Búsqueda Imágenes Maps Play YouTube Noticias Gmail Drive Más »
Iniciar sesión
Usuarios de lectores de pantalla: deben hacer clic en este enlace para utilizar el modo de accesibilidad. Este modo tiene las mismas funciones esenciales pero funciona mejor con el lector.

Patentes

  1. Búsqueda avanzada de patentes
Número de publicaciónUSRE31743 E
Tipo de publicaciónConcesión
Número de solicitudUS 06/294,251
Fecha de publicación20 Nov 1984
Fecha de presentación19 Ago 1981
Fecha de prioridad15 Sep 1980
Número de publicación06294251, 294251, US RE31743 E, US RE31743E, US-E-RE31743, USRE31743 E, USRE31743E
InventoresMulk R. Arora, John J. Randall, Jr.
Cesionario originalSprague Electric Company
Exportar citaBiBTeX, EndNote, RefMan
Enlaces externos: USPTO, Cesión de USPTO, Espacenet
AC Etching of aluminum capacitor foil
US RE31743 E
Resumen
Aluminum electrolytic capacitor foil is etched in a bath containing 0.7 to 2.0 M hydrochloric acid, 0.2 to 0.5 M hydrated aluminum trichloride, and 0.02 to 0.4 M phosphate ion while subjected to the action of alternating current at 35° to 55° C.
Imágenes(1)
Previous page
Next page
Reclamaciones(4)
    What is claimed is: .[.1. A process for the electrolytic etching of aluminum electrolytic capacitor foil comprising passing the foil between electrodes supplied with alternating current in a bath containing 0.7 to 2 moles/liter hydrochloric acid, 0.2 to 0.5 moles/liter hydrated aluminum trichloride, and 0.02 to 0.4 moles/liter phosphate ion at a temperature of 35° to 55° C..]. .[.2. A process according to claim 1 wherein the anodic current density is 1.6 to 4 amps/in2 and the
  1. frequency of the alternating current is 20 to 40 Hz..]. 3. A process according to claim .[.1.]. .Iadd.8 .Iaddend.wherein the concentration of said hydrochloric acid is 1.4 M, the concentration of said hydrated aluminum chloride is 0.4 M, the concentration of said phosphate ion is 0.2
  2. M, and said temperature is 45° C. 4. A process according to claim .[.1.]. .Iadd.8 .Iaddend.wherein the etching time is 2 to 6 minutes. .Iadd.5. In a method for producing electrodes for use in an aluminum electrolytic capacitor whose effective surface area is enlarged by electrochemically etching aluminum foil in an aqueous solution consisting essentially of hydrogen chloride and an additive capable of anodizing said aluminum foil with electric power supplied in alternating current, an improvement characterized in that the concentration of the hydrogen chloride in said solution is set at a range between 0.7N and 2N, the concentration of said additive is set at a range between 0.02 mole/liter and 0.4 mole/liter, the frequency of said alternating current power supply is ranging from 20 Hz to 40 Hz and its current density is ranging from 1.6 A/in2 to 4 A/in2, while the temperature of said solution is
  3. being maintained at 30° to 45° C. .Iaddend. .Iadd.6. A method as claimed in claim 5, further characterized in that said additive is selected from an inorganic acid capable of anodizing (forming an oxide protecting layer on the surface of) aluminum. .Iaddend. .Iadd.7. A method as claimed in claim 6, further characterized in that said additive is
  4. phosphoric acid. .Iaddend. .Iadd.8. A process for the electrolytic etching of aluminum electrolytic capacitor foil comprising passing the foil between electrodes supplied with alternating current in a bath consisting essentially of 0.7 to 2 moles/liter hydrochloric acid, 0.2 to 0.5 moles/liter hydrated aluminum trichloride, and 0.02 to 0.4 moles/liter phosphate ion at a temperature of 30° to 45° C. and an alternating current frequency of 20 to 40 Hz. .Iaddend. .Iadd.9. A process according to claim 1 wherein the anodic current density is 1.6 to 4 amps/in2. .Iaddend.
Descripción
BACKGROUND OF THE INVENTION

This invention relates to the etching of aluminum foil for electrolytic capacitors, and in particular to a process utilizing alternating current and a chloride electrolyte bath containing phosphate ions.

