JP2018037622A - Aluminum porous body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum porous body having a wide superficial area.SOLUTION: The present invention is directed to an aluminum porous body having many cavities 2 communicating from its surface to the inside thereof. The porous body is 2.3 g/cmor more in apparent density, and 90 mass% or more in aluminum purity, of which the rate of pores of 1-10 μm in diameter measured by a mercury penetration method is 90% or more in terms of pore volume.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an aluminum porous body suitably used as a material for an electrode material in, for example, an aluminum electrolytic capacitor and an aluminum solid electrolytic capacitor, and a related technique.

  Since aluminum electrolytic capacitors and aluminum solid electrolytic capacitors are relatively inexpensive and have a high capacity, they are widely used for home appliances such as personal computers and television sets and on-vehicle electrical products. An aluminum electrolytic capacitor is generally manufactured by winding an anode foil and a cathode foil with a separator interposed therebetween to form a capacitor element, impregnating the capacitor element with an electrolytic solution, storing the case in a case, and sealing. ing. For example, an anode foil is subjected to a surface expansion treatment by chemical or electrochemical etching on a valve action metal foil such as aluminum, and an oxide film layer is formed by subjecting the surface of the surface expansion treatment to chemical conversion. Is formed.

  Many techniques have been proposed in the past for the purpose of improving capacitance, which is one of the most important performances of capacitors. For example, based on the technology related to the development of an aluminum foil material as shown in Patent Documents 1 and 2, and the technology related to the development of an etching processing technology as shown in Patent Document 3, high capacity can be achieved by approaching various surface expansion treatments It has been advanced.

JP 2006-169629 A JP 2007-146301 A JP 2001-244153 A JP 2006-302917 A Japanese Patent Laid-Open No. 63-62890 JP 2006-22365 A

  However, the increase in the capacity of aluminum electrolytic capacitors by the techniques of Patent Documents 1 to 3 has slowed in recent years, and it has become difficult to significantly increase the capacitance with the extension of the prior art.

  On the other hand, for the purpose of significantly increasing the capacity of an aluminum electrolytic capacitor, as shown in Patent Document 4, as shown in Patent Document 4, in order to arrange the etching positions regularly, the technique of injecting the powder of valve action metal onto the anode foil is shown in Patent Document 5. A technique using a printing method and a technique using lithography as shown in Patent Document 6 have been proposed. However, any of the techniques in Patent Documents 4 to 6 has a problem such as high cost, and is not practical. Not reached.

  The present invention has been made in view of the above problems, and has a sufficient surface area. For example, when it is used as an anode body of an aluminum electrolytic capacitor, an aluminum porous material capable of greatly improving the capacitance is provided. The purpose is to provide the body and related technology.

  In order to achieve the above object, the present invention has the following structure.

[1] An aluminum porous body having a large number of voids communicating from the surface to the inside,
The apparent density is 2.3 g / cm ³ or more, the aluminum purity is 90% by mass or more, and the ratio of pores having a diameter of 1 μm to 10 μm measured by mercury porosimetry is 90% or more of all pores in terms of pore volume. An aluminum porous body characterized in that there is.

[2] The porous aluminum body according to item 1, wherein the apparent density is 2.4 g / cm ³ or more.

[3] The aluminum porous body according to 1 or 2 above, wherein the apparent density is 2.5 g / cm ³ or more.

  [4] The aluminum porous body according to any one of items 1 to 3, wherein the aluminum purity is 94% by mass or more.

  [5] The aluminum porous body according to any one of items 1 to 4, wherein the aluminum purity is 99% by mass or more.

  [6] The aluminum porous body according to any one of items 1 to 5, having a void penetrating in the thickness direction.

[7] An electrode material for a capacitor constituted by an aluminum porous body having a large number of voids communicating from the surface to the inside,
The apparent density is 2.3 g / cm ³ or more, the aluminum purity is 90% by mass or more, and the ratio of pores having a diameter of 1 μm to 10 μm measured by mercury porosimetry is 90% or more of all pores in terms of pore volume. An electrode material for a capacitor, characterized in that there is.

[8] The capacitor electrode material according to item 7, wherein the apparent density is 2.4 g / cm ³ or more.

[9] The electrode material for capacitors as described in 7 or 8 above, wherein the apparent density is 2.5 g / cm ³ or more.

