【発明の詳細な説明】[Detailed description of the invention]
本発明は酸化水銀、酸化銀、二酸化マンガン、
酸素又は空気等を陽極とし、亜鉛を陰極、苛性カ
リ溶液を電解液とするアルカリ電池において、ゲ
ル状陰極体のゲル化剤としてのゲル化性能に優れ
ており、かつ耐アルカリ性の優れたエーテル化度
2.4〜3.0のカルボキシメチルセルロースアルカリ
塩（以下CMCと略す）に関するものである。
従来、アルカリ電池の陰極体保持方法として陰
極部の電解液をゲル化させ、それに陰極活性物質
である粉末亜鉛を混入して保持させる方法は良く
知られている。これは亜鉛を効率よく放電させる
ため、粉末にして表面積を大きくし、さらに陰極
内に均一に分散せしめて、ゲル化剤を含む水酸化
カリウム水溶液から成る電解液をゲル化させ、陰
極体としたものである。
また、そのゲル化剤としてCMCが用いられる
ことも良く知られている。しかし、一般に使用さ
れているCMCはエーテル化度0.50〜1.70と比較的
低いものであり、このものを使用した電池は種々
の欠点を有していた。
電池陰極体として望ましいゲルの条件は、まず
粉末亜鉛を保持し得るほどの固さを持ついるこ
と、次に電解液の電導度を低下しないようCMC
濃度はできるだけ低い方が良く、又、放電及びス
トツクによる経時変化が小であること、粘着性が
少なく取り扱いが容易であること等である。
一方、アルカリ電池用電解液はそのイオン電導
度の点から通常苛性カリ水溶液が用いられ、この
苛性カリ水溶液は苛性カリ濃度約25〜50％（以下
重量パーセント）のものが用いられる。従来のエ
ーテル化度0.50〜1.70で平均重合度約350のCMC
を用いて電解液をゲル化させる場合、CMC濃度
を約３〜８％としないと亜鉛粉末を保持し得るほ
どの固さを持つたゲルは得られない。また、この
CMC濃度ではゲルはかなり粘着性を有し、取り
扱いが容易でないのみならず、CMC添加による
苛性カリ電解液の電導度の低下をもたらす。
これらの欠点を克服する意味で、高分子量の
CMCを用いる方法もあるが、この方法はアルカ
リ電池の放電及びストツク中にCMCの分子量低
下が顕著であり、それによりゲルは容易にこわ
れ、漏液の原因となる等の欠点を持つている。従
来のエーテル化度0.50〜1.70で平均重合度約350
のCMCを用いた場合でもストツク中のCMCの分
子量低下はさけがたく、CMCの最大の欠点と考
えられていた。
本発明者らはアルカリ電池のゲル状陰極体のゲ
ル化剤として、ゲル化性能に優れ、かつ耐アルカ
リ性の優れたCMCを開発すべく鋭意検討した結
果、エーテル化度2.4〜3.0、好ましくは2.7以上の
CMCがゲル化性能および耐アルカリ性が著しく
優れていることを見い出し、本発明を完成するに
到つたものである。
すなわち、本発明はエーテル化度2.4〜3.0のカ
ルボキシメチルセルロースアルカリ塩を用いるこ
とを特徴とするアルカリ電池用ゲル化剤に関する
ものである。
本発明のエーテル化度2.4〜3.0のCMCは公知の
方法（Canadian Journal of Research 28，Sec.