AC etching has been used to produce aluminum articles such as lithographic plates and capacitor foil. It also has been used to electropolish aluminum articles prior to metal plating.

The prior art has discussed the difficulties in obtaining an even or uniform etch structure and has overcome these difficulties in a variety of ways, e.g., interrupting the etch process to apply protective coatings, carrying out the etch process in stages of differing degrees of aggressiveness, and using additives in the electrolyte bath to control pit size or to increase mechanical strength of the foil. Another problem has been to prevent the precipitation of aluminum hydroxide, formed during etching, on or into the etched surfaces.

The resolution of these problems has led to processes in which the etch conditions are carefully controlled to provide the desired increase in surface area and, particularly for capacitor foil, little change in mechanical strength.

SUMMARY OF THE INVENTION

A process of etching aluminum capacitor foil utilizes AC current to give a uniform etch structure while maintaining the strength of the foil. The process also provides a greater etch pit density than prior art processes. The above results are accomplished by using an etchant solution containing hydrochloric acid, hydrated aluminum trichloride, and a phosphate ion source at 35° to 55° C. and alternating current of 20 to 40 Hz frequency.

The concentration of the hydrochloric acid in the etchant is 0.7 to 2.0 M to provide strongly acidic conditions that prevent the formation and precipitation of aluminum hydroxide on the foil. The concentration of the hydrated aluminum trichloride is 0.2 to 0.5 M to prevent wide variations of aluminum ion concentration, especially with fresh etchant solution. The concentration of phosphate ion is 0.02 to 0.4 M to give the desired uniformity and etch density (number of pits/unit area of foil). It is postulated that the phosphate ion serves to passivate sites that have already been started so that etching will proceed at different sites, giving the desired etch density, rather than concentrating at started sites. More than 0.4 M phosphate ion was found to be detrimental, as it appears to cause excessive inhibition of new etch sites.

The current density is maintained at 1.6 to 4 A/in2 to provide the desired number of sites. If the current density is too low, i.e., below 1.6 A/in2, there will not be the desired number of sites; if too high, i.e., above 4 A/in2, the etch structure becomes fragile leading to a smooth, polished surface rather than an etched one. Foil is also thinned in the latter case. The frequency of the alternating current is maintained at 20 to 40 Hz as this frequency gives etched foil with optimum capacitance. The voltage, a function of current density and etch cell design, is ±7 V. With a different cell design, the voltage will differ also.

The temperature of the etchant solution is maintained at 35° to 55° C. to provide pores of suitable size and density. Lower temperatures result in fewer, larger pores while higher temperatures give more pores but narrower pits and lower capacitance. Etching time is 2 to 6 min.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE shows foil being etched by the process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aluminum foil 10 is passed over roller 20 into tank 30 containing the hydrochloric acid-aluminum chloride-phosphate etchant solution of the present invention. Electrodes 31, 32, 33, 34, 35, 36 and 37 are connected to an AC source (not shown). Foil 10 passes between electrodes 31 and 32 and under roller 21, thence between electrodes 32 and 33 and out of the etchant over roll 22, back into the etchant between electrodes 33 and 34, under roller 23, between electrodes 34 and 35, over roller 24, between electrodes 35 and 36, under roller 25 and finally between electrodes 36 and 37 out of tank 30 and over roller 26.

