US2780879A - Stiffening of shoe uppers and stiffening elements therefor - Google Patents

Description

Feb. l2, 1957 R. a, HARRISON Erm. 2,780,879

STIFFENING oF SHOE URPERS AND STIFFENING ELEMENTS THEREFOR Filed Nov. 16, 1953 IN VENTORS nitcd States Patent STIFFENING OF SHOE UPPERS AND STIFFENING ELEMENTS THEREFOR Raymond B. Harrison, Arlington, and Russell G. Edwards, Quincy, s., assignors to Stedfast Rubber Company, Inc., Boston, Mass.

Application November` 16, 1953, Serial No. 392,302 2 Claims. (Cl. i6-46.5)

This invention relates to the stiilenng of a portion of the upper of a shoe. More particularly, it pertains to means and procedure `by which a stiiening blank containing a rubber composition can be maintained limp during the upper assembly and shoe lasting operations and become fully vulcanized in lasted shape to a permanently resilient condition while in the iinished shoe and before wear. Y

The invention is applicable to box toes, counters, and other similar stiifening elements. It may best be understood by describing its application to box toes for which it has been employed with outstanding success.

Self-conforming box toes are generally classified as rigid and soft The rigid type includes all kinds, whether thermoplastic, or solvent activatable, or water activatable, that produce iir-m toe Wallsand dome portions upon dissipation of the activating medium used to soften the box toe blank to a condition of workable plasticity directly before shoe lasting operations. The soft types comprise all box toes that do not ultimately become fully rigid in the shoe. They embrace a wide range of commercial box toe sheet materials providing a variety of degrees of softness or exibility for the shoe manufacturers choice. They are described by the shoe industry as soft, semi-soft, flexible and semi-ilexible in order to classify these many box toe materials by the end character of the lasted toe in terms of specific degrees of resilience. The degrees of resilience vary with the box toe material itself, the latex or other cement used to attach the box toe to shoe parts, and the cementing technique used. The range extends from a lifeless softness to a degree of rmness just short of rigidity, and considered exible only by reason of the yielding of thel dome and wall portions to thumb pressure to an extent sufficient to locate the toes of a wearer within the shoe.

All soft box toes, except certain light weight pyroxylin types that are self-adhering upon activation by solvent, must be cemented into the shoe upper. Various cements are employed for this Vpurpose and the cementing techniques vary widely in accordance with the value of the shoe and the personal preference of the shoe manufacturer. In most cases, la-tex cements of natural or synthetic rubber are used to attach the box toe to one or more of its co-engaging shoe parts. In some cases, box toes are cementedA on one side with latex and attached thereby to the esh of the leather upper in the stitching room, and again cemented on the opposite side at the pulling-over operation to `engage and permanentlyV affix the shoe lining thereto. A brush applied, naphtha-rubber cement is often employed for this purpose at the pullingover operation.

Where box toes are cemented into unlined footwear latex cements are almost universally used in preference to the more viscous naphtha-rubber cements.

These attaching cements have an important bearing on the resilience and strength of the finished lasted box toe. lf of proper viscosity, their lilms aid and support 2,780,879 Patented Feb. l2, 1957 the impregnant used in Vthe box toe itself and their eiec- Itiveness in causing the toe to be permanently integrated with the co-engaging shoe parts causes the entire structure of vamp, box toe and shoe lining to become a laminate, thus greatly increasing the box toe wall strength. Many lightweight soit box toes having ilannel or other textile bases depend nearly as much upon the iilms which attach the box toe to the shoe lining and/ or shoe vamp as upon the box toe itself for the support given the finished lasted toe.

Box toe sheetngs containing either natural or synthetic rubber as the principal component of the impregnant used have always been made either partially or fully vulcanized in their finished state, though the liquid irnpregnant employed has been either entirely uncured or only partially cured such as in the case when impregnants are constructed from pre-vulcanized latices. Box toes cut from partially vulcanized box toe sheetings do not function in the shoe with any degree of permanence though offering theY advantage of being more readily conformable at lasting operations than box toes cut from fully precured sheetings. A fully precured box toe, being non-thermoplastic and being unactivatable by any solvent not injurious to other shoe parts cannot be softened to a condition of limpness or static pliability directly before the Shoe lasting operations, and permitted to set-up through dissipation of the activating medium as is common practice in preparing rigid box toe types for pulling over and bed-lasting. A fully precured box toe tights Vthe conforming action of the bed-lasting wipers and often develops unsightly pin wrinkles in the exterior wall of the shoe toe.

