Leak resistant galvanic cell and process for the production thereof

Galvanic cells having at least a portion of their sealing surfaces and/or corrodible members coated with a sputtered or plasma polymerization deposited layer of polymeric material no more than 2000 angstroms thick demonstrate increased resistance to electrolyte leakage and/or increased resistance to corrosion.

FIELD OF THE INVENTION 
This invention relates to a sealed galvanic cell wherein at least a portion 
of the surface of at least one of the components of the cell's housing or 
of a corrodible cell component is coated with a tightly adhering layer of 
polymeric material which is no thicker than about 2000 angstroms, such 
layer having been deposited by plasma polymerization or sputtering. Such 
cell demonstrates enhanced resistance to electrolyte leakage and/or 
enhanced resistance to corrosion. Also provided is a process for treating 
cell components so as to produce a cell exhibiting enhanced resistance to 
corrosion and/or electrolyte leakage. 
BACKGROUND OF THE INVENTION 
A continuing concern in the manufacture of galvanic cells is that 
electrolyte may creep through a sealed interface of the cell and leak out 
of the cell. Electrolyte leakage may shorten cell life and can also cause 
a corrosive deposit to form on the exterior surface of the cell which 
detracts from the cell's appearance and marketability. These corrosive 
salts may also damage the device in which the cell is housed. Electrolyte 
leakage occurs in cell systems having aqueous or nonaqueous electrolytes, 
such as organic solvent-based electrolytes and liquid inorganic 
cathode-electrolytes, for example those based on thionyl chloride and 
sulfuryl chloride. Electrolytes such as alkaline electrolytes have an 
affinity for wetting metal surfaces and are known to creep through a 
sealed interface of a galvanic cell. 
In the prior art it has been a conventional practice to incorporate an 
insulating gasket 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, the cell gasket must possess sufficient flexibility and 
resistance to cold flow under pressure as well as being able to maintain 
these characteristics so as to insure a proper seal during long periods of 
storage. Materials such as nylon, polypropylene, and high density 
polyethylene have been found to be suitable as gasket materials for most 
applications. 
However, the use of a compressible gasket alone has not proved sufficient 
to reduce cell leakage to commercially acceptable standards. Accordingly, 
several approaches have been taken in the prior art in order improve the 
leakproofness of galvanic cells. Among the approaches which have been 
taken in the past is the deposition of a polymeric layer at the cell 
container/gasket and/or cover/gasket interface. 
For example, U.S. Pat. No. 4,282,293 discloses an improved seal for 
alkaline cells wherein a film of a substituted organosilane is disposed 
and compressed between the interface of the cell cover and a coated 
gasket, such film being deposited utilizing a solvent which is 
subsequently evaporated. Preferably such film has a thickness of between 
10 and 100 angstroms. 
Japanese Patent Application No. 90146/1978 discloses the formation of a 
fluoropolymer film by sputtering or plasma deposition onto the surfaces of 
electrochemical cells in order to reduce electrolyte leakage. This patent 
application indicates that the thickness of the film deposited should be 
at least 3000 angstroms in order to avoid pinholes. 
However, even these cell constructions are not successful in stopping cell 
leakage. Although not wishing to be held to any theory, applicants surmise 
that a major reason for the failure of the prior art ultra thin films to 
successfully prevent electrolyte leakage is that such films do not 
sufficiently adhere to the cell container and/or cover and/or gasket 
substrate. 
It is believed that the resistance to chemical reactions which take place 
at the interface of a substrate and a polymeric coating and, hence the 
resistance of such interface to electrolyte leakage, can be considered to 
be dependent on four major factors: (1) the permeability of the coating to 
the electrolyte solvent; (2) the electrolyte repellency of the coating; 
(3) the adhesion of the coating to the substrate; and (4) the passivation 
effect on the interface caused by the coating. In the case of thick film 
coatings the permeability of the coating and the electrolyte repellence of 
the coating itself play predominant roles, with the third and fourth 
factors mentioned above playing a relatively minor roles. 
However, in ultrathin film coatings, the role of the permeability factor 
becomes minimal due to the fact that the overall transport resistance is 
the ratio of the film thickness to permeability. For instance, water 
molecules pass through most organic polymers rather easily, and the time 
lag of diffusion of water through a 0.1 mm thick layer is well below a 
fraction of a second and it is nearly impossible to stop the penetration 
of water to the substrate/film interface. Consequently the adhesion 
characteristics, particularly the wet adhesion properties, become a 
vitally important factor in the overall chemical resistance of the 
interface. The adhesion and passivation effects of an ultrathin film are 
often closely related and are often inseparable characteristics of such a 
coating. 
