JPH0587828B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus, and more specifically, the present invention relates to an image forming apparatus that transfers an image on an image carrier carrying a developed image to an intermediate transfer member, and further transfers the image on the intermediate transfer member to a transfer material. The present invention relates to an image forming apparatus.

Conventionally, in image forming apparatuses such as transfer-type color electrophotographic apparatuses, which sequentially form different color images on an image bearing member such as a photoreceptor drum, and multiple-transfer each color image onto a transfer material, Various types of multiple transfer devices have been proposed.

These methods can be classified into two types: one is to wrap the transfer material around a transfer roller or transfer belt made of rubber, metal, plastic, film, etc., and apply a bias voltage to the back surface of the roller or belt to carry the image; The image on the body is sequentially transferred onto a transfer material multiple times to obtain a multicolor image on the transfer material.

The other method uses a transfer roller or a transfer belt similar to the above as an intermediate transfer member, and directly transfers the image on the image carrier multiple times in sequence onto the intermediate transfer member to form a multicolor image on the intermediate transfer member. Thereafter, the multicolor image is transferred all at once onto a final transfer material.

The former method requires means for wrapping the transfer material around a transfer roller, etc., and means for preventing the transfer material from shifting during multiple transfer steps.
For example, extremely complicated means such as a gripper device for gripping the leading edge of the transfer material and an electrostatic adsorption device for adsorbing and holding the transfer material to a transfer roller or the like are required.

In addition, in the latter method, although positional shift during multiple transfer can be easily prevented, the following problems arise.

That is, in order to obtain a uniform transferred image on the intermediate transfer drum, it was necessary to press the intermediate transfer drum against the image carrier with considerable pressure. This was also necessary to increase the transfer efficiency by widening the contact width (transfer width) between the intermediate transfer drum and the image carrier.

The necessity of the above-mentioned pressure also applies to the method of wrapping the transfer material around the transfer drum, etc., but when using an intermediate transfer drum, there is no transfer material interposed between the image carrier and the transfer drum. This is even more problematic.

Intermediate transfer drum (hereinafter simply referred to as transfer drum)
If it is made of a rigid body or a material close to it, the above-mentioned pressing force is required to be approximately 500 g/cm ² to 2000 g/cm ² , and even in this case, the contact width is around 2 mm. Moreover, even if the material is made of an elastic body such as rubber to reduce the pressure, the pressure still needs to be about 1/2 of the above amount in order to widen the contact width to some extent.

Therefore, in the center of a high-density image area, some of the toner is pressed against the image carrier by the pressure of the transfer drum and remains untransferred by the transfer electric field.
The so-called hollow phenomenon, in which the image after transfer becomes white, tends to occur.

Further, when the pressing force is high, the toner tends to stick on the transfer drum, resulting in lower transfer efficiency when re-transferring to a transfer material, and also lowering the cleanability of the surface of the transfer drum. Furthermore, when the pressing force is high, the bias voltage applied to the transfer drum tends to leak to the image carrier, which may damage the image carrier.

In view of the above problems, the present invention provides a new and excellent transfer device.

The present invention provides an image forming apparatus that sequentially superimposes and transfers a plurality of color developed images formed on an image carrier onto an intermediate carrier, and retransfers the developed image on the intermediate carrier onto a transfer material. The carrier includes a flexible sheet member that supports the transfer material, and a support member that includes a pair of cylinder members facing each other to support the flexible sheet member, and the support member includes a pair of cylinder members facing each other to support the flexible sheet member. The member and the cylinder member are fixed, and an elastic member is provided between the flexible sheet member and the cylinder member.

With the above configuration, the present invention elastically holds the image bearing surface of the transfer drum and prevents pressure on the image bearing member, for example.
100g/cm ² or less, which makes it extremely small compared to conventional devices, and the contact width with the image carrier can be made sufficiently wide, resulting in high-quality transferred images and a high transfer rate. That's what you get. Furthermore, the image bearing surface of the transfer drum has good cleaning properties.

