GB2103008A

GB2103008A - Galvanic dry cell and method for sealing same

Info

Publication number: GB2103008A
Application number: GB8209114A
Authority: GB
Inventors: Brooke Schumm
Original assignee: Union Carbide Corp
Current assignee: Union Carbide Corp
Priority date: 1981-03-30
Filing date: 1982-03-29
Publication date: 1983-02-09
Also published as: DE3211331C2; GB2103008B; JPS57210563A; FR2502849A1; FR2502849B1; DE3211331A1

Abstract

There is disclosed a galvanic dry cell comprising a consumable anodic container 2 housing the remaining active components and having a closure 14 disposed over the container's open end and wherein a heat-shrinkable tape 22 is adhesively secured to and shrunk about the upstanding wall of the container and at least the peripheral edge of the closure thereby adhesively securing and sealing the closure to the container. There is also disclosed a method for sealing the closure to a galvanic dry cell using heat-shrinkable tape and adhesive. <IMAGE>

Description

SPECIFICATION Galvanic dry cell and method for sealing same The invention relates to sealed galvanic dry cells and more particularly to a cylindrical consumable anodic container having disposed therein a depolarizer mix separated from the container by a separatc ,-, a current collector (carbon rod) centrally embedded in said depolarizer mix, a closure having an opening at its center through which the current collector passes and having a peripheral portion disposed on top of the upper rim of the container. The invention also relates to a method for sealing such galvanic cells.

Conventional galvanic dry cells for use in flashlights, toys or other sundry devices generally comprise a cylindrical container, such as a zinc anode can, with a depolarizer mix filling most of the container and having a carbon rod in the center which functions as the current collector for the depolarizer mix. The cells are generally sealed by inserting a support washer over the cathode depolarizer mix and then dispersing hot molten asphalt onto the washer thereby providing an asphalt seal for the cells while also providing an airspace above the depolarizer mix and below the asphalt seal to accommodate the discharge gases and exudate of the cells.

Although asphalt seals have been employed with some success in sealing galvanic dry cells, they do have a number of drawbacks or disadvantages. For example, several assembly procedures are required such as placing a support washer down into the cell, pouring an asphaltic pitch onto the support washer, placing a vent washer on top of the asphaltic pitch and then finally placing a terminal cap on top of the cell and locking it in place. The vent washer is usually required to prevent the terminal cap from becoming embedded in the pitch which could possibly result in forming a gastight seal which could prevent venting. In addition, it is possible that the inside surface of the container could become dirty due to chemical contamination, prior to dispensing the asphaltic pitch.This could result in a pseudo-seal which, over a period of time, could eventually lead to moisture loss from the cell and/or oxygen ingress to the cell because of insufficient adhesion of the pitch to the can or container. It is also possible that during the heating of the asphalt pitch to cause a meniscus to form at the can-asphalt interface, pin holes may form in the pitch as a result of expansion of the air in the void volume below the support washer which would allow moisture loss and/or oxygen ingress to the cell. Another disadvantage in the use of asphalt seals is that they physically take up a relatively large space in the cell thereby limiting the size of the airspace into which the reaction products of the cells can discharge.In addition, asphalt seals are not particularly suited for high temperature environments since the seal at the asphalt-can interface is subject to degradation at high temperatures which could possibly cause paths through which moisture loss) and/or oxygen (ingress) could travel.

In the abovedescribed cells, the venting of the gases from within the cell can take place through a porous current collector such as a carbon rod-or the like. Although a properly prepared asphalt seal will effectively minimize electrolyte or moisture loss through evaporation and minimize air or oxygen ingress to the cells, the assembly and quality control techniques required to insure good seals are rather expensive and time consuming.

The finished cells that do not meet the minimum quality standards for one reason or another are usually dissembled or detubed so that the raw cell components can be reused. However, in constructions where the container is adhered by asphalt or the like to the outer finish, recovery of the raw cell components is messy and expensive.

Furthermore, when a top centering seal washer is employed as part of the finished cell, the detubing operation (removal of the outer jacket) may disturb this centering washer which in turn may cause the depolarizer mix contact to be somewhat loosened.

