JP7809534B2 - alkaline batteries - Google Patents

Description

The present invention relates to alkaline batteries.

In alkaline batteries, manganese dioxide is used as the active material for the positive electrode, and zinc is used as the active material for the negative electrode. The electrolyte is an alkaline electrolyte in which potassium hydroxide is dissolved. Furthermore, alkaline batteries use a resin gasket to seal the opening of the battery can.

The resins most commonly used in alkaline battery gaskets are PA (PolyAmide) 66 (also known as 6,6-nylon, nylon 66, etc.) and PA 612 (also known as 6,12-nylon, nylon 612, etc.).

In recent years, as a measure to combat global warming, countries around the world have been moving forward with "carbon neutral" initiatives to curb the rise in carbon dioxide concentrations, which are a cause of global warming. This has led to calls for carbon neutrality and reduced environmental impact in the development of various products.

It is known that fluorene-based materials can be used as flow improvers to improve the fluidity of polyamide resins (see, for example, Patent Document 1).

International Publication No. 2016/139826

The PA66 and PA612 resins currently used in alkaline battery gaskets are petroleum-derived resins, and 0% of the carbon in the resin (polymer structure) is derived from renewable resources. This makes it difficult to reduce the amount of carbon dioxide emitted (achieving carbon neutrality).

In addition, plant-derived polyamide resins containing carbon derived from renewable resources have low fluidity in the molten plastic state, and if this resin is used as is, it is difficult to mold gaskets with complex shapes, which reduces the productivity of alkaline batteries.

In one aspect, the present invention aims to provide an alkaline battery that is highly productive while minimizing environmental impact.

In one embodiment, an alkaline battery is provided that includes a resin gasket, the gasket containing a plant-derived polyamide resin and a fluorene-based flow improver.

In one aspect, the present invention can improve the productivity of alkaline batteries while reducing the environmental impact.

1 is a cross-sectional view showing an example of an alkaline battery according to an embodiment of the present invention. FIG. 10 is a diagram showing evaluation results.

Hereinafter, embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of an alkaline battery according to the present embodiment.
In the example of FIG. 1, a cylindrical alkaline dry battery is shown as the alkaline battery 10.

In an alkaline battery 10, a positive electrode material (also called a positive electrode mixture) 12, a separator 13, a negative electrode material (also called a negative electrode mixture) 14, and an alkaline electrolyte are housed in a cylindrical metal positive electrode can 11 with a bottom. The opening of the positive electrode can 11 is sealed using a negative electrode terminal plate 16 with a rod-shaped current collector 15 fixed to the inside and a resin gasket 17. The current collector 15 is inserted into the negative electrode material 14.

The positive electrode can 11 has a layered structure, for example, in which an iron material, an alloy layer, a nickel plating layer, and a conductive film are layered in this order from the inside of the battery. A rare metal coating layer made of a rare metal may be provided between the nickel plating layer and the conductive film. The positive electrode can 11 also functions as a positive electrode current collector and positive electrode terminal, and a convex positive electrode terminal portion 11a is formed on the bottom. The positive electrode material 12 is, for example, a mixture of manganese dioxide and graphite, molded into a ring shape. The separator 13 is, for example, made of a cellulose product.

The negative electrode material 14 is a mixture of zinc alloy powder, which is an active material, and an electrolyte solution or the like, which is gelled.
In alkaline battery 10 of the present embodiment, gasket 17 contains a plant-derived polyamide resin and a fluorene-based flowability improver.

To further advance carbon neutrality and reduce environmental impact, it is desirable to use plant-derived polyamide resins whose carbon content (hereafter referred to as "carbon ratio") is 70% or more derived from renewable resources. Examples of plant-derived polyamide resins with a carbon ratio of 70% or more derived from renewable resources include PA410 and PA1010. PA410's carbon ratio from renewable resources is 70%, while PA1010's is 100%. PA410 and PA1010 are made from castor oil.

As mentioned above, plant-derived polyamide resins containing carbon derived from renewable resources have low fluidity in the molten plastic state, and if this resin is used as is, it is difficult to mold gaskets 17 with complex shapes. The reason for this low fluidity is the hydrogen bonding between the hydrogen and oxygen in the amino groups.

In the alkaline battery 10 of this embodiment, a fluorene-based flow improver is used as described above to improve the fluidity of the molten plastic when producing the gasket 17. By mixing the flow improver with the plant-derived polyamide resin, the flow improver penetrates between the hydrogen bonds, weakening the hydrogen bonds, resulting in a highly fluid molten plastic.

This effect is particularly effective when using a plant-derived polyamide resin with a renewable resource-derived carbon ratio of 70% or more, which has particularly low fluidity as a molten plastic.
Examples of fluorene-based flow improvers that can be used include 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3-phenylphenyl)fluorene, and 9,9-bis(2,4-dihydroxyphenyl)fluorene.

