JPH01316774A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image of good quality stably by arranging a control means which controls the press-contact state of the press-contact nip part between an image carrier and a transfer roller when a transfer material passes between the image carrier and transfer roller. CONSTITUTION:The transfer roller 2 is arranged nearby the image carrier 1 which rotates as shown by an arrow A, both ends of the shaft 5 of the transfer roller are supported by springs 7 and 7 incorporated in form bodies 6 and 6 provided on the appropriate fixed part in the device, and the transfer roller 2 is displaced toward the image carrier 1 at all time and pressed so as to form the nip part with proper length. The shaft 5 is provided with control rolls 10 and 10 made of rigid materials such as metal rotatably outside both ends of the transfer roller 2 and outside the image area L of the image carrier. Therefore, the length of the press-contact nip part in the running direction of the transfer material is maintained as desired. Consequently, deterioration in picture quality such as void and image staining is prevented and the image of good quality is obtained stably for a long period without the fusion of toner.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(Prior Art and Problems to be Solved) In a well-known image forming apparatus that includes a step of transferring a transferable toner image formed on the surface of an image carrier to a sheet-like transfer material such as paper that comes into contact with the transferable toner image, the toner image is A structure has already been proposed in which a transfer roller is brought into pressure contact with an image carrier carrying a toner image, and a transfer material is passed through a nip between the two to transfer a toner image onto the transfer material.

FIG. 7 is a schematic side view of such an image forming apparatus, particularly showing a portion of the transfer site, and shows a cylindrical image carrier having an axis perpendicular to the plane of the paper and rotating in the direction of arrow A. 2
0, and the transfer roller 21 is arranged close to this.

The transfer roller 21 is made up of a core metal 21b and a surface layer 21a made of conductive rubber.The core metal 21b is supported by a spring 24 disposed on a frame 23 fixed at a suitable position in the image forming apparatus, and the transfer roller 21 is rotated. By pressing upward in the figure, the surface layer 21a of the transfer roller 21 is brought into pressure contact with the image carrier 20, thereby forming a lengthwise nip portion when viewed in the direction of arrow A.

A toner image T is formed on the surface of the image carrier, and at the same time, a transfer material P is inserted into the nip portion from the direction of arrow B. At the same time, a transfer bias is applied to the transfer roller to form an image. It is assumed that the toner image on the carrier side is transferred to the transfer material.

It goes without saying that around the image carrier 20 there are provided a negative charger, an image information providing means, a developing device, a cleaning device, and other members necessary for forming fine images. All of these are omitted as they are not relevant to the above explanation.

In such a device, since the transfer material is firmly held at the transfer site from start to finish, image quality deterioration due to transfer misalignment and vibration is more likely to occur compared to known transfer means that use a transfer charger. However, since the transfer bias applied during transfer can be applied at a relatively low voltage, this greatly contributes to the miniaturization and cost reduction of this type of device, but it is not free from the following drawbacks.

To briefly explain this, in principle, toner is transferred from the image carrier to the transfer material at the nip section, but the length of this nip section depends on the strength of the spring 24 and aging due to long-term use. Variations occur due to various causes such as changes in the transfer roller's hardness, curvature of the transfer roller, wear, etc., and this affects the transfer effect.

As shown in FIG. 8, the distance between the image carrier 20 and the transfer material P in the transfer area is d1, the potential difference between them is V, the mass of the toner particles is m, and the charge is q. The time τ for moving from the body side to the transfer material P is (1/2) (qV/ma) τ2=d ■The time the toner exists in the transfer area, the length of the transfer area, the speed of the relevant part, and V Then, t=sentence/V (2) In order for transcription to be performed sufficiently, it is necessary that τ≦t, and from this and the above two equations, the following relationship is obtained.

The toner on the actual image carrier is, of course, not a single particle, but in order to perform sufficient transfer, the length of the nip must be determined by the size of the image carrier, transfer material, developer material, etc. at the transfer site. It can be seen that it is necessary to have a value greater than a certain value so that the relationship shown in the above equation holds true.

Therefore, if the above-mentioned conditions are not satisfied and the length of the transfer area becomes smaller than a certain value, a transfer defect will occur.

