JP3741810B2 - Fixing heater, fixing device, and image forming apparatus - Google Patents

Description

【００２４】
そして、抵抗発熱体１２は例えば長さ約２３０mm，厚さ約１０μｍの銀・パラジウム（Ａｇ・Ｐｄ）合金やニッケル・錫（Ｎｉ・Ｓｎ）合金，ＲｕＯ_２合金等を主体とする厚膜により形成されている。
【００２５】
抵抗発熱体１２はその一端部，または両端部に、その一部上に重ねて、銀あるいは銀・白金合金（Ａｇ・Ｐｔ），銀・パラジウム合金（Ａｇ・Ｐｄ）等の良導電体からなる膜を形成して一対の電極１３ａ，１３ｂを形成して、抵抗発熱体１２に電気的に接続している。一対の電極１３ａ，１３ｂには図示しないコネクタを介して抵抗発熱体１２に通電するようになっている。
【００２６】
そして、抵抗発熱体１２と一対の電極１３ａ，１３ｂの内端部外表面の全面を、電気絶縁性を有する保護層であるガラス質のオーバーコート層１４により被覆して、耐摩耗性や耐衝撃性などの機械的強度の向上と、硫化や酸化等からの耐蝕保護と、後述する加圧ローラ等との電気的絶縁を図っている。
【００２７】
一方、図２，図３に示すように基板１１は、その裏面（他面）１１ｂ側に、一対の配線導体１５ａ，１５ｂを並設している。これら配線導体１５ａ，１５ｂは銀（Ａｇ）、白金（Ｐｔ）、金（Ａｕ）や銀・白金（Ａｇ・Ｐｔ）合金、銀・パラジウム（Ａｇ・Ｐｄ）合金などを主体とし、膜厚が５〜３０μｍである。これら配線導体１５ａ，１５ｂの一端（図２では左端）に端子部１６ａ，１６ｂを一体に連成している。
【００２８】
そして、配線導体１５ａ，１５ｂの各先端部は基板裏面１１ｂのほぼ中央部（基板表面１１ａの抵抗発熱体１２の中央部真裏）で終端し、これら終端部上にチップ状のサーミスタ１７を跨架し、その両側端部を基板裏面１１ｂに例えばエポキシ系等の接着剤１８により固着している。
【００２９】
サーミスタ１７は抵抗発熱体１２の温度を基板１１を介して検出し、この検出温度信号を図示しない温度制御回路にフィードバックして抵抗発熱体１２に印加する電力を制御することにより抵抗発熱体１２の温度を一定に保持するものである。
【００３０】
図４に示すように、サーミスタ１７は例えばアルミナ（Ａｌ_２Ｏ_３）セラミックスからなる厚さ約２５０μｍの矩形平板状の基体１７ａの図中上面の中央部上に、マンガン、コバルト、ニッケルなどの酸化物（ＭｎＯ_２、Ｃｏ_３Ｏ_４、ＮｉＯ）を混合して形成した薄膜からなる感温部１７ｂを形成し、この感温部１７ｂの両端部に連接して例えば白金（Ｐｔ）層もしくはＡｕ層などからなる薄膜電極１７ｃ，１７ｄを形成している。感温部１７ｂの外面（図４では上面）は、この膜が大気中の温度や不純物ガスにより特性劣化を起こすのを防ぐために、例えば酸化硅素（ＳｉＯ_２）からなる層厚が５〜６０μｍのオーバーコート層１７ｅにより全面的に被覆されている。
【００３１】
なお、図４中、符号１９は導電性接着剤である。また、上記の各膜、層は基板１１やサーミスタ基体１７ａに対比して薄膜であるが、図１では説明の便宜上、誇張して厚く示しており、寸法上比例しているものでもない。
【００３２】
このチップ形状のサーミスタ１７は、温度係数が負の大きな値を有する電気抵抗体を用いたもので、温度上昇したときに抵抗値が大きく低下し、温度を抵抗値の大小に変換する熱検出素子からなるセンサである。
【００３３】
したがって、図示しないコネクタを介して一対の電極１３ａ，１３ｂ間に所定の電圧が印加されると、抵抗発熱体１２が通電されて発熱し、この発熱がガラス質のオーバーコート層１４の頂面上を図１に示すように入側ｉｎから出側ｏｕｔへ幅方向に摺動する被定着体であるコピー用紙Ｐを加熱して、トナー像をコピー用紙Ｐに定着させることができる。
【００３４】
そして、基板１１を熱膨張係数が小さく、かつ曲げ強度が高い窒化硅素により形成しているので、抵抗発熱体１２の昇温時、または抵抗発熱体１２の長さよりも幅寸法が小さい複写用紙等被定着物Ｐを加熱することにより抵抗発熱体１２を部分的に使用する場合に、基板１１に発生する部分的な温度差による熱膨張差を縮小させることができる。
【００３５】
したがって、基板１１の反りを低減ないし防止することができると共に、その反りによる曲げや割れを低減ないし防止することができる。このために、オーバーコート層１４の外面と接する加圧ローラ（図示せず）との加圧面を軸方向でほぼ均等圧にすることができるので、このオーバーコート層１４の外面と加圧ローラの外面との間を通過するコピー用紙Ｐをほぼ均等に加圧することができ、加熱ないし定着むらを低減ないし防止することができる。
【００３６】
また、基板１１の熱膨張係数が小さいので、基板１１の部分的な温度差に伴う熱膨張差による応力が、サーミスタ１７を基板裏面１１ｂに固着している樹脂製接着剤１８に作用して基板１１から剥離させるのを防止することができる。つまり、サーミスタ１７が基板１１から脱落するのを防止することができる。
【００３７】
さらに、基板１１を形成する窒化硅素は熱伝導性が低いので、この基板１１上で通電加熱される抵抗発熱体１２の温度を所定の発熱温度に素早く到達させることができ、温度の立上げを早めることができる。
【００３８】
図５は本発明の第２の実施形態に係る定着ヒータ２０の斜視図、図６は図５の正面図、図７は図６のVII−VII線断面図である。この定着ヒータ２０は基板２１をアルミナセラミックス（Ａｌ_２Ｏ_３）またはムライト（３Ａｌ_２Ｏ_３・２ＳｉＯ_２）セラミックス等の耐熱性・電気絶縁性材料により細長中空円柱状、つまり円筒に形成した点に特徴がある。
【００３９】
つまり、この円筒状基体２１は例えばその両端を開口させた円筒体よりなり、その円弧状頂部の外表面には、上記実施形態とほぼ同様に、抵抗発熱体２２を銀・パラジウム（Ａｇ・Ｐｄ）合金やニッケル・錫（ＮｉＳｎ）合金，ＲｕＯ_２合金等を主体とする厚膜により所定幅の帯状に軸方向に沿って形成固着すると共に、この抵抗発熱体２２の長手両端部上に一部を重ねて電気的に接続された膜状の一対の電極２３ａ，２３ｂを形成している。また、抵抗発熱体２２の全外表面には基体２１の外表面上にて、保護層であるガラス質のオーバーコート層２４により被覆するように形成している。
【００４０】
