JPH0876553A - Recording method and recording apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] When stacking toner images onto an intermediate transfer body,
To provide a recording method and a recording device capable of suppressing the occurrence of a reverse transfer phenomenon of a toner image without adding a new device or the like. A recording method and a recording apparatus for electrically transferring a toner image on a latent image bearing medium 1 onto an intermediate transfer medium 6 and recording it on a recording medium 11. Each time when the latent image carrier medium 1 is transferred to the intermediate transfer medium 6, the surface of the intermediate transfer medium is charged by the charging means 8 to the same polarity as the toner image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method and apparatus for electrically transferring a toner image developed on a latent image bearing medium onto an intermediate transfer medium and recording it on a recording medium.

[0002]

2. Description of the Related Art As a recording device, for example, an electrophotographic printer, an electrostatic latent image formed on a photoconductor is developed, and the developed toner image is sequentially electrically transferred to an intermediate transfer medium to form a plurality of laminated layers. Then, the stacked toner images are collectively fixed and recorded on a recording medium such as recording paper, for example, Japanese Patent Laid-Open No. 1-22
A color electrophotographic apparatus disclosed in Japanese Patent No. 82571 is known.

In such a conventional recording apparatus, when the toner image developed on the photosensitive member is transferred and laminated on the intermediate transfer medium, the following two conditions must be satisfied.

First, to secure a transfer electric field sufficient to electrically transfer a toner image from a photoreceptor to an intermediate transfer medium. Usually, this electric field is obtained by applying a bias voltage between the photoreceptor and the intermediate transfer medium.

Secondly, the so-called reverse transfer phenomenon in which the toner image transferred onto the intermediate transfer medium returns to the photosensitive member side when the toner image of the next color is transferred does not occur.

By the way, in the above-mentioned conventional recording apparatus, when the toner images are stacked and transferred onto the intermediate transfer medium,
By performing the static elimination processing for canceling the polarity of the previous toner image, the transferability of the subsequent toner image is improved.

This is because the toner image previously transferred to the intermediate transfer medium is charged to the same polarity as the subsequent toner image, and the potential of the surface of the intermediate transfer medium is changed to the toner by the charge of the previous toner image. This is because it is considered that the charge fluctuates in the same polarity as the charge of the image and acts in the direction of hindering the transfer of the subsequent toner image.

[0008]

The above static elimination treatment meets the first condition because it also removes the charges held by the insulating layer on the surface of the intermediate transfer medium.

However, when the charge eliminating process is performed, the charge of the toner image is reduced or the polarity is reversed, and as a result, the electrostatic attraction between the toner image and the intermediate transfer medium is reduced. Therefore, the toner image is easily separated from the intermediate transfer medium, and when the next toner image is transferred from the photoconductor to the intermediate transfer medium,
There is a problem that the previous toner image is reversely transferred to the photoconductor.

The present invention has been made in view of the above points, and suppresses the occurrence of the reverse transfer phenomenon of the toner image at the time of stack transfer of the toner image onto the intermediate transfer medium without adding a new device or the like. It is an object of the present invention to provide a recording method and an apparatus for the recording method.

[0011]

According to a recording method of the present invention for achieving the above object, a method of electrically transferring a toner image on a latent image bearing medium onto an intermediate transfer medium and recording it on the recording medium. The surface of the intermediate transfer medium is charged to the same polarity as the toner image each time the latent image bearing medium is transferred to the intermediate transfer medium.

Further, according to the recording apparatus of the present invention, the toner image on the latent image carrying medium is electrically transferred onto the intermediate transfer medium and recorded on the recording medium. The charging means is provided for charging the surface of the intermediate transfer medium to the same polarity as the toner image each time the image is transferred to the intermediate transfer medium.

Further, the recording apparatus of the present invention comprises means for forming an electrostatic latent image based on recording information on the latent image carrying medium, means for developing the electrostatic latent image, means for conveying the recording medium, and A means for fixing the transferred image to the recording medium is provided, and the surface of the intermediate transfer medium is uniformly charged to the same polarity as the toner image each time the latent image bearing medium is transferred onto the intermediate transfer medium. It is configured to include means.