In all shoes which are toe lasted with latex cement and in which the attachment of the overlasted margin of the toe portion of the upper depends upon the latex cement alone for permanent engagement to the insole, the active resilience of the fully precured box toe attempting to return to unlasted shape often acts instantly to pull away from the partially .coagulated cementiilm applied to the surface ofthe insole only seconds earlier.

Therefore, while the finished soft box toe shoe would Y be greatly enhanced by the complete curing of the rubprovidingit with a box toe or other upper stiieningelement embodying fully cured rubber materialV havingV a high degree `of permanent resilience, and yet at the same time avoiding all problems of conforming such ele-V ments to the shoe last and of varying or increasing shoe manufacturing operations,v or costs, such as derived from the customary practices followed in incorporating fully cured orpartially cured box toes or similar stiffening elements.

In the accomplishment of this general objective there has beendeveloped a shoe stiiening sheet material impregnated with an uncured rubber and a curing agent, from which to cut the skive box toes, counters, and the like for incorporation in the upper of a shoe through the use of various rubber cen-rents containing self-curing, migratory vulcanizing accelerators operative at room temperatures. Particularly advantageous in use and commercially available arethe dithiocarbamate type room temperature accelerators. In one special instance to be mentioned the use of the curing agent is unnecessary.

Vulcanization or curing of the impregnant composition does not loccur at room temperature until the dithiocarbamate or other accelerator migrates from the adtoe. thus bringing together the sulphur or a curing agent l and the accelerator essential for self-curing of the rubber. Various perfecting agents may be used with the sulphur to enhance' the powerful action ofthe dithioca-rbamate on the rate of reaction between rubber and sulphur. The irnpregnant composition is thus changed physically from a plastic condition to a resilient mass creating a lively rebound in the toe structure.

It is a further and specic object of this invention to provide shoe stiffener sheet material of the character indicated with an auxiliary saturantor coating that will add a different uncured rubber component to the sheet material for preventing blocking or welding of the sheet material to itself particularly while being dinked or cut. The shoe stiffener sheet material having such an auxiliary saturant or coating for preventing blocking or Welding is the subject of our copending application Serial No. 629,988, tiled December 2l, 1956.

These and other features of the invention will be particularized and more fully understood from the following detailed descriptions of preferred embodiments, when taken in connection with the accompanying drawing in which:

Fig. l is a plan View of a cut and skived toe stiffener blank formed of the sheet material of this invention;

Fig. 2 is a plan view of the inside of the toe portion of a shoe vamp to which the toe stiifener blank of Fig. l has been partially applied in the required position by means of adhesive;

Fig. 3 is a plan view of the outer side of a quarter lining partially covered by a counter stiiening blank,l made in accordance with this invention, and adhesively joined thereto;

Fig. 4 is a perspective view of the quarter lining of Fig. 3 with the counter stiffening blank adhesively secured to the outer side thereof, the assembly being partially formed to shape for incorporation in the heel end portion of a shoe;

Fig. 5 is a side view of the toe end portion of a lasted shoe of conventional type welt, partially sectioned to show the last and details of box toe construction;

Fig. 6 is a similar side view of the heel end portion of a lasted shoe of welt construction, sectioned to illustrate details of counter stiifening construction; `and Fig. 7 is a bottom perspective View of a last to which a welt insole has been attached, and in which` a lining including upper assembly is having cement manually applied to the lining face of the toe blank immediately prior to the pulling-over operation. Y

In the drawing, 10 refers to the toe stiffener blank which has a skived edge portion 12, and refers to the counter stifener blank having a peripheral skived edge portion 22 interrupted Vby a dart 24 for preforming with a quarter lining 26 by use of stitching 28 as shown in Fig. 4.

The shoe stiffener sheet material fromy which the toe i stifener blank 10 and the Vcounter stiffener blank 20 are formed may be made of any suitable base material such as carded felt, napped or unnapped woven textiles, paper and the like, although only the use of a preferredannel yard goods will be described in detail. Entirely suitable finished sheet materials in a desired range can beV produced from four basic flannels having yardtopound relationships of 4.18, 3.00, 2.35 and 1.60.

