JP2007025453A - Separating member and fixing device and image forming apparatus provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive separating member which doesn't have a risk of injuring a surface of a fixing member or damaging a recording medium having high surface smoothness and glossiness and a fixed image and doesn't bring about disturbance of an image on the recording medium or poor secondary transfer, due to dew condensation, and a fixing device and an image forming apparatus provided with the same. <P>SOLUTION: A separating member 11 for separating a recording medium P ejected from a nip part 5 formed by a fixing member 2 and a pressure member 6 pressed to the fixing member, from the fixing member is formed like a wire and is disposed in proximity to the fixing member in parallel with a direction of a revolving shaft of the fixing member so that a diameter of the separating member 11 is smaller than a maximum amount of rise of the recording medium ejected from the nip part and a nip formed between the separating member 11 and the fixing member is smaller than a minimum amount of rise of the recording medium ejected from the nip part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separation member for a fixing device provided in a copying machine, a facsimile machine, a multifunction machine, etc., a fixing device and an image forming apparatus provided with the separation member, and more specifically, a sheet at a nip portion between a pair of fixing members Alternatively, in a device that allows a recording medium such as a sheet to pass through and applies heat and pressure to the toner of the toner image when passing through the recording medium and fixes the toner image to the recording medium, the recording medium after fixing can be easily separated from the fixing member. It relates to a separating member that can be produced. As an application field of the fixing device provided with the separating member, an image forming apparatus adopting an electrophotographic method such as PPC, LBP, and facsimile can be cited.

  In a color image forming apparatus configured as a copying machine, a facsimile, a printer, a printing machine, or a multifunction machine having at least two of these functions capable of reproducing multiple colors by applying electrophotography, it is heated. A fixing member and a pressure member that is in pressure contact with the fixing member, and a recording medium carrying a toner image to be fixed is pressed against the fixing member in a direction in which the toner image is in contact with the fixing member. An image forming apparatus that employs a fixing device that passes through a nip formed by pressure contact with a member and fixes the toner image onto a recording medium by the action of heat and pressure is generally used. In the fixing device of this type, when the toner carried on the recording medium passes through the nip portion formed by the fixing member and the pressure member, the toner melts in the nip portion. There is a possibility that the recording medium that has come out of the portion is wound around the surface of the fixing member without being separated from the surface. In particular, in an image forming apparatus that forms a full-color image, a plurality of toner images of different colors are superimposed on each other on a recording medium, and such a superimposed toner image is fixed by a fixing device. This melts the toner, which increases the adhesive strength of the toner and makes the recording medium more easily wound around the fixing member. Further, the discharge direction of the recording medium after passing through the nip portion changes depending on the shape of the nip portion, and the possibility of winding around one of the fixing roller and the pressure roller as a fixing member increases.

  Therefore, conventionally, a separating means composed of a plurality of separating claws is brought into contact with the surface of the recording medium passing area on the fixing member side where the recording medium may be wound, and the recording medium that has come out of the nip portion is separated by the separating claws. A fixing device that is separated from the surface of the fixing member and prevents the recording medium from being wound around the surface of the fixing member has been employed (see, for example, Patent Documents 1, 2, and 3). However, since the tip of the separation claw is in contact with the surface of the fixing member on the recording medium passage area, the surface of the fixing member may be damaged by the separation claw. When a flaw occurs on the surface of the fixing member, the toner image passing through the nip portion is disturbed, and the image quality of the toner image after fixing is deteriorated.

  In order to eliminate such defects, there has been proposed a fixing device in which the function of the separation claw is separated from the surface of the fixing member and disposed as a separation plate (see, for example, Patent Documents 4 and 5). However, in the separation plate arranged in a non-contact state with respect to the surface of the fixing member, the recording medium exiting the nip portion enters between the fixing member and the separation plate while adhering to the surface of the fixing member. There is a possibility that the recording medium is wound around the fixing member, the separation function of the recording medium is lowered, and the possibility that the recording medium is wound around the fixing member is increased. In addition, when a metal separation plate having a thickness of about 0.2 mm as used in Patent Document 5 is used, the metal separation plate is extremely thin, so that the edges are rounded. It is difficult to process, and when the recording medium comes into contact with the edge of the metal separator, the recording medium with high surface smoothness and glossiness, such as an OHP sheet or coated paper, is fixed. There has been a problem that the full color image may be damaged like a scratch. Furthermore, the fixing device using the separator plate uses a metal separator plate with a large volume to secure a gap between the fixing member and the separator plate. Below, when the moisture-containing air in the fixing device or the recording medium comes close to the metal separation plate, the moisture in the air or the recording medium gradually accumulates on the surface of the separation plate to form water droplets (condensation). There is a problem that water droplets accumulated on the surface of the separation plate may flow backward to the recording medium and disturb the print image fixed on the recording medium. In addition, when water droplets accumulated on the surface of the separation plate flow back to the recording medium, the moisture content of the recording medium increases and the resistance value decreases, so that in the case of duplex printing, the toner image is secondarily transferred to the back side. At this time, there is a problem that a secondary transfer failure may occur and the image quality may deteriorate.

