JP2003095475A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To comparatively inexpensively prevent image stain when carrying paper, securing sufficient carrying force for a recording medium. SOLUTION: This image forming device is provided with a carrier path 30 for printing both sides for leading the recording medium after printing one side to a transfer part again after reversing the recording medium. At least surface parts of driving rollers 36, 37 and 38 of a pair of carrying rollers arranged within the carrier path 30 for printing both sides are made of a material containing rubber or thermal plastic elastomer and having a comparatively high coefficient of friction. At least surface parts of driven rollers 27, 28 and 29 are made of a material having a relatively low coefficient of friction. The driven rollers 27, 28 and 29 and the driving rollers 36, 37 and 38 are arranged on an image carrying surface side of the recording medium moving in the carrier path for printing both sides and a non-image carrying surface side, respectively.

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 an electrophotographic printer, a facsimile, and a copying machine having a double-sided printing function, and more particularly to a conveying roller thereof.

[0002]

2. Description of the Related Art As an example of a conventional image forming apparatus having a double-sided printing function, a conveyance guide before and after a transfer section and a double-sided sheet re-feeding path are integrally formed.
The configuration disclosed in the issue can be mentioned. A problem with such an image forming apparatus is that the image on the first surface (front surface) is rubbed against a conveyance guide plate or a conveyance roller in the re-feeding path after printing on the first side, and the stain is generated on the next transfer sheet. May get dirty.

[0003]

Regarding the problem of such roller contamination, there may be a problem with the material of the conveying roller. As a material normally used, rubber having a high coefficient of friction or thermoplastic elastomer is essential for the drive roller. The driven roller may be a rubber roller, an elastomer, a metal roller, or a resin roller. When the driving roller is driven, the driven roller is rotated together. However, when a transfer sheet is interposed between these rollers, a slight slip occurs between the driving roller and the transfer sheet and between the transfer sheet and the driven roller. Therefore, on the transfer paper on which the image is placed on the first surface, when the image rubs against the roller, dirt is transferred to the roller. Here, the rubber roller is generally made of EP rubber, klurprene rubber, urethane rubber, or the like, but has a high friction coefficient, poor surface properties, and has adhesive additives such as oil and plasticizer on the surface. Due to the nature of the rubber roller, the releasability of the toner from the toner is poor, and the toner is likely to adhere when rubbed against the image on the first surface. On the other hand, in the case of resin or metal, since the friction coefficient is low and the surface characteristics can be improved, the releasability is considerably better than that of rubber. Particularly in the case of a resin, it is possible to reduce the toner adhesion by selecting a resin such as a fluororesin which is expensive but has a particularly good releasing property. In terms of cost, the resin is suitable for mass production and has the advantage that it can be used at the lowest cost.

The present invention takes the above situation into consideration,
A main object is to prevent image stains when a sheet is conveyed at a relatively low cost while ensuring a sufficient conveying force for a transfer sheet (recording medium).

Further, during double-sided printing, the transfer paper is skewed (diagonal feeding or curving) in the re-feeding path after the first-side printing.
May occur. If skew occurs in the re-feeding path after printing on the first side, there is a problem that the image position on the second side is displaced. As one of the causes of the skew in the re-feeding path, it is conceivable that the pair of conveying rollers is obliquely fed. The configuration shown in FIG. 5 is generally known, but since both ends of the driven roller 27 are pressed against the drive roller 36 by the two springs 51 via the bearings 50, respectively. Deviations tend to occur on the left and right due to variations in the individual loads of. Normally, the variation in the load of a spring that can be mass-produced is about 5 to 10%, and the dimensions at the time of each attachment also vary depending on the quality of the attached parts, which causes further deviations, and the deviations cause a difference in the left and right feed amounts. Occurs, and diagonal feed occurs. Further, in the case of manufacturing such a conveying roller at low cost, it is not possible to make the roller so wide that it is axially wide, and another measure must be taken into consideration. Proposing this measure is the first sub-task.

Further, it prevents image stains for a long period of time,
The second sub-task is to improve the image quality for a long time.

[0007]

SUMMARY OF THE INVENTION The main problem is that an image forming apparatus is provided with a double-sided print conveyance path for reversing a recording medium having one side printed and then guiding it to the transfer section again. Of the pair of conveying rollers arranged in the path, at least the surface portion of the drive roller is made of a material containing rubber or thermoplastic elastomer and having a relatively high coefficient of friction, and at least the surface portion of the driven roller is relatively frictionally rubbed. The problem can be solved by arranging the driven roller on the image bearing surface side and the driving roller on the non-image bearing surface side of the recording medium which is composed of a material having a low coefficient and which moves in the double-sided printing conveyance path.

