JPH08101587A - Transferring device - Google Patents

Abstract

PURPOSE: To prevent a toner image from causing the transfer void at the time of pressurizing transfer for transferring by bringing the transfer roller into press contact with the latent image carrier. CONSTITUTION: The transfer device 1 has the transfer roller 13 in press contact with the latent image carrier 30 and the toner image on the latent image carrier 30 is transferred to the transfer material by allowing the transfer material to pass between the both. The nip width (mm) and the nip pressure (gf/mm<2> ) of the transfer roller 13 at the time of passing the transfer material have correlation with the rubber hardness and the pressing pressure of the transfer roller 13, and the rubber hardness and the pressing pressure of the transfer roller 13 against the latent image carrier 30 are respectively set so as to satisfy the condition shown by the next numerical formula, nip width × nip pressure <=2.8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device applied to an electrostatic image forming apparatus such as a copying machine, a laser beam printer and other electrostatic recording devices, and more particularly to a toner image formed on an image carrier. The present invention relates to a transfer device that transfers an image onto a transfer material using a transfer bias roller.

[0002]

2. Description of the Related Art As a transfer device of this type, the following technology (J01) is conventionally known. (J01) (Technology described in Japanese Patent Laid-Open No. 59-46664) The transfer device described in this publication electrostatically transfers a toner image formed on the surface of an image carrier to a sheet-shaped transfer material such as paper. In the transfer device, a rubber roller having low hardness and excellent recovery from deformation is used as the transfer roller, the transfer roller to which a bias voltage is applied is pressed against the image carrier, and the transfer material is passed between them, The toner image on the image carrier side is transferred to a transfer material. Such a transfer device can positively press and support the transfer material at the transfer portion, as compared with a transfer device using a corona device that has been put into practical use, so that the transfer roller can be used to support the image carrier. The pressure contact area can be enlarged. For this reason, there is less risk of synchronization failure due to the transfer material transporting means and transfer deviation due to loops, curls, etc. occurring in the transfer material, and shortening of the transfer material transporting path due to downsizing of the transfer device in the future, It has the advantage that it can easily respond to requests for miniaturization.

[0003]

However, the conventional technique (J01) has the following problems. (Problem of (J01)) Although the transfer roller that performs transfer by pressure contact with the image carrier has the advantages as described above, the transfer current must be supplied from the pressure contact part. It is necessary to apply a certain pressing force to the transfer roller to bring it into contact with the carrier. When a pressing force is applied to the transfer roller, a pressure is also applied to the toner image on the image carrier, and the toner image is aggregated. Further, when the surface of the image bearing member is formed of resin, the toner aggregates may adhere to the image bearing member, which may hinder the transfer of the toner image to the transfer material. In an extreme case, the strongly adhered portion is not transferred at all, resulting in a phenomenon that the image quality is lost.

This phenomenon is particularly remarkable in the line portion of 0.1 to 2 mm. This is edge development at the line portion, and a large amount of toner adheres to the edge portion. In this case, aggregation due to pressure contact of the transfer roller is likely to occur, and defects due to transfer are likely to occur. In addition, the image output at this time is a copy in which an image of only the contour is formed, and is called so-called "transfer void". FIG. 11 shows examples of images formed by different types of transfer, FIG. 11A is an image transferred by corona transfer, and FIG. 11B is a hollow image transferred by a transfer roller. "Transmission void" is 100 g / m2
It appears remarkably at the time of transfer to the above thick paper or OHP film having high smoothness. In thick paper and OHP film, since the transfer material is thick, the effect of the transfer electric field is small,
It is considered that the pressure applied to the toner becomes stronger and the toner easily falls out.

As described above, in the case of transfer by pressure contact of the transfer roller, there are many advantages such as downsizing of the apparatus and reduction of power consumption, but on the other hand, the condition for the transfer material for performing good transfer becomes narrow. There is. In view of the above-mentioned circumstances, the present invention has the following contents. (O01) In a transfer device that uses a transfer roller, prevent "middle transfer failure" from occurring.

