JP4454404B2 - Fixing apparatus, image forming apparatus, and toner fixing method - Google Patents

Description

  The present invention relates to a fixing device, an image forming apparatus, and a toner fixing method.

  Conventionally, a fixing device built in an electrophotographic image forming apparatus has a heater such as a halogen lamp which generates heat when supplied with power, and a hollow cylindrical heating roller heated by the heater, The toner on the recording paper sheet is heated by a heating roller and fixed to the sheet.

  In this fixing device, if there is a difference (unevenness) in the surface temperature in the axial (longitudinal) direction of the heating roller, the degree of fixing of toner differs in one sheet of recording paper, and in particular, in terms of image quality such as uneven glossiness. In the case of a color image, irregularities in glossiness and tint appear prominently in the case of a color image, and various ideas have been conventionally made to make the temperature distribution in the axial direction of the heating roller uniform ( For example, see Patent Documents 1 to 4.)

For example, at the start-up stage of the apparatus, that is, at the initial stage of passing paper immediately after starting the image formation,
Assuming that the thickness of the heating roller is constant in the axial direction and the light distribution (heat generation) distribution of the heater is uniform in this axial direction, the axial end of the heating roller is delayed in temperature rise compared to the center. The end portion does not reach the predetermined temperature, and the fixing ability is insufficient. For this reason, the light distribution of the heater is made larger at the end than at the center of the heating roller (see, for example, Patent Document 1).

  However, when the paper is continuously passed, the temperature of the end portion of the heating roller tends to be higher than the central portion. The countermeasure for adjusting the light distribution as described above promotes the temperature rise at the end portion, so that the toner adheres to the surface of the heating roller, and the toner moves to the succeeding paper, causing the image stain. It was.

  On the other hand, if the light distribution at the end of the heater is made smaller to eliminate the rise in end temperature during continuous paper feeding, the end temperature shortage at the start-up stage of the device will worsen, which may lead to poor fixing at the end. Has occurred.

  As countermeasures against such problems, the thickness of the central portion of the heating roller is increased, and the light distribution of the heater is increased correspondingly in the central portion of the heating roller, thereby making the temperature distribution of the heating roller uniform. (For example, refer to Patent Documents 1 to 3.)

No. 7-13004 Japanese Patent Laid-Open No. 11-24469 JP 2002-82559 A JP-A-5-341679

  However, even if the above measures are taken, there is a case where better fixing of the toner is required.

  The inventor investigated the cause of the occurrence of the fixing failure, and found that when the cooling mechanism inside the apparatus such as a fan or a duct provided for the purpose of preventing the temperature inside the image forming apparatus was provided, the cooling mechanism resulted. As a result, an air flow was generated around the fixing device, and the air flow caused the temperature distribution in the longitudinal direction of the heating roller to become non-uniform, and it was found that a fixing failure occurred. In addition, the air flow makes the temperature distribution in the longitudinal direction of the pressure roller in pressure contact with the heating roller non-uniform, thereby causing the temperature distribution in the longitudinal direction of the heating roller to become non-uniform, resulting in poor fixing. . In addition, as shown in Patent Document 4, fins are provided inside the heating roller to generate an airflow in a direction that opposes the airflow generated by the cooling fan. Depending on the rotation speed of the heating roller, the temperature distribution may be uniform. It was difficult.

  The present invention has been made in view of the above problems in the prior art, and can provide a fixing device capable of uniforming the temperature distribution in the axial direction of the heating roller, an image forming apparatus including the fixing device, and An object is to provide a toner fixing method.

The present invention provided to solve the above-described problems includes a heat generating means that generates heat when supplied with power, a heating means that is heated by the heat generating means, and a pressurizing means that is pressed against the heating means. In a fixing device which is built in a main body of a forming apparatus and sandwiches a sheet carrying toner by the heating unit and the pressing unit and heat-fixes the toner on the sheet, the heating unit and / or the pressing unit includes the image forming unit. device heat capacity of the leeward portion much larger than the windward portion with respect to air flow of the sheet width direction of the heating means or pressure means generated by provided a device inside the cooling mechanism to the body, the heating means, said heating means wherein among the portion corresponding to the end regions of the sheet width direction, the fixing device, wherein the amount of heat generation in the leeward portion is greater than the windward portion for a stream of That (claim 1).

