JP2012083419A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that solves a problem of likelihood of decrease in collection performance of a collection member due to the presence of a portion to be kept in proper temperature and a portion to be cooled inside a fixing unit, the portion to be kept in proper temperature being a collecting member that is required to be kept in temperature between a melting point and a sublimation point of a mold release wax, the portion to be cooled being a rotor inside the fixing unit for heat fixing that is required to be cooled to address temperature rise of an end portion thereof generated by successive feeding of small-sized sheets.SOLUTION: Cooling means is disposed downstream side in the rotational direction of a rotor in a fixing unit for heat fixing, rather than a collecting member area.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic recording system.

  In an image forming apparatus using an electrophotographic recording method, there is an apparatus that uses toner containing release wax in order to cope with a phenomenon in which toner is offset by a fixing device. By embedding the release wax in the toner, the release wax moves to the interface between the molten toner and the fixing roller during heat fixing, and prevents the molten toner from crying to the fixing roller side, thereby improving the anti-offset performance. ing.

  However, the release wax contained in the toner is liquefied at the time of heat fixing, and a part of the wax is sublimated to become a gas. The wax component cooled immediately after vaporization solidifies again and moves on the wind flowing in the machine. Then, there was a phenomenon that the solidified wax component was liquefied again and adhered at various points in the machine where the temperature rose by passing paper. In the machine, the temperature tends to rise at the point where the recording material comes into contact. That is, the wax component tends to adhere to the recording material conveyance guide and the conveyance roller. If wax components adhere to the recording material conveyance guide or conveyance roller, the recording material conveyance may be hindered or the friction coefficient of the roller may be reduced. A special response was necessary.

  In recent years, users tend to use recording materials of various sizes. In particular, small envelopes and postcard sizes are widely used. However, when fixing is performed by continuously passing a small-size recording material, the surface temperature of the non-sheet passing area on the fixing roller side may excessively increase and damage parts in the apparatus. In order to cope with this phenomenon, Patent Document 1 proposes a technique in which a cooling fan is provided at the end of the fixing roller.

JP 2008-32904 A

  Recently, laser beam printers have become very demanding for high speed, downsizing, and media flexibility. In order to satisfy the fixing performance at a higher speed in image formation, higher heat energy and pressure are required than ever before. If an attempt to increase the speed is achieved only by increasing the pressing force, a structure that can withstand the pressing force is required, and thus there is a possibility that the request for miniaturization may not be sufficiently satisfied.

  In order to satisfy the miniaturization, a method of increasing the heating time and a method of increasing the heating temperature are conceivable as methods for increasing the thermal energy applied to the recording material. However, in both cases, the thermal energy given to the toner on the recording material increases. As the heat energy applied to the toner increases, the amount of the release wax that vaporizes also increases.

  It is conceivable to provide a member for collecting the vaporized component inside the fixing device. However, when a fan for cooling the non-sheet passing portion is also attached, the cooling air affects the collection member, and the vaporized component by the collecting member There is a concern that the collection ability will decrease.

  In order to solve the above-described problems, the present invention provides a rotating body for heat-fixing a toner image formed using toner containing a release wax on a recording material, and the recording material is nipped and conveyed together with the rotating body. A fixing nip portion forming member that forms a fixing nip portion, and a cooling member that cools an end region of the rotating body that is not in contact with a recording material having a width smaller than the maximum recording material usable in the apparatus. In the apparatus, the vaporized component of the release wax generated by heating the toner at the fixing nip is maintained at a temperature between the melting point of the release wax and the sublimation point of the release wax. An area of the rotating body that has a collecting member and is downstream of the fixing nip portion in the rotation direction of the rotating body serves as a collecting member heating area for heating the collecting member, and the collecting member heating area Before The downstream side in the rotational direction is characterized in that it is a cooling region cooled by the cooling member.

  According to the present invention, the vaporized component can be collected with a simple configuration of providing a collecting member that maintains the temperature between the melting point and the sublimation point of the release wax, and further downstream in the rotational direction than the collecting member heating region. By disposing the cooling means, the influence on the collecting member can be suppressed, and the decrease in the vaporization component collecting ability of the collecting member can be suppressed.

1 is a cross-sectional view of an image forming apparatus. Sectional drawing of a fixing unit. The perspective view which showed the structure of the fixing unit. FIG. 3 is an internal top view of the fixing unit. FIG. 9 is a perspective view illustrating a structure of a fixing unit according to a second embodiment. FIG. 6 is a cross-sectional view of a fixing unit according to a second embodiment. The measurement figure of melting | fusing point and sublimation point of a mold release wax.