In order to solve the above-mentioned problems, the inventors of the present invention have proposed a void phenomenon in transfer occurring when a line-shaped toner image in the process direction formed on an image carrier is transferred onto a transfer material under pressure. We have been conducting various surveys and studies. That is, the inventors of the present invention operate the electrostatic image forming apparatus while changing various combinations of the rubber hardness of the roller outer layer of the transfer roller and the pressing force Q to the image carrier, which are estimated to have an influence on the void during transfer. Then, the image evaluation test was performed. The evaluation test was conducted under the following conditions. Toner: Diameter 7 μm Transfer paper: Thick paper (100 g / square m) Electric field in transfer area: Adjust in the range of 20 to 60 KV / mm \ u Peripheral speed difference between image carrier and transfer roller: 0

7 and 8 are obtained by the above evaluation test,
FIG. 7 is a graph showing the relationship between the frequency of occurrence of voids in transfer, the contact pressure (nip pressure) between the transfer roller and the image carrier, and the nip width W, where the horizontal axis represents the nip pressure P (gf / mm 2). The vertical axis represents the nip width W (mm). Codes Gi (i = 1 to 5) in the figure are evaluations of the occurrence frequency of voids in transcription, which are classified into the following five levels from G1 (grade 1) to G5. (G1) No transfer voids occur (G2) Transfer voids of 10 μm or less that cannot be visually confirmed occur (G3) Transfer voids of 10 μm to 100 μm occur (G4) Transfer voids of 100 μm to 1 mm or less Occurrence (G5) Transfer dropout larger than 1 mm occurred

Curves a, b, c, and d in FIG. 8 represent the sponge rubber forming the outer layer of the roller, with the pressing force Q (gf) of the transfer roller and the image carrier being constant in the image evaluation test. 9 is a curve showing an example in which transfer rollers having different hardnesses are used and the nip width is not controlled. Here, the curve a is a rubber hardness of 25 °, the curve b is 29 °, and the curve c is 33 °.
The product and the curve d are curves showing the relationship between the nip width and the nip pressure when the transfer roller 13 of the 38 ° product (measured by JIS hardness) is used.

The left side or the lower side of the curve A in FIGS. 7 and 8 indicates a region in which a void in the transfer can not be visually confirmed, or an image in which a better image can be obtained at a level G2 or better, and the boundary is the curve. It can be represented by A. This curve A shows the nip width W (mm) and the nip pressure P (gf /
It is shown that the product of mm2) is approximately 2.8, and linear pressure (nip width W (m
m) and nip pressure P (gf / mm2)) PW 2.8
It can be seen that it may be set to (gf / mm) or less. Further, from FIG. 8, it is possible to easily understand an appropriate range of the nip pressure P and the nip width W at which the phenomenon of void in transfer does not occur when the rubber hardness is determined. Therefore, if the hardness of the rubber forming the outer layer of the transfer roller to be used is determined, it is possible to determine from P in FIG.
Appropriate values for the nip pressure P and the nip width W at which W is 2.8 (gf / mm) or less are easily determined.

[0010]

The present invention has been completed as a result of the above studies. Next, the present invention devised to solve the above problems will be described. The elements of the present invention include:
In order to facilitate correspondence with the elements of the embodiments described below, the reference numerals of the elements of the embodiments are enclosed in parentheses. In addition,
The reason why the present invention is described in association with the reference numerals of the embodiments described below is to facilitate understanding of the present invention and not to limit the scope of the present invention to the embodiments.

(First Invention) In order to solve the above problems,
The transfer device of the first invention of the present application comprises an image carrier (30),
An image carrier (30) is formed by passing a transfer material between the transfer roller (13) and the image carrier (30) and the transfer roller (13).
In a transfer device that transfers the above toner image to a transfer material,
(Y01) a transfer roller support member (51) for rotatably supporting the transfer roller (13), and (Y02) the transfer roller support member (5) characterized by having the following requirements.
Guide member (57) for guiding 1) to and from the image carrier (30) in a predetermined distance range, and (Y03) the transfer roller support member (51) to the image carrier (30).
The spring strength of the spring member (63), (Y04), which is pressed toward, is such that the nip width of the contact portion between the image carrier (30) and the transfer roller (13) is W. (Mm)
And the nip pressure is P (gf / mm2), the product PW of the nip width W and the nip pressure P is 2.8 (gf /
mm) or less.

(Embodiment 1 of the first invention) A transfer device of embodiment 1 of the first invention is characterized in that the transfer device of the first invention has the following requirements: (Y00
1) A means for adjusting the strength of the pressing force of the spring member (63) for pressing the transfer roller supporting member (51) toward the image carrier (30), that is, a pressing force adjusting means (61).
b, 62) is provided.