JP 2001-215825 A JP 2003-107953 A JP 2005-010218 A JP 2004-226815 A Japanese Patent Laid-Open No. 11-184300

  Therefore, the present invention solves the problems of the conventional one, and there is no possibility of damaging the surface of the fixing member, damaging a recording medium or a fixed image having high surface smoothness and glossiness, and dew condensation. An object of the present invention is to provide an inexpensive separation member, a fixing device including the separation member, and an image forming apparatus that do not disturb an image on a recording medium or cause a secondary transfer failure. To do.

  In order to solve the above-mentioned problem, the invention according to claim 1 separates, from the fixing member, a recording medium discharged from a nip portion composed of a fixing member and a pressure member pressed against the fixing member. A separating member that is formed in a wire shape and is arranged close to and parallel to the rotation axis direction of the fixing member, the diameter of which is smaller than the maximum lifting amount of the recording medium discharged from the nip portion, and fixing. The gap formed with the member is arranged so as to be smaller than the minimum lifting amount of the recording medium discharged from the nip portion.

According to a second aspect of the present invention, in the first aspect, the wire-shaped wire main body arranged in parallel to the rotation axis direction of the fixing member, and the surface of the wire main body outside the sheet passing range of the fixing member; A gap holding member provided in contact with a surface outside the sheet passing range of the fixing member at a corresponding portion, and the wire main body is provided with a shaft center different from that of the gap holding member. Features. The invention according to claim 3 is characterized in that, in claim 1 or 2, the linear thermal expansion coefficient is 8.0 × 10 ⁻⁶ / K or less.

  According to a fourth aspect of the present invention, the separation member according to any one of the first to third aspects is provided, and the separation member is rotatable in the same direction as the rotation direction of the fixing member. It is a fixing device. According to a fifth aspect of the present invention, in the fourth aspect, the cleaning member for cleaning the separation member is provided. A sixth aspect of the present invention is characterized in that, in the fifth aspect, the cleaning member is mounted on the wire body of the separating member and is slidable in the axial direction of the wire body. According to a seventh aspect of the present invention, in the fifth aspect, the cleaning member comes into contact with the wire main body when the gap between the wire main body and the fixing member is increased by rotation of the gap holding member. It is mounted at a position. According to an eighth aspect of the present invention, in any one of the fourth to seventh aspects, a static elimination member for neutralizing the separation member is provided. A ninth aspect of the present invention is the method according to any one of the fourth to eighth aspects, wherein the separation member is composed of one layer or a plurality of layers, and the outermost layer is a fluororesin having a releasability or a fluorine having a releasability. It is characterized by being covered with rubber.

  According to a tenth aspect of the present invention, there is provided an image forming apparatus comprising the fixing device according to any one of the fourth to ninth aspects.

  The present invention is as described above, wherein the separation member is formed in a wire shape, and is arranged in close proximity to and parallel to the rotation axis direction of the fixing member, and the maximum diameter of the recording medium discharged from the nip portion. Since the gap formed between the fixing member and the fixing member is smaller than the minimum lifting amount of the recording medium discharged from the nip portion, the volume is reduced as compared with the conventional one. . Therefore, since the heat capacity of the separation member is reduced and the temperature rise time of the separation member due to heat radiation or heat transfer by the heating source in the fixing device is shortened, the surface of the fixing member is damaged, the surface smoothness and There is no possibility of damaging a recording medium or a fixed image having a high glossiness, which contributes to a high durability of the fixing member. In addition, it is possible to suppress the occurrence of condensation on the surface of the separating member, thereby preventing the image on the recording medium from being disturbed or causing a secondary transfer failure or the like, thereby contributing to preventing a deterioration in quality such as a fixing failure. Further, since the separating member is in the form of a wire (wire), the installation space in the fixing device is not easily limited, and the cost of the fixing device is reduced. In addition, the gap between the separation member and the fixing member can be easily ensured, which contributes to increase the reliability of the separation function of the separation member.

