JP7011936B2 - Manufacturing method of positive electrode mixture for alkaline batteries - Google Patents

Description

The present invention relates to a method for producing a positive electrode mixture for an alkaline battery.

Alkaline batteries contain an alkaline power generation element consisting of a positive electrode mixture, a separator, and a gel-like negative electrode (hereinafter, also referred to as negative electrode gel) in a bottomed cylindrical metal battery can, and the opening of the battery can. The part has a structure that is airtightly sealed using a sealing gasket made of resin. FIG. 1 shows an LR6 type alkaline battery as an example of a general alkaline battery. FIG. 1 is a vertical cross-sectional view when the extension direction of the cylindrical shaft 100 of the cylindrical battery can 2 is the vertical direction or the vertical direction. The alkaline battery 1 shown in FIG. 1 has a so-called inside-out type structure, and is a metal battery can 2 having a bottomed cylindrical shape and a positive electrode terminal 9 formed on the outer surface of the bottom portion which also serves as a positive electrode current collector. A positive electrode mixture 3 formed in an annular shape, a bottomed cylindrical separator 4 arranged inside the positive electrode mixture 3, a negative electrode gel 5 containing a zinc alloy and filled inside the separator 4, and this negative electrode gel. It is composed of a rod-shaped negative electrode current collector 6 inserted in 5, a dish-shaped metal negative electrode terminal plate 7, a sealing gasket 8, and the like. In this structure, the power generation element of the alkaline battery 1 is formed by the positive electrode mixture 3, the separator 4, the negative electrode gel 5, and the electrolytic solution.

Further, the negative electrode current collector 6 is erected and fixed to the lower surface of the negative electrode terminal plate 7 by welding with the bottom of the battery can 2 facing downward. The negative electrode terminal plate 7, the negative electrode current collector 6, and the sealing gasket 8 are integrally combined in advance as a sealing body, and the outer peripheral portion of the sealing gasket 8 is a peripheral portion between the opening edge portion of the battery can 2 and the peripheral edge portion of the negative electrode terminal plate 7. The battery can 2 is sealed by being pinched by being crimped between them.

The procedure for assembling the alkaline battery 1 is described in Non-Patent Document 1 below. Generally, after inserting the annular positive electrode mixture 3 into the battery can 2, the separator 4 is inserted inside the positive electrode mixture 3. Next, a liquid injection step is performed in which the electrolytic solution is injected into the battery can 2 and the separator 4 and the positive electrode mixture 3 are impregnated with the electrolytic solution. Then, after filling the inside of the separator 4 with the negative electrode gel 5, a sealing step of sealing the battery can 2 with a sealing body is performed.

As a method for producing the positive electrode mixture 3, first, a positive electrode active material such as electrolytic manganese dioxide (EMD) is used as a powder material, and a binder such as graphite or polyacrylic acid is used as a conductive material, and the powder material thereof is, for example, for example. The electrolytic solution consisting of a 40 wt% KOH aqueous solution is mixed at a predetermined mass ratio (for example, EMD: graphite: binder: electrolytic solution = 91.4: 6.0: 0.1: 2.5). Next, this mixture (hereinafter, also referred to as a raw material mixture) is rolled to obtain a raw material mixture (hereinafter, also referred to as a dense pressure mixture) which is densely pressed into flakes. Further, the dense pressure mixture is sequentially treated in each step of crushing, granulating, and then classified to obtain positive electrode mixture granules screened in a range of, for example, an average particle size of 180 μm to 1000 μm. Then, the positive electrode mixture particles are compressed with a mold to form an annular shape.

The technique for improving the characteristics of the positive electrode mixture is described in, for example, Patent Documents 1 and 2 below. Further, Patent Document 1 describes a method for producing a positive electrode mixture in which the amount of water contained in the mixture of raw materials is defined in order to improve the moldability of the positive electrode mixture. Further, in Patent Document 2 below, in order to improve the liquid absorbency of the positive electrode mixture, an alkaline battery in which the positive electrode mixture is preheated and dried before filling the annular positive electrode mixture in the battery can is manufactured. The method is described.

