US2612679A - Filaments containing fillers - Google Patents

Description

Oct. 7, 1952 R. K. LADISCH FILAMENTS CONTAINING FILLERS '2 SHEETS-SHEET 1 Filed Aug. 21, 1951 INVENTOR A AD/SCY/ 6m ATTORNEY Patented Oct. 7, 1 952 7 2,612,679 IFIILAMENTS ICQNTAINING' FILLERS -Rolf Karl Ladisch, Drexel Pa.

*Originalapplication October 23, 1950, Serial {No. 1915672. Divided and this application E'August 21, 1951,-'Serial N0. 242 ,972 I I v .11 Claims. (01. 28-32,)

(Granted under -the act oLMarch .11-883, is r amended April so, 1928;.1370.1.0..G. 757) The invention described herein, if "patented, maybe manufactured and used by .or "tor-the Government for governmental purposes without thexpayment tome of anyroyalty-thereon.

This invention relates to artificial fibers or filaments'containing solid fillers.

This application is adivision of my pending application Serial "No. 191,672, filed October 23, 1'950,'entit1ed Method of Spinning Filaments? now'PatentNo.'2,5'71;45'7, datedOctober 16, 1951.

According to the novel method of said parent application, a relatively small amount of energy put into an elastic fluid israpidly concentrated to atheoretically'infinitevaluejper space unit by causing the elastic fiuid to spiral'towards the vertex of a hollow cone; a filament-forming liquid? as hereafter defined, flows to this location.

ofhigh energy concentration the conduit for the filament-forming liquid is unconventionally large in diameter, that is',"it may ,be'sc-ores or hundreds of times larger than 'theiapertures, in

conventional .sp'inn'erets; .and' the ffilament iormfationoccurs near the vertex in, the midst. of surrounding elastic jfiuid, unobstructed by .apparatus,"..with violent force. and at a rate of production" ,not I known heretofore. with comparably simple apparatus. and "low input of energy. The lower the viscosity of the filament-'formingliquid,"o the farther removed .from the vertexfthe disrupture into filaments willjoccur. ,The higher the viscosity of the filament-forming liquid, .the nearer .to the vertex the disruption.intoiilaments willloccur. JH'o'wever, suchdisrupture ,willfinall cases beoutside oi the conduit through whichthe ffilame'riteforming' liquid. flows but within the cone'shaped figure jbounded by the ispiraling elastic fluid. The elasticfluid mayibeheatedor cooled ;Iit,wil1be.under pressure; and, ingeneral, it'willlhave those physical conditions which facilitate. "fiber formation. .In consideration of this type of spinning, the method may ,be termed .cyclone-spinning and the products of the. inyentionmay be termed ,cyclone-- spun, products. iThe expression f-filament-forming '1iq1iid.. ,in-o eludes any liquidflcapable of iorminga fiberor filament when permitted tofallireely as, aistream through. an elastic} fluid, said liquid being ,generally limited to those materials which exhibit a transformation interval; such liquids will generally produce fibersor filamentshaving a substantially; amorphous character immediately atterformation. of said fibers ,or filaments. It ;is to lbe kund erstood that such .a liquid may be; but does nothave tobe, a vpure substance; .11; may: be

molten mixture, and'may contain other ingredients; such as solvents, plastici'zereand solid fillers. It may consist of any combination of the aforesaid orequivalent constituents, The expression"to fall freely as a-stream means that the material in the liquid state is able to" fall solely under the action of'gravity. To the category oi filament-forming liquids belong many arti fi-cia'l resinsysuch as cellulose propionate -polyamides of the nylon type, polystyrene; polyvinyl acetate, and cellulose acetate; -natural-resins', such as shellac andcolophonium; someinorganic glasses! organic glasses, such as sucrose"oct'aacetate '(C28H38 Ol9 glassy chemicalsyis ichf as boron trioxide (B203) and sodium metapho'sph'ate (Na-P0911; other vitreous materia1s,;sucihas-cer' tain types of candy; and -metalloicls,-such selenium. The members of this group, although departing from each other often widely in their chemical nature, are related closely by their rheological properties.

