US2560924A - Photoflash lamp - Google Patents

Description

July 17, 1951 F. G. BROCKMAN PHOTOFLASH LAMP Filed July 26, 1947 FIG! FIG.2

FRANK e. BROCKMAN INVENTOR AGENT types ofalloys.

Patented July 17, 1951 UNITED STATES AT E N-T' OF Fl C-E,

PHOTOFLASH LAMP Frank G. Brockman, DObbSiFBIIX, N:'Y., assignor' to PhilipsLaboratories, l'nc'., Irvington on Hudson, N. Y1

My invention relates to. photoflash lamps of the typewhich employ a solid. combustible material .and more particular to. the combustible material itself. and. to a method of. placing, the same in the lamps.

The majority of. present-day photofiash lamps comprise-a filling material in the. form of a wire composed of a material which is combustible with the production of light rays of good actinic properties. Such. a material is, for; example, aluminum or alloys of aluminumand magnesium. This wire filling materialmay be. of various cross-sections, for instance circular or rectangular, and is madein various ways.

In. some'cases, the wireismade. by a drawing processwhereas in. other cases. it ismade by cutting foil into wire of rectangular or square crosssections. While the drawing, process produces wire. which gives exceptionally good results, this process is somewhat expensive Whenusing; some The process of making the wire from foil has the disadvantage that. it is diiflcult to obtain wire of very small cross-section. Moreover, the metal or alloy used is restricted tocertain types' having, the requisite physical characteristics', for example, ductility.

It is an obj ect of my invention to provide a new and novel photoflash lamp, and a method. of manufacture. thereof.

It is another object of the inventiontoprovide a" filling material which is economical to manufacture.

Another object ofthe invention is toimprove the manufacture of photoflashlamps.

A further object of my invention. is to provide a novel filamentary filling materialfor photoflash lamps, and a method of making the same.

A further object of my invention is toprovide a filling material for a photofiash lamp which may be given a desired predetermined aotinic property.

Other objects, advantages, and novel features of the invention. will become apparent as the specification progresses;

In accordance with my invention, I provide a photofiash lamp having a filling material of a mixture ofa cementing or plastic material anda high percentage ofv a finely-divided actinicallyreactive material. The material, according to the invention, may be made by forming the mixture into a thin foil, and if desired; then cutting, or shredding wires therefrom. However, I prefer to extrude the mixture into a filament, preferalbly' of a circular cross-section. The actinicallyreactive material may be a mixture of a metallic material and an oxidizing agent; However, Ipre- 2, for to use a metallicmaterial consisting ofa finelydivided metal or mixtures of'metal.

In some. cases, I'prefer to extrude the, wire-at the opening, of the bulb to be filled and carry the wire into the bulb by means; of a stream of gas, as described in the United States. Patent to Cornelis Korver, No. 2,115,423, issued Aprilf26, 1938.

In order that theinvention' may be more clearly understood and readily carried. into effect, it will now be described with reference to the accompanying drawing in which:

Figure l is. a cross-sectionalviewof one. form of apparatus for making aphotoflash lampiin'accordance with the invention; and r Fig. 2 is a. cross-sectional view of aphotoflash lamp in. accordance with the invention.

As. a. preferred method of production of the combustible fi1ling, a plastic binding material is first put in liquid solution, and a quantity of finely-divided. metal is mixed therewith. The solvent is dried and the mixture is extruded into filamentary form to produce the filament for the lamp. Preferably, I extrude the filament directly into the envelope of 'thelamp to be manufactured. The following examples will provide more specific information whereby the invention may be practiced:

ErampZe1.--One gram of polyethylene is dissolvedin 15 cc. of toluene (CsI-IeCI-Is) to form a viscous solution" at a temperature of approximately 100 C. preferably near the boiling" point of toluene. A quantity of'powdered, atomized, fial ze,v or other finely-divided aluminum is screened in a 325' mesh screen havinga nominal pore size of .0017 inch and nine grams thereof are homogeneously mixed with the polyethylenetoluene solution. The toluene is" then evaporated with occasionalstirring of the mixture to assure uniform dispersion of the comminuted metal. Whenthe'solventhas been evaporated, I find it convenient'to compress the resulting mixture into a block suitable to use as a charge in an extrusion press. This charge is then-placed'i'n an extrusion press, suchas the press Iii of Fig. 1, preferably having heating means such as a heating coil I2 to maintain the temperature of the charge at approximately l to l 6G C., whereupon moderate pressure of the order of 2,000pounds on piston I 4, which has-a diameter of inch, may be applied 7 and the charge extruded through the'die-aperture results "are'obtained when theal'uminum constiw -tutesapproximately by" weight of the exwith its extrusion from the die hole i6.

