US2154204A - Rayon structures and their method of preparation - Google Patents

Description

April 11, 1939.

G.\B. HOFF ET AL RAYON STRUCTURES AND THEIR METHOD OF PREPARATION Filed Juye 2, 1954 s Sheets-Sheet; 1

INVENTOR5 V GEORGE Peas-few Hon- Frql.

:K. E M A D. R Y m i rT N A E April 1939- s. P. HOFF ET AL RAYON STRUCTURES AND THEIR METHOD OF PREPARATION Filed June 2,-1954 s Sheets-Sheet 2 INVENTORS Games-a Peas-row HOFF' BY HAROLD HENRY PAIEKER O MM! 7 2% ATTORNEY.

April 11, 1939. G. P. HOFF ET- AL RAYON STRUCTURES AND THEIR METHOD OF PREPARATION Filed Jun e 2, 1934 3 Sheets-Sheet 3 M Fig.5

INVENTORS B: GEOQGE. Per-:sroN Hon- HARO LD HENRY PARKER ATTORNE Patented Apr. 11, 1939 PATENT, orr cs BAYON sranorunns AND 'rmtm mnon or raarm'rron George Preston H01! and Harold Henry Parker,

Kenmore, N. Y., assignors, by memo assignments, to E. I. du Pont de Nemours J: Company, Wilmington, DeL, a corporation of Delawere Application June 2, 19:4. No. 728,802- 3 Claims. (01. 51-151).

This invention relates to artificial yarn and particularly to the preparation of twisted structures such as strands and; cords from strong artificial yarn of the regenerated cellulose type,

5 and to their use in the manufacture of reinforced rubber articles such as rubber vehicle tires.

Strong rayon yarn is already known for use in reinforcing cord for rubber vehicle tires.

Cotton cord, commonly used in the manufacture of rubber vehicle tires, may be produced by twisting together five threads of 23 count cotton to about 20 turns per inch, then 3 strands thus formed are combined to form a cable by twisting them to 10 turns in a direction opposite to the strand twist. Such cord is commonly referred to as 23-5-3 construction. In making a comparable cord from strong rayon 5 threads of 275 denier-120 filament strong rayon twisted to '1 turns per inch are twisted together to about 20 turns per inch in a direction opposite to the twist of the threads. Three strands thus formed are then combined to form a cord by twisting them 10 turns per inch in a direction opposite to the strand twist and thus in the same direction 5 as the thread twist. Such a cord will hereinafter be referred to as a 275-5-3 construction, the num-- 'ber 275 designating the thread denier; .5, the number of threads making up the strand; and 3, the number of strands in the cable. For the sake 30 of facilitating a discussion of the invention, this construction is frequently referred to in the examples and throughout the specification, al-

though it is to be understood that the invention is in no way limited thereto.

35 According to one known method of preparing a strong rayon cord. of the abovetype, five 275- denier threads are led from a creel to the feed-in rolls ,by which they are delivered at a uniform rate.

40 being twisted together, passes from the feed roll to a. pigtail guide centered directly above the take-up spool and from it through the traveller on a ring, tothe spool. The required twist, which may be .20 turns per inch right, is inserted dur- 45 ing the thread travel from the feed rolls to the spool. Following this operation, three spools of the twisted strands are placed on a creel and the strands are twisted together in the ,reverm direction to about 10 turns per inch. However, if

.50 the doubling and twisting operation is conducted the strands are characterized by marked irregularity of surface and the resulting.

as above.

This bundle of threads, which is rapidly.

for rubber tires, it is frequently necessary to impart a high degree of twist, both while forming the intermediate strands, and also while plying the strands into the cord, in order that the cord may possess that degree of elongation and resilience essential to the emcient operation and long service life of the tires. Contrary to the experience and practice in the twisting of ordinary rayon and of cotton, the imparting of a high twist to strong rayon by conventional methods is accompanied by a great loss of strength (com-.

pared with what should reasonably be expected from the great initial strength of strong rayon), severe degradation of the thread, comparatively short service life, as well as other accompanying disadvantages. The marked difference between strong rayon and ordinary rayon, upon being given a high degree of twist, can be explained by p the fact that the materials are essentially differ- Strongrs on Normal rayon three thread Dry tenacity, g. p. d.- 2.95 l. 64 Dry elongation, percent 8. 0 21. 5 Wet tenacity. g. p. (1-. 1. 66 0. 82 Wet elongation, percent 12.0 30. 8

As further illustrative examples of strong rayon thread, we refer to those described in co-pending application of Harold H. Parker, Serial No. 676,463, flied June 19, 1933.