According to one aspect, of this invention} cyclone-spun polymeric fibers and filaments have finely divided solids physically incorporated therein -at=spaced-intervals, the "discrete 'solid par ticles-always'being enveloped by atubular-polymeric casing. 'Some'or all of thesesolid -particles may "have diameters or lateral dimensions materially-greater than the-{normal "internal diameter of the surrounding 'tubuiarenvelope, yet thepolymer will completelyenca-se t-he particles which, being spaced apart longitudinally of the envelope,-wi1l form spaced bulbous swellings or bulges; an advantageous characteristic for some uses of the products. In another aspect of the invention, the solid particlesowithin' the envelope'areso close togetheras'toflform What is visually a continuous corep'which may be nonmetallic or' metallic, and if preferredQthe-fiiaments so formedmay have-relatively iargecores so as to be predominantly:metallic'or metallo'i'dal in structure and -charadteristics,-, :while having.

thin, continuous, unbroken walls :013 the ,pure

polymer, orrthe polymerunited'with aplasticizen In othercases theqfiberspor filaments :each have interior cavities or voidsatirequent; intervals,

these cavities apparently being partiall evac'uated by the action of the solid particles which move at high velocity during formationi'oflthe filaments, the exterior walls of. thelfilaments, however, remaining smooth and'funbroken'and sealing joii the cavities as ,well as the soIidJParticles adjoining the ends of the, cavities A .Among other objects, theinvention: aimsj.:to

provide fibers or filamentsjsuitableifor making threads, yarns, mats or matting, batts,"woo1-1ike masses, woven or unwoven sheets, panels, and the like. A number of the products of the invention because of their extreme light weight combined with their high heat-insulating quality will be valuablefor stufiing or lining articles of clothing,

sleeping bags, heating pads, electric blankets,

pads and the like; also for insulating'the walls of refrigerators and refrigeratorcars and trucks,

, passenger cars, airplanes, ships and other vehicles, portable shelters, houses, and industrial buildingsp Some of the products of the invention may have such insulating qualities as to be useful in acoustics and/or in the insulation of articles.

subjectedto electrical stresses. Other products of the invention consist of extremely fine and curly fibers and are believed .to be particularly suitable for gas masks, industrial air filters, air conditioning equipment, etc. Also, woven or knitted fabrics suitable for certain articles of clothing may be made fromthreads drawn or twisted from several of the filaments. Insulating mats or wovenifabrics made from the filaments may form linings or paddings within clothin and other articles subjected to flexure to give'a' pronounced heat-insulating effect without being destroyed or rendered-valueless by repeated bending, folding or twisting; Additionally, the products of the invention may be relatively inexpensive and in certain cases are readily adaptable to coloring as by conventional means. Filaments of the invention may be of increased resilience and flexibility, and when matted may form filter bodies giving improved results. .The electrostatic, magnetic and insulating qualities, and the weight, ,feel, curliness, and other physicalcharacteristics may be materially changed bythe addition of properly selected solid particles, to effect considerable improvements over filaments made from a pure polymer, copolymer, or polymeric mixture.

In th accompanying drawings forming a part of this specification- .Fig. 1 is a longitudinal section through a nozzle usefulfor making the fibers or filaments of the invention, the scale being nearly full size;

Fig. 2 is a reproduction of part of a photornicrograph of cellulose propionate filament containing 4% by weight of iron powder, magnificationabout 150:1; I

.Fig'. 3 is a reproduction of part of a photomicrograph ofcellulose propionate filament containing 2% silica gel powder, magnification about Fig. 4 is a reproduction ofpart of a photomicrograph' of several cellulose propionate filaments containing the same silica gel asfiri Fig, 3, the magnification being about 20:1;

Fig. 5 is a reproduction of partof a photomi- I crographshowing the filaments of. Fig.4 in cross section, the magnification being about 315:1

. Fig. 6 is a reproduction of part of photomicro- I graph showing polyvinyl acetate filaments combined with 5% by weight of iron powder, the magnification beingabout 90:1;

Fi g.-7 'is' a reproduction of part of a photomicrograph' showing a few nylon filaments combined with2.5% by {weight of-iron powder, the magnification beingabout 90: 1'; v

Fig. 8 is a reproduction of a pho'tomicrograph 1 of two cellulose propionate fibers having continuous tin cores, the magnification being about 8551;

*FigJQ is a reproduction of a photomicrograph of cellulosepropionate fibers with solid cores of facilitate the formation of fibers orfilaments tin shown in cross section, the magnification be ing about 625:1; r

Fig. 10 is a greatly enlarged fragmentary lon- {nally extending cavities and solid particles of silic'a gel at the larger ends of said cavities.

