US2278888A - Artificial structure and process for producing same - Google Patents

Description

April 7, 1942- E. v. LEWIS 2,278,888

ARTIFICIAL STRUCTURE AND PROCESS FOR PRODUCING SAME Filed Nov. 2, 1938 fverE/f Vernon [aw/Is INVENTOR BY ATTORNEY Patented Apr. 7, 1942 ARTIFICIAL STRUCTURE AND PROCESS FOR PRODUCING SAME Everett Vernon Lewis, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application November 2, 1938, Serial No. 238,316

Claims.

This invention relates to the production of dyed filaments, yarns, ribbons, films, fabrics and the like, comprising synthetic linear polyamides, having novel effects and appearances.

These synthetic linear polyamides are of two types: those obtainable from monoaminomonocarboxylic acids or their amide-forming derivatives, and those obtainable from the reaction of suitable diamines and dibasic-carboxylic acids or their amide-forming derivatives. These synthetic polyamides may be prepared, for example, by a process of condensation-polymerization such as is described in U. S. Patent No. 2,071,250. The diamine-dibasic type of synthetic polyamides is more fully described in U. S. Patent No. 2,130,948.

These synthetic linear polyamides are capable of being spun into filaments, yarns and the like directly from melt. These filaments as spun are capable of being cold drawn (stretched in the solid state) to 400-500 per cent of their original length whereupon their elongation is greatly reduced and they exhibit orientation of the crystals along the fiber axis as evidenced by -X-ray investigation. For example, filaments spun from polyhexamethylene adipamide, a synthetic linear polyamide having a melting point of about 265 C. and which can be obtained by the reaction of hexamethylene diamine and adipic acid, can be cold drawn approximately 400 per cent whereupon they exhibit an elongation of approximately per cent. Similarly in the case of films, wide ribbons or other formed structures where it is not convenient to cold draw (application of tensile stress) they may be cold rolled (application of compressive stress) to obtain orientation in the same manner. These oriented synthetic linear polyamide filaments, yarns, films, ribbons, and the like have a strong afilnity for dyes and can be dyed with acid and direct dyes.

It has now been found that the affinity of these synthetic linear polyamide filaments for dyes is dependent to a very great extent upon the degree to which the yarn has been cold drawn or cold rolled. In general undrawn (unoriented) yarn hasa greater affinity for dyestuffs than the drawn (oriented) yarn. When two yarns are drawn to different degrees the yarn drawn to the lesser degree usually has the greater afiinity for dyestuffs. These difi'erences in dye affinity are particularly apparent with direct dyes. These differences in dye affinity of undrawn and drawn filaments are very marked tently reciprocating bar 25.

and in many instances constitute the difference between strong and substantially zero afllnities,

respectively.

It is, therefore, an object of this invention to prepare dyed filaments, fibers, ribbons, yarns, films, fabrics, and the like having novel optical effects. It is a further object of this invention to prepare filaments, fibers, ribbons, films, yarns, fabrics, and the like having varying optical effects by a single dyeing operation.

Other objects of this invention will be apparent from the description which follows.

For convenience the invention shall be discussed with particular reference to cold drawn filaments and yarns produced from polyhexamethylene adipamide, although it is obviously not so limited. For example, the invention is not limited to cold drawing since other methods of imparting the desired orientation to the structure can be employed. The invention can be applied to films and ribbons as well as filaments and yarns. The invention is furthermore broadly applicable to structures composed of synthetic linear polyamides.

The details of the present invention will be more clearly apparent by reference to the following description and the accompanying diagrammatic illustration of one embodiment of apparatus suitable for imparting non-uniform orientation of crystals along the length of the filaments preparatory to dyeing the same.

Referring to the illustration, reference numeral N designates a wound yarn package. The yarn I3 is withdrawn from the package II and is passed upwardly through stationary yarn guide l5 and then abount drawing rolls l1, l9 and 2|, 23. The yarn is passed about the drawing rolls a sufficient number of times to prevent any material amount of slippage. The drawing rolls 2|, 23 are rotatedat a greater speed than rolls l1, i! so as to draw out the yarn to a reduced denier, thereby orienting the crystals along the fiber axis.

