JPH03155584A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the slip and positional deviation of a transfer material which is carried to the contacting part of an image carrier and a transfer means from the image carrier by making the peripheral speed of the transfer means higher than that of the image carrier at a transfer position when a transfer is performed. CONSTITUTION:The transfer means 2 has a ASKER-C hardness 20' - 40', its pressure-contacting power to the image carrier 1 is 50g/cm<2> - 200g/cm<2>, and the peripheral speed of the transfer means 2 is higher than that of the image carrier 1 at the transfer position when the transfer is performed. In other words, a visible image formed on the image carrier is moved to a contacting part with the transfer part 2 by the rotation of the image carrier 1. The peripheral speed of the transfer means 2 is higher than that of the image carrier 1 at the contacting part. Thus, slip and positional deviation which occur between a transfer material and an image carrier in the case of a transfer are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus using an electrophotographic method, such as a copying machine, a laser printer, or the like.

(Prior Art) Conventionally, as shown in FIG. 6, there is a transfer device for an image forming apparatus in which an image carrier 100 and a roller type transfer means 101 are arranged in contact with each other. That is, the visible image formed on the surface of the image carrier 100 by toner or the like is
By rotation in the direction of the arrow 00, the image moves to the transfer position 102, which is the contact portion 102 between the image carrier 100 and the transfer means 101, and is transferred onto the transfer material 103 that is conveyed in a timely manner. By the way, in such a transfer device 104, the transfer material 103 cannot keep up with the rotational speed of the image carrier 100, resulting in chronic problems such as transfer voids and transfer defects.

In order to solve such problems, for example,
No. 126872 takes the following measures.

An elastic roller to which a voltage is applied is used as the transfer means, and the peripheral speed of the roller is set to be faster than the peripheral speed of the image carrier, depending on the hardness of the roller and the contact pressure to the image carrier. However, the circumferential speeds at the contact portion between the roller and the image carrier are made to match.

(Problem to be Solved by the Invention) However, even if the circumferential speeds of the image carrier and the roller at the contact portion are made to match as described above, there is a problem at the contact portion caused by differences in the material of the transfer material, friction coefficient, etc. This method cannot deal with slippage or misalignment between the transfer material and the image carrier, and cannot be an essential solution.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a transfer device that can prevent slippage or misalignment between the transfer material conveyed to the contact portion between the image carrier and the transfer means and the image carrier. It is said that

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a rotatable image carrier, an image forming means for forming an image on the image carrier, and a transfer position on the image carrier. In the image forming apparatus, the image forming apparatus includes a transfer means that can be contacted and transfers the image formed by the image forming means to the transfer material by conveying the transfer material together with the image carrier at the transfer position, the transfer means , its height is 20″~ in ASKER-C hardness.
40° Pressure force to the above image carrier is 50 g/cm2 to 2
00 g/cm'', and the peripheral speed of the transfer means at the transfer position during transfer is larger than the peripheral speed of the image carrier at the transfer position.

(Function) Based on the above structure, the visible image formed on the image carrier is transferred to the contact portion with the transfer means by rotation of the image carrier. In the contact portion, The peripheral speed of the transfer means is faster than the peripheral speed of the image carrier.

(Example) Next, the present invention will be explained based on the example shown in FIGS. 1 to 5.

Embodiment 0 FIG. 2 shows a schematic configuration of an image forming apparatus to which a transfer device B according to the present invention is applied. In the figure, 1 is a photoreceptor as an image carrier, and this photoreceptor l is an organic photoconductor (O
DC), which is rotated in the direction of the arrow by a driving means (not shown). The photoreceptor 1 is charged by a charging roller 23 connected to a power source 24, and an image-modulated laser beam 25 is projected onto the photoreceptor 1 to form an electrostatic latent image on its surface.

