US3550369A - Steamed coupled-process nylon yarn - Google Patents

Description

Dec. 29, 1970 a rrz 3,550,369

STEAMED COUPLED-PROCESS NYLON YARN Filed Sept. 10, 1969 5 Sheets-Sheet l FIG. Ml

INVENTOR GILBERT PITZ L ATTORNEY Dec. 29, 1970 G. PITZL 3,550,369

STEAMED COUPLED-PROCESS NYLON YARN Filed Sept. 10, 1969 5 Sheets-Sheet 2 Flt-.3

INVENTOR GiLBERT PITZL BY fizz m ATTORNEY Dec. 29,1970

Filed Sept." 10, 1969 G. PITZL STEAMED COUPLED-PROCESS NYLON YARN F IG. 4

z '2 gnoo r E 90 Q V E x 40 so so 10 STEM mum SURFACE mm, c

3 Sheets-Sheet 3 INVENTOR GILBERT PITZL ATTORNEY United States Patent O 3,550,369 STEAMED COUPLED-PROCESS NYLON YARN Gilbert Pitzl, Chattanooga, Tenn., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Continuation-impart of application Ser. No. 754,160, June 17, 1968, which is a division of application Ser. No. 451,822, Apr. 29, 1965. This application Sept. 10, 1969, Ser. No. 864,256

Int. Cl. D02g 3/02 US. Cl. 57140 2 Claims ABSTRACT OF THE DISCLOSURE In a coupled process for making nylon yarn, steaming of the yarn after quenching and before drawing gives the filaments a rougher surface as compared to unsteamed, coupled-process yarns, but does not affect the core of the filaments. Thus, the yarn exhibits the ad vantages of coupled-process yarns, viz, superior strength, modulus, and rate and depth of dyeing, relative to splitprocess yarns, without the disadvantage of increased yarn-to-guide friction in processing. The filaments, as viewed in electron micrographs of shadowed crosssections, exhibit a smooth core surrounded by a grainy skin. The skin is more nighly crystalline and exhibits higher birefringence than the core.

RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 754,160, filed June 17, 1968, now abandoned, which is in turn a division of application Ser. No. 451,822, Apr. 29, 1965, now US. Pat. 3,414,646, issued Dec. 3, 1968.

BACKGROUND OF THE INVENTION This invention relates to improved nylon yarn.

Commercially available nylon yarn is usually produced by melt-spinning polyamide filaments, winding the undrawn yarn into a package, and subsequently unwinding and drawing the yarn. Due to the separation of the spinning and drawing steps, this practice may be termed a split process. Split process yarns are usually subjected to a steam treatment as taught by Babcock in US. 2,289,860 to provide satisfactory package formation on winding the undrawn yarn.

The need for increased yarn production at decreased cost has led to the development of processes wherein the spinning and drawing steps are operated continuously, i.e., are not separated by an intermediate packaging step. Such an operation is termed a coupled process. In addition to operating economies, the coupled process, under optimum conditions, produces yarn which is superior in some respects to split-process yarns, particularly in strength, modulus and rate and depth of dyemg.

However, coupled-process filaments tend to have a very smooth surface which, in turn, leads to high yarnto-guide friction in processing the yarn into fabrics. This high level of friction results in higher and more variable tension which in turn causes undesirable nonuniformities such as streaks in the fabric. This difiiculty is avoided with split process yarns by aging the undrawn yarn for several hours before drawing. The surface roughness of the filaments is appreciably increased by this procedure.

SUMMARY OF THE INVENTION The novel product of the invention is a low friction yarn comprising synthetic polymer filaments of a polycarbonamide. The filaments are characterized by a rough texture on their surface and, as viewed in electron micrographs of shadowed cross-sections, as having a smooth central portion surrounded by a rough, grainy peripheral area. This structure will be best understood by reference to the photomicrographs to be described hereinafter. The filaments are further characterized by a ratio of CD for the skin to CD for the whole filament of at least 1.04 and by a skin-to-core birefringence ratio in excess of 1.01. CD is percent crystallinity by density determined as hereinafter described.

