JP4430440B2 - Manufacturing method of anode body for solid electrolytic capacitor - Google Patents

Description

  The present invention relates to a method for producing an anode body for a solid electrolytic capacitor.

  The anode body used in the conventional solid electrolytic capacitor is prepared by granulating the valve metal powder 3 by mixing the valve metal powder 3 and a binder as shown in FIG. It can be obtained by sintering the anode lead 2 on the molded body at a high temperature and under vacuum sintering.

  In the solid electrolytic capacitor anode body, the valve action metal powder 3 is granulated using a liquid or mist binder such as polyvinyl alcohol (PVA) to improve the flowability and formability of the valve action metal powder, It is manufactured by performing pressure forming and sintering (see, for example, Patent Document 1).

  Furthermore, if the valve metal powder granulated with a liquid or mist binder is used as it is, the anode metal body after sintering is in close contact with the valve metal powder. There is a problem that the path (path) for impregnating the solid electrolyte mother liquor (for example, manganese nitrate solution) into the body becomes narrow and the tan δ value and ESR value increase. As a countermeasure, as shown in FIG. A technique of further mixing the solid binder 7 as it is with the granulated powder and expanding the path is used (for example, see Patent Document 2).

In general, as a method for removing the binder from the molded body, thermal decomposition and scattering at high temperature and vacuum are used.
JP-A-5-65502 JP-A-9-134854

  As described above, in the conventional method in which the valve action metal powder 3 obtained by granulating once with a liquid binder and then mixing the solid binder 7 as it is, the path through which the solid electrolyte mother liquor is impregnated into the anode body is expanded. Although it is possible to increase the capacity appearance rate and reduce the tan δ value and the ESR value to some extent, the mechanical strength partially decreases due to the density variation of the sintered body 8, and the manufacturing process of the solid electrolytic capacitor There is a problem that leakage current increases due to post-manufacture stress.

  This is because the solid binder 7 has an extremely small specific gravity with respect to the valve metal powder 3, and when the mixed powder of both is introduced into the molding die, the solid binder 7 is upward and the valve metal powder 3 is downward. This is due to bias and non-uniform dispersion. And after sintering, since there is variation (bias) in the pores 11 inside the sintered body (FIG. 6), there is also a problem that variation occurs in the tan δ value and ESR value of the solid electrolytic capacitor.

  Further, when the solid binder 7 is not used, by increasing the amount of the liquid binder at the time of granulation, the path through which the solid electrolyte mother liquor is impregnated into the anode body is expanded, the capacity appearance rate is increased, the tan δ value, the ESR value However, in this case, the mechanical strength of the entire sintered body is lowered, and the leakage current increases due to the solid electrolytic capacitor manufacturing process or post-manufacture stress. There's a problem.

  Because of the above problems, there has been a demand for a method for manufacturing an anode body for a solid electrolytic capacitor that can suppress an increase in leakage current, reduce a tan δ value and an ESR value, and suppress variations.

The present invention solves the above-described problems, and provides a method for producing an anode body for a solid electrolytic capacitor that improves tan δ and ESR characteristics, reduces variations, and improves leakage current characteristics.
That is, in a method for producing an anode body for a solid electrolytic capacitor having a step of pressure-molding a powder of a valve action metal mixed with a binder, and a step of sintering the molded body,
The step of pressure forming includes the first step of granulating the first valve action metal powder with the first binder and then implanting and pressing the anode lead 2, The second valve action metal powder is granulated with the second powder, and the second step is press-molded. The mixing ratio of the first binder to the valve action metal powder is 3.0 to 3.0. It is 30.0 wt%, and the mixing rate of a 2nd binder is 0.1-3.0 wt%, It is a manufacturing method of the anode body for solid electrolytic capacitors characterized by the above-mentioned.

  Furthermore, the first and / or second binder is in a liquid or mist form and is mixed with a valve action metal powder. This is a method for producing an anode body for a solid electrolytic capacitor.

  The binder may be polyvinyl alcohol, polyvinyl butyral, acrylic resin, benzoic acid, or camphor, which is a method for producing an anode body for a solid electrolytic capacitor.

