【発明の詳細な説明】[Detailed description of the invention]
本発明は感湿素子、更に詳しくは広範囲の湿度
領域で使いやすい電気的抵抗値を有し、かつ長時
間に亘つて安定使用可能な湿度センサに関する。
大気中の湿度を測定・検出する湿度センサは、こ
れまでに極めて多数の方式が提案され、かつ実用
化されている。特に近年は電気的に直接湿度を検
出できる方式の湿度センサが提案されてきてい
る。前記の如く湿度を直接電気的に検出する方式
の湿度センサは、検出のみならず湿度の制御をも
簡便に電気的信号で処理できるという特長があ
り、かつ安価なものも提案・実用化されてきてお
り注目を浴びている。ところでこの方式の湿度セ
ンサのうち一部実用化、市販されているもののう
ち安価なものは、大気中の湿度を測定するため
に、大気中の水分を感湿体の表面に物理吸着させ
電気的抵抗値を読み取るものが一般的であり、か
くの如き湿度センサは感湿体が高分子、或いは金
属酸化物の焼結体、さらには基板上に金属酸化物
を焼付けたものが用いられている。ところで前記
２者の湿度センサは高湿度領域では比較的使いや
すい抵抗を有しており、或る程度精度良くしかも
簡便に湿度を検知し、さらには制御が可能となつ
ているが低湿度領域（20〜30％Ｒ，Ｈ，以下）で
はその抵抗値が1MΩないしは10MΩ以上と極め
て大きくなり、通常の電気的検出装置では容易に
湿度を検知できないし精度も極めて悪くなる。一
方後者のタイプの湿度センサは低湿度領域では湿
度に対する抵抗値変化が殆んどなく、やはり同様
に低湿度を精度良く検出できるとはいい難い。こ
のように安価でかつ低湿度を比較的精度良く検出
でき、かつ長期に亘つて安定な湿度センサはまだ
得られていない。
ところで低湿度領域を簡便にかつ精度の良い検
出制御を必要とする分野は産業用・民生用と極め
て多岐にわたつており、これらの用途に適する湿
度センサの開発が強く望まれている。前記要望を
満たすべく鋭意研究も行なつた結果、本発明者ら
は広範囲の湿度領域で使いやすい電気的抵抗値を
有し、かつ長時間に亘つても比較的安定して使用
可能な湿度センサを見出した。
すなわち、LiMeVO4が15〜１モル％（Me＝
Cu，Fe，Mnから選ばれた少くとも１種）ZnOが
30〜80モル％、およびCr3O3か55〜19モル％を必
須成分とした焼結体から成る感湿素子である。
本発明による感湿素子は周囲温度25℃で相対湿
度10％で電気的抵抗値は約500KΩと従来の湿度
センサよりも２桁以上低くなり、極めて使いやす
い値となつている。また相対湿度90％では約
3KΩという値になり、広範囲の湿度領域にわた
つて使いやすい抵抗値を有している。ところで本
発明による感湿素子は組成比にも依存するが、焼
結温度によつて感湿特性が変化することが確認で
き、比較的使いやすい抵抗値を有する感湿素子
は、本発明の場合焼結体のポロシテイが15〜30％
の範囲にあることがわかつた。
以下実施例１について詳しく説明する。
まず出発原料としては炭酸リチウム，酸化銅，
酸化バナジウム，酸化亜鉛，酸化クロムの微粉末
を用いた。この原料粉末をLiCuVO4，酸化亜鉛，
酸化クロムとしてモル比で各々10％，45％，45％
になるように秤量を行い、しかるのちにポツトミ
ルで24時間湿式混合した。この後混合物を120℃
で12時間乾燥した後900℃で仮焼を行なつた。こ
の後さらにポツトミルで湿式で24時間粉砕を行な
つた後120℃で12時間再たび乾燥を行なつて原料
粉末を調整した。
次いでかくして得られた調整粉末に粘結剤とし
てポリビニルアルコールを２重量％加えライカイ
機で造粒を行い、この後に加圧成形を行なつた。
加圧成形は500Kg／cm2の圧力で行い成形体として
直径５mm厚み約４mmの円盤状のものを得た。かく
して得られた成形体を温度1300℃で２時間焼結を
行い、得られた焼結体の両主面を2000番のホワイ
トアランダムで研磨し直径５mm厚み３mmの焼結体
とした。次いでこの焼結体の両主面に酸化ルテニ
ウムペーストをスクリーンで印刷付与し、その後
700℃の温度で焼付け電極を形成し、第１図の如
く感湿素子を得た。
かくして得られた本発明による感湿素子の湿度
特性を第２図に示す。この感湿素子は周囲温度25
℃で相対湿度10％で450KΩ、相対湿度90％で
3KΩと広範囲の湿度領域で極めて使いやすい抵
抗値となつている。またこの時得られた焼結体の
ポロシテイを水銀圧入法で測定したところポロン
テイは18％であることがわかつた。
本発明による感湿素子の安定性を調べるため
に、高湿度（40℃90％Ｒ，Ｈ，）及び低湿度（10
℃10％Ｒ，Ｈ，）の各条件に感湿素子を放置した
際の結果をそれぞれ第３図及び第４図に示すが放
置後しばらくはわずかに抵抗値が変化するもの
の、400時間以降は安定した抵抗値を示し、長期
に亘つても感湿素子は充分安定しており、精度良
く湿度を検出可能であることが確認された。その
他の実施例及び比較例については実施例１を含め
て組成，及びその場合の感湿特性（感湿特性とし
ては25℃10％Ｒ，Ｈ，及び90％Ｒ，Ｈ，の抵抗値
で示す）を表に示す。
The present invention relates to a humidity sensor, and more particularly to a humidity sensor that has an electrical resistance value that is easy to use in a wide range of humidity and can be stably used for a long time.
