JP3264688B2 - Electrolytic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic capacitor having electrolytic paper interposed between an anode foil and a cathode foil.
Particularly, in an electrolytic capacitor for medium and high pressure, the use of electrolytic paper mixed with whiskers improves the impedance characteristic without lowering the withstand voltage.

[0002]

2. Description of the Related Art In general, an electrolytic capacitor, particularly an aluminum electrolytic capacitor, is formed by winding an electrolytic paper as a separator between an anode aluminum foil and a cathode aluminum foil to form a capacitor element. It is immersed in the electrolyte solution of the above to impregnate the electrolyte, and sealed. As the electrolyte, ethylene glycol (EG) is usually used.
Using dimethylformamide (DMF) or γ-butyrolactone (GBL) as a solvent, and dissolving an organic acid salt such as boric acid, ammonium adipate or ammonium hydrogen maleate in such a solvent, penetrate from both ends of the capacitor element. I make it.

[0003] In these conventional aluminum electrolytic capacitors, an electrolytic solution is impregnated in electrolytic paper, so that the impedance characteristics of the capacitor, particularly the equivalent series resistance (hereinafter referred to as ESR), are obtained.
Therefore, in order to improve impedance characteristics, it is conceivable to lower the resistance of the electrolytic solution or to make the electrolytic paper thinner or lower in density. However, lowering the resistance value of the electrolytic solution causes corrosiveness to the aluminum foil.On the other hand, if the electrolytic paper is made thinner or lower in density, the short-circuit defect rate increases when winding it on the capacitor element, Even if short-circuiting does not occur, there is a problem that the short-circuit defect rate after being commercialized and put on the market increases.

Therefore, in order to improve impedance characteristics, the shape and orientation of the constituent fibers of electrolytic paper have been studied. In the case of the same thickness and the same density, it is desirable that voids in the electrolytic paper efficiently penetrate from the front surface to the back surface of the electrolytic paper. Therefore, the raw material of the electrolytic paper is required to have two points, that is, the fiber diameter is as small as possible and close to a circle, and the fiber has high rigidity. From these points, means for changing the raw material of the electrolytic paper from ordinary wood kraft pulp to synthetic fiber, manila hemp pulp, and esparto pulp has been used.

[0005] However, synthetic fibers are circular and have the most ideal fiber form. However, when mixed with cellulosic fibers such as manila hemp pulp, the synthetic fibers and cellulose are poorly blended with each other and the formation is poor. And low tensile strength. On the other hand, if manila hemp pulp or esparto pulp is used as a raw material, low-density paper can be easily made, so that the impedance characteristics are good, and the low-density paper has sufficient tensile strength. It is widely used and has a corresponding effect.

However, these are all low-density papers and are not suitable for improving the impedance characteristics of a medium-to-high pressure electrolytic capacitor. Conventionally, in a medium-to-high voltage electrolytic capacitor, electrolytic paper having a density and a thickness high enough to secure a withstand voltage has been used even if electric characteristics are sacrificed.

[0007]

In general, when the rated voltage of a capacitor to be manufactured is increased, short circuit accidents caused by contact between anode foils are prevented, and oxygen gas generated at the anode and hydrogen gas generated at the cathode are prevented from passing therethrough. For this purpose, it is customary to increase the density and thickness of the electrolytic paper. It is also effective to increase the density and increase the thickness in order to increase the withstand voltage of the electrolytic paper itself.

[0008] Densification of electrolytic paper is achieved by CSF (Canad) according to JIS P8121, which indicates the degree of beating of raw material of electrolytic paper.
This is achieved by lowering the value of ian Standard Freeness to promote the fibrillation of the fibers, increase the contact points between the fibers, and reduce the porosity to densify the obtained electrolytic paper.

