JPH05291080A - Electrolytic capacitor - Google Patents

Abstract

PURPOSE:To improve an electrolytic capacitor in impedance characteristics without making it deteriorate in withstand voltage and increase in fraction defective due to short circuits by a method wherein an electrolytic paper containing organic fine powder is used in the capacitor, where the electrolytic capacitor of intermediate or high voltage is composed of an anode foil, a cathode foil, and an electrolytic paper interposed between the foils. CONSTITUTION:An electrolytic capacitor is composed of an anode foil, a cathode foil, and an electrolytic paper interposed between the foils, where the electrolytic paper contains organic fine powder. The organic powder is round, as small as 0.01-20mum in diameter, and in the mixing ratio 1-70%.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an electrolytic capacitor constructed by interposing electrolytic paper between an anode foil and a cathode foil,
In particular, in an intermediate- and high-voltage electrolytic capacitor, by using an electrolytic paper mixed with organic fine powder, the impedance characteristics are improved without lowering the withstand voltage and without increasing the short-circuit defect rate. ..

[0002]

2. Description of the Related Art Generally, an electrolytic capacitor, particularly an aluminum electrolytic capacitor, is formed by winding electrolytic paper as a separator between an anode aluminum foil and a cathode aluminum foil to form a capacitor element, and then forming this capacitor element in a liquid state. It is manufactured by immersing it in the electrolyte solution of 1 above, impregnating it with an electrolyte, and sealing it. The electrolyte is usually ethylene glycol (EG),
Dimethylformamide (DMF) or γ-butyrolactone (GBL) is used as a solvent, and organic acid salts such as boric acid, ammonium adipate, and ammonium hydrogen maleate are dissolved in these solvents, and the solution is permeated from both ends of the capacitor element. Is produced.

In these conventional aluminum electrolytic capacitors, since electrolytic paper is impregnated with an electrolytic solution, impedance characteristics as a capacitor, particularly equivalent series resistance (hereinafter referred to as ESR).
Is abbreviated), and there is a possibility that it will deteriorate over time during use. Therefore, in order to improve the impedance characteristics, it is possible to reduce the resistance of the electrolytic solution, or to thin the electrolytic paper or reduce the density. However, lowering the resistance value of the electrolytic solution causes corrosiveness to the aluminum foil, while thinning the electrolytic paper or lowering the density increases the short-circuit failure rate when winding the electrolytic element, Even if no short circuit occurs, there is a drawback that the short circuit defect rate after being commercialized and put on the market is high.

Therefore, in order to improve the impedance characteristics, the shape and orientation of the fibers constituting the electrolytic paper have been studied. When the thickness and the density are the same, it is desirable that the voids in the electrolytic paper penetrate efficiently 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, the fiber diameter is close to a circle, and the fiber rigidity is high. From these points, means for changing the raw material of electrolytic paper from ordinary wood kraft pulp to synthetic fiber, manila hemp pulp, or esparto pulp is used.

However, although the synthetic fibers are circular and have the most ideal fiber form, when the synthetic fibers are mixed with the cellulosic fibers such as Manila hemp pulp, the synthetic fibers and the cellulose are not well compatible with each other and are not well formed. And the tensile strength is low. On the other hand, when 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 even 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 medium- and high-voltage electrolytic capacitors. Conventionally, electrolytic paper having a sufficiently high density and thickness for ensuring a withstand voltage has been used in medium- and high-voltage electrolytic capacitors even at the expense of electrical characteristics.

[0007]

Generally, when the rated voltage of a capacitor to be manufactured becomes high, the purpose is to prevent a short circuit accident due to contact between anode foils, to prevent passage of oxygen gas generated at the anode and hydrogen gas generated at the cathode. Therefore, it is customary to increase the density of the electrolytic paper and increase its thickness. Further, in order to increase the withstand voltage of the electrolytic paper itself, it is effective to increase the density and increase the thickness.