  In addition to the above, in the ratio with the conventional separation claw or separation member, the separation claw cannot avoid physical damage to the fixing member such as the fixing belt because of contact separation, but the separation member is in the form of a wire. The fixing member is disposed in proximity to each other, and there is no physical damage to the fixing member due to non-contact separation. Although the separation plate is non-contact separation, its volume is large and its heat capacity is large.Therefore, when the apparatus starts up, moisture in the atmosphere in the apparatus and the recording medium is condensed, but the separation member has a small volume and heat capacity. Is small and therefore no condensation occurs. The separation claw and the separation plate are preferably cleaned because they are contaminated by the scattered toner in the apparatus and the toner on the recording medium, but it is difficult to install a cleaning mechanism because the separation point is fixed. Since the separation member is rotatable, it is easy to add a cleaning mechanism. Further, the separation performance is improved as compared with the separation claw and the separation plate, and the space saving is excellent, so that the layout in the apparatus is easy and the degree of freedom of the apparatus is high.

  An embodiment of the present invention will be described with reference to the drawings.

  1 is a side view of the belt fixing device, and FIG. 2 is an enlarged view of a portion A in FIG. Reference numeral 1 denotes a belt fixing device, an endless fixing belt 2, a fixing roller 3 and a heating roller 4 as a pair of belt conveying rollers that rotatably support the fixing belt, and a fixing belt 2 below the fixing roller 3. And a pressure roller 6 that forms a nip portion 5 and presses an unfixed recording medium against the belt. The nip portion 5 may be formed by a pair of fixing members, and may be formed by, for example, the fixing roller 3 and the pressure roller 6.

  The heating roller 4 has a heater 7 as a heat source therein. The pressure roller 6 has a cored bar and at least one of an elastic layer and a release layer on its surface, and has a heater 8 as a heat source inside. The fixing belt 2 is driven and rotated in the direction of the arrow by the fixing roller 3. The fixing belt 2 has a surface layer made of a thin film release material such as a belt base composed mainly of polyimide and a mixed coat of PTFE (polytetrafluoroethylene resin) and PFA (perfluoroalkyl vinyl ether resin). The fixing belt 2 may have a multilayer structure in which an elastic layer made of silicone rubber is sandwiched between a belt substrate and a release layer, and the release layer material may be either PTFE or PFA.

  As described above, the recording medium P discharged from the nip portion 5 is separated from the fixing belt 2 on the downstream side in the conveyance direction of the recording medium P of the nip portion 5 formed by the fixing belt 2 and the pressure roller 6. The wire-shaped separating member 11 is disposed so as to be rotatable in the same direction as the moving direction of the surface of the fixing belt 2. A rotating mechanism such as a motor or a spring may be provided for rotating the separating member.

  4 and 5, the separating member 11 has a wire main body 12 arranged in parallel to the rotation axis direction of the fixing roller 3, and the surface of the wire main body outside the sheet passing range of the fixing belt 2 is provided. A gap holding member 13 that abuts the surface outside the sheet passing range of the belt is held at the corresponding end portions by holding the gap 14 between the surface of the wire body 12 and the surface of the fixing belt 2. It is provided with a heart. It is desirable that the gap 14 does not change greatly even if the ambient temperature in the fixing device 1 changes by about 200 ° C. Therefore, it is necessary to use a material having a low coefficient of linear thermal expansion for the wire body 12 and the gap holding member 13. Examples of the material having a low linear thermal expansion coefficient include an Invar alloy made of Fe-36Ni and a Kovar alloy made of Fe29Ni-17Co. The wire body 12 is composed of one layer or a plurality of layers, and the outermost layer is covered with a fluororesin having a releasability or a fluororubber having a releasability.

  The separation member 11 has a diameter smaller than the maximum lifting amount of the recording medium P discharged from the nip portion 5, and the recording medium P from which the gap 14 formed between the separation member and the fixing belt 2 is discharged from the nip portion 5. Are arranged close to each other in a non-contact state so as to be smaller than the minimum lifting amount.