Furthermore, the structure is simple and can be manufactured at low cost.

The details of the present invention will be explained below using specific examples with reference to the drawings. FIG. 1 is an explanatory diagram of an example in which the transfer device of the present invention is applied to a color copying machine.

In FIG. 1, reference numeral 1 denotes an electrophotographic photosensitive drum having an insulating layer on its surface, which is rotatably supported by a shaft 2, and starts rotating in the direction of an arrow 3 in response to a copy command. When the drum 1 rotates to the normal position, the original 0 placed on the original platen glass 4 is illuminated by an illumination lamp 6 integrated with the first scanning mirror 5.
The reflected light is scanned by a second scanning mirror 7. The first scanning mirror 5 and the second scanning mirror 7 move at a speed ratio of 1:1/2, so that the original is scanned while the optical path length from the original 0 to the lens 8 is always kept constant. The reflected light image above is the lens 8 and third mirror 9.
After passing through, the color is separated by a color separation filter 10 ,
An image is formed on the drum 1 by the exposure section 11.

The drum 1 is previously neutralized by a lamp 13 and a charger 14, and then charged (for example, positively) by a primary charger 15, after which the image irradiated by the illumination lamp 6 is slit-exposed in the exposure section 11. At the same time, AC or charge removal with a polarity opposite to the primary one (for example, negative) is performed using the secondary charger 16, and then the entire surface is exposed using the full-surface exposure lamp 17, thereby forming an electrostatic latent image on the drum 1.

The electrostatic latent image on the photosensitive drum 1 is then visualized as a toner image by a developing device 18 . The developing device 18 has 3 colors: yellow 18 ₁ , magenta 18 ₂ , and cyan 18 ₃
The toner image is composed of several developing devices, and the designated developing device works in accordance with the color separation filter used for exposure to obtain a toner image of the required color.

The developed image formed on the photosensitive drum 1 is charged by a pre-transfer charger 19 at the same time as the lamp 20 uniformly exposes the developed image to an alternating current or primary charge with a polarity opposite to that (for example, negative).
electrification is performed. A predetermined bias voltage is applied for each color to a grid wire provided at the opening of the pre-transfer charger 19, and the photosensitive drum 1 is charged, for example, from approximately 0V to a negative value. In the case of full-color copying, if the charge is increased, for example, to the negative side, in the order of the first color, second color, and third color, the transfer rate of each color can be made almost constant.

Next, the developed image on the photosensitive drum 1 is transferred to a first transfer corona charger 22 in a transfer drum 22 rotatably supported by a shaft 21, which will be described in detail later.
₁ onto the image bearing sheet 22 ₂ on the surface of the transfer drum 22 and are sequentially transferred to form a multicolor image. A grid wire is tightly stretched in the opening of the first transfer charger 22 ₁ in close proximity to the back surface of the image bearing sheet 22 ₂ , and the back surface of the sheet is almost completely covered by the bias voltage applied to the grid wire. It is charged to a constant potential (for example, positive). However, in the case of full color copy, the first color →
It is effective to equalize the transfer rate of each color by increasing the bias voltage applied to the grid wire in the order of transfer from the second color to the third color and increasing the charge potential on the back side of the sheet. This is not particularly necessary if the bias voltage applied to the grid wires of the filter 19 is controlled for each color.

After the transfer, the surface of the photosensitive drum 1 is cleaned by a cleaning device 12 composed of an elastic blade, and the process proceeds to the next cycle.

Next, the 1 transferred by the first transfer charger 22 ₁
The toner images of each color, second color, and third color are transferred to an AC charger 2 together with an image bearing sheet 22 ₂ .
Static electricity is removed each time by 2 ₃ and 22 ₄ . Charger 22
₃ and 22 ₄ are opposed to each other, and the phases of the AC voltages applied to the respective discharge wires are 180° different from each other, thereby enhancing the static elimination effect.

