JP2010153427A - Separator and solid electrolytic capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator which can be enhanced in productivity by achieving high-density packing of a conductive high polymer and securing continuity of the conductive high polymer, thereby improving electric characteristics such as impedance characteristics, especially, equivalent series resistance (hereinafter ESR); and to provide a solid electrolytic capacitor using the separator. <P>SOLUTION: The present invention relates to: the separator for the solid electrolytic capacitor formed by interposing and winding a separator between an anode foil and a cathode foil, and holding the conductive high polymer as a solid electrolyte layer after carbonizing the separator, the separator containing 50% by weight of natural cellulose fiber, 10 to 40% by weight of heat-resistive fiber of ≥450°C in thermal decomposition point, and a predetermined amount of a binder; and the solid electrolytic capacitor using the separator. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention creates a capacitor element by winding a separator between an anode foil and a cathode foil, a solid electrolytic capacitor having a solid electrolyte layer formed in the capacitor element, and a solid using the separator With regard to the electrolytic capacitor, in particular, it is possible to achieve a high filling of the conductive polymer and ensure the continuity of the conductive polymer, thereby improving impedance characteristics, particularly equivalent series resistance (hereinafter abbreviated as ESR), capacitance. This improves the electrical characteristics and improves productivity.

  In general, an electrolytic capacitor, specifically, a wound aluminum electrolytic capacitor, is formed by winding a separator between an anode aluminum foil and a cathode aluminum foil to form a capacitor element. It is manufactured by dipping in a liquid, impregnating with an electrolyte, and sealing. As the electrolytic solution, ethylene glycol (EG), dimethylformamide (DMF), or γ-butyrolactone (GBL) is usually used as a solvent, and solutes such as boric acid, ammonium adipate, and ammonium hydrogen maleate are dissolved in these solvents. It is manufactured by infiltrating from both ends of the capacitor element.

  Various digital electronic devices for commercial and consumer use such as flat-screen TVs, Blu-ray discs, and high-performance home video game devices have dramatically increased the operating frequency, and the power consumption of the electronic devices as a whole has also increased. The current situation is strongly demanded. Therefore, electrolytic capacitors, which are parts constituting these electronic devices, are also small in size and large in capacitance, particularly in equivalent series resistance (hereinafter abbreviated as ESR) in order to increase the operating frequency and save power. Things are sought.

  However, it is difficult to sufficiently reduce ESR in a high frequency range in an electrolytic capacitor using the above-described electrolytic solution as an electrolyte. This is because the specific resistance of the electrolytic solution itself cannot be lowered. For this reason, electrolytic capacitors using manganese dioxide or TCNQ complexes have been developed as electrolytes with lower specific resistance.

  Further, recently, solid electrolytic capacitors using conductive polymers having conductivity such as polypyrrole and polythiophene as electrolytes have been developed. Since the specific resistance of these conductive polymers is smaller than the specific resistance of manganese dioxide or TCNQ complex, it is possible to manufacture a capacitor having good ESR of the electrolytic capacitor itself. The conductive polymer refers to a polymer that has conductivity and can be used as an electrolyte of an electrolytic capacitor.

  Conventionally, a solid electrolytic capacitor using such a conductive polymer as an electrolyte has been mainly used for a low voltage application of 10 WV or less for digital home appliances such as a personal computer application, but further, a low voltage of 4 WV or less and 100 μF or more. There is a demand for an increase in capacitance. On the other hand, as a further application development in recent years, for example, it has been used for in-vehicle applications and the like. For in-vehicle applications, a high withstand voltage of 25 WV is required at high temperatures. With the progress of electrification of vehicles such as hybrid cars and electric cars, it is predicted that the withstand voltage of electrolytic capacitors for in-vehicle use will continue to increase.

  In recent years, lead-free solder has been introduced since lead in solder has an adverse effect on the environment. Along with this, the solder reflow temperature has increased from the conventional 180 ° C. to about 260 ° C., and it is indispensable to inevitably increase the heat resistance of various electronic components used in electronic devices. ing.

  However, when an electrolytic capacitor, particularly a wound aluminum solid electrolytic capacitor is manufactured using a conductive polymer as an electrolyte, natural cellulose used in an aluminum electrolytic capacitor that uses an electrolytic solution as a conventional electrolyte. There is a problem that a separator made of fiber cannot be used as it is. This is because the cellulose in the separator has a hydroxyl group (OH group) and impedes impregnation with the polymerization solution of the conductive polymer or polymerization of the conductive polymer. Furthermore, since the oxidizing agent (such as p-toluenesulfonic acid ferric acid) contained in the polymerization solution causes a chemical reaction with the separator made of natural cellulose fiber, it may damage the separator and cause a short circuit. Therefore, in a solid electrolytic capacitor using a conductive polymer as an electrolyte, there is a problem that a separator made of natural cellulose fibers cannot be used as it is.

  In order to suppress the influence of such cellulose, an attempt has been made to remove the above-described adverse effects of cellulose by heat treating the wound capacitor element and carbonizing the separator. However, a capacitor element using a separator made of natural cellulose fiber has a problem that the shape of the element is lost due to carbonization or short-circuit defects are increased due to stress caused by heat treatment. Therefore, there is provided a separator made of natural cellulose fiber that has practical utility to satisfy the recent requirements for electrolytic capacitors even though the harmful effects of cellulose can be removed by carbonization, and a solid electrolytic capacitor using the separator. Absent.

  Accordingly, various attempts have been made to develop a separator that does not use natural cellulose fibers and a solid electrolytic capacitor that uses the separator. For example, it has been proposed to use a separator using glass fibers instead of cellulose fibers, but it is difficult to reduce the thickness of glass fiber paper, which makes the capacitor element large and difficult to wind. The problem arises.

  It has also been proposed to use a separator using chemical fibers as a raw material for the separator. An electrolytic capacitor using a vinylon fiber as a separator (Patent Document 1) or a solid electrolytic capacitor using a polyester fiber as a separator (Patent Document) 2) A wound electrolytic capacitor using an acrylic fiber as a separator (Patent Document 3) is provided. A solid electrolytic capacitor using a 100% synthetic fiber separator made of aramid floc and / or aramid fibrid having higher heat resistance has also been proposed (Patent Document 4). According to the separators described in these Patent Documents 1 to 4, at least the above problems can be solved.

  On the other hand, as a means for removing the adverse effects caused by carbonization of a separator made of cellulose as a raw material and improving the dimensional stability of the carbonization process, a separator mixed with acrylic fibers has been proposed (Patent Document 5). By using a raw material in which acrylic fiber, which is a heat-resistant fiber having no melting point, is blended with natural cellulose fiber as a raw material for the separator, the shrinkage of dimensions during heat treatment is suppressed. An object of the present invention is to obtain a solid capacitor in which the external dimensions of the capacitor element are unlikely to change.

In addition, a separator composed of at least two components having different pyrolysis temperatures is used, and before the formation of the solid electrolyte layer, the capacitor element is not less than the pyrolysis temperature of the low pyrolysis temperature of the components of the separator. A separator formed by heating to a temperature to decompose and remove at least part of a low pyrolysis temperature component and reducing the amount of the separator has been proposed (Patent Document 6). Specifically, aramid fiber and cellulose are disclosed as two types of constituent components.
Japanese Patent No. 3319501 JP 2001-155967 A JP 2001-332451 A JP 2002-203750 A JP 2004-146707 A JP 2004-193402 A

  In order to realize a reduction in ESR in a high frequency range, it is an effective means to use a conductive polymer having a small specific resistance as a solid electrolyte, and a means for carbonizing a separator made from a conventional natural cellulose fiber. Instead, various developments such as those described in Patent Documents 1 to 6 have been attempted, but all have problems to be solved and do not satisfy the recent requirements for solid electrolytic capacitors. .

  The solid electrolytic capacitor (Patent Document 1) using the vinylon fiber has a problem that the product expands when used in a surface mount electrolytic capacitor. Further, in the solid electrolytic capacitor using the polyester fiber (Patent Document 2), the solder reflow temperature has been increased to about 260 ° C. in recent years, and the polyester having a melting point of 260 ° C. has a problem in terms of heat resistance.