In actual practice ideal results have been obtained by the use of two saturations and a iinal spread coating on one side of the saturated base material. pears desirable because it has been found diiicult to obtain the ounce load required with a single saturation. Further, Y

a second saturation permits. the use of aidiiferenteompound, which, though subject to full curing by the room temperature accelerators contained in the cement, acts to decrease the tendency of the iinished stiiener sheetY to block to other adjacent sheets, as would occur in packaging and also in cut box toe and counter blanks when die cut in multiple thicknesses on a beam dinker or clicking. ma-

Double saturatingfap-y 4 chine. Final insurance against blocking is obtained by spread coating a l'm of the nraterial` comprising the second saturating compound on one side of the finished sheet goods. It is possible, however, to obtain adequate impregnation of the saturable base material with only a single saturation of either saturating.` compound.

An exemplary formula for the rst saturating compound is as follows:

F rst Saturant Parts by Trade Weight; Naines Crude Rubber (smoked sheet)v 100 10 Amborex-S.

Zinc Oxide 5 Calcium Carbonate.. 90 Atounto. Titanium Dioxide 15 Antioxidant i Antox.

Petroleum Naphtha 200 Denatured Alcohol 6 In the above formula, which is a preferred one, the vulcani'zed vegetable oil may range from l0 to 20 parts, the sulphur from 2 to 3.5 parts, the zinc oxide from 5 to l0 parts, and lthe inertfcalcium carbonate particlesfrom 30 to l5() parts. GR-S synthetic rubber (butadiene-styrene copolymer) may be used in place of the crudo rubber pro viding the sulphur is increased, to 4 5 to 5 parts.

It will be noted that the above compound includes, in addition to sulphur and' other vulcanizing agents, a predominant amount of crude rubber and a very substantial portion of calcium carbonate which acts as a filler. Other lrubbers may be employed in the unvulcanized form.

This rst saturating compound may be made by premas ticating the crude rubber'on a rubber mill and thereafter adding the other solid ingredients until all are uniformly milled together. Usiugthe petroleum naphtha asl a solvent for'the rubber andv denatured alcohol as a viscosity reducer, the mill'ed material is finally churned to a viscosity suitable for saturation.

The second'saturatingcompound which is used also as a ilnalV spreading compound differsk in that the predominant elastomeric component is an unvulcanized synthetic rubberwhich is a rubbery copolymer of butadiene and acrylonitrile. YThis compound, an exemplary formula of which is as follows, also contains a substantial portion of aresinous copolymer of'styrene and butadiene:

' Second; satura/1t'nnd'spreadng compound In the preceding formulan, which is a preferred one,v the zine'oxid'e may range from 2 to- 10 parts, the sulphur from 2.5 to 3.5' parts, the styrene-butadiene copolymer from l0 to 35 parts, the calcium carbonate yfrom 20. to 70parts, the steari'c 'acid1from l to 2, parts, and the wax from 4 to -part's. l Y

In this instance the compound may be'produced by permasticating the synthetic butadiene elastomer on a rubber mill, land thenV addingallother solid' components until a. uniformly milled condition is obtained. Employing toluol as a solvent, the milled material i`s churned to a suitable saturating or spreading viscosity.

It has been found that an entirely satisfactory shoe stiffening blank material is obtained by saturating and coating a 1.60 double-napped flannel with the above compounds in the following manner: The flannel is saturated with the saturant of the first compound, `and thereafter it proceeds through a drier having a temperature of the order of 180 F. The thus dried saturated material in rolled form is then fed to the second saturant, after which it also travels through a drier having a temperaturecf the order of 180 F. This roll of dried, double saturated base material is then fed through a knife spreader, which imparts alight coating to one surface only, using the same compound employed in the second saturating treatment. The spreading operation is continuous and the base material coated with the spreading compound proceeds through a drying zone having a temperature of the order of 190 F.

