US 3645663 A
A percussive-type photoflash lamp, the primer of which comprises a wire anvil partially coated with fulminating material and coaxially supported within a tube in a manner providing a clearance between the coating of fulminating material and the inner wall of the tube. The fulminating material includes a red phosphorus fuel, a chlorate salt oxidizer, a powder combustible, incandescible metal, and a powdered carbon additive for facilitating propulsion of the powdered metal from the primer tube into the lamp envelope when ignited. The fulminating material is prepared and applied in the following manner: the red phosphorus, powdered metal and powdered carbon area dispersed in water to provide an aqueous slurry; the anvil wire is dipped into this aqueous slurry; the coating is dried; a dissolved chlorate salt solution is prepared; and the coated wire is dipped into the chlorate solution so as to permeate the previously applied coating.
Description (OCR text may contain errors)
United States Patent Shaffer 5] Feb. 29, 1972 Primary Examiner-Edward .1. Michael Attorney-Norman J. O'Malley and Edward J. Coleman  ABSTRACT A percussive-type photollash lamp, the primer of which comprises a wire anvil partially coated with fulminating material and coaxially supported within a tube in a manner providing a clearance between the coating of fulminating material and the inner wall of the tube. The fulminating material includes a red phosphorus fuel, a chlorate salt oxidizer, a powder combustible, incandescible metal, and a powdered carbon additive for facilitating propulsion of the powdered metal from the primer tube into the lamp envelope when ignited. The fulminating material is prepared and applied in the following manner: the red phosphorus, powdered metal and powdered carbon area dispersed in water to provide an aqueous slurry; the anvil wire is dipped into this aqueous slurry; the coating is dried; a dissolved chlorate salt solution is prepared; and the coated wire is dipped into the chlorate solution so as to permeate the previously applied coating.
12 Claims, 1 Drawing Figure PAIENTEDFEBZS I972 I 3, 645,663
JOHN W SHAFFER VENTOR AGENT PHO'IOFLASII LAMP AND METHOD OF PREPARING AND APPLYING FULMINATING MATERIAL This invention relates to the manufacture of percussive-type photoflash lamps and more particularly to the composition of the fulminating material employed therewith, especially as associated with the method of preparing and applying the fulminating material.
Generally speaking, a percussive-type photoflash lamp comprises an hermetically sealed, light transmitting envelope containing a source of actinic light and having a primer secured thereto. More particularly, the percussive-type photoflash lamp comprises a length of glass tubing constricted to a tip at one end thereof and having a primer sealed therein at the other end thereof. The length of glass tubing which defines the lamp envelope contains a combustible, such as shredded zirconium foil, and a combustion supporting gas, such as oxygen. The primer comprises a metal tube and a charge of fulminating material on a wire anvil coaxially supported therein. Operation of the lamp is initiated by an impact onto the tube of the primer to cause deflagration of the fulminating material on the wire anvil up through the tube to ignite the combustible disposed in the lamp envelope.
Two significant and conflicting demands are made of the fulminating material for percussive flashlamps. The material must be very sensitive so as to flash reliably upon impact. Deflagration of the fulminating material must be intense enough to reliably ignite the shredded metallic combustible located at a distance from the fulminating material. On the other hand, highly sensitive fulminating materials tend to be violent burning, and when present in sufficient amounts to assure shred ignition, the light output of the lamp and reliability of containment become unacceptable. For example, a violet burning fulminating material can cause up to 50 percent reduction in lamplight output.
Basically, fulminating material employed in percussive-type photoflash lamps comprises a mixture of percussively reactive materials, a fuel and an oxidizer, arranged to ignite upon interparticle movement, such as a blend of red phosphorus and potassium chlorate. lntermixed with the percussively reactive materials is a powdered combustible, incandescible metal, such as titanium. When the materials react, they ignite the powdered metal and force incandescent particles thereof to spew into the body of the envelope and ignite the shredded combustible metal.
During the course of development of the percussive flashlamp, it was found that different metallic constituents in the fulminating material had differing abilities to attenuate its explosive nature while maintaining high ignition reliability and sensitivity. Listed in order of increasing attenuation ability are the metals zirconium, titanium, silicon, and boron. Extensive testing showed titanium to be the best available choice with regard to overall explosive attenuation ability and shred ignition reliability.