  Table 1 summarizes the decomposition temperatures and melting points of vinylon fibers (Patent Literature 1), polyester fibers (Patent Literature 2), acrylic fibers (Patent Literatures 3 and 5), and aramid fibers (Patent Literatures 4 and 6).

  As shown in Table 1, the vinylon fiber (Patent Document 1) has a problem that its decomposition temperature is 240 ° C. and its heat resistance is low. That is, the vinylon fiber undergoes a desorption phenomenon of water molecules in the air at a temperature of 240 ° C. or higher, generates gas, and the main chain of the polymer is cut, separated, and thermally decomposed. Therefore, there is a problem that the case expands after the solder reflow. Polyester fibers (Patent Document 2) also have a low melting point of 260 ° C. and low heat resistance, and are not suitable for temperature when the solder reflow temperature is 260 ° C.

  On the other hand, acrylic fibers (Patent Documents 3 and 5) are heat-resistant fibers having no melting point and have a decomposition temperature of 300 ° C. Therefore, the solder reflow at 260 ° C. has been problematic for vinylon fibers and polyester fibers. Can also be used. However, the acrylic fiber has a problem that the fiber contracts in the length direction by heating, and the dimensional change of the separator occurs. Acrylic is heated and stretched in the spinning process and spun to a specified fiber diameter, but has the property of restoring its original size by heating the fiber again. Therefore, the acrylic fiber shrinks in the length direction depending on the temperature during heating and polymerization in the carbonization process, so the size of the separator changes, and when the amount of acrylic fiber used increases, the size shrinkage of the separator during heating increases. When the shrinkage in the thickness direction is large, the element-stopping tape is cut and the element is separated, so that there is a problem that the characteristics of the heat-resistant fiber cannot be exhibited.

  On the other hand, aramid fiber is also a heat-resistant fiber having no melting point, and it can be used in 260 ° C. solder reflow, which has been a problem with vinylon fiber and polyester fiber, and the decomposition temperature is 450 ° C. or higher. Aramid fibers do not have the property of being restored by heating unlike acrylic fibers. A solid electrolytic capacitor using a 100% synthetic fiber separator made of aramid floc and / or aramid fibrid disclosed in Patent Document 4 is a monomer, 3,4-ethylenedioxythiophene (EDT) is an oxidizing agent. Polyethylene dioxythiophene (PEDT) obtained by polymerization with ferric p-toluenesulfonate is used as a solid electrolyte, and the maximum temperature of the heat treatment is the temperature of the polymerization step, which is less than 200 ° C. Does not deteriorate.

  However, the separator according to Patent Document 4 is a 100% synthetic fiber separator made of aramid floc and / or aramid fibrid. If the blending ratio of the aramid fiber, which is a heat resistant fiber, is too high, the density is decreased and the voids are increased. It becomes impossible in principle, and since there are not enough gaps to hold the conductive polymer in the separator, the conductive polymer cannot be held sufficiently, so further electrical characteristics such as higher capacitance and improved ESR I cannot expect improvement.

Similarly, Patent Document 6 using an aramid fiber as a raw material discloses an example in which an aramid fiber and a cellulose fiber are 50:50 by weight and have a thickness of 40 μm and a basis weight of 10 g / m ^2. In general, a binder is indispensable for making a synthetic fiber paper having a practical tensile strength that can withstand element winding using fibers. When a separator is made without using a binder as in Patent Document 6, hydrogen bonds generated between the hydroxyl groups of cellulose are reduced, so that the tensile strength is reduced. In order to confirm this, in the blended composition of natural cellulose fiber and aramid fiber, a separator was made with a thickness of 40 μm and a density of 0.45 g / cm ³ without using a binder, and the blended amount of natural cellulose fiber and aramid fiber. The tensile strength was measured while changing. The results are shown in Table 2.

  As shown in Table 2, the tensile strength of the separator decreases as the blending amount of the aramid fiber is increased from 100% by weight of the natural cellulose fiber. In the case of only natural cellulose fibers, the tensile strength was 12.7 N / 15 mm. However, when the blending amount of aramid fibers was increased without using a binder, for example, 80 wt% of natural cellulose fibers and 20 wt% of aramid fibers were used. In the separator, the tensile strength is reduced to 6.9 N / 15 mm. A separator is interposed between the anode foil and the cathode foil, and the minimum tensile strength necessary for winding the capacitor element is 7.8 N / 15 mm or more when wound at a low speed, and is wound at a high speed. In this case, 9.8 N / 15 mm or more is necessary, and preferably a tensile strength of 11.8 N / 15 mm or more is necessary.

  In the example of Patent Document 6, a raw material in which 50% by weight of aramid fiber is blended without blending a binder is used, and a tensile strength of 7.8 N / 15 mm or more cannot be obtained. When the separator disclosed in the example of Patent Document 6 was actually manufactured and its tensile strength was measured, it was only 2.6 N / 15 mm, and an element could not be practically produced with this strength.

  Moreover, in the Example of patent document 6, it is suitable that the porosity of a separator shall be 85% or more, especially 85-95% of range, and it is trying to remove a cellulose completely by heat processing. Therefore, in the examples, the aramid fiber and cellulose that were in a weight ratio of 50:50 before the heat treatment are 100: 0 after the heat treatment, and the cellulose is supposed to be completely lost by the heat treatment. That is, it is shown that the above-mentioned porosity is achieved by making the portion where the cellulose existed in the separator into a complete void, and the cellulose is unnecessary. Certainly, at first glance, it is considered that the higher the porosity and the more voids in the separator, the better the impregnation property of the conductive polymer polymerization solution and the greater the amount of impregnation.

  However, in order to uniformly and sufficiently impregnate the polymerization solution between the anode foil and the cathode foil by a vacuum impregnation method or the like, a path for the polymerization solution to flow and a medium for holding the polymerization solution are required. The fiber constituting the separator plays the role. In addition, a medium is necessary to hold the conductive polymer formed by polymerization of the monomer solution of the conductive polymer and the oxidant solution in the polymerization solution.

  Therefore, as in Patent Document 6, when the porosity of the separator is extremely increased, or the portion where the cellulose is present in the separator is made a complete void, the fiber in the separator serving as a medium is an aramid that is a chemical fiber. On the other hand, the impregnation property of the polymerization solution is deteriorated. Moreover, since the medium for holding the conductive polymer formed by polymerization is also reduced, the continuity is lost.

  Natural cellulose fiber cannot be used as a separator for a solid electrolytic capacitor as it is, and carbonization by heat treatment is necessary to suppress the influence of cellulose, but even if carbonization can suppress the influence of cellulose, the element New adverse effects such as collapse of the shape will occur. Therefore, a practical separator using cellulose as a raw material has not been provided. On the other hand, cellulose is widely used as a raw material for separators of electrolytic capacitors using an electrolytic solution as an electrolyte, and has inherently excellent advantages as a raw material for separators such as having a high porosity. Heat-resistant fibers with a thermal decomposition temperature of 450 ° C or higher, including aramid fibers, are attractive materials as separator raw materials from the viewpoint of improving the heat resistance of solid electrolytic capacitors. There are many disadvantages from the viewpoint of securing and improving the impregnation property of the polymerization liquid, and the single substance is not suitable as a raw material for the separator.

  Therefore, the present invention eliminates various problems of conventional separators for solid electrolytic capacitors and solid electrolytic capacitors using the separators, and uses a separator mainly composed of natural cellulose fibers to provide conductivity. Improve impedance characteristics, especially electrical characteristics such as ESR, and obtain solid electrolytic capacitors with improved productivity by ensuring high polymer packing and ensuring the continuity of conductive polymers. Specifically, an object of the present invention is to obtain a separator for a solid electrolytic capacitor that realizes an electrostatic capacity of 100 μF or more and an ESR of 20 mΩ or less after aging, and a solid electrolytic capacitor using the separator.

  In order to achieve the above object, the present inventors have earnestly studied the combination of natural cellulose fiber and heat resistant fiber, and obtained the following knowledge. In order to secure a large number of voids for holding the conductive polymer polymerization solution in the separator, it is effective to increase the blending amount of the natural cellulose fiber and increase the degree of carbonization. However, when the blending amount of natural cellulose fiber is increased, the dimensional stability of the separator is lost due to carbonization, and when the carbonization degree is too strong, the fiber shape of the natural cellulose fiber itself for holding the conductive polymer is lost. It disappears excessively, and it becomes difficult to act as a medium for holding the polymerization solution and a medium for holding the polymerization solution and a medium for holding the polymerization solution. Furthermore, when the blending amount of the heat resistant fiber is small, it is impossible to ensure the dimensional stability of the separator by carbonization.

