Dust reduction for electrode plates

Start of patent period: 1980 06 15 Longest possible duration:

© Lost on: 1981 01 26 © inventor:

© dependence:

© Pamphlets considered to delineate the prior art:

DE-AS1946398

Nr.360606

The invention relates to an electrode plate for lead-acid batteries whose surface is provided with a dust-fixing coating.

In the accumulator industry, various steps in the production of the electrode plates, in particular after intermediate drying, are accompanied by a harmful development of lead pulp. Based on experience, the vast amount of lead dust is produced by formed positive plates on their further production path until they are installed in the battery.

In view of the stricter provisions of environmental protection and occupational hygiene, it is necessary to remedy this situation.

The invention therefore pursues the purpose, by .A surface treatment of Elektro10 denplatten, which can be incorporated without difficulty in the production process to stem the formation of lead or to bind the lead dust so that when handling the electrodes at most a very low abrasion.

US Pat. No. 905,829 discloses a process which provides for the treatment of freshly pasted electrode plates by brushing or spraying on an aqueous solution of water-soluble organic polymer compounds, including immersion in such a solution. These water-soluble polymers include polyvinyl alcohol, polyethylene oxide, alkyl cellulose and starch. After the evaporation of water on the surface of the plates, they leave a thin film that binds the lead dust particles. However, because of the water-solubility of the film-forming products, their dust-binding effect only temporarily persists until subsequent washing treatment largely removes the coating again.

Does not occur with the applied organic polymer compounds during the formation process, no radical oxidation to carbonic acid, so could remain as residual other acids such as acetic acid, formic acid, citric acid and others, as they are soluble

Lead salts form, lead to corrosion.

If, on the other hand, the dust fixing treatment is carried out on the already formed and then particularly dust-prone positive plates, it can not be avoided that at least some of the water-soluble organic substances are introduced into the battery electrolyte, with undesirable effects on the electrochemical processes during the La30 de / unloading operation can not be foreseen. Very often, the presence of soluble organic substances in the battery electrolyte is also adversely affected by foaming.

The invention is therefore an object of the invention to provide a dust-free electrode plate, which has only a slight tendency to dust formation by surface treatment with a layer-forming material, wherein the coating formed chemically largely indifferent

Should be 35 and does not affect the electrical properties of the battery.

The object is achieved in that the coating contains a silicate as a film-forming component.

The electrode plates according to the invention are preferably positive grid plates which are either dry or moist for a few seconds in dilute solutions 40 of, for example, sodium silicate, Na ₂ SiO₃ (Sodium water glass), dipped and then dried for about 1 h at 60 ° C in a convection oven. Optionally, the solution can also be applied by spraying. Of course, both positive and negative electrode plates can be treated according to the invention u.zw. both after pasting and after formation; Preferably, the treatment is done after pasting.

Under the name "soda-waterglass" a wide range of varieties of sodium silicate solutions is commercially available. The chemical composition and physical properties of these products are approximately in the following frame: 22 to 37% SiO 2₂, 6 to 18% Na₂O, 28 to 55% solids, density 1.26 to 1.75 g / cm³ and viscosity (20 ° C) 20 to 2000 cP. For the application according to the invention, a soda-waterglass has proved to be particularly favorable, whose analysis values ​​consistently coincide approximately with the lower limits of the mentioned ranges.

Such a water glass is either undiluted or diluted with water in the ratio 1: 1, applied by dipping on the plates, the dipping time up to 1 min, preferably

- 3 no. 360606 s. The mixture is then dried at 60 ° C for 1 to 2 h. The dry plate surface appears glazed afterwards.

In factories in which the plates are formed in the block box, the water glass treatment is preferably performed on the freshly pasted plates, since the mounting work 5 is practically completed even before the formation step. As has been shown, the curing following the fasting is in no way adversely affected by the waterglass film. In addition, a lower tendency of the plates to blow off is discernible.

To evaluate the dust-binding capacity of coatings of the invention, the panels are subjected to either a vibration test or a rub-off test. It can be seen that the amount of dust emitted by an impregnated electrode plate is only about 5 to 10% of the amount of dust released by an impregnated electrode plate

Dust on an untreated electrode plate amounts.

The amount of water glass taken up by the plate depends on the concentration of the solution, the viscosity of the solution also being important, since low-viscosity solutions penetrate deeper into the pores, but higher-viscosity solutions can flow out of the solution more slowly after removal. On the other hand, the amount of water glass consumed depends on the moisture of the plate. It has been found, for example, that a dry flask of a relatively high viscosity undiluted water glass takes up about 10 g in 1 s, whereas a wet plate absorbs only 5 g in 10 s. In dilute, low-viscosity waterglass solutions, the amounts of fixer taken up by the plate after a treatment time of 201 min at less than 3 g (dry plate) or less than 1 g (wet plate) (these values ​​are based on 149 x 106 x 1.6 mm electrode plates). This finding is easily explained by the fact that even during the relatively long treatment period, the water present in the interior of the porous plate can not be exchanged so quickly. Nevertheless, the subsequently developed amounts of dust remain about equally low, u.zw. reduced to values ​​of less than 1.4 mg / plate, while the dust accumulation without fixative approaches 10 mg / plate.

