JP3903633B2 - Image forming apparatus - Google Patents

Description

【００５５】
表１に示すように、中間転写体の発泡層を予備加熱することで、必要電力量を約８０％に落とすことができることがわかる。
【００５６】
次に、発泡層の熱伝導率と必要電力量との関係を調査する実験を行った。
この実験では、発泡層の材料を変えることによって熱伝導率を変化させ、上記実験と同じ条件（予備加熱あり）で定着に必要な電力を測定した。その結果を図３に示す。
【００５７】
図３に示すように、熱伝導率が約０．１（Ｗ/ ｍＫ）以下であれば、電力を低減する効果があることがわかる。これは、熱伝導率が０．１（Ｗ/ ｍＫ）より大きいと発泡層への熱流入量が多くなるためであると考えられる。
【００５８】
次に、中間転写体の予備加熱温度を変化させたときの転写定着時における中間転写体及びトナーの温度変化を測定する実験を行った。
この実験では、一次元熱解析により中間転写体の予備加熱温度を変え、その時トナーが記録材と接触した時の温度が予備加熱してないときの温度とほぼ同じになるように投入電力（必要電力）を調整し、中間転写体及びトナーの各工程における温度を測定した。この実験の結果を表２に示す。
なお、このときの発泡層の熱伝導率は０．０４（Ｗ/ ｍＫ）である。また、予備加熱の方法は、前記実験の予備加熱方法と同様に、１サイクル分だけ記録材なしで１００Ｗ程度（中間転写体の設定温度によって多少異なる）の電力を投入して行った。
【００５９】
【表２】

【００６０】
表２から中間転写体の予備加熱温度を上げていくと、投入電力（必要電力）は減少していくことがわかる。また、この結果は上述した実機での結果とよく一致している。
【００６１】
また、予備加熱温度を上げていった場合、ある温度になると投入電力（必要電力）は減少していき飽和していくようである。このことをより明確にするため、中間転写体の初期温度と必要電力との関係を図４に、中間転写体の初期温度と中間転写体のニップ後温度との関係を図５に示す。
【００６２】
図４に示すように、中間転写体の予備加熱温度が５５℃のとき、必要電力は４８０Ｗで済むことがわかる。また 図５に示すように予備加熱温度が５５℃のときは、中間転写体のニップ後温度も約５５℃となっている。このことは、中間転写体上のトナー像を記録材に転写定着した後、次の一次転写プロセスまでの間に中間転写体の発泡層を冷却しなくてもよいことになる。
【００６３】
次に、この条件で画像形成装置を連続使用し、画像の状態を確認する実験を行なった。
この実験の条件として、中間転写体の予備加熱温度は５５℃がよいのであるが、５５℃という温度は画像形成装置内の他のシステムへの支障や、トナーの現像装置内でのブロッキング現象などを引き起こす懸念があるので、この実験での予備加熱温度は５０℃とし、５００Ｗの投入電力で行なった。また、トナー像が記録材に転写定着された後の中間転写体の温度を５０℃にすべく、冷却装置であるファンを用いて温度調整を行なった。
この実験は富士ゼロックス社製用紙Ｊ紙Ａ４を横送りで１０００枚連続挿通し、トナーとして前記トナーを１．８ｇ/ ｍ² の５×５ｃｍのベタ画像を定着させた。その結果、すべて満足できる定着状態であることが確認された。
【００６４】
〈実験−２〉
図１に示す画像形成装置の比較例として、中間転写体を赤外線ランプにより予備加熱する方式の画像形成装置を用い、そのときの投入電力を調査する実験を行った。
図８は、比較のために用いた画像形成装置を示す概略構成図である。この画像形成装置は、図１に示す画像形成装置の電磁誘導加熱装置１２に変えて、赤外線ランプ１１２を二次定着ロール１０８と対向して配置し、中間転写体１０５を輻射熱によって加熱するものである。なお、この画像形成装置は、図１に示す装置と同様に、一次転写ロール１０６と、画像形成ユニット１０７Ｙ，１０７Ｍ，１０７Ｃ，１０７Ｋと、駆動ロール１０９と、テンションロール１１０と、加圧ロール１１１と、ぺーバーガイド１１３と、剥離爪１１４と、案内部材１１５と、冷却装置１１６とを備えており、これらの構成は図１に示す装置と同じである。
【００６５】
上記赤外線ランプ１１２による輻射加熱方式の画像形成装置を用い、中間転写体の予備加熱を行った場合と、予備加熱を行わない場合との投入電力を比較した。評価基準は実験−１と同じ条件である。この実験の結果を表３に示す。
【００６６】
【表３】

【００６７】
表３に示すように、予備加熱を行った場合は、行わない場合と比較して投入電力が減少し、電磁誘導作用による加熱方式によらず予備加熱の効果があることがわかる。一方、表３と前記表１の結果とを比較すると、電磁誘導加熱装置に比べて赤外線ランプで加熱する場合は著しく投入電力が大きくなっている。したがって、電磁誘導加熱方式を用いることにより、投入電力を低減する効果が非常に大きいことがわかる。
【００６８】
なお、本実施形態の画像形成装置では、電磁誘導加熱装置１２を中間転写体５の外側に配置しているが、中間転写体の内側に配置したり、あるいは、内側と外側の両方に配置して加熱してもよく、これにより同様の電力低減効果を得ることができる。
【００６９】
【発明の効果】
以上説明したように、本願発明に係る画像形成装置では、中間転写体裏面に発泡層を設け、これを予備加熱することで、本サイクルで中間転写体上のトナー像を加熱するときの使用エネルギーを低減することができる。また、この発泡層により、裏面側へ流出する無駄なエネルギーを激減できるため、エネルギーの高効率化を図ることができる。さらに、加熱工程で中間転写体上のトナー像を加熱し、この加熱工程を行う領域と連続した領域でトナー像を常温状態の記録材に圧接するので、記録材が冷却部材として作用し、トナー像を瞬時に記録材上に転写・定着することが可能となる。このため、記録材を中間転写体から剥離する時にトナーの温度を十分に低下させることができ、オフセットの発生を防止できるとともに、定着性の良い高品質な画像を得ることができる。
具体的には以下のようなメリットを有しており、その利用価値は大きい。
（１）全消費エネルギーが少なく、限られた電力で高速の画像形成が可能となる。
（２）中間転写体を予備加熱することで、中間転写体を冷却することが不要となるか、もしくは冷却する温度差を小さくすることができるので、廃熱が少なくてすみ効率的である。
（３）記録材が冷却部材として作用し中間転写体の温度が急激に低下するので、像担持体側に支障をきたすことがない。
（４）加熱手段を構成する部材の表面に断熱弾性体層を形成することにより、従来のソフトロールを用いた定着装置で定着した画質と同等の高品位の転写定着画像を得ることができる。
（５）シャープメルトのオフセットしやすいトナーでもオフセット現像が全く生じることがないため、白黒複写機だけでなくカラー複写機用にも十分に適用可能である。
（６）記録材の加熱量が非常に少ないため、記録材の厚みや熱容量に転写定着性がほとんど影響されず、さらにカールや紙しわの発生が少ない。
（７）ウォームアップタイムが大幅に短縮可能であり、その結果スタンバイ時に加熱手段を設定温度に維持しておくために投入していた電力を削除することができる。
（８）カラートナーの場合、従来、トナーを中間転写体から剥離するために必要であった、オイルなどの離型剤を使用することなく、定着画像を良好に剥離することが可能となる。
【図面の簡単な説明】
【図１】本願発明の一実施形態である画像形成装置を示す概略構成図である。
【図２】図１に示す画像形成装置で用いられる中間転写体を示す部分拡大図である。
【図３】図１に示す画像形成装置における中間転写体の熱伝導率と必要電力との関係を示すグラフである。
【図４】図１に示す画像形成装置における中間転写体の初期温度と必要電力との関係を示すグラフである。
【図５】図１に示す画像形成装置における中間転写体の初期温度と、転写定着後の中間転写体の温度との関係を示すグラフである。
【図６】中間転写体の予備加熱を行った場合の転写定着領域におけるトナー及び中間転写体の温度変化を示す図である。
【図７】中間転写体の予備加熱を行わない場合の転写定着領域におけるトナー及び中間転写体の温度変化を示す図である。
【図８】比較例である画像形成装置を示す概略構成図である。
【符号の説明】
１ 像担持体
２ 帯電装置
３ 露光装置
４ 現像装置
５、１０５ 中間転写体
６、１０６ 一次転写ロール
７、１０７ 画像形成ユニット
８、１０８ 二次転写ロール
９、１０９ 駆動ロール
１０、１１０ テンションロール
１１、１１１ 加圧ロール
１２ 電磁誘導加熱装置
１３、１１３ ペーパーガイド