As the photoreceptor 1 rotates, this electrostatic latent image is made visible by toner (not shown) in the developing device 26, and is applied to the contact portion W with the roller 2 as a transfer means, that is, the transfer position. Transition. Meanwhile, at the same time, the conveyance path 27
A transfer material P is conveyed from there, and a transfer bias, which is a DC voltage of opposite polarity to the toner, is applied to the roller 2 from a power source 24, so that the visible image on the photoreceptor 1 is transferred onto the transfer material P. Thereafter, the transfer material P is conveyed to a fixing section (not shown). Further, the toner remaining on the photoreceptor 1 is scraped off by a cleaner 28 in preparation for subsequent image formation.

Here, the roller 2 will be explained in detail.

The roller 2 is provided with a conductive elastic layer on the outer periphery of the core metal,
The core metal at the longitudinal end of the roller 2 is urged in the direction toward the photoreceptor 1 by means of urging means such as a spring, and foamed EPDM rubber is used as the material of the conductive elastic layer. The EPDM has an Asker-C hardness of 28 degrees, and conductive ZnO is dispersed to provide conductivity.

Other materials used for the conductive elastic layer of the roller 2 include CR rubber, NBR, and urethane rubber.

Examples include Si rubber and fluororubber.

The hardness of the transfer roller is ASKER C.
A hardness of 20' to 40' is desirable.

In order to perform uniform transfer in the longitudinal direction of the transfer roller, it is necessary to form and ensure a uniform electric field at the transfer nip. When a sponge roller with a hardness of less than 20 @ is used as the transfer roller, the foaming rate of the roller is high, so when trying to obtain a transfer nip to obtain a uniform electric field, the foaming opening of the roller will not be blocked too much. In this way, the pressing force against the photosensitive drum must be reduced. If this is done, the conveyance force against the transfer material P will also be reduced, and as a result, the transfer material will slip in the transfer nip, causing image blurring and making it difficult to obtain a normal image.

Further, in order to ensure a sufficient transfer nip for a transfer roller having a hardness exceeding 40@, it is necessary to increase the pressing force against the photosensitive drum. In this case, the transfer roller strongly presses the toner particles on the photosensitive drum onto the photosensitive drum via the transfer material P, resulting in a state in which voids are very likely to occur.

On the other hand, examples of the conductive substance dispersed in the roller 2 for the purpose of imparting conductivity include carbon and ZnO.

Examples include metal fillers such as 5nOa, but a metal filler that has a relatively high specific resistance so as not to be affected by environment and fluctuations, and can be easily controlled by the number of parts to be dispersed, preferably ZnO.

The present invention having the above-mentioned structure is designed so that the circumferential speed Vrn of the roller 2 at the contact portion W is faster than the circumferential speed V+tg of the photoreceptor 1, as shown in FIG. 1(a). The circumferential speed (■, 1) determined from the diameter is adjusted. A method for calculating the circumferential velocity V tn+V rg of the roller 2 will be explained using FIG. 1(b).

First, the radius of the photoreceptor 1 is R[mml, the radius of the roller 2 is r[n+ml, and the circumferential length of the contact portion W is η[mml].
Then, find the radius r' [mml] of the roller 2 at the center point ξ of the contact portion during contact deformation. Then, the length of the string aβ formed by the photoreceptor 1 and roller 2 is λ[mml,
The distances from the center 0 of the photoreceptor 1 and the center 0' of the roller 2 to the string αβ are respectively Q and m [mml].

If the entrance point α and the center point of the contact portion W are the angle θ [radl where the center 0 of the photoreceptor 1 is set, then j2 = Rcos θ η = Rcos () R...(1) Nichi = Rsin θ = Rsin (-) R...(2) From formulas (1) and (2), = A + m-R. Therefore, if the circumferential speed of roller 2 is Vr, the contact portion W
The circumferential velocity V r at the time of contact with the photoreceptor 1 at the center point ξ
n is found. Furthermore, even if there is a transfer material between the photoreceptor 1 and roller 2 in FIG. The roller speed at the contact point when there is a transfer material in the area is almost the same as Vrn.

Example 1 In the image forming apparatus shown in FIG. 2, the diameter of the photoreceptor 1 was 30φ, the diameter of the roller was 20φ, and the roller 2 was driven from the rotation axis of the photoreceptor 1. In addition, the pressing force of the roller 2 against the photoconductor 1 is controlled in the range of 50 to 200 g/cm2 when the circumferential length of the contact part is 4 mm and the axial length is 220 mm, and from the viewpoint of transportability of the transfer material P. 120-14
It was set at 0 g/cm2.