Thin films produced by evaporation methods, such as that employed in U.S. 
Pat. No. 4,282,293 are subject to pinhole formation, whereas films formed 
by sputtering or plasma polymerization do not generally contain pinholes. 
See Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 10 at page 275, 
John Wiley & Sons (3d Ed. 1980). Thus evaporation produced films such as 
those described in U.S. Pat. No. 4,283,293 will provide poorer protection 
for the substrate surface due to the presence of such pinholes. Moreover, 
such lower energy film deposition processes result in the polymeric film 
having a relatively poor adhesion to the substrate. 
While Japanese Patent Application No. 90146/1978 employs higher energy 
means of coating the fluoropolymers on the cell surfaces, thin layers of 
about 300 angstroms of such fluoropolymers possess relatively poor 
maintenance of wet adhesion notwithstanding said application means as 
evidenced by the relatively poor wet adhesion exhibited by plasma 
polymerized tetrafluoroethylene and hexafluoroethane in Example 1 below. 
A further problem which may be encountered during the lifetime of a 
galvanic cell is that of internal or external corrosion. Internal 
corrosion of interior corrodible cell members may undesirably increase the 
internal resistance of the cell, particularly during high temperature 
storage. External corrosion may detract from the cell's marketability or 
interfere wih the cell's contact with the device into which such cell is 
to be inserted. As is apparent to those skilled in the art, conventional 
coating of the external surfaces of the components of the cells housing or 
the internal surfaces of interior corrodible cell components with a 
protective layer is precluded as such layer will interfere with the cell's 
operation due to the high electrical resistance of such coating. 
Therefore, there is a need for a galvanic cell having internal and/or 
external surfaces which exhibit increased resistance to corrosion, which 
corrosion resistance means does not interfere with the effective operation 
of the cell. 
Accordingly, it is an object of the present invention to provide a galvanic 
cell which exhibits improved resistance to electrolyte leakage. 
It is another object of this invention to provide a galvanic cell which 
exhibits increased resistance to internal and/or external corrosion, which 
cell does not exhibit increased internal resistance or impaired contacts 
due to such corrosion resistance means. 
It is a yet another object of this invention to provide a process for 
treating at least a portion of at least one surface of at least one 
component of a galvanic cell such that, when assembled, said cell will 
exhibit increased resistance to electrolyte leakage and/or to corrosion. 
The foregoing and additional objects of this invention will become apparent 
from the following description and accompanying drawings and examples. 
DESCRIPTION OF THE INVENTION 
This invention relates to a sealed galvanic cell comprising a cathodic 
material, an anodic material and an electrolyte housed in a container 
having an open end and a container sealing surface, said container being 
sealed at its open end by a cover having a cover sealing surface with a 
non-conductive gasket compressively disposed therebetween, said gasket 
having a first gasket sealing surface and a second gasket sealing surface, 
said first gasket sealing surface and said second gasket sealing surface 
being in interfacial sealing contact with the container sealing surface 
and the cover sealing surface respectively; characterized in that at least 
a portion of at least one of the cover sealing surface, the container 
sealing surface, the first gasket sealing surface and the second gasket 
sealing surface is coated with a tightly adhering layer of polymeric 
material which is no thicker than about 2000 angstroms, such polymeric 
layer being comprised of at least one component selected from the group 
consisting of hydrocarbons, oxygen-containing hydrocarbons, 
nitrogen-containing hydrocarbons, sulfur-containing hydrocarbons, 
phosphorous-containing hydrocarbons and organometallic compounds, said 
polymeric layer having been deposited by plasma polymerization or 
sputtering. 
In another aspect this invention relates to a sealed galvanic cell 
comprising a cathodic material, an anodic material, a corrodible component 
and an electrolyte housed in a container having an open end and a 
container having an open end, said container being closed at its open end 
by a cover with a non-conductive gasket compressively disposed between 
said cover and container; characterized in that at least a portion of at 
least one of the surfaces of the cover, the container, the gasket or the 
interior corrodible component is coated with a tightly adhering layer of 
polymeric material which is no thicker than about 2000 angstroms, such 
polymeric layer being comprised of at least one component selected from 
the group consisting of hydrocarbons, oxygen-containing hydrocarbons, 
nitrogen-containing hydrocarbons, sulfur-containing hydrocarbons, 
phosphorous-containing hydrocarbons and organometallic compounds, said 
polymeric layer having been deposited by plasma polymerization or 
sputtering. 
