JP2004157462A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent toner from sticking to the leading end of a fixation entrance guide. <P>SOLUTION: The image forming apparatus is provided with a transport guide 4 for guiding a sheet material to a fixing device and an entrance guide 10 for guiding the sheet material into a fixation nip part. A projection P is arranged on the transport part of the entrance guide, and an angle β formed by a straight line linking a point PL on the transport guide farthest away from a straight line LN linking between the downstream point of a transfer nip and the upstream point of the fixation nip and also in the most downstream position in the transport direction and a projection apex PH and a horizontal plane is made larger than an angle α formed by a straight line linking between the most downstream point on the transport guide farthest away from the straight line linking between the downstream point of the transfer nip and the upstream point of the fixation nip and also in the most downstream position in the transport direction and the most downstream point positioned closest to the pressure roller 7 on the transport surface of the entrance guide and the horizontal plane. Besides, an angle γ formed by a straight line linking between the projection apex and the most downstream point PE positioned closest to the pressure roller on the transport surface of the entrance guide and the horizontal plane is controlled so as not to be larger than an angle δ formed by a straight line linking the upper and lower streams of the fixation nip and the horizontal plane. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for preventing toner from adhering to a transport guide disposed below an upstream side of a fixing device of an image forming apparatus.
[0002]
[Prior art]
As an example of the related art, a printer that is an image forming apparatus that records an image on a sheet material using an electrophotographic process will be described with reference to FIGS. FIG. 8 is a schematic sectional view showing a printer main body, and FIG. 9 is a schematic sectional view showing a state during transfer and fixing.
[0003]
Hereinafter, the operation of the printer 100 will be described.
[0004]
First, the face-down discharge of one-sided printing will be described. As the paper feed roller 102 rotates, the sheet material S is fed out one by one from the paper feed cassette 101 in the paper feed direction, and is conveyed to the registration roller pair 104 via the intermediate roller pair 103. The sheet material S is sent between a photosensitive drum 106 and a transfer roller 107 built in a toner cartridge 105 constituting an image forming unit by a pair of registration rollers 104 rotating at a predetermined timing.
[0005]
A latent image is formed on the photosensitive drum 106 by a laser beam from the laser scanner unit 108, and the toner image is developed on the photosensitive drum 106 by attaching toner to the latent image. Then, the toner image on the photosensitive drum 106 is transferred to the sheet material S by the transfer roller 107.
[0006]
The sheet material S on which the transfer of the toner image has been completed is sent to the fixing device 109 by the conveyance force of the photosensitive drum 106 and the transfer roller 107, where the toner image on the sheet material S is fixed. The sheet material S that has completed the fixing is stacked on the stacking tray 111 via the sheet discharging roller pair 110.
[0007]
Next, the operation during automatic double-sided printing will be described.
[0008]
As in the case of face-down discharge, after each of the paper feeding, transfer, and fixing processes is completed, the sheet is conveyed by a pair of discharge rollers 110, and the rear end of the sheet material passes through a pair of fixing discharge rollers 112 of the fixing device 109. Then, at a predetermined timing, the rotation direction of the sheet discharge roller pair 110 is reversed, and the sheet material is conveyed in the direction of being drawn into the main body.
[0009]
At this time, the sheet material is nipped between the double-sided roller 113 and the fixing discharge roller 112A, and the sheet material is transported into the double-sided unit 114. The sheet material that has passed through the duplex unit 114 is again sent to the intermediate roller pair 103 by the refeed roller pair 115, and printing on the second surface is started. The print on the second side is transferred face-down to the stacking tray 111 by the discharge roller pair 110 through transfer and fixing similarly to the first side.
[0010]
Here, the behavior of the sheet material during transfer and fixing will be described. The sheet material on which the toner image has been transferred by the photosensitive drum 106 and the transfer roller 107 is conveyed along a transfer guide 116 and a fixing entrance guide 117.
[0011]
The transfer guide 116 and the fixing entrance guide 117 are located below a line connecting the transfer nip formed by the photosensitive drum 106 and the transfer roller 107 and the fixing nip formed by the pressing roller 118 and the fixing roller 119.
[0012]
After the transfer and before the fixing nip enters, the paper is made slack along the transfer guide 116 and the fixing entrance guide 117. It is necessary to prevent the unfixed image on the sheet material from touching other members such as the toner cartridge 105 during transfer and fixing, thereby causing image rubbing.