Incidentally, because polyamide resin is permeable to moisture, it has been confirmed that moisture can penetrate into alkaline batteries that use polyamide resin gaskets, resulting in leakage during long-term storage. Therefore, even when using plant-derived polyamide resin, from a safety perspective, it is desirable to use a material with as low a water absorption rate (≒ moisture permeability) as possible (for example, a material with a water absorption rate of 2.0% or less). For example, PA410 and PA1010 are plant-derived polyamide resins with a water absorption rate of 2.0% or less.

An example of a method for manufacturing the alkaline battery 10 shown in FIG. 1 will now be described.
First, electrolytic manganese dioxide, graphite, a binder, and a potassium hydroxide solution are mixed together to prepare the cathode material 12 .

Then, a gel-like negative electrode material 14 is produced using zinc alloy powder, electrolyte, etc. The zinc in each zinc alloy powder may be alloyed with aluminum or indium in addition to bismuth. The zinc alloy powder is powdered using, for example, centrifugal atomization or gas atomization.

Next, a ring-shaped piece of cathode material 12 is fitted into the cathode can 11, which serves as the outer casing. Then, beading is applied to the top end of the body of the cathode can 11, and a sealant is applied to the contact surface between the current collector 15 and the cathode can 11.

Then, a separator 13 is inserted inside the ring-shaped positive electrode material 12 fitted into the positive electrode can 11, and a process is carried out in which potassium hydroxide electrolyte is impregnated into the separator 13. Then, the inside of the separator 13 is filled with negative electrode material 14. The opening of the positive electrode can 11 is sealed by a negative electrode terminal plate 16 to which a current collector 15 is fixed, and a gasket 17.

The gasket 17 is produced, for example, by extrusion molding. In extrusion molding, the plant-derived polyamide resin and the fluorene-based flow improver are mixed and heated to produce a molten plastic, which is then extruded into a mold, where it is molded into the shape of the gasket 17, and then extruded from the mold into a cooling layer where it is cooled.

The alkaline battery 10 is fabricated by the above-described method.
In this alkaline battery 10, the gasket 17 contains a plant-derived polyamide resin, which promotes carbon neutrality and reduces environmental impact. Furthermore, the gasket 17 contains a fluorene-based flow improver, which improves the flow of molten plastic during the production of the gasket 17 and enhances the formability of the gasket 17, thereby improving the productivity of the alkaline battery 10.

(Evaluation results)
Next, we will show the results of various evaluations conducted to determine the desirable range of blend ratios of plant-derived polyamide resin and fluorene-based flow improver suitable for gasket 17. 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene was used as the fluorene-based flow improver. For comparison, evaluations were also conducted using resins other than plant-derived polyamide resin (PA612 and PA66).

The evaluation included the results of MFR (Melt Flow Rate) measurement, the results of water absorption rate measurement, the results of a storage test under high temperature and humidity conditions, and the presence or absence of burrs.
The MFR measurement was carried out in accordance with JIS K 7210-1. The test temperature was 230°C and the load was 2.16 kg. For samples in which the mixing ratio of the flowability improver was not 0 wt%, the resin and the flowability improver were kneaded together.

The water absorption rate was measured in accordance with JIS K 7209. The water absorption rate was calculated from the weight of the sample when it was thoroughly dried at 50°C and the weight when it was immersed in water at 23°C for 24 hours.
The high-temperature, high-humidity storage test was conducted on 100 alkaline batteries assembled using gaskets prepared with different blend ratios of resin and flow improver. More specifically, the alkaline batteries were stored for 100 days in an atmosphere at a temperature of 60°C and a humidity of 90%, and then the presence or absence of leakage was confirmed.

The 100 gaskets produced as described above were visually inspected for the presence or absence of burrs.
FIG. 2 is a diagram showing the evaluation results.

Comparative Example 1 represents a case where PA612 was used and the mixing ratio of the fluorene-based flowability improver was 0 wt % (that is, no flowability improver was included).
As shown in Figure 2, in Comparative Example 1, the MFR measurement result was 50 g/10 min, indicating sufficient fluidity, the water absorption rate was low at 1.3%, and the leakage rate was 0%, which were good results. In addition, no burrs were observed.

However, PA612 is a petroleum-derived material and contains 0% carbon derived from renewable resources, meaning it does not contribute to reducing carbon dioxide emissions.
Comparative Example 2 represents a case where PA66 was used and the mixing ratio of the fluorene-based flowability improver was 0 wt % (that is, no flowability improver was included).