Thus, since the fixation of dust is also possible with the use of wet plates, there is the advantage of being able to treat shaped plates immediately after washing without having to dry them first. This is interesting from the point of view of energy saving.

Only a small influence on the dust binding has the treatment time. It does not significantly change the treatment success at dive times between 10 s and 1 min, so that the treatment time of 10 s is considered to be fully sufficient.

The effect of the dust-binding coating according to the invention is enhanced by the fact that water glasses in acidic solutions with the formation of Si-O-Si bridges in a short time to

Polysilicic acids codensieren and thereby tend to crosslinks.

The electrical behavior of the electrode plate is practically unaffected by the coating according to the invention. An additional advantage is achieved by mixing the waterglass solution with a highly dilute aqueous dispersion of an organic polymer compound 40. The coating formed in this way is characterized by an increased elasticity due to the organic constituent. The organic additives, which are all water-insoluble, may be either simple polymers such as polyvinyl acetate, polystyrene, polyacrylates, polyvinyl chloride or copolymers whose components are formed from, for example, styrene and acrylic esters, styrene and butadiene or vinyl acetate and maleic acid esters. They belong to the group of "thermoplastic polymerization plastics and are otherwise used as coating raw materials in the coatings industry

Use.

In the application according to the invention, the commercially available approximately 50% aqueous dispersion of the polymeric plastic is diluted to a ratio of 1:10 and this dilution is mixed with the commercial waterglass solution in the ratio 1: 1. The treatment liquid 50 then has a total solids content of 15 to 27 wt .-%. The application of the water glass solution with the plastic additive to the electrode plate and its drying is carried out in the same manner as described above.

The result is a coating that optimally reduces the formation of dust to a residual of about 2.5% of the dust accumulation of an untreated plate.

- 4 No.360606

An overview of the results of treatment both with pure water glass solutions and with a combination of waterglass / acrylic acid ester-styrene copolymer according to dry and wet plates is given in Tables 1 and 2 below. In both cases, positive-shaped plates were used and a dust-proofing test was carried out ,

Table 1

Dry plates, dipped for 1 min; Dried at 60 ° C for 2 h

<td>attempt No.</td><td>Solids content of the original water glass solution (%)</td><td>dilution</td><td>amount of substance (G / disk)</td><td>amount of dust (Mg / plate)</td>

<td>1</td><td>untreated</td><td></td><td>0</td><td>9.70</td>

<td>2</td><td>28</td><td>1: 1</td><td>2, QQ</td><td>0.63</td>

<td>3</td><td>35</td><td>1: 0</td><td>2.50</td><td>0.76</td>

<td>4</td><td>38</td><td>1: 1</td><td>2.90</td><td>0.46</td>

<td>5</td><td>45</td><td>1: 3</td><td>1.50</td><td>0.60</td>

<td>6</td><td>Original water glass solution off Vers. Nr.2 + Copoiymerisat acrylic ester styrene 1:10 verd.</td><td>1: 1</td><td>2.20</td><td>1.0</td>

Table 2

Wet plates, dipped for 1 min; 2 h at 60^pC dried

<td>attempt No.</td><td>Solids content of the original water glass solution (%)</td><td>dilution</td><td>amount of substance (G / disk)</td><td>amount of dust (Mg / plate)</td>

<td>7</td><td>28</td><td>1: 0</td><td>0.80</td><td>0.76</td>

<td>8th</td><td>35</td><td>1: 0</td><td>0.35</td><td>0.93</td>

<td>9</td><td>38</td><td>l; l</td><td>Q.56</td><td>1.00</td>

<td>10</td><td>45</td><td>i; 3</td><td>0.25</td><td>2.90</td>

<td>11</td><td>Original water glass solution Vers.Nr.2 resp. 7 + copolymer acrylic ester-styrene 1:10 verd.</td><td>1: 1</td><td>0.35</td><td>0.9</td>

- 5 No.360606

It is interesting to compare Experiment No. 3 (dry plate) with Experiment No. 7 (wet plate): in both cases the same protection value is achieved with a dust amount of 0.76 mg / plate, although less with the wet plate Water glass was applied in the treatment liquid and reached the layer-forming substance amount only about 1/3 of those in the tracke nen plate.

In addition to the plastics mentioned, cane sugar and sodium sulfate have proven to be suitable additives to soda water glass. They have the role of pore-forming agents, since they are later dissolved out of the insoluble silica coating by the electrolyte and thus prevent excessive coverage of the electrochemically active electrode surface 10. Water glass is also in addition to these additives main component of the dust-binding layer and thus the actual film former.

A 30% cane sugar solution, mixed with undiluted water glass solution in the ratio 1: 1, was able to reduce the amount of dust to 1% of that of an untreated plate, the immersion time was 8 min.

Was the sodium silicate solution with 15% Na ₂SO "solution diluted in a ratio of 1: 1 resulted after 10 s immersion time and drying only half the amount of dust, as they are at the same dilution, but without Na₂SQ ",

PATENT CLAIMS:

1. electrode plate for lead-acid batteries, the upper surface is provided with a dust-fixing coating, characterized in that the coating as a film-forming component

2 ° contains a silicate.

2. Elektrcdenplatte according to claim 1, characterized in that the coating of alkali metal silicate, in particular of sodium silicate, consists ·

3. Electrode plate after the