Fixing device and image forming apparatus

A fixing device includes a fixing belt, a pressuring member, a driving member and a slide contact member. The fixing belt is arranged rotatably. The pressuring member comes into pressure contact with the fixing belt to form a fixing nip and is arranged rotatably. The driving member is arranged so as to sandwich the fixing belt with the pressuring member and rotates the fixing belt. The slide contact member is arranged so as to sandwich the fixing belt with the pressuring member and comes into slide contact with the fixing belt. The fixing belt is engaged around the driving member and slide contact member with a state having looseness at least partially.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority from Japanese Patent application No. 2013-216934 filed on Oct. 18, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a fixing device fixing a toner image onto a recording medium and an image forming apparatus including the fixing device.

Conventionally, an electrographic image forming apparatus, such as a copying machine or a printer, includes a fixing device fixing a toner image onto a recording medium, such as a sheet. In the fixing device, a heat roller manner is widely applied. The heat roller manner is a manner making a pair of rollers come into pressure contact with each other to form a fixing nip. However, in order to sufficiently ensure a nip width (a width of a fixing nip) by the heat roller manner, it is necessary to enlarge an external diameter of each roller forming the fixing nip, and accordingly, heat capacity of components forming the fixing nip is increased. Because of this, a restoring time of the fixing device (a time until it is restored to a condition capable of fixing the toner image onto the sheet) is elongated to obstruct energy saving. If the external diameter of each roller forming the fixing nip is enlarged, a problem of deteriorating separability of the recording medium from each roller is brought.

Recently, in order to solve the above-mentioned problem, a belt fixing manner is applied. The belt fixing manner is a manner making a fixing belt and a pressuring member (e.g. a pressuring roller) come into pressure contact with each other to form a fixing nip. By applying the belt fixing manner, the nip width may be sufficiently ensured without enlarging external diameters of the fixing belt and pressuring member.

For example, there is a fixing device including a fixing belt arranged rotatably, a pressuring member coming into pressure contact with the fixing belt to form a fixing nip, a tensioning roller arranged to sandwich the fixing belt with the pressuring member and a slide contact member arranged to sandwich the fixing belt with the pressuring member.

In such a fixing device, the fixing belt is stretched across the tensioning roller and slide contact member and constant tension strength is applied to the whole area of the fixing belt. In such a condition, when the fixing belt is rotated, a sliding load of the fixing belt (a load required for sliding the fixing belt with respect to the slide contact member) becomes large. According to this, there is a possibility that the fixing belt is rapidly worn and durability of the fixing belt is deteriorated. If the fixing belt is rotated in a condition having the large sliding load, and is repeatedly bent in accordance with a shape of the slide contact member, there is a possibility of bringing damage of the fixing belt.

In order to rotate the fixing belt in a condition where the constant tension strength is applied to the whole area of the fixing belt, it is necessary to increase a nip pressure (a pressure of the fixing nip), and accordingly, drive torque of the fixing belt (torque required for rotating the fixing belt) is increased. If the nip pressure is increased as mentioned above, because each component of the fixing device must be enlarged in order to ensure strength withstanding the increased nip pressure, there is a possibility of bringing enlargement of the entire fixing device. In addition, if the nip pressure is increased as mentioned above, because the force shifting the fixing belt to one side in a longitudinal direction is strengthened, there is a possibility that an end part of the fixing belt interferes with other components and is damaged.

SUMMARY

In accordance with an embodiment of the present disclosure, a fixing device includes a fixing belt, a pressuring member, a driving member and a slide contact member. The fixing belt is arranged rotatably. The pressuring member comes into pressure contact with the fixing belt to form a fixing nip and is arranged rotatably. The driving member is arranged so as to sandwich the fixing belt with the pressuring member and rotates the fixing belt. The slide contact member is arranged so as to sandwich the fixing belt with the pressuring member and comes into slide contact with the fixing belt. The fixing belt is engaged around the driving member and slide contact member with a state having looseness at least partially.