However, on the other hand, reducing the numerical value of CSF by advancing the degree of beating deteriorates the electrical characteristics of the electrolytic capacitor. That is, the increase in the air density of the electrolytic paper impairs ion conduction, the increase in ESR due to the redundancy of the ion current path, and the increase in ESR due to the decrease in the amount of electrolyte that can be impregnated and held due to the decrease in porosity.
In addition, the decrease in the amount of the electrolyte solution that can be impregnated and held also accelerates the characteristic deterioration due to the decrease with time of the electrolyte solution when used for a long time. Therefore, in spite of the deterioration of these electrical characteristics, especially in medium-to-high voltage electrolytic capacitors, accident prevention due to short-circuit of electrode foil, oxygen gas generated inside the capacitor,
Since the top priority is to prevent small explosion and ensure withstand voltage by mixing hydrogen gas, the density and thickness of electrolytic paper have been increased. To ensure the withstand voltage, the impedance characteristics and the life are sacrificed.

Therefore, the present invention simply changes the electrolytic paper without changing the withstand voltage of the electrolytic capacitor and increasing the short-circuit failure rate without changing the high impedance which was the fate of the conventional medium-to-high voltage electrolytic capacitor. And to provide a new electrolytic capacitor having good electric characteristics.

[0011]

According to the present invention, there is provided an electrolytic capacitor in which electrolytic paper is interposed between an anode foil and a cathode foil.
Provided is an electrolytic capacitor in which aluminum borate whiskers of 1 to 10 µm are mixed and internally added. The mixing ratio of the aluminum borate whiskers is 1 to 60% by weight.

[0012]

According to the present invention having the above construction, the diameter is 0.1 to 10 mm.
μm aluminum borate whiskers are circular, have a very small cross section, and have high rigidity, so that voids can efficiently penetrate from the surface to the back of the electrolytic paper obtained by blending with pulp, and achieve dense paper quality. As a result, impedance characteristics can be improved as compared with electrolytic paper made of conventional natural pulp having the same thickness and the same density.
In addition, since the aluminum borate whisker itself has a high electric resistance, a high withstand voltage can be maintained. Therefore, the impedance characteristic can be improved without lowering the withstand voltage particularly in the electrolytic capacitor for medium and high voltage.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the present invention will be described below together with various embodiments. The electrolytic paper according to the present invention has a diameter of 0.1 to 10 μm.
It is characterized that the whiskers are added in混抄
I have . In order to reduce the impedance of the electrolytic capacitor, the raw material fibers of the electrolytic paper are required to have as small a fiber diameter as possible, close to a circle, and high rigidity of the fibers. Therefore, the inventor paid attention to whiskers as an inorganic material from such a demand, and invented a mixed paper of whiskers and pulp as electrolytic paper.

A whisker is a general term for a substance having a needle-like crystal structure, and is called a whisker-like substance. Its tensile strength is greater than any other material. This is thought to be because the whiskers have an ideal crystal structure and have no defects as a material. The fibers of the whiskers are small in cross section and nearly circular, and some whiskers have a fiber diameter of about 1 μm, which is extremely small as compared with esparto pulp having a fiber diameter of about 10 μm. In addition, since it is an acicular crystal, the rigidity is high. Therefore, the two requirements required for the raw material fiber of the electrolytic paper are satisfied at a high level. In addition, such fine particles are well-known even when mixed with the pulp raw material that has been beaten. Therefore, the papermaking properties are also good. Therefore, since the whisker has a circular and extremely minute cross section and a high rigidity, the whisker can efficiently penetrate the void from the front surface to the back surface by mixing with pulp, and can obtain dense paper quality.

If the fiber diameter of the whisker to be mixed is too small, the effect of improving the impedance is small, and if it is too large, the papermaking properties are poor. Therefore, the fiber diameter of the whisker is 0.1.
Range of 1~10μm is Ri optimum der,該U for the electrolytic paper
The mixing rate of the whiskers is 1 to 60% by weight. Whiskers
A fiber length of 1 to 400 μm can be used, but if the fiber length is short or long, the papermaking property is poor and the short defect rate increases.
Therefore, the length of the whisker is optimally 5 to 50 μm.

