JPH04322280A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a faulty image from being produced caused by peeling discharge or the generation of the wrinkles of a paper in accordance with the heating of a fixing roller before fixing and to stably carry the paper to a fixing part from a transfer part. CONSTITUTION:The side end part A of the transfer part of a guide 10-1 is shaped so as to form a projection on an image surface side (image carrier 8 side) with respect to a tangent line drawn on the outer circumference of the carrier 8 at the nip part M1 of the carrier 8 and a transfer electrostatic charger 9. Simultaneously, the guide surface 10-1a of the guide 10-1 is shaped so as to be curved in a recessed state. Since the deflection of the paper P is absorbed by the curvature of the surface 10-1a of the guide 10-1, the paper P is stably carried to the fixing part from the transfer part. Besides, since the peeling discharge when the paper P is peeled from the carrier 8 is prevented from occurring and the paper P enters a fixing roller 10-2 from a fixing roller 10-4 side, a heat quantity that the paper P receives from the roller 10-2 before the fixing is suppressed to the minimum and the faulty image caused by the peeling discharge or the wrinkles of the paper P is prevented from being produced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam printer or an LED printer.

0002

2. Description of the Related Art In recent years, there has been an increasing demand for image forming apparatuses such as laser beam printers and LED printers that record images using an electrophotographic process to save space and improve operability for users.

FIG. 6 shows an example of a printer that meets such requirements.
Shown below. In this printer, sheets P loaded in a cassette 60 are conveyed to an image carrier 8 of an image forming section by a paper feed roller 2 and a conveyance roller 7.

On the other hand, the image carrier 8 is connected to the scanner unit 5.
A latent image is formed on its surface by being irradiated with light L from zero, and this latent image is developed as a toner image by a developing device (not shown). This toner image is then transferred onto the paper P by the transfer charger 9. In addition, the transfer charger 9 is
It is made of a conductive rubber roller and is brought into contact with the image carrier 8 with light pressure, and a predetermined voltage is applied thereto.

[0005] Then, the paper P to which the above toner image was transferred
The toner image is formed by passing between an aluminum fixing roller 10-2 that rotates at a predetermined speed and a rubber pressure roller 10-4 that comes into contact with the fixing roller 10-2 and rotates as a result. After being fixed, the paper ejection guide 10-
5 to the paper ejection roller 100, and the paper ejection roller 1
00, the paper is discharged from the machine and stacked on the paper stacking section 110. Note that the fixing roller 10-2 is equipped with a heater 10-2.
3 and a temperature sensor (not shown), and is rotatably supported by a fixing frame 10-0 by a bearing (not shown), and the pressure roller 10-4 is heated to a predetermined temperature by a temperature sensor (not shown). It is brought into contact with the roller 10-2 with a predetermined pressure.

[0006]

[Problems to be Solved by the Invention] By the way, the paper P to which the toner image has been transferred by the transfer charger 9 is
The paper P is separated from the image carrier 8 due to the curvature of the paper P and the rigidity of the paper P. However, if the rigidity of the paper P is small, the adhesion force that the paper P receives from the transfer charger 9 to the image carrier 8 is relatively strong. Therefore, there is a delay in the timing at which the paper P is separated from the image carrier 8, and the paper P is suddenly separated from the image carrier 8. When the paper P is suddenly separated from the image carrier 8 in this way, a separation discharge occurs between the paper P and the image carrier 8, and as shown in FIG. A problem arises in that the toner t scatters and causes image defects.

[0007] In order to solve the above problem, guide 10-
1 as close to the image carrier 8 as possible to prevent the paper P from being suddenly peeled off. However, Guide 10-1
If the guide 10-1 approaches the image carrier 8 too closely, the paper P cannot be guided to the nip N2 between the fixing roller 10-2 and the pressure roller 10-4. A straight line is formed slightly along the non-image surface side (lower right side in FIG. 6) of the straight line L3 connecting the nip part N1 with the device 9 and the nip part N2 between the fixing roller 10-2 and the pressure roller 10-4. The guide surface is located at.

On the other hand, the transport speed V0 of the paper P coming out of the transfer charger 9 is set to be higher than the transport speed V1 of the paper P at the fixing section (V0≧V1). The reason for this is that the conveyance force on the fixing side is much stronger than that on the transfer side, so if the conveyance speed V0 on the transfer side is smaller than the conveyance speed V1 on the fixing side, the paper P is pulled on the fixing side and the image is This is because problems such as stretching and image fraying occur.