(Second Invention) The transfer device according to the second invention of the present application is an image carrier (30) and a transfer roller (13).
And a transfer device for passing a transfer material between the image carrier (30) and the transfer roller (13) to transfer the toner image on the image carrier (30) to the transfer material, which has the following requirements. (Y05) transfer roller support members (51), (Y) that rotatably support the transfer roller (13).
06) A guide member (57) for guiding the transfer roller supporting member (51) so that the transfer roller supporting member (51) can move back and forth within a predetermined distance range with respect to the image carrier (30), and (Y07) the transfer roller supporting member (51). Spring members (63), (Y08) for pressing toward the image carrier (30), the transfer roller support member (5)
The outer diameter of the tracking roll, which is rotatably supported by 1) and is in rotary contact with the image carrier (30), and (Y09) the tracking roll, are the same as those of the contact portion between the image carrier (30) and the transfer roller. When the nip width is W (mm) and the nip pressure is P (gf / mm2), the product PW of the nip width W and the nip pressure P is set to be 2.8 (gf / mm) or less. Was it.

(Embodiment 1 of the second invention) The transfer device of the embodiment 1 of the second invention is characterized in that the transfer device of the second invention has the following requirements.
2) Means for adjusting the position of the rotation axis of the tracking roll with respect to the image carrier (30), that is, tracking roll position adjusting means (57a, 58b, 68, 6).
9) is provided.

[0015]

Next, the operation of the present invention having the above features will be described. (Operation of the First Invention) In the transfer device of the first invention of the present application having the above-mentioned characteristics, the spring member (63) directs the transfer roller supporting member (51) toward the image carrier (30). Press. The transfer roller support member (51) advances toward the image carrier (30) while being guided by the guide member (57). The transfer roller (1) rotatably supported by the transfer roller support member (51)
3) advances together with the transfer roller supporting member (51) toward the image carrier (30) and is pressed against the image carrier (30).

By the way, when the transfer roller (13) is pressed against the image carrier (30) by the spring member (63) in a state where the surface hardness of the transfer roller (13) is fixed, the pressure contact area S (mm 2) is transferred. Roller (13) nip width W (m
It is represented by the product of m) and the length L (mm). That is, S =
It is WL. Here, when the force (pressing force) by which the spring member (63) presses the transfer roller supporting member (51) toward the image carrier (30) is Q (gf), the nip is large when the pressing force Q is large. The width W (mm) becomes wider, and when the pressing force Q is small, the nip width W (mm) becomes narrower. On the other hand, the pressure per unit area of the pressure contact portion between the image carrier (30) and the transfer roller (13), that is, the nip pressure P (gf / mm2)
Is subject to some resistance due to the member interposed between the spring member (63) and the transfer roller (13), but it has a correlation with the pressing force Q, and if the resistance is ignored, P = Q / S = Q / WL. In this case PW =
It becomes Q / L, and the value of PW (= Q / L) is called linear pressure. The spring strength of the spring member (63) is
When the nip width of the transfer roller (13) is W (mm) and the nip pressure is P (gf / mm2), the product PW (= Q / L) of the nip width W and the nip pressure P is 2.8. (Gf
/ Mm) or less. When a transfer material is passed between the image carrier (30) and the transfer roller (13) and the toner image on the image carrier (30) is transferred to the transfer material, a transfer image without a void in transfer occurs. Is obtained.

(Operation of Embodiment 1 of First Invention) In the transfer device of the second invention of the present application, the pressing force adjusting means (61) is used.
b, 62), the spring member (6) for pressing the transfer roller support member (51) toward the image carrier (30).
The strength of the pressing force of 3) can be adjusted. Since the nip pressure P can be adjusted by adjusting the strength of the pressing force, the product PW of the nip width W and the nip pressure P is 2.8 (gf / mm) or more due to manufacturing error or the like. Even so, it is easy to set it to 2.8 or less.

(Operation of the Second Invention) In the transfer device of the second invention of the present application having the above-mentioned characteristics, the spring member (63) is
The transfer roller support member (51) is connected to the image carrier (3
Press toward 0). This transfer roller support member (5
1) advances toward the image carrier (30) while being guided by the guide member (57). The transfer roller (13) and the tracking roll, which are rotatably supported by the transfer roller support member (51), move forward together with the transfer roller support member (51) toward the image carrier (30), and the transfer roller (13). ) And the tracking roll are pressed against the image carrier (30).

