Process for ultrasonic sealing an anode cup into a gasket for electrochemical cells

A gasket-cover assembly for use as a closure for an electrochemical cell which is produced by a process in which an extended wall of the cover is ultrasonically forced into a flange of a gasket such that the flange of the gasket makes a "U" shaped enclosure about the bottom wall of the cover.

FIELD OF THE INVENTION 
The Invention relates to the sealing of a cover, such as an anode cup for 
electrochemical cell, into a gasket using ultrasonic means to produce a 
cover-gasket assembly ideally suited for sealing a container, such as a 
container for an electrochemical cell. 
BACKGROUND OF THE INVENTION 
The miniaturization of electronic devices has created a demand for small 
but powerful electrochemical cells. Cells that utilize an alkaline 
electrolyte are known to provide high energy density per unit volume, and 
are therefore well suited for applications in miniature electronic devices 
such as hearing aids, watches and calculators. However, alkaline 
electrolytes, such as aqueous potassium hydroxide and sodium hydroxide 
solutions, have an affinity for wetting metal surfaces and are known to 
creep through the sealed metal interface of an electrochemical cell. 
Leakage in this manner can deplete the electrolyte solution from the cell 
and can also cause a corrosive deposit on the surface of the cell that 
detracts from the cell's appearance and marketability. These corrosive 
salts may also damage the device in which the cell is housed. Typical cell 
systems where this problem is encountered include silver oxide-zinc cells, 
nickel-cadmium cells, air depolarized cells, and alkaline manganese 
dioxide cells. 
Many liquid electrolytes used in galvanic cells will form a corrosive salt 
deposit on the exterior surface of the cells in which the electrolyte is 
used if the electrolyte leaks out of the cell. Such a corrosive deposit 
detracts from the appearance and marketability of the cell. These 
corrosive deposits may also damage the electronic device in which the cell 
is housed and short the cell. Therefore such galvanic cells are sealed to 
prevent electrolyte leakage. 
In the prior art it has been a conventional practice to incorporate 
insulating gaskets between the cell container and cover so as to provide a 
seal for the cell. Generally, the gasket must be made of a material inert 
to the electrolyte contained in the cell and the cell environment. In 
addition, it had to be flexible and resistant to cold flow under pressure 
of the seal and maintain these characteristics so as to insure a proper 
seal during long periods of storage. Materials such as nylon, 
polypropylene, ethylene-tetrafluoroethylene copolymer and high density 
polyethylene have been found to be suitable as gasket materials for most 
applications. Typically, the insulating gasket is in the form of a "J" 
shaped configuration in which the extended wall of the cover is inserted 
so that upon being radically squeezed, the bottom portion of the gasket 
forms a "U" shaped seal for the bottom portion of the wall of the 
container. To better insure a good seal, a sealant is generally deposited 
in the "J" shaped seal so that upon insertion of the cover into the 
gasket, the edge of the extended wall of the cover will seat in the 
sealant and then upon the application of a radical squeeze, the gasket 
will be compressed against the bottom portion of the extended cover wall. 
The sealant will thereby act as a further seal for the cover-gasket 
assembly. In addition, the sealant can also function as a gap filler to 
compensate for variances in the manufacture of the gasket and cover 
components. It is possible that deviation from the ideal component sizes 
of the gasket and cover could result in the active battery materials 
and/or electrolyte being trapped between the edge of the wall of the cover 
and the sealant. This could result in cell leakage. Consequently, since 
component parts of the gasket-cover assembly are difficult to manufacture 
to exact specifications and it is difficult to apply the sealant with 
precision to the gasket on a continuous operational basis, there is always 
the possibility that the assembled cells will leak. This is particularly 
true of small miniature cells. 
It is an object of the present invention to provide a process for producing 
a good gasket-cover seal assembly for electrochemical cells. 
