JP2004014286A

JP2004014286A - Heating element

Info

Publication number: JP2004014286A
Application number: JP2002165811A
Authority: JP
Inventors: Masayuki Terakado; 寺門　誠之; Kazuyuki Obara; 小原　和幸; Mitsuru Yoneyama; 米山　充; Takahito Ishii; 石井　隆仁; Keiko Yasui; 安井　圭子
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2002-06-06
Filing date: 2002-06-06
Publication date: 2004-01-15
Anticipated expiration: 2022-06-06
Also published as: JP3979188B2

Abstract

【課題】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、人体が快適と感じられるような低温度域で急速かつ安定に飽和する発熱体を、高温環境に強い高融点の結晶性樹脂を使用して形成する。
【解決手段】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６と第２の面状発熱体７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７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。
【選択図】　図１A heating element which rapidly rises in temperature by applying a positive resistance temperature characteristic and rapidly and stably saturates in a low temperature range in which a human body is felt comfortable can be converted into a high melting point crystal which is strong in a high temperature environment. It is formed using a conductive resin.
At the start of energization, a first sheet-like resistor and a second sheet-like heating element electrically connected in series generate heat with high electric power over a wide area, and a positive resistance temperature characteristic at saturation. Only the second planar heating element 7 having the above structure generates heat. At the start of energization, heat of high power can be obtained over a large area of the heating element, and therefore, it is particularly excellent in quick heat. In addition, it is possible to saturate in a low temperature range where the user feels comfortable even though the temperature rises rapidly with high power. In addition, this heating element has a low saturation temperature, but can maintain the stability of resistance characteristics even when exposed to a high environmental temperature.
[Selection diagram] Fig. 1