Ignition pastes for conventional filament type flash lamps use nitrocellulose as a binding resin, and organic solvents such as amyl acetate as the vehicle. In an effort to increase the handling safety of percussive fulminating material, water was evaluated as the vehicle for applying the fulminating material to the primer anvil, in conjunction with water soluble binding resins such as hydroxyethyl cellulose. The fulminating material deposited from such an aqueous suspension was found to be much more sensitive to impact than a similar material deposited from organic solvents. This enhanced sensitivity was attributed to deposition of the potassium chlorate onto the particles of red phosphorus, resulting in a more intimate mixture. Although these gains in lamp sensitivity and reliability were significant, the new water based materials were found to retain a degree of hazard. It was found, for example, that a crust of dried material, generated enough heat during flashing to ignite the adjacent aqueous suspension, and that the latter would burn to completion. The burning violence of the wet material varied inversely with the amount of water present.
Accidental drying or partial drying of the sensitive fulminating material constituted an ever present danger of fire or explosion in the production process. In order to restrict the danger involved in handling and using the fulminating material it was prepared in small batches. The amount allowed in any one container was Iimitated to a fraction of an ounce of solid ingredients. The high cost of preparing numerous small batches was completely overshadowed by the lost machine production time required for frequent replacement or refilling of the small fulminating material dip cups.
In an effort to avoid the use of such hazardous materials in production, a two layer technique for applying fulminating material was evaluated in which the potassium chlorate and red phosphorus were not mixed. In this technique. separate coatings of potassium chlorate and of the red phosphorusmetal mixture were applied one over the other. Each component was prepared as a milled aqueous slurry containing the chosen ingredients along with a quantity of binding resin. Extensive testing and effort, however, failed to attain the degree of lamp reliability and photometric performance with this two layer system that had been achieved with the aqueous completely mixed material. The shortcomings of such two layer structures is that only single-surface contact exists between the red phosphorus and potassium chlorate layers, whereas in completely mixed material intimate bulk contact is attained.
A significantly improved technique for applying the fulminating material was then developed which proved to be safer and more economical for large scale production, while at the same time providing an impact sensitivity such that the flashlamps had a high degree of ignition reliability and photometric performance. Referred to as an absorbed oxidizer process," the technique involves the deposition of an oxidizer-free layer made up primarily from red phosphorus and titanium, drying that coating, then dipping the coated anvil into a concentrated solution of dissolved sodium chlorate which permeates the phosphorus-containing layer. when dried, a sensitive deposit of fulminating material results which is similar in behavior to that deposited initially from a complete mixture. The chlorate salt component of fulminating material applied in this manner is referred to as an absorbed oxidizer."
In a small percentage of the lamps employing absorbed oxidizer fulminating materials, however, the fulminating material failed to ignite the shredded combustible, even though the composition of the dried fulminating material was quantitatively the same as that of the completely mixed materials that gave good shred ignition reliability. The difference in performance is apparently caused by the nonhomogeneous distribution of the absorbed sodium chlorate throughout the thickness of the fulminating material layer.
In view of the foregoing, the principal object of this invention is to provide a fulminating material for percussive flashlamps that gives improved shred ignition reliability while maintaining high impact sensitivity, good lamplight output characteristics, and manufacturing safety and economy. Another object is to provide a safer more reliable percussivetype photoflash lamp. A further object of the invention is to provide an improved method of preparing and applying fulminating material on the primer anvil wire of a percussivetype photoflash lamp which is safe and economical for large scale production and at the same time provides improved shred ignition reliability without decreasing impact sensitivity or lamplight output.
I have discovered that the addition of a small quantity of powdered carbon to the fulminating material of percussive flashlamps significantly reduces the incidence of shred ignition failure. When the carbon burns upon ignition of the charge of fulminating material, it produces carbon dioxide, which facilitates propulsion, or transport, of the incandescent titanium particles from the primer tube into the lamp envelope where the filamentary combustible shreds are located. Of particular importance, carbon achieves this result without at the same time incurring the detrimental explosiveness that results when the red phosphorus content is increased for the same rnrno: (HR l purpose. The addition of soluble organic materials or more binding resin, even though being gas generators, is detrimental to the impact sensitivity and ignition reliability of the composition because of the resulting insulating" layer surrounding the particles of red phosphorus.