The room temperature, ultra-accelerators that will ultirnately contact the surface of the finished box toes, counters, and like shoe stifiening elements will cure both the natural and synthetic rubbers of the two saturating compounds. The particular reason for using the crude rubber impregnant iirst is that more bounce, as a characteristic of the finished box toe, develops from the finally cured crude than from the finally cured synthetic rubber. The uncured crude rubber, however, is slightly tacky and prone to weld or block to itself. By using it as a first impregnant and then covering it with the second impregnant comprising a synthetic rubber which, though curable, has much less tendency to weld in its uncured state, welding of either uncured sheet goods or uncured cut shoe stiffener blanks is successfully avoided. It is possible also to use only the second saturant compound by following the previously described procedure with the second saturant compound used for each impregnation. The resulting cured box would have moderately less life and bounce as compared to one embody ing the crude rubber saturant. In this connection it will be rec-alled that the shoe stiffening, sheet material will in each instance remain uncured until it is incorporated into the shoe with accelerator-laden cement.

lt has been found that an ideal latex cement can be made from the following exemplary formula:

Parts by Trade Names Weight Natural latex (60% Solids) 167.0 Potassium Hydroxidc 0. 5 Water-dispersible vulcanizing aceeler- 30.0 Setsit- (R. .'l. ator (a dithiocarbamate). Vanderbilt). W ater 65.

Since a latex cement is used on the leather en aUin side ofthe stiffening blank, the ultra-accelerator must be dispersible by ball milling or must be water soluble in order to be miscible with the natural latex. Dupont accelerators 89 and Tepidone have been tested and found i to satisfy these requirements as well as the others involved. Tepidone is a 47% water solution of sodium dibutyl dithiocarbamate, according `to Dupont.

An entirely satisfactory naphtlra-rubberv cement has been produced from the following exemplary formula:

It is permissible to use from l5 to 30 parts of the accelerator in the above formula.

Denatured alcohol may also be used in the above formula.

The foregoing naphtha-rubber cement compound isA produced by masticating crude rubber on a cold rubber mill, after which the batch is put into solution with a petroleum naphtha having a distillation range of 2 04-220 F. and a Kauri-Butanol index of 45. A closed churn is used for .this purpose to prevent solvent loss. The vulcanizing ultra-accelerator is added after the cement is fully churned to blended smoothness, after which further churning is continued until the vulcanizing accelerator is uniformly mixed throughout the cement which, when finished, should contain l8l9% rubber and have a viscosity of approximately 20,000 centipoises. The similar accelerator of Monsanto, N-2l26-A, which is also a brown liquid for addition to solvent cements, may also be used. The solid dithiocarbamate Dupont Accelerator 552 is also suitable, but would have to be milled into the rubber before 4the cement is made.

Selective use of the two types of cement will depend upon the shoe construction involved. For instance, the latex type will be preferred for attaching Abox toes to the inner face of the vamp on all unlined footwear, since it is cleaner to handle and will function in cementing machines. VIn lined footwear, the latex cement can be used on both sides of the box toe with the vamp, box toe and vamp lining all cemented together in the stitching room, or the box toe can be cemented to the vamp with the latex type in .the stitching room, wit-h the lining left unce-` mented to the box toe until the pulling-over operation. There the operator, before pulling the shoe, can manually brush a coat of either the latex or the naphtharubber cement over the exposed surface of the box toe, engaging the lining to the wet cement film and causing all three parts to become unitary during the course of ensuing shoe making operations.

The naphtha-rubber cement may be preferred for use at pulling-over since many lined shoes are given a brush coat of rubber cement, called vamp former, between the vamp and the vamp lining in their side portions, and also directly behind the back edge of the box toe, to help avoid vamp lining wrinkles and to hold the lining against the vamp during shoe wear. `The naphtha-rubber cement of this invention lwill act as a vamp former as well as to cause curing of the box toe. Thus,'the brush coating of the vamp and the coating of the box toe can be accomplished with a Vsingle cement in a single work step of the operator, as opposed to using the latex type cement to coat the box-toe and a vamp forming cement to unite vamp and vamp lining rearward of the box` toe.

It is `to be understood that either the latex type or the naphtha-rubber type cement will cure the box toe, and

the latex may be used on one side of the box toe and the naphtha-rubber on the other'. It will be apparent that the vulcanization of the rubber components of the box toe will occur more rapidly if the curing media ismigrating into the box toe from both sides. with the latex type cement alone, as used in an unlined shoe, will vulcanize more slowly, though as completely,

The box toe cemented andere as box toes in lined footwear having either cement on both surfaces.

Adhesion of the box `toe material to the vamp lining is of a character to indicate that the adhesive itself becomes vulcanized, even though it contains no curing agents except the accelerator. It is thought that enough sulphur may be present at the interface to cure the thin adhesive film.