１４、１１４ 剥離爪
１５、１１５ 案内部材
１６、１１６ 冷却装置
２１ 基材
２２ 導電層
２３ 表面層
２４ 発泡層
３１ 励磁コイル
３２ 励磁回路
１１２ 赤外線ランプ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic process, and in particular, after a toner image formed on an image carrier is transferred to an intermediate transfer member, the toner image on the intermediate transfer member is transferred onto a recording material. The present invention relates to an image forming apparatus that fixes and records images.
[0002]
[Prior art]
Conventionally, as an image forming apparatus, toner on an image carrier is primarily transferred to an intermediate transfer member having releasability, and the toner image on the intermediate transfer member is melted onto a recording material by heating / pressurizing means. Those which are fixed simultaneously with the next transfer are known. As this pressurizing / heating means, a heating roll and a pressurizing roll that are press-contacted via an intermediate transfer member are known, and the toner on the intermediate transfer member is melted by a heating roll at the press-contacting portion of both and used as a recording material. The recording material is permeated and peeled off from the intermediate transfer member using the releasing effect of the intermediate transfer member.
[0003]
In such an image forming apparatus, there are various severe conditions for transferring the toner image on the intermediate transfer member to the recording material and fixing it at the same time, and it is considerable to achieve good transfer and fixing of the toner image. It is difficult to. For this reason, as means for improving the transfer and fixing of the toner image, for example, Japanese Patent Publication No. 46-41679, Japanese Patent Laid-Open No. 49-78559, Japanese Patent Laid-Open No. 50-107936, and Japanese Patent Laid-Open No. 57-57. Techniques described in Japanese Patent No. 163264, Japanese Patent Publication No. 64-1027, and Japanese Patent Laid-Open No. 10-63121 have been proposed.
[0004]
In the technique described in Japanese Patent Publication No. 46-41679, the recording material is heated without heating the toner image on the intermediate transfer member, and the toner image is melted by the heat of the recording material and transferred onto the recording material. It is to fix.
[0005]
Further, the techniques described in JP-A-49-78559 and JP-A-50-107936 select the toner on the intermediate transfer member up to its melting temperature by radiant heating means without heating the recording material. The toner image on the intermediate transfer member is pressed against the recording material and transferred and fixed.
[0006]
In the technique described in Japanese Patent Application Laid-Open No. 57-163264, the intermediate transfer member and the toner image transferred to the intermediate transfer member are heated in advance, and the recording material is heated and pressed together to place the toner image on the recording material. Transfer and fix.
[0007]
The technique described in Japanese Patent Publication No. 64-1027 is a technique in which toner is preliminarily heated before a nip portion (transfer fixing area) where a toner image on an intermediate transfer body is pressed against a recording material. In other words, a belt-shaped intermediate transfer member is wound on the heating roll by 90 ° or more, and the toner is preliminarily heated using the heat of the heating roll on the near side of the nip portion with the recording material, and the toner is heated to the vicinity of the melting temperature of the toner. Increase temperature. Thereafter, in the nip portion, the toner is further heated and melted to transfer and fix the toner image onto the recording material.