In accordance with an embodiment of the present disclosure, an image forming apparatus includes the above-mentioned fixing device.

DETAILED DESCRIPTION

First Embodiment

First, with reference toFIG. 1, the entire structure of a printer1(an image forming apparatus) will be described.

The printer1includes a box-like formed printer main body2. In a lower part of the printer main body2, a sheet feeding cartridge3storing sheets (recording mediums) is installed and, in a top face of the printer main body2, an ejected sheet tray4is formed. To the top face of the printer main body2, an upper cover5is openably/closably attached at a lateral side of the ejected sheet tray4and, below the upper cover5, a toner container6is installed.

In an upper part of the printer main body2, an exposure device7composed of a laser scanning unit (LSU) is located below the ejected sheet tray4. Below the exposure device7, an image forming part8is arranged. In the image forming part8, a photosensitive drum10as an image carrier is rotatably arranged. Around the photosensitive drum10, a charger11, a development device12, a transfer roller13and a cleaning device14are located along a rotating direction (refer to an arrow X inFIG. 1) of the photosensitive drum10.

Inside the printer main body2, a conveying path15for the sheet is arranged. At an upstream end in the conveying path15, a sheet feeder16is positioned. At an intermediate stream part in the conveying path15, a transferring part17composed of the photosensitive drum10and transfer roller13is positioned. At a downstream part in the conveying path15, a fixing device18is positioned. At a downstream end in the conveying path15, a sheet ejecting part19is positioned. Below the conveying path15, an inversion path20for duplex printing is arranged.

Next, the operation of forming an image by the printer1having such a configuration will be described.

When the power is supplied to the printer1, various parameters are initialized and initial determination, such as temperature determination of the fixing device18, is carried out. Subsequently, in the printer1, when image data is inputted and a printing start is directed from a computer or the like connected with the printer1, image forming operation is carried out as follows.

First, the surface of the photosensitive drum10is electrically charged by the charger11. Then, exposure corresponding to the image data is carried out to the photosensitive drum10by a laser light (refer to a two-dot chain line P inFIG. 1) from the exposure device7, thereby forming an electrostatic latent image on the surface of the photosensitive drum10. Subsequently, the development device12develops the electrostatic latent image to a toner image by a toner (a developer).

On the other hand, a sheet fed from the sheet feeding cartridge3by the sheet feeder16is conveyed to the transferring part17in a suitable timing for the above-mentioned image forming operation, and then, the toner image on the photosensitive drum10is transferred onto the sheet in the transferring part17. The sheet with the transferred toner image is conveyed to a downstream side in the conveying path15to be inserted to the fixing device18, and then, the toner image is fixed onto the sheet in the fixing device18. The sheet with the fixed toner image is ejected from the sheet ejecting part19to the ejected sheet tray4. The toner remained on the photosensitive drum10is collected by the cleaning device14.

Next, with reference toFIGS. 2 and 3, the fixing device18will be described in detail. Hereinafter, it will be described so that the front side of the fixing device18is positioned at the near side onFIG. 2, for convenience of explanation. An arrow Y inFIG. 2indicates a conveying direction of the sheet. An arrow Fr inFIG. 3indicates the front side of the fixing device18.

As shown inFIG. 2, the fixing device18includes a fixing belt21, a pressuring roller22(a pressuring member), a driving roller23(a driving member), a heater (a heat source) and a slide contact member25. The pressuring roller22is arranged below (outside) the fixing belt21. The driving roller23is arranged inside the fixing belt21. The heater24is contained in the driving roller23. The slide contact member25is arranged inside the fixing belt21and at a left side (an upstream side in the conveying direction of the sheet) of the driving roller23.

The fixing belt21is formed in a roughly cylindrical shape elongated in the forward and backward directions. The fixing belt21is rotatably arranged. An arrow A inFIG. 2indicates a rotating direction of the fixing belt21. The fixing belt21has flexibility and is endless in a circumference direction. The fixing belt21is engaged (wound) around the driving roller23and slide contact member25with a state having looseness at an upper part21a. That is, the fixing belt21is not stretched across the driving roller23and slide contact member25.