Japanese Unexamined Patent Publication No. 61-208752 Japanese Unexamined Patent Publication No. 7-12265

FDK Corporation, "Until Fujitsu Alkaline Dry Batteries are Made", [online], [Search on November 29, 2017], Internet <URL: http://www.fdk.co.jp/denchi_club/denchi_story/arukari. htm>

If the types of raw materials contained in the raw material mixture and the mixing ratio of the raw materials are the same, the discharge performance of the alkaline battery can be improved by increasing the density of the positive electrode mixture. That is, when the density of the positive electrode mixture is increased, the conductivity between the positive electrode active materials in the positive electrode mixture is increased, and the discharge performance is improved. However, if the press pressure at the time of molding is increased in order to obtain a high-density positive electrode mixture, there arises a problem that the die wears faster. Therefore, it is desirable to produce high-density positive electrode mixture grains in the rolling process.

It is also conceivable to increase the density of the positive electrode mixture particles by uniformly dispersing the binder. As a method for uniformly dispersing the binder, for example, there is a method of spraying a binder solution obtained by dissolving the binder in a large amount of solvent on a mixture of a powdery positive electrode active material and a conductive material. However, in this method, even if the binder can be uniformly dispersed in the raw material mixture, the raw material mixture containing a large amount of solvent is rolled. Therefore, it becomes difficult to increase the density of the positive electrode mixture particles. In addition, a drying step for removing the solvent after the granulation step is also required, which increases the manufacturing time and the manufacturing cost of the positive electrode mixture. As a result, the manufacturing cost of alkaline batteries is also increased.

In the invention described in Patent Document 1, the formability is improved by impregnating the raw material mixture with water in a proportion of 2 to 5 wt% and then rolling the mixture. Further, even in a general alkaline battery, a positive electrode mixture prepared from a raw material mixture containing 2 to 5 wt% of water is used. However, the raw material mixture containing about 2 to 5 wt% of water is close to a dry state, and it is difficult to uniformly mix the binder. If the binder is not mixed uniformly, the raw material mixture tends to aggregate and form "lumps". If the raw material mixture containing lumps is rolled, the yield will decrease in the subsequent classification step. Further, the positive electrode mixture obtained by forming the positive electrode mixture granules containing lumps in a ring shape has a non-uniform density and moldability. Then, in the process of assembling the alkaline battery after molding the positive electrode mixture, the yield may decrease due to the positive electrode mixture being chipped due to insufficient strength, or the performance of the assembled alkaline battery may vary.

On the other hand, if the density of the positive electrode mixture is increased in order to improve the performance of the alkaline battery, the electrolytic solution of the positive electrode mixture is absorbed in the liquid injection step of filling the battery can with the electrolytic solution when assembling the alkaline battery. The problem that the liquid rate drops occurs. If the liquid absorption rate of the positive electrode mixture decreases, the time for impregnating the positive electrode mixture with the electrolytic solution becomes longer. Therefore, the manufacturing time of the alkaline battery becomes long. In addition, it is necessary to store the alkaline batteries in the process of assembling, which are waiting for the liquid injection process. That is, a space for storing the alkaline battery in the process of assembly is required. In addition, lengthening the manufacturing time and securing storage space are factors that increase the manufacturing cost. Furthermore, there is a possibility that "contamination" may occur in which foreign matter enters the alkaline battery during storage or the manufacturing equipment is contaminated by various materials in the alkaline battery during storage. In the invention described in Patent Document 2, the liquid absorption rate can be increased, but an additional step of heating the positive electrode mixture before being fitted into the battery can is required, which increases the manufacturing time and lengthens the production time. Manufacturing costs increase.
Therefore, an object of the present invention is to provide a method for producing a positive electrode mixture for an alkaline battery, which can secure liquid absorption, have high molding strength, and can improve the discharge performance of the alkaline battery.

The present invention for achieving the above object is a method for producing an inside-out type positive electrode mixture for an alkaline battery.
A rolling step of rolling a raw material mixture obtained by adding an electrolytic solution to a powder material containing a positive electrode mixture, a conductive material and a binder and mixing them to obtain a dense pressure mixture is included.
In the rolling step, a roller type rolling apparatus equipped with a roller capable of temperature adjustment is used, and the temperature of the dense pressure mixture is adjusted to be 1/3 or more and 90 ° C. or less of the temperature of the glass transition point of the binder. At the same time, the method for producing a positive electrode mixture for alkaline batteries is characterized in that the density of the dense pressure mixture is adjusted to 2.5 g / cm ³ or more and 3.5 g / cm ³ or less.