In view of the great potential importance of rayon cord and the like made from strong rayon, I

the disadvantages following from the practice of known methods for twisting strong rayon present a very serious problem to the art. The problem is particularly serious in view of the fact that strong rayon, due to its many valuable properties, offers considerable promise in the reinforcement of rubber tires and other reinforced rubber structures.

Byway of illustrating; the ineffectiveness of the methods now used for the twisting of strong rayon threads, when flve 275 denier-120 filament strong rayon threads, having an initial twist of 7 turns per inch left, were plied and twisted to gether to 20 turns per inch right, and three such strands then plied and twisted together to 16 ..ous methods of forming twisted rayon structures from strong rayon have been discovered which produced strands, cords, and the like, having tenacities, durability, service life, et cetera, greatly in excess of those obtainable by prior art methods, and havingasmooth, uniform structure.

One object this invention relates to the productlon-oi a twisted rayon structm'e ng high tensile strength.

An additional object of this invention is to provide a rayon cord having high tensile strength and exceptional durability.

' Another object of this invention is to provide a twisted structure formed of strong rayon in which the elements are uniformly spaced, and lie in place so that the resulting strand or cord possesses a high degree of uniformity.

A further object of this inveniion is to provide a method for twisting strong rayon on standard twisting machinery oi the heavy duty type without substantially increasing the cost.

Another object of the invention relates to twisting of strong rayon yarn at a low relative humidity for the production oi strong, uniform structures. a

A still further obiect'oi the invention is the production of strong, uniform rayon strands and cords by a twisting operation in which twisting of an element is eiifected in a pluralityot stages in the same direction.

Another object relates to the reinforcement of rubber structures. for example, rubber tires, by means of. the strands and cords produced in accordance with this invention.

Other-objectsoi the invention will appear from the description and the claims.

Referring to the drawings, Figure 1 represents a side elevation, partially in section, of a twisting machine adaptable for the practice of the invention. Figure 2 represents a front elevation. partially in section, of the same machine. ligure 3 is a side and detail view, partially in section, of some of the' details of the machine. Figure 4 represents a detail view of a forming device which maybeusedinlieuoi thatshowninl'lguresl and 3. Figure 5 is a front view of a pulley comprising the forming device shown in Figure 4.

Figure Bisaviewoiastrandtwisted in accordance with the present invention.

In accordance with this invention, it has been discovered that a strand of even structure and high strength can be obtained without resortins to more than one operation by subjecting the thread during twisting to the action 01, "forming device comprising preferably a non-rotatable rod, but which may alternatively comprise a pulley, or any other equivalent appliance having a smooth surface, the forming device being placed between the twister iced rolls and the spool and 'overwhichthethreadsaredrawnastheyare 75 bythemotionoithestrand. 'lheuae'otmcha 20-turnsper twisted into a strand or cord. The forming device crowds the threads as they pass thereover evenly and uniformly around the center line of the finished strand or cord. -Where a pulleyisused as the forming device, it is preferably mounted sothatit can rotateireelyandeanbedriven pulley minmiles the abrasive contact and is believed to have a definite beneficial shaping action on the bundle oithreads as they roll or turn in the pulley groove while being twisted. The forming device may alternatively be a pulley which is directly driven from any suitable source of power, for example. by a frictional drive arangement from the feed roll. In this modification, the amount of slippage is controlled by the effectiveness of tbe'pulley drive and the relative sizes oi iced roll and pulley.

In the carrying out of the invention, the position of the forming device in relation to the feedin rolls is not a critical factor within reasonable limits. Thus, it may be placed in the same horizontal plane as the feed-in roll and 2" or 3" in front of the roll so that the bundle of threads passes from the iorming device vertically downward to the spool. If desired, the forming device may be placed 8", 10", 12", or even 14" above the feed-in roll instead otin the same horizontal plane.

It is preferred, however, that the front portion of the periphery of the forming device be disposed directly above the spool so that the thread. after passing over the forming device, travels towards the guide which leads the thread on to the spool, in substantially a plumb direction.