truded mixture. A greater proportion of aluminum, for example over 95%, tends to make the resultant filament brittle. Quantities of aluminum significantly less than 90%, for example less than 75%, result in such a high oxygen requirement in the finished bulb as to be impractical, partly because the gas in the bulb after reaction will be at appreciably higher pressures than before reaction, tending to bulb breakage.

The bulb 18 may be filled by blowing the extruded filamentous material into the envelope thereof as described in the aforesaid patent to Cornelis, Korver, or the filamentary material maybe separately collected, for example on a spool, and thereafter placed in the bulb by any conventional method. In Fig. 1, I have illustrated the former method, which I consider preferable, whereby warmed air is blown through the jet chambers 20 to carry the extruded filament 2! into the envelope it) simultaneously This processing has the further advantage that it tends to remove the last remaining traces. of the solvent from the extruded mixture. The usual ignition charge and igniting electrodes are then inserted in place in the envelope and the bulb sealed.

Example 2.--The filamentous material 2| of the bulb I8 is produced in the same manner as in Example 1 except that I use as the comminuted metallic material particles of carbonyl iron of a nominal particle size of eight microns (.008 mm.). Again, the best results have been obtained with a mixture of about 90% by weight of said iron with respect to the total weight of the filament.

Example 3.--One gram of a polyamide, for

, example that commercially sold as Nylon No. FM

101 noted on page 215 in Modern Plastic Encyclopedia, 1946 Plastics Catalogue, published by Plastics Catalogue Corporation, New York, is dissolved in 20 cc. of normal butyl alcohol at an elevated temperature. About nine grams of comminuted screened aluminum of one of the types above mentioned is mixed in the solution in a manner similar to that in which the aluminum is mixed in Example 1. The resultant mixture, after evaporation of the butyl alcohol, is compressed into a slug as a charge for insertion in the die and then extruded at a temperature of about 210 C. A die aperture having a diameter of about .004 inch is also used in this example, and in other respects, the filling of the bulb 18 may be completed as before. At the present time, I have achieved the best results by utilizing a die pressure near the lowest reasonable flow pressure at slightly elevated temperatures. Thus, in this example, I find that the pressure is preferably higher than that utilized in Example 1 when extruding the polyethylene, and that a pressure of about 4000 pounds force on the piston M has been found to produce the desired results.

Referring now to Fig. 2', there is illustrated a photofiash lamp l8 which may be manufactured in accordance with the invention. As a specific example, a combustible filling 22 of filamentous material is inserted in lamp I8. Material 22 is composed of polyamide and comminuted aluminum dispersed in the polyamide, the aluminum constituting about 90% by weight of the said material. In this example, the bulb l8 encloses about '70 cc. of volume, and the filamentous material 22 weighs about 58 milligrams. A pulveriz ed igniting mixture 24 of the usual type is inserted in the lamp and electrodes 26 leading thereto are sealed at 28 into the base of the tube. When the mixture 2 3 is flashed by application of a suitable potential to the electrodes 26, sufficient concentrated energy is produced to start the reaction of adjacent particles of the combustible filling material with the oxygen in the envelope. As the reaction progresses, the binder or plastic of the filling material is volatilized by the energy released and the actinically-reactive metallic material is freed to react with the oxygen. It is probable that the plastic simultaneously reacts to produce actinic radiation. In any event, I obtain a flash lamp of good actinic properties.

The filaments produced by the foregoing methods have a diameter approximating the diameter of the aperture of the die, and in the above examples, the maximum diameter is about .006 inch. The binders for the metal powder, as above described, have generally the property of forming strong fibers by themselves. This property may be attributed to the fact that the molecules of the fibers or filaments may be oriented lengthwise thereof to provide comparatively high tensile strength and I have found that the use of such binders is preferable in order to produce a filament having a high ratio of metal to binder. Furthermore, I have found it preferable, as noted above, to insert the filamentous material immediately after its extrusion into the envelope of the lamp whereby a greater uniformity of distribution of the filament in the envelope is achieved, and deleterious changes of the properties of the filament are avoided. Another advantage of placing the filament directly into the envelope is that such changes in the flexibility of the material with time, as may occur, take place after the material has assumed its final position in the envelope and, therefore, breakage of the filament due to brittleness is avoided and proper distribution of the filament in the envelope is facilitated.

