JPH03156480A - 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) Purpose of the Invention (Field of Industrial Application) This invention relates to image forming apparatuses that utilize an electrostatic transfer process, such as electrostatic copying machines and printers, and particularly to contact-type transfer means. The present invention relates to an image forming apparatus to be used.

(Prior art and issues to be solved) An electrostatic latent image is formed by irradiating an image-modulated laser beam, an LED array, etc. onto the charged surface of the image carrier surface, and this is charged with the same polarity as the latent image. A toner image is formed by supplying the lower toner by a reversal development method, and a sheet-like transfer material such as paper is placed on a transfer site configured by contacting the image carrier with a transfer means such as a conductive transfer roller or a transfer belt. An image forming apparatus has already been proposed in which the toner image is supplied at the same time as the toner image, and a transfer bias is applied to the transfer means to transfer the toner image on the image carrier side to the transfer material.

The above-mentioned transfer means is more susceptible to discharge unevenness due to dirt on the discharge wire due to dust and floating toner inside the device than the transfer means using a corona discharger which is widely used in this type of device. There are various advantages such as no uneven transfer, scattering of unfixed toner, image blurring due to instability of transfer material support at the transfer site, and extremely low generation of ozone and nitrogen oxides due to high-pressure discharge. However, on the other hand, if the transfer means such as the transfer roller is contaminated with toner, it is difficult to clean it.For example, in the method of using a known blade or felt material to clean the transfer roller, etc. are flexible, so paper dust can get stuck between the cleaning material such as the blade and the transfer roller, resulting in poor cleaning and stains on the back of the transfer material. The dirt is noticeable.

The present invention has been made to deal with such a situation, and in an image forming apparatus that uses a transfer means that comes into contact with an image carrier, such as a transfer roller, the interval at which the transfer material is fed and the transfer means are adjusted. Provided is an image forming apparatus that can perform good leaning without providing a special cleaning member in the transfer means by setting the relationship between the outer periphery, the width of the nip portion between the two, and the respective speeds at the opposing portions of the two. The purpose is to

(2) Structure of the invention (technical means for solving the problem, its effects) (Description of embodiments) FIG. The image-modulated laser beam passes through a reflecting mirror 2 and is applied to an OPC photoreceptor 1 whose surface has been negatively charged in advance to about 1,700 V by a wide charger 4 and which is arranged to extend perpendicularly to the plane of the paper. After being projected, the potential of the projected part is -100 to 2
The voltage is attenuated to about 00V and an electrostatic latent image is formed.

As the photoconductor 3 rotates, when the latent image reaches a development area close to the developing device 5, toner charged to the same polarity as the latent image, that is, negative polarity, is supplied, and by reversal development, the attenuation is Toner adheres to the area and a toner image is formed.

Further, the photoconductor 3 rotates, and the toner image is transferred to the photoconductor 3.
When reaching the transfer site, which is a pressure nip between the transfer roller 6 and the transfer roller 6, the transfer material supplied from the cassette 7 is guided to the transfer site in synchronization with the toner image. A positive transfer bias having a polarity opposite to that of the toner is applied to the transfer roller 6 by the power source, and the toner image on the photoreceptor side is transferred to the transfer material.

Thereafter, the transfer material passes through a fixing section (not shown), fixes and fixes the toner image, and is then discharged from the apparatus.

After the transfer is completed, the residual toner remaining on the photoreceptor is removed by the cleaner 9, and the residual charge is removed by the discharge lamp 10, and the photoreceptor is ready for the next process.

Next, FIG. 2 shows the configuration of the transfer roller.

This will be explained with reference to Fig. 73.

The one shown in the second figure has a urethane sponge on the core bar 21,
The layer 22 has a thickness of 3 to 5011 IIl and has a volume resistance adjusted to 104 to 10' Ωcm by dispersing carbon or metal powder in a sponge such as NBR.

A bias voltage having a polarity opposite to that of the toner, which is positive in the case of the above-mentioned apparatus, is applied to such a transfer roller 6 during transfer. The applied voltage varies depending on the resistance value of the transfer roller and the process speed, but in the case of the above device, it is +5
It is determined as appropriate in the range of 00 to 4000 V, and generally a current of several μA needs to flow through the transfer roller.

