JPH04357814A - Sealing rubber for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To make a sealing rubber for aluminum electrolytic capacitors usable even at a high temperature and producible at a low price. CONSTITUTION:A sealing rubber is molded by resin-curing butyl rubber. In this case, halogen compounds are used as a resin curing agent and a resin curing assistant. This sealing rubber is dipped in the good solvent for the halogen compounds, or in the solution, wherein this solvent and a solvent for swelling rubbers are blended, and is left as it is in a whole day and night. Then, the halogen compounds included in the sealing rubber are dissolved in the solvent. In this manner, the halogen compounds included in the sealing rubber can be removed. This sealing rubber is excellent in its thermal resistance and in its quality as a gas barrier, and does not corrode aluminum. Therefore, this sealing rubber is usable for the aluminum electrolytic capacitors in vehicles and computers, etc., which are exposed to certain high temperatures. Also, the time of a bridge formation in this sealing rubber is short in comparison with conventional resin-cured sealing rubbers too, and no secondary curing is required. Therefore, the productivity of this sealing rubber is very excellent and its price is low.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] Aluminum electrolytic capacitors are small capacitors mainly used in televisions, videos, radios, etc. Recently, it has been used in cars, computers, etc., and the number of products produced is increasing year by year. Aluminum electrolytic capacitor has a diameter of 3 to 20 mm and a height of 10 mm.
It has a cylindrical shape of ~50mm. The cylindrical part is a small can-shaped case made of aluminum foil that contains a paste electrolyte. One side of the aluminum case is open and has a rubber stopper. The rubber stopper therefore has a cylindrical shape with the same diameter as the aluminum case and a lower height than the case. The rubber stopper has two thin holes through which lead wires from outside the container to inside the container pass. The present invention relates to this sealing rubber.

0002

BACKGROUND OF THE INVENTION Sealing rubber is mainly required to have the following three properties. ○Does not corrode aluminum. If the sealing rubber contains something that corrodes aluminum, it will cause holes in the aluminum foil. Examples of corrosive materials include chloroprene rubber and halogen compounds. Such materials must not be present in the sealing rubber.

[0003] Aluminum electrolytic capacitors, which have high heat resistance, have come to be widely used in cars, computers, etc. in recent years. For this reason 100~
May be exposed to high temperatures of 150°C for long periods of time. There is now a demand for a sealing rubber that can withstand such use. ○High gas barrier properties. Ethylene glycol, dimethylformamide, γ-butyrolactone, etc. are used in the paste electrolyte solution of aluminum electrolytic capacitors. Recently, γ-butyrolactone has been widely used to improve the characteristics of aluminum electrolytic capacitors. This tends to volatilize at temperatures above 60°C. If the sealing rubber has low gas barrier properties, γ-butyrolactone will volatilize through the sealing rubber. In particular, for aluminum electrolytic capacitors that are used at high temperatures, gas barrier properties are strongly required for the sealing rubber.

Next, conventional sealing rubber will be described. Previously, aluminum electrolytic capacitors were mainly used in TVs, videos, etc. Ethylene glycol was mainly used as the electrolyte. At this time, the base rubber for sealing rubber was inexpensive natural rubber. Natural rubber lacks heat resistance and gas barrier properties, but no problems occurred under the usage conditions described above. However, when it began to be used in cars and other products, heat resistance was required. Therefore, ethylene propylene diene rubber, which has high heat resistance, replaced natural rubber as the base rubber for sealing rubber. Furthermore, when γ-butyrolactone came to be used in electrolytes, gas barrier properties were also required. Therefore, butyl rubber became the base rubber for sealing rubber in place of ethylene propylene diene rubber, which has poor gas barrier properties.

[0005] Butyl rubber has the highest gas barrier property among all rubbers. A sealing rubber using this as a base rubber can prevent volatilization of γ-butyrolactone. However, general-purpose butyl rubber has lower heat resistance than ethylene propylene diene rubber. Therefore, butyl rubber with high heat resistance is used as sealing rubber. It is either partially crosslinked butyl rubber crosslinked with peroxide or butyl rubber vulcanized with a resin. Although both satisfy all of the above-mentioned properties, there is a problem in terms of productivity.

Peroxide crosslinked partially crosslinked butyl rubber is
The base rubber is partially crosslinked. This causes poor flow during kneading and molding, making it difficult to handle. Therefore, it is difficult to increase productivity. Additionally, partially cross-linked butyl rubber cross-linked with peroxide is susceptible to cracking. When assembling the sealing rubber into the aluminum case,
There are things that can break.