By the relatively small amount of the binder of the valve action metal powder 5 used for the second pressure molding covering the outer peripheral portion, it becomes a sintered body outer peripheral portion that is strong against the process of forming the solid electrolytic capacitor or the stress after the formation, The mechanical strength of the base portion of the anode lead 2 planted portion is also increased.
Moreover, the amount of the binder of the valve action metal powder 4 used for the first pressure forming for planting the anode lead 2 is relatively increased, and the porosity inside the anode body which is difficult to be impregnated with the solid electrolyte mother liquor is made uniform. By increasing the capacity, the capacity appearance rate can be increased, and the tan δ value and the ESR value can be reduced.
Therefore, an increase in leakage current due to the solid electrolytic capacitor manufacturing process or post-manufacture stress can be suppressed.
Furthermore, when only the liquid binder is used, the valve action metal powder 3 can be uniformly coated, and uniform voids are formed in the sintered body without unevenness. There is no reduction in mechanical strength.
As described above, it is possible to obtain an anode body for a solid electrolytic capacitor that is excellent in level / variation in leakage current, tan δ, and ESR characteristics, has a high capacity appearance rate, and has a stable leakage current value even in a heat resistance test.

  Next, embodiments of the present invention will be described with reference to the drawings.

[Example 1]
An anode body for a solid electrolytic capacitor according to the present invention was produced as follows.
First, a liquid binder (first binder) obtained by dissolving 10.0 wt% of polyvinyl alcohol in water with respect to the weight of the valve metal in tantalum powder 3 which is a valve metal having a particle size distribution of about 1 to 400 μm. By mixing, granulated powder 4 was obtained.
Further, a liquid binder (second binder) in which 1.0 wt% of polyvinyl alcohol is dissolved in water is mixed with tantalum powder 3 having the same particle size distribution with respect to the weight of the valve metal, and granulated powder 5 is obtained. Obtained.

  Next, the anode lead 2 was planted using the granulated powder 4 described above, and first compaction was performed to form a compact.

  And the outer peripheral part of the said molded object was covered with the granulated powder 5, the 2nd press molding was performed, and the molded object 1 shown in FIG. 1 was formed.

Thereafter, the binder in the molded body was thermally decomposed and scattered in a high vacuum atmosphere at 1325 ° C., and then sintered at 1325 ° C. to obtain a tantalum anode body 8.
Furthermore, this anode body was converted to 18 V in a 0.1 wt% phosphoric acid solution to form a tantalum oxide film, and a manganese dioxide layer as a solid electrolyte layer, and a carbon layer and a silver paste layer as a cathode lead layer were sequentially formed thereon. Thus, a tantalum solid electrolytic capacitor element was obtained.
Then, the anode lead 2 of the capacitor element was connected to the anode terminal by welding, and the cathode layer was connected to the cathode terminal by a conductive paint, and then a chip type tantalum solid electrolytic capacitor was produced by applying an exterior resin.

[Examples 3, 4, 7, 8 and Comparative Examples 2, 5, 6, 9 ]
As shown in Table 1, the amount of liquid binder is mixed in the range of 1.0 to 40.0 wt% with respect to the weight of valve action metal to form granulated powder 4, and the amount of liquid binder is based on the weight of valve action metal. In the range of 0.05 to 5.0 wt%, granulated powder 5 is obtained, and in the same manner as in Example 1, the first pressure molding with granulated powder 4 and the second with granulated powder 5 are performed. The chip-shaped tantalum solid electrolytic capacitors of Examples 3 , 4, 7, and 8 and Comparative Examples 2, 5 , 6 , and 9 were manufactured by performing pressure molding, heat treatment, sintering, chemical conversion, and assembly.

(Comparative Example 1 )
As shown in Table 1, the amount of liquid binder is mixed at 3.0 wt% with respect to the weight of the valve action metal to obtain granulated powder 4, and the amount of liquid binder is 10.0 wt% with respect to the weight of the valve action metal. A granulated powder 5 is mixed, and in the same manner as in Example 1, the first pressure molding with the granulated powder 4, the second pressure molding with the granulated powder 5, heat treatment, sintering, chemical conversion, assembly The chip type tantalum solid electrolytic capacitor of Comparative Example 1 was produced.