Preferably, in the recording method and apparatus of the present invention, the surface of the intermediate transfer medium has a dielectric thickness of 5 μm.
The following surface insulating layer is formed.

[0015]

In the recording method and the recording apparatus of the present invention, when the toner image is transferred from the latent image bearing medium onto the intermediate transfer medium, the surface of the intermediate transfer medium is charged to the same polarity as the toner image. The electrostatic attraction between the toner image transferred onto the medium and the intermediate transfer medium is increased, and the occurrence of the reverse transfer phenomenon of the previous toner image onto the photoconductor during subsequent transfer of the toner image is reduced. .

At this time, if a dielectric layer is formed on the surface of the intermediate transfer medium, generally, the toner images transferred in layers are easily physically peeled off and the transferability onto the recording medium is improved.
Moreover, if the dielectric thickness of the surface insulating layer is 5 μm or less,
The electrostatic capacitance between the surface of the intermediate transfer medium and the conductive portion in the intermediate transfer body becomes large, and fluctuations in the potential on the surface of the intermediate transfer medium due to the accumulation of charges on the surface due to the above charging are suppressed.

As a result, when the surface of the intermediate transfer medium is charged, the transfer bias electric field of the toner image from the latent image carrier to the intermediate transfer medium is not impaired, and the toner image from the latent image carrier to the intermediate transfer medium is not impaired. Transferability is also improved.

In this case, when the dielectric thickness exceeds 5 μm, the capacitance becomes small, and the potential fluctuation due to the accumulation of electric charges on the surface is apt to increase, so that the latent image bearing medium and the intermediate transfer medium are separated from each other. It acts in the direction of reducing the applied transfer bias electric field of the toner image. Therefore, the thinner the dielectric thickness of the surface insulating layer, the better, preferably 4 μm or less, and most preferably 3 μm or less. However, if it is extremely thin, the electric field due to the above-mentioned charging increases, and dielectric breakdown easily occurs. Therefore, the limit of the preferable range on the thin side of the surface insulating layer is determined by the material forming the surface insulating layer.

Here, the dielectric thickness referred to in this specification means a value (d / ε) obtained by dividing the thickness d of the surface insulating layer formed on the surface layer of the intermediate transfer member by its relative permittivity ε.

In the present invention, the surface insulating layer is a surface layer portion formed of an insulator formed between the outermost portion which is electrically connected to the main body of the intermediate transfer medium and should have the same potential, and the surface. Point to. For example, in an intermediate transfer medium, a conductive rubber layer is provided on the surface of a metal drum, an adhesive layer made of an adhesive is laminated on the surface, and a dielectric layer made of a dielectric material such as silicone rubber is further formed on the surface of the adhesive layer. A laminate of is used. In this case, the surface insulating layer is a combination of the adhesive layer and the dielectric layer. Further, the dielectric thickness of the surface insulating layer in the case where the surface insulating layer is formed by laminating a plurality of layers of insulators as described above, is obtained as the sum of the dielectric thickness of each layer.
For example, in the case of the above layer structure, assuming that the thickness of the adhesive layer is d1, its relative permittivity is ε1, the thickness of the dielectric layer is d2, and its relative permittivity is ε2, the dielectric thickness of the surface insulating layer is d2 / ε1.
+ D2 / ε2. This is because the electrostatic capacitance between the surface of the intermediate transfer medium and the main body of the intermediate transfer medium is the same as the capacitance in the case where the two capacitors of the adhesive layer and the dielectric layer are connected in series.

Even if the surface of the intermediate transfer medium is charged to the same polarity as the toner image under such conditions of the dielectric thickness, the potential variation of the surface is small due to this charging, and the toner images are laminated on the intermediate transfer medium. Impact on

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS.

FIG. 1 shows an electrophotographic printer according to an embodiment of the recording method and apparatus of the present invention.

