US 3893798 A
A miniature high performance flashlamp is disclosed which includes an improved primer material that is more stable in handling during lamp manufacture and further improves performance of the lamp in operation. Said primer material comprises a mixture in percentages by weight of 1-5% sodium chlorate, 1-6% sodium perchlorate, and the balance being zirconium, which mixture can be bonded to form a unitary mass with a polyvinyl pyrrolidone binder. An aqueous solution of the primer material which includes the polyvinyl pyrrolidone binder remains substantially gel-free for long time periods and provides a tough and adherent coating in the lamp.
Description (OCR text may contain errors)
United States Patent [191 Sterling PHOTOFLASH LAMP  Inventor: Vaughn C. Sterling, Cleveland, Ohio  Assignee: General Electric Company,
 Filed: Dec. 15, 1972  App]. No: 315,663
[ July 8,1975
Schupp 431/95 McDonough 431/95 5 7} ABSTRACT A miniature high performance flashlamp is disclosed which includes an improved primer material that is more stable in handling during lamp manufacture and further improves performance of the lamp in operation. Said primer material comprises a mixture in percentages by weight of l5% sodium chlorate, l-6% sodium perchlorate, and the balance being zirconium, which mixture can be bonded to form a unitary mass with a polyvinyl pyrrolidone binder. An aqueous solution of the primer material which includes the polyvinyl pyrrolidone binder remains substantially gel-free for long time periods and provides a tough and adherent coating in the lamp.
1 Claim, 1 Drawing Figure 1 PHOTOFLASH LAMP BACKGROUND OF THE INVENTION This invention relates in general to miniature photoflash lamps of the all-glass type. and more particularly. to those of the so-called electricahignition type. Such photoflash lamps in general use at present comprise a hermetically sealed light-transmitting envelope usually made of glass and containing a combustion-supporting gas such as oxygen together with a filling of a suitable light-producing combustible material such as shredded foil zirconium or hafnium. for example. which upon ig nition, produces a high intensity flash of actinic light. A stem press base is located at one end of the lamp envelope to form a hermetic seal with a pair of electrical lead-in wires having a metal resistance filament connected therebetween. In such electrical-ignition type photoflash lamps in general use at present. the inner ends of these lead-in wires are coated with a charge of heat sensitive primer material so that when electrical current is passed through the resistance filament there will be deflagration of the primer material causing the shredded combustible foil in the lamp envelope to burn rapidly with incandescence.
With increasing miniaturization of a photoflash lamp such as that disclosed and claimed in U.S. Pat. 3.506.385 to Weber et al and assigned to the assignee of the present invention. more difficulties are encountered with the primer material of the electrical-ignition system both as affects lamp manufacture and the lamp operation. More particularly, a smaller bead size of the primer material on the electrical in-lead elements is required for lamps having an internal volume of less than about 2 cubic centimeters. and reliable manufacture of these lamps further necessitates not depositing the primer material on the inside wall of the tubular glass envelope during manufacture. Additionally. the high blast primers developed for larger diameter photoflash lamps contain a sufficient proportion of oxidizer in the primer material to generate a fire ball covering much of the inside lamp volume. Because the commonly used oxidizing materials are also generally not very soluble in the liquid coating compositions used to obtain the primer coating on the in-leads. it further became necessary to increase the oxidizer concentration even more so that enough oxidizer was present throughout the primer coating to cause complete combustion of the available fuel. The percussion-sensitive nature of these oxidizer substances makes handling them hazardous so that it would be desirable to reduce their concentration in the solid primer material.
Certain primer materials are already known which can be applied as coatings from a water-base suspension to reduce the hazards of handling the primer solids. A known primer material comprises a mixture in percentages by weight of 440% phosphorus. 3-87: potassium chlorate. 630% potassium perchlorate. and the remainder being titanium which is described and claimed in copending patent application. Ser. No. 198.547, filed Nov. 15. l97l in the name of Lewis J. Schupp, now US. Pat. 3.724.991 and assigned to the assignee of the present invention. Such primer mixture can be suspended in an aqueous solution of polyvinyl alcohol to provide a coating which is subsequently bonded to the envelope with the polyvinyl alcohol binder. A related primer material comprises a mixture in percentages by weight of 4-507r phosphorus.