  On the other hand, in order to ensure the dimensional stability of the separator after carbonization, the blending amount of natural cellulose fibers is reduced, the blending amount of heat-resistant fibers is increased, and the degree of carbonization is weakened. However, if the blending amount of natural cellulose fibers is reduced and the blending amount of heat-resistant fibers is increased, sufficient voids cannot be secured even if carbonized, and the tensile strength at the time of element winding is lost. Further, if the degree of carbonization is insufficient, the harmful effects of the hydroxyl group of natural cellulose cannot be removed. Furthermore, in order to mix heat resistant fibers, it is indispensable to add a binder in order to ensure the tensile strength when the element is wound.

  These findings are summarized as follows, focusing on separators made from natural cellulose fibers. Separators made from natural cellulose fibers have the disadvantage of hindering the polymerization of the conductive polymer by hydroxyl groups, but it is easy to obtain a high porosity and carbonized fibers flow in the polymerization solution to suppress the influence of hydroxyl groups. And a medium for holding the polymerization solution and a medium for holding the polymerized conductive polymer. By carbonizing a separator made of natural cellulose fiber as a raw material, the adverse effects of the hydroxyl group can be removed and the porosity can be increased. However, if the degree of carbonization is excessive, the fiber form of the cellulose fiber will disappear. The medium holding the conductive polymer is lost, and the dimensional stability of the separator is deteriorated. Thus, when heat-resistant fibers are blended with the raw material fibers, the dimensional stability during carbonization can be improved, but the tensile strength when winding the element is insufficient. In order to ensure the tensile strength, it is necessary to blend a binder for joining the entanglement points of the heat-resistant fibers.

  On the other hand, natural carbon fibers that are not carbonized leave the harmful effects of hydroxyl groups, and an increase in the amount of natural cellulose fibers adversely affects dimensional stability during carbonization. In addition, an increase in the amount of heat-resistant fiber has an adverse effect on ensuring the porosity, holding the conductive polymer, and ensuring the tensile strength. Furthermore, an increase in the amount of the binder adversely affects the increase in porosity. As described above, natural cellulose fiber, heat-resistant fiber and binder have advantages and disadvantages as raw materials for separators of solid electrolytic capacitors, respectively, and realize high packing of conductive polymer and conductivity. In order to achieve low ESR by ensuring the continuity of the polymer, it is necessary to ensure a balance between these, and the present inventors provide the following separator and a solid electrolytic capacitor using the separator To do.

  In order to achieve the above object, the present invention provides a solid electrolytic capacitor in which a separator is interposed between an anode foil and a cathode foil, and the separator is carbonized to carbonize the separator and then hold a conductive polymer as a solid electrolyte layer. As a separator, a separator containing 50% by weight or more of natural cellulose fiber, 10% to 40% by weight of heat-resistant fiber having a thermal decomposition temperature of 450 ° C. or more, and a predetermined amount of binder is basically used. As offered. And the structure which carbonizes so that a fiber form body may remain while removing the hydroxyl group of a natural cellulose fiber, and by carbonizing natural cellulose fiber by heating, while forming a space in a separator, the fiber form body of a natural cellulose fiber remains When heating for carbonization, the natural cellulose fiber is carbonized in a state where the shape of the separator is maintained by the heat-resistant fiber, thereby forming voids in the separator and leaving the fibrous body of the natural cellulose fiber. Provide a configuration to be made. In addition, the conductive polymer is continuously held along the fiber shaped body, and partially unoxidized cellulose fibers remain together with the fiber shaped body.

  Further, as natural cellulose fibers, one or more fibers selected from Manila hemp pulp, sisal hemp pulp, esparto pulp, cotton pulp, jute pulp, hemp pulp, and wood pulp are used. One or more fibers selected from aramid fiber, amideimide fiber, polyimide fiber, fibrillated aramid fiber, aramid fibrid, fibrillated amidimide fiber, alumina fiber, boron fiber, carbon fiber, and glass fiber are used as the heat resistant fiber. To do. As the binder, 10 wt% to 30 wt% of wet heat fusion resin is contained, and polyvinyl alcohol is used as the wet heat fusion resin. Further, 2% by weight to 10% by weight of polyacrylamide resin is contained as a binder.

  Then, the separator having the above-described configuration is wound between an anode foil and a cathode foil, and after carbonizing the separator, a solid electrolytic capacitor is provided that retains a conductive polymer as a solid electrolyte layer. Further, the separator is carbonized by heating at a temperature of 250 ° C. to 350 ° C. for 60 minutes to 120 minutes, and at least one of polypyrrole, polythiophene, polyaniline, or a derivative thereof is used as the conductive polymer.

  According to the separator obtained by the present invention and the solid electrolytic capacitor using the separator, the natural cellulose fiber is changed from hydrophilic to hydrophobic by carbonizing the capacitor element, and the conductive polymer due to the hydroxyl group of cellulose. Inhibition of the impregnation of the polymerization solution and polymerization of the conductive polymer can be suppressed. Further, the carbonized cellulose expands the porosity of the separator, and after carbonization, the fibrous structure and partially unoxidized cellulose fibers remain so that the polymerization solution flows through the fibrous structure and unoxidized fibers. And a medium for holding the polymerization solution and a medium for holding the polymerized conductive polymer.

  At the same time, by blending heat-resistant fibers having a thermal decomposition temperature of 450 ° C. or higher with natural cellulose fibers at a specific blending ratio, it is possible to ensure the dimensional stability of the separator against heating during carbonization. In addition, by blending the binder at a specific ratio, it is possible to obtain the tensile strength required for element winding without adversely affecting the porosity, and maintain the strength required as a solid electrolytic capacitor, resulting in a short circuit failure. The rate can be improved.

  Therefore, by increasing the porosity of the separator, which has been considered difficult in the past, it is possible to ensure the impregnation of the polymerization solution, the high filling of the conductive polymer and the continuity, and the dimensional stability of the separator against heating during carbonization. Can be improved at the same time. The polymerized conductive polymer is continuously held in the separator as a conductive polymer layer along the voids and carbonized fibers after carbonization and unoxidized fibers, which adversely affects other characteristics of the solid electrolytic capacitor ESR and the like in the high frequency range can be improved without any problems. Specifically, to obtain a solid electrolytic capacitor that realizes a capacitance of 100 μF or more and an ESR of 20 mΩ or less in the capacitor element characteristics after aging (finished product) without adversely affecting other characteristics such as short circuit defects. Can do.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best embodiment of a separator according to the present invention and a solid electrolytic capacitor using the separator will be described. The present invention is a solid electrolytic capacitor separator in which a conductive polymer is held as a solid electrolyte layer, 50% by weight or more of natural cellulose fibers, and 10% to 40% by weight of a heat decomposition temperature of 450 ° C. or more. It is characterized by containing fibers and a predetermined amount of binder.

  Since natural cellulose fiber has a hydroxyl group, it impedes impregnation of the polymerization solution of the conductive polymer or polymerization of the conductive polymer, but it is possible to suppress the harmful effects of the hydroxyl group by carbonization. In addition, the porosity itself is further expanded by carbonization, and by leaving the fiber-shaped body after carbonization, the path for the polymerization solution to flow, the medium for holding the polymerization solution, and the polymerized conductivity It can function as a medium for holding a polymer. Therefore, in the present invention, 50% by weight or more of natural cellulose fiber is blended as the main fiber, and further blended in the range of 50% by weight to 88% by weight.

  The natural cellulose fiber is not particularly limited as long as it is a natural cellulose fiber that can be used as a separator for an aluminum electrolytic capacitor that uses an electrolyte as an electrolyte. Manila hemp pulp, sisal pulp, esparto pulp, cotton pulp, jute pulp, Use one or more fibers selected from hemp pulp, wood pulp, etc. Adding 50% by weight or more of natural cellulose fiber ensures a large space for holding the polymer solution of the conductive polymer in the separator, and holds the route for the polymer solution to flow after carbonization and the polymer solution. It is for functioning as a medium for holding the polymerized conductive polymer.

