JP5919583B1 - Alkaline battery - Google Patents

Abstract

The alkaline battery has a case having an opening, a power generation element housed in the case together with an alkaline electrolyte, and a sealing unit having a gasket mainly composed of polyamide resin and sealing the case opening. . The gasket includes a thin portion that functions as an explosion-proof valve. The polyamide resin includes a first polyamide resin and a second polyamide resin having the same monomer unit chemical structure as the first polyamide resin and having a number average molecular weight smaller than that of the first polyamide resin.

Description

  The present invention relates to an alkaline battery, and more particularly to a gasket for sealing an alkaline battery.

  The alkaline battery includes a case, an alkaline electrolyte, a power generation element, and a sealing unit. The power generation element is housed in the case together with the alkaline electrolyte. The sealing unit having a gasket is disposed in the opening of the case, and the alkaline dry battery is sealed by caulking the opening of the case against the sealing unit.

  The gasket is generally manufactured by an injection molding method in which a resin melted at a high temperature is poured into a mold at a high pressure. As a resin used for the gasket, a polyethylene resin having excellent chemical resistance has been used in the past, but at present, a polyamide resin having excellent heat resistance is mainly used.

  Alkaline batteries are widely used as a power source for various devices. Nowadays, it is used as an emergency power source during natural disasters such as typhoons and earthquakes, and may be stored for a long time after purchasing alkaline batteries. For this reason, the alkaline dry battery is required to have a liquid leakage resistance exceeding, for example, 10 years at room temperature.

  Therefore, the gasket is required not to be brittle with respect to the alkaline electrolyte and not to crack so that the sealing performance can be maintained over a long period of time.

  Moreover, the thin part which functions as an explosion-proof valve is formed in the gasket. The battery may be short-circuited or charged due to incorrect use of the battery or abnormality on the device side. At this time, it is avoided that the thin-walled portion is broken (explosion-proof valve is activated) due to a significant increase in internal pressure, and the battery is ruptured.

  However, when a large number of batteries are connected in series, significant heat generation may occur. In addition, the usage environment may be high. When the temperature of the alkaline battery increases in such a situation, the gasket softens and expands, the explosion-proof valve does not operate, and the alkaline battery may burst. For this reason, the gasket is required to have a characteristic that the explosion-proof valve operates stably even at high temperatures.

  Patent Document 1 describes a gasket composed of a mixture of 6,6 polyamide resin and 6,10 polyamide resin in order to improve leakage resistance.

  Patent Document 2 describes a gasket composed of a polymer alloy made of 6,6 polyamide resin, polyphenyl ether, and an elastomer in order to improve leakage resistance.

Special table 2013-527864 gazette Special table 2001-351586

  The present invention provides an alkaline battery having a gasket including an explosion-proof valve that maintains hermeticity for a long period of time and operates stably even at high temperatures.

  The alkaline dry battery of the present invention includes a case having an opening, a power generation element housed in the case together with an alkaline electrolyte, a gasket mainly composed of polyamide resin, and a sealing unit that seals the opening of the case And have. The gasket includes a thin portion that functions as an explosion-proof valve. The polyamide resin includes a first polyamide resin and a second polyamide resin having the same monomer unit chemical structure as the first polyamide resin and having a number average molecular weight smaller than that of the first polyamide resin.

  In the alkaline dry battery having this configuration, the gasket maintains the sealing performance for a long time, and the explosion-proof valve operates stably even at high temperatures.

FIG. 1 is a partially cutaway sectional view of an alkaline battery according to an embodiment of the present invention. FIG. 2A is an explanatory view showing a cross section of the gasket before the short-circuit test. FIG. 2B is an explanatory diagram showing an operation state of the explosion-proof valve in the cross section of the gasket after the short-circuit test is performed in a high-temperature environment following FIG. 2A.

  Prior to the description of the embodiments of the present invention, problems in conventional alkaline batteries will be briefly described. In Patent Document 1 and Patent Document 2, gaskets are made of resins having different components. In such a gasket, there are portions where resins of different components are not dissolved and phase-separated, or there are portions where resins of the same component are aggregated. Such a locally peculiar part and the interface part between the surroundings are easily embrittled with the alkaline electrolyte, and there is a possibility that the gasket may crack. This crack causes leakage. Patent Document 1 and Patent Document 2 do not consider the operation of the explosion-proof valve of the gasket at high temperatures.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a partially cutaway sectional view of an alkaline battery according to an embodiment of the present invention.

  The alkaline battery includes a bottomed cylindrical case 1, a positive electrode 2, a negative electrode 3, a separator 4, and a sealing unit 9. The positive electrode 2 contains manganese dioxide and graphite. The negative electrode 3 contains zinc. The separator 4 is interposed between the positive electrode 2 and the negative electrode 3. The positive electrode 2, the negative electrode 3, and the separator 4 constitute a power generation element.

