Separator with longitudinal and transverse ribs for use in accumulators

Separators for use in accumulators are provided with integral longitudinal and transverse ribs. The separators have an increased transverse and longitudinal rigidity thus permitting a clear reduction in the sheet thickness. They are preferably provided in the form of rolls with the rib structure preventing a permanent distortion of the separators.

The invention relates to separators for accumulators preferably in the form 
of material taken from the roll not cut to size. The separators are 
provided at least on one side with a pattern of longitudinal and 
transverse ribs which increases the rigidity of the separators both in the 
longitudinal and transverse directions and prevents a distortion of the 
separator sheet by coiling operations. 
The separators which are used today in accumulators are formed from 
microporous sheets, which prevent short circuits between the plates and 
the falling out of plate material. However, by reason of their pore 
structure they permit an ionic flow of current in the electrolyte. 
Separators of this type are normally provided at least on one side with 
longitudinal ribs which should prevent the direct contact of the separator 
sheet with the positive electrode plate. At the same time these ribs give 
the separator a certain rigidity in the longitudinal direction. The 
separators consist generally of a thermoplastic material and are formed 
into pockets, into which the positive or negative electrode plate is 
inserted. The height of the ribs is usually greater than the thickness of 
the separator sheet which results in a relatively unfavourable torque for 
forces acting at the ribs which in conjunction with the plasticity of the 
plastics used frequently results in distortions of the separator. 
Distortions of this type occur particularly when the finished separator 
tracks are rolled up. As a result of this the separators are no longer 
even which causes serious problems during subsequent cutting to size and 
further processing into pockets. Their low rigidity in the transverse 
direction is also a disadvantage on the known separators. 
Rigid separators for electrical accumulators are described in German patent 
specification DE-PS 28 47 453, for which a microporous base material is 
thermally bound to a network structure made of stretch plastic. The webs 
of the stretch plastic have different thicknesses and thus facilitate the 
escape of electrolytic gases. These separators have an increased bending 
strength in all surface directions. A disadvantage of these separators is 
that the network structure and the base material are manufactured 
independently of each other and then have to be joined together in an 
additional process step. In addition the network structure of the stretch 
plastic layer does not allow the electrolytic gases to rise in a straight 
line but forces the gas bubbles into a zig-zag shaped pattern. The battery 
separators disclosed in the German patent specification DE-PS 28 47 463 
are rigid separators which are inserted in sheet form into the accumulator 
housing. The handling of rigid separators of this type is relatively 
difficult so that interest in them is decreasing. Furthermore the 
structure of the separators disclosed in DE-PS 28 47 463 does not allow 
them to be further processed to form pockets as is usual currently. 
The object of the present invention is to provide separators for 
accumulators which have an increased rigidity both in the longitudinal and 
transverse directions and which are provided with ribs which can be 
manufactured integrally, i.e. at the same time as the porous separator 
sheet and which enable the charging gases to escape rapidly and in a 
straight line. The separators should preferably be provided in the form of 
rolls which are simple to handle and which can easily be further processed 
to form pockets. 
The subject matter of the invention is a separator for accumulators which 
in addition to the longitudinal ribs which run in the direction of 
manufacture is provided with ribs which run transversally to it. The 
transverse ribs have a smaller height by comparison with the longitudinal 
ribs. The separators are disposed in the accumulator in such a way that 
the longitudinal ribs run vertically and the transverse ribs horizontally 
so that a channel is created by the reduced height of the transverse ribs 
which enables the charging gases to escape easily and in a straight line. 
The transverse ribs can be produced at the same time as the longitudinal 
ribs and do not require any additional working step. 
In principle, all acid-resistant thermoplastic materials are suitable for 
the manufacture of the separators according to the invention. Preferred 
materials are polyvinyl chloride, polyethylene and polypropylene, 
polyethylene of high molecular weight is particularly preferred. The 
separators are preferably manufactured with the addition of inorganic 
fillers such as amorphous silicic acid with the composition and 
manufacture of separators of this type being known from the prior art 
(e.g. DE-PS 1 267 423, DE-PS 1 298 712, DE-AS 1 496 123 and DE-PS 39 28 
468).