This particular arrangement provides for a minimum number of electrodes as electrodes 31 and 32 form a pair as do 32 and 33, 33 and 34, 34 and 35, 35 and 36, and 36 and 37. A complete pass is defined as the path between the adjacent rolls that are out of the tank, i.e. between 20 and 22, 22 and 24, and 24 and 26. Hence, in the arrangement shown, there are three complete passes utilizing a total of seven electrodes. More electrodes may be used for a greater number of passes per tank or other arrangements may be used. The rolls 21-25 are preferably the same size as the distance between electrodes and so arranged that the foil passes vertically between electrodes.

The etched foil obtained by the method of the present invention has a metallic core, that gives good mechanical properties and low-temperature capacitance retention.

In the examples below, soft foil of 99.99% purity was used. Hard foil can be etched by this process, as can foil of different purity, but satisfactory capacitance is obtained without resorting to hard foil.

EXAMPLE 1

A series of runs were made using as etchant a solution of 1.5 M hydrochloric acid, 0.2 M aluminum chloride, and 0.02 M ammonium phosphate. The frequency of the alternating current was 45 Hz. Soft 2.9 mil aluminum foil was used; thickness refers to final thickness in mils. Capacitance per unit area (Cap) is given in microfarads per square inch, μF/in2, and etch time in minutes.

              TABLE 1______________________________________                  Temp.  Wt-loss                               Thick- 30 VSample Amps/in.sup.2           Time   °C.                         %     ness   Cap______________________________________1     2.03      2.5    62.5   29.9  2.6    36.82     2.03      3.0    62.5   36.7  2.6    46.03     3.05      1.8    63.0   29.3  2.5    32.74     3.05      2.0    63.0   33.1  2.5    39.65     1.02      6.0    60.0   31.7  2.1    20.0______________________________________
EXAMPLE 2

Another series of runs were made at a frequency of 30 Hz and a current density of 2.8 A/in2. The etchant solution was 1.4 M hydrochloric acid, 0.4 M aluminum trichloride, and 0.2 M phosphoric acid. Soft 3.3 mil foil was used, and thickness given is the final thickness. The other units are as given in Example 1.

              TABLE 2______________________________________         Temp.     Wt-lossSample Time   °C.                   %     Thickness 30 V Cap______________________________________1      2.7    44.5      29.2  3.15      71.22      3.0    44.5      31.7  3.10      64.83      3.3    44.0      37.5  3.05      81.5______________________________________
EXAMPLE 3

Foil 2.9 mil thick was etched at 30° C., at 30 Hz and 3 A/in2 current density for 2.5 min in an etchant solution of 2.2 M hydrochloric acid, 0.6 M aluminum trichloride, and 0.4 M phosphoric acid. Higher hydrochloric acid and aluminum chloride concentrations gave less reproducible results. Average results are presented below.

              TABLE 3______________________________________Thickness      Wt-loss % 30 V Cap______________________________________2.75 mil       27.1      68.7______________________________________
EXAMPLE 4

In this example, average results are presented for 2.9 mil thick foil etched at 70° C., 3.5 A/in2 current density, 30 Hz frequency for 2.2 min in an etchant solution of 0.75 M hydrochloric acid, 0.2 M aluminum trichloride, and 0.11 M phosphoric acid.

              TABLE 4______________________________________Thickness      Wt-loss % 30 V Cap______________________________________2.7 mil        30.5      53.7______________________________________
EXAMPLE 5

In this example, etching was carried out at 4 A/in2 current density, 30 Hz, and 45° C. for 1.9 min using an etchant solution of 1.3 M hydrochloric acid, 0.36 M aluminum trichloride, and 0.2 M phosphoric acid. Average results on 2.9 mil foil are given below.

              TABLE 5______________________________________Thickness      Wt-loss % 30 V Cap______________________________________2.7 mil        35.3      71.2______________________________________
EXAMPLE 6

This run was carried out at 20 Hz frequency, 2.8 A/in2 current density, and 45° C. using an etchant solution of 1.4 M hydrochloric acid, 0.39 M aluminum trichloride, and 0.22 M phosphoric acid. Foil 2.9 mil thick was etched at two different etch times.