  The gap 14 is closely related to the amount of floating when the recording medium P reaches the wire body 12 of the separating member 11 and the margin length of the leading end of the recording medium P. The relationship between the two depends on the size of the margin portion. Is set in consideration of changes. That is, since the adhesive force of the toner acts on a portion that is not a margin portion, the amount of lift of the tip portion decreases as the margin portion becomes shorter. In order to set the maximum lifting amount and the minimum lifting amount, a recording medium (paper medium) having a different margin length is passed through the fixing device 1 and a position discharged from the nip portion 5 after fixing is photographed using a high-speed camera, for example. After that, the amount by which the leading end of the paper medium is lifted from the fixing belt 2 is obtained using image processing software. In any case, the maximum and minimum meanings are within the range where the margin length is changed. FIG. 3 shows the relationship between the margin length of the recording medium P and the height at which the tip is lifted.

  FIG. 3 shows the relationship between the leading edge margins of the three types of recording media P and the lifting height h (see FIG. 2) immediately after discharge from the nip portion 5. In this example, the second mark shown by ◆. Ricoh type 6200 of Ricoh Co., Ltd. indicated by the original drawing and ■, and a postcard indicated by ▲ were used. As can be seen from FIG. 3, the thick paper is relatively separated from the surface of the fixing belt 2, and the thin paper tends to adhere to the fixing belt 2. This difference is due to the paper strain, and the leading edge of the recording medium P discharged in this way is slightly lifted. For this reason, the wire body 12 of the separating member 11 is set to have a diameter equal to or less than the maximum paper lifting amount, and the gap 14 formed between the wire body and the fixing belt 2 is made smaller than the minimum paper lifting amount. By disposing the recording medium P, the recording medium P can be separated from the surface of the fixing belt 2.

  In the fixing device 1 as described above, the recording medium P carrying the unfixed toner image passes through the nip portion 5 to fix the toner to the recording medium, and then is disposed on the downstream side of the nip portion 5. 11 and separated by the paper transport guides 16 and 17 to the discharge port.

  Since the separating member 11 has the wire body 12 as described above, even when the same material as the conventional separating plate is used, a significant reduction in heat capacity can be obtained compared to the conventional separating plate, and the wire body 12 The thermal response of becomes higher. Therefore, it is easy to raise the temperature of the wire main body 12 by heat transfer from the fixing member, and even if water vapor present in the atmosphere in the apparatus or in the recording medium P contacts the wire main body 12, it forms water droplets and forms dew. Has the advantage of eliminating

  In FIG. 4, reference numeral 23 denotes a cleaning member, which comprises a central hole and a groove opened outward from the hole. The central hole is fitted into the wire body 12 through the groove, and the wire body 12 is indicated by an arrow. It is possible to move in the axial direction. When the cleaning member 23 is moved, it is desirable that the separation member 11 can rotate in the direction opposite to the rotation direction for the separation so that the gap 14 can be formed large. FIG. 5 shows the gap in this case. The gap 14a at the time of cleaning in (B) is larger than the gap 14 at the time of separation in (A). Therefore, in this case, the cleaning member 23 moves along the wire body 12 when the wire body 12 of the separating member 11 is separated from the fixing belt 2 so as to form the gap 14 a by the rotation of the gap holding member 13. Thus, cleaning is performed.

  6 and 7 show a modified example of the cleaning member, and the cleaning member 28 of this modified example is provided so as to be able to contact over almost the entire length of the wire body 12 of the separating member 11. Also in this case, it is desirable that the separation member 11 can be rotated in the direction opposite to the rotation direction for the separation. Therefore, also in this case, when the wire main body 12 of the separating member 11 is separated from the fixing belt 2 so as to form the gap 14 a by the rotation of the gap holding member 13, the cleaning member 28 is formed on the track surface drawn by the wire main body 12. Cleaning is performed by physical contact.

  FIG. 8 shows a cleaning member 38 of the same type as that of the cleaning member 23 with a function of discharging the wire body 12 of the separating member 11, and a discharging brush on the inner surface of the central hole that fits the wire body 12 of the cleaning member 38. An example with 40 attached is shown. When the cleaning member 38 that also functions as a static elimination function is used, the wire body 12 uses a spring, a crank mechanism, a cam mechanism, or the like to form a gap 14a formed between the wire body and the fixing belt 2. It is desirable to have a variable mechanism. As a result, the cleaning member 38 can be cleaned over the entire outermost surface of the wire body 12 without damaging the fixing belt 2, thereby improving the durability of the fixing belt 2, improving the fixing image quality, and The cleaning performance of the cleaning member 38 and the reliability of the charge removal performance can be improved.

