JPH02304585A - Image transfer 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 [Object of the Invention] (Industrial Application Field) The present invention relates to an image transfer device provided in, for example, an electrophotographic apparatus.

(Prior Art) Currently, in electrophotographic devices, the main method for transferring an image formed on an image carrier such as a photoreceptor to a transfer material such as paper is a method using a corona charger (
Corona transfer method) is used.

However, the corona transfer method has problems such as image scattering, transfer failure in humid environments, and the need for an expensive power source to generate high voltage.

Therefore, there are methods such as pressing a transfer roller against the image bearing member and transferring the image using pressure, and methods of pressing an elastic roller against the image bearing member and applying a bias voltage to transfer the image using pressure and electrostatic force. has been devised.

In particular, a method in which an elastic roller is pressed against the image carrier, a bias voltage is applied, and the image is transferred using pressure and electrostatic force does not cause image scattering, has good environmental stability, and does not damage the image carrier. Good transfer can be performed.

However, even with this method, problems such as image omission occurred during transfer to special transfer materials such as OHP sheets and cardboard.

This is because multiple sets of paper such as OHP sheets, cardboard, and envelopes have higher electrical resistance than a single sheet of plain paper.

However, in the past, a constant bias voltage was applied regardless of the type of the transfer material, which resulted in the phenomenon of hollow areas where toner was not transferred in the center of line images such as characters.

The rate at which hollow spots occur is related to the magnitude of the current that flows from the transfer roller to the transfer target material and to the transfer section.

That is, in the case of transfer materials with high resistance such as OHP sheets and envelopes, the transfer current becomes low, resulting in an increase in the incidence of hollow images.

Here, the percentage of hollow spaces is the ratio of the area of the blank portion of the text portion to the entire area of the text portion of the image.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image transfer device that does not cause transfer defects such as image voids when transferring to special transfer materials such as OHP sheets and cardboard.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides electrostatic transfer of a developer image carried by an image carrier onto a transfer material using a conductive transfer member. The image transfer apparatus is characterized in that it includes a voltage applying means for applying a voltage having a value depending on the type of the material to be transferred.

(Function) By the means described above, it is possible to obtain a stable transferred image that does not cause transfer defects such as image hollowing out, regardless of the type of transfer material.

(Example) The present invention will be described below with reference to an example shown in the drawings.

FIG. 1 shows an image transfer device, in which reference numeral 1 denotes a photosensitive drum as an image carrier. A transfer roller 2 made of a conductive rubber roller, which is an electrode structure serving as a transfer member, is pressed into contact with the photoreceptor drum 1. This transfer roller 2 has a resin layer 3 with a thickness of 100Ω and a surface resistance of about 106 to 108Ω, a conductive resin layer 4 with a thickness of 100Ω and a surface resistance of about 104Ω, and a conductive resin layer 4 made of silicone rubber. It is composed of a substrate roller 5 in which particles are dispersed to make it conductive. The hardness of the surface of the transfer roller 2 having the multilayered structure is preferably in the range of 20 degrees to 60 degrees in order to obtain an appropriate nip width with the photoreceptor drum 1.

Further, a high voltage generating circuit 11 as a voltage applying means is electrically connected to the transfer roller 2.

This high voltage generating circuit 11 is configured to apply voltages of different values to the transfer material 8 depending on the type thereof.

During image formation, a toner image 7 is formed on the photoreceptor drum 1 by an image transfer means (not shown), and this toner image 7 is transferred to the toner transfer portion (A-B section) as the photoreceptor drum 1 rotates (in the direction of the arrow). will be transferred to. The toner image 7 is pressed against the transfer material 8 at the toner transfer section. During this time, a high voltage with a polarity opposite to the charge polarity of the toner image 7 supplied by the high voltage generation circuit 11 acts on the toner image 7, and the toner image 7 is electrostatically transferred to the transfer material 8. An image 9 is formed on top.

Incidentally, the contact width between the transfer roller 2 and the transferred material 8 is 1 to 2■■.

Note that in roller transfer, if the transfer pressure by the transfer roller 2 is too large, a hollow phenomenon occurs in which the toner in the center of a line drawing such as a character or an image is not transferred to the transfer material 8.