It will be apparent that by choosing the metallic particles suitably, or by suitable mixtures thereof, the actinic radiation of the lamp may be controlled to a degree not hitherto possible without great practical difficulties.

Thus, many desirable materials which cannot be drawn to small diameters or made into thin foils may be utilized in the filamentous material of the invention.

One may also use as the actinically-reactive substance mixed in the plastic a mixture of a metal or metals and an oxidizing agent. For example, a mixture of aluminum and sodium chlorate by about by weight is mixed with a suitable plastic, for example, one of those noted hereinbefore, by about 10% by weight. The proportion of plastic may be increased, particularly if enough excess of oxidizing agent is included to oxidize the plastic material, and the bulb may then be completely evacuated.

In those instances where the filament upon extrusion is wound on a spool, it is preferable to apply a slight tension to the emerging filament during its extrusion to assist in the fiow of material through the die aperture.

Instead of extruding the filament in a hot state as described above, it is possible to extrude the filament in a cold state by controlling the prior evaporation of the solvent from the mixture of plastic, solvent, and :actinically-reactive particles, so that the solution i of the proper plasticity to be extruded through the die aperture. The metallic particles may be mixed in the plastic material by heating the plastic material to a liquid state, and thereafter mixing the metallic particles into the liquid, no solvent being used.

While I have described my invention with specific examples, and in a specific embodiment, I do not wish to be limited thereto since obvious modifications will suggest themselves to those skilled in the art without departing from the scope and spirit of the invention.

What I claim is:

1. A photofiash lamp comprising an envelope having an actinic light transmitting portion and a filamentous material distributed within said envelope, said filamentous material comprising a plastic binding material and a major proportion of finely-divided actinically-reactive metallic particles dispersed in said plastic, said filamentous material having a diameter of less than about .006 inch, said particles having a particle size of less than about .002 inch.

2. A combustible filling material for a photoflash lamp comprising a filament of polyethylene and a comminuted actinically-reactive metallic material dispersed in said polyethylene, said filament consistin of about by weight of polyethylene and about 90% by weight of said metallic material.

3. A combustible filling material for a photofiash lamp comprising a filament of polyamide and comminuted metallic material dispersed in said polyamide, said filament consisting of about 10% by weight of polyamide and about 90% by weight of said metallic material.

4. In the manufacture of a photoflash lamp, the method of producing an actinically-reactive filament for insertion in said lamp, comprising the steps of dissolving a plastic and a solvent, mixing in said solution finely comminuted metallic material in the ratio of about three parts to about nineteen parts by weight of metallic material to about one part by Weight of plastic, evaporating the solvent from said mixture, and extruding the mixture in fine diameter into a filament of substantial length for insertion in said lamp.

5. In the manufacture of a photofiash lamp, the method of producing an actinically-reactive filament for insertion in said lamp, comprising the steps of dissolving polyethylene in toluene, mixing a finely-divided metallic material in said solution, evaporating the toluene from said mixture, and extruding the mixture in fine diameter into a filament of substantial length for insertion in said lamp.

6. In the manufacture of a photofiash lamp, the method of producing an actinically-reactive filament for insertion in said lamp, comprising the steps of dissolving a polyamide in normal butyl alcohol, mixing a finely-divided metallic material in said solution, evaporating the normal butyl alcohol from said mixture, and extruding the mixture in fine diameter into a filament of substantial length for insertion in said lamp.

FRANK G. BROCKMAN.

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

UNITED STATES PATENTS Number Name Date 594,594 Bostwick Nov. 30, 1897 613,021 Schwartz Oct. 25, 1898 2,115,423 Korver Apr. 26, 1938 2,149,694 Vollrath Mar. 7, 1939 2,158,415 Formhals May 16, 1939 2,205,081 Burrows et al June 18, 1940 2,272,779 Sarbey Feb. 10, 1942 2,363,569 Caldwell et a1. Nov. 28, 1944

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