  [10] The capacitor electrode material according to any one of items 7 to 9, wherein the aluminum purity is 94% by mass or more.

  [11] The electrode material for capacitors as described in any one of 7 to 10 above, wherein the aluminum purity is 99% by mass or more.

  [12] The electrode material for capacitors as described in any one of 7 to 11 above, which has a gap penetrating in the thickness direction.

  [13] A capacitor comprising the capacitor electrode material as described in any one of 7 to 12 above.

  According to the porous aluminum body, the electrode material for a capacitor, and the capacitor of the present invention, since it has a desired porous structure having a large number of fine voids, it has a sufficient surface area and greatly improves the capacitance. Can do.

FIG. 1 is an optical micrograph showing a cross section of a solidified structure in an aluminum porous body obtained in an example of the present invention.

  In general, an aluminum electrolytic capacitor is formed by sandwiching a dielectric coating made of aluminum oxide formed on an anode material made of aluminum between an anode and a cathode facing the anode.

  By using the porous aluminum body of the present invention as an anode material, a dielectric film is formed on the anode material, and a separator infiltrated with an electrolyte solution serving as a cathode is placed on the dielectric film, whereby an aluminum electrolytic capacitor is obtained. Can be formed. The separator may not be used depending on the structure of the capacitor.

  In the present invention, a known separator such as a cellulose porous membrane can be used as the separator.

  In the present invention, known electrolytes can be used. The electrolytic solution generally comprises a cation component, an anion component, and a solvent. Examples of the anion component include weak acids such as boric acid and carboxylic acid, and examples of the cation component include organic bases such as ammonia and amines. Examples of the solvent include ethylene glycol and γ-butyrolactone. As the cathode, a conventional surface-expanded Al foil or the like can be used.

  The anode material obtained by this invention is constituted by an aluminum porous body (porous material). This aluminum porous body has an aluminum alloy cast body formed by casting solidification as a precursor. Then, by eluting (etching) a required portion of the precursor, an aluminum porous body having a large number of voids (pores) open to the surface and communicating from the surface to the inside is obtained.

  An aluminum alloy as a precursor is expressed as an Al—X alloy in which “X” as an additive component (additive element) is added to Al (aluminum) as a main component (main element) as described later. it can.

  The solidified structure of the precursor has an α phase composed of primary crystals (that is, an α-Al phase) and a second phase having a eutectic formed continuously with the α phase. The primary crystal refers to a crystal that is first formed from a molten metal during casting solidification. The second phase has a eutectic of Al and the additive element “X”. The second phase is virtually all connected. However, the isolated second phase may remain as long as the effects of the present invention are not impaired.

  In the present invention, the casting method for obtaining the precursor is not particularly limited, and may be casting into a mold or continuous casting method. As the continuous casting method, for example, a DC casting method, a horizontal continuous casting method, an electromagnetic field casting method, a roll type continuous casting method, a belt casting method, or the like can be applied.

  Furthermore, in the present invention, a directional solidification casting method can be suitably used as casting for obtaining the precursor. By applying the directional solidification casting method, a precursor having a uniform structure can be obtained, and a porous body having a large surface area can be obtained by elution of the second phase of the precursor.

  Among the directional solidification casting methods, it is preferable to apply the unidirectional solidification casting method. That is, when the unidirectional solidification casting method is used, the porous body having a large surface area is more reliably obtained by leaving the α-Al phase of the precursor having a structure extending in one direction and dissolving the second phase with the eluent. Is obtained.

  In the present invention, the unidirectional solidification casting method is not particularly limited. For example, as described in Reference Document 1 below, continuous casting in which the ingot surface is solidified right outside the mold outlet end using a heating mold. As described in the method, Reference 2, a closed mold placed on a cooling plate is filled with molten metal without voids, and the molten metal is unidirectionally solidified by cooling from the cooling plate, Reference 3, a twin roll continuous casting method or the like can be applied.