The thickness of the separator sheet is approximately 0.10 to 0.50 mm and 
the height of the longitudinal ribs between 0.3 and 2.0 mm so that the 
total thickness of the separator is up to approximately 2.50 mm. 
Separators with a total thickness of between 1.0 and 2.0 mm are preferred 
however. The transverse ribs have a lower height by comparison with the 
longitudinal ribs. Their height is approximately between 1/10 and 1/2 and 
preferably approximately 1/3 of the height of the longitudinal ribs and is 
approximately between 0.1 and 0.7 mm. The longitudinal ribs are preferably 
approximately 0.7 mm in width and the transverse ribs approximately 0.35 
mm in width. 
The distance between two adjacent longitudinal or transverse ribs depends 
on the desired rigidity of the separator. With a sheet thickness of 0.25 
mm, a longitudinal rib height of 1.0 mm and a transverse rib height of 0.4 
mm distances of 8 mm to 15 mm for the longitudinal ribs and between 3 mm 
and 8 mm for the transverse ribs have proved satisfactory for use in 
starter batteries. 
In a preferred embodiment longitudinal and transverse ribs form angles of 
90.degree. to each other. Embodiments with angles other than 90.degree. 
are however conceivable. In this connection all transverse ribs can run 
parallel to each other so that all transverse ribs intersect the 
longitudinal ribs at the same angle. It is also possible, however, to have 
the transverse ribs form several groups of parallel ribs which groups 
amongst themselves are at angles of approximately 90.degree. to 
.ltoreq.180.degree. to each other as is known for example from the 
so-called herringbone pattern. 
Separators with transverse ribs at right angles to the longitudinal ribs 
with a height of approximately 1/3 of the height of the longitudinal ribs 
have a transverse rigidity which is approximately three times greater by 
comparison with separators without transverse ribs with it being possible 
to increase or reduce this value further by varying the transverse rib 
dimensions and spacings. The longitudinal rigidity of the separators 
according to the invention with a width of 100 mm normally reaches values 
of 5 mJ and the transverse rigidity values of 2.5 mJ. 
The longitudinal and transverse ribs can have both a round and an angular 
cross section with equal-sided trapezoidal cross sections being preferred. 
The separators according to the invention can be manufactured in the same 
way as conventional polyethylene separators. With this method the plastic 
material containing filler is extruded through a slot die and then run 
through two calender rolls by means of which both the longitudinal and the 
transverse ribs are produced and the separator sheet is reduced to the 
desired thickness. 
Tests have shown that the separators according to the invention have a 
better machine workability than those without transverse ribs. A 
significantly better guidance of the separator tracks can be achieved as a 
result of the increased transverse rigidity and the processability for 
placing the electrode plates in pockets is considerably improved because 
of the increased transverse rigidity. In addition, production of 
separators with a considerably reduced sheet thickness and consequently 
with a reduced electrical resistance becomes possible which is of 
significance particularly in relation to efforts constantly to increase 
the output further with a constant battery volume. The separators 
according to the invention can be processed to form pockets without 
difficulty on conventional machines. The additional transverse ribs do not 
cause any problems either with the welding of the pockets by the use of 
heat or ultrasonic means or with the mechanical process for producing 
pockets. 
The separators according to the invention are preferably provided in the 
form of material taken from the roll not cut to size. Tests have shown 
that neither during the coiling operation or upon storing of the rolls are 
distortions caused to the separators. Rolls with a diameter of 
approximately 0.8 m were examined and they had approximately 200 separator 
layers located one above the other. 
FIGS. 1A and 1B show perspective views of a separator according to the 
invention with transverse ribs running at right angles to the longitudinal 
ribs.