The fixing belt21is composed of, for example, a base material layer, an elastic layer provided around the base material layer and a release layer covering the elastic layer in order from the inside. The base material layer of the fixing belt21is made of, for example, resin, such as polyimide (PI), or metal, such as steel special use stainless (SUS) or nickel. The base material layer of the fixing belt21has, for example, a thickness of 15 μm-100 μm. The elastic layer of the fixing belt21is made of, for example, a silicone rubber. The elastic layer of the fixing belt21has, for example, a thickness of 50 μm-500 μm. The release layer of the fixing belt21is made of, for example, a perfluoro alkoxy alkane (PFA) tube. The release layer of the fixing belt21has, for example, a thickness of 15 μm-70 μm. Incidentally, each figure shows the respective layers (the base material layer, elastic layer and release layer) of the fixing belt21without distinguishing.

The pressuring roller22is formed in a roughly cylindrical shape elongated in the forward and backward directions. The pressuring roller22is rotatably arranged. The pressuring roller22faces to the fixing belt21and comes into pressure contact with the fixing belt21.

The pressuring roller22is composed of, for example, a cylindrical core metal26, an elastic layer27provided around the core metal26and a release layer (not shown) covering the elastic layer27in order from the inside. The core metal26of the pressuring roller22is made of, for example, metal, such as aluminum. The elastic layer27of the pressuring roller22is made of, for example, a foamed silicone rubber (a foamed body). The elastic layer27of the pressuring roller22has, for example, a thickness of 1 mm-10 mm. The release layer of the pressuring roller22is made of, for example, a PFA tube. The release layer of the pressuring roller22has, for example, a thickness of 15 μm-70 μm.

The driving roller23is made of, e.g. metal, such as aluminum, SUS or iron. The driving roller23has, for example, a thickness of 0.3 mm-0.7 mm. An external diameter of the driving roller23is smaller than an external diameter of the pressuring roller22. The external diameter of the driving roller23is, preferably, 20%-80% of the external diameter of the pressuring roller22. Both front and rear end parts of the driving roller23are extended to the outside of both front and rear end parts of the fixing belt21in the forward and backward directions (refer toFIG. 3).

As shown inFIG. 2, the driving roller23is connected to a drive source28composed of a motor or the like and it is configured so as to rotate the driving roller23by the drive source28. The driving roller23is arranged so as to sandwich the fixing belt21with the pressuring roller22.

The heater24is composed of, for example, a halogen heater or a carbon heater. The heater24is configured so as to generate heat by energization and to heat the driving roller23.

The slide contact member25is composed of, for example, a base material layer and a surface layer covering the base material layer. The base material layer of the slide contact member25is made of, for example, metal, such as aluminum, SUS or iron, or heat resistant resin, such as liquid crystal polymer (LCP) or polyphenylene sulfide (PPS). The surface layer of the slide contact member25partially comes into slide contact with an inner circumference face of the fixing belt21. The surface layer of the slide contact member25is, for example, made of fluorine coating or ceramic coating having heat resistance and slidability, or made of non-woven fabric. Incidentally, each figure shows the respective layers (the base material layer and surface layer) of the slide contact member25without distinguishing.

The slide contact member25has a first guide portion31, a second guide portion32and a third guide portion33. The second guide portion32is bent from a left end part (an end part at the upstream side in the conveying direction of the sheet) of the first guide portion31to an upper side (a side separating from the pressuring roller22). The third guide portion33is bent from an upper end part (an end part at the side separating from the pressuring roller22) of the second guide portion32to a right side (the downstream side in the conveying direction of the sheet). A boundary portion Z1 between the first guide portion31and second guide portion32and a boundary portion Z2 between the second guide portion32and third guide portion33are curved without an edge.