  As described above, the separation member 11 that separates the recording medium P after passing through the nip portion 5 from the fixing belt 2 is disposed in a non-contact state with respect to the recording medium passage region of the fixing belt, and is formed into a wire shape. The separation member having a reduced heat capacity and the apparatus configuration of a fixing device using the same are shown. As a result, it is possible to simultaneously solve the problem of deterioration of the image quality due to physical damage of the fixing member such as the fixing belt and the fixing roller and condensation of the separating member, and it is possible to improve the degree of design freedom by downsizing the separating member. . As a result, it provides a highly durable and highly reliable fixing device characterized by high durability of the fixing member, improved separation performance, and improved fixing image quality, and contributes to improving customer satisfaction.

  FIG. 9 shows another embodiment in which the separating member 41 is also disposed near the base end of the lower transport guide 17. Other configurations are the same as those in the above embodiment. When the separating members 11 and 41 are arranged near the base ends of the pair of conveying guides 16 and 17, that is, near both the fixing members 2 and 6, the recording medium P that has floated after passing through the nip portion 5 is separated. Even when the paper is separated and transported downward, it is separated by the separating member 41 and guided to the paper transport path in both guides by the lower transport guide 17.

  Hereinafter, further detailed experimental examples, comparative examples, and evaluation examples will be described based on the embodiment.

<Experimental example 1>
The diameter of the wire body 12 of the separating member 11 was set to 2.5 mm, and the gap 14 was set to be 0.3 mm larger than the minimum lifting amount of the paper. As the material of the separating member 11, cast iron having a linear thermal expansion coefficient of 10.0 × 10 ⁻⁶ [/ K] was used. In the configuration of the fixing device 1, the pressure roller 6 has a structure in which a cored bar, an elastic layer made of silicone rubber and a release layer made of PFA are formed on the surface thereof. The fixing belt 2 has a belt base composed mainly of polyimide (PI) and a thin film release layer made of PFA as an outermost layer, and has an elastic layer made of silicone rubber between the PI base and the release layer. A three-layer structure was adopted.

<Experimental example 2>
In the separation member 11 of Experimental Example 1, the gap 14 formed between the wire main body 12 and the fixing belt 2 was disposed so as to be smaller than the minimum lifting amount of the recording medium P.

<Experimental example 3>
In the separation member 11 of Experimental Examples 1 and 2, an Invar alloy made of Fe-36Ni was used as the material of the wire body 12 and the gap holding member 13. Invar alloy is known as a material having a low coefficient of linear thermal expansion, and the coefficient of linear thermal expansion at 200 ° C. or lower of the Invar alloy used in this experimental example was 2.0 × 10 ⁻⁶ [/ K].

The fixing device configuration is the same as the material of the wire body 12 and the gap holding member 13, but the temperature dependence of the gap 14 in the fixing device configuration using each wire body when other materials are used as the wire body 12. Table 1 shows the results of the examination. In addition, the linear thermal expansion coefficient of each material is as follows. ^{Stainless, 15.0 × 10 -6 [/K];Alloy903,8.0×10 -6} [/ K]; Invar ^{alloy, 2.0 × 10 -6 [/ K} ].

部材温度170℃において、ステンレスとAlloy903を用いたワイヤ本体12では、ギャップ14が得られなくなっていた。一方、インバー合金を用いたワイヤ本体12では、部材温度170℃においても0.06[mm]のギャップを維持していた。このことから、インバー合金などの線熱膨張係数の低い部材を用いることによって、定着装置１内におけるワイヤ本体12の温度変化範囲内で、ギャップを確保できることがわかる。このことは、定着装置１の通常使用範囲内では、ワイヤ本体12と定着ベルト２が常に非接触状態を保つことを示しており、定着ベルト２の損傷を防止し、定着ベルトの高耐久性、定着画質の高信頼性を向上させる。

At a member temperature of 170 ° C., the gap 14 could not be obtained in the wire body 12 using stainless steel and Alloy 903. On the other hand, in the wire body 12 using Invar alloy, a gap of 0.06 [mm] was maintained even at a member temperature of 170 ° C. From this, it is understood that a gap can be secured within the temperature change range of the wire body 12 in the fixing device 1 by using a member having a low linear thermal expansion coefficient such as an Invar alloy. This indicates that the wire main body 12 and the fixing belt 2 are always kept in a non-contact state within the normal use range of the fixing device 1, which prevents the fixing belt 2 from being damaged, and the fixing belt has high durability. Improves the reliability of fixing image quality.