The roller shown in FIG. 3 has carbon or metal powder dispersed on the outside of the core bar 21 to increase the volume resistance to 10' to 10".
An inner layer 22 with a thickness of 3 to 50 mm is made of urethane sponge, silicone sponge, NBR sponge, or even rubber with low hardness adjusted to about ΩC11,
The outside is composed of Teflon (product name), nylon,
Resin selected from polyurethane rubber, polyethylene, polyester, silicone rubber, NBR, acrylic, etc.
Preferably, it is made of a material that is charged to the opposite polarity to the toner by friction with the transfer material, and is made of a material with a thickness of 0.01 mm.
~0.3 mm and an outer layer 23 adjusted to have an insulating property with a volume resistivity of 10" Ωcm or more. In this case, for example, Teflon, polyethylene, polyester, etc. are dried to have a negative polarity, while nylon is charged to a positive polarity. In addition, since the transfer roller is placed in contact with or in close proximity to the photoreceptor, it is necessary to select a material for its surface that does not adversely affect the photoreceptor.

The bias voltage applied to the transfer roller 6 during transfer depends on the resistance value of the transfer roller and the process speed, but the bias voltage applied to the transfer roller 6 depends on the resistance value of the transfer roller and the process speed.
It is also possible to apply a superimposed alternating current of 0 to 2000 V and a frequency of 500 Hz to 3 KHz.

FIG. 4 shows the photoreceptor 3 and transfer roller 6 of the apparatus shown in FIG.
This is an enlarged view of the vicinity of the transfer site formed by contact between the photoreceptor 3 and the transfer roller 6, in which the photoreceptor 3 and the transfer roller 6 are in pressure contact to form a nip portion having a length m when viewed in the traveling direction of the transfer material. .

The photoreceptor 3 and the transfer roller 6 each have a voltage of V++ug+/sec.
.

It is assumed that the transfer roller 6 is running in the direction of the arrow at a circumferential speed of V t n+m/sec, the diameter of the transfer roller 6 is r, the circumferential length is 2, and a predetermined bias voltage is applied to the roller 6 by the power source 35. do.

The distance between the rear end of the preceding transfer material 32 and the leading edge of the adjacent and succeeding transfer material 31 is defined as d.

At the transfer site, transfer materials of various widths arrive at the photoconductor and transfer roller, so for some reason the toner supplied from the developer remains attached to the photoconductor. This toner is bound to exist on the surface of the toner, and it is also inevitable that this toner will adhere to the transfer roller, resulting in staining of the back side of the transfer material.

It has been found that the following conditions are necessary to avoid such a situation. In the illustrated device, approximately one rotation of the transfer roller ((2+ m
) is (β” m ) / V
t, and the distance the photoreceptor moves within this time is (l + m
) / V t + V note, (g + m )
The relationship between x V / V t and the transfer material spacing d is expressed as (1
2+m) XV/Vt<d.

Furthermore, as shown in the operating sequence of the device shown in FIG. While the material is not present at the transfer site, its polarity is reversed to negative so that the toner on the transfer material roller is electrostatically returned to the photoreceptor. However, in addition to toner charged to a predetermined negative polarity, there is so-called reverse fog toner, which is charged to an opposite polarity to a positive polarity, and this toner exists between the transfer material and the primary transfer material. This reverse fog toner may also adhere to the surface of the photoconductor corresponding to the area, so if a bias voltage of the same polarity as the latent image is applied to the transfer roller for too long, this reverse fog toner may adhere to the transfer roller. .

According to experiments, the time for applying a bias of the same polarity as the latent image to the transfer roller is preferably 5 to 10 rotations at the upper limit, preferably 5 rotations or less in terms of the number of times the transfer roller is rotated, that is, d<5l. It is preferable that

In addition, in the sequence shown in FIG. 5, the transfer bias is
+500 to 400 when there is a transfer material at the transfer site
0V, and when there is no transfer material at the transfer site and it is in direct contact with the photoreceptor, -1000 to +300V, preferably about -1000-OV, is suitable.

