Note: Descriptions are shown in the official language in which they were submitted.
, 1 17630~
Back ound of the Invention
The present invention i5 directed to a battery separator formed from
an acid-stable sheet and to a battery, in particular to a lead-acid battery,
which has the separator located between adjacent plates of opposite polarity.
Storage batteries have been known and used for over a century. A
conventional storage battery is formed of one of more units or cells, each of
whicll has a positive electrode, a negative electrode, separator elements between
electrodes of opposite polarity and an electrolyte, such as aqueous sulfuric
acid solutions.
Separators for a lead-acid battery should prevent contact between
electrodes of opposite polarity yet permit contact between electrode and excess
electrolyte to produce efficient electrochemical reactions. For example, elec-
trodes formed from lead and lead oxide must be maintained in contact with an
excess of sulfuric acid electrolytic solution to permit the double sulfate
reaction to occur between the electrode's material and the acid during discharge
while also providing sufficient electrolyte for ionic transfer. Further, sepa-
rators should permit the removal of gaseous products which are formed on the
plate surfaces during the charging operation of any charge/discharge cycle.
Oxygen i5 normally formed and evolved at the positive plates and hydrogen at
~ the negative plates. The gaseous products are generally in the form of minute
bubbles and may form at any point on an electrode plate surface. These bubbles
are impediments to electrolyte/electrode contact required to have efficient
battery operation.
In early battery designs, where compactness and energy density were
not a prime objective, electrode elements of opposite polarity were maintained
sufficiently apart by separator pins or posts which readily allowed the flow
of electrolyte and egress of formed gaseous products.
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In a modern storage batteryg a group of interconnected plates form-
ing the positive electrode is intermeshed with another group oE interconnected
plates which act as the negative electrode to give alternating positive/negative
plate orientation within each cell of the battery. Each plate must be maintain-
ed apart from adjacent plates of opposite polarity by some ~orm of separation
means. Contact may be due to imperfections in plate structure or due to warping
or wrinkling of a plate which normally occurs during operation of the battery
as well as by other chemical or physical phenomena. The desire to develop
batteries of compact, high specific capacity (electrlcal energy/unit weight) in
which the separator membranes are sandwiched between electrodes of opposite
polarity requires a separator ~hich is capable of being formed from thin, light
weight sheet material; providing means for the removal of gases; providing for
elec~rode/electrolyte contact within a minimum spacing; and exhibiting the
abili~y to withstand the compressive forces encountered from adjacent electrode
plates. Such forces may tend to distort and sometimes permanently collapse the
gaseous egress means designed in conventional separators. The separator com-
ponent is recognised as a key element in forming a highly efficient battery.
Prior art separators used in lead-acid storage batteries have in-
cluded various designs which provide spacer arrangements such as separators which
~20 are laminated with glass mat or which have armour ribs or projections formed on
at least one major surface. Such separators are costly to form and add material
and weight to the battery system. Further, separators which have glass mats as
part of their structure have the defect of permitting gas bubbles to be lodged
and retained within the mat's fiberous structure. ~seful armour ribbed sepa-
rators have heretofore only been formed from thick sheet stock since thin sheet
material have been found ~oo flexi~le from precluding effective alignment of
the separator between adjacent electrode plates of opposite polarity.
Separators with spacing arrangements have alsD been formed from
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f :~ 7~3~7
embossed sheet. yarious embossments are kno~n and include straight corrugated
configurations, such as described in Vnited States 2,662,106, or projections,
as described in United States Patents 2,382,829; 2,465,493; 4,072,802; and
4,153,759. The known corrugated type of separators does not have structural
integrity whcn formed from thin sheet stock. Thin corrugated separators have
the defect of succumbing to the compressive forces and collapsing against a
plate surface. Separators of straight corrugated design are suitable for gas
release only when formed from rigid and thicker than desired stock. Separators
llaving embossed separate projections, such as shown in United States Patents
2,382,829 and 2,465,493, tend to trap gaseous products in their individual
cavities. Separators such as shown in United States 4,072,802 and 4,153,759,
are capable of being formed from thin sheet stock, but have conical projections
which tends to block the egress of gaseous products. United States Patent
4,228,225 is directed to a separator capable of being formed from thin sheet
material and provides an embossed configuration having continuous vertically
orientated gas egress paths. The presently described separator sheet has
a design ~hich further enhances and promotes the removal of formed gaseous pro-
ducts while providing the other desired properties.
An object of the present invention is to provide a battery separator
wllicll has paths on both sides for providing for and enhancing the removal of
gaseous products formed within the battery.
A further object of the present invention is to provide a battery
separator which provides means for enhancing the removal of gaseous products
~hile also providing substantial electrolyte to electrode contact to form an
effective battery.