U.S. Patent 3,967,977 discloses a closure for sealed galvanic dry cells in which the closure has a a centrally disposed tubular neck adapted to be snugly slid over and be adhesively secured to a current collector centrally embedded in a depolarizer mix within a cylindrical container and has a peripherally disposed tubular skirt or apron adapted to snugly slide on and be adhesively secured to the upper rim of the container thereby providing a seal for the container.

The invention broadly relates to a galvanic dry cell comprising in combination a cylindrical consumable anodic container having an open end, an electrode comprising a depolarizer mix disposed within said container and separated therefrom by a separator, a current collector partially embedded, preferably centrally, in said depolarizer mix and a closure covering the open end of said container, said closure having an opening, preferably at its center, and being disposed such that the upper portion of the current collector passes through and is secured (joined} to the wall defining the opening in the closure and the peripheral portion of the closure sits on the upper rim of the open end of the container, the improvement wherein a heatshrunk tape is adhesively secured to and shrunk about the upstanding cylindrical wall of the container and is shrunk and adhesively secured onto at least the peripheral portion of the closure thereby sealing said closure to the container.

The current collector could be secured to the opening in the closure by having at least a snug fit therein, preferably a forced fit, and/or by being secured therein through the use of a separate medium such as an adhesive or sealant.

Preferably, the tape should extend onto at least a , portion of the bottom of the cell's container to prevent any spew from escaping through perforations that may form at the corner of the container during discharge. If desired, a disc or the like could be disposed on the bottom of the container and secured to the container using the shrink tape.

The invention also relates to a method for sealing a galvanic dry cell comprising the steps:~ a) placing in a cylindrical consumable anodic container having an open end, an electrode comprising a depolarizer mix, a separator disposed between said depolarizer mix and said inner container wall, a current collector partially embedded in said depolarizer mix and extending out through the open end of said container, and an electrolyte; b) placing a closure having an opening therein on top of the open end of the container such that the upper end of the current collector passes through and becomes secured to the wall defining the opening in the closure, and the peripheral portion of the closure sits on the upper rim of the open end of the container;; c) enveloping the upstanding wall of the container and at least the peripheral portion of the closure with an adhesive and a heat-shrinkable tape such that the adhesive is disposed between said tape and the container and the at least peripheral portion of the closure; and d) heating the tape enveloped containerclosure assembly sufficiently to shrink said tape around the container wall and onto said closure thereby providing a heat-shrunk tape adhesively secured to said container and adhesively secured onto the closure thereby sealing said closure to said container.

By the present invention there may be provided a means for entrapping and preventing any spew within a cell employing a consumable anodic container from leaking out through the container.

The use of the present invention may have increased internal volume to accommodate the cell's active components and discharge products, and may be easily and inexpensively be assembled.

Further by use of the present invention raw cell's may be sealed through the use of heat shrinkable adhesive tape while also providing a means for preventing the leakage of any spew out through an opening in the cell's consumable container formed during storage or cell discharge.

Preferably, the heat-shrinkable tape should have an adhesive side thereby eliminating the need for a separate step of applying the adhesive to the appropriate cell components. A suitable heat-shrinkable adhesive tape would be Electrical Tape 1320 obtainable from Industrial Electrical Products Division of 3M Company, St. Paul Minn.

This tape is a heat-shrinkable polyester film tape with acrylic, pressure-sensitive adhesive having good flagging resistance and solvent resistance.

In addition to securing the closure to the container, the heat-shrunk tape being adhesively secured around the upstanding wall of the consumable anodic container will cover any openings formed in the container during discharge and thereby retain any spew within the cell from leaking out between the shrunk tape and the container. With the tape adhesively secured around the entire upstanding wall of the container, an adhesive barrier is formed which prevents any spew exiting from an opening in the container to flow between the tape and container.

Consequently, the adhesively secured tape entraps and confines any spew from leaking out of the cell where it could cause damage to the device in which it is being used. Additionally, the adhesively secured shrunk tape extends onto at least the outer periphery of the closure thereby securing the closure through the bond of the adhesive material and the continuing force exerted by the heat shrunk tape. This latter force will exert a continuing compressive force onto the closure thereby securing and sealing the closure to the container.