また、円筒状基体２１の内面には図示しないサーミスタを抵抗発熱体２２の中央部裏側にて固着する一方、一対の電極２３ａ，２３ｂには図示しないコネクタを介して抵抗発熱体２２に通電するようになっている。
【００４１】
そして、このように構成された定着ヒータ２０を図示しない複写機等の筺体の所定位置に基体２１を回転させないように固定して取り付ける。
【００４２】
したがって、図示しないコネクタを介して一対の電極２３ａ，２３ｂ間に所定の電圧が印加されると、抵抗発熱体２２が通電されて発熱し、この発熱がガラス質のオーバーコート層２４の円弧状頂面上を入側ｉｎから出側ｏｕｔへ幅方向に摺動する被定着体であるコピー用紙Ｐを加熱して、トナー像をコピー用紙Ｐに定着させることができる。
【００４３】
そして、基体２１を曲げ強度を増強させることができる円筒状に形成しているので、抵抗発熱体２２の昇温時または部分的使用に伴う温度差により基体２１に反りが発生しようとしても、その反りを低減ないし防止することができる。したがって、基体２１の反りが極端に進行した場合の基体２１の曲げや割れを低減ないし防止することができる。このために、上記平板型の定着ヒータ１０と同様に被定着物の定着むらを低減ないし防止することができる。
【００４４】
図８は本発明の第３実施形態に係る定着ヒータ２０Ａの一部切欠正面図、図９は図８の左側面図であり、この定着ヒータ２０Ａは図５〜図７で示す実施形態に係る円筒状基体２１の軸方向両端部に、一対の取付溝２５ａ，２５ｂをそれぞれ形成した点に特徴がある。
【００４５】
各取付溝２５ａ，２５ｂは例えば円筒状基体２１の両端中心を直径方向に通るように、基体２１の両端面を所定幅の溝でそれぞれ切り欠いて形成されている。
【００４６】
したがって、これら取付溝２５ａ，２５ｂに、図示しない複写機等の組込機器の筺体の取付用突部に係合させることにより、定着ヒータ２０Ａの位置決めの容易性と精度とを共に向上させることができる。
【００４７】
図１０は本発明の第４の実施形態に係る定着ヒータ２０Ｂの一部切欠正面図、図１１は図１０の左側面図であり、この定着ヒータ２０Ｂは図５〜図７で示す実施形態に係る円筒状基体２１の軸方向両端部に、一対の取付用切欠２６ａ，２６ｂをそれぞれ形成した点に特徴がある。
【００４８】
各取付用切欠２６ａ，２６ｂは例えば円筒状基体２１の両端において、その中心を直径方向に通る水平中心線よりも下方の下半部を切り欠いて形成されている。
【００４９】
したがって、これら取付用切欠２６ａ，２６ｂに、図示しない複写機等の組込機器の筺体の取付用突部に係合させることにより、定着ヒータ２０Ｂの位置決めの容易性と精度とを共に向上させることができる。
【００５０】
なお、上記取付溝２５ａ，２５ｂや取付用切欠２６ａ，２６ｂの形状はこれらに限定されるものではなく、これら定着ヒータ２０Ａ，２０Ｂを組み込もうとする組込機器の取付部の形状に係合し得る形状に形成すればよく、外方に突出する突部でもよい。
【００５１】
また、上記各実施形態では基体２１を円筒状に形成した場合について説明したが、本発明はこれに限定されるものではなく、例えば図１２で示すかまぼこ状基体２１Ａのように、少なくとも基体の一部を円弧状に形成してもよい。これによっても基体２１Ａの曲げ強度を増強することができるので、基体２１Ａの反りや割れを低減ないし防止することができる。
【００５２】
また、図１２ではかまぼこ状基体２１Ａの円弧状部２１ｂの外表面に抵抗発熱体２２を形成した場合を図示しているが、抵抗発熱体２２の形成位置はこれに限定されるものではなく、例えばかまぼこ状基体２２の平坦状底面２１ｃの外面に抵抗発熱体２２を形成してもよく、さらに、上記各基体２１，２１Ａを中実に形成してもよい。
【００５３】
図１３は本発明の第５実施形態に係る画像形成装置の一種である電子式複写機３１の実施形態の全体構成を示しており、この複写機３１は筐体３２内に、カセット３３内の複写用紙Ｐを引き込み、これに図示しない原稿の画像に対応したトナー画像を形成する画像形成部３４と、このトナー画像を複写用紙Ｐに定着させる定着装置３５とを内蔵している。
【００５４】
定着装置３５は例えば図１４に示すように構成され、回転する加圧ローラ３６に対向させて上記定着ヒータ１０，２０，２０Ａ，２０Ｂのいずれか、例えば１０を外接させて並設しており、この定着ヒータ１０を樹脂製円柱状のホルダー３７の取付溝の底部上に固着している。定着ヒータ１０の外周面には加圧ローラ３６のシリコーンゴム層３８を弾性的に圧接させている。
【００５５】
そして、定着ヒータ１０は一対の電極１３ａ，１３ｂに接触した燐青銅板等からなる弾性が付与されたコネクタを通じて通電されて抵抗発熱体１２が発熱し、この発熱は基板１１全体とオーバーコート層１４とに与熱される。したがって、このオーバーコート層１４の図示しない耐熱シートの外面と加圧ローラ３６のシリコーンゴム層３８との間で、トナー像Ｔを形成した複写用紙Ｐを定着ヒータ１０により加熱しつつ送ることにより、未定着トナー像Ｔを溶融し、複写用紙Ｐに定着させることができる。
【００５６】
そして、この定着ヒータ１０は上記したように、その基板１１を熱膨張率が小さく、かつ曲げ強度の大きい窒化硅素により形成しているので、基板１１の反りや曲げ、割れを低減ないし防止することができる。このために、定着ヒータ１０の長寿命化を図ることができると共に、この定着ヒータ１０と、加圧ローラ３６との加圧面を定着ヒータ１０のほぼ全長に亘って均圧化することができる。このために、複写用紙Ｐの加熱むら、ひいては定着むらを低減ないし防止することができる。
【００５７】
また、定着ヒータ２０，２０Ａ，２０Ｂを定着装置３５に組み込む場合にも、これらヒータ２０，２０Ａ，２０Ｂの基体２１，２１Ａが曲げ強度の大きい円筒体により形成されているので、定着ヒータ１０とほぼ同様の作用効果を奏するこくとができる。
【００５８】
【発明の効果】
以上説明したように請求項１の発明は、基体が中空円筒状であるので、曲げ強度が一般的に平板状基板等に比して大きい。したがって、この中空円筒状基体に形成された抵抗発熱体の昇温時または部分使用に伴う温度差により部分的な熱膨張差が発生し、仮に反りが発生しようとしても、中空円筒状基体にはそもそも曲がりが発生しにくい。このために、基体の反りや割れを低減ないし防止することができる。
【００５９】
請求項２記載の発明によれば、中空筒状基体の少なくとも一部を円弧状に形成しているので、この中空筒状基体の曲げ強度は平板状基板よりも大きい。したがって、抵抗発熱体の昇温時または部分的使用により部分的な温度差が発生しても、この基体には曲がりがそもそも発生しにくい。