[0013]
Therefore, the speed of conveyance by the pressure roller 118 and the fixing roller 119 is lower than the upper and lower tolerances of component dimensions, the thermal expansion during operation, and The fixing device 109 pulls the sheet material at a constant speed in consideration of abrasion.
[0014]
If the speed of the transfer unit is high, the sheet material is pushed into the fixing device 109, and the paper further sags and contacts a part of the toner cartridge 105, so that the unfixed image on the sheet material is rubbed. For this reason, as shown in FIG. 9, the fixing nip enters the fixing nip obliquely from below along the transfer guide 116 and the fixing entrance guide 117.
[0015]
Thereafter, the fixing device 109 conveys the sheet slightly earlier than the transfer section, eliminates slack between transfer and fixing, and conveys the sheet while preventing the unfixed image on the sheet material from rubbing. In addition, the tip of the fixing entrance guide 117 is as close as possible to the pressure roller so that the tip of the sheet material enters the fixing nip stably without waving, and the tip is often formed flat in the axial direction. .
[0016]
[Problems to be solved by the invention]
However, the conventional configuration has the following problems.
[0017]
This will be described with reference to FIGS. The thickness of the sheet material, the stiffness, and the state of the sheet material during transfer and fixing are different. The thin and weak paper is conveyed along the transfer guide and the fixing entrance guide. Conversely, thick and stiff sheet materials are conveyed relatively linearly without much along these guides.
[0018]
Since the conveyance state of the sheet material varies depending on the sheet material, the sheet material often touches the leading end of the fixing entrance guide 117 even during conveyance other than immediately before the sheet material enters the fixing nip.
[0019]
Since the end of the fixing entrance guide 117 is close to the pressure roller 118, the temperature becomes extremely high at a maximum of about 150 degrees when the sheet is passed. In this high temperature situation, the toner is likely to be dissolved and adhere to the tip of the fixing entrance guide 117. In particular, in the case of double-sided printing, in the case of printing on the second side, the first side on which printing has already finished contacts the fixing entrance guide 117.
[0020]
On the first side, not only the print image but also the fog image is transferred to the sheet material. The fogged image is easily peeled off due to a minute amount of toner. The toner adhered on the first side rubs against the tip of the fixing entrance guide 117 at the time of printing on the second side, so that the toner gradually adheres and accumulates.
[0021]
FIG. 10 shows a state in which the toner is deposited. 10Z is a lump of deposited toner. Since the surface on which the toner is deposited is roughened, it becomes a resistance to conveyance, and causes various problems such as jam and paper wrinkles. These problems are likely to occur when printing a large number of sheet materials such as bond paper and cardboard, which have poor fixability and are easily peeled off by toner.
[0022]
SUMMARY OF THE INVENTION The present invention has been devised for the purpose of solving the above problems, and it is an object of the present invention to provide a mechanism for preventing toner from adhering to the tip of a fixing entrance guide and suppressing the occurrence of jams and paper wrinkles.
[0023]
[Means for Solving the Problems]
The present invention is directed to an image forming apparatus in which an unfixed toner image is transferred and a sheet material is pressed and heated by a fixing device to fix the sheet material to the sheet material.
A transfer guide having a shape curved in the transfer direction for guiding the sheet material to the fixing device after transfer, and an entrance guide for introducing the sheet material to a fixing nip formed by a pressure roller and a fixing roller in the fixing device,
A projection shape is provided on the transport section of the entrance guide,
A straight line connecting the downstream point of the transfer nip formed by the photosensitive drum and the transfer roller and the upstream point of the fixing nip to the furthest point on the conveyance guide and the most downstream point in the conveyance direction and the projection vertex The angle β to make with the horizontal plane is
The most distant point on the conveyance guide from the straight line LN connecting the downstream point of the transfer nip and the upstream point of the fixing nip, the most downstream point in the conveyance direction, and the most downstream point closest to the pressure roller on the conveyance surface of the entrance guide. Is larger than the angle α between the straight line connecting the horizontal line and the horizontal plane, and the angle γ between the horizontal line and the line connecting the most downstream point closest to the pressure roller on the transfer surface of the entrance vertex and the entrance guide,
The angle is not larger than an angle δ formed between a straight line connecting the upstream and downstream of the fixing nip and a horizontal plane.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the present invention will be described based on an embodiment shown in the drawings.