B，P731〜736〈1950〉）でも得ることができるが、
本発明者らが発明した特願昭57−60576号の方法
により容易に工業的に製造することができる。す
なわち、エーテル化に必要な水酸化ナトリウムを
分割添加してエーテル化反応を少量のアルカリ存
在下で行なう水酸化ナトリウム多段添加反応法を
採用することにより、容易に置換度2.4〜3.0の
CMCを得ることができる。
本発明に用いるエーテル化度2.4以上のCMCの
平均重合度は150〜800の範囲のものが適当であ
る。平均重合度が150以下の低重合度のCMCで
は、亜鉛粉末を保持し得るほどの固さを持つたゲ
ルを得るには高濃度のCMCが必要となり、電解
液の電導度が低くなる欠点がある。逆に平均重合
度800以上の高重合度CMCはアルカリ電池の放電
又はストツク時の重合度低下が著しく、ゲルがこ
われて漏液の原因となり好ましくない。
本発明のエーテル化度2.4以上のCMCはナトリ
ウム塩、リチウム塩、カリウム塩、アンモニウム
塩その他いずれのアルカリ塩でもよい。また使用
する電解液も濃度25〜50％の苛性カリ水溶液が通
常用いられるが、他のアルカリ水溶液でもよい。
本発明のゲル化剤の電解液に対する添加量は、
亜鉛粉末を保持し得るほどの固さのゲルが得られ
る最少の量が望ましく、電解液の種類、濃度など
により変化するが、通常電解液に対し0.5〜５％、
好ましくは１〜３％の範囲である。
以下に本発明のエーテル化度2.4〜3.0のCMCが
アルカリ電池のゲル状陰極体のゲル化剤として、
ゲル化性能および耐アルカリ性の優れていること
を実施例により説明する。
実施例１〜３，比較例１〜３
46％KOH水溶液に対しエーテル化度の異なる
CMCをCMC濃度１％および２％添加溶解し、各
CMC濃度におけるゲル化性能を比較した。ゲル
化性能は300mlの円筒型ガラス容器にゲル状液を
200ml仕込み、ゲルの流動性で評価した。また、
各CMCの２％添加で生成したゲル状液を300mlの
円筒型ガラス容器に200mlとり、密閉後23℃に１
ケ月放置し、ゲルの流動性の経時変化を調べた。
第１表にみられるように、実施例１〜３のエー
テル化度2.4〜3.0のCMCは、CMC濃度１〜２％
の低濃度でもアルカリ電池のゲル状陰極体に適し
たゲルが得られ、しかも１ケ月経過後もそのゲル
化性能に変化がなかつた。
これに対し、比較例１〜３のエーテル化度2.3
以下のCMCの場合は、１％濃度ではほとんどゲ
ル化せず、２％濃度では一部ゲル化するが、本発
明のエーテル化度2.4〜3.0のCMCに較べて、その
ゲル化性能は著しく劣つたものであつた。また、
２％濃度のゲルの１ケ月経過後はゲルとKOH水
溶液に分離する離水現象が生じ不安定なものであ
つた。
実施例４〜６，比較例４〜６
エーテル化度の異なるCMCを27％KOH水溶液
に１％添加し、溶解した溶液の粘度を、BL型粘
度計（60rpm、25℃）により測定し、純水に
CMCを１％溶解した水溶液の粘度と比較した。
これらのCMCの27％KOH水溶液を300mlの円筒
型ガラス容器に200mlづつとり、密閉して23℃で
放置して14日後および30日後に粘度を測定し、粘
度の経時変化からCMCの耐アルカリ性を比較し
た。結果を第２表に示す。
The present invention includes mercury oxide, silver oxide, manganese dioxide,
In alkaline batteries that use oxygen or air as the anode, zinc as the cathode, and caustic potash solution as the electrolyte, it has excellent gelling performance as a gelling agent for the gelled cathode, and has a high degree of etherification with excellent alkali resistance.
This relates to carboxymethyl cellulose alkali salt (hereinafter abbreviated as CMC) of 2.4 to 3.0. Conventionally, as a method for holding a cathode body of an alkaline battery, a method of gelling an electrolyte in a cathode portion and mixing powdered zinc as a cathode active substance therein to hold the cathode body is well known. In order to efficiently discharge zinc, it is made into a powder to increase its surface area, and then uniformly dispersed within the cathode.The electrolyte, which is made of an aqueous potassium hydroxide solution containing a gelling agent, is gelled to form a cathode body. It is something. It is also well known that CMC is used as a gelling agent. However, commonly used CMC has a relatively low degree of etherification of 0.50 to 1.70, and batteries using this CMC have various drawbacks. The desirable conditions for the gel to be used as a battery cathode are, first, that it be hard enough to hold powdered zinc, and second, that it be hard enough to hold the CMC so as not to reduce the conductivity of the electrolyte.