【００６０】
このために、基体の反りや割れを低減ないし防止することができる。
【００６１】
請求項３記載の発明によれば、請求項１または２記載の定着ヒータを有するので、これらとほぼ同様の作用効果を奏することができる。また、基体の反りや曲げを低減することができるので、この基体を有する定着ヒータに外接する加圧ローラとの加圧面を軸方向でほぼ均等圧にすることができる。このために、この定着ヒータによる加熱むらないし定着むらを低減ないし防止することができる。
【００６２】
請求項４記載の発明によれば、請求項３記載の定着装置を有するので、これとほぼ同様の作用効果を奏することができる。
【図面の簡単な説明】
【図１】 本発明の第１の実施形態に係る定着ヒータの表面側の平面図。
【図２】 図１で示す定着ヒータの基板の一部切欠裏面図。
【図３】 図１のIII−III線断面図。
【図４】 図３のサーミスタ回りの拡大図。
【図５】 本発明の第２の実施形態に係る定着ヒータの斜視図。
【図６】 図５で示す実施形態の正面図。
【図７】 図６のVII−VII線断面図。
【図８】 本発明の第３の実施形態に係る定着ヒータの一部切欠正面図。
【図９】 図８の左側面図。
【図１０】 本発明の第４の実施形態に係る定着ヒータの一部切欠正面図。
【図１１】 図１０の左側面図。
【図１２】 本発明の第５の実施形態に係るかまぼこ形定着ヒータの横断面図。
【図１３】 本発明の第６の実施形態に係る画像形成装置である電子式複写機の全体構成図。
【図１４】 図１３で示す定着装置の要部拡大構成図。
【図１５】 従来の平板型定着ヒータの平面図。
【図１６】 図１５のXVI−XVI線断面図。
【符号の説明】
１０ 平板形定着ヒータ
１１ 基板
１１ａ 基板表面
１１ｂ 基板裏面
１２，２２ 抵抗発熱体
１３ａ，１３ｂ、２３ａ，２３ｂ 一対の電極
１４，２４ オーバーコート層
２０，２０Ａ，２０Ｂ 円筒形定着ヒータ
２１ 円筒形基体
２５ａ，２５ｂ 一対の取付溝
２６ａ，２６ｂ 一対の取付用切欠
３１ 電子式複写機
３２ 筐体
３３ カセット
３４ 画像形成部
３５ 定着装置
３６ 加圧ローラ
３７ ホルダー[0001]
BACKGROUND OF THE INVENTION
The present invention is used for thin fixing heaters that are used by being mounted on small devices such as OA equipment, household electrical equipment and precision manufacturing equipment, and toner fixing of copying machines, facsimiles, and the like in which this fixing heater is mounted. The present invention relates to a fixing device and an image forming apparatus using the fixing device.
[0002]
[Prior art]
In general, in an electronic copying machine, a copy sheet on which a toner image is formed is passed between a fixing heater and a pressure roller while directly or indirectly through a heat-resistant sheet, and the copy sheet is heated by heating the heater. The upper toner is heated, melted and fixed.
[0003]
As a conventional fixing heater of this type, Japanese Patent Publication No. 7-11606 and a plate-shaped one as shown in FIGS. 15 and 16, for example, have been put into practical use. The fixing heater 1 shown in FIGS. 15 and 16 has, for example, an elongated strip-shaped thick film resistance heating element 3 on the surface 2a of an elongated flat plate-like heat-resistant / electrically insulating substrate 2 made of alumina (Al ₂ O ₃ ) ceramics. Are formed by, for example, thick film printing. A pair of electrodes 4a and 4b are formed on the substrate surface 2a by thick film printing or the like and electrically connected to, for example, both ends in the longitudinal direction of the resistance heating element 3, and are electrically connected to the electrodes 4a and 4b. The resistance heating element 3 is energized through the connector (not shown).
[0004]