A still further object of the present invention is to provide a bat-
tery separator ~hich has means to provide for and enhance the removal of gaseous
products, proyiding for good elect~oly*e to electrode contact and having suffi-
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1 ~ 76307
cient resistance to mechanical forces encountered to maintain its configuration
during use.
Another object of the present invention is to provide a battery sepa-
rator comprising a porous sheet which has substantially uniform thickness
throughout; having a configuration which provides gaseous egress means on both
major surfaces and which can be formed into a wrap-around or enveloping confi-
guration ~hile maintaining the same improved gaseous egress means in said
configurations~
A further object of the present invention is to provide an acid battery
having a container, an electrolyte at least one pair of electrode plates of
opposite polarity and a separator formed from a seperator sheet of this invention
positioned between and at least coextensive with each pair of electrode plates.
According to the present invention there is provided a battery sepa-
rator for an acid battery which separator comprises an acid-stable porous sheet,
the sheet having first and second faces, formed within spaced planes con~aining
the faces and formed into a plurality of separate continuous open channels on
each of the faces, each channel on each face defining a separation betwesn two
channels on the other face, each of the channels defining an imaginary median
line, at least some portions of at least some of the channels extending laterally
with respect to the median line, and the channels being so configured that a
tangent to substantially any portion of each of the channels is oriented at an
acute angle of no greater than 70 degrees with respect to an imaginary vertical
line oriented from bottom to top of a battery,when in place therein.
Conveniently the planes are spaced substantially parallel planes and
the cross sectional area of any one of the channels taken perpendicular to the
channels imaginary median line may be substantially the same along the tctal
extension of the channel. In a preferred embodiment substantially every portion
of each of the channels is oriented at an angle of not greater than 50 degrees
~ ~763~7
and at least some of the channels may be generally of a sinusoidal configuration
when viewed on either of the first face or the second face.
The sheet may be comprised of from about 20 to about 75 weight percent
of a thermoplastic resin, and from about 25 to about ~0 weight percent of an
acid resistant inorganic filler and conveniently the thickness of the sheet may
be from 0.025 mm to about 1 mm, the maximum spacial thickness being from about
0.25 n~l to about 5 mm and the sheet may have at least two channels on each of
the faces per 25 mm horizontal dimension of each sheet.
In a further preferred configuration, the separator may be contained
in an acid battery between a pair of electrode plates of opposite polarity and
the sheet may have dimensions which are at least coextensive with the dimension
of the pair of electrode plates between which it is to be positioned. Conve-
niently the outermost portion of each separation between channels on each of
the faces is capable of being at least 75 percent in continuous contact with
an adjacent electrode plate when contained in a battery. The separator may be
substantially planar or of a substantially U-shape configuration.
In another aspect, the invention provides a battery comprising a
container, an acidic electrolyte, at least one pair of electrode plates of
opposite polarity and a separator positioned between each pair of electrode
plates of opposite polarity.
Tl~e ollowing is a description by way of example of certain embodiments
of the present invention reference being had to the accompanying drawings in
which;
Figure 1 is a cut-away view of a storage battery cell containing a
separator membrane located between a positive and a negative elec~rode plate.
Figure 2 is a cross-sectional view of a portion of a sheet product
of the present invention.
~ g 76307
Figure 3 is a planar view of a portion of the sheet product along
plane P3-P3 of Figure 2,
Figure 4 is a planar view of a portion of a sheet product according
to an embodiment of the present invention.
Figure 5 is an enlarged geometric contour drawing of a portion of the
face of the sheet product of Figure 4.
Figure 6 is a planar view of a portion of a first major face of a
sheet product according to one embodiment of the present invention.
Figure 7 is a planar view of a portion of a second major face of the
sheet product of Figure 6.
Figure 8a, is a cross-sectional view of a portion of the sheet product
of Figure 4 along line 4-4.
Figures Sb and 8c are cross-sectional views of alternate configurations
of sheet products of the present invention.
Figure 9 is a perspective view of a single separator sheet element of
the present invention.
Figure 9a is a perspective view of a single envelope-shaped separator
formed from a sheet product of the present invention which has an electrode
plate contained therein.
Figure 10 is a cross~sectional view of a portion of a separator of
the present invention engaged between electrode plates of opposite polarity.
Detailed Description of Preferred Embodiments
The present invention is directed to a battery separator. The
separator is formed from a sheet having a structural configuration which provides
continuous and enabling egress paths for the removal of gaseous products from
a battery, provides a means of permitting good electrolyte/electrode contact
while at the same time providing structural strength to resist compression
forces even when the separator sheet is formed from thin stock material. The
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separator can be formed from a microporous sheet and can be formed into indivi-
dual substantially planar sheets or wrap-around U shape design while providing
the continuous upward egress paths on all major surfaces of the separator.
Figure 1 illustrates a cell of a storage battery, such as a conven-
tional lead-acid automotive type battery, formed from outer container 1 and cover
2 wi~h its associated terminal post 3, vent plug 4 and inter cell connector 5.