Densification of electrolytic paper indicates the degree of beating of electrolytic paper raw material by CSF (Canad according to JIS P8121).
It is realized 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.

On the other hand, however, if the degree of beating is advanced and the value of CSF is reduced, the electrical characteristics of the electrolytic capacitor are deteriorated. That is, the increase in the airtightness of the electrolytic paper impedes the ionic conduction, the increase in the ESR due to the redundancy of the ion current path, and the increase in the ESR due to the decrease in the amount of the electrolytic solution that can be impregnated and held with the decrease in the porosity.
In addition, the decrease in the amount of the electrolytic solution that can be impregnated and held also accelerates the deterioration of the characteristics due to the decrease in the electrolytic solution over time when used for a long time. Therefore, in spite of the deterioration of these electrical characteristics, especially in medium- and high-voltage electrolytic capacitors, accident prevention due to short circuit of electrode foil, oxygen gas generated inside the capacitor,
Since the highest priority is given to the prevention of small explosions and the securing of withstand voltage by mixing hydrogen gas, the density and thickness of electrolytic paper have been increased. Impedance characteristics and life are sacrificed to secure the withstand voltage.

Therefore, according to the present invention, the high impedance, which has been the fate of the conventional medium and high voltage electrolytic capacitors, is simply changed without lowering the withstand voltage of the electrolytic capacitor and increasing the short circuit defect rate. It is an object of the present invention to provide a new electrolytic capacitor which has a reduced electric field and excellent electric characteristics.

[0011]

In order to solve the above problems, the present invention provides an electrolytic capacitor comprising an electrolytic paper interposed between an anode foil and a cathode foil, wherein the electrolytic paper contains finely powdered organic matter and is internally added. The electrolytic capacitor is provided. The organic fine powder has a circular shape and an extremely fine cross section, the organic fine powder has a diameter of 0.01 to 20 μm, and the mixing ratio of the organic fine powder is 1 to 70%. To do.

[0012]

According to the present invention having the above structure, since the organic fine powder has a circular shape and an extremely small cross section and has high rigidity, voids are efficiently formed from the front surface to the back surface of the electrolytic paper obtained by mixing with pulp. Electrolyte consisting of conventional natural pulp of the same thickness and the same density can be obtained because it penetrates well and the fine particles of organic matter are agglomerated and filled in the voids between the fibers, so that the paper quality of appearance is dense. Impedance characteristics can be improved compared to paper. Moreover, since the organic fine powder itself has a high electric resistance, a high withstand voltage can be maintained. Therefore, it is possible to improve the impedance characteristics of the electrolytic capacitor for medium- and high-voltage without lowering the withstand voltage.

[0013]

EXAMPLES The constitution of the present invention will be described below together with various examples. The electrolytic paper according to the present invention is one in which organic fine powder is added in a mixed paper. In order to reduce the impedance of the electrolytic capacitor, the raw material fibers of the electrolytic paper are required to have two points: the fiber diameter is as small as possible, the fiber diameter is close to a circle, and the fiber rigidity is high. Therefore, the inventor paid attention to the organic fine powder from such requirements, and invented a mixed paper of the organic fine powder and pulp as the electrolytic paper.

The organic fine powder according to the present invention has a very small cross section such as a sphere, a spine, and a column, which is close to a circle, and has a high rigidity. Therefore, the two requirements required for the raw material fibers of the electrolytic paper are satisfied at a high level. When the mixed paper is added to the electrolytic paper, the organic fine powder is present at the contact points between the fibers. As a result, the contact between the organic fine powder and the fibers and the contact between the organic fine powders are close to point contact, and the voids are efficiently and continuously penetrated from the front surface to the back surface. Further, since the organic fine powder is agglomerated and filled in the voids between the fibers, it is possible to obtain an electrolytic paper having a dense paper quality in appearance. In addition, such a minute material is well suited to be mixed with a pulp material that has been beaten. Therefore, the papermaking property is also good. Therefore, since the organic fine powder has a circular shape with an extremely small cross section and high rigidity, it is possible to efficiently penetrate the voids from the front surface to the back surface and obtain a dense paper quality by mixing with pulp.