<Experimental example 4>
In the separation member 11 of Experimental Examples 1 to 3, a motor was installed at the end of the wire body 12 so that it could rotate in the same direction as the moving direction of the surface of the fixing belt 2. The rotational speed of the wire main body 12 was set by motor control so that the linear outermost linear velocity of the wire main body 12 and the surface linear velocity of the fixing belt 2 opposed thereto were substantially equal. As a result, there is no difference in the speed between the outermost part of the wire main body 12 and the recording medium P in contact therewith, or the difference becomes extremely small, so that the wire main body 12 scratches the toner image on the recording medium. It is possible to prevent the generation of streaking in the toner image without applying force. Further, when the wire main body 12 rotates in the same direction as the movement direction of the surface of the fixing belt 2, the recording medium is separated from the fixing belt 2 when the recording medium P contacts the wire main body 12. Rotational torque can be given in the direction to be caused. Therefore, the separation performance of the wire body 12 can be further improved.

<Comparative Example 1>
Although it is the same as the apparatus configuration of the fixing apparatus 1 of the experimental example 1 described above, a separation claw that is a contact type separation means is used as a separation member.

<Comparative example 2>
Although it is the same as the apparatus configuration of the fixing apparatus 1 of the above-described experimental examples 1 and 2, a separation plate which is another non-contact type separation means was used as a separation member.

<Evaluation Example 1>
In Experimental Examples 1 to 4 and Comparative Examples 1 and 2 described above, the paper separation performance of the recording medium P after fixing the unfixed toner, the fixing belt durability, and the disturbance of the fixed image due to condensation on the surface of the separation member were evaluated. The results are shown in Table 2. The explanation of each rank symbol and the judgment criteria are as shown in Table 3. To evaluate the disturbance of the fixed image caused by condensation, leave the fixing device with each configuration in a low-temperature, high-humidity environment of 10 ° C and 70% where condensation is likely to occur, and start up the device. In this case, it was examined whether the initial fixed image was disturbed by condensation.

From the above results, Experimental Example 4 was the best evaluation result as the separating member.
In Experimental Example 1, there was paper separation performance, there was no disturbance in the fixed image due to condensation, and the evaluation result showed that there was little damage to the fixing belt 2. In Experimental Example 1, the heat capacity of the separation member was reduced without greatly impairing the paper separation function, so that the thermal responsiveness was superior to the separation plate method with respect to the temperature rise of the fixing member due to the start-up of the apparatus. It depends. That is, even if dew condensation occurs on the wire body 12, as soon as the fixing member rises in temperature when the apparatus is started up, the separation member also rises in temperature, and the water droplets are changed to water vapor again.
On the other hand, Experimental Example 1 was slightly inferior in paper separation performance as compared with Comparative Example 1. On the other hand, compared with Comparative Example 2, the durability and paper separation performance of the fixing belt 2 were slightly inferior. However, it is superior to the other comparative examples 1 and 2 as a separation member that achieves paper separation performance without damaging the fixing belt 2 and does not induce disturbance of the fixed image due to condensation.

  In Experimental Example 2, the paper separation performance was improved as compared with Experimental Example 1. This is because, in Experimental Example 2, the wire body 12 can more reliably supplement the recording medium P wound around the fixing belt 2.

  In Experimental Example 3, the durability of the fixing belt 2 was improved as compared with Experimental Example 2. This is because, in Experimental Example 3, since the wire body 12 is made of a material having a low coefficient of linear thermal expansion, the gap 14 can be held even if the temperature changes in the fixing device 1. It is.

  In Experimental Example 4, compared with Experimental Example 3, the paper separation function was further improved. This is because when the wire body 12 of the separating member 11 rotates in the same direction as the moving direction of the surface of the fixing belt 2, the recording medium is fixed to the recording medium when the recording medium P contacts the wire body 12. This is because rotational torque can be applied in the direction of separation from the belt.

From the above, it has been found that the wire body 12 is excellent as a separating member that simultaneously satisfies the high durability of the fixing member, the improvement of the separation performance, and the improvement of the fixing image quality, and Experimental Example 4 is the best. However, when the fixing device composed of the separation member used in these experimental examples is used, it is caused by various factors such as electrostatic adhesion of scattered toner in the fixing device and toner adhesion due to contact during separation of the recording medium. Deterioration of the fixing image quality due to toner adhesion to the wire body 12 was induced, resulting in a malfunction in the performance of the fixing device 1.
Therefore, the following experimental examples were evaluated.

