US3739464A

US3739464A - Making disposable electric devices

Info

Publication number: US3739464A
Application number: US00113163A
Authority: US
Inventors: S Eilenberger
Original assignee: Progressive Products Corp
Current assignee: Progressive Products Corp
Priority date: 1969-07-24
Filing date: 1971-02-08
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19

Abstract

A method for making disposable electric devices, such as flashlights, which includes providing a casing having one or more battery compartments; coating one or more surfaces of each compartment with an electrode overlay, such as zinc; coating one or more surfaces of each compartment with another electrode overlay such as carbon; providing serial or parallel electric connection between the compartments; filling the compartments with a battery mix; inserting the operative electrical elements of the device, such as a bulb and lens assembly, in connection with the electrodes and sealing the device.

Description

United States Patent Appl. No.: 1 13,163

Related 1.1.8. Application Data Division of Ser. No. 844,592, July 24, 1969, Pat. No. 3,601,601.

U.S. Cl 29/592, 136/175, 136/131 Int. CL. H0lm 1/00 Eilenberger 11mm 19, 1973 [54] MAKING DISPOSABLE ELECTRIC DEVICES 3,007,994 1 [/1961 Urry 136/126 2,745,774 5/1956 Reid 117/216 [75] Inventor Stanley Mmdlemwm 3,400,020 9/1968 comm, et a1. 136/120 Conn' 2,931,894 4/1960 Bruehl 240/1061 [73] Assignee: Progressive Products Corporation, 1

Kensington, Conn. Primary Examiner-Charles W. Lanham 1 Assistant Examiner-D. C. Crane [22] Flled' 1971 Attorney-Russell & Nields 1 57 ABSTRACT A method for-making disposable electric devices, such as flashlights, which includes providing a casing having one or more battery compartments; coating one or more surfaces of each compartment with an electrode overlay, such as zinc; coating one or more surfaces of each compartment with another electrode overlay such as carbon; providing serial or parallel electric connection between the compartments; filling the compartments with a battery mix; inserting the operative electrical elements of the device, such as a bulb and lens assembly, in connection with the electrodes and sealing the device.

16 Claims, 16 Drawing Figures PATENTED g 13. T39 ,464

SEE! 1 [If 3 IIIIIIIIIIIIIIII IIIIIIII v/////////////// ///////)/r 8 6 gi SEN 1 4 7 a FIG. 3

STANLEY D. EILENBERGER ATTORNEYS 1 MAKING DISPOSABLE ELECTRIC DEVICES CROSSREFERENCE TO RELATED APPLICATION This application is a divisional application of my copending application, Ser. No. 844,592, filed July 24,

1969, now US Pat. No. 3,60l,60l.

BACKGROUND OF THE DISCLOSURE mize the amount of mix which ban be encased. See for example US. Pat. Nos. 2,561,532; 2,494,265; and 2,794,904. Such devices, however, apparently have not realized widespread commercial success. Recently a disposable flashlight battery has achieved commercial success, but this is of the design illustrated in expired U.S. Pat. No. 2,401,349, wherein two battery cells of ordinary design are encased in a plastic container having the customary bulb and wiring. Indeed, this device is hardly more than a conventional flashlight, having a plastic case, that becomes permanently useless as soon as the batteries expire.

The present invention results in an electrical device having a very high yield of battery mix per unit volume, and which is truly disposable in the sense that the total cost of the unit is competitive with the cost of ordinary cell batteries capable of delivering similar electrical output. The low total cost is due in part to the present method, which is readily adapted to high-speed automated procedures.

It is therefore the major objective of the invention to i provide electrical devices in which a battery mix is encased within the device in a high yield per unit volume. Another objective is to provide electrical devices, of long life, having a battery mix encased by the device casing. It is a further objective to provide such a method. which entails a series of simple process steps capable of high-speed automatic performance in order that a minimum of time and of hand-assembly operations is necessary. Other objectives, as well as advantages, of the invention will become apparent as the invention is further described below.