Any standard make of down twister may be used in carrying out our process. The size of the twister, the speed of the spindles, the amount of twisting tension, or the particular design employed does not appear to alter the relationship between the results obtained with our improved 'method and those obtained by the previous method of twisting. While the relative results may thus be the same, it is preferable, in order to' obtain the maximum strength to use twisters of the heavy duty type particularly designed for rubber vehicle fire cord work. 7

Where a non-rotatable rod is used as the forming device, we prefer to use a 7 diameter rod although successful results may be obtained with $5" diameter rods and with rods as large as 2" in diameter. Likewise. it does not appear that the diameter of the pulley, where a pulley is used as the forming device, is a critical factor since good results can be obtained with sizes, having a thread contacting periphery, ranging from /4" to 1%".

j Various materials of construction may be used tor the rods or pulleys, for example, glass, porcelain, brass, steel, "Bakelitefl or hard rubber. The rod or pulley should, of course, be smooth.

In the preferred embodiment of our invention, theuse of a forming device of the character de-. scribed has its greatest advantage in the twisting of the threads into strands. It can likewise be applied with advantage, however, to the cabling or cord-forming operation.

the drawings illustrate theuse 01' a rod or a pulley as the forming device in the twisting operatlon: 1

Example I.Five threads I of 275 denierfilament strong rayon, having '7 turns initial twist left, and a dry strength of about 3 grams per denier at room temperature, are led downward from bobbins I mounted on a suitable creel II, are gathered together on a convergence guide it and then fed by means of positively driven teed rolls ii and I3 and frictionaliy driven intermediate roll it to the travelers ii on ring is and wound onto suitably driven spools I! with about inch right twist. A non-rotatable 4 9,154,204, .glass rod is, having a diameter of is mountto and slightly above the teed-in rolls Ii and l3.

The threads pass over rod i8 and are firmly held against it by the tension on the threads. Three spools of strands 24 prepared in this manner are then taken andv placed on the creel and are likewise twisted together on the same or on a similar twisting machine to give a final twist of 10 turns perinch, in a direction opposite to the twist in the strand. The rod or other forming device need not be used during the twisting of the strands into cord. The cord prepared bythis method possesses a dry tensile strength at-room temperature oi about 18 pounds, i. e. 1.68 grams per denier, as determined by as Scott testing machine, as compared to a tensile strength oi about 16.2 pounds, i. e. 1.44 grams per denier, for the best cord obtainable from strong rayon by prior art methods.

Example H.--The procedure is the same as for Example I'except that instead oi'a rod, a pin rality of axially aligned, freely rotatable pulleys 25, having 1%" outside diameter and having 1%" thread contacting diameter, are freely mounted on a fixed rod 25' held in place in the same way as rod id, as shown in Figure 4, and

' with the front extremity of the thread contacting periphery of the pulleys being disposed directly 5 opposite of that of the initial twist in the thread.

iii

Our process may also be conducted to prepare a cord in which the first two twists, i. e., the thread twist and the strand twist, are in the same direction and the cable twist the reverse of the preceding or strand twist. This type of construction is ,commonly referred to as the hawser type.

Example V.--The procedure is the same as for Example I except that the five threads making up the strand are twisted to 18 turns and the three strands are then twisted to 9 turns.

Example VL-I'hb procedure is the same as for Example Ior 11 except that four threads instead of five are combined to make up the strand.

Three strands are then twisted to form a cord. This construction is known as the 2'75-4-3 type. In this case, the strand twist is 23 turns instead of 20 and the cable twist upwards of 10.5-turns.

\ We find that strands prepared according to the processes of the above examples possess 10% 15%, and even 20% greater strength than is obtained by conventional processes. Likewise,

cords prepared from such strands show upwards of 20% increased strength with attendant-increase in durability.

In addition to the increase in strength, the strands and cords prepared by the methods described above possess higher strength at elevated temperatures. As an example, the strength o! cords, prepared as described in the above exam ples, measured at. 250 F.,' may'be 16 pounds (1.42 grams per denier) or above, as compared to 13.7 pounds (1.21 grams per denier) for cord made by a conventional process.

ing 10 additional turns right.