Referring to Fig. 1, the preferred nozzl comprises a generally frusto-conical body l5 having a hollow frusto-conical chamber 16 on theinside and having an inlet I1 for-an elastic fluid, the inlet opening tangentially at the larger and of said chamber, said nozzle having a coupling it to couple a supply pipe of elastic fluid (not shown). The elastic fluid will usually be air,but it may be nitrogen, carbon dioxide, steam, a volatilized organic solvent, or any other gas or vapor or combination of gases'and/or vapors which will from filament-forming liquids. Generally the elastic fluid will be, and in many cases itmust be, heated. A layer of insulation i9 is shown surrounding the nozzle to minimize heat losses. At higher operating temperatures of the nozzlea heating element, consisting of electrical heating wires or other means for heating, is preferred to, and is used in placeof, the insulation i9.

Arranged coaxially oi the nozzle is a'straight materiahfeeding tube or conduit 20 connected with a vessel, pipe, or conduit (not shown) feeding a supply of filament-forming liquid, said tube having a smooth bore 2! of uniform diameter and having its discharge end beveled as at 22 and projecting slightly v beyond the discharge opening- 23 of the nozzle. Discharge opening 23 is a narrow annular opening'defined by the in-' side walls of the body l5 at its smaller end and the outer walls of tube 26. It will be noted that this discharge opening is directed toward a point outside the nozzle marked Vertex, which is the vertex of the cone that coincides with the inner frusto-conical walls of chamber it. The filament-forming liquid is disrupted and drawn into fibers and/orfilaments .near this Vertex. It will be understood that the phrase near the Vertex includes any and all points within the hollow cone having its tip at the Vertex" and its base coinciding with the outer edges of discharge opening 23,. in which cone contact is made between the filament-forming liquid and the spiraling elastic fluid. Y

The bore 2| of the feeding tube has a diameter which is extremely large in comparison with the passageways provided in spi-nnerets or othercon ventional extrusion apparatus; this diameter may exceed one-fourth of 'an'inch and frequently is large-enough to permit 'free gravity flow of the filament-forming liquid by. merely directing the nozzle downwardly. This large feeding tube presents a solid stream of the filament-forming liquid which in comparison withthe portion of the aforesaid cone that lies outside the nozzle is very massive, being usually of a diameter exceeding one-half thebase diameter of that cone portion. A nut 24' threaded on tube 2|} and swiveled on the nozzle bodymay be used to adjust the size of the discharge opening 23 by shift ing the position of slidable tube 20 longitudinally. Other apparatus used with the nozzle is disclosed in the aforesaid R. K. Ladisch patent.

The described nozzle 'may be modified in a number'of ways, for example, the feeding tube 20 may be shaped on its outside substantially similar to the frusto-conical chamber l6 though in smaller dimensions The bore 21 may be constricter! near its-lower endaoritmray extendmmnelelike toward ':the discharge :end. .Instead of "being beveled asaat 22,;the ;.discharge=:end :of'tube 20 may be squaredofi, aand itslopeningpmaybe; in substantially .thesame. .plane as discharge opening 23. .Instead of pointing.directlydownwardly, the'nozzle may point downwardly:.at;,an..angle of d5 .touthe horizontal, or -..at. any.;.other tangle. Clood-rresults have been obtained with the 45 angleswhen making matting. aUsuallyeven when the nozzle :..ispointed rdirectly downwardly .low pressure will be employed .to. iorce: the ffilamentforming 'liquidout :of- :the '"feedf tube. J Forming .oi :thedilaments may. take. place in atmospheric air, i or: in a chamber filled-with nitrogen .or :other non-oxidizing aelastic :flul'd. :The muzzle l:;discharges :a .spiraling flow of :elastic fluldi-from discharge :opening 2 3 :and: this .::spiraling :fluid :en-

"counters the solidstream'ot (filament-formin on a moving belt or within a chamber (not.

shown) 'untila suflicient mass 515 collected, after which the .layer or mass :may be removed for other-processing.

.To" incorporate-solid particlesdn the rfilaments lormed' by .the described inozzle, pow.dered silica el, or powdered ffrozen'.solids,.such as aluminum, .icopper, iron, nicke1 ...-eobalt, and tin, are added in small-amounts tothe "filament-form- -ing.liquid-prior to :feeding itto'ithe nozzle. In lieu of powdered frozen metals, moltenmetals of .low :melting points, such as tin, m'etalloids, such as selenium, :and .low melting alloys, :such as soft .solder and Woods metal, may beadded-in 'small'amounts to :a molten resin. Due to the peculiar nozzle eonstructiomnocclogging is possible if the heat is'maintained .to preventsolidiiicatlon, and-relatively. coarse particles may be added which will cause'very pronounced bulges in the filament, if present in small percentages .(0.5"to 10% by weight).