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、複数に分割された抵抗要素を発熱体面に展開してなる第１の面状抵抗体と、複数に分割された抵抗要素を前記発熱体面に展開してなる第２の面状抵抗体と、前記発熱体面に形成される少なくとも一対の電極からなり、前記第１の面状抵抗体の各抵抗要素は、前記第２の面状抵抗体の何れかの抵抗要素を直列に経由して前記一対の電極に接続され、前記一対の電極は電源に接続可能であり、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の抵抗値が拮抗状態にあるために共に発熱し、高電力の面状熱源を形成するとともに、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するために、前記第２の面状抵抗体の各抵抗要素が主に発熱し、正抵抗温度特性による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、複数に分割された抵抗要素を発熱体面に展開してなる第１の面状抵抗体と、複数に分割された抵抗要素を前記発熱体面に展開してなる第２の面状抵抗体と、前記発熱体面に形成される少なくとも一対の電極からなり、前記第１の面状抵抗体の各抵抗要素は、前記第２の面状抵抗体の何れかの抵抗要素を直列に経由して前記一対の電極に接続され、前記一対の電極は電源に接続可能であり、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の抵抗値が低抵抗の拮抗状態にあるために共に発熱し、高電力の面状熱源を形成するとともに、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するために、前記第２の面状抵抗体の各抵抗要素が主に発熱し、正抵抗温度特性による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の面状抵抗体の抵抗要素の展開面積を第２の面状抵抗体の抵抗要素の展開面積よりも大きくしたものである。第１の面状抵抗体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。一方、第２の面状抵抗体は飽和時の発熱面積を制限し、飽和時の電力を抑制する。第１の面状抵抗体の抵抗要素の展開面積を第２の面状抵抗体の抵抗要素の展開面積よりも大きくすることにより、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。そして、飽和時には第１の面状抵抗体が実質的に発熱しなくなることによって、第２の面状抵抗体による発熱面積を通電開始時の２分の１以下に縮小することができる。
【００１３】
請求項３に記載の発明は、第１の面状抵抗体の抵抗要素が発熱体面に対して面状あるいは帯状に展開されるのに対して、第２の面状抵抗体の抵抗要素は相対的に点状あるいは線状に展開されるものである。第１の面状抵抗体の抵抗要素を発熱体面に対して面状あるいは帯状に展開することによって、通電開始直後の発熱面積を確保し、高電力を発熱体の全面で発生させ、十分な速熱性を付与することができる。一方、第２の面状抵抗体の抵抗要素を発熱体面に対して点状あるいは線状に展開することによって、飽和時の発熱面積を制限し、飽和時の電力を抑制することができる。さらに、第２の面状抵抗体の各抵抗要素をできる限り１次元的な形状とすることによって、各抵抗要素からの放熱熱抵抗を高めることができる。この結果、被加熱体へ伝達される熱量が局部的に集中しなくなるので、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、支障のない発熱分布を得ることができる。
【００１４】
請求項４に記載の発明は、通電開始時点において、第１の面状抵抗体の抵抗要素の抵抗値を第２の面状抵抗体の抵抗要素の抵抗値よりも大きくしたものである。双方の抵抗要素は直列接続されているために電力は抵抗値に比例する。通電開始時点において、第１の面状抵抗体の抵抗要素の抵抗値を第２の面状抵抗体の抵抗要素の抵抗値よりも大きくすることにより、第１の面状抵抗体は第２の面状抵抗体よりも大きい電力を発熱体の全面で発生させることができ、十分な速熱性を発揮することができる。また、第２の面状抵抗体の電力は第１の面状抵抗体よりも小さくなり、第２の面状抵抗体の温度上昇が緩やかになり、抵抗値の増大が遅れ、発熱体全体の抵抗値上昇も遅くなる。結果的に、高電力を持続する時間が長くなるために、投入電力の積算値が増大し、速熱性が大幅に改善される。
【００１５】
請求項５に記載の発明は、通電開始時点において、第１の面状抵抗体の抵抗要素の電力密度を第２の面状抵抗体の抵抗要素の電力密度よりも大きくしたものである。発熱体の速熱性は電力密度が決定づける。通電開始時点において、第１の面状抵抗体の抵抗要素の電力密度を第２の面状抵抗体の抵抗要素の電力密度よりも大きくすることにより、第１の面状抵抗体の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ことができる。
【００１６】
請求項６に記載の発明は、第１の面状抵抗体及び第２の面状抵抗体が共に正抵抗温度特性を示し、温度上昇に伴って抵抗値が増大するが、飽和温度に至るまでの温度域において、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。
【００１７】
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。
【００１８】
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。
【００１９】
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。
【００２０】
請求項７に記載の発明は、少なくとも通電開始近傍の温度において、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となるようにしたものである。通電開始時点で、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るために、均一な昇温特性が得られる。また、通電開始時点で第１の面状抵抗体よりも第２の面状抵抗体の電力密度が明らかに大きい場合、発熱体全体の温度が上昇する前に第２の面状抵抗体の温度が上昇し、早期に低電力で飽和するために速熱性が発揮される温度域が低温域に限定される。
【００２１】
また、その逆の場合、第１の面状抵抗体の温度が上昇しているのに第２の面状抵抗体の温度上昇が緩やかになり、電力が低下する時間が遅れるために、一旦、高温になってから飽和する。通電開始時の両者の電力密度を略同一にすれば、昇温特性と速熱性の一つの調和点が得られる。
【００２２】
請求項８に記載の発明は、飽和温度に至るまでの温度域において、前記第１の面状抵抗体の抵抗値の増大率が低下するものである。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。
【００２３】
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は増大するが、第１の面状抵抗体の抵抗値は増大率が低下するために、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。
【００２４】
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。
【００２５】
請求項９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。
【００２６】
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。
【００２７】
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。
【００２８】
請求項１０に記載の発明は、飽和温度近傍以上の温度域において、第１の面状抵抗体が実質的に有効な正抵抗温度特性を示すようにしたものである。飽和までは請求項９の発明の実施の形態と同様の作用と効果を示すものであるが、何らかの想定されない原因によって発熱温度が飽和温度を大きく越えた場合、第１の面状抵抗体が実質的に有効な正抵抗温度特性を示し、抵抗値が急激に増大する。第１の面状抵抗体の抵抗値が増大すれば、第２の面状抵抗体と共に該当する直列回路の抵抗値を大きく増大させることができるので、危険を未然に防止できる。
【００２９】
請求項１１に記載の発明は、発熱体面に形成される一対の電極が、共に主電極と前記主電極から分岐された複数の枝電極から構成され、前記一対の枝電極の部分を交互に対向させることによって対となる電極を複数形成し、前記一対の各枝電極の間に、第１の面状抵抗体と第２の面状抵抗体の各抵抗要素を形成してなるものである。主電極は電圧損失を極力抑制しつつ枝電極に給電するものであり、主電極から給電を受けた一対の枝電極間に第１の面状抵抗体と第２の面状抵抗体が形成される。この電極構成は、発熱体の全面に多数の対となる電極を合理的に形成することが可能であり、この多数の対となる枝電極間に、第１の面状抵抗体と第２の面状抵抗体の抵抗要素からなる直列回路が形成される。対となる枝電極は多数存在するので、第１の面状抵抗体と第２の面状抵抗体の抵抗要素が直列に接続されるとともに複数に分割された抵抗要素が多数形成される。
【００３０】
また、対となる枝電極間内で抵抗体を分割することにより、さらに細分割することができる。このようにして多数に分割された抵抗要素を発熱体全体に均等に分散することが容易にできる。
【００３１】
請求項１２に記載の発明は、電源に接続することのできる一対の電極とは別に、電源に接続されない中間電極を発熱体面に形成し、前記中間電極の介在によって、第１の面状抵抗体と第２の面状抵抗体の各抵抗要素が接続されて形成されてなるものである。電源に接続されない中間電極を介在することによって、第１の面状抵抗体と第２の面状抵抗体の電気的結合が安定化する作用があり、結合点の電位も安定化する。特に、第１の面状抵抗体と第２の面状抵抗体の幅が異なる場合にも電気的結合を可能にする。
【００３２】
請求項１３に記載の発明は、第１の面状抵抗体及び第２の面状抵抗体が電圧印加直交方向に所定の間隔で非発熱部を形成することによって分割されて電気的に並列に接続されてなるものである。抵抗体の電圧印加直交方向に所定の間隔で非発熱部を形成することによって、抵抗体を電気的に独立な複数の抵抗要素に分割することができる。抵抗体を電気的に独立な複数の抵抗要素に分割することによって、抵抗要素を均等に分散して配置することが可能となる。特に、多数の抵抗要素を発熱体全体に均等に分割することによって発熱体全体としての温度の平準化及び平均化がはかれる。
【００３３】
請求項１４に記載の発明は、第１の面状抵抗体及び第２の面状抵抗体の少なくとも一方が電圧印加直交方向に所定の間隔で非発熱部を形成するとともに、中間電極が前記非発熱部に対応して分割されてなるものである。第１の面状抵抗体及び第２の面状抵抗体を電圧印加直交方向に所定の間隔で非発熱部を形成することによって、電気的に独立な複数の抵抗要素に分割することができる。合わせて、第１の面状抵抗体と第２の面状抵抗体の間に介在する中間電極を分割することによって、抵抗体を電気的に独立な複数の抵抗要素に分割することが可能になる。また、分割された第１の面状抵抗体及び第２の面状抵抗体からなる直列回路が独立の回路として形成される。特に、直列回路が独立することにより、発熱体の各部の発熱や放熱状態に応じて、独立に電力が制御されるため、飽和時の温度分布を均一に保つことができる。
【００３４】
請求項１５に記載の発明は、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ものである。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により、第１の面状抵抗体に比較して、第２の面状抵抗体の形状を線状に近づけ、展開面積をより小さくする。この結果、飽和時に主体的に発熱する第２の面状抵抗体の電力をより小さくすることができる。また、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が、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力を配分することが可能になる。
【００３５】
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状態では、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。またこの寸法関係を裏返せば、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大きくすることであり、第２の面状抵抗体が形成される間隔が広げられることになり、第２の面状抵抗体が主体的に発熱する飽和時においては、その間隔に形成される第１の面状抵抗体の温度を低下させることができる。この結果、飽和時の発熱体の平均発熱温度を下げることができる。
【００３６】
請求項１６に記載の発明は、第１の面状抵抗体の各抵抗要素の電圧印加直交方向寸法と、第２の面状抵抗体の各抵抗要素の電圧印加直交方向寸法を異なる寸法とするものである。第１の面状抵抗体及び第２の面状抵抗体の面積抵抗値は、特に、正抵抗温度特性が必要な場合等、材料組成によって制約があり、最適な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。この電圧印加方向寸法と電圧が決まれば、電力密度は面積抵抗値によって決定されることになり、第１の面状抵抗体と第２の面状抵抗体の微妙な調整ができなくなる。直列回路の場合には、電圧印加直交方向寸法が同一ならば、電圧印加方向寸法を調整しても電力密度は面積抵抗値を変えない限り変わらない。
【００３７】
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。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。
【００３８】
【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。
【００３９】
（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。
【００４０】
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。
【００４１】
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。
【００４２】
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。
【００４３】
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。
【００４４】
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。
【００４５】
（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。
【００４６】
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。
【００４７】
（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。
【００４８】
（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。
【００４９】
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。
【００５０】
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。
【００５１】
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。
【００５２】
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。
【００５３】
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。
【００５４】
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。
【００５５】
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。
【００５６】
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。
【００５７】
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。
【００５８】
（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。
【００５９】
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。
【００６０】
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。
【００６１】
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。
【００６２】
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。
【００６３】
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。
【００６４】
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。
【００６５】
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。
【００６６】
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。
【００６７】
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。
【００６８】
【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]
TECHNICAL FIELD 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 a heating element of this type, for example, as described in JP-A-53-143047 and FIG. 5, a heat-conductive substrate on which a heat-conductive plate 18 is mounted via an insulating film 17 has a positive resistance. The heating element material 19 and the electrode 20 having a self-temperature control function based on temperature characteristics are applied and dried, and the temperature is rapidly increased with a large inrush power, and a predetermined saturation temperature is maintained to form a heating element having a uniform temperature distribution. Things.
[0003]
[Problems to be solved by the invention]
However, when using the conventional positive resistance temperature characteristic heating element, for example, to form a fast-heating, human body contact type heating product such as a heating mat, the surface temperature at which 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 generation temperature of the heating element at around 50 ° C. is sufficient. Therefore, when the power is turned on, high power is generated with a low resistance, but the power rapidly decreases due to a sharp increase in the resistance value near 50 ° C., and a positive resistance that can maintain 50 ° C. by self-temperature controllability. A heating element material exhibiting temperature characteristics is required. For this reason, a low melting point crystalline resin is used as the heating element material, and the conductive material dispersed therein loses conductivity due to a sudden increase in specific volume just below the melting point of the crystalline resin. It is necessary to adjust the temperature range in which the resistance value rapidly increases to around 50 ° C. described above. Although ordinary crystalline resins can increase the specific volume even below the melting point, the rate of increase sharply increases as the temperature approaches the melting point, so sufficient positive resistance temperature characteristics can be obtained in the temperature range away from the melting point. Absent. In the case of the above-mentioned heating application of the human body contact type, 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 having excellent controllability can be obtained. When the melting point of the crystalline resin is higher than this, the ratio of the resistance value near 50 ° C. to the resistance value at the time of turning on the power decreases, and when the resistance value near 50 ° C. is fixed, the resistance value at the time of turning on the power increases. , Quick heat is impaired. Further, if the resistance value at power-on is fixed, the self-control temperature becomes higher than 50 ° C. When the melting point of the crystalline resin exceeds 80 ° C., it is extremely difficult to achieve both rapid heating and self-controllability at around 50 ° C. From the situation described above, it is considered that the melting point of the crystalline resin is desirably as low as possible in the above applications.
[0004]
On the other hand, when a crystalline resin having a low melting point is specifically selected, from the viewpoint of crystallinity, the crystallinity decreases as the melting point decreases, and sufficient positive resistance temperature characteristics tend not to be obtained. If a material having a melting point on the order of 60 ° C. is selected from among the most useful olefin-based resins as the heating element material at present, an ethylene-vinyl acetate polymer having a high vinyl acetate content will be selected. The crystallinity of the ethylene vinyl acetate polymer tends to decrease in proportion to the content of vinyl acetate, and the ethylene vinyl acetate polymer having a melting point on the order of 60 ° C. often cannot provide sufficient positive resistance temperature characteristics. Therefore, from the viewpoint of crystallinity, it is considered that a grade having a higher melting point is more desirable.
[0005]