Reference 1: Atsumi Ohno, Report of the Japan Institute of Metals, 23 [9], 773-778, 1984
Reference 2: JP-A-8-155627 Reference 3: JP-A-2007-268547 In this embodiment, the content (mass%) of the additive component “X” in the second phase is the content in the α phase. More than

  When the precursor is brought into contact with a solution that dissolves the additive component “X”, the additive component “X” is preferentially eluted, and as a result, the α phase remains and at least a part, preferably all, of the second phase remains. By elution, a large number of continuous voids (pores) are formed in the precursor from the surface to the inside, and the porous aluminum body of the present embodiment is obtained.

  As the additive component “X”, Mg can be suitably used because it has a melting point close to that of Al and is easy to handle. The additive component “X” is not limited to one type, and two or more types may be added.

  The Al—X-based alloy constituting the precursor can be considered to have a hypoeutectic composition in which the addition amount of “X” is Al or less than the eutectic point. Thus, in the case of a hypoeutectic composition, an Al-rich alloy phase is crystallized inside the solidification cell constituting the α phase, while being added to the final solidification portion of the solidification cell formed on the outer periphery of the α phase. Since the alloy phase (second phase) containing a large amount of the component “X” is crystallized, the second phase is preferentially eluted by the eluent. Therefore, a desired gap can be formed reliably.

  The α phase may also be slightly eluted, but this is not a problem as long as a continuous void is formed and the shape of the porous body is maintained.

  In the case where the precursor has a hypereutectic composition in which the addition amount of “X” exceeds the eutectic point, a crystallized product whose primary crystal is composed of the additive component “X” or an alloy containing a large amount of the additive component “X” Since it becomes a crystallized product of the phase, many parts of the primary crystal are eluted by the eluent. In this case, the voids are too large, and the surface area cannot be sufficiently expanded or the porous structure cannot be maintained.

  Further, an element other than “X” (third component) may be added to the Al—X-based alloy as the precursor within the range of the eutectic composition as necessary or unavoidable.

  The general addition amount of “X” in the precursor is not more than the eutectic composition and is 1% by mass or more, desirably 5% by mass or more, and more desirably 10% by mass or more. That is, when “X” is added in this amount, as described above, an alloy phase containing a large amount of the additive component “X” crystallizes on the outer periphery of the α phase. When the preferential elution is performed and the second phase is eluted, a porous structure having a desired void can be formed. The eutectic composition in the present invention is 35% by mass with the smallest amount of Mg in the phase diagram in the case of an Al—Mg alloy, and 36% by mass in the case of an Al—Zn alloy.

  Further, since the second phase is preferentially eluted, the surface area can be increased as the solidification cell composed of the α phase during casting is smaller. Therefore, it is preferable to reduce the solidification cell during casting solidification. In general, the greater the amount of additive component “X” added, and the faster the cooling rate near the freezing point, the smaller the solidification cell, and the solidification cell becomes a granular (circular or elliptical) crystallized product. Since it changes into a complex shape into a crystal, the surface area can be enlarged. For example, the cooling rate in the vicinity of the freezing point may be adjusted to 1 ° C./sec or higher, preferably 5 ° C./sec or higher, more preferably 10 ° C./sec or higher.

  It is preferable to form dendrites in at least a part of the α-phase solidification cell, and it is more preferable to form all of them into dendrites.

  For example, as shown in FIG. 1, in the porous aluminum body related to the present invention, the primary α phase 1 (the light gray portion in the figure) is composed of dendritic crystals, and between the α phases 1, The void 2 (the dark gray portion in the figure) formed by the elution of the second phase is continuously formed. As will be described in detail later, the photograph in FIG. 1 is an aluminum porous body having a specific apparent density and a specific pore ratio, and is an observation of an axial cross section of an aluminum alloy casting. .

  As long as the solidified structure at the time of casting solidification remains in the cast aluminum alloy as the precursor, mild processing with a small deformation rate may be performed. For example, the precursor may be subjected to a drawing process or a rolling process for shaping the outer shape.

  However, if the precursor is processed with a high deformation rate, the solidified structure collapses, and the crystallized product as the second phase is divided, and when the crystallized product is eluted, the porous material has a desired void. There is a possibility that the structure cannot be obtained.

  The surface of the precursor (cast solidified surface) may be cut as it is or to a size that facilitates the next process. Further, the cast solidified surface may be cut (deleted) so that the etching (elution) of the second phase can be performed quickly and uniformly.