[0008]
In the technique described in Japanese Patent Laid-Open No. 10-63121, a heating member is disposed so as to be in contact with the inner peripheral surface of an endless belt-shaped intermediate transfer member, and the toner on the intermediate transfer member is in a region in contact with the heating member. The image is heated so that it is 1.5 to 2.5 times the toner softening point temperature. Further, a pressure member is disposed in the most downstream portion of the region of the intermediate transfer member that contacts the heating member, and a normal temperature recording material is sent between the pressure member and the intermediate transfer member to press-contact the toner image. The toner image is transferred onto a recording material and fixed.
[0009]
[Problems to be solved by the invention]
However, the conventional techniques as described above have the following problems.
The technique described in Japanese Examined Patent Publication No. 46-41679 is preferable in that it can prevent the intermediate transfer member from being overheated and can prevent the image carrier from being adversely affected by heat. It is necessary to apply a considerable amount of heat energy to a recording material which is low and made of ordinary paper. Furthermore, when transferring and fixing a toner image at a high speed, it is necessary to give a larger amount of thermal energy to the recording material. As a result, energy consumption increases, and the recording material cannot be smoothly conveyed and jammed. In some cases, the risk of ignition is high.
[0010]
Further, the techniques described in Japanese Patent Application Laid-Open Nos. 49-78559 and 50-107936 use radiant heating as a means for selectively heating only the toner, so that the substantial thermal efficiency is achieved by the heating roll. It becomes lower than the conductive heating means such as. In addition, most of the thermal energy absorbed by the toner is transferred to the intermediate transfer body having a low temperature during the period from the radiant heating area to the transfer fixing area where the recording material is brought into contact with the recording material. Must be heated, and the total thermal energy efficiency is low. Further, since the radiant heating means is used, there is a risk of burning paper when a jam occurs.
[0011]
On the other hand, the technique described in JP-A-57-163264 has an advantage that the temperature of the intermediate transfer member can be set low because the intermediate transfer member, the toner and the recording material are heated together. In addition, since there is little heat transfer between the toner image on the intermediate transfer member and the recording material at the press contact portion, there is little decrease in the fluidity of the toner, and the toner sufficiently penetrates the recording material and is transferred from the intermediate transfer member. The However, since the temperature of the toner when separated from the intermediate transfer member is higher than the toner softening point temperature and is in a fluid state, the toner tends to be divided and easily offset to the intermediate transfer member. Further, since all of the intermediate transfer member, toner, and recording material need to be heated, the total energy consumption increases. In addition, there is a problem that heat is transferred to the image carrier side by the circular movement of the intermediate transfer member heated by the heating roll, and the temperature around the intermediate transfer member rises to hinder the charging function. If such a mechanism is followed to prevent the heat of the intermediate transfer member from being transmitted to the image carrier side, a considerably large cooling device is required, resulting in an increase in the cost of the device.
[0012]
In the technique described in Japanese Patent Publication No. 64-1027, since the toner is preheated before the nip portion (transfer fixing area), the set temperature of the heating roll can be lowered. Since the toner and the recording material are reheated, the total energy consumption becomes large as in the above-described conventional example.
[0013]
As a solution to these problems, there is a technique described in Japanese Patent Application Laid-Open No. 10-63121. However, a heating member is disposed so that the heat generating member is in contact with the inner peripheral surface of the intermediate transfer member. Since the heat is supplied by this, a transition time (rise time) from room temperature to the set temperature is inevitably required at least about 30 seconds. Therefore, in order to supplement this point, it is only necessary to always warm at a temperature lower than the set temperature and higher than the room temperature during standby, but this requires power during standby, which is not preferable from the viewpoint of energy saving.
In addition, the intermediate transfer member must have a large heat capacity because the toner on the intermediate transfer member is instantaneously raised to the melting temperature of the toner and brought into contact with a normal temperature recording material to remove heat and solidify the toner. Inevitably thin. For this reason, the mechanical strength is weak and wrinkles are likely to occur, image defects are likely to occur, and in the long term, they are broken, resulting in poor reliability.
[0014]
As described above, the image forming apparatus using the conventional fixing method has a common problem that a large amount of power is required, and the normal power supply is 1.5 kVA, so that the energy distribution in the fixing system is limited. Therefore, power reduction in high-speed machines is an important issue.
[0015]
The present invention has been made in view of the above-described problems, and an object of the present invention is to reliably transfer and fix a toner image on an intermediate transfer member onto a recording material, and at high speed with limited power. An object of the present invention is to provide an image forming apparatus capable of printing.
[0016]
[Means for Solving the Problems]
  In order to solve the above problems, the invention according to claim 1 is directed to an image carrier on which a toner image is formed by selectively adhering toner to an endless peripheral surface, and a circulation of the endless peripheral surface. An intermediate transfer member to which the toner image is transferred at a portion whose outer peripheral surface is opposed to the image carrier, and the toner image on the intermediate transfer member is transferred to a recording material and fixed at the same time In the image forming apparatus, the intermediate transfer member has an endless belt-like base and a foam layer formed on the inside thereof.
  A pressure member that presses the recording material against the intermediate transfer member, and a heating unit that heats the intermediate transfer member on the upstream side in the circumferential direction of the intermediate transfer member from a position where the pressure member is provided. Provided, and the heating means includesImmediately before the main cycle in which the toner image is transferred from the image bearing member to the intermediate transfer member, the intermediate transfer member is driven around to perform preliminary heating of the intermediate transfer member, and after entering the main cycle,It is assumed that the toner image is set to be heated to a temperature at which fixing is performed at the same time as the transfer to the recording material.