10-25% potassium chlorate. 4l071 sodium chlorate. and the remaining being titanium which is described and claimed in pending application. Ser. No. 198.587. filed Nov. I5. 1971 in the name of the same inventor. now US. Pat. 3.724.990 and also assigned to the assignee of the present invention. The solid primer coating can also be applied from an aqueous suspension containing the polyvinyl alcohol binder.
SUMMARY OF THE INVENTION An improved primer material has now been discovered which can be applied reliably as a coating for the in-lead members of an electrical-ignition type flashlamp from a water-base suspension wherein all oxidizer constituents of the primer material are dissolved in the liquid suspension. The present primer material exhibits proper ignition sensitivity along with low blast characteristics upon actuation which makes it especially suitable for miniaturized photoflash lamps of the all-glass type which are described in the aforementioned US. Pat. No. 3.506.385. In such lamps having an internal volume of approximately 0.3-0.4 cubic centimeters it becomes possible to flash the lamps reliably with a high constant light output by using the present primer material at a primer weight range between 0.5 and 2.5 milligrams. Additionally. the lower ratio of oxidizer to fuel in the present primer material reduced the hazards of handling the primer solids.
An improved flashlamp construction of the present invention thereby comprises a hermetically sealed light-transmitting envelope. a quantity of filamentary combustible material distributed within said envelope. a filling of combustion-supporting gas in said envelope. and an electrical ignition system in communication with the interior of said envelope. said electricalignition system including a quantity of primer material which comprises an adhesively bonded solid mixture in percentages by weight of l-S7r sodium chlorate. l-67z sodium perchlorate, and the balance being zirconium. The combined weight percent of sodium chlorate and sodium perchlorate in the primer mixture does not exceed l07r in the preferred compositions so that a water-base coating composition can be used in applying the primer material having all of said oxidizer substances completely dissolved in the coating composition. By having the oxidizer constituents fully dissolved in the coating composition there are a number of benefits which include eliminating oxidizer segregation. reducing any flocculation and lumping tendency in the coating composition. and maintaining constancy of the oxidizer-fuel proportions throughout the life of the liquid coating composition. The present primer mixture is adhesively bonded to the envelope member with a polyvinyl pyrrolidone binder instead of the polyvinyl alcohol binder employed in the referenced primer formulations. Substitution of a polyvinyl pyrrolidone binder provides additional advantages of lesser foam tendency. a more rewettable nature. and higher tolerance to the dissolved oxidizers in the coating composition that was experienced with polyvinyl alcohol.
The coating compositions for the primer material of the present invention comprises a suspension of the afore-mentioned solid mixture in an aqueous solution of commercially available polyvinyl pyrrolidone which can have an average molecular weight in the range from 40.000-l60,000. Certain optional materials such as dispersants and preservatives can be added to the coating compositions in minor amount including polyvinyl alcohol which improves the toughness and chip resistance of the final solid coating. In a preferred coating composition. the powdered zirconium fuel is suspended by mixing with a colloidal silica suspending agent in an aqueous solution containing up to approximately l% polyvinyl alcohol binder until a uniform smooth dispersion has been obtained. The sodium chlorate and sodium perchlorate oxidizers are separately dissolved with a fungicide in an aqueous solution containing up to 20% polyvinyl pyrrolidone binder which provides safe handling of the oxidizer substances prior to mixing with the liquid fuel suspension when the final coating composition is to be applied. One part of said oxidizer solution can be added to about 6 parts of said fuel suspension to provide the final coating composition.