' The following table "shows-.itheresults-obtained in twelve runs :during which cellulose propionate was cyclone-spun alone and then mixed successively'with' aluminum, copper, :iron, tin and silica gel-powders and cyclone-spun, the pressure .with- 'infthe feeding tube .being 3 p.-.s.- i., the temperature of said tube being about 250 C., the temperature of the elastic fluid (atmosphericv air) being .about 270 Cmand its pressure being about v15 .p.s: i. ('superatmospheric) measured at the nozmelted :811'5' 230 0.1118101? imixingswith stir-cam :dered materials. The aluminum -powder .fMa'llinckrodt -;3 116; athe .::o.opper {powder 1 seeds Eimer ;& Amend. ;H.-;reduced.. C. 12:2; ,athe;iron powder was .Mallinckrodt; 5304,5Degreased.';;= the .tin was FEimer & Amend, :1e129; finest=owden Pure"; and thesilicargel xwas .Ei-mer lh S4156, dried at: 500"v C. for seightihours toa expel practicallyall moisture. :Thewolumeipen-meight ratios are believed to b.e..:accurate. to.;t10%afifl were determined by: filling aivessel'ofdmownwol- .ume rand weight with ;;the entangled .1 filaments and ascertaining the weightrtofitheafilamentous mass, which was..:not gcompressed; exceptlbyiilts own-weight.

flwhengmore thansil %;of.-'-'alummum.zpowderztwas added, :resiliency. and-flexibility of-iithe filaments.

were reduced. The color of all zthreealumlnumcontainingfilaments was silvery grey. wanna aluminum adde'd, thefilament; "had a' sli feel. Copper -powder (2-"4 'i-mparted af-i reddish tinge to thefilamentsand enhanceddiheir heat-insulatingefllciency. This=powder was-- apparently distributed evenly along thelengthsfbf the color to grey. .The sllica gel was distributed as beads alongthe fibers .se,e Fig.3 (magnification' 150:1) while the fibers themselves varied considerably in diameter'asshown in'fFfig. I4"( magnification, 20 :1) Fig.6 shows fhow iib ers incorporating silica .gel particles iloolced jin v cross sec-- tion (magnification 315:1), the openareasbeing voids or partially evacuated areaaapp'arehtly 'fo'rmed because of the bullet-like .yelocityof "the solid ,particles when picked ,llp by t esp al n'z air 1 et. In longitudinal section,fthese voids. were elongated, misshapen cones asyiewedunder the microscope,- with the .large end or .eachconead-r jacent Ito a.sol id.par-.ticle. .See fl g.;.10. sections through these .yoids thereiorewaried greatly in diameter, as Fig. 5,.indicatesr In lieu of metallic iron powderas a. filler -1 contemplateusing powdered magnetite or ferrous ferric oxide (Fe3Q4) ,iI1 the; same p poruss;.;g

.zle inlet. 1

th ic p w rs; on I s av-maenetlze meta Substnnce Added,.Arnt. and Particle 1 y tigffie h gggg Resin Size "Der-wet. (microns) (ca/gm.) r