The prongs 21 and 29 of the forked member 3| are positioned on opposite sides of the yarn. The forked member 3| is attached to an intermit- As the yarn is drawn between rolls II, I! and 2|, 23 the bar 25 is intermittently reciprocated to impart, at intervals, an additional stretch or draw to the yarn.

The yarn is passed from the drawing rolls 2|, 23 to a yam guide 33 and thence to a follower 35 which is positioned on ring 31 of a ring twisting apparatus to be wound onto pirn 39.

As above indicated, the invention in its broad aspect comprises subjecting filaments or yarns comprising these synthetic linear polyamides to stresses in such a manner that the orientation along the fiber axis is non-uniform, and afterwards dyeing the filaments and yarns so produced.

These differences in the extent of orientation over various regions of these filaments or yarns may be produced in various manners. In general, these can be divided into three classes. In the first, filaments or yarns spun with uniform denier are drawn varying amounts by intermittently or periodically changing the extent to which the yarn is cold drawn during the drawing operation. In the second process, th yarn may be spun of non-uniform denier, or of uniform denier and of non-uniform drawing characteristics, and relatively large sections drawn a uniform amount, thereby causing the regions of smaller denier, or those sections which will draw most readily, to draw to a greater extent than those of greater denier. The third process is the combination by doubling, plying, twisting or the like of filaments or yarns drawn to various extents to form composite yarns.

Yarns produced by any of these methods are then dyed whereupon a novel appearance is obtained due to the varying dye affinity of the components. It is apparent that the yarns produced by the first and second processes will be of non- .uniform denier.

If a yarn of substantially uniform denier is desired, the yarns produced may be redrawn after the dyeing step to obtain yarns of substantially uniform denier. The novel optical effects produced upon dyeing. are not destroyed during this redrawing step. The optical effects produced are not to be confused with slight differences in appearance which accompany differences in denier of other textile filaments. Were these differences in optical appearance of these synthetic polyamide filaments due solely to denier difference, these differences would be destroyed upon redrawing.

The following examples are directed to a few illustrative processes showing, in detail, the preferred steps in carrying out the invention. The invention is not to be limited, however, to the details set forth in these examples.

Example I A 170-denier, 20-filament bright polyhex-amethylene adipamide yarn was drawn by passing it a plurality of times around a cylindrical drawing roll 2 inches in diameter, thence to an idenvent slippage of the yarn. These two rolls were positively driven, the second at a rate 4.1 times that of the firstroll (ratio 1:4.1). This differential speed continuously subjected the yarn between the rolls to stress, thus drawing it under normal conditions to 410 per cent of its original length (4.1 times its original length). The first roll was then subjected to random increases in speed over short periods such that the ratio of speeds momentarily became 1:1, care being taken that the source of supply of yarn permitted such changes in speed without causing drawing. The yarn passed from the lower roll to a down twister and was wound on a pirn. As a result of this variation in speed the yarn produced showed over long lengths an average denier of 50, but in the short sections drawn when the ratio of the speeds of the two rolls became 1:1 the denier was 170. This yarn was then boiled off in the usual manner used for silk or wool and dyed in a solution containing 0.1 per cent of Pontamine Skyblue 63X, Color Index No. 518, 1 per cent Pontacyl Light Yellow GX. Color Index No. 639. (respectively direct and acid dyes) and per cent common salt. The yarn was then rinsed and dried in the usual manner. Upon dyeing, the

region of higher denier (substantially undrawn) has assumed a deep green color while the region of lower denier (substantially fully drawn) showed a pale yellow color. "The short sections of varying denier where the denier was changing (partial drawing), showed a gradation of color from green to yellow and vice versa.

Another sample of the undyed yarn was knitted into a fabric and the fabric itself dyed in a similar manner. A fabric of attractive appearance was produced, the regions of contrasting color giving very; novel effects. A fabric knit in the same manner from the dyed yarn had a similar appearance.