The product of the invention is provided by an improved coupled-process for the continuous production of drawn synthetic polymer filaments from a melt of a polycarbonamide, which involves the sequential steps of extruding said melt in the form filaments, at least partially quenching the melt in a gaseous, nonaqueous cooling medium to solidify the filaments and then drawing the filaments to at least twice their as-spun length. The improvement comprises intermediate said quenching and drawing steps treating the filaments with steam while their surface temperature is in the range of T to Tfd+60 C., wherein T is the force-to-draw transition temperature of the filaments.

The term sequential used in describing the steps of the above process is intended to connote that the operations of extruding, quenching, steaming and drawing occur in that order prior to windup of the filaments. It will be understood that intermediate operations in the continuous process, especially between steaming and drawing or between drawing and windup, are not meant to be excluded. A typical intermediate operation of this nature would be the application of a lubricant or finish to the filaments. In any case there is no intermediate packaging or other appreciable delay, e.g., aging, prior to the drawing step.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more readily understood by reference to the drawings wherein:

FIG. 1 shows photomicrographs of filament crosssections, that of A being a product of the invention and B and C being prior art products;

FIG. 2 shows photomicrographs of filament surfaces,

I that of A being a product of the invention and B and C being prior art products;

FIG. 3 is a schematic drawing showing the various steps of the process for obtaining the product of the present invention;

FIG. 4 is a graph, to be explained in connection with Example 2, showing the effect upon tension when the filament surface temperature is varied in the steaming step.

DETAILED DESCRIPTION As shown in FIG. 3, filaments 1 freshly extruded from spinneret 2, pass into cooling chimney 3 where they are contacted by cross flow air 4. Convergence guide 5, adjustable in position to assist control of filament temperature, leads the yarn at the desired temperature out of chimney 3 and into steamer 6 where a cross flow of steam 7 contacts the still hot filaments. After passing out of steamer 6, the yarn passes over finish roller 8 to apply a lubricating finish and then around a pair of rolls 10. The yarn is continuously drawn by wraps around a pair of heated rolls 12 moving at higher speed. The yarn then. passes over driven roll 13 and finally advances through guide 15 to a package 20 where it is wound on cylindrical core 21 which is surface driven by drive roll 22.

The process, in particular the application of steam to the filaments at a critical period in the consolidation of their structure, promotes crystal growth at and near the filament surface and as a result a very rough, bumpy surface, as illustrated in FIG. 2A, is formed when the yarn is drawn. Unlike split-process yarns, however, this effect does not extend throughout the filament cross-section and, as a consequence, the improved properties of the yarn relative to split-process yarn are retained.

When a nucleating agent, such as the kaolinite particles exemplified hereinafter or other finely divided particulate material, is added to the polymer before extrusion, spherulites are formed near the filament surface when the yarn is steamed and this leads to a somewhat rougher surface than obtained With steaming alone. As is well known to those experts in the polymer art, spherulites are crystalline aggregates of more or less spherical shape which form when certain polymer melts are cooled. Excessive spherulitic growth, i.e., throughout the filament cross-section, is undesirable from the standpoint of obtaining optimum fiber properties and is usually avoided by rapid cooling of the extruded filaments to a temperature below the glass-or second-order transition temperature which is referred to herein as the force-todraw transition temperature.

If the temperature of the filaments entering the steaming zone is allowed to drop below the force-to-draw transition temperature, which is about 59 C. for 6-6 nylon yarn prepared as described herein, the desired filament-surface roughening is not achieved.

The initial modules of the yarn is indicative of the rate of which the yarn elongates with increasing load in the early stages of elongation. Practically, it is determined from the stressstrain curve by multiplying the load in grams at 1% elongation on the loading curve by 100 and dividing by the denier of the yarn.

Measurements of yarn friction as reported herein are made by passing the yarn at 250 y.p.m. (228.5 meters/ min.) over a inch (9.5 mm.) diameter polished chrome pin. The yarn contacts the pin over an angle of 164 degrees. The yarn is passed from a supply package over a magnetic brake to apply the desired tension, then downwardly to and around a small pulley attached to a Statham strain gauge. From the pulley, the yarn is passed up and over the chrome pin and then down to a second pulley attached to another strain gauge. From the second pulley, the yarn is passed upwardly to a power-driven roller and an associated idler roller where it is given several passes around these rollers to avoid slippage. The yarn is passed from the power-driven roller to an aspirator, which carries the yarn to a waste container. The input tension, T is adjusted to 10 grams as measured on the first strain gauge. The output tension, T is measured by the second strain gauge, the strain gauges being connected to suit able recorders for this purpose. For comparative purposes, the output tension developed may be compared when the input tension is constant. The coeificient of friction may be calculated from the equation.

wherein T is the input tension, T the output tension, a is the angle of yarn contact in radians and e is the base of the natural log.