The first guide portion31comes into slide contact with the inner circumference face of the fixing belt21. The first guide portion31is arranged so as to sandwich the fixing belt21with the pressuring roller22. The first guide portion31is curved in an arc shape along an outer circumference face of the pressuring roller22. A right end part (an end part at the downstream side in the conveying direction of the sheet) of the first guide portion31faces to an outer circumference face of the driving roller23at a distance34.

The second guide portion32is extended in a straight line shape roughly along upward and downward directions (to be exact, a direction inclined to the slightly left side as going upwardly). The second guide portion32comes into slide contact with an inner circumference face of the fixing belt21. The third guide portion33has a length shorter than those of the first guide portion31and second guide portion32. The third guide portion33is separated from the inner circumference face of the fixing belt21.

As shown inFIG. 2, in a pressure contact portion between the fixing belt21and pressuring roller22, a fixing nip35is formed. The force applied to the fixing nip35is set to 100N or less as a whole.

The fixing nip35has a first nip portion36, a second nip portion37arranged at the left side of the first nip portion36and a third nip portion38arranged between the first nip portion36and second nip portion37.

The first nip portion36is formed in a part where the pressuring roller22and driving roller23sandwich the fixing belt21. The first nip portion36is backed up from the inside of the fixing belt21by the driving roller23.

The second nip portion37is formed in a part where the pressuring roller22and first guide portion31of the slide contact member25sandwich the fixing belt21. The second nip portion37is backed up from the inside of the fixing belt21by the first guide portion31of the slide contact member25. The second nip portion37is arranged at the upstream side from the first nip portion36in the rotating direction (refer to the arrow A inFIG. 2) of the fixing belt21. The first nip portion36and second nip portion37are configured so that the sum total of the force applied to the second nip portion37is larger than the sum total of the force applied to the first nip portion36. That is, the force sandwiching the fixing belt21by the pressuring roller22and first guide portion31of the slide contact member25is larger than the force sandwiching the fixing belt21by the pressuring roller22and driving roller23.

The third nip portion38is arranged at a position corresponding to the distance34. Therefore, the third nip portion38is not backed up from the inside of the fixing belt21.

In the fixing device18configured as mentioned above, in order to fix the toner image onto the sheet, as indicated by an arrow B inFIG. 2, the drive source28works to rotate the driving roller23. According to this, as indicated by arrows A and C inFIG. 2, the fixing belt and pressuring roller22are co-rotated with the rotation of the driving roller23. That is, the driving roller23rotates the fixing belt21and pressuring roller22. At this time, the fixing belt21is rotated from a side of the slide contact member25to a side of the driving roller23in a state of being sandwiched by the pressuring roller22and driving roller23.

Moreover, in order to fix the toner image onto the sheet, the heater24is activated (lighted). When the heater24is thus activated, the driving roller23is heated from the inside by the heater24and the fixing belt21is heated from the inside by heat conduction from the driving roller23. In such a condition, when the sheet is passed through the fixing nip35, the toner image is heated and melted, and then, fixed onto the sheet.

In the embodiment, as mentioned above, the fixing belt21is engaged around the driving roller23and slide contact member25with the state having the looseness at the upper part21a(an opposite portion to a portion forming the fixing nip35). Therefore, it is possible to decrease a sliding load of the fixing belt21as compared with a case where constant tension strength is applied to the whole area of the fixing belt21. According to this, it is possible to restrain wear of the fixing belt21and to improve durability of the fixing belt21. Even if the fixing belt21is repeatedly bent in accordance with a shape of the slide contact member25accompanying to the rotation of the fixing belt21, the fixing belt21is hardly damaged.