By the way, when the transfer roller (13) is pressed against the image carrier (30) by the spring member (63) in a state where the surface hardness of the transfer roller (13) is fixed, the pressure contact area S (mm2) is transferred. Roller (13) nip width W (m
It is represented by the product of m) and the length L (mm). That is, S =
It is WL. Although the length L is constant, the value of the nip width W changes depending on the outer diameter of the tracking roll and the position of the rotation center. When the rotation center of the tracking roll is fixed (for example, when it coincides with the rotation center of the tracking roll), the value of the nip width W changes depending on the outer diameter of the tracking roll. In this case, the outer diameter of the tracking roll is such that the nip width of the transfer roller (13) is W (mm) and the nip pressure is P.
(Gf / mm2), the product PW (= Q / L) of the nip width W and the nip pressure P is 2.8 (gf / mm).
It is set as follows. The rotation center position of the tracking roll can be arranged at a position different from the rotation center position of the transfer roller (13). In that case,
The rotation center position of the tracking roll can be adjusted. The outer diameter or the center of rotation of the tracking roll is adjusted to adjust the nip width W and the nip pressure P.
And a product PW (= Q / L) of 2.8 (gf / mm) or less, a transfer material is passed between the image carrier (30) and the transfer roller (13) to carry the image. When the toner image on the body (30) is transferred onto a transfer material, a transfer image without a void phenomenon in transfer can be obtained.

(Operation of Embodiment 1 of Second Invention) Second Operation
In the transfer device according to the first embodiment of the invention, the nip width W and the nip pressure P can be easily adjusted by the tracking roll position adjusting means (57a, 58b, 68, 69). Since the nip width W and the nip pressure P can be easily adjusted in this way, the value of the product PW of the nip width W and the nip pressure P is 2.8 (gf / m) due to manufacturing error or the like.
Even if m) or more, it is easy to set 2.8 or less.

[0021]

EXAMPLES Examples of the present invention will now be described with reference to the drawings, but the present invention is not limited to the following examples. (Embodiment 1) FIG. 1 is an overall explanatory view of Embodiment 1 of an image forming apparatus of the present invention. FIG. 2 is an enlarged explanatory view of the main part of FIG. FIG. 3 is a sectional view taken along line III-III of FIG. FIG. 4 is a view seen from the arrow IV in FIG. FIG. 5 is a sectional view taken along line VV of FIG. FIG. 6 shows the arrow V in FIG.
It is the figure seen from I.

In order to facilitate understanding of the following description, orthogonal coordinate axes X-axis, Y-axis and Z-axis are defined in the directions of arrows X, Y and Z which are orthogonal to each other in the drawings, and the direction of arrow X is forward. , The arrow Y direction is left, and the arrow Z direction is up.
In this case, the direction opposite to the X direction (front) (-X direction, that is, the opposite X direction) is backward, and the direction opposite to the Y direction (left) (-Y).
The direction, that is, the anti-Y direction) is to the right, and the direction opposite to the Z direction (upward) (-Z direction, that is, anti-Z direction) is downward. In addition, the direction including the front (X direction) and the rear (−X direction) is referred to as the front-back direction or the X-axis direction, and the left (Y direction) and the right (−
The Y direction) is referred to as the left-right direction or the Y-axis direction, and the upper direction (Z direction) and the lower direction (-Z direction) are referred to as the up-down direction or the Z-axis direction. Furthermore, in the figure, the ones with "・" in the "○" mean the arrows from the back of the paper to the front, and the ones with "X" in the "○" are from the front of the paper. It means an arrow pointing to the back.

In FIG. 1, an image forming apparatus U in which the first embodiment of the transfer device of the present invention is incorporated is a digital printer. The digital printer U is a printer main body (that is, an image forming apparatus main body) U1 and a process cartridge U2 that is detachable by inserting or pulling out the printer main body U1 from the front side (X side, front side of the paper surface).
It consists of and. The printer body U1 has a sheet supply tray 1 at the bottom. A laser writing device 2 is arranged above the right side portion of the sheet supply tray 1, and an electric circuit portion 3 is arranged above the laser writing device 2. On the left side of the laser writing device 2 and the electric circuit portion 3, there is provided a space in which the detachable process cartridge U2 is arranged.

A sheet take-out roll 4 for taking out the sheets one by one from the sheet feed tray 1 is arranged at the upper left end of the sheet feed tray 1. A drive roll 6a and a retard roll 6b are provided on the left side of the sheet take-out roll 4.
The sheet transport roll 6 is arranged.
The sheet guide 7 for guiding the sheet conveyed by the sheet conveying roll 6 is composed of a fixed guide 8 and a movable guide 9.

