JP3979188B2

JP3979188B2 - Heating element

Info

Publication number: JP3979188B2
Application number: JP2002165811A
Authority: JP
Inventors: 誠之寺門; 和幸小原; 充米山; 隆仁石井; 圭子安井
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 2002-06-06
Filing date: 2002-06-06
Publication date: 2007-09-19
Anticipated expiration: 2022-06-06
Also published as: JP2004014286A

Description

【０００１】
【発明の属する技術分野】
本発明は、暖房、加熱、乾燥などの熱源として用いることのできる発熱体に関するものである。
【０００２】
【従来の技術】
従来、この種の発熱体としては、例えば、特開昭５３−１４３０４７号公報や図５に記載されるように、絶縁フィルム１７を介して熱伝導板１８を装着した熱伝導性基板に正抵抗温度特性による自己温度制御機能を有する発熱体材料１９及び電極２０を塗布、乾燥し、大きな突入電力で急速に昇温すると共に、所定の飽和温度を保ち、均一な温度分布の発熱体を形成するものである。
【０００３】
【発明が解決しようとする課題】
しかしながら、前記従来の正抵抗温度特性発熱体を用いて、例えば、暖房マットのような速熱性で人体接触型の暖房製品を形成する場合、人体が快適に感じる表面温度は４０℃近辺であり、表面材による温度低下を１０Ｋ程度見込んでも、発熱体の発熱温度としては、５０℃近辺で十分である。したがって、電源投入時は低抵抗で高電力を発生するが、５０℃近辺で抵抗値が急激に増大することによって電力が急激に低下し、自己温度制御性によって５０℃を保持できるような正抵抗温度特性を示す発熱体材料が必要となる。このために、発熱体材料としては、低融点の結晶性樹脂を用い、その中に分散された導電性材料が、結晶性樹脂の融点の直下での急激な比容積の増大によって導電性を失い、抵抗値が急激に増大する温度域が上記の５０℃近辺となるように調整する必要がある。通常の結晶性樹脂は融点以下でも比容積の増加は得られるが、融点に近い程その増加率が急激に増す性質があるため、融点から離れた温度域では十分な正抵抗温度特性は得られない。上記のような人体接触型の暖房用途の場合、結晶性樹脂の融点としては６０℃台が理想的で、このような樹脂を使用すれば、速熱性に優れるとともに、５０℃近辺での自己温度制御性に優れた発熱体材料が得られる。結晶性樹脂の融点がこれより高くなると、５０℃近辺の抵抗値と電源投入時の抵抗値の比率が小さくなり、５０℃近辺の抵抗値を固定した場合、電源投入時の抵抗値が大きくなり、速熱性が損なわれる。また、電源投入時の抵抗値を固定すると、自己制御温度が５０℃よりも高温になってしまう。結晶性樹脂の融点が８０℃を越えると、速熱性と５０℃近辺での自己温度制御性を両立させることは極めて困難になる。以上に示した状況から、上記のような用途では、結晶性樹脂の融点としてはできる限り低融点の方が望ましいと考えられる。
【０００４】
一方、具体的に低融点の結晶性樹脂を選定するとなると、結晶性の観点からは、低融点になるほど結晶性が低下し、十分な正抵抗温度特性が得られなく傾向にある。現状で発熱体材料として最も有用とされるオレフィン系樹脂の中で融点が６０℃台の材料を選定するとなると、酢酸ビニルの含有量の多いエチレン酢酸ビニル重合体を選定することになる。エチレン酢酸ビニル重合体は酢酸ビニルの含有量に比例して結晶性が低下する傾向があり、融点が６０℃台のエチレン酢酸ビニル重合体では十分な正抵抗温度特性が得られない場合が多い。したがって、結晶性の観点からは、融点が高いグレードの方が望ましいと考えられる。
【０００５】
また、このような暖房製品がさらされる環境条件を考慮すると、通電による自己発熱の場合は、正抵抗温度特性による自己温度制御性によって上限温度が規制されるので特に問題はないが、例えば、他の高温熱源を有する機器との併用、直射日光を浴びるような環境、倉庫での保管条件や輸送条件、車載用途などを考慮すると、製品としては少なくとも６０℃以上、用途によっては８０℃以上の温度に耐える性能が要求される。６０℃近辺に融点を持つ結晶性樹脂を主成分とする発熱体材料をこのような条件にさらせば、通常、発熱体の変形、抵抗特性の変化、寿命の低下など、好ましくない結果を生ずる。このために、従来の技術では、製品の表面材をさらに厚くしたり、発熱体の装着面積を減らしたりするなどして、熱伝導あるいは熱伝達を妨げることによって、表面温度は４０℃近辺であるが、発熱体温度を例えば６０℃近辺まで高め、より高融点の結晶性樹脂を使用できるようにする方法。速熱性あるいは自己温度制御性による温度の安定性を犠牲にして、より高融点の結晶性樹脂を使用できるようにする方法等が選択されている。熱伝導を妨げる構成であれば、表面温度の達成は可能であるが、熱伝導を妨げることによって、製品の表面温度の昇温速度が大きく低下する欠点があった。また、発熱体の装着面積を減らして平均表面温度を下げる構成では、飽和時の適切な表面温度は達成できるものの、発熱体と製品表面との間の熱抵抗を増大させることに変わりはなく、製品の昇温速度が大きく低下する欠点があった。
【０００６】
本発明は、前記従来の課題を解決するもので、正抵抗温度特性を応用することによって、急速に昇温すると共に、所定の表面温度で急速かつ安定に飽和する発熱体を提供することを目的とし、合わせて、結晶性が高く、高温環境に強い高融点の結晶性樹脂を使用できる技術手段を提供するもので、特に、低温域の表面温度を有する正抵抗温度特性発熱体を形成する場合に極めて有用である。
【０００７】
【課題を解決するための手段】
前記従来の課題を解決するために、本発明の発熱体は、基板上に形成した一対の電極から電圧が印加されて発熱する抵抗要素を前記基板上に形成してなる発熱体であって、
前記抵抗要素は第１の面状抵抗体と、前記第１の面状抵抗体より面積が小さい第２の面状抵抗体とに細分割されており、かつ、前記第１の面状抵抗体と前記第２の面状抵抗体は交互に配設され、隣接する少なくとも１組毎に直列に電気的に接続されて発熱体全面を形成したものであり、通電開始時点では前記第１の面状抵抗体及び前記第２の面状抵抗体の各抵抗要素が略同一電力密度で共に発熱して高電力の面状熱源となり、その後の温度上昇に伴って少なくとも前記第２の面状抵抗体の抵抗値が増大し、前記第１の面状抵抗体の各抵抗要素よりも前記第２の面状抵抗体の各抵抗要素が高抵抗化し、前記第２の面状抵抗体の各抵抗要素が主に発熱することにより、正抵抗温度特性による小面積の定温熱源であると同時に散在熱源となって低電力で飽和し、少なくとも、前記第２の面状抵抗体が、人体が直接接触した場合に、実用上、温度分布を感じないだけの形状にまで細かく分割されてなり、前記定温熱源の自己制御温度にかかわらず、体感的に快適と感じることのできる低い温度域で飽和するようにしたものである。
【０００８】
【発明の実施の形態】
請求項１に記載の発明は、基板上に形成した一対の電極から電圧が印加されて発熱する抵抗要素を前記基板上に形成してなる発熱体であって、前記抵抗要素は第１の面状抵抗体と、前記第１の面状抵抗体より面積が小さい第２の面状抵抗体とに細分割されており、かつ、前記第１の面状抵抗体と前記第２の面状抵抗体は交互に配設され、隣接する少なくとも１組毎に直列に電気的に接続されて発熱体全面を形成したものであり、通電開始時点では前記第１の面状抵抗体及び前記第２の面状抵抗体の各抵抗要素が略同一電力密度で共に発熱して高電力の面状熱源となり、その後の温度上昇に伴って少なくとも前記第２の面状抵抗体の抵抗値が増大し、前記第１の面状抵抗体の各抵抗要素よりも前記第２の面状抵抗体の各抵抗要素が高抵抗化し、前記第２の面状抵抗体の各抵抗要素が主に発熱することにより、正抵抗温度特性による小面積の定温熱源であると同時に散在熱源となって低電力で飽和し、少なくとも、前記第２の面状抵抗体が、人体が直接接触した場合に、実用上、温度分布を感じないだけの形状にまで細かく分割されてなり、前記定温熱源の自己制御温度にかかわらず、体感的に快適と感じることのできる低い温度域で飽和するようにしてなる発熱体である。
【０００９】
通電開始時点では、第１及び第２の面状抵抗体の各抵抗要素の抵抗値が共に低い状態にあり、双方の抵抗値が比較的近接している。このために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、その抵抗値配分によって電力に差があるものの全ての各抵抗要素は高電力で発熱する。全ての各抵抗要素が発熱することにより、高電力の面状発熱体が形成され、広域発熱による急速加熱を可能にする。温度が上昇するに伴い、第２の面状抵抗体の抵抗値が増大するために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、第２の面状抵抗体の各抵抗要素の抵抗値が明らかに高くなり、第２の面状抵抗体の各抵抗要素の電力の配分が高まる。
【００１０】
この時、直列回路の抵抗値が増大するために全体の電力は低下し、電力の配分が低下する第１の面状抵抗体の電力は大きく低下するが、第２の面状抵抗体の電力が大きく低下することはなく、第２の面状抵抗体の各抵抗要素部分の温度は上昇を続ける。この結果、第２の面状抵抗体の抵抗値がさらに増大するために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、第２の面状抵抗体の各抵抗要素の抵抗値が決定的に高くなり、第２の面状抵抗体の各抵抗要素が主体的に発熱するようになる。この状態は第２の面状抵抗体の正抵抗温度特性による自己温度制御発熱であり、第２の面状抵抗体は、温度の上昇によって、急激な抵抗値増大及び電力低下がもたらされるので、比較的少ない温度上昇で飽和温度に到達する。
【００１１】
このように、飽和温度においては、実質的に第２の面状抵抗体のみが発熱し、自己温度制御発熱による定温の熱源が散在する発熱体が形成される。この飽和状態においては、発熱部の温度が多少高くなっても発熱面積が限定されるために平均温度はむしろ低下し、電力をより低下させることができる。したがって、正抵抗温度特性による自己制御温度が高い抵抗体材料であっても低温の発熱体を形成することができる。また、第２の面状抵抗体の各抵抗要素は複数に分割され、散在しているために、発熱体全体としては温度の一様性がくずれることはなく、実用上、支障のない温度分布を形成することができる。