  These natural cellulose fibers need to be carbonized by heat treatment in order to suppress the influence of hydroxyl groups, but the dimensional stability of the separator deteriorates due to carbonization as the blending amount of the natural cellulose fibers is increased. Therefore, in order to ensure dimensional stability by carbonization even when 50% to 88% by weight of natural cellulose fiber is blended, 10% to 40% by weight of heat resistant fiber having a thermal decomposition temperature of 450 ° C. or higher is used for the separator. Blend as a raw material. Specifically, one or more fibers selected from aramid fiber, amideimide fiber, polyimide fiber, fibrillated aramid fiber, aramid fibrid, fibrillated amidimide fiber, alumina fiber, boron fiber, carbon fiber, and glass fiber are used. Is possible.

  As shown in Table 3, these heat resistant fibers all have a heat resistance of 450 ° C. or higher. The heat resistance of 450 ° C. or higher is required to maintain the basic form of the separator without being affected by the heating temperature during carbonization, as well as being able to be used in solder reflow at 260 ° C. is there. In addition, the blending amount is set to 10% to 40% by weight, even when natural cellulose fibers are reduced by carbonization, to maintain the basic form while maintaining the dimensional stability of the separator without being affected by it, It balances the increase in porosity due to carbonization of natural cellulose fibers.

  Compared with the acrylic fiber shown in Patent Document 3, the dimensional stability of the separator can be secured against heating during carbonization by blending natural cellulose fiber with heat-resistant fiber having a thermal decomposition temperature of 450 ° C. or higher such as aramid fiber. And clarify. Aramid fibers and amideimide fibers were used as heat resistant fibers at 450 ° C. or higher. In the experiment, with respect to acrylic fiber, aramid fiber, and amideimide fiber, the blending amount with respect to natural cellulose fiber was changed from 0% to 100%, respectively, and the thickness dimension retention ratio and the area dimension retention ratio after heating at 260 ° C. for 60 minutes. Was measured as an evaluation of dimensional stability. The results are shown in Tables 4 and 5.

[Evaluation of thickness dimension retention]
The thickness retention is such that 10 test pieces of 250 mm × 15 mm are folded and the tip is fixed with a staple. The measurement was performed with a micrometer defined in the old JIS C2301 (electrolytic capacitor paper) and calculated from the following equation.
Thickness retention (%) = Thickness after treatment / Thickness before treatment × 100
Thickness retention is a value indicating the rate of change when the thickness before processing is set to 100. If the value exceeds 100, it indicates an increase, and the greater the value, the greater the change in thickness. ing. When the change in the thickness direction is large, there is a problem that the tape stopper is cut and the element can bounce or collapse.

[Evaluation of area dimension retention]
A test piece of 100 mm × 100 mm was used as the area retention rate. The measurement was performed using a caliper and calculated from the following formula.
Area retention ratio (%) = area after treatment / area before treatment × 100
The area retention ratio is a value indicating the area retention when the area before processing is 100, and the smaller the value, the larger the change. The smaller the retention ratio, the greater the change in the external dimensions of the capacitor element, and the short circuit. The defect rate and the variation of LC and ESR increase.

  As shown in Table 4, when acryl is blended with natural cellulose fiber, the thickness direction dimension greatly increases with respect to the thickness before heating, and when acryl is blended with 20% by weight, the thickness dimension retention is 108.0. %, Exceeding the thickness before heating. On the other hand, when amideimide or aramid was blended with natural cellulose fiber, the thickness dimension retention ratio approached 100% from 88% in the case of natural cellulose alone as the blending ratio increased. That is, thickness shrinkage decreases as the amount of amideimide or aramid increases.

  As shown in Table 5, when acrylic is blended with natural cellulose fibers, the separator shrinks in the surface direction, and the area size retention rate that was 99.7% with natural cellulose fibers alone is blended with 20% by weight of acrylic. 85.3%. Since acrylic does not lose weight due to oxidation / dehydration reactions, etc., its volume can be regarded as constant. Therefore, it is considered that the thickness inevitably increases as the surface contracts. In other words, the increase in thickness indicates a large shrinkage in the surface direction as a separator, that is, a decrease in area. When acrylic is mixed as shown in Table 5, the area size increases before heating as the blending ratio increases. It has decreased greatly with respect to the area. On the other hand, when amideimide or aramid is blended with natural cellulose fiber, the thickness change tends to decrease as the blending amount increases, indicating that the dimensional stability against heating is large.

  From these facts, heat-resistant fibers having a heat resistance of 450 ° C. or more compensate for loss of dimensional stability of the separator due to oxidation and dehydration of cellulose by carbonizing a separator made of natural cellulose fibers. be able to. That is, the outer skeleton structure of the separator can be maintained by the heat resistant fiber, and the adverse effects caused by carbonizing the natural cellulose fiber to suppress the hydroxyl group can be eliminated.

  When the separator is interposed between the anode foil and the cathode foil, and the minimum tensile strength necessary for winding the capacitor element is 9.8 N / 15 mm or more when wound at a high speed. However, when heat resistant fibers are blended with natural cellulose fibers, hydrogen bonds generated between the hydroxyl groups of cellulose are reduced as shown in Table 2 above, so that the tensile strength decreases as the amount of heat resistant fibers increases. . Therefore, in the present invention, in order to ensure a tensile strength of 9.8 N / 15 mm or more, a predetermined amount of binder is blended with the raw material of the separator together with natural cellulose fibers and heat resistant fibers.

  As the binder, wet heat fusion resin such as polyvinyl alcohol (PVA) or polyacrylamide resin (PAM) is used. In the case of using a wet heat fusion resin, the content is suitably 10% by weight to 30% by weight. This is because wet heat fusion resin exists in the form of fibers and is less soluble in water at room temperature, so it can be blended up to 30% by weight with little sticking to the paper machine, and to obtain a binder effect This is because it is necessary to contain at least 10% by weight. On the other hand, when a polyacrylamide resin is used, the content is suitably 2 to 10% by weight. This is because polyacrylamide resin (PAM) is a water-soluble resin used as a solution, and if the content is excessive, sticking to the paper machine occurs, so 10% by weight is considered the maximum amount, and This is because it is necessary to contain at least 2% by weight in order to obtain the effect.

  Heat-resistant fibers having a thermal decomposition temperature of 450 ° C. or higher, such as aramid fibers used in the present invention, are not affected by heating at 250 ° C. to 350 ° C., so that the entanglement points of the fibers are joined. This is the cause that the tensile strength required for element winding cannot be obtained. In the present invention, by blending the above-described binder, the binder joins the entanglement points of the heat-resistant fibers, so that the tensile strength necessary for element winding can be expressed. In addition, since the heat-resistant fibers are continuous with each other through the entanglement points joined by the binder, the structure maintained by the heat-resistant fibers is also a medium for impregnating the polymer solution of the conductive polymer or the conductive high-temperature fibers. It becomes a medium for holding molecules.

  Using the above-mentioned raw materials, carbonization is performed by heating a separator having a predetermined thickness and a predetermined density at a temperature of 250 ° C. to 350 ° C. for 60 minutes to 120 minutes using a known paper machine such as a circular net paper machine. . If the carbonization temperature and time are much less than 250 ° C for 60 minutes, carbonization will be insufficient and uncarbonized cellulose will remain, so the harmful effects of cellulose hydroxyl groups cannot be removed or gas will be generated after aging. As a result, the continuity of the conductive polymer is cut, so that the ESR deteriorates and the electrostatic capacity decreases. In addition, when the carbonization temperature and time greatly exceed 350 ° C. for 120 minutes, the residual amount of the fibrous form of the cellulose fiber for holding the conductive polymer decreases, and the conductive polymer intended for the present invention has a high content. Filling and continuity cannot be realized, and since the impregnation of the polymerization solution is reduced from the stage after carbonization, the ESR is deteriorated and the capacitance is reduced. Therefore, in the present invention, a medium for impregnating the polymerization solution by carbonization and a fiber-shaped body as a medium for holding the conductive polymer are appropriately left in a separator made from the above raw material in a temperature range of 250 ° C. to 350 ° C. Carbonization was performed by heating at a temperature of 60 ° C. for 60 minutes to 120 minutes.