DESCRIPTION OF THE DRAWINGS The invention isillustrated in the attached drawings, which serve to illustrate the present method. These drawings include:

FIG. I, a cross-sectional view in side elevation of a flashlight case having two compartments, with two controde overlay of carbon have been applied to the exposed zinc surfaces, and after battery mix has been added;

FIG. 4, across-sectional view along lines 44 of FIG. 3;

H (6) filling the battery compartment(s) with a battery FIG. 5, a side elevation view, partly in cross-section, of the case after paper washers and an end seal of wax have been put in place;

FIG. 6, a side elevation view, partly in cross-section, of the case after the contacts have been given their final shape and the lamp and lens assembly have been attached;

FIGS. 7 and 8, cross-sectional views in end elevation showing an alternative case arrangement in two pieces with interlocking means;

FIGS. 9 and 10, elevation views partly in cross ment having conductive means between opposite walls,

eight of which are used in the case arrangement of FIG. 11;

FIG. 13, a cross-sectional view showing in elevation another alternative case arrangement wherein the contacts need not extend into the battery compartments;

FIG. 14, a cross-sectional view along lines 14-14 of FIG. 13;

FIG. 15, a cross-sectional view of the case of FIGS. 13 and 14, after the zinc and carbon electrode overlays have been applied, after the paper barriers and battery mix have been inserted, after the sealing means of FIGS. 9 and 10 has been inserted, and after contacts have been inserted; and

FIG. 16, a cross-sectional view partially broken away along lines 1616 of FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a novel method of making disposable electric devices which is at once simple and efficient. In brief, the method involves incorporating in a certain way battery mix and operative electrical elements in a casing, the structure of which will of course vary depending upon the ultimate use of other, similar devices, such as night lights, candleY sticks, bicycle lights or horns, cigarette lighters, desk calendars, alarms, and the like.

The present method includes in combination the following steps: (I) providing a casing for electrodes, battery mix and the operative electrical elements of the device, preferably composed of a strong, inert plastic material, and containing at least one battery compartment; (2) inserting two electrical contacts into the cas ing to provide conductive means from the battery compartment(s) to the electrical elements; (3) coating partly or completely at least one wall of each battery compartment with an electrode (e.g., zinc) overlay and providing electrical contact between an overlay and at least one of the electrical contacts; (4) coating partly or completely at least one other wall of each battery compartment with another electrode (e.g., carbon) overlay and providing electrical contact between that overlay and one of the electrical contacts: (5) preferably, coating substantially completely the former (zinc) overlay(s) of each compartment with a paper barrier;

mix; (7) sealing the battery compartment(s); (8) and attaching and electrically connecting the operative electrical elements to the two electrical contacts.

The particular order in which all of the above steps are performed is not critical, but it is preferred that steps 1 (3), (4), (5), (6) and 7 are performed at least in part in that order. Step (2) can be performed whenever it is convenient to insert the contacts in conductive relationship with the compartment(s). Further, in order to ensure good electrical contact, it may be preferable to coat two or more walls of each compartment with a zinc overlay and at the same time to provide electrical contact between electrical contacts and the two different zinc overlays, and then to coat one zinc overlay of each compartment with a carbon overlay. This procedure is illustrated in the drawings and will be described fully below. In addition, where a plurality of battery compartments is to be used, it is of course necessary to provide electrical contact between the zinc overlay of one compartment and the carbon overlay of the next. Various ways of simply achieving such contact are described hereafter.

The casings for the present electrical devices are preferably made of a strong, inert plastic. The material should be strong enough to withstand the impact of normal usage, which inevitably would result in dropping from heights up to several feet, without breaking or otherwise leaking the battery mix. And it must be chemically resistant to the battery mix, i.e., noncorroding or inert. Of course, the casing should not be electrically conductive to the extent of defeating its purpose. Several well-known plastics have suitable properties; among them are mediumor high-impact polystyrene, phenolics, vinyls, polyamides, polycarbonates and similar plastics. The casings may be fabricated by any suitable technique, many of which are well known, such as compression or injection molding.

