question.

24. Av composition for use in dyeing cellulose acetate with acid dyes, characterized by containing an aqueous solution o1' a dye acid, an inorganic acid and an organic acid solvent of cellulose acetate, said solution having an effective concentration with reference to the material treated between its threshold value and its critical point with reference to de-lustering. at the temperatures and for the period of dyeing in question.

LUIGI C. GALATIOTO.

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