This electrophotographic printer comprises a latent image carrying medium 1, a first charging means 2, an exposing means 3, a developing means 4, a pre-transfer charging means 5, an intermediate transfer medium 6, a second charging means 8 and a thermal transfer means 10. The cleaning unit 13 and the charge removing unit 14 are provided, and each is configured as follows.

The latent image carrying medium 1 is an organic photoconductive drum (photosensitive drum having an organic photoconductor layer on its surface). In addition, a photosensitive drum having a photoconductive layer such as selenium or amorphous silicon on its surface can be used. In addition to the photosensitive drum, a photosensitive belt can be used.

The first charging means 2 uses a corona charger to uniformly charge the surface of the latent image carrying medium 1. Other than the corona charger, a contact charging device using a conductive roller can be used.

The exposing means 3 is a laser optical system, which exposes the surface of the latent image carrying medium 1 with light corresponding to color image information to sequentially form electrostatic latent images. LE as the exposure means
A D optical system or the like can also be used. The arrow A in the figure indicates the position of image exposure by the exposure means 3.

The developing means 4 is a liquid developing device using a known roller developing method, and is composed of four independent developing devices containing yellow, magenta, cyan, and black liquid toners. It is movable in the direction of arrow B in the figure. The developing device may have a structure of two units of black and magenta, three units of yellow, magenta, and cyan, or may have a configuration of five or more units to which another mixed color is added. The four developing units include developing rollers 41, 43, 45, 47 whose lower part is immersed in liquid toner, and diaphragms for removing excess liquid toner adhering to the latent image carrying medium 1 during development. Rollers 42, 44, 46 and 48 are provided independently of each other. As the liquid toner, a liquid carrier in which toner particles are dispersed is used.

The pre-transfer charging means 5 is a corona charger that charges the surface of the latent image carrying medium 1 together with the developed toner image to the same polarity as the charge polarity of the toner image. By this pre-transfer charging, the toner image is pressed by the electric field force, the attraction force between the latent image carrying medium 1 and the toner image is increased, and the toner image flow or thickening in the process of transferring the toner image to the intermediate transfer medium 6 is prevented. suppress. At the same time, the surface of the latent image carrying medium 1 is charged to the same polarity as the toner image, and as a result, it also acts as a transfer bias to the intermediate transfer member.

As shown in FIG. 2, the intermediate transfer medium 6 includes a metal drum 6a made of, for example, aluminum or stainless steel, a conductive rubber layer 6b, an adhesive layer 6c made of an insulating material, and a dielectric layer 6d. The layers are formed in order. Here, the rubber layer 6b is a layer that exhibits a function of improving the adhesion to the latent image bearing medium 1, and there is no particular limitation on the material as long as it can exhibit this function. Examples of the material of the rubber layer 6b include fluororubber, silicone rubber,
Ethylene propylene rubber, nitrile rubber, butyl rubber,
Acrylic rubber etc. can be used. In addition, the surface dielectric layer 6
d is not particularly limited in terms of material as long as the transferability of the color images transferred in layers onto a recording medium such as recording paper is good.
For example, materials such as silicone, tetrafluoroethylene and vinylidene fluoride are used. A bias voltage having a polarity opposite to that of the toner particles is applied to the intermediate transfer medium 6 by an application unit (not shown) that applies a transfer bias. The intermediate transfer medium 6 may have an appropriate diameter depending on the size of the recording medium. Further, as the intermediate transfer medium 6, a transfer belt can be used instead of the roller. The adhesive layer 6c is not always necessary when the rubber layer 6b and the dielectric layer 6d have high adhesion. In this embodiment, the surface insulating layer has, for example, a dielectric layer 6d (thickness: 3 μm) made of silicone rubber (thickness: 3 μm) and a surface insulating layer configured to use an adhesive layer (thickness: 1 μm) having a relative dielectric constant of 4. .
In this case, the dielectric thickness is 1.25 μm.