Here, it is preferable that the heat capacity of the heating unit and / or the pressurizing unit is gradually increased from the windward portion toward the leeward portion of the airflow.
The heating means and the pressure means are respectively a cylindrical heating roller and a pressure roller, and the heat capacity of the heating roller and / or the pressure roller is preferably adjusted by the thickness of the roller .

The present invention provided to solve the above-mentioned problems comprises the fixing device according to any one of claims 1 to 3 , wherein a sheet on which a toner image is formed by an electrophotographic method is sent to the fixing device. (Claim 4 ).

The present invention provided to solve the above-described problems is a toner fixing method in which the fixing unit is heated by the heat generated by the heating unit, the sheet carrying the toner is heated by the fixing unit, and the toner is fixed to the sheet. The fixing unit is cooled by an airflow in the width direction of the sheet, and uses a fixing unit having a larger heat capacity in the leeward part than the upwind part with respect to the airflow , and a portion corresponding to an end region of the fixing unit in the heating unit of a toner fixing method which comprises causing heat the heat generating means so the amount of heat generated in the leeward portion is greater than the windward portion for air flow (claim 5).

According to the fixing device of the present invention, a large temperature balance in the sheet width direction (roller axial direction) of the heating unit (heating roller) can be prevented at the time of startup of the apparatus, and in particular, both end portions of the heating unit (heating roller). It is possible to reduce the difference in the degree of heating at both ends. In addition, the temperature distribution in the sheet width direction (roller axis direction) of the heating means (heating roller) can be made more uniform even during continuous paper feeding.
According to the image forming apparatus of the present invention, since the fixing device is provided, stable fixing can be achieved without causing poor fixing at the end portion, and good image quality can be obtained.
According to the toner fixing method of the present invention, a large temperature balance in the sheet width direction (roller axial direction) in the heating means (heating roller) can be prevented when the apparatus is started up, and in particular, both ends of the heating means (heating roller). The difference in the degree of heating of the parts (both shaft ends) can be reduced. In addition, the temperature distribution in the sheet width direction (roller axis direction) of the heating means (heating roller) can be made more uniform even during continuous paper feeding.

The configuration of the image forming apparatus according to the present invention will be described below.
FIG. 1 is a cross-sectional view showing an overall schematic configuration of a laser printer (hereinafter referred to as a printer) which is an electrophotographic image forming apparatus as an image forming apparatus according to the present invention.
The printer 100 has a photosensitive drum 1 as a latent image carrier. The surface of the photosensitive drum 1 is uniformly charged by a charging roller 50 as uniform charging means that comes into contact with the photosensitive drum 1 while being driven to rotate in the direction of arrow A in the figure. Thereafter, scanning exposure is performed based on image information by an optical writing unit 51 as a latent image forming unit, and an electrostatic latent image is formed on the surface of the photosensitive drum 1. As the uniform charging unit and the latent image forming unit, those different from the charging roller 50 and the optical writing unit 51 can be used.

  The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 2 to form a toner image on the photosensitive drum 1. A toner image formed on the photosensitive drum 1 is an aspect of a sheet conveyed from a sheet feeding cassette 54 via a sheet feeding roller 55 and a registration roller pair 56 by a transfer unit as a transfer unit including a transfer roller 53. Is transferred onto the transfer paper 52.

  After the transfer, the transfer paper 52 is fixed with a toner image by a fixing device 57 unitized as a fixing means, and is discharged outside the apparatus. The untransferred toner remaining on the photosensitive drum 1 without being transferred is removed from the surface of the photosensitive drum 1 by a cleaning unit 58 as a cleaning unit. Further, the residual charge on the photosensitive drum 1 is removed by a static elimination lamp 59 as a static elimination means.