It is preferable to use a method for producing a positive electrode mixture for an alkaline battery in which the binder is polyacrylic acid.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for producing a positive electrode mixture for an alkaline battery, which has high molding strength, excellent liquid absorption, and can improve the discharge performance of the alkaline battery.

It is a figure which shows the structure of a general alkaline battery. It is a figure which shows the procedure of the manufacturing method of the positive electrode mixture for alkaline batteries which concerns on Example of this invention.

=== Process to reach the present invention ===
In order to obtain a positive electrode mixture having high molding strength and little variation in performance using a powder material in a dry state, it is necessary to uniformly diffuse the binder in the powder material. By the way, the viscosity of the binder decreases as the temperature rises, and it becomes easier for the binder to enter the gaps between the particles of the positive electrode active material or the conductive material in the rolling process. The rolling process and the forming process are both steps of compressing the supplied materials, but the thickness of the raw material mixture supplied in the rolling process is thinner than the thickness of the positive electrode mixture grains supplied in the forming process. Therefore, in the rolling process, the force is more easily transmitted to the center of the supplied raw material. That is, even if the pressure in the molding step is low, the density and molding strength of the positive electrode mixture can be increased by increasing the density of the dense pressure mixture after the rolling step. Therefore, if the viscosity of the binder is lowered in the rolling step, the binder can surely enter between the particles of the positive electrode active material and the conductive material in the dense pressure mixture, and the particles can be firmly bonded to each other. As a result, the molding strength of the positive electrode mixture is improved. Therefore, the present inventor has considered maintaining the temperature of the binder at a high temperature at least after the rolling step in the manufacturing process of the positive electrode mixture. Furthermore, considering the possibility that the water present in the raw material mixture evaporates and the strength of the positive electrode mixture after molding decreases, or the discharge performance of the alkaline battery using the positive electrode mixture decreases, rolling is performed. It was considered necessary to set an upper limit on the temperature in step s4. Specifically, considering that the temperature at which water evaporates is 100 ° C., it is desirable to keep the temperature of the raw material mixture at 90 ° C. or lower in the rolling process.

However, when an attempt was made to improve the performance of the positive electrode mixture and the alkaline battery by maintaining the temperature of the binder at a high temperature based on the above considerations, it was found that it was difficult to maintain the temperature of the raw material mixture constant. It was also found that the temperature at which the characteristics improve differs depending on the type of binder. For example, when the raw materials of the positive electrode active material are mixed to obtain a raw material mixture, the electrolytic solution composed of the positive electrode active material EMD and the KOH aqueous solution reacts to generate heat, but the calorific value is small. In addition, the raw material mixture is cooled in the transportation route to the rolling process, and the temperature returns to about room temperature. The raw material mixture may be continuously heated, but it is not realistic considering the manufacturing cost. Further, in the rolling process, the raw material mixture generates heat due to frictional heat, but the heat generation temperature of each material constituting the raw material mixture differs depending on the applied pressure. Therefore, it is difficult to strictly control the temperature of the positive electrode mixture during the rolling process.

Next, if the present inventor can find a wide and appropriate temperature range without strict temperature control in the rolling process, the binder is uniform among the particles of the positive electrode active material or the conductive material which is a powder material. It was thought that it would be possible to improve the discharge performance of alkaline batteries while ensuring molding strength and liquid absorption. Of course, it is possible that the appropriate temperature range differs depending on the type of binder, so it is possible to uniquely identify the appropriate temperature range based on the physical characteristics of the binder, not the type of binder. I also thought it was necessary.

Then, the present inventor paid attention to the glass transition point (hereinafter, also referred to as Tg) as a physical property related to viscosity and temperature in the binder. When the binder is Tg or more, the viscosity rapidly decreases and the binder softens. Therefore, if the raw material mixture can be maintained at a temperature of Tg or higher, the characteristics of the positive electrode mixture and the alkaline battery can be improved. However, the Tg of the binder is often 100 ° C. or higher at which water evaporates, and the positive electrode mixture cannot be heated to Tg during rolling. Next, the present inventor focused on the fact that the viscosity of the binder, which is a polymer material, decreases as the temperature rises even if it does not reach Tg. We also paid attention to the pressure in the rolling process. The higher the pressure in the rolling process, the more the binder penetrates between the particles of the powder material. Of course, the pressure in the rolling process also affects the molding strength and liquid absorption of the positive electrode mixture. Then, the present inventor appropriately sets the temperature range related to Tg in the rolling process and some parameter related to the pressure applied to the raw material mixture in the rolling process, so that the liquid absorption property and the forming strength of the positive electrode mixture can be improved. I thought that it would be possible to secure it and improve the discharge performance of alkaline batteries. The present invention has been made as a result of repeated diligent research based on the above considerations.