Further, as shown in FIG. 16, the thermistor 5 is fixed to the back surface 11b of the substrate 11 with an adhesive 6, the temperature of the resistance heating element 3 is detected by the thermistor 5, and the resistance heating element 3 is detected by a temperature control circuit (not shown). The temperature is controlled.
[0005]
The outer surface of the resistance heating element 3 is covered with a glassy overcoat layer 7 as a protective layer to improve mechanical strength such as wear resistance and impact resistance, and to protect against corrosion from sulfidation and oxidation. In addition, electrical insulation between the overcoat layer 7 and a rotatable pressure roller (not shown) in contact with the overcoat layer 7 is achieved. On the top surface of the overcoat layer 7, for example, a copy paper P on which a toner image is formed slides in the width direction of the resistance heating element 2 from in to out as indicated by an arrow in the figure as shown in FIG. The toner image is fixed on the copy paper P by heating.
[0006]
[Problems to be solved by the invention]
However, in such a conventional flat-type fixing heater 1, the strip-shaped resistance heating element 3 is formed on one surface (surface 2 a) of the substrate 2 made of alumina ceramics. The substrate surface 2a side on which the resistance heating element 3 is formed has the problem that the substrate 2 is thermally expanded first to cause warping of the substrate 2, and in an extreme case, the substrate 2 is also cracked.
[0007]
Further, not only when the temperature of the resistance heating element 3 is raised, but also when the width of the copy paper P to be fixed is small so that only a part of the resistance heating element 3 is used, Since the heat is easily taken away and the heat is not easily escaped in the unused portion, the temperature gradient is increased, and the substrate 2 tends to be easily warped or cracked. Further, it is necessary to reduce the amount of heat escaped through the substrate by appropriately reducing the thermal conductivity of the substrate so that the amount of heat generated by the resistance heating element is effectively transferred to the copy paper P.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a highly efficient fixing heater, fixing device, and image forming apparatus that can reduce or prevent warping and cracking of a substrate. is there.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 is a hollow cylindrical base having at least an outer surface formed of a heat-resistant electrical insulating layer; a resistance heating element fixed in a belt shape to at least the outer surface of the base; and both ends of the resistance heating element A pair of electrodes that are electrically connected; and an electrically insulating protective layer that covers at least the outer surface of the resistance heating element.