  According to the present invention having the above-described configuration, it is possible to achieve high filling of the conductive polymer, ensure the continuity of the conductive polymer, without adversely affecting other characteristics of the solid electrolytic capacitor, Electrical characteristics such as reduction of ESR can be improved in a high frequency range. Therefore, the relationship between the present invention and the high filling and continuity of the conductive polymer will be described.

  In order to achieve a high packing of the conductive polymer, first, a larger porosity in the separator is preferable in order to impregnate more polymerization solution for polymerizing the conductive polymer. In addition to the large porosity, it is necessary that a path for the polymerization solution to flow and a medium for holding the polymerization solution exist in the separator.

  In order to increase the continuity of the conductive polymer, in order to first impregnate more polymerization solution for polymerizing the conductive polymer, it is preferable that the porosity in the separator is larger. Moreover, it is necessary not only to have a high porosity, but also to have a medium for holding the polymerized conductive polymer in the separator. The continuity of the conductive polymer requires that the medium for holding the conductive polymer is continuous in the separator. That is, it is necessary that some fiber for holding the conductive polymer is continuous in the separator. When the fiber which is the holding medium for the conductive polymer is intermittent, the conductive polymer is not continuous at the portion where the fiber is broken.

In separators made from natural cellulose fibers, if carbonization proceeds excessively, the portion lost to cellulose fibers will increase due to heating, and the fiber-shaped skeleton will gradually become fragmented and cut. lose. When carbonization is advanced to the maximum and most of the cellulose fibers disappear, the voids increase but the polymerization solution is retained, and there is no medium to retain the polymerized conductive polymer. Will be inhibited. Therefore, as the carbonization proceeds, the voids increase, but the polymerization solution and the medium holding the conductive polymer are lost, and excessive carbonization worsens the ESR.

  Therefore, in the present invention, 50% by weight or more of natural cellulose fiber is blended as the main fiber of the separator, and the polymerization solution is sufficiently impregnated by heating and carbonizing at a temperature of 250 ° C. to 350 ° C. for 60 minutes to 120 minutes. Therefore, the voids in the separator are secured, and the fiber shaped skeleton of the natural cellulose fibers is left after carbonization by the balance between the temperature and time of carbonization and the heat resistant fiber and binder mixed in the natural cellulose fibers. In addition, by using the partially unoxidized cellulose fiber as a path for the polymerization solution to flow and a medium for holding the polymerization solution, high filling and continuity are ensured.

  For securing the dimensional stability of the separator that will be adversely affected by carbonization to remove the adverse effects caused by hydroxyl groups of natural cellulose fibers blended in an amount of 50% by weight or more, the temperature is from 250 ° C. to 350 ° C. for 60 minutes to It is supposed to be ensured by blending 10% to 40% by weight of heat-resistant fiber having a heat resistance of 450 ° C. or higher that is not affected by heating for 120 minutes of carbonization. That is, the basic shape of the separator is secured by heat resistant fibers. Furthermore, about the fall of the tensile strength by mix | blending a heat resistant fiber, it is a predetermined amount (in the case of a wet heat fusion resin, 10 weight%-30 weight%, in the case of a polyacrylamide resin, 2 weight%-10 weight% ) Is included, the entanglement points of the fibers of the heat-resistant fiber are joined to ensure the necessary tensile strength when the element is wound. The heat-resistant fiber in which the entanglement points of the fibers are joined by a binder also acts as a path for the polymerization solution to flow and a medium for holding the polymerization solution. Thus, the high filling which the present invention intends to achieve does not simply achieve the porosity of the separator by the numerical value. This can only be achieved by creating a balanced blend of natural cellulosic fiber shapes that have been reduced in mass by carbonization and partially unoxidized cellulose fibers in heat-resistant fibers that maintain the basic shape of the separator. is there.

  Next, based on the embodiment, the solid electrolytic capacitor according to the present invention secures high filling and continuity of the conductive polymer, and thus does not adversely affect the other characteristics of the solid electrolytic capacitor, and the high frequency region. It is clarified in comparison with the conventional example and the comparative example that ESR and the like can be improved.

[Examples 1 to 3]
Using a circular paper machine, the raw material is 88% by weight of sisal pulp as natural cellulose fiber, 10% by weight of fibrillated aramid fiber as heat-resistant fiber, and 2% by weight of polyacrylamide resin (hereinafter referred to as PAM) as binder. A paper separator having a thickness of 40 μm and a density of 0.45 g / cm ³ was made and carbonized by heating at 250 ° C. (Example 1), 300 ° C. (Example 2), and 350 ° C. (Example 3) for 60 minutes. .

[Examples 4 to 6]
Sinus hemp pulp 50% by weight as natural cellulose fiber, 40% by weight of fibrillated aramid fiber as heat-resistant fiber, and 10% by weight of PAM as binder, using a circular paper machine, thickness 40μm, density 0.33g / A cm ³ separator was paper-made and carbonized by heating at 250 ° C. (Example 4), 300 ° C. (Example 5), and 350 ° C. (Example 6) for 60 minutes.

[Examples 7 to 9]
Circular paper making using 70% by weight of sisal pulp as natural cellulose fiber, 20% by weight of fibrillated aramid fiber as heat-resistant fiber, and 10% by weight of polyvinyl alcohol (hereinafter referred to as PVA) which is a wet heat fusion resin as binder. Paper is made into a separator having a thickness of 40 μm and a density of 0.45 g / cm ³ using a machine and heated at 250 ° C. (Example 7), 300 ° C. (Example 8), and 350 ° C. (Example 9) for 60 minutes. And carbonized.

[Example 10 to Example 12]
Sinus hemp 50% by weight as natural cellulose fiber, 20% by weight of fibrillated aramid fiber as heat-resistant fiber, and 30% by weight of PVA as binder, using a circular paper machine, thickness 40μm, density 0.35g / A cm ³ separator was paper-made and carbonized by heating at 250 ° C. (Example 10), 300 ° C. (Example 11), and 350 ° C. (Example 12) for 60 minutes. In Examples 1 to 12, the fibrillated aramid fiber used was a fiber sold by Teijin Techno Products Limited under the trade name “Teijin Twaron”. Moreover, what is generally marketed for paper manufacture was used for PAM and PVA.

[Examples 13 to 22]
Using a circular paper machine, a separator with a thickness of 40 μm and a density of 0.45 g / cm ³ is prepared using 75% by weight of sisal pulp as natural cellulose fiber, 20% by weight of heat-resistant fiber, and 5% by weight of PAM as a binder. Paper was made and carbonized by heating at 300 ° C. for 60 minutes. The heat resistant fiber used was changed as follows in each Example. Example 13 is a fibrillated aramid fiber, Example 14 is an aramid fiber, Example 15 is an aramid fibrid, Example 16 is a fibrillated amidimide fiber, Example 17 is an amidimide fiber, Example 18 is a polyimide fiber, Example 19 Is a micro glass fiber, Example 20 is carbon fiber, Example 21 is boron fiber, and Example 22 is alumina fiber as heat resistant fiber.

[Examples 23 to 32]
A separator with a thickness of 40 μm and a density of 0.40 g / cm ³ using a circular net paper machine with 60% by weight of sisal pulp as natural cellulose fiber, 20% by weight of heat-resistant fiber and 20% by weight of PVA as a binder. Paper was made and carbonized by heating at 300 ° C. for 60 minutes. The heat resistant fiber used was changed as follows in each Example. Example 23 is a fibrillated aramid fiber, Example 24 is an aramid fiber, Example 25 is an aramid fibrid, Example 26 is a fibrillated amidimide fiber, Example 27 is an amideimide fiber, Example 28 is a polyimide fiber, Example 29 Is a micro glass fiber, Example 30 is carbon fiber, Example 31 is boron fiber, and Example 32 is alumina fiber as heat resistant fiber.

[Example 33]
As a natural cellulose fiber similar to Example 23, 60% by weight of sisal pulp, 20% by weight of fibrillated aramid fiber as heat-resistant fiber, and 20% by weight of PVA as a binder are used as raw materials, and the thickness is 40 μm using a circular paper machine. A separator having a density of 0.40 g / cm ³ was made and carbonized by heating at 300 ° C. for 120 minutes.