In yet another aspect, this invention relates to a process for treating at 
least one member of a galvanic cell housing such that the assembled cell 
will exhibit increased resistance to electrolyte leakage, said process 
comprising the steps: 
(a) providing at least one member of a cell housing said member having a 
portion which is adapted to function as a sealing surface; and 
(b) depositing a tightly adhering layer of polymeric material composed of 
at least one component selected from the group consisting of hydrocarbons, 
oxygen-containing hydrocarbons, nitrogen-containing hydrocarbons, 
sulfur-containing hydrocarbons, phosphorous-containing hydrocarbons and 
organometallic compounds, said layer being no thicker than about 2000 
angstroms, by plasma polymerization or sputtering onto at least a portion 
of said portion of said cell housing which is adapted to function as a 
sealing surface. 
In another aspect this invention is directed to a process for treating at 
least one corrodible component of a galvanic cell such that the assembled 
cell will exhibit increased resistance to corrosion, said process 
comprising the steps: 
(a) providing at least one corrodible component of a galvanic cell; and 
(b) depositing a tightly adhering layer of polymeric material comprised of 
at least one component selected from the group consisting of hydrocarbons, 
oxygen-containing hydrocarbons, nitrogen-containing hydrocarbons, 
sulfur-containing hydrocarbons, phosphorus-containing hydrocarbons and 
organometallic compounds, said layer being no thicker than about 2000 
angstroms, by plasma polymerization or sputtering onto at least a portion 
of at least one surface of said cell component. 
It is within the scope of this invention to coat a portion of or the entire 
outside surface of an assembled galvanic cell. Thus the term "at least one 
corrodible component" encompasses components which have already been 
assembled into a galvanic cell. 
As is employed herein the term "cell housing" encompasses the cell cover, 
container and sealing gasket. The term "sealing surface" refers to a 
portion of a member of the cell's housing which portion is adapted to be 
disposed opposite a portion of a second member of the cell's housing such 
that a seal is formed at the interface of such portions, whereas the term 
"corrodible component" refers to a component of the cell which is subject 
to internal and/or external corrosion in the assembled cell. Such 
corrodible components include interior components, such as anode or 
cathode collectors, or components of the cell's housing. Moreover, as is 
employed herein the term "cathodic material" encompasses solid, liquid and 
gaseous cathodes, as well as materials adapted to serve as conductive 
substrates for gases such as are employed in air-depolarized cells. 
Sputtering is a process in which material is removed from a source or 
target by a plasma and deposited on a substrate. The use of 
radio-frequency (r-f) sputtering of polymers is known in the art and is 
described in some detail in Kirk-Othmer Encyclopedia of Chemical 
Technology, Volume 10, at pages 258-260, John Wiley & Sons (3d Ed. 1980). 
Because sputtering is a high energy process, polymeric materials which are 
made to adhere to substrates by the sputtering method will typically 
exhibit good adherence to such substrate. It is noteworthy that the 
coating produced by the sputtering of organic polymeric targets will have 
"marked differences" from the original polymeric target. According to 
Kirk-Othmer, supra, page 260 at lines 4-6, at least in the case of 
polytetrafluoroethylene (and likely parylene) "evidence of amorphous 
structure and increased hardness appears to indicate that sputter coatings 
contain a greater amount of cross-linking and molecular disorientation." 
Thus, sputtered coatings differ markedly from coatings of similar 
composition accomplished by different processes. 
The process of plasma polymerization or glow-discharge polymerization is 
also known in the art and is described in Kirk-Othmer, Encyclopedia of 
Chemical Technology, Volume 10 at pages 262-265 John Wiley & Sons (3d Ed. 
1980). In plasma polymerization, a substance in the vapor phase is excited 
to luminescence by an electric discharge, and a solid film is deposited on 
surfaces exposed to the luminous plasma. According to Kirk-Othmer at pages 
264-265, the product deposited by plasma polymerization is highly 
branched, cross-linked and unsaturated regardless of the starting vapor. 
