US2421624A - Method of conditioning artificial silk thread - Google Patents

Description

June 3, 194-7 H. B. KLINE ET AL 2,421,624

METHOD OF CONDITIONING ARTIFICIAL SILK THREAD Original Filed Oct. 9, 1941 5 Sheets-Sheet l IQ a a I 72 f I 7| 3 I 7 r1 "2 I (A. 62 I t I 62 I l l I l I 70 o o H 9 9 68 68 66 E I INVENTO/PS HAYDEN BKLl/VE KENNETH M. McLELLA/V I I v, 65 I WW1;

ArroRA Er June 3, 1947.

H. B. KLINE ET AL METHOD OF CONDITIONING ARTIFICIAL SILK THREAD 3 Sheets-Sheet 3 Original Filed Oct. 9, 1941 W A .I I 3 L 8 5 5 E M 5 W LM W 3 2 N T m I E W N wflw s I WWW. 42 1.1 27 25 Y R B 2 5 4 32 2 2 I ATTORNEY Patented June 3, 1947 METHOD OF CONDITIONING ARTIFICIAL SILK THREAD Hayden B. Kline and Kenneth M. McLellan, Cleveland, Ohio, assignors to Industrial Rayon Corporation, Cleveland, Ohio, a corporation of Ohio Original application October 9, 1941, Serial No. 414,325. Divided and this application July 13, 1944, Serial No. 544,720

4 Claims.

This invention relates to the manufacture of filaments, bands, ribbons, thread and the like, hereinafter referred to as thread; particularly, artificial silk thread characterized by a high tensile strength. I

This application is a division of application Serial No. 414,325, filed October 9, 1941.

Artificial silk thread, especially multiple filament viscose artificial silk thread, which is characterized by a high tensile strength is not easy to manufacture. When produced by ordinary methods, such thread is markedly nonuniform in its physical and physicochemical properties, varying noticeably not merely from batch to batch but even within the same batch. As a rule; excessive manipulation of the thread incident to the conventional process of manufacturing it results in undue waste of partially processed material.

In all usua1 methods of manufacturing multiple filament viscose artificial silk thread of high tensile strength, the necessary stretch is imparted to the thread only after it has had time to become set. A high stretch cannot be imparted to such thread without causing rupture of'some of the filaments thereof, bringing about a concomitant reductionin the tensile strength of the thread as a whole. Prior art methods of stretching thread to increase its tensile strength have been seriously limited by this seemingly inherent inability of the thread to withstand more than a moderate amount of stretching:

The present invention not only simplifies the process as a whole but permits extremely high stretches to be imparted to the thread without detrimental effects upon its quality. This is accomplished by employing a plurality of stretching operations, such operations being performed on thread which has been treated so as to enhance its capacity for stretching. thread is, in a somewhat plastic state whenthe stretching operations are performed upon it. Inasmuch as all operations, including stretching operations, are performed upon the thread in one continuous sequence, many of the difficulties found in prior !art methods are obviated.

Apparatus suitable for the purposes of the invention comprises, among other things, a thread source, a catena of thread-advancing thread store devices upon each of which the thread is continuously but temporarily stored in substantially helical turns while the desired processing operations are performed upon it, and appropriate collecting means. After leaving the source, the thread. passes in succession to each of the Pref enably, thev several thread-adwancing thread store devices comprising the catena. From the last threadadvancing thread store device of the catena, the processed thread passes directly to thecollecting means.

Figure 1 of the drawings shows an end elevlation of apparatus with which the invention may be employed, such apparatus embodying two oppositely inclined banks made up of laterally adjacent catenae. Figure 2 is a side elevation of the apparatus of Figure 1 from line 2-2 thereof showing in detail one of the inclined banks. Figure 3 is a substantial sectional elevation of the apparatus.

In the drawings, severlal laterally adjacent catenae individually made up of ten threadadvancing reels ofcantilever construction are represented more or less diagrammatically. Actually, each reel in each oatena comprises two cagelike reel members of substantially circular cross section which occupy substantially the same space, the periphery of each reel member being made up of a plurality of longitudinally extending thread-supporting bars. The bars of each reel member interdigitate with and are alternately disposed with respect to the bars of the other reel member. The reel members of each reel rotate about axes displaced from each other, for instance, they may be andpreferably are in inclined relation in parallel planes.