In addition, in consideration of environmental conditions to which such heating products are exposed, in the case of self-heating due to energization, there is no particular problem because the upper limit temperature is regulated by self-temperature controllability by the positive resistance temperature characteristic. Considering combined use with equipment having a high-temperature heat source, environments exposed to direct sunlight, storage and transport conditions in warehouses, and in-vehicle applications, the temperature of the product is at least 60 ° C or higher, and 80 ° C or higher depending on the application. It is required to withstand performance. If a heating element material containing a crystalline resin having a melting point around 60 ° C. as a main component is subjected to such conditions, undesired results such as deformation of the heating element, a change in resistance characteristics, and a shortened life are usually produced. For this reason, in the prior art, the surface temperature is around 40 ° C. by preventing the heat conduction or heat transfer by further increasing the thickness of the surface material of the product or reducing the mounting area of the heating element. However, a method in which the temperature of the heating element 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 the stability of the temperature due to rapid heating or self-temperature control. If the configuration prevents heat conduction, the surface temperature can be achieved. However, there is a disadvantage that the rate of temperature rise of the surface temperature of the product is greatly reduced by hindering the heat conduction. In the configuration in which the average surface temperature is reduced by reducing the mounting area of the heating element, an appropriate surface temperature at the time of saturation can be achieved, but the thermal resistance between the heating element and the product surface is still increased, There was a drawback that the rate of temperature rise of the product was greatly reduced.
[0006]
An object of the present invention is to solve the above-mentioned conventional problems, and to provide a heating element that rapidly rises in temperature and rapidly and stably saturates at a predetermined surface temperature by applying a positive resistance temperature characteristic. In addition, it provides technical means that can use a crystalline resin with high crystallinity and high melting point that is resistant to high temperature environment, especially when forming a positive resistance temperature characteristic heating element having a surface temperature in a low temperature range. Is extremely useful.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned conventional problems, a heating element of the present invention includes a first planar resistor formed by developing a plurality of divided resistance elements on a heating element surface, and a plurality of divided resistance elements. It comprises a second planar resistor developed on a heating element surface, and at least a pair of electrodes formed on the heating element surface, and each resistance element of the first planar resistor is the second planar resistor. One of the resistance elements of the resistor is connected in series to the pair of electrodes, the pair of electrodes is connectable to a power supply, and the first planar resistor and the second Since the resistance values of the respective resistance elements of the sheet resistance element are in an antagonistic state, they generate heat together, form a high-power sheet heat source, and at least increase the resistance of the second sheet resistance element with a rise in temperature. The value of the second planar resistor is larger than that of each resistance element of the first planar resistor. In order to increase the resistance of each resistance element of the body, each resistance element of the second planar resistor mainly generates heat, and is a constant-temperature heat source based on the positive resistance temperature characteristic, and at the same time becomes a scattered heat source and has a low power It is intended to be saturated.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the first aspect of the present invention, a first planar resistor formed by developing a plurality of divided resistance elements on a heating element surface, and a first planar resistor formed by developing a plurality of divided resistance elements on the heating element surface. And at least one pair of electrodes formed on the surface of the heating element, wherein each resistance element of the first sheet resistance is any one of the resistance elements of the second sheet resistance. Are connected in series to the pair of electrodes, and the pair of electrodes can be connected to a power supply. At the time of starting the energization, each resistance of the first planar resistor and the second planar resistor is Since the resistance values of the elements are in an antagonistic state of low resistance, they generate heat together and form a high-power planar heat source, and at least the resistance value of the second planar resistor increases with increasing temperature, Each of the resistance elements of the second planar resistor is larger than each of the resistance elements of the first planar resistor. In order to make the resistance, each of the resistance elements of the second planar resistor mainly generates heat, and becomes a constant-temperature heat source based on the positive resistance temperature characteristic, and at the same time, becomes a scattered heat source and saturates with low power. Body.
[0009]
At the start of energization, the resistance values of the respective resistance elements of the first and second planar resistors are both low, and the two resistance values are relatively close to each other. For this reason, in the series circuit composed of the respective resistance elements of the first and second sheet resistors, although there is a difference in power due to the distribution of the resistance values, all the resistance elements generate high power and generate heat. I do. When all the resistance elements generate heat, a high-power planar heating element is formed, thereby enabling rapid heating by wide-area heat generation. As the temperature rises, the resistance value of the second planar resistor increases. Therefore, in the series circuit including the resistance elements of the first planar resistor and the second planar resistor, the second The resistance value of each resistance element of the sheet resistor is significantly increased, and the power distribution of each resistance element of the second sheet resistor is increased.
[0010]
At this time, the total power decreases because the resistance value of the series circuit increases, and the power of the first planar resistor whose power distribution decreases decreases greatly, but the power of the second planar resistor decreases. Does not drop significantly, 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, the second planar resistor in the series circuit including the respective resistive elements of the first planar resistor and the second planar resistor has a second planar resistance. 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 planar resistor, and the second planar resistor has a sudden increase in resistance and power due to a rise in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0011]
As described above, at the saturation temperature, substantially only the second planar resistor generates heat, and a heating element in which a constant-temperature heat source is scattered due to self-temperature controlled heat generation is formed. In this saturated state, even if the temperature of the heat-generating portion is slightly increased, the heat-generating area is limited, so that the average temperature is rather lowered, and the power can be further reduced. 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. Further, since the respective resistance elements of the second planar resistor are divided into a plurality of parts and are scattered, the uniformity of the temperature does not deteriorate as a whole of the heating element, and the temperature distribution does not hinder practical use. Can be formed.
[0012]
According to a second aspect of the present invention, the development area of the resistance element of the first planar resistor is larger than the development area of the resistance element of the second planar resistor. The first planar resistor expands the heat generation area immediately after the start of energization, generates high power over the entire surface of the heat generator, and exhibits sufficient rapid heat resistance. On the other hand, the second planar resistor limits the heat generation area at the time of saturation and suppresses the power at the time of saturation. By making the expansion area of the resistance element of the first sheet resistor larger than the expansion area of the resistance element of the second sheet resistor, the first sheet resistor sufficiently exerts the function of generating heat over a wide area. can do. Then, when the first planar resistor does not substantially generate heat at the time of saturation, the heating area of the second planar resistor can be reduced to half or less of that at the start of energization.
[0013]
According to the third aspect of the present invention, the resistance element of the first planar resistor is developed in a plane or a band shape with respect to the heating element surface, whereas the resistance element of the second planar resistor is relatively developed. It is developed in a point-like or linear manner. By developing the resistance element of the first planar resistor in a planar or strip shape with respect to the heating element surface, a heating area immediately after the start of energization is secured, high power is generated over the entire heating element, and sufficient speed is achieved. Thermal properties can be imparted. On the other hand, by developing the resistance element of the second planar resistor in a dotted or linear manner with respect to the heating element surface, the heating area at the time of saturation can be limited, and the power at the time of saturation can be suppressed. Furthermore, by making each resistance element of the second planar resistor as one-dimensional as possible, the heat radiation resistance from each resistance element can be increased. As a result, the amount of heat transferred to the object to be heated is not concentrated locally, so that the uniformity of temperature does not deteriorate for the entire heating element, and a heat generation distribution that does not hinder practical use can be obtained.
[0014]
According to a fourth aspect of the present invention, the resistance value of the resistance element of the first planar resistor is made larger than the resistance value of the resistance element of the second planar resistor at the start of energization. Since both resistance elements are connected in series, the power is proportional to the resistance value. At the start of energization, the resistance value of the resistance element of the first planar resistor is set to be larger than the resistance value of the resistance element of the second planar resistor, so that the first planar resistor becomes the second planar resistor. Electric power greater than that of the planar resistor can be generated on the entire surface of the heating element, and sufficient rapid heat can be exhibited. Further, the power of the second sheet resistor becomes smaller than that of the first sheet resistor, the temperature rise of the second sheet resistor becomes slow, the increase of the resistance value is delayed, and the entire heating element becomes The resistance value rises slowly. As a result, since the time during which the high power is maintained becomes longer, the integrated value of the input power increases, and the rapid heat property is greatly improved.
[0015]
According to a fifth aspect of the present invention, at the start of energization, the power density of the resistance element of the first planar resistor is made higher than the power density of the resistance element of the second planar resistor. The power density determines the rapid heating of the heating element. At the start of energization, the power density of the resistance element of the first sheet resistor is set to be higher than the power density of the resistance element of the second sheet resistor, thereby increasing the high power of the first sheet resistor. It is generated on the entire surface of the heating element, and can exhibit sufficient rapid heat resistance.
[0016]
According to a sixth aspect of the present invention, the first planar resistor and the second planar resistor both exhibit positive resistance-temperature characteristics, and the resistance value increases as the temperature rises. In the temperature range described above, the rate of increase in the resistance value of the second sheet resistor exceeds the rate of increase in the resistance value of the first sheet resistor, and Also, each of the resistance elements of the second planar resistor has a high resistance. At the start of energization, the resistance values of the respective resistance elements of the first and second planar resistors are both low, and the two resistance values are relatively close to each other.