As a further improvement ever known proccases for twisting rayon filaments, thread, cords, and the like, in accordance with this invention, it has been discovered that .the tendency of strong rayon, when given a high twist by previously known methods, (e. g., a twist oi 18-22 turns per inch in the formation of a strand from 5 threads of 275 denierfilament strong rayon), to assume a rough, snarled appearance, can be overcome by carrying on the twisting operation in two or more stages. The following example illustrates a mode of applying this feature of the invention:

Example VII.-Five threads of 275 denier-120 filament strong rayon, having 7 turns-left initial twist and a dry strength at room temperature oi about 3 grams per denier, are led downward from a suitable creel and then led by means of positively driven feed rolls through the traveler of a ring twister and are wound onto a spool with a twist ofabout 10 turns per inch right. This operation-is conducted in the same manner as regular ring twisting of cotton thread and standard equipment may be used throughout the process. The strand having 10 turns twist is then taken and placed on the creel, and, in the same manner as the above, ten additional turns of twist are inserted in the same direction to give a final twist of 20 turns per inch right. 'Ihe strand sov prepared shows a strength at room temperature on a Scott tester oi between 5 and 6 pounds (between 1.40 and 1.68 grams per denier) as compared to 3.5 to 4 pounds (0.98 to 1.12 grams per denier) which is the strength of a strand of.

strong rayon which has been given its final twist in a single conventional twisting operation.

The variations stated in Examples 111 to V1 above may likewise be applied to the two-stage method of twisting with the same beneficial results obtained by the process of Example VII.

The multiple stage twisting operation may be,

eiiectively and conveniently carried out, however. in conjunction with the use of rollers or pulleys .as "forming devices as'descrlbed in the preceding part of this specification.

The prior art twisting of strong rayon threads results in a rough, snarled strand in which the threads do not lie evenly in the strand structure,

1 Referring to Figure 6 of the drawings, this figure represents astrand, magnified 25 diameters, prepared from five threads of strong rayon yarn having seven turns initial leit twist by first imparting to the threads 10 turns twist right, and then, in a separate twisting operation, impart- Figure 6 clearly indicates the advantages to be derived by the two-stage twisting operation of the present in: vention, the strand having an even, uniform structure and possessing a high strength and durability. The new strandsfurthermore possess a strength which may be 25%, 35% and even 50% higher than the prior art "twisted strands, together with a far greater durability, length of service life, and resistanceto failure, the uni-- equal portion of. the load at all times. Similarly, cords prepared from the new strands have correspondingly greater tenaclty,'service life, durability, resistance to failure, and when used as reinforcing fabric in rubber tires, eliminate blow outs and other similar failures to a far greater extent than cords prepared from the prior art strands. Strands having satisfactory physical characteristics comparable to thou of the strand shown in-Figure 6, with a similar even, smooth surface, result from the use of the forming devices described in Examples I to V1, even where the twisting of the threads in the strand is ac- 'complished in a single twisting operation.

The following table further illustrates the improvements realized by twisting strong rayon in the same direction in two or more stages, the letters A and 3" representing two types of strong rayon cord prepared by twisting three strands prepared as described in Example VII so as to form a cord havinglO turns in a direction opposite to the strand twist, the single twisting operation being designated as "one, rep- .resenting the prior art twisting method:

The type of strong rayon thread designated "A" in the above tableiwas formed from'stron rayon filaments coagulated in the usual sulfuric acid-sodium sulfate coagulating bath. The type designated as B in the above table was formed from strong rayon filaments coagulated as described in co-pending application of Harold B. Parker, Serial No. 676,463, in a bath which contained zinc sulfate and glucose in addition to the usual sulfuric acid and sodium sulfate.

As explained above, it is usually desirable to twist the five threads of 2'15 denier yarn, which make up the strand, to about turns per inch. It is to be noted that though the expression 20 tumsperin "hastheappearanceofalow twist, it is, in fact, a very high twist. The twist for different deniers required to produce a given strain in the thread varies indirectly with the denier. 20 turns per inch for flve threads 01'275 denier strong rayon yarn represent an extremely high twist for this type of yarnand result in a strand having a hard, compact structure. This hardness of structure makes it particularly necessary that the methods of this invention be used for high twist strands since in these cases, readjustment in position of the threads cannot readily take place once they are twisted together. Our new two-stage twisting method produces strands and cords having improved hot strength as compared with prior art cords. Thus, cords prepared in accordance with the method of Example VII have a strength, measured at 250' I"., of 17.4 pounds (1.54 grams per denier) as compared to 13.7 pounds (1.21 grams per denier) for strong rayon cords made by prior art methods.