Example 1
First, the overall configuration of the image forming apparatus will be outlined with reference to FIG. In the image forming apparatus illustrated in FIG. 1, a sheet feeding unit 80 is disposed at the lowest level. A registration roller unit 50 that arranges and conveys the leading end of the recording material P is disposed above the sheet feeding means 80. Further, a laser scanner unit 30 for forming an electrostatic latent image on the photosensitive member is provided above the paper feeding means 80. A scanner frame 31 is disposed immediately above the laser scanner unit 30, and the laser scanner unit 30 is fixed to the scanner frame 31. The process cartridge guide 32 (32Y, 32M, 32C, 32Bk) is disposed on the scanner frame 31. Above the scanner frame 31, four color process cartridges 10 (10Y, 10M, 10C, 10Bk) are arranged. The intermediate transfer unit 40 is disposed above the process cartridge 10 (10Y, 10M, 10C, 10Bk) so as to face the process cartridge 10 (10Y, 10M, 10C, 10Bk). The intermediate transfer unit 40 includes an intermediate transfer belt 41. Inside the intermediate transfer belt 41, a primary transfer roller 42 (42Y, 42M, 42C, 42Bk), a driving roller 43, a secondary transfer counter roller 44, a tension roller 45, and a cleaning roller are provided. Means 46 are provided. A secondary transfer unit 90 is disposed on the right side of the intermediate transfer unit 40. The secondary transfer unit 90 includes a secondary transfer roller 91 so as to face the secondary transfer counter roller 44. The fixing unit 20 is disposed above the intermediate transfer unit 40 and the secondary transfer unit 90. A paper discharge unit 60 is disposed at the upper left of the fixing unit 20. The paper discharge unit 60 includes a paper discharge roller pair 61 (61a, 61b), a double-sided conveyance unit 62, a reverse roller pair 63 (63a, 63b), and a double-sided flapper 64 serving as a branching unit. Each process cartridge includes a photosensitive drum 11 (11Y, 11M, 11C, 11Bk), and a charging roller 12 (12Y, 12M) is disposed around the photosensitive drum 11 (11Y, 11M, 11C, 11Bk). , 12C, 12Bk), developing device 14 (14Y, 14M, 14C, 14Bk), and cleaning device 16 (16Y, 16M, 16C, 16Bk). Since the image forming process is well known, a description thereof will be omitted.

  Next, a detailed configuration of the fixing unit 20 of the image forming apparatus will be described with reference to FIGS. FIG. 2 is a cross-sectional view of the fixing unit 20, and FIG. 3 is a perspective view showing an internal structure of the fixing unit 20.

  In the fixing unit 20, 101 is a heating unit, and 102 is a pressure roller (fixing nip portion forming member). The heating unit 101 has a heater 103. The heater 103 is supported by a heater holder 104 as a support member. The heater holder 104 is formed of a heat-resistant resin having heat resistance and slidability, such as a liquid crystal polymer, in a substantially semicircular bowl shape. The heater holder 104 is provided with a sleeve-shaped fixing sleeve 105. The fixing sleeve 105 has an endless configuration having substantially the same peripheral length as the pressure roller 102, and both end portions are rotatably held on the outer periphery of the pair of sleeve flanges 106. Further, both end portions of the heater holder 104 are also held by the sleeve flange 106. The pair of sleeve flanges 106 are supported by the side plate pair 107. The pressure roller 102 is brought into pressure contact with the fixing sleeve 105 with a predetermined pressing force T so as to face the heater 103 supported by the heater holder 104. As a result, a fixing nip portion N that heats and fixes the toner image onto the recording material is formed while the recording material is nipped and conveyed between the heater 103 and the pressure roller 102 via the fixing sleeve 105.