2, in Comparative Example 2, the MFR measurement result was 30 g/10 min, indicating relatively good fluidity. In addition, no burrs were observed.
However, in Comparative Example 2, the water absorption rate was high at 2.5%. As a result, moisture penetrated into the battery during long-term storage as an alkaline battery, resulting in a high leakage rate of 50%, as shown in Figure 2. Furthermore, like PA612, PA66 is also a petroleum-derived material, with 0% of its carbon content derived from renewable resources. Therefore, it is not effective in reducing carbon dioxide emissions.

Comparative Example 3 represents a case where PA610 was used and the mixing ratio of the fluorene-based flowability improver was 0 wt % (that is, no flowability improver was included).
Although PA610 contains carbon derived from renewable resources, the carbon ratio is only 50%. In addition, in Comparative Example 3, the MFR measurement result was 10 g/10 min, indicating poor fluidity.

In Comparative Example 3, the water absorption rate was 1.5% and the leakage rate was 0%. No burrs were observed.
Comparative Example 4 represents a case where PA410 was used and the mixing ratio of the fluorene-based flowability improver was 0 wt % (that is, no flowability improver was included).

PA410 has a carbon content of 70% derived from renewable resources, which can reduce the amount of carbon dioxide emitted. On the other hand, in Comparative Example 4, the MFR measurement result was 10 g/10 min, indicating poor fluidity.

In Comparative Example 4, the water absorption rate was 2.0%, which was higher than that of Comparative Example 3, but the leakage rate was 0%, meaning no leakage was observed. In addition, no burrs were observed.
Comparative Example 5 shows the case where PA410 was used and the mixing ratio of the fluorene-based flowability improver was set to 4 wt %.

In Comparative Example 5, a fluorene-based flow improver was used, but the MFR measurement result was 20 g/10 min. Although the flowability was improved compared to Comparative Example 4, it was still inferior to Comparative Examples 1 and 2 and was not sufficient.

In Comparative Example 5, the water absorption rate was 2.0%, and the leakage rate was 0%, meaning no leakage was observed, as in Comparative Example 4. Furthermore, no burrs were observed.
Example 1 shows the case where PA410 was used and the mixing ratio of the fluorene-based flowability improver was set to 5 wt %.

In Example 1, due to the effect of the fluorene-based flow improver, the MFR measurement result was 35 g/10 min, which was inferior to Comparative Example 1 but improved over Comparative Example 2.
In Example 1, the water absorption rate was 2.0%, and the leakage rate was 0%, meaning no leakage was observed, as in Comparative Examples 4 and 5. In addition, no burrs were observed.

Example 2 shows the case where PA410 was used and the mixing ratio of the fluorene-based flowability improver was set to 10 wt %.
In Example 2, due to the effect of the fluorene-based flowability improver, the MFR measurement result was 50 g/10 min, and good flowability equivalent to that of Comparative Example 1 was obtained.

In Example 2, the water absorption rate was 2.0%, and the leakage rate was 0%, similar to Comparative Examples 4 and 5 and Example 1, meaning no leakage was observed. Also, no burrs were observed.
Comparative Example 6 represents a case where PA410 was used and the mixing ratio of the fluorene-based flowability improver was set to 11 wt %.

In Comparative Example 6, due to the effect of the fluorene-based flow improver, the MFR measurement result was 60 g/10 min, achieving higher flowability than Comparative Example 1. However, the flash occurrence rate was 55%, confirming that flash occurred due to molten plastic seeping into the parting portions of the mold. For this reason, it can be said that the flowability of Comparative Example 6 is too high.

In Comparative Example 6, similar to Comparative Examples 4 and 5 and Examples 1 and 2, the water absorption rate was 2.0%, the leakage occurrence rate was 0%, and no leakage was observed.
Comparative Example 7 represents a case where PA1010 was used and the mixing ratio of the fluorene-based flowability improver was 0 wt % (that is, no flowability improver was included).

PA1010 has a 100% carbon content derived from renewable resources, making it possible to significantly reduce the amount of carbon dioxide emitted. On the other hand, Comparative Example 7 had a measured MFR of 15 g/10 min, indicating poor fluidity.

In Comparative Example 7, the water absorption rate was 1.5%, the leakage rate was 0%, and no leakage was observed. Also, no burrs were observed.
Comparative Example 8 shows the case where PA1010 was used and the mixing ratio of the fluorene-based flowability improver was set to 4 wt %.

In Comparative Example 8, a fluorene-based flow improver was used, but the MFR measurement result was 25 g/10 min. While the flowability is improved compared to Comparative Example 7, it is still inferior to Comparative Examples 1 and 2 and is not sufficient.