19 This shows an increase of 26% in hot strength.

7 pie twisting operation, is superior to previous cord All other tests used in the tire industry to evaluate cords for pneumatic tires, for example, fatigue and durability tests, show that cord prepared as described in Example VII, by the multito an extent which may even be greater than would be expected to accompany the increase in tensile strength.

The twisting operations described in Examples I to VII are carried out at a relative humidity of above 60% and at a room temperature of about 75 F.

A major feature of this invention resides in the further discovery that when strong rayon threads are given a high degree of twist, it the twistins operation is carried out at a low-relative humidity, that is to say, of less than 50%, a product is produced having a substantially higher cold and hot strength and a much -greater uniformity and evenness of structure than where normal humidities, such as 65% and higher, are used, as in conventional twisting operations. This improvement is substantial even where ordinary single-stage twisting is used. The use of low relative humidity during twisting furthermore adds greatly to the improvement which follows from the use of forming devices such as rods or pulleys as is described in a preceding portion of this specification, or where the twisting of the threads into strands takes place in two or more twisting operations. The range of relative humidities used in order to get the best results will ordinarily be between 35% and 50%, although in some cases, relative humidities lower than 35% may be used. The temperatures maintained during twisting under low relatiye humidities will ordinarily range from about 75 to 95 F. v I

The following examples illustrate the use of low humidity in twisting operations: Example VIII .-2'75 denier-120 filament regenerated cellulose thread having a dry strength of about 3 grams per denier, is finished in a suitable way with a solution containing about of 7 sodium oleate soap andtwisted on a down-twister to 7 turns per inch left- Five of these threads are led downward from a suitable creel and then led I by positively driven feed rolls to a traveler of a. ring twister and ontoa spool to give about 10 turns per inch right. A glass rod, having a diameter of approximately is placed directly over the spool and under the thread parallel to and slightly above the feed-in rolls in the manner indicated in Figure 1 of the drawings. The threads pass over'this rod and are held firmly against it by .the twisting tension. This operation is conducted in the same manner as regular ring twisting of cotton thread, and standard equipment, other than the glass rod above noted, may be used throughout the process. 'Ihe strands having 10 turns twist are then taken and placed on the creel, and, in the same manner as described in Example VII above, 10 additional turns or twists are inserted in the same direction to given. final twist of 20 turns right per inch.

l The operation of Example VIII is carried out at a relative humidity of 45% and a temperature of 75 F. A strand prepared as described in this example has a strength on the Scott testing machine of between 5 and 6 pounds, as compared with strength of strands previously obtained of 3.5 to 4 pounds. Three of these strands are next twisted in a similar manner to 10 turns per inch in the reverse direction. The resulting cord has a dry strength at room temperature of over 21 pounds (1.85 grams per denier), as compared with previous cords having a strength of about 16 pounds (1.42 grams per denier). Furthermore. this cord has a hot strength of approximately 18 pounds (1.68 grams per denier), as compared with the maximumpreviously obtainable hot proved durability and the smoc h, uniform structure shown in Figure 6. i

, It is to be noted that in carrying out our invention in its preferred form, that isto say, with the use of low relative humidity, a number of improvements are combined, each of which contribute to the excellent result which is obtained.

It is to be understood, of course, that it is not tioned heretofore to obtain results which are appreciably better than the results obtained by the prior art methods. To demonstrate this, we give below the following examples:

Example lX.Five threads of 275 denier-120 filament strong rayon, which have not been twisted, are twisted to 7 turns on the customary rayon throwing machine. Five of these threads are then led downward from a suitable creel by means of positively driven feed rolls and through a traveler of a ring twister onto a spool to give a twist of about turns per inch, the twist being in the reverse direction to that of the elemental thread twist. Three strands so produced are then doubled and twisted in the reverse direction in a similar manner to 10 turns per inch. All these operations are conducted on the standard downtwister of the heavy duty type such as is commonly used for twisting and doubling cotton thread.

so The twisting is carried out at room temperature and at a relative humidity of 45%. The cord so obtained has a strength at room temperature of approximately 17.1 pounds (1.51 grams per denier) at' 60% relative humidity and a hot strength of approximately 15 pounds (1.33 grams per denier). It is to be'noted that this mere change in humidity condition without the use of other improvements described throughout this specification improves the strength of the cord at room temperature and also the hot strength,

each in the neigborhood of 1 to 2 pounds, as compared with the results obtained when the relative humidity is 65% at room temperature as is customary in the twisting of rayon and cotton 45 thread.