The |values for force-to-draw transition temperatures, as reported herein, are determined by measuring the force-to-draw at different yarn temperatures and plotting a curve of force-to-draw vs. yarn temperature. The lowest temperature above room temperature at which a definite break in the curve is observed is taken as the transition temperature for the particular yarn. Since the force-todraw transition temperature for nylon varies with the degree of crystallinity, orientation and moisture content, the force-to-draw is determined by passing yarn directly after quenching to a heated feed roll of 6.72 inches (17 cm.) diameter, passing the yarn around the feed roll for 16 turns to insure temperature equilibration, then passing the yarn to a draw roll and drawing to a 2.2 draw ratio.

The force-to-draw transition temperature of the 6-6 nylon yarns referred to herein is about 59 C. in all cases. The surface temperature of the filaments is determined with a compensating thermocouple arrangement in which one of a pair of thermocouples is placed in contact with the running filament and the other thermocouple is heated electronically until the two are in balance. A commercially available instrument of this type and manufactured by the Hastings-Radist Company Was used in measuring the filament temperatures reported herein.

The rate and depth of dyeing of yarns, as reported herein, are determined using an aqueous solution of anthraquinone blue SWF at a concentration of 1% based on the weight of the yarn to be immersed in the dye bath and a temperature of 55 C. The depth of dyeing is reported in terms of the number of shades difference in depth of one sample relative to another. Plus signs indicate deeper dyeing, while minus signs indicate slighter dyeing. The rate of dyeing is calculated on a basis of the percent dye, based on the weight of the yarn, taken up in a unit of time.

Examination of shadowed filament-cross-sections in the electron microscope is carried out as follows: the filament is embedded in a copolymer of methyl and butyl methacrylate. Cross sections of 0.3-0.5 micron thickness are then cut using a microtome with a glass knife. Knives other than glass, particularly diamond, should be avoided. The embedded filament cross-section is then placed on a metal grid or screen and placed under a bell jar where a high vacuum is created. A mixture of gold and palladium is then deposited on the cross-section from a heated goldpalladium filament mounted at an angle with respect to the surface of the filament cross-section. If the surface of the cross-section is completely smooth, an even coating of the metal results. However, if the cross-section is rough or irregular, then more metal is deposited on the side adjacent the heated metal filament and an irregular coating results. The cross-section is then examined in the electron microscope and an electron micrograph prepared using conventional techniques with the electron beam perpendicular to the surface of the filament.

Surface replicas of filaments are prepared as follows: the filament is mounted on a microscope slide, placed in vacuum and exposed to metal vaporization at an angle to the surface of the filament following the procedure described above for shadowed cross-sections. The filament is then dipped in polyacrylic acid to embed one side. After the polyacrylic acid hardens, the slide is removed, leaving the metal-coated filament with one side (the metalcoated side) embedded in the hardened polyacrylic acid. The filament is then peeled out of the metal coating which remains adhered to the polyacrylic acid. The polyacrylic acid is then dissolved with water and an electron micrograph made of the metal surface replica.

In the following examples all parts and percentages are by weight unless otherwise stated.

EXAMPLE I Polyhexamethylene adipamide having a relative viscos ity of 36.5 is melt extruded in the conventional manner to form 34 filaments. By an arrangement similar to that illustrated in FIG. 3, the filaments are passed downwardly through a quenching chimney where they are cooled by transverse air flow. When the filaments reach an external temperature of -85 C., they are converged by passing over a convergence guide and then immediately through a 12-inch length steamer where steam at essentially atmospheric pressure is passed across the yarn. The yarn is then passed over a finish roller where a lubricating finish is applied, then around a feed roller and its associated idler roller, then around a draw roller having a sufiiciently higher peripheral speed than the feed roller to draw the yarn to a ratio of 3.2. The draw roller is located in a heated compartment having an air temperature of C. and the peripheral speed of the draw roller is 3,500

y.p.m. From the draw roller, the yarn is passed around a second roller in the heated compartment and then back around the draw roller, the second roller having the same peripheral speed as the draw roller so that the yarn is subjected to a constant-length heat treatment. The yarn then passes from the heated compartment directly to and around a roller having a lower peripheral speed to permit the yarn to retract slightly and thereby the winding tension. The yarn is then passed to a rotating bobbin where it is wound into a package in the conventional manner.