【００１２】
請求項２に記載の発明は、第１の面状抵抗体および第２の面状抵抗体は共に正抵抗温度特性を有し、温度上昇に伴って抵抗値が増大するが、少なくとも通電開始近傍の温度においては、第１の面状抵抗体の抵抗要素の電力密度と第２の面状抵抗体の抵抗要素の電力密度が略同一であり、一方、飽和温度に至るまでの温度域においては、前記第２の面状抵抗体の抵抗値の増大率が前記第１の面状抵抗体の抵抗値の増大率を上回り、前記第１の面状抵抗体の各抵抗要素よりも前記第２の面状抵抗体の各抵抗要素が高抵抗化するようにしたものである。
【００１３】
このために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、各抵抗要素は全て高電力で発熱する。温度が上昇するに伴い、第１の面状抵抗体及び第２の面状抵抗体の双方の抵抗値が増大するために電力は低下するが、双方の抵抗値が比較的近接していることに変わりはなく、双方の各抵抗要素が全て発熱する状態がこの時点でも継続している。温度がさらに上昇するに伴い、第２の面状抵抗体の抵抗値の増大率が第１の面状抵抗体の抵抗値の増大率を上回り、第１の面状抵抗体の各抵抗要素よりも第２の面状抵抗体の各抵抗要素が明らかに高抵抗化する。この時点で第２の面状抵抗体の各抵抗要素の電力の配分が高まり、その部分の温度は上昇を続ける。
【００１４】
その結果、第２の面状抵抗体の抵抗値がさらに増大するために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、第２の面状抵抗体の各抵抗要素の抵抗値が決定的に高くなり、第２の面状抵抗体の各抵抗要素が主体的に発熱するようになる。この状態は第２の面状抵抗体の正抵抗温度特性による自己温度制御発熱であり、第２の面状抵抗体は、温度の上昇によって、急激な抵抗値増大及び電力低下がもたらされるので、比較的少ない温度上昇で飽和温度に到達する。
【００１５】
このように、飽和温度においては、実質的に第２の面状抵抗体のみが発熱し、自己温度制御発熱による定温の熱源が散在する発熱体が形成される。この飽和状態においては、発熱部の温度が多少高くなっても発熱面積が限定されるために平均温度はむしろ低下し、電力をより低下させることができる。したがって、正抵抗温度特性による自己制御温度が高い抵抗体材料であっても低温の発熱体を形成することができる。また、第２の面状抵抗体の各抵抗要素は複数に分割され、散在しているために、発熱体全体としては温度の一様性がくずれることはなく、実用上、支障のない温度分布を形成することができる。
【００１６】
請求項３に記載の発明は、第１の面状抵抗体は飽和温度近傍までの温度域では実質的に有効な正抵抗温度特性を示さず、第２の面状抵抗体が実質的に有効な正抵抗温度特性を示すものである。通電開始時点では、第１及び第２の面状抵抗体の各抵抗要素の抵抗値が共に低い状態にあり、双方の抵抗値が比較的近接している。このために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、各抵抗要素は全て高電力で発熱する。温度が上昇するに伴い、第１の面状抵抗体の抵抗値は大きく変化しないが、第２の面状抵抗体の抵抗値のみが増大するために第１の面状抵抗体の各抵抗要素よりも第２の面状抵抗体の各抵抗要素が明らかに高抵抗化する。
【００１７】
この時点で第２の面状抵抗体の各抵抗要素の電力の配分が高まり、その部分の温度はさらに上昇する。その結果、第２の面状抵抗体の抵抗値がさらに増大するために、第１の面状抵抗体及び第２の面状抵抗体の各抵抗要素からなる直列回路において、第２の面状抵抗体の各抵抗要素の抵抗値が決定的に高くなり、第２の面状抵抗体の各抵抗要素が主体的に発熱するようになる。この状態は第２の面状抵抗体の正抵抗温度特性による自己温度制御発熱であり、第２の面状抵抗体は、温度の上昇によって、急激な抵抗値増大及び電力低下がもたらされるので、比較的少ない温度上昇で飽和温度に到達する。
【００１８】
このように、飽和温度においては、実質的に第２の面状抵抗体のみが発熱し、自己温度制御発熱による定温の熱源が散在する発熱体が形成される。この飽和状態においては、発熱部の温度が多少高くなっても発熱面積が限定されるために平均温度はむしろ低下し、電力をより低下させることができる。したがって、正抵抗温度特性による自己制御温度が高い抵抗体材料であっても低温の発熱体を形成することができる。また、第２の面状抵抗体の各抵抗要素は複数に分割され、散在しているために、発熱体全体としては温度の一様性がくずれることはなく、実用上、支障のない温度分布を形成することができる。
【００１９】
【実施例】
以下、本発明の実施例について、図面に基づいて詳細に説明する。
【００２０】
（実施例１）
図１は本発明における実施例１の発熱体の一部を拡大した平面図であり、図２はその全体を示す平面図である。図１及び図２において、１は基板であり、１８８μｍ厚みのポリエチレンテレフタレートフィルムを用いている。２、２’は一対の電極であり、エポキシ樹脂中に銀粉末を分散した導電性銀ペーストを、厚膜印刷によって基板１上に形成している。電極２、２’は主電極３、３’と主電極３、３’から分岐される枝電極４、４’から構成され、一対の枝電極４、４’が交互に対向するように配置されている。また、５は中間電極であり、一対の枝電極４、４’の間に電極２、２’とは独立に基板１上に形成されている。中間電極５は、電極２、２’と同様に導電性銀ペーストを厚膜印刷することによって形成されている。そして、６は第１の面状抵抗体であり、共重合ポリエステル樹脂と高ストラクチャーのカーボンブラックからなるペーストを、厚膜印刷によって枝電極４と中間電極５の間に形成したものである。また、７は第２の面状抵抗体であり、融点９２℃のエチレン酢酸ビニル共重合体と低ストラクチャーのカーボンブラックの混練物を、ゴム系のバインダーと高沸点の芳香族系溶剤を用いてペースト化したものを、厚膜印刷によって枝電極４’と中間電極５の間に形成したものである。なお、第１の面状抵抗体６、第２の面状抵抗体７、中間電極５は、それぞれ非発熱部８によって分割されて、各枝電極４、４’間に電気的に並列に形成されている。
【００２１】
分割されて形成された第１の面状抵抗体６、第２の面状抵抗体７、中間電極５は、それぞれ、幅寸法すなわち電圧印加直交方向寸法が３０ｍｍであり、幅３ｍｍの非発熱部８によって分割されている。第１の面状抵抗体６が形成される枝電極４と中間電極５の間の距離すなわち電圧印加方向寸法は１５ｍｍである。また、第２の面状抵抗体７が形成される枝電極４’と中間電極５の間の距離、すなわち電圧印加方向寸法は５ｍｍである。第１の面状抵抗体６、第２の面状抵抗体７、中間電極５は、１つの対となる枝電極４、４’間に５個に分割されて隣接され、対となる枝電極４、４’は発熱体全体で２０形成されている。第１の面状抵抗体６と第２の面状抵抗体７は中間電極５を介して直列に接続されているが、発熱体全体ではこのような直列回路が１００回路形成され、これらが電気的に並列に接続されている。
【００２２】
分割されて形成される第１の面状抵抗体６と第２の面状抵抗体７の分割単位での２０℃における抵抗値は、２５０Ω及び２５０Ωであった。面積抵抗値を算出すると、それぞれ５００Ω及び１５００Ωとなる。第１の面状抵抗体６と第２の面状抵抗体７からなる直列回路の分割単位での抵抗値は５００Ωとなり、発熱体全体では１００回路が並列であるから５Ωとなる。ここにＤＣ１５Ｖの電圧を印加すると、電圧印加直後の電力は４５Ｗが得られる。なお、第１の面状抵抗体６は温度が上昇しても抵抗値は実質的に一定であるが、第２の面状抵抗体７は融点９２℃の結晶性樹脂中に低ストラクチャーのカーボンブラックを分散しているために温度の上昇とともに抵抗値が増大する特性に優れ、大きな正抵抗温度特性を示す。第２の面状抵抗体７の分割単位での抵抗値は２０℃で２５０Ωであるが、５０℃では７５０Ω、６０℃では１７５０Ωとなる。したがって、分割単位での直列抵抗は２０℃で５００Ω、５０℃で１０００Ω、６０℃で２０００Ωとなる。
【００２３】
発熱体が２０℃の時にＤＣ１５Ｖを印加すると４５Ｗの電力が得られるが、直列回路における電力の比率は抵抗値に比例するので、第１の面状抵抗体６は２２．５Ｗ、第２の面状抵抗体７は２２．５Ｗを発熱する。また、この時点で、第１の面状抵抗体６には７．５Ｖ、第２の面状抵抗体７には７．５Ｖが印加されている。発熱体の温度が上昇するにつれ、第２の面状抵抗体７の抵抗値が増大するために直列回路の抵抗値も増大し、全体の電力は低下する。しかしながら、例えば発熱体が５０℃の時にＤＣ１５Ｖを印加すると、そのときの電力は２２．５Ｗであるが、第２の面状抵抗体７の抵抗値が明らかに高くなるために、第１の面状抵抗体６の電力５．６Ｗに対し、第２の面状抵抗体７は１６．９Ｗとなり、電力の不均衡が生じる。この時点で、第１の面状抵抗体６の昇温速度は極めて緩やかになるが、第２の面状抵抗体７はなおも昇温を続けるために、やがて、その抵抗値の差は決定的になる。発熱体が６０℃の時にＤＣ１５Ｖを印加すると、そのときの電力は１１．２Ｗであるが、第２の面状抵抗体７の抵抗値が決定的に高くなるために、第１の面状抵抗体６の電力１．４Ｗに対し、第２の面状抵抗体７は９．８Ｗとなり、第２の面状抵抗体７が主体的に発熱する状態となる。
【００２４】
２０℃の室温に発熱体をなじませ、ＤＣ１５Ｖを印加して飽和するまで通電してみたところ、通電開始時は第１の面状抵抗体６及び第２の面状抵抗体７の抵抗値が近接しているために両者が発熱し、発熱体は広域で高電力を得て、面全体で急速に昇温することを確認した。また、温度が上昇するにつれ、上記の過程を経て、第２の面状抵抗体７が主体的に発熱する状態になることを確認した。なお、この経過の観察は輻射温度計を用いて行った。最終的に第２の面状抵抗体７は６０℃で飽和せずに、なおも昇温を続け、最終的に６３℃で飽和した。そのときの発熱体の電力は７．７Ｗであった。第２の面状抵抗体７は、６０℃以上では抵抗値増大率が極めて急峻となり、比較的少ない温度上昇であっても電力が大きく低下するために、発熱と放熱が釣り合うものと考えられる。
【００２５】
飽和状態において温度分布を確認したところ、輻射温度計では温度分布が観測されたが、人間が直接座ったりしても温度分布は感じられず、実用上、均一発熱と考えられる。面状抵抗体を細かく分割し、発熱体の面に散在させたために、実用上、均一と見なせる発熱体を形成することができたものと考えられる。
【００２６】
（比較例１）