If the electrodes are to be applied by spraying, it ordinarily is necessary to treat the casing surface, for example by sand blasting, to render it capable of adhering with the sprayed electrode film. Finally, if the case is originally in two pieces, or more, they must be sealed to prevent leakage, preferably by ultrasonic sealing. Case sealing is most conveniently performed after the electrode overlays are applied, and may be done before the battery mix is added and the battery compartments are sealed. If ultrasonic sealing is employed, the edges must be clean, which would be achieved also by sand blasting. One of the advantages of the present method is its speed, which in ordinary operation is sufficient to ensure that the casing, after the original sand blasting, remains clean until sealing. The electrode overlays are formed from suitable electrode materials. A preferred .anode material is zinc, which may be applied by any suitable method, such as spraying, coating or otherwise applying the electrode layer. The term overlay, as used here, is not intended to limit the method of application, for example, to spraying, although this method is a preferred component of the invention. The overlay may be applied to the battery compartment surface(s) even as a preformed layer, provided that in use it is in intimate contact with the surface(s).

A zinc overlay preferably is 99.9 percent pure, and should preferably be free of iron, tin, arsenic, antimony, magnesium, copper and other detrimental impurities. Because of the nature of this invention, impurities which affect only the mechanical properties of zinc, such as lead or cadmium, may be tolerated, but

those which adversely affect electrical properties, in particular iron and copper, should be avoided. A zinc overlay may be applied by flame spraying, which is preferred, arc spraying, sputtering or plasma spraying, methods which are generally known to those of the art, as well as by electrodeposition and vacuum metallizing. Flame spraying is a preferred method in part because it results in a high surface area for the zinc, which is advantageous. Since, unlike ordinary battery cells, the zinc is not used for mechanical strength, the zinc overlay need only be thick enough to provide good potential and a complete reaction when the battery is exhausted, although for practical reasons some excess is usually desired. An overlay thickness of about 0.009 inch is adequate, and a thickness in the range of about 0.0030.02 is normally suitable.

The cathode ordinarily used in conjunction with zinc anodes is, of course, carbon. A carbon overlay may be applied by any of several suitable methods. In this invention the carbon overlay preferably is applied from what has become to be known to the art as an electrically conductive carbon dispersion, a dispersion of fine carbon particles in a suitable vehicle, e.g., alcohol or trichloroethylene. Preferably, a carbon overlay is applied as a pressure spray, sometimes referred to as airless, in a thickness of about 0002-0005 inch, or more. Since a carbon overlay, expecially in this thickness range, is a poor electrical conductor, it is preferred to apply a zinc overlay beneath the carbon electrode, so that conductivity is needed only through the carbon overlay thickness, and not along its length. If this is done, however, it is important that the carbon layer on top of the zinc be continuous, with no discontinuities, in order that contact between the battery mix and the zinc sublayer be avoided.

A preferred method of ensuring a continuous carbon layer on a zinc sublayer is to apply the carbon with a resin binder, although this approach may make difficult spray application. Alternatively, the carbon may be applied as a continuous, preformed film on a substrate of carbon on a vinyl sheet to form a duplex electrode.

As will be apparent from the description hereafter, the zinc and carbon overlays are applied to one or more walls of the battery compartments, but not to all of the wall surfaces. Hence, it is necessary while applying the overlays by any of the spraying methods to mask those walls not to be covered, preferably with a material to which the overlay will not adhere, such as, for example, zinc, glass or chrome-plated steel.

