Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Utilizing nonaqueous bath
Reexamination Certificate
2001-12-10
2003-11-25
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Utilizing nonaqueous bath
C205S322000, C205S332000, C252S062200, C361S504000, C361S505000
Reexamination Certificate
active
06652729
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to electrolytes for use in electrolytic capacitors.
BACKGROUND OF THE INVENTION
With the development by Ruben (U.S. Pat. No. 1,710,073) in the mid 1920's of largely non-aqueous “working” or “fill” electrolytes containing glycerine and borax (sodium tetraborate decahydrate), the working voltage of aluminum electrolytic capacitors was extended to 200+ volts. Ruben's electrolytes also made possible the modern wound foil and paper separator construction in which the electrolyte is absorbed into the porous separator paper. The use of ammonia/glycerol borate is described on page 72 of the volume, “The Electrolytic Capacitor” Alexander M. Georgiev, Technical Books Division, Murray Hill Books, Inc., New York, 1945.
By the late 1920's, Ruben developed a series of fill electrolytes based upon ethylene glycol, boric acid, and ammonia solutions (U.S. Pat. No. 1,891,207). These so called “glycol-borate” fill electrolytes were found to be capable of satisfactory performance at operating voltages up to about 600 volts. In order to operate above about 450 volts, the ethylene glycol/glycerol and boric acid must be fully esterified and the water removed, and the maximum operating temperature of the capacitor limited to 65 C. or less.
In the 1930's, Lilienfeld patented a series of fill electrolytes (U.S. Pat. Nos. 2,013,564 and 1,986,779) based upon the condensation products of one or more polyethylene glycols with one or more polyfunctional acids to which finely powdered conductive solids, such as Lamp black, copper powder, or aluminum powder, and a small amount of an ionizable alkali metal salt were added. A typical composition described in these patents is a mixture of the polyester formed from triethylene glycol and boric acid with powdered aluminum (“aluminum black”) and a very small amount of borax.
The electrolytes of Lilienfeld, described above, have several advantages over earlier electrolytes. The polyesters formed between polyethylene glycols, such as triethylene glycol, and boric acid may be used to anodize to over 1,500 volts, which is far higher than the maximum voltage attainable with the ethylene glycol/boric acid polyester. The electrolytes of Lilienfeld are thick pastes in the normal operating range of high voltage capacitors and capacitors fabricated with them do not require separator papers or may employ reduced thickness and density of separator papers. Capacitors containing the electrolytes of Lilienfeld are much less susceptible to positive tab corrosion from anodic oxidation products than are capacitors containing ethylene glycol-based electrolytes (tab corrosion by the anodic oxidation products of ethylene glycol is discussed in the paper entitled: “The Potential For Positive Tab Corrosion In High Voltage Aluminum Electrolytic Capacitors Caused By Electrolytic Decomposition Products” Brian Melody, Proceedings, 13th Capacitor And Resistor Technology Symposium, Costa Mesa, Calif., pages 199-205, 1993).
Unfortunately, the fill electrolytes of Lilienfeld, described above, have some serious disadvantages from the standpoint of capacitor fabrication on a mass production basis. The consistency of the polyethylene glycol polyesters is such that it is very difficult to wet pre-rolled cartridges with them unless very high impregnation temperatures, i.e., approximately 150° C., are employed. The conductive solids added to reduce the effective resistivity of these electrolytes tend to separate from suspension when the electrolytes are heated to reduce the viscosity to levels which facilitate traditional vacuum impregnation. The combination of these viscosity and suspension properties is such that wet assembly of the capacitor cartridges or stacks is necessary resulting in much lower manufacturing rates and efficiency than is possible with the electrolytes of Ruben, described above. Additionally, the ionizable salts added to the polyethylene glycol polyesters in order to increase oxide film formation efficiency (see U.S. Pat. No. 1,986,779, page 4, Col 2, lines 40-60) tend to reduce the maximum breakdown voltage of the electrolyte.
Perhaps the largest drawback to the use of Lilienfeld's electrolytes is the need to employ anode foil which has been anodized so as to produce a duplex anodic film having a relatively thick layer of non-insulting oxide covering a thinner layer of barrier (insulating) oxide in order to prevent shorting due to the conductive particles present in the electrolyte. The thickness of duplex anodic oxides is such as to preclude the use of modem highly etched aluminum anode foils due to the blockage of the etch tunnels by the non-insulating portion of the duplex anodic oxide; only coarsely etched, relatively low capacitance foils lend themselves to use with Lilienfeld's polyester electrolyte compositions.
The maximum operating voltage of fill electrolytes capable of being use in connection with wound foil and paper cartridges remained at the approximately 600 volt level achieved by Ruben and Lilienfeld until the late 1980's. Clouse, et al., developed a series of fill electrolytes based upon substituted pyrrolidones and poly-pyrrolidones, some variations of which were found to be capable of operation at voltages in excess of 700 volts (U.S. Pat. No. 5,160,653, Example 8 and column 11, lines 22-36).
More recently, Marshall, et. al., developed a series of electrolytes based upon hydrogen bonded (fumed silica-polar solvent) solutions of certain acrylic monomers which are polymerized in situ (i.e., after absorption by the capacitor cartridges). The resulting electrolytes are claimed to be useful to voltages in excess of 700 volts. Unfortunately, the use of reactive monomeric materials may necessitate the use of glove boxes and other moisture control techniques. The polymerization initiators, such as persulfate compounds, may give rise to corrosive by-products, such as sulfates, which may negatively impact device reliability.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to a new electrolyte for electrolytic capacitors capable of use at very high voltage, that is 800 or more volts. In one embodiment, the electrolyte of the invention is relatively unaffected by exposure to the atmosphere. Another embodiment provides protection against damage due to hydration of the anodic oxide, and provides good service with aluminum foil of much lower purity than is normally used for the fabrication of electrolytic capacitors.
The present invention is directed to an electrolyte comprising a polyester condensation product of 2-methyl-1,3-propane diol and boric acid; and further comprising dimethyl amino ethoxy ethanol. The amine reduces the resistance of the electrolyte.
In another embodiment, the electrolyte further comprises ortho-phosphoric acid and at least one substituted pyrrolidone or lactone. The at least one pyrrolidone or lactone is preferably at least one of N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-hydroxy ethyl-2-pyrrolidone or 4-butyrolactone, more preferably, N-hydroxy ethyl-2-pyrrolidone. The ortho-phosphoric acid prevents hydration of anodic aluminum oxide in contact with the solution. The pyrrolidone or lactone reduces the resistance of the electrolyte.
In another embodiment, the electrolyte further comprises sodium silicate. The sodium silicate increases the breakdown voltage of the electrolyte.
Although water is generally not added to the electrolyte, minor amounts of water may be present due to the chemicals used.
The invention is further directed to a method of anodizing or healing any faults or cracks in the dielectric oxide covering the anode surfaces of capacitors impregnated with the electrolyte.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present invention as claimed.
DETAILED DESCRIPTION OF THE INVENTION
It is desirable to produce an electrolyte having a high breakdown voltage, preferably in excess of 800 volts. It is also d
Kinard John Tony
Melody Brian John
Wheeler David Alexander
Banner & Witcoff , Ltd.
Kemet Electronics Corporation
King Roy
Leader William T.
LandOfFree
Electrolyte for very high voltage electrolytic capacitors does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrolyte for very high voltage electrolytic capacitors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrolyte for very high voltage electrolytic capacitors will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3181920