Each time the toner image is transferred from the latent image carrier medium 1 to the intermediate transfer medium 6, the second charging means 8 uniformly charges the surface of the intermediate transfer medium 6 to the same polarity as the transferred toner image. What is processed, for example, a corona charger is used. Since the dielectric thickness of the surface insulating layer of the intermediate transfer medium 6 is suppressed to 5 μm or less, even if electric charges are accumulated on the surface of the dielectric layer 6d due to such charging, the surface potential does not greatly change. When a scorotron type corona charger having a grid is used as the second charging means 8,
By controlling the grid voltage, the fluctuation of the surface potential of the intermediate transfer medium 6 can be further suppressed, which is preferable.

Further, since the surface of the latent image carrying medium 1 is charged to the same polarity as the toner image by the pre-transfer charging means 5, a repulsive force acts between the latent image carrying medium 1 and the toner image on the intermediate transfer medium 6 to cause reverse transfer. Can be further suppressed.

The thermal transfer means 10 is a roller incorporated in a heater (not shown), and is pressed against the intermediate transfer medium 6 by a pressing mechanism (not shown), and a color toner image is transferred and laminated on the intermediate transfer medium 6. Is heated and pressed to transfer it onto the recording medium 11.

Here, the pressing mechanism is the latent image carrier medium 1.
Therefore, when the toner image is transferred to the intermediate transfer medium 6, the thermal transfer means 10 is separated from the intermediate transfer medium 6. Then, the heat fixing unit 10 is pressed against the intermediate transfer medium 6 by a predetermined pressing force by the pressing mechanism by the time the final toner image transferred portion of the four types of toner images arrives. As a result, the thermal transfer means 10 heats and pressurizes the color toner images laminated and transferred onto the intermediate transfer medium 6,
The four types of toner images are transferred onto the recording medium 11 supplied from the conveying unit 12 at once.

The cleaning means 13 is provided with a sponge roller (not shown) and a cleaning blade (not shown) in the cartridge. When the cartridge is mounted on the recording apparatus, the sponge roller and the cleaning blade carry a latent image. Contact the medium 1. The cleaning unit 13 scrapes off the toner image and the liquid toner remaining on the latent image carrying medium 1 after the transfer to the intermediate transfer medium 6 by the sponge roller or the cleaning blade. As a result, the latent image bearing medium 1 is cleaned.

The static eliminating means 14 is a tungsten lamp or L
By exposing the entire surface of the latent image bearing medium 1 with an ED array or the like, residual charges on the latent image bearing medium 1 are removed.

In FIG. 1, reference numeral 9 is the recording medium 1.
1 is a preheater that preheats the color toner image transferred onto the image forming apparatus 1 to improve transferability.

The recording apparatus constructed as described above forms a color image by the following recording method.

In the recording apparatus, first, the latent image bearing medium 1 rotates in the direction of the arrow in the figure, and the surface of the latent image bearing medium 1 is uniformly charged by the first charging means 2.

Next, the yellow image information to be visualized first is written on the latent image carrying medium 1 by the exposing means 3.

The electrostatic latent image thus obtained is developed by the developing device of the developing means 4 with the yellow liquid toner. The development is performed by rotating the developing roller 41 whose lower part is immersed in the yellow liquid toner and supplying the liquid toner to the latent image carrying medium 1. Excess liquid toner attached to the latent image bearing medium 1 by this development is removed by the aperture roller 42. The developing rollers 43, 45, 47 and the squeezing roller 4 provided in the developing device containing the liquid toner of another color.
4, 46 and 48 also operate in the same manner when the developing operation is performed using the developing device.

Then, the pre-transfer charging means 5 charges the surface of the electrostatic latent image carrying medium 1 together with the developed yellow toner image. By this charging, the electrostatic attraction force of the toner image to the latent image carrying medium 1 is increased, and the flow and thickening of the image in the transfer step of transferring the toner image to the intermediate transfer medium 6 are suppressed.

The obtained yellow toner image is transferred onto the intermediate transfer medium 6 by applying a transfer bias voltage having a polarity opposite to the charge polarity of the toner image from the back surface of the intermediate transfer medium 6. When the yellow toner image is transferred onto the intermediate transfer medium 6 in this way, the surface of the intermediate transfer medium 6 is uniformly charged with the same polarity as the transferred toner image by the second charging means 8. .