However, in the toner transfer device used in this example, 20 to 2
At a transfer pressure of 0.00 g/c-, in the case of plain paper, the appearance rate of voids in the transferred image is 2% or less, and a problem-free image can be obtained.

Next, in this example, recording currents were measured during transfer to various transfer materials such as plain paper and OHP sheets, which will be described below.

Three types of transfer materials were used: two types of plain paper with a resistivity of around 10Ω(2) and an OHP sheet with a resistivity of 1012 to 1017Ωl.

In FIG. 1, a bias voltage was applied to the transfer roller 2 by the high voltage generating circuit 11, and the current flowing into the photosensitive drum 1 was measured at normal temperature and normal humidity, and this was taken as the recording current during transfer.

FIG. 2 shows a method for measuring the resistance of a transfer material. An aluminum tube 12 having the same shape as the photoconductor drum 1 is used instead of the photoconductor drum 1, the transfer material 8 is sandwiched between the transfer roller 2 and the aluminum tube 12, and electric power is applied by the high voltage generating circuit 11. The current flowing from the aluminum tube 12 to the ground was measured with an ammeter 13. Here, the resistance of the transferred material is measured in 2. The voltage was set to OKV.

FIG. 3 shows the relationship between the resistance of the transfer material and the recording current, and shows the results when the voltage applied to the transfer roller 2 was 1.6 KV and 2.4 KV.

However, the resistance of the transferred material is 2. This is the value at the OKV voltage, and the change in resistance of the transferred material due to voltage change was considered to be constant.

When the resistance of the transfer material increases, the recording current tends to decrease, but by increasing the bias voltage applied to the transfer roller 2, the recording current increases.

FIG. 4 shows the relationship between the recording current and the percentage of the transferred image on the transfer material. The transfer blanking rate was determined by n1 using an image processing device, which was obtained by magnifying the ratio of the area of the blank portion of the character portion to the entire area of the character portion in the image sample using a microscope.

It can be seen from FIG. 4 that the transfer rate tends to decrease as the recording current increases. When the transfer blanking rate is about 2% or less on plain paper, the blanking out is hardly noticeable when visually inspected.

OHP sheets have a higher rate of transfer voids than plain paper, but when images were projected with a projector, no voids were observed even when the transfer rate was around 6%.

When the bias voltage is set to 2.4 KV, even in the case of an OHP sheet, the transfer blanking rate is 2%, which is a good condition.

Looking at FIG. 4, it can be seen that the recording current is about 3
．． It can be seen that when OnA/c or more, the transfer blanking rate is 2% or less.

Furthermore, in the case of envelopes and cardboard, the resistance of the transfer material is higher than that of plain paper, as is the case with OHP sheets, so increasing the bias voltage lowers the transfer rate.

As explained above, with plain paper, a bias voltage of 1.6 KV can produce an image with very few hollow areas in the transferred image, but with transfer materials with high resistance such as OHP sheets, the bias voltage is 2.4 KV.
By increasing the bias voltage as shown in FIG.

However, according to this example, the bias voltage value and recording current value in the transfer as described above were appropriate, but these may vary depending on the diameter of the photoreceptor drum and transfer roller 2, the process speed,
The appropriate range varies depending on the contact pressure of the transfer roller 2 and the like.

As in this embodiment, by changing the bias voltage applied to the transfer roller 2 in at least two levels depending on the type of transfer material such as plain paper, OHP sheet, envelope, etc., the occurrence of missing transferred images is extremely reduced. can do.

[Effects of the Invention] As explained above, the present invention applies a voltage of a value depending on the type of material to be transferred, so that it is possible to obtain a stable image without transfer defects such as hollow areas in the transferred image. The effect of being able to do it is effective.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is an explanatory diagram showing the state of transfer of a toner image, FIG. FIG. 4 is a graph showing the relationship between the recording current and the transfer blanking rate in the transferred image. 1... Photosensitive drum (image bearing area), 2... Transfer roller (transfer member), 7... Toner image (developing material image), 8...
...Transfer member, 11... Voltage application means (high voltage generation circuit). Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In an image transfer device that electrostatically transfers a developer image carried on an image carrier to a transfer material using a conductive transfer member, a voltage that applies a voltage having a value depending on the type of the transfer material An image transfer device characterized by comprising an application means.