The transfer paper 25 in the cassette 24 is transferred to the paper feed roller 26.
is sent into the machine by register rollers 27, 27.
The multicolor image on the image bearing sheet 22 ₂ is transferred all at once onto the transfer paper 25 by the corona discharge action of the second transfer charger 28 at the transfer position. At this time, if the toner image has the same polarity as the toner image from the inside of the transfer drum 22 (that is, if corona discharge is performed during transfer by the second transfer charger 22 ₅ , even for a thick toner layer where two or three colors overlap), The toner can be transferred to the transfer paper extremely efficiently. Therefore, the toner in the lowest layer of the transfer drum 22 is also sufficiently transferred, and an image with good color balance can be obtained.

Furthermore, the improved transfer rate facilitates cleaning of the surface of the image bearing sheet 22 ₂ in a later step. Immediately after the transfer paper 25 is transferred and charged by the transfer charger 28, the transfer paper 25 is charged by the AC charger 29.
5 Separation and static elimination is performed on the back side, and the transfer paper is separated from the transfer drum 22 and delivered to the conveyor belt 30,
Furthermore, it is guided to a heat roller fixing device 31 coated with silicone oil, where it is pressurized and heated, and then the tray 3
It is discharged to 2.

On the other hand, on the surface of the image bearing sheet ₂₂ of the transfer drum, there is a fur brush cleaning device 2 that can freely come into contact with and separate from it.
3 comes into contact and the image bearing surface of the sheet is cleaned. A cleaning brush 22 ₆ is provided opposite to the fur brush cleaning device 23 and in contact with the back surface of the image bearing sheet 22 ₂ .
When the fur brush cleaning device 23 operates, it performs mechanical back-up and also cleans the back surface of the image bearing sheet ₂₂₂ .

It is advantageous for the fur brush cleaning device 23 and the cleaning brush 22 ₆ to be electrically conductive, since unnecessary charging will not occur on the front and back sides of the image bearing sheet 22 ₂ . However, the cleaning device 23
If an AC charger is further provided between the first transfer charger 22 ₁ and the front and back sides of the image bearing sheet 22 ₂ , charging by the cleaning device 23 and the cleaning brush 22 ₆ will occur. There is no problem.

As mentioned above, the color electrophotographic apparatus shown in FIG. 1 sequentially transfers developed images carried on the surface of the photosensitive drum 1 onto the transfer drum 22 , and transfers the obtained multicolor images all at once onto the transfer paper 25. It is equipped with a transfer device for transferring.

In the illustrated embodiment, the transfer device includes a transfer drum 22 that moves endlessly and a first transfer charger 22 ₁ that applies a transfer corona discharge from the back side of the image bearing sheet 22 ₂ of the transfer drum 22. There is. The transfer drum 22 , as shown in a perspective view in FIG.
₂ , a support member 22 ₇ that supports this film at its edge, and an elastic member 22 ₈ interposed between the edge of the film 22 ₂ and the support member 22 ₇ (see FIG. 2). It consists of the shaded part). Third
The figure shows a part of a cross section of the transfer drum 22 in the axial direction.

Plastic films such as polyester, polypropylene, and triacetate are used as the above-mentioned insulating film. The thickness is 25μ to 300μ, preferably around 100μ.

In addition, in order to prevent as much as possible transfer unevenness, toner scattering, and charge-up development on the image bearing surface due to peeling discharge that tends to occur immediately after separation from the photosensitive drum during transfer, the resistance value is 1 × 10 ⁹ Ω・cm to 1. ×10 ¹² cm relatively low resistance resin or
Film 22 ₂ of photoconductive resin such as PVK, ZnO, etc.
A better transferred image can be obtained by coating the image bearing image. The elastic member 22 ₈ that adheres the film 22 ₂ and the cylinder support member 22 ₇ is, for example, a low hardness rubber with a JIS hardness of 40 or less (urethane rubber, ethylene, propylene rubber, chloroprene rubber, NBR, natural rubber, silicone rubber). etc.) or rubber and plastic foams (foamed butyl rubber, foamed polyurethane, foamed polyethylene, foamed polystyrene, foamed vinyl chloride, etc.) are used. The thickness of the elastic member 22 ₈ is 0.5
A range of approximately 5 mm is suitable.