Example 11 A 240-denier, 30-filament unoriented dull polyhexamethylene adipamide yarn was drawn nonuniformly in the same manner as described for Example 1 except that the normal relative rates of rotation of the rolls was in the ratio of 1:3. The drawn yarn was then wet with water and passed through a bath of turbine oil held at 150 C. at a rate of 100 feet per minute and a bath travel of 5 inches. The yarn was thenwashed and rinsed free of oil and cold drawn while wet with water an additional 13 per cent, skeined and allowed to dry, whereupon it crimped. The skein was then dyed by a standard dye procedure with an acid blue dye having the composition 1- amino-2-sulfo-4-ortho-sulfo-para-tolyl aminoanthroquinone. The resulting yarn showed a variation or shades of blue from section to section accompanying the differences in orientation.

Example III A 20-filament bright polyhexamethylene adipamide yarn was spun directly from melt. The extrusion and draw-off rates were adjusted to yield a yarn having an average denier of 170, but at intervals the pumping rate was abruptly increased to increase the denier to approximately 340 over one inch lengths of the yarn. This unoriented yarn was then pretwisted to 4'turns per inch and drawn between two cylindrical rolls 2 and 3 inches in diameter respectively, located with their centers 12 inches apart and operating at a constant peripheral speed ratio of 124.1. The speeds of the rolls irr this instance were not subjected to any changes. Upon examination of the yarn it was found that the average denier over long lengths was approximately 50, indieating an effective drawing ratio of approximately 1:3.4. It was found, however, that the denier of the heavier portions of the yarn was approximately 200 corresponding to an effective ratio of approximately 1 1.7, due to the fact that the substantially uniform tension supplied drew the several sections in varying amounts.

The resulting yarn was dyed in the same manner as'described in Example I, and it was again found that the regions of low orientation (drawn less than 340 per cent) had assumed a deep green "color while the regions of high orientation (drawn more than 340 per cent) showed a pale yellow color. In the intermediate regions bevice versa, drawing the yarn showed a gradation I from yellow to green and vice versa.

Example IV device was provided which g ipped the yarn se-' curely at desired intervals and for a desired period. This device was adjusted to grip the yarn at points corresponding to every 15 inches of drawn yarn and for the period required to produce inch of normally drawn yarn. The resulting yarn showed an average denier of 50. When examined carefully in the order in which it was drawn, short sections were found in which the denier dropped abruptly, followed by short section in which the denier increased to more than 50, which in turn was followed by still another section in which the denier decreased again to the average value of 50.

The yarn was then dyed in a normal manner with Pontacyl Fast Blue 5 R Conc., Color Index No. 289. The resulting yarn showed a much lighter shade of blue in the areas of high orientation than in those of low orientation. This difference in appearance was due to a true difference in dye affinity.

Example V A 1'70-denier, 20-fllament dully polyhexamethylene adipamide yarn was drawn between rolls having two inch diameters, mounted on 6-inch centers and operating at a constant drawing ratio of 3:1. At a point one inch below the first roll a rod of elliptical cross-section having a one inch major axis and a 4 inch minor axis, heated to a temperature of 100 C., was mounted and rotated in such a manner that it was'brought intermittently into intimate contact with the yarn. When the yarn so drawn was examined it was found that the average denier over long lengths was approximately 58, but accompanying each contact with the heated rod the denier first dropped rapidly and then increased abruptly, and finally returned to the average value of 58. When this yarn' was dyed in the manner described in Example I it was found thatthe yarn had a mild green color interspersed with sections showing a pale yellow color, and others showing 'a deep green color.