However, the difference between the transport speeds V0 and V1 (
=V0-V1) is large, as shown in FIG.
is largely bent between the transfer section and the fixing section, that is, at the guide 10-1 portion. Then, the paper P approaches the fixing roller 10-2 at the entrance portion of the fixing roller 10-2, and the paper P is heated by the fixing roller 10-2 even before it is bitten by the fixing roller 10-2, and the paper P is heated by the fixing roller 10-2. The moisture becomes water vapor and evaporates, causing minute wrinkles on the paper P. When such minute wrinkles occur on the paper P, as shown in FIG. 7, tree branch-like gloss unevenness a appears in the fixed toner area, resulting in a significant deterioration in image quality. .

[0010] Furthermore, when the amount of water vapor evaporated from the paper P during fixing increases, the amount of curl of the paper P increases,
Problems such as poor stacking of the paper P on the discharged paper stacking section 110 occur. In order to solve this problem, the position of the tip of the guide 10-1 on the fixing roller 10-2 side is changed to the pressure roller 10-4.
When the paper P is lowered to the side, the paper P first hits the pressure roller 10-4 side, making it difficult for the paper P to enter the nip N2 between the fixing roller 10-2 and the pressure roller 10-4. There have been problems in that wrinkles occur and the paper P is more likely to jam. For this reason, the actual situation is that there are significant restrictions on the paper P and environment that can be used.

The present invention has been made in view of the above problems, and its purpose is to prevent image defects caused by peeling discharge and wrinkles caused by heating of the fixing roller on the paper before fixing, and to improve the quality of the paper. An object of the present invention is to provide an image forming apparatus that can stably transport images from a transfer section to a fixing section.

0012

[Means for Solving the Problems] In order to achieve the above object, the present invention has an image bearing member and a transfer device in a transfer section, a fixing roller and a pressure roller in a fixing section, and an image bearing member and a transfer device that are discharged from the transfer section. In an image forming apparatus provided with a guide member that guides paper to a fixing unit, an end of the guide member on the transfer unit side is aligned with a tangent to the outer periphery of the image carrier at a contact point between the image carrier and the transfer device. In contrast, the guide member has a convex shape toward the image plane, and the guide surface of the guide member has a concavely curved shape.

[0013]

[Operation] According to the present invention, since the end of the guide member on the side of the transfer section is formed in a convex shape, peeling discharge when the paper is peeled off from the image bearing member is prevented, and conventionally caused by peeling discharge. This eliminates the problem of image defects.

Further, according to the present invention, since the deflection of the paper is absorbed by the curvature of the guide member, the paper is stably conveyed from the transfer section to the fixing section. Moreover, since the paper always enters the fixing roller from the pressure roller side that is far from the fixing roller surface, the amount of heat that the paper receives from the fixing roller before fusing can be minimized, making it possible to minimize the amount of heat that the paper receives from the fixing roller. This solves the problem that minute wrinkles occur on the paper because the paper is heated by the fixing roller even before it is bitten by the fixing roller, and the water contained therein turns into water vapor and evaporates. This prevents deterioration of image quality such as uneven gloss.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of a transfer section and a fixing section of an image forming apparatus according to the present invention, FIG. 2 is a diagram showing the positional relationship between a transfer section, a fixing section, and a guide, and FIG. 3 is a cross-sectional view of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view of the device (laser beam printer).

First, the general structure of the image forming apparatus will be explained based on FIG.
The paper P stored in the cassette 1 is separated one by one by the paper feed roller 2 and the separation claw 3 at a predetermined timing, and then separated by the paper guide 4 provided in the paper cassette 1 and the paper guides 5 and 6 provided in the main body of the apparatus. Timing rollers 7a, 7
be guided by b. Note that a paper detection sensor s is provided immediately in front of the timing rollers 7a, 7b, and this paper detection sensor s controls the rotation of the timing rollers 7a, 7b, the timing of laser emission, etc.

The paper P sent out by the timing rollers 7a and 7b passes between an image carrier 8 rotatably housed in a process cartridge C and a transfer charger 9 that comes into contact with the image carrier 8 and rotates as a result. By passing through, the toner image formed on the image carrier 8 is transferred. still,
The process cartridge C is configured by housing a plurality of process units for image formation in one housing. A predetermined voltage is applied to transfer the image.