On the other hand, if the sentences are not long, problems as shown schematically in Figure 9 will occur.

As schematically illustrated in the figure, the transfer material P that advances in the direction of arrow B and passes through the nip portion between the image carrier 20 and the transfer roller 21, which is the transfer area, is normally moved in the same direction as the direction of the transfer material P1. However, if the pressing action of the transfer roller 21 against the image carrier changes for some reason as mentioned above, and as a result, the length of the transfer area becomes excessive, this causes the transfer material to As the curling occurs, the traveling direction of the transfer material passing through the transfer site also changes upward in the figure, so that the transfer material tends to change as shown by the symbol P2 in FIG.

Therefore, the transfer material that has left the transfer site comes close to the bottom of the cleaning device 22, which is usually located near the downstream side of the site, and depending on its path, the charge remaining on the transfer material may cause it to become part of the cleaning device. This may cause the inconvenience that the cleaning device may rub against the cleaning device, disturbing the image, or even come into direct contact with the cleaning device, causing a jam.

The above-mentioned defects are due to variations in the length of the transfer area, but in addition to these, there are also image defects due to changes in the suppression effect in the transfer area.

To briefly explain this, if the pressing force of the spring 24 is too strong in the device shown in FIG. A phenomenon called dropout occurs.

In the case of normal transfer, as shown in FIG. 10A, most of the toner T forming the toner image on the image carrier 20 is transferred to the transfer material P at the transfer site, and only a small amount of it is transferred to the transfer material P. The toner will then be removed by a cleaning procedure as residual toner.

However, if the pressing force is too strong, the surface of the image carrier and the toner aggregate and adhere firmly to the image carrier, and the adhesion force is greater than the effect of the electric field that attempts to transfer the toner to the transfer material. As a result, the toner in the center of one image is not transferred, resulting in a transfer failure called hollowing out, as shown in Figure 10C. Become.

Further, toner present as a fog on the image carrier when the transfer material is not passed may fuse to the image carrier or the transfer roller due to long-term use.

Normally, in order to avoid such a situation, the direction of the electric field at the transfer site is switched when the paper is not passing to electrostatically prevent toner from adhering to the transfer roller.
If the pressure of the transfer roller on the image carrier is too strong, the resulting mechanical adhesion force becomes greater than the electrostatic force, causing the toner to fuse to the transfer roller and be drawn back to the image carrier. Toner also adheres strongly to the image bearing member due to the excessive pressing force of the transfer roller, and cannot be removed even by a cleaning device, which may lead to image defects.

The present invention has been made in order to cope with such a current situation, and is intended to constantly and accurately maintain the pressure contact between the image bearing member and the transfer roller that is in pressure contact with the image forming apparatus in an image forming apparatus that has a transfer means that is in pressure contact with the image carrier. It is an object of the present invention to provide an image forming apparatus that can stably obtain high-quality images without causing the above-mentioned defects by adjusting the image quality.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention comprises an image bearing member and an elastic transfer roller that comes into pressure contact with the image carrier, and a pressure nip between the two. In an image forming apparatus configured to transfer a transferable toner image on the surface of an image carrier to the transfer material by inserting a transfer material through the transfer material, there is a The present invention is characterized in that a regulating means for regulating the pressure-welding state of the pressure-welding nip portion is provided.

With this configuration, it is possible to stably obtain high-quality images without image defects due to hollow spots, stains on the transfer material, and the like.

(Description of Embodiments) FIGS. 1 and 2 are a side view and an end view of a main part showing a transfer site of an image forming apparatus equipped with an image carrier and a flexible transfer roller that is in pressure contact with the image carrier, A transfer roller 2 is disposed adjacent to an image carrier 1 extending perpendicular to the plane of the paper and rotating in the direction of arrow A, and both ends of a shaft 5 of this transfer roller are placed at appropriate positions in a stationary part of the apparatus. The transfer roller 2 is supported by springs 7 and 7 built into the arranged frames 6 and 6, and the transfer roller 2 is always biased in the direction of the image carrier 1 so that a nip portion of an appropriate length is formed. It is in pressure contact with the

Regulating rollers 10.10 made of a rigid material such as metal are rotatably disposed on the shaft 5 on both sides of the transfer roller 2 and outside the image area of the image carrier.

