【発明の詳細な説明】[Detailed description of the invention]
本発明は金属酸化物からなり、湿度の変化を電
気抵抗の変化として検出する感湿素子に関する。
従来この種の感湿素子としては金属酸化物の微
粉末を無機質絶縁基板の表面に塗着して感湿膜を
形成したものや金属酸化物の焼結体に電極を付与
したものがあり、いずれも湿度の変化に応じてそ
の電気抵抗が変化することを利用したものであ
る。しかしながら上記感湿素子は初期に於ては優
れた感度を有するものもあるがいずれも長期間の
使用において抵抗値の経時変化が大きいという欠
点があつた。この欠点を克服するために、金属酸
化物の焼結体よりなる感湿素子にヒーターを設
け、使用前に１時的に感湿素子を加熱し、高温状
態として感湿素子表面を再生した後、湿度を検出
するものも知られている。
つまり、金属酸化物の焼結体の熱安定性を利用
し、湿度を検出する直前に高温にすることによ
り、感湿素子を初期の状態に戻し再現性を確保し
ている。しかしながらこの感湿素子では湿度検出
の直前に加熱を行う必要があるために連続的な湿
度検出は不可能である。またヒータ、ヒータ制御
回路という複雑な機構が必要という欠点を有して
いる。
また連続的な湿度検出を可能とするため種々の
感湿素子材料が研究されており、例えば経時特性
を改良したものとしてZnO―LiZnVO4から成る感
湿素子（特願昭49―97020（特開昭51−25183
号））が挙げられる。この感湿素子はヒーター等
の再生処理を施すことなく、高湿度中において優
れた経時変化を有するものの常温常湿（25℃，50
〜60％R.H.）条件下で長期間使用した場合、必
ずしも充分な経時特性、再現性を得られない場合
があつた。
本発明は以上の欠点を除去し、通常の環境条件
（０℃〜40℃，30％R.H.〜90％R.H.）で長期間使
用しても感湿素子の抵抗変化は殆んど無く、さら
に再現性・信頼性にすぐれた感湿素子を提供する
ことを目的とするものである。
すなわち本発明は、酸化亜鉛（98.5〜78モル
％）と酸化亜鉛・炭酸リチウム・酸化バナジウム
からなるLiZnVO4（スピネル化合物）（0.5〜10モ
ル％）と酸化マグネシウム・酸化バリウムから選
ばれた少くとも１種の酸化物（1.0〜12モル％）
とを含有する焼結体からなる感湿素子である。
なお本発明に於いて組成範囲を限定した理由は
LiZnVO4からなるスピネル化合物が1.0モル％未
満になると湿度に対する感度（湿度変化に対する
抵抗値の変化巾）が小さくなり実用上不適当とな
る。一方10モル％をこえると常温常湿での抵抗の
変化（経時変化）が大きくなり再現性、信頼性に
乏しくなる。また酸化マグネシウム、酸化バリウ
ムが1.0モル未満では、感度は小さく、12モル％
をこえると感湿素子の抵抗値が大きくなり抵抗値
変化の検出が実用上不適当となるためである。ま
たZnOは98.5〜78モル％の範囲外では充分な感湿
特性が得られないためこの範囲とした。
以上本発明を実施例をあげて詳細に説明する。
次に本発明について具体例を挙げて説明する。先
ずLi2Co3，ZnOおよびV2O5をモル比で１：２：
１の組成比に正確に秤取し、ボールミルによつて
よく混合した。しかる後にこの混合物を700℃１
時間予備焼成してからボールミルによつて粉砕し
てLiZnVO4の粉末を得た。
かくして得たLiZnVO4の粉末をMgO，BaOの
粉末を所定量秤取した後混合し、原料を調整・用
意した。
次いで上記原料粉末にポリビニルアルコール
（粘結剤）を加え1.0トン／cm2の圧力でプレス成形
してから加熱焼結した。この時焼成温度が1100℃
未満では感湿素子の強度は弱く、また1300℃を越
えると感湿特性が低下するため1100〜1300℃の範
囲とする事が好ましい。
感湿素形の形状は第１図乃至第２図に示すよう
に厚さ１mm径10mmの円板形１とし、この円板形の
両主面に金ペーストを格子状に焼付け１対の電極
２，２′を設ける一方リード線３を熱圧着して接
続し、感湿素子をそれぞれ作成した。次に上記の
如く製造した実施例および比較例としての38種の
感湿素子についてそれぞれ求めた25℃，30％R.