There is no intention to limit this invention to the electrode overlays here described in detail, i.e., zinc and carbon. Equivalent electrode materials, such as magnesium or nickel-cadmium, may also be used, with suitable modification to the battery mix composition and method of overlay application, these modifications being within the ordinary skill of the art. It is desirable to interpose' a barrier between the zinc electrodes and the battery mix, to prevent chemical reaction between the mix and the zinc. This barrier may be a gel of cereal paste, such as a mixture of cornstarch and flour which may be directly applied to the zinc anode by spraying or other means, or a gel-coated paper. Alternately, this paste may be prepared from such materials as locust bean flour or guar flour. The purpose of this gel is to provide a thin film between the electrolyte and the zinc anode. Paper coated with cereal paste, usually about 0.005 inch thick is preferred. When wetted by the electrolyte the coating becomes conductive for electric current but prevents chemical action between the ammonium chloride and the zinc. The barrier should be continuous and sealed at the edges, if contact between the zinc and mix is to be avoided.

The composition of the battery mix is not critical, many different suitable compositions being wellknown; some are described in the literature and some are trade secrets of others. A typical composition would contain about 55-65 percent manganese dioxide, 5-25 percent graphite or acetylene black, 8-15 percent ammonium chloride, 0.5-4 percent zinc chloride, and -15 percent water. Equivalent ingredients may, of course, be substituted for the ingredients of the above composition, and equivalent compositions are also known and may be used.

Inhibitors to reduce gassing, such as mercuric chloride or potassium dichromate, may be added to the battery mix. Mercuric chloride is preferred unless the device is to be used at elevated temperature, and may be added in a concentration of up to 0.1 percent, or even more. Since the mercuric chloride forms an amalgam with zinc, thereby weakening the metal, ordinarily it is used only in small amount, usually about 0.025 percent. Here, however, such restriction is not so critical, since the zinc is not needed for mechanical strength.

With reference to the drawings, FIGS. 1 and 2 show a flashlight casing 1, composed of a strong, inert plastic material, having outer walls 2, a cutout 3, designed to receive a switch button not shown, a center dividing wall 4, and recessed tracks 5 and 6. The casing walls define two

battery compartments

7 and 8 having wall surfaces 7a-e and Sa-e. Inserted into recessed tracks 5 and 6, respectively, are preformed

electrical contacts

9 and 10.

FIGS. 3 and 4 show the device after several further steps of the method have been performed, as follows.

The first step is the application of zinc overlays Ila-e, by a method such as flame spraying, to

contacts

9 and 10, wall surfaces 7d and 8a, and to frontend surface 12 of center wall 4. The purpose of this last zinc overlay lle is to provide electrical contact between

battery compartments

7 and 8. Zinc overlays 11a and 110 ultimately are to be the anodes of the two battery cells to be

providedin compartments

7 and 8, while overlay 11b is to provide contact between overlay lle and a cathode, and overlay 1 1d is to provide contact between contact 10 and another cathode. While the zinc overlay is being applied, walls 7b, c, e, and 812, c, e, are masked, in order to restrict application to the desired areas.

The next step of the method, shown in FIGS. 3 and i 4, is the application of carbon overlays l3a-b, by spraying, for example, on zinc overlays 11a and 11c, respectively. These carbon overlays provide the cathodes for the two battery cells. While the carbon overlay is being applied, walls 7b, 0, e and 8b,'c, e, as well as zinc overlays 11b and d, are masked, in order to restrict application to the desired areas, zinc overlays 11a and.

cation of paper barriers l4a-b on the remaining exposed zinc overlays 11b and lid of the battery compartments; and the addition of battery mix 15 to

compartments

7 and 8. FIG. 5 shows the device after paper washers l6 and wax seal 17 are applied to provide an airtight seal of the battery compartments.

The next steps, shown in FIGS. 3 and 4, are the appli- After the battery compartments have been sealed, 1

the electrical elements may then be incorporated into the device, and the remaining steps of the method carried out. First, as shown in FIG. 6, contacts 9 and II) are formed into their final shape, then lamp assembly 18, consisting of lamp l9 and reflector 2%, is inserted into the casing 1 against shoulder 121i. The lamp assembly may be a separate'subassernbly made by a light press fit of lamp flange 22 into collar 23 of relfector 12ft. After insertion, center contact 24' of lamp 11%" is permanently connected to contact at nipple Switch an operates, by lateral sliding, to engage end 2'7 or contact 9 with lamp shell 28 oflamp 3119, thereby completing the circuit and activating the lamp. After lamp assembly 118 is inserted, finally, lens assembly 29 is inserted to form a tight press fit with casing l at wall 30. Preferably the flashlight device is then sealed to prevent disasscmbly,