The bottom of container 1 normally has means 6, such as ribs, to support an
electrode assembly. The assembly is made up of a negative electrGde formed
from a number of negative electrode plates 7 which are spaced from one another
and connected by a negative connecting strap 8J and a positive electrode formed
by a number of positive electrode plates 9 which are spaced from one another
and connected by a positive connecting strap 10. The negative plates 7 are
positioned in the space between each of two positive plates 9 to form an alter-
nating sequence of negative-positive plates. Between each pair of plates of
opposite polarity of the electrode assembly is separator 11 to prevent contact
between the plates. The separator of the present invention can be used as
individual sheets between each pair of plates of opposite polarity as shown in
Figure 1 or can be wrapped around each of the positive or each of the negative
plates such as in an open sided U configuration (edges of the separator sheet
~ adjacent to the vertical side of battery container 1) or a closed sided, known
in the art as an "envelope," configuration as shown in Figure 9a and described
in detail hereinbelow.
Figures 2 and 3 are described herein for purposes of identifying
certain terms used throughout this specification and in the appended claims.
Figure 2 is an enlarged view of a typical cross-section of a portion of a
species of a separator sheet according to the present invention, and Figure 3
is a planar view of the plane P3-P3 of Figure 2. Figure 2 represents a partial
and enlarged cross-sectional view of a separator sheet 20 contained within
. ~, . , :
,
~ ~7~30~
boundary plane Pl-Pl and boundary plane P2-P2. The spatial relationship bet-
ween planes Pl-Pl and P2-P2 defines the sheets maximum spatial distance 25,
which is the maximum spatial thickness of the sheet 20. Sheet 20 has a first
major face 21 and a second major face 22. Sheet 20 has a body thickness 25'
which is the thickness between surfaces 21 and 22. The body thickness is
generally of a substantially thin uniform dimension throughout sheet 20.
Each of the major faces of the sheet 20 forms a surface which has
multiple extensions from its boundary plane towards the other boundary plane.
Specifically, major face 21 is in the form of a surface which has apex portions
23 which are in closest spatial relationship to boundary plane Pl-Pl relative
to facial surfaces adjacent to each portion 23. Each apex portion 23 is general-
ly contiguous with boundary plane Pl-Pl. Major face 21 has extended surface
areas 26 which do not lie in plane Pl-Pl but extend in the direction towards
plane P2-P2 within the maximum spatial distance 25. Each extended surface
area 26 is normally ~with the possible exception of one which is adjacent to an
edge of the separator sheet) bound by spaced adjacent apex portions 23 of face
21. Therefore, each of such surface areas 26 forms an open channel on major
face 21. Each portion of surface area 26 of face 21 which is bounded by two
adjacent apex portions 23 has a nadir portion 23' which is the portion of surface
area 26 extending closest to boundary plane P2-P2. The terms "raised surface
area" and "depressed surface area" as used in this description and the appended
claims are relative terms which define points on a surface of a sheet product
of the present invention with respect to another point on the same surface and
within the bounds of two adjacent apex points on that surface as viewed from
a cross-sectional configuration with the surface apex points being positioned
upwardly.
Similarly, face 22 forms a surface which has multiple apex portions
24 which have the greatest extension towards or are contiguous with boundary
1 ~ 7 ~ 3 0 7
plane P2-P2 relative to facial surfaces adjacent to each portion 24. Major
face 22 has extended surface areas 27 which extend within spatial distance 25
and from apex portions 24 toward plane Pl-Pl. Each extended surface area 27 is
normally [with the possible exception of one which is adjacent to an edge of
the separator sheet) bound by spaced, adjacent apex portions 24 of face 22 which
are closest to plane P2-P2 and, therefore, each of such extended surface areas
27 forms an open channe] on major face 22. Each portion of surface area 27
forming a separate open channel bounded by two adjacent apex portions 24 has a
nadir portion 24' which is a portion of surface 27 extending closest to boundary
plane Pl-Pl. It can be seen that each extendad surface area 26 which forms a
channel on face 21 has a nadir portion 23' which corresponds, on face 22, to
apex area 24 on extended surface 27 so that the channels on one major face form
a separation on the other major face. The channel on one major face forms a
separation between two adjacent channels on the other major face of the separa-
tor sheet. ~Figure 2 further shows an imaginary plane P3-P3 which is one of a
number of planes which lies within planes Pl-Pl and plane P2-P2 and intersects
major face 21 at points 28, 28', 2-8 " , 28 " ', 28 " " and 28 " "' of the extended
surface areas of the face.