  In the present invention, when a large amount of the additive component “X” remains in the porous body, there are concerns that defects in the oxide film may become a problem depending on the application, and there are too many impurities in the porous body. In the present invention, in order to reduce the residual amount of “X” in the porous body, heat treatment is performed in a process after the aluminum alloy cast body is manufactured. By this heat treatment, “X” evaporates, and the residual amount of “X” in the porous body finally obtained can be reduced.

The atmosphere of the heat treatment is preferably performed in a vacuum in order to promote evaporation of “X”. The degree of vacuum in the heat treatment in vacuum is preferably 0.1 Pa or less, more preferably 1 × 10 ⁻² Pa or less, and particularly preferably 5 × 10 ⁻³ Pa or less.

  The heat treatment is a temperature at which “X” evaporates in the heat treatment atmosphere, and is preferably 550 ° C. or less. If the heat treatment temperature is too low, “X” does not evaporate, and if the heat treatment temperature is too high, the aluminum surface is oxidized inhomogeneously. When “X” is Mg, the heat treatment temperature is preferably from 400 ° C. to 550 ° C., more preferably from 450 ° C. to 550 ° C.

  In the present embodiment, an acid aqueous solution can be exemplified as an eluent for dissolving the additive component “X” of the precursor. As an acid contained in the acid aqueous solution, hydrochloric acid, sulfuric acid, nitric acid and the like can be used.

  In the present invention, when the heat treatment is performed in a state where the additive component “X” is dissolved from the precursor and the area is expanded, evaporation of “X” is promoted. Therefore, the heat treatment is performed by contact with the eluate. It is preferable to carry out after dissolution of “X”.

  In the present invention, the precursor may be made porous by performing at least one of contact with the eluate and heat treatment a plurality of times.

  In addition, if the contact with the eluate is performed after the first contact with the eluate, heat treatment is performed, and then the second eluate is contacted. If it is possible, the second contact with the eluate may be performed in such a short time that the oxide film can be removed.

  In the porous aluminum body of the present invention, the ratio of pores having a diameter of 1 μm to 10 μm (1 μm or more and 10 μm or less) measured by mercury porosimetry is used in order to have a large surface area and suitable for applications such as capacitors. It is necessary to make it 90% or more in terms of volume. When the pore diameter is too small, the area reduction rate when the porous body is subjected to chemical conversion treatment for use as an anode material becomes too high. Conversely, when the pore diameter is too large, the surface area expansion of the porous body itself is insufficient.

The apparent density of the porous aluminum body of the present invention needs to be 2.3 g / cm ³ (g · cm ⁻³ ) or more. This apparent density is the density obtained from the volume of the overflowing liquid and the mass of the porous body when the porous body is placed in a water tank filled with liquid to the full volume.If there are few closed pores and many open pores, the apparent density Density increases. Therefore, it is preferable that the apparent density is high and close to the density of pure aluminum (2.7 g · cm ⁻³ ). Since the porous aluminum body of the present invention is obtained by dissolving the second phase communicating to the surface, open pores are developed. The apparent density of the aluminum porous body is preferably 2.4 g / cm ³ (g · cm ⁻³ ) or more, and more preferably 2.5 g / cm ³ (g · cm ⁻³ ) or more.

  The aluminum purity of the porous aluminum body of the present invention needs to be 90% by mass or more. In the present invention, the aluminum purity (% by mass) is defined as a value obtained by subtracting the total of Fe, S, Cu and additive component “X” concentrations from 100% by mass. If the aluminum purity becomes too low, defects are generated in the oxide film, which is not preferable. The aluminum purity of the aluminum porous body is preferably 94% by mass or more, and more preferably 99% by mass or more.

  An aluminum porous body obtained by treating the precursor with an eluent can be used as an electrode material for a capacitor. When an aluminum porous body is used as a capacitor anode material, a dielectric coating is formed on the anode body. The method for forming the dielectric film is not particularly limited, but it is preferable to apply a chemical conversion treatment by anodic oxidation.

  In general, hydration is performed in pure water as pre-chemical treatment. Other pretreatment methods include immersion in hydrogen peroxide, cleaning with an acid or alkaline treatment solution, vacuum or atmospheric heat treatment, dechlorination treatment, hydration treatment in an aqueous solution to which an amine is added, thermal oxide film It can be applied alone or in combination from known pretreatment methods including treatment with an acid or alkali solution after formation, and hydration treatment performed after electrolytic etching is applied to the aluminum foil.