[0017]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the intermediate transfer member has a heat generating layer made of a conductive material outside the base, and the heating means It has an exciting circuit that forms an alternating magnetic field substantially orthogonal to the surface of the intermediate transfer member and performs electromagnetic induction heating, and the heating means moves the intermediate transfer member carrying the toner image above the softening point temperature of the toner. And the temperature of the toner that contacts the intermediate transfer member and the recording material is less than the softening point temperature of the toner before passing through the nip portion where the recording material is pressed against the intermediate transfer member by the pressure member. It is assumed that the intermediate transfer member is heated so that
[0018]
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the thermal conductivity of the foam layer is 0.1 W / mK or less.
[0019]
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the preheating performed by the heating unit is set so that the temperature of the intermediate transfer member is equal to or higher than normal temperature and lower than a toner softening point temperature. It shall be.
[0020]
According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the intermediate transfer member is placed at a temperature equal to or higher than normal temperature on the downstream side in the moving direction of the intermediate transfer member from the position where the pressure member is provided. It is assumed that a cooling device for adjusting the temperature to be lower than the softening point temperature is provided.
[0021]
In the image forming apparatus as described above, the intermediate transfer member is an endless belt-like member. The toner is softened by heating at least the intermediate transfer member with a heating unit, and the transfer is performed by pressing the toner onto the recording material. And fixing can be performed simultaneously. Therefore, the belt-shaped member having a small heat capacity can be heated in a short time, and the rise time at the start of the apparatus is shorter than that of an apparatus that heats and fixes a member having a large heat capacity such as a roll.
[0022]
Since the foam layer is provided on the inner side of the intermediate transfer body, the belt-shaped member is preheated by preheating, so that it is possible to reduce the amount of power used when transferring and fixing the toner image. . In other words, Fourier's law
dq = −λ (dθ / dx) dA
dq: heat transfer amount
λ: thermal conductivity
dθ / dx: Rate of temperature change
dA: Unit area
If the temperature change rate is small, the movement of thermal energy is small. Therefore, if the temperature of the foamed layer is increased by the preheating, the amount of heat energy dissipated from the heat generating layer is reduced.
[0023]
In general, the amount of electric power used is increased in order to rapidly heat the intermediate transfer member, which is a belt-like member, to a temperature at which the toner is softened before transferring and fixing, but the belt-like member is preheated as described above. Accordingly, the dissipation of heat energy from the heat generating layer can be reduced, and the amount of power used for fixing can be reduced. In addition, when performing the said preheating, while a foaming layer functions as a livestock heat layer, heat dissipation is reduced by the heat insulation effect.
Further, by providing the foam layer, the functional rigidity of the intermediate transfer member is increased, the belt-like intermediate transfer member is hardly wrinkled, and the reliability and durability are improved.
[0024]
Further, the belt-shaped intermediate transfer member and the toner are heated by the heating means, and after this is finished, the softened toner is pressed against the recording material, so that the temperature of the toner in contact with the recording material is lowered and solidified and fixed on the recording material. Will be. Therefore, good transfer and fixing are performed.
[0025]
As described above, the image forming apparatus is configured to heat at least the endless belt-shaped intermediate transfer member and heats the belt-shaped intermediate transfer member. Further, since the heat capacity of the belt-shaped intermediate transfer member is small, the toner temperature is lowered in the nip portion where the recording material is pressed against the intermediate transfer member, and good transfer / fixing is performed.
With such a configuration, it is possible to achieve both reduction in energy used for fixing, reduction in power consumption during fixing, and reduction in the rise time of the apparatus.
[0026]
According to the second aspect of the present invention, an intermediate transfer member having a heat generating layer outside the substrate is used to form an alternating magnetic field substantially orthogonal thereto, and an eddy current is generated in the heat generating layer to cause a toner image by electromagnetic induction. The method of heating is adopted. FIG. 6 shows the interface temperature between the intermediate transfer member and the toner when preheating is performed by the image forming apparatus according to the present invention (the surface temperature of the intermediate transfer member after the toner leaves the intermediate transfer member by the recording material). It is the schematic diagram which looked at with respect to the change of time.
[0027]
In this heating method, the heat generating layer can instantaneously self-heat above the toner softening point temperature by electromagnetic induction without contact with the intermediate transfer member from the outside, whereby the toner image on the intermediate transfer member is rapidly heated. Soften. Next, the toner on the intermediate transfer body is cooled below the toner softening point temperature by bringing the toner image into contact with a normal temperature recording material sent between the intermediate transfer body and the pressure member. It becomes solidified and fixed. At this time, since the intermediate transfer member is preheated before the main cycle for performing the primary transfer of the toner image, the initial temperature of the intermediate transfer member becomes relatively high as shown in FIG. 6, and the toner image is heated rapidly. It is possible to reduce the amount of power when doing so. In other words, the input energy substantially only heats the thin film intermediate transfer member to melt the toner, and it is not necessary to apply energy to the foam layer and the back surface member. It can be carried out.
[0028]
On the other hand, as shown in FIG. 7, in the case where no preheating is performed in the image forming process, the intermediate transfer member is heated suddenly from near normal temperature in the transfer fixing process, and the temperature is from normal temperature to the maximum toner temperature. The energy consumption increases. Therefore, the method of preheating the intermediate transfer member as in the present invention has a great effect of reducing the energy used for fixing in this cycle. For this reason, it is possible to perform high-speed image formation with limited power.