When the adhesive material is not provided as an integral part of the tape, then any suitable adhesive could be used that could withstand the temperatures required to shrink the tape. For example, temperatures between about 700C and about 3000C for a period of time between about 2 seconds and about 30 minutes would generally be suitable for most heat-shrinkable tape applications. Suitable adhesives are disclosed in the textbook titled "Handbook of Adhesives" edited by Irving SkeistReinhold Publishing Corporation, New York (1962). Examples of suitable adhesives are the polyamide resins which are either the thermoplastic heat seal or heatactivated adhesives.

Another class of suitable adhesives is the fatty polyamides which are produced from dibasic fatty acids. As defined in the "Encyclopedia of Polymer Science and Technology", Vol. 10, Interscience Publishers, a division of John Wiley and Sons, Inc., fatty polyamides are condensation products of di- and polyfunctional amines and di- and polybasic acids obtained by the polymerization of unsaturated vegetable oil acids or their esters.

Fatty polyamide adhesives, in addition to being excellent adhesives, also resist wetting by electrolytes and, therefore, can retard "creep" of such electrolytes within or from the cells over a long period of time. The use of fatty polyamides in galvanic cells is disclosed in U.S. Patent No.

3,922,1 78 by Jerrold Winger.

The closure for use in this invention could be made of an insulating material such as plastic, for example, polyethylene, polypropylene, rigid vinyl, polycarbonate, high impact polystyrene, copolymers made from acrylonitrile, butadiene and styrene and nylon. Of the above, polypropylene or polystyrene would be the preferred materials. The opening disposed in the center of the closure should preferably be of a size sufficiently small so as to provide a force fit for the current collector. The opening in the closure could also be defined by a tubular neck which could be adhesively secured to the current collector, if desired, for particular applications.

The closure has a sufficient diameter so that its peripheral portion can seat on the upper rim of the container, and preferably should be larger in diameter than the upper rim of the container so that it extends slightly over the rim. If desired, the peripheral portion of the closure could extend in a tubular skirt or apron which could fit on or over and contact the rim of the container. The closure could also be a flat disc. Whatever the shape of the closure, it has to be such that it seats or sits on the rim of the container so that the heatshrinkable tape can be at least adhesively secured to and shrink onto the peripheral portion of the closure thereby securing and sealing the closure to the container. Suitable types of closures are disclosed in U.S. Patents, 3,967, 977 and 3,802,923. The disclosures made in both of these patents are incorporated herein by reference.

The invention will now be further described by way of example with reference to the accompanying drawings in which:~ Figure 1 is an elevational view in cross-section of a primary galvanic dry cell incorporating an embodiment of the present invention.

Figure 2 is an elevational view in cross-section of a primary galvanic dry cell incorporating another embodiment of the present invention.

Figure 3 is an elevational view, partly in cross section, of a seal closure suitable for use in this invention.

Figure 4 is an elevational view, partly in cross section, of a seal closure suitable for use in this invention.

Figure 5 is an elevational view, partly in cross section, of a completely assembled cell of this invention.

Referring to Figure 1, there is shown a galvanic dry cell which includes a cylindrical container 2 made of an electro-chemical consumable metal such as zinc and which serves as the anode of the cell. Included in container 2 are an insulator disc and/or cup 4 disposed at the bottom of container 2, a separator 6 lining the vertical wall of the container, a cathode electrode comprising a depolarizer mix 8 disposed within but separated from said container by insulator disc and/or cup 4 and separator 6 and a current collector 10 centrally embedded in the depolarizer mix 8. The insulator disc or cup could be made of plastic, paper, or any other suitable material. The separator 6 may comprise a thin electrolyte paste layer or may be a thin film separator containing electrolyte, for example, a thin bibulous paper coated with an electrolyte gel paste.The cathode depolarizer mix 8 is an electrochemically active cell component and may contain, for example, manganese dioxide, a conductive carbonaceous material such as carbon black or graphite and an electrolyte. The depolarizer mix 8 may be molded around a central carbon cathode collector rod 10 before being inserted into container 2 or preferably the depolarizer mix 8 could be first inserted into container 2 whereupon current collector 10 could then be forced into the mix. A conventional centering washer (not shown) could be employed to maintain the current collector 10 in an upright axial position.