The optimum percentage of carbon to be added varies with the dimensions and mechanical construction of the percussive flashlamp in which the fulminating material is to be used. I prefer approximately 1 percent based on the weight of dried solids exclusive of the oxidizer, although quantities from 0.1 percent to 10.0 percent may be preferable with other lamp types.
While not limited to such use, the addition of powdered carbon for facilitating propulsion of the incandescent powdered metal is particularly advantageous when employed in conjunction with the absorbed oxidizer process for applying fulminating material. That is, the advantages of safety and economy provided by the absorbed oxidizer techniques are retained and further enhanced by an improvement in ignition reliability.
Accordingly, an example of a very satisfactory method of preparing and applying fulminating material in accordance with the invention is given below.
First, an aqueous slurry is prepared having the following dried composition: titanium, 69.31 percent, red phosphorus 27.21 percent, hydroxyethyl cellulose, 1.19 percent, magnesium oxide, 061 percent; magnesium montmorillonite, 0.60 percent; carbon, 1.02 percent; sulphur, 0.06 percent; and trichlorophenol, 0.01 percent. Water content is adjusted to give the desired coating thickness. The anvil is dipped into this aqueous slurry and the resulting coating is dried.
The coated anvil wire is then dipped into an aqueous solution containing about 25 percent by weight of dissolved sodium chlorate. Upon drying a very sensitive fulminating material coating results.
Alternative materials that can be used in place of powdered carbon include combustible materials that are insoluble in the liquid vehicle used to apply the fulminating material to the primer and which give gaseous products of combustion. Further, the material must be stable for extended periods of time in intimate contact with sodium chlorate. In particular, the substance for facilitating propulsion of the powdered metal may comprise any nonacidic carbon-containing compound which is substantially insoluble in liquid vehicles commonly used in applying fulminating material to the primer, such as water or amyl acetate. Finely powdered polymers such as, for example, cellulose or cellulose nitrate could be used.
Other chlorate salts which have cations not catalytically reactive toward red phosphorus and which are soluble to the extent of l percent or greater by weight in water may be used as the oxidizers; for example, calcium chlorate, lithium chlorate, magnesium chlorate, and zinc chlorate, however, the extreme deliquescence of these materials may render their use in flashlamps more difficult with regard to drying and maintaining the coating dry prior to hermetic closure of the flashlamp. Similarly phosphorus sesquisuli'ide may be used in place or red phosphorus, if desired, although a slight loss in sensitivity may be noted. Further, although titanium is preferred, other powdered combustible, incandescible metals may be employed, such as zirconium or boron.
In the accompanying drawing, the single FIGURE is an elevational view partly in section of a percussive-type photoflash lamp with which a charge of fulminating material prepared in accordance with this invention may be employed. The lamp comprises a length of glass tubing defining an hermetically sealed lamp envelope 2 constructed at one end to define an exhaust tip 4 and shaped to define a seal 6 about a primer 8 at the other end thereof. The primer 8 comprises a metal tube 10 a wire anvil 12 coated with a charge of fulminating material 34. A combustible such as filamentary zirconium 16 in a combustion supporting gas such as oxygen are disposed within the lamp envelope. The wire anvil 12 is centered within the tube 10 and held in place by a crimp 18 just above the head 20 of the anvil. Additional means, such as lobes 22 on wire anvil 12, are also used to aid in stabilizing and supporting it substantially coaxial within the primer tube 10 and insuring clearance between the fulminating material 14 and the inside wall of the tube 10. A refractory bead 24, fused to the wire anvil 12 just above the inner mouth of the primer tube 10, eliminated burn-through and functions as a deflector to deflect and control the ejection of hot particles of fulminating material from the primer.
In conclusion, the present invention incorporates an additional gas generating fuel in the fulminating material for percussive flashlamps in order to provide efficient transport to the incandescent particles from the primer to the envelope to thereby promote high shred ignition reliability without decreasing impact sensitivity or lamp light output. Such a propellant is particularly advantageous in the primer structure illustrated in the drawing. Of additional significance, the inventive principles described significantly enhance the commercial manufacture of percussive flashlamps by the much safer absorbed oxidizer process.