(Conventional example 1)
As in Example 1, a tantalum powder 3 having a particle size distribution of about 1 to 400 μm is mixed with a liquid binder obtained by dissolving 3.0 wt% of polyvinyl alcohol in water with respect to the weight of the valve action metal. Obtained.
Next, a polyvinyl alcohol having a solid binder 7 of 3.0 wt% with respect to the valve action metal weight and a particle size of 200 μm or less was mixed with the granulated powder 6.

  Using the mixed tantalum powder, the anode lead 2 was planted and pressure-molded to form a molded body 8 shown in FIG.

  Next, in the same manner as in Example 1, heat treatment, sintering, chemical conversion, and assembly were performed to produce a chip-type tantalum solid electrolytic capacitor.

(Conventional example 2)
Similar to Example 1, tantalum powder 3 having a particle size distribution of about 1 to 400 μm was mixed with a liquid binder in which 10.0 wt% of polyvinyl alcohol was dissolved in water with respect to the weight of the valve metal, and granulated powder 4 was obtained. Obtained.

  Using the granulated powder 4, the anode lead 2 was planted and pressure-molded to form a molded body 1 shown in FIG.

  Next, in the same manner as in Example 1, heat treatment, sintering, chemical conversion, and assembly were performed to produce a chip-type solid electrolytic capacitor.

  1 to 3 are schematic cross-sectional views showing a tantalum molded body 1 (after pressure forming of tantalum granulated powder and before binder removal). FIG. 1 shows Example 1, FIG. 2 shows Conventional Example 2, and FIG. It is sectional drawing of the prior art example 1. FIG.

  4 to 6 are schematic cross-sectional views showing a tantalum sintered body 8 (before tantalum oxide film formation). FIG. 4 is a schematic cross-sectional view of Example 1, FIG. 5 is Conventional Example 2, and FIG. It is.

  FIG. 7 is a diagram comparing the relationship between the hole diameter and the hole volume ratio of the tantalum sintered body 8 in Example 1 and Conventional Examples 1 and 2.

Next, the results of comparing the characteristics of Example 1 and Conventional Examples 1 and 2 of the chip-type solid electrolytic capacitor produced as described above are shown in FIGS.
8 shows the leakage current value (applied with rated voltage, 1 minute later), FIG. 9 shows the capacity appearance rate at 120 Hz, FIG. 10 shows the tan δ value, and FIG. 11 shows the result of comparison of the ESR value at 100 kHz.
FIG. 12 is a diagram comparing the changes in leakage current values before and after the heat resistance test (260 ° C., 10 seconds air reflow × 3 times).

Further, FIG. 13 shows the amount of the liquid binder of the granulated powder 4 used in Examples 1 , 3 , 4, 7, and 8, Comparative Examples 2, 5, 6, 9, and Comparative Example 1 in Table 1, It is a figure which shows the relationship between the amount of liquid binders, and an electrical property.

First, the schematic cross-sectional views (FIGS. 1 to 3) of the molded bodies will be compared.
As shown in FIG. 3, since the specific gravity of the solid binder 6 is extremely small with respect to the valve action metal powder 6 in the molded body 1 of the conventional example 1, when the mixed powder of both is molded with a mold, the solid binder 7 is upward. The valve action metal powder 6 is biased downward and the pores are in a non-uniform dispersion state.
Moreover, in the prior art 1, as shown in FIG. 2, the void | hole is in the uniform distribution state as a whole.
On the other hand, in Example 1, as shown in FIG. 1, the pores are in a uniform dispersed state inside and outside the sintered body.

Next, comparison will be made with respect to schematic sectional views (FIGS. 4 to 6) of the sintered bodies.
In FIGS. 4 to 6, the dispersed state of the binder is as it is after the binder is removed.
In Example 1 and Conventional Examples 1 and 2, pores that are impregnated with the solid electrolyte mother liquor are formed, but the states are different.
In the sintered body 8 of Conventional Example 1, as shown in FIG. 6, the holes 11 are biased upward, and the mechanical strength of the upper part is weak.
Moreover, in the prior art 2, as shown in FIG. 5, although it is in the uniform dispersion state as a whole, the mechanical strength of the whole sintered compact is falling.
On the other hand, in Example 1, as shown in FIG. 4, the pores are uniformly dispersed inside and outside the sintered body, and the base portion of the sintered body outer peripheral portion and the planted portion of the anode lead 2 is empty. There are few holes, and the strength is strong against the stress of the solid electrolytic capacitor formation process or after the formation.