On the other hand, resin-vulcanized butyl rubber does not have the disadvantage of being easily cracked. However, this also poses a productivity problem. General resin-vulcanized butyl rubber requires stannous chloride or a halogenated polymer as a vulcanization aid. Among them, if stannous chloride is not added, the crosslinking time will be extremely long. However, if a halogen compound is present in the sealing rubber, the halogen will be liberated and corrode the aluminum. Therefore, current sealing rubbers using resin-vulcanized butyl rubber use a resin vulcanizing agent containing bromine. Bromine compounds are less likely to corrode aluminum than chlorine compounds, but they take longer to crosslink. This sealing rubber requires 1.5 to 2 times as much crosslinking time as general-purpose butyl rubber, and also requires secondary crosslinking to allow crosslinking to proceed sufficiently. Therefore, productivity is poor. Also, if this sealing rubber is used at high temperatures for a long period of time, it may corrode the aluminum.

[0008] In view of these problems, sealing rubber made by gluing rubber and plastic together has been considered. This is sulfur-vulcanized butyl rubber coated with Teflon. This sealing rubber has the properties of Teflon, that is, high heat resistance and impermeability to γ-butyrolactone, added to butyl rubber. However, this sealing rubber also has the following problems.

[0009] There are variations in the performance of aluminum electrolytic capacitors. Teflon has no elasticity. When the sealing rubber is assembled into an aluminum case, if there is a slight burr on the Teflon part of the sealing rubber, a gap will be created between the aluminum case and the Teflon part of the sealing rubber. In such an aluminum electrolytic capacitor, γ-butyrolactone quickly volatilizes. Also, when assembling, the hard Teflon part may wrinkle. The Teflon part and the rubber part gradually peel off. If the Teflon has peeled off, the gas barrier properties of the sealing rubber will deteriorate. In this way, applying a sealing rubber made of Teflon may result in an aluminum electrolytic capacitor with poor performance.

○ It is expensive. The material Teflon is expensive and the manufacturing process is complicated. This sealing rubber is about 5 to 7 times more expensive than sealing rubber that uses only butyl rubber as a base rubber. ○This sealing rubber can only be made in a cylindrical shape. In recent years, sealing rubbers that are not simply cylindrical in shape but have small cylinders attached to the circular surface of the sealing rubber have come into use. This shape has an uneven circular surface. Due to the manufacturing process, it is difficult to mold this type of Teflon one by one and glue it together with rubber.

[0011]

[Problems to be Solved by the Invention] The problems solved by the sealing rubber of the present invention are summarized below. ○ Can withstand long-term use at high temperatures. High heat resistance. Furthermore, the sealing rubber does not volatilize γ-butyrolactone even when used at high temperatures. Of course, it will not corrode aluminum. ○It is inexpensive. This sealing rubber has a simple manufacturing process and can be mass-produced. Therefore, it is inexpensive. Additionally, aluminum electrolytic capacitors with this rubber seal do not exhibit any variation in performance. In other words, the rate of rejected products is low. In this respect as well, it is an inexpensive sealing rubber. ○No restrictions on shape. You can make something with a small cylinder attached to the circular surface of the sealing rubber.

0012

Means for Solving the Problems The sealing rubber of the present invention is manufactured as follows. ■Butyl rubber as base rubber,
A halogen compound is added and a sealing rubber is molded by resin vulcanization. ■Remove halogen compounds from molded sealing rubber. This will be explained in detail below.

(2) Using butyl rubber as a base rubber, a halogen compound is added, and a sealing rubber is molded by resin vulcanization. First, set the composition. Table 1 shows formulations suitable for the sealing rubber of the present invention. The formulation basically consists of butyl rubber, resin vulcanizing agent, vulcanizing aid, and filler. Each is described below.