[0029]
Further, as in the invention described in claim 3, it is desirable that the thermal conductivity of the foam layer is set to 0.1 W / mK or less. As the thermal conductivity of the foam layer itself is smaller, the heat transfer is smaller. Therefore, the energy reduction effect is further enhanced by selecting a material having a lower thermal conductivity. In addition, since the foamed layer is difficult to warm up, but once warmed up, it is difficult to cool down. Therefore, the foamed layer is saturated at a temperature higher than normal temperature by a constant input energy. As a result, an apparatus that does not require the cooling process as much as possible is possible, and the energy required in the cooling process can be minimized.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. This image forming apparatus includes an endless belt-shaped intermediate transfer body 5 supported so that the circumferential surface thereof can circulate, and yellow, magenta, cyan, and black toner images are placed at positions facing the intermediate transfer body 5. Four image forming units 7Y, 7M, 7C and 7K to be formed are arranged. Each image forming unit has an image carrier 1 on the surface of which an electrostatic latent image is formed. Charging for almost uniformly charging the surface of the image carrier 1 around each image carrier 1 An apparatus 2; an exposure device 3 that forms a latent image by irradiating image light onto the surface of the image carrier; and a development that selectively transfers toner to the latent image formed on the image carrier to form a toner image. An apparatus 4 and a primary transfer roll 6 for transferring the toner image on the image carrier onto the intermediate transfer member 5 are provided.
[0031]
A secondary transfer roll 8, a drive roll 9, and a tension roll 10 are disposed inside the intermediate transfer body 5, and the intermediate transfer body 5 is stretched around these so as to be able to go around.
In addition, a pressure roll 11 that presses the intermediate transfer body 5 against the secondary transfer roll 8 is provided at the most downstream portion of the contact area with the secondary transfer roll 8 in the circumferential direction of the intermediate transfer body 5. An electromagnetic induction heating device 12 for heating the toner image transferred onto the intermediate transfer member 5 is provided on the upstream side of the pressure contact portion with the pressure roll 11 in the circumferential direction of the intermediate transfer member 5.
[0032]
Further, in the apparatus, a paper guide 13 for feeding the recording material P to the pressure contact portion between the pressure roll 11 and the intermediate transfer member 5, a peeling claw 14 for peeling the recording material that has passed through the pressure contact portion, and a recording material are illustrated. And a guide member 15 that conveys the paper to the paper discharge unit.
Further, a cooling device 16 for cooling the intermediate transfer body 5 is provided on the downstream side of the pressure contact portion with the pressure roll 11 in the circumferential direction of the intermediate transfer body 5 and on the upstream side of the image forming unit 7Y. .
[0033]
As shown in FIG. 2, the intermediate transfer member 5 has a conductive layer 22 that self-heats by electromagnetic induction on the peripheral surface of an endless belt-like base material 21 with high heat resistance, and a release agent from the toner. And a surface layer 23 having good properties, and further, a foam layer 24 is provided inside the base material 21. The intermediate transfer member 5 is rotated in the direction of the arrow shown in FIG. 1 at a speed of 160 mm / s by the rotation of the drive roll 9.
[0034]
For example, a film of polyester, polyimide, aromatic polyamide, polyacrylate, polyetherimide, polyethersulfone, polyetheretherketone, polybaravanic acid, or the like can be used as the base material 21. In view of ease of use and usability, polyimide having a circumferential length of 800 mm and a width of 320 mm is employed. As for the thickness at this time, it is better to consider the workability and mechanical strength. However, considering the heat capacity when the recording material takes away heat, the thickness is better. In view of these points, a thickness of 15 μm is adopted.
[0035]
For the conductive layer 22, a metal having high magnetic permeability is used. For example, nickel, iron, copper, gold, silver, aluminum, steel, or the like can be selected. Of these, considering cost, heat generation performance, and workability, copper, nickel, aluminum, and iron are suitable, and copper is particularly suitable, so copper is adopted.
[0036]
The surface layer 23 is preferably a coat layer having good heat resistance and releasability. For example, fluororesin, silicone rubber, or fluororubber can be selected. Considering moldability and durability, PFA (polytetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) is considered to be optimal, and this is adopted in this embodiment. The thickness of the surface layer is adjusted to a thickness of 5 μm in consideration of long-term reliability against wear and to minimize the heat capacity.
[0037]
The foam layer 24 needs to have heat resistance. For example, a foam such as PET, a styrene foam, a silicone sponge, a rubber sponge, or the like can be used. In this embodiment, foamed PET is used. Used. The thermal conductivity is preferably set to 0.1 W / mK or less, and is set to 0.04 W / mK in this embodiment. The thickness of the foam layer 24 is desirably 1 mm or less, and is set to 200 μm in this embodiment.
[0038]
The secondary transfer roll 8 is made of a resin having a diameter of 50 mm and a core thickness of 8 mm, and the intermediate transfer member 5 is wound around about half of the peripheral surface.
A fan, a heat sink, a heat pipe, a Peltier element, or the like can be selected as the cooling device 16. However, since the fan is optimal in terms of cost, space, and structure, a fan is used in this embodiment.
[0039]
The electromagnetic induction heating device 12 includes an exciting coil 31, an exciting circuit 32, and the like, and heats the conductive layer 22 of the intermediate transfer member 5 by electromagnetic induction. The principle of heat generation of the conductive layer 22 by this electromagnetic induction action will be described below.
When an alternating current is applied to the exciting coil 31 by the exciting circuit 32, the magnetic flux repeatedly generates and disappears around the exciting coil 31. When this magnetic flux crosses the conductive layer 22 of the intermediate transfer member 5, an eddy current is generated in the conductive layer 22 so as to generate a magnetic field that hinders the change of the magnetic flux. Joule heat is generated by the eddy current and the specific resistance of the conductive layer 22.
[0040]
Due to the skin effect, the eddy current flows almost concentrated on the surface of the conductive layer 22 on the side of the exciting coil 31, and the skin resistance R of the conductive layer 22._SGenerates heat with power proportional to
Here, when the angular frequency is ω, the magnetic permeability is μ, and the specific resistance is ρ, the skin depth δ is expressed by the following equation.
δ = (2ρ / ωμ)^1/2
Furthermore, skin resistance R_SIs expressed by the following equation.
Rs = ρ / δ = (ωμρ / 2)^1/2
[0041]
The electric power P generated in the conductive layer 22 of the intermediate transfer member 5 is expressed by the following equation, where Ih is the current flowing through the intermediate transfer member.