It is another object of the present invention to provide a process using 
ultrasonic means for producing a good gasket-cover seal assembly for 
electrochemical cells, such as alkaline cells. 
It is another object of the present invention to provide an efficient and 
cost effective process that uses ultrasonic means for producing a 
gasket-cover seal assembly for alkaline cells. 
The foregoing and additional objects of the present invention will become 
more fully apparent from the following description and accompanying 
drawings. 
DISCLOSURE OF THE INVENTION 
The invention relates to a process for ultrasonically sealing a cover into 
a gasket comprising the steps; 
(a) preparing a compressible gasket comprising a tubular wall with a flange 
extending inwardly at one end; 
(b) preparing a cover with a wall extending downwardly and terminating with 
a bottom edge; 
(c) inserting said cover into said gasket such that the bottom edge of the 
wall of the cover contacts the flange of the gasket; and 
(d) ultrasonically forcing the cover into the flange of the gasket until 
the flange and a bottom portion of the wall of the gasket forms a U-shaped 
enclosure about a portion of the bottom segment of the wall of the cover. 
As used herein, the term tubular means circular, oval, square, rectangular 
or any polygonal shaped tubular wall. 
Elastic waves of frequencies beyond the range of audibility are called 
ultrasonic waves. These waves are conventionally produced by quartz 
crystal oscillators designed for producing frequencies ranging from up to 
200 to 300 kilocycles per second or higher. These ultrasonic waves can be 
used to produce a steady force against an object. It is this force means 
that are used in the present invention to insert the extended wall of a 
cover into a flange of a gasket to provide an excellent seal between the 
gasket and the bottom wall of the cover. The force to be applied to insert 
the bottom portion of the cover wall into the flange of the gasket has to 
be sufficient so that the gasket forms a "U" shaped seal about the bottom 
portion of the wall of the cover. Thus the settings of an ultrasonic 
welder has to be adjusted depending on the material of the cover and the 
composition of the gasket. Once these data are selected, a conventional 
ultrasonic welder can be used to insert the bottom wall of a cover into 
the flange of a gasket. 
Preferably, the thickness of the flange measured parallel to the 
longitudinal axis of the wall of the gasket would be thicker than the 
thickness of the wall of the gasket so that the edge of the wall of the 
cover could easily be forced fitted within said flange using ultrasonic 
means. Preferably, the flange thickness should be at least 1.5 times 
thicker than the thickness of the wall of the gasket and more preferably 
at least 3 times thicker than the thickness of the wall of the gasket. 
Preferably, the insertion of the edge of the cover wall should be inserted 
into the gasket by at least 0.01 inch and more preferably by at least 
0.015 inch to insure a good seal. It should be appreciated that the 
distance that the edge is inserted into the flange will depend on the 
material composition of the gasket-cover components and in some 
applications the cell system that the gasket-cover assembly will be used. 
In some applications, a sealant may be used between the edge of the cover 
wall and the flange of the gasket. Once the gasket-cover assembly is 
produced, it is preferable to assemble the anode of the cell into the 
gasket-cover assembly and then the gasket-cover-anode assembly is placed 
within a container of a cell housing other active and inactive components 
of the cell system. The container is then squeezed against the 
gasket-cover assembly forming a seal for the cell. Specifically, the 
gasket-cover assembly could be sealed to a container of the cell by 
turning the top portion of the container sidewall over the outer 
upstanding wall of the gasket thereby compressing the gasket between the 
container and cover so as to effectively seal said cover to and 
electronically insulating said cover from the container. 
