DE2238245A1 - METHOD OF TREATMENT OF ALUMINUM FOIL FOR ELECTROLYTE CAPACITORS - Google Patents

Description

Method of treating aluminum foil for electrolytic capacitors.

Me invention "relates to a method for treating

ment of aluminum foil for electrolytic capacitors j on through this. procedure treated film and on one made of such a film th capacitor-.

The electrode surfaces of aluminum folds for electrolytic capacitors are preferably roughened by etching vioduroh the effective surface area and thus the capacitance of the capacitor is increased, when aluminum is exposed to the air, forms ^^ nter the. Influence of water ¹ a layer consisting of an oxide hydrate. This hydrate of oxide, which may be built into aluminum oxide, increases the capacity of the foil. Since the hydrate of oxide is a dielectric, albeit a 1 / iolektriifura with high losses »it is evident that among these uranium Minden capacitors with stable eLiioia, capacities: Zltlttr.iWer't, not received

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can be. This manifests itself in the fact that it takes a very long time before Formed film kept in stock for some time with a constant supply Current reaches the forming voltage again.

It was therefore proposed (see German © patent specification 966.477) »to apply a boehmite layer to an etched aluminum foil. As a result, the foil is protected from corrosion in an appropriate manner and the electrolytic capacitor made from this foil has favorable electrical properties. This is achieved by treatment with distilled water at a temperature above 75 ^° C. after washing in distilled water at a lower temperature, the pH of the hot water being kept at 5 to 6 by adding chlorine-free acidic buffer substances and a layer with a thickness of 0, 02 to 0.1 / um is produced, which is dewatered by drying while gradually increasing the temperature to a maximum of 2.0 ^° C. in such a way that it finally has a water content of at most 20 ^ a. It turns out, however, that this process only results in a relatively small increase in capacity after formation.

from British Patent 504,559 is a traveller. known, after which the aluminum foil for a few minutes or! linger treated in distilled water at a temperature up to boiling point will. This often results in a significant increase in capacity after the Fortaierur. but, as mentioned above, that turns out to be achieved Capacity is not stable, which manifests itself in the fact that a lot of electrical ■ Energy is required to bring the film to tension.

According to the invention, eiiu?

Stable oxide skin on the aluminum foil is preserved and after forming. " a Kupasittitserhöhim /: and c; Lue reduction of the dielectric ■ 'Vfcrl; .u-. : n

BAD ORIGINAL 3Q98Q7 / Q969 ^% '"-

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reached, 'both of 5 to 10 ⁰ Jo with respect to film treated only in distilled water. In addition, the improvement is obtained that fewer coulombs are required in the reforming process.

The method for treating aluminum foil for electrolytic capacitors, which treatment is carried out in deionized water at elevated temperature up to the boiling point of the treatment liquid, is characterized according to the invention in that the treatment takes place in two baths, the first of which consists of deionized water and the second is a liquid, the clipboard 0,0t a lot and 0.5 wt. ■ "/" contains a normal or acid phosphate with a pH Veri 2 to 8.5, said second treatment before the formation of the dielectric Oxide layer and / or between the formation and the reforming is carried out, in the latter case optionally the film is held at a tension which is a fraction of the forming tension.

It should be noted that the treatment between the formation and reforming to a tension that is a fraction of the forming tension is known per se from the German patent specification I..IO3.IO4 is-Indem Now, according to the invention, a normal or acidic phosphate is added to the required solution, a considerable improvement in the so-called • Obtain a depolarization effect, as given below by way of an example will be shown. The phosphate mentioned above can be an electrolyte solution in the Forming composition used to-be added while also a Solution of the phosphate alone can be used.

Immersing a formed aluminum foil in a solution

of monoammonium phosphate without tension as the last processing, thus after the formation, is from the German Offenlegungsschrift 1 · 9? 5 · 914 "got *

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It has proved to be advantageous if the formation is performed after the pretreatment according to the invention in a Formierelektrolyten which contains besides the usual components an addition of phosphoric acid in an amount from 0.001 to 0.05 wt. Γο.

The invention is explained in more detail below using a few exemplary embodiments.
Example 1 ,

Made of aluminum foil with a thickness of 100 μm and

With a purity of>99> 98 ^c / ° Al, round disks with a diameter of ^ O mm were cut with a connecting lug. These discs was treated by the fact that they were 2 minutes immersed in deionized water of 100 ⁰ C. A portion of the wafers was then immersed 2, 4 or 6 min in deionized water to which was added 0.1 wt. Ammoniur. fo-bisphosphate [ΉΕ H PO) (pH = 4).

It was in a bath vcn 90 ⁰ C formed, the boric acid, ammonia (i) and optionally 0.004? ° phosphoric acid (il).

The disks were made with a current density of I50 mA per

Disk (= 7.5 mA / cm) and then for one hour at 4OO V nit molded final current value. There were two scribers each. formed at the same time in different baths under the same conditions as possible, the total current being kept constant at 300 mA during the forming process while the two substreams were checked separately. During the molding process, the common supply was supplied to a stabilized anode voltage device taken, with the partial streams also read separately could become.