Figure 3 is a planar view Or intersect plane P3-P3 of Figure 2 in
~0 ~hich intersect contour lines 28a, 28b, 28c, 28d, 28e and 28f are the intersect
lines of plane P3-P3 which extend from points 28, 28'~ 28 ", 28 "', 28 " " and
28 " "', respectively, on face 21. Imaginary contour lines 23a, 23b and 23c
are each apex contour lines of each apex facial point 23, respectively, on
face 21 as depicted in Figure 2. Distance 29 between intersect contour lines
28b and 28c and distance 30 between intersect contour lines 28d and 28e repre-
sent the dimensional width of each open channel 26' on face 21 between paired
points 28' and 28 " and pair points 28 "' and 28 " ", respectively. Distance
29' between imaginary apex contour lines 23a and 23b and, similarly, distance
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30' between imaginary apex contour lines 23b and 23c represent the facial dimen-
sional widtll of each open channel 26'.
Each channel has a pattern. Each portion of the pattern of each
channel can be defined with the aid of a pair of spaced contour lines formed by
the intersect of an imaginary plane, such as P3-P3, with a facial surface of
the separator sheet. For example, contour lines 28b and 28c are spaced and
define a channel pattern. The pattern bounded by intersect contour line 28b
between points 31 and 32 and by intersect contour line 28c between points 33
and 34 represents a single cycle of a pattern which may again repeat itself
along a segment of the open channel's extension. A channel pattern related
area 31, 32, 33, 34 can be defined by connecting by straight lines each of the
paired points 31, 32; 32, 33; 33, 34 and 34, 31. Any other pair of planar
contour lines, either facial, such as by Pl-Pl, or intersecting, such as by
P3-P3, can aid in defining the channel pattern. Line 35 is an imaginary median
line of channel 26 such that, over any one cycle of the channel's pattern the
imaginary median line 35 is straight and bisects the total area 31, 32, 33, 34
of the channel into equal average ~arithmetic mean) areas. Imaginary median
line may be curved or straight over the total extent of the sheet products.
Channel 26' has, as a part'of its pattern, extensions 36 which extend laterally
from the median line to a greater distance than the minimum dimension 37 of the
channels lateral extension. The channel's minimum lateral extension may be
of a positive or negative value or substantially zero. When all lateral exten-
sions of a pattern cycle of a contour line are located on the same side of an
imaginary median line the minimum lateral extension is taken as a positive
value. When all lateral extensions of a pattern cycle of a contour line are
located on the same side of an imaginary median line and the minimum lateral
extension touches the median line, the minimum lateral extension will be zero.
l~hen lateral extensions of a pattern cycle projects across the imaginary median
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line, the minimum lateral extension shall be considered a negative value and
extensions on the opposite side as of positive value. A separator sheet in
which all of the channels have all lateral extensions equidistant from an ima-
ginary median line does not exhibit the desired properties which are unexpect-
edly attained by the separator sheet of the present invention.
Each of the channels of the separator sheet 20 has a pattern such that
any apex contour line and any intersect contour line of any plane P3-P3 within
the boundary planes Pl-Pl and P2-P2 has all sections at an acute angle of not
greater than about 70 degrees from a vertical orientation line when contained
in a battery. For example, line 28d is an intersecting contour line of plane
P3-P3 with respect to extended surface 26 of face 21. The sheet product 20
of Figure 3 is orientated such that lines 38 each represent an imaginary vertical
orientation line of the sheet product from bottom to top of a battery in use in
which the separator sheet is contained. The angle theta ~p) is an acute angle
from imaginary vertical line 38 to a tangent line of contour line 28d at the
point of intersection with line 38. A preferred configuration of sheet 20 will
have an imaginary median line 35 of at least some of its channels in the form
of straight lines, and the imaginary median line 35 is substantially vertically
oriented when the separator sheet 20 is contained in a battery.
Figure 4 is an enlarged view of a portion of one of the two major
faces of a specie of a separator sheet 40 of the present invention. The other
major face of this specie is of a reverse configuration which is of substantially
the same overall configuration as the face illustrated in Figure 4. The shown
portion of sheet product 40 has a major face 41 which contains continuous apex
surface areas 42a, 42b, 42c, 42d and 42e in the form of apex contour lines which
are the contour lines contiguous with or closest to an imaginary boundary plane
of face 41. The apex surface areas 42a, 42b, 42c, 42d, and 42e separate adja-
cent extended surface areas 43a, 43b, 43c and 43d and their respective nadir
I ~ 763~7
contour lines 43a', 43b', 43c' and ~3d'. That is to say 'hat apex surface area,
such as 42b forms an apex contour line which separates adjacent extended surface
area 43a from adjacent extended surface area 43b. Each of the extended surface
areas forms an open, continuous channel. The terms "open" and "continuous" are
separate and distinct terms, not meant to modify each other. The term "open"
is meant herein and in the appended claims to define a channel which opens out
from the face of the sheet product. The term "continuous" is meant herein and
in the appended claims to define a continuous, non-segmented channel from one
end to the other capable of having a continuous rising gaseous egress configu-
ration when in use position.