<Experimental example 5>
In the fixing device 1 composed of the separating member 11 used in Experimental Example 4, as shown in FIG. 4, cleaning is performed by periodically driving the wire body 12 in the long axis direction to clean the wire body. A member 23 was provided. When the cleaning member 23 is provided in the wire main body 12 of the separating member 11 as in the present experimental example, the fixing belt 2 should have a mechanism in which the gap 14 formed by the wire main body 12 and the fixing belt 2 can be changed. Efficient cleaning is possible without damaging. In the present experimental example, as shown in FIG. 5, a mechanism for changing the gap 14 by adopting eccentricity within the circular cross section of the gap holding member 13 was adopted. As a result, the initial gap 14 changes to the gap 14a as the gap holding member 13 rotates 180 degrees in the same direction as the surface movement direction of the fixing belt 2 from the initial state. By installing the cleaning member 23 at the displacement position of the wire main body 12 when the gap holding member 13 rotates 180 degrees, the cleaning function can be performed without damaging the fixing belt 2.

  The cleaning member 23 may be a cleaning member 28 having a length over the entire length of the wire body 12 as shown in FIGS. In this case, the cleaning member 28 is arranged so as to be applied on the displacement locus of the wire body when the gap between the wire body 12 and the fixing belt 2 changes from the gap 14 to the gap 14a.

<Experimental example 6>
In the fixing device 1 composed of the separating member 11 used in Experimental Example 4, the neutralizing brush 40 shown in FIG. 8 is attached on the inner cavity surface of the cleaning member 23 to simultaneously perform the cleaning function and the neutralizing function. Became possible. This prevents scattered toner or the like in the fixing device 1 from electrostatically adhering to the wire body 12, thereby preventing deterioration of the fixed image quality and contributing to improving the reliability of the fixed image quality.

<Experimental example 7>
In the fixing device 1 including the separating member 11 used in Experimental Example 4, the outermost layer of the wire body 12 was coated with PFA. As a result, the releasability of the surface layer of the wire body 12 is further improved, and toner adhesion to the wire body due to various causes is prevented, thereby preventing deterioration of the fixed image quality and improving the reliability of the fixed image quality. Contribute.

<Experimental Example 8>
Experimental examples 5 and 6 were provided.

<Experimental Example 9>
Examples 5 and 7 were provided.

<Experimental example 10>
Experimental examples 6 and 7 were provided.

<Experimental example 11>
Experimental examples 5, 6 and 7 were provided.

<Evaluation Example 2>
In Experimental Examples 4 to 11, a toner smear evaluation of a fixed image was performed. As a criterion for judgment, whether or not toner stains are observed in a fixed image after 100 k continuous paper feeding is determined by ranking as shown in Table 5.

  From the above results, Experimental Examples 8 to 11 were the best evaluation results. In Experimental Example 5, the surface of the wire main body 12 can be regularly maintained without toner adhesion due to physical contact. Experimental Example 6 can prevent the scattered toner in the fixing device 1 from adhering to the surface of the wire body due to the charging of the wire body 12. Experimental Example 7 can prevent unfixed toner from sticking to the surface of the wire body. In each of Experimental Examples 5, 6 and 7, the fixed image after passing 100k was found to have a somewhat disturbed image due to toner contamination, but the fixed image quality was within an allowable range. In Experimental Examples 8 to 11 in which these Experimental Examples 5 to 7 were combined, no image distortion due to toner contamination was observed in the fixed image after 100 k paper was passed. This is due to the combination of Experimental Examples 5 to 7, and the toner adhesion on the surface of the wire main body due to various factors such as electrostatic adhesion of scattered toner in the fixing device 1 and toner adhesion due to contact at the time of separation of the recording medium. This indicates that it was possible to prevent In particular, in Experimental Example 11, image disturbance due to toner smearing was not observed in the fixed image even after 200 k paper was passed.

  From the above results, it is possible to completely prevent toner stains on the fixed image by using Experimental Examples 5 to 7 or these Experimental Examples in combination. This does not induce deterioration of the fixed image quality due to remelting of the adhered toner, and contributes to improving the reliability of the fixed image quality. Therefore, by using the fixing device 1 using the separating member 11, a highly durable and highly reliable fixing device characterized by high durability of the fixing member, improvement of separation performance, and improvement of fixing image quality is provided. And contribute to the improvement of customer satisfaction.

  Next, a characteristic effect of the invention described in claim 2 and the following claims will be described. According to the second aspect of the present invention, since the wire main body can be moved away from the fixing member by the rotation of the gear-up holding member, it is convenient to avoid buffering with the fixing member, for example, when cleaning the wire main body. It will be a thing. According to the invention described in claim 3, since the linear thermal expansion coefficient of the separation member is low, a change in the gap between the separation member and the fixing member due to a temperature change in the fixing device can be reduced. This contributes to increasing the durability of the fixing member, improving the fixing image quality, and increasing the reliability of the separating function of the separating member.