Thus a material which has been deposited by means of plasma polymerization 
will differ markedly from conventional polymers of the monomer or monomers 
employed. 
As employed herein the term "plasma polymerization" encompasses the 
technique of chemical vapor deposition. 
As used herein the term "polymeric material" when used in connection with 
sputtering methods will refer to the coating produced when a polymer is 
employed as the target in the sputtering technique. When used in 
connection with plasma polymerization methods, the term "polymeric 
material" will refer to the coating produced when low molecular weight 
compounds are fed into the plasma polymerization reaction chamber. 
The polymers which may be employed as the target for sputtered coatings are 
comprised of at least one component selected from the group consisting of 
hydrocarbons, oxygen-containing hydrocarbons, nitrogen-containing 
hydrocarbons, sulfur-containing hydrocarbons, phosphorous-containing 
hydrocarbons and organometallic compounds. In this context the term 
hydrocarbons encompasses both saturated and unsaturated aliphatic 
hydrocarbons, aromatic hydrocarbons, saturated and unsaturated cyclic 
hydrocarbons, as well as mixtures thereof. Representative of the 
organometallic compounds which may be employed are organosilicon and 
organotin compounds. Illustrative of such target polymers are 
polypropylene, polyethylene, and the like. The particular polymer target 
which is most preferably employed will vary with the particular cell 
system selected. 
The low molecular weight compounds which may be employed for plasma 
deposited coatings comprise at least one member selected from the group 
consisting of hydrocarbons, oxygen-containing hydrocarbons, 
nitrogen-containing hydrocarbons, sulfur-containing hydrocarbons, 
phosphorous-containing hydrocarbons and organometallic compounds. In this 
context the term hydrocarbons encompasses both saturated and unsaturated 
aliphatic hydrocarbons, aromatic hydrocarbons, saturated and unsaturated 
cyclic hydrocarbons, as well as mixtures thereof. Representative of the 
organometallic compounds which may be employed are organosilicon and 
organotin compounds. Illustrative of the low molecular weight compounds 
which may be employed are methane, ethane, propane, propylene, siloxanes 
and the like. Moreover, a mixture of one of the above compounds and a 
halogen-substituted compound may be employed. The amounts of 
halogen-substituted compound which may be incorporated will depend upon 
various factors including the substrate selected, the halogen-substituted 
compound employed, the low molecular weight compound employed, the voltage 
employed in the polymerization deposition, and other similar factors. 
However, the optimum proportions for a given situation may be determined 
by one skilled in the art by simple experimentation. A process for the 
plasma deposition of such mixed coatings is detailed in U.S. Pat. No. 
4,366,208. The choice of compound which is selected will depend in large 
part upon the cell system employed. For alkaline cells methane and 
propylene have been found to be particularly advantageous. 
The polymeric material layer in either sputtering or plasma deposited 
coatings is no more than about 2000 angstroms thick as coatings thicker 
than about 2000 angstroms are frequently too brittle so as to cause 
cohesive failure during cell construction. Although the preferable 
thickness of the polymeric layer will vary in accordance with the 
composition of such layer, in general such layer is preferably no more 
than about 500 angstroms and is most preferably between about 75 angstroms 
and about 125 angstroms thick. 
Because of the extreme thinness (i.e., less than about 2000 angstroms) of 
the layer of polymeric material employed in the cell of this invention, it 
is possible to coat the surfaces of those cell components which are to 
function as conductive surfaces without materially impairing cell 
operation. Thus, the surfaces of internal components, such as anode 
collectors or cathode collectors, or of external contacts may be protected 
from corrosion without increasing the internal resistance of the cell to 
undesirable levels. Thus, if desired, the entire surface of any of the 
housing components of the cell may be coated without adverse effect. 
Additionally, it is within the scope of this invention to coat the thin 
layer of polymeric material with a second polymeric layer. Such a second 
polymeric layer is particularly applicable where the sealing surfaces of 
the cell are coated in accordance with this invention. The second 
polymeric layer may be applied by any technique including evaporation, 
sputtering or plasma polymerization, independently of whether the first 
layer was deposited by sputtering or plasma polymerization. Illustrative 
of the compounds which may be employed are parylene (poly-p-xylylene), 
polytetrafluoroethylene, siloxane and the like. 
