JPH0661012B2 - Image forming device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image forming apparatus utilizing an electrostatic transfer process such as an electrophotographic copying machine and a printer, and more particularly to effectively using a conveying device thereof.

(Technical background) A transferable toner image is formed on the surface of a running image carrier, and a transfer material mainly composed of paper, which runs in synchronization with the image carrier, is brought into proximity with or in contact with the toner image on the surface of the image carrier, An image forming apparatus configured to transfer the toner image to a transfer material, separate the transfer material from the image carrier, and transfer the toner image to a fixing portion through an appropriate transfer unit is well known in the art.

By the way, various fixing devices for fixing a toner image to a transfer material have been proposed, but recently, a pair of rollers are pressed against each other and at least one roller is heated to melt the toner on the transfer material. Heat and pressure method to fix,
Alternatively, a pressure fixing method of fixing only by pressure without heating means has been widely put into practical use.

In other words, when such an image forming apparatus is viewed from the transfer material side, the transfer material is given a conveying action in order to move synchronously with the transfer position at a transfer position close to the image carrier, and then, after separation, a transfer belt or the like. The transporting action also acts on the transfer material by the transporting means, and the transporting action also acts on the transfer material by passing between the pair of rollers that are in pressure contact with each other at the fixing portion. The force will act.

Of course, when the image forming apparatus is large in size or the transfer material is extremely small and each of these parts acts on the transfer material independently, there is no particular problem. However, for example, as seen in an electrophotographic copying machine. With the rapid downsizing of equipment in recent years, even when a sheet of A4 size or smaller, which is usually most frequently used, is used as a transfer material, the tip of the transfer material after transfer is a roller at a fixing portion. It is unavoidable that a state in which the rear end is still present at the transcription site occurs even though the pair has been reached.

In such a state, the respective parts that apply the conveying force to the transfer material affect each other as described above, and this is an unstable condition that is simply applied to the transfer material by the electrostatic attraction force. Inconvenience of disturbing a large toner image occurs.

For example, if the transfer material enters the pressure contact roller pair at the fixing portion, the load applied to the roller pair at that moment becomes large, and the rotational speed of the roller rapidly decreases, which causes the transfer material to move toward the transfer portion of the image carrier. Therefore, the image carrier and the transfer material are temporarily out of synchronization with each other, which adversely affects the transfer.

Further, particularly when pressure fixing means is adopted, as is well known, the pair of rollers which are in pressure contact with each other are provided in order to make the pressing force on the transfer material as uniform as possible over the entire length thereof.
It is well known that some rollers are arranged so that their axes intersect at a slight angle. However,
In such a case, if the transfer material is sandwiched between the rollers, a uniform conveying action does not work in the width direction of the transfer material (longitudinal direction of the roller), and it tends to deviate from the original traveling direction. For this reason, one side edge of the transfer material is curved and deformed on the upstream side (as viewed in the running direction of the transfer material), which is coupled with the elasticity of the transfer material itself and is displaced from the image bearing surface at the transfer material portion in the transfer portion. May occur and adversely affect the image quality.

Further, in this type of image forming apparatus, it is usual to provide a space as wide as possible in the upper part of the conveying means so that the transfer material does not accidentally collide with various parts inside the apparatus. If the size is reduced, this also becomes difficult, and the curved transfer material may collide with the internal member.

In order to avoid the above-mentioned drawbacks, it has been proposed to provide a spur means having a needle-shaped projection on the periphery.
Suitable when the transfer material is smaller than the device,
As described above, when the transfer material is present from the transfer portion to the fixing portion, the force is weak with the spur-like means, and therefore the transfer material having a strong rigidity such as a thick transfer paper or a plastic sheet cannot be pressed down. In addition, as another method, a method has been proposed in which a pressing roller is provided in the transport section to press the transfer material. surely,
The pressing roller prevents the influence of irregular running of the transfer material, which occurs in the fixing portion when the transfer material is pressed by a certain pressure, from reaching the transfer portion. However, since the pressing roller comes into contact with the unfixed toner image on the transfer material, the toner adheres to the pressing roller and leaves a trace on the transfer material, resulting in an image defect.

(Objects and Constituents) An object of the present invention is to solve the above-mentioned drawbacks so that the effect of irregular running of the transfer material that occurs in the fixing section can be reached by sufficiently supporting the transfer material in the transport section with pressure rollers. This prevents the toner from adhering to the surface of the pressure roller by preventing static electricity from being removed from the back surface of the transfer material corresponding to the pressure roller in the transport section when the surface of the transfer material is neutralized after transfer. To prevent.

(Embodiment) FIG. 1 is a sectional view showing an embodiment of the present invention. A visible image is formed on the surface of the image carrier 1 (hereinafter referred to as a photosensitive drum) via the electrostatic latent image forming unit 2 and the developing unit 3. The visible image on the photosensitive drum 1 is transferred onto a transfer material (not shown) sent from a transfer guide 6 by a transfer corona of a transfer charger 5. After the transfer material holding the visible image is transferred, the charge of the opposite polarity to the toner is removed by the charge removal needle 8 on the back surface of the transfer material. The charge eliminating step has the effect of facilitating the separation of the transfer material from the photosensitive drum 1, and if the charge remains on the back surface after being transported to the transport portion, the charge leaks to the adjacent conductor portion and the surface is not fixed. There is an effect of preventing the toner image from being disturbed by removing the charge. The static elimination needle applies a bias voltage of the opposite polarity to the ground or the transfer corona. After that, the transfer material is sent from the transfer inlet guide 9 to the transfer portion, and the pressing roller 11 and the pressing roller 1 are used to prevent irregular transfer of the transfer material.
It is pressed by 2 and sent to the fixing unit, and the unfixed toner is fixed by the fixing roller 14 and discharged to the outside of the apparatus.