[0017]
For this reason, in the series circuit composed of the respective resistive elements of the first planar resistive element and the second planar resistive element, all the resistive elements generate heat with high power. As the temperature rises, both the first sheet resistance and the second sheet resistance increase in resistance value, so that the power decreases, but the two resistance values are relatively close to each other. , And the state in which all the resistance elements generate heat continues at this point. As the temperature further rises, the rate of increase in the resistance of the second sheet resistor exceeds the rate of increase in the resistance of the first sheet resistor, and the resistance of each of the resistance elements of the first sheet resistor increases. Also, each of the resistance elements of the second planar resistor clearly has a higher resistance. At this time, the power distribution of each resistance element of the second planar resistor increases, and the temperature of that portion continues to rise.
[0018]
As a result, the resistance value of the second planar resistor further increases, so that the second planar resistor is connected in the series circuit including the first and second planar resistors. 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 planar resistor, and the second planar resistor has a sudden increase in resistance and power due to a rise in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0019]
As described above, at the saturation temperature, substantially only the second planar resistor generates heat, and a heating element in which a constant-temperature heat source is scattered due to self-temperature controlled heat generation is formed. In this saturated state, even if the temperature of the heat-generating portion is slightly increased, the heat-generating area is limited, so that the average temperature is rather lowered, and the power can be further reduced. 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. Further, since the respective resistance elements of the second planar resistor are divided into a plurality of parts and are scattered, the uniformity of the temperature does not deteriorate as a whole of the heating element, and the temperature distribution does not hinder practical use. Can be formed.
[0020]
The power density of the resistive element of the first planar resistor and the power density of the resistive element of the second planar resistor are substantially the same at least at a temperature near the start of energization. It was made. At the start of energization, the power density of the resistance element of the first sheet resistor and the power density of the resistance element of the second sheet resistor are substantially the same, so that a uniform temperature rise characteristic can be obtained. If the power density of the second planar resistor is clearly higher than that of the first planar resistor at the start of energization, the temperature of the second planar resistor is increased before the temperature of the entire heating element rises. Rises, and the temperature range in which rapid heat is exhibited because of early saturation with low power is limited to the low temperature range.
[0021]
In the opposite case, the temperature of the first sheet resistor is rising, but the temperature of the second sheet resistor is gradually increased, and the time for reducing the electric power is delayed. Saturates at high temperatures. If the power densities of the two at the start of energization are made substantially the same, one harmony point of the temperature rising characteristic and the rapid thermal characteristic can be obtained.
[0022]
In the invention according to claim 8, the rate of increase in the resistance value of the first planar resistor decreases in a temperature range up to the saturation temperature. At the start of energization, the resistance values of the respective resistance elements of the first and second planar resistors are both low, and the two resistance values are relatively close to each other. For this reason, in the series circuit composed of the respective resistive elements of the first planar resistive element and the second planar resistive element, all the resistive elements generate heat with high power. As the temperature rises, both the first sheet resistance and the second sheet resistance increase in resistance value, so that the power decreases, but the two resistance values are relatively close to each other. , The resistance values of the two resistance elements are relatively close to each other, and the state in which all the resistance elements generate heat continues at this point.
[0023]
As the temperature further increases, the resistance of the second sheet resistor increases, but the rate of increase of the resistance of the first sheet resistor decreases. Each of the resistance elements of the second planar resistor has a clearly higher resistance than each of the resistance elements. At this point, the power distribution of each resistance element of the second planar resistor increases, and the temperature of that portion further increases. As a result, the resistance value of the second planar resistor further increases, so that the second planar resistor is connected in the series circuit including the first and second planar resistors. 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 planar resistor, and the second planar resistor has a sudden increase in resistance and power due to a rise in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0024]
As described above, at the saturation temperature, substantially only the second planar resistor generates heat, and a heating element in which a constant-temperature heat source is scattered due to self-temperature controlled heat generation is formed. In this saturated state, even if the temperature of the heat-generating portion is slightly increased, the heat-generating area is limited, so that the average temperature is rather lowered, and the power can be further reduced. 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. Further, since the respective resistance elements of the second planar resistor are divided into a plurality of parts and are scattered, the uniformity of the temperature does not deteriorate as a whole of the heating element, and the temperature distribution does not hinder practical use. Can be formed.
[0025]
According to a ninth aspect of the present invention, the first planar resistor does not exhibit a substantially effective positive resistance temperature characteristic in a temperature range up to a saturation temperature, and the second planar resistor is substantially effective. It shows a good positive resistance temperature characteristic. At the start of energization, the resistance values of the respective resistance elements of the first and second planar resistors are both low, and the two resistance values are relatively close to each other. For this reason, in the series circuit composed of the respective resistive elements of the first planar resistive element and the second planar resistive element, all the resistive elements generate heat with high power. As the temperature rises, the resistance of the first sheet resistor does not change significantly, but only the resistance of the second sheet resistor increases, so that each resistance element of the first sheet resistor is increased. The resistance of each resistance element of the second planar resistor is clearly increased.
[0026]
At this point, the power distribution of each resistance element of the second planar resistor increases, and the temperature of that portion further increases. As a result, the resistance value of the second planar resistor further increases, so that the second planar resistor is connected in the series circuit including the first and second planar resistors. 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 planar resistor, and the second planar resistor has a sudden increase in resistance and power due to a rise in temperature. The saturation temperature is reached with a relatively small temperature rise.
[0027]
As described above, at the saturation temperature, substantially only the second planar resistor generates heat, and a heating element in which a constant-temperature heat source is scattered due to self-temperature controlled heat generation is formed. In this saturated state, even if the temperature of the heat-generating portion is slightly increased, the heat-generating area is limited, so that the average temperature is rather lowered, and the power can be further reduced. 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. Further, since the respective resistance elements of the second planar resistor are divided into a plurality of parts and are scattered, the uniformity of the temperature does not deteriorate as a whole of the heating element, and the temperature distribution does not hinder practical use. Can be formed.
[0028]
According to a tenth aspect of the present invention, the first planar resistor has a substantially effective positive resistance temperature characteristic in a temperature range near the saturation temperature or higher. Until the saturation, the same operation and effect as those of the embodiment of the ninth embodiment are exhibited. However, if the heat generation temperature greatly exceeds the saturation temperature due to some unexpected reason, the first planar resistor is substantially not changed. It shows an effective positive resistance temperature characteristic, and the resistance value sharply increases. If the resistance value of the first planar resistor increases, the resistance value of the series circuit corresponding to the second planar resistor can be greatly increased, so that danger can be prevented beforehand.
[0029]
According to an eleventh aspect of the present invention, the pair of electrodes formed on the surface of the heating element each include a main electrode and a plurality of branch electrodes branched from the main electrode, and the pair of branch electrodes alternately face each other. In this way, a plurality of pairs of electrodes are formed, and each resistance element of a first planar resistor and a second planar resistor is formed between the pair of branch electrodes. The main electrode supplies power to the branch electrodes while minimizing voltage loss, and a first planar resistor and a second planar resistor are formed between a pair of branch electrodes supplied from the main electrode. You. With this electrode configuration, a large number of pairs of electrodes can be rationally formed on the entire surface of the heating element, and the first planar resistor and the second pair of electrodes are provided between the multiple pairs of branch electrodes. A series circuit composed of the resistance elements of the sheet resistor is formed. Since there are many pairs of branch electrodes, the resistance elements of the first sheet resistance and the second sheet resistance are connected in series and a large number of divided resistance elements are formed.
[0030]
Further, the resistor can be further subdivided by dividing the resistor between the pair of branch electrodes. In this way, the resistance elements divided into a large number can be easily distributed evenly over the entire heating element.
[0031]
According to a twelfth aspect of the present invention, in addition to a pair of electrodes that can be connected to a power supply, an intermediate electrode that is not connected to a power supply is formed on the surface of the heating element, and the first planar resistor is formed by the intermediate electrode. And the respective resistance elements of the second planar resistor are connected to each other. The interposition of the intermediate electrode not connected to the power supply has the effect of stabilizing the electrical coupling between the first planar resistor and the second planar resistor, and also stabilizes the potential at the coupling point. In particular, even when the width of the first planar resistor and the width of the second planar resistor are different, electrical coupling is enabled.
[0032]