[0010]
Here, the columnar shape includes a prism or cylinder, and may be hollow or solid. Further, the columnar substrate may be one in which the outer surface of a metal substrate is coated with a heat-resistant and electrically insulating film .
[0011]
According to the present invention, since the base is a hollow cylinder, the bending strength is generally higher than that of a flat substrate or the like. Therefore, when the resistance heating element formed on the columnar substrate is heated or when a partial temperature difference occurs due to partial use, a partial difference in thermal expansion occurs, and even if warpage is to occur, the columnar substrate is bent in the first place. Hard to do. For this reason, it is possible to reduce or prevent warping or cracking of the substrate.
[0012]
Furthermore, according to this invention, it is possible to energize the resistance heating element through the pair of electrodes. Also, since the outer surface of the resistance heating element is covered with an electrically insulating protective layer, mechanical improvement such as wear resistance and impact resistance, corrosion protection from oxidation and sulfurization, and resistance heating element outer surface It is possible to achieve electrical insulation.
[0013]
According to a second aspect of the invention, at least the outer surface is formed on the heat-resistant electrically insulating layer, at least a part of a hollow cylindrical body which is formed in an arc shape; is secured to the strip on at least the outer surface of the base resistor And a heating element.
[0014]
According to the present invention, since at least a part of the hollow cylindrical substrate is formed in an arc shape, the bending strength of the hollow cylindrical substrate is larger than that of the flat substrate. Therefore, even if a partial temperature difference occurs due to the temperature rise or partial use of the resistance heating element, the substrate is unlikely to bend in the first place.
[0015]
For this reason, it is possible to reduce or prevent warping or cracking of the substrate .
[0016]
According to a third aspect of the present invention, the fixing heater according to the first or second aspect is disposed so as to be in pressure contact with the fixing heater, and heat from the fixing heater is applied to the toner forming the image of the fixing body. And a pressure roller for transporting the member to be fixed.
[0017]
According to the present invention, since the fixing heater according to the first or second aspect is provided, substantially the same operational effects as those described above can be obtained. Further, since the warping and bending of the substrate can be reduced, the pressure surface with the pressure roller that circumscribes the fixing heater having the substrate can be made substantially uniform in the axial direction. For this reason, it is possible to reduce or prevent heating unevenness and fixing unevenness by the fixing heater.
[0018]
According to a fourth aspect of the present invention, there is provided the fixing device according to the third aspect ; forming a reverse image by attaching toner to the electrostatic latent image formed on the medium; And means for forming the image.
[0019]
According to the present invention, since the fixing device according to the third aspect is provided, substantially the same operational effects as this can be achieved.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 14, the same or corresponding parts are denoted by the same reference numerals.
[0021]
1 is a top plan view of a fixing heater 10 according to a first embodiment of the present invention, FIG. 2 is a partially cutaway rear view of FIG. 1, and FIG. 3 is a sectional view taken along line III-III of FIG. In the figure, the fixing heater 10 has a long strip-like and resistive heating element 12 formed along the longitudinal direction on a surface 11a of an elongated substrate 11 having heat resistance and an electrical insulating material.
[0022]
The substrate 11 is made of silicon nitride (Si ₃ N ₄ ), for example, a rectangular flat plate having a length of about 300 mm, a width of about 8 mm, and a thickness of about 0.6 to about 1 mm. Silicon nitride has a smaller coefficient of thermal expansion and a higher bending strength as shown in the table below than alumina (Al ₂ O ₃ ).
[0023]
[Table 1]

[0024]
The resistance heating element 12 is formed of a thick film mainly composed of, for example, a silver / palladium (Ag / Pd) alloy, nickel / tin (Ni / Sn) alloy, RuO ₂ alloy having a length of about 230 mm and a thickness of about 10 μm. Has been.
[0025]
The resistance heating element 12 is made of a good conductor such as silver, silver / platinum alloy (Ag / Pt), silver / palladium alloy (Ag / Pd) or the like on one end or both ends thereof. A film is formed to form a pair of electrodes 13 a and 13 b and are electrically connected to the resistance heating element 12. The pair of electrodes 13a and 13b are energized to the resistance heating element 12 via a connector (not shown).
[0026]
Then, the entire surface of the outer surface of the inner end portion of the resistance heating element 12 and the pair of electrodes 13a and 13b is covered with a vitreous overcoat layer 14 which is a protective layer having electrical insulation properties, and wear resistance and impact resistance. Improvement of mechanical strength such as resistance, protection against corrosion from sulfidation, oxidation, etc., and electrical insulation from a pressure roller or the like to be described later.
[0027]
On the other hand, as shown in FIGS. 2 and 3, the substrate 11 has a pair of wiring conductors 15a and 15b arranged in parallel on the back surface (other surface) 11b side. These wiring conductors 15a and 15b are mainly composed of silver (Ag), platinum (Pt), gold (Au), silver / platinum (Ag / Pt) alloy, silver / palladium (Ag / Pd) alloy, etc., and have a film thickness of 5 ˜30 μm. Terminal portions 16a and 16b are integrally connected to one end (the left end in FIG. 2) of the wiring conductors 15a and 15b.
