JPS6262450B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a separator for an electrolytic capacitor. Conventionally, porous paper has been used for the separator of electrolytic capacitors, but this case has the following problems. There are many pinholes, which causes many short-circuit accidents between capacitor electrodes. The hole diameter of the paper hole is large, and the leakage current of the capacitor is large. Chemical resistance to electrolyte is insufficient, and mechanical strength decreases when impregnated with electrolyte. In order to solve these problems, it has been considered to form the separator with a thin film of cellulose plastic, but it has not been possible to obtain satisfactory results. This invention was made in view of the above circumstances,
The purpose is to provide a method for manufacturing electrolytic capacitor separators that are free from pinholes, have appropriate pore diameters, and have excellent chemical resistance to electrolytes. 30 to 30% of the following silica powder
This method is characterized by impregnating and coating a synthetic fiber web with a dispersion liquid dispersed in a dispersion medium at a ratio of 80 wt%, and then drying this. This invention will be explained in detail below. The silica-based powder used in this invention includes:
Mineral powder whose main component is SiO ₂ , such as silica powder, silica powder, activated clay, etc. These powders are used with a maximum particle size of 30μm or less, and from the viewpoint of leakage current and ion movement of the electrolyte, 30μm or less is used.
A powder having a particle size distribution with m as the maximum particle size is desirable, and powders without a particle size distribution need to be used by mixing powders of different particle sizes. When the maximum particle size of the silica-based powder exceeds 30 μm, the particles become large and easily fall off from the separator to form pinholes, and the pore size becomes large, causing problems. Note that when activated clay is used as the silica-based powder, it is necessary to use one that has been pickled several times to remove impurities. As a dispersion medium for dispersing silica powder, water,
In solvents such as ethanol, methanol, acetone, and isopropanol, and mixtures of these solvents, binders that are soluble in these solvents and insoluble in electrolyte solutions for electrolytic capacitors, such as polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC),
A solution containing soluble starch or the like is used. The best binder concentration is the lowest concentration at which the silica-based powder does not come off from the web.As the concentration increases, the silica-based powder will no longer come off, but the separator will become a film, with no pores and no ion movement, resulting in increased resistance. As the amount increases, the permeability of the electrolyte tends to deteriorate, so 2 to 10 wt% is generally suitable. Silica-based powder is added to the dispersion medium formed by dissolving the binder in a proportion of 30 to 80 wt% and mixed to form a silica-based powder dispersion. If the amount of silica-based powder is less than 30wt%, the fixation rate of the silica-based powder to the web will be poor,
This is undesirable because the number of pinholes increases. Also,
If it exceeds 80 wt%, pinholes will not occur, but processability will deteriorate, and a low-density separator will not be formed, resulting in a separator with high resistance, which is inconvenient. The silica powder dispersion is then impregnated and applied to a synthetic fiber web. The synthetic fiber web used here is a woven fabric made of synthetic fibers such as polyethylene fiber, polypropylene fiber, polyester fiber, polyamide fiber, Vinylon (trademark) fiber, or a non-woven fabric made of these synthetic fibers. Examples include knitted fabrics. The permissible operating temperature of the resulting separator is related to the material of the synthetic fiber web, so the material of the web should be selected with this point in mind. If the separator has an allowable operating temperature of 100°C or higher, it is preferable to use polyester fiber, polyamide fiber, vinylon fiber, or polypropylene fiber, and if the operating temperature is lower than 100°C, it is desirable to form the wep with polyethylene fiber. .
Furthermore, the thickness of the resulting separator is determined by the thickness of the webbing, and the thickness of the webbing is determined by the fiber diameter of the synthetic fibers that compose it. must be used. Generally, it is sufficient to use fibers having a thickness of 1/2 to 1/3 of the thickness of the separator. To impregnate and apply the silica-based powder dispersion to a web made of synthetic fibers, a conventional dipping impregnation method or a coating method using a roll coater, doctor knife, or squeeze knife is used. The suitable amount of the silica-based powder dispersion to be applied is 50g to 100g per 1 m ² of wet cloth.
If the coating amount is less than this, the dispersion will not be uniformly spread over the entire surface of the web, and if it is greater than this, the thickness of the separator will become undesirably thicker than necessary. The wet coated with a silica-based powder dispersion is then dried to remove the solvent in the dispersion.
The silica-based powder is fixed to the web to obtain a separator. Since the separator for electrolytic capacitors obtained as described above has a web made of synthetic fibers having high mechanical strength and good chemical resistance as a base material, it does not deteriorate due to electrolytic solution and has improved durability. In addition, since the fine silica-based powder is filled into the voids between the fibers of the web, it has micropores with a suitable pore size as a separator, and the silica-based powder is not dissolved by the electrolyte, so the capacity of the capacitor is Change never occurs. Furthermore, since the hole diameter is appropriate, leakage current can be reduced. Hereinafter, this invention will be specifically explained based on Examples. Example 1 A nonwoven fabric made of polyethylene terephthalate fibers with a fiber diameter of approximately 15 μm, a thickness of 60 μm, and a basis weight of 30 g/m ² was used as a web, and a dispersion containing 40 wt% of silica powder of various maximum particle sizes was mixed into the web at 70 to 80 g/m2. m ² was applied and dried to create a separator. The airtightness (according to JIS-C-2111), pinholes, and maximum pore diameter of these separators were measured. The results are shown in Table 1.

[Table] As is clear from Table 1, when the particle size of the silica-based powder is 50 μm or more, the number of pinholes increases significantly. Additionally, the maximum pore diameter also increases. Example 2 In Example 1, the particle size of the silica-based powder was kept constant at 20 μm or less, and the concentration of the silica-based powder in the dispersion was varied to create separators. Similar tests were conducted on these separators. The results are shown in Table 2.

[Table] As is clear from Table 2, if the silica powder concentration is too low, the number of pinholes will increase significantly, and if the concentration is 90wt%, the airtightness will increase rapidly, ion movement will deteriorate, and the electrolytic capacitor It is not preferable for use as a separator. Example 3 A nonwoven fabric made of Vinylon (trademark) fibers with a fiber diameter of approximately 15 μm, a thickness of 50 μm, and a basis weight of 20 g/m ² was used as a web, and various silica-based powders with a particle size of 25 μm or less were added.
A dispersion containing a concentration of 40 wt% was applied at 70 to 80 g/m ² and dried to obtain a separator. The same tests as in Example 1 were conducted on these separators. The results are shown in Table 3.

[Table] *Product Name Silica Fine Powder Manufactured by Nippon Silica Co., Ltd. From Table 3, it can be seen that a separator with excellent properties can be obtained no matter what type of silica powder is used. As explained above, the manufacturing method of the electrolytic capacitor separator of the present invention has a maximum particle size of 30 μm.
A synthetic fiber web is impregnated with a dispersion of the following silica-based powder dispersed in a dispersion medium at a ratio of 30 to 80 wt%, and then dried, so the separator obtained has no pinholes and is suitable for electrodes. There are no short circuit accidents. Furthermore, since the hole diameter is appropriate, leakage current is small, ion movement is sufficient, and the withstand voltage of the capacitor is increased. Furthermore, it is highly durable as there is no deterioration caused by electrolyte.
Since the mechanical strength is also maintained high, it has advantages such as improved vibration resistance of the capacitor.

Claims (1)

[Claims] 1 30% of silica powder with a maximum particle size of 30μm or less
A method for producing a separator for an electrolytic capacitor, characterized by impregnating and applying a dispersion liquid dispersed in a dispersion medium at a ratio of ~80 wt% onto a web made of synthetic fibers, and drying the same.