With respect to each of the open continuous channels formed from ex-
tended surface areas 43a, 43b, 43c and 43d, one can form an imaginary median
line 44a, 44b, 44c and 44d, which each bisect each of the extended surface areas,
respectively. The channel of surface area 43a, as well as each of the other
channels, has lateral extensions 45 with respect to the imaginary median line
44a which extends beyond the channel's minimum lateral extension 46 to form a
channcl 43a which has a curvilinear conriguration. 'I'he curvilinear configuration
is substantially sinusoidal. Similarly) channel 43b ~the channel identification
number in the present specification is the identlfication number of the extended
surface forming the channel) has lateral extensions 47 with respect to its
imaginary median line 44b which extend beyond the minimum lateral extension 4~
of channel 43b with respect to median line 44b. Chamlel 43b is curvilinear in
the form of a sinusoidal configuration. Channels 43c and 43d are of the same
configurational nature as channels 43a and 43b. Each of channels 43a, 43b, ~3c
and 43d is nested with respect to each other or, stated another way, each of
the chalmels 43a, ~3b, ~3c and 43-1 laterally extends to substantially the same
extent in the same direction as the next adjacent channel on a line perpendi-
cular to a median line. Although not illustrated, it is understood that other
~ ~630~
channels of sh~et 40 can haYe curvilinear configuration which are not sinusoidal
and/or nested ~ut which still meet the requirements of the present invention.
Separator sheet 40 provides substantial electrolyte/electrode contact;
resists compressive forces exerted on the major faces of the formed sheet pro-
duct; and provides, when properly oriented within a battery~as described here-
inbelow, an improved gas egress means.
The separator sheet is capable of being placed in a ~attery in an
orientation such that imaginary vertical orientation lines running from bottom
to top of the battery in its use position and substantially (at least 85 per-
cent, preferably at least 90 percent and more preferably 100 percent with any
remaining amount forming an acute angle of from 70 to 90 degrees) all lines
tangent to the contour lines of each of the channels of the sheet form an acute
angle of up to 70 degrees and preerably up to 50 degrees at their point of
intersection. For example, channel 43d of sheet 40 has a contour line 49 which
is one of a multiplicity of contour lines that can be formed on the surface of
face 41 between the apex contour line 42e of the raised surface area and the
nadir contour line 43d' of the depressed surface area. If an imaginary line 51,
having vertical orientation with respect to the top to bottom use position of
a battery in which the sheet 40 is contained, intersects with the tangent line
5~ of contour line 49 the lines form an acute angle of up to 70 degrees from
the vertical line 51 at substantially any point along the curvilinear contour
line 49.
~igure 5 is an expanded view of a section of ~igure 4 to show, in
greater detail, the contour orientation of the walls of the open channels of
the sheet of the present invention. Between nadir contour line 43d' and apex
contour line 42e is drawn an intersect contour line 49 which is the intersecting
line of the separator sheet with a plane which is ~n substantially parallel
relationship to at least one boundary plane of the sheet 40. rmaginary lines
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! 11 76307
51 are facially superimposed on contour line 49 of sheet 40 at a vertical
orientation with respect to the battery in which sheet 40 is contained. Lines
52 are tangent lines of contour line 49 at the point of intersection with verti-
; cal line 51. The angle theta (0) is the acute angle formed between the imagina-
ry vertical line 51 and imaginary tangent line 52. (The term "tangent line" as
used in this disclosure refers to a straight line passing through two adjacent
points on a curved or s~raight line segment of the contour line). The separator
sheets of the present invention should have open channels of a curvilinear
design. Such design should have lateral extensions which extend beyond any
minimum lateral extension with respect to the channel's median line. Fu-.ther
the design must provide an acute angle theta of up to 70 degrees at substantially
all points on any of each channel's contour lines. Apex or nadir contour lines
are convenient contour lines to determine angle theta.
The imaginary vertical lines can be substantially parallel to an
imaginary median line of one or more channels of alseparator sheet or can be at
an angle thereto provided that the sheets use orientation permits the fulfill-
ment of the channel's angular requirement as described above.
The channels of the separator sheet should have curvilinear configu-
rations which, in combination with each other, produce resistance to compression
forces exerted on the sheet. It is preferred that at least about 20 and
preferably about 50 percent of the curvilinear configuration of all the channels
on any sheet laterally extend beyond the minimum lateral extension for each
respective channel. Channels which, therefore, have substantially uniform
lateral extension may be disposed between channels of more than one lateral
extension. Alternatively, some or all channels may have extended segments
which have a uniform lateral extension.
The separator sheet is preferably formed from a sheet stock of substan-
tially uniform thickness. The overall configuration of the other major surface
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~ ~ 763~7
(not shown) of sheet 40 is, therefore, substantially the reverse of major
surface 41 shown in Figure 4. The configuration of the first major surface is
symmetrically opposite to that of the second major surface.