A large number of humidity sensors that measure and detect atmospheric humidity have been proposed and put into practical use. Particularly in recent years, humidity sensors that can directly detect humidity electrically have been proposed. As mentioned above, humidity sensors that directly detect humidity electrically have the advantage of not only detecting humidity but also easily processing humidity control using electrical signals, and inexpensive ones that have been proposed and put into practical use. It is attracting attention. By the way, some of the humidity sensors using this method have been put into practical use and are commercially available, but inexpensive ones measure atmospheric humidity by physically adsorbing moisture in the atmosphere onto the surface of a humidity sensing element and then electrically absorbing it. Humidity sensors such as those that read resistance are common, and the moisture sensing element used is a polymer, a sintered body of metal oxide, or even a metal oxide baked onto a substrate. . By the way, the above two types of humidity sensors have resistances that are relatively easy to use in high humidity areas, and can detect and control humidity with a certain degree of accuracy and ease, but in low humidity areas ( (20 to 30% R, H, or less), the resistance value becomes extremely large, such as 1 MΩ or 10 MΩ or more, and a normal electrical detection device cannot easily detect humidity and the accuracy becomes extremely poor. On the other hand, the latter type of humidity sensor has almost no change in resistance value with respect to humidity in a low humidity region, and similarly cannot be said to be able to accurately detect low humidity. In this way, a humidity sensor that is inexpensive, can detect low humidity with relatively high accuracy, and is stable over a long period of time has not yet been obtained. By the way, the fields that require simple and accurate detection control in low humidity regions are extremely diverse, including industrial and consumer applications, and there is a strong desire to develop humidity sensors suitable for these applications. As a result of intensive research to meet the above needs, the inventors of the present invention have developed a humidity sensor that has an electrical resistance value that is easy to use in a wide range of humidity ranges, and that can be used relatively stably even over long periods of time. I found out. That is, LiMeVO4 is 15-1 mol% (Me=
At least one type selected from Cu, Fe, Mn) ZnO
This is a moisture-sensitive element made of a sintered body whose essential components are 30 to 80 mol% and 55 to 19 mol% of Cr3O3 . The humidity sensing element according to the present invention has an electrical resistance value of approximately 500 KΩ at an ambient temperature of 25° C. and a relative humidity of 10%, which is more than two orders of magnitude lower than that of conventional humidity sensors, making it extremely easy to use. Also, at a relative humidity of 90%, approximately
It has a resistance value of 3KΩ, making it easy to use over a wide range of humidity. By the way, although it depends on the composition ratio, it has been confirmed that the humidity sensing characteristics of the humidity sensing element according to the present invention change depending on the sintering temperature, and the humidity sensing element according to the present invention has a resistance value that is relatively easy to use. Porosity of sintered body is 15-30%
It was found that it was within the range of Example 1 will be described in detail below. First, the starting materials are lithium carbonate, copper oxide,
Fine powders of vanadium oxide, zinc oxide, and chromium oxide were used. This raw material powder is mixed with LiCuVO 4 , zinc oxide,
10%, 45%, 45% respectively in molar ratio as chromium oxide
The mixture was weighed and then wet mixed in a pot mill for 24 hours. After this the mixture was heated to 120°C.
After drying for 12 hours, calcination was performed at 900°C. Thereafter, the powder was further wet-pulverized in a pot mill for 24 hours, and then dried again at 120°C for 12 hours to prepare a raw material powder. Next, 2% by weight of polyvinyl alcohol was added as a binder to the prepared powder thus obtained, and granulation was performed using a Raikai machine, followed by pressure molding.