As the chemical conversion treatment solution, known ones can be used, and examples include an aqueous solution in which one or more of boric acid, ammonium borate, adipic acid, ammonium adipate, phosphoric acid and its salt, citric acid and its salt, etc. are mixed. it can.

  As the chemical conversion method, the EIAJ method can be exemplified, but is not limited thereto. The chemical conversion treatment may be performed a plurality of times, the chemical conversion liquid may be changed for each chemical conversion treatment according to a known method, and heat treatment or washing may be performed between the chemical conversion treatment and the chemical conversion treatment. In addition, the conversion voltage may be set to different values in a plurality of conversion processes.

  In the present invention, the precursor may be formed in any shape such as a columnar shape, a cylindrical shape, an elliptical columnar shape, an elliptical cylindrical shape, a prismatic shape, a rectangular cylindrical shape, a flat shape such as a plate shape, or the like. For example, in order to effectively utilize the surface of the precursor and enlarge the surface area, it is advantageous to form the surface in an elliptical shape or a flat shape. Further, when the precursor is hollow like a cylinder or the like, it can be preferentially eluted from the inner peripheral surface, so that a higher surface area can be obtained.

  An aluminum electrolytic capacitor can also be formed by sequentially stacking and placing a semiconductor layer and a conductor layer on the dielectric coating.

  The semiconductor layer can be formed of an inorganic semiconductor such as manganese dioxide or an organic semiconductor such as a conductive polymer, and these can be generally produced by a known method. In the case of forming with a conductive polymer, it can be formed using, for example, a chemical polymerization method and / or an electrolytic polymerization method. The solution for forming the semiconductor layer is not particularly limited as long as the solution can form a semiconductor by dipping and / or energization. For example, a solution containing aniline, thiophene, pyrrole, and a substituted derivative thereof (for example, 3,4-ethylenedioxythiophene) can be used. Further, a dopant may be added to this solution. Although it does not specifically limit as a dopant, For example, arylsulfonic acid or its salt, alkylsulfonic acid or its salt, various polymeric sulfonic acid or its salt, etc. can be used. From the conductive polymer (for example, polyaniline, polythiophene, polypyrrole, polymethylpyrrole, and derivatives thereof) on the dielectric layer by immersing and / or energizing using such a solution for forming a semiconductor layer. A semiconductor layer can be formed.

  For example, carbon, silver, or the like having high conductivity can be used for the conductor layer, and the conductor layer can be manufactured by solidifying paste-like carbon or silver. These may be laminated.

<Example 1>
A molten alloy having the composition shown in Table 1 was cast by casting into a mold as shown in Table 2 to obtain a cylindrical (round bar) cast aluminum alloy. The cast body thus obtained was cut at a thickness of 0.9 mm perpendicularly in the axial direction as shown in Table 3, degreased with ethanol, immersed in 5N hydrochloric acid solution at a liquid temperature of 10 ° C. for 24 hours, and vacuumed. Heat treatment at 400 ° C. for 5 hours in the inside (1 × 10 ⁻³ Pa) and immersion for 10 minutes in a 5N hydrochloric acid aqueous solution at a liquid temperature of 10 ° C. were sequentially performed to obtain an aluminum porous body of Example 1.

When the obtained aluminum porous body was evaluated by a mercury intrusion method, the specific surface area was 0.41 m ² / g, and the ratio of pores of 1 μm or more and 10 μm or less was 90% or more of all pores in terms of volume. It was. Furthermore, the apparent density of this porous body was 2.58 g / cm ³ . Moreover, as shown in Table 5, the aluminum purity (100% by mass-Mg: 7.2% by mass-Fe: 0.002% by mass-Si0.003-Cu: less than 0.001% by mass) exceeds 90% by mass. It was.

  Further, it was confirmed that the obtained aluminum porous body penetrated in the axial direction by blowing air into the porous body in water.

  Next, the obtained aluminum porous body was immersed in boiling pure water for 5 minutes for chemical conversion pretreatment.