and it is possible, if desired, to form a waterproof seal joined together after the various overlays are applied,

as described above for casing. l, to the inner surfaces of

walls

34 and 35 and to both surfaces of center wall 32, by inserting peripheral. edge 36 and center-wall edge 37 of the top and center wall into recessed peripheral groove 38 and center groove 39 respectively, with suitable adhesive means not shown, for example by ultrasonic sealing.

FIGS. 9 and 10 illustrate an alternative sealing mean for the battery compartments. This type of seal is preferred because it alleviates the buildup of by-product gases, principally hydrogen, of the electric discharge of the battery. Preferably the sealing means, consisting of molded seal 40, having an aperture 41, and backing sheet 42, is composed of a plastic material permeable to hydrogen, in order to vent such gas through the backing sheet 42 and aperture 41, and substantially imt permeable to water vapor, in order to retard drying of the battery mix, which would deactivate the battery. Such plastic material include certain polyvinyl chlorides; low density polyethylenes, such as DINl-I diameter of aperture may be about inch. Preferably the backing sheet 42 is heat s-ealed to the back of molded seal40, or alternatively the two may be molded together as a single molded seal, not shown.

FIGS. 11 and 12 illustrate an alternative battery cell arrangement in a casing having eight battery compartments. FIG. 11 shows the main casing 43, consisting of,

side walls

44 and 45, end wall 46 and center wall 47. FIG. 12 shows detail of a separator wall 49, provided with connector 50 for electrical contact between the opposite sides of the wall. The eight compartments 48a-h are formed by inserting eight separator walls 49, the connection being between tongue 51 of the separator walls and grooves 52 a-h of the

side walls

44 and 45 of casing 43, and between tongue 53a-h ofcenter wall 47 and grooves 54 of the separator walls 49.

The coating of the surfaces of casing 43 with the various overlays is somewhat complicated by the presence of so many compartments. Initially, surface 46a of the end wall is coated with a zinc overlay and surface 46b, with a carbon overlay, and an electrical contact 55 is provided between these two end wall overlays. Then six separator walls 49, having a carbon overlay on one side and a zinc overlay on the other, are inserted, in the locations between tongues 53b, 0, d, f, g and h and grooves 52 b, c, d,f, g andh, shown in FIG. 11, as above described. Finally, a separator wall 49, having a carbon overlay on its interior wall, is inserted between tongue 53a and groove 52a, and another separator wall 49, having a zinc overlay on its interior wall, is inserted between tongue 53e and groove 52e. Contacts (not shown) similar to

contacts

9 and 10, used in casing 1 above, may then be connected to the connectors 50 or the last two separator walls 49 and to the lamp assembly in the conventional manner.

FIGS. 13-l6 illustrate an alternative flashlight device, prepared by a method somewhat different from that used as illustrated in FIGS. 1-6. With reference to FIGS. 13 and 14, battery case 56 is provided with

side walls

57 and 58, end wall 59 and center wall 60, and contains two battery compartments, 61 and 62. In the forward part of the case, ahead of the battery compartments, are recessed

tracks

72 and 73, for the insertion of contacts. The battery compartments have wall surfaces 61a-e and 62a-e.