Pressure molding was performed at a pressure of 500 kg/cm 2 to obtain a disc-shaped molded product with a diameter of 5 mm and a thickness of about 4 mm. The thus obtained compact was sintered at a temperature of 1300° C. for 2 hours, and both main surfaces of the obtained sintered compact were polished with No. 2000 white arundum to obtain a sintered compact with a diameter of 5 mm and a thickness of 3 mm. Next, ruthenium oxide paste was applied by screen printing to both main surfaces of this sintered body, and then
Baked electrodes were formed at a temperature of 700°C to obtain a humidity sensing element as shown in FIG. The humidity characteristics of the humidity-sensitive element according to the present invention thus obtained are shown in FIG. This moisture sensing element is suitable for ambient temperature 25
450KΩ at 10% relative humidity and 90% relative humidity at °C
It has a resistance value of 3KΩ, which is extremely easy to use in a wide range of humidity. Furthermore, when the porosity of the sintered body obtained at this time was measured by mercury intrusion method, it was found that the porosity was 18%. In order to investigate the stability of the humidity sensing element according to the present invention, high humidity (40°C, 90% R,H,) and low humidity (10
Figures 3 and 4 show the results when the humidity sensing element was left under various conditions (℃10%R, H, ), respectively.The resistance value changed slightly for a while after being left, but after 400 hours it changed. It was confirmed that the humidity sensing element exhibited a stable resistance value, was sufficiently stable even over a long period of time, and was capable of detecting humidity with high accuracy. For other Examples and Comparative Examples, including Example 1, the composition and the moisture sensitivity characteristics (humidity sensitivity characteristics are shown as resistance values at 25°C, 10% R, H, and 90% R, H) ) are shown in the table.
【表】【table】
【表】
表からわかる如く、いずれも広範囲な湿度で使
いやすい抵抗値を有していることが確認できた。
さらに実施例１と同じ条件で長期安定性を調べた
ところ、実施例１と殆んど同じような変化を示
し、長期に亘つて安定であることが確認できた。
ところで実施例１の組成について各種の湿度で
焼結を行なつたところ、焼結体のポロシテイは焼
結湿度と共に単調な変化をせずに第５図に示す如
く変化した。またこの時の25℃50％Ｒ，Ｈ，の抵
抗値を併せて示しておく。他の実施例についても
同様な操作を行なつたところ、広範囲の湿度領域
で良好な抵抗値を得るには、焼結体のポロシテイ
が15〜30％の間にあるのが好ましいことがわかつ
た。
以上本発明による感湿素子は広範囲の湿度領域
で抵抗値は極めて使いやすい値を有しており、か
つ長期に亘つても安定した湿度の検出が可能であ
ることが確認でき、その効果は極めて顕著なもの
といえる。[Table] As can be seen from the table, it was confirmed that all of them had resistance values that were easy to use over a wide range of humidity.
Furthermore, when long-term stability was examined under the same conditions as in Example 1, it was confirmed that changes were almost the same as in Example 1, and that it was stable over a long period of time. By the way, when the composition of Example 1 was sintered at various humidities, the porosity of the sintered body did not change monotonically with the sintering humidity, but changed as shown in FIG. The resistance values at 25°C, 50% R and H at this time are also shown. When similar operations were performed for other examples, it was found that in order to obtain good resistance values in a wide range of humidity, it is preferable that the porosity of the sintered body be between 15 and 30%. . As described above, it has been confirmed that the humidity sensing element according to the present invention has a resistance value that is extremely easy to use in a wide range of humidity ranges, and can stably detect humidity even over a long period of time, and its effectiveness is extremely high. This can be said to be remarkable.
【図面の簡単な説明】[Brief explanation of drawings]
第１図本発明に係る感湿素子の斜視図、第２図
本発明に係る感湿素子の感湿特性を示す曲線図、
第３図40℃90％Ｒ，Ｈ、に放置した場合の感湿特
性の安定性を示す曲線図、第４図10℃10％Ｒ，
Ｈ、に放置した場合の感湿特性の安定性を示す曲
線図、第５図焼結温度と25℃50％Ｒ，Ｈ、の抵抗
値およびポロシテイの量の関係を示す曲線図。
FIG. 1 is a perspective view of a moisture-sensitive element according to the present invention; FIG. 2 is a curve diagram showing the moisture-sensitive characteristics of the moisture-sensitive element according to the present invention;
Fig. 3 A curve diagram showing the stability of moisture sensitivity when left at 40°C, 90% R, H, Fig. 4: 10°C, 10% R,
FIG. 5 is a curve diagram showing the relationship between the sintering temperature and the resistance value and amount of porosity at 25° C. 50% R and H.