=== Example ===
<Procedure for manufacturing positive electrode mixture>
FIG. 2 shows the manufacturing procedure of the positive electrode mixture. First, the powder materials EMD, graphite, and binder are weighed and then dry-mixed (s1), and then ion exchange is performed to adjust the water content in the raw material mixture into an electrolytic solution consisting of the mixture and a KOH aqueous solution. Wet-mix with water-added (s2, s3). Here, the amount of ion-exchanged water is adjusted so that the water content in the raw material mixture obtained by wet mixing is about 3%. Then, the raw material mixture obtained by the wet mixing step (s3) is rolled using a roller type rolling apparatus (s4). The dense pressure mixture obtained in the rolling step s4 is subjected to each step of pulverization (s5), granulation (s6), and classification (s7) to obtain granular positive electrode mixture grains. Then, the positive electrode mixture particles are formed into an annular shape (s8) to complete the positive electrode mixture 3. The above procedure is the same as the conventional procedure for producing a positive electrode mixture. However, according to the method for producing a positive electrode mixture for an alkaline battery according to an embodiment of the present invention, parameters related to the temperature related to Tg of the binder and the pressure applied to the raw material mixture in the rolling process are appropriately set. There is. Thereby, a positive electrode mixture having high molding strength can be obtained without deteriorating the liquid absorption performance. In addition, the alkaline battery using the positive electrode mixture has high discharge performance.

<Sample preparation conditions>
In order to evaluate the performance of the positive electrode mixture prepared by the method according to the embodiment of the present invention and the alkaline battery 1 using the positive electrode mixture, the Tg is different in the procedure for producing the positive electrode mixture shown in FIG. Various types of binders were prepared, various positive electrode mixtures having different types of binders to be contained in the raw material mixture and the implementation conditions of the rolling step s4 were prepared, and alkaline batteries using the various positive electrode mixtures were prepared as samples. Specifically, the production line of the positive electrode mixture 3 used for the general LR6 type alkaline battery 1 provided as the product shown in FIG. 1 and the product assembly line were used. Then, in steps other than the dry mixing step s1 and the rolling step s4, a sample was prepared under the same conditions as the product. In the dry mixing step s1, the EMD and the conductive material were mixed with a binder of the type corresponding to the sample. In the rolling step s4, a rolling roller type rolling mill equipped with a roller having a built-in heater was used, and the temperature at which the raw material mixture was heated in the rolling step s4 and the pressure (linear pressure) applied to the raw material mixture by the rollers were changed.

The two types of binders prepared are polyacrylic acid, and Tg differs depending on the degree of polymerization. Here, prior to preparation of the sample, the Tg of each binder was measured using a differential scanning calorimeter (DSC). When measuring Tg, an alumina is used as a reference sample, a binder and a reference sample are placed in the sample chamber of the DSC, and the atmosphere is introduced into the sample chamber at a flow rate of 100 mL / min, and the room temperature is 10 ° C./min. The temperature of the sample chamber was raised from 1 to 400 ° C. As a result of the measurement, the Tg of the two kinds of binders was 134.0 ° C and 166.4 ° C.

When the rolling step s4 was carried out, the temperature and linear pressure of the rollers in the rolling apparatus were adjusted according to the sample, but the temperature and linear pressure of the rollers were not adopted as the parameters for evaluating the performance of the sample. rice field. Regarding the temperature, the raw material mixture in the rolling step s4 does not reach the roller temperature within the process time of the rolling step s4, and the raw material mixture itself generates heat due to the pressure. The temperature cannot be specified. Therefore, the temperature of the dense pressure mixture immediately after the rolling step s4 was used as a parameter related to the temperature. The temperature of the roller set in the rolling step s4 was set to any of 80 ° C. and 120 ° C. without heating, depending on the sample.

Regarding the temperature of the dense pressure mixture, since the raw material mixture is formed as a thin scaly dense pressure mixture in the rolling step s4, it is not necessary to consider the temperature gradient in the thickness direction. Therefore, the temperature of the surface of the tight pressure mixture was measured. The surface temperature can be measured in a non-contact manner using, for example, an infrared thermometer.