The movable guide 9 is supported by a left cover 12 which rotates around a fulcrum 11, and when the left cover 12 rotates from the closed position shown by the solid line in FIG. It is adapted to rotate counterclockwise together with the cover 12. When the movable guide 9 rotates counterclockwise, the sheet passage formed between the fixed guide 8 and the movable guide 9 is opened. Therefore, the jammed sheet can be easily removed in the sheet passage. A transfer roller 13 is supported on the left cover 12 by a transfer roller supporting device T, which will be described in detail later, and is arranged in contact with the surface of the image carrier of the process cartridge U2 at the solid line position shown in FIG. The transfer roller 13 and the transfer roller supporting device T that supports the transfer roller 13 are also rotated counterclockwise integrally with the left cover 12 when the left cover 12 is opened so as to be separated from the surface of the image carrier of the process cartridge U2. It has become.

In the printer body U1, a fixing device 16 having a heating roll 16a and a pressure roll 16b on the upper left side,
The fixing device 16 is provided with a conveying path 17 for conveying the sheet on which the toner image is transferred by the transfer roller 13. Further, the printer body U1 includes a discharge roll 18 including a driving roll 18a and a driven roll 18b,
Sheet guides 19a and 19b forming a conveyance path 19 for conveying the sheet on which the toner image is fixed from the fixing device 16 to the discharge roll 18 are supported. Further, on the upper surface of the printer body U1, there is formed a sheet discharge tray 21 for containing the sheets discharged from the discharge roll 18.

The process cartridge U2 is mounted between the transfer roller 13 and the laser writing device 2 and in the space above the sheet supply tray 1 (that is, the space for mounting the process cartridge U2). . The process cartridge U2 includes an image carrier 30, an erase device 31 that eliminates static electricity on the surface of the image carrier 30, a charging roll 32 that uniformly charges the surface of the image carrier 30, and a developing device 33. There is. The developing device 33 is the developing container 3
4, a developing roll 36 supported by the developing container 34, a toner supply roll 37 that supplies toner to the developing roll 36, and a stirring member 3 that stirs the toner in the developing container 34.
It has 8, 39 etc.

Further, the process cartridge U2 has a cleaning device 41 above the image carrier 30. In FIG. 2, the cleaning device 41 has a toner storage container 42. The toner container 42 is provided with the blade holder fixing portion 43. A metal blade holder 44 is fixed to the blade holder fixing portion 43. A sheet-shaped cleaning blade 46 made of resin is fixed to the tip of the blade holder 44.
The edge portion of the cleaning blade 46 is in contact with the surface of the image carrier 30. A film seal 47 is provided on the opposite side of the cleaning blade 46. Inside the toner container 42, the film seal 47 and the cleaning blade 46.
When the toner is collected in the toner collection space in the vicinity (the left side in FIG. 1) in which is arranged, and the collected toner accumulates, the toner collected earlier is pushed by the toner collected later. And move to the right.

Next, the transfer roller 13 and the transfer roller supporting device T that supports the transfer roller 13 will be described with reference to FIGS. In FIG. 3, the transfer roller 13 is composed of a cylindrical member 13a made of aluminum (made of a conductive member) and a roller outer layer 13b made of rubber covering the surface of the cylindrical member 13a. The outer roller layer 13b is made of rubber having a JIS hardness of 33 ° (see FIG. 8). A bias voltage for transfer is applied to the cylindrical member 13a of the transfer roller 13 from a bias power source (not shown). As the rubber material forming the roller outer layer 13b,
Butadiene rubber, isoprene rubber, SBR (styrene-
Butadiene rubber), NBR (nitrile-butadiene rubber), chloroprene rubber and the like are used.

The transfer roller support device T, which supports the transfer roller 13 while pressing it against the image carrier 30, has a transfer roller support member 51 that rotatably supports the transfer roller 13. The transfer roller support member 51 is composed of a roller support shaft 52 and bearings 53, 53 mounted on the roller support shaft 52. The transfer roller 13 is rotatably supported by the bearings 53, 53. At both ends of the roller support shaft 52, a supported portion 52a is formed by cutting the surface so that the cross section becomes rectangular.