The concentration should be as low as possible, and changes over time due to discharge and stock should be small, and the adhesive should be low and easy to handle. On the other hand, as the electrolyte for alkaline batteries, a caustic potassium aqueous solution is usually used in view of its ionic conductivity, and the caustic potassium aqueous solution has a caustic potassium concentration of about 25 to 50% (hereinafter referred to as weight percent). CMC with a conventional degree of etherification of 0.50 to 1.70 and an average degree of polymerization of approximately 350
When gelling an electrolyte using CMC, a gel with enough hardness to hold zinc powder cannot be obtained unless the CMC concentration is approximately 3 to 8%. Also, this
At CMC concentrations, the gel is quite sticky and is not only not easy to handle, but also leads to a decrease in the conductivity of the caustic potash electrolyte due to the addition of CMC. In order to overcome these drawbacks, high molecular weight
Although there is a method using CMC, this method has drawbacks such as a significant drop in the molecular weight of CMC during discharge and storage of an alkaline battery, which causes the gel to break easily and cause leakage. The average degree of polymerization is about 350 with the conventional degree of etherification of 0.50 to 1.70.
Even when CMC is used, it is inevitable that the molecular weight of CMC in the stock will decrease, and this was considered to be the biggest drawback of CMC. The present inventors conducted intensive studies to develop CMC with excellent gelling performance and alkali resistance as a gelling agent for gelled cathodes of alkaline batteries, and found that the degree of etherification is 2.4 to 3.0, preferably 2.7. More than
It was discovered that CMC has extremely excellent gelling performance and alkali resistance, leading to the completion of the present invention. That is, the present invention relates to a gelling agent for alkaline batteries characterized by using a carboxymethyl cellulose alkali salt having a degree of etherification of 2.4 to 3.0. The CMC of the present invention having a degree of etherification of 2.4 to 3.0 can be obtained by a known method (Canadian Journal of Research 28, Sec.
B, P731-736〈1950〉) can also be obtained, but
It can be easily produced industrially by the method disclosed in Japanese Patent Application No. 57-60576 invented by the present inventors. That is, by adopting a multistage sodium hydroxide addition reaction method in which sodium hydroxide necessary for etherification is added in portions and the etherification reaction is carried out in the presence of a small amount of alkali, it is easy to obtain a substitution degree of 2.4 to 3.0.
You can get CMC. The average degree of polymerization of the CMC having a degree of etherification of 2.4 or more used in the present invention is suitably in the range of 150 to 800. CMC with a low degree of polymerization (average degree of polymerization of 150 or less) requires a high concentration of CMC to obtain a gel hard enough to hold zinc powder, which has the disadvantage of lowering the conductivity of the electrolyte. be. On the other hand, CMC with a high degree of polymerization having an average degree of polymerization of 800 or more is undesirable because it causes a significant decrease in the degree of polymerization during discharge or storage of an alkaline battery, causing the gel to break and leakage. The CMC of the present invention having a degree of etherification of 2.4 or more may be a sodium salt, a lithium salt, a potassium salt, an ammonium salt, or any other alkali salt. Further, the electrolyte used is usually a caustic potassium aqueous solution with a concentration of 25 to 50%, but other alkaline aqueous solutions may be used. The amount of the gelling agent of the present invention added to the electrolyte is as follows:
The minimum amount is desirable to obtain a gel hard enough to hold zinc powder, and although it varies depending on the type and concentration of the electrolyte, it is usually 0.5 to 5% of the electrolyte.