Regarding the pressure, there is a possibility that the linear pressure actually applied to the raw material mixture in the rolling process s4 will be different even if the linear pressure set value for the rolling apparatus is the same due to the difference in the model of the rolling apparatus or the individual difference of the same model. There is. Therefore, the density of the dense pressure mixture obtained in the rolling step s4 was adopted as a parameter related to the pressure. The roller type rolling apparatus rolls the raw material mixture by passing the supplied raw material mixture between two rollers arranged in parallel with a predetermined gap. Then, the linear pressure applied to the raw material mixture is adjusted by the gap between the two rollers (hereinafter, also referred to as the roller spacing) and the pressure applied to the two rollers in the directions facing each other (press pressure). In the rolling apparatus used in the rolling step s4, the roller spacing was fixed at 0.8 mm, and in the rolling step s4, only the press pressure was adjusted. In order to obtain a dense pressure mixture having a predetermined density in the rolling step s4, the relationship between the linear pressure set in the rolling apparatus to be used and the density of the dense pressure mixture may be investigated in advance.

<Performance evaluation test>
The liquid absorption performance, molding strength (kgf), and discharge performance of the positive electrode mixture 3 were examined for various samples assembled using the various positive electrode mixture 3 having different production conditions as described above. Regarding the liquid absorption performance, in the liquid injection step in the assembly process of the alkaline battery 1, a predetermined amount of electrolytic solution is injected into the battery can 2 in which the positive electrode mixture 3 and the separator 4 are arranged inside. When the positive electrode mixture 3 and the separator 4 are impregnated with the electrolytic solution over a long period of time, if the injected electrolytic solution is completely impregnated as in the case of the product, the result is passed, and the inside of the battery can 2 is not impregnated with the electrolytic solution. If it remained in, it was rejected.

Regarding the molding strength of the positive electrode mixture 3, a load test was performed on the positive electrode mixture 3 by applying a load (kgf) perpendicular to the direction of the cylindrical axis 100 and increasing the load (kgf). Was evaluated by the load (kgf) when it was cracked or chipped. Regarding the discharge performance, a discharge test was performed in which the sample was discharged at a current of 1500 mA for 2 seconds and then discharged at a current of 650 mA for 28 seconds as one cycle, and a discharge test was repeated for 10 cycles per hour, and the final voltage (for example, 1. It was evaluated by measuring the number of cycles up to 05V).

<Performance evaluation result>
Table 1 below shows the preparation conditions for each sample and the performance evaluation results for each sample.

Of the samples 1 to 30, samples 1 to 15 are samples using a binder having a Tg = 134 ° C, and samples 16 to 30 are samples using a binder having a Tg = 166.4 ° C. Then, the sample 1 and the sample 16 are samples produced by the same procedure as the alkaline battery 1 provided as a product, only the type of the binder is different.

Further, in the evaluation results of each sample, regarding the liquid absorption performance, the passed samples are indicated by "○" and the rejected samples are indicated by "x". As for the molding strength, as described above, the load (kgf) when the positive electrode mixture 3 is damaged by the load test is shown. As for the discharge performance, the relative value when the discharge performance of the sample 1 is 100 is shown. In addition, in Table 1, the water content in the tight pressure mixture (hereinafter, also referred to as water content) is also shown, and this water content is the water content contained in the raw material mixture and the raw material before and after the rolling step s4. It can be obtained from the mass ratio of the mixture and the tight pressure mixture.

In Table 1, first, looking at the characteristics of the samples 1 to 15 using the binder at Tg = 134 ° C., the samples 4, the samples 7 to 9, and the samples 7 to 9 and the samples 7 to 9 and the heating temperature of the rollers in the rolling step s4 were not affected. In the samples 12 to 14, the liquid absorbing performance was ensured, and the molding strength of the positive electrode mixture 3 was 1.0 kgf or more, which was 2.5 times or more that of the sample 1. The discharge performance is improved by 20% or more with respect to the sample 1. The temperature of the tight pressure mixture (hereinafter, also referred to as temperature) in these samples 4, 7 to 9, and 12 to 14 is in the range of 45.5 ° C. to 88.3 ° C., and the tight pressure mixture is in the range of 45.5 ° C. to 88.3 ° C. The density (hereinafter, also referred to as density) is in the range of 2.5 g / cm ³ to 3.5 g / cm ³ . If the density is less than 2.5 g / cm ³ , it can be considered that the conductivity between the active materials is insufficient, and as a result, the discharge performance is not improved. Of course, if the density is low, it is difficult to improve the molding strength. On the other hand, if the density is larger than 3.5 g / cm ³ , it can be considered that the liquid absorption performance is deteriorated and, as a result, the discharge performance is also deteriorated.