  The principle by which the collecting member 130 collects the components vaporized from the wax at the fixing nip is as follows. The wax component heated and vaporized in the fixing nip portion is cooled immediately after vaporization and solidifies again. The melting point Tm of the release wax contained in the toner used in this embodiment is 76.08 ° C. and the sublimation point Ts is 140 ° C. Therefore, the release wax is liquid in the region of 76.08 to 140 ° C. It becomes a phase state. In the liquid phase state, “wetting” occurs on the collection member 130, and an intermolecular force acts between the release wax and the collection member, thereby making it possible to adsorb the release wax. That is, by setting the temperature of the collecting member to the melting point Tm or higher and re-solidifying the wax component after vaporization, the release wax can be collected by the collecting member. When the temperature of the collecting member is equal to or lower than the melting point Tm, the release wax is in a solid phase, and “wetting” does not occur on the collecting member. Since the intermolecular force acting between the release wax and the collection member is very small, the release wax cannot be adsorbed to the collection member. Moreover, if the temperature of the collection member exceeds the sublimation point Ts, the collected release wax will sublimate again from the collection member. For the above reasons, by keeping the temperature of the collecting member in the same region (76.08 to 140 ° C.), the release wax that has been solidified after being heated and sublimated in the fixing nip is liquefied again by the collecting member. Can be absorbed. In addition, in order to collect the release wax stably even when printing a small number of sheets such as when performing single sheet printing intermittently, the temperature of the collecting member is rapidly raised after the print signal is input, and recording is performed. It is preferable that the temperature of the collecting member is allowed to reach the melting point Tm of the release wax before the leading end of the material P reaches the nip portion N. By allowing the temperature of the collecting member to reach the melting point Tm of the release wax before the leading edge of the recording material P reaches the nip portion N, the release wax is stably collected in any paper passing mode. It can be adsorbed to the member.

  Here, the melting point and sublimation point of the release wax contained in the toner will be described with reference to FIG. The peak temperature of the maximum endothermic peak of the release wax is measured according to ASTM (American Society for Testing 82) using a differential scanning calorimetry (DSC) apparatus “Q1000” (manufactured by TA INSTRUMENTS). To measure. The temperature correction of the device detection unit uses the melting points of indium and zinc, and the correction of heat uses the heat of fusion of indium. Specifically, about 10 mg of toner is precisely weighed (precisely weighed), placed in an aluminum pan, and an empty aluminum pan is used as a reference. Measurement is performed at a temperature elevation rate of 1 ° C./min. In the measurement, the temperature is once raised to 200 ° C., subsequently lowered to 30 ° C., and then the temperature is raised again. The maximum endothermic peak of the DSC curve in the temperature range of 30 to 200 ° C. in the second temperature raising process is defined as the maximum endothermic peak of the endothermic curve in the DSC measurement of the release wax, and this temperature is defined as the melting point (Tm). To do.

  The sublimation point of the release wax is measured using a particle counter “Handheld 3016” (manufactured by Lighthouse). Specifically, in a space sealed by a box of 30 cm × 30 cm × 30 cm, 10 mg of “toner containing a release wax” precisely weighed is heated and measured. In this measurement, the temperature at which counting starts at the particle counter is defined as the sublimation point (Ts). That is, the temperature when the “component first vaporized from the release wax” is detected by the particle counter is defined as the sublimation point of the release wax. The release wax used in this example has a melting point Tm of 76.08 ° C. (a in FIG. 7) and a sublimation point Ts of 140 ° C. (b in FIG. 7).

  In order to quickly raise the temperature of the collecting member 130 to a temperature equal to or higher than the melting point of the release wax contained in the toner when printing is started, the collecting member 130 is almost between the object to be attached (in this example, the upper cover 111 as described later). Is insulated with an air layer to reduce heat capacity. In order to insulate with an air layer, it has a structure that floats with a plurality of legs against the object to be attached. In addition, the collecting member is disposed in the immediate downstream portion with respect to the rotation direction of the fixing sleeve 105 as viewed from the fixing nip portion N in the vicinity of the fixing sleeve 105 immediately after being heated by the heater 103. Further, it is held about 3 mm away from the fixing sleeve 105. Furthermore, the collection member 130 is manufactured with glass-filled PBT (polybutylene phthalate) having a thickness of 1 mm so as to have a very small heat capacity. With respect to the holding destination, the fixed portion to be contacted is held as small as possible so as not to take heat from the collecting member 130. As shown in FIG. 2, the collection member 130 is held by the upper cover 111, but may be held by the stay 108, the duct 141 shown in FIG. 2, or the side plate pair 107 shown in FIG.

  Here, if the duct 141 can integrally hold the collecting member 130, the cost can be reduced by reducing the number of parts, and the fixing unit 20 can be downsized. Furthermore, since it is not necessary to consider the tolerance of parts and the interference margin due to the deformation due to the temperature change of the duct 141 and the collecting member 130, the area of the collecting member 130 can be set larger. For example, when the duct 141 and the collecting member 130 are each made of resin parts that are easily thermally deformed, the clearance between the duct 141 and the collecting member 130 is required to be about 3 to 6 mm. The collection member 130 can be enlarged by the clearance.