実施例１の比較例として、第１の面状抵抗体６を面積抵抗１０Ω／□の抵抗体に置き換えて同様の発熱体を作製した。この抵抗体はフェノール樹脂にグラファイトを多量に分散させたものであり、抵抗特性を測定したところ、第１の面状抵抗体６の抵抗値は実質的に０であり、第２の面状抵抗体７の抵抗特性のみが測定された。この比較例の発熱体にＤＣ１５Ｖを印加して昇温特性を測定した。実施例１と比較すると、通電開始時の電力は９０Ｗに増大したが、飽和時の電力には差異が見られなかった。また、通電開始直後の電力の減衰が極めて速く、初期電力は実施例１の２倍程度あるにもかかわらず、所定時間までの積算電力は逆に低下した。さらに、体感的には速熱性は感じられず、温度データでは飽和までに長い時間を必要とすることが判明した。この原因は通電開始直後の発熱面積が不足すると、熱が面方向に拡散するための時間が必要になり、いくら電力を投入しても速熱性が改善されないという現象によるものと思われる。
【００２７】
実施例１では、通電開始時には、第１の面状抵抗体６と第２の面状抵抗体７の双方を発熱させるようにしているために発熱面積が広く、熱が面方向に拡散するための時間が不要となる。このことから速熱性の面では特に有利となると考えられる。また、正抵抗温度特性を有する面状抵抗体は多くの電力を投入すると、急速に温度が上がるが、それだけ急速に電力が低下する特性があり、面状の熱源の場合、できる限り広い面積に展開させないと速熱性の面では逆効果となる。実施例１では、通電開始時には、正抵抗温度特性のない第１の面状抵抗体６を発熱させようにしているために、投入電力を高めても急速に電力が低下することはなく、速熱性の面では特に有利になると考えられる。
【００２８】
（比較例２）
実施例１の別の比較例として、全面が第２の面状抵抗体によって構成される発熱体を作製した。抵抗値が実施例１と同一になるように、中間電極を廃止し、各枝電極間の距離を１４ｍｍとし、対となる枝電極を発熱体全体で２８形成し、２０℃の抵抗値が５Ωとなるようにした。この発熱体の抵抗値は２０℃で５Ω、５０℃で１５Ω、６０℃では３５Ωとなった。この比較例の発熱体にＤＣ１５Ｖを印加したところ、実施例１に比較して、通電開始時の電力は４５Ｗで同一であったが、飽和時の電力は１３Ｗであり、明らかに大きくなった。飽和時の温度を測定したところ、発熱体の温度は極めて均一であり、実施例１よりも低い５３℃で飽和していた。しかしながら、発熱体の平均温度としては実施例１よりは明らかに高く、直接座ってみても熱く感じられる温度であった。なお、速熱性は非常に優れ、飽和温度及び飽和電力が大きい以外、明確な欠点はなかった。
【００２９】
（比較例３）
実施例１の別の比較例として、全面が別の面状抵抗体によって構成される発熱体を作製した。実施例１では、第２の面状抵抗体には融点９２℃のエチレン酢酸ビニル共重合体を使用したが、より低温で大きな正抵抗温度特性が得られるように、融点７４℃のエチレン酢酸ビニル共重合体を用いて抵抗体を作製した。面積抵抗値が高くなったために、各枝電極間の距離を１０ｍｍとし、対となる枝電極を発熱体全体で３７形成し、２０℃の抵抗値が５Ωとなるようにした。この発熱体の抵抗値は２０℃で５Ω、５０℃で２３Ω、６０℃では６５Ωとなった。この比較例の発熱体にＤＣ１５Ｖを印加して昇温特性を測定した。実施例１に比較すると、通電開始時の電力は４５Ｗで同一であり、飽和時の電力も７Ｗと、ほぼ同一の電力で飽和した。速熱性や温度分布には何ら遜色なく、飽和時の体感温度も低く感じられた。ただし、この発熱体を８０℃の雰囲気に曝した後に抵抗値を測定すると、抵抗値変化率が＋５０％を超え、熱サイクルによってさらに抵抗値が増大する傾向が見られた。
【００３０】
この発熱体は非常に正抵抗温度特性に優れているために、それ自身では８０℃を超える温度まで発熱することは有り得ないが、使用環境や保存環境を考えると少なくとも８０℃までは安定に使用できることが望ましい。結晶性樹脂をその融点以上の温度まで曝すことは、特に、抵抗値の安定性を考慮すると、避けるべきであるという結果となった。
【００３１】
以上、実施例１に示したように、本発明の発熱体は通電開始時には広域で高電力を発生し、速熱性に優れている。また、体感的に快適と感じることのできる低い温度域で飽和させることができる。しかも、通常の使用条件で考えられる８０℃までの環境温度に曝されても抵抗特性の安定性を保つことができるものであり、極めて有用であると考えられる。
【００３２】
なお、実施例１では、第１の面状抵抗体６と第２の面状抵抗体７の分割単位での２０℃における抵抗値は、２５０Ω及び２５０Ωで同一であったが、この発熱体の抵抗値を室温−２０℃で測定した結果、それぞれ２５０Ω及び１５０Ωになり、第１の面状抵抗体６の方が高抵抗となっていることが判明した。−２０℃の環境下で通電したところ、通電開始直後は５６Ｗの電力が得られ、その近辺での電力がしばらく持続してから、電力が低下する現象が見られた。このように、正抵抗温度特性を実質的に示さない抵抗体の方を高抵抗値に設定することにより、正抵抗温度特性を示す抵抗体の電力をかなり低く抑えることができる。この状態であれば、正抵抗温度特性を示す抵抗体の温度がなかなか上がらないために、通電開始時の電力をしばらく持続することができる。この発熱体は体感試験でも極めて優れた速熱性を発揮することを確認できた。また、通電開始時の電力を必要以上に高めることなく、限られた電力で速熱性を確保できることも確認できた。実施例１の発熱体は、第１の面状抵抗体６の方が高抵抗となる０℃以下の低温域では、通電開始時の電力をしばらく持続するが、２０℃では殆ど持続しないことも判明した。速熱性を確保したい場合には、第１の面状抵抗体６の方が高抵抗となるようにすることがより好ましいと言える。
【００３３】
また、実施例１では、第１の面状抵抗体６は４５０ｍｍ^２、第２の面状抵抗体７は１５０ｍｍ^２の面積の比率で形成したが、第１の面状抵抗体６は通電開始直後の発熱面積を拡大し、高電力を発熱体の全面で発生させ、十分な速熱性を発揮するのが目的であるから、可能な限り面積が大きい方が望ましい。一方、第２の面状抵抗体７は飽和時の発熱面積を制限し、飽和時の電力を抑制するのが目的であるから、可能な限り面積が小さい方が望ましい。したがって、少なくとも、第１の面状抵抗体６の展開面積は、第２の面状抵抗体７の展開面積よりも大きくすることが望ましく、その比率が大きいほど、第１の面状抵抗体の広域発熱の機能を十分に発揮することができる。
【００３４】
また、実施例１では、第１の面状抵抗体６は３０ｍｍ×１５ｍｍの長方形、第２の面状抵抗体７は３０ｍｍ×５ｍｍの細い長方形であったが、第１の面状抵抗体６は通電開始直後の発熱面積を確保するのが目的であるから、正方形に近い面形状が望ましい。また、第２の面状抵抗体７は飽和時の発熱面積を制限するのが目的であるから、縦横比の大きな細長い形状が望ましい。さらに、第２の面状抵抗体７は細長い形状とすることによって、その抵抗要素からの放熱熱抵抗が高まるので、発熱体表面あるいは被加熱体へ伝達される熱量が局部的に集中しなくなる。この現象は特に体感温度として感じられるものであって、そのように熱源を散在させた発熱体は、実質的に温度が一様となる。このことから、第２の面状抵抗体７は少なくとも第１の面状抵抗体６よりも細長い形状、すなわち、線状に近い形状にすることが望ましい。さらに好ましくは、点状に近い形状にすることが望ましい。
【００３５】
このような観点から、第２の面状抵抗体の各抵抗要素の電圧印加方向寸法を、第１の面状抵抗体の各抵抗要素の電圧印加方向寸法よりも小さくすることが望ましい。また、別の観点からであるが、第２の面状抵抗体は大きな正抵抗温度特性を付与するために高い面積抵抗値となる傾向にある。電圧印加方向寸法を小さくすると抵抗値を下げやすくなり、直列回路を組む第１の面状抵抗体の方により大きな電圧及び電力を配分することが可能になる。さらに、正抵抗温度特性を有する面状発熱体は、熱拡散が不十分な条件では、電圧集中を伴う局部発熱現象を生じる可能性があるが、電圧印加方向寸法を小さくすれば熱拡散が格段に改善されるため、このような現象を防止できる。
【００３６】
また、実施例１では、第１の面状抵抗体６は３０ｍｍ×１５ｍｍ、第２の面状抵抗体７は３０ｍｍ×５ｍｍであって、同一の電圧印加直交方向寸法を有していたが、それぞれの抵抗体の電力密度を調整するためには電圧印加直交方向寸法を変更することが望ましい。実施例１ではそれぞれの抵抗体の面積抵抗値が５００Ω／□、１５００Ω／□であり、抵抗値は２５０Ω、２５０Ω、電圧は７．５Ｖ、７．５Ｖ、電力は２２．５Ｗ、２２．５Ｗ、電力密度は５００Ｗ／ｍ^２、１５００Ｗ／ｍ^２であって、特に、電力密度のバランスは必ずしも最適値ではなかった。電力密度は発熱体の昇温能力であるために、通電開始直後の電力密度は一様であることが望ましい。しかしながら、実施例１のように、正抵抗温度特性が必要な場合には、材料組成によって制約があり、最適な面積抵抗値が得られない場合が多い。また、各抵抗要素の電圧印加方向寸法については、発熱面積、電圧集中、発熱間隔等の制約があり、自由に設定できない。
【００３７】
この電圧印加方向寸法と電圧が決まってしまえば、電力密度は面積抵抗値に依存して決定されてしまう。しかし、直列回路の場合、電圧印加直交方向寸法を変えることによって、電力密度を調整できる特徴がある。面積抵抗値が高い抵抗体は電圧印加直交方向寸法を大きく、面積抵抗値が低い抵抗体は電圧印加直交方向寸法を小さくすることによって電力密度を近づけることができる。実施例１の第１の面状抵抗体６及び第２の面状抵抗体７寸法をそれぞれ２０ｍｍ×１５ｍｍ、３０ｍｍ×５ｍｍとするだけで、電力密度は７２０Ｗ／ｍ^２、９６０Ｗ／ｍ^２となる。電圧印加直交方向寸法を変更することによって、必要に応じて電力密度を調整することができる。なお、電圧印加直交方向寸法の異なる抵抗体を電気的に接続する場合、中間電極は極めて有効である。
【００３８】
また、実施例１では、第１の面状抵抗体６は正抵抗温度特性を全く示さない抵抗体材料を使用していたが、第１の面状抵抗体６の抵抗体を融点１３０℃の高密度ポリエチレンを用いた材料に変更することによって有用な発熱体が形成できる。高密度ポリエチレンを用いた抵抗体は８０℃以上で有効な正抵抗温度特性を示すが、８０℃以下の温度域では実質的に正抵抗温度特性を示さない。したがって、実施例１の第１の面状抵抗体６を高密度ポリエチレンを用いた抵抗体に置き換えても、実施例１と全く同様の発熱特性を得ることができる。しかしながら、何らかの原因で発熱体が８０℃以上に過熱した場合、この抵抗体の抵抗値が急激に増大して、それ以上の過熱を防止することができる。
【００３９】
（実施例２）