When electron micrographs of shadowed cross-sections, prepared as previously described, are examined, the area in the center is found to be relatively smooth while the area near the skin is rough and grainy as illustrated in FIG. 1A. An electron micrograph of a replica of the filament surface shows it to be rough and bumpy as illustrated in FIG. 2A.

For comparison, electron micrographs of shadowed cross-sections and skin replicas of a filament from a yarn prepared as above except for omission of the steaming are illustrated, respectively, in FIGS. 1B and 2B. Here the entire cross-section is smooth and the surface of the filament is smooth relative to the steamed filament. Also for comparison, a yarn is prepared by the split process, the yarn being steamed after quenching using an 82 inch (208 cm.) steamer in the usual manner. The filament temperature at steaming is 50 C. After steaming, the undrawn yarn is wound into a package in the conventional manner. The undrawn yarn is then drawn immediately using the drawing stage of the coupled-process machine as described above so that drawing conditions are identical with those of the coupled-process yarn. Electron micrographs of a shadowed cross-section and a filament surface replica are prepared and illustrated in FIGS. 1C and 2C. As can be seen from these figures, the rough, grainy structure appears throughout the shadowed cross-section and the surface, although rough and striated, appears smoother than that of the yarn of this invention. Shadowed crosssections and surface replicas are also prepared from split process yarns which have been aged for more than 8 hours before drawing and are found to be identical with those of FIGS. 10 and 2C.

Properties of the above three yarns are shown for comparison in Table I 'below. As can be seen therefrom, the yarn of this invention, i.e., the coupled-process steamed yarn, retains the high tenacity, initial modulus and good dyeability of the unsteamed coupled-process yarn and is superior in this respect to the split-process steamed yarn. On the other hand, the coeflicient of friction of the yarn of this invention is substantially lower than either of the other two.

When the yarn of this invention is used as a filling in a fabric having a conventional 70-denier nylon warp, the quilling tension being 20 grams, the quill barr is judged to be at an acceptable level. Under the same conditions, the unsteamed coupled-process yarn produces 35 grams quilling tension and an unacceptable level of quill barr.

*Number shades difference in depth. NorE.Yarn A=coupled process, steamed, Yarn B=coupled process,

unsteamed; Yarn C=split process, steamed.

EXAMPLE II Coupled-process yarns of various filament deniers are prepared as in Example I except that the temperature of the yarn at the point of steaming, i.e., as the yarn enters the steamer, is varied in the range 4590 C., by changing the location of the steamer or the convergence guide. When these yarns are subjected to friction tests as previously described with a constant input tension of 10 grams, the output tension varies with the temperature of the yarn at steaming as shown by the curve in FIG. 4. As can be seen, the output tension drops sharply as the temperature exceeds 50 C., but becomes constant again at temperatures of 60-65 C. and higher. At temperatures above about C. the process becomes inoperable due to the filaments becoming sticky and fusing together. Conditions employed in preparing the yarns of FIG. 4 are given in Table II below.

Two hundred parts of a commercially available kaolinite powder (Al O -2SiO- '2H O), purified by an ultra flotation process (US. Pat. No. 2,990,958) to substantially eliminate metal oxides other than aluminum and silicon oxide and classified by centrifugation to provide an average maximum dimension of 0.55 micron, are mixed with 300 parts water and 1.2 parts tetrasodiumpyrophosphate decahydrate in a high-shear mixing mill. After milling for 1 hour, the mixture is diluted with 300 parts water, transferred to a tank and stirred for 24 hours. The slurry is allowed to settle for 20 hours, then decanted from the settled materials and diluted with water to a concentration of 20% solids. The diluted slurry is then passed through a standard commercial filter having an average pore size of 5 microns and continuously stirred until used.

Several 450 pound batches of polyhexamethylene adipamide having a relative viscosity of about 37 are prepared in an autoclave in the conventional manner except that to certain batches sufficient amounts of the kaolinite slurry are added during the polymerization cycle to give the concentrations indicated in Table III below. The kaolinite slurry is added to the autoclave when the temperature reaches 200 C. The polymer is extruded from the autoclave and cut into flake in the conventional manner.