FIGS. and 16 illustrate the battery case 56 of FIGS. 13 and 14, after the battery compartments have been filled and sealed and contacts inserted, but before the electrical elements have been incorporated. The method is first to

coat surfaces

61a, 61d, 62a and 62d with an electrode, such as zinc by the manner described above, to form overlays 63a-d; to coat zinc overlays 63a and c with the second electrode, carbon, to form overlays 64a and b; and to cover the remaining zinc overlays 63b and d with paper barriers 65a and b. Connection between

battery compartments

61 and 62 is again provided by extending the zinc overlay 63e between overlays 63b and c. In addition, the application of zinc overlay is extended beyond the battery compartments into the forward part of the case by conducting overlays 66a and b on forward surfaces 67a and b of case 56. With the various overlays in place, battery mix 68 and washers 69 are added, and hydrogenpermeable sealing means 70 (similar or identical to that illustrated in FIGS. 9 and 10) is force-fitted against shoulder 71, and held in place in part by the

ends

72a and 73a of recessed

tracks

72 and 73. This sealing means 70 provides a seal for the battery compartments that is permeable to hydrogen and substantially impermeable to water vapor. After sealing of the battery compartments,

contacts

74 and 75 are inserted into recessed

tracks

72 and 73, in intimate conducting contact with overlays 66a and b, respectively. The electrical components of the device, i.e., the switch, lamp and lens assembly, not shown, may be subsequently inserted in a manner similar to that used for the device earlier described.

It is apparent that in the device just illustrated in FIGS. 13-16 zinc overlays are applied directly onto the outer walls and extended beyond the battery compartments into the vicinity of the operative electrical elements, and contact made there between the elements and the zinc overlay. This arrangement may be preferred, expccially where an effective seal may be difficult to maintain due to the extension of the contacts into the battery compartments. In any case, this latter procedure should be deemed equivalent to the procedure of inserting contacts into the battery compartments shown in FIGS. I-6.

It will be evident that devices other than flashlights, or flashlights or" different construction, may be similarly prepared by the present method, perhaps if desired by altering the dimensions and shape of the case, and by employing suitably different operative electrical components.

A number of variations of the above devices are possible still within the present method. As sometimes desired with batteries, it is possible to provide for the release of pressure due to the formation of gas during the battery discharge. This may be accomplished by substituting a gas-permeable, liquid-impermeable seal for the wax seal, as above described. It also may be accomplished by the use of inhibiters, as above described, or by employing an expansive seal, made for example of elastic material, in place of the customary seal. Alternatively, a conventional gas vent may be employed to avoid the problem of gas pressure buildup.

The above specification has described preferred embodiments of the invention, namely various two-cell and eight cell disposable flashlights. There is no intention to limit the invention to the illustrated embodiments, which is applicable as well to others.

I claim:

1. A method for making electrical devices, which comprises providing a strong, inert casing having at least one battery compartment, coating at least one wall surface of said compartment with a first electrode overlay while masking the remaining wall surfaces, coating at least one wall surface of said compartment with a second electrode overlay while masking the remaining surfaces, in a manner such that at least one wall surface is covered with said first electrode overlay and at least one separate wall surface is coated with said second electrode overlay, filling said battery compartment with a battery mix to provide a potential difference between said first and second electrode overlays, sealing said battery compartment, and inserting operative electrical elements into the casing in connection with the electrodes.

2. The method of claim 1, wherein said first electrode overlay is zinc, and said second electrode overlay comprises a carbon overlay.

3. The method of claim 2, wherein said zinc overlay is applied by flame spraying, and said zinc overlay is coated with a barrier.

4. The method of claim 2, wherein said zinc overlay is applied to at least two wall surfaces of said battery compartment and said carbon overlay is applied thereafter to one of said wall surfaces covered with said zinc overlay.

5. The method of claim 2, wherein at least one electrical contact is inserted into said battery compartment along a recessed track, to provide electrical connection with said operative electrical components, and a zinc overlay is applied to said contact.

6. The method of claim 2, wherein said zinc overlay is extended beyond said battery compartment into a forward compartment of said casing, and electrical connection is there made with said operative electrical elements.

7. The method of claim 2, wherein said casing comprises at least two battery compartments, and electric cal elements comprise a switch, a light bulb and a lens assembly.

9. The method of claim 1, wherein said casing is constructed of molded, high-impact polystyrene.

10. The method of claim 1, wherein said battery cornpartment is sealed by a sealing means permeable to hydrogen and substantially impermeable to water vapor.