Moreover, it is also within the scope of this invention to treat the thin 
layer of polymeric material with a halogen-containing and/or 
silicon-containing plasma in order to deposit halogen and/or silicon on 
the surface of such layer. A particularly preferred treatment is to 
subject the polymeric film to C.sub.2 F.sub.6 plasma. This treatment will 
provide the film with hydrophobic layer without destroying the improved 
adherence of the underlying layer relative to plasma deposited 
fluorine-containing materials (see Example 1). 
The cell cover and container of the cells of this invention may be composed 
of metals such as nickel, steel, copper, copper-clad steel, monel (an 
alloy of copper and nickel), brass, nickel-plated steel and the like. 
The cells of this invention employ compressible gaskets which are typically 
composed of nylon, polypropylene, ethylene-tetrafluoroethylene copolymer, 
high density polyethylene and the like. When a portion of the surface of a 
cell component other than the sealing gasket has been treated in 
accordance with this invention a particularly preferred gasket is that 
described in copending U.S. patent application Ser. No. 564,250 filed on 
Dec. 22, 1983, which gasket has been plasma treated with a saturated 
fluorocarbon to increase its electrolyte repellence. 
When the sputtering method of deposition is employed, the coating of a 
desired portion of a surface of a cell component is typically accomplished 
as follows. When components having metal surfaces are to be treated in 
accordance with the process of this invention the surfaces to be coated 
are first degreased by washing with trichloroethylene followed by rinsing 
with distilled water. Such surfaces may then be prepared for reception of 
the sputtered coating by appropriate gas plasma treatment. For example, 
treatment with O.sub.2 plasma will remove organic material while treatment 
with H.sub.2 plasma will reduce oxides present on the surface. Other 
cleaning methods could also be used. The metallic component having such 
cleaned surfaces (or a nonmetallic cell component) is placed on the base 
plate portion of the apparatus opposite the target polymer. Argon gas is 
introduced into the system and sputtering initiated by subjecting the 
polymer to r-f radiation. If desired, areas of the cell component may be 
masked so that only the desired portion of such component is coated. 
When plasma polymerization deposition is employed, this process is 
typically accomplished as follows. When components having metal surfaces 
are to be treated such surfaces are first degreased by washing with 
trichloroethylene followed by rinsing with distilled water. Such metallic 
surfaces may then be prepared for reception of the plasma polymerized 
coating by appropriate gas plasma treatment, as is described above, or 
other cleaning methods may be employed. The cell component having such 
cleaned metal surfaces or the nonmetallic cell component is placed into 
the plasma polymerization reactor. The low molecular weight compounds to 
be used are then introduced into the reactor and plasma polymerization 
initiated. If desired, areas of the cell component may be masked so that 
only the desired portion of such cell component is coated.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to FIG. 1 there is shown a cell cover 2. A portion of the 
sealing surface of cover 2 is coated with plasma polymerization desposited 
layer 4. If desired the entire sealing surface of cover 2 could be coated. 
Moreover, if desired, the entire inner and/or outer surfaces could be 
coated with a layer of polymeric material deposited by plasma 
polymerization or sputtering. Polymeric layer 4 is no more than about 2000 
angstroms thick. 
FIG. 2 shows a cross-sectional view of cell container 6. The sealing 
surface of container 4 is coated with plasma polymerization deposited 
polymeric layer 8. If desired, only a portion of the sealing surface or, 
alternatively, the entire inside and/or outside surfaces of container 6 
could be coated. Polymeric layer 8 is no more than about 2000 angstroms 
thick. 
FIG. 3 shows a cross-sectional view of a sealing gasket 17, having portions 
of the first gasket sealing surface and second gasket sealing surface 
covered with tightly adhering layers of sputter-deposited polymeric 
material, 18B and 18A respectively. Alternatively these layers could be 
deposited by plasma-polymerization techniques. Such polymeric layers are 
not thicker than about 2000 angstroms. 