  The cooling fan 140 is attached so as to cool the end portion of the fixing sleeve 105, and has a duct 141 in order to enhance the cooling effect. The duct 141 is disposed close to the fixing sleeve 105 and is separated from the fixing sleeve 105 by about 1 to 2 mm so as not to contact the fixing sleeve 105. As shown in FIG. 4, at least the length of the duct 141 is arranged from the end of the fixing sleeve 105 to the position of the end of the recording material with the minimum width through which the image forming apparatus can pass. The duct 141 is disposed further downstream of the collecting member 130 with respect to the rotation direction of the fixing sleeve 105 when viewed from the fixing nip portion N.

  The heating unit 101 and the pressure roller 102 are surrounded by a pair of side plates 107, a stay 108, and a base plate 109, and are all sheet metal members. These three parts are frames constituting the fixing unit 20 and ensure the rigidity of the fixing unit 20. The side plate pair 107, the stay 108, and the base plate 109 are surrounded by the rear cover 110, the upper cover 111, the front lower cover 112, and the left and right covers 117, and the user connects the side plate pair 107, the stay 108, and the base plate 109 from the outside. It cannot be touched.

  Next, cooling of the fixing sleeve 105 by the cooling fan 140 will be described. As the air flow for cooling the fixing sleeve 105, outside air is taken into the fixing unit 20 from the louver shape of the left and right covers 117 by the cooling fan 140 as shown by arrows in FIG. 3. The taken-in air flows through a space surrounded by the fixing sleeve 105 and the duct 141. At that time, the end of the fixing sleeve 105 is cooled. Air heated by cooling the end of the fixing sleeve 105 is exhausted out of the fixing unit 20 from the louver shape of the front lower cover 112. Warm air exhausted to the outside of the fixing unit 20 is exhausted to the outside of the image forming apparatus by an exhaust duct shape (not shown).

  As described above, since the collecting member 130 is made with a very small heat capacity, it is sensitive to temperature changes. In order to stabilize the temperature of the collecting member 130, it is necessary to not disturb the ambient temperature around the collecting member 130. By arranging the duct 141 further downstream of the collecting member 130 with respect to the rotation direction of the fixing sleeve 105 when viewed from the fixing nip portion N, the air forcedly flowing by the cooling fan 140 is supplied to the collecting member 130. On the other hand, the temperature change can be reduced because the contact is not made positively and the ambient temperature around the collecting member 130 is not disturbed. Thereby, since the temperature fall of the collection member 130 by cooling air can be suppressed, the vaporization component collection capability fall of a collection member can be suppressed.

  A heater drive control circuit as a control means includes a power feeding device and a CPU for controlling the power feeding device. In the heater drive control circuit, the CPU inputs a print signal and performs on / off control of the power supply device, thereby energizing and heating the heating resistor of the heater 103. The heater 103 is rapidly heated by energization heating of the heating resistor. The heater 103 is heated to a predetermined target set temperature based on the temperature detected by a thermistor (not shown) as temperature detecting means provided on the back surface (the surface opposite to the nip portion N) of the heater 103. And the fixing sleeve 105 is heated to that temperature. The set temperature in this embodiment is 180 ° C.

  Next, the fixing operation of the recording material P will be described. First, the case where the width of the recording material P is near the maximum width that can be used in the image forming apparatus will be described. The recording material P is transferred with the toner image (unfixed) transferred by the intermediate transfer unit 40 and the secondary transfer unit 90. The conveyed recording material P is sent to the fixing unit 20 where the toner image is fixed by the heated fixing sleeve 105 and the pressure roller 102 and conveyed to the paper discharge unit 60. At that time, since the recording material P removes heat from almost the entire width of the nip portion of the fixing sleeve 105, it is not necessary to cool the end region of the fixing sleeve 105. Therefore, the cooling fan 140 does not operate. On the other hand, the collection member 130 is rapidly heated by the fixing sleeve 105 heated by the heater 103 and reaches the melting point of the release wax. As a result, the release wax solidified after being heated and sublimated by the fixing sleeve 105 and the pressure roller 102 is liquefied again and can be adsorbed.