P∝Rs∫ | Ih |²dS
[0042]
Therefore, skin resistance R_SIf the current Ih is increased or the current Ih is increased, the power P can be increased and the amount of heat generated can be increased.
Here, the skin depth δ (m) is expressed by the following equation using the frequency f (Hz) of the excitation circuit, the relative permeability μr, and the specific resistance ρ (Ωm).
δ = 503 (ρ / (f μr))^1/2
[0043]
This shows the depth of absorption of electromagnetic waves used for electromagnetic induction, and the intensity of electromagnetic waves is less than 1 / e deeper than this, and conversely most energy is absorbed up to this depth. Yes.
[0044]
Here, the thickness of the conductive layer 22 is thicker than the skin depth represented by the above formula (1 to 100 μm), and 5 μm or less in view of the balance of heat capacity with the recording material in the heating process and cooling process according to the present embodiment. It is preferable to make it. On the other hand, when the thickness of the conductive layer 22 is smaller than 1 μm, most of the electromagnetic energy cannot be absorbed, resulting in poor efficiency. In view of these points, the present embodiment is adjusted to a thickness of 2 μm, which is considered to be the best.
The heat capacity of the intermediate transfer member 5 is about 2.5 joules / ° C. in the area of A4 size, which corresponds to about 40% of the heat capacity of the recording material.
[0045]
Next, the toner used in the image forming apparatus will be described.
As the toner, any of oilless toner containing wax, which is frequently used in conventional black and white copying machines, and sharp melt toner used in color copying machines can be used. By combining them, it becomes possible to further extract the features of the present invention. When forming a color image or a full color image, by using a sharp melt toner, the color reproduction range of the copying machine can be widened, and a color copy faithful to the original multicolor or full color image can be obtained satisfactorily. The color toner preferably uses, for example, a polyester resin as a sharp melt binder resin in consideration of color developability and fixability. The toner has a softening point of 75 to 150 ° C., preferably 80 to 125 ° C., and a low temperature softening point.
[0046]
Here, the toner having sharp melt property means an apparent melt viscosity of 10.^ThreeT is the temperature at which Pa · s is indicated.₁The apparent melt viscosity is 5 × 10²T is the temperature at which Pa · s is indicated.₂T₁= 80-140 ° C, T₂-T₁= Satisfying the condition of 5 ° C to 20 ° C. The sharp melt resin having these temperature-melt viscosity characteristics is characterized in that the viscosity is lowered extremely sharply when heated. Such a decrease in viscosity causes an appropriate mixing of the uppermost toner layer and the lowermost toner layer on the intermediate transfer member, and further sharply increases the transparency of the toner layer itself, thereby causing good subtractive color mixing. .
[0047]
In addition, the flow of the sharp melt toner causes the air contained in the powder to escape and the thermal conductivity in the toner layer increases, so that even when the color toners are superimposed, the entire toner layer can be heated in a short heating time. It can be melted and is particularly effective in the image forming apparatus of this embodiment. Further, such a sharp melt color toner has a high affinity and is likely to be offset during fixing. However, in the present invention, the toner is peeled off from the intermediate transfer member 5 at a temperature equal to or lower than the toner softening point, so that no offset occurs at all.
[0048]
Next, the operation of the image forming apparatus as described above will be described.
In this image recording apparatus, before entering this cycle, the intermediate transfer member 5 is moved by one cycle, and an alternating electric field is formed by the electromagnetic induction heating device 12 with a lower power (for example, 100 W) than this cycle. The intermediate transfer body 5 is preheated by generating heat by the electromagnetic induction effect on the conductive layer 22 of the transfer body 5. As a result, the temperature of the intermediate transfer member 5 is raised to about 50.degree.
[0049]
On the other hand, the image information is decomposed into four color images of cyan (C), magenta (M), yellow (Y), and black (K), and the image forming units 1Y, 7M, 7C, 7K Different color toner images are formed on the top. The pre-heated intermediate transfer member 5 enters this cycle and circulates in a certain direction, and the toner image is transferred from the image carrier 1 by the action of the primary transfer roll 6. After the toner images are sequentially transferred from the four image forming units, the superimposed four color toner images are conveyed to a region facing the electromagnetic induction heating device 12 by the movement of the intermediate transfer body 5.
[0050]
In this region, the four color toner images on the intermediate transfer member 5 are melted by the heat generation of the conductive layer 22 due to electromagnetic induction. The melted toner is brought into pressure contact with the recording material P at room temperature at a position facing the pressure roll 11, and the toner image instantaneously penetrates into the recording material P to be transferred and fixed. At the exit of the nip, the toner temperature is lowered by contact with the recording material, and the toner cohesive force is increased, so that the toner image is almost completely transferred and fixed on the recording material without causing an offset. The
After the toner image is transferred and fixed, the intermediate transfer member 5 passes through a position facing the cooling device 16, the temperature of the intermediate transfer member 5 is cooled to about 50 ° C., and is conveyed again to the position facing the image forming unit. Then, the primary transfer of the toner image is performed in the next process.
[0051]
Next, an experiment conducted for confirming the effect of the image forming apparatus will be described.
<Experiment-1>
A comparative test was performed between the preheated and non-preheated image forming apparatus.
In the preheating, immediately before this cycle, 100 W, which is lower than the current cycle, was applied, and the intermediate transfer member 5 was heated for one cycle without a recording material. However, since the foam layer 22 has a property that it is difficult to warm but is difficult to cool, there is no particular problem even if some time (several seconds) is allowed between the preliminary cycle and the main cycle. Therefore, it is possible to start this cycle by taking an adjustment time so that the temperature of the foamed layer 22 becomes the temperature shown below, and the experiment was conducted by adjusting the preheating temperature as such.
[0052]
Further, in the experiment, the lower limit electric power was compared when the toner fixed on the recording material and the recording material were easily separated and the fixing property of the fixed toner was good. The results are shown in Table 1.