Moreover, since the fixing belt21is engaged around the driving roller23and slide contact member25with the state having the looseness at the upper part21a, it is possible to sufficiently ensure a nip width without increasing a nip pressure. According to this, it is possible to decrease drive torque of the fixing belt21. In addition, since it is unnecessary to increase the nip pressure as mentioned above, it is unnecessary to enlarge each component of the fixing device18in order to make the component have strength withstanding the increased nip pressure. Therefore, it is possible to achieve minimization of the entire fixing device18and to produce the fixing device18at low cost. By preventing the nip pressure from being increased, since it is possible to weaken the force shifting the fixing belt21to one side in forward and backward directions, it is possible to prevent an end part of the fixing belt21from coming into contact with other components and from being damaged.

Since the fixing belt21is sandwiched between the pressuring roller22and driving roller23, it is possible to securely conduct drive force of the driving roller23to the fixing belt21. Therefore, even if the upper part21aof the fixing belt21is loosened, it is possible to stably rotate the fixing belt21.

By sandwiching the fixing belt21between the pressuring roller22and driving roller23and between the pressuring roller22and first guide portion31of the slide contact member25, it is possible to improve adhesion between the fixing belt21and pressuring roller22in the fixing nip35. Therefore, it is possible to ensure suitable nip pressure and to restrain image deterioration caused by fixing failure.

During rotating the fixing belt21, in the first nip portion36, the force rotating the fixing belt21acts from the driving roller23to the fixing belt21. On the other hand, in the second nip portion37, the force holding the fixing belt21in a stopping state acts from the first guide portion31of the slide contact member25to the fixing belt21. Therefore, by arranging the second nip portion37at the upstream side from the first nip portion36in the rotating direction of the fixing belt21, in the third nip portion38formed between the first nip portion36and second nip portion37, constant tension strength is applied to the fixing belt21. Accordingly, it is possible to restrain the fixing belt21from being loosened at the third nip portion38and to prevent image deterioration caused by fixing failure.

The sum total of the force applied to the second nip portion37is larger than the sum total of the force applied to the first nip portion36. Therefore, it is possible to securely fix the toner image onto the sheet at the second nip portion37and to more efficiently prevent image deterioration caused by fixing failure.

It is configured so that, when the driving roller23is rotated by the drive source28, the fixing belt21and pressuring roller22are co-rotated with the rotation of the driving roller23. By applying such a configuration, it is possible to stabilize rotation speed of the fixing belt21and pressuring roller22.

By curving the first guide portion31of the slide contact member25in the arc shape along the outer circumference face of the pressuring roller22, it is easy to deform the fixing belt21to a shape along the outer circumference face of the pressuring roller22and it is possible to ensure wide nip width. According to this, it is possible to securely fix the toner image onto the sheet at the fixing nip35. In addition, by curving the boundary portion Z1 between the first guide portion31and second guide portion32and the boundary portion Z2 between the second guide portion32and third guide portion33, it is possible to restrain catching between the fixing belt21and the slide contact member25.

The pressuring roller22has the elastic layer27made of the foamed silicone rubber (the foamed body). By applying such a configuration, it is possible to decrease heat capacity of the pressuring roller22as compared with a case where the elastic layer27of the pressuring roller is made of solid material (solid wood material). Therefore, it is possible to reduce heat quantity taken by the pressuring roller22and to more quickly heat the fixing belt21.

In the embodiment, since the external diameter of the driving roller23is smaller than the external diameter of the pressuring roller22, it is possible to reduce heat capacity of the driving roller23and to heat the driving roller23at a short time.

Since the fixing nip35is formed by using the fixing belt21, it is possible to ensure sufficient nip width without enlarging external diameters of the fixing belt21and pressuring roller22. Therefore, it is possible to reduce heat capacity of components constituting the fixing nip35and to achieve energy saving and shortening of restoring time of the fixing device18. Further, by reducing the external diameter of the fixing belt21, it is possible to easily separate the sheet from the fixing belt21.

The surface layer of the slide contact member25is made of the fluorine coating or the ceramic coating having the heat resistance and the slidability, or made of the non-woven fabric. Therefore, it is possible to decrease the sliding load of the fixing belt21, to decrease the drive torque of the fixing belt21and to restrain the wear of the fixing belt21.

