JPH03214174A - Electrostatic printing method and electrostatic printing device - Google Patents

Abstract

PURPOSE:To effectively carry out selection between color printing and monochromatic printing by sequencially transferring and superimposing monochromatic toner images of different colors sequencially formed on a toner image carrier to an intermediate transfer body at a time of color printing and by directly transferring a monochromatic toner image on the toner image carrier to a recording body at a time of monochromatic printing. CONSTITUTION:The color toner image is formed on the intermediate transfer body 85 by sequencially transferring and superimposing the monochromatic toner images of different colors sequencially formed on a toner image carrier 40 to the intermediate transfer body 85 in the color printing. After that, this color toner image is transferred to the recording body 84 to obtain a color printed matter. In the monochromatic printing, the monochrome toner image on the toner image carrier 40 is transferred to the recording body 84 to obtain a monochromatic printed matter. Thus, the effective selection between color printing and monochromatic printing can be carried out.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) This invention is a method for transferring a toner image formed on a toner image carrier onto plain paper according to recorded information such as characters and images. Relating to electrostatic printing methods and electrostatic printing devices for obtaining printed images,
In particular, the present invention relates to an electrostatic printing method and an electrostatic printing apparatus that selectively perform color printing and monochrome printing.

(Prior Art) As information processing and communication networks become more sophisticated, the demand for color hard copies is increasing. Color printers that output color hard copies can be roughly divided into those that mainly output full-color hard copies, such as full-color photographs, printed matter, or color computer graphics, and those that output both monochrome or color hard copies at any time. Color devices are now being introduced in business offices, which are a large market for notebook devices, and in addition to single-color output with recording quality equal to or better than conventional single-color copiers and single-color laser printers, high-quality color output is now possible. requested. Recording methods for color printers include electrophotographic recording, thermal transfer recording, and inkjet recording, but the electrophotographic recording method is superior in terms of high-speed recording performance and high image quality.

FIG. 7 shows an example of a conventional apparatus using a color electrophotographic method. This device consists of a part that generates a monochrome toner image in response to an image signal, and a part that transfers the monochrome toner image onto recording paper to form a full-color toner image.

First, in the case of full-color printing, a photosensitive layer (not shown) of a photosensitive drum 1 is uniformly charged by a charging corona charger 2.

A laser beam scanning system 3 scans and exposes the photosensitive layer with a laser beam 4 in accordance with a recording signal corresponding to a yellow toner image, thereby forming an electrostatic latent image. The electrostatic latent image is reversely developed by a yellow toner two-component magnetic brush developer 5 to form a yellow toner image.

At this time, the magnetic brushes of other developing devices are separated from the photosensitive layer. The yellow toner image is transferred onto a recording paper (not shown) wrapped around a transfer sleeve 6 by a transfer corona charger 7 that generates corona ions of opposite polarity to the toner image. After the toner image has been transferred to the recording paper, the photosensitive layer is reused after the remaining toner is removed by a blade cleaner 8.

Next, in the same process as before, a magenta toner image is formed by the magenta toner two-component magnetic brush developer 9 in accordance with the recording signal corresponding to the magenta toner image. This magenta toner image is transferred onto the recording paper in a superimposed manner on the yellow toner image previously transferred. Similarly, a cyan toner image formed by the cyan toner two-component magnetic brush developing device 10 in accordance with a recording signal corresponding to the cyan toner image is superimposed on the yellow toner image and magenta toner image that have been previously transferred onto the recording paper. Copy them together. Further, if necessary, a black toner image formed by the two-component magnetic brush developing device 11 for black toner is superimposed and transferred in accordance with a recording signal corresponding to the black toner image.

The recording paper on which the completed color toner image has been formed is separated from the transfer sleeve 6 by the peeling charger 12 and the recording paper separation claw 13, and the color toner image on the recording paper is
The image is fixed on the recording paper by the fixing device 14.

In the case of monochrome printing, after transferring one toner image to the recording paper,
The recording paper is immediately peeled off and the toner image is fixed.

In the apparatus shown in FIG. 7, in order to wrap and fix the recording paper around the transfer sleeve 6, a "gripping margin" for the recording paper is required, and a portion where recording cannot be performed occurs at the leading edge and both ends of the recording paper. In addition, in the case of "stiff" or small-sized recording paper, the recording paper may not be sufficiently fixed to the transfer sleeve 6, resulting in image quality deterioration such as color shift and toner falling.
The range of recording paper that can be used is limited.

FIG. 8 shows another example of a conventional apparatus using a color electrophotographic method. This device consists of a part that generates a monochrome toner image in response to an image signal, a part that forms a color toner image by superimposing and transferring the monochrome toner image onto a transfer belt, and a part that transfers the color toner image onto recording paper. to form a full-color toner image.