The practice of the shoemaking method involved in the use of `the impregnated toe stifening blank 10 of this invention is specifically illustrated in Figs. 1, 2, and 7.

VThe prepared and skived blank having an adhesive coating 14 of active latex rubber cement containing a room temperature curing ultra-accelerator is positioned and applied to the inner surface of the cut shoe vamp 30. Subsequently an upper assembly including a lining 32 as well as the vamp 30 and adhered toe stiffener blank 10 are placed over the toe end of a last L having a welt insole 34 secured to the last bottom. Thereupon the operatorturns back the toe end part of liningV 32 and applies an adhesive coating 16 of naphtha-rubber cement containing a room temperature curing ultra-accelerator to the face of the blank 10 engageable by the lining. With the lining 32 adhered to the toe blank 1G, the upper assembly is drafted over the last on a pulling over machine and subsequently finally conformed on a bed lasting machine, and the marginal edge portions of the lining, blank and Vamp 3i) are secured to the welt insole 34, thus conforming the toe stiiener to the last L as shown in Fig. 5.

It will now be fully understood .that by reason of the room temperature curing accelerators used as components of each of the two types of cement, and the action of such accelerators on the sulphurV contained in the box toe or other stiifening element material when brought into mutual contact or migrating relation when the cement is applied to the box toe or other stiffening element, cause the lasted box toe or other stitfening element progressively to vulcanize to as complete a cure-state as would have been obtained in the event that the impregnated sheet material had been cured before the box toe or other upper stitfening element were cut therefrom` Since the novel sheet material of this invention is uncured, though latently curable through the presence of sulphur in its impregnant, no resistance is otfered to the conforming action of lasting equipment. ln uncured condition, the shoe stiffeners are limp and extensible, and shape readily to the last. Depending upon whether the cement and its curing accelerators are presented to one or both sides of the stitener blank, the cure is progressive to a final end point in from 10 to 15 days. This is clear evidence that no degree of immediate cure, consistent with the production speeds of normal shoe manufacturing practice, can impair the susceptibility of the box toe to shoe lasting operations.

The shoe stifening material of this invention also has excellent adaptability for stiffening the rearward por. tion ofa shoe upper in the region where a molded counter is normally used. Consistent with the increasing demand for flexible box toes, there is a growing interest in soft or flexible heel end structures, particularly for juvenile footwear.

With specific reference to Figs. 3, 4 and 6, it 'has been -found that a very satisfactory result in this direction can be obtained by cutting the quarterj lining blank 26 from leather or imitation leather material and cementing with either the latex or naphtha-rubbervulcanizing cementV hitherto disclosed the blank of stifening material that has been suitably skived around its marginal edges, to the inner face of the quarter lining blank in theV region to be stiffened, assembling the unitary quarter lining and stifening blank into the shoe upper 30 by stitching it in place in the usual manner, and thereafter, before the as-l sembling operation in the lasting room, brush coating the inner and previously uncemented surface of the stiffening material with the naphtha-rubber cement to cause the vulcanization of the Vrubberous saturant contained therein to occur from both surfaces of the stitfening material blank 20.

In a variation of this method the stilening blank would be cemented in position on the quarter itself, and directly thereafter the quarter lining would be cemented to the stilfening blank to produce a unitary construction of three parts before the unit becomes attached to the vamp to form a completed upper. It has been found that the latex type cement is preferable in this procedure.

In a still further variant, satisfactory results can be obtained by merely dipping the cut and skived stifening blank into the latex type cement and inserting it into the pocket formed by the bottom free and open common marginal edges of the quarter and quarter lining. The

cement securely anchors the blank in place and the vulcanizing action proceeds as heretofore described.

As in the case of the box toes, the shaping and conforming action of shoemaking operations will cause the counter blank stitening element as well as the shoe upper to correspond to the contours of the heel end portion of the shoe last. Having been thus self-conformed, the ultimate self-curing attained will cause preservation of the shape imparted by the dwell on the shoe last. It will be readily appreciated that the counter portions of shoes stitfened in this manner to a bouncy resilience afford great comfort to growing feet since there is no rigid encasement of the upper portion of the heel bones to restrict foot growth, and no hard, knife-like edges to abrade against the wearers foot with resulting discomfort. The complete vulcanization of the rubber components of the stif`r`ening material, coupled with its complete conformability in an uncured state is particularly enefcial in this additional utilization. The contours essential to the character of the heel portion of the shoe are preserved without progressive collapse and fatigue of the stitr'ening medium that occurs when rubber stiffening blanks are used in an either completely unvulcanized or only partially vulcanized condition.