If the fiber diameter of the organic fine powder to be mixed is too small, the effect of improving the impedance is small, and conversely if it is too large, the paper-making property is poor and the texture is broken, and large particles fall off the paper surface, Becomes a pinhole, and it is easy to increase the short circuit defect rate. Therefore, the particle size is 0.0
The optimum range is 1 to 20 μm. In addition, the organic fine powder does not contain impurities that elute in the electrolytic solution, is stable with respect to the electrolytic solution, and heat when incorporated into an electrolytic capacitor,
It should be one that does not deteriorate with time due to stress such as pressure.

As the organic fine powder to be mixed under these conditions, regenerated cellulose fine powder such as rayon fine powder, natural cellulose fine powder which has been pulped or before pulp, fine powder of chemical fiber or synthetic fiber is suitable. is there. As a method for producing these organic fine powders, regenerated cellulose fine powders are produced by coagulating and regenerating spherically a cellulose derivative dissolved in various solvents in a coagulation bath. Natural fiber
In the case of fine powder of chemical fiber / synthetic fiber, the fiber has high rigidity with a cross section close to a circular shape and a diameter of 20 μm or less, for example, dry crushed material of bamboo such as natural cellulose, dry crushed material such as esparto and hemp pulp, and chemical fiber. In the case of viscose rayon fiber, in the case of synthetic fiber, polyacrylonitrile fiber, polyethylene terephthalate fiber, aromatic polyamide fiber are pulverized by dry or wet method.

The paper quality changes as follows depending on the mixing ratio of the organic fine powder. If the mixing ratio is increased, the ESR is lowered without lowering the withstand voltage, which is favorable. However, if the mixing ratio is too high, the tensile strength will be low. The decrease in tensile strength leads to an increase in paper breakage and short circuit defect rate in the element winding process, and aging short circuit rate after incorporation into a capacitor. Therefore, in order to have a practical tensile strength, the mixed papermaking ratio must be up to 70% by weight. If it is less than 1% by weight, the improving effect for achieving the object of the present invention does not occur.

The raw material pulp to which the fine organic powder is added in the papermaking process is not particularly limited in its type 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. Is also good. The mixing ratio of the organic fine powder is determined in the range of 1 to 70% by weight based on the electrolytic paper, depending on the CSF value of the raw material pulp, the thickness and density of the electrolytic paper to be obtained.

The electrolytic paper according to the present invention is prepared by subjecting the hemp pulp, esparto pulp, kraft pulp, etc., which are conventional raw materials for electrolytic paper, to known adjustments such as washing, dehydration and beating to remove impurities. Fine organic powder is added and mixed in an amount of 1 to 70% by weight with respect to the electrolytic paper. Next, an electrolytic paper having a predetermined thickness is prepared from this adjusted raw material by a paper machine such as a cylinder paper machine, a fourdrinier paper machine, a fourdrinier cylinder combination machine, and a cylinder / reticular combination machine. The electrolytic paper thus obtained is interposed between an anode foil and a cathode foil and wound up to produce a capacitor element, which is then impregnated with a liquid electrolyte and sealed to produce an electrolytic capacitor. The obtained electrolytic paper has a thickness of 10 to 130 μm and a density of 0.
Good results were obtained at 40 to 0.90 g / cm ³ .