The case of full color printing will be explained. Photosensitive belt 2
0 photosensitive layer (not shown) is a charged corona charger 21
is uniformly charged.

A laser beam scanning system 22 scans and exposes the photosensitive layer with a laser beam 23 in accordance with a recording signal corresponding to a yellow toner image.
Forms an electrostatic latent image. The electrostatic latent image is reversely developed by a yellow toner two-component magnetic brush developer 24 to form a yellow toner image. At this time, the magnetic brushes of other developing devices are separated from the photosensitive layer. The yellow toner image is transferred to the transfer belt 25. After the toner image has been transferred to the transfer belt 25, the photosensitive layer is reused after the remaining toner is removed by a blade cleaner 26.

Next, in the same process as before, a magenta toner image is formed by the magenta toner two-component magnetic brush developer 27 according to the recording signal corresponding to the magenta toner image, and the magenta toner image is first transferred to the transfer belt 25. The yellow toner image is superimposed and transferred. Similarly, a cyan toner image formed by the cyan toner two-component magnetic brush developer 28 in accordance with a recording signal corresponding to the cyan toner image is superimposed on the yellow toner image and magenta toner image previously transferred to the transfer belt 25. Copy them together. Further, if necessary, a black toner image formed by a two-component magnetic brush developer for black toner is superimposed and transferred in accordance with a recording signal corresponding to the black toner image. The completed color toner image is transferred to a recording paper 30 and fixed by a fixing device 31. The transfer belt 25 to which the color toner image has been transferred is reused after the toner remaining after transfer is removed by a blade cleaner 32.

In the case of monochrome printing, as in the case of full-color printing, one toner image is transferred to the transfer belt 25 and further transferred to recording paper, and then the toner image is fixed.

In the apparatus shown in FIG. 8, since the recording paper is not fixed to the transfer belt 25, the problems encountered in the conventional apparatus shown in FIG. 7 do not occur. However, even in monochrome printing where character images that require sharp edges are often recorded, the toner image is transferred from the photosensitive layer of the photosensitive belt 20 to the transfer belt 25, and from the transfer belt 25 to the recording paper. Since it is necessary to perform the transfer twice, it becomes difficult to obtain a character image with sharp edges.

In addition, in the process of transferring a toner image from an intermediate transfer body to recording paper, conventional equipment uses a corona charger transfer device as a transfer means and applies corona ions directly to the recording paper, but in a high humidity environment, leakage of corona ions may occur. There was a problem that the transfer efficiency was significantly reduced and the image quality was deteriorated.

(Problems to be Solved by the Invention) As mentioned above, in the first conventional device, in order to wrap and fix the recording paper around the transfer sleeve, a "grasp" of the recording paper is required, and the leading edge of the recording paper and Not only will there be areas on both ends that cannot be recorded, but if the recording paper is "stiff" or small in size, it will not be secured properly to the transfer sleeve, resulting in deterioration of image quality such as color shift and toner dropping. Therefore, there is a problem that the range of usable recording paper is limited.

The second conventional device does not have the problem of the first conventional device because the recording paper is not fixed to the transfer belt, but it does not have the problem of recording character images that require sharp edges. Even in monochrome printing, which is often the case, the toner image transfer process is required twice, making it difficult to obtain character images with sharp edges.

In addition, if a corona charger transfer device is used to transfer the toner image from an intermediate transfer body to recording paper, corona ions will act directly on the recording paper, so the transfer efficiency will significantly decrease due to leakage of corona ions in a high humidity environment. However, there is a problem that image quality deteriorates.

This invention was made in view of the above-mentioned problems, and its purpose is to eliminate the need to fix the recording medium to an intermediate transfer body, to obtain high-quality images in color printing, and to provide sharp edges in monochrome printing. An object of the present invention is to provide an electrostatic printing method and an electrostatic printing device that can obtain a character image.

Another object of the present invention is to provide an electrostatic printing device that can transfer a toner image to both an intermediate transfer member and recording paper using one transfer means.

Still another object of the second invention is to provide an electrostatic printing device that can prevent corona ions from directly acting on a recording medium even when a corona charger transfer device is used, thereby increasing transfer efficiency and obtaining high-quality images. It's about doing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned problems, the present invention, in color printing, sequentially forms monochromatic toner images of different colors on a toner image carrier and sequentially transfers them to an intermediate transfer member. After a color toner image is formed on an intermediate transfer member by transferring and overlapping, this color toner image is transferred to a recording member to obtain a color printed matter.In monochrome printing, a monochrome toner image on a toner image carrier is is transferred to a recording medium to obtain a monochrome printed matter.

