JP2005208321A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device equipped with a fixing roller making the extension of fixing nip width compatible with the securement of prescribed pressuring force required for fixing. <P>SOLUTION: In the fixing device constituted of the fixing roller, a heating roller, an endless fixing belt stretched and laid between the fixing roller and the heating roller, and a pressure roller opposed to the fixing roller and holding and pressuring the fixing belt, the fixing roller has two-layer structure having a 1st heat resistant elastic member formed on a core bar as a base layer and equipped with a 2nd heat resistant elastic member as the outer layer of the base layer, and set so that the hardness of the 2nd heat resistant elastic member (outer layer) is lower than that of the 1st heat resistant elastic member (base layer). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device in an image forming apparatus such as an electrophotographic copying machine or a printer. More specifically, the present invention relates to a belt fixing device that heats an endless fixing belt and presses and fixes an unfixed toner image on a recording sheet.

  As a fixing device used in an image forming apparatus, a pressure roller is pressed against a fixing roller having a heat source therein to form a fixing nip portion, and an unfixed toner image on a recording sheet is formed at the fixing nip portion. A heat roller fixing method for fixing is known.

  In the heat roller fixing system, it is necessary to suppress the heating time to the fixing temperature (warm-up time) from being prolonged. For a fixing roller with a heat source inside, it is not possible to increase the thickness of the heat resistant elastic layer beyond a certain level. Can not. Therefore, a predetermined nip width required for fixing cannot be secured, and the fixing range is narrowed.

  This is because in such a heat roller fixing device, the fixing performance is determined by the condition of the nip portion formed by the roller pair. The fixing performance depends on the roller temperature at the nip portion, the width and passing time of the nip portion, the pressure applied to the nip portion, and the like.

  For example, when it is intended to realize low temperature fixing by lowering the roller temperature in consideration of energy saving, it is necessary to increase the nip width and increase the nip passage time of the recording paper. Also, in order to increase the fixing speed, it is necessary to increase the roller temperature corresponding to the speed and to increase the nip width. Note that the pressure applied to the nip portion requires a predetermined pressure in any case.

  However, the enlargement of the nip width as described above leads to an increase in the roller diameter, which is a limit on the apparatus configuration.

  Therefore, for example, a belt fixing method for solving the problems of the heat roller fixing method described in Patent Document 1 has been put into practical use. In this belt fixing device, an endless fixing belt having high heat conductivity is stretched between a fixing roller and a heating roller, and the fixing belt heated by the heating roller is opposed to the fixing roller via the fixing belt. And a pressure roller that presses to form a nip portion. The fixing roller is formed of a heat-resistant elastic member of a foam layer on a core metal, and the pressure roller is composed of a high-hardness roller or a metal roller. It is the structure which forms a part.

  Therefore, in the belt fixing device, a heat resistant elastic layer having a lower hardness can be used for the fixing roller of the heat roller fixing device. Therefore, when a fixing roller and a pressure roller having the same diameter as the heat roller fixing device are used. It is possible to obtain a larger nip width.

  For this reason, the belt fixing device can satisfy the fixing performance without lowering the diameter of the roller because the fixing temperature is lowered and the fixing speed is high.

JP 09-281824 A

  However, the configuration of the belt fixing device described above can satisfy the fixing performance for a specific toner image, but is insufficient for fixing color toner or the like. The reason for this is that the pressure contact force between the fixing roller made of the heat-resistant elastic member of the foam layer and the pressure roller via the belt is dispersed and absorbed by the foam layer of the fixing roller, so that sufficient pressing force is obtained for fixing. Because there is no.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a fixing device having a fixing roller having both a wide fixing nip width and securing a predetermined pressure required for fixing in a fixing roller structure of a belt fixing device.

  In order to achieve the above object, the invention described in claim 1 is directed to a fixing roller, a heating roller, an endless fixing belt stretched between the fixing roller and the heating roller, and the fixing roller. In the fixing device constituted by a pressure roller that sandwiches and presses the fixing belt, the fixing roller has a first heat-resistant elastic member formed on a core metal as a base layer, and a second heat-resistant layer as an outer layer. An elastic member is provided, and the second heat-resistant elastic member (outer layer) has a two-layer structure whose hardness is lower than the hardness of the first heat-resistant elastic member (base layer).

  The invention according to claim 2 is the invention according to claim 1, wherein the first heat-resistant elastic member (base layer) of the fixing roller has an Asker C hardness of 30 ° to 60 °, and the second heat-resistant elastic member (outer layer). ) Is formed of a foam layer having a hardness lower than that of the first heat-resistant elastic member (base layer).

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the second heat-resistant elastic layer (outer layer) of the fixing roller is constituted by a foam layer having a layer thickness of 3 mm or more which becomes 1 mm or less at the maximum strain. It is characterized by that.

  According to the present invention, since the fixing roller in the belt fixing device has a two-layer structure, the expansion of the nip width by the foam layer as the outer layer and the maximization of the pressure contact force by the elastic layer of the inner layer can be achieved. It is possible to cope with high-speed fixing and shorten the warm-up time without increasing the diameter of the fixing roller, and the range of the types of toner that can be fixed, the types of recording paper, and the like is expanded.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  First, the above-described conventional belt fixing device will be described with reference to FIG.

  In FIG. 5, reference numeral 53 denotes an endless film fixing belt made of nickel or polyimide, and the fixing belt 53 is stretched between the fixing roller 51 and the heating roller 52. The heating roller 52 is a cylindrical roller having a heat source such as a heater inside. The fixing roller 51 is a roller formed by covering a cored bar 51a with a heat-resistant elastic layer 52b having a low thermal conductivity, and a foamed material such as silicon rubber is used as the heat-resistant elastic layer.

