NO150657B - DISPENSER FOR ELECTRICAL ACCUMULATORS CONSISTING OF A MICROPOROUS BASIC MATERIAL, AND PROCEDURE FOR THE PREPARATION OF THE DISPENSER - Google Patents

Description

The invention relates to a separating device for electric accumulators, in particular lead accumulators, of a porous material where the side facing the positive electrode is connected to a net structure of stretch plastic, as well as a method for producing the separating device.

The use of separating devices in accumulator technology includes, depending on the cell structure and electrode shape, an extensive spectrum of diaphragms, which extends from simple spacers to microporous space structures. The separation devices today, especially for use in lead accumulators, are predominantly made of acid-resistant thermoplastic plastics.

The simplest method for producing such separators is sintering plastic powders. In this case, e.g. polyvinyl chloride powder applied to a steel strip in a thin layer and passed through a sintering furnace. At an air temperature in the oven of 200 - 350°C, the powder band is sintered together into a solid body with a relatively high porosity.

By cutting or punching, the plates can be given a desired built-in size, which, however, in close, surface-wise contact with the electrode plates, leaves no room for an unimpeded escape of the gases that arise during charging.

The sintered powder band is therefore, prior to cutting at a reduced temperature, reshaped between rollers into a wavy body, or it is given a profile using ribs or steps which, before sintering, are shaped using shaping rollers or ironing knives (squeegee knives) from the band or ribs applied afterwards.

Usually it is sufficient that there are only ribs on one side of the separating device, which side faces the positive electrode, while the other side of the separating device lies immediately against the negative electrode. Arrangements both of this type and also with undulating foils between the positive and negative battery electrodes are e.g. known from DE-AS 1771227. The ribs, respectively the spacers, are provided here by punching out a foil material of the desired thickness and glued, welded on or pressed in with force in parallel running paths on the actual separator. According to another known method according to De-AS 1269212, a heat-hardening synthetic resin mixture is applied by means of an extruder in the form of parallel strands to the actual porous separating film and the product is passed through an air circulation oven with a set temperature, in which the strands melt on the substrate and here - there completely out at the same time as this which is impregnated with partially hardened phenol-formaldehyde synthetic resin.

As the ribs can only run in longitudinal paths for

to ensure the rising oxygen bubbles a necessary passage, the separating device only has a good mechanical stability in one direction, while in the other direction it can easily be folded or pressed in.

The task that is therefore the basis of the invention is to provide a separation device, particularly for lead accumulators, respectively starter batteries, which, in addition to its actual function as a highly porous diaphragm, also has a good rigid

hot over the entire surface area and, despite a tight installation, enables the charging gases from the electrolyte to escape without problems.

This task is solved according to the invention by a device of the type mentioned at the outset, the characteristic features of which appear from the application's requirements.

The connection with the actual base material must

in and of itself is only maintained until the separating device has taken its place permanently in the cell between electrodes of different polarity. The network has the task of attaching an extremely flexible base material that can be manipulated to the rigid separation device during fabrication.

The basic material in the separating device can be

a highly porous foil, which consists of an acid-resistant, thermoplastic plastic. As suitable material comes into question

polyethylene, preferably, however, polypropylene. A known polypropylene film has e.g. a thickness of approx. 25 li and a porosity of 3 5%, whereby the diameter of the pores is less than 0.1 y. The pores of this foil can be understood as discrete, slightly curved channels from one surface to the other. The resulting particularly even structure gives the foil extremely favorable mechanical and electrical properties for the intended purpose of use.

On one side of the base material for the separation device and permanently connected to it, a net structure of a synthetic material is applied, which is suitably selected from the same group of thermoplastics, but can optionally also be a thermosetting plastic.

The net structure plays the role of a spacer, whereby the separation device in all surface directions gets an increased bending strength which the known laminar structures in the initially mentioned step separation devices only have to an incomplete extent. Only in connection with the net-like spacer layer over which the skin-thin foil is stretched in a way, can the device optimally perform its separation function.

The net structure itself can be formed from mutually intersecting parallel bands of plastic rods or threads.

The mesh structure can be a stretch plastic which is produced from a smooth strip material in the same way as a stretch metal. The basis for this stretch processing is a stretch process known in and of itself which gives the plastic material, which forms the net structure, its shape stability. When stretched, most linear polymeric plastics experience a significant increase in strength with a simultaneous decrease in expansion. The fixation is due to the fact that the usually clumped thread molecules under the influence of a tensile stress

ning arranges itself into crystal-like structures within which the intermolecular binding forces become more effective.

Deformation during stretching is possible with glass-amorphous thermoplastics as well as semi-crystalline thermoplastics such as polyethylene and polypropylene at room temperature. With the latter, it is advantageous to carry out the stretching at a higher temperature in the range of 100 - 150°C (hot form temperature), which is already close to the melting range for the crystallites. In any case, the deformation temperature should be chosen so high that a rapid cooling can then be carried out to below the so-called freezing temperature, whereby the thermoelastic state range is undercut. The change in shape is thereby fixed to the crystal melting area, at least at the usual operating temperatures.

Steps with a smaller thickness are arranged within the stretch grid, so that in the preferred directions passing stretches appear for avoiding the electrolytic gases after the separation device is tightly embedded between the electrode plates. Such a design of the stretch plastic is possible in different ways. For example the slots with which the plastic foil is equipped in a completely similar way as in the case of a metallic strip material to be stretched, can be offset from each other according to a predetermined pattern in such a way that with the help of the knives of the stretching tool the surfaces arranged between the slots are pressed out partially stronger , partly less strongly to the sides. Thereby, paths with less thick steps with a zigzag-shaped course can be achieved. Another possibility for providing larger and smaller step thicknesses next to each other is that the otherwise similar, comb-like arranged slotting knives in the stretching tool are partially and in a specific order replaced by punching knives.

The connection of the net structure with the microporous base material into a uniform body can, due to the special properties of the thermoplastic plastics, take place in such a way that the surfaces to be connected are heated to initial softening and compressed under weak pressure, respectively that the base material is ironed onto the mesh structure. However, the heating time should be made so short and the temperature set so that the surface is just adhesive and when pressure is applied causes a weld together.

For this purpose, it is advantageous to feed the micro-porous base material and the stretch plastic, both in strip form, over separate superheatable rollers, which give them the temperature required for bonding on the contact side against the roll surface. The strips are immediately then taken up by two closely spaced bending rolls and lightly compressed between them. The gap width between the bending rolls should be somewhat narrower than the height of the finished product to avoid an unwanted flat rolling of the attached stretch plastic.

Fig. 1 shows a composite separator according to the invention, consisting of the microporous base foil 1 and a stretch plastic layer 2. The dashed lines lead over preferred passages for gas, which are formed by reducing the step thickness in these areas.

The entire layer thickness of the separator corresponds to the thickness of normal separators in the starter battery.

Claims (3)

1. Separation device for electric accumulators, in particular for lead accumulators, of a porous base material, where the side facing the positive electrode is connected to a net structure of a stretch plastic material, characterized in that the stretch plastic material has steps of different thickness, whereby in preferred directions only arranged step with less thickness. 2. Method for producing a separation device according to claim 1 for electric accumulators, in particular lead accumulators, from a porous base material, where the side facing the positive electrode is connected to a net structure of stretch plastic, characterized in that the stretch plastic is thermally connected to the microporous the basic material. 3. Method for manufacturing a separation device according to claim 2, characterized in that the stretch plastic is stretched during the design of different thick steps.