図３は本発明における実施例２の発熱体の一部を拡大した平面図であり、図４はその全体を示す平面図である。図３及び図４において、９は基板であり、１８８μｍ厚みのポリエチレンテレフタレートフィルムを用いている。１０、１０’は一対の電極であり、エポキシ樹脂中に銀粉末を分散した導電性銀ペーストを、厚膜印刷によって基板１上に形成している。電極１０、１０’は主電極１１、１１’と主電極１１、１１’から分岐される枝電極１２、１２’から構成され、一対の枝電極１２、１２’が交互に対向するように配置されている。また、１３は中間電極であり、一対の枝電極１２、１２’の間に電極１０、１０’とは独立に基板９上に形成されている。中間電極１３は、電極１０、１０’と同様に導電性銀ペーストを厚膜印刷することによって形成されている。そして、１４は第１の面状抵抗体であり、融点９２℃のエチレン酢酸ビニル共重合体と高ストラクチャーのカーボンブラックからなるの混練物を、ゴム系のバインダーと高沸点の芳香族系溶剤を用いてペースト化したものを、厚膜印刷によって枝電極１２と中間電極１３の間に形成したものである。また、１５は第２の面状抵抗体であり、融点９２℃のエチレン酢酸ビニル共重合体と低ストラクチャーのカーボンブラックの混練物を、ゴム系のバインダーと高沸点の芳香族系溶剤を用いてペースト化したものを、厚膜印刷によって枝電極１２’と中間電極１３の間に形成したものである。なお、第１の面状抵抗体１４、第２の面状抵抗体１５、中間電極１３は、それぞれ非発熱部１６によって分割されて、各枝電極１２、１２’間に電気的に並列に形成されている。
【００４０】
分割されて形成された第１の面状抵抗体１４、第２の面状抵抗体１５、中間電極１３は、それぞれ、幅寸法すなわち電圧印加直交方向寸法が３０ｍｍであり、幅３ｍｍの非発熱部１６によって分割されている。第１の面状抵抗体１４が形成される枝電極１２と中間電極１３の間の距離すなわち電圧印加方向寸法は８ｍｍである。また、第２の面状抵抗体１５が形成される枝電極１２’と中間電極１３の間の距離、すなわち電圧印加方向寸法は３ｍｍである。第１の面状抵抗体１４、第２の面状抵抗体１５、中間電極１３は、１つの対となる枝電極１２、１２’間に５個に分割されて隣接され、対となる枝電極１２、１２’は発熱体全体で３４形成されている。第１の面状抵抗体１４と第２の面状抵抗体１５は中間電極１３を介して直列に接続されているが、発熱体全体ではこのような直列回路が１７０回路形成され、これらが電気的に並列に接続されている。
【００４１】
分割されて形成される第１の面状抵抗体１４と第２の面状抵抗体１５の分割単位での２０℃における抵抗値は、６２０Ω及び２３０Ωであった。面積抵抗値を算出すると、それぞれ２３２０Ω及び２３２０Ωで同一となる。なお、第２の面状抵抗体１５の抵抗体構成材料は実施例１と同じであるが、印刷膜厚を薄くすることによって面積抵抗値を高め、第１の面状抵抗体１４の面積抵抗値と同一となるようにしたものである。第１の面状抵抗体１４と第２の面状抵抗体１５からなる直列回路の分割単位での抵抗値は８５０Ωとなり、発熱体全体では１７０回路が並列であるから５Ωとなる。ここにＤＣ１５Ｖの電圧を印加すると、電圧印加直後の電力は４５Ｗが得られる。なお、第１の面状抵抗体１４は融点９２℃の結晶性樹脂を用いているために温度の上昇とともに抵抗値が増大する特性を示すが、高ストラクチャーのカーボンブラックを用いているために導電パスが安定で、正抵抗温度係数は全般に余り大きくなく、特に高温域での温度係数が控え目になる傾向にある。第２の面状抵抗体１５は、融点９２℃の結晶性樹脂中に低ストラクチャーのカーボンブラックを分散しているために導電パスの変化幅が大きく、温度の上昇とともに抵抗値が増大する特性に優れ、大きな正抵抗温度係数を示す。
【００４２】
第１の面状抵抗体１４の分割単位での抵抗値は２０℃で６２０Ωであるが、５０℃では９９０Ω、６０℃では１５５０Ωとなる。第２の面状抵抗体１５の分割単位での抵抗値は２０℃で２３０Ωであるが、５０℃では６９０Ω、６０℃では１６１０Ωとなる。したがって、分割単位での直列抵抗は２０℃で８５０Ω、５０℃で１６８０Ω、６０℃で３１６０Ωとなる。
【００４３】
発熱体が２０℃の時にＤＣ１５Ｖを印加すると４５Ｗの電力が得られるが、直列回路における電力の比率は抵抗値に比例するので、第１の面状抵抗体１４は３２．８Ｗ、第２の面状抵抗体１５は１２．２Ｗを発熱する。また、この時点で、第１の面状抵抗体１４には１０．９Ｖ、第２の面状抵抗体１５には４．１Ｖが印加されている。第１の面状抵抗体１４の発熱量が大きく、バランスが崩れているように思われるが、この時点での電力密度は共に８００Ｗ／ｍ^２であり、昇温能力の均衡がとれている。発熱体の温度が上昇するにつれ、第１の面状抵抗体及び第２の面状抵抗体の抵抗値が増大するために直列回路の抵抗値も増大し、全体の電力は低下する。しかしながら、例えば発熱体が５０℃の時にＤＣ１５Ｖを印加すると、そのときの発熱体の電力は２２．８Ｗが得られるが、第１の面状抵抗体１４と第２の面状抵抗体１５の電力はそれぞれ１３．４Ｗ、９．４Ｗとなる。実施例１と比較すると、この時点での第１の面状抵抗体１４の電力が大きく、全ての面状抵抗体が実質的に発熱状態にあると言える。また、電力密度はそれぞれ３３０Ｗ／ｍ^２、６１０Ｗ／ｍ^２となり、昇温能力の均衡が崩れ始めていて、第２の面状抵抗体１５の昇温能力の方が勝っている。この時点で、第１の面状抵抗体１４の昇温速度は緩やかになるが停止はしない。
【００４４】
しかし、第２の面状抵抗体１５の方が昇温速度は大きいために、そのまま通電を続けると、第２の面状抵抗体１５の方が高温となり、明確な抵抗値の差が生じる。第１の面状抵抗体１４及び第２の面状抵抗体１５が６０℃の時にＤＣ１５Ｖを印加すると、そのときの電力は１２．１Ｗであるが、第２の面状抵抗体１５の抵抗値の増大率が高いために、第１の面状抵抗体１４の電力５．９Ｗに対し、第２の面状抵抗体１５は６．２Ｗとほとんど同一になる。また、電力密度はそれぞれ１５０Ｗ／ｍ^２、４１０Ｗ／ｍ^２となり、昇温能力は不均衡となり、そのまま通電を続けると、即座に第２の面状抵抗体１５の方が高温となり、高抵抗となって主体的に発熱するようになる。
【００４５】
２０℃の室温に発熱体をなじませ、ＤＣ１５Ｖを印加して飽和するまで通電させてみたところ、通電開始時は第１の面状抵抗体１４及び第２の面状抵抗体１５の抵抗値が近接しているために両者が発熱し、電力密度が同一であり、均一な発熱分布が得られることを確認した。また、広域で高電力が発生するために、面全体で急速に昇温することを確認した。また、温度が上昇するにつれ、徐々に第２の面状抵抗体１５の発熱の比率が高まり、その後、実施例１と同様に面状抵抗体１５が主体的に発熱するようになることを確認した。最終的に第２の面状抵抗体１５は６０℃で飽和せずに、なおも昇温を続け、最終的に６２℃で飽和した。そのときの電力は７Ｗであった。第２の面状抵抗体１５は、６０℃以上では抵抗値増大率が極めて急峻となり、比較的少ない温度上昇であっても電力が大きく低下するために、発熱と放熱が釣り合い、飽和するものと考えられる。なお、実施例２の発熱体は実施例１に比べると、第１の面状抵抗体１４の電力の低下速度が遅く、積算電力も大きくなることを確認した。実施例２の構成は最終的には低電力で飽和するが、一旦、発熱体全体の温度が５０℃近辺まで上がる時期があり、体感実験では、速熱感を強く感じるものであった。飽和状態において温度分布を確認したところ、輻射温度計では温度分布が観測されたが、人間が直接座ったりしても温度分布は全く感じられず、実用上、均一発熱と考えられる。
【００４６】
実施例１よりも面状抵抗体を細かく分割し、発熱体の面に散在させたために、実用上、均一と見なせる発熱体を形成することができたものと考えられる。
【００４７】
以上、実施例２に示したように、本発明の発熱体は通電開始時のみならずある程度温度が上昇する時点まで、広域で高電力を発生させることできるもので、特に速熱性に優れている。また、体感的に快適と感じることのできる低い温度域で飽和させることができる。しかも、通常の使用条件で考えられる８０℃までの環境温度に曝されても抵抗特性の安定性を保つことができるものであり、極めて有用であると考えられる。
【００４８】
以上、実施例に基づいて説明を加えたが、本発明はこれらの実施例に限定されるものではなく、特に抵抗体材料に関しては以下に示す材料が選択できる。抵抗体の抵抗温度特性を設定するための調整ポイントは、結晶性樹脂の融点及びカーボンブラックのストラクチャーだけではなく、結晶性樹脂では、結晶化度、分子量分布、官能基、分子構造等があり、カーボンブラックでは、比表面積、粒子径、官能基等がある。これらの観点から多彩な材料が使用可能である。本実施例では、結晶性樹脂にエチレン酢酸ビニル共重合体及び高密度ポリエチレンを示したが、低密度ポリエチレン、リニア低密度ポリエチレン、エチレンエチルアクリレート、アイオノマなどのオレフィン系の結晶性樹脂でも同様の作用と効果がある。さらに、ポリ弗化ビニリデン、ナイロン、ポリエステル、ポリウレタン、シリコン樹脂など、オレフィン系以外の結晶性樹脂でも同様の作用と効果がある。
【００４９】
【発明の効果】
以上のように、本発明によれば、発熱体は、通電開始時には、電気的に直列に接続された第１の面状抵抗体と第２の面状発熱体が広い面積で共に高電力で発熱し、飽和時には正抵抗温度特性を有する第２の面状発熱体のみが発熱するようにしてなるものである。通電開始時には、発熱体の広い面積で高電力の発熱が得られるために、特に、速熱性に優れている。また、高電力で急速に昇温するにもかかわらず、体感的にも快適と感じられる低温度域で飽和させることが可能である。しかも、この発熱体は、飽和温度は低いが、高温の環境温度に曝されても抵抗特性の安定性を保つことができる。
【図面の簡単な説明】
【図１】本発明の実施例１の発熱体の構造を示す平面図
【図２】本発明の実施例１の発熱体の構造を示す平面図
【図３】本発明の実施例２の発熱体の構造を示す平面図
【図４】本発明の実施例２の発熱体の構造を示す平面図
【図５】従来の発熱体の構造を示す外観図
【符号の説明】
１、９基板
２、２’、１０、１０’ 電極
３、３’、１１、１１’ 主電極
４、４’、１２、１２’ 枝電極
５、１３中間電極
６、１４第１の面状抵抗体
７、１５第２の面状抵抗体
８、１６非発熱部[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a heating element that can be used as a heat source for heating, heating, drying, and the like.