              TABLE 6______________________________________Etch Time Thickness    Wt-loss % 30 V Cap______________________________________  3 min   2.65         36.7      73.63.5 min   2.45         42.7      80.2______________________________________

The range of etchant solution composition and process variables that give the desired etching, as reflected by capacitance, is 0.7 to 2 M hydrochloric acid, 0.2 to 0.5 M aluminum trichloride, 0.02 to 0.4 M phosphate ion, 35° to 55° C., 20 to 40 Hz frequency and 1.6 to 4 amps/in2 current density.

Citas de patentes
Patente citada Fecha de presentación Fecha de publicación Solicitante Título
US3193485 *28 May 19646 Jul 1965Plessey Co LtdElectrolytic treatment of aluminium for increasing the effective surface
US3887447 *27 Sep 19733 Jun 1975Alcan Res & DevProcess of electrograining aluminium
US4276129 *25 Jun 198030 Jun 1981Matsushita Electric Industrial Co., Ltd.Method for producing foil electrodes for electrolytic capacitor
US4297184 *19 Feb 198027 Oct 1981United Chemi-Con, Inc.Method of etching aluminum
JP4536701B2 Título no disponible
JP4636291B2 Título no disponible
JP4940537B2 Título no disponible
JP5264659B2 Título no disponible
JP45036701A * Título no disponible
JP46036291A * Título no disponible
JPS4940537A * Título no disponible
JPS5264659A * Título no disponible
JPS50159430A * Título no disponible
JPS52133043A * Título no disponible
JPS52141444A * Título no disponible
Citada por
Patente citante Fecha de presentación Fecha de publicación Solicitante Título
US72569837 Nov 200314 Ago 2007Nippon Chemi-Con CorporationElectrolytic capacitor
US7262953 *7 Nov 200328 Ago 2007Nippon Chemi-Con CorporationElectrolytic capacitor
US74301087 Nov 200330 Sep 2008Nippon Chemi-Con CorporationElectrolyte for electrolytic capacitor and electrolytic capacitor containing the same
US74925727 Nov 200317 Feb 2009Nippon Chemi-Con CorporationElectrolytic capacitor manufacturing method
US20060098384 *7 Nov 200311 May 2006Nippon Chemi-Con Corporation Tokyo JapanElectrolytic capacitor
US20060127566 *7 Nov 200315 Jun 2006Nippon Chemi-Con CorporationElectrolytic capacitor manufacturing method
US20060152882 *7 Nov 200313 Jul 2006Masayuki TakedaElectrolytic capacitor
US20060164791 *7 Nov 200327 Jul 2006Masashi OzawaElectrolytic capacitor
US20060250751 *7 Nov 20039 Nov 2006Masashi OzawaElectrolyte for electrolytic capacitor and electrolytic capacitor containing the same
US20080030926 *10 Jul 20077 Feb 2008Masashi OzawaElectrolytic capacitor
US20140326595 *4 Nov 20136 Nov 2014Chung Shan Institute of Science and Technology, Armaments Bureau, Ministry of National DefenseRoll-to-roll electrochemical polish apparatus
USRE3251228 Jun 198229 Sep 1987Matsushita Electric Industrial Co., Ltd.Method for producing foil electrodes for electrolytic capacitor
Clasificaciones
Clasificación de EE.UU.205/139, 205/658, 205/682, 205/153
Clasificación internacionalH01G9/04, H01G9/055, C25F3/04
Clasificación cooperativaC25F3/04, H01G9/055
Clasificación europeaC25F3/04, H01G9/055
Eventos legales
FechaCódigoEventoDescripción
5 Abr 1993ASAssignment
Owner name: UNITED CHEMI-CON MANUFACTURING, INC., NORTH CAROLI
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:SPRAGUE ELECTRIC COMPANY;REEL/FRAME:006483/0442
Effective date: 19920903