Although, in the embodiment, a case where the fixing belt21is composed of the base material layer, elastic layer and release layer was described, in another embodiment, the fixing belt21may be composed of a base material layer and a release layer. That is, the fixing belt21may be made without the elastic layer. In such a case where the elastic layer is not arranged in the fixing belt21, for example, instead of the PFA tube with a thickness of 15 μm-70 μm, fluorine coating with a thickness of 15 μm-70 μm may be used as the release layer of the fixing belt21.

In the embodiment, a case where the elastic layer of the pressuring roller22is made of the foamed silicone rubber (the foamed body) was described. On the other hand, in another embodiment, the elastic layer27of the pressuring roller22may be made of a solid rubber (solid material).

Although, in the embodiment, a case of using the heater24composed of the halogen heater or the carbon heater as the heat source was described, in another embodiment, a ceramic heater, an IH (Induction Heating) coil or the like may be used as the heat source.

The embodiment was described in a case of applying the configuration of the present disclosure to the printer1. On the other hand, in another embodiment, the configuration of the disclosure may be applied to another image forming apparatus, such as a copying machine, a facsimile or a multifunction peripheral.

Second Embodiment

Next, a fixing device41according to a second embodiment of the present disclosure will be described with reference toFIGS. 4 and 5. Hereinafter, it will be described so that the front side of the fixing device41is positioned at the near side onFIG. 4, for convenience of explanation. An arrow Y inFIG. 4indicates the conveying direction of the sheet. An arrow Fr inFIG. 5indicates the front side of the fixing device41. Incidentally, other components except for winding rollers42(winding members) have similar or corresponding configurations to the first embodiment, and therefore, the other components will be denoted by the same reference numerals in the figures and their explanation will be omitted.

As shown inFIG. 4, the winding rollers42are located at an opposite side to the pressuring roller22across the driving roller23. The winding rollers42are arranged so as to sandwich the fixing belt21with the driving roller23. The winding rollers42are rotatably arranged around a roller shaft43extending in the forward and backward directions.

As shown inFIG. 5, the fixing belt21has a sheet passing region (a recording medium passing region) R1, on which the sheet is passed, and sheet non-passing regions (recording medium non-passing regions) R2, on which the sheet is not passed, arranged both front and rear sides of the sheet passing region R1 (outside the sheet passing region R1). Each winding roller42does not come into contact with the sheet passing region R1 of the fixing belt21, but comes into contact with the sheet non-passing regions R2 of the fixing belt21.

Each winding roller42is composed of, for example, a cylindrical core metal and a surface layer covering a surface of the core metal. The core metal of each winding roller42is made of, for example, metal, such as aluminum, SUS or iron. The surface layer of each winding roller42is made of, for example, fluorine resin coating or fluorine resin tube.

By arranging each winding roller42as mentioned above, it is possible to make the fixing belt21securely come into contact with the driving roller23from a lower side (an area of a side of the pressuring roller22) of the driving roller23to an upper side (an area of an opposite side to the pressuring roller22) of the driving roller23. According to this, it is possible to quickly heat the fixing belt21by the heat conduction from the driving roller23, to shorten the restoring time of the fixing device41and to achieve energy saving.

Each winding roller42comes into contact with the sheet non-passing regions R2 of the fixing belt21. Therefore, it is possible to prevent heat of the sheet passing region R1 from being taken by each winding roller42.

In the embodiment, a case where each winding roller42comes into contact with the sheet non-passing regions R2 of the fixing belt21was described. On the other hand, in another different embodiment, as shown inFIG. 6, the winding roller42may come into contact with the sheet passing region R1 and sheet non-passing regions R2 of the fixing belt21(roughly whole area of the fixing belt21). By applying such a configuration, it is possible to make both the sheet passing region R1 and sheet non-passing regions R2 of the fixing belt21securely come into contact with the driving roller23and to improve heat conduction efficiency from the driving roller23to the fixing belt21.

While the present disclosure has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present disclosure.