[0028]
And each front-end | tip part of wiring conductor 15a, 15b terminates in the approximate center part of substrate back surface 11b (just behind the center part of resistance heating element 12 of substrate surface 11a), and chip-like thermistor 17 is straddled on these termination parts. Then, both end portions thereof are fixed to the substrate back surface 11b with an adhesive 18 such as epoxy.
[0029]
The thermistor 17 detects the temperature of the resistance heating element 12 via the substrate 11, feeds back the detected temperature signal to a temperature control circuit (not shown), and controls the power applied to the resistance heating element 12 to control the resistance heating element 12. The temperature is kept constant.
[0030]
As shown in FIG. 4, the thermistor 17 is formed of an oxide such as manganese, cobalt, or nickel on the central portion of the upper surface of a rectangular flat substrate 17a made of alumina (Al ₂ O ₃ ) ceramics and having a thickness of about 250 μm. A temperature sensitive portion 17b made of a thin film formed by mixing materials (MnO ₂ , Co ₃ O ₄ , NiO) is formed, and connected to both ends of the temperature sensitive portion 17b, for example, a platinum (Pt) layer or an Au layer The thin film electrodes 17c and 17d are formed. The outer surface (the upper surface in FIG. 4) of the temperature sensing portion 17b has a layer thickness of 5 to 60 μm, for example, made of silicon oxide (SiO ₂ ), in order to prevent the film from deteriorating characteristics due to atmospheric temperature or impurity gas. The entire surface is covered with an overcoat layer 17e.
[0031]
In FIG. 4, reference numeral 19 denotes a conductive adhesive. Each of the films and layers described above is a thin film as compared with the substrate 11 and the thermistor base 17a. However, in FIG. 1, it is exaggerated and thick for convenience of explanation, and is not proportional in size.
[0032]
This chip-shaped thermistor 17 uses an electrical resistor having a large negative value of the temperature coefficient, and the resistance value is greatly reduced when the temperature rises, and the heat detection element converts the temperature into a resistance value. It is a sensor which consists of.
[0033]
Therefore, when a predetermined voltage is applied between the pair of electrodes 13a and 13b via a connector (not shown), the resistance heating element 12 is energized to generate heat, and this heat generation is generated on the top surface of the glassy overcoat layer 14. As shown in FIG. 1, the toner image can be fixed on the copy paper P by heating the copy paper P, which is a member to be fixed, that slides in the width direction from the input side in to the output side out.
[0034]
Since the substrate 11 is formed of silicon nitride having a low coefficient of thermal expansion and high bending strength, copy paper having a width dimension smaller than the length of the resistance heating element 12 when the resistance heating element 12 is heated or the like. When the resistance heating element 12 is partially used by heating the article to be fixed P, the difference in thermal expansion due to the partial temperature difference generated on the substrate 11 can be reduced.
[0035]
Therefore, the warpage of the substrate 11 can be reduced or prevented, and bending or cracking due to the warpage can be reduced or prevented. For this reason, the pressure surface of the pressure roller (not shown) in contact with the outer surface of the overcoat layer 14 can be made substantially uniform pressure in the axial direction, so that the outer surface of the overcoat layer 14 and the pressure roller The copy paper P passing between the outer surfaces can be pressurized almost evenly, and heating or fixing unevenness can be reduced or prevented.
[0036]
Further, since the thermal expansion coefficient of the substrate 11 is small, the stress due to the thermal expansion difference due to the partial temperature difference of the substrate 11 acts on the resin adhesive 18 that fixes the thermistor 17 to the substrate back surface 11b. 11 can be prevented from being peeled off. That is, it is possible to prevent the thermistor 17 from dropping from the substrate 11.
[0037]
Furthermore, since the silicon nitride forming the substrate 11 has low thermal conductivity, the temperature of the resistance heating element 12 that is energized and heated on the substrate 11 can quickly reach a predetermined heating temperature, and the temperature can be raised. You can expedite.
[0038]
5 is a perspective view of a fixing heater 20 according to the second embodiment of the present invention, FIG. 6 is a front view of FIG. 5, and FIG. 7 is a sectional view taken along line VII-VII of FIG. The fixing heater 20 is formed by forming a substrate 21 into an elongated hollow columnar shape, that is, a cylinder by a heat-resistant and electrically insulating material such as alumina ceramic (Al ₂ O ₃ ) or mullite (3Al ₂ O ₃ .2SiO ₂ ) ceramics. There are features.
[0039]
That is, the cylindrical base body 21 is formed of, for example, a cylindrical body having both ends opened, and the resistance heating element 22 is formed on the outer surface of the arcuate top portion of silver / palladium (Ag · Pd) in the same manner as in the above embodiment. ) Along with a thick film mainly composed of an alloy, nickel-tin (NiSn) alloy, RuO ₂ alloy, etc., it is formed and fixed along the axial direction in a band shape of a predetermined width, and partly on both longitudinal ends of the resistance heating element 22 A pair of film-like electrodes 23a and 23b that are electrically connected to each other are formed. Further, the entire outer surface of the resistance heating element 22 is formed on the outer surface of the substrate 21 so as to be covered with a glassy overcoat layer 24 as a protective layer.