According to a thirteenth aspect of the present invention, the first planar resistor and the second planar resistor are divided by forming a non-heat generating portion at a predetermined interval in a direction orthogonal to the voltage application, and are electrically connected in parallel. They are connected. By forming the non-heat generating portions at predetermined intervals in the voltage application orthogonal direction of the resistor, the resistor can be divided into a plurality of electrically independent resistance elements. By dividing the resistor into a plurality of electrically independent resistor elements, the resistor elements can be evenly distributed and arranged. In particular, by equally dividing a number of resistance elements into the entire heating element, the temperature of the entire heating element can be equalized and averaged.
[0033]
According to a fourteenth aspect of the present invention, at least one of the first planar resistor and the second planar resistor forms a non-heating portion at a predetermined interval in a direction perpendicular to the voltage application, and the intermediate electrode has the non-heat generating portion. It is divided according to the heat generating part. By forming the non-heat-generating portions at predetermined intervals in the direction perpendicular to the voltage application, the first planar resistor and the second planar resistor can be divided into a plurality of electrically independent resistance elements. In addition, by dividing the intermediate electrode interposed between the first planar resistor and the second planar resistor, it is possible to divide the resistor into a plurality of electrically independent resistance elements. Become. Further, a series circuit composed of the divided first and second sheet resistors is formed as an independent circuit. In particular, since the series circuit is independent, the power is independently controlled according to the heat generation and the heat radiation state of each part of the heating element, so that the temperature distribution at the time of saturation can be kept uniform.
[0034]
According to a fifteenth aspect of the present invention, the dimension in the voltage application direction of each resistance element of the second planar resistor is smaller than the dimension in the voltage application direction of each resistance element of the first planar resistor. By making the dimension of each resistance element of the second sheet resistor in the voltage application direction smaller than the dimension of each resistance element of the first sheet resistor in the voltage application direction, it can be compared with the first sheet resistor. Then, the shape of the second planar resistor is approximated to a linear shape, and the developed area is further reduced. As a result, it is possible to further reduce the electric power of the second planar resistor that generates heat mainly at the time of saturation. Further, the second planar resistor tends to have a high sheet resistance in order to provide a large positive resistance temperature characteristic. However, when the dimension in the voltage application direction is reduced, the resistance is easily reduced, and the second planar resistor is formed in a series circuit. It is possible to distribute more power to one sheet resistor.
[0035]
Furthermore, a sheet heating element having a positive resistance temperature characteristic may cause a local heating phenomenon with voltage concentration in a state where heat diffusion is insufficient, but if the dimension in the voltage application direction is reduced, the heat diffusion becomes remarkable. Because of the improvement, such a phenomenon can be prevented. If this dimensional relationship is reversed, the dimension in the voltage application direction of each resistance element of the second planar resistor is made larger than the dimension in the voltage application direction of each resistance element of the first planar resistor. The interval at which the second planar resistor is formed is widened, and at the time of saturation when the second planar resistor mainly generates heat, the first planar resistor formed at the interval is saturated. Can be lowered. As a result, the average heating temperature of the heating element at the time of saturation can be reduced.
[0036]
According to a sixteenth aspect of the present invention, the dimension in the voltage application orthogonal direction of each resistance element of the first planar resistor is different from the dimension in the voltage application orthogonal direction of each resistance element of the second planar resistor. Things. The sheet resistance of the first and second sheet resistors is limited by the material composition, especially when positive resistance temperature characteristics are required, and an optimum value is often not obtained. . In addition, the dimensions of each resistance element in the voltage application direction cannot be freely set due to restrictions such as a heating area, voltage concentration, and a heating interval. If the dimensions in the voltage application direction and the voltage are determined, the power density is determined by the sheet resistance value, and fine adjustment of the first and second sheet resistors cannot be performed. In the case of a series circuit, if the dimensions in the voltage application orthogonal direction are the same, the power density does not change even if the dimension in the voltage application direction is adjusted, unless the area resistance value is changed.
[0037]
However, in the case of a series circuit, the power density can be adjusted by changing the dimension in the voltage application orthogonal direction. A resistor having a high sheet resistance has a large dimension in the voltage application orthogonal direction, and a resistor having a low sheet resistance has a small dimension in the voltage application orthogonal direction, whereby the power density can be made closer.
[0038]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0039]
(Example 1)
FIG. 1 is an enlarged plan view of a part of a heating element according to a first embodiment of the present invention, and FIG. 2 is a plan view showing the entire heating element. 1 and 2, reference numeral 1 denotes a substrate, which uses a polyethylene terephthalate film having a thickness of 188 μm. Reference numerals 2 and 2 ′ denote 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, 2 'are composed of main electrodes 3, 3' and branch electrodes 4, 4 'branched from the main electrodes 3, 3', and a pair of branch electrodes 4, 4 'are arranged so as to face each other alternately. 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 similarly to the electrodes 2 and 2 ′. Reference numeral 6 denotes a first planar resistor, which is formed by thick-film printing between the branch electrode 4 and the intermediate electrode 5 by using a paste made of a copolymerized polyester resin and high-structure carbon black. Reference numeral 7 denotes a second planar resistor, which is obtained by kneading a kneaded product of an ethylene vinyl acetate copolymer having a melting point of 92 ° C. and low-structure carbon black by using a rubber-based 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 planar resistor 6, the second planar resistor 7, and the intermediate electrode 5 are each divided by the non-heating portion 8 and are formed in parallel between the branch electrodes 4, 4 '. Have been.
[0040]
Each of the divided first planar resistor 6, second planar resistor 7, and intermediate electrode 5 has a width dimension, that is, a dimension in a direction perpendicular to voltage application of 30 mm, and a non-heating portion having a width of 3 mm. 8 divided. The distance between the branch electrode 4 on which the first planar resistor 6 is formed and the intermediate electrode 5, that is, the dimension in the voltage application direction is 15 mm. The distance between the branch electrode 4 'on which the second planar resistor 7 is formed and the intermediate electrode 5, that is, the dimension in the voltage application direction is 5 mm. The first planar resistor 6, the second planar resistor 7, and the intermediate electrode 5 are divided into five pairs between one pair of branch electrodes 4 and 4 ′, adjacent to each other, and formed as a pair of branch electrodes. Reference numerals 4 and 4 ′ are formed 20 in the entire heating element. The first planar resistor 6 and the second planar resistor 7 are connected in series via the intermediate electrode 5, but 100 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 6 and the second planar resistor 7 formed by division were 250Ω and 250Ω. When the sheet resistance value is calculated, they are 500Ω and 1500Ω, respectively. The resistance value of the series circuit composed of the first planar resistor 6 and the second planar resistor 7 in divided units is 500Ω, and 5Ω because 100 circuits are parallel in the entire heating element. When a voltage of 15 V DC is applied here, 45 W of power is obtained immediately after the application of the voltage. Although the first sheet resistor 6 has a substantially constant resistance value even when the temperature rises, the second sheet resistor 7 has a low-structure carbon resin in a crystalline resin having a melting point of 92 ° C. Due to the dispersion of black, the resistance is increased as the temperature rises, and the resistance is increased. The resistance value of the second planar resistor 7 in divided units is 250Ω at 20 ° C., but is 750Ω at 50 ° C. and 1750Ω at 60 ° C. Therefore, the series resistance in division units is 500Ω at 20 ° C, 1000Ω at 50 ° C, and 2000Ω at 60 ° C.
[0042]
When DC 15 V is applied when the heating element is at 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 and the second surface is The resistor 7 generates 22.5 W. At this point, 7.5 V is applied to the first sheet resistor 6 and 7.5 V 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 that the resistance value of the series circuit also increases, and the overall power decreases. However, if, for example, 15 V DC is applied when the heating element is at 50 ° C., the power at that time is 22.5 W, but the resistance value of the second planar resistor 7 is clearly high, so the first surface The electric power of the second planar resistor 7 is 16.9 W with respect to the electric power of the planar resistor 6 of 5.6 W, resulting in an imbalance in electric power. At this point, the rate of temperature rise of the first sheet resistor 6 becomes extremely slow, but since the temperature of the second sheet resistor 7 still continues to rise, the difference between the resistance values is eventually determined. Become When 15V DC is applied when the heating element is at 60 ° C., the power at that time is 11.2 W. However, since the resistance value of the second sheet resistance element 7 becomes decisively high, the first sheet resistance The power of the body 6 is 1.4 W, and the power of the second sheet resistor 7 is 9.8 W, so that the second sheet resistor 7 mainly generates heat.
[0043]
When the heating element was adapted to a room temperature of 20 ° C., and 15 V DC was applied to energize until saturation, the resistance values of the first planar resistor 6 and the second planar resistor 7 at the start of energization were reduced. Because of the proximity, both generated heat, and it was confirmed that the heating element obtained high power over a wide area and rapidly heated over the entire surface. In addition, it was confirmed that as the temperature rose, the second planar resistor 7 was in a state of mainly generating heat through the above process. The observation of the progress was performed using a radiation thermometer. Finally, the second planar resistor 7 did not saturate at 60.degree. C., but continued to rise in temperature, and finally saturated at 63.degree. The power of the heating element at that time was 7.7 W. The heat resistance and the heat radiation of the second planar resistor 7 are considered to be balanced because the rate of increase in the resistance value becomes extremely steep at 60 ° C. or higher, and the power greatly decreases even with a relatively small temperature rise.
[0044]
When the temperature distribution was confirmed in the saturated state, the temperature distribution was observed with the radiation thermometer. However, the temperature distribution was not felt even when a person sat directly, and it is considered that the heat generation was uniform in practical use. It is probable that, since the planar resistor was finely divided and scattered on the surface of the heating element, a heating element that could be regarded as uniform in practice could be formed.
[0045]