After molding, the disks were wrapped in paper for a long time and then in a 0.75 % ammonium _{pentaborate solution;} r

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in water at a temperature of 30 ⁰ C on voltage, the current strength was 1 mA per disk. · '

The measurement results are summarized in Table I below. The capacitance was measured in relation to a cathode made of plat-iniea tem silver at a distance of 2 cm in an electrolyte (il) of the above , Composition measured.

TABLE I.

phi ;. 5759.

Sieaezeiten (Hin) Anmoniua Por-
ffiier-
liquid- Pormieren Impression. direct I. ■! Measurement Measurement after 1 week
and on tension
bring tg Π-0 on tension
bring
I. Time
(Min) entienis. bifoaf. solution speed Time current
(ΐαά) ■ Chap. tg d ( ^c / a) Kar.
(/ uF / cm ² ) 3.5 ι Span
tion
(Volts) 55 ■ water - I. (Min) 6th A> - 0.343 3.2 43 23
- 2 2 I. 3i 6th 0.354 3.7 0.372 3.2 42 13th i 4 ■ I. 32 6th 0.367 3.8 0.377 ht on
/ notice)
3.9 42 (10)
29 ί
2 2 TT
TT 31 6th
5 0.374 3.8
4.4 (never got
si
0.359 3.5 7th
428 16 _it • j
i ρ 4th II 30th
30th 5 0.356
0.359 4.4 0.364 3.0 430 31 5 II 31 6th 0.364 I 4.1 - 0.362 ^ don't come out !
Tension) 452 (10)
* a. S. II 30th 5 0.362 > 3.4 ' 169 2 29 0.362

OO

cn «0

(O

NJ Ni

QQ

cn

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This shows that with a treatment duration in the

Ammonium biphasic solution of 4 to 6 minutes an optimal value for the speed! speed is obtained, with that when clamping with constant current the forming tension is reached.

Samples 4 ^υη & 8 did not reach their voltage within a useful time, which can be seen from the fact that only a very low voltage was reached in these two samples after 10 minutes. A voltage should be reached dr.nn which is at least 90 ^c ß> the forming voltage. These samples were therefore terminated after 10 minutes.

Example 2

Aluminum disks of the aforesaid kind and having the above mentioned dimensions initially 2 Hinxjten were immersed in deionized water of ', 00 ⁰ C, "then contained at 400 V in a liquid, the boric acid unc. Ammonium and was heated to 90 ⁰ C, at a constant current strength of 35 mA / cm ² and then molded to 0.5 mA / cm ² .

Subsequently, according to the invention for 4 minutes,

a depolarization treatment with anodically connected foil disks with a voltage of +15 V (sample T-) and +200 V (sample 2) in a solution of '" ¹ OO ⁰ C, which contained 0.2 ^ ammonium dihydrogen phosphate, with a cathode made of stainless steel was used. Finally, it was reformed to a current of 0.2 raA / cm ". .

Comparison White some slices were depolarized by the fact that they were immersed between the formation and the Kachformierung for 4 minutes in deionized water of 100 ⁰ C (Sample j) j that some disks 4 minutes at a voltage of -I5 V in the above-mentioned solution _{ -: were obtained (sample 4), and that some slices 4 '

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PHN. 5769

^{Were held at 100 °} C. for minutes without tension in a solution of ammonium dihydrogen phosphate (sample 5).

It was made in an electrolyte solution containing glycol, boric acid

and ammonium pentaborate, the time was measured to test the film, in which a voltage of 400 V is reached at a constant current of 5 mA / cm became.

The measurement results are given in Table II below.

TABLE Il

sample Number of coul.
after formation Time
sample
komiat (lake.
on )in the
tension / capacity
(100Hz / uF / dm ²
/ W * 1 6370 15th - 29.8 2.8 2 29OO 26th 51.7 2.9 5 694O 23 32.1 5.1 4th I78OO ■ 27 30.5 5.2 VJl 5O8O 23 52.1 2.9

From this table it can be seen that Depolaris? .Erung ·

on a tension that is a fraction of the forming tension, faster al :; the other procedure is going on, and fast th when the stress is about 3 to 5 ° / ° of the forming stress (sample 1) compared to the case where the stress is about 50 ^ of the forming stress (sample 2) .

309807/0969

Claims (5)

ί 1 , J Process for the treatment of aluminum foil for electrolytic capacitors, in which the foil is immersed in deionized water at an elevated temperature up to the boiling point of the treatment liquid, characterized in that the treatment takes place in two baths, the first of which is made of deionized water, and the second consists of a liquid containing an amount between 0.01 and 0.5 wt. <fo of a normal or acidic phosphate with a pH value between 2 and 8.5, this second treatment prior to formation the dielectric oxide layer and / or between the formation and the reforming is carried out, in the latter case optionally the film is held at a voltage which is a fraction of the forming voltage. 2. The method according to claim 1, characterized in that the treatment between the formation and the Kachforraierung takes place at a voltage which is 3 to 5 f »of the forming voltage. 3. The method according to claim 1, characterized in that the forming is carried out after the pretreatment in a forming electrolyte which, in addition to the usual constituents, contains an addition of phosphoric acid in an amount between 0.001 and 0.05 wt. Fo . 4. Aluminum foil treated by the method of any preceding claim. . 5. 'Electrolytic capacitor made with an aluminum anode foil is provided, which by the method according to any one of claims 1 to 3 is treated. 30 9 807/0969