[Conventional Example 1 to Conventional Example 5]
Paper separators having a thickness of 40 μm and a density of 0.40 g / cm ³ were produced using a circular net paper machine using 100% by weight of sisal pulp as a natural cellulose fiber, and 200 ° C. (conventional example 1) and 250 ° C., respectively. (Conventional Example 2), heated at 300 ° C. (Conventional Example 3), 350 ° C. (Conventional Example 4), and 400 ° C. (Conventional Example 5) for 60 minutes for carbonization.

[Conventional Example 6 to Conventional Example 7]
As natural cellulose fibers, 100% by weight of sisal pulp (conventional example 6) and 100% by weight of kraft pulp (conventional example 7) are used as raw materials, respectively, using a circular paper machine and having a thickness of 40 μm and a density of 0.40 g / cm. The separator ³ was paper-made and heated at 350 ° C. for 120 minutes for carbonization.

[Equivalent to Conventional Example 8 to Conventional Example 12 / Patent Document 6]
Paper making a separator with a thickness of 40 μm and a density of 0.40 g / cm ³ using a circular paper machine with 50% by weight of sisal pulp as natural cellulose fiber and 50% by weight of fibrillated aramid fiber as heat resistant fiber Then, carbonization was performed by heating at 200 ° C. (Conventional Example 8), 250 ° C. (Conventional Example 9), 300 ° C. (Conventional Example 10), 350 ° C. (Conventional Example 11), and 400 ° C. (Conventional Example 12) for 60 minutes. It was.

[Compatible with Comparative Example 1, Comparative Example 2 / Examples 1 to 3]
Using the same raw materials as in Examples 1 to 3, separators made with the same thickness and density with a circular paper machine were changed to 200 ° C. (Comparative Example 1) and 400 ° C., respectively, except for carbonization conditions. Carbonization was performed by heating at 0 ° C. (Comparative Example 2) for 60 minutes.

[Compatible with Comparative Example 3, Comparative Example 4 / Examples 4 to 6]
Using the same raw material as in Examples 4 to 6, separators made with a circular net paper machine to the same thickness and density have different temperatures only at 200 ° C. (Comparative Example 3), 400 Carbonization was performed by heating at 60 ° C. (Comparative Example 4) for 60 minutes.

[Compatible with Comparative Example 5, Comparative Example 6 / Examples 7 to 9]
Using the same raw materials as in Examples 7 to 9, separators made with a circular mesh paper machine to the same thickness and density have different carbonization conditions only, and are 200 ° C. (Comparative Example 5) and 400 respectively. Carbonization was performed by heating at 60 ° C. (Comparative Example 6) for 60 minutes.

[Compatible with Comparative Example 7, Comparative Example 8 / Examples 10 to 12]
Using separators made of paper having the same thickness and density using a circular paper machine, using the same raw materials as in Examples 10 to 12, except for carbonization conditions, 200 ° C. (Comparative Example 7), 400 Carbonization was performed by heating at 0 ° C. (Comparative Example 8) for 60 minutes.

[Comparative Examples 9 to 13]
Sinus hemp pulp 45% by weight as natural cellulose fiber, 45% by weight of fibrillated aramid fiber as heat-resistant fiber, and 10% by weight of PAM as binder, using a circular paper machine, thickness 40μm, density 0.40g / A paper separator of cm ^{3 was made} and 60 ° C. (Comparative Example 9), 250 ° C. (Comparative Example 10), 300 ° C. (Comparative Example 11), 350 ° C. (Comparative Example 12), and 400 ° C. (Comparative Example 13), respectively. Carbonized by heating for a minute.

  Table 6 shows the heat-resistant fibers used and the fibers used as the binder in Examples, Conventional Examples, and Comparative Examples. As natural cellulose fiber, sisal pulp and wood kraft pulp were appropriately beaten with a refiner. Further, the degree of beating of the natural cellulose fiber and the fibrillated heat-resistant fiber may be set within an appropriate range depending on the characteristics of the separator to be obtained. Further, the PAM as a binder may be added by means of internal addition at the time of papermaking or coating after papermaking, but papermaking was carried out in the above examples and comparative examples.

  Next, using the separators shown in these examples, conventional examples, and comparative examples, the separator was interposed between the anode foil and the cathode foil, and the separator was carbonized. A solid electrolytic capacitor impregnated with a molecular polymerization solution and polymerized and held as a solid electrolyte layer was fabricated and evaluated. First, an anode aluminum foil and a cathode aluminum foil were formed in a slit shape having a desired size, and then a lead bar was attached to each anode aluminum foil and the cathode aluminum foil, and a capacitor element was produced by winding it through each separator. . Next, the capacitor element was heated at a predetermined temperature for a predetermined time to carbonize the separator. At this stage, since the oxide film is not formed on the end face of the aluminum foil of the capacitor element, chemical conversion treatment is performed in an aqueous solution of ammonium adipate at 60 ° C. and 1.0% by weight, and thereafter, 3,4-ethylenedioxythiophene and After dipping in a polymerization solution (monomer: oxidant = 1: 1.5, molar ratio) in which p-toluenesulfonic acid iron (3) is dissolved in i-propanol, the mixture is kept at a temperature of 100 ° C. for 60 minutes for chemistry. A solid electrolyte layer of polyethylene dioxythiophene (PEDT) was formed by polymerization. A capacitor element having a solid electrolyte layer obtained by repeating this solid electrolyte layer forming method twice is dried and heated and then placed in a case, the opening is sealed with a sealing member, and a surface mounting seat plate is provided on the sealing member side. Attached. After that, the DC voltage is gradually increased from 0 at a temperature of 105 ° C. for 120 minutes, and an aging treatment is performed by applying a voltage of 6V, which is 1.5 times the rated voltage, and the rated voltage is 4 WV and the rated capacitance is 100 μF. Each of 1000 surface mount type solid electrolytic capacitors was manufactured.

  Evaluation of raw materials and characteristics of separators according to Examples, Conventional Examples and Comparative Examples, and solid electrolytic capacitors manufactured using these separators are shown in Table 7 for Examples 1 to 6, and Examples 7 to 12 are used. In Table 8, Examples 13 to 22 in Table 9, Examples 23 to 33 in Table 10, Conventional Examples 1 to 12 in Table 11, Comparative Examples 1 to 13 in Table 11. 12 shows.

  Each measured value and evaluation method of the separator and the obtained solid electrolytic capacitor in each example, conventional example and comparative example are as follows.

[Evaluation of separator / thickness, density, tensile strength]
The thickness, density, and tensile strength of the separator were measured by the methods specified in the old JIS C2301 (electrolytic capacitor paper). The test conditions for tensile strength are as follows.
Test conditions: A separator having a width of 15 mm was immersed in pure water for 30 seconds, and then tested according to the item of tensile strength of JIS C2111 (electrical insulation paper test method).

[Evaluation of separator / weight retention]
The weight retention after carbonization of the separator was measured by weight after carbonization / weight before carbonization × 100. The method for measuring the thickness retention ratio and area retention ratio is as described above.

[Evaluation of separator / porosity]
When using a separator containing natural cellulose fiber and heat-resistant fiber, the heat-resistant fiber retains the outer shape of the separator, so it is assumed that the outer shape and dimensions of the separator do not change. Was measured by the following formula (see “Science of Paper”, page 330 (1) / Taku Kadoya et al.).
Porosity = (1−density of paper / density of material constituting paper) × 100 (1)
In addition, the density of the separator after carbonization was calculated by the following formula (Equation 1). By calculating the density of the separator after carbonization according to the degree of carbonization for each example, the conventional example, and the comparative example by this mathematical formula (Equation 1), and substituting the density of paper into the formula (1), The porosity of the separator was calculated.

[Short defect rate]
The short-circuit failure rate of the capacitor element after carbonization was confirmed by a tester for continuity due to a short between both electrodes. First, regarding the short-circuit defect rate of the capacitor element after polymerization of the conductive polymer, a conductive polymer layer was formed on the capacitor element after carbonization, and then continuity due to a short between both electrodes was confirmed by a tester. The short defect rate was inspected for 1000 elements, and the ratio of the short elements to the total number of elements was defined as the short defect rate. Moreover, it performed similarly about the short defect after aging.

[ESR, capacitance]
The ESR was measured before and after aging with an LCR meter at a frequency of 20 ° C. and 100 kHz. The capacitance was measured by an LCR meter at 20 ° C. and a frequency of 120 Hz.