Since the radius D2 of the regulating roller IO is smaller than the radius DI of the transfer roller 2 in its natural state by a predetermined dimension, the transfer roller 2 is pressed against the image carrier and deformed by an amount determined by DI-D2''. This forms a nip, that is, a transfer area.

With this structure, as long as the spring 7 has sufficient strength to reliably press the regulating roller 10 against the image carrier l, the above-mentioned manufacturing Even if there are variations in assembly errors, hardness of the transfer roller, spring force, etc., the length of the transfer area can be maintained at a substantially predetermined length, and the occurrence of image defects as described above can be suitably prevented. It becomes possible to do so.

Furthermore, when the transfer roller is actively driven, it is normally configured so that the driving force is applied to one end. In the present invention, transfer defects that occur in the width direction (perpendicular to the paper surface of the second drawing) can also be avoided by reducing the roller pressure 1 at both ends.
i! This can be prevented since the amount is equalized at the extreme end.

Next, an experimental example of the above device will be described.

An image carrier having a photosensitive layer made of an organic photoconductor with a diameter of 30+ mm and a transfer roller having a specific resistance of 103 to 10
A foamable polyurethane rubber (manufactured by Toyo Polymer Co., Ltd., Rubicel registered trademark) with an Ωc, m and Asker-C hardness of 20 to 40 degrees is integrally molded onto a shaft with a diameter of 8 m, and the outer diameter in its natural state is 19. 5-20. A 5m long intestine was used.

As the regulating roller, a pole bearing was processed to have an outer diameter of 17.5 to 18.5 mm and attached to the shaft of the transfer roller.

The circumferential speed of the image carrier was set to 100 rats/sec, the dark potential was set to -700 V, and the bright potential was set to -100 V to carry out reversal development, and a transfer bias of +500 V was applied to the transfer roller via a support spring. , 60-400gr
/rn' transfer paper was passed through.

For all the transfer papers within the above-mentioned range, good images without image defects such as transfer omission 1 image stain and hollow omission were obtained.

3 and 4 show other embodiments of the present invention, in which FIG. 3 is a side view of the transfer site, and FIG. 4 is a sectional view taken along line BB' in FIG. 3.

In this device, the frame 6° supporting the shaft 5 and the spring 7 of the transfer roller 2 has a closed upper side, and the position of the shaft 5 is regulated by the sugar chain portion 11. Thus, the pressure nip portion between the image carrier 1 and the transfer roller 2, which is the transfer area, is determined.

In this device, the frame body 6', the shaft 5, and the spring 7, which are members that define the length of the transfer area, are interconnected to form a regulating means, so double-sided printing and multiple printing can be performed on thick transfer materials. Depending on the type of developer used, voids are likely to occur, so it is necessary to improve the processing and assembly accuracy of each component, but in the case of single-sided printing, which is commonly used, Depending on the configuration, it is sufficiently durable for practical use and can stably obtain good images.

In addition, in this case, since the frame body serving as the regulating member does not come into contact with the image carrier, the toner is fused to the roller serving as the regulating member, as in the case of the above embodiment, and the image carrier and the transfer roller are connected to each other. It is possible to prevent the deterioration of the function as a spacer between the layers and the occurrence of transfer defects due to this.

Note that an appropriate number of members including the image carrier 1 and the transfer roller 2 are
When using an integral cartridge configuration, it is often sufficient for this type of device to have limited durability, so in such cases, as shown by the dotted line in Fig. It is also possible to configure the upper side of the frame 6' to come into contact with the image carrier and rub against the image carrier, which is advantageous in terms of cost.

To briefly describe the experimental example, the same image carrier and transfer roller as in the above experimental example were used, and the distance between the center of the shaft 5 of the transfer roller and the center of the image carrier 1 was 18.9 to 19.1 mm.
When the frame body was fixed at 6 degrees so that There was no occurrence of

5 and 6 show still another embodiment of the present invention, FIG. 5 is a side view of the transcription site, and FIG. 6 is a side view of the transcription site, and FIG.
FIG. 3 is a cross-sectional view taken along line c'.