[0014]

[Table 1]

Any butyl rubber may be used as long as it does not contain halogen. The resin vulcanizing agent is
Use one for butyl rubber. Examples include alkylphenol formaldehyde resins, alkylphenol sulfide resins, and the like. These require a halogen compound as a vulcanization aid. The vulcanization aid may be an organic or inorganic compound as long as it serves as a halogen donor. Among them, metal halides are suitable for the present invention. Specific examples include stannous chloride, zinc chloride, aluminum chloride, zinc bromide, and aluminum bromide. Resin vulcanizing agents containing halogens can also be used in the present invention. For example, chlorinated alkylphenol formaldehyde resin, brominated alkylphenol formaldehyde resin, etc. Since these contain halogen, it is not necessary to add a vulcanization aid, or the above-mentioned vulcanization aid may be added. Add compounding ingredients, knead, and mold sealing rubber using a mold. The crosslinking conditions are 160-1
The temperature is 80°C for about 7 to 15 minutes.

(2) Remove halogen compounds from the molded sealing rubber. Remove the halogen compounds used as resin vulcanizing agents and vulcanizing aids from the molded sealing rubber. First, choose a solvent in which the halogen compound used will dissolve well. For example, when stannous chloride is used as a vulcanization aid, the solvent is selected from ethyl acetate, acetone, diethyl ether, alcohol, water, and the like. You can choose from alcohol or ether for zinc chloride, water or almost any organic solvent for aluminum chloride, and water, alcohol, acetone, benzene, etc. for aluminum bromide. When a halogenated alkylphenol formaldehyde resin is used as the resin vulcanizing agent, the solvent is selected from ethyl acetate, acetone, etc. Two or more types of solvents may be used in combination. The molded sealing rubber is immersed in the selected solvent and left at room temperature for 3 to 10 hours. A reflux condenser may be attached to warm the solvent to 50-80°C. If you warm it up, the leaving time can be shortened to 1 to 4 hours. After removing the rubber seal from the solvent, it is best to wash it with fresh solvent. This is dried to evaporate the solvent.

Among the solvents mentioned above, water and alcohol do not penetrate the sealing rubber at all. Ether and ethyl acetate also do not penetrate well. When these solvents are used, the halogen compounds on the surface of the sealing rubber can be removed, but the halogen compounds inside the sealing rubber cannot be removed. To remove all internal halogen compounds, do the following: Prepare a solvent that penetrates well into the sealing rubber. Such solvents include n-hexane, xylene, toluene, and the like. A solvent that penetrates the sealing rubber and a solvent that dissolves the halogen compound mentioned above are mixed. Choose solvents that mix well with each other. The ratio of mixing solvents is
The ratio of the solvent that permeates into the sealing rubber to the good solvent of the halogen compound is 3:7 to 7:3. Two or more types of either solvent may be used in combination. A sealing rubber is immersed in a solution containing both solvents and left at room temperature for 20 to 30 hours. Replace the solution with a new one and leave for 3-8 hours. The solution is exchanged 2 to 4 times. The leaving time for each time is 3~
8 hours is appropriate. As mentioned above, by attaching a reflux condenser and raising the temperature of the solution to 50 to 80°C, the standing time can be shortened. After the immersion, the sealing rubber is left to stand to volatilize all the solvent that has penetrated into the sealing rubber. This operation takes 20 to 30 hours at room temperature, 50 to 80℃.
That would take 5 to 10 hours.

[0018]

[Operation] The sealing rubber of the present invention is obtained by adding a halogen compound and crosslinking and molding butyl rubber using a conventional resin vulcanization method. In normal resin vulcanization, the rubber flows well during the kneading and molding stages. Furthermore, when a halogen compound, especially stannous chloride, is blended, crosslinking will proceed sufficiently in the same crosslinking time as the sulfur crosslinking of butyl rubber. Resin-vulcanized butyl rubber has higher heat resistance than its sulfur-crosslinked counterpart.

In the sealing rubber of the present invention, a halogen compound is used as a resin vulcanizing agent or a vulcanizing aid during crosslinking. Halogen compounds corrode the aluminum parts of aluminum electrolytic capacitors because they liberate halogen over time. Therefore, in the present invention, the molded sealing rubber is post-treated to remove the halogen compound from the sealing rubber. The molded sealing rubber is immersed in a good solvent for halogen compounds, such as alcohol or acetone, and left to stand. Then, the halogen compound on the surface of the sealing rubber migrates toward the solvent. After leaving it for a certain period of time, the sealing rubber is dried. Since the rubber part is cross-linked, it will not change during this operation. In this way, the halogen compound on the surface of the sealing rubber can be removed.