The sealing gasket of this invention comprises a material selected with 
consideration given to its stability in the presence of the electrolyte, 
its resiliency, and its resistance to cold flow. Suitable polymeric 
materials are selected from the group consisting of nylon, 
polytetrafluoroethylene, fluorinated ethylene-propylene, ethylene 
copolymer with fluorinated ethylene-propylene, chlorotrifluoroethylene, 
perfluoro-alkyoxy polymer, polyvinyls, polyethylene, polypropylene, 
polystyrene and the like. Other suitable materials would be recognizable 
by one skilled in the art. In some applications, additional precautions 
can be used in conjunction with the gasket of this invention to provide a 
more effective seal, such as coating the flange of the gasket surfaces 
with an adhesive agent such as a fatty polyamide resin. The sealing gasket 
of this invention is amenable to production techniques such as injection 
molding. The configuration of the surfaces of the gasket flanges is well 
suited for ease of removal from dies, punches and the like. Preferably the 
gasket would be nylon. The cover could be made of monel, copper, clad 
stainless steel, or some other conductive material. Preferably, the cover 
would be a triclad cover made of nickel, stainless steel and copper. 
However, the cover should be made of a conductive material that will not 
corrode or otherwise deteriorate when in contact with the materials of the 
cell. The container for the cell could be made of stainless steel, iron, 
nickel, nickel-plated steel, or some other conductive material. 
Typical cell systems in which this invention can be used are alkaline 
manganese dioxide cells, air depolarized cells, nickel-cadmium cells and 
silver oxide-zinc cells.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows a cylindrical gasket 2 comprising an upstanding cylindrical 
wall 4 terminating with an inwardly extended flange 6. The thickness X of 
flange 6 is thicker than the thickness Y of upstanding wall 4. FIG. 2 
shows an anode cup 8 comprising a top cover 10 and extended cylindrical 
side wall 12. This anode cup 8 is shown as one material but preferably 
would be composed of two or more layers of different materials and most 
preferably would be a triclad of nickel, stainless steel and copper. 
FIG. 3 shows the cover 8 of FIG. 2 inserted in gasket 2 of FIG. 1 so that 
the bottom edge 16 of cover 8 rest on flange 6. FIG. 4 shows the edge 16 
of cover 8 imbedded in flange 16 after being ultrasonically forced into 
flange 16. As can be seen from FIG. 4, flange 6 forms a "U" shaped seal 
encasement about edge 16 of the cover. If desired, a sealant could be 
disposed between the edge 16 and flange 6. In addition, to facilitate the 
insertion of edge 16 into flange 6, the edge 16 of cover 8 could be 
tapered to form a blunt edge surface. Preferably the taper would be less 
than 45.degree. as measured from the longitudinal axis of the gasket and 
more preferably between 15.degree. and 30.degree.. 
Shown in FIG. 5 is a zinc air cell 19 in which the largest component of the 
cell 19 is an open ended metal container 20 identified as a cathode cup. 
The cathode cup 20 is generally made from nickel plated steel that has 
been formed such that it has a relatively flat central region 22 which is 
continuous with and surrounded by an upstanding wall 24 of uniform height. 
Two small holes 26 are punched into the bottom 22 of cup 20 to act as 
air-entry ports. A layer of porous material 28 covers the interior surface 
of the air holes 26 and acts as an air distribution membrane 28. A layer 
of polytetrafluoroethylene 30 covers the entire bottom of cathode cup 20 
including the air distribution membrane 28. The second major component is 
an air electrode 32 which is positioned adjacent the inside surface of the 
polytetrafluoroethylene layer 30. This electrode 32 contains several 
components, including: a metal screen 34; a mixture of manganese oxides 
and carbon embedded in screen 34; a barrier film 36 which prevents the 
anode's electrolyte from moving into the cathode 32; and a soak up 
separator 38. The third component is a generally cup-shaped metal cover 40 
which forms the top of the cell and is generally referred to as the anode 
cup. In FIG. 5 the edge 42 of the anode cup 40 has been ultrasonically 
inserted into the flange 44 of gasket 46 according to this invention. The 
anode cup 40 can be made from a trilaminate material comprising copper 48 
that has been laminated to the bare side of a nickel-clad steel strip. A 
nickel layer 50 protects the exterior surface of steel strip 52 which is 
located between nickel layer 50 and copper layer 48. Other laminated 
materials from which anode cups may be made include: a bilaminate of 
copper on a stainless steel substrate or a laminate made from more than 
three layers. Round disks punched from this laminated metal strip are then 
formed into anode cups. The copper layer forms the inside surface of the 
anode cup and directly contacts the anodic mixture. The fourth component 
is the anodic mixture 54 which can comprise a mixture of zinc particles, 
electrolyte and organic compounds such as binders and corrosion 
inhibitors, which make up the battery's anode. The cathode cup 20 along 
with the inserted air electrode 32 and associated membranes, are inverted 
over and pressed against the anode cup/gasket assembly which is 
preassembled according to this invention and containing the anode. While 
inverted, the edge of the cathode cup 20 is collected inwardly. The rim 56 
of the cathode cup is then compressed against the elastomeric gasket 46 
between the cathode up 20 and the anode cup 40 thereby forming a seal and 
an electrical barrier between the anode cup 40 and the cathode cup 20. A 
suitable tape 58 can be placed over the opening 26 until the cell is ready 
for use. 
