JPH09288434A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the rib mark of a guide member and a circular void image from being formed. SOLUTION: As for the guide member 3 guiding a recording material S to a nip part between a fixing roller 1 and a pressure roller 2, the central part of the roller 1 in the axial direction is formed to a thick part 4 projecting upward from both side parts and the tick part 4 is shaped flat. Thus, the conventional rib mark caused by the contact pressure of the recording material on a rib and the splash of a toner image occurring when the guide member is charged are eliminated. Then, the circular void image is prevented from being formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic or electrostatic photography type image forming apparatus such as a copying machine or a laser printer, which is characterized by a fixing device.

[0002]

2. Description of the Related Art Conventionally, a recording material is nipped and conveyed at a nip portion formed between a fixing roller heated by a heating source and a pressure roller rotating in pressure contact with the fixing roller, thereby recording the recording material on the recording material. 2. Description of the Related Art A fixing device that makes an unfixed toner image formed on a toner image a permanent image is often used in image forming apparatuses such as a copying machine and a laser printer.

In such a fixing device, in order to prevent paper wrinkles from occurring on the recording paper after passing through the fixing device due to variations in the arrival point of the recording material to the nip portion and the posture of the recording material entering the nip portion, the recording material is nipped. In most cases, a guide member for accurately guiding the member is installed.

FIG. 6 shows an example of a conventional fixing device having such a guide member. In the figure, the fixing device 10
Is a fixing roller 1 having a heater H therein, a pressure roller 2 which is in pressure contact with the fixing roller 1 and is driven or driven to rotate,
Further, a guide member 3 for guiding the recording material S to a pressure contact portion (nip portion) N formed between the pair of rollers 1 and 2 is provided.

The recording material S is accurately guided by the guide member 3 to the nip portion N while preventing the occurrence of paper wrinkles, and the unfixed toner image formed on the recording material S is conveyed under a nipping pressure to be a permanent image. It is fixed.

Here, the cause of paper wrinkles is shown in FIG.
A brief explanation will be given with reference to.

The leading edge of the recording material S that has approached the vicinity of the nip portion N contacts the fixing roller 1 or the pressure roller 2 slightly earlier and is nipped by the nip portion N.

At this time, the front end of the recording material S is fixed to the fixing roller 1.
In many cases, it is not a straight line but a wavy shape in the axial direction. Therefore, at the tip portion, the fixing roller 1
There is a part that first comes into contact with the pressure roller 2 and a part that comes into contact with the pressure roller 2 first.

On the other hand, the fixing roller 1 and the pressure roller 2 have different surface materials in most cases, so that the recording material S
The friction coefficient for is different.

Therefore, the time to reach the nip portion N is different between the portion contacting the fixing roller 1 and the portion contacting the pressure roller 2 first. Therefore, the timing at which the conveyance is started by the nip portion N in one sheet of recording material S varies, so that the recording material S is internally stressed, and the recording material S largely undulates. The large undulations are crushed by being sandwiched by the nip portion N, which causes paper wrinkles.

Therefore, generally, a method of guiding the recording material S to either the fixing roller 1 or the pressure roller 2 is adopted. In most conventional fixing devices, the friction coefficient of the outer peripheral surface of the pressure roller 2 with respect to the recording material S is larger than that of the fixing roller 1. Therefore, the tip of the recording material S comes into contact with the pressure roller 2 first. If so, the variation in the time for reaching the nip portion N partially increases due to the waviness of the leading end of the recording material S.

In consideration of the above, in the prior art, since the leading end of the recording material S is made to enter the nip portion N at the same time without variation, the leading end of the recording material S is positively brought into contact with the fixing roller 1 having a small friction coefficient. Prevents wrinkles.

The attitude of the recording material S is another cause of paper wrinkles. FIG. 8 shows a diagram for explaining another mechanism of paper wrinkling.

When the leading end portions of the left and right recording materials S with respect to the recording material advancing direction enter the nip portion N while being raised above the central leading end portion of the recording material S, the left and right recording material leading end portions are recorded. The pressure is nipped at the nip portion N slightly earlier than the central tip portion. Since the left and right parts of the recording material in the traveling direction are fixed and conveyed while being pinched, internal stress is accumulated in the central part of the recording material and paper wrinkles occur.

In consideration of this, conventionally, a paper wrinkle is formed by forming the central portion of the guide member 3 for guiding the recording material S to the nip portion N in the axial direction of the fixing roller 1 to be raised above both side portions. To prevent.

