Abstract:
An electrolytic capacitor having an electrolyte consisting essentially of a solution in ethylene glycol of 8-12% by weight of ammonium benzoate, 2.5-4% by weight of ammonium azelate, 1.5-3% by weight of ammonium sebaccic, and 2-3% by weight of water.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a new and novel electrolytic capacitor particularly useful for mid-volt applications. The term &#34;mid-volt&#34; being defined for the purposes of the instant invention as the 100-325 volt range. 
     Electrolytic capacitors that are frequently employed for use in mid-volt applications present the problems of employing as electrolytes materials that are environmentally undesirable. Such materials include dimethylforamide, dimethylacetamide, boric acid and other environmentally undesirable materials. 
     Also many electrolytic capacitors that are used in the mid-volt range suffer from the deficiency of having relatively poor properties when employed at elevated temperatures, for example, at temperatures of from 90° C. to 120° C. Additionally, some of these known capacitors have undesirably short life usefulness. Japanese Kokai No. 56-51821 shows a low resistivity electrolyte for use in capacitors having a good chemical stability. However, the electrolytes shown include as an essential ingredient a boric acid or a salt of boric acid which are considered to be environmentally undesirable materials. 
     BRIEF SUMMARY OF THE INVENTION 
     A principal object of this invention is to provide an electrolytic capacitor free of environmentally undesirable ingredients which is particularly useful for the mid-volt range. 
     These and other objects of the invention will be apparent from the description that follows. 
     According to the invention, the applicant has developed a new and novel electrolytic capacitor comprising an anode provided with a dielectric insulated layer, a cathode and an electrolyte, the electrolyte consisting essentially of a solution in ethylene glycol of the ammonium salts of sebaccic, azelaic and benzoic acids and a minor amount of water. 
     The capacitors of the invention have the advantage of being free of environmentally undesirable ingredients. Additionally these capacitors have low internal resistances and demonstrate a high capacitance and a high degree of capacitive retention even when operating at a high operating temperature for an extended period of time. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be described in greater detail with reference to the following examples and tables. 
     In the novel capacitors of the invention, the anode and cathode may be formed of such known valve metals as aluminum, titanium, niobium, and tantalum. 
     Preferably the capacitors of the invention are aluminum impregnated cartridge type capacitors of conventional design. In such a capacitor an aluminum foil anode and an aluminum foil cathode, at least one of which has an oxide film thereupon is separated by a paper spacer impregnated with the electrolyte and wound into a cylindrical shape and sealed in a container of aluminum. 
     It is found that in general the most improved results are produced with an electrolyte of the invention containing 8-12% by weight of ammonium benzoate, 0.5-4.5% by weight of ammonium azelate, 1.5-3.5% of ammonium sebacate and 2-3% of water dissolved in ethylene glycol. In a particularly useful embodiment the electrolyte of the invention contains about 2% by weight of ammonium zebacate, 2.5% of ammonium azelate, 5% of ammonium benzoate and 2% by weight of water. 
    
    
     EXAMPLE 
     An electrolyte was prepared by dissolving 2% by weight of ammonium sebacate, 2.5% by weight of ammonium azelate, 5% by weight of ammonium benzoate and 2% by weight of dionized water, 89.5% by weight of ethylene glycol at 85° C. 
     The resultant electrolyte exhibited the following properties, resistivity at 25° C.=396 ohms-cm, pH at 100% concentration=6.52, pH at 10% concentration=5.47, K.F. % H 2  O=3.0% scintillation voltage at 85° C.=340 volts. 
     A number of capacitors were prepared and subjected to life tests. Each capacitor consisted of an anode foil of aluminum provided with a dielectric oxide layer, in a cathode aluminum foil. The anode foil was etched and formed at 325 volts and the cathode foil was etched and formed at 9 volts. Both the anode foil and the cathode foil were provided with a contact lug and together were formed into a roll and separated from each other by a separator of porous paper impregnated with the electrolyte of the example and sealed in an aluminum container. The resultant capacitors had a diameter of 1.375 and a length of 3.125. They were all aged at 260 V at 85° C. 
     The following tables show the results of life tests carried out at 105° C. and 200 volts DC on a number of properties of these capacitors. 
     