[0002]
[Prior art]
  Conventionally, as this type of heating element, for example, as described in Japanese Patent Application Laid-Open No. 53-143047 and FIG. 5, a positive resistance is applied to a heat conductive substrate on which a heat conductive plate 18 is mounted via an insulating film 17. The heating element material 19 and the electrode 20 having a self-temperature control function based on the temperature characteristics are applied and dried, and the temperature is rapidly increased with a large inrush power, while maintaining a predetermined saturation temperature, and a heating element having a uniform temperature distribution is formed. Is.
[0003]
[Problems to be solved by the invention]
  However, using the conventional positive resistance temperature characteristic heating element, for example, when forming a human body contact type heating product such as a heating mat, the surface temperature that the human body feels comfortable is around 40 ° C., Even if the temperature drop due to the surface material is expected to be about 10K, the heat generating temperature of the heating element is sufficient around 50 ° C. Therefore, when the power is turned on, a high resistance is generated with a low resistance, but a positive resistance that can maintain 50 ° C. by self-temperature controllability due to a sharp decrease in power due to a sudden increase in resistance near 50 ° C. A heating element material exhibiting temperature characteristics is required. For this reason, a low melting crystalline resin is used as the heating element material, and the conductive material dispersed therein loses its conductivity due to a sudden increase in specific volume immediately below the melting point of the crystalline resin. It is necessary to adjust the temperature range in which the resistance value increases rapidly to be around 50 ° C. Normal crystalline resin can increase the specific volume even below the melting point, but since the rate of increase increases rapidly as the melting point is approached, sufficient positive resistance temperature characteristics can be obtained in a temperature range away from the melting point. Absent. In the case of the above human body contact type heating application, the melting point of the crystalline resin is ideally in the range of 60 ° C., and if such a resin is used, the heat resistance is excellent and the self-temperature around 50 ° C. A heating element material excellent in controllability can be obtained. If the melting point of the crystalline resin is higher than this, the ratio between the resistance value near 50 ° C and the resistance value when the power is turned on decreases, and when the resistance value near 50 ° C is fixed, the resistance value when the power is turned on increases. , The rapid thermal properties are impaired. Moreover, if the resistance value at the time of turning on the power is fixed, the self-control temperature becomes higher than 50 ° C. When the melting point of the crystalline resin exceeds 80 ° C., it becomes extremely difficult to achieve both rapid thermal properties and self-temperature controllability near 50 ° C. From the situation shown above, it is considered that the melting point of the crystalline resin is preferably as low as possible in the above-described applications.
[0004]
  On the other hand, when a crystalline resin having a low melting point is specifically selected, from the viewpoint of crystallinity, the lower the melting point, the lower the crystallinity and there is a tendency that sufficient positive resistance temperature characteristics cannot be obtained. If a material having a melting point in the range of 60 ° C. is selected from among olefin resins that are most useful as heating element materials at present, an ethylene vinyl acetate polymer having a high vinyl acetate content is selected. The ethylene vinyl acetate polymer tends to decrease in crystallinity in proportion to the vinyl acetate content, and an ethylene vinyl acetate polymer having a melting point in the range of 60 ° C. often does not provide sufficient positive resistance temperature characteristics. Therefore, from the viewpoint of crystallinity, a grade having a high melting point is considered desirable.
[0005]
  Considering the environmental conditions to which such a heating product is exposed, in the case of self-heating due to energization, there is no particular problem because the upper limit temperature is regulated by the self-temperature controllability by the positive resistance temperature characteristic. Considering the combination with equipment having a high temperature heat source, direct sunlight, storage conditions in warehouses, transportation conditions, in-vehicle use, etc., the temperature of the product is at least 60 ° C or higher, and depending on the application temperature of 80 ° C or higher Performance to withstand is required. If a heating element material mainly composed of a crystalline resin having a melting point near 60 ° C. is subjected to such conditions, it usually causes undesirable results such as deformation of the heating element, change in resistance characteristics, and reduction in life. For this reason, in the prior art, the surface temperature is around 40 ° C. by preventing the heat conduction or heat transfer by increasing the surface material of the product or reducing the mounting area of the heating element. However, the heating element temperature is increased to, for example, around 60 ° C. so that a crystalline resin having a higher melting point can be used. A method has been selected in which a crystalline resin having a higher melting point can be used at the expense of temperature stability due to rapid thermal properties or self-temperature controllability. If the configuration prevents the heat conduction, the surface temperature can be achieved, but there is a drawback that the rate of temperature rise of the surface temperature of the product is greatly reduced by preventing the heat conduction. In addition, in the configuration where the average surface temperature is lowered by reducing the mounting area of the heating element, an appropriate surface temperature at the time of saturation can be achieved, but there is no change in increasing the thermal resistance between the heating element and the product surface, There was a drawback that the heating rate of the product was greatly reduced.
[0006]
  The present invention solves the above-described conventional problems, and an object thereof is to provide a heating element that rapidly rises in temperature by using a positive resistance temperature characteristic and that saturates rapidly and stably at a predetermined surface temperature. In addition, it provides technical means that can use a high melting point crystalline resin that has high crystallinity and is resistant to high temperature environments, especially when forming a positive resistance temperature characteristic heating element having a surface temperature in a low temperature range. Very useful.
[0007]
[Means for Solving the Problems]
  In order to solve the conventional problem, the heating element of the present invention is:A heating element in which a resistance element that generates heat when a voltage is applied from a pair of electrodes formed on a substrate is formed on the substrate,
The resistance element includes a first sheet resistor and a second sheet having a smaller area than the first sheet resistor. The first sheet resistors and the second sheet resistors are alternately arranged, and are electrically connected in series at least every adjacent pair. And formed the entire heating element,At the start of energization, each resistance element of the first sheet resistor and the second sheet resistorAt approximately the same power densityBoth feverTheHigh power planar heat sourceAnd thenAs the temperature rises, at least the resistance value of the second sheet resistor increases, and each resistance element of the second sheet resistor has a higher resistance than each resistor element of the first sheet resistor. ConversionShiThe resistance elements of the second planar resistor mainly generate heat.ByDepends on the positive resistance temperature characteristicsSmall areaIt is a constant temperature heat source and at the same time a scattered heat sourceLowSaturated with electric power, and at least when the second sheet resistor is in direct contact with the human body, it is subdivided into a shape that practically does not feel the temperature distribution, and self-control of the constant temperature heat source Regardless of the temperature, it is designed to saturate in a low temperature range where you can feel comfortable.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
  The invention described in claim 1A heating element in which a resistance element that generates heat when a voltage is applied from a pair of electrodes formed on a substrate is formed on the substrate, wherein the resistance element includes a first planar resistor and the first element It is subdivided into a second sheet resistor having a smaller area than the sheet resistor, and the first sheet resistor and the second sheet resistor are arranged alternately and adjacent to each other. And at least one set electrically connected in series to form the entire heating element,At the start of energization, each resistance element of the first sheet resistor and the second sheet resistorAt approximately the same power densityBoth feverTheHigh power planar heat sourceAnd thenAs the temperature rises, at least the resistance value of the second sheet resistor increases, and each resistance element of the second sheet resistor has a higher resistance than each resistor element of the first sheet resistor. ConversionShiThe resistance elements of the second planar resistor mainly generate heat.ByDepends on the positive resistance temperature characteristicsSmall areaIt is a constant temperature heat source and at the same time a scattered heat sourceLowSaturated with electric power, and at least when the second sheet resistor is in direct contact with the human body, it is subdivided into a shape that practically does not feel the temperature distribution, and self-control of the constant temperature heat source It is a heating element that saturates in a low temperature range where it can be felt comfortably regardless of temperature.
[0009]
  At the start of energization, the resistance values of the resistance elements of the first and second planar resistors are both low, and both resistance values are relatively close. For this reason, in the series circuit composed of the resistance elements of the first sheet resistor and the second sheet resistor, all the resistance elements generate heat with high power although there is a difference in power depending on their resistance value distribution. To do. When all the resistance elements generate heat, a high-power planar heating element is formed, enabling rapid heating by wide-area heat generation. Since the resistance value of the second sheet resistor increases as the temperature rises, the second circuit element in the series circuit composed of the first sheet resistor and the resistor element of the second sheet resistor The resistance value of each resistance element of the planar resistor is clearly increased, and the power distribution of each resistor element of the second planar resistor is increased.
[0010]
  At this time, since the resistance value of the series circuit increases, the overall power decreases, and the power of the first planar resistor whose power distribution decreases decreases greatly, but the power of the second planar resistor decreases. Is not greatly reduced, and the temperature of each resistance element portion of the second planar resistor continues to rise. As a result, since the resistance value of the second planar resistor further increases, in the series circuit including the resistance elements of the first planar resistor and the second planar resistor, the second planar resistor is used. The resistance value of each resistance element of the resistor becomes decisively high, and each resistance element of the second planar resistor mainly generates heat. This state is self-temperature-controlled heat generation due to the positive resistance temperature characteristic of the second sheet resistor, and the second sheet resistor has a sudden increase in resistance value and power reduction due to an increase in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0011]
  Thus, at the saturation temperature, substantially only the second sheet resistor generates heat, and a heating element is formed in which constant temperature heat sources are scattered by self-temperature controlled heat generation. In this saturated state, even if the temperature of the heat generating portion is somewhat increased, the heat generating area is limited, so that the average temperature is rather decreased, and the power can be further decreased. Therefore, a low-temperature heating element can be formed even with a resistor material having a high self-control temperature due to the positive resistance temperature characteristic. In addition, since each resistance element of the second planar resistor is divided into a plurality of parts and scattered, the temperature uniformity of the entire heating element is not impaired, and there is no practically troublesome temperature distribution. Can be formed.
[0012]
  The invention described in claim 2Both the first sheet resistor and the second sheet resistor have a positive resistance temperature characteristic, and the resistance value increases as the temperature rises, but at least at the temperature near the start of energization, the first surface resistor The power density of the resistor element of the sheet resistor is substantially the same as the power density of the resistor element of the second sheet resistor. On the other hand, in the temperature range up to the saturation temperature, the second sheet resistor The rate of increase of the resistance value exceeds the rate of increase of the resistance value of the first sheet resistor, and each resistance element of the second sheet resistor is greater than each resistor element of the first sheet resistor. Is designed to increase the resistance.
[0013]
  For this reason, in the series circuit composed of the resistance elements of the first planar resistor and the second planar resistor, all the resistive elements generate heat with high power. As the temperature increases, the resistance value of both the first sheet resistor and the second sheet resistor increases, so the power decreases, but the resistance values of both are relatively close. There is no change, and the state where all the resistance elements of both of them generate heat continues at this time. As the temperature further rises, the increase rate of the resistance value of the second sheet resistor exceeds the increase rate of the resistance value of the first sheet resistor, and is greater than each resistance element of the first sheet resistor. However, each resistance element of the second planar resistor is clearly increased in resistance. At this point, the power distribution of each resistance element of the second planar resistor increases, and the temperature of that portion continues to rise.