Example VI Another portion ofthe same original yarn was drawn 200 per cent and given the same treatment in the tetrachlorethylene bath, wet with water and drawn an additional 183 per cent and kept wet. These two yarns were then plied with one turn 8 twist, skeined and allowed to dry. Upon drying the yarn crimped. The crimped yarn so prepared was then'dyed as in Example 11. The resulting yarn had a pleasing two-tone effect in blue as a result of the difference in the 2,278,888 tween regions of maximum and minimum, and

extent of drawing or the t o plies, and since the denier was constant this e ect could not be attributed to differences in denier.

Example VII Some of the same unoriented yarn used in Example VI was cold drawn 200 per cent, wet with methanol, and passed through a tetrachlorethylene bath as described in Example VI. This yarn was then wet with water and divided into two parts, one of which was drawn an additional 183 per cent while the other was drawn an additional 130 per cent. The two portions, kept wet, were then plied with 4 turns 8 twist per inch, skeined and allowed to dry whereupon they became crimped. The skein was dyed as in Example VI whereupon a similar two-toned effect I was obtained.

Example VIII Some of the unoriented yarn used in Example I was drawn between two rolls, the first having an elliptical cross-section with a major axis of two and seven eighths inches and a minor axis of one and seven eighthsinches, the second being of cylindrical cross-section with a diameter of two inches. The two rolls were positively driven at a ratio of speeds of 123.8. The oriented yarn produced showed an average denier of 50, but upon close examination showed a cyclical variation in denier above and below this value corresponding to the elliptical circumference of the first drawn roll. The yarn was dyed as in Example IV. The dyed yarn showed a cyclical variation from light to dark blue accompanying the differences in orientation. This variation in optical appearance in a predetermined manner was very attractive.

Example IX A portion of the oriented, dyed yarn produced in Example I was redrawn between rolls 2 inches in diameter mounted with their centers 24 inches apart and operated at a constant drawing ratio of 1:12. This drawing with widely separated rolls produced a yarn of substantially uniform denier with an optical appearance similar to that of the original dyed yarn of non-uniform denier.

This yarn so treated Examples of other dyes which show particularly notable variations in dye affinity with the du Pont Anthraquinone Rubine R cone In general these differences in dye aflinity are most pronounced at relatively low concentrations of the dye baths. At high concentrations, especially at excessive concentrations, the differences in appearance while still apparent are less pronounced.

The examples illustrate various methods of obtaining non-uniformly drawn yarn from yarn of uniform or non-uniform denier, but it is to be understood that the invention is not so limited. The peripheral rates of either or both of the draw rolls may be varied to change the effective draw ratio. Likewise, the draw rolls may be cylindrical and either or both mounted of! center and driven at speeds of a constant or variable ratio. Similarly, draw rolls of elliptical crosssections or other non-circular cross-sections mounted and driven in various ways may be used. Similarly, various other combinations may be used.

While the preceding examples illustrate the invention by the use of dye baths containing one or two dyestuffs, it is within the scope of theinvention to use dye baths of more than two dye components. Similarly the filaments, yarns, fabrics, films, ribbons, etc., of the invention may be dyed in a plurality of dye baths -to obtain these novel effects. a

The elongation of these polyamides and/or the force required to cold draw them may also be varied by varying the conditions under which they are spun, e. g., variation in rate of spinning and/or rate of cooling. For example, during the spinning operation the rate of chilling of the freshly extruded filamentary streams may be varied abruptly and rapidly. The rate of cooling' and resultant crystal formation affects the force required to cold draw. As a result, when this non-uniformly chilled yarn is cold drawn at a constant draw ratio certain sections will draw more easily resulting in a drawn yarn of non-uniform denier. Advantage may also be taken of these properties by doubling such yarns or varying the treatment on the same yarns, and then subjecting them to cold drawing. The resulting yarns will have some regions drawn more than others or many of the filaments may break with attendant dyeing differences.

While the differences in degrees of dyeing in many of the yarns illustrated by the examples are accompanied by differences in denier the invention is not so limited. The differences in denier may be reduced considerably by redrawing th dyed yarns at constant tension or with widely separated rolls. Drawing at constant tension may conveniently be done by the use of slip drives on the draw rolls; these may be operated mechanically, hydraulically or electrically. The

redrawn yarns will be of a much more uniform denier and elongation as a result of this redrawing operation and their attractive and novel ap pearance will not be seriously affected.