Figure 6 shows a portion of a specie of formed sheet 53 according to
the instant invention having a major face 53' with channels 54. Each individual
channel 54a, 54b, 54c, 54d and additional ones are in the form of open, conti-
nuous channels. As shown with respect to channel 54a, the channel has a
curvilinear configuration of substantially a toroidal design which defines an
imaginary median line 55. The channel 54a has lateral extensions 56 which are
greater than the minimum lateral extension 57 of the chalmel in relation to
its imaginary median line 55. The lateral extensions 56 from one minimum
extension 57 to the next is in the form of a section of a circle. Channel 54a
has facial apex contour line 58 and facial apex contour line 59 which together
define the surface area forming channel 54a. Adjacent channel 54b has a facial
apex contour line 60 which is closest to apex contour line 59. The apex contour
lines 59 and 60 of the two adjacent channels 54a and 54b, respectively, form
an apex area 61 which is substantially planar and contiguous with an imaginary
boundary plane of face 53'. Apex area 61 separates channels 54a from 54b. If
the sheet 53 is placed in a battery in a position such that the vertical orien-
~0 tation lines of the battery are parallel to each channel's imaginary medianline 55, it can be readily observed that substantially all sections of contour
lines 58, 59 and 60 are at acute angles of up to 70 degrees from the vertical.
A segment of the second major face of sheet 53 is illustrated in
Figure 7. Figure 7 shows a major face 62 which has open continuous channels
63a, 63b, 63c, 63d and other similar channels thereon. Each of the channels
63a, 63b~ 63c and 63d are separated from each other by apex surface areas 64a,
64b, and 64c and others which are the compliment of the nadir areas 54a', 54b'
and 54c', respectively, of the channels of major face 53' shown in Figure 6.
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~ ~ 763~
Each channel is of substantially the same configuration as the next adjacent
channel and is in nested relationship. The apex planar portions 61 of face
53' form the nadir planar portions 63a', 63b~, 63c', and 63d' of each channel
63a, 63b, 63c and 63d, respectively. Using one channel to further describe the
channel's configuration it is readily seen that imaginary median line 65 divides
the average area of channel 63b into two equal areas. Channel 63b has lateral
extensions 66 periodically along the channel on both sides of the median line.
The nadir area 63b' of channel 63b on face 62 corresponds to the apex area 61
of face 53' of the same sheet 53. The apex contour lines of channel 63b are
lines 67 and 68. Lines 67 and 68 form the boundary of the surface area on face
62 which forms channel 63b. An apex contour line 69 along with apex contour
line 68 defines the boundary of the apex area 64b which is substantially planar
and contiguous with the boundary plane of face 62 and forms a separation between
channels 63b and 63c. This apex area 64b corresponds to the nadir area of
channel 54b on face 53'.
It can be seen that the separator sheets illustrated in Figures 4, 6
and 7 have each channel member on each of their two major surfaces of a con-
figuration which, although having the required lateral extension, which extension
is greater than any minimum extension of the channel, provides for essentially
all of each channel's surfaces to be ~a) open, Ib) of a continuous upward orien-
tation and (c) have all surface areas forming each channel capable of being at
an acute angle of up to 70 degrees from an imaginary vertical orientation line
of from bottom to top of a battery in which the sheet is contained.
Figure 8a is a cross-sectional view of the sheet product of Figure 4
along line 8a-8a. Sheet 40 has a first major face 41 and a second major face
42 which defines a substantially uniform body thickness 80. It is understood
that the thickness 80 can have some variation over sheet 40 expanse. Such
variation may be due to the processing of the starting material into the subject
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~ ~ 7~307
sheet. The cross-sectional configuration can be continuously curvilinear of
substantially sinusoidal form. Other alternate configurations are shown in
Figures 8b and 8c as described below. Face 41 of sheet 40 has apex points 81
which are individually indicated as 81a, 81bJ 81c, 81d, and 81e and nadir points
82 which are individually indicated as 82a, 82b, 82c and 82d. Each of the apex
points 81 are substantially coplanar and contiguous with an imaginary boundary
facial plane of the sheet 20. Further, each of the apex points 81a, 81b, 81c,
81d and 81e corresponds to a point on the apex contour line 42a, 42b, 42c, 42d
and 42e respectively, which are shown in Figure 4. Each of the nadir points
82 on face 41 are in spatial relationship with the imaginary facial plane of
face 41. The facial surface areas 83 which are individually indicated as 83a-a,
83a-b, 83b-b, 83b-c, 83c-c, 83c-d, 83d_d~and 83d-e are surface areas which
extend between the apex points 81 and nadir points 82 on surface 21. The
surfaces 83 along with nadir points 82 form channels 43a, 43b, 43c and 43d.