The electrolytic paper, which is a mixed paper of the organic fine powder and pulp, has the following features. The withstand voltage of conventional electrolytic paper is largely borne by 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 preparation stage and making paper with pure cellulose fiber. In the present invention, an organic fine powder other than cellulose is mixed and made, but the electric fineness of the organic fine powder itself is high, and if a fine one is selected, the denseness of the paper can be maintained, and thus a high withstand voltage mixed paper can be obtained. .. Since the organic fine powder has a circular shape with an extremely small cross section and high rigidity, voids penetrate efficiently from the front surface to the back surface of the electrolytic paper obtained by mixing with pulp, and a dense paper quality is obtained. Therefore, the impedance characteristic can be improved. Also, the short-circuit failure rate of electrolytic paper depends on strength, thickness, density, compactness and the presence or absence of pinholes. Generally, if the strength is low, the short-circuit failure rate will be high, and if the pinhole is large or large, the short-circuit failure rate will be high. In the present invention, when the mixed papermaking ratio is 1 to 70% by weight, the strength of the organic fine powder mixed paper is small and the papermaking property of the organic fine powder is good, so that the mixed paper can maintain the compactness. , There are no pinholes. As a result, when compared with the same thickness and the same density, it is possible to obtain a good result in the short-circuit defect rate for the paper made with 100% natural pulp.

Tables 1 to 5 below show specific examples and thicknesses, densities, withstand voltages, tensile strengths, rated voltages, and short-circuit defect rates of practical examples and comparative examples produced to have approximately the same thickness and density. , ESR etc. are shown. The method of making the electrolytic capacitor and the method of measuring the electrolytic capacitor in the above examples are as follows.

Evaluation method of electrolytic paper The thickness, density and tensile strength of electrolytic paper are JIS C2301.
It was measured by the method specified in (Electrolytic capacitor paper). The withstand voltage and airtightness of the electrolytic paper were measured by the methods specified in JIS C2111 (Testing method for electrical insulating paper).

Method of Evaluating Electrolytic Capacitor Short Circuit Defect Ratio Electrolytic paper was wound together with an anode foil and a cathode foil to form an electrolytic capacitor element, and conduction by a short circuit between both electrodes was confirmed with a tester without impregnating an electrolytic solution. The short circuit defect rate was inspected for about 1000 elements, and the ratio of the short circuit elements to the total number of elements was defined as the short circuit defect rate.

Aging Short Failure Rate The electrolytic capacitor element manufactured by the above method was impregnated with a predetermined electrolytic solution and sealed to manufacture an electrolytic capacitor. About 100 of these electrolytic capacitors were aged at about 1.1 times the rated voltage, and the ratio of the shorted electrolytic capacitors to the number of test electrolytic capacitors was taken as the aging short-circuit rate.

ESR (Equivalent Series Resistance) 20 ° C., 1 k of the electrolytic capacitor subjected to the aging treatment
ESR at Hz was measured by LCR meter.

In Example 1, kraft pulp was beaten to a CSF value of 0 cc to obtain an organic fine powder having an average diameter of 5 μm.
This is an electrolytic capacitor using electrolytic paper obtained by mixing regenerated cellulose fine powder of m in a fourdrinier paper machine as a separator. Comparative Example 1 is an electrolytic paper made only from kraft pulp, and Comparative Example 2
Is 5 μm in minor axis and 10 in major axis instead of regenerated cellulose fine powder.
Electrolytic paper mixed with scaly mica of μm and length of 2 μm
Comparative Example 3 is an electrolytic capacitor using electrolytic paper mixed with regenerated cellulose fine powder having an average particle diameter of 30 μm. The mixing ratio in each example is 40% by weight with respect to the electrolytic paper.