The evaluation of the fixing performance is 1 m²Per toner mass is 1.8 (g / m²) Was fixed, and the image part at that time was folded and then opened, and even if the evaluation image was rubbed with white paper, the image where both the unbent part and the bent part remained firmly was regarded as acceptable.
[0053]
The process speed was 160 mm / s and the nip width was 10 mm. The foam layer 22 is foamed PET, and its thermal conductivity is 0.04 (W / mK).
The power was measured using a wattmeter WT2010 manufactured by Yokogawa Electric Corporation.
Further, the temperature of the foam layer is obtained by measuring the surface temperature of the portion where the foam layer surface of the intermediate transfer member is exposed with a radiation thermometer R2-D2 manufactured by Keyence Corporation.
[0054]
[Table 1]

[0055]
As shown in Table 1, it can be seen that the required power can be reduced to about 80% by preheating the foam layer of the intermediate transfer member.
[0056]
Next, an experiment was conducted to investigate the relationship between the thermal conductivity of the foam layer and the required electric energy.
In this experiment, the thermal conductivity was changed by changing the material of the foam layer, and the electric power required for fixing was measured under the same conditions (with preheating) as in the above experiment. The result is shown in FIG.
[0057]
As shown in FIG. 3, it can be seen that if the thermal conductivity is about 0.1 (W / mK) or less, there is an effect of reducing power. This is considered to be because when the thermal conductivity is greater than 0.1 (W / mK), the amount of heat flowing into the foamed layer increases.
[0058]
Next, an experiment was conducted to measure temperature changes of the intermediate transfer member and the toner during transfer fixing when the preheating temperature of the intermediate transfer member was changed.
In this experiment, the preheating temperature of the intermediate transfer member is changed by one-dimensional thermal analysis, and the input power (necessary so that the temperature when the toner contacts the recording material is almost the same as the temperature when the preheating is not performed) The temperature of each step of the intermediate transfer member and the toner was measured. The results of this experiment are shown in Table 2.
At this time, the thermal conductivity of the foam layer is 0.04 (W / mK). In addition, the preheating method was performed by supplying power of about 100 W (a little different depending on the set temperature of the intermediate transfer member) without a recording material for one cycle, similarly to the preheating method in the experiment.
[0059]
[Table 2]

[0060]
From Table 2, it can be seen that the input power (required power) decreases as the preheating temperature of the intermediate transfer member increases. Moreover, this result is in good agreement with the result of the actual machine described above.
[0061]
Further, when the preheating temperature is increased, the input power (required power) seems to decrease and become saturated at a certain temperature. In order to clarify this, FIG. 4 shows the relationship between the initial temperature of the intermediate transfer member and the required power, and FIG. 5 shows the relationship between the initial temperature of the intermediate transfer member and the post-nip temperature of the intermediate transfer member.
[0062]
As shown in FIG. 4, it can be seen that when the pre-heating temperature of the intermediate transfer member is 55 ° C., the required power is 480 W. Further, as shown in FIG. 5, when the preheating temperature is 55 ° C., the post-nip temperature of the intermediate transfer member is also about 55 ° C. This means that it is not necessary to cool the foam layer of the intermediate transfer body after the toner image on the intermediate transfer body is transferred and fixed on the recording material and before the next primary transfer process.
[0063]
Next, an experiment was conducted to confirm the state of the image by continuously using the image forming apparatus under these conditions.
The condition for this experiment is that the pre-heating temperature of the intermediate transfer member should be 55 ° C. However, a temperature of 55 ° C. may interfere with other systems in the image forming apparatus, or a toner may be blocked in the developing device. Therefore, the preheating temperature in this experiment was set to 50 ° C. and the input power was 500 W. The temperature of the intermediate transfer member after the toner image was transferred and fixed on the recording material was adjusted to 50 ° C. using a fan as a cooling device.
In this experiment, 1000 sheets of J paper A4 made by Fuji Xerox Co., Ltd. were continuously inserted by lateral feed, and the toner was 1.8 g / m as the toner.²A solid image of 5 × 5 cm was fixed. As a result, it was confirmed that the fixing state was satisfactory.
[0064]
<Experiment-2>
As a comparative example of the image forming apparatus shown in FIG. 1, an image forming apparatus of a type in which the intermediate transfer member is preheated with an infrared lamp was used, and an experiment was conducted to investigate the input power at that time.
FIG. 8 is a schematic configuration diagram showing an image forming apparatus used for comparison. In this image forming apparatus, instead of the electromagnetic induction heating device 12 of the image forming apparatus shown in FIG. 1, an infrared lamp 112 is disposed opposite to the secondary fixing roll 108, and the intermediate transfer member 105 is heated by radiant heat. is there. As in the apparatus shown in FIG. 1, the image forming apparatus includes a primary transfer roll 106, image forming units 107Y, 107M, 107C, and 107K, a drive roll 109, a tension roll 110, and a pressure roll 111. The paper guide 113, the peeling claw 114, the guide member 115, and the cooling device 116 are provided, and these configurations are the same as those shown in FIG.
[0065]
Using the radiant heating type image forming apparatus using the infrared lamp 112, the input power was compared between when the intermediate transfer member was preheated and when it was not preheated. The evaluation criteria are the same conditions as in Experiment-1. The results of this experiment are shown in Table 3.
[0066]
[Table 3]

[0067]
As shown in Table 3, when the preheating is performed, the input power is reduced as compared with the case where the preheating is not performed, and it can be seen that the effect of the preheating is obtained regardless of the heating method based on the electromagnetic induction action. On the other hand, when Table 3 is compared with the results in Table 1, the input power is remarkably increased when heating with an infrared lamp as compared with the electromagnetic induction heating device. Therefore, it can be seen that the effect of reducing the input power is very large by using the electromagnetic induction heating method.