By this charging process, the yellow toner image transferred onto the intermediate transfer medium 6 has an increased electrostatic attraction between the yellow toner image and the intermediate transfer medium 6, and a reverse transfer phenomenon occurs when the magenta toner image is subsequently transferred. Is reduced.

Moreover, in the intermediate transfer medium 6, the surface insulating layer composed of the adhesive layer 6c and the dielectric layer 6d has a dielectric thickness of 5 μm.
Since it is as follows, even if charges are accumulated in the dielectric layer 6d, the fluctuation of the surface potential is suppressed. As a result, the reverse transfer of the yellow toner image is further suppressed, and the transferability of the magenta toner image from the latent image carrying medium 1 to the intermediate transfer medium 6 is improved.

After the yellow toner image is transferred onto the intermediate transfer medium 6, the latent image carrying medium 1 has the liquid toner and the residual charge remaining on the surface thereof removed by the cleaning unit 13 and the charge eliminating unit 14.

Next, after the surface of the latent image bearing medium 1 is uniformly charged again by the first charging means 2, this time, magenta image information to be visualized second is written.

The magenta electrostatic latent image thus obtained is developed by a developing device containing magenta liquid toner in the developing means 4 to remove excess liquid toner on the latent image carrying medium 1. After that, charging is performed by the pre-transfer charging unit 5.

The magenta toner image on the latent image bearing medium 1 thus obtained is transferred onto the intermediate transfer medium 6 onto which the yellow toner image has already been transferred.

Thereafter, by the same process, after the cyan toner image is layer-transferred onto the intermediate transfer medium 6, the black toner image is finally layer-transferred. Here, it goes without saying that when the toner images are stacked and transferred to the intermediate transfer medium 6, the registration of the superposition is performed.

After the color toner images of four colors are laminated on the intermediate transfer medium 6 in this way, the thermal transfer means 10 is pressed against the intermediate transfer medium 6 by the pressing mechanism.
The recording medium 11 conveyed from the conveying unit 12 is sandwiched between the thermal transfer unit 10 and the intermediate transfer medium 6, and the color toner images formed in layers are transferred onto the recording medium 11.

Here, each toner image is transferred from the latent image carrier medium 1 to the intermediate transfer medium 6, and the surface of the intermediate transfer medium 6 is transferred.
A comparison was made between the method of the present invention in which the transferred toner image is uniformly charged to the same polarity and the conventional method in which the surface of the intermediate transfer medium is discharged.

For comparison, yellow 100 is obtained by each method.
%, Magenta 100%, and cyan 100%, three-color toner images are superimposed, so-called process black is printed, and the reflection density thereof is measured, and unevenness is visually observed. The dielectric thickness of the surface insulating layer of the intermediate transfer medium 6 at this time was 1.25 μm according to the above-mentioned configuration.

As a result, in the process black printed by the method of the present invention, the reflection density was 1.8 and even printing was possible, whereas in the process black printed by the conventional method, the color superimposition was not good and there was unevenness. The reflection density was 0.4, which was yellowish brown which was not black.

The transfer rate was measured by changing the dielectric thickness of the dielectric layer 6d while fixing the thickness of the adhesive layer 6c on the surface of the intermediate transfer medium 6. The transfer rate was measured by the following series of procedures.

That is, the recording device is stopped during the transfer of the toner image from the latent image carrying medium 1 to the intermediate transfer medium 6, and the toner image on the intermediate transfer medium 6 and the residual toner immediately after the transfer on the latent image carrying medium 1 are transferred. Each of the images was dried with warm air.

Next, the toner images on the latent image bearing medium 1 and the intermediate transfer medium 6 were peeled off with an adhesive tape and stuck on a white paper, and the toner images were measured with a reflection densitometer.

The density of the toner image on the intermediate transfer medium 6 is a, the density of the residual toner image on the latent image carrying medium 1 immediately after the transfer is b, and a / (a + b) is the transfer rate.