Here, the pressure contact force is the total pressure applied by the urging means to urge the transfer roller against the photoreceptor, divided by the contact area between the photoreceptor and the transfer roller.

The hardness of the transfer roller is 20° to 40 according to the Asker-C hardness mentioned above.
When the pressure contact force is less than 50 g/cm'', the clamping force between the photosensitive drum and the transfer roller decreases, and the conveying force decreases ( Of course, the registration rollers, fixing rollers, etc. are susceptible to shocks when they enter the transfer material nipping member or are ejected, and image blurring is likely to occur.

On the other hand, if the contact force exceeds 200 g/cm, the toner will be strongly pressed against the photoreceptor, causing voids, and the core metal of the transfer roller will also bend, causing the toner to fall out at both ends and the center in the longitudinal direction of the transfer roller. The width of the transfer nip formed at each section is different.This nip width is thicker because both ends of the core of the transfer roller are pressed by the biasing means, and the distance from the photoreceptor becomes larger in the center part, which is not biased by the biasing means. As a result, a uniform electric field cannot be obtained because the nip width is different.Also, the transfer material conveyance speed differs in the longitudinal direction, resulting in problems such as not being able to obtain a normal image. arise.

As mentioned above, pressure contact force and hardness are closely related in terms of securing the nip, but they are independently effective factors in terms of conveyance and hollowing out, so it is desirable to set optimal values for each. .

This configuration has been selected to be considered optimal. The process speed equal to the circumferential speed V4 of the photoreceptor 1 is 50 [
mm/5ecl.

In addition, in this experimental example, the circumferential velocity V rn of the center point ξ of the contact portion W of the roller 2 is set to 2
% faster. Its circumferential speed Vrn is 1.02X 50
= 51 (mm/5eal).The circumferential velocity Vr required to obtain a circumferential velocity of 51 [mm/5ec] at the center point ξ is 52.
7 [mm/5ecl. Therefore, in an experimental example in which the drive is taken from the rotating shaft of the photoreceptor 1, the radius of the drive gear (not shown) of the roller 2 and the gear ratio of the drive gear (not shown) of the photoreceptor 1 are adjusted. realized by.

As described above, the circumferential speed yrn of the roller 2 at the center point ξ of the contact portion W is set to be 2% lower than the circumferential speed Vp1g of the photoreceptor l.
By increasing the speed, there is no slippage or misalignment between the transfer material P and the photoreceptor 1 during transfer, and it is possible to perform transfer at almost the same circumferential speed.
g/m” paper, envelope.

The major problem of transfer voids in various paper types such as OHP sheets made of polyethylene terephthalate can be solved, and in addition, stable paper transport prevents image shift and paper wrinkles. Good images can now be provided regardless of environmental changes. As mentioned above, the circumferential speed of the roller 13 is
It is thought that the reason why hollow spots can be prevented by increasing the circumferential speed of the photoconductor 1 is that a force is applied to scrape off the toner on the photoconductor 1 with the transfer material conveyed by the roller 13.

Furthermore, the rate at which the circumferential speed V f,l of roller 2 is increased is 0.5.
When we conducted a similar experiment by changing the circumferential speed from % to 5% in 0.5% steps, we found that increasing the peripheral speed by 1% to 3% had a sufficient effect, but when it was less than 1%, hollowing occurred and 3 %, in addition to hollow spots, image elongation became noticeable, impeding image accuracy. In addition, in this example,
The gear diameter and gear ratio are changed in order to increase the circumferential speed, but similar results can also be achieved by increasing the circumferential speed by increasing the roller diameter itself, or by driving the photoreceptor and roller separately. Needless to say, it is effective.

0 Second Embodiment FIG. 2 shows a schematic configuration when the present invention is applied to an image forming apparatus E using a transfer/transport belt 42 and an electrode roller 43 as transfer means.