Example X.The doubling and twisting operation is carried out as in Example IX on a twisting machine similar to that shown in Fig. 1 of the drawings and equipped with a glass rod. The cord so formed has a dry strength at room temperature and a hot strength each about 3' lb. higher than the cord of Example 1,

Example XI.--A twisting operation is carried out as described in Example IX with the exception that the intermediate strand twist is conducted in two stages as is described in Example VII. The cord so produced has a cold strength and a hot strength about equal to those of the cords produced in the previous example.

Example XII.-The process is carriedout'as in Example XI with the exception that the elementary threads are twisted on a downtwister to 7 turns per inch. Animprovement of about one-half pound in cord strength is obtained.

The variations described in Examples 111 to VI may, of course, be applied to the low humidity twisting process referred to in the examples immediately preceding this paragraph.

While it is in general preferred to carry out the twisting operation at a relative-humidity of 40-45%, it is desired to state that the lower the humidity, he greater is the tenacity of the twisted strand or cord. The relationship between decrease in humidity during twisting and increase in the tenacity of the cord is a straight necessary to include each and every element men-' line function. This is illustrated in the following table which refers to a cord prepared by twisting 5 threads of 275 denier-.120 filament strong rayon having a strength of about 3 grams per denier and having an initial twist of 7 turns left, into strands with 20 turns right, this operation being carried out in two stages, during each of which 10 turns is given the strands, three of the strands then being given 10 turns left in'order to-iorm the cord.

Dry tenacity in rats se msr tensile test) Per cent 45 i8. 7 19. 1 24 19. 5

The foregoing examples quite clearly demonstrate the beneficial eiTect-of the various features a denier as low as 30, or as high as 1100. or even I 1600 or higher, or the number of threads twisted into strands, or the number-of strands twisted into cords may be varied. Likewise the number of plying operations to produce the final product may be three or more. especially where low denier threads are used. Similarly, the new methods 'may be applied to the twisting of threads having a low filament denier, e. g. 30 denier-30 filament,

' 120 denier-100 filament, 275 denier-250 filament, and other threads having 'a filament denier of the same order of magnitude. To indicate these factors in an example not yet disclosed, our new method. 01' twisting may be applied to the twisting of three threads of 450 denier strong rayon into a strand and then to the twisting of three of the strands into cord, with the-same beneficial results already described. They may be'applied to the twisting of yarns obtained from diflerent kinds of viscose, to the twisting of strong artificial yarn produced by the cuprammonium process, or of any other artificial yarn having physical characteristics comparable to those of strong rayon. While the processes described in this invention are of most marked advantage in the case of strong rayon yarns having a low dry elongation, i. e. 12% or lower, at room temperature, strong rayon yarns having a high dry elongation, for

. example, 16%, can be twisted according to the novel methods with advantage.

The amount of twist which is inserted in the various twisting operations may be varied, or the number of twisting steps in the multiple-twisting operation-may be increased to 3 or more. The

new twisting methods may likewise be used in' conjunction with the various common devices,

such as tensioning weights on the creel.

Thetwi'sting methods of the present invention involving the use of "forming devices" or multiple 01d H. Parker, Serial No. 728,801, filed 01' even' date herewith.

In the above methods for carrflng out our invention, we prefer to use any suitable finish on the thread, and particularly prefer one which impartstothethreadahi'ghdegreeofsoftness and slipperiness, e. g., soap, vegetable oil, or other lubricating material. As an example of a iinish giving very satisfactory results, we may cite a solution containing simply about 59% of soap, calculated as sodium We find that the threads, when soaked in this solution and dried, have the desired characteristics which permit themtobereadiiytwistedintosmooth,even strand structures. by our preferred process. Fur: thermore, the use of a finish substantially lessens degradation in the threat during twisting, and increases tenacity of the twisted structure.