[0027]

[Table 1]

As is clear from Table 1, there is a large difference in the electrical characteristics of the capacitors even though the electrolytic paper has substantially the same thickness and the same density. That is, the ESR of the capacitor of Example 1 using the electrolytic paper in which regenerated cellulose fine powder was mixed as the organic fine powder was 0.112Ω,
Compared with the ESR of 0.214Ω of the capacitor using the electrolytic paper not mixed with the organic fine powder shown in Comparative Example 1, this is remarkably improved. Moreover, the withstand voltage of Example 1 is 990V,
Comparative Example 1 was 950 V, and the withstand voltage did not decrease even when the organic fine powder was mixed. The tensile strength is also 2.0 kg, which is the same. That is, by mixing an organic fine powder having an extremely small thickness and a substantially circular cross section even if the thickness and the density are substantially the same, the ESR can be improved without affecting the withstand voltage, and the short-circuit defect rate can be improved. Can also be reduced. On the contrary, in the mixed paper of mica having a non-circular cross section in Comparative Example 2, the ESR was as high as 0.571Ω. In Comparative Example 3 in which regenerated cellulose fine powder having an average particle diameter of 30 μm was mixed, the dielectric breakdown strength did not decrease and the ESR was improved to 0.108Ω, but the particle diameter of the organic fine powder was too large. Tensile strength is 1.6Kg
As a result, large particles fell off the paper surface, and the short-circuit defect rate increased to 0.4%.

Examples 2 to 5 are electrolytic capacitors using, as a separator, electrolytic paper obtained by beating kraft pulp with a CSF value of 0 cc and mixing various organic fine powders with a 20% by weight Fourdrinier paper machine. The size of each organic fine powder used in Examples 2 to 5 is as follows: regenerated cellulose fine powder has a spherical shape with an average particle size of 5 μm, and PET (polyethylene terephthalate) fine powder has an average long fiber bundle called a strand with a diameter of 10 μm. It is a fine powder called milled fiber that is dry-ground to a length of 50 μm and has a cylindrical shape. Acrylic fine powder (polyacrylonitrile fine powder) has a diameter of 10 μm.
Made of milled fiber with an average length of 50 μm and has a cylindrical shape,
Aromatic polyamide fine powder has a diameter of 12 μm and a length of 60 μm
It is a milled fiber and has a cylindrical shape. Comparative Example 4 is an electrolytic paper produced by using a raw material obtained by beating kraft pulp to a value of 0 cc with a CSF value and making the paper have substantially the same thickness and the same density as those of Examples 2 to 5, and the fine organic powder is a mixed paper. I haven't.

[0030]

[Table 2]

As is clear from Table 2, by mixing the fine organic powders regardless of the kind of the fine organic powders to be mixed, the ESR is definitely improved as compared with Comparative Example 4 in which the fine powders are not mixed.

Examples 6 to 11 use kraft pulp as CSF.
Of the regenerated cellulose fine powder having an average particle diameter of 5 μm as an organic fine powder mixed with a Fourdrinier paper machine, two electrolytic papers are stacked to form a separator, and an electrolytic capacitor having a rating of 300 V is used. Is. In Comparative Example 5, the mixed papermaking ratio was 70% by weight, and in Comparative Example 6, organic fine powder was not mixed.

[0033]

[Table 3]

As is clear from Table 3, by mixing finely divided organic matter powders even if they have substantially the same thickness and the same density,
The ESR can be improved without affecting the withstand voltage. Further, it can be seen that the mixed effect ratio is improved from 1% by weight shown in Example 6, and that the effect is increased as the mixed effect ratio becomes higher. However, as shown in Comparative Example 5, when the mixing ratio of the organic fine powder was 80% by weight, the aging short circuit defect rate of the capacitor was as high as 4%. This is because when the mixing ratio exceeds 70%, the mechanical strength such as flexibility and tensile strength of the paper decreases, and workability deterioration such as paper breakage in the capacitor winding process and mechanical strength decrease increase the aging short circuit defect rate. This is because it is considered to cause Therefore, the optimum mixing ratio should be determined in consideration of the effect of improving the electric characteristics and other characteristics, but the range of 1 to 70% by weight is suitable.
If it is a mixed paper of up to 70% by weight, it has a practical tensile strength.