(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 was obtained by dispersing a large amount of graphite in a phenol resin. When the resistance characteristics were measured, the resistance of the first sheet resistor 6 was substantially 0, and the resistance of the second sheet resistor 6 was substantially zero. Only the resistance properties of body 7 were measured. DC15V 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 no difference was observed in the power at saturation. Also, the power decay immediately after the start of energization was extremely fast, and although the initial power was about twice that of the first embodiment, the integrated power up to the predetermined time was conversely reduced. In addition, it was found that quick heat was not felt, and temperature data required 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, time is required for heat to diffuse in the surface direction, and even if power is applied, the rapid heat property is not improved.
[0046]
In the first embodiment, at the start of energization, both the first planar resistor 6 and the second planar resistor 7 generate heat, so that the heat generation area is large and heat is diffused in the plane direction. Time is not required. This is considered to be particularly advantageous in terms of quick heat. In addition, a sheet-like resistor having a positive resistance temperature characteristic has a characteristic that the temperature rises rapidly when a large amount of power is applied, but the power decreases rapidly as much as possible.In the case of a sheet-like heat source, the area is as large as possible. If it is not developed, it will have the opposite effect in terms of quick heat. In the first embodiment, at the start of energization, the first planar 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 decrease rapidly, and It is thought to be particularly advantageous in terms of thermal properties.
[0047]
(Comparative Example 2)
As another comparative example of Example 1, a heating element including the entire surface formed of the second planar resistor was manufactured. The intermediate electrode was abolished, the distance between the branch electrodes was set to 14 mm, and the pair of branch electrodes were formed 28 in the entire heating element so that the resistance value became the same as that in Example 1. The resistance value at 20 ° C. was 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 15 V DC was applied to the heating element of this comparative example, the power at the start of energization was 45 W, which was the same as in Example 1, but the power at saturation was 13 W, which was clearly higher. 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 in 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, the rapid heat property was very excellent, and there was no clear defect except for the saturation temperature and the saturation power.
[0048]
(Comparative Example 3)
As another comparative example of Example 1, a heating element whose entire surface was formed of another planar resistor was manufactured. In Example 1, the ethylene vinyl acetate copolymer having a melting point of 92 ° C. was used for the second planar resistor, but the ethylene vinyl acetate having a melting point of 74 ° C. was obtained so that a large positive resistance temperature characteristic could be obtained at a lower temperature. A resistor was prepared using the copolymer. Because the area resistance value was increased, the distance between the branch electrodes was set to 10 mm, and the pair of branch electrodes was formed 37 by the whole 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. DC15V 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 was 45 W, which was the same, and the power at the time of saturation was 7 W, which was saturated with almost the same power. The quick heat and the temperature distribution were comparable, and the perceived temperature at saturation was also felt low. However, when the resistance was measured after exposing this heating element to an atmosphere at 80 ° C., the rate of change in resistance exceeded + 50%, and there was a tendency that the resistance further increased due to thermal cycling.
[0049]
Since this heating element has a very good positive resistance temperature characteristic, it cannot generate heat to a temperature exceeding 80 ° C by itself, but it is stably used at least up to 80 ° C in consideration of a use environment and a storage environment. Desirable. Exposing the crystalline resin to temperatures above its melting point should be avoided, especially in view of the stability of the resistance.
[0050]
As described above, as shown in the first embodiment, the heating element of the present invention generates high power over a wide area at the start of energization, and is excellent in quick heat property. In addition, saturation can be achieved in a low temperature range where the user can feel comfortable. In addition, it is possible to maintain the stability of the resistance characteristics even when exposed to an environmental temperature up to 80 ° C. which is considered under normal use conditions, and it is considered to be extremely useful.
[0051]
In the first embodiment, the resistance values at 20 ° C. in the division unit of the first planar resistor 6 and the second planar resistor 7 were 250Ω and 250Ω, which were the same. As a result of measuring the resistance at room temperature of −20 ° C., the resistance was 250 Ω and 150 Ω, respectively, and it was found that the first planar resistor 6 had a higher resistance. When electricity was supplied in an environment of −20 ° C., a power of 56 W was obtained immediately after the start of electricity supply, and a phenomenon in which the power was reduced was observed after the power in the vicinity of the power continued for a while. As described above, 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 suppressed to a considerably low level. In this state, since the temperature of the resistor exhibiting the positive resistance temperature characteristic does not readily rise, power at the time of starting the energization can be maintained for a while. It was also confirmed that this heating element exhibited extremely excellent rapid heat properties in a bodily sensation test. In addition, it was also confirmed that rapid heating can be ensured with limited power without increasing the power at the start of energization more than necessary. In the heating element of the first embodiment, the power at the start of energization is maintained for a while in a low temperature range of 0 ° C. or less where the first planar resistor 6 has a higher resistance, but it is hardly maintained at 20 ° C. found. When it is desired to ensure rapid heat resistance, it can be said that it is more preferable that the first planar resistor 6 has a higher resistance.
[0052]
In the first embodiment, the first planar resistor 6 is 450 mm. ² The second planar resistor 7 is 150 mm ² However, the first planar resistor 6 has a purpose of enlarging the heating area immediately after the start of energization, generating high power over the entire surface of the heating element, and exhibiting sufficient rapid heat resistance. Therefore, it is desirable that the area be as large as possible. On the other hand, since the purpose of the second planar resistor 7 is to limit the heat generation area at the time of saturation and to suppress the power at the time of saturation, it is desirable that the area is as small as possible. Therefore, it is desirable that at least the developed area of the first planar resistor 6 is larger than the developed area of the second planar resistor 7, and the larger the ratio, the larger the area of the first planar resistor 6 is. The function of wide-area heat generation can be sufficiently exhibited.
[0053]
In the first embodiment, the first planar resistor 6 has a rectangular shape of 30 mm × 15 mm, and the second planar resistor 7 has a narrow rectangular shape of 30 mm × 5 mm. The purpose is to secure a heat generation area immediately after the start of energization, so that a surface shape close to a square is desirable. Further, since the purpose of the second planar resistor 7 is 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 planar resistor 7 has an elongated shape, the heat dissipation heat resistance from the resistance element increases, 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 the perceived temperature, and the temperature of the heating element in which the heat sources are dispersed is substantially uniform. For this reason, it is desirable that the second planar resistor 7 has a shape that is longer than at least the first planar resistor 6, that is, a shape close to a linear shape. More preferably, it is desirable to make the shape close to a point shape.
[0054]
From such a viewpoint, it is desirable that the dimension in the voltage application direction of each resistance element of the second planar resistor is smaller than the dimension in the voltage application direction of each resistance element of the first planar resistor. Further, from another viewpoint, the second sheet-like resistor tends to have a high sheet resistance in order to provide a large positive resistance temperature characteristic. If the dimension in the voltage application direction is reduced, the resistance value can be easily reduced, and it becomes possible to distribute a larger voltage and power to the first planar resistor forming the series circuit. Furthermore, a planar heating element having a positive resistance temperature characteristic may cause a local heating phenomenon accompanied by voltage concentration when the heat diffusion is insufficient, but if the dimension in the voltage application direction is reduced, the heat diffusion is remarkable. Therefore, such a phenomenon can be prevented.
[0055]
In the first embodiment, the first planar resistor 6 is 30 mm × 15 mm, and the second planar resistor 7 is 30 mm × 5 mm, and has 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 / m ² 1500W / m ² In particular, the power density balance was not always the 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 are many restrictions on the material composition, and an optimum sheet resistance value cannot be obtained in many cases. In addition, the dimensions of each resistance element in the voltage application direction cannot be freely set due to restrictions such as a heating area, voltage concentration, and a heating interval.
[0056]
If the dimensions in the voltage application direction and the voltage are determined, the power density is determined depending on the sheet resistance. However, in the case of a series circuit, there is a characteristic that the power density can be adjusted by changing the dimension in the voltage application orthogonal direction. A resistor having a high sheet resistance has a large dimension in the voltage application orthogonal direction, and a resistor having a low sheet resistance has a small dimension in the voltage application orthogonal direction, whereby the power density can be made closer. The power density is 720 W / m by simply setting the dimensions of the first planar resistor 6 and the second planar resistor 7 of Example 1 to 20 mm × 15 mm and 30 mm × 5 mm, respectively. ² , 960W / m ² It becomes. By changing the dimension in the voltage application orthogonal direction, the power density can be adjusted as needed. When electrically connecting resistors having different dimensions in the voltage application orthogonal direction, the intermediate electrode is extremely effective.
[0057]
In the first embodiment, the first sheet-like resistor 6 is made of a resistor material that does not exhibit any positive resistance temperature characteristic. However, the resistor of the first sheet-like resistor 6 having a melting point of 130 ° C. By changing to a material using high-density polyethylene, a useful heating element can be formed. A resistor using high-density polyethylene exhibits an effective positive-resistance temperature characteristic at 80 ° C. or higher, but does not substantially exhibit a positive-resistance temperature characteristic in a temperature range of 80 ° C. or lower. Therefore, even if the first planar resistor 6 of the first embodiment is replaced with a resistor using high-density polyethylene, it is possible to obtain exactly the same heat generation characteristics as the first embodiment. However, if the heating element overheats to 80 ° C. or more for some reason, the resistance value of this resistor rapidly increases, and further overheating can be prevented.
[0058]