The various batches of polymer are melt extruded and processed into 70-denier, 34-filament yarn by the coupled process following the procedure described in Example I. As indicated in Table III below, yarns I and I were steamed as described in Example I while the other yarns were not steamed. When friction measurements are made as previously described at a constant input tension of 10 grams, the output tension varies for the different yarns as shown in Table III. As can be seen, yarn I which combines the use of 0.5% kaolinite with steaming gives the lowest friction.

As illustrated by the foregoing examples, the product of this invention has a structure such that when examined microscopically at a magnification of at least 1600X, the outer surface of the filament is rough to provide low yarn to guide friction which is needed in textile processing operations, while the internal or core structure is apparently unchanged so that advantages in strength and modulus are retained. Also, even though the outer portion of the filament cross-section is changed, the enhanced dyeability of the coupled filament is retained. This desirable structure is obtained by steaming the filaments at a temperature above the force-to-draw transition temperature. Preferably, the temperature of the filaments as they enter the steaming zone is at least C. above the force-to-draw transition temperature in order to insure the maximum reduction in friction as well as uniformity in this respect. The temperature should not exceed the softening temperature of the filaments. For best results, the temperature of the filaments should be in the range of 5-40" C. above the force-to-draw transition temperature. The preferred temperature range for 6-6 nylon is 65100 C. The temperature referred to is, in all cases, the surface temperature of the filaments, since this is the only temperature which can be measured practically.

The yarns of this invention may be prepared from any polyamide which crystallizes readily in the presence of heat and moisture. The preferred polyamides are 6-6 and 6 nylon; that is, poly(hexamethylene adipamide) and poly(epsiloncaproamide), respectively. Other suitable polyamides for this purpose are those disclosed in U.S. Pats. 2,071,253, 2,130,523 and 2,130,948.

The duration of steaming is not highly critical however, for reasons of economy and operability, steaming times in the range of 0.0040.02 second are preferred. Particularly with the shorter steaming periods, the steam should be applied uniformly and with minimum turbu lence in order to prevent nonuniformities in the resulting filaments. For this purpose, a steamer of the type disclosed and claimed in U.S. Pat. No. 3,316,741 is preferred. The particular temperature and degree of saturation of the steam do not affect the results obtained.

Intermediate packaging of the yarn, or other appreciable delay, between steaming and drawing must be avoided in order to obtain the product of this invention. Thus, the split process is not suitable for this purpose regardless of the method of steaming employed.

EXAMPLE IV This example compares, as in Example I, a split-process yarn and an unsteamed coupled-process yarn with a steamed coupled-process yarn of this invention and illustrates the unique skin/ core differences and the advantages of the yarn of this invention.

In each case, polyhexamethylene adipamide with a relative viscosity of 38 is melt-extruded in the conventional manner to form 17 filaments. The steamed coupledprocess yarn is prepared as described in Example I, the draw-ratio in a hot-chest at 160 C. being 3.2, the draw speed being 2500 yd./ min. (2290 m./min.), and the yarntemperature at the prior point of steaming being 90 C. The comparison coupled-process product is formed in identical fashion except that it is not steamed before drawing. Both of these drawn yarns have a denier of 71.

The conventional split-process yarn is steamed at a yarn-temperature of 55C. and then Wound up. Subsequently, it is unwound, drawn at 560 yd./min. (512 m./ min.) to a draw ratio of 3.1, and packaged at a final denier of 70. Thus, except for the processing differences being illustrated, these three yarns are as nearly compara ble as is reasonably possible.

Properties of the three yarns are given in Table IV, being obtained as described hereinbefore.

TABLE IV.YARN PROPERTY COMPARISON Tenacity Percent (gm./ Percent Quilling shrink- Dye Yarn* denier) elongation tension age" depth*** *Yarn A=eoupled-pr0cess, steamed; Yarn B=coupled-process. unsteamed; Yarn O=split-process, steamed.

Loss in length from treatment in boiling water.