While the examples illustrate novelty effecfs produced on crimped polyamide yarns by variation of the extent of cold drawing, it is apparent that other modifications are possible including uneven or non-uniform treatment with wetting agents, varying baths, bath concentrations and/ or temperatures.

Novelty effects other than those resulting from dye affinity may be produced in'a variety of other ways. For example, if the filaments contain insoluble pigments, delusterants, etc., other differences in the amount of cold drawing become apparent. This may be reflected by an increased luster with greater degrees of cold drawing or even in speckled effects at higher ratios. Likewise this insoluble matter may be itself capable of orientation with respect to the surface of the filaments, yarns, ribbons and the like, e. g., pearlessence, aluminum powder, etc. It is also apparent that novel optical effects will be attained by combination of the variable dye effects with these pigments.

Other similar novelty effects can be produced by combining these pigmented or. delustered yarns with unpigmented yarns, or spinning yarns ity of these polyamide products is somewhat de- Y creased by hot water or steam treatments. Advantage can be taken of this by doubling undyed yarns at least two of which have been steamed varying amounts, or undyed yarns may be steamed non-uniformly along their length or undyed fabrics may be steamed non-uniformly When the resulting structures are dyed novel effects are produced. These novel effects may be further varied by the application of the process of the invention.

Other novelty effects may be produced by the combination of yarns, filaments and the like having varying dye affinity due to their chemical composition. For example, various dye modifiers may be added either to the molten filamentforming composition or to the monomeric reactants from which the polymer is prepared. Likewise the various monofunctional carboxylic acids or nitrogenous bases, added to the monomeric reactants from which the polymer is formed to obtain polymers which do not undergo appreciable viscosity changes when maintained at elevated temperatures, affect the dye amnity. Filaments or yarns containing these different compounds may be plied or fabrics may be knit from them and subsequently dyed. Likewise polymers having different dye aflinities may be blended before spinning or spun simultaneously from the same or adjacent 'spinnerets and .ioinedginto the same yarn.

As indicated above, yarns prepared according to this invention have a very pleasing appear-,- ance and are useful for a variety of purposes, and advantage may be taken of these dyeing differences in the reparation of various fabrics of novel appearance. The yarns of this invention, like synthetic polyamide yarns uniformly dyed, are useful both as continuous filament yarns or they may be cut into staple length fibers and gspun into yarns. 'Both the crimped and uncrimped yarns are,valuable for these purposes. These synthetic polyamide yarns may be used singly or they may be combined with other yarns by well-known processes of doubling, twisting, and/or plying Spiral yarns may be prepared by winding a coarse yarn about a finer yam as a core to give the effect of a spiral. For example, an uncrimped synthetic polyamide yarn may be wound around another crimped or uncrimped yarn or around a yarn of another material such as a silk, cotton wool or cellulosic rayon yarn. Similarly, the crimped synthetic polyamide yarn might be wound about a crimped or uncrimped yarn as a core, or the crimped or uncrimped yarn may be used as the core about which any other type ing the formation of nubs spaced at intervals. Similarly, loop or boucl yarns may be prepared by a twisting operation wherein one of the ends is loose thus causing it to twist on itself forming a loop. The diameter of the loop is governed by the speed at which the two yarns are fed to the twister. Various combinations of uncrimped and crimped synthetic polyamide yarns in combination with themselves or other com-' mercial yarns are useful in'this connection.

Flake or slub yarns may also be prepared the outstanding characteristic of which is that one of the plies is very coarse and forms bunches. The flakes may comprise tufts or roving inserted between binder yarns at intervals or they may be formed from continuous yarns. Various combinations of uncrimped and crimped synthetic polyamide yarns (staple or continuous filament) may be combined with present commercial yarns in various manners. Attractive yarn of this type may be prepared taking advantage of dyeing differences due to cold'drawing.