FIG. 4 shows an assembled miniature cell having a housing comprised of 
cover 2, a portion of the sealing surface of which is coated with plasma 
polymerization deposited layer 4, and container 6, the sealing surface of 
which is coated with plasma polymerization deposited layer 8. The sealing 
surface of container 6 is disposed in interfacial sealing contact with the 
first gasket sealing surface of gasket 16 while the sealing surface of 
cover 2 is disposed in interfacial sealing contact with the second gasket 
sealing surface of gasket 16. Disposed within cover 2 and in electrical 
contact therewith is anode 10, thereby adapting cover 2 as the anodic or 
negative terminal of the cell. Disposed within container 6 and in 
electrical contact therewith is cathode 12, thereby adapting container 6 
as the cathodic or positive terminal of the cell. Anode 10 is separated 
from cathode 12 by separator 14. Compressively disposed between cover 2 
and container 6 is nonconductive sealing gasket 16. Optionally, the 
sealing surfaces of gasket 16 could be covered with a plasma 
polymerization deposited or a sputtering deposited layer of polymeric 
material. The presence of the layer of polymeric material at the sealing 
surfaces of the cell will reduce the ability of the cell's electrolyte to 
creep along such surfaces and leak from the cell. 
FIG. 5 shows a cross-sectional view of an assembled galvanic cell wherein 
the entire outside surface of the cell has been coated with a layer of 
polymeric material by plasma polymerization after assembly of the cell. 
Cell 20 is comprised of anode 22 and cathode 24 with separator 26 disposed 
therebetween. Anode 22 is in contact with cover 28 thereby adapting cover 
28 as the anodic or negative terminal of the cell. Similarly, cathode 24 
is in contact with container 30 thereby adapting container 30 as the 
cathodic or positive terminal of cell 20. Compressively disposed between 
cover 28 and container 30 is nonconductive sealing gasket 32. Layer of 
polymeric material 34, which has been deposited by plasma polymerization 
coats the entire outside surface of cell 20 thereby protecting the cell 
from external corrosion. Alternatively, layer 34 could be disposed by 
sputtering. 
FIG. 6 shows an elevational view of an electrode assembly which is adapted 
to be coiled and inserted into a cell having a jellyroll construction. 
Electrode assembly 40 is comprised of separator 42 which extends between a 
positive electrode (not shown) and negative electrode 44, and, optionally, 
which extends about the exterior of such electrodes, encapsulating them. 
Connective tab 46 extends to the positive electrode. 
As is shown in enlarged detail in FIG. 7, negative electrode 44 is 
comprised of expanded metal screen 48, which is coated with layer of 
polymeric material 50, layer 50 having been deposited by plasma 
polymerization. Anodic material 52 is pressed onto the coated screen 48. 
Layer of polymeric material 50 protects metal screen 48 from corrosion 
while avoiding materially increasing the internal resistance of the cell. 
EXAMPLES 
The following Examples are intended to further illustrate the invention and 
are not intended to limit the scope of the invention in any manner. 
EXAMPLE 1 
Several copper-clad stainless steel plates, each measuring 2 cm in height 
and 2 cm in width were cleaned with trichloroethylene and rinsed with 
distilled water to remove grease from the copper surface. Oxides present 
on the surface were removed by plasma treatment with hydrogen gas. This 
treatment was accomplished in a capacitively coupled bell jar plasma 
reactor having a fixed frequency of 10 KHz. The gas flow rate during this 
treatment was 3 cc (STP)/min. and the electrical discharge power was 30 
watts. The moving plate on which the sample plates were mounted was 
rotated at a speed of 50 r.p.m. so that the substrate passed between the 
electrodes on each rotational cycle thereby ensuring a uniform coating. 
The cleaned and deoxidized plates were plasma-coated utilizing the 
compounds listed in Table 1 below until the thickness of the coating was 
determined to be about 300 angstroms. In order to produce such coating the 
power was varied from 30-120 watts and the compound flow rate varied from 
0.5-3.0 cc(STP)/min. depending on the compound used. As is shown in Table 
1, several of the samples were subsequently treated with C.sub.2 F.sub.6 
plasma. In this context it is worth noting that treatment with C.sub.2 
F.sub.6 plasma alone will result in the deposition of fluorine atoms on 
the polymeric layer in a reaction which is in a practical sense 
self-limiting, whereas treatment with a mixture of C.sub.2 F.sub.6 and 
H.sub.2 plasma will produce a polymeric layer of C.sub.2 F.sub.6 material. 
