Method for producing conductive polymer and method for producing solid electrolyte capacitor

Abstract

A solid electrolytic capacitor is obtained by a method comprising dissolving a polymerizable material for being converted into a conductive polymer in a water-soluble organic solvent to obtain a solution, adding the solution to water while homogenizing the solution to obtain a sol, immersing an anode body having a dielectric layer in the surface of the anode body in the sol, and applying voltage using the anode body as a positive electrode and a counter electrode as a negative electrode placed in the sol to electropolymerize the polymerizable material. An electropolymerizable liquid for producing a conductive polymer, the liquid composed of a sol comprising water, a water-soluble organic solvent, and a polymerizable material for being converted into the conductive polymer.

Claims

1. A method for producing a solid electrolytic capacitor, wherein the method comprises performing a production method of conductive polymer in the presence of an anode body, which has a dielectric layer in the surface of the anode body, to form a conductive polymer layer on the dielectric layer in the surface of the anode body, wherein the production method of conductive polymer comprises dissolving a polymerizable material to be converted into the conductive polymer in a water-soluble organic solvent to obtain a solution, mixing the solution with water to obtain a sol, and electropolymerizing the polymerizable material in the sol.

2. The method according to claim 1, wherein the electropolymerization is performed using the anode body as a positive electrode and a counter electrode as a negative electrode which are placed in the sol.

3. The method according to claim 1, wherein the method further comprises immersing the anode body in a water-soluble organic solvent solution comprising the polymerizable material, pulling the anode body out of the solution, and then immersing the anode body in the sol.

4. The method according to claim 1, wherein the polymerizable material is at least one selected from the group consisting of compounds having a thiophene skeleton and compounds having a pyrrole skeleton.

5. The method according to claim 1, wherein a content of the polymerizable material is from 2 g/L to 7 g/L in the sol.

6. The method according to claim 1, wherein the mixing is conducted by adding the solution to the water.

7. The method according to claim 1, wherein a dispersoid in the sol has a 50% diameter of 0.5 nm to 1,000 nm in volumetric basis particle size cumulative distribution.

8. The method according to claim 1, wherein the sol further comprises a dopant.

9. The method according to claim 1, wherein the water-soluble organic solvent is polyhydric alcohols or polyalcohol derivatives.

10. The method according to claim 1, wherein the water-soluble organic solvent has a boiling point of not less than 150° C.

Description

EXAMPLES

(1) The present invention is explained in more detail below with reference to Examples. Note that they are merely examples for explanation, and the present invention is not limited thereto.

(2) The characteristics, etc., were measured as follows.

(3) (Capacitance)

(4) Conductor wires connected to an LCR meter (produced by Agilent Technologies) were brought into contact with the conductor layer of a capacitor element and a lead wire implanted in the capacitor element. The capacitance at 120 Hz was measured by the LCR meter.

(5) (Leakage Current)

(6) Voltage of 2.5 V was applied to a capacitor element at room temperature. When 30 seconds passed from the start of voltage application, the electric current value (leakage current) of a circuit of the plus terminal of a power supply across the lead wire of the capacitor element, the conductor layer of the capacitor element, and the minus terminal of the power supply was measured.

(7) (ESL)

(8) Conductor wires connected to an LCR meter (produced by Agilent Technologies) were brought into contact with the conductor layer of a capacitor element and a lead wire implanted in the capacitor element. ESL at 500 kHz was measured by the LCR meter.

Example 1

(9) [Preparation of Electropolymerizable Liquid]

(10) In 250 parts by mass of ethylene glycol, 3.7 parts by mass of 3,4-Ethylenedioxythiophene was dissolved to prepare a solution. The solution was added to 525 parts by mass of water while homogenizing the solution with a homogenizer (NS-51, produced by Microtec Co., Ltd.). Then, 7.5 parts by mass of anthraquinonesulfonic acid dopant was added while homogenizing. The thus-obtained sol was homogeneous and transparent. The sol was placed in a stainless steel container as an electropolymerizable liquid.