Furthermore, the relationship diagram (FIG. 7) between the hole diameter and the hole volume ratio of the tantalum sintered body 8 will be compared.
Conventional Example 2 has one type of pore diameter, whereas Example 1 has two types of pore size, and separate pore states are formed in the sintered body and on the outer periphery. I understand that.
Although Conventional Example 1 has two types of pore diameters, one is an extremely large pore diameter due to the solid binder 7, and it can be seen that there is a large density variation.

Next, the leakage current value of the chip type tantalum solid electrolytic capacitor will be compared.
As shown in FIG. 8, Example 1 shows better results than both of Conventional Examples 1 and 2 in terms of level and variation.
In Example 1, it is considered that the mechanical strength of the outer periphery of the sintered body, which is weak against the stress in the process of forming the solid electrolytic capacitor, and the base portion of the anode lead 2 planting portion is increased, and the leakage current is suppressed to a low level. It is done.

Further, the capacity appearance rate, tan δ value, and ESR value of the chip-type tantalum solid electrolytic capacitor will be compared.
As shown in FIGS. 9 to 11, Example 1 shows better results in terms of both level and variation than Conventional Examples 1 and 2.
In Example 1, it is considered that a uniform and sufficient amount of pores are formed inside the sintered body so that the solid electrolyte mother liquor is easily impregnated.

Next, a change in leakage current value before and after the heat resistance test of the chip-type tantalum solid electrolytic capacitor will be compared.
As shown in FIG. 12, Example 1 showed better results in both level and variation than Conventional Examples 1 and 2.
In Example 1, it is considered that the mechanical strength of the sintered body outer peripheral portion weak against stress after the formation of the solid electrolytic capacitor and the anode lead 2 planted portion base portion is increased, and the leakage current is suppressed to a low level. It is done.

Next, Examples 3 , 4, 7, and 8, Comparative Examples 2 , 5 , 6 , and 9 in Table 1, the amount of liquid binder of granulated powder 4 used in Comparative Example 1 , the amount of liquid binder of granulated powder 5 and FIG. 13 showing the relationship with the electrical characteristics will be described.
When the amount of the liquid binder used for the granulated powder 4 is less than 3.0 wt% with respect to the weight of the valve metal, pores formed inside the sintered body are reduced, and the capacity appearance rate, tan δ characteristics, The effect of improving the ESR characteristic cannot be obtained.
Further, if it exceeds 30.0 wt% with respect to the weight of the valve metal, the mechanical strength of the molded body after pressurization becomes extremely weak, and the leakage current after the formation of the chip-type solid electrolytic capacitor increases. The amount of the liquid binder used for the powder 4 is preferably in the range of 3.0 to 30.0 wt% with respect to the weight of the valve action metal.
The amount of the liquid binder used for the granulated powder 4 is 3.0 wt% with respect to the valve action metal, and the amount of the liquid binder used for the granulated powder 5 is 10.0 wt% with respect to the valve action metal (comparison). Example 1 ) When the mixing ratio is reversed from that in Example 8, the capacity appearance rate, the tan δ characteristic, and the leakage current characteristic are deteriorated, which is not preferable.