(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 entire heating element. 3 and 4, reference numeral 9 denotes a substrate, which uses a polyethylene terephthalate film having a thickness of 188 μm. Reference numerals 10 and 10 ′ denote 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, 10 'are composed of main electrodes 11, 11' and branch electrodes 12, 12 'branched from the main electrodes 11, 11', and a pair of branch electrodes 12, 12 'are arranged so as to face each other alternately. ing. Reference numeral 13 denotes an intermediate electrode, which is formed on the substrate 9 between the pair of branch electrodes 12, 12 'independently of the electrodes 10, 10'. The intermediate electrode 13 is formed by printing a thick conductive silver paste in the same manner as the electrodes 10 and 10 '. Reference numeral 14 denotes a first planar resistor, which is obtained by mixing a kneaded product of an ethylene-vinyl acetate copolymer having a melting point of 92 ° C. and a high-structure carbon black with a rubber-based binder and a high-boiling 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 prepared by kneading a kneaded product of an ethylene vinyl acetate copolymer having a melting point of 92 ° C. and a low-structure carbon black using a rubber-based 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 planar resistor 14, the second planar resistor 15, and the intermediate electrode 13 are each divided by the non-heating portion 16 and are formed in parallel between the branch electrodes 12 and 12 '. Have been.
[0059]
Each of the divided first planar resistor 14, second planar resistor 15, and intermediate electrode 13 has a width dimension, that is, a dimension in a direction perpendicular to voltage application of 30 mm, and a non-heating portion having a width of 3 mm. It is divided by 16. The distance between the branch electrode 12 on which the first planar resistor 14 is formed and the intermediate electrode 13, that is, the dimension in the voltage application direction 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 dimension in the voltage application direction is 3 mm. The first planar resistor 14, the second planar resistor 15, and the intermediate electrode 13 are divided into five pairs between one pair of branch electrodes 12 and 12 ′, adjacent to each other, and formed as a pair of branch electrodes. Numerals 12 and 12 'are formed of 34 in the entire heating element. The first planar resistor 14 and the second planar resistor 15 are connected in series via the intermediate electrode 13, but 170 series circuits are formed in the entire heating element, and these are electrically connected. Are connected in parallel.
[0060]
The resistance values at 20 ° C. in division units of the first planar resistor 14 and the second planar resistor 15 formed by division were 620 Ω and 230 Ω. When the sheet resistance values are calculated, they are the same at 2320Ω and 2320Ω, respectively. The material constituting 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 set to be the same as the value. The resistance value of the series circuit including the first planar resistor 14 and the second planar resistor 15 in divided units is 850Ω, and is 5Ω for the entire heating element because 170 circuits are parallel. When a voltage of 15 V DC is applied here, 45 W of power is obtained immediately after the application of the voltage. Although the first planar resistor 14 uses a crystalline resin having a melting point of 92 ° C., it exhibits a characteristic that the resistance value increases with an increase in temperature. However, since the first planar resistor 14 uses a high-structure carbon black, it has a conductive property. The path is stable, the temperature coefficient of positive resistance is generally not so large, and the temperature coefficient especially in a high temperature region tends to be conservative. The second planar resistor 15 has a characteristic in which the width of change in 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 increases. Excellent, showing large temperature coefficient of positive resistance.
[0061]
The resistance value of the first planar resistor 14 in divided units is 620Ω at 20 ° C, 990Ω at 50 ° C, and 1550Ω at 60 ° C. The resistance value of the second planar resistor 15 in divided units is 230Ω at 20 ° C., 690Ω at 50 ° C., and 1610Ω at 60 ° C. Therefore, the series resistance in division units is 850Ω at 20 ° C, 1680Ω at 50 ° C, and 3160Ω at 60 ° C.
[0062]
When 15 V DC is applied when the heating element is at 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 14 is 32.8 W and the second surface is The resistor 15 generates 12.2 W of heat. At this point, 10.9 V is applied to the first sheet resistor 14 and 4.1 V is applied to the second sheet resistor 15. Although the heat value of the first planar resistor 14 is large and it seems that the balance has been lost, the power density at this time is 800 W / m. ² And the heating capacity is balanced. As the temperature of the heating element rises, the resistance of the series circuit also increases because the resistances of the first and second sheet resistors increase, and the overall power decreases. However, for example, if DC15V is applied when the heating element is at 50 ° C., the power of the heating element at that time can be 22.8 W, but the power of the first sheet resistance 14 and the second sheet resistance 15 can be obtained. Are 13.4 W and 9.4 W, respectively. Compared with the first embodiment, it can be said that the power of the first planar resistor 14 at this point is large, and all the planar resistors are substantially in a heat generating state. The power density is 330 W / m each. ² , 610 W / m ² As a result, the balance of the temperature-raising ability has begun to collapse, and the temperature-raising ability of the second planar resistor 15 is superior. At this time, the temperature rising rate of the first planar resistor 14 becomes slow but does not stop.
[0063]
However, since the temperature rise rate of the second planar resistor 15 is higher than that of the first planar resistor 15, if the current is continued, the temperature of the second planar resistor 15 becomes higher and a clear difference in resistance value occurs. When DC15V is applied when the first and second sheet resistors 14 and 15 are at 60 ° C., the power at that time is 12.1 W, but the resistance value of the second sheet resistor 15 is Is high, the power of the first planar resistor 14 is 5.9 W, and the power of the second planar resistor 15 is almost the same as 6.2 W. The power density is 150 W / m each. ² , 410W / m ² The temperature raising capability becomes unbalanced, and if the current is continued, the temperature of the second planar resistor 15 immediately becomes higher, the resistance becomes higher, and heat is mainly generated.
[0064]
When the heating element was adjusted to a room temperature of 20 ° C., and DC 15 V was applied to energize it until saturation, the resistance values of the first planar resistor 14 and the second planar resistor 15 at the start of energization were reduced. Because of the close proximity, both generated heat, the power density was the same, and it was confirmed that a uniform heat distribution was obtained. In addition, it was confirmed that the temperature increased rapidly over the entire surface due to high power generation in a wide area. Also, as the temperature rises, it is confirmed that the rate of heat generation of the second planar resistor 15 gradually increases, and thereafter, the planar resistor 15 mainly generates heat as in the first embodiment. did. Finally, the second planar resistor 15 did not saturate at 60.degree. C., but continued to rise in temperature, and finally saturated at 62.degree. The power at that time was 7W. The second planar resistor 15 has a very sharp increase in resistance value at 60 ° C. or higher, and a large decrease in power even with a relatively small temperature increase, so that heat generation and heat radiation are balanced and saturated. Conceivable. In addition, it was confirmed that the heating element of Example 2 had a slower reduction rate of the power of the first planar resistor 14 and a larger integrated power than that of Example 1. Although the configuration of Example 2 eventually saturates at low power, the temperature of the entire heating element once rises to around 50 ° C., and in a bodily sensation experiment, a quick feeling of heat was strongly felt. When the temperature distribution was confirmed in the saturated state, the temperature distribution was observed with the radiation thermometer. However, even if a person sits directly, the temperature distribution is not felt at all, which is considered to be uniform heat generation in practical use.
[0065]
It is considered that since the sheet-like resistor was finely divided and scattered on the surface of the heating element as compared with the first embodiment, a heating element that can be regarded as uniform in practical use could be formed.
[0066]
As described above, as shown in Embodiment 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 up to a point when the temperature rises to some extent, and is particularly excellent in quick heat property. . In addition, saturation can be achieved in a low temperature range where the user can feel comfortable. In addition, it is possible to maintain the stability of the resistance characteristics even when exposed to an environmental temperature up to 80 ° C. which is considered under normal use conditions, and it is considered to be extremely useful.
[0067]
As described above, the description has been made based on the embodiments. However, the present invention is not limited to these embodiments. In particular, the following materials can be selected for the resistor material. 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 carbon black, but also the crystalline resin has crystallinity, molecular weight distribution, functional group, molecular structure, etc. Carbon black has a specific surface area, a particle diameter, a functional group, and the like. From these viewpoints, various materials can be used. In this embodiment, the crystalline resin is an ethylene-vinyl acetate copolymer and a high-density polyethylene. It is effective. Further, a crystalline resin other than an olefin resin, such as polyvinylidene fluoride, nylon, polyester, polyurethane, and silicone resin, has the same function and effect.
[0068]
【The invention's effect】
As described above, according to the present invention, at the start of energization, the first planar resistor and the second planar heater electrically connected in series have a large area and a high power at the start of energization. It generates heat, and when saturated, only the second planar heating element having the positive resistance temperature characteristic generates heat. At the start of energization, heat of high power can be obtained over a large area of the heating element, and therefore, it is particularly excellent in quick heat. In addition, it is possible to saturate in a low temperature range where the user feels comfortable even though the temperature rises rapidly with high power. In addition, this heating element has a low saturation temperature, but can maintain the stability of resistance characteristics even when exposed to a high environmental temperature.
[Brief description of the drawings]
FIG. 1 is a plan view showing the structure of a heating element according to a first embodiment of the present invention.
FIG. 2 is a plan view showing the structure of the heating element according to the first embodiment of the present invention.
FIG. 3 is a plan view showing a 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' electrodes
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 first planar resistor formed by developing a plurality of divided resistance elements on a heating element surface; a second planar resistor formed by developing a plurality of divided resistance elements on the heating element surface; It consists of at least a pair of electrodes formed on the heating element surface, and each resistance element of the first sheet resistor is connected in series with any one of the resistance elements of the second sheet resistor. The pair of electrodes can be connected to a power supply, and at the start of energization, the resistance values of the respective resistance elements of the first planar resistor and the second planar resistor are low resistance. Since both are in a state, they generate heat and form a high-power planar heat source, and at least the resistance value of the second planar resistor increases with an increase in temperature. In order for each resistance element of the second planar resistor to have a higher resistance than each resistance element, Heating element each resistive element of the second planar resistive element is mainly fever, it is the is the constant temperature heat source by positive resistance-temperature characteristics and scattered heat source simultaneously saturated at low power.