Yarns of attractive appearance may also be prepared by plying together two or more ends of crimped synthetic polyamide yarns in one direction, and then plying together two or more ends of the yarn so produced an equal number of turns in the opposite direction.

Other yarns may be prepared by plying two or more ends of crimped or uncrimped synthetic polyamide yarns, at least one of which is undrawn and at least one other drawn to some extent or in which at least two have been drawn difierent amounts so that they retain varying amounts of residual elongation, and then redrawing a sufficient amount so that one end breaks and leaves loose ends sticking from the yarn. If the yarn produced by plying the ends which have been drawn varying amounts is dyed before further drawing occurs the pleasing optical efiects of this invention are produced. If more level dyeing effects are desired the amount of original drawing of the two components should be so adjusted that the unbroken filaments will be almost completely drawn. The yarn should then be dyed after the drawing operation.

Advantage may be taken of the ability of these synthetic polyamide yarns to be cold drawn to produce yarns and fabrics with various other novel effects. Undrawn or partially drawn synthetic polyamide yarns may be combined with feeding crimped and uncrimped yarns to the twister at the same rate. When such yarns are 1 subjected to stress, the uncrimped yarn bears the tension and prevents the crimped yarn from straightening out. Yarns having similar utility may be prepared by doubling two yarns of these crimped synthetic polyamide yarns and feeding them to the twister at different speeds. The composite yarns so produced may then be doubled in the reverse direction with similarly prepared yarns. The resulting yarn has high bulk of the loose crimped elements; i. e., those fed at a greater rate are intimately held so they will not slip over the tighter element.

Twistless yarns may also be produced. Such yarns may be prepared from staple length fibers, either the crimped or uncrimped synthetic polyamide yarns. These yarns are prepared in a manner similar to ordinary spinning except that instead of giving the yarn the usual amount of twist necessary for strength the yarn is impregnated with a suitable adhesive. The adhesive imparts to the yarn sufficient strength for adequate knitting without the introduction of twist, and the fabrics so produced have improved fullness of handle, a softer feel, and there is a complete lack of spirality in the fabric produced, i. e., no curling of the fabric edges after cutting.

Various woven or knitted fabrics may be prepared from these synetheic linear polyamide filaments, yarns, ribbons and the like. For example, fabrics may be woven entirely or in part from transparent ribbons of these synthetic linear polyamides used in combination with the crimped or uncrimped yarns or with other commercial type yarns. Similarly, yarns may be prepared by coating one side of a transparent ribbon with a metal powder and winding it spirally around a other yarns which are not capable of beingv drawn I so that the latter are broken during a subsequent drawing operation. Likewise two or more synthetlc polyamide yarns drawn varying amounts may be combined with other textile yarns, fibers, and filaments and then drawn. Also, drawn or. partially drawn synthetic polyamide yarns may be cut into staple length and spun into yarn'followed by cold drawing (or, optionally, further twisting). The resulting yarn has a rabbit fur effect resembling Angora'type yarn since some of the staple will project from the yarn being drawn toa lesser extent in the drawing operation. Due to these differences in the extent of drawing these yarns will show the differences in dyeing affinity of this invention, e. g., the projecting filaments will be more deeply dyed. Alternatively, the synthetic polyamide staple fibers may be spun with staple fibers of other materials. Other novelty yarns may be prepared by doubling two or more ends of synthetic polyamide staple drawn varying amounts and subsequently dyed.

Yarns may be prepared having a full hand by continuous filament with the coated side inside to give a metallic appearance or pearly yarn for decorative purposes. In like manner yarns may be prepared by passing the crimped or uncrimped synthetic polyamide yarns intermittently through cellulose acetate or other solutions in such a manner that the yarn is coated in regular or irregular intervals with cellulose acetate. These will have varying appearances and additional dyeing differences may be introduced. Similarly, suede-like fabrics may be prepared by weaving or knitting fabrics with staple or continuous yarns comprising crimped or uncrimped synthetic polyamide yarn or in combination with other yarns, followed by napping by any suitable method. Due to the remarkably high tenacity and resistance to abrasion of these synthetic polyamide yarns the fabrics are not injured irretrievably and are very valuable. Yarns having these novel effects may also be prepared in a similar manner.