[0025]
(1st Embodiment)
FIGS. 1, 2, 3, and 4 show a first embodiment of the present invention. FIG. 1 is a schematic cross-sectional view during transfer and fixing of a printer as an example of an image forming apparatus, FIG. 2 is a schematic cross-sectional view of a part of a fixing device and a transfer guide of the printer, and FIG. FIG. 4 shows a schematic cross-sectional view of a part of the fixing device and the transfer guide.
[0026]
In these figures, 1 is a toner cartridge, 2 is a photosensitive drum, 3 is a transfer roller, 4 is a transfer guide, 5 is a transfer frame, 6 is a fixing device, 7 is a pressing roller, 8 is a fixing roller, and 9 is a fixing discharger. A pair of paper rollers 10 is an entrance guide, and 10a is a transport rib of the entrance guide 10, respectively.
[0027]
Also, NA is a point on the downstream side of the nip formed by the photosensitive drum 2 and the transfer roller 4, NB is an upstream point of the nip formed by the pressure roller 7 and the fixing roller 8, and W is a point between the transport ribs 10a of the entrance guide 10. The minimum interval, PH is the apex of the projection P provided on the transport rib 10a, PE is the most downstream point of the transport rib 10a, PL is the lowest and downstream point on the transport surface of the transfer guide 4, and LN is the pressure roller. A straight line connecting the upstream and downstream points of the nip formed by the fixing roller 7 and the fixing roller 8 represents a conveying direction of the sheet material by the fixing roller pair.
[0028]
α is the angle made between the straight line connecting PL and PE and the horizontal plane, β is the angle made between the straight line connecting PL and PH and the horizontal plane, γ is the angle formed between the straight line connecting PE and PH and the horizontal plane, δ is It represents the angle between LN and the horizontal plane.
[0029]
The angle β formed by the straight line connecting PL and PH and the horizontal plane is larger than the angle α formed by the straight line connecting PL and PE and the horizontal plane, and the nip formed by the pressure roller 7 and the fixing roller 8 is formed. The angle γ formed by LN and the horizontal plane is lower than or equal to the angle δ formed by the straight line connecting PE and PH and the horizontal plane. The projection shape P is provided so as to be smaller than an angle α formed between a straight line connecting PL and PE and a horizontal plane and an angle β formed between a straight line connecting PL and PH and a horizontal plane.
[0030]
Further, the position of the vertex PH of the projection shape P of the transport rib 10a is set at a position 1 mm or more and 5 mm or less upstream of the most downstream point PE in the transport direction. The transport ribs 10a are disposed in the axial direction of the entrance guide 10, but the maximum distance W between the ribs is 13 mm, that is, each transport rib is disposed at an interval of 13 mm or less.
[0031]
The most downstream point PE of the transport rib 10a is very close to the pressure roller 7, and reaches a maximum of about 150 ° C. during the printing operation. However, the apex PH of the protruding shape P provided on the transport rib 10a, which is slightly away from PE, remains at a much lower temperature than PE because it is far from the pressure roller. From this, it can be said that PH is a place where toner is less likely to adhere than PE.
[0032]
Further, if the PH is too close to PE, the temperature becomes high, which is disadvantageous for toner adhesion. If the PH is too far, the sheet material often comes into contact with PE, and the effect of preventing toner adhesion is weakened. Therefore, the distance between PH and PE is preferably in the range of 1 to 5 mm. Further, if the interval between the transport ribs is too wide, the sheet material is loosened between the ribs and the chance of touching the PE increases, so the interval is preferably 13 mm or less.
[0033]
Next, the behavior of the sheet material near the entrance guide 10 during printing will be described. The sheet material after the transfer is conveyed along the transfer guide 4 and the entrance guide 10 and guided to the fixing nip.
[0034]
After the sheet material touches PH, the angle δ between LN and the horizontal plane is larger than the angle α between the straight line connecting PL and PE and the horizontal plane, and the angle β between the straight line connecting PL and PH and the horizontal plane. Because of its small size, it often rushes directly into the fixing nip without contacting the PE.
[0035]
When the sheet is conveyed by the pressure roller 7 and the fixing roller 8 after entering the fixing nip, since the entrance guide 10 is located below the LN, the sheet material does not always rub against the conveyance rib of the entrance guide. However, even after the leading edge of the paper enters the fixing nip, the behavior of the thin paper is likely to be rampant, and the thin paper may lightly contact PH or PE. In the case of transporting thick paper, even if the behavior of the paper is violent due to the strong stiffness, the paper may slightly contact the PH but hardly touch the PE.