[Impregnation]
The impregnation property is that a capacitor element wound up and carbonized is taken out and 10 parts are taken out separately and immersed in a polymerization solution, and then the capacitor element is disassembled to suck up the least sucked up part. I measured the height.

[Appearance swelling]
Regarding the appearance swelling, the capacitor element after aging was visually inspected.

  Conventional Example 1 to Conventional Example 5 shown in Table 11 are obtained by heating a heating temperature at 200 ° C. to 400 ° C. for 60 minutes using a separator made of 100% by weight of sisal pulp as natural cellulose fiber. It is considered that as the heating temperature rises, the weight retention ratio and thickness retention ratio decrease, and the voids in the separator increase. For example, in the conventional example 2 heated at 250 ° C., the weight retention rate and the thickness retention rate are 90.0% and 90.9%, respectively, whereas in the conventional example 3 heated at 300 ° C., 30. It has decreased to 4% and 51.1%. On the other hand, since the dimensional stability is lost, the short-circuit defect rate increases from 10% in the conventional example 2 to 30% in the conventional example 3 in the capacitor element characteristics after forming the conductive polymer layer after carbonization. In the conventional example 5 heated at 400 ° C., it is 60%. Thus, since the separator made only of the conventional natural cellulose fiber lacks dimensional stability due to carbonization, there are many short-circuit defects, the ESR value is also deteriorated, and it can be used as a separator for a solid electrolytic capacitor. Can not.

  Conventional Example 6 and Conventional Example 7 are examples in which the heating temperature and heating time for carbonization are set to 120 minutes at 350 ° C. to increase the heating time, and Conventional Example 7 is an example in which wood kraft pulp is used instead of sisal hemp pulp. However, like the conventional examples 1 to 5, the dimensional stability is lacking, and both the ESR and the short-circuit defect rate are not usable values. Specifically, it is impossible to realize an electrostatic capacity of 100 μF or more and an ESR of 20 mΩ or less in both the capacitor element characteristics after forming the conductive polymer layer after carbonization and the capacitor element characteristics after aging (finished product). . Further, by proceeding carbonization, the weight retentions of Conventional Example 6 and Conventional Example 7 are reduced to 16.1% and 16.1%, but the weight does not become 0%.

  Conventional Example 8 to Conventional Example 12 are examples in which sisal pulp as natural cellulose fiber and fibrillated aramid fiber as heat resistant fiber are blended by 50% by weight, and corresponds to Patent Document 6. In either case, the tensile strength was only 2.6 N / 15 mm, and an attempt was made to produce a capacitor element. However, the capacitor element could not be produced due to frequent paper breaks during cutting.

  In Examples 1 to 3, a separator in which 88% by weight of sisal pulp was mixed with 10% by weight of fibrillated aramid fibers and 2% by weight of PAM was carbonized at a temperature of 250 ° C., 300 ° C., and 350 ° C. for carbonization. Heated for a minute. Since 88% by weight of sisal pulp, which is a natural cellulose fiber, is contained, the weight retention decreases to 92.1%, 42.5%, and 33.2% as the heating temperature increases, and the porosity is 70. The basic shape of the separator is maintained by fibrillated aramid fibers that are not affected by heating, which is increased by 6%, 77.8%, and 78.1%, but the area retention rate is respectively 99.3%, 82.1%, and 80.2% are secured. Therefore, the short-circuit defect rate was 0% in all cases. The capacitor element characteristics after forming the carbonized conductive polymer layer (hereinafter referred to as element characteristics after carbonization) and the capacitor element characteristics after aging (hereinafter referred to as element characteristics after aging) are both electrostatic capacitances of 100 μF or more. The capacity is achieved, and from this, it can be seen that high packing of the conductive polymer is realized. Furthermore, since the carbonized sisal fiber functions as a path for the polymerization solution to flow, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer, ESR is also 20 mΩ or less. It can be seen that the continuity of the conductive polymer is secured.

  On the other hand, Comparative Example 1 and Comparative Example 2 are examples in which the same separator as in Examples 1 to 3 was used and heated at a carbonization temperature of 200 ° C. and 400 ° C. for 60 minutes. In Comparative Example 1, since the carbonization temperature is low, the weight retention is 99.8% and the carbonization is insufficient, the adverse effects of the hydroxyl group of sisal hemp pulp cannot be removed, and swelling occurs after aging, As characteristics after carbonization and aging, ESR is also deteriorated to 22 mΩ and 30 mΩ. On the other hand, in Comparative Example 2, since the carbonization temperature is too high, the weight retention rate is extremely reduced to 30.5% and the impregnation property is as good as 4 mm. However, the remaining fiber form of the sisal pulp is insufficient. As a result, the continuity of the conductive polymer cannot be ensured, so that the element characteristics after aging deteriorated to 26 mΩ, and the short-circuit defect rate increased to 6%. This means that if the carbonization conditions are exceeded, the continuity of the conductive polymer is interrupted, both ESR and electrostatic capacity deteriorate, and a short circuit due to the conductive polymer partially connected between the electrodes occurs. It shows that it gets worse. Therefore, as a condition for carbonization for the natural cellulose fiber to function as a path for the polymerization solution to flow, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer, 250 ° C. A temperature of ˜350 ° C. is suitably 60 minutes to 120 minutes.

  In Examples 10 to 12, a separator prepared by blending 50% by weight of sisal pulp with 20% by weight of fibrillated aramid fibers and 30% by weight of PVA was used for carbonization at temperatures of 250 ° C., 300 ° C., and 350 ° C., respectively. Heated for a minute. Since 50% by weight of sisal pulp, which is a natural cellulose fiber, is contained, the weight retention decreases to 93.2%, 57.8%, and 40.9% as the heating temperature increases, and the porosity is also 75.%. Since the basic shape of the separator is maintained by the fibrillated aramid fiber which is increased by 4%, 80.7% and 81.3%, and is not affected by heating that is blended by 20% by weight, the area retention rate is 99.1%, 93.6% and 89.2%, respectively. Therefore, the short-circuit defect rate was 0% in all cases. And as for the element characteristic after carbonization and the element characteristic after aging, both have achieved a capacitance of 100 μF or more. From this, it can be seen that high packing of the conductive polymer is realized. Further, since the carbonized sisal fiber functions as a path for the polymerization solution to flow, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer, the conductive polymer In both the post-carbonization device characteristics and the post-aging device characteristics, the ESR shows a good value of 18Ω or less. Therefore, in order to function as a path for the polymerization solution to flow after carbonization, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer, the natural cellulose fiber is at least 50% by weight. It turns out that it is necessary to mix | blend more than%.

  On the other hand, Comparative Example 7 and Comparative Example 8 are examples in which the same separator as in Examples 10 to 12 was used and heated at a carbonization temperature of 200 ° C. and 400 ° C. for 60 minutes. In Comparative Example 7, since the carbonization temperature is low, the weight retention rate is 99.6%, and the carbonization is insufficient, the adverse effect of the hydroxyl group of sisal hemp pulp cannot be removed, and the ESR is 33 mΩ as a characteristic after aging. It is getting worse. On the other hand, in Comparative Example 8, since the carbonization temperature is too high, the weight retention rate is extremely reduced to 32.2% and the impregnation property is as good as 4 mm. However, the fiber shape of the sisal pulp is not sufficiently remained. The continuity of the conductive polymer could not be ensured, the element characteristics after aging deteriorated to 28 mΩ, and the short-circuit defect rate increased to 5%. Therefore, as a condition for carbonization for the natural cellulose fiber to function as a path for the polymerization solution to flow, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer, 250 ° C. A temperature of ˜350 ° C. is suitably 60 minutes to 120 minutes.

  Next, in order to confirm that carbonization for 60 minutes to 120 minutes at a temperature of 250 ° C. to 350 ° C. is appropriate, using the separator according to Example 22, 200 ° C., 250 ° C., 300 ° C., 350 ° C. , Heated at 400 ° C. for 10 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 120 minutes, and 300 minutes, with the same rated voltage of 4 WV and rated capacitance of 100 μF as in the examples. A surface mount type solid electrolytic capacitor was manufactured, and evaluations of capacitance, ESR, short-circuit defect rate, and appearance swelling as element characteristics after aging are shown in Table 13 as ◯. The evaluation criteria are as shown in Table 14.