The heating element according to claim 1, wherein a development area of the resistance element of the first planar resistor is larger than a development area of the resistance element of the second planar resistor.

While the resistance element of the first sheet resistor is developed in a plane or a band with respect to the heating element surface, the resistance element of the second sheet resistor is developed relatively in a point or line. The heating element according to claim 1, wherein the heating element is formed.

The heating element according to any one of claims 1 to 3, wherein a resistance value of the resistance element of the first sheet resistor is larger than a resistance value of the resistance element of the second sheet resistor at the time of energization start. .

The heating element according to any one of claims 1 to 4, wherein the power density of the resistance element of the first planar resistor is higher than the power density of the resistance element of the second planar resistor at the start of energization. .

Both the first planar resistor and the second planar resistor exhibit positive resistance temperature characteristics, and the resistance value increases as the temperature rises. However, in the temperature range up to the saturation temperature, the second planar resistor has the second resistance. The rate of increase of the resistance value of the sheet resistor exceeds the rate of increase of the resistance value of the first sheet resistor, and the resistance of the second sheet resistor is larger than that of each resistance element of the first sheet resistor. The heating element according to claim 1, wherein each of the resistance elements has a high resistance.

7. The heating element according to claim 6, wherein the power density of the resistance element of the first sheet resistor and the power density of the resistance element of the second sheet resistor are substantially the same at least at a temperature near the start of energization.

The heating element according to claim 6, wherein a rate of increase in a resistance value of the first planar resistor decreases in a temperature range up to a saturation temperature.

The first planar resistor does not exhibit substantially effective positive resistance temperature characteristics in a temperature range up to a saturation temperature, and the second planar resistor exhibits substantially effective positive resistance temperature characteristics. The heating element according to any one of claims 1 to 5.

The heating element according to claim 9, wherein the first planar resistor exhibits substantially effective positive resistance temperature characteristics in a temperature range near or above the saturation temperature.

A pair of electrodes formed on the surface of the heating element are both composed of a main electrode and a plurality of branch electrodes branched from the main electrode, and a plurality of pairs of electrodes are formed by alternately opposing the pair of branch electrodes. 11. The device according to claim 1, wherein each of the first and second sheet resistors is formed between the pair of branch electrodes. 12. Heating element.

In addition to a pair of electrodes that can be connected to a power supply, an intermediate electrode that is not connected to a power supply is formed on the surface of the heating element, and the intermediate electrode interposes the first planar resistor and the second planar resistor. The heating element according to claim 11, wherein the heating element is formed by connecting the respective resistance elements.

12. The first planar resistor and the second planar resistor are divided by forming a non-heat generating portion at a predetermined interval in a direction orthogonal to the voltage application and are electrically connected in parallel. Heating element.

At least one of the first planar resistor and the second planar resistor forms a non-heat generating portion at a predetermined interval in a voltage application orthogonal direction, and the intermediate electrode is divided corresponding to the non-heat generating portion. The heating element according to claim 12.

The heat generation according to any one of claims 11 to 14, wherein a dimension in a voltage application direction of each resistance element of the second planar resistor is smaller than a dimension in a voltage application direction of each resistance element of the first planar resistor. body.

16. The dimension in the voltage application orthogonal direction of each resistance element of the first planar resistor and the dimension in the voltage application orthogonal direction of each resistance element of the second planar resistor are different from each other. Heating element.