For example, the transfer drum of the present invention may have a drum diameter of 200 mm,
When the insulating film is made of 100 μ thick polyester film (width 340 mm) and the elastic member is made of 5 mm thick foamed butyl rubber (width 12 mm on one side), a surface potential is applied to the back side of the polyester film of the transfer drum by the first transfer charger 22 ₁ . When charged so that the voltage becomes 2000V, the pressure of the transfer drum on the photosensitive drum is approximately 10g/ ^cm2 , and the transfer width is approximately 8.
It became mm.

At this time, the first color toner image on the photosensitive drum was transferred onto the transfer drum at a transfer rate of about 90%. The second and third color toner images on the photosensitive drum were also superimposed and transferred onto the transfer drum at a transfer rate of 85% or more.

Further, the third color toner image thus formed on the transfer drum was transferred onto the transfer paper by the second transfer charger 28 and the charger ₂₂₅ at a transfer rate of about 90%. The transferred multicolor image was a high-quality image free of uneven transfer, missing areas, and positional deviation.

For comparison, the transfer drum was constructed by wrapping a 50μ thick polyester film around the surface of a conductive rubber roller with a JIS hardness of 30, and a bias voltage of 3000V was applied to the conductive rubber portion to ensure even transfer. When attempting to obtain an image, the pressure of the transfer drum against the photosensitive drum was required to be approximately 150 g/cm ² , and the transfer width in this case was approximately 6 mm.

At this time, the first color toner image on the photosensitive drum was transferred onto the transfer drum at a transfer rate of about 85%.

Further, when the third color toner image on the transfer drum was transferred all at once onto the transfer paper by corona transfer with the bias voltage of the transfer drum turned OFF, the transfer rate was about 80%. In the transferred multicolor image, the color transfer of the layer close to the surface of the transfer drum was poor in the overlapped portion of the third color, and a mixed color image with good color balance could not be obtained. In addition, uneven transfer and a phenomenon of missing parts were also observed.

In this way, since the toner is transferred onto the film supported by a pair of cylinder members, it is possible to prevent hollow spots, and by fixing the film and the cylinder member, the film does not shift in the rotational direction of the intermediate transfer drum. It is possible to prevent color misregistration of toner on the transfer drum. Further, by providing an elastic member between the film and the cylinder member, even if the film and the cylinder member are fixed, distortion of the film due to heat or long-term use can be absorbed by the elastic member.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of a color electrophotographic apparatus to which a transfer device according to the present invention is applied;
1 is a perspective view of a transfer drum used in the transfer device shown in FIG. 1, and FIG. 3 is a diagram showing a part of an axial cross section of the transfer drum. 1...Photosensitive drum, 4...Original table glass, 5...
...First scanning mirror, 6...Illumination lamp, 7...Second scanning mirror, 8...Lens, 9...Third mirror, 10 ...Color separation filter, 22 ...Transfer drum, 22 ₇ ...Support Member, 22 ₈ ...Elastic member.

Claims (1)

[Scope of Claims] 1. An image forming apparatus that sequentially superimposes and transfers developed images of a plurality of colors formed on an image carrier onto an intermediate carrier, and retransfers the developed images on the intermediate carrier onto a transfer material. In this, the intermediate carrier includes a flexible sheet member that supports the transfer material, and a support member that includes a pair of cylinder members facing each other to support the flexible sheet member, and An image forming apparatus characterized in that a flexible sheet member and the cylinder member are fixed, and an elastic member is provided between the flexible sheet member and the cylinder member.