  As shown in Table 13, a solid electrolytic capacitor using a separator carbonized by heating at 250 to 350 ° C. for 60 to 120 minutes has a capacitance of 100 μF or more and an ESR of 20 mΩ as element characteristics after aging. Hereinafter, the short-circuit defect rate is 1% or less, and there is no blistering. Therefore, all of the four evaluation items show good values of ○. On the other hand, in the case of carbonization conditions that deviate from the range of the carbonization temperature and time, at least one of the items of capacitance, ESR, short-circuit defect rate, and blistering is outside the value of the above ○, and as a solid electrolytic capacitor The value is inappropriate x. From this, as a condition for carbonization for the natural cellulose fiber to function as a path for the polymerization solution to flow, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer, It can be seen that 60 minutes to 120 minutes is suitable at a temperature of 250 ° C to 350 ° C.

  Comparative Example 3 and Comparative Example 4 are Examples 4 to 6, and Comparative Example 5 and Comparative Example 6 are the same separators as in Examples 7 to 9, with carbonization temperatures of 200 ° C. and 400 ° C. This is an example of heating for 60 minutes. Each measured value shows the relationship between Comparative Example 1 and Comparative Example 2 and Examples 1 to 3, and the same relationship as Comparative Example 7 and Comparative Example 8 and Examples 10 to 12.

  In Comparative Examples 9 to 13, the amount of sisal pulp was reduced to 45% by weight, and separators containing 45% by weight of fibrillated aramid fibers and 10% by weight of PAM were carbonized at 200 ° C. and 250 ° C., respectively, for carbonization. , 300 ° C., 350 ° C., and 400 ° C. for 60 minutes. When fibrillated aramid fiber is added in an amount of more than 40% by weight and 45% by weight, even when 10% by weight of the maximum amount of PAM added as a binder is added, the tensile strength is manifested only at a minimum allowable value of 7.8 N / 15 mm. . Moreover, since only 45% by weight of sisal pulp is less than 50% by weight, no matter how carbonization proceeds, the capacitance remains at 80 μm to 92 μF, and the impregnation property is as bad as 1 mm or 2 mm. As the characteristics after aging, the ESR deteriorates to 25 mΩ to 30 mΩ. Therefore, it is necessary that 50% by weight or more of natural cellulose fiber is blended.

  In Examples 13 to 22, heat resistant fibers to be blended with sisal pulp are fibrillated aramid fibers, aramid fibers, aramid fibrids, fibrillated amidimide fibers, amideimide fibers, polyimide fibers, micro glass fibers, carbon fibers, boron. The separator used was a mixture of 75% by weight of sisal pulp, 20% by weight of heat-resistant fiber, and 5% by weight of PAM, which was changed to fiber and alumina fiber, and heated at 300 ° C. for 60 minutes. Moreover, Example 23-Example 32 mix | blends 60 weight% of sisal pulp, 20 weight% of heat resistant fibers, and 20 weight% of PVA using the same heat resistant fiber as Examples 13-22, respectively, 300 A separator heated at 60 ° C. for 60 minutes is used.

  Each of Examples 13 to 32 and Example 33 achieves a capacitance of 101 μF or more and an ESR of 19 mΩ or less, and the short-circuit defect rate is 0%. Therefore, heat-resistant fibers with a heat resistance of 450 ° C or higher are not particularly affected by the fiber type, and maintain the basic shape of the separator during carbonization and ensure dimensional stability by carbonizing natural cellulose fibers. Is possible. The carbonized natural cellulose fiber functions as a path for the polymerization solution to flow, a medium for holding the polymerization solution, and a medium for holding the polymerized conductive polymer. Can be ensured.

  According to the present invention, the impregnating property of the polymerization solution by increasing the porosity of the separator, which has been considered difficult in the past, ensuring a high filling and continuity of the conductive polymer, and the size of the separator against heating during carbonization. Ensuring stability can be improved at the same time. The polymerized conductive polymer is continuously held in the separator as a conductive polymer layer along the voids and carbonized fibers after carbonization and unoxidized fibers, thus realizing a high packing of the conductive polymer. In addition, the continuity of the conductive polymer can be ensured, and ESR and the like in the high frequency region can be improved without adversely affecting other characteristics of the solid electrolytic capacitor. Specifically, to obtain a solid electrolytic capacitor that realizes a capacitance of 100 μF or more and an ESR of 20 mΩ or less in the capacitor element characteristics after aging (finished product) without adversely affecting other characteristics such as short circuit defects. Can do.

Claims (15)

In a separator for a solid electrolytic capacitor that holds a conductive polymer as a solid electrolyte layer after winding the separator foil between an anode foil and a cathode foil, and carbonizing the separator.
A separator comprising 50% by weight or more of natural cellulose fiber, 10% by weight to 40% by weight of heat-resistant fiber having a thermal decomposition temperature of 450 ° C. or more, and a predetermined amount of binder as the separator. In a separator for a solid electrolytic capacitor that holds a conductive polymer as a solid electrolyte layer after winding the separator foil between an anode foil and a cathode foil, and carbonizing the separator.
The separator contains 50% by weight or more of natural cellulose fiber, 10% by weight to 40% by weight of heat-resistant fiber having a thermal decomposition temperature of 450 ° C. or more, and a predetermined amount of binder to remove hydroxyl groups of the natural cellulose fiber. And carbonized so that the fiber shape remains. In a separator for a solid electrolytic capacitor that holds a conductive polymer as a solid electrolyte layer after winding the separator foil between an anode foil and a cathode foil, and carbonizing the separator.
The separator contains 50% by weight or more of natural cellulose fiber, 10% to 40% by weight of heat-resistant fiber having a thermal decomposition temperature of 450 ° C. or more, and a predetermined amount of binder, and carbonizes the natural cellulose fiber by heating. By making it form, while forming a space | gap in a separator, the fibrous form body of a natural cellulose fiber remains, The separator characterized by the above-mentioned. In a separator for a solid electrolytic capacitor that holds a conductive polymer as a solid electrolyte layer after winding the separator foil between an anode foil and a cathode foil, and carbonizing the separator.
The separator contains 50% by weight or more of natural cellulose fiber, 10% by weight to 40% by weight of heat-resistant fiber having a thermal decomposition temperature of 450 ° C. or more, and a predetermined amount of binder. A separator characterized by carbonizing natural cellulose fibers in a state in which the shape of the separator is maintained by heat resistant fibers, thereby forming voids in the separator and leaving the fibrous form of the natural cellulose fibers.   The separator according to claim 2, 3 or 4, wherein the conductive polymer is continuously held along the fiber-shaped body.   The separator according to claim 2, 3, 4 or 5, wherein partially unoxidized cellulose fibers remain together with the fiber-shaped body.   The natural cellulose fiber uses one or more fibers selected from Manila hemp pulp, sisal pulp, esparto pulp, cotton pulp, jute pulp, hemp pulp, and wood pulp. Or the separator of 6.   One or more fibers selected from aramid fiber, amideimide fiber, polyimide fiber, fibrillated aramid fiber, aramid fibrid, fibrillated amidimide fiber, alumina fiber, boron fiber, carbon fiber, and glass fiber are used as the heat resistant fiber. The separator according to claim 1, 2, 3, 4, 5, 6 or 7.   The separator according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein 10% by weight to 30% by weight of a wet heat fusion resin is contained as a binder.   The separator according to claim 9, wherein polyvinyl alcohol is used as the wet heat fusion resin.   The separator according to claim 1, 2, 3, 4, 5, 6, 7, or 8 containing 2% by weight to 10% by weight of a polyacrylamide resin as a binder.   The separator according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the separator is carbonized by heating at a temperature of 250 ° C to 350 ° C for 60 minutes to 120 minutes.   The separator according to any one of claims 1 to 11, wherein the separator is wound between an anode foil and a cathode foil, and after carbonizing the separator, the conductive polymer is held as a solid electrolyte layer. Solid electrolytic capacitor.   The solid electrolytic capacitor according to claim 13, wherein the separator is carbonized by heating at a temperature of 250 ° C. to 350 ° C. for 60 minutes to 120 minutes.   The solid electrolytic capacitor according to claim 13 or 14, wherein at least one of polypyrrole, polythiophene, polyaniline, or a derivative thereof is used as the conductive polymer.