In the fixing device 57 that is a toner fixing unit, a heating roller 57A that is one mode of the heating unit and a pressure roller 57B that is one mode of the pressure unit are arranged in the apparatus casing. The heating roller 57A is a roller having a hollow cylinder made of a good thermal conductor disposed on the side in contact with the toner image carried on the transfer paper 52 and a release layer on the surface of the hollow cylinder. It is formed by applying Teflon (registered trademark) to the surface of an Al roller having a shape. In addition, a heater (not shown) such as a halogen lamp is disposed in the hollow inside of the heating roller 57A, with the heating roller 57A as one form of heat generation means (heat source), and the heating roller 57A is heated by light emission of the halogen lamp. It is like that. Further, the halogen lamp can adjust the surface temperature distribution in the axial direction of the heating roller 57A by changing the light emission distribution in the sheet width method (axial direction) of the transfer paper 52. The surface temperature of the heating roller 57A is monitored by a temperature sensor such as a thermocouple, and is controlled so that the surface temperature of the heating roller 57A is within a temperature range that does not cause a problem in the fixing process by turning on and off the halogen lamp. .
The pressure roller 57B is a roller member having an elastic layer on the surface of the core metal, and can be configured to form a fixing nip portion when the transfer paper 52 is nipped and conveyed by rotating in conjunction with the heating roller 57A while being in pressure contact. It is like that.
The toner image carried on the transfer paper 52 is heated and fixed by the action of heat and pressure when being nipped and conveyed by the heating roller 57A and the pressure roller 57B, and then the transfer paper 52 on which the toner image is fixed is The paper is discharged and stacked on the paper discharge tray 61 by the paper discharge roller pair 60.

  Further, the image forming apparatus main body 10 is provided with a cooling fan F as a cooling mechanism for preventing an excessive temperature rise around the fixing device 57. The position of the cooling fan F is less flexible due to cost reduction and space saving of copying machines and laser printers, and airflow tends to occur at positions that affect the temperature distribution of the fixing device 57. is there. An example is shown in FIG. Due to the air flow generated by the cooling fan F, the heat held in the windward portion A, which is one end region of the heating roller 57A, is drawn toward the leeward side. A certain leeward part B will be affected by the heat.

  Here, a conventional heating roller having a uniform wall thickness in the axial direction has a uniform temperature distribution in the sheet width method (roller axial direction) when the apparatus starts up. Considering the temperature distribution after the influence, as shown in FIG. 3, the temperature of the heating roller in the leeward part B tends to be higher than that of the leeward part A. Depending on the conditions, the temperature of the leeward part B can fix the toner. The upper limit temperature is exceeded, and a problem of image smearing occurs.

  As shown in FIG. 4, a countermeasure is taken to reduce the light distribution in the axial direction of the heater from the windward portion A toward the leeward portion B of the heating roller, as shown in FIG. Although it is conceivable to make the temperature distribution uniform, this time, the surface temperature distribution of the heating roller when the apparatus starts up is significantly affected by the light distribution of the heater, causing another problem. That is, as shown in FIG. 5, the leeward portion B tends to be lowered in the axial direction of the heating roller, and the temperature of the leeward portion B falls below the lower limit temperature at which toner can be fixed, resulting in poor fixing.

  The present invention solves this problem, and the upwinding of the heating roller 57A against the airflow in the sheet width direction (roller axial direction) in the heating roller 57A generated by the cooling fan F provided in the image forming apparatus main body 10. The heat capacity of the leeward part B is made larger than that of the part A.

  Specifically, as shown in FIG. 6, the outer diameter φ of the heating roller 57 </ b> A is constant in the axial direction, and the thickness is gradually increased from the leeward portion A toward the leeward portion B. . As a result, the heat roller 57A has an asymmetric heat capacity in the axial direction such that the heat capacity of the heat roller 57A gradually increases from the windward portion A to the leeward portion B of the airflow.