[0036]
After the sheet material has passed through the nip between the photosensitive drum 2 and the transfer roller 3, when the rear end of the paper passes through the entrance guide 10, the toner touches the PH but hardly touches the PE. The rate of adhesion is much lower.
[0037]
Next, since the interval W between the transport ribs 10a of the entrance guide is set to 13 mm or less, it is possible to prevent the sheet material from loosening between the ribs and coming into contact with the PE.
[0038]
As described above, by providing the projection P on the entrance guide 10 in the fixing device 6, the time for which the sheet material comes into contact with the leading end PE closest to the pressure roller 7 is reduced, so that the entrance guide 10 This has the effect of preventing toner adhesion.
[0039]
(Second embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a schematic cross-sectional view during transfer and fixing of the printer, FIG. 6 is a schematic cross-sectional view of a part of the fixing device and the transfer guide of the printer, and FIG. 7 is a view taken in the direction of arrow T2 in FIG.
[0040]
4A is a transfer guide, 4a is a transfer rib of the transfer guide 4A, W2 is a minimum distance between the transfer ribs 4a of the transfer guide 4A, PH2 is an apex of the projection P2 provided on the transfer rib 4a, and PE2 is a top end of the transfer rib 4a. The downstream point, PL2, is the lowest and downstream point on the transfer surface of the transfer guide 4, α2 is the angle between the straight line connecting PL2 and PE2 and the horizontal plane, and β2 is the angle between the straight line connecting PL2 and PH2 and the horizontal plane. The angle, γ2, is the angle formed between the horizontal line connecting PE2 and PH2 and the horizontal plane, and δ2 is the straight line connecting the upstream and downstream points of the nip formed by the pressure roller 7 and the fixing roller 8, and the direction of conveyance of the sheet material by the pair of fixing rollers. Represents an angle formed between LN and a horizontal plane. The description of the same parts as in the first embodiment will be omitted.
[0041]
In the present embodiment, since the entrance guide and the transfer guide are formed integrally, in addition to the effect of preventing toner adhesion shown in the first embodiment, the transfer guide and the entrance guide as in the first embodiment are provided. Since there is no step required to transfer the sheet material between them, there is an effect that the sheet material can be stably conveyed and an effect that leads to a cost reduction by reducing the number of parts.
[0042]
Embodiments of the present invention include the following embodiments 2, 3, and 4 in addition to embodiment 1.
[0043]
(Embodiment 1)
In an image forming apparatus in which an unfixed toner image is transferred and the sheet material is pressurized and heated by a fixing device 6 and fixed to the sheet material,
After the transfer, a conveyance guide 4 having a shape curved in a conveyance direction for guiding the sheet material to the fixing device 6, and an inlet for introducing the sheet material into a fixing nip formed by the pressure roller 7 and the fixing roller 8 in the fixing device 6. Having a guide 10,
A projection P is provided on the conveyance section of the entrance guide 10, and the conveyance guide 4 is formed from a straight line LN connecting the downstream point NA of the transfer nip formed by the photosensitive drum 2 and the transfer roller 3 and the upstream point NB of the fixing nip. The angle β formed between the horizontal plane and the straight line connecting the point PL at the farthest and most downstream in the transport direction and the projection apex PH is
The point PL on the conveyance guide 4 that is farthest from the straight line LN connecting the downstream point NA of the transfer nip and the upstream point of the fixing nip, and the point that is the most downstream in the conveyance direction and the conveyance surface of the entrance guide 10 that is closest to the pressure roller 7. Greater than the angle α between the straight line connecting the most downstream point PE and the horizontal plane,
An angle γ formed between a horizontal line and a straight line connecting the protrusion apex PH and the most downstream point PE closest to the pressure roller 7 on the conveyance surface of the entrance guide is:
The angle is not larger than an angle δ formed between a straight line connecting the upstream and downstream of the fixing nip and a horizontal plane.
[0044]
(Embodiment 2)
The image forming apparatus according to the first embodiment, wherein the protrusion apex PH is located at a distance of 1 mm to 5 mm upstream from the most downstream point PE closest to the pressure roller 7 on the conveyance surface of the entrance guide 10.
[0045]
(Embodiment 3)
2. The image forming apparatus according to claim 1, wherein the protrusions P are provided on the ribs in a direction perpendicular to the conveying surface of the entrance guide 10, and the interval between the ribs 10a is 13 mm or less.