The following example is provided to illustrate the concept of the 
invention and is not intended to limit the scope of the invention which is 
recited in the appended claims. 
EXAMPLE 
It was discovered that a 0.008 inch thick triclad (nickel, stainless steel, 
copper) straight walled anode cup with an overall height of 0.163 inch 
could be inserted approximately 0.006 inch into a 0.020 inch flanged ("J" 
channeled) gasket (constant thickness gasket) with the use of a ultrasonic 
welder. The anode cup and gasket were mated by hand and placed under the 
horn of a welder with the anode cup facing the horn. Pressure and 
ultrasonic waves were then applied and the total downward travel 
controlled by a positive stop. This yielded an anode/gasket assembly with 
an overall height of 0.177 inch instead of the normal mated height of 
0.183 inch. The welder was a Branson Welder series 800 model 8400 equipped 
with a flat horn. Settings for the welder for inserting the cover into the 
gasket were as follows: 
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Down Speed 6 
Pressure 10 psi 
Weld Time &lt;0.2 sec. 
Hold Time 0.3 sec. 
Trigger Setting 5 
Power 100 
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Zinc air cells were manufactured using this gasket-cover assembly and 
showed good sealing characteristics. 
Molded thick flanged (0.040 inch) gaskets were then made. These gaskets had 
a thicker flange (X) than the wall thickness (Y) such that X was 0.040 
inch and Y was 0.010 inch. An 0.008 inch triclad anode cup with an overall 
height of 0.174 inch was used with these gaskets. It was found that the 
initial settings for the ultrasonic welder used for the 0.020 inch flange 
gaskets would not accomplish the necessary insertion of the cover. Thus 
the settings were changed as follows: 
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Down Speed 6 
Pressure 14 
Weld Time 0.8 sec. 
Hold Time 0.3 sec. 
Trigger Setting 5 
Power 100 
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These settings yielded an overall height of the anode/gasket assemblies of 
0.184 inch which represented an insertion of 0.030 inch and an effective 
gasket flange thickness under the edge of the cover of 0.010 inch. It was 
observed during this test that some deformation of the gasket's outer 
gasket diameter could occur and to correct this the gasket could be held 
in place by the use of a carrier which had the desired gasket outer 
dimensions while the cover was ultrasonically inserted into the flange of 
the gasket. 
The data from the test demonstrate that (1) better and more accurate fit 
can be obtained between the gasket and anode cover; (2) assembly heights 
can be maintained and controlled; (3) tolerance of component parts become 
less critical; (4) easier manufacturing means can be employed to produce 
the "L" shaped gasket; and (5) the sealing area increases due to deeply 
seated cover insertion into the flange of the gasket. 
It is to be understood that modifications and changes to the preferred 
embodiment of the invention herein shown and described can be made without 
departing from the spirit and scope of the invention.