In Comparative Example 8, the water absorption rate was 1.5%, and the leakage rate was 0%, meaning no leakage was observed, as in Comparative Example 7. Furthermore, no burrs were observed.
Example 3 shows the case where PA1010 was used and the mixing ratio of the fluorene-based flowability improver was set to 5 wt %.

In Example 3, due to the effect of the fluorene-based flowability improver, the MFR measurement result was 35 g/10 min, which was inferior to Comparative Example 1 but improved over Comparative Example 2.
In Example 3, the water absorption rate was 1.5%, and the leakage rate was 0%, meaning no leakage was observed, as in Comparative Examples 7 and 8. Furthermore, no burrs were observed.

Example 4 shows the case where PA1010 was used and the mixing ratio of the fluorene-based flowability improver was set to 10 wt %.
In Example 4, due to the effect of the fluorene-based flowability improver, the measured MFR result was 55 g/10 min, and even better flowability than in Comparative Example 1 was obtained.

In Example 4, the water absorption rate was 1.5%, and the leakage rate was 0%, meaning no leakage was observed, similar to Comparative Examples 7 and 8 and Example 3. Furthermore, no burrs were observed.
Comparative Example 9 shows the case where PA1010 was used and the mixing ratio of the fluorene-based flowability improver was set to 11 wt %.

In Comparative Example 9, due to the effect of the fluorene-based flow improver, the MFR measurement result was 65 g/10 min, achieving higher flowability than Comparative Example 1. However, the flash occurrence rate was 60%, confirming that flash occurred due to molten plastic seeping into the parting portions of the mold. For this reason, it can be said that the flowability of Comparative Example 9 is too high.

In Comparative Example 9, similar to Comparative Examples 7 and 8 and Examples 3 and 4, the water absorption rate was 1.5%, the leakage occurrence rate was 0%, and no leakage was observed.
From the above results, the following can be said:

To mold a gasket 17 with a complex shape such as that shown in Figure 1, it is desirable to achieve fluidity at least equal to or greater than that achieved when using PA66, which is sometimes used as a gasket resin. As in Comparative Example 2, the measured MFR when using PA66 was 30 g/10 min, and only Examples 1 to 4 and Comparative Examples 6 and 9 achieved a fluidity higher than this. However, as mentioned above, burrs were generated in Comparative Examples 6 and 9. Such burrs could have adverse effects when assembling alkaline batteries 10, which have complex structures.

For this reason, when 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene is used as a fluorene-based flow improver, it is desirable to set the mixing ratio of the flow improver to 5 wt% or more and 10 wt% or less, as in Examples 1 to 4.

In addition, when using other fluorene-based flow improvers such as 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, 9,9-bis(4-hydroxy-3-phenylphenyl)fluorene, and 9,9-bis(2,4-dihydroxyphenyl)fluorene, the desirable mixing ratio is likely to be in the same range as above.

As long as no flash occurs, the higher the fluidity, the better the moldability of the gasket 17. In the example of Figure 2, in Examples 2 and 4, the MFR measurement results were 50 g/10 min or higher, and no flash occurred. In other words, if the mixture ratio of the flow improver is 10 wt%, as in Examples 2 and 4, the moldability of the gasket 17 can be further improved.

Furthermore, a water absorption rate of 2.0% or less is desirable as this prevents leakage. The results in Figure 2 show that water absorption rate depends on the type of resin. When PA410 or PA1010 is used as in Examples 1 to 4, the water absorption rate is 2.0% or less, so it is preferable to use such resins as plant-derived polyamide resins.

Furthermore, because PA1010 contains 100% carbon derived from renewable resources, using PA1010 can further advance carbon neutrality and reduce environmental impact compared to using PA410.

While one aspect of the alkaline battery of the present invention has been described above based on the embodiment, this is merely an example and the present invention is not limited to the above description.
For example, the specific material names given above are merely examples, and other materials may be used.

10 alkaline battery 11 positive electrode can 11a positive electrode terminal portion 12 positive electrode material (positive electrode mixture)
13 Separator 14 Negative electrode material (negative electrode mixture)
15 Current collector 16 Negative electrode terminal plate 17 Gasket

Claims (4)

An alkaline battery including a resin gasket,
The gasket is
Plant-derived polyamide resin,
a fluorene-based flow improver;
and
The mixing ratio of the flow improver in the gasket is 5 wt% or more and 10 wt% or less.
Alkaline batteries. The alkaline battery described in claim 1, wherein the proportion of carbon derived from renewable resources in the carbon contained in the plant-derived polyamide resin is 70% or more. The alkaline battery according to claim 1 or 2, wherein the plant-derived polyamide resin has a water absorption rate of 2.0% or less. 4. The alkaline battery according to claim 1 , wherein the plant-derived polyamide resin is PA410 or PA1010.