[0014]
  As a result, in order to further increase the resistance value of the second planar resistor, in the series circuit composed of the resistance elements of the first planar resistor and the second planar resistor, The resistance value of each resistance element of the resistor becomes decisively high, and each resistance element of the second planar resistor mainly generates heat. This state is self-temperature-controlled heat generation due to the positive resistance temperature characteristic of the second sheet resistor, and the second sheet resistor has a sudden increase in resistance value and power reduction due to an increase in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0015]
  Thus, at the saturation temperature, substantially only the second sheet resistor generates heat, and a heating element is formed in which constant temperature heat sources are scattered by self-temperature controlled heat generation. In this saturated state, even if the temperature of the heat generating portion is somewhat increased, the heat generating area is limited, so that the average temperature is rather decreased, and the power can be further decreased. Therefore, a low-temperature heating element can be formed even with a resistor material having a high self-control temperature due to the positive resistance temperature characteristic. In addition, since each resistance element of the second planar resistor is divided into a plurality of parts and scattered, the temperature uniformity of the entire heating element is not impaired, and there is no practically troublesome temperature distribution. Can be formed.
[0016]
  Claim3The first sheet resistor does not exhibit a positive resistance temperature characteristic which is substantially effective in the temperature range up to the saturation temperature, and the second sheet resistor has a substantially effective positive resistance. It shows temperature characteristics. At the start of energization, the resistance values of the resistance elements of the first and second planar resistors are both low, and both resistance values are relatively close. For this reason, in the series circuit composed of the resistance elements of the first planar resistor and the second planar resistor, all the resistive elements generate heat with high power. As the temperature rises, the resistance value of the first sheet resistor does not change greatly, but only the resistance value of the second sheet resistor increases, so that each resistance element of the first sheet resistor is increased. As a result, the resistance elements of the second planar resistor are clearly increased in resistance.
[0017]
  At this time, the power distribution of each resistance element of the second planar resistor increases, and the temperature of that portion further increases. As a result, in order to further increase the resistance value of the second planar resistor, in the series circuit composed of the resistance elements of the first planar resistor and the second planar resistor, The resistance value of each resistance element of the resistor becomes decisively high, and each resistance element of the second planar resistor mainly generates heat. This state is self-temperature-controlled heat generation due to the positive resistance temperature characteristic of the second sheet resistor, and the second sheet resistor has a sudden increase in resistance value and power reduction due to an increase in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0018]
  Thus, at the saturation temperature, substantially only the second sheet resistor generates heat, and a heating element is formed in which constant temperature heat sources are scattered by self-temperature controlled heat generation. In this saturated state, even if the temperature of the heat generating portion is somewhat increased, the heat generating area is limited, so that the average temperature is rather decreased, and the power can be further decreased. Therefore, a low-temperature heating element can be formed even with a resistor material having a high self-control temperature due to the positive resistance temperature characteristic. In addition, since each resistance element of the second planar resistor is divided into a plurality of parts and scattered, the temperature uniformity of the entire heating element is not impaired, and there is no practically troublesome temperature distribution. Can be formed.
[0019]
【Example】
  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0020]
  Example 1
  FIG. 1 is an enlarged plan view of a part of the heating element according to the first embodiment of the present invention, and FIG. 2 is a plan view showing the whole. 1 and 2, reference numeral 1 denotes a substrate, and a polyethylene terephthalate film having a thickness of 188 μm is used. 2, 2 'are a pair of electrodes, and a conductive silver paste in which silver powder is dispersed in an epoxy resin is formed on the substrate 1 by thick film printing. The electrodes 2 and 2 ′ are composed of main electrodes 3 and 3 ′ and branch electrodes 4 and 4 ′ branched from the main electrodes 3 and 3 ′, and the pair of branch electrodes 4 and 4 ′ are arranged so as to alternately face each other. ing. Reference numeral 5 denotes an intermediate electrode which is formed on the substrate 1 between the pair of branch electrodes 4 and 4 'independently of the electrodes 2 and 2'. The intermediate electrode 5 is formed by thick film printing of a conductive silver paste in the same manner as the electrodes 2 and 2 '. Reference numeral 6 denotes a first planar resistor, in which a paste made of a copolyester resin and high-structure carbon black is formed between the branch electrode 4 and the intermediate electrode 5 by thick film printing. Reference numeral 7 denotes a second planar resistor, which is a kneaded mixture of ethylene vinyl acetate copolymer having a melting point of 92 ° C. and low structure carbon black, using a rubber binder and a high boiling aromatic solvent. The paste is formed between the branch electrode 4 ′ and the intermediate electrode 5 by thick film printing. The first sheet resistor 6, the second sheet resistor 7, and the intermediate electrode 5 are each divided by the non-heat generating portion 8 and are electrically formed in parallel between the branch electrodes 4, 4 ′. Has been.
[0021]
  The first sheet resistor 6, the second sheet resistor 7, and the intermediate electrode 5, which are divided and formed, each have a width dimension, that is, a voltage application orthogonal direction dimension of 30 mm, and a non-heat generating portion having a width of 3 mm. It is divided by 8. The distance between the branch electrode 4 and the intermediate electrode 5 where the first planar resistor 6 is formed, that is, the voltage application direction dimension is 15 mm. Further, the distance between the branch electrode 4 ′ on which the second planar resistor 7 is formed and the intermediate electrode 5, that is, the voltage application direction dimension is 5 mm. The first sheet resistor 6, the second sheet resistor 7, and the intermediate electrode 5 are divided into five pieces between the pair of branch electrodes 4 and 4 ′, and are adjacent to each other. 4 and 4 'are formed 20 by the whole heat generating body. The first sheet resistor 6 and the second sheet resistor 7 are connected in series via the intermediate electrode 5, but 100 series of such series circuits are formed in the entire heating element, and these are electrically connected. Are connected in parallel.
[0022]
  The resistance values at 20 ° C. in divided units of the first sheet resistor 6 and the second sheet resistor 7 formed by division were 250Ω and 250Ω. When the sheet resistance values are calculated, they are 500Ω and 1500Ω, respectively. The resistance value in the division unit of the series circuit composed of the first sheet resistor 6 and the second sheet resistor 7 is 500Ω, and the entire heating element is 5Ω because 100 circuits are in parallel. When a voltage of DC 15 V is applied here, 45 W is obtained immediately after the voltage application. The resistance value of the first planar resistor 6 is substantially constant as the temperature rises, but the second planar resistor 7 is a low structure carbon in a crystalline resin having a melting point of 92 ° C. Since black is dispersed, the resistance value increases as the temperature rises, and a large positive resistance temperature characteristic is exhibited. The resistance value in the divided unit of the second planar resistor 7 is 250Ω at 20 ° C., but becomes 750Ω at 50 ° C. and 1750Ω at 60 ° C. Therefore, the series resistance in divided units is 500Ω at 20 ° C., 1000Ω at 50 ° C., and 2000Ω at 60 ° C.
[0023]
  When DC15V is applied when the heating element is 20 ° C., 45 W of power is obtained. However, since the ratio of power in the series circuit is proportional to the resistance value, the first planar resistor 6 is 22.5 W, the second surface. The resistor 7 generates 22.5 W. At this time, 7.5V is applied to the first sheet resistor 6 and 7.5V is applied to the second sheet resistor 7. As the temperature of the heating element rises, the resistance value of the second planar resistor 7 increases, so the resistance value of the series circuit also increases and the overall power decreases. However, for example, when DC 15 V is applied when the heating element is 50 ° C., the power at that time is 22.5 W, but the resistance value of the second planar resistor 7 is clearly increased, so that the first surface The second planar resistor 7 is 16.9 W with respect to the power 5.6 W of the sheet-like resistor 6, and an imbalance of power occurs. At this point, the rate of temperature rise of the first sheet resistor 6 becomes very slow, but the second sheet resistor 7 continues to rise in temperature, so that the difference in resistance value is determined over time. Become. When DC 15 V is applied when the heating element is 60 ° C., the power at that time is 11.2 W. However, since the resistance value of the second sheet resistor 7 becomes decisively high, the first sheet resistance The second sheet resistor 7 becomes 9.8 W with respect to the electric power 1.4 W of the body 6, and the second sheet resistor 7 mainly generates heat.
[0024]
  When the heating element was applied to a room temperature of 20 ° C. and DC15V was applied to energize until it was saturated, the resistance values of the first sheet resistor 6 and the second sheet resistor 7 were at the start of energization. It was confirmed that both of them generated heat because they were close to each other, and the heating element gained high power over a wide area and rapidly heated up over the entire surface. Further, it was confirmed that as the temperature rose, the second sheet resistor 7 mainly generated heat through the above process. In addition, observation of this progress was performed using the radiation thermometer. Finally, the second sheet resistor 7 did not saturate at 60 ° C., but continued to rise in temperature, and finally saturated at 63 ° C. The electric power of the heating element at that time was 7.7 W. The second sheet resistor 7 has an extremely steep increase in resistance value at 60 ° C. or higher, and the power is greatly reduced even with a relatively small increase in temperature. Therefore, it is considered that heat generation and heat dissipation are balanced.
[0025]
  When the temperature distribution was confirmed in the saturated state, a temperature distribution was observed with the radiation thermometer, but even if a person sat directly, the temperature distribution was not felt, and it is considered that the heat generation was practically uniform. It is considered that a heating element that can be considered practically uniform could be formed because the planar resistor was finely divided and scattered on the surface of the heating element.
[0026]
  (Comparative Example 1)
  As a comparative example of Example 1, a similar heating element was manufactured by replacing the first planar resistor 6 with a resistor having a sheet resistance of 10Ω / □. This resistor is obtained by dispersing a large amount of graphite in a phenol resin. When the resistance characteristic is measured, the resistance value of the first sheet resistor 6 is substantially 0, and the second sheet resistance Only the resistance characteristics of the body 7 were measured. DC 15V was applied to the heating element of this comparative example, and the temperature rise characteristics were measured. Compared with Example 1, the power at the start of energization increased to 90 W, but there was no difference in power at saturation. In addition, the power decay immediately after the start of energization was extremely fast, and the integrated power until a predetermined time decreased conversely even though the initial power was about twice that of the first embodiment. Furthermore, it has been found that temperature does not feel rapid heat, and the temperature data requires a long time until saturation. This is considered to be due to the phenomenon that if the heat generation area immediately after the start of energization is insufficient, it takes time for the heat to diffuse in the surface direction, and the rapid thermal performance is not improved no matter how much power is applied.
[0027]
  In the first embodiment, at the start of energization, since both the first sheet resistor 6 and the second sheet resistor 7 are caused to generate heat, the heat generation area is wide and heat is diffused in the surface direction. Is no longer necessary. This is considered to be particularly advantageous in terms of rapid heating. In addition, a sheet resistor having positive resistance temperature characteristics rises rapidly when a large amount of power is applied, but the power decreases rapidly, and a planar heat source has as large an area as possible. If it is not deployed, it will have the opposite effect in terms of rapid heating. In the first embodiment, when the energization is started, the first sheet resistor 6 having no positive resistance temperature characteristic is caused to generate heat. Therefore, even if the input power is increased, the power does not rapidly decrease, and the speed is reduced. This is considered particularly advantageous in terms of thermal properties.