  According to the fourth aspect of the present invention, the torque acts on the recording medium in the direction in which the recording medium is separated from the fixing member, and the reliability of the separating function of the separating member is increased, thereby improving the reliability of the fixing device. Contributes to increase. According to the fifth aspect of the present invention, it is possible to periodically clean the separation member so that the surface of the separation member is free from toner adhesion due to physical contact. For this reason, it is possible to prevent the toner from adhering to the recording medium from the separating member, so that the fixed image is not disturbed, and the quality of the fixed image is improved.

  According to the sixth aspect of the invention, the wire body can be cleaned by sliding the cleaning member in the axial direction of the wire body. According to the seventh aspect of the present invention, the wire body can be cleaned without the need to dispose the cleaning member on the separating member side.

  According to the eighth aspect of the present invention, the separation member can be periodically neutralized to prevent the scattered toner in the fixing device from adhering to the surface of the separation member due to charging of the separation member. For this reason, it is possible to prevent the toner from adhering to the recording medium from the separating member, so that the fixed image is not disturbed, and the quality of the fixed image is improved. According to the ninth aspect of the present invention, since the releasability of the outermost layer of the separation member is good, the fixation of unfixed toner to the separation member is suppressed, so that the fixed image is not disturbed and the fixed image quality is improved. It contributes to the improvement. According to the tenth aspect of the present invention, it is possible to provide an image forming apparatus equipped with the fixing device according to any one of the fourth to ninth aspects.

1 is a schematic side view showing a belt fixing device according to an embodiment of the present invention. It is the A section enlarged view of FIG. 5 is a graph showing a relationship between a leading edge margin for each recording medium and a leading edge lifting height after fixing. It is the perspective view which looked at the wire-shaped separation member from the nip part discharge side. (A) is the principal part enlarged view which shows the gap at the time of isolation | separation, (B) is the gap at the time of cleaning, respectively. It is a principal part enlarged view which shows the modification of a cleaning member. It is a perspective view same as the above. It is a principal part enlarged view which shows the example which added the static elimination function to the cleaning member. It is a principal part enlarged view which shows another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Belt fixing apparatus 2 Fixing belt 3 Fixing roller 4 Heating roller 5 Nip part 6 Pressure roller 7, 8 Heater (heat source)
11, 41 Wire-like separation member
12 Wire body
13 Gap retaining member
14, 14a gap
16, 17 Paper transport guide
23, 28, 38 Cleaning member
40 Static elimination brush P Recording medium

Claims (10)

A separation member for separating a recording medium discharged from a nip portion formed of a fixing member and a pressure member pressed against the fixing member from the fixing member;
It is formed in the shape of a wire and is arranged close to and parallel to the rotation axis direction of the fixing member. The diameter is smaller than the maximum lifting amount of the recording medium discharged from the nip portion and is formed between the fixing member and the fixing member. The separation member is disposed so that the gap is smaller than the minimum lifting amount of the recording medium discharged from the nip portion.   A wire body arranged in parallel to the rotation axis direction of the fixing member, and a portion of the wire body corresponding to a surface outside the sheet passing range of the fixing member, on a surface outside the sheet passing range of the fixing member The separation member according to claim 1, further comprising a gap holding member provided in contact with the wire body, wherein the wire main body is provided with a shaft center different from that of the gap holding member. The separation member according to claim 1 or 2, wherein a linear thermal expansion coefficient is 8.0 × 10 ^-6 / K or less.   A fixing device comprising the separation member according to claim 1, wherein the separation member is rotatable in the same direction as the rotation direction of the fixing member.   The fixing device according to claim 4, further comprising a cleaning member for cleaning the separation member.   The fixing device according to claim 5, wherein the cleaning member is attached to the wire body of the separating member and is slidable in the axial direction of the wire body.   The fixing device according to claim 5, wherein the cleaning member is mounted at a position in contact with the wire main body when the gap is formed between the wire main body and the fixing member by a rotation of the gap holding member. .   The fixing device according to claim 4, further comprising a static elimination member for neutralizing the separation member.   9. The fixing device according to claim 4, wherein the separating member is composed of one layer or a plurality of layers, and the outermost layer is covered with a fluororesin having releasability or a fluororubber having releasability. .   An image forming apparatus comprising the fixing device according to claim 4.

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