The photoreceptor 1 is in contact with a belt 42 that is suspended between a support roller 46 and a drive roller 45 driven by a drive means (not shown) and runs in the direction of the arrow in the figure. The transfer material P passes through a transfer position formed by contact between the photoreceptor 1 and the belt 42 in synchronization with the visible image on the surface of the photoreceptor 1 . The visible image on the photoreceptor 1 is transferred onto the transfer material P by a voltage supplied from a power source 44 to a roller electrode 43 disposed on the opposite side of the photoreceptor 1 at the transfer position.

Thereafter, the belt 42 is cleaned by a cleaning blade 48.

The material of the belt 42 is PVdF or PET thermoplastic elastomer, Mariolefin thermoplastic elastomer, polyurethane thermoplastic elastomer, or polyethylene thermoplastic elastomer.

A single-layer semiconducting material selected from polyamide thermoplastic elastomer, fluorine thermoplastic elastomer, ethylene-vinyl acetate thermoplastic elastomer, polyvinyl chloride thermoplastic elastomer, etc., the volume resistivity of which is hydroxyl group, Conductivity is imparted by a polar group such as the 27th mino group, and the conductivity is adjusted within the range of 1011 to 10'8 Ω·clTl.

In the illustrated image forming apparatus E, a urethane thermoplastic elastomer is used as the material of the transfer belt, the volume resistivity is 1014 Ω·cm, the thickness is 150 μm, and the hardness is 50 to 70 degrees of Shore hardness.

0 Experimental Example 2 In FIG. 3, the diameter of the photoreceptor 1 is 60φ, and the electrode roller 43
The diameter of the roller was 8φ, the material was a conductive EPDM roller, and the hardness was 25° in terms of Asker-C hardness. The belt 42 has a circumference of 2
The transfer belt was 20 mm wide, 210 mm wide, and the length of the contact part with the photoreceptor 1 was 4 mm, and the contact pressure was set within the range of 50 to 80 g/cm.Here, the thickness of the transfer belt was determined by the diameter of the electrode roller. The hardness was so small that it could be ignored in comparison, and even when the hardness of the electrode roller and transfer belt was measured together, it was no different from the hardness of the electrode roller alone.

In this embodiment, the photoreceptor 1 and the belt 42 are driven separately. As in Experimental Example 1, there is no problem in carrying out the experiment by changing the circumferential speed depending on the diameter and ratio of the gear.

In the experimental example configured as described above, an experiment was conducted while changing the type of transfer material P. As a result, the peripheral speed difference between the photoreceptor 1 and the transfer belt was set to 0.5% between 0.5% and 5%.
When it was increased by 5 steps, it was found that a sufficient effect in reducing transfer voids was obtained in the range of 1 to 3%, as in the case of the roller. If it exceeds 3%, stable conveyance of the transfer material P cannot be obtained due to the relationship between the curvature of the photoreceptor 1 and the belt 42 and the pressure contact force, and transfer misalignment frequently occurs. Also, 1
% or when there was a circumferential speed difference of more than 3%, there was almost no effect on the transfer voids.

03rd Embodiment In FIGS. 4 and 5, a member 53 for abutting against the photoreceptor 1 is provided at the end of a roller 51 serving as a transfer means. 54 is a metal core, and the abutting member 53 made of a rigid body and the transfer member 52 having elasticity are adhered to the metal core 54.

The purpose of this embodiment is to maintain a constant distance between the axes of the photoreceptor 1 and the roller 51. Figure 5 shows when the photoreceptor l and roller 51 are not in contact and when they are in contact (during transfer).
As shown in the figure, the transfer member 52 made of a material such as foamed rubber is depressed by the photoreceptor 1 upon contact, and the photoreceptor 1 enters the abutment member 53, which is a rigid body, up to position A.

When the photoreceptor l enters point A, the amount of contact formed with the transfer member 52 can be adjusted by changing the diameter r of the abutment member 53. Alternatively, the diameter r of the abutment member 53 may be constant and the thickness of the transfer member 52 may be varied.