The halogen compound used in the present invention is not dissolved in the rubber portion of the sealing rubber, but is dispersed or scattered. If the temperature at which the aluminum electrolytic capacitor is used is up to about 80° C., the halogen compounds scattered inside the sealing rubber will not migrate to the surface of the sealing rubber. Therefore, if the halogen compound on the surface of the sealing rubber is removed, aluminum will not be corroded by the sealing rubber.

However, when used at a higher temperature of 80 to 150° C., the rubber molecules of the sealing rubber and the halogen compound molecules become very active. Then, the halogen compound inside the sealing rubber moves to the surface of the sealing rubber over time. In such a case, it is also necessary to remove the halogen compound inside the sealing rubber. For this purpose, a mixture of a solvent that penetrates into the sealing rubber and a good solvent for the halogen compound is used. Since the former penetrates into the sealing rubber, the latter also penetrates into the sealing rubber. Then, the halogen compound inside the sealing rubber is dissolved in the latter solvent. Dissolved halogen compounds migrate to lower concentrations. In this way, the halogen compound inside the sealing rubber can be transferred to the solution in which the sealing rubber is immersed. After sufficiently removing the halogen compound from the sealing rubber, the sealing rubber is taken out from the solution. This sealing rubber absorbs the solution and swells. When the sealing rubber is left at room temperature or gently heated, the solution evaporates and the sealing rubber returns to its original size.

In the present invention, a halogen compound is used as a resin vulcanizing agent or a vulcanizing aid. Any of the ones mentioned above may be used. However, if a resin vulcanizing agent that does not contain a halogen compound is combined with stannous chloride as a vulcanization aid, mass production is easier. This is due to the following reason.

[0023] This combination requires 7 to 11 minutes for crosslinking, which is shorter than other combinations. Further, there is no need for secondary vulcanization. In this way, the process is simple and the daily production amount can be increased. ○Stannous chloride dissolves quickly in solvents, so it is easy to remove from sealing rubber. The time required to immerse the sealing rubber in a solvent can be shortened.

The sealing rubber of the present invention is almost the same in price as the conventional butyl rubber sealing rubber. This is due to the following reason. ○The existing molds can be used. The new equipment is only related to immersing the sealing rubber in solvent and volatilizing the solvent, and is inexpensive. ○Since the time required for crosslinking is short and secondary vulcanization is not required, the daily production amount can be increased. ○The sealing rubber of the present invention does not break when assembled into an aluminum electrolytic capacitor. Therefore, the rate of rejected products is low.

[0025]

EXAMPLES Four types of sealing rubbers, Examples A to D, will be described. According to the formulation shown in Table 1, butyl rubber was used as a base rubber and compounding agents were added and kneaded. And height 2mm, line 3
．． A 5 mm cylindrical sealing rubber was molded. Each of these was treated as follows to remove the halogen compound from the sealing rubber.

Example A) Example using an alkylphenol formaldehyde resin as the resin vulcanizing agent and stannous chloride as the vulcanization aid. Compounding and kneading according to Table 1, Example A, and crosslinking at 170° C. for 7 minutes to form a sealing rubber. Molded. Acetone was used as the solvent for dipping the sealing rubber. The sealing rubber was immersed in acetone and left at room temperature for one day and night while being gently stirred. The sealing rubber removed from the acetone was washed with fresh acetone. This was left at room temperature for 5 hours to dry the acetone.

Example B) Example of using an alkylphenol formaldehyde resin as the resin vulcanizing agent and zinc chloride as the vulcanization aid.The compositions were blended and kneaded according to Table 1, Example B, and a sealing rubber was molded under crosslinking conditions at 170°C for 12 minutes. . The solvent in which the sealing rubber was immersed was a mixture of ethyl alcohol and toluene in a ratio of 1:1. The sealing rubber was immersed in the mixed solvent and left at room temperature for one day and night while being gently stirred. Replace the mixed solvent (same solvent type and solvent ratio) with new one twice,
It was left for 5 hours each time. At this stage, the sealing rubber absorbs the mixed solvent and swells. This sealing rubber is left at room temperature for one day and night to volatilize the absorbed solvent. Then,
The rubber seal returned to its original size.

Example C) Example of using brominated alkylphenol formaldehyde resin as resin vulcanizing agent Compounding and kneading were carried out according to Table 1, Example C, and a sealing rubber was molded under crosslinking conditions of 180° C. for 13 minutes. Acetone was used as the solvent for dipping the sealing rubber. The sealing rubber was immersed in acetone and left at room temperature for one day and night. The sealing rubber was removed from the acetone and washed with fresh acetone. This was left at room temperature for 5 hours to dry the acetone.