As can be seen from the above explanation, the speed of the photoreceptor 1, the transfer roller, the length of the nip portion which is the transfer site, the circumference of the transfer roller,
By setting the distance between adjacent transfer materials as (β+m)×V/Vt<cl, the transfer roller can be kept clean at all times without using a special cleaning member.

The above-mentioned phenomenon applies to toner with an average particle size of 10 to 15 μm, but fine toner with an average particle size of 4 to 8 μm, which has recently been used to improve image quality, is It is easy to adhere to the transfer roller, and once adhered, it is difficult to separate, but it has been found that the present invention is extremely effective in such cases.

FIG. 6 is an operational sequence showing another embodiment of the present invention.

In a laser beam printer, in order to keep the light intensity of the beam constant at all times, the intensity of the laser beam is corrected and controlled by turning it on between sheets of paper where there is no transfer material at the transfer site (APC: Automatic Power
Control) is being carried out.

In this APC exposure section, the photoreceptor is exposed and then developed, so as shown in the figure, when the APC exposure section reaches the development position, the alternating current component of the development bias is cut off. It is inevitable that some toner will stick to the surface.

Of course, in this case, it would be more effective if the DC component was also capped, but the rise of the voltage at that time,
Considering that the fall time is several tens of milliseconds and that the nip of the transfer roller, that is, the transfer area is about 1 to 3IIIffl, it is difficult to control as a practical matter.

Therefore, in such a case, toner will remain in the form of a streak between each sheet of paper, but by applying a voltage with the opposite polarity to that of the toner between sheets, and at the same time reducing the area d° between the APC part shown in the figure and the subsequent transfer material. , (Q+m)×V/V, <d'<5l, the toner attached to the transfer roller is
The next time it comes into contact with the photoreceptor, it can be returned to the photoreceptor.

The embodiments in which the present invention is applied to a transfer roller have been described above, but the present invention is not limited thereto, and can also be applied to a transfer roller. It is easy to understand that the present invention can also be applied to a device configured to be transferred.

(3) As described in detail, according to the present invention, the feeding of the transfer material is adjusted in an image forming apparatus such as a printer using a so-called image exposure or reversal development method that exposes the portion to which toner is to be attached. However, by changing the developing bias, there is a remarkable effect in reducing back stains, preventing image blurring and poor separation of transfer materials as much as possible, and obtaining high-quality images.

[Brief explanation of the drawing]

Fig. 1 is a side view of the main parts showing an embodiment in which the present invention is applied to a printer, Figs. 2 and 3 are sectional views showing the structure of the transfer roller, and Fig. 4 shows the vicinity of the first transfer site. An enlarged side view; FIG. 5 is a diagram showing the operation sequence of the device shown in FIG. 1; FIG. 6 is an operation sequence showing another embodiment of the present invention. 3... Photoreceptor, 6... Transfer roller. Fig. Fig. Fig. Fig. 1

Claims (3)

[Claims] (1) An image forming apparatus that is equipped with a traveling image carrier and a transfer means that travels in contact with the image carrier, and performs development by a reversal development method, and a transfer region where the image carrier and the transfer means come into contact with each other. In the case where transfer is performed by passing the transfer material continuously, the distance between adjacent transfer materials is d, the speed of the image carrier at the portion where the image carrier and the transfer means contact is V, and the speed of the transfer means is V. When the speed is V_t, the length of the abutting nip between these two as seen in the running direction of the transfer material is m, and the circumferential length of the transfer means is l, (l+m)×V/V_t<d<5l, and An image forming apparatus comprising means for applying a bias voltage having the same polarity as a latent image to a transfer means in a portion where no transfer material is present. (2) In an image forming apparatus that uses a laser beam as a light source to form an electrostatic latent image, and controls the amount of light by exposing the light source during pre-rotation or paper spacing, the distance between the exposure section and the subsequent transfer material The image forming apparatus according to claim 1, wherein d' is set to (l+m)×V/V_t<d'<5l. (3) The image forming apparatus according to claim 1 or 2, wherein the toner has an average particle size of 8 μm or less.