The driving roller of the pair of conveying rollers is composed of two rollers extending away from each other in a direction perpendicular to the recording medium conveying direction and a shaft penetrating these rollers, and the driven rollers are respectively contacted with the driving roller rollers. It is preferable that the first sub-problem can be solved by forming the two integral resin rollers in contact with each other and arranging the pressurizing means for pressing these rollers against each other in the central region of the two resin rollers. . It is preferable to additionally provide a member for cleaning the surface of the driven roller, because the second sub problem can be solved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be described based on an example shown in the drawings. First, the image forming apparatus according to the present invention will be described. The configuration of the entire image forming apparatus is basically the same as that of the conventional one, and in FIG. 1, around the photoconductor 9 which is an electrostatic latent image carrier, a charging for charging the surface of the photoconductor is performed. A roller 11, a writing unit (multi-beam writing) for forming a latent image on the uniformly charged surface, and a developing device (developing roller) 10 for forming a toner image by attaching charged toner to the latent image on the surface of the photoconductor. A transfer device (transfer roller) 13 for transferring the formed toner image on the photoconductor to a transfer paper (recording sheet) 15, a cleaning device (cleaning blade) 12 for removing residual toner on the photoconductor, A static eliminator (not shown) for removing the residual potential on the photoconductor is sequentially arranged.

In the image forming apparatus having such a structure at its central portion, the entire structure of the apparatus will be described along the flow of the transfer paper. The transfer paper 15 is formed from the paper feed tray 14 by the paper feed roller 1 and the friction pad 2. Registration rollers 3 sheet by sheet
And is sent to the transfer roller 13 in synchronization with the image on the photoconductor 9 by the registration roller 3. Instead of the transfer paper from the paper feed tray 14, the manual paper feed roller 18 and the manual friction pad 34 are opened from the open manual feed stand 17.
By the transfer rollers 29, 38 to the registration roller 3
It is well known that it may be sent to. It may be fed through the relay roller 4.

The transfer paper sent to the transfer roller section has an image transferred there, and is sent to the upper fixing roller 6 and the pressure roller 7, and the image is fixed by heat and pressure. Next, in the case of discharging as it is (single-sided printing), the branch claw 33 on the downstream side does not operate, and the branch claw 33 (shown by a dotted line)
The fixed transfer paper is sent to the paper discharge roller 8 through the lower side and is discharged onto the paper discharge tray 25. In the case of double-sided printing, the branch claw 33 is operated by a DC solenoid (not shown) to send the transfer paper to the switchback roller 31.
When the reversing sensor 42 detects the trailing edge of the transfer sheet, the switchback roller 31 starts reverse rotation and switches back the transfer sheet to send it to the duplex unit. Although not shown in the double-sided unit, the driving conveyance rollers 36, 37, 38 are rotated by a stepping motor, and the transfer sheet is sent downward by the conveyance rollers and again sent to the registration roller 3. After that, the sheet is discharged to the sheet discharge tray 25 through the registration roller 3 and the same operation as described above.

In the double-sided unit whose path is defined by the double-sided printing guide plate 30, the driving and conveying rollers 36, 3 are used.
7, 38 are those in which rubber rollers are pressed into a metal shaft. At the respective facing positions of the drive transport rollers 36, 37, 38, driven transport rollers 27, 28, 29 (provided with a driven roller cleaning means 39) having at least rollers made of resin are pressed against the drive transport rollers. It is provided to do. The driven conveyance roller may be made of an integral resin. The material is polyacetal or AB, which has a lower friction coefficient than that of the driving and conveying rubber roller.
S, fluororesin, etc. are selected according to the cost. In this example, PPE containing glass fiber is used. The drive conveyance rollers 36, 37, 38 are arranged on the non-image surface side of the transfer sheet, and the driven rollers 27, 28, 29 are arranged on the image surface side, as can be understood from the illustrated switchback path.

Next, the case where the driven conveying rollers 27, 28, 29 are integrally formed of resin will be described in detail with reference to FIGS. As shown in FIG. 2, the driven roller 2
7, 28, 29 are slidably attached to the guide plates of the double-sided unit via bearings 40 at both ends, and the substantially central portion thereof is pressed by the pressurizing means 41 to drive and convey rollers 36, 37, 38. Pressed. In this example, FIG.
As can be understood from the above, a leaf spring is used as the pressing means 41, and a low-cost method of directly pressing the driven rollers 27, 28, 29 is adopted, but the leaf spring and the driven roller are brought into contact with each other. If you are concerned that the roller will be scraped,
A shoe made of a resin having a low friction coefficient (for example, polyacetal) may be provided below the leaf spring. The pressurizing means 41
Is not limited to a leaf spring, and any means such as a compression spring or a tension spring may be used as long as the both transport rollers can be pressed against each other. As shown in FIG. 3, in the leaf spring of this example, the driven rollers 27, 2 are screwed to the guide plate.
It also serves as a retainer for 8,29. By pressing the center part of the driven roller, the driven roller made of resin bends, so that even if there is a warp or a deflection of the roller during resin molding, the driven roller can be flexibly deformed and adhered to the drive roller. Has become. Further, in this example, the contact surface between the leaf spring 41 and the driven rollers 27, 28, 29 (ideally the tangent line)
Has a width of about 10 mm, but in order to avoid a deviation in the pressing force in the roller axis direction (left and right direction in FIG. 2) even when the leaf spring is twisted and attached, It is preferable that this contact surface (tangent line) is as small (short) as possible. In this example, the pressing force of the leaf spring 41 is set to 2N.
It is about degree. This is the minimum value for stably transporting the transfer paper, and if it is smaller than 2N, the grip force is reduced, and the skew is apt to occur, and the grip force is increased as the pressing force is increased. However, there is a problem in that the deflection of the roller becomes large, and the shaving and abnormal noise easily occur.