[0016]

As described above, the fixing device often uses the fixing roller 1 in order to prevent paper wrinkles.
The leading edge of the recording material S is positively brought into contact with the vicinity of the nip portion. Further, paper wrinkles are further prevented by forming the central portion of the guide member 3 for guiding the recording material S to the nip portion N in the axial direction of the fixing roller 1 so as to be raised above both side portions.

At this point, the mounting position accuracy and the shape accuracy of the guide member 3 for guiding the recording material S to the contact point are very strictly required.

On the other hand, since the rib #A at the central portion of the guide member 3 in the axial direction of the fixing roller is raised above the portions on both sides, when the recording material S is nipped and conveyed by the nip N, the guide member 3 is guided. The contact pressure of the recording material S on all the high ribs in the center of the recording medium 3, especially on the ribs 3a on both side edges becomes strong, the guide member 3 is electrified, and the unfixed image scatters. In some cases, a circular outline image was generated.

Therefore, an object of the present invention is to provide an image forming apparatus provided with a fixing device capable of preventing the generation of a trace of ribs on a guide member and a circular white image.

[0020]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
The recording material is pinched and conveyed at a nip portion formed between a fixing roller heated by a heating source and a pressure roller rotating in pressure contact with the fixing roller, thereby undecidedly formed on the recording material. In an image forming apparatus having a fixing device for making a toner image a permanent image, a guide member for guiding a recording material to the nip portion is provided, and a central portion of the guide member in an axial direction of the fixing roller is located above both side portions thereof. The image forming apparatus is characterized in that the thick portion is raised up and the thick portion has a planar shape.

[0021] It is preferable that the top portion of the thick portion has an R shape, and the portion connecting the top portion and the both side portions has a gentle R shape. Both of the R shapes have a radius of 10
mm or more.

The apex portion is located upstream of the downstream end of the guide member in the recording material conveying direction, and the inclined surface connecting the apex portion and the downstream end of the guide member conveys the recording material at the nip portion. The dip angle is 30 ° to 60
° is preferred. The distance from the downstream end of the guide member to the top portion is preferably 4 to 10 mm.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. In the embodiments described below, the present invention is described as being embodied in an electrophotographic image forming apparatus as shown in, for example, FIG. 5, but the present invention is not limited to this.

In FIG. 5, the electrophotographic image forming apparatus has a photosensitive drum 11 as an image carrier rotatably provided, the photosensitive drum 11 is uniformly charged by a primary charger 12, and then, for example, like a laser. The light emitting element 13 exposes the information signal to form an electrostatic latent image, and the developing device 14 visualizes it. Next, the visible image is transferred onto the transfer paper S by the transfer charger 15 and further fixed by the fixing device 10 to obtain a permanent image. Further, the transfer residual toner on the photosensitive drum 1 is removed by the cleaning device 16.

Example 1 Example 1 of the fixing device according to the present invention will be described with reference to FIGS. 1 and 2. The same members as those described above are designated by the same reference numerals. 1 and 2, the fixing device 10 includes a fixing roller 1 having a heater H therein,
The fixing roller 1 is provided with a pressure roller 2 that is driven or driven to rotate by pressure, and a guide member 3 that guides the recording material S to a pressure contact portion (nip portion) N formed between the pair of rollers 1 and 2. ing. The guide member 3 is provided with a raised portion 4 in a planar shape at the central portion in the axial direction of the fixing roller.

The fixing device of this embodiment operates as follows. The pressure roller 2 is in pressure contact with the fixing roller 1 and is driven or driven to rotate. Such one
Pressure contact portion N (nip portion) formed between the pair of rollers 1 and 2
At, the unfixed image is fixed as a permanent image by conveying the recording material S having the unfixed toner image while being heated and nipped.

In this embodiment, in the guide member 3 that guides the recording material S to the contact point P, the thick portion 4 that is raised above the portions on both sides in the central portion of the guide member 3.
Is present in the shape of a plane, the rib mark as described above does not occur.