Further, the transfer roller supporting device T has a fixed supporting member 56 fixed to the left cover 12. The fixed support member 56 extends in the front-rear direction (X-axis direction), and guide members 57, 57 are fixed to both front and rear ends thereof. The guide member 57 is formed with an elongated slit 57a for supporting the supported portion 52a of the roller support shaft 52 so that the supported portion 52a can move forward and backward with respect to the image carrier 30. A portion of the fixing member 57 near the image carrier 30 is bent outward, and two bent slits are formed in the bent portion as shown in FIG. The two slits and the portion left between them form a spring locking portion 57b.

A moving member 58 is fixed to the outer end portion of the supported portion 52a of the roller support shaft 52 penetrating the slit 57a of the fixed member 57. On the side of the moving member 58 remote from the image carrier 30, a spring locking piece support portion 58a bent outward is formed. A spring locking piece 61 is fixed to the spring locking piece support portion 58a. The spring locking piece 61 has a spring locking bent portion 61a formed at one end and a screw 61b formed at the other end. This screw 6
1b passes through the spring locking piece support portion 58a, and two nuts 62 are screwed into the screw 61b. The spring lock piece 61 is fixed to the spring lock piece support part 58a by tightening the spring lock piece support part 58a from both sides with these two nuts. The screw 61b and the two nuts 62 constitute pressing force adjusting means (means for adjusting the force for pressing the transfer roller 13 against the image carrier 30).

The spring locking piece 61 and the spring locking portion 57b.
A tension spring (spring member) 63 is provided between the tension spring 63 and the spring locking piece 6 (see FIG. 6).
1, the moving member 58 and the roller support shaft 52 are always urged toward the image carrier 30. Therefore, the image carrier 3
0 and the transfer roller 13 are in contact with each other with a pressing force Q (gf). In this case, assuming that the length (nip length) L of the contact portion between the image carrier 30 and the transfer roller 13 is W and the contact width W, the area S of the contact portion is S = LW, and the nip pressure P at this time is P. Is P =
(Q / LW) [gf / mm2]. The pressing force Q is a value determined by the strength of the tension spring 63, and the linear pressure PW is determined by the value of Q, the hardness of the roller outer layer 13b and the nip length L. Therefore, the roller outer layer 1
When the hardness of 3b and the nip length L are determined, by setting the strength of the tension spring 63 that determines the pressing force Q and the extension length during operation to predetermined values,
The value of the linear pressure PW can be set to 2.8 (gf / mm) or less.

That is, in Example 1, the rubber forming the roller outer layer 13b had a JIS hardness of 33 ° (see FIG. 8).
Value), the value of linear pressure PW is 2.8 (gf / m
m) or less, the nip width W = 1.5 m from FIG.
m, nip pressure P = 1.3 (gf / mm2) is adopted. In this case, PW = 1.95 (gf / mm). If the nip length L is 250 mm, the pressing force Q is Q = PW
L = 1.95 (gf / mm) × 250 (mm) = 487.
It becomes 5 (gf). One tension spring 63 is provided at each end of the transfer roller 13, and a total of two tension springs 63 are provided.
Since there are two springs, the pressing force generated by one of the tension springs 63 is (487.5 / 2) = 243.75.
(Gf) is required. Therefore, one tension spring 6
The strength of 3 is set so as to generate a force of about 243.75 (gf) when the transfer roller 13 is in contact with the image carrier 30 and the length thereof is extended.

(Operation of First Embodiment) Next, the operation of the image forming apparatus incorporating the first embodiment of the transfer device of the present invention having the above-described structure will be described. The surface of the image carrier 30 is charged by the charging roll 32. Next, the laser writing device 2 irradiates the surface of the image carrier 30 with a laser beam, exposes the surface of the image carrier 30 to write out image information, and then causes the toner in the developing device 33 to adhere to the surface of the developing roll 36. hand,
A toner image is formed on the image carrier 30. Next, the toner image on the image carrier 30 is transferred onto the transfer material while passing the transfer material such as paper from the sheet supply tray 1 between the image carrier 30 and the transfer roller 13. At this time, the image carrier 30 and the transfer roller 13 rotate at substantially the same peripheral speed, and the transfer roller 13 has the nip width W (mm) and the nip pressure P (gf).
/ Mm2) and press contact with the image carrier 30. The transfer material is then supplied to the fixing device 16 and the toner image 13 is fixed to form the original image information. On the other hand, the toner remaining on the surface of the image carrier 30 is cleaned and removed by the cleaning device 41.