                                           TABLE 1__________________________________________________________________________(0 Hours)Unit    IL 5  CAP(UF)        % D           ESR  % CAP RT                       REF ESR                              WEIGHT                                    % REF WT.__________________________________________________________________________1   0.045  432   2.46           75.60                100.000                       100.000                              96.49 100.002   0.016  433   2.62           80.10                100.000                       100.000                              91.35 100.003   0.019  429   2.31           71.50                100.000                       100.000                              90.00 100.004   0.018  427   2.42           75.10                100.000                       100.000                              96.37 100.005   0.028  424   2.66           83.20                100.000                       100.000                              91.40 100.006   0.048  442   2.39           71.70                100.000                       100.000                              98.54 100.007   0.017  455   2.49           72.60                100.000                       100.000                              97.67 100.008   0.012  424   3.15           98.40                100.000                       100.000                              93.27 100.009   0.017  437   2.47           75.00                100.000                       100.000                              90.70 100.0010  0.019  447   2.37           70.30                100.000                       100.000                              99.72 100.0011  0.015  436   2.39           72.60                100.000                       100.000                              93.85 100.00AVG 0.023  435   2.54           77.54                100.000                       100.000                              94.57 100.00__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________1500 TEST HOURS COMPLETEDUnit    IL 5  CAP(UF)        % D           ESR  % CAP RT                       % REF ESR                              WEIGHT                                    % REF WT.__________________________________________________________________________1   0.006  432   2.47           75.80                99.845 100.265                              96.19 99.682   0.006  432   2.68           82.20                99.808 102.622                              91.05 99.673   0.006  428   2.40           74.50                99.851 104.196                              89.68 99.654   0.006  426   2.50           77.70                99.801 103.462                              96.08 99.695   0.006  424   2.64           82.60                99.995  99.279                              91.12 99.706   0.006  441   2.47           74.40                99.824 103.766                              98.28 99.737   0.005  455   2.60           75.70                99.917 104.270                              97.36 99.698   0.005  421   2.42           76.30                99.340  77.541                              93.03 99.749   0.005  437   2.60           79.10                99.911 105.467                              90.41 99.6710  0.006  447   2.51           74.60                99.920 106.117                              99.44 99.7111  0.005  436   2.50           76.00                100.030                       104.683                              93.55 99.68AVG 0.006  434   2.53           77.17                99.840 101.061                              94.20 99.69__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________4500 TEST HOURS COMPLETEDUnit    IL 5  CAP(UF)        % D           ESR  % CAP RT                       % REF ESR                              WEIGHT                                    % REF WT.__________________________________________________________________________1   0.005  431   2.59           79.70                99.688 105.423                              95.79 99.272   0.005  432   2.79           85.70                99.628 106.991                              90.66 99.253   0.005  427   2.52           78.40                99.657 109.650                              89.28 99.204   0.005  425   2.61           81.30                99.602 108.256                              95.62 99.225   0.005  423   2.94           92.30                99.769 110.938                              90.70 99.246   0.005  440   2.58           77.60                99.627 108.229                              97.91 99.367   0.005  454   2.67           78.00                99.732 107.438                              96.97 99.298   0.005  421   2.52           79.40                99.208  80.691                              92.68 99.379   0.005  436   2.69           81.70                99.771 108.933                              90.03 99.2610  0.005  446   2.73           81.20                99.736 115.505                              99.01 99.2911  0.005  435   2.64           80.30                99.851 110.606                              93.11 99.21AVG 0.005  434   2.66           81.42                99.661 106.605                              93.80 99.27__________________________________________________________________________ 
    
     In these tables, IL 5 is the leakage current in milliamps after 5 minutes; CAP is the capacitance in microfarads, %D is the loss factor; ESR is the equivalent series resistance in ohms; %CAP RT is the percentage of the initial capacitance retained; %REF ESR is the percentage of the initial equivalent series resistance; WEIGHT is the weight of the capacitor in grams and %REF WT. is the percentage of the initial weight of the capacitor. 
     As these tests show, even after the life tests as long as 4500 hours, the capacitors of the invention exhibited excellent retention capacitance with only very slight increases in equivalence of series resistances together with almost imperceptible increases in the loss tangent. 
     It will be apparent to those skilled in the art that various modifications of the present invention may be made without departing from its scope as defined by the following claims.