Whiskers mixed under these conditions include Al ₂ O ₃ , BeO, Cr ₂ O ₃ , MgO, ZnO, C
dS, B ₄ C, SiC, Si ₃ N ₄ , AlN, BN, Cr ₂
N, TiN, Mg ₂ B ₂ O ₅ , NaCa ₂ P ₂ O ₁₈ , CaC
O ₃ , aluminum borate and potassium titanate are used. The whiskers used in the present invention are not particularly limited as long as the whiskers are in the above-described fiber diameter and length range and do not contain impurities for the electrolytic capacitor. For example, natural products such as sepiolite, chrysotile and wallastrite can also be used. However, in this case, pretreatment such as washing with water for removing impurities is required. Among these, Al ₂
O ₃ , MgO, SiC, Si ₃ N ₄ , aluminum borate,
Potassium titanate is particularly preferred.

The paper quality changes as follows depending on the mixing ratio of whiskers. When the mixing ratio is increased, the ESR is lowered without lowering the withstand voltage, and the mixture becomes favorable. However, if the mixing ratio is too high, on the other hand, the tensile strength also decreases.
Therefore, in order to have a practical tensile strength, the mixing rate is 6%.
It must be up to 0%. However, the electrical characteristics may be more important than the tensile strength, in which case there is no limitation on the mixing ratio.

The raw material pulp to which whiskers are mixed and incorporated is not particularly limited in its kind and CSF value, and may be any of manila hemp pulp, sisal pulp, kraft pulp, esparto pulp or a mixture of these pulp raw materials. good. The mixing ratio of whiskers is determined by the numerical value of the CSF of the raw pulp and the thickness and density of the electrolytic paper to be obtained.

The electrolytic paper according to the present invention is prepared by subjecting a conventional raw material for electrolytic paper, such as manila hemp pulp, esparto pulp and kraft pulp, to a known adjustment such as washing, dehydration, beating, etc., and removing impurities therefrom. Whiskers of 0.1 to 10 μm are added and mixed so as to be 1 to 60% by weight based on the electrolytic paper. Next, electrolytic paper having a predetermined thickness is formed from the adjusted raw material on a paper machine such as a round paper machine, a fourdrinier machine, a fourdrinier combination machine, or a round net combination machine. The electrolytic paper thus obtained is interposed between the anode foil and the cathode foil and wound up to produce a capacitor element, then impregnated with a liquid electrolyte and sealed to produce an electrolytic capacitor.

The electrolytic paper made of the mixed paper of whiskers and pulp has the following characteristics. The withstand voltage of conventional electrolytic paper depends largely on the withstand voltage of pure cellulose. That is, the conventional electrolytic paper can have a large withstand voltage by removing conductive ions and fine particles at the raw material adjustment stage and making the paper with pure cellulose fiber. In the present invention, whiskers other than cellulose are mixed, but the whiskers have a diameter of 0.1 .
The electric resistance of the whisker itself of 1 to 10 μm is high,
Since the density of the paper can be maintained, a mixed paper having a high withstand voltage can be obtained. Since this whisker has a circular, extremely minute cross section and high rigidity, it is possible to efficiently penetrate voids from the front side to the back side of the electrolytic paper obtained by mixing with pulp, and obtain dense paper quality. As a result, the impedance characteristics can be improved. Further, the short-circuit failure rate of the electrolytic paper depends on strength, thickness, density, denseness, and the presence or absence of pinholes. In general, when the strength is small, the short-circuit failure rate increases, and when the pinhole is large or large, the short-circuit failure rate increases. In the present invention, the decrease in the strength of the whisker-mixed paper is small and the whisker has good paper-making properties, so that the mixed paper can maintain its denseness and has no pinholes. As a result, natural pulp 10
With respect to paper made at 0%, a good short defect rate can be obtained.