The top of the cathode depolarizer mix 8 is disposed a fixed distance below the open end of container 2 to provide airspace 12 to accommodate any liquid spew that may be formed during storage or cell discharge.

An electrically insulating closure 14 is provided for sealing the open end of container 2. The closure 14 has a centrally disposed opening 16 which is slightly smaller in diameter than the diameter of rod 10 so that is provides a friction fit when it is forced down on rod 10. The peripheral portion 18 of closure 14 seats on the upper crimped in rim 20 of container 2. A heatshrinkable tape 22 with an adhesive disposed between the tape 22 and container 2 is wrapped around the container 2 and extends onto the peripheral portion 18 of closure 14 and onto the bottom of container 2. The assembly is suitably heated whereupon the tape is shrunk around the upstanding wall of container 2 and onto the peripheral portion 18 of closure 14 thereby securing and sealing closure 14 to the container 2.Thus closure 14 is sealed and secured to container 2 through the compressive force of the shrunk tape and also the adhesive bond between the tape and the closure. As evident from Figure 1, the use of the heat-shrinkable tape and adhesive will provide for increased internal volume for the active components of the cell system, for the containment of liquid formed during discharge, and for the expansion of the cathode mix during discharge. As also evident from Figure 1, if the consumable zinc container should fail as by forming perforations in its upstanding wall, then the adhesively secured shrunk tape will contain any spew discharging through such perforations. Thus the subject invention will provide an improvement in containing and preventing spew from escaping from a galvanic dry cell.

Figure 2 shows a similar galvanic dry cell as in Figure 1 except that it employs a different closure 30 than the closure 14 shown in Figure 1. The remaining components of the cell in Figure 2 are identical to those shown in Figure 1 and are, therefore, identified with the same reference numbers. Closure 30 is of the type disclosed in U.S. Patent 3,802,923.

Figures 3 and 4 show two embodiments of closures 32 and 34, respectively, suitable for use in the subject invention.

Figure 5 shows the raw cell of Figure 1 enclosed in an outer assembly including an outer tubular noncorrodible jacket 36. The upper end of the tubular jacket 36 extends beyond closure 14 and is locked in engagement with the outer peripheral edge of a one piece top cover 38 in the conventional manner. The outer cell assembly includes means for venting any gas released from inside the container 2 to the outer atmosphere.

Such means may be provided, for example, by making the locking engagement between the top cover plate 38 and jacket 36 permeable to gas.

Thus the invention provides a taped closure means for the open end of a cylindrical container used in sealed galvanic dry cells which requires the minimum number of parts and which is, therefore, relatively inexpensive to assemble. The taped closure can be easily and accurately assembled during manufacture of the dry cells and give highly reliable and reproducible results in containing and confining gases and cell exudate during cell storage and discharge.

The taped closure of this invention offers a number of advantages such as: 1. The raw cell may be aged independent of the jacket: 2. The taped closure would limit moisture loss and oxygen ingress to the cell; 3. The adhesive is on the outside of the container (zinc) rather than on the inside, thus a potentially better sealed closure is formed because the outside of the container can be kept clean and free of contamination from the depolarizer mix or the like; 4. The adhesive shrink tape provides an area contact rather than a line contact, thus an increased leakage resistant path; 5. The taped closure allows appearance rejects to be reclaimed without disturbing the raw cell assembly; 6. The closura may be thin to provide minimum material cost and can be formed at high production rates; and 7.The taped closure can provide an increase in void volume of the raw cell for spew containment or an increase in mix height and service capacity compared to an asphalt sealed cell.

Example Several hundred "D" size raw cells (without the tubular jacket and top terminal cover cap) were constructed substantially as shown in Figures 1 and 2 except the closure shown in Figure 1 had a slight semi-circular recess disposed approximately midway between the center of the collector rod and the edge of the cover.