  Next, the case where the width of the recording material P is near the minimum width that can be used in the image forming apparatus will be described. The recording material P enters the fixing unit 20, is fixed, and is conveyed to the paper discharge unit 60. Here, when the number of printed sheets is about several, the cooling fan 140 does not operate because the temperature rise at the end of the fixing sleeve 105 is moderate. However, in the case of continuous printing of 10 sheets or more, since the portion of the fixing sleeve 105 that contacts the recording material P is continuously deprived of heat by the recording material P, the heater 103 continues to generate heat by a thermistor (not shown). As a result, the temperature of the end region of the fixing sleeve 105 that is not deprived of heat by the recording material P rises. Therefore, the cooling fan 140 is operated, and air is blown to the end region of the fixing sleeve 105 to be cooled, so that the temperature distribution in the entire fixing sleeve 105 becomes uniform. The end of the fixing sleeve 105 can be cooled by about 30 ° C. to 50 ° C. by controlling the rotation speed of the cooling fan 140. On the other hand, the collecting member 130 is rapidly heated by the fixing sleeve 105 heated by the heater 103 in the same manner as the printing near the maximum width that can be passed through the image forming apparatus, and reaches the melting point of the release wax. As a result, the release wax solidified after being heated and sublimated by the fixing sleeve 105 and the pressure roller 102 pair is liquefied again and can be adsorbed.

(Example 2)
FIG. 5 is a perspective view of the inside of the fixing unit 220 of the second embodiment, and FIG. 6 is a sectional view of the fixing unit 220 of the second embodiment. Description of the same part as Example 1 is omitted. As shown in FIG. 5, the cooling fan 140 is attached in the direction of exhausting the air in the image forming apparatus.

  The cooling of the fixing sleeve 105 by the cooling fan 140 will be described. As the air flow for cooling the fixing sleeve 105, the warm air in the space surrounded by the fixing sleeve 105 and the duct 141 is discharged out of the fixing unit 20 by the cooling fan 140 as shown by the arrow in FIG. 5. By the exhaust operation, the cool air of the outside air is taken into the fixing unit 20 from the louver shape of the left and right covers 117. Thereby, the fixing sleeve 105 can be cooled.

  At this time, as shown in FIG. 6, air slightly flows from the collection member 130 in the direction of the arrow in the direction of the duct 141 through a gap S of about 1 to 2 mm between the duct 141 and the fixing sleeve 105. Thereby, the cold air of outside air does not hit the collection member 130, and does not disturb the ambient temperature around the collection member 130. Thereby, the temperature change of the collection member 130 can be made very small.

  As described above, in Examples 1 and 2, the vaporization component of the release wax generated by heating the toner at the fixing nip portion while maintaining the temperature between the melting point of the release wax and the sublimation point of the release wax. A region of the rotating body downstream of the fixing nip portion in the rotation direction of the rotating body is a collecting member heating region for heating the collecting member, and from the collecting member heating region In addition, the downstream side in the rotation direction is a cooling region cooled by the cooling member. This makes it possible to collect vaporized components with a simple configuration of providing a collecting member that maintains the temperature between the melting point and the sublimation point of the release wax, and cooling means downstream of the collecting member heating region in the rotational direction. By arrange | positioning, the influence which it has on a collection member can be suppressed, and the fall of the vaporization component collection capability of a collection member can be suppressed.

101 Heating Unit 103 Heater 105 Fixing Sleeve 130 Collection Member 140 Cooling Fan 141 Duct

Claims (2)

A rotating body for heat-fixing a toner image formed using toner containing a release wax on a recording material; and a fixing nip portion forming member for forming a fixing nip portion for nipping and conveying the recording material together with the rotating body; A fixing member having a cooling member that cools an end region of the rotating body that does not come into contact with a recording material having a width smaller than the maximum recording material usable in the apparatus,
A collecting member that collects a vaporized component of the release wax generated by heating the toner at the fixing nip portion, maintained at a temperature between the melting point of the release wax and the sublimation point of the release wax. A region of the rotating body downstream of the fixing nip portion in the rotational direction of the rotating body is a collecting member heating region for heating the collecting member, and the region of the rotating member is more than the collecting member heating region. A fixing device in which a downstream side in a rotation direction is a cooling region cooled by the cooling member.   2. The cooling unit according to claim 1, wherein the cooling unit includes a cooling fan and a duct for guiding the ventilation of the cooling fan to the rotating body, and the duct and the collecting member are integrally formed. The fixing device described.

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