BRIEF DESCRIPTION OF THE DRAWING In the drawing, the single FIGURE is a crosssectional view partly in elevation of a preferred flashlamp of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing. a preferred flashlamp, according to the invention comprises a glass bulb or envelope l which. as shown. may be formed of a short length of glass tubing. for example. about A inches outside diameter, which is constricted and rounded off at one end as indicated at 2 and closed off thereat by an exhaust tip 3 and is formed at the other or base end 4 with a stem press base. The lead-in wires 6 are sealed in opposite corners 7 of the stern press base which provides a longer path length of the in-leads through the lamp envelope and less likelihood of leakage and loss ofthe hermetic seal. The envelope 1 is preferable made of a borosilicate hard glass which is capable of forming a good hermetic seal to the preferred iron-nickel cobalt alloys employed for the in-leads 6. The preferred glass compositions consist essentially of the following constituents in about the range stated by weight: 60 to 75% SiO to B 0 l to 10% A1 0 4 to l0% total alkali oxides. and O to 5% BaO except for incidental impurities and residual fluxes and refining agents, and having a mean coefficient of linear thermal expansion between 0 and 300C about in the range of to X 10 per C. The preferred alloys for at least one electrical inlead being hermetically sealed through said glass wall include commercial products known by the names Kovar, Rodar. Therlo. Fernico I, Fernico ll. Nicoseal, Nilok. Sealvac A and others. Generally. these are allows predominantly of iron, nickel and cobalt. and optionally contain manganese in amounts generally less than I% preferably less than 0.5%, along with incidental impurities. The general range of composition for such alloys is 27 to 32% Ni. l4 to 19% Co. less than 1.0 Mn, the balance iron. except for incidental impurities. The composition of Kovar. a suitable lead material is about 54% Fe. 29% Ni, 17% Co; 0.5% Mn, 0.2% Si. and 0.06% C. The inner ends of the leads are coated with the primer material 8 and have an electrical filament 9 connecting them. This filament may be a fine tungsten wire or preferably constructed of a 97% tungsten 3% rhenium alloy. A quantity of filamentary combustible material 10 such as a shredded foil of zirconium or hafnium. for example, is distributed within the interior space of the envelope 1 which also contains a filling ofa suitable combustiomsupporting gas such as oxygen generally at high pressure in excess of several atmospheres.
The solid coating of primer material in the above embodiment can be applied to the in-lead members as a stabilized aqueous suspension of the present invention in various known ways. For example. the in-lead members can be dipped into the aqueous slurry followed by drying in the air or with heat to remove the liquid and produce a solid adhered coating having the desired characteristics previously described. Alternately, the aqueous slurry can be sprayed on the in-lead members and thereafter processed to provide a solid coating exhibiting comparable performance.
As an example of suitable coating compositions which are prepared as generally above described in two portions so as to maintain the oxidizer and fuel constituents separately until the final coating composition is to be applied. there is listed below a typical formulation together with permissible variation in the individual constituents as follows:
For the above coating compositions approximately one part of the oxidizer solution can be added to about 5-6 parts of the liquid fuel suspension in the manufacturing plant by conventional means to provide the primer coating composition. After mixing the individual por tions to produce a smooth even blend of the constituents. there is obtained a liquid coating composition which is stable in storage up to l week. The zirconium fuel material should have a particle range from a fine mesh size to a micron size to provide the final smooth and uniform primer coating.
While the best mode of carrying out the present invention has been set forth above, it will be understood that additions. changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. For example. it will be apparent that still another optional constituents can be added to the liquid coating compositions if desired so long as in minor amount to modify the film-forming characteristics of the final solid coating when necessary for a particular lamp construction. Likewise, it will be apparent that other electricalignition type flashlamp constructions other than herein specifically disclosed can employ the primer materials of the present invention. It is intended to limit the present invention, therefore, only the scope of the following claims.
What I claim as new and desire to secure by Letters Patent of the United States is:
1. In a miniature flashlamp comprising a hermetically sealed light-transmitting envelope having an internal volume of approximately 0.4cc or less. a quantity of filsively bonded solid primer mixture which comprises in percentages by weight of 1-57: sodium chlorate. 1-47: polyvinyl pyrrolidone. l-67( sodium perchlorate, and the balance being zirconium with said primer mixture having been applied as an aqueous suspension of zirconium having the sodium chlorate, sodium perchlorate and polyvinyl pyrrolidone dissolved therein.