The strong rayon referred to in the above examples and to which the twisting processes of this invention may be most beneficially applied, is prepared as described in co-pending application of Harold H. Parker, Serial No. 676,463, filed June 19, 1933, and has a strength of, about 3 grams per denier. This thread is prepared by the use oi a spinning bath containing zinc sulfate and glucose in additionto the usual sulfruic acid and sodium sulfate. while strong rayon prepared 'inthismannerispreferred,anyotherstrong rayon prepared by any other method, for example, by precipitating in the conventional sulfuric acid-sodium sulfate bath,maybeused.

Bythepracticeofthisinvmtiomthereare producedstrongrayoncordshavingadrytenacity at room temperature'of ldpounds and higher. and having a hot strength of well above 15 pounds. of about 16 pounds andabout 18.1 pounds respecappreci but they also have the further effect of decreasing the spread between maximum and minimum. Thus, for cord A of the table givenon page 4, the maximum tenacity is 18.1 1b., and the minimum is 16.6 lb., and for cord 3". the maximum is 19.9 lb. and the minimum is 17.5

' lb. This narrow spread between maximum and minimum, compared with a spread between maximum and minimum tenacities of prior art cords of some two to three times that of cords prepared by the twisting processes of the present invention, is very important since cord failures occurat points of minimum strength.

The term room temperature" whmever referred to throughout the specification and claims is intended to be F.

when the terms elongation" and percentage elongation are referred to, they signify elongation at the breaking load.

It has been stated that the invention can be applied with great advantage to the production of rayon structures having a high twist. Thus, for example, in producing strong rayon, cord for useinrubbertires,where thecordisto be ofthe 'z'zs-s-a type, the intermediate strand may be givenatwistofzoturnsperinch. Itistobe noted that though the expression "20 turns per inch" has the appearance of a low twist, it is, in fact, a very high twist. The twist for different deniers required toproduce a given strain in the thread varies indirectly with the denier. The most satisfactory method for determining whetheratwistisahightwistoralowtwistis byreierencetothehelix angle as deflnedinan article "An introduction to the micro-analysis of yarn twist by E. R. Schwarz, published in the Journal of the Textile Institute for March, 1933, wherein itisstated onpage 109:

Barker and Midgley state, for example, that a Helix angle of 30 corresponds to a hard twist,

'andthataI-Ielixangleofibrepresentsnormally an extremely high twist." Using the equation developed by the above anthor,thehellxangle forthestrandspreparedin accordance with the instant invention, i. e., 5 threads of 275 denierfilament, twisted to 20 turns per inch, is approximately 40'. We have calculated the twist required for structures of different denier to produce this same helix angle. These values are summarised below:

Toisttogivesamehdironnleondthaeforesam decree of twist with structures of diflereat denier mcmx ANGLE, 40-

. 353 ens-a Thus,itisseenthat mturnsperlnch inaply of five threads of 275 denier is in fact an extremeiy high twist.

The twisting methods of the present invention enable strong rayon yarn to be given a highdegree of twist to produce a smooth, uniform surface with resulting increase in tenacity.

Ibr the purposes of this invention,-a high twist significsahelixangleinthetwistedstructure, i. e. whetherstrand or cord, of above 35', as deby the equatlon referred to in said tained by conditioning at 60% relative humidity- 45 turns per inch. It is preferred that the strong thread have 7 turns per inch. It will be understood, however, that in some cases, this invention may be practiced with advantage with a strong rayon thread having no substantial twist.

In referring throughout the specification or claims to dry thread strength at room temperature, or its equivalent, this is intended to indicate the tenacity obtained in the following manner:

The thread is reeled under uniform tension in 450-meter skeinszlthese skeins are conditioned for 3 hours in an atmosphere maintained at 60% relative humidity and 75 I".; the skeins are then weighed to determine the denier which is defined as the weight in grams of 9000' meters.

The tests for determining tenacity and elongation are made on a Suter single strand strength and elasticity tester with an oil plunger con-.

each of the above skeins are tested separately.

These are clamped in the tester and stretched until the yarn breaks. Both the breaking load in grams and the percent elongation may be read directly from scales on the machine.

Grams per denier are obtained by dividing the scale reading in grams by the denier of the thread.

The average of 50 dry breaks on threads selected at random is considered to be the tensile strength for any given lilo-pound lot of yarn.

The dry strength of the strands or cords is oband 7c" Ffand testing according to the a s. 'r. M. procedure D-1'I9-30 (see A. B. T. M. Standard. vol. 2, 1930, page 1085).