Then, the paper P to which the toner image has been transferred is
The toner image is transported along the guide 10-1 to the fixing device 10, where the toner image is fixed. Note that the fixing device 10 is
An aluminum fixing roller 10-2 is disposed above the image carrier 8 and the transfer charger 9, and is heated to a predetermined temperature by a heater 10-3 and a temperature sensor (not shown).
A pressure roller 10-4 is disposed facing the fixing roller 10-2, and is brought into contact with the fixing roller 10-2 with a constant pressure by a spring (not shown) and rotates as a result. The guide 10-1 is made of a semiconductive molded member having a predetermined electrical resistance, and includes a thin metal charge-eliminating core for dissipating the electric charge applied to the paper P during transfer. is provided.

In this embodiment, as shown in FIG. 2, the nip N2 between the fixing roller 10-2 and the pressure roller 10-4 is the same as the nip between the image carrier 8 and the transfer charger 9. Part N1
It is located on the image surface side (diagonally to the left in FIG. 2) with respect to a tangent L1 drawn to the outer circumferential circle of the image carrier 8 and the transfer charger 9.

Also, a portion of the guide 10-1 close to the exit of the transfer section (nip portion N between the image carrier 8 and the transfer charger 9)
1) has a convex shape on the image carrier 8 side with respect to the tangent L1. If the amount of protrusion of the portion A of this guide 10-1 from the tangent line L1 is Δt1 as shown in the figure, then this amount of protrusion Δt1 is the same as that between the image carrier 8 and the transfer charger 9.
nip portion N1, fixing roller 10-2, and pressure roller 10
The value is set such that the portion A does not exceed the straight line L3 connecting the nip portion N2 of -4, and in this embodiment, Δt1 is set to 0 to 2 mm.

Furthermore, the guide surface 10-1 of the guide 10-1
a has a concave shape curved toward the non-image side (right side in FIG. 2). The amount of curvature of the guide surface 10-1a is basically determined by the conveyance speed V0 of the paper P at the transfer section and the conveyance speed V0 at the fixing section.
1 (=V0-V1) and the distance between the nip parts N1 and N2. In this example, the speed difference ratio (=(V0-V1/V0)) is 1%, and the nip part N1 and N
2 is about 50mm, the amount of curvature is straight line L
3 to 5 to 10 mm.

Further, the tip B of the guide 10-1 on the fixing side is located below the tangent L2 drawn to the outer circumference of the fixing roller 10-2 and the pressure roller 10-4 at the nip N2 (the pressure roller 10 -4 side), and if the distance of the tip B from the tangent L2 is Δt2 as shown in the figure, Δt2=0 to 1.5 mm. and,
This tip B is configured to form a slight straight line to guide the paper P, and if the extension of the straight line is L4 as shown in the figure, then this extension L4 is the nip part N2.
Δt3 shown in the image side (fixing roller 10-
2 side).

The paper P, on which the toner image has been transferred by passing through the nip N1 between the image carrier 8 and the transfer charger 9, is discharged to the fixing side approximately along the straight line L3.
As described above, the portion A of the guide 10-1 close to the exit of the transfer section (the portion close to the nip N1 between the image carrier 8 and the transfer charger 9) is on the image carrier 8 side with respect to the tangent L1. Because of the convex shape, even if the rigidity of the paper P is small, peeling discharge when the paper P is peeled off from the image carrier 8 is prevented, and the problem of image defects that conventionally occurred due to peeling discharge is avoided. It will be resolved.

[0025] Then, the leading end of the paper P is guided by the guide 10-1.
When the guide surface 10-1a comes into contact with the guide surface 10-1a, the guide surface 1
It is conveyed to the fixing side along 0-1a. At this time, since the guide surface 10-1a is curved downward from the straight line L3 as described above, the leading edge of the paper P conveyed along the guide surface 10-1a has a negative angle with respect to the tangent L2. The paper P enters the fixing roller 10-2 at an angle of , and is caught between the fixing roller 10-2 and the pressure roller 10-4, where the toner image is fixed by heat and pressure. In this case, paper P
The conveyance speed V0 at the transfer section is the conveyance speed V1 at the fixing section.
(V0>V1), the paper P gradually bends at the guide 10-1 portion, but this bending of the paper P is absorbed by the curvature of the guide surface 10-1. Therefore, the paper P always enters the nip portion N2 from the side of the pressure roller 10-4 that is distant from the surface of the fixing roller 10-2, and the paper P is transferred to the fixing roller 10-2 before fixing.
The amount of heat received from the fixing roller 10-2 can be minimized, and the paper P is heated by the fixing roller 10-2 even before it is bitten by the fixing roller 10-2 as in the conventional case, and the water contained therein turns into water vapor and evaporates. Therefore, the problem of minute wrinkles occurring on the paper P is solved, and deterioration in image quality such as uneven image gloss due to wrinkles is prevented.