  Here, in the end region of the heating roller 57A, the windward portion A, which is a thin portion, has a small heat capacity, so that the surface temperature is raised to a predetermined temperature and maintained with a small amount of heat, that is, with a low heater luminous efficiency. Is possible. In order to set the target portion of the heating roller 57A as the target temperature, heat loss due to heat conduction in which heat is transmitted in the axial direction through the heating roller 57A itself, heat loss due to radiation from the heating roller 57A, heating roller due to the airflow The heat generation amount (light emission rate) of the heater is set in consideration of the heat balance such as heat loss due to the cooling effect on the surface of 57A and the heat capacity of the heating roller 57A. Since the heat mobility due to heat conduction slows down, the heater conditions may be set by mainly considering other factors.

  On the other hand, in the end region of the heating roller 57A, the leeward part B which is a thick part has a relatively large heat capacity. Therefore, even if the airflow is affected by the heat from the leeward part A, the temperature of that part It becomes difficult to rise, and abnormal temperature rise can be prevented. Moreover, since the amount of heat conduction in the axial direction is large due to the thick wall, the temperature in the vicinity of the portion is averaged and hardly rises. Note that the heater conditions may be set in consideration of the fact that the heat capacity of the portion is large and it is difficult to raise the temperature when the apparatus is started up. In continuous paper passing, the heater conditions may be set in consideration of heat loss due to heat conduction in the axial direction, heat loss due to radiation from the heating roller 57A, heat input from the windward due to the airflow, and the like.

  In addition, as an example of a dimension of the heating roller 57A, the total length is 250 to 450 mm, and the outer diameter is 25 to 100 mm. Moreover, the thickness is in the range of 0.3 to 20 mm, and the difference in thickness between the leeward portion A and the leeward portion B may be set within the range of 0.1 to 10 mm.

Further, as shown in FIG. 7, the heating roller 57A is gradually increased in thickness from the windward portion A toward the leeward portion B at a constant ratio while the outer diameter φ of the heating roller 57A is constant in the axial direction. It is good also as a structure which is thick.
Or it is good also as the heating roller 57A arrange | positioned so that the heat capacity of the leeward part B may become larger than the leeward part A on the inner diameter side of a roller with constant outer diameter and wall thickness.

  As a heater condition for the heating roller 57A having the above-described cross-sectional shape, for example, as shown in the light distribution shown in FIG. The heater luminous rate for the windward portion A) may be lower than the heater luminous rate for the end portion on the thick wall side (windward leeward portion B). Here, the reason why the light distribution at both ends is increased is to compensate for heat loss due to bearings, gears, and the like at both ends of the heating roller 57A in the initial stage of heating. Further, the reason why the heater luminous rate of the windward portion A is made lower than that of the leeward portion B of the heating roller 57A is to balance the difference in heat capacity. If the temperature drop in the central portion of the heating roller 57A is large during continuous paper feeding, the heater light emission rate in the central portion of the heater light distribution in FIG. 8 may be increased.

  Further, the technology of the present invention may be applied to the pressure roller 57B. That is, the heat capacity of the leeward portion B of the pressure roller 57B relative to the airflow in the sheet width direction (roller axial direction) of the pressure roller 57B generated by the cooling fan F provided in the image forming apparatus main body 10 rather than the windward portion A of the pressure roller 57B. Should be increased.

Specifically, as in the case of the heating roller 57A shown in FIG. 6, the pressure roller 57B has a stepped thickness from the leeward portion A toward the leeward portion B while the outer diameter φ is constant in the axial direction. The structure is thicker. Alternatively, as with the heating roller 57A shown in FIG. 7, the pressure roller 57B has an outer diameter φ constant in the axial direction, and gradually increases in thickness from the windward portion A toward the leeward portion B at a constant ratio. It is good also as a structure thickened. In this case, the thickness of the cored bar and / or the elastic layer constituting the pressure roller 57B may be adjusted.
The application of the technology of the present invention to the pressure roller 57B may be performed simultaneously with the application of the technology of the present invention to the heating roller 57A or independently.