(11) Tantalum powder having 250,000 CV/g was compressed together with tantalum wires (lead wires) having a diameter of 0.29 mm. The compacts were vacuum-fired at 1,290 ° C. for 30 minutes, thereby obtaining a plurality of sintered bodies having a size of 1.0 mm×1.5 mm×4.5 mm. Each of the lead wires having a diameter of 0.29 was implanted in the center of the 1.0 mm×1.5 mm surface of each of the obtained sintered bodies so that 8 mm of the lead wire projected from the sintered body and 3.2 mm of the lead wire was buried in the sintered body. A tetrafluoroethylene washer having an inner diameter of 0.26 mm, an outer diameter of 0.80 mm, and a thickness of 0.20 mm was attached to the lead wire in a position 0.20 mm apart from the sintered body.

(12) [Chemical Conversion Treatment]

(13) The sintered body was immersed in a 2% by mass phosphoric acid aqueous solution so that the entire sintered body sank in the solution and the upper surface of the washer was in contact with the solution. And electrolytic oxidation was performed at 80 ° C. at 8 V for 300 minutes, thereby chemically converting the surface layer of the sintered body into a dielectric.

(14) The sintered body formed with a dielectric layer was immersed in a 10% by mass iron (III) toluenesulfonate aqueous solution. The sintered body was pulled out of the aqueous solution, and dried at room temperature. The immersion-drying operation was further repeated 4 times (5 times in total).

(15) Then, the sintered body was immersed in a 20% by mass 3,4-ethylenedioxythiophene monomer ethanol solution. The sintered body was pulled out of the ethanol solution, and dried at room temperature.

(16) [Electropolymerization]

(17) Subsequently, the sintered body was immersed in the electropolymerizable liquid so that the entire sintered body sank in the liquid and the lower surface of the washer was in contact with the liquid. Using the lead wire as a positive and the stainless steel container as a negative, electropolymerization was performed by applying electric current at room temperature first at 40 μA for 15 minutes, then at 80 μA for 45 minutes, and finally at 120 μA for 10 minutes. The sintered body was pulled out of the electropolymerizable liquid, washed, and dried (1st treatment). This immersion—electropolymerization—washing—drying operation was performed once again (2nd treatment).

(18) The immersion—electropolymerization—washing—drying operation was performed twice in the same manner as above, except that the electric current pattern was changed to 80 μA for 30 minutes, and then 120 μA for 30 minutes (3rd and 4th treatments).

(19) The immersion—electropolymerization—washing—drying operation was performed twice in the same manner as above, except that the electric current pattern was changed to 120 μA for 30 minutes, and then 140 μA for 40 minutes (5th and 6th treatments).

(20) The immersion—electropolymerization—washing—drying operation was performed once in the same manner as above, except that the electric current pattern was changed to 80 μA for 15 minutes, then 60 μA for 50 minutes, and finally 40 μA for 30 minutes (7th treatment).

(21) Thus, a conductive polymer was formed on the dielectric layer on the surface of the sintered body.

(22) [Additional chemical conversion treatment]

(23) Thereafter, the sintered body with a conductive polymer formed on the dielectric layer was immersed in a 2% by mass phosphoric acid aqueous solution, and electrolytic oxidation was performed at 80° C. at 5 V for 20 minutes.

(24) Subsequently, a carbon paste layer and a silver paste layer were sequentially laminated, thereby producing a capacitor element.

(25) The two capacitor elements were placed in parallel in the same direction so that the 1.5 mm×4.5 mm surface of each element was in contact with a cathode part of a lead frame having a thickness of 100 μm made of a copper alloy having the under plating layer of 0.6-μm-thick nickel and the outermost plating layer of 5-μm-thick tin, and they were connected with silver paste. The lead wire cut into a predetermined size was connected by welding to an anode part of the lead frame. The capacitor elements were sealed with a resin, while leaving a part of the lead frame unsealed. The lead frame protruding from the side of the resin-sealed body was cut at a predetermined position, and folded twice along the resin-sealed body. Thus, 320 chip-like solid electrolytic capacitors were obtained in which each capacitor has a size of 7.3 mm×4.3 mm×1.8 mm and a rating of 2.5 V and has a cut end of the lead frame on the undersurface of the resin-sealed body. The yield of capacitors with an LC of 0.1 CVμA or less was 90% or more. Table 1 shows the performance of the obtained capacitors. The numerical values in Table 1 are the average value of capacitors with a leakage current (LC) of 0.1 CVμA or less among the produced 320 capacitors. The capacitance was measured at 120 Hz, and ESL was measured at 500 kHz. The measurements were performed using an LCR meter produced by Agilent Technologies.