As a result, the transfer rate of the toner image in magenta was 85% when the dielectric thickness of the surface insulating layer of the intermediate transfer medium 6 was 3 μm, whereas it was 70% and 10 μm when it was 5 μm. If it exceeds, it will be less than 50%.

As described above, according to the recording method of the present invention, it has been found that a good toner image can be obtained without any influence on the laminated formation of the toner image on the intermediate transfer medium 6. . Preferably, by setting the dielectric thickness of the surface insulating layer of the intermediate transfer medium 6 to 5 μm or less, a good transfer rate can be obtained.

[0061]

As is apparent from the above description, according to the recording method and apparatus of the present invention, when the toner images are laminated and transferred onto the intermediate transfer medium, the surface of the intermediate transfer medium is replaced with the static elimination which has been conventionally performed. By charging the toner image with the same polarity as that of the toner image, the electrostatic attraction between the toner image transferred onto the intermediate transfer medium and the intermediate transfer medium is increased, and the toner image is transferred without adding a new device or the like. It has an excellent effect that the occurrence of the reverse transfer phenomenon can be suppressed.

At this time, if a dielectric layer is formed on the surface of the intermediate transfer medium, the toner images transferred in layers are easily physically separated, and the transferability to the recording medium is improved. Moreover,
When the dielectric thickness of the surface insulator layer is 5 μm or less, the fluctuation of the surface potential of the intermediate transfer medium in the direction of the same polarity as the toner image is suppressed even if charges are accumulated on the surface of the intermediate transfer body. As a result, when the surface of the intermediate transfer medium is charged, the transferability of the toner image from the latent image bearing medium to the intermediate transfer medium is improved.

[Brief description of drawings]

FIG. 1 is a front view of an electrophotographic printer showing an embodiment of a recording method and apparatus of the present invention.

FIG. 2 is a sectional view partially showing a structure of an intermediate transfer medium.

[Explanation of symbols]

 1: Latent image carrying medium 2: First charging means 3: Exposure means 4: Developing means 5: Pre-transfer charging means 6: Intermediate transfer medium 6a: Metal drum 6b: Rubber layer 6c: Adhesive layer 6d: Dielectric layer 8: Second charging means (intermediate transfer medium) 9: Preheater 10: Thermal transfer means 11: Recording medium 12: Conveying means 13: Cleaning means 14: Charge removing means 41: Developing roller 42: Aperture roller 43: Developing roller 45: Developing roller 47 : Developing roller 44: Aperture roller 46: Aperture roller 48: Aperture roller

Claims (5)

[Claims] 1. A method of electrically transferring a toner image on a latent image bearing medium onto an intermediate transfer medium and recording the image on a recording medium, wherein each time the transfer from the latent image bearing medium to the intermediate transfer medium is performed. A recording method, wherein the surface of the intermediate transfer medium is charged to the same polarity as the toner image. 2. The intermediate transfer medium has a dielectric thickness of 5
2. The recording method according to claim 1, wherein a recording layer having a surface insulating layer of .mu.m or less is used. 3. A device for electrically transferring a toner image on a latent image bearing medium onto an intermediate transfer medium and recording the image on a recording medium, wherein the latent image bearing medium is transferred to the intermediate transfer medium every time. A recording apparatus comprising a charging unit that charges the surface of the intermediate transfer medium to the same polarity as the toner image. 4. An apparatus for electrically transferring a toner image on a latent image bearing medium onto an intermediate transfer medium and recording it on a recording medium, the electrostatic latent image based on recording information on the latent image bearing medium. A means for forming an electrostatic latent image, a means for developing the electrostatic latent image, a means for transporting the recording medium, and a means for fixing the transfer image on the recording medium, and A recording apparatus comprising means for uniformly charging the surface of the intermediate transfer medium to the same polarity as that of the toner image each time it is transferred. 5. The recording apparatus according to claim 3, wherein the intermediate transfer medium has a surface insulating layer having a dielectric thickness of 5 μm or less formed on the surface thereof.