The number of turns of thread per unit of length on a given reel is a function of the angle of inclination of the axes of rotation of the two reel members. Such angle of inclination is determined in part by the size of the thread to {be stored on the reel. As viewed from a plane parallel to the two parallel planes in which the axes lie, the apparent intersection of the axes of rotation of the two reel members may be at any point along the reel as a whole but preferably near the center of the thread-bearing portion thereof. In the drawings, the number of turns of thread and thespacing between turns on the illustrated. reels are not to scale.

Reels of the type described and apparatus of the kind illustrated as embodying them are shown in Ratent 2,225,642 to Walter F. Knebusch et al. i The laterally adjacent catenae going to make up the two oppositely inclined banks shown in Figure 1 are supported on each side of an A- shaped frame I 2. In each catena, the unsupported end of each reel is directed toward the working face of the bank with which it is associated. Reels 2 to II), inclusive, are disposed in stepped relation as shown in Figures 1 and 3 with the thread-discharge portion of each reel in juxtaposition to the thread-receiving portion of the succeeding reel. Such an arrangement oifers constructional and operative advantages which will appear more clearly hereinafter.

As shown in Figure 3, reels l and 2 may, if desired, be constructed with a flared contour so that thread being advanced therealong will bestretched as it is advanced. These reels need not necessarily be flared, for either or both may be substantially cylindrical. If desired, other reels included among reels 3 to H), inclusive, maybe of such flared contour; also, any of reels 3 to in, inclusive, may be of tapered contour so that the thread may contract in passing thereover. Preferably, however, reels 3 to 10, inclusive, are sub-- stantially cylindrical.

Reels l to Hi, inclusive, are driven through change speed mechanism M by means of a motor [3 located at the drive end of the apparatus, i. e, the end at the left in Figure 2. Speed reduction unit i5, driven by change speed mecha-' nism l8, actuates a drive shaft [.8 extending longitudinally of the machine which shaft serves to drive all reels I through suitable gear boxes H. In similar fashion, speed reduction unit [8, also driven by motor [3' through change speed mechanism l4, actuates the two longitudinally extending drive shafts i3 which, through gear boxes 2| and inclined drive shafts 22, serve to drive reels 2' to it), inclusive.

Gears 23, mounted on inclined drive shafts 22, mesh with gears 24 mounted on reels 2v to ID, inclusive. Gears 23 and 24 are demountable, consequently, changes may be made in the speeds of reels 2: to. to, inclusiveby changing these gears. If desired, the gear ratios of the gears. for each reel may be maintained constant and a peripheral speed. diiferential between successive reels obtained by using successive reels of different diameters; In either case, successive reels in the catena. may be. rotated at peripheral speeds greater or less than preceding reels, thereby imparting stretch to or allowing for contraction of the thread, as the case may be, while it is passing from reel to reel.

- By employing a driving arrangement of this kind; reels l and reels 2 to [0, inclusive, may be driven at different speeds by suitable adjustment of change speed mechanism Hi. If it is desired to. stop rotation. of any reel l, the corresponding clutch handle. 25 may be turned to disengage the coupling through, which such reel is driven from shaft Hi. Similarly, any catena of reels 2 to H), inclusive, may be stopped by operating clutch handle 23. If desired, one or more reels in each of the several catenae may be provided with a slip clutch device so that rotation of any one of the reels thus equipped may be interrupted without affecting, the rotation of other reels in the catena.

Since the illustrated apparatus is adapted to produce the thread as well as to process it, a particularly convenient arrangement is one pursuantv to: which. motor I3, through change. speed mechanism 14., speed reduction unit 2-! and shafts 28, drives gear pumps 29 disposed at intervals along the; front. of the apparatus. Gear pumps 29 are connected to spinning solution supply pipes, 3[ in: such manner that a coagulable spinning solution, i.. e., viscose, can be fed at a uniform rate. through feed pipes 32 and pivotally mounted mass. tubes 33- to spinnerets 34. As the spinning solution is extruded into precipitating bath 35 in trough 36, it is coagulated to form a multiple filament artificial silk thread 31.