  Case 1 has an opening and houses a power generation element together with an alkaline electrolyte. The sealing unit 9 has a negative electrode current collector 6, a negative electrode terminal plate 7 electrically connected to the negative electrode current collector 6, and a gasket 5, and seals the opening of the case 1. The gasket 5 includes a thin portion 5a that functions as an explosion-proof valve when the internal abnormal pressure rises. The outer surface of the case 1 is covered with an exterior label 8.

  The gasket 5 is formed of a resin mainly composed of a polyamide resin. This polyamide resin includes a first polyamide resin and a second polyamide resin. The second polyamide resin has the same monomer unit chemical structure as the first polyamide resin, and has a smaller number average molecular weight than the first polyamide resin.

  In the gasket 5 configured in this manner, there are regions where the molecular weights are locally different. In this region, the molecular chain entanglement is slightly weakened and the mechanical strength is slightly weakened. For this reason, before the gasket 5 is softened and stretched at a high temperature, the thin portion 5a functioning as an explosion-proof valve is broken. For this reason, the explosion-proof valve operates stably.

  In addition, since the chemical structures of the monomer units are the same, the first polyamide resin and the second polyamide resin are more easily compatible than when mixed with resins of different components. Therefore, there are fewer interfaces that are easily embrittled with the alkaline electrolyte. As a result, the gasket 5 can maintain the sealing performance for a long time.

  Specifically, the difference between the number average molecular weight of the first polyamide resin and the number average molecular weight of the second polyamide resin is preferably 300 or more and 4000 or less.

  If the difference in number average molecular weight is 300 or more, a substantial effect can be obtained. Considering the kneading time of the polyamide resin before injection molding into the gasket 5, the difference in the number average molecular weight may be 4000 or less. If it does in this way, it will suffice if it knead | mixes in the time comparable as the kneading | mixing time in the case of producing the gasket formed with the single component polyamide resin, and does not affect productivity.

  In addition, the number average molecular weight of a polyamide resin can be calculated | required by gel permeation chromatography, for example using Tosoh Corporation HLC-8220GPC.

  For example, a polyamide resin having a number average molecular weight of 5000 to 50000 may be used.

  For example, 6,6 polyamide or 6,10 polyamide resin may be used as the polyamide resin.

  Moreover, the gasket 5 can contain a plasticizer, a heat stabilizer, an antioxidant, a lubricant, a filler, a colorant, a combustion inhibitor, and the like as long as the object of the present invention is not impaired.

  Hereinafter, the effect by this Embodiment is demonstrated in detail using a specific example.

  In producing a sample of an alkaline battery, gaskets are produced by injection molding using various resins. The composition of the gasket at that time is shown in (Table 1) and (Table 2).

  The gaskets of samples C1 and C2 shown in (Table 1) are composed of resins having different components described in Patent Documents 1 and 2 described above. The gasket of sample C1 is composed of a mixture of 6,6 polyamide resin and 6,10 polyamide resin. The gasket of sample C2 is composed of a polymer alloy made of 6,6 polyamide resin, polyphenyl ether, and elastomer.

  The gaskets of Sample C3 and Sample C4 shown in (Table 2) are general gaskets composed of a single 6,10 polyamide resin and 6,6 polyamide resin, respectively.

  On the other hand, the gaskets of the samples E1 to E5 are composed of a first polyamide resin and a second polyamide resin. For example, in sample E1, the first polyamide resin and the second polyamide resin are 6,10 polyamide resins. The number average molecular weights of the first polyamide resin and the second polyamide resin are 14000 and 13700, respectively.

  In addition, Asahi Kasei CM2001 is used as 6,10 polyamide resin. As 6,6 polyamide resin, 1300s manufactured by Asahi Kasei is used. In producing the gasket, a plurality of lots of the above-mentioned resins were obtained, and by performing gel permeation chromatography, 6,10 polyamide resins having number average molecular weights shown in (Table 1) and (Table 2), 6,6 polyamide resin is prepared.

  Then, the materials shown in (Table 1) and (Table 2) are respectively melted, kneaded and injection-molded in composition ratios to produce gaskets having the shapes shown in FIG. Specifically, the melting temperature of the material is about 280 ° C. The kneaded product is put into an injection molding machine, injected into a molding die maintained at about 80 ° C. under a pressure of 100 MPa in 2 seconds, held for 2 seconds, and further cooled in the die for 5 seconds. Yes. In this way, a gasket is produced.

  Using these gaskets, LR6 (AA) size alkaline dry battery samples similar to the structure shown in FIG. 1 were prepared and evaluated as follows.

<Evaluation test of long-term storage characteristics>
In order to examine the long-term sealing performance of the gasket, 50 samples of each alkaline battery are stored in a constant temperature bath in an environment of 80 ° C. and an environment of 90% relative humidity (90% RH) at 60 ° C. . At 1.5 and 3 months, the number of leaking batteries is visually confirmed.

  According to the above evaluation, it is judged that it is excellent in long-term storage when it does not leak for 3 months in an environment of 80 ° C. and an environment of 60% at 90% relative humidity. The results of this evaluation test are shown in (Table 3).

  According to Table 3, no leakage occurred in any of the samples in a storage period of 1.5 months under an environment of 80 ° C. and an environment of 60% at 90% relative humidity.

