JPH0445471A - image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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) A moving image carrier is provided with a contact type transfer means such as a transfer roller and a transfer belt that are in pressure contact with the image carrier, and a paper or the like is placed in the transfer area formed as a pressure nip between the two. A transfer material is supplied, and a transfer bias is applied to the transfer means, so that the toner image previously formed on the surface of the image carrier is transferred to the transfer material by the action of the electric field formed. Image forming apparatuses configured as follows have been widely used in the past.

The transfer rollers, transfer belts, etc. used as transfer means used in such image forming apparatuses are made by dispersing carbon or metal oxide powder in rubber, sponge, etc. and adjusting the volume resistance appropriately. However, with this method, it is not necessarily easy to form the resistance value uniformly over the entire area, and it is difficult to avoid local differences in the resistance value. This situation is noticeable in the resistance value range of 10' to 1010Ω.

In addition, the surfaces of transfer rollers, transfer belts, etc. are extremely rough, and for this reason, the contact conditions at the contact surfaces between these transfer means, transfer materials, and image carriers are different from each other when viewed locally. Therefore, from the viewpoint of the formation of the electric field, it must be said that the situation is considerably different from the expected state.

Because of the existence of such local changes in resistance value, electric field strength, etc., the actual transfer performance is as follows: ■ In areas where there is a local excess electric field, the charge passes through the transfer material from the transfer means and carries the image. Due to body leakage, a transfer electric field is not formed, resulting in white spots appearing in this area, or deterioration of image quality such as toner scattering and blurring of the image when leaking.

■In addition, the transfer means and the image carrier come into direct contact between sheets during continuous printing, and in areas where paper does not pass when intermediate transfer materials are used. If excessive electrolysis is applied to the image bearing member, the image carrier will become excessively charged, and this part will not disappear until the next image forming process and will become a charged memory, and this part will be developed and cause black spot-like image stains. This causes stains on the contacting transfer means and stains on the back side of the subsequent transfer material.

Furthermore, in contact type transfer means, there is a problem of hollowing out in linear images such as characters (as is well known).

The present invention has been made in view of the current situation, and the present invention has been made in an image forming apparatus equipped with a contact-type transfer means as described above, in which image deterioration due to local changes in the electrical characteristics of the transfer means is avoided. The purpose of this is to create an image forming apparatus that can prevent problems and obtain high-quality images.

(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 a transfer member made of an elastic material that comes into pressure contact with the image bearing member, so that both While passing the transfer material through the transfer site formed as a pressure contact part,
At this time, the image forming apparatus performs the transfer by applying a transfer bias to the transfer means, and is characterized in that the transfer bias is a pulsating DC voltage.

With this configuration, it is possible to prevent image quality from deteriorating due to local changes in the electrical characteristics of the transfer member 5 and from staining the transfer material, and to obtain high-quality images.

(Description of Embodiments) FIG. 1 is a schematic side view showing the main parts of an image forming apparatus suitable for applying the present invention.

The surface of the image carrier 1, which has an axis perpendicular to the plane of the paper and rotates in the direction of the arrow shown in the figure, is uniformly charged by a primary charging means (not shown), and image exposure is projected onto this charged surface to generate an electrostatic charge. After a latent image is formed, this latent image is visualized at a development site and becomes a toner image.

Furthermore, as the image carrier rotates, when this toner image reaches a transfer site formed as a nip portion where the transfer roller 2 contacts the image carrier 1, the transfer material is transferred from the conveyance path 5 at the same timing. is transported to the transcription site,
At the same time, a transfer bias is applied by the power source 3 via the transfer roller 2, and the toner image on the image carrier side is transferred to the transfer material.

The transfer material carrying the toner image is then separated from the image carrier and conveyed to a fixing site (not shown), and the residual toner on the surface of the image carrier is cleaned by a cleaner, making it ready for the next process.

More specifically, the transfer roller 2 is made up of a core bar 2a made of a conductive material such as metal, and an elastic layer 2b made of EPDM rubber with carbon dispersed therein so as to have a volume resistivity of 10'' to 104ΩcI11. It is assumed that a transfer bias is applied to the core metal 2a by the power source 3.