Liquid for coagulating the spinning solution as it is extruded into precipitating bath 35 is supplied to trough 36 from the end of the apparatus opposite the drive end. It passes to trough 36 through weir box 38, header boxes 39, and inlet pipes 4|, which parts are connected together as shown in Figure 3. The coagulating liquid passes into trough 36 through orifices 42 disposed at intervals along inlet pipe M. Inasmuch as there is preferably a continuous flow of coagulating liquid into coagulating trough 36, the excess liquid is permitted to pass therefrom through overflow pipe 43 and return pipe 44 to suitable make-up and recirculation means.

The freshly formed thread 31 passes substantially vertically upward from the precipitating bath to the thread-receiving end of reel I, passing through thread guide 45. Guide 45 not only leads thread 3'! to reel I but also serves to strip therefrom a considerable amount of the entrained coagulating liquid. Although a. considerable quantity of coagulating liquid is stripped from thread 3'! in this manner before it passes toreel' i, enough remains so that coagulation of the freshly formed thread continues while the thread is being advanced over the periphery of the reel.

It is sometimes desirable to apply an oleaginous material to reels l to inhibit deposition of deposits thereon; accordingly, oil supply pipes 46 and drip pipes 41 may be employed to drip oil or the like onto reels I After thread 31 has been advanced to the thread-discharge end of reel I, it passes from reel l vertically downward through channel 48, part of which isshown as broken away in order to show the path of the thread. From the lower end of channel 48 the thread passes under thread guide 5i or, as in Figure 3, under guide 5| and over thread guide 52. Guide 5| or 52, as the case may be, serves to locate the point at which thread 31 starts to wind onto the succeeding reel. For convenience, guide 52 is adjustably mounted to provide for the storage on reel 2. of varying amounts of thread.

similar threadv guides 53 are disposed between adjacent reels 2 to 10, inclusive; however, the thread usually passes between two adjacent reels in a substantially straight line,

The. thread; is subjected. to the desired processing operations as it advances in closely spaced, substantially helical turns. over each of reels 2 to Ill, inclusive. Collecting, troughs 5B are disposed beneath each horizontal seriesv of reels 2 to Ii), inclusive, to collect any excess of the liquid applied to the thread: these troughs operate to return the collected liquid through outlets 51. Troughs. 56 have formed therein near the forward edges thereof supply conduits 58 adapted to conduct processing liquid through distributor pipes- 55 to the reels inthe horizontal series disposed immediately below each of such troughs. A pipe- 54- extends longitudinally of the apparatus above reels 2 to supply suitable treating liquid through. distributor pipes. 55 to the thread 3-1 stored on reels 2-.

Ordinarily, only one set of conditions is employed at one time on one and the same apparatus; for this reason, the left and right-hand banks. appearing in Figure 3 constitute imagesof each. other.

After having been processed as desired onreels 1' to l, inclusive, the. thread on reaching reel (H's stage.

treated with an oil emulsion to enhance its flexibility' in preparationior'the twisting operation. In order that no unnecessary excess emulsion will remain onthe'thread, reel 9is utilized as a drip As will hereinafter appear, the ratio of the peripheral speed of reel 8 to that 'of reel 9 afiects the efiectiveness of the drip stage. The latter is intended to accomplish the removal of a'substantial amount. of the liquid which would otherwise cling to the thread; indeed, by the time the thread reaches the discharge end of reel 9, it should have a comparatively low, constant moisture content so that it may be dried without undue difiiculty.

Reels [0, on which the thread is dried, may be heated internally by hot water, oil, steam, etc. to a temperature high enough to dry the threads substantially completely but in any event to an extent sufiicient to permit it to be collected in finished form on cap twisters 62, to which the threads proceed through thread guides 6| after leaving the unsupported end of reels l0. "Ordinarily, a temperature of 80 C. to 100 C. is suflicient to accomplish the drying of the thread in a reasonable time. Reels suitable for drying multiple filament artificial silk thread of the kind to which the present invention relates are shown, described and claimed in Jordan Patent 2,207,739.

Cap twisters 62 are disposed below the horizontal series of reels l0, one cap twister being associated with each descending catena of reels l to II], inclusive.

Motor 63 actuates the cap twisting mechanism through cam 64 and cam-following lever 65 which effects vertical reciprocation of lifter rail 66. The same motor 63 actuates driving drum 6! around which whorl belt 68 passes. While lifter rail 66 reciprocates in a vertical direction, whorls 69 are rotated by belt 68 which passes therearound. Thus the thread passing to the cap twister 62 is simultaneously twisted and collected on bobbins Ill. Shields H are disposed between adjacent cap twisters 62 to prevent entanglement of the respective threads 31 as they balloon about the cap twisters, such shields being attached to the bottom of housings 12 which enclose dryer reels I0.