What I claim is:
1. A photoflash lamp comprising:
an hermetically sealed, light-transmitting envelope;
a quantity of filamentary combustible material located within said envelope;
a combustion-supporting gas in said envelope;
and a primer secured to one end of said envelope and in communication therewith, said primer including a charge of percussively ignitable fulminating material comprising a phosphorus fuel, a chlorate salt oxidizer, a powdered combustible, incandescible metal, and a substance for facilitating the propulsion of said powdered metal from said primer into said envelope when said charge is ignited, said last-mentioned substance consisting of powdered carbon or a powdered, nonacidic carbon-containing compound which is substantially insoluble in liquid vehicles commonly used in applying said fulminating material to said primer.
2. The combination of claim 1 in which said chlorate salt is an absorbed oxidizer having a water solubility greater than 15 percent by weight and a cation not catalytically reactive toward phosphorus.
3. The combination of claim 1 in which said last-mentioned substance consists of powdered carbon or a powdered, nonacidic organic carbon compound which is substantially insoluble in liquid vehicles commonly used in applying said fulminating material to said primer.
4. The combination of claim 3 in which said powdered carbon or carbon compound comprises not less than 0.1 percent and not more than 10 percent of the dry weight of said fulminating material exclusive of said oxidizer.
5. The combination of claim 3 in which said fuel is red phosphorus, said oxidizer is sodium chlorate, and said powdered metal is titanium.
6. The combination of claim 1 in which said primer includes a tube sealed in said end of said envelope and having an exposed segment outside said envelope, and a wire anvil located substantially coaxial within said tube, said fulminating material being a coating on said wire anvil located intermediate its ends and on that segment of said wire anvil located in said exposed segment of said tube but spaced from the inside wall thereof.
7. The combination of claim 6 in which said fuel is red phosphorus, said oxidizer is absorbed sodium chlorate, said powdered metal is titanium, and said propulsion facilitating substance is powdered carbon or a powdered, nonacidic organic compound which is substantially insoluble in liquid vehicles commonly used in applying said fulrninating material to said wire anvil.
8. The combination of claim 6 in which the dried composition of said fulminating material exclusive of said oxidizer comprises about 69.31 percent titanium, about 27.21 percent red phosphorus, about l.l9 percent hydroxyethyl cellulose, about 0.61 percent magnesium oxide, about 0.60 percent magnesium montmorillonite, about 1.02 percent carbon, about 0.06 percent sulfur, and about 0.01 percent trichlorophenol.
9. The method of preparing fulminating material and applying said fulminating material on a primer anvil wire of a percussive-type photoflash lamp, said method comprising:
Preparing a slurry comprising a liquid vehicle, red
phosphorus, a powdered combustible, incandescible metal, and powdered carbon or a powdered, nonacidic carbon-containing compound which is substantially insoluble in said liquid vehicle;
coating said wire with said slurry;
drying said coated wire;
and permeating said coating on said wire with a chlorate salt solution containing at least percent by weight of dissolved chlorate salt.
10. The method of claim 9 in which the step of coating said wire is performed by dipping said wire into said slurry, and the last step is performed by dipping said coated wire into said chlorate salt solution.
11. The method of claim 9 in which said slurry is prepared by using water as the liquid vehicle, said powdered metal is titanium, and said powdered carbon or carbon compound comprises not less than 0.1 percent and not more than 10 percent of the weight of the materials in said slurry when dried.
12. The method of claim 10 in which said slurry is prepared by using water as the liquid vehicle and has a dried composition comprising about 69.31 percent titanium, about 27.21 percent red phosphorus, about l.l9 percent hydroxyethyl cellulose, about 0.61 percent magnesium oxide, about 0.60 percent magnesium montomorillonite, about 1.02 percent carbon, about 0.06 percent sulfur, and about 0.01 percent trichlorophenol, and in which said chlorate salt solution is prepared by dissolving sodium chlorate in water to provide an aqueous solution containing about 25 percent by weight of said chlorate.