In Examples 12 to 14, two kinds of kraft pulps having different beating degrees were used as organic fine powder, and the average particle size was 5 μm.
m regenerated cellulose fine powder was mixed and made into paper by a Fourdrinier combination machine and formation voltage 450
It is a capacitor using V foil. Kraft pulp C
The SF is 0 cc on the long net side and 100 cc on the circular net side. In Example 12, 30% by weight of regenerated cellulose fine powder was used as the raw material on the long net side and Example 13 on the cylinder side.
No. 4 is an electrolytic paper prepared by mixing 15% by weight of regenerated cellulose fine powder with the raw materials on the Fourdrinier and the cylinder side, respectively. Comparative Example 7 is an electrolytic capacitor using electrolytic paper which is a double paper obtained by making a kraft pulp not mixed with regenerated cellulose fine powder with a Fourdrinier combination machine.

[0036]

[Table 4]

As is clear from Table 4, even when fine powder of organic matter is mixed into the raw materials of the long-net side, the cylinder side or both, E
SR has been improved. According to Example 12, a thickness of 9
Even with a thick high-density paper having a thickness of 0.2 μm and a density of 0.599 g / cm ² , the ESR is 0.488 Ω, and the ESR of Comparative Example 7 having substantially the same thickness and density is 0.751 Ω.
Has been greatly improved.

Example 15 uses Manila hemp pulp as CSF50.
Beated to 0 cc, as an organic fine powder, average particle size 5 μm
It is an electrolytic capacitor using electrolytic paper obtained by mixing the regenerated cellulose fine powder of No. 1 with 20% by weight with a cylinder paper machine. In Comparative Example 8, only Manila hemp pulp beaten to CSF 500 cc was used, and in Comparative Example 9, 40% of esparto pulp was added to Manila hemp pulp beaten to CSF 500 cc to make paper having substantially the same thickness and the same density as the electrolytic paper of Example 15. It is an electrolytic capacitor using electrolytic paper.

[0039]

[Table 5]

As is clear from Table 5, even with the low density paper of Example 15 having a density of 0.500 g / cm ³ , the ESR of 0.099Ω was obtained by mixing the organic fine powder.
This is an improvement from 0.141 Ω in Comparative Example 8 in which no paper was mixed. Further, due to the dense paper quality, the short-circuit defect rate is 0%, which is a great improvement from 0.8% in Comparative Example 8. Therefore, the present invention is effective for E
It is possible to improve both the SR and the short circuit defect rate.

[0041]

As described in detail above, the electrolytic capacitor according to the present invention uses the electrolytic paper mixed with the organic fine powder, and the organic fine powder has a circular shape and an extremely fine cross section, and also has rigidity. Since it is high, voids can be efficiently penetrated from the front surface to the back surface of the electrolytic paper obtained by mixing paper with pulp, and since a dense paper quality can be obtained, conventional natural pulp of the same thickness and the same density can be obtained. The impedance characteristic can be improved as compared with the electrolytic paper made of
Moreover, since the organic fine powder itself has a high electric resistance, a high withstand voltage can be maintained. Further, even when the organic fine powder is mixed and produced, the decrease in strength is small, and since the fine organic powder has a good paper-making property, the mixed paper can maintain the compactness and has no pinhole. As a result, when compared with the same thickness and the same density, it is possible to obtain a good result in the short-circuit defect rate for the paper made with 100% natural pulp. Therefore, it is possible to improve the impedance characteristics of the electrolytic capacitor for medium- and high-voltage without lowering the withstand voltage.

Claims (4)

[Claims] 1. An electrolytic capacitor comprising an electrolytic paper interposed between an anode foil and a cathode foil, wherein the electrolytic paper contains finely divided organic powder mixed therein. 2. The electrolytic capacitor according to claim 1, wherein the organic fine powder is circular and has an extremely small cross section. 3. The organic fine powder has a diameter of 0.01 to 20.
The electrolytic capacitor according to claim 1, which has a thickness of μm. 4. The electrolytic capacitor according to claim 1, 2 or 3, wherein the mixing ratio of the organic fine powder is 1 to 70% by weight.