As can be seen from FIG. 8, an appropriate range of the nip width W and the value of the nip pressure P is determined according to the rubber hardness of the roller outer layer 13b of 33 °, and selected from the appropriate range. The corresponding nip width W (= 1.5 mm) and nip pressure P (= 1.3 gf / mm) value and nip length L (= 250 mm) value Q (= PWL =
The value of 243.75 gf) is determined. This Q value (= 24
Since the strength of the tension spring 63 and the elongation at the time of operation are determined so as to obtain 3.75 gf), the hollow transfer does not occur at the time of transfer.

(Second Embodiment) Next, a second embodiment of the image forming apparatus of the present invention will be described with reference to FIG. FIG. 9 is an explanatory diagram of Embodiment 2 of the image forming apparatus of the invention. In the description of the second embodiment, constituent elements corresponding to those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The second embodiment differs from the first embodiment in the following points, but is configured similarly to the first embodiment in other points. (S01) The tracking roller 66 is rotatably supported at both ends of the roller support shaft 52 of the transfer roller 13 of the first embodiment. The outer diameter of the tracking roll 66 is set to be slightly smaller than the outer diameter of the transfer roller 13.

(Operation of Embodiment 2) Next, the operation of Embodiment 2 of the present invention having the above-mentioned structure will be described. Example 2
In the image forming apparatus of, the outer diameter of the tracking roll 66 is
By properly setting the outer diameter of the transfer roller 13, the nip width W and the nip pressure P can be easily determined. That is, when the transfer roller 13 and the tracking roll 66 are pressed against the surface of the image carrier 30, the transfer roller 13 first contacts the image carrier 30 and the surfaces thereof are elastically deformed. At this time, the transfer roller 13 comes into surface contact with the image carrier 30. When the transfer roller 13 is further pressed, the amount of elastic deformation of the surface of the transfer roller 13 increases and the nip width W increases. Since the surface layer of the image carrier 30 is sufficiently hard as compared with the surface layer of the transfer roller 13, its deformation amount can be ignored. As the amount of deformation of the transfer roller 13 increases, the tracking roll 66
When comes into contact with the image carrier 30, no further increase in the elastic deformation amount of the transfer roller 13 occurs. In that state, the nip width W is constant. The nip pressure P in that state is the elastic deformation amount (that is, the transfer roller 1
3 and the outer diameter of the tracking roll 66) and the material of the outer surface of the transfer roll 13. That is, in the second embodiment, the amount of elastic deformation of the surface of the transfer roller 13 and the value of the nip width W are determined by the outer diameter dimensions of the transfer roller 13 and the tracking roll 66. The nip pressure P at that time is equal to the transfer roller 13
It depends on the material of the surface. That is, the transfer roller 1
It is possible to adjust the values of the nip pressure P and the nip width W by appropriately setting the outer diameter difference between the transfer roller 13 and the tracking roll 66 according to the material of the three surface layers. As a result, it is possible to prevent the occurrence of hollow transfer during transfer.

(Third Embodiment) Next, a third embodiment of the image forming apparatus of the present invention will be described with reference to FIG. FIG. 10 is an explanatory diagram of Embodiment 3 of the image forming apparatus of the invention. In addition,
In the description of the third embodiment, constituent elements corresponding to those of the second embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. The third embodiment differs from the second embodiment in the following points, but is configured similarly to the second embodiment in other points. (S02) In the second embodiment, the tracking roll 67 is rotatably supported at both ends of the roller support shaft 52 of the transfer roller 13, whereas in the third embodiment, the rotation support shaft 68 of the tracking roll 67 is transferred. It is provided separately from the rotation axis of the roller 13. (S03) The rotation support shaft 6 of the tracking roll 67
The position of 8 is adjustable with respect to the image carrier 30. That is, the rotation support shaft 6 of the tracking roll 67
A screw is formed on the outer end portion of No. 8, and the screwed outer end portion penetrates the slit 57 a of the fixed member 57 and the slit 58 b formed on the moving member 58 to screw the nut 69. I am fit. The rotation support shaft 68 of the tracking roll 67 is fixed to the moving member 58 by tightening the nut 69. Tracking roll position adjusting means for adjusting the position of the tracking roll 67 with respect to the image carrier 30 is constituted by the elements 57a, 58b, 68 and 69.