11. A method for making electrical devices, which comprises providing a strong, inert, two-piece, plastic casing capable of being sealed and having at least one battery compartment, sand blasting said casing, coating at least one wall surface of said compartment with first electrode overlay while masking the remaining wall surfaces, coating said first electrode overlay with a barrier, coating at least one separate wall surface of said compartment with a second electrode overlay, comprising a conductive overlay on said separate wall surface and a dissimilar overlay on said conductive overlay, while masking the remaining surfaces, in a manner such that at least one surface is covered witha first electrode overlay and at least one separate surface is coated with a second electrode overlay, joining and sealing the two parts of the casing by ultrasonic sealing,

filling said battery compartment with a battery mix to provide a potential difference between said first and second electrode overlays, sealing the battery compartment, and inserting operative electrical elements into the casing in connection with the electrodes.

12. The method of claim ll, wherein said first elec trode overlay is zinc, and said second electrode overlay comprises a zinc conductive overlay and a carbon dissimilar overlay.

13. The method of claim 12, wherein said zinc over lays are applied by flame spraying.

14. The method of claim 12, wherein said zinc overlays are applied at once to at least two walls of each

Claims

2. The method of claim 1, wherein said first electrode overlay is zinc, and said second electrode overlay comprises a carbon overlay.
3. The method of claim 2, wherein said zinc overlay is applied by flame spraying, and said zinc overlay is coated with a barrier.
4. The method of claim 2, wherein said zinc overlay is applied to at least two wall surfaces of said battery compartment and said carbon overlay is applied thereafter to one of said wall surfaces covered with said zinc overlay.
5. The method of claim 2, wherein at least one electrical contact is inserted into said battery compartment along a recessed track, to provide electrical connection with said operative electrical components, and a zinc overlay is applied to said contact.
6. The method of claim 2, wherein said zinc overlay is extended beyond said battery compartment into a forward compartment of said casing, and electrical connection is there made with said operative electrical elements.
7. The method of claim 2, wherein said casing comprises at least two battery compartments, and electric connection between said two compartments is provided by a zinc overlay.
8. The method of claim 1, wherein said casing is the external casing of a flashlight and said operative electrical elements comprise a switch, a light bulb and a lens assembly.
9. The method of claim 1, wherein said casing is constructed of molded, high-impact polystyrene.
10. The method of claim 1, wherein said battery compartment is sealed by a sealing means permeable to hydrogen and substantially impermeable to water vapor.
11. A method for making electrical devices, which comprises providing a strong, inert, two-piece, plastic casing capable of being sealed and having at least one battery compartment, sand blasting said casing, coating at least one wall surface of said compartment with first electrode overlay while masking the remaining wall surfaces, coating said first electrode overlay with a barrier, coating at least one separate wall surface of said compartment with a second electrode overlay, comprising a conductive overlay on said separate wall surface and a dissimilar overlay on said conductive overlay, while masking the remaining surfaces, in a manner such that at least one surface is covered with a first electrode overlay and at least one separate surface is coated with a second electrode overlay, joining and sealing the two parts of the casing by ultrasonic sealing, filling said battery compartment with a battery mix to provide a potential difference between said first and second electrode overlays, sealing the battery compartment, and inserting operative electrical elements into the casing in connection with the electrodes.
12. The method of claim 11, wherein said first electrode overlay is zinc, and said second electrode overlay comprises a zinc conductive overlay and a carbon dissimilar overlay.
13. The method of claim 12, wherein said zinc overlays are applied by flame spraying.
14. The method of claim 12, wherein said zinc overlays are applied at once to at least two walls of each battery compartment, and said carbon overlay is applied thereafter to one of said walls of each compartment covered with said zinc overlay.
15. The method of claim 11, wherein said casing is constructed of molded, high-impact polystyrene.
16. The method of claim 11, wherein said battery compartment is sealed by a sealing means permeable to hydrogen and substantially impermeable to water vapor.