In all the Examples contained herein a plus sign "+" when used in 
conjunction with C.sub.2 F.sub.6 will indicate that C.sub.2 F.sub.6 is 
employed in the plasma along with the other compound listed. The use of a 
slash "/" when used in conjunction with C.sub.2 F.sub.6 will indicate a 
subsequent treatment with C.sub.2 F.sub.6 polymer alone of the plasma 
deposited coating listed. During such C.sub.2 F.sub.6 treatment the gas 
flow varied from 3-5 cc (STP)/min. and the electrical discharge varied 
from 15-30 watts. 
The adhesion of the coated polymers was measured by a pressure sensitive 
tape test ANSI/ASTM D-3359-76 under the conditions shown in Table 1 below. 
TABLE 1 
______________________________________ 
Adhesion quality by pressure sensitive tape test* 
After 
Immersion After 
In Cold Immersion 
(about 20.degree. C.) 
in Boiling 
Water Water 
In for for 
Coating Air 15 Hrs. 2 Hrs. 
______________________________________ 
methane O O O 
methane/C.sub.2 F.sub.6 
O O O 
tetramethyl- O O O 
disiloxane 
tetramethyl- O O O 
disiloxane/C.sub.2 F.sub.6 
O O O 
propylene 
Propylene/C.sub.2 F.sub.6 
O O O 
C.sub.2 F.sub.6 + H.sub.2 mixture 
O O X 
tetrafluoro- O O X 
ethylene 
______________________________________ 
*O pass equivalent to 5A on ASTM scale 
X fail equivalent to 4A or less on ASTM scale 
The above results indicate the relatively poor maintenance of wet adhesion 
after immersion in boiling water demonstrated by fluorine-containing 
polymers which have been plasma deposited. 
Several additional samples were prepared as above. The coated plates were 
scratched in a cross-hatched pattern, presoaked in cold (i.e. about 
20.degree. C.) water for 30 days, and their subsequent peeling-off time in 
boiling water measured. The results of such testing are shown in Table 2. 
TABLE 2 
______________________________________ 
Peeling-off Time in Boiling 
Water after 3-Day Presoak in about 20.degree. C. Water 
Polymeric Material 
Peeling-off Time (Minutes) 
______________________________________ 
tetrafluoroethylene 
2 
methane 7 
methane/C.sub.2 F.sub.6 
12 
propylene 120 
tetramethyldisiloxane 
120 
propylene/C.sub.2 F.sub.6 
120 
______________________________________ 
These results further indicate the relatively poor maintenance of wet 
adhesion of plasma-deposited fluoropolymers. 
Several additional plates were prepared as above except that certain plates 
(as indicated in Table 3) were not precleaned by washing in 
trichloroethylene. The plates were then placed in a 41 weight percent KOH 
solution, such that the lower edge of the plate just touched the liquid. A 
voltage of -1.15 vs. Hg/HgO was applied to the plates, and the increase in 
height along the copper surface after 6 hours measured. The results of 
such creepage tests are shown in Table 3 below. 
TABLE 3 
______________________________________ 
Creepage Distance, cm/6 Hrs 
Cleaned Uncleaned 
Coating Plates* Plates* 
______________________________________ 
Control (None) .941 -- 
Propylene .492 .798 
Propylene/C.sub.2 F.sub.6 
.254 .868 
Tetramethyldisiloxane 
.497 .577 
Methane .452 .458 
Methane/C.sub.2 F.sub.6 
.356 .356 
Tetrafluoroethylene 
.871 .829 
______________________________________ 
*Average Values 
The above results indicate that a correlation between sustained wet 
adhesion and resistance to creepage exists as tetrafluoroethylene exhibits 
poorer creepage resistance as well as poorer sustained wet adhesion. The 
results also demonstrate the improvement obtained by washing the substrate 
to be treated with trichloroethylene. 