Although the invention may be employed in the manufacture of other types of artificial silk thread, it will be described hereinafter as applied to the manufacture of viscose artificial silk thread having a dry tensile strength of at least 2.5 grams per denier.

A thread of relatively high tensile strength may be produced by subjecting it in the early stages of regeneration to a plurality of successive stretchin operations each of which stretches the thread but none of which is great enough to break the filaments of which the thread is composed. In this state, i. e., before regeneration proceeds to completion, an inherent tendency to contract exists in multiple filament viscose artificial silk thread, regardless of whether it is passing along the peripheries of the reels or passing between reels.

If, for example, the peripheral speeds of reels l and 2 are the same, a normal tension due entirely to the aforementioned inherent tendency to contract will exist in the thread, which tension may be as much as 50 grams or more as measured by a thread deflection tensiometer. A similar tension exists in the thread passing between reels 2 and 3 even if the peripheral speedsof those reels are equal. A like state of affairs obtains in varying degrees on and between the subsequent reels of each catena. This normal tension is to 6 be distinguished .from tensions introduced by stretching operations as hereinafter described.

In these circumstances, if two or more stretching operations are introduced, the tension developed in viscose artificial silk thread during the later oftwo stretching operations will be much greater than that developed during the earlier stretching operation, without regard to the fact that the second may not be as drastic as the first. Not only this, but where two or more stretching operations are employed, the total tension in the thread in a given stretching stage, i. e., that tension induced by the stretching operation together with the tension due to the inherent tendency of the thread to contract, will vary in different stretching stages even though the magnitude of the respective stretching efforts may be the same.

The inherent contraction of viscose artificial silk thread is dependent upon a number of factors including the amount of stretching in the preceding stages and the length of elapsed time between extrusion and stretching. The amount of inherent contraction may, however, be increased, decreased, or otherwise controlled by subjecting the thread to certain processing treatments before or during the stretching operations. Among other things, it is possible to provide thread of comparatively high tensile strength by reducin inherent contraction to a minimum in at least one of a plurality of stretching operations while imparting the desired amount of stretch to the thread.

When, for instance, the thread is stretched between reels l and 2, the inherent tendency to contract limits the extent to which the thread may be stretched. Likewise, inherent contraction limits the amount of stretch which can normally be imparted between reels 2 and 3. Accordingly, before the thread is stretched between reels 2 and 3, it is preferably conditioned as hereinafter described so as to render it capable of being stretched to the desired extent without deleteriously affecting the individual filaments of which the thread is composed.

For the most part, best results are obtained a when the highest tension developed in any of a plurality of separate stretching stages is maintained at a minimum, this being achieved by applying to the thread, preferably immediately prior to the stage'in which such tension is developed, a suitable treating fluid at a temperature between 10 and 60 C. The medium applied to the thread may-be water or other treating fluid, for example, an aqueous solution of a strong acid. If water is employed, it is desirable to treat the thread for a somewhat longer period of time or at a somewhat higher temperature than if an acid is used. The length of time of treatment may be increased or decreased by increasing or decreasing the number of turns of thread on the reel.

The methods described herein may also be performed in the absence of the step of continuously but temporarily storing the freshly formed thread on reel I. I In the following example, the freshly formed thread travels a distance of approximately fifteen inches in the coagulating bath and approximately 2.6 inches in the air before 'it comes into contact with the first reel of the catena. The distance between the point at which the thread leaves the first reel and that at which it winds onto the second reel is approximately eighty-one inches. The distance between succeeding reels is approximately nine inches. The length of in the example.

Example As shown in Figure 3, thread 31 is drawn vertically upward out of the coagulating bath by a flared reel I which imparts a stretch of approximately to the freshly formed thread as it advances thereover from the supported to the unsupported end of the reel.