Next, when the temperature range in Samples 4, 7 to 9, and 12 to 14 is examined, the densities of Samples 3, 8, and 13 are both 3.0 g / cm ³ and the above 2.5 g / cm. It is in the range of cm ³ to 3.5 g / cm ³ . However, it cannot be said that the molding strength and the discharge performance of the sample 3 are superior to those of the sample 1 which is a standard for performance evaluation. On the other hand, although the water content of the samples 8 and 13 is smaller than that of the sample 3, both the molding strength and the discharge performance are excellent. Therefore, it can be considered that there is a threshold value for improving the molding strength and the discharge performance between the temperature of the sample 3 in which the improvement in performance is not observed at 40.1 ° C. and the lower limit of the temperature range of 45.5. can.

Next, in order to confirm the presence or absence of the above threshold value, when the molding strength and the discharge performance of the samples 1 to 4 are compared, the temperature of the sample 2 is 5.7 ° C higher than the temperature of the sample 1, and the temperature of the sample 3 is It is 7.9 ° C higher than the temperature of sample 2. However, the differences in molding strength and discharge performance between the samples 1 to 3 are small. Moreover, among the samples 2 and 3, the sample 3 having a higher temperature was inferior in the discharge performance. On the other hand, the temperature of the sample 4 is 4.6 ° C. higher than the temperature of the sample 3 and smaller than the temperature difference between the samples 1 and 2 or the samples 2 and 3. However, the discharge performance of the sample 4 is double that of the sample 3, and the molding strength is improved by 18%. Therefore, it is reasonable to consider that there is a threshold between 40.1 ° C and 45.5 ° C. Then, when the above threshold value was examined while considering the above-mentioned "temperature range related to Tg", the temperature of sample 4 was 45.5 ° C., which was 1/3 of Tg (= 134.0 ° C.), 44. It turned out to be very close to 7 ° C.

Next, in order to confirm whether or not 1/3 of the above Tg is a threshold value related to performance, the characteristics of the samples 1 to 16 using the binder of Tg = 134.0 ° C. and Tg = 166.4 ° C. Comparing the characteristics of 16 to 30 using the binder of No. 4, Sample 4 and Sample 19 have the same density and moisture, and the temperature is almost the same. However, although the sample 4 has excellent molding strength and discharge performance, the sample 23 using the binder at Tg = 166.4 ° C. has the same molding strength as the sample 4, but the discharge performance is high. No improvement was seen. That is, it can be seen that the lower limit of the temperature range for improving the discharge performance is not the absolute value of the temperature but the temperature related to the characteristics of the binder. Of the samples 16 to 30, the samples 23, 24, sample 27, and sample 28 have ensured liquid absorption performance, and the molding strength of the positive electrode mixture is 1.0 kgf or more, which is 2.5 times or more that of sample 1. Met. Moreover, the discharge performance of each of these samples is improved by 20% or more with respect to the sample 1. The densities of the samples 23, 24, 27, and 28 are in the range of 2.5 g / cm ³ to 3.5 g / cm ³ , and the liquid absorption performance of the samples 1 to 16 is ensured. Consistent with the density range of Samples 4, 7-9, and 12-14, which have excellent molding strength and discharge performance.