For example, channel 43a is formed by surface areas 83a-a and 83a-b which, along
with nadir point 82a extends from apex point 81a to apex point 81b. Channel
43a is separated from channel 43b by apex point 81b. Each other channel is
similarly formed and separated from adjacent channel(s). It is readily seen
that surface area 83aa and 83ab are each a "depressed surface area" with respect
to apex points 81a and 81b respectively and can also be viewed as a "raised
surface area" with respect to nadir point 82a.
The other major face 42 of sheet 40 is substantially the reverse
configuration of face 21. Each apex point 81 of surface 41 has a corresponding
nadir point 84 which is individually indicated on Figure 8a as 84a, 84b, 84c,
84d and 84e at corresponding points on face 42. Similarly, each nadir point 82
on surface 41 has a corresponding apex point 85 which is individually indicated
as 85a, 85b, 85c and 85d on face 22. It is readily seen that any one channel
on one surface forms a separation between adjacent channels on the other surface
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~ 1 763~7
of the separator sheet.
Figures 8b and 8c are illustrative examples of other cross-sectional
configurations that can be used to form the open continuous channels of the
separator sheet. Figure 8b illustrates a cross-sectional configuration wherein
one surface 86 has a single apex point 87 separa~ing adjacent channels and the
surface 86 has a multiple of nadir points which forms a nadir planar section 88
for each channel. The other surface 89 has a reverse coniguration which, by
definition, has a single nadir point 90 for each channel which corresponds to
each apex point 87 on surface 86. Surface 89 has a multiple of adjacent apex
points which forms apex planar sections 91 which, in turn, correspond to each
nadir planar sections 88 on surface 86. Each apex section on one surface forms
a separation between adjacent channels on the other surface.
Figure 8c illustrates a cross-sectional configuration wherein for
eacil channel on each face there is a multiple of nadir points forming a nadir
planar section 92 as part of the channel and there is a multiple of apex points
forming apex planar sections 93 separating adjacent channels.
It is realized that different channels formed on each face of a
separator sheet can be of different cross-sectional configuration. Further,
the facial configuration of each channel of the sheet can be different from the
70 configuration of an adjacent channel. For example, certain channels on one
face of a sheet can have a sinusoidal configuration as described with respect
to Figure 4 hereinabove while other channels on the same face may have a toroidal
configuration as illustrated in Figure 6. Alternately, each channel on one face
of a separator sheet can have sections of one configuration and sections of
another configuration.
It is to be also understood that any one channel of one face of the
separator sheet may have a configuration wherein its lateral extension of at
least one surface forming the channel is of a substantially equal distance with
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3 1! 76307
respect to the channel's imaginary median line for some distance along the
channel. However, such channels of equal lateral extension shall not form a
part of the separator sheet to a degree which would show any substantial decrease
in compressive force resistance. The exact degree of channel or channel segment
of equal lateral displacement permitted depends on the particular configuration
of the remaining and, particularly, the adjacent channels, as well as the parti-
cular composition of the sheet to produce non-collapsing compressive force resis-
tance as can be determined by those skilled in ~his art. It is preferred that
the sheet forming a battery separator should have less than about 50 percent
of all channels or channel segments of equal lateral displacement configuration.
The separator sheets are all formed from a porous sheet material of a
substantially uniform thickness of from about 0.025 mm to about 1 mm, and
preferably from about 0.1 mm to about 1 mm. The desired sheet can be formed by
embossing, pressing, or the like conventional processing techniques of a
material that has a substantially uniform body thickness (providing for stretch-
ing and the like during formation). The maximum spatial thickness of the formed
sheet can range from about 0.25 mm to about 5 mm although greater or lesser
maximum spatial thickness may be formed for particular applications,
The sheet material used to form the separator must be formed of an
~0 acid-stable composition. The composition preferably comprises a thermoplastic
pol~ymer and an acid resistant inorganic filler. The preferred compositions
include from about 20 to about 75 percent and preferably from about 30 to
about 60 percent by weight of a thermoplastic polymer and from about 25 to 80
percent and preferably from about 30 to 75 percent by weight of an acid resistant
inorganic filler. The preferred thermoplastic polymer is a resin containing
at least one resin selected from a polymer or copolymer of ethylene, propylene,
butylene, vinyl chloride, acrylic or styrene. The more preferred polymer would
contain at least 50 percent ethylene units. The preferred composition may
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~ ~ 76307
contain additional materials such as plasticizer, oil, stabilizers, wetting
agents and the like.
The sheet material used to form the separator can also be formed
from thermoset resinous compositions. The composition must be formed into the
proper configuration prior to or while being subjected to sufEicient elevated
temperature conditions to cause curing of the resinous material. Thermoset
compositions capable of forming the present sheet product include compositions
containing thermoset resins as, for example, phenolics, EPDM (ethylene/propylene/
diene), sulfur cured isoprene, butadiene, styrene and the like, as well as those
described in United States 3,551,362.