  In the storage period of 3 months, the samples C3, C4, and the samples E1 to E5 were not leaked in an environment of 80 ° C. and an environment of 90% relative humidity at 60 ° C. The storage characteristics are shown.

  However, in an environment of 80 ° C. and a storage period of 3 months under an environment of 60 ° C. and a relative humidity of 90%, the sample C1 and the sample C2 composed of the resin of different components leaked in the sample. doing.

  Among the alkaline dry batteries composed of the gaskets of Sample C1 and Sample C2, when the sample that had leaked was disassembled, it was found that all leaked due to cracks in the gasket. The gaskets of sample C1 and sample C2 are made of resins having different components. Therefore, it is considered that there are many portions where the resin components are not compatible but phase-separated. The interface between different resins tends to become brittle with respect to the alkaline electrolyte, and it is assumed that cracks occurred in the gasket during long-term storage, leading to leakage.

<Short-circuit test>
In order to investigate the operability of the explosion-proof valve in a high temperature environment, 30 sets of assembled batteries in which four samples of each alkaline battery are connected in series are prepared. These were stored in a 60 ° C. constant temperature bath for 8 hours, and then each set was short-circuited and left as it was for 24 hours. After that, the number of batteries that have ruptured is confirmed.

  Further, the extent of gasket expansion during the above test is examined by the following method. The body of each alkaline battery is cut in the radial direction of the battery so as to be roughly divided into two parts, and the negative electrode and the positive electrode are removed from the case sealed with the gasket and washed. In order to fix the gasket in this, an epoxy resin adhesive is poured, cured for 24 hours, and then cut in the axial direction of the battery so as to be roughly divided into two parts, and the cut surface is polished.

  In this way, 10 cut surfaces are prepared, and the length of the curve X′Y ′ shown in FIG. 2B is measured with a digital microscope. 2A and 2B are explanatory views of a cross section including a gasket of an alkaline battery. FIG. 2A shows the state before the short-circuit test, and the length of the line segment XY is 2.2 mm. FIG. 2B shows a state after the short-circuit test, and shows that the line segment XY before the test is extended by heat and deformed into a curve X′Y ′.

  As an evaluation index of the degree of expansion of the gasket, a difference in length between the line segment XY (2.2 mm) and the curve X′Y ′ is obtained, and an average value of 10 pieces is calculated for each. Table 4 shows the results of the short-circuit test and the results of evaluating the gasket extension.

  From Table 4, the batteries of sample C1 and sample C2 are not ruptured, and the elongation of the gasket is smaller than the other samples. The gaskets of Sample C1 and Sample C2 are composed of resins having different components, and it is considered that there are many portions that are not compatible but phase-separated. Since the interface between different resins is weak in mechanical strength, it is presumed that the thin-walled portion that functions as an explosion-proof valve was likely to break before the gasket softened and extended at high temperatures.

  In general gasket samples C3 and C4 formed of a single component, the elongation of the gasket is large and rupture occurs.

  In contrast to the above results, the samples E1 to E5 do not rupture, and the elongation of the gasket is significantly smaller than those of the samples C3 and C4.

  As described above, in samples E1 to E5, polyamide resins having the same monomer unit chemical structure and different number average molecular weights are used. Therefore, the gasket 5 has regions having different molecular weights. In this region, the molecular chain entanglement is slightly weakened, and the mechanical strength is considered to be slightly weakened. Therefore, it is considered that the explosion-proof valve works better than the samples C3 and C4 using the conventional single-component gasket.

  Further, the elongation of the gasket of sample E4 is smaller than that of the gasket of sample E2. Therefore, it is considered that mixing a small amount of a polyamide resin having a small number average molecular weight is more effective for stable operation of the explosion-proof valve at high temperatures. Thus, the polyamide resin preferably contains more first polyamide resin than the second polyamide resin.

  The alkaline dry battery of the present invention has excellent liquid leakage resistance and safety, and is suitably used for all devices using the dry battery as a power source.

1 Case 2 Positive electrode 3 Negative electrode 4 Separator 5 Gasket 5a Thin part (explosion-proof valve)
6 Negative Current Collector 7 Negative Terminal Board 8 Exterior Label 9 Sealing Unit

Claims (3)

A case having an opening;
A power generation element housed in a case together with an alkaline electrolyte;
A sealing unit having a gasket mainly composed of 6,6 polyamide resin or 6,10 polyamide resin and sealing the opening,
The gasket includes a thin portion that functions as an explosion-proof valve,
The polyamide resin includes a first polyamide resin, a second polyamide resin having the same monomer unit chemical structure as the first polyamide resin, and having a smaller number average molecular weight than the first polyamide resin; including,
Alkaline battery. The difference between the number average molecular weight of the first polyamide resin and the number average molecular weight of the second polyamide resin is 300 or more and 4000 or less.
The alkaline dry battery according to claim 1. The polyamide resin contains more of the first polyamide resin than the second polyamide resin,
The alkaline dry battery according to claim 1.

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