Further, the temperatures of the sample 23, the sample 24, the sample 27, and the sample 28 are in the range of 59.9 ° C to 82.2 ° C, and the lower limit of this temperature range of 55.9 ° C is Tg = 166 of the binder. It is very close to 55.5 ° C, which is 1/3 of 0.4 ° C. Therefore, in order to obtain excellent molding strength and discharge performance while ensuring liquid absorption performance, the lower limit of the temperature is 1/3 or more of Tg, and the density is 2.5 g / cm ³ to 3.5 g /. The requirement is cm ³ . As described above, it is appropriate to set the upper limit of the temperature range to 90 ° C. in consideration of evaporation of water. In fact, the temperature of the sample 14 is 88.3 ° C., which is close to the upper limit temperature of 90 ° C. in consideration of evaporation of water, and the water content is reduced to 2.2 wt%, but the molding strength is 3 of the sample 1. It was 1.2, which was double, and the discharge performance was improved by 35% compared to sample 1. The liquid absorption performance was also ensured. On the other hand, looking at the characteristics of the sample 29, although the density of the sample 29 was 3.5 g / cm ³ and was in the above numerical range, the temperature was 93.2 ° C and exceeded 90 ° C. Although the molding strength was 1.1 kgf, the liquid absorption performance and the discharge performance were deteriorated. Therefore, it can be said that it is appropriate to specify the upper limit of the appropriate temperature range at 90 ° C. Of the samples 1 to 30, the discharge performance of the samples 15 and 30 was significantly deteriorated.

Based on the above, the method for producing the positive electrode mixture for alkaline batteries according to the embodiment of the present invention is such that the density of the dense pressure mixture is 2.5 g / cm ³ or more and 3.5 g / cm ³ or less in the rolling step s4. In addition to adjusting, the temperature is adjusted to be 1/3 or more and 90 ° C. or less of Tg of the binder used. Further, as shown in Table 1, in the samples 16 to 30 using the binder having a Tg of 166.4 ° C., the samples 16 to 20 in which the rollers were not heated in the rolling step s4 had a compacted mixture temperature of Tg. It was less than 1/3. Therefore, it is more preferable to surely adjust the temperature of the dense pressure mixture to 1/3 or more of Tg by heating the rollers and performing the rolling step s4. In order to obtain a dense pressure mixture having an appropriate temperature in the rolling step s4, the relationship between the linear pressure set in the rolling apparatus to be used and the temperature of the rollers may be investigated in advance.

=== Other Examples ===
In the above example, polyacrylic acid was used as the binder. Polyacrylic acid is widely used in alkaline batteries provided as products. Then, in the above embodiment, polyacrylic acid was used as the binder in order to clarify the performance difference from the product. Of course, if the binder contained in the positive electrode mixture of the alkaline battery is a polymer binder like polyacrylic acid, the viscosity drops sharply at Tg or more. Therefore, even with a binder other than polyacrylic acid, in the rolling step s4, the temperature of the tight-pressure mixture is 1/3 or more and 90 ° C. or less of Tg, and the density of the close-pressure mixture is 2.5 g / cm ³ or more. If the pressure is adjusted to 5 g / cm ³ or less, the liquid absorption performance is ensured and a positive electrode mixture having excellent molding strength can be produced, and the alkaline battery using the positive electrode mixture has excellent discharge performance. It is easily expected that it will be. Examples of the binder include polyacrylic acid salt, polyvinyl alcohol, carboxymethyl cellulose, styrene butadiene rubber, methyl cellulose, alginic acid, polyethylene, polypropylene and the like.

In the above embodiment, a rolling apparatus having a heater built in the roller was used, and the temperature of the dense pressure mixture was adjusted to be within a predetermined temperature range. Of course, it is also possible to separately install a heater for adjusting the temperature of the dense pressure mixture to heat the raw material mixture supplied to the rolling step s4 or to heat the roller from the outside.

1 Alkaline battery, 2 Battery can, 3 Positive electrode mixture, 4 Separator, 5 Negative electrode gel,
6 Negative electrode current collector, 7 Negative electrode terminal board, 8 Seal gasket, 9 Positive electrode terminal,
s1 dry mixing process, s3 wet mixing process, s4 rolling process s8 molding process

Claims (2)

This is a method for manufacturing an inside-out type positive electrode mixture for alkaline batteries.
A rolling step of rolling a raw material mixture obtained by adding an electrolytic solution to a powder material containing a positive electrode mixture, a conductive material and a binder and mixing them to obtain a dense pressure mixture is included.
In the rolling step, a roller type rolling apparatus equipped with a roller capable of temperature adjustment is used, and the temperature of the dense pressure mixture is adjusted to be 1/3 or more and 90 ° C. or less of the temperature of the glass transition point of the binder. At the same time, the density of the dense pressure mixture is adjusted to be 2.5 g / cm ³ or more and 3.5 g / cm ³ or less.
A method for manufacturing a positive electrode mixture for an alkaline battery. The method for producing a positive electrode mixture for an alkaline battery according to claim 1 , wherein the binder is polyacrylic acid.

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