' te- None...' 280 34,68 5 dfafiTfi??? Aluminum 0.5%,.Passes 140 mesh 190 3 3 H Aluminum 1.0%,Passes 1.40- mesh 2m 22.92 4 .Aluminum2.0%,Passes 140 mesh... r 1346 a" Copper, 2.0%,,Passes 250 mesh. 200 36-46 6 Copper, 4.0%, Passes 250 mesh .1140. 5 7 Iron, 2.0%, Passes250me5h..- ,zt-go 8 Iron, 4.0%,Passes 250 mesh..- 423760 9 'Iron, 10.0%, Passes 250 mesh 0 v .3846 16 Tin, 6.(l%, .Iasses 325 mesh 1 50 ill-23.35 11' Silica e1,'2.0%, 250 to 300 me 516796- 12 Silica gel, 4.0%, 250 to300 mesh 50, A340 The cellulose propionate was thevarietyknown toithe trade as Forticicl 28102 and contained 9% plasticize'r "of unknown composition; being -pre 11 iron or'-'-stee1-*-particles 1encased indilan ents by placing -the filaments "in a strong. magnetic field. The resultant magnetic-filaments "may-be tWisted into yarns' and the i yarns may i be woven 'to i form rabrics which maybeuseful as filter oloth having -ia.dual function, viz., mechanical mtr'auen' ana inagneticsep'aration of iron parlticle's :too'small'to be caught upon the meshes of .the'woven-filter' fabric. 'A -*filter containing a sufiicientpropo'rtion of magnetized particles may fialsoibe desirable because it can be lifted ad a support without rupture by bringing a strong :magnet close to: it. This technique will be de- In-ffurther runs, I found that fillers amount-.- ing to as much as 80% of the total weight of the resinous-filaments may be ,added without c10g-' gingthe nozzle or. preventing the formationof tube-:like'filaments. Thus the described process makes possibleior the first time the .formation of filamentsheavilydaden with a metallic-or mete alloidal core :orcpntent, so that the filaments are more metallic or metalloidalfin theircharacter- .istics than resinous. l/Vhen. selenium: infinely divided iorm (100% passing through a 250 mesh sieve) was added toythe extent of- 80% by weight topolyvinyl acetate (Mowilith 30) ,with an indicated nozzle temperature of 240 C. and an indicated airpressure of 20 p. s. 1., the filaments rormed had a volume per weight ratio of 23 and aoiameter ranging from 1 to 18 microns. The selenium was such a large pr'oportion of the fibers that it impartedadark brown appearance and gave a rather harsh feel to them, besides making themf'quit'e brittle. Each fiber, however, con;- sisted'ofacontinuou's thin tubular envelope sur roundingthe 'metalloidalfcore. The mixing of polyvinyl acetate with molten selenium in a 50-50 volume'ratio results in a'homogeneous viscous mixture at 2 i C,"which readily forms filaments, again with, the metalloid forming a continuous core "sheathed by the resin.

Fig. 8 shows the ends of'two cellulose propion'at'e' fibers containing tin cores, enlarged 85 times. Cellulosefpropionate (Forticel 28102) was mixed with tin powder passing a 325' mesh sieve, and the mixture was cyclone-spun with an indicated air pressure of "15 p. s. and 3 p. s. i. in the feed tube.' Temperatures were 250 C. in the feed'tube and 270C. for the'compressed air; While part 'of the mixture'left' the VerteX in the form of pmn-resmeus fibers and separate tin pellets, a considerablepercentage of plastic tubular fibers with tin'cores were formed. These tin cores were not of uniform diameter but varied as Fig. 2 3 shows, and some were-as short as 2 mm., while others were'50 mm. long. Fig. 9 (magnification 625:1) shows in'section solid tin cores which were a major partof the'fibers, but insome sections the tin cores were so fine they could only be seen under a microscope after dissolving away the resinous envelope with methyl acetate. Microscopic examination failed'to disclose :a single tin fiber free from an enveloping polymeric sheath or tube.

Solutions of various polymers mixed with powdered fillers may be spun into filaments, as dis- 5 closed in my pending application Serial No. 122,343, filed October 19,1949.

Thus, polyvinyl acetate (Mowilith 30) was dis-.. solved in 15% acetone (the percentage being based on the total weight of the solution) and 5% by weight of iron powder (300 mesh) was addedv and the mixture thoroughlystirred and then introduced into tube 20. The nozzle temperature FY35 iq ifi-eed the a rp e su sup r'r 8 atmospheric). Filaments cerami- 1811'70 481.1111- crons were obtained, with a volume weight' ratio, as explained above,.of 65. Some of .the'larse filaments, magnified 90 times, are'shown in' Fig. 6, which omits the finest filaments because'no details of theirstructure were apparent from the photomicrograph. I A Again, nylon molding powder (duPontiCode 10001) was dissolved in formic acid (thep'ercentage being based on the total weightxof the solution) and 2.5% by weight of iron powder passing a 300 mesh sieve was mixed in thB'SOllI-r tion. The nozzle temperature was 70? CQandth'e air pressure 15 p. s. i. Filaments ranging-from 2 to 12 microns in diameter were obtained,.with a volume-weight ratio, as explained above, of,1 5. Several of the coarser nylon filamentsproduced under these conditions as shown in a photomicrograph (:1) are reproduced in Figj 'l. ..Bette'r results would be obtained by spinning completely under nitrogen. The filament in each case were collected and put in a dessicator, which was evacuated by a Water" injection pump for three days to remove traces of solvent which had not been lostduring thespinning process itself.