H.の抵抗値R1，25℃90％R.H.の抵抗値R2および
感度R1／R2を次表に示す。
The present invention relates to a humidity sensing element made of metal oxide and detecting changes in humidity as changes in electrical resistance. Conventional moisture-sensitive elements of this type include those in which a moisture-sensitive film is formed by applying fine metal oxide powder to the surface of an inorganic insulating substrate, and those in which electrodes are attached to a sintered body of metal oxide. All of these utilize the fact that their electrical resistance changes in response to changes in humidity. However, although some of the above-mentioned moisture-sensitive elements have excellent sensitivity in the initial stage, all of them have the drawback that the resistance value changes significantly over time during long-term use. In order to overcome this drawback, a heater is installed in the humidity sensing element made of a sintered body of metal oxide, and the humidity sensing element is temporarily heated before use, and the surface of the humidity sensing element is regenerated into a high temperature state. , devices that detect humidity are also known. In other words, by utilizing the thermal stability of the sintered body of metal oxide and raising the temperature to a high temperature immediately before detecting humidity, the humidity sensing element is returned to its initial state and reproducibility is ensured. However, since this humidity sensing element needs to be heated immediately before detecting humidity, continuous humidity detection is not possible. It also has the disadvantage of requiring a complicated mechanism such as a heater and a heater control circuit. In addition, various moisture - sensing element materials are being researched to enable continuous humidity detection. Showa 51-25183
)). This moisture-sensing element does not require any regeneration treatment such as a heater, and has excellent aging performance in high humidity.
When used for a long period of time under conditions (~60% RH), there were cases in which sufficient aging characteristics and reproducibility were not always obtained. The present invention eliminates the above drawbacks, and even when used for long periods under normal environmental conditions (0°C to 40°C, 30% RH to 90% RH), there is almost no change in resistance of the moisture sensing element, and it is even more reproducible. The purpose of this invention is to provide a moisture-sensitive element with excellent performance and reliability. That is, the present invention provides at least one material selected from zinc oxide (98.5 to 78 mol%), LiZnVO 4 (spinel compound) (0.5 to 10 mol%) consisting of zinc oxide, lithium carbonate, and vanadium oxide, and magnesium oxide and barium oxide. One type of oxide (1.0-12 mol%)
This is a moisture-sensitive element made of a sintered body containing. The reason for limiting the composition range in the present invention is
If the spinel compound consisting of LiZnVO 4 is less than 1.0 mol %, the sensitivity to humidity (the range of change in resistance value with respect to changes in humidity) will be small, making it unsuitable for practical use. On the other hand, if it exceeds 10 mol%, the change in resistance at room temperature and humidity (change over time) becomes large, resulting in poor reproducibility and reliability. In addition, when magnesium oxide and barium oxide are less than 1.0 mol, the sensitivity is small and is 12 mol%.
This is because if the resistance value exceeds this value, the resistance value of the humidity sensing element increases, making it practically inappropriate to detect a change in resistance value. Furthermore, ZnO was set in this range because sufficient moisture sensitivity characteristics cannot be obtained outside the range of 98.5 to 78 mol %. The present invention will be described in detail with reference to examples.
Next, the present invention will be explained by giving specific examples. First, Li 2 Co 3 , ZnO and V 2 O 5 were mixed in a molar ratio of 1:2:
The mixture was weighed accurately to a composition ratio of 1, and thoroughly mixed using a ball mill. After that, heat this mixture to 700℃1
After pre-calcining for an hour, it was ground by a ball mill to obtain LiZnVO 4 powder. The thus obtained LiZnVO 4 powder was mixed with predetermined amounts of MgO and BaO powders to adjust and prepare raw materials. Next, polyvinyl alcohol (binder) was added to the raw material powder, which was press-molded at a pressure of 1.0 tons/cm 2 and then heated and sintered. At this time, the firing temperature is 1100℃
If it is less than 1,300°C, the strength of the moisture-sensitive element will be weak, and if it exceeds 1,300°C, the moisture-sensing properties will deteriorate, so it is preferably in the range of 1,100 to 1,300°C. As shown in Figures 1 and 2, the shape of the moisture-sensitive element is a disc 1 with a thickness of 1 mm and a diameter of 10 mm, and a pair of electrodes are attached to both main surfaces of the disc by baking gold paste in a lattice pattern. 2 and 2' were provided, and the lead wires 3 were connected by thermocompression bonding, thereby producing moisture-sensitive elements. Next, 25°C and 30% R were determined for each of the 38 types of humidity-sensitive elements manufactured as examples and comparative examples as described above.
The following table shows the resistance value R 1 of H., the resistance value R 2 at 25°C and 90%RH, and the sensitivity R 1 /R 2 .
【表】【table】
【表】
この結果本発明に係る感湿素子は実用上充分な
感度および抵抗値を有する事が確認された。
次に本発明に係わる感湿素子の経時変化を調べ
た。
まず高湿中における経時特性として、試料No.