The image carrier 1 is formed by forming an OPC photosensitive layer 1b on the surface of a cylindrical substrate 1a made of aluminum, and is uniformly charged to approximately 1600 V by a charging means.

This charged surface is irradiated with an image signal such as an image-modulated laser beam, and the potential of the area is attenuated to form an electrostatic latent image, and the negatively charged toner from the developer is applied to the electrostatic latent image. The toner is supplied and adheres to the latent image portion to form a toner image.

When this toner image reaches the transfer site where the image carrier 1 and the transfer roller 2 come into pressure contact, the transfer material P is supplied from the conveyance path 4 at the same timing, and at the same time, a transfer bias is applied by the power source 3. However, in this case, the applied bias was DC +600V, and the best result was obtained in terms of transfer efficiency, but due to the local fluctuations in the electrical characteristics of the transfer roller as described above, White spots and toner scattering occur due to leakage, and localized charging memory occurs in areas where paper does not pass, resulting in black spot-like stains and stains on the back of the transfer material.

Therefore, in the present invention, as shown in Fig. 2, when applying a pulsating DC voltage with a 400V bias in the positive direction and a peak-to-peak voltage of 600μ, the same transfer as when +600V DC was applied. Not only was efficiency achieved, but also high-quality images without the above-mentioned defects could be obtained.

By pulsating the applied voltage, this requires a lower voltage than in the case of normal direct current, and the pulsating electric field
This is thought to be because leakage in the transfer material and excessive charging on the surface of the image carrier are less likely to occur.

Next, to explain another embodiment, a device as shown in the figure is used, and as the transfer roller and its elastic layer,
Images were produced using EPDM rubber in which carbon and zinc oxide were dispersed and the volume resistivity was adjusted to about 10' cffl.

In this case, the best transfer efficiency was obtained with a transfer bias of approximately +2000V, but in this case as well, the same problem as in the previous case was made more pronounced due to changes in the local electrical characteristics of the transfer roller. It occurred in

On the other hand, +t 400v as shown in FIG.
It was confirmed that by applying a pulsating DC voltage with a peak-to-peak voltage of 2000V with a DC bias to the voltage, the same transfer efficiency as when applying a normal +2ooov voltage could be obtained, and the above-mentioned problems would not occur. .

Although the case where a transfer roller is used as the transfer means has been described above, the same effect can be achieved when a transfer belt is used as a contact type transfer means.

The waveform of the bias voltage applied to the transfer means superimposes alternating current on direct current, and in this case, the peak-to-peak voltage of the alternating current is 100% of the direct current voltage that shifts the alternating current to the positive side.
Those with peak-to-peak voltages of ~200% are preferred.

If the peak-to-peak voltage is lower than this, the oscillating electric field is too weak to achieve the desired effect; if it is too high, the toner image itself vibrates, causing toner scattering.

(3) As described in detail, according to the present invention, an image carrier;
In an image forming apparatus that uses a transfer roller or a contact type transfer means that is in pressure contact with the transfer roller, white spot images, toner scattering, black spot-like image stains, etc. may occur due to local fluctuations in the electrical characteristics of the transfer means. This method has a remarkable effect in obtaining high-quality images by effectively preventing the occurrence of blemishes, and also preventing hollow lines in linear images such as characters.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of the main parts of an image forming apparatus suitable for applying the present invention, and FIGS. 2 and 3 are waveforms of a transfer bias applied to the transfer means of the same apparatus. l... Image carrier, 2... Monocycle roller, 3. Pressure V Bη t in the figure.

Claims (4)

[Claims] (1) An image bearing member and a transfer means made of an elastic material that is in pressure contact with the image carrier are provided, and the transfer material is passed through a transfer region formed as a pressure contact portion between the two, and at this time, a transfer bias is applied to the transfer means. What is claimed is: 1. An image forming apparatus that performs transfer using a pulsating DC voltage as a transfer bias. (2) The peak-to-peak voltage of the AC component of the transfer bias is 100 to 20% of the DC component for biasing the transfer bias to DC.
The image forming apparatus according to claim 1, which is within the range of 0%. (3) Claim 1 in which the transfer means is a transfer roller
2. The image forming apparatus according to claim 1 or 2. (4) Claim 1 in which the transfer means is a transfer belt
2. The image forming apparatus according to claim 1 or 2.