Example D) Example using brominated alkylphenol formaldehyde resin as the resin vulcanizing agent and stannous chloride as the vulcanization aid.Blend and knead according to Table 1, Example D, and seal under crosslinking conditions at 170°C for 7 minutes. Molded rubber. The solvent in which the sealing rubber was immersed was a mixture of acetone and toluene in a ratio of 1:1. The sealing rubber was immersed in the mixed solvent and left at room temperature for one day and night while being gently stirred. The mixed solvent (the type of solvent and the solvent ratio were the same) was replaced with a new one three times, and the mixture was left for 5 hours each time. At this stage, the sealing rubber absorbs the mixed solvent and swells. This sealing rubber is left at room temperature for one day and night to volatilize the absorbed solvent. Then, the sealing rubber returns to its original size.

(Experiment) The sealing rubber of the present invention is made by vulcanizing butyl rubber with a resin. Since butyl rubber has high gas barrier properties, γ-butyrolactone hardly permeates through it even at high temperatures. Therefore, regarding the sealing rubber of the present invention, an experiment was conducted to examine the heat resistance and corrosion resistance of aluminum. The details of the experiment are described below. Example A ~ in a glass ampoule with an inner diameter of about 7.5 mm
Enclose one sealing rubber of Example D and one sheet of aluminum foil. Aluminum foils were cut from those used in aluminum electrolytic capacitors so that each sheet weighed approximately 1 mg. Examples A and C are left at about 80°C, and Examples B and D are left at about 150°C. After one month, observe the state of the aluminum foil and sealing rubber. As a control, a sealing rubber molded in the same manner as in Example A was used as it was, ie, without being immersed in a solvent.

The results are shown in Table 2. None of the aluminum foils sealed in glass ampoules together with the sealing rubber of the present invention had any holes or scratches. However, the aluminum foil encapsulated with the sealing rubber of Example A, which had not been immersed, was scratched and had holes. This is thought to be due to chlorine released from the sealing rubber. None of the sealing rubbers was softened or sticky. As described above, the sealing rubber of the present invention has high heat resistance and does not corrode aluminum. If the halogen compound is removed from the entire sealing rubber as in Examples B and D, these effects will be even more remarkable. The aluminum electrolytic capacitor provided with this rubber seal can be used continuously at 150°C.

[0032]

[Table 2]

[0033]

[Effects] The sealing rubber of the present invention is molded by vulcanizing butyl rubber with a resin. Therefore, the heat resistance of this sealing rubber is higher than general-purpose butyl rubber and comparable to ethylene propylene diene rubber. Gas barrier properties are much higher than ethylene propylene diene rubber. However, when molding the sealing rubber, halogen compounds are used that corrode aluminum. Therefore, in the present invention, the sealing rubber is post-treated to remove the halogen compound. Therefore, the sealing rubber of the present invention does not corrode aluminum.

[0034] During post-treatment, if a solvent that permeates into the sealing rubber is mixed and used, the halogen compound from the entire sealing rubber can be removed. This sealing rubber can be used continuously at high temperatures. Such sealing rubber has hitherto been made by subjecting partially crosslinked butyl rubber to peroxide crosslinking, or by vulcanizing butyl rubber with a resin. However, these had poor productivity. The sealing rubber of the present invention has better rubber flow during kneading and molding and is easier to handle than partially crosslinked butyl rubber. Furthermore, since a halogen compound is added during crosslinking, the time required for crosslinking is shorter than that of conventional resin-vulcanized sealing rubbers. In this way, productivity is also excellent. Therefore, the sealing rubber of the present invention is inexpensive. Furthermore, since the rubber is molded using a mold, it can be made into any shape. In other words, compared to sealing rubber made by bonding Teflon,
There are no restrictions on shape. In this way, the sealing rubber of the present invention solves all of the problems that have hitherto been encountered with various sealing rubbers.

Claims (2)

[Claims] Claim 1: A sealing rubber for an aluminum electrolytic capacitor is molded by resin vulcanization of butyl rubber, and a halogen-containing compound is removed from the surface of the sealing rubber or the entire sealing rubber using a solvent. Features a sealing rubber for aluminum electrolytic capacitors. 2. The sealing rubber according to claim 1, wherein stannous chloride is used as a vulcanization aid when vulcanizing the butyl rubber with a resin.