EXAMPLE 2 
Employing an apparatus similar to that described in Example 1, the copper 
side of several triclad (i.e., copper-stainless steel-nickel) plates was 
coated with a layer of plasma polymerization deposited polymeric material 
as shown in Table 4 below. As a control, one plate remained untreated. As 
noted in Table 4, the copper surface of several of the samples was 
pretreated with H.sub.2 plasma and the layer of plasma deposited polymeric 
material treated with C.sub.2 F.sub.6 plasma. The sample plates were 
placed in a fixture contacting both surfaces with a cross-sectional area 
of 1/2 inch.sup.2 at a pressure of 80 grams and resistances from one 
contact to the other were measured after zeroing the fixed resistance. The 
results of such testing are summarized in Table 4 below: 
TABLE 4 
__________________________________________________________________________ 
RESISTANCE OF PLASMA-COATED TRICLAD SAMPLES 
Hydrogen- 
Composition of C.sub.2 F.sub.6 Plasa 
Plasma Monomer Forming 
Thickness of 
Treatment Measured 
Sample 
Pretreatment 
Polymeric Layer 
Polymer Layer* 
of Polymeric Layer 
Resistance* 
__________________________________________________________________________ 
1 (control) 
No None None No 8 
2 No Propylene 100 No 18 
2 Yes Methane 100 Yes 11 
4 Yes Methane 500 Yes 13 
5 Yes Propylene 1000 Yes 64 
__________________________________________________________________________ 
*In angstroms 
**In milliohms 
The above results indicate that the presence of a thin layer of polymeric 
material deposited by plasma polymerization does not materially increase 
the measured resistence of the samples to commercially unacceptable 
levels. 
EXAMPLE 3 
Several lots of miniature Zn/Ag.sub.2 O cells employing a potassium 
hydroxide electrolyte, each cell measuring about 0.31 inch (about 0.79 cm) 
in diameter and about 0.14 inch (about 0.36 cm) in height, were 
constructed. The anode cups of said cells had a thin layer of polymeric 
material deposited on their sealing areas utilizing the plasma 
polymerization reactor of Example 1. This layer was deposited after 
washing the surfaces with trichloroethylene and rinsing with distilled 
water, followed by a deoxidizing hydrogen plasma treatment. Several lots 
of cells were sealed employing a C.sub.2 F.sub.6 plasma-treated nylon 
gasket as described in copending U.S. patent application Ser. No. 564,520 
filed on Dec. 22, 1983, followed by coating with a fatty polyamide. Other 
lots employed only fatty polyamide coated gaskets. 
The cells so produced were stored for nine weeks at 90% relative humidity 
and elevated temperature (45.degree. C. and 60.degree. C.). The negative 
terminal leakage of such cells is indicated in Tables 5 and 6 below. 
TABLE 5 
______________________________________ 
Negative Terminal Leakage Characteristics 
After 9 Weeks at 60.degree. C., 90% R.H. 
No. 
Anode Cells Per- 
Cup Gasket No. Showing cent 
Treatment 
Treatment Cells Salting 
L* H** Salt*** 
______________________________________ 
Control polyamide- 12 11 1 10 92 
(None) coated 
Methane.sup.1 / 
polyamide- 15 8 5 3 53 
C.sub.2 F.sub.6 
coated 
Methane.sup.1 / 
C.sub.2 F.sub.6 treated, 
13 4 3 1 30 
C.sub.2 F.sub.6 
polyamide- 
coated 
Propylene.sup.2 / 
polyamide- 15 4 1 3 27 
C.sub.2 F.sub.6 
coated 
Propylene.sup.2 / 
C.sub.2 F.sub.6 -treated, 
15 13 5 8 87 
C.sub.2 F.sub.6 
polyamide- 
coated 
______________________________________ 
*L = number of cells showing light salting (i.e. visible at 20x 
magnification but not with the naked eye) at negative terminal 
**H = number of cells showing heavy salting (i.e. visible with the naked 
eye) at negative terminal 
***Percent Salt = percent of total cells showing salting 
.sup. 1 = polymer thickness 100 Angstroms 
.sup.2 = polymer thickness 500 Angstroms 
TABLE 6 
______________________________________ 
Negative Terminal Leakage Characteristics 
After 9 Weeks at 45.degree. C., 90% R.H. 
No. 
Anode Cells Per- 
Cup Gasket No. Showing cent 
Treatment 
Treatment Cells Salting 
L H Salt 
______________________________________ 
Control polyamide-coated 
14 7 2 5 50 
(None) 
Methane/ 
polyamide-coated 
15 3 2 1 20 
C.sub.2 F.sub.6 
Methane/ 
freon-treated, 
15 0 0 0 0 
C.sub.2 F.sub.6 
polyamide-coated 
Propylene/ 
polyamide-coated 
15 1 1 0 7 
C.sub.2 F.sub.6 
Propylene/ 
freon-treated, 
15 3 2 1 20 
C.sub.2 F.sub.6 
polyamide-coated 
______________________________________ 
The above results indicate that using the coatings of this invention, a 
substantial reduction in leakage was obtained.