The term rubber as used broadly herein comprehends synthetic as well as natural rubber.

Where in the specification and claims reference is made to room temperature curing accelerators of the dithiocarbamate type it is specifically intended to include all dithiocarbamate-producing compounds such as those xanthates that when used with an amine form a dithiocarbamate, in addition to the commercial dithiocarbamate accelerator described in the material relating to the specific examples of adhesive-containing accelerators.

In the formulasl set forth herein satisfactory results are obtainable when any combination from the ranges specified is utilized.

The scope of this Ainvention is further demonstrated by the proven fact that a neoprene saturant will cure at room temperature without the use of a curing agent in the saturant by the migration of an xanthate contained in the adhesive.

The following formulas have been used successfully:

Note: The neoprene is milled with the calcium carbonate and napthenic oil until completely blended whereafter the compound is churned in toluol until a smooth saturable solution is achieved.

Note: The above cement is produced by masterbatching 50 parts of premasticated natural rubber with 50 parts of ZBX whereafter the compound is constructed by using 50 parts of the master batch with 75 parts of milled natural rubber resulting in a total of 100 parts rubber to 25 parts of ZBX. The final compound is then churned in 220 parts of the petroleum naphtha (type 2220, having a distillation range of 204-220 deg. and a Kauri-Butanol index of 45). The butyl alcohol is then added, causing the cement to achieve a desired viscosity.

lt has been further discovered that a neoprene saturant containing a curing agent can also be cured at room temperature by utilizing the migration of an aldehyde amine accelerator contained in the adhesive.

The formulas which follow exemplify such a modification of curing action:

Saturant Parts by Trade Weight Names Neoprene (chloroprene polymer). 100 Type GN. Calcium Carbonate (ller) 40 Light Calcinecl Magnesia (stabil 4 Litharge (curing agent) 5 High Napthenic Oil 8 Toluol 200 Note: The compounding of the above formula is accomplished in identical fashion to the description given in the immediately prior saturant formula.

Note: Accelerator 833 which is a butyraldehyde-monobutylamine condensation product, also a migratory room temperature ultra-accelerator curing medium, and also a Dupont product may be substituted for Accelerator 808 at equal parts by weight.

Either single or multiple applications of the two neoprene saturants can be made.

The advantages attained through the use of the stifening blank material of this invention are without increase in the cost of shoemaking operations, and are accompanied by such an enhanced superiority of shoe product, that any increase in impregnated blank material and cement costs is more than compensated by satisfaction to the users of such shoes.

It will be understood that variations, changes, and adaptations can be made in the invention set forth without departing from rthe principles thereof and the scope of the appended claims.

Having thus described our invention, what we claim as novel and desire to secure by Letters Patent of the United States is:

1. A prepared shoe upper for lasting in which a particular portion is provided with a limp, conformable, eXtensible sheet of saturable base material impregnated with vulcanizable rubber containing a vulcanizing agent and in which all of said rubber is unvulcanized, said vulcanizing agent being present in amount suicient for subsequent curing of the vulcanizable rubber, and said sheet being adhesively joined to an inner surface of the upper by a rubber-containing cement which includes in its composition a room temperature curing accelerator in amount capable in coaction with the said vulcanizing agent of causing complete curing of the vulcanizable rubber contained in the sheet whereby the shoe in which said upper is incorporated will have a permanent highly resilient stiifening portion.

2. The combination of claim 1 in which the upper includes a lining member to which said sheet is also adhesively joined by a rubber-containing cement.

References Cited in the tile of this patent UNITED STATES PATENTS 1,573,978 Levine Feb. 23, 1926 1,722,967 Bennett et al July 30, 1929 1,777,544 Beckwith Oct. 7, 1930 1,831,689 Swett Nov. 10, 1931 2,197,928 Finn Apr. 23, 1940 2,201,931 Sullivan May 31, 1940 2,363,981 Lissig Nov. 28, 1944 2,512,003 Wedger lune 20, 1950 2,541,748 Daly Feb. 13, 1951 2,611,195 Brophy et al. Sept. 23, 1952 2,646,379 Poschel July 2l, 1953

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