[0068]
In the image forming apparatus according to the present embodiment, the electromagnetic induction heating device 12 is disposed outside the intermediate transfer member 5, but is disposed inside the intermediate transfer member or both inside and outside. The same power reduction effect can be obtained.
[0069]
【The invention's effect】
As described above, in the image forming apparatus according to the present invention, the energy used when the toner image on the intermediate transfer member is heated in this cycle by providing the foam layer on the back surface of the intermediate transfer member and preheating it. Can be reduced. Moreover, since this foamed layer can drastically reduce the useless energy flowing out to the back side, energy efficiency can be improved. Further, the toner image on the intermediate transfer member is heated in the heating process, and the toner image is pressed against the recording material in a room temperature state in an area continuous with the area where the heating process is performed. It becomes possible to transfer and fix an image on a recording material instantly. For this reason, the temperature of the toner can be sufficiently lowered when the recording material is peeled from the intermediate transfer member, the occurrence of offset can be prevented, and a high-quality image with good fixability can be obtained.
Specifically, it has the following advantages and its utility value is great.
(1) Total energy consumption is small, and high-speed image formation is possible with limited power.
(2) By preheating the intermediate transfer member, it becomes unnecessary to cool the intermediate transfer member, or the temperature difference for cooling can be reduced, so that waste heat is reduced and efficient.
(3) Since the recording material acts as a cooling member and the temperature of the intermediate transfer member is rapidly lowered, there is no problem on the image carrier side.
(4) By forming a heat insulating elastic layer on the surface of the member constituting the heating means, a high-quality transfer-fixed image equivalent to the image quality fixed by a fixing device using a conventional soft roll can be obtained.
(5) Since offset development does not occur at all even with toner that is easily offset by sharp melt, it is sufficiently applicable not only to black-and-white copying machines but also to color copying machines.
(6) Since the heating amount of the recording material is very small, the transfer fixing property is hardly influenced by the thickness and heat capacity of the recording material, and further, the occurrence of curling and paper wrinkles is small.
(7) The warm-up time can be greatly shortened, and as a result, the electric power that has been applied to keep the heating means at the set temperature during standby can be deleted.
(8) In the case of a color toner, it is possible to peel a fixed image satisfactorily without using a release agent such as oil, which has been conventionally required for peeling the toner from the intermediate transfer member.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention.
2 is a partially enlarged view showing an intermediate transfer member used in the image forming apparatus shown in FIG.
3 is a graph showing the relationship between the thermal conductivity of the intermediate transfer member and the required power in the image forming apparatus shown in FIG.
4 is a graph showing a relationship between an initial temperature of an intermediate transfer member and required power in the image forming apparatus shown in FIG.
5 is a graph showing the relationship between the initial temperature of the intermediate transfer member and the temperature of the intermediate transfer member after transfer fixing in the image forming apparatus shown in FIG.
FIG. 6 is a diagram illustrating temperature changes of toner and an intermediate transfer member in a transfer fixing region when the intermediate transfer member is preheated.
FIG. 7 is a diagram illustrating temperature changes of toner and an intermediate transfer member in a transfer fixing region when preheating of the intermediate transfer member is not performed.
FIG. 8 is a schematic configuration diagram illustrating an image forming apparatus which is a comparative example.
[Explanation of symbols]
1 Image carrier
2 Charging device
3 Exposure equipment
4 Development device
5, 105 Intermediate transfer member
6,106 Primary transfer roll
7, 107 Image forming unit
8,108 Secondary transfer roll
9, 109 Drive roll
10, 110 Tension roll
11, 111 Pressure roll
12 Electromagnetic induction heating device
13, 113 Paper guide
14,114 Peeling nails
15, 115 Guide member
16, 116 Cooling device
21 Base material
22 Conductive layer
23 Surface layer
24 Foam layer
31 Excitation coil
32 Excitation circuit
112 Infrared lamp

Claims (5)

An image carrier on which a toner image is formed by selectively adhering toner to an endless peripheral surface;
An intermediate transfer member to which the endless peripheral surface is supported so as to be capable of circular movement, and the toner image is transferred at a portion of the outer peripheral surface facing the image carrier,
In the image forming apparatus that fixes the toner image on the intermediate transfer body at the same time as transferring to the recording material,
The intermediate transfer body has an endless belt-like substrate and a foam layer formed on the inside thereof.
A pressure member that presses the recording material against the intermediate transfer member;
Heating means for heating the intermediate transfer member on the upstream side in the circumferential direction of the intermediate transfer member from a position where the pressure member is provided;
The heating means drives the intermediate transfer member to rotate around immediately before the main cycle in which the toner image is transferred from the image carrier to the intermediate transfer member, and performs preliminary heating of the intermediate transfer member. The image forming apparatus is set to be heated to a temperature at which the toner image is transferred to the recording material and fixed at the same time. The intermediate transfer member has a heat generating layer made of a conductive material on the outside of the substrate,
The heating means includes an excitation circuit that forms an alternating magnetic field substantially orthogonal to the surface of the intermediate transfer member and performs electromagnetic induction heating.
The heating unit heats the intermediate transfer member carrying the toner image to a temperature equal to or higher than the softening point temperature of the toner and passes the nip portion where the recording material is pressed against the intermediate transfer member by the pressure member. 2. The intermediate transfer member is set to be heated so that a temperature of toner in contact with the intermediate transfer member and a recording material is lower than a softening point temperature of the toner. The image forming apparatus described.     The image forming apparatus according to claim 1, wherein the foam layer has a thermal conductivity of 0.1 W / mK or less.     The image forming apparatus according to claim 1, wherein the preheating performed by the heating unit is set so that the temperature of the intermediate transfer member is equal to or higher than normal temperature and lower than a toner softening point temperature.     A cooling device for adjusting the intermediate transfer member to a temperature not lower than a normal temperature and lower than a softening point temperature of the toner is provided downstream of the position where the pressure member is provided in the moving direction of the intermediate transfer member. The image forming apparatus according to claim 1.

Images