[0040]
A thermistor (not shown) is fixed to the inner surface of the cylindrical base 21 at the back side of the central portion of the resistance heating element 22, while the pair of electrodes 23a and 23b are energized to the resistance heating element 22 via a connector (not shown). It has become.
[0041]
Then, the fixing heater 20 configured as described above is fixed and attached to a predetermined position of a housing such as a copying machine (not shown) so as not to rotate.
[0042]
Therefore, when a predetermined voltage is applied between the pair of electrodes 23a and 23b via a connector (not shown), the resistance heating element 22 is energized to generate heat, and this heat generation is caused by the arc-shaped top of the glassy overcoat layer 24. It is possible to heat the copy paper P, which is a member to be fixed, sliding in the width direction from the input side in to the output side out on the surface, thereby fixing the toner image on the copy paper P.
[0043]
Since the base body 21 is formed in a cylindrical shape capable of enhancing the bending strength, even if the base body 21 is warped due to a temperature difference caused by the temperature rise or partial use of the resistance heating element 22, Warpage can be reduced or prevented. Therefore, it is possible to reduce or prevent bending and cracking of the base body 21 when the warpage of the base body 21 is extremely advanced. For this reason, the fixing unevenness of the fixing object can be reduced or prevented as in the case of the flat type fixing heater 10.
[0044]
8 is a partially cutaway front view of a fixing heater 20A according to a third embodiment of the present invention, FIG. 9 is a left side view of FIG. 8, and the fixing heater 20A is according to the embodiment shown in FIGS. The cylindrical base 21 is characterized in that a pair of mounting grooves 25a and 25b are formed at both ends in the axial direction.
[0045]
Each mounting groove 25a, 25b is formed by, for example, notching both end surfaces of the base body 21 with a groove having a predetermined width so as to pass through the center of both ends of the cylindrical base body 21 in the diameter direction.
[0046]
Therefore, by engaging the mounting grooves 25a and 25b with mounting protrusions of a housing of a built-in device such as a copying machine (not shown), both the ease and accuracy of positioning of the fixing heater 20A can be improved. it can.
[0047]
10 is a partially cutaway front view of a fixing heater 20B according to a fourth embodiment of the present invention, FIG. 11 is a left side view of FIG. 10, and the fixing heater 20B is in the embodiment shown in FIGS. The cylindrical base body 21 is characterized in that a pair of mounting notches 26a and 26b are formed at both ends in the axial direction.
[0048]
Each of the mounting cutouts 26a and 26b is formed, for example, at both ends of the cylindrical base 21 by cutting out the lower half part below the horizontal center line passing through the center in the diameter direction.
[0049]
Therefore, both the ease and accuracy of positioning of the fixing heater 20B are improved by engaging the mounting notches 26a and 26b with mounting protrusions of a housing of a built-in device such as a copying machine (not shown). Can do.
[0050]
Note that the shapes of the mounting grooves 25a and 25b and the mounting notches 26a and 26b are not limited to these, but are engaged with the shape of the mounting portion of the built-in device to which the fixing heaters 20A and 20B are to be assembled. What is necessary is just to form in the shape which can do, and the protrusion which protrudes outside may be sufficient.
[0051]
In each of the above-described embodiments, the case where the base 21 is formed in a cylindrical shape has been described. However, the present invention is not limited to this. For example, like the kamaboko-shaped base 21A shown in FIG. The part may be formed in an arc shape. Also by this, the bending strength of the base 21A can be increased, so that warping and cracking of the base 21A can be reduced or prevented.
[0052]
12 shows the case where the resistance heating element 22 is formed on the outer surface of the arc-shaped portion 21b of the semi-cylindrical base 21A, but the position where the resistance heating element 22 is formed is not limited to this. For example, the resistance heating element 22 may be formed on the outer surface of the flat bottom surface 21c of the semi-cylindrical base 22, and the bases 21 and 21A may be formed solid.
[0053]
FIG. 13 shows the overall configuration of an embodiment of an electronic copying machine 31 which is a kind of image forming apparatus according to the fifth embodiment of the present invention. The copying machine 31 is placed in a housing 32 and in a cassette 33. An image forming unit 34 for drawing in the copy paper P and forming a toner image corresponding to an image of a document (not shown), and a fixing device 35 for fixing the toner image on the copy paper P are incorporated.
[0054]
The fixing device 35 is configured, for example, as shown in FIG. 14, and is arranged in parallel with one of the fixing heaters 10, 20, 20A, 20B, for example, 10 facing the rotating pressure roller 36, The fixing heater 10 is fixed on the bottom of the mounting groove of the resin cylindrical holder 37. A silicone rubber layer 38 of the pressure roller 36 is elastically pressed against the outer peripheral surface of the fixing heater 10.
[0055]
The fixing heater 10 is energized through an elastic connector made of a phosphor bronze plate or the like in contact with the pair of electrodes 13a and 13b, and the resistance heating element 12 generates heat. This heat generation is caused by the entire substrate 11 and the overcoat layer 14. And is heated. Therefore, the copy paper P on which the toner image T is formed is sent while being heated by the fixing heater 10 between the outer surface of the heat-resistant sheet (not shown) of the overcoat layer 14 and the silicone rubber layer 38 of the pressure roller 36. The unfixed toner image T can be melted and fixed on the copy paper P.