[0026] Further, the tip end B of the guide 10-1 is connected to the tangent L2.
Since the angle of the paper P is set lower than that of the fixing roller 10-2, when the trailing edge of the paper P leaves the transfer section, the angle of the paper P is set lower than that of the fixing roller 10-2.
is determined by the nip portion N2 of the pressure roller 10-4, and the paper P is stably conveyed without rubbing against the tip portion B of the guide 10-1.

As a result of the above, it has become possible to use paper, which was previously impossible, and there is no longer any need for environmental restrictions.

[0028]The paper P, on which the toner image has been fixed in the fixing section, is separated from the fixing roller 10-2 by the separating claw 10-6 shown in FIG.
and the paper ejection roller section 10 guided by the paper ejection outer guide 10-7.
0, is discharged outside the machine by the paper discharge roller section 100, and is stacked on the paper stacking section 110.

Next, the second and third embodiments of the present invention are shown in FIG.
Each is shown in FIG. 4 and 5 are cross-sectional views of a transfer section and a fixing section of the image forming apparatus, and in these figures, the same elements as shown in FIG. 1 are given the same reference numerals.

In the second embodiment shown in FIG. 4, the guide 10-1 has a two-part structure, and the guide 10-1 is divided into a guide piece 10-1A attached to the transfer charger 9 side and a fixing device. 10 and a guide piece 10-1B attached to the guide piece 10-1B.

Furthermore, in the third embodiment shown in FIG.
A press-formed product such as a sheet metal is used as 0-1. still,
The guide 10-1 is not directly fixed to the fixing device 10 or the transfer unit, but may be attached to another frame, or a rib directly integrally molded from the frame.

[0032]

Effects of the Invention As is clear from the above description, according to the present invention, the transfer section includes an image bearing member and a transfer device, the fixing section includes a fixing roller and a pressure roller, and an image is discharged from the transfer section. In an image forming apparatus provided with a guide member that guides paper to a fixing unit, an end of the guide member on the transfer unit side is aligned with a tangent to the outer periphery of the image carrier at a contact point between the image carrier and the transfer device. The guide member has a convex shape toward the image surface, and the guide surface of the guide member is curved in a concave shape to prevent image defects due to peeling discharge and wrinkles caused by heating of the fixing roller of the paper before fixing. In addition to preventing this, the paper can be stably transported from the transfer section to the fixing section.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a transfer section and a fixing section of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the positional relationship between a transfer section, a fixing section, and a guide.

FIG. 3 is a sectional view of an image forming apparatus (laser beam printer) according to the present invention.

FIG. 4 is a sectional view of a transfer section and a fixing section of an image forming apparatus showing a second embodiment of the present invention.

FIG. 5 is a sectional view of a transfer section and a fixing section of an image forming apparatus showing a third embodiment of the present invention.

FIG. 6 is a sectional view of a conventional image forming apparatus.

FIG. 7 is a diagram showing uneven gloss and toner scattering on paper.

FIG. 8 is a sectional view of a transfer section and a fixing section of a conventional image forming apparatus.

[Explanation of symbols]

8 Image carrier 9 Transfer charger (transfer device) 10
Fixing device 10-1 Guide (guide member) 10-1a
Guide surface 10-2 Fixing roller 10-4 Pressure roller A Transfer section side end B of guide
Fusing side tip L1 of guide
Tangent line L2 Tangent line L3 Straight line N1 Nip part (contact point between image carrier and transfer device) N2 Nip part (contact point between fixing roller and pressure roller) P Paper

Claims (3)

[Claims] Claim 1: The transfer section includes an image carrier and a transfer device,
In an image forming apparatus including a fixing roller and a pressure roller in a fixing section, and a guide member that guides a sheet discharged from a transfer section to the fixing section, an end of the guide member on the transfer section side is connected to the image carrier. The guide member has a shape that is convex toward the image surface side with respect to a tangent drawn to the outer periphery of the image carrier at the contact point between the body and the transfer device, and the guide surface of the guide member is curved in a concave shape. image forming device. 2. The image forming apparatus according to claim 1, wherein the guide surface of the guide member is curved toward a non-image surface side. 3. The tip of the guide member on the fixing unit side is located on the non-image surface side with respect to a tangent drawn to the outer circumference of the fixing roller at the contact point between the fixing roller and the pressure roller. The image forming apparatus according to claim 1.