In this example, the peripheral speed at point A is Rw +
> r W *, and the relationship is 1 to 3 from Rw 1
It is desirable that %rW2 be fast.

0 Experimental example 3 The roller 51 described above was applied to the image forming apparatus shown in FIG.

The diameter of the photoreceptor 1 is 30φ, and the diameter of the roller 51 is 20φ.
A foamed EPDM rubber having a diameter of φ and an Asker-C hardness of 28° is used. The diameter of the abutment member 53 is 4 m in contact length.
In order to make m, r=9.7 mm from equation (4).

At this time, the contact pressure of the roller 51 against the photoreceptor l is 50
~60 g/cm2. The contact pressure can be adjusted by the pressure of a spring (not shown) that biases the core metal of the roller 51.

In this experimental example, the driving of the roller and the driving of the photoreceptor 1 were separately driven, and the peripheral speed was varied from 0.5 to 5% in 0.5% increments, and the transfer material P was 48 to 135 g/m. ``When we conducted a paper-threading experiment with paper, envelopes, two postcards, etc., roller 51
The state in which the circumferential speed of the photoreceptor 1 was made 1 to 3% faster than the circumferential speed of the photoreceptor 1 was most effective in preventing transfer defects, and when it was less than 1% or more than 3%, there was no effect. In this example, , the contact part is always formed in a stable state, and even when the drive is taken from the rotating shaft of the photoreceptor 1, it is possible to reliably control the peripheral speed of the central part of the contact part, so that the contact part is always formed in a good state. Transferability is obtained.

In the above embodiments, the developing material preferably contains toner and fine powder treated with silicone oil or silicone varnish. This is because this fine powder improves the releasability of the toner from the image carrier during transfer, and prevents hollow spots.

In addition, in order to obtain high-resolution images, it is preferable that the volume average particle size of the toner shown above be 8 μm or less, but in this case, the cohesive force of the toner increases and the hollowing phenomenon is likely to occur. At this time, it is effective to apply the present invention.

(Effects of the Invention) Since the present invention is configured as described above, it is possible to prevent slippage or misalignment between the transfer material and the image carrier that occurs during transfer. Therefore, the image can be transferred to the transfer material without any environmental differences, and on various paper types such as thin paper, thick paper such as postcards, envelopes, and OHP sheets, the image can be transferred excellently without any hollow transfer.

[Brief explanation of the drawing]

1 to 5 show embodiments of the present invention, and FIG.
1, (b) and 5(a), fb) are schematic front views, FIGS. 2 and 3 are schematic configuration diagrams when applied to an image forming apparatus, and FIG. 4 is a perspective view of the roller. , FIG. 6 is a schematic front view showing a conventional example. Explanation of symbols 1...Photoreceptor (image carrier) 2.15...Roller (transfer means) 42...Belt (transfer means) B...Transfer device P...Transfer material W... Contact part Fig. 1 (CI) Fig. 2 Fig. 1 (b) Fig. 3 54 (a) When Azusa touches Fig. 5 (b) 1 fist Kaku Nikka Fig.

Claims (4)

[Claims] (1) A rotatable image carrier, an image forming means for forming an image on the image carrier, and a transfer material that can be brought into contact with the image carrier at a transfer position, and a transfer material together with the image carrier at the transfer position. In the image forming apparatus, the transfer means transfers the image formed by the image forming means to a transfer material by conveying the image forming means, the transfer means has a hardness of 20° to 40° in terms of ASKER-G hardness. , the pressing force to the image carrier is 50 g/
cm^2 to 200 g/cm^2, and the peripheral speed of the transfer means at the transfer position during transfer is greater than the peripheral speed of the image carrier at the transfer position. . (2) The image forming apparatus according to claim 1, wherein the peripheral speed of the transfer means is set to be 1.0 to 3.0% faster than the peripheral speed of the image carrier. (3) The image forming apparatus according to claim 1 or 2, wherein the transfer means is a roller. (4) The image forming apparatus according to claim 1 or 2, wherein the transfer means includes a belt that contacts the image carrier, and a roller that contacts the belt on a side opposite to the image carrier. .