At the thread-receiving end of reel I, the peripheral speed thereof is 43.7 meters per minute, while at the thread-discharge portion thereof, the peripheral speed is 50.3 meters per minute. Additional stretch is imparted to the thread as it passes between reels I and 2, the latter having, for instance, a peripheralspeed of 58.8 meters per minute at the thread-receiving end thereof. A third stretch is imparted to the thread as it advances over the periphery of flared reel 2, which has a peripheral speed at its thread-discharge end of 67.7 meters per minute. Reels 3 to 8, inclusive, rotate at a peripheral speed the same as that of reel 2 at the thread-discharge end thereof; viz., 67.7 meters per minute.

When a liquid is applied to the thread stored on reel 2 as hereinafter explained, the thread passing between reels I and 2 preferably has approximately 110 grams tension, while that passing between reels 2 and 3 preferably has 80 grams 2 tension.

Under preferred conditions, no processing liquid is applied to the thread stored on. reel I but a dilute acid solution comprising water, 2.5% H2504, 5% NazSO4 and 0.05% ZnSO4 is applied at a temperature of C. and at a rate of approximately 300 c. e. per minute to the thread stored on reel 2. The application of the treating liquid to the thread. stored on reel 2 not only increases the ability of the thread to withstand greater stretching but also reduces the inherent tension in the thread during and. after the stretching operation. The same treating solution is applied to the thread while it is being advanced on reel 3, the temperature and rate of application being the same as that applied to the thread on reel 2. From the thread-discharge end of reel 3 the thread passes to'the thread-receivin-g end of reel 4, where approximately 60 turns of thread are stored while a faintly acid aqueous washing liquid (02% H2SO4) is applied to the thread at a temperature of 30 C.

The thread is then passed from reel 4 to reel 5 where it is stored in approximately '70 turns while fresh water is applied thereto at a temperature of 30 C. to wash free of excess acid, salts, etc.

If it is found desirable to remove the sulphur contained in the thread by a desulfurizing process, the thread is passed to reel 6, upon which approximately 60 turns of thread may be stored while a .35% aqueous solution of sodium'sulfide is applied thereto at a temperature of 50 C. While it is not in all cases necessary to employ such a desulfurizing operation, if it is employed, the excess of such-desulphurizing solution should be washed from the thread on reel I. The thread is stored upon reel I in approximately 60 turns while water is applied thereto at a'temperature of 30 C.

The twisting operation to which the thread is subjected in the final stage requires a certain amount of lubrication of the thread. Accordingly, thread 31 passes from reel 1 to reel 8, where an oil emulsion is applied to the thread while approximately 60 turns of thread are stored thereon.

The emulsion may consist of a mixture of mineral oil and a sulfonated hydrocarbon dispersed in an aqueous medium. The emulsion applied to the reel is preferably maintained at a temperature of approximately 40 G.

Since it is undesirable to have an undue amount of moisture in the thread immediately prior to the drying operation, reel 9 acts as a drip stage for the thread: in such stage, approximately 36 turns of thread are stored on the reel.

It has been found that by decreasing the peripheral speed of reel 9 with respect to that of reel 8; for instance, by making the diameter of reel 9 less than that of reel 8 while maintaining the'angular velocity the same as that of reel 8, more liquid can be removed from the thread in the drip stage than if the peripheral speed of the two reels were equal or if the peripheral speed of reel 9 were greater than that of reel 8. For this surprising state of affairs no satisfactory explanation is available at the present time. Ordinarily a reduction of approximately 2% in peripheral speed is sufficient to achieve the desired results.

The optimum percentage of reduction in peripheral speed usually is determined by the amount of tension which has been developed in the thread during the previous stages. For example, if the peripheral speed of reel 8 is 67.7 meters per minute and a total stretch of 55% has been imparted to the thread in the first stages of regeneration, reel 9 should have a peripheral speed of approximately 66.4 meters per minute. In general, the greater the amount of tension developed in the thread during the stretching operation, the greater should be the difference in peripheral speeds of reels 8 and 9.

In order that the desired residual shrinkage and elongation properties may be imparted to the finished thread, the moist thread is stretched slightly while it passes from the,thread discharge end of drip reel 9 to the thread-receiving end of drying reel I0. Preferably the amount of stretch imparted to the thread between reels 9 and I0 is less than the amount of let-ofi in the thread between reels 8 and 9. In the instant example, drying reel I0 should have a peripheral speed of approximately 67 meters per minute, whereby approximately 1% stretch is imparted to the thread while it passes from reel 9 to reel I0. Of course, the peripheral speeds of the reels may be varied in any desirable manner such as decreasing the speed of the intermediate reel. and increasing the speed of the drying reel over both previous reels or either one, depending on the final required yarn characteristics.