The sheet material used to form the separator should be porous, that
is to say have an open pore structure. The pores should be generally between
about 0.01 and about 40 microns in diameter. The sheet must be formed in a
manner which does not fuse or close the structure of the pores. The complete
collapse of the pores or even the collapse or closure of the pore structure
at the surface of the formed separator sheet would exhibit increased electrical
resistance characteristics. It is understood that some reduction in pores'
aggregate si~e may occur during processing and formation of the sheet. Such
reduction can be tolerated.
The subject sheets have been found to provide an improved battery
separator, particularly for use in an acid battery system. ~ne preferred
embodiment of the separator is that it be in the form of individual sheets.
Each sheet has boundary edges which define dimensions of the major surfaces
of the sheet~such that the dimensions are at least substantially equal to the
electrode plates between which it is contemplated that the seperator sheet is
to be positioned. Referring to Figure 9, sheet 92 has a substantially rectan-
gular facial configuration bound by top edge 93a, bottom edge 93b and side
edges 94. The terms "top", "bottom" and "side" refer to orientation with
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~ ~ 7~3V7
respect to a battery in which the separator sheet is used. The top edge 93a is
contemplated to be the edge of *he separator in closest spa~ial relationship to
the top of the battery when it is in its normal use orientation. Similarly,
bottom edge 93b is the edge contemplated to be in closest spatial relationship
with the bottom of the battery when it is in its normal use orientation. The
separator should be formed such that each channel on both major faces of the
separator are open, continuous channels which have their surface areas continous-
ly open or directed upwardly in its use orientation.
The configuration requirements of the separator not only provide the
de~ired properties discussed above but also provide a separator sheet which can
interchange its top edge g3a with its bottom edge 93b when placed between plates
of opposite polarity without sacrificing any of the desired properties. This
further provides one with the ability to form a separator of a wrap around
or U configuration from a single piece of sheet. Figure 9a illustrates a
separator 95 wrapped around an electrode plate 96 in a U configuration. The
separator 95 is formed by forming a fold from a point 97 on one side edge to a
point 98 on the opposite side edge, wherein points 97 and 98 are approximately
equidistant from one top edge 99 of the separator. The side edges on each side
of the separator which are contiguous with other portions of the same side edge
~0 can be sealed together to form sealed edges 99 and 100, such as by conventional
heat sealing or ultrasonic welding of thermoplastic sheet. Such "pocket"
design further eliminates battery failure problems caused by contact of plates
of opposite polarity via precipitate or scale material conventionally known as
"shed" or "mud" material which has accumulated at the bottom of the battery
container.
The separator sheet provides good electrolyte/electrode contact;
improved gas egress means; good resistance to deformation by compressive forces;
and can urther facilitate formation of a battery due to i~s ability to be
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~ ~7~3~7
reverse oriented from top to bottom when placed in use position, or can facili-
tate forming a still further improved battery by its ability ~o be formed into
a U configuration capable of inhibiting contact of plates of opposite polarity
via shedded active material and the like accumulation.
Figure 10 shows a cross-sectional view of a pair of electrode plates
of opposite polarity with a separator membrane positioned there between as in
an operating battery. The positive plate 101 and negative plate 102 are con-
tiguous with the imaginary boundary facial planes of the separator such that the
surfnce areas separating each of the adjacent channels on each of the faces are
la in substantial contact with the electrode plate adjacent to that face. It is
preferred that the separator be oriented to provide surface areas of reduced
porosity 104 (due to compression and the like processing parameters) toward or
in contact with the positive electrodeplate 101 while surface areas of greater
porosity 105 are orientated toward or in contact with the negative electrode
plate 102. However, the battery separator's performance is almost equal when
the battery separator's surface areas in contact with each plate member are
reversed such that surface areas 104 engage the negative plate 102 and surface
areas 105 engage the positive plate 101.
Each of the apex areas separating adjacent channels on any one surface
of the separator sheet is substantially contiguous with a boundary facial plane
of the sheet, It is preferred that each apex area separating adjacent channels
on any one face of a sheet is at least about 75 percent, or preferably about 90
percent, and still more preferred substantially 100 percent, continuous and
contiguous with its boundary facial plane from the bottom to the top of the
battery separator face. Each continuous apex surface area should be completely
isolated from other apex surface areas on the same face of the separator sheet.
Adjacent apex surface areas on a face of the sheet can have a spatial relation-
ship of equal distance ~such as formed by the nested configuration of the sheet
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I ~76307
of Figure 4) or of varied distances (such as formed by an unnested configura-
tion) from one apex surface area to the next over the total extension of each
apex surface area. The apex surface area on any one battery plate should not
exceed abou* 50 percent, and preferably about 30 percent, of the total surface
area of the major face adjacent to the plate. Further, the spatial distance
between adjacent apex surface areas may be such as to provide at least two
open continuous channels per ~5 mm although less channeis may be suitably
formed by certian configuration and still retain the desired properties.