***Using structuresensitive Milling Blue B dye.

From the results shown in Table IV, it is apparent that tenacity of the coupled-process yarns is at least as high as for split-process, and percent elongation is improved. The coupled-process yarns have desirability lower shrinkages on boil-off and are dyeable to many shades greater dye-depth. The unsteamed coupled-process yarn (Yarn B), however, has a quilling tension so high as to cause unacceptable quill barr, but the steamed coupled-process yarn (Yarn A) has a quilling tension at least as loW as for conventional split-process yarn (Yarn C). The observation that steamed coupled-process yarn retains the property-advantages characteristic of coupledprocess yarn without its surface-friction deficiencies suggests a unique skin/core character.

In order to separately study skin and core character, the skin is carefully pulled from a filament sample. The sample is glued to a glass slide under 0.1 gm./ den. tension. After notching the surface slightly with a razor blade, the skin can be peeled off using tweezers, 2.0 to 2.5 cm. long peels of skin being relatively easily obtained when working under 10X magnification. The first 0.5 cm. of each skin peel usually has some core attached and it is out 01f. In all cases, the skin comprises from 5 to 10% of the weight of the whole filament. It is much easier to remove the skin from steamed coupled-process yarn than from either unsteamed coupled-process yarn or splitprocess yarn.

Small differences in density of nylon samples are excellent measures of differences in percent crystallinity, the densities for amorphous and crystalline polyhexamethylene adipamide being given by H. W. Starkweather and R. E. Moynihan in J. Polymer Sci, 22 (1956), pp. 363-368. Percent crystallinity by density, CD, is calculated using Equation 1 dd,, d-1.069 d,d,, 1.2201.069 (1) Densities are in -gm./ml., d denoting amorphous density and d the 100%-crystalline density. Density, d, of a specimen under test is obtained in a density gradient tube containing benzene and carbon tetrachloride calibrated using glass beads of known density. Fine nylon samples are easily seen in the liquid if observed using crossed polaroids. The standard deviation of repetitive CD measurements by this technique is only 0.3

For practical reasons, and because the skin is such a small percentage of the total filament, crystallinities by the above technique are obtained for skin specimens and whole-filament specimens rather than to isolate core specimens. The ratio of CD for the skin to CD for the whole filament is computed in each case. For the steamed coupled-process yarn, this ratio is 1.09 indicating significant increase in crystallinity of the skin over that of the core. For the unsteamed coupled-process yarn and the splitprocess yarn the ratios are 1.00 and 1.01, respectively, in-

CD X 100 X 100 dicating no significant difference in crystallinity between skin and core. The absolute percent crystallinities given in (skin)/ (core) form are: 47.2/43.2 for steamed coupled-process yarn, 45 .5 45.4 for unsteamed coupledprocess yarn, and 44.3/43.7 for split-process yarn.

To verify the unique skin/core differences in the yarns of this invention, birefringence profiles across whole filaments are determined. An interference microscope which, in the absence of a sample, sets up a field of parallel interference fringes one wavelength of light apart is used in this measurement. When a filament of different refractive index is immersed in the liquid, the interference fringes shift proportionally to the optical-path differences caused by the filament. The change in optical-path length at any point is proportional to sample thickness and its refractive index at that point. The effect of sample thickness is eliminated by photographing the fringes when the sample is immersed in each of two liquids of known different refractive indices. With a polarizing analyzer parallel to the fiber axis, n (the parallel refractive index) is computed from the fringe distortions and the known refractive indices of the two liquids, the computations being made for spaced points across the width of each filament. In the same way, n; is computed from fringe shifts obtained when the polarizing analyzer is perpendicular to the fiber axis. Birefringence, An, is computed from An==n=-n (3) For each of the three types of yarn, ten specimens are so measured and the results are averaged. The split-process and unsteamed coupled-process yarns show no increase in skin birefringence over core birefringence. The steamed coupled-process yarn of this invention, however, shows a marked decrease in birefringence on passing from the outer skin to the core. Skin/core birefringence ratios for these yarns are 1.03 for steamed coupled-process 0.99 for unsteamed coupled-process 0.99 for splitprocess.

References Cited UNITED STATES PATENTS 2,834,093 5/1958 Woodell 57l40X 2,860,480 11/1958 Cox 57140 3,019,509 2/1962 Cox et al. 16l177X 3,158,983 l/l964 Tlamicha 161l80X 3,291,880 12/1966 Pitzl 264-176 3,360,424 12/1967 Tlamicha l61180 JOHN PETRAKES, Primary Examiner US. or. x. l61180

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