Comparative Example 1

(26) To obtain a mixed solvent, 250 parts by mass of ethylene glycol, 525 parts by mass of water, and 7.5 parts by mass of anthraquinonesulfonic acid dopant were mixed together. To the mixed solvent, 3.7 parts by mass of 3,4-ethylenedioxythiophene was added, and homogenized with a homogenizer (NS-51, produced by Microtec Co., Ltd.). The 3,4-ethylenedioxythiophene was not completely dissolved, and a solution with two separate phases was obtained. Solid electrolytic capacitors were obtained in the same manner as in Example 1, except that the solution was used as the electropolymerizable liquid. The yield of capacitors with an LC of 0.1 CVμA or less was 90% or more. Table 1 shows the performance of the obtained capacitors.

Example 2

(27) Solid electrolytic capacitors were obtained in the same manner as in Example 1, except that 250 parts by mass of ethylene glycol was changed to 388.5 parts by mass of propylene glycol, the amount of 3,4-ethylenedioxythiophene was changed to 4.5 parts by mass, the amount of water was changed to 375 parts by mass, and the amount of anthraquinonesulfonic acid dopant was changed to 9.2 parts by mass. The electropolymerizable liquid was a homogeneous and transparent sol. The yield of capacitors with an LC of 0.1 CVμA or less was 90% or more. Table 1 shows the performance of the obtained capacitors.

Comparative Example 2

(28) Solid electrolytic capacitors were obtained in the same manner as in Comparative Example 1, except that 250 parts by mass of ethylene glycol was changed to 388.5 parts by mass of propylene glycol, the amount of 3,4-ethylenedioxythiophene was changed to 4.5 parts by mass, the amount of water was changed to 375 parts by mass, and the amount of anthraquinonesulfonic acid dopant was changed to 9.2 parts by mass. The electropolymerizable liquid was a solution with two separate phases. The yield of capacitors with an LC of 0.1 CVμA or less was 90% or more. Table 1 shows the performance of the obtained capacitors.

Example 3

(29) Solid electrolytic capacitors were obtained in the same manner as in Example 1, except that 3.7 parts by mass of 3,4-ethylenedioxythiophene was changed to 3.3 parts by mass of pyrrole, and the amount of anthraquinonesulfonic acid dopant was changed to 7.0 parts by mass. The electropolymerizable liquid was a homogeneous and transparent sol. The yield of capacitors with an LC of 0.1 CVμA or less was 90% or more. Table 1 shows the performance of the obtained capacitors.

Comparative Example 3

(30) Solid electrolytic capacitors were obtained in the same manner as in Comparative Example 1, except that 3.7 parts by mass of 3,4-ethylenedioxythiophene was changed to 3.3 parts by mass of pyrrole, and the amount of anthraquinonesulfonic acid dopant was changed to 7.0 parts by mass. The electropolymerizable liquid was a solution with two separate phases. The yield of capacitors with an LC of 0.1 CVμA or less was 90% or more. Table 1 shows the performance of the obtained capacitors.

(31) The results of the Comparative Examples suggest that the amounts of the above polymerizable materials are in excess of their solubility in the solvents, and are basically undissolved amounts. However, all of the electropolymerizable liquids obtained in the Examples are homogeneous and transparent. Accordingly, it was determined that the electropolymerizable liquids obtained in the Examples were “sols,” rather than “solutions.”

(32) TABLE-US-00001 TABLE 1 Capacitance ESL [μF] [nH] Ex. 1 2100 1.8 Comp. Ex. 1 2120 3.9 Ex. 2 2230 2.2 Comp. Ex. 2 2210 3.7 Ex. 3 1990 2.7 Comp. Ex. 3 1980 4.8

(33) As shown in Table 1, the solid electrolytic capacitors obtained by the production method of the present invention (Examples) have significantly lower ESL (equivalent series inductance) than the solid electrolytic capacitors obtained by a conventional method (Comparative Examples).