As described above, the driven rollers 27, 28, 2
Cleaning means 39 is provided so as to abut the surface of 9. As can be seen from FIG. 4, the cleaning means 39 is 0.1
A leaf spring of ~ 0.2 mm is attached to the guide plate.
The cleaning means 39, which is a leaf spring, is set so that the tip of the cleaning means 39 is pressed against the surface of the driven rollers.
When 8 and 29 rotate, they come into contact with each other in the direction of hitting the counter. The cleaning means 39 may be a polyester film or sponge-like polyurethane foam, but when the toner after fixing the first surface of the transfer paper adheres, the toner once melted by heat is solidified. Because,
The cleaning effect is greater when a hard member such as a leaf spring is brought into contact.

[0015]

According to the present invention, of the pair of conveying rollers arranged in the conveying path for double-sided printing, at least the surface portion of the driving roller contains rubber or thermoplastic elastomer and has a relatively high friction coefficient. At least the surface portion of the driven roller is made of a resin having a relatively low coefficient of friction, and the driven roller on the image bearing surface side of the recording medium moving in the double-sided printing conveyance path is set to the non-image bearing surface side. By disposing the drive roller, it is possible to prevent the image after the first surface transfer and fixing from adhering to the conveying roller in the re-feeding path, so that it is possible to prevent the recording medium from being contaminated next time.

The driving roller of the conveying roller pair is composed of two rollers extending away from each other in the direction perpendicular to the recording medium conveying direction and a shaft penetrating these rollers, and the driven roller abuts against the driving roller roller. If it is composed of two integrated resin rollers and the pressing means for pressing these rollers against each other is arranged in the central region of the two resin rollers, the occurrence of skew in the re-feeding path can be prevented. . Further, since the driven roller is made of an integral resin, it can be realized at a lower cost than the conventional type in which the roller of rubber or resin is attached to the metal shaft.

By attaching a member for cleaning the surface of the driven roller, it becomes easy to continue to prevent toner adhesion (dirt) to the conveying roller even with time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a schematic front view of a pair of conveyance rollers for double-sided printing according to the present invention.

3 is a conceptual cross-sectional view of a pair of conveyance rollers in FIG.

FIG. 4 is a conceptual cross-sectional view of an example in which a cleaning unit is attached to a conveyance roller.

FIG. 5 is a schematic front view of a conveyance roller pair according to a conventional example.

[Explanation of symbols]

1 paper feed roller, 2 friction pad, 3
Registration rollers, 4 relay rollers, 6 fixing rollers, 7 pressure rollers, 8 paper discharge rollers,
9 photoconductor, 10 developing roller, 11 charging roller, 12 cleaning blade, 13 transfer roller, 14 paper feed tray, 15 transfer paper,
17 Manual Feed Stand, 18 Manual Feed Roller, 25 Paper Ejection Tray, 27, 28, 29 Driven Conveyor Rollers, 30
Double-sided printing guide plate, 31 switch back roller, 33 branching claws, 36, 37, 38 drive conveying roller, 39 driven roller cleaning means, 42 reversing sensor

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H072 CA01 CB00 JA02 JC02                 3F049 AA01 CA12 CA15 CA16 DA11                       DA12 LA01 LB03                 3F100 AA02 BA13 CA15                 3F101 AB01 AB09 LA03 LA05 LA07                       LB03

Claims (3)

[Claims] 1. An image forming apparatus having a double-sided print transport path for reversing a recording medium after printing on one side and then guiding the recording medium to a transfer section again, wherein a pair of transport rollers arranged in the double-sided print transport path. Among them, at least the surface portion of the drive roller is made of a material having a relatively high friction coefficient containing rubber or thermoplastic elastomer, and at least the surface portion of the driven roller is made of a material having a relatively low friction coefficient, An image forming apparatus characterized in that a driven roller is arranged on the image bearing surface side of a recording medium moving on a double-sided printing conveyance path, and a drive roller is arranged on the non-image bearing surface side. 2. A driving roller of the conveying roller pair is composed of two rollers extending apart from each other in a direction perpendicular to the recording medium conveying direction and a shaft penetrating the two rollers, and the driven roller is the driving roller roller. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is composed of two integral resin rollers that are in contact with each other, and a pressing unit that presses both rollers is arranged in the central region of the two resin rollers. 3. The image forming apparatus according to claim 1, further comprising a member for cleaning the surface of the driven roller.