Specifically, the cells were fabricated using a zinc can, a kraft paper bottom cup and a plastic insulator disc disposed in the bottom of the can, a separator lining the vertical wall of the zinc can, a positive electrode of depolarizer mix composed of manganese dioxide, carbon black and zinc chloride-containing electrolyte disposed in and separated from the zinc can by the bottom separators and the vertical lining, and a porous carbon rod centrally embedded in the depolarizer mix. A polypropylene closure was placed over the open end of the zinc can and an adhesive shrinkable tape (Tape 1320) was wound about the can and cover. The assembly was heated at 2000C for 3 to 5 seconds whereupon the tape shrunk as shown in Figure 1. The cells were then stored at 21 0C and some were short circuited for 21 days. The cells were visually examined after 21 days on short circuit and found to exhibit no leakage of liquid spew from within the cell.

Claims

1. A galvanic dry cell comprising in combination a cylindrical consumable anodic container having an open end, an electrode comprising a depolarizer mix disposed within said container and separated therefrom by a separator, a current collector partially embedded in said depolarizer mix, and a closure covering the open end of said container, said closure having an opening and being disposed such that the upper portion of the current collector passes through and is secured to the wall defining the opening and the peripheral portion of the closure sits on the upper rim of the open end of the container; and a heat shrunk tape adhesively secured to and shrunk about the upstanding cylindrical wall of the container and shrunk and adhesively secured onto at least the peripheral portion of the closure thereby sealing said closure to the container.

2. A galvanic dry cell as claimed in claim 1, wherein the current collector is force fitted into the opening in the closure.

3. A galvanic dry cell as claimed in claim 1, wherein the current collector is secured to the opening in the closure using an adhesive or sealant.

4. A galvanic dry cell as claimed in any one of the preceding claims, wherein the closure has a peripheral skirt that seats onto the upper rim of the container.

5. A galvanic dry cell as claimed in any one of the preceding claims, wherein the tape is shrunk and adhesively secured to at least a portion of the bottom of the container.

6. A galvanic dry cell as claimed in any one of the preceding claims, wherein the tape is shrunk tape having an adhesive side.

7. A galvanic dry cell as claimed in any one of the preceding claims, wherein the consumable anodic container is zinc and the depolarizer mix comprises manganese dioxide and a carbonaceous material.

8. A method for sealing a galvanic dry cell comprising the steps:~ a) placing in a cylindrical consumable anodic container having an open end an electrode comprising a depolarizer mix, a separator disposed between said depolarizer mix and said inner container wall, a current collector partially embedded in said depolarizer mix and extending out through the open end of said container, and an electrolyte; b) placing a closure having an opening on top of the open end of the container such that the upper end of the current collector passes through and becomes secured to the wall defining the opening in the closure and the peripheral portion of the closure sits on the upper rim of the open end of the container;; c) enveloping the upstanding wall of the container and at least the peripheral portion of the closure with an adhesive and a heat shrinkable tape such that the adhesive is disposed between said tape and said container and said at least peripheral portion of the closure; and d) heating the tape enveloped container closure assembly sufficiently to shrink said tape around the container and onto the closure thereby providing a heat shrunk tape adhesively secured and shrunk around the container wall and adhesively secured and shrunk onto the closure thereby sealing said closure to the container.

9. A method as claimed in claim 8, wherein in step c) the tape is a heat shrinkable adhesive tape.

10. A method as claimed in claim 8 or 9, wherein in step d) the heating is carried out at a temperature between about 7000 and about 3000C for between about 2 seconds and about 30 minutes.

11. A method as claimed in claim 8, 9 or 10, wherein in step b) the current collector is secured to the wall defining the opening in the closure by being force fitted into said opening.

12. A method as claimed in claim 8, 9 or 10, wherein in step b) the current collector is secured to the wall defining the opening in the closure by an adhesive or sealant.

13. A method as claimed in any one of claims 8 to 12, wherein in step c) the tape and adhesive extends at least onto the bottom of the container.

14. A galvanic dry cell substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.

15. A galvanic dry cell substantially as hereinbefore described in the foregoing Example.

1 6. A method for sealing a galvanic dry cell substantially as hereinbefore described with reference to and as illustrated in any one of the accompanying drawings.

17. A method for sealing a galvanic dry cell substantially as hereinbefore described in the foregoing Example.