Furthermore, when the amount of the liquid binder used in the granulated powder 5 is less than 0.1 wt% with respect to the weight of the valve metal, the granulation effect of the valve metal powder is small, and the flowability of the powder is deteriorated.
If the weight exceeds 3.0 wt% with respect to the weight of the valve metal, the mechanical strength of the outer periphery of the sintered body is reduced, and the chip-type solid electrolytic capacitor forming process and the effect of improving the leakage current characteristics after forming cannot be obtained. Therefore, the amount of the liquid binder used for the granulated powder 5 is desirably in the range of 0.1 to 3.0 wt% with respect to the valve action metal weight.
As a liquid binder for the granulated powders 4 and 5 in the above examples, polyvinyl alcohol was used in liquid form, but the same effect can be obtained by using polyvinyl butyral, acrylic resin, benzoic acid, and camphor.
Moreover, although the liquid binder of the granulated powder 4 and 5 in the said Example all used polyvinyl alcohol in the liquid state, the liquid binder of the granulated powder 4 and the liquid binder of the granulated powder 5 are polyvinyl alcohol, polyvinyl butyral, acrylic. The same effect can be obtained even when two or more types of resin, benzoic acid, and camphor are used in combination.
And in the said Example, although the binder was liquid and mixed with the valve action metal, the same effect will be acquired even if it mixes in mist form.

  Although tantalum was used as the valve action metal powder in the above example, the same effect can be obtained by using niobium, aluminum, titanium or the like.

  Moreover, although manganese dioxide was used as the solid electrolyte of the above-mentioned example, a known conductive polymer such as polythiophene, polypyrrole or polyaniline can be used.

1 is a schematic cross-sectional view of a tantalum powder pressure-formed body according to an embodiment of the present invention. It is a schematic cross section of a tantalum powder pressure-formed body according to a conventional example. It is a schematic cross section of a tantalum powder pressure-formed body according to another conventional example. It is a schematic cross section of the tantalum sintered body 8 by the Example of this invention. It is a schematic cross section of the tantalum sintered compact by a prior art example. It is a schematic cross section of a tantalum sintered body according to another conventional example. It is the figure which compared the relationship between the hole diameter of a tantalum sintered compact of Example 1 of this invention, and the prior art examples 1 and 2, and a void | hole volume ratio. It is the figure which compared the chip-type tantalum solid electrolytic capacitor leakage current value of Example 1 of this invention, and the prior art examples 1 and 2. FIG. It is the figure which compared the capacity | capacitance appearance rate of the chip-type tantalum solid electrolytic capacitor of Example 1 of this invention, and the prior art examples 1 and 2. FIG. It is the figure which compared the tan-delta value of the chip-type tantalum solid electrolytic capacitor of Example 1 of this invention and the prior art examples 1 and 2. FIG. It is the figure which compared the ESR value of the chip-type tantalum solid electrolytic capacitor of Example 1 of this invention and the prior art examples 1 and 2. FIG. It is the figure which compared the leakage current value before and behind the heat test of the chip-type tantalum solid electrolytic capacitor of Example 1 of the present invention and Conventional Examples 1 and 2. Examples 1 , 3 , 4, 7, 8 of the present invention , Comparative Examples 2, 5, 6, 9 , 9, the amount of liquid binder of granulated powder 4 used in Comparative Example 1 , the amount of liquid binder of granulated powder 5, It is the figure which showed the relationship with an electrical property.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molded body 2 Anode lead 3 Valve action metal powder 4 Granulated powder of liquid binder 10.0 wt% 5 Granulated powder of liquid binder 1.0 wt% 6 Granulated powder of liquid binder 3.0 wt% 7 Solid binder 8 Sintered Body 9 Sintered body part with many pores 10 Sintered body part with few pores 11 Holes with solid binder

Claims (3)

In the method for producing an anode body for a solid electrolytic capacitor, comprising: a step of pressure-molding a powder of a valve action metal mixed with a binder; and a step of sintering the molded body.
A step of pressure forming, after granulating the first valve action metal powder with a first binder, a first step of planting the anode lead and pressure forming;
The molded body comprises a second step of covering and pressing with a granulated powder obtained by granulating the second valve action metal powder with a second binder,
Solid electrolysis characterized in that the mixing ratio of the first binder with respect to the valve action metal powder is 3.0 to 30.0 wt%, and the mixing ratio of the second binder is 0.1 to 3.0 wt%. A method for producing a capacitor anode body. A method for producing an anode body for a solid electrolytic capacitor, wherein the first and / or second binder according to claim 1 is in a liquid or mist form and is mixed with a valve action metal powder . The method for producing an anode body for a solid electrolytic capacitor , wherein the binder according to claim 1 is polyvinyl alcohol, polyvinyl butyral, acrylic resin, benzoic acid, or camphor .

Images