(Operation of Third Embodiment) Next, the operation of the third embodiment of the present invention having the above-described structure will be described. This Example 3
Then, depending on the position of the rotation support shaft of the tracking roll 67 (position with respect to the image carrier 30), the transfer roller 1
The elastic deformation amount of 3 and the value of the nip width W are determined. The nip pressure P at that time is determined by the material of the surface of the transfer roller 13. That is, the values of the nip pressure P and the nip width W can be adjusted by appropriately setting the position of the rotation support shaft of the tracking roll 67 according to the material of the surface layer of the transfer roller 13. As a result, it is possible to prevent the occurrence of hollow transfer during transfer.

(Modifications) The embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-mentioned embodiments, and is within the scope of the gist of the present invention described in the claims. Thus, various changes can be made. A modified embodiment of the present invention is illustrated below. (H01) Although the tension spring 63 is used in FIG. 1 as the means for pressing the transfer roller 13, the transfer roller 13 is used as the image carrier 30.
If it is an elastic member that can be appropriately pressed against, the tension spring 6
It is not limited to three. (H02) The image carrier 30 can be configured by an endless belt that runs endlessly instead of the rotating cylindrical drum.

[0042]

The present invention has the following effects. (E01) It is possible to easily manufacture a transfer device in which a “transfer void” of a toner image does not occur at the time of transfer in which a transfer roller is pressed against an image carrier and transferred with the transfer material being sandwiched.

[Brief description of drawings]

FIG. 1 is an overall explanatory view of an image forming apparatus in which a first embodiment of a transfer device of the present invention is incorporated.

FIG. 2 is an enlarged explanatory view of a main part of FIG.

3 is a sectional view taken along line III-III of FIG.

FIG. 4 is a view seen from an arrow IV in FIG.

FIG. 5 is a sectional view taken along line VV of FIG. 3;

FIG. 6 is a view seen from an arrow VI in FIG.

FIG. 7 is a graph showing the relationship between the occurrence frequency of voids in transfer, the pressure contact area of the transfer roller, and the pressure contact pressure.

FIG. 8 is a graph showing a relationship between a nip width and a nip pressure when a plurality of sponge rubber rollers having different rubber hardness are used as a transfer roller.

FIG. 9 is an explanatory diagram of a second embodiment of the image forming apparatus of the present invention.

FIG. 10 is a third embodiment of the image forming apparatus of the present invention.
FIG.

11A and 11B show images formed by different types of transfer, FIG. 11A is a copy image by corona transfer, and FIG. 11B is an intermediate void copy image by a transfer roller.

[Explanation of symbols]

13 ... Transfer roller, 30 ... Image carrier, 51 ... Transfer roller support member, 57 ... Guide member, 63 ... Spring member, (61
b, 62) ... pressing force adjusting means, (57a, 58b, 68,
69) ... Tracking roll position adjusting means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norichika Hirohashi, 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Minoru Ueki, 2274, Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) ) Inventor Akihiro Takafuji 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Akio Arai 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (2)

[Claims] 1. An image carrier, a transfer roller, and a transfer device for passing a transfer material between the image carrier and the transfer roller to transfer the toner image on the image carrier to the transfer material, which have the following requirements. A transfer device, (Y01) a transfer roller support member that rotatably supports the transfer roller,
(Y02) A guide member that guides the transfer roller support member so as to move back and forth within a predetermined distance range with respect to the image carrier.
(Y03) A spring member that presses the transfer roller support member toward the image carrier, and (Y04) the spring strength of the spring member is equal to the nip width of the contact portion between the image carrier and the transfer roller. The product PW of the nip width W and the nip pressure P is set to 2.8 (gf / mm) or less when W (mm) and the nip pressure are P (gf / mm2). 2. An image carrier, a transfer roller, and a transfer device for passing a transfer material between the image carrier and the transfer roller to transfer the toner image on the image carrier to the transfer material, which have the following requirements. A transfer device, (Y05) a transfer roller support member that rotatably supports the transfer roller,
(Y06) A guide member that guides the transfer roller support member so as to advance and retreat within a predetermined distance range with respect to the image carrier.
(Y07) A spring member that presses the transfer roller support member toward the image carrier, (Y08) A tracking roll that is rotatably supported by the transfer roller support member and is in rotary contact with the image carrier, (Y09) The outer diameter of the tracking roll is the nip width W and the nip pressure when the nip width of the contact portion between the image carrier and the transfer roller is W (mm) and the nip pressure is P (gf / mm2). The product PW of P is set to be 2.8 (gf / mm) or less.