  Further, a pressure roller 54 is provided so as to face the fixing roller 51. The pressure roller 54 is a roller provided with a metal pipe or an elastic member having a high hardness on the surface layer of the pipe, and is pressed against the fixing roller 51 via a fixing belt 53 by a pressing means (not shown). Further, there is an example in which a heat source 56 is disposed inside the pressure roller 54 as necessary.

  In the belt fixing device configured as described above, the nip portion (nipA) in the drawing is formed by the pressure contact between the fixing roller 51 and the pressure roller 54. In the figure, P is a recording sheet on which an unfixed toner image is transferred, and is conveyed from the direction of the arrow to the fixing device with the image surface facing upward.

  Next, the fixing device according to the present invention will be described with reference to FIG.

  In FIG. 1, 1 is a fixing belt, 2 is a fixing roller embodying the present invention, and details will be described later. 3 is a heating roller provided with a heater 4 inside, and 5 is a pressure roller having a heater 6 inside. This pressure roller 5 faces the fixing roller 2 and is attached to the fixing roller 2 by a pressing means (not shown). It is in pressure contact.

  Here, an embodiment of the fixing roller of the present invention will be described with reference to FIGS. 2 is an enlarged view of the nip portion (nipB) in FIG.

  The fixing roller 2 is formed into a two-layer structure in which a first heat-resistant elastic layer 2b (base layer) is provided on a core metal 2a and a second heat-resistant elastic layer 2c is provided on the outer layer.

  The first heat-resistant elastic layer 2b is a solid elastic layer formed of silicon rubber or the like, and preferably has a layer thickness of 3 mm or more, and the rubber hardness is 30 ° to 60 ° in Asker C hardness. Since the rubber hardness corresponds to the hardness of the elastic layer of the pressure roller used in the heat roller fixing device, when a predetermined pressure is applied, the deformation 2n shown in FIG. 2 is obtained.

  Next, the second heat-resistant elastic layer 2c, which is an outer layer, is a foam layer made of silicon rubber or the like, and is formed of an elastic layer having a layer thickness of 3 mm or more that becomes 1 mm or less at the maximum collapse. The elastic layer 2c has a hardness lower than that of the elastic layer 2b. For example, when the elastic layer 2b has an Asker C hardness of 50 °, the elastic layer 2c may have a hardness of about 20 ° to 30 °.

  FIG. 2 is an enlarged view of the nip portion (nipB) formed in FIG.

  As shown in the figure, when the pressure roller 5 is pressed with a predetermined pressure through the fixing roller 2 and the fixing belt 1, the outer elastic layer 2c is deformed to the maximum collapse amount (1 mm or less), and the pressure is further increased. Accordingly, the first elastic layer is deformed (2d) to have a maximum deformation amount. Therefore, the pressure contact portion formed at the time of the maximum deformation forms a nip portion (nipB).

  FIG. 3 is a diagram showing the relationship between the nip width formed by the above-described fixing roller of the present invention and the pressing force. The nip width is large and the maximum pressing force is concentrated in the center. .

  FIG. 4 is a diagram showing the relationship between the applied pressure and the nip width as in FIG. 3. Here, the nip (nipB) formed in the present invention is indicated by a dotted line, and at the same time, the nip (nipA) formed by the conventional belt fixing device. ) And the nip of a general heat roller fixing device.

  As is apparent from the figure, the shape of the nip formed by the fixing roller of the present invention is as wide as the nip width formed by a conventional single-layer fixing roller of foam, and in a general heat roller fixing device. A pressing force equivalent to the pressing force can be secured.

  Therefore, in the belt fixing device to which the fixing roller of the present invention is applied, since the nip width is increased and the appropriate pressure is ensured at the same time, the fixable range is widened, and the warm-up time can be shortened and the high speed response can be achieved. It becomes possible.

  The present invention is highly applicable to a belt fixing device that heats an endless fixing belt and presses and fixes an unfixed toner image on a recording sheet.

It is a block diagram of the belt fixing device which implemented this invention. FIG. 4 is an enlarged view of a nip portion in the fixing roller of the present invention. FIG. 4 is a diagram showing the relationship between the nip width and the applied pressure in the fixing roller of the present invention. It is a comparison diagram of the relationship between nip width and applied pressure. It is a block diagram of the conventional belt fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing belt 2 Fixing roller 2a Core metal of fixing roller 2b First heat-resistant elastic layer in base layer of fixing roller 2c Second heat-resistant elastic layer in outer layer of fixing roller 2n Deformation of first heat-resistant elastic layer in base layer of fixing roller Indicates.

3 Heating roller 4 Heat source such as heater 5 Pressure roller 6 Heater

Claims (3)

A fixing roller, a heating roller, an endless fixing belt stretched between the fixing roller and the heating roller, and a pressure roller facing the fixing roller and sandwiching and pressing the fixing belt. In the configured fixing device,
The fixing roller includes a first heat-resistant elastic member formed on a core metal as a base layer, and an outer layer provided with a second heat-resistant elastic member. The hardness of the second heat-resistant elastic member (outer layer) is the first heat-resistant elastic member. A fixing device having a two-layer structure lower than the hardness of an elastic member (base layer).   The first heat resistant elastic member (base layer) of the fixing roller has an Asker C hardness of 30 ° to 60 °, and the second heat resistant elastic member (outer layer) is lower than the hardness of the first heat resistant elastic member (base layer). 2. The fixing device according to claim 1, wherein the fixing device is formed of a foam layer having hardness.   3. The fixing device according to claim 1, wherein the second heat-resistant elastic layer (outer layer) of the fixing roller is formed of a foam layer having a layer thickness of 3 mm or more which is 1 mm or less at the maximum strain.

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