Tables 1 to 3 show the thickness, density, tensile strength, withstand voltage, blending ratio, and short-circuit defect ratio of specific examples and comparative examples which were formed to have substantially the same thickness and the same density as the examples. , ESR are shown. In addition, the manufacturing method and the measuring method of the electrolytic capacitor in the said Example are as follows.

Evaluation method of electrolytic paper The thickness, density and tensile strength of electrolytic paper were measured according to JIS C2301.
(Electrolytic capacitor paper). The withstand voltage of the electrolytic paper was measured by a method specified in JIS C2111 (electrical insulating paper test method).

Evaluation Method of Electrolytic Capacitor Aging Short Failure Rate Electrolytic paper was wound together with an anode foil and a cathode foil to form an electrolytic capacitor element, which was then impregnated with a predetermined electrolytic solution and sealed to produce an electrolytic capacitor. About 100 electrolytic capacitors were aged at 1.1 times the rated voltage. At that time, the ratio of the short-circuited electrolytic capacitors to the number of test electrolytic capacitors was defined as the aging short ratio.

ESR (Equivalent Series Resistance) Aged electrolytic capacitor at 20 ° C., 1 kHz
Was measured by an LCR meter.

In Examples 1 to 6, 50% by weight of manila hemp pulp was used.
Raw material obtained by mixing 50% by weight of esparto pulp with CSF
Beat to 500 cc, and add aluminum borate whiskers having an average diameter of 1 μm and an average whisker length of 20 μm to 1 to 6
Rated 4 using 2 sheets of electrolytic paper mixed with 0% by weight as separator
It is a 00V capacitor. In Comparative Example 1, a raw material obtained by mixing 50% by weight of Manila hemp pulp and 50% by weight of esparto pulp was beaten to 500 cc of CSF, and two electrolytic papers each containing 70% by weight of aluminum borate whiskers having an average diameter of 1 μm and an average whisker length of 20 μm were prepared. This is a 400V rated capacitor used as a separator. Comparative Example 2 is Comparative Example 1
The whisker is not mixed with the raw material.

[0026]

[Table 1]

As is evident from Table 1, there is a large difference in the electrical characteristics of the capacitors despite the fact that they are electrolytic papers having substantially the same thickness and the same density. That is, the electrical characteristics of the capacitor using electrolytic paper mixed with whiskers are remarkably improved as compared with the capacitor using electrolytic paper not mixed with whiskers shown in Comparative Example 2. For example, mixing rate 1
The ESR of Example 3 at 0% is 0.454Ω, which is much lower than 0.664Ω of Comparative Example 2 which is not mixed. Moreover, the withstand voltage was 632 V in Example 3 and 633 V in Comparative Example 2, and the withstand voltage did not decrease even when whiskers were mixed. The tensile strength is also 3.5 Kg, which is equivalent.
That is, even if the whiskers are mixed even if they have substantially the same thickness and the same density, the ES can be formed without affecting the withstand voltage.
R can be improved. The improvement effect can be seen from the blending rate of 1% by weight, and it can be seen that the effect increases as the blending rate increases. However, as shown in Comparative Example 1, when the mixing ratio of whiskers was 70% by weight, the aging short defect rate of the capacitor was increased. This is considered to be because mechanical strength such as tensile strength decreases when the mixing ratio increases. Therefore, the optimum blending ratio must be determined in consideration of the effect of improving the electrical characteristics and other various characteristics, but a range of 1% by weight to 60% by weight is appropriate. If mixed up to 60% by weight, the tensile strength hardly decreases.