９，24，33（実施例）及び試料No.38（比較例）を
それぞれ25℃90〜95％R.H.条件下に1000時間放
置した際の抵抗変化率（％）は第３図に示す如く
であつた。なお第３図中曲線（Ａ）は試料No.９の
実施例の場合を曲線(b)は試料No.38の場合をそれぞ
れ示す。また試料No.24，33は上記曲線（Ａ）と同
様の結果を示した。さらに常温常湿中における経
時特性として25℃，50％R.H.条件下に1000時間
放置した際の抵抗変化率（％）を第４図乃至第８
図に示す。
第４図及び第８図は比較例の場合であり、第４
図は試料No.38を、第８図は試料No.16または37の場
合をそれぞれ示す。
一方第５図乃至第７図は本発明に係る実施例の
経時変化を示し、第５図中曲線A′は試料No.４，
８，または12を、第５図中曲線A2は試料No.5.9，
10，または13、第６図中曲線A3は試料No.19，
23，または28を、第６図中曲線A4は試料No.20，
24，25または29を、第７図中曲線A5は試料No.31
または32を、第７図中曲線A6は試料No.33または
36をそれぞれ示す。
上記の結果から明らかな如く、本発明に係わる
実施例においては、1000時間で高に２％以下の抵
抗値変化しか示さず、安定性に優れたものである
ことが確認された。なお表示中において試料No.
16，37は高い温度を有しているが経時特性が悪
く、また試料No.２，26は抵抗値が高すぎて実用困
難なものを示す。
さらに実施例としての試料No.９及び比較例とし
ての試料No.45について25℃で30％R.H，〜90％R.
H.の湿度サイクルを1000回繰り返した結果、実
施例においては高々２〜５％程度の抵抗変化しか
なく、比較例においては５〜８％程度であつた。
この結果本発明に係る感湿素子は実用範囲の抵
抗値域において高感度を有し、かつ高湿度及び常
湿範囲での経時特性に優れ、さらに湿度サイクル
に対しても安定した特性を有する事が確認され
た。この様に安定した感湿特性を有するために連
続的に正確な湿度検出が可能となり、実用上利用
価値の大きなものといえる。[Table] As a result, it was confirmed that the moisture sensitive element according to the present invention has practically sufficient sensitivity and resistance value. Next, the change over time of the humidity sensing element according to the present invention was investigated. First, as for the aging characteristics in high humidity, sample No.
The resistance change rate (%) of Sample No. 9, 24, 33 (Example) and Sample No. 38 (Comparative Example) when they were left for 1000 hours at 25°C and 90% to 95%RH is as shown in Figure 3. It was hot. In FIG. 3, curve (A) shows the case of Example No. 9, and curve (b) shows the case of Sample No. 38. Moreover, samples No. 24 and 33 showed the same results as the above curve (A). Furthermore, as the aging characteristics at room temperature and humidity, the resistance change rate (%) when left for 1000 hours at 25℃ and 50%RH is shown in Figures 4 to 8.
As shown in the figure. Figures 4 and 8 are comparative examples;
The figure shows sample No. 38, and FIG. 8 shows the case of sample No. 16 or 37, respectively. On the other hand, FIGS. 5 to 7 show the changes over time of Examples according to the present invention, and in FIG. 5, curve A' indicates sample No. 4,
8, or 12, curve A2 in Figure 5 is sample No. 5.9,
10, or 13, curve A3 in Figure 6 is sample No. 19,
23 or 28, curve A4 in Figure 6 is sample No. 20,
24, 25 or 29, curve A 5 in Figure 7 is sample No. 31.
or 32, curve A 6 in Figure 7 is sample No. 33 or
36 are shown respectively. As is clear from the above results, the examples according to the present invention exhibited only a 2% or less change in resistance value over 1000 hours, and were confirmed to have excellent stability. In addition, sample No. is displayed.
Samples Nos. 16 and 37 have high temperatures but have poor aging characteristics, and samples Nos. 2 and 26 have too high resistance values to be practical. Furthermore, sample No. 9 as an example and sample No. 45 as a comparative example were heated to 30% RH and ~90% R at 25°C.
As a result of repeating the humidity cycle of H. 1000 times, there was only a resistance change of about 2 to 5% at most in the Examples, and about 5 to 8% in the Comparative Examples. As a result, the humidity sensing element according to the present invention has high sensitivity in the practical resistance value range, excellent aging characteristics in high humidity and normal humidity ranges, and stable characteristics against humidity cycles. confirmed. Having such stable moisture sensitivity characteristics enables continuous and accurate humidity detection, and can be said to be of great practical value.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図及び第２図は本発明に係る感湿素子の構
造例を示す斜視図及び断面図、第３図、第５図、
第６図および第７図は本発明に係る感湿素子の特
性例を示す曲線図、第４図および第８図は比較例
の特性例を示す曲線図。
1 and 2 are perspective views and cross-sectional views showing structural examples of the moisture sensing element according to the present invention, FIGS. 3 and 5,
FIGS. 6 and 7 are curve diagrams showing characteristic examples of the moisture sensitive element according to the present invention, and FIGS. 4 and 8 are curve diagrams showing characteristic examples of comparative examples.