Protective coating for electrolytic capacitors
A solid electrolytic capacitor that comprises an anode that contains a valve-action metal (e.g., tantalum, niobium, and the like) and a dielectric film overlying the anode is provided. The capacitor also comprises a protective coating overlying the dielectric film, wherein the protective coating contains a relatively insulative, resinous material. For example, in one embodiment, the resinous material can be a drying oil, such as olive oil, linseed oil, tung oil, castor oil, soybean oil, shellac, and derivatives thereof. The capacitor also comprises a conductive polymer coating overlying the protective coating. As a result of the present invention, it has been discovered that a capacitor can be formed that can have a relatively low leakage current, dissipation factor, and equivalents series resistance.
1. A method for forming a solid electrolytic capacitor, said method comprising:
forming an anode that contains a valve-action metal;
anodizing a surface of said anode to form a dielectric film;
forming a protective coating on said dielectric film, said protective coating containing a relatively insulative, resinous material; and
forming a conductive polymer coating.
2. A method as defined in claim 1 , wherein said resinous material contains esters of unsaturated or saturated fatty acids.
3. A method as defined in claim 1 , wherein said resinous material contains at least one drying oil or derivatives thereof.
4. A method as defined in claim 3 , wherein said drying oil is selected from the group consisting of olive oil, linseed oil, tung oil, castor oil, soybean oil, shellac, and derivatives thereof.
5. A method as defined in claim 1 , wherein said protective coating contains shellac or derivatives thereof.
6. A method as defined in claim 1 , wherein said protective coating is formed by from a solution containing said relatively insulative, resinous material.
7. A method as defined in claim 6 , wherein said solution further contains a non-aqueous solvent having a boiling point greater than about 80° C.
8. A method as defined in claim 6 , wherein said solution further contains a non-aqueous solvent having a boiling point greater than about 120° C.
9. A method as defined in claim 6 , wherein said solution further contains a non-aqueous solvent having a boiling point greater than about 150° C.
10. A method as defined in claim 6 , wherein said protective coating is formed by dipping said anode into said solution.
11. A method as defined in claim 1 , further comprising applying a curing agent to the protective coating before forming said conductive polymer coating.
12. A method as defined in claim 10 , wherein said curing agent contains sulfuric acid.
13. A method as defined in claim 1 , wherein said protective coating includes multiple layers.
14. A method as defined in claim 13 , wherein each protective coating layer is dried at a temperature ranging from about 30° C. to about 300° C.
15. A method as defined in claim 13 , wherein each protective coating layer is dried at a temperature ranging from about 50° C. to about 150° C.
16. A method for forming a solid electrolytic capacitor, said method comprising:
forming an anode that contains a valve-action metal;
anodizing a surface of said anode to form a dielectric film;
applying a solution to said anodized anode that contains a conductive polymer catalyst and a relatively insulative, resinous material; and
thereafter, applying a conductive monomer to said anodized anode, wherein said conductive monomer polymerizes to form a conductive polymer coating.
17. A method for forming a solid electrolytic capacitor, said method comprising:
forming an anode that contains a valve-action metal;
anodizing a surface of said anode to form a dielectric film;
applying a solution to said anodized anode that contains a conductive monomer and a relatively insulative, resinous material; and
thereafter, applying a conductive monomer catalyst to said anodized anode, wherein said conductive monomer polymerizes to form a conductive polymer coating.
18. A method for forming a solid electrolytic capacitor, said method comprising:
forming an anode that contains a valve-action metal;
anodizing a surface of said anode to form a dielectric film;
applying a solution to said anodized anode that contains a conductive monomer, a catalyst for said conductive monomer, and a relatively insulative, resinous material, wherein said conductive monomer polymerizes to form a conductive polymer coating.