[0028]
  (Comparative Example 2)
  As another comparative example of Example 1, a heating element having the entire surface constituted by the second planar resistor was produced. The intermediate electrode is abolished so that the resistance value is the same as in Example 1, the distance between each branch electrode is 14 mm, and 28 paired branch electrodes are formed in the entire heating element, and the resistance value at 20 ° C. is 5Ω. It was made to become. The resistance value of this heating element was 5Ω at 20 ° C., 15Ω at 50 ° C., and 35Ω at 60 ° C. When DC15V was applied to the heating element of this comparative example, compared with Example 1, the power at the start of energization was the same at 45 W, but the power at saturation was 13 W, which was clearly increased. When the temperature at the time of saturation was measured, the temperature of the heating element was extremely uniform and was saturated at 53 ° C. lower than that of Example 1. However, the average temperature of the heating element was clearly higher than that of Example 1, and was a temperature that felt hot even when sitting directly. In addition, quick heat property was very excellent, and there was no clear fault except a saturation temperature and saturation power being large.
[0029]
  (Comparative Example 3)
  As another comparative example of Example 1, a heating element having the entire surface made of another planar resistor was produced. In Example 1, an ethylene vinyl acetate copolymer having a melting point of 92 ° C. was used as the second planar resistor, but an ethylene vinyl acetate having a melting point of 74 ° C. was obtained so as to obtain a large positive resistance temperature characteristic at a lower temperature. A resistor was prepared using the copolymer. Since the area resistance value was increased, the distance between the branch electrodes was set to 10 mm, and 37 branch electrodes were formed as a whole in the heating element so that the resistance value at 20 ° C. was 5Ω. The resistance value of this heating element was 5Ω at 20 ° C., 23Ω at 50 ° C., and 65Ω at 60 ° C. DC 15V was applied to the heating element of this comparative example, and the temperature rise characteristics were measured. Compared to Example 1, the power at the start of energization was the same at 45 W, and the power at the time of saturation was 7 W, which was saturated at almost the same power. There was no inferiority to the rapid thermal properties and temperature distribution, and the temperature at saturation was felt to be low. However, when the resistance value was measured after the heating element was exposed to an atmosphere of 80 ° C., the resistance value change rate exceeded + 50%, and the resistance value tended to further increase due to thermal cycling.
[0030]
  Since this heating element is extremely excellent in positive resistance temperature characteristics, it cannot generate heat up to a temperature exceeding 80 ° C by itself, but it can be used stably at least up to 80 ° C in consideration of the use environment and storage environment. It is desirable to be able to do it. As a result, exposure of the crystalline resin to a temperature higher than its melting point should be avoided, especially considering the stability of the resistance value.
[0031]
  As described above, as shown in the first embodiment, the heating element of the present invention generates high power in a wide area at the start of energization, and is excellent in rapid thermal performance. Moreover, it can saturate in the low temperature range which can be felt comfortably. Moreover, even when exposed to an environmental temperature up to 80 ° C., which is considered under normal use conditions, the stability of the resistance characteristics can be maintained, which is considered extremely useful.
[0032]
  In Example 1, the resistance values at 20 ° C. in the divided units of the first planar resistor 6 and the second planar resistor 7 were the same at 250Ω and 250Ω. As a result of measuring the resistance value at room temperature −20 ° C., it became 250Ω and 150Ω, respectively, and it was found that the first planar resistor 6 had a higher resistance. When energized in an environment of −20 ° C., a power of 56 W was obtained immediately after the energization was started, and a phenomenon in which the power decreased was observed after the power in the vicinity thereof was maintained for a while. In this way, by setting the resistor that does not substantially exhibit the positive resistance temperature characteristic to a higher resistance value, the power of the resistor that exhibits the positive resistance temperature characteristic can be significantly reduced. In this state, since the temperature of the resistor showing the positive resistance temperature characteristic does not rise easily, the power at the start of energization can be maintained for a while. It was confirmed that this heating element exhibited extremely excellent rapid heating properties even in a sensation test. It was also confirmed that rapid heat performance could be secured with limited power without increasing the power at the start of energization more than necessary. In the heating element of Example 1, the electric power at the start of energization is sustained for a while in the low temperature range of 0 ° C. or lower where the first planar resistor 6 has a higher resistance, but it may hardly last at 20 ° C. found. It can be said that it is more preferable that the first planar resistor 6 has a higher resistance when it is desired to ensure rapid thermal performance.
[0033]
  In Example 1, the first sheet resistor 6 is 450 mm.²The second sheet resistor 7 is 150 mm²However, the first sheet resistor 6 is intended to expand the heat generation area immediately after the start of energization, generate high power over the entire surface of the heat generator, and exhibit sufficient heat resistance. Therefore, it is desirable that the area be as large as possible. On the other hand, the second planar resistor 7 is intended to limit the heat generation area at the time of saturation and suppress the power at the time of saturation, and therefore it is desirable that the area be as small as possible. Therefore, it is desirable that at least the development area of the first planar resistor 6 is larger than the development area of the second planar resistor 7, and the larger the ratio, the greater the ratio of the first planar resistor 6. The function of wide-area heat generation can be fully exhibited.
[0034]
  In the first embodiment, the first sheet resistor 6 is a 30 mm × 15 mm rectangle, and the second sheet resistor 7 is a 30 mm × 5 mm thin rectangle. Since the purpose is to secure a heat generation area immediately after the start of energization, a surface shape close to a square is desirable. In addition, since the second planar resistor 7 is intended to limit the heat generation area at the time of saturation, an elongated shape having a large aspect ratio is desirable. Furthermore, since the second sheet resistor 7 has an elongated shape, the heat radiation resistance from the resistance element is increased, so that the amount of heat transmitted to the surface of the heating element or the object to be heated does not concentrate locally. This phenomenon is particularly felt as a sensible temperature, and the temperature of the heating element in which the heat sources are scattered is substantially uniform. For this reason, it is desirable that the second planar resistor 7 has an elongated shape, that is, a shape close to a linear shape, at least as compared with the first planar resistor 6. More preferably, it is desirable to make the shape close to a dot shape.
[0035]
  From such a viewpoint, it is desirable that the voltage application direction dimension of each resistance element of the second planar resistor is smaller than the voltage application direction dimension of each resistance element of the first planar resistor. Moreover, although it is from another viewpoint, since the 2nd planar resistor gives a big positive resistance temperature characteristic, it exists in the tendency for it to become a high sheet resistance value. If the dimension in the voltage application direction is reduced, the resistance value can be easily lowered, and a larger voltage and electric power can be distributed to the first planar resistors that form a series circuit. Furthermore, a planar heating element having a positive resistance temperature characteristic may cause a local heat generation phenomenon with voltage concentration under conditions where thermal diffusion is insufficient. Therefore, this phenomenon can be prevented.
[0036]
  Further, in Example 1, the first planar resistor 6 was 30 mm × 15 mm, and the second planar resistor 7 was 30 mm × 5 mm, and had the same voltage application orthogonal direction dimension. In order to adjust the power density of each resistor, it is desirable to change the dimension in the voltage application orthogonal direction. In Example 1, the area resistance value of each resistor is 500Ω / □, 1500Ω / □, the resistance value is 250Ω, 250Ω, the voltage is 7.5V, 7.5V, the power is 22.5W, 22.5W, Power density is 500W / m²1500W / m²In particular, the balance of power density is not necessarily an optimum value. Since the power density is the heating capability of the heating element, it is desirable that the power density immediately after the start of energization is uniform. However, when the positive resistance temperature characteristic is required as in the first embodiment, there is a limitation depending on the material composition, and an optimum sheet resistance value is often not obtained. Further, the voltage application direction dimension of each resistance element cannot be freely set because of restrictions such as heat generation area, voltage concentration, and heat generation interval.
[0037]
  If the voltage application direction dimension and voltage are determined, the power density is determined depending on the area resistance value. However, in the case of the series circuit, there is a feature that the power density can be adjusted by changing the dimension in the voltage application orthogonal direction. A resistor having a high area resistance value can be made closer to the voltage density in the voltage application orthogonal direction, and a resistor having a lower area resistance value can be made close to the power density by reducing the voltage application orthogonal direction dimension. The power density is 720 W / m only by setting the dimensions of the first sheet resistor 6 and the second sheet resistor 7 of Example 1 to 20 mm × 15 mm and 30 mm × 5 mm, respectively.²960W / m²It becomes. By changing the voltage application orthogonal direction dimension, the power density can be adjusted as necessary. Note that the intermediate electrode is extremely effective when electrically connecting resistors having different dimensions in the voltage application orthogonal direction.
[0038]
  In the first embodiment, the first sheet resistor 6 is made of a resistor material that does not exhibit any positive resistance temperature characteristics. However, the resistor of the first sheet resistor 6 has a melting point of 130 ° C. A useful heating element can be formed by changing to a material using high-density polyethylene. A resistor using high-density polyethylene exhibits effective positive resistance temperature characteristics at 80 ° C. or higher, but does not substantially exhibit positive resistance temperature characteristics at a temperature range of 80 ° C. or lower. Therefore, even if the first planar resistor 6 of Example 1 is replaced with a resistor using high-density polyethylene, exactly the same heat generation characteristics as in Example 1 can be obtained. However, when the heating element overheats to 80 ° C. or higher for some reason, the resistance value of the resistor increases rapidly, and further overheating can be prevented.
[0039]
  (Example 2)
  FIG. 3 is an enlarged plan view of a part of the heating element according to the second embodiment of the present invention, and FIG. 4 is a plan view showing the whole. 3 and 4, 9 is a substrate, and a polyethylene terephthalate film having a thickness of 188 μm is used. 10 and 10 'are a pair of electrodes, and a conductive silver paste in which silver powder is dispersed in an epoxy resin is formed on the substrate 1 by thick film printing. The electrodes 10 and 10 'are composed of main electrodes 11 and 11' and branch electrodes 12 and 12 'branched from the main electrodes 11 and 11', and a pair of branch electrodes 12 and 12 'are arranged so as to alternately face each other. ing. Reference numeral 13 denotes an intermediate electrode, which is formed on the substrate 9 between the pair of branch electrodes 12 and 12 'independently of the electrodes 10 and 10'. The intermediate electrode 13 is formed by thick film printing of a conductive silver paste in the same manner as the electrodes 10 and 10 '. Reference numeral 14 denotes a first sheet resistor, a kneaded material composed of an ethylene vinyl acetate copolymer having a melting point of 92 ° C. and a high structure carbon black, a rubber binder and a high boiling point aromatic solvent. The paste formed by using this is formed between the branch electrode 12 and the intermediate electrode 13 by thick film printing. Reference numeral 15 denotes a second planar resistor, which is a kneaded mixture of an ethylene vinyl acetate copolymer having a melting point of 92 ° C. and a low structure carbon black, using a rubber binder and a high boiling aromatic solvent. The paste is formed between the branch electrode 12 ′ and the intermediate electrode 13 by thick film printing. The first sheet resistor 14, the second sheet resistor 15, and the intermediate electrode 13 are each divided by a non-heat generating portion 16 and are electrically formed in parallel between the branch electrodes 12, 12 ′. Has been.