  By using the image forming apparatus including the fixing device having such a configuration, a large temperature balance in the axial direction of the heating roller 57A can be prevented when the apparatus starts up, and in particular, heating of both shaft ends of the heating roller 57A can be prevented. The difference in degree can be reduced. Further, even during continuous paper feeding, the temperature distribution in the axial direction of the heating roller 57A can be made more uniform as shown in FIG. 9, so that the image was transferred to the transfer paper without causing poor fixing at the end. The toner image can be fixed.

  Although FIG. 2 shows an example in which the cooling fan F is arranged in the roller axial direction of the fixing device, the present invention is not limited to the arrangement position of the cooling fan F, and the air flow generated by the cooling fan F This effectively acts when the heat held in the windward portion A which is one end region of the heating roller 57A and / or the pressure roller 57B is drawn toward the leeward side. For example, the cooling fan F may be disposed at an upper or lower corner portion of the image forming apparatus main body 10 in FIG.

1 is a cross-sectional view showing a configuration in an embodiment of an image forming apparatus according to the present invention. FIG. 6 is a cross-sectional view illustrating a relationship between an air flow by a cooling fan and a temperature distribution of the fixing device. It is a figure which shows the temperature distribution (1) of the conventional heating roller. It is a figure which shows the light distribution of the conventional heater. It is a figure which shows the temperature distribution (2) of the conventional heating roller. FIG. 3 is a cross-sectional view illustrating a configuration of an embodiment of a heating roller of a fixing device according to the present invention. It is sectional drawing which shows the structure in other embodiment of the heating roller of the fixing device which concerns on this invention. It is a figure which shows the light distribution example of a heater in the fixing device of this invention. It is a figure which shows the temperature distribution of the heating roller in the fixing device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Developing apparatus 10 Image forming apparatus main body 50 Charging roller 51 Optical writing unit 52 Transfer paper 53 Transfer roller 54 Paper feed cassette 55 Paper feed roller 56 Registration roller pair 57 Fixing device 57A Heating roller 57B Pressure roller 58 Cooling Unit 59 Static elimination lamp 60 Paper discharge roller 61 Paper discharge tray 100 Laser printer (image forming apparatus)

Claims (5)

A heating unit that generates heat when supplied with electric power, a heating unit that is heated by the heating unit, and a pressurizing unit that is pressed against the heating unit. The heating unit and the pressurizing unit that are built in the main body of the image forming apparatus In a fixing device that sandwiches a sheet carrying toner by means and heat-fixes the toner on the sheet,
The heating unit and / or the pressurizing unit is a leeward part rather than an upwind part for the airflow in the sheet width direction in the heating unit or the pressurizing unit generated by a cooling mechanism inside the apparatus provided in the image forming apparatus main body. the heat capacity of the rather large,
The fixing device according to claim 1, wherein the heat generation unit has a larger amount of heat generation in a leeward portion than an upwind portion with respect to an airflow among portions corresponding to an end region in the sheet width direction of the heating unit.   The fixing device according to claim 1, wherein the heat capacity of the heating unit and / or the pressurizing unit is gradually increased from an upwind portion to an leeward portion of the airflow.   The heating means and the pressure means are respectively a cylindrical heating roller and a pressure roller, and the heat capacity of the heating roller and / or the pressure roller is adjusted by the thickness of the roller. Item 4. The fixing device according to Item 1. A fixing device according to any one of claims 1 to 3, the image forming apparatus characterized by sending a sheet to form a toner image on the fixing device by an electrophotographic method. In the toner fixing method in which the fixing unit is heated by the heat generated by the heating unit, the sheet carrying the toner is heated by the fixing unit, and the toner is fixed to the sheet.
The fixing unit is cooled by an airflow in the width direction of the sheet ;
Using fixing means having a larger heat capacity of the leeward part than the leeward part against the airflow ,
A toner fixing method in which the heat generating means is caused to generate heat so that the amount of heat generated in the leeward portion of the heat generating means corresponding to the end region of the fixing means is larger than that of the airward portion with respect to the airflow .

Images