In this embodiment, the diameter of the regulating rollers 10 disposed on the outside of both ends is larger than the outer diameter of the transfer roller 2, and in a natural state, the photosensitive layer 12 formed on the surface of the image carrier and the A gap d is formed between the transfer rollers 2, and this gap d is smaller than the thickness of the transfer material.

With this structure, when the transfer material passes during transfer, a suppressing effect acts on it and the transfer is executed, and when the paper does not pass, the image carrier does not come into contact with the transfer roller, so there is no possibility of jamming. In some cases, the toner image on the image carrier may be transferred to the transfer roller, or the toner that has adhered to the non-image area as background fog may adhere to the transfer roller and cause stains on the back of the next transfer material. can be prevented.

Further, as shown in the figure, by configuring the regulating roller 10 to abut against the photosensitive layer of the image carrier at a position outside the photosensitive layer, damage to the photosensitive layer can be prevented.

The same image carrier as in the original experimental example, and
Using a transfer roller with an outer diameter of 19.98 to 20.02 cm in its natural state, use high-density polyethylene acid to transfer a roller with an outer diameter of 20.09 to 20.02 cm.
20.11+e+s regulating rollers were brought into contact with the aluminum background portion outside the photosensitive layer on the surface of the image carrier. As a result, although paper was passed under the same process conditions as in the experimental example, it was possible to obtain good images free of jams, toner fusion, hollow spots, and back stains.

(3) As described in detail, according to the present invention, an image carrier;
In an image forming apparatus that is equipped with a transfer roller that is in pressure contact with the transfer roller, and transfers the transfer material by passing the transfer material through the pressure nip between these two rollers, the length of the pressure nip as seen in the running direction of the transfer material is set to the desired length. It effectively prevents deterioration of image quality such as hollow spots and image stains, and has a large mechanism that helps to stably obtain high-quality images over a long period of time without toner fusing. be.

[Brief explanation of the drawing]

FIG. 1 is a side view of the main parts of an image forming apparatus to which the present invention is applied, showing the configuration near the transfer site, FIG. 2 is a cross-sectional view of the top end of the same, and FIGS. 3 and 4 are other examples, respectively. FIGS. 5 and 6 are a side view and an end sectional view of the vicinity of the transfer site showing still another embodiment, and FIG. 7 is a side view and an end sectional view of the vicinity of the transfer site, respectively, and FIG. A side view showing the vicinity of the transfer site of the device for explaining the operation of the device;
FIG. 8 is a schematic diagram for explaining the state in which toner is transferred from the image carrier to the transfer material, and FIG. 9 is a schematic side view for explaining the direction of movement of the transfer material in a known image forming apparatus. Figure 1.
The OC diagram is a schematic diagram illustrating a mode of toner transfer in an image forming apparatus using a transfer roller. l...image bearing member, 2-...transfer roller, 5...shaft,
6＠φ・Frame, 7...Spring, 10...-Regulation roller. Figure 1 Z 2 Figure Town 84 Prisoner Figure 5 Figure 6 Prisoner Figure 7 Figure 8 Figure 9 Figure 10A

Claims (4)

[Claims] (1) It is configured to include an image carrier and an elastic transfer roller that is in pressure contact with the image carrier, and to insert a transfer material into the pressure nip between the two to transfer the transferable toner image on the surface of the image carrier to the transfer material. An image forming apparatus comprising: a regulating means disposed between the image carrier and the transfer roller to regulate the pressure contact state of a pressure nip portion between the image carrier and the transfer roller when the transfer material passes through the image forming apparatus. (2) The image forming apparatus according to claim 1, wherein the regulating means is a roller having a diameter smaller than the diameter of the transfer roller. (3) Claims in which the regulating means is a roller whose diameter is set so as to press the transfer roller against the image carrier to form a nip only when the transfer material passes through the nip. The image forming apparatus according to item 1. (4) regulating means are disposed at both ends of the transfer roller;
Claim 1, which is a frame body that pivotally supports the transfer roller.
The image forming apparatus described in .