Further, a portion 4b connecting the top portion 4a of the thick portion 4 in which the central portion of the guide member 3 is raised above both side portions thereof and the both side portions 3b thereof is gently connected with a radius of 10 mm or more, so that As described above, the contact pressure of the recording material S to each one of the high ribs in the central portion becomes strong, the guide member is charged, the unfixed image is scattered, and the rib mark and the circular blank image are not generated. It was

Second Embodiment Next, a second embodiment of the fixing device of the present invention will be described with reference to FIGS. In both figures, the fixing device 10 is
Recording is performed on a fixing roller 1 having a heater H therein, a pressure roller 2 which is pressed against the fixing roller 1 and is driven or driven to rotate, and a pressure contact portion (nip portion) N formed between the pair of rollers 1 and 2. The guide member 3 for guiding the material S is provided. In the guide member 3, a thick portion 4 is formed in a planar shape in the central portion of the fixing roller 1 in the axial direction, and the thick portion 4 has a top portion 4a formed on the nip side thereof and a guide member downstream end 4c. The inclined surface 5 has a connecting surface, and the inclined surface 5 has a dip angle α = 3 with respect to the direction in which the recording material S is conveyed in the nip portion N.
It is set to 0 ° to 60 °.

The fixing device of this embodiment operates as follows. The pressure roller 2 is in pressure contact with the fixing roller 1 and is driven or driven to rotate. Such one
Pressure contact portion N (nip portion) formed between the pair of rollers 1 and 2
At, the unfixed image is fixed as a permanent image by conveying the recording material S having the unfixed toner image while being heated and nipped.

In the present embodiment, the inclined surface 5 connecting the top portion 4a of the thick portion 4 and the downstream end 4c of the guide member 3 in the central portion of the guide member 3 is raised. Since the dip angle α is 30 ° to 60 ° relative to the direction in which the material S is being conveyed in the nip portion, the thick paper or O
The thicker portion 4 is the rear end portion of the recording material S such as HT that is hard and has a strong elasticity.
It is possible to prevent a sudden drop immediately after passing the top portion 4a of the sheet, and to prevent a trailing edge scattered image that has been generated due to the rapid drop immediately after passing the top portion 4a of the thick portion 4 in the related art. .

[0032]

As is apparent from the above description, the image forming apparatus of the present invention has the guide member for guiding the recording material to the nip portion, and the central portion of the guide member in the fixing roller axial direction is on both sides thereof. By forming the thick portion raised above the portion and forming the thick portion in a planar shape, it is possible to prevent rib marks of the guide member and the generation of a circular outline image, and therefore a high quality image. Can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a fixing device according to a first exemplary embodiment.

FIG. 2 is a cross-sectional view of the fixing device of FIG.

FIG. 3 is a perspective view illustrating a fixing device according to a second exemplary embodiment.

FIG. 4 is a sectional view of the fixing device shown in FIG.

FIG. 5 is a schematic configuration diagram showing an example of an image forming apparatus to which an embodiment is applied.

FIG. 6 is a perspective view showing an example of a conventional fixing device.

FIG. 7 is a perspective view showing an example of a working state of the fixing device of FIG.

FIG. 8 is a perspective view showing another example of the operating state of the fixing device in FIG.

[Explanation of symbols]

 1 Fixing Roller 2 Pressure Roller 3 Guide Member 4 Thick Part 4a Top Part 5 Inclined Surface 10 Fixing Device H Heater (Heating Source) S Transfer Paper (Recording Material)

Claims (5)

[Claims] 1. A recording material is nipped and conveyed at a nip portion formed between a fixing roller heated by a heating source and a pressure roller rotating in pressure contact with the fixing roller, thereby conveying the recording material on the recording material. An image forming apparatus having a fixing device for making an unfixed toner image formed on a recording medium a permanent image has a guide member for guiding a recording material to the nip portion, and a central portion of the guide member in the fixing roller axial direction is provided. An image forming apparatus characterized in that a thick portion is raised above both side portions thereof, and the thick portion has a planar shape. 2. The top portion of the thick portion has an R shape, and the portion connecting the top portion and the both side portions has a gentle R shape.
The image forming apparatus according to claim 1, wherein the image forming apparatus has a shape. 3. The image forming apparatus according to claim 2, wherein both of the R shapes have a radius of 10 mm or more. 4. The apex portion is located upstream of a downstream end of the guide member in the recording material conveying direction, and an inclined surface connecting the apex portion and a downstream end of the guide member has a recording material in the nip portion. Angle of dip of 30 ° to 6 relative to the direction in which it is conveyed
The image forming apparatus according to claim 2, wherein the image forming apparatus has an angle of 0 °. 5. The image forming apparatus according to claim 4, wherein the distance from the downstream end of the guide member to the top portion is 4 to 10 mm.