Glasses of a number of difierent'compositions may also be cyclone-spun by the described nozzle,

as is disclosed in the R. G. H. Siu application Serial No. 180,686 filed August 21, 1950. Theresult is inherently curly glass filaments ofaifineness of less than one micron up to -.micro'ns. Molten glass, whose temperature is at least250 higher than its softening point, is fed into the fed tube 20 at low pressure. The temperature of the compressed'elastic fluid operatingzthe nozzle should be about 100 C. higher than. the temperature of the glass as it enters the feed tube; The relatively large feed tube permitsthe feedinginot only of molten glass towards the Vertex but also mixtures of molten glass with powdered metals, such as platinum (for. soft glass),:tungsten (for Pyrex glass) and other metals and metallic alloys; These mixtures will form filaments near the"Vertex, providedthe metals or'alloys haveabout the same c'oefiicientof expansion as the glass and are not chemicallychanged thereby. The size of the particles of the filler may be'small or largerrthan the average diameters of the glass filaments; if larger, the glassfilaments' will form envelopes having spaced bulbous enlargements'like the polymeric filaments disclosed inthe foregoing. Of course, the size of the'filler particles must never equal the diameter of theipassageway 21 of the feed tube l Substantially pure selenium may also. be cycione spun by the described nozzle, as is disclosed in the pending application of R. G. H. siu serial No. 127,479, filed November 15, 1949. Selenium powder (Eimer & Amend, 8-137) was melted in feed tube of the nozzle: Air at 20 p. s; iwas employed as the gas. The nozzle was heated to 240 C. and was directed vertically downward. The molten selenium was disrupted readily by the spiraling jet of air and formed a rapidly moving stream of filaments whichcollected as a curly mass in the open air below the nozzle. The filaments varied from one to 30 microns in diameter,

7 with a considerable proportion below 10 microns.

In color they were dark grey with'a metallic sheen .when viewed as a mass. I he same selenium pow der was mixed with 5% by weight of iron powder (300 mesh), also with iron powder of 45 mesh, and the two mixtures were separately cyclone-spun. In each case the iron particles were encased with s.

' 9 in the selenium and formed enlargements or bulges spaced along the filaments. In a further test, silica gel powder (45 mesh, Eimer & Amend, S-156) was mixed with powdered selenium to the extent of by weight, and the mixture was cyclone-spun, obtaining dark brownish-grey filaments with no appreciable metallic sheen but with the silica gel appearing as glistening beads having a metallic appearance because of the enveloping selenium. All of the described selenium products were curly.

What I claim is:

1. Artificial filaments containing solid particles which lie wholly on the inside of the filament, many of said solid particles being larger than the diameter of the filament. 7

2. Artificial filaments each consisting of a polyenlarged or bulged out and inclosing or sheathing a particle of a solid material at each of said spaced points.

4. The invention defined in claim 3, wherein the particle of solid material is metallic.

5. The invention defined in claim 3, wherein the particle of solid material is silica gel.

6. An artificial filament consisting of continuous unbroken walls of a polymer having bulbous enlargements at frequent intervals along its length, and a solid particle within each of the bulbous enlargements.

'7. The invention defined in claim 6, wherein the major proportion of the solid particles are 10 each adjoining the larger end of an elongated cavity wholly within the filament,

8. Artificial filaments each composed of a generally tubular envelope formed from a filamentforming liquid and encasing a plurality of spaced solid particles, at least.some of which are larger than the average diameter of the tubular envelope so that they cause the walls of the envelope to bulge out.

9. The invention defined in claim 8, wherein the solid particles are present in the range of 0.5

to 10% by weight of the encasing tubular en velope. r

10. The invention defined in claim 9, wherein the solid particles are metallic.

11. The invention defined in claim 9, wherein.

the solid particles are silica gel.

ROLF KARL LADISCH.

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

UNITED STATES PATENTS Number Name Date 1,394,270 Brandenberger Oct. 18, 1921 1,629,241 Ubbelohde May 17, 1927 1,884,069 Mendel Oct. 25, 1932 2,005,360 Boggs June 18, 1935 2,042,702 Dreyfus June 2, 1936 2,072,858 Ellis Mar. 9, 1937 2,200,946 Block May 14, 1940 2,207,157 Neville et a1 July 9, 1940 2,280,135 Ward Apr. 21, 1942 2,328,998 Radford Sept. 7, 1943 2,385,890 Spanagel Oct. 2, 1945 2,411,660 Manning Nov. 26, 1946 2,466,951 Hunter Apr. 12, 1949 2,485,589v Gray Oct. 25, 1949 2,566,441

Camras Sept. 4, 1951

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