In Examples 7 to 10, the kraft pulp was treated with CSF.
Beating to 0 cc with a numerical value of 200 V, with one sheet of electrolytic paper mixed with 10% by weight of various whiskers as a separator
Of the capacitor. The size of the whiskers used in Examples 7 to 10 was such that potassium titanate had an average diameter of 1 μm.
m, average whisker length is 30 μm, alumina has an average diameter of 1 μm, average whisker length is 25 μm, silicon carbide has an average diameter of 0.1 μm, and average whisker length is 15 μm.
m, silicon nitride has an average diameter of 1 μm and an average whisker length of 20 μm. Comparative Example 3 uses kraft pulp with CSF
This is a 200 V rated capacitor using electrolytic paper that has been beaten to 0 cc and made into paper.

[0029]

[Table 2]

As is clear from Table 2, the whiskers of Examples 7 to 10 and the comparative examples 3 of which whiskers were not mixed were substantially the same in thickness and density, but were not mixed in Examples 7 to 10.
10 has improved RSR. For example, while the ESR of Comparative Example 3 is 0.577Ω, the ESR of Example 9 is
R is improved to 0.413Ω.

In Examples 11 to 13, two types of kraft pulp having different degrees of beating were mixed with aluminum borate whiskers, and a 450 V rated capacitor was used in which one sheet of double paper made by a fourdrinier combination machine was used as a separator. is there. Kraft pulp CSF is 0c on the fourdrinier side
c, 600cc on the mesh side. Example 11 is a fourdrinier side, Example 12 is a 10% by weight aluminum borate whisker as a raw material on the round side, and Example 13 is 5% by weight of an aluminum borate whisker as a raw material on the long net and the round net side.
This is an example in which electrolytic paper mixed and paper-formed is used. Comparative Example 5 is an example in which electrolytic paper which is a double paper made of kraft pulp in which aluminum borate whiskers are not mixed by a fourdrinier combination machine is used.

[0032]

[Table 3]

As is evident from Table 3, even if whiskers are mixed with the raw material side, the circular net side, or both, the ES
R has been improved. According to the eleventh embodiment, the thickness 90.
Even with a high-density paper having a thickness of 3 μm and a density of 0.603 g / cm ² , the ESR is 0.497Ω, which is a significant improvement over the ESR of 0.748Ω of Comparative Example 5 having substantially the same thickness and density. I have.

[0034]

As described [Effect Invention above in detail, the electrolytic capacitor according to the present invention, the diameter 0.1~10μm borate al
There are characterized Miniumu whiskers on the use of electrolytic paper was混抄internally added in混抄rate of 1 to 60 wt%, the borate Al
Minium whiskers are circular and have a very small cross section,
Since the rigidity is high, voids can efficiently penetrate from the front surface to the back surface of the electrolytic paper obtained by blending with pulp, and it is possible to obtain dense paper quality, so that the conventional paper of the same thickness and the same density The impedance characteristics can be improved as compared with electrolytic paper made of natural pulp. And boric acid
Since the electrical resistance of the aluminum whisker itself is high, a high withstand voltage can be maintained. In addition, aluminum borate
Decrease in strength even if混抄Umm whisker is small, also boric
Since the papermaking properties of aluminum acid whiskers are also good, the mixed papermaking can keep its density and there are no pinholes. As a result, when compared with paper having the same thickness and density, natural short pulp can be used. Therefore, the impedance characteristic can be improved without lowering the withstand voltage particularly in the electrolytic capacitor for medium and high voltage.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-76114 (JP, A) JP-A-51-23660 (JP, A) JP-A-63-268214 (JP, A) JP-A-60-76 43811 (JP, A) JP-A-55-146872 (JP, A) JP-A-59-149017 (JP, A) JP-A-5-74660 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H01G 9/00-9/02

Claims (2)

(57) [Claims] 1. An electrolytic capacitor having electrolytic paper interposed between an anode foil and a cathode foil, wherein aluminum borate whiskers having a diameter of 0.1 to 10 μm are mixed and added to the electrolytic paper. Electrolytic capacitor. 2. The electrolytic capacitor according to claim 1, wherein the mixing ratio of the aluminum borate whisker is 1 to 60% by weight.