Printed effects may be obtained by weaving these synthetic polyamide filaments in combination with cellulose, acetate, cellulosic rayon or wool, dissolving or partially dissolving the latter by suitable means such as solvents, alkalis and the like. The fact that these polyamide filaments are very resistant to chemical reagents and are insoluble in most solvents makes them especialduced by using alternate shrunk and unshrunk yarns in the fabric.

Since it is obvious that many changes and modifications can be made in the details of the present invention without departing from the denier and exhibiting different color character istics along the length thereof. 1

3. A dyed yarn comprising synethetic linear polyamide filaments of substantially uniform denier and having variations in degree of orientation along the length thereof and having variations in color characteristics corresponding to said variations in degree of orientation.

4. A dyed yarn comprising polyhexamethylene adipamide filaments of substantially uniform denier and having variations in degree of orientation along the length thereof and having variations in color characteristics corresponding to said variations in degree of orientation.

5. A spiral yarn comprising dyed synethetic linear polyamide filaments spirally arranged about a core, said filaments of substantially uniform denier and having variations in color characteristics along the length thereof.

6. Applied yarn comprising a plurality of strands of dyed synthetic linear polyamide filaments, at least one strand of which has a different degree of orientation along the length thereof than the remaining strands, said yarn having a substantially uniform denier and exhibiting variations in color characteristics corresponding to said variations in degree of orientation.

7. A dyed yarn comprising continuous synthetic linear polyamide filaments of substantially uniform denier and broken filaments, said polyamide filaments exhibiting variations in color characteristics along the length thereof.

8. A dyed yarn comprising staple length linear polyamide fibers, said fibers of substantially uniform denier and having variations in color characteristics along the length thereof.

9. The process of producing vari-colored synthetic linear polyamide yarn. which comprises spinning said yarn, subjecting said yam to nonuniform drawing conditions which will impart to the yarn variations in denier, dyeing said yarn and re-drawing the same to substantially eliminate variations in denier of the filaments.

10..The process of producing a vari-colored polyhexamethylene adipamide yarn which comprises spinning said yarn, subjecting said yarn to non-uniform drawing conditions which will impart to the yarn variations in denier, dyeing said yarn and re-drawing the same ,to substantially eliminate variations in denier of the filaments.

11. The process of producing a vari-oolored synthetic linear polyamide yarn which comprises spinning said yarn of non-uniform denier, subjecting said yarn to uniform drawing conditions whereby to draw thesections of the yarn having a smaller denier to a greater extent than the sections of yarn having a larger denier, and dyeing the same.

12. The process of producing a vari-colored synthetic linear polyamide yarn which comprises spinning said yarn of non-uniform denier, subjecting said yarn to uniform drawing conditions whereby to draw the sections of the yarn having a smaller denier to a greater extent than the sections of yarn having a larger denier, dyeing said yarn, and redrawing said yarn to reduce the non-uniformity of denier thereof.

13. The process of producing a vari-colored synthetic linear polyamide yarn which comprises spinning said yarn of uniform denier, non-uniformly drawing said yarn, dyeing said yarn, and redrawing said yarn to reduce the non-uniformity of denier thereof. v

14. The process of producing a vari-colored synthetic linear polyamide yarn which comprises spinning said yam and subsequently drawing the same to form a yarn having variations in orientation and denier along the length thereof, dyeing said yarn, and redrawing the same to substantially eliminate said variations in denier.

15. The process of producing a vari-colored polyhexamethylene adipamide yarn which comprises spinning said yam and subsequently drawing the same to form a yarn having variations in orientation and denier along the length thereof, dyeing said yarn, and redrawing the same to substantially eliminate said variations in denier.

EVERETT VERNON LEWIS.

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