When the unfixed toner image is pressed by the pressing roller 11 in the conveying portion, the toner adheres to the surface of the pressing roller 11 and the image on the transfer material is disturbed as described above. In order to prevent the toner from adhering to the surface of the pressing roller 11, a charge having a polarity opposite to that of the toner, that is, a charge having the same polarity as the transfer corona remains on the back surface of the transfer material, so that the unfixed toner image is pressed by the pressing roller 11. However, the charge on the back surface of the transfer material and the toner attract each other. Therefore, the toner image on the transfer material is not disturbed, and the toner hardly adheres to the surface of the pressing roller 11. The slightly adhered toner is cleaned on the surface of the pressing roller by a cleaning member 15 such as felt or sponge.

When the back surface of the transfer material is not discharged after transfer and the transfer corona charge remains, the unfixed toner image due to the pressing roller is not disturbed, but the separation failure occurs as described above.
Therefore, 8a corresponding to the pressing roller as shown in FIG.
By cutting the part of the needle, the back surface of the transfer material with which the pressing roller 11 is in contact is not neutralized, but the transfer corona charge remains, and the other back surface is neutralized. Since the charge is removed from the portion other than the portion corresponding to the pressing roller 11, the separation is favorably performed, and the back surface charge does not leak to the adjacent conductor in the transport portion to disturb the image. On the other hand, the back surface of the transfer material corresponding to the pressing roller 11 does not adhere to the pressing roller 11 because the charge having the opposite polarity to the toner, which is the transfer corona charge, attracts the oner. Leakage of charges on the back surface of the transfer material corresponding to the pressing roller to the adjacent conductor is lightly fixed on the transfer material by the pressure of the pressing roller 11, so that the toner image on the surface is not disturbed even if the leakage occurs.

FIG. 4 shows another embodiment of the present invention, which covers the static elimination needle. As shown in FIG. 4 (a), the upper portion of the charge eliminating needle corresponding to the pressing roller is covered with the insulator 7a and the charge is not eliminated only in that portion. As shown in FIG. 4 (b), the insulator 7 is extended to the side of the transport guide 9 to cover the static elimination needle 8 at two places (7a in the figure).

The width of the static elimination needle cutting portion 8a and the insulating eaves 7a is about 5 times the width of the pressing roller 11, that is, the width of the pressing roller 5 in this embodiment.
Since it is mm, a width of 5 to 25 mm is suitable.

FIG. 5 shows another embodiment of the present invention, which is a case where the electrostatic separation charging device 18 removes electricity. Transport entrance guide 19
Extends the portion corresponding to the pressing roller on the separation charger 18 to eaves 19a.
Coated with. Therefore, since only the portion corresponding to the pressing roller is not discharged, the image is not disturbed by the pressing roller. In addition, the case where the entire conveying portion is the conveying belt, not the pressing roller, is shown, and the transfer material is sent between the pressing roller 11 and the wide belt 21 that is rotated by being supported by the base 20, and is undetermined by the fixing roller. The deposited toner image is fixed and conveyed outside the machine.

(Effect) According to the present invention, even if the copying operation is repeated, a good image is always obtained without any deviation from the original on the image.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention. FIG. 2A is a plan view of the transport unit. FIG. 2B is a cross-sectional view of the transport section. Third
The figure shows a static elimination needle used in the present invention with the needle partially cut. Fourth
The figure is a view of another example of the static elimination needle used in the present invention. FIG. 5 is a sectional view showing another embodiment of the present invention. FIG. 6 is a plan view of the static eliminator used in the present invention. 1 is a photosensitive drum, 2 is an electrostatic latent image forming unit, 3 is a developing unit, 4
Is a cleaning unit, 5 is a transfer charger, 5 is a transfer guide,
7 is an insulating member, 8 is a static elimination needle, 9 is a conveyance inlet guide, 10
Is a corona wire, 11 is a pressing roller, 12 is a pressing roller, 13 is a fixing inlet guide, 14 is a fixing roller pair, and 15 is a fixing roller pair.
Is a cleaning member, 16 is a transport guide, 17 is a transport belt, 18 is a separation charger, 19 is a transport inlet guide, 20
Is a belt support plate, and 21 is a wide conveyance belt.

Claims (1)

[Claims] 1. A transfer device comprising a discharging unit for discharging a rear surface of a transfer material after transferring a visible image of the transfer material, and a transfer unit for carrying and fixing unfixed toner on the transfer material after passing through the discharging unit. In a device having means for pressing and rotating the unfixed surface of the material, in order to prevent the rear surface of the transfer material with which the pressing and rotating means is in contact from being neutralized, the static elimination means of the corresponding portion with which the pressing and rotating means is in contact An image forming apparatus characterized by reducing or eliminating the ability.