The hot strength of cords given in this application are measured as follows:

A testing machine-is provided with means for heating and maintaining the temperature of the cord during the tensile test at 250 F.; the cord is clamped between jaws initially 30 centimeters apart under an initial load of 4 ounces, and is then heated to 250 F. when that temperature is reached, the cord is loaded at the rate of 10 lbs.

the time to break the cordis measured. with a stop-watch and the breaking load is computed from thistime, knowing the quantity of water that has flowed into the bucket. The initial load of 4 ounces is added to the measured load to give the total tensile strength of the cord in pounds. Where methods of testing, other than those specifically referred to herein, are used, difi'erent numerical results may be obtained, but the relative improvement over the prior art will be of the same order, regardless of the method of testing used. I

It will be'readily understood from a study of the specification that by the practice of the various features of this invention, there are obtained rayon strands and rayon cords from strong rayon which have highly improved physical char- 7 aeteristics, as compared with strong rayon twisted according to -conventional twisting methods. Rayon strands, and more particularly rayon cords, produced according to this invention, are extremely useful as reinforcing means in the production of various articles which may or may not'contain rubber. Thus, they may be used as reinforcing cord or fabric in rubber tires,

, in hose, in belts, such asfan belts or. other power belts and conveyer belts, in loom harness, -and generally in the manufacture of articles where. it

is desired to utilize the properties of the novel twistedstructures. The highhot strength of our new strands and cords make them of particular value when used in reinforced articles which operate at a high temperature, such as pneumatic vehicle tires, steam hose, and conveyer belts used for the handling of hot materials. Rubber vehicle tires reinforced with the strands and cords prepared in accordance with this invention, as compared with tires reinforced with prior art cord. exhibit greater durability, longer service life, a lower rate of growth, a greater resistance to blow-outs, consume less power and thus lower the fuel consumption per mile,and operate at 'a-lower temperature, since the tires reinforced with the new cords generate less heat, during the operation of the vehicle. -Anyvariation or modification which conforms to the spirit of the invention is intended to be included within the scope of the claims. I We claim: I

l. A method of twisting strong rayon of the regenerated cellulosetype and. having a. dry tenacity at ordinary room temperature of at least 2.5 grams per denier into a strand for use as a reinforcement for rubber structures which comprises imparting to'= the strong rayon a substantial twist and then, in a separate step.

parting an additional twist in the same direction.

2. 'The method of twisting strong rayon into a strand which comprises imparting a twist of about 2 to '7 turns per inchto threads of 275 denier-120 filament strong rayon, then twisting five threads in two steps to at least 18 turns per inch in the direction opposite to the twist of the threads.

3. A method of twisting strong rayon of the regenerated cellulose type and having a dry .a separate step, imparting additional twists in thesame direction, and then twisting the result:-

per minute by means of water flowing through 1 mg strand an orifice under a constant head into a bucket: j

comprises producing a strand by imparting a twist of about .2 to '7 turns per inch to strong rayon threads of 275 denier-120 filaments, then twisting five threads in two steps to at least 18 turns per inch in the direction opposite to the twist of the threads, and then twisting the resulting strand into a cord by imparting 9 turns per inch in the cord in a direction opposite to the strand twist. r

- 6. The method oi twisting strong rayon oi the regenerated cellulose type and having a dry tenacity at ordinary room temperature of at least 2.5 grams per denier into a strand for use .as a reinforcement for rubber structures which comprises imparting a substantial twist to a bundle of threads of strong rayon filaments, then further twisting the strand so formed by an additional twisting step in which the twist is in the same direction, further characterized in that the twist in at least one step is accompanied by apassage of the strand over a smooth curved surface disposed between the feed-rolls and the spool.

7. The process of twisting strong rayon threads of the regenerated cellulose type and having a dry tenacity at ordinary room temperature of at least 2.5 grams per denier into strands for use as a reinforcement [or rubber structures which comprises carrying out the twisting opmm at a relative humidity of less than 50% and. at a temperature of about 75-95 F., further characterised in that the twisting operationiscarriedoutaoastogiveatwistintwo successive stages in the samedirection.

8. The process of twisting strong rayon threads of the regenerated ceilulose'type and stages in the same direction. the strand during atleastoneoisaidstagesbeingpassed overa smooth curved surface.

GEORGE PRESTON HOPE.

HARDL'D HENRY Pm. 2o

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