The aluminum porous body subjected to the chemical conversion pretreatment was immersed in 11 L of pure water to which 1100 g of boric acid and 9.9 g of ammonium pentaborate octahydrate were added, and the initial current value was 500 mA / cm ² at 90 ° C., constant voltage. Chemical conversion treatment was carried out by holding at 150 V for 10 minutes.

  The aluminum porous body subjected to chemical conversion treatment is immersed in 360 ml of pure water to which 28.8 g of ammonium pentaborate octahydrate is added, and below the surface of the stainless steel container (area: bottom diameter 60 mm × height 150 mm) As a counter electrode, 30 ° C., measurement frequency 120 Hz, measurement voltage 0.5 Vr. m. s. When the capacitance was measured at 50 μF, it was 50 μF.

<Examples 2 to 6>
As shown in Table 2, molten alloys of the alloys having the compositions shown in Table 1 were cast by a heating mold type continuous casting method to obtain cylindrical (round bar) aluminum alloy castings. Each cast body thus obtained was cut in a thickness of 0.9 mm perpendicular to the axial direction as shown in Table 3, and then treated under the conditions shown in Table 3 to obtain porous aluminum bodies of Examples 2-6.

  FIG. 1 shows an optical micrograph of a cross section of the solidified structure in the precursor of the porous aluminum body of Example 2. As shown in the figure, α-phase 1 of the primary crystal (light gray portion in the figure) is formed in dendritic crystals, and is formed by elution of the second phase between the α-phases 1. The void 2 (the dark gray portion in the figure) is continuously formed.

Further, as shown in Table 4, in any of the porous bodies of Examples 2 to 6, the ratio of the pores of 1 μm or more and 10 μm or less is 90% or more of the total pores in terms of volume, and the apparent density is 2.3 g. / Cm ³ or more.

  Further, it was confirmed that the obtained aluminum porous body penetrated in the axial direction by blowing air into the porous body in water.

  As is clear from the above examples, the porous aluminum body of the present invention has an apparent density and a specific pore ratio specific to the present invention, and therefore has a large number of fine voids communicating from the surface to the inside. Therefore, it can be used as an electrode material having a high electrostatic capacity, and can be suitably used as an anode material for an aluminum electrolytic capacitor or an aluminum solid electrolytic capacitor.

  The porous aluminum body of the present invention can be suitably used as an anode material for aluminum electrolytic capacitors and aluminum solid electrolytic capacitors.

1: α phase 2: void

Claims (13)

An aluminum porous body having a large number of voids communicating from the surface to the inside,
The apparent density is 2.3 g / cm ³ or more, the aluminum purity is 90% by mass or more, and the ratio of pores having a diameter of 1 μm to 10 μm measured by mercury porosimetry is 90% or more of all pores in terms of pore volume. An aluminum porous body characterized in that there is. The aluminum porous body according to claim 1, wherein the apparent density is 2.4 g / cm ³ or more. The aluminum porous body according to claim 1 or 2, wherein the apparent density is 2.5 g / cm ³ or more.   The aluminum porous body according to any one of claims 1 to 3, wherein the aluminum purity is 94% by mass or more.   The aluminum porous body according to any one of claims 1 to 4, wherein the aluminum purity is 99% by mass or more.   The aluminum porous body according to any one of claims 1 to 5, which has voids penetrating in the thickness direction. An electrode material for a capacitor constituted by an aluminum porous body having a large number of voids communicating from the surface to the inside,
The apparent density is 2.3 g / cm ³ or more, the aluminum purity is 90% by mass or more, and the ratio of pores having a diameter of 1 μm to 10 μm measured by mercury porosimetry is 90% or more of all pores in terms of pore volume. An electrode material for a capacitor, characterized in that there is. The electrode material for a capacitor according to claim 7, wherein the apparent density is 2.4 g / cm ³ or more. The capacitor electrode material according to claim 7 or 8, wherein the apparent density is 2.5 g / cm ³ or more.   The electrode material for capacitors according to any one of claims 7 to 9, wherein the aluminum purity is 94% by mass or more.   The electrode material for capacitors according to any one of claims 7 to 10, wherein the aluminum purity is 99% by mass or more.   The electrode material for a capacitor according to any one of claims 7 to 11, which has a gap penetrating in the thickness direction. The capacitor | condenser electrode material of any one of Claims 7-12 was integrated, The capacitor | condenser characterized by the above-mentioned.