Preferably it is in the range of 1 to 3%. Below, the CMC of the present invention with a degree of etherification of 2.4 to 3.0 is used as a gelling agent for a gelled cathode body of an alkaline battery.
The excellent gelling performance and alkali resistance will be explained by examples. Examples 1 to 3, Comparative Examples 1 to 3 Different degrees of etherification for 46% KOH aqueous solution
CMC was dissolved by adding CMC concentration of 1% and 2%, and each
The gelation performance at different CMC concentrations was compared. The gelling performance is measured by pouring a gelatinous liquid into a 300ml cylindrical glass container.
200ml was charged and the fluidity of the gel was evaluated. Also,
Pour 200 ml of the gel-like liquid produced by adding 2% of each CMC into a 300 ml cylindrical glass container, and after sealing, store at 23℃ for 1 hour.
The gel was left to stand for several months, and changes in the fluidity of the gel over time were examined. As seen in Table 1, the CMC of Examples 1 to 3 with a degree of etherification of 2.4 to 3.0 has a CMC concentration of 1 to 2%.
A gel suitable for a gel cathode body of an alkaline battery was obtained even at a low concentration of , and there was no change in its gelling performance even after one month had passed. In contrast, the degree of etherification in Comparative Examples 1 to 3 was 2.3.
In the case of the following CMC, it hardly gels at a concentration of 1%, and partially gels at a concentration of 2%, but its gelling performance is significantly inferior to that of the CMC of the present invention with a degree of etherification of 2.4 to 3.0. It was wet. Also,
After one month of using the 2% gel, a syneresis phenomenon occurred in which the gel and the KOH aqueous solution separated, and the gel was unstable. Examples 4 to 6, Comparative Examples 4 to 6 1% of CMC with different degrees of etherification was added to a 27% KOH aqueous solution, and the viscosity of the dissolved solution was measured using a BL viscometer (60 rpm, 25°C). in water
The viscosity was compared with that of an aqueous solution containing 1% CMC.
Put 200 ml of each of these 27% KOH aqueous solutions of CMC into 300 ml cylindrical glass containers, seal them and leave them at 23°C. The viscosity was measured after 14 and 30 days, and the alkali resistance of CMC was determined from the change in viscosity over time. compared. The results are shown in Table 2.
【表】【table】
【表】
エーテル化度2.3以下のCMCでは、純水溶液粘
度に比し27％KOH水溶液粘度が著しく低く、か
つ経時粘度低下も顕著であるのに対し、エーテル
化度2.4〜3.0のCMC、特にエーテル化度2.7以上
のCMCでは27％KOH水溶液中でも比較的高い粘
度を示し、経時粘度低下はほとんどないか、あつ
ても比較的少なかつた。
以上のようにエーテル化度2.4〜3.0、好ましく
は2.7以上のCMCは低濃度でゲル化能を有するた
め、電解液の電導度の低下が少なく、かつ粘着性
がないため取扱いが容易であり、さらに耐アルカ
リ性が優れていることから、放電またはストツク
時の漏液のおそれがないため、アルカリ電池のゲ
ル状陰極体のゲル化剤として優れた適性を有して
いる。[Table] For CMC with an etherification degree of 2.3 or less, the viscosity of a 27% KOH aqueous solution is significantly lower than that of a pure aqueous solution, and the viscosity decreases significantly over time. CMC with a chemical degree of 2.7 or higher showed a relatively high viscosity even in a 27% KOH aqueous solution, and the viscosity decreased little or not over time. As mentioned above, CMC with an etherification degree of 2.4 to 3.0, preferably 2.7 or higher, has gelation ability at low concentrations, so there is little decrease in the conductivity of the electrolyte, and it is easy to handle because it is not sticky. Furthermore, since it has excellent alkali resistance, there is no risk of liquid leakage during discharge or storage, making it excellently suited as a gelling agent for gelled cathodes of alkaline batteries.