[0046]
(Embodiment 4)
The image forming apparatus according to any one of the first to third embodiments, wherein the entrance guide 10 and the transport guide 4 are integrally formed.
[0047]
【The invention's effect】
As described above, the provision of the protrusion on the fixing entrance guide has an effect of preventing the toner from adhering to the entrance guide by reducing the time in which the sheet material comes into contact with the leading end closest to the pressure roller. Thus, a mechanism for suppressing the occurrence of jams and paper wrinkles can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view during transfer and fixing of a printer showing a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a part of a fixing device and a transfer guide of the printer of the present invention. FIG. 4 is a schematic sectional view of a part of a fixing device and a transfer guide of a printer according to a first embodiment of the present invention. FIG. 5 is a view showing a second embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of a printer during transfer and fixing. FIG. 6 is a schematic cross-sectional view of a part of a fixing device and a transfer guide of the printer according to a second embodiment of the present invention. FIG. 8 is a schematic sectional view of a printer showing a conventional technique. FIG. 9 is a schematic sectional view of a printer showing a conventional technique during transfer and fixing. FIG. 10 is a schematic view of a fixing device showing a conventional technique. Cross-sectional view [Explanation of reference numerals]
DESCRIPTION OF SYMBOLS 1 Toner cartridge 2 Photosensitive drum 3 Transfer roller 4 Transfer guide 5 Transfer frame 6 Fixing device 7 Pressure roller 8 Fixing roller 9 Fixing discharge roller pair 10 Inlet guide 10a Conveyance rib NA of inlet guide 10 With photosensitive drum 2 and transfer roller 4 The point NB on the downstream side of the nip to be formed The point W on the upstream side of the nip formed by the pressure roller 7 and the fixing roller 8 The minimum distance PH between the conveying ribs 10a of the entrance guide 10 The vertex PE of the protrusion provided in the shape of the conveying rib 10a The conveying rib The lowest point PL on the conveying surface of the transfer guide 4 and the point LN on the downstream side of the transfer guide 4 represents a straight line connecting the upstream and downstream points of the nip formed by the pressing roller 7 and the fixing roller 8, and conveying the sheet material by the fixing roller pair. The angle between the straight line connecting the direction α PL and PE and the horizontal plane β The angle between the straight line connecting PL and PH and the horizontal plane γ The straight line connecting the PE and PH Δ LN formed between the horizontal plane and the angle δ LN formed between the horizontal plane and the angle T, T2 Arrow direction 4A Transfer guide 4a Transfer rib W2 of transfer guide 4 Minimum distance PH2 between transfer ribs 4a of transfer guide 4 Provided on transfer rib 4a The peak apex PE2 of the projection The most downstream point PL2 of the transport rib 4a The lowest and the downstream point α2 on the transport surface of the transfer guide 4 The angle β2 formed between the straight line connecting PL2 and PE2 and the horizontal plane The straight line connecting PL2 and PH2 and the horizontal plane Angle γ2 Angle between the straight line connecting PE2 and PH2 and the horizontal plane δ2 Angle between LN and the horizontal plane

Claims (1)

In an image forming apparatus in which an unfixed toner image is transferred and the sheet material is pressed and heated by a fixing device and fixed to the sheet material,
A transfer guide having a shape curved in the transfer direction for guiding the sheet material to the fixing device after transfer, and an entrance guide for introducing the sheet material to a fixing nip formed by a pressure roller and a fixing roller in the fixing device,
A projection shape is provided on the transport section of the entrance guide,
A straight line connecting the downstream point of the transfer nip formed by the photosensitive drum and the transfer roller and the upstream point of the fixing nip to the furthest point on the conveyance guide and the most downstream point in the conveyance direction and the projection vertex Angle to make with horizontal plane,
From the straight line connecting the downstream point of the transfer nip and the upstream point of the fixing nip, the furthest point on the conveyance guide and the most downstream point in the conveyance direction and the most downstream point closest to the pressure roller on the conveyance surface of the entrance guide The angle formed between the horizontal line and the straight line connecting the most downstream point closest to the pressure roller at the projection apex and the conveyance surface of the entrance guide is larger than the angle formed between the connected straight line and the horizontal plane,
An image forming apparatus characterized in that the angle is not larger than an angle formed between a straight line connecting the upstream and downstream of the fixing nip and a horizontal plane.

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