[0040]
  The first sheet resistor 14, the second sheet resistor 15, and the intermediate electrode 13 that are divided and formed have a width dimension, that is, a voltage application orthogonal direction dimension of 30 mm, and a non-heat generating portion having a width of 3 mm. 16 is divided. The distance between the branch electrode 12 where the first planar resistor 14 is formed and the intermediate electrode 13, that is, the voltage application direction dimension is 8 mm. The distance between the branch electrode 12 ′ on which the second planar resistor 15 is formed and the intermediate electrode 13, that is, the voltage application direction dimension is 3 mm. The first sheet resistor 14, the second sheet resistor 15, and the intermediate electrode 13 are divided into five pieces between the pair of branch electrodes 12 and 12 ′, and are adjacent to each other. 12 and 12 'are formed 34 by the whole heat generating body. The first sheet resistor 14 and the second sheet resistor 15 are connected in series via the intermediate electrode 13, but 170 series of such series circuits are formed in the entire heating element, and these are electrically connected. Are connected in parallel.
[0041]
  The resistance values at 20 ° C. in divided units of the first planar resistor 14 and the second planar resistor 15 formed by division were 620Ω and 230Ω. When the sheet resistance values are calculated, they are the same at 2320Ω and 2320Ω, respectively. The resistor constituting material of the second sheet resistor 15 is the same as that of the first embodiment, but the sheet resistance is increased by reducing the printed film thickness, and the sheet resistance of the first sheet resistor 14 is increased. It is the same as the value. The resistance value in the division unit of the series circuit composed of the first planar resistor 14 and the second planar resistor 15 is 850Ω, and 5Ω because the entire heating element has 170 circuits in parallel. When a voltage of DC 15 V is applied here, 45 W is obtained immediately after the voltage application. The first planar resistor 14 has a characteristic that the resistance value increases as the temperature rises due to the use of a crystalline resin having a melting point of 92 ° C. The path is stable and the temperature coefficient of positive resistance is not so large in general, and the temperature coefficient tends to be conservative particularly in a high temperature range. The second planar resistor 15 has a characteristic that the change width of the conductive path is large because the low structure carbon black is dispersed in the crystalline resin having a melting point of 92 ° C., and the resistance value increases as the temperature rises. Excellent, large positive resistance temperature coefficient.
[0042]
  The resistance value in the division unit of the first planar resistor 14 is 620Ω at 20 ° C., but becomes 990Ω at 50 ° C. and 1550Ω at 60 ° C. The resistance value in the division unit of the second planar resistor 15 is 230Ω at 20 ° C., but becomes 690Ω at 50 ° C. and 1610Ω at 60 ° C. Therefore, the series resistance in divided units is 850Ω at 20 ° C., 1680Ω at 50 ° C., and 3160Ω at 60 ° C.
[0043]
  When DC15V is applied when the heating element is 20 ° C., 45 W of power can be obtained. However, since the power ratio in the series circuit is proportional to the resistance value, the first planar resistor 14 is 32.8 W, the second surface. The resistor 15 generates 12.2 W. At this time, 10.9 V is applied to the first sheet resistor 14 and 4.1 V is applied to the second sheet resistor 15. The amount of heat generated by the first sheet resistor 14 is large and seems to be out of balance, but the power density at this point is 800 W / m.²Therefore, the heating capability is balanced. As the temperature of the heating element rises, the resistance value of the first planar resistor and the second planar resistor increases, so the resistance value of the series circuit also increases, and the overall power decreases. However, for example, when DC 15 V is applied when the heating element is 50 ° C., the power of the heating element at that time is 22.8 W. The power of the first planar resistor 14 and the second planar resistor 15 is obtained. Are 13.4W and 9.4W, respectively. Compared with Example 1, it can be said that the electric power of the first sheet resistor 14 at this time is large, and all the sheet resistors are substantially in a heat generation state. The power density is 330 W / m.²610W / m²Thus, the balance of the temperature raising ability is beginning to collapse, and the temperature raising ability of the second planar resistor 15 is better. At this point, the rate of temperature rise of the first planar resistor 14 becomes slow but does not stop.
[0044]
  However, since the temperature rise rate of the second sheet resistor 15 is larger, if the energization is continued as it is, the second sheet resistor 15 becomes higher temperature and a clear difference in resistance value occurs. When DC 15V is applied when the first sheet resistor 14 and the second sheet resistor 15 are 60 ° C., the power at that time is 12.1 W, but the resistance value of the second sheet resistor 15 Therefore, the second sheet resistor 15 is almost the same as 6.2 W with respect to the electric power 5.9 W of the first sheet resistor 14. The power density is 150 W / m each.²410W / m²As a result, the temperature rise capability becomes unbalanced, and if the current is continued as it is, the second planar resistor 15 immediately becomes higher in temperature and becomes higher in resistance and mainly generates heat.
[0045]
  When the heating element was applied to a room temperature of 20 ° C. and DC15V was applied and energized until saturation, the resistance values of the first sheet resistor 14 and the second sheet resistor 15 were at the start of energization. Since they are close to each other, both of them generate heat, the power density is the same, and it was confirmed that a uniform heat generation distribution can be obtained. In addition, since high power is generated in a wide area, it was confirmed that the temperature rises rapidly over the entire surface. Further, as the temperature rises, it is confirmed that the ratio of heat generation of the second sheet resistor 15 gradually increases, and thereafter the sheet resistor 15 mainly generates heat similarly to the first embodiment. did. Finally, the second sheet resistor 15 did not saturate at 60 ° C., but continued to rise in temperature, and finally saturated at 62 ° C. The power at that time was 7W. The second planar resistor 15 has an extremely steep increase in resistance value at 60 ° C. or higher, and the power is greatly reduced even with a relatively small temperature rise. Conceivable. In addition, it was confirmed that the heating element of Example 2 had a lower power reduction rate and a higher integrated power than the first sheet resistor 14 as compared to Example 1. The configuration of Example 2 eventually saturates at low power, but once the temperature of the entire heating element rises to around 50 ° C., the sensation experiment felt a strong sense of rapid heat. When the temperature distribution was confirmed in the saturated state, a temperature distribution was observed with the radiation thermometer, but even if a person sat directly, the temperature distribution was not felt at all, and it was considered that the heat generation was practically uniform.
[0046]
  It is considered that a heating element that can be regarded as practically uniform could be formed because the planar resistor was more finely divided than in Example 1 and scattered on the surface of the heating element.
[0047]
  As described above, as shown in Example 2, the heating element of the present invention can generate high power in a wide area not only at the start of energization but also until the temperature rises to some extent, and is particularly excellent in rapid heat performance. . Moreover, it can saturate in the low temperature range which can be felt comfortably. Moreover, even when exposed to an environmental temperature up to 80 ° C., which is considered under normal use conditions, the stability of the resistance characteristics can be maintained, which is considered extremely useful.
[0048]
  As mentioned above, although description was added based on the Example, this invention is not limited to these Examples, Especially regarding a resistor material, the material shown below can be selected. Adjustment points for setting the resistance temperature characteristics of the resistor are not only the melting point of the crystalline resin and the structure of the carbon black, but in the crystalline resin, there are crystallinity, molecular weight distribution, functional group, molecular structure, etc. Carbon black has specific surface area, particle diameter, functional group, and the like. From these viewpoints, various materials can be used. In this example, ethylene vinyl acetate copolymer and high-density polyethylene were shown as the crystalline resin. However, the same effect can be obtained with olefin-based crystalline resins such as low-density polyethylene, linear low-density polyethylene, ethylene ethyl acrylate, and ionomer. And effective. Furthermore, crystalline resins other than olefins such as polyvinylidene fluoride, nylon, polyester, polyurethane, and silicone resin have the same action and effect.
[0049]
【The invention's effect】
  As described above, according to the present invention, when the energization is started, the first sheet resistor and the second sheet heater that are electrically connected in series are both high power with a large area. Only the second planar heating element that generates heat and has positive resistance temperature characteristics at the time of saturation generates heat. At the start of energization, high power heat can be obtained over a wide area of the heating element, so that it is particularly excellent in rapid thermal performance. In addition, it is possible to saturate in a low temperature range in which the user feels comfortable even though the temperature is rapidly increased with high power. Moreover, this heating element has a low saturation temperature, but can maintain stability of resistance characteristics even when exposed to a high ambient temperature.
[Brief description of the drawings]
FIG. 1 is a plan view showing a structure of a heating element according to a first embodiment of the present invention.
FIG. 2 is a plan view showing the structure of a heating element of Example 1 of the present invention.
FIG. 3 is a plan view showing the structure of a heating element according to a second embodiment of the present invention.
FIG. 4 is a plan view showing the structure of a heating element according to a second embodiment of the present invention.
FIG. 5 is an external view showing the structure of a conventional heating element.
[Explanation of symbols]
  1, 9 substrate
  2, 2 ', 10, 10' electrode
  3, 3 ', 11, 11' main electrode
  4, 4 ', 12, 12' branch electrode
  5, 13 Intermediate electrode
  6, 14 First planar resistor
  7, 15 Second planar resistor
  8, 16 Non-heating part

Claims

A heating element in which a resistance element that generates heat when a voltage is applied from a pair of electrodes formed on a substrate is formed on the substrate,
The resistor element is subdivided into a first sheet resistor and a second sheet resistor having a smaller area than the first sheet resistor, and the first sheet resistor. And the second sheet resistors are alternately arranged, and are electrically connected in series for each adjacent pair to form the entire heating element,
At the start of energization, each of the resistance elements of the first sheet resistor and the second sheet resistor generates heat at substantially the same power density and becomes a high power sheet heat source ,
As the temperature rises thereafter, at least the resistance value of the second sheet resistor increases, and each resistance element of the second sheet resistor is more than the resistance element of the first sheet resistor. The resistance is increased, and each resistance element of the second planar resistor mainly generates heat, so that it becomes a constant temperature heat source with a small area due to the positive resistance temperature characteristic and at the same time becomes a scattered heat source and is saturated with low power,
At least when the second sheet resistor is in direct contact with the human body, it is practically finely divided into a shape that does not feel the temperature distribution, regardless of the self-control temperature of the constant temperature heat source, A heating element that saturates in a low temperature range where you can feel comfortable.

Both the first sheet resistor and the second sheet resistor have a positive resistance temperature characteristic, and the resistance value increases as the temperature rises, but at least at the temperature near the start of energization, the first surface resistor The power density of the resistor element of the sheet resistor is substantially the same as the power density of the resistor element of the second sheet resistor. On the other hand, in the temperature range up to the saturation temperature, the second sheet resistor The rate of increase of the resistance value exceeds the rate of increase of the resistance value of the first sheet resistor, and each resistance element of the second sheet resistor is greater than each resistor element of the first sheet resistor. The heating element according to claim 1, wherein the resistance increases .

The first sheet resistor does not exhibit a substantially effective positive resistance temperature characteristic in a temperature range up to a saturation temperature, and the second sheet resistor exhibits a substantially effective positive resistance temperature characteristic. The heating element according to 1 or 2 .