Drying reel I0 may be heated to a temperatur of 90 C. by hot water, oil or other suitable heating fluid while approximately 1.00 turns of thread are stored thereon. Inasmuch as reel I0 is substantially cylindrical and the thread is restrained somewhat from shrinking during the drying thereof, the dried thread may have a residual capacity to shrink of 6% or more based on. the original length of the finished thread. Since the shrinkage is uniform throughout all parts of the thread, the quality thereof is not in any way lowered because of such relatively high residual shrinkage capacity.

The dried thread is collected on cap-twisting apparatus of the type hereinbefore described, approximately two and one half turns per inch twist being imparted to the thread. I

Thread manufactured according to the pro- 9 cedure hereinbefore set forth has the following physical properties:

Under similar conditions, a thread of 100 denier, 40 filaments, may be produced by decreasing the delivery rate of the viscose pumps to 7.8 grams per minute. The physical properties of such thread are:

. r Denier Filaments Elongation Shrinkage T211259 T331716 Per cent Per cent G./d.. G./d. 100 40 9. 3 c. 75 1.89 3. 20

Since thread of the latter type will require less spacing between turns on the respective reels, the following table may be taken as giving the preferred number of turns of thread to be stored on the reels.

Also, the inherent contraction and total tensions will be only about /3 of the values stated for a thread of 275 denier, 120 filaments.

Although thread-advancing reels are preferred for the purposes of the invention, it is possible to substitute therefor sets of inclined, spaced rollers, particularly in handling freshly spun thread. At points where only one or two turns of thread are to be handled, it is possible to employ godet wheels. If, however, a processing medium is to be applied to the thread or if it is desired to store the thread for a relatively long time, thread-advancing reels of the type illustrated are preferred, principally because a large number of turns may be stored thereon in a small space. Numerous other modifications may be made in the methods and apparatus herein described without departing from the spirit of the invention.

It is intended that the patent shall cover, by suitable expression in the appended claims, whatever features of patentable novelty reside in the invention.

We claim:

1. The method of processing regenerated cellulose artificial silk thread comprisng applying a liquid to the thread while it is continuously but temporarily stored on a first thread store device in a plurality of substantially helical turns, passing the wet thread to a second thread store device upon which the thread is stored continuously but temporarily in a plurality of substantially helical turns and to which thread no further liquid is applied, and rotating said second thread store device at a peripheral speed less than that of said first thread store device whereby the liquid carried by the thread from said first device drips from the thread, said steps being performed in a continuous sequence of operations.

2. The method of processing regenerated cellulose artificial silk thread comprising applying a liquid to the thread, continuously but temporarily storing the wet thread on a first thread store device in a pluraltiy of substantially helical turns, passing the wet thread to a second thread store device upon which the thread is continuously but temporarily stored in a plurality of generally helical turns, rotating the second thread store device, at a peripheral speed less than the peripheral speed of said first thread store device, passing the moist thread to a thread store device adapted to store the thread continuously but temporarily during drying thereof; and rotating the drying device at a peripheral speed greater than that of said second thread store device, said steps being performed in a continuous sequence of operations.

3. The method described in claim 2 wherein the peripheral speed of the drying device is greater than that of said first device.

4. The method of manufacturing viscose artificial silk thread comprising applying a liquidprocessing medium to the thread while said thread is being continuously but temporarily stored upon a thread store device in substantially helical turns, drawing the wet thread from said thread store device by means of a succeeding thread store device which has a peripheral speed less than the former device, advancing the thread over the periphery of said succeeding thread store device in a plurality of substantially helical turns while no liquid-processing medium is applied to the thread stored thereon, drawing the moist thread from said succeeding thread store device to a thread store device adapted to dry the: moist thread, said thread store device adapted to dry the thread having a peripheral speed greater than that of said succeeding thread store device but less than the first-mentioned thread store device, said steps being performed in a continuous sequence of operations.

HAYDEN B. KLlNE.

KENNETH M. McLELLAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,189,195 Burkholder Feb. 6, 1940 2,002,996 Hoefinghoif et a1. May 28, 1935

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