[0056]
In the fixing heater 10, as described above, the substrate 11 is formed of silicon nitride having a low coefficient of thermal expansion and a high bending strength, so that warping, bending, and cracking of the substrate 11 can be reduced or prevented. Can do. Therefore, the life of the fixing heater 10 can be extended, and the pressure surfaces of the fixing heater 10 and the pressure roller 36 can be equalized over almost the entire length of the fixing heater 10. For this reason, it is possible to reduce or prevent uneven heating of the copy paper P, and consequently fixing unevenness.
[0057]
Further, when the fixing heaters 20, 20A, 20B are incorporated in the fixing device 35, the bases 21, 21A of the heaters 20, 20A, 20B are formed of a cylindrical body having a high bending strength. The same effects can be achieved.
[0058]
【The invention's effect】
As described above, according to the first aspect of the present invention , since the base is a hollow cylinder , the bending strength is generally larger than that of a flat substrate or the like. Therefore, a partial thermal expansion difference occurs due to the temperature difference of the resistance heating element formed on the hollow cylindrical substrate at the time of temperature rise or partial use. In the first place, bending is hard to occur. For this reason, it is possible to reduce or prevent warping or cracking of the substrate.
[0059]
According to invention of Claim 2, since at least one part of a hollow cylindrical base is formed in circular arc shape, the bending strength of this hollow cylindrical base is larger than a flat substrate. Therefore, even if a partial temperature difference occurs due to the temperature rise or partial use of the resistance heating element, the substrate is unlikely to bend in the first place.
[0060]
For this reason, it is possible to reduce or prevent warping or cracking of the substrate .
[0061]
According to the third aspect of the present invention, since the fixing heater according to the first or second aspect is provided, substantially the same operational effects as these can be achieved. Further, since the warping and bending of the substrate can be reduced, the pressure surface with the pressure roller that circumscribes the fixing heater having the substrate can be made substantially uniform in the axial direction. For this reason, it is possible to reduce or prevent heating unevenness and fixing unevenness by the fixing heater.
[0062]
According to the fourth aspect of the present invention, since the fixing device according to the third aspect is provided, substantially the same operational effects can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view of a surface side of a fixing heater according to a first embodiment of the present invention.
FIG. 2 is a partially cutaway rear view of the fixing heater substrate shown in FIG.
3 is a sectional view taken along line III-III in FIG.
4 is an enlarged view around the thermistor in FIG. 3;
FIG. 5 is a perspective view of a fixing heater according to a second embodiment of the present invention.
6 is a front view of the embodiment shown in FIG.
7 is a sectional view taken along line VII-VII in FIG.
FIG. 8 is a partially cutaway front view of a fixing heater according to a third embodiment of the present invention.
9 is a left side view of FIG.
FIG. 10 is a partially cutaway front view of a fixing heater according to a fourth embodiment of the present invention.
11 is a left side view of FIG.
FIG. 12 is a cross-sectional view of a kamaboko type fixing heater according to a fifth embodiment of the present invention.
FIG. 13 is an overall configuration diagram of an electronic copying machine that is an image forming apparatus according to a sixth embodiment of the present invention.
FIG. 14 is an enlarged configuration diagram of a main part of the fixing device shown in FIG.
FIG. 15 is a plan view of a conventional flat plate type fixing heater.
16 is a sectional view taken along line XVI-XVI in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Flat type fixing heater 11 Board | substrate 11a Board | substrate surface 11b Board | substrate back surface 12, 22 Resistance heating element 13a, 13b, 23a, 23b A pair of electrode 14,24 Overcoat layer 20,20A, 20B Cylindrical fixing heater 21 Cylindrical base | substrate 25a, 25b A pair of mounting grooves 26a, 26b A pair of mounting cutouts 31 Electronic copying machine 32 Housing 33 Cassette 34 Image forming unit 35 Fixing device 36 Pressure roller 37 Holder

Claims (4)

A hollow cylindrical base having at least an outer surface formed of a heat-resistant electrical insulating layer;
A resistance heating element fixed to at least the outer surface of the substrate in a strip shape ;
A pair of electrodes electrically connected to both ends of the resistance heating element;
An electrically insulating protective layer covering at least the outer surface of the resistance heating element;
A fixing heater comprising: A hollow cylindrical substrate having at least an outer surface formed in a heat-resistant electrical insulating layer and at least a part formed in an arc shape;
A resistance heating element fixed to at least the outer surface of the substrate in a strip shape ;
A fixing heater comprising: A fixing heater according to claim 1;
A pressure roller that is disposed so as to be in pressure contact with the resistance heating element of the fixing heater and causes the heat from the fixing heater to act on the toner forming the image of the fixing body, and for conveying the fixing body; ;
A fixing device. A fixing device according to claim 3 ;
Means for attaching a toner to an electrostatic latent image formed on a medium to form a reverse image, and transferring the reverse image to a fixing member to form a predetermined image;
An image forming apparatus comprising:

Images