According to one embodiment, the electrostatic printing device of the present invention selectively performs color printing and single-color printing based on such a method, in which a toner carrying a toner image obtained by developing an electrostatic latent image is used. an image carrier, an intermediate transfer member having a portion facing the toner image carrier, a first transfer means for directly transferring the toner image on the toner image carrier to a recording member, and The apparatus includes a second transfer means that transfers the toner image onto the intermediate transfer member, and a third transfer means that transfers the toner image on the intermediate transfer member onto the recording member.

According to another aspect, the operation of transferring the toner image on the toner image carrier to the intermediate transfer body, and the operation of transferring the toner image on the toner image carrier to the intermediate transfer body, with a part of the front surface facing the toner image carrier, are performed. One type of transfer that selectively performs the operation of transferring the toner image of 1 to a recording medium inserted between the toner image bearing member and the intermediate transfer member, and the operation of directly transferring the toner image on the toner image bearing member to the recording medium. Means are provided.

When this common transfer means is, for example, a corona charger transfer device, first and second power supplies with different polarities and a switching means are provided to selectively switch between them, and the toner image on the toner image carrier is intermediately transferred. In the case of transferring the toner image to a recording medium inserted between the toner image carrier and the intermediate transfer body, the first power source is connected to the transfer means, and the toner image on the intermediate transfer body is transferred to the recording body. The transfer means has a second
The configuration is such that the power supply is connected.

(Function) In the electrostatic printing method and apparatus according to the present invention, a recorded matter can be obtained in a recording process with a smaller number of steps in monochrome printing than in color printing. Specifically, the toner transfer process is performed once during monochrome printing and twice during full-color printing. Therefore, the edge sharpness of character images, which is particularly important in monochrome printing, is improved.

In addition, in the case of monochrome printing, the toner image is directly transferred to the recording medium, and even in the case of color printing, the toner images of each color are superimposed on the intermediate transfer body and then transferred to the recording body, so the recording medium is transferred to the intermediate transfer body. There is no need to fix it on the transfer body. Therefore,
The areas on the edges of the recording paper that cannot be recorded are reduced, and there is no need to consider image quality deterioration such as color shift or toner drop due to insufficient fixation to the transfer sleeve, and there is a high degree of freedom in the recording paper that can be used.

Furthermore, a recording body is inserted between the toner image bearing member and the intermediate transfer body, and a toner image is transferred from the toner image bearing body or the intermediate transfer body to the recording body by one transfer means provided on the back surface of the intermediate transfer body, or If the toner image is transferred from the toner image carrier to the intermediate transfer member, even if a corona charger transfer device is used as the transfer means, since the intermediate transfer member is located between the recording paper and the corona charger transfer device, the recording paper Corona ions do not act directly on This increases transfer efficiency,
High quality images can be obtained.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a laser printer which is a first embodiment of an electrostatic recording apparatus according to the present invention. This electrostatic recording device is
The configuration of the transfer station that transfers the toner image onto recording paper differs between color printing and monochrome printing. A corona charger 41, a two-component magnetic brush developer 42 for black toner, yellow toner, and magenta toner are arranged around a photosensitive drum 40 whose photosensitive layer (not shown) is an organic photoreceptor serving as a toner image carrier. Two-component magnetic brush developers 43, 44 and 45 for cyan toner, a corona charger transfer device 46 as a first transfer means, and a cleaner 47 are provided along the rotational direction of the photosensitive drum 40. A laser beam scanning system 48 scans the photosensitive drum 4 with a laser beam 49.
This is only for scanning and exposing 0.

Adjacent to the photosensitive drum 40, there is a transfer drum 50 as an intermediate transfer member, in which a polyester film is suspended in the form of a sleeve.
is installed. The circumference of this transfer drum 50 is A3
It is set slightly longer than the vertical length of the size. A corona charger transfer device 51 as a second transfer means and a pair of corona charger static eliminators 52 are arranged inside the transfer drum 50 (Ill), and a far plan cleaner 53 and a conductive elastic A roller transfer device 54 serving as a third transfer means including a roller is arranged.The fixing device 55 is constituted by a pair of heat rollers in this example.

The cassettes 56 and 66, which are recording medium holding means, hold special paper 57, which is recording paper for full-color printing with good surface smoothness, and plain paper 67, which is recording paper for monochrome printing, respectively. There is.

First, the recording operation during color printing will be explained. First, the photosensitive layer of the photosensitive drum 40 is connected to the corona charger 4
1, it is uniformly charged to -600V. Next, a laser beam 49 modulated according to yellow image information supplied from an image information source (not shown) is transmitted by a laser beam scanning system 48 to a uniformly charged photosensitive drum 40 that is transported by rotation. The layer is scanned and exposed to reduce the surface potential of the exposed areas to -150 cm to form a yellow electrostatic latent image. This electrostatic latent image is reversely developed by a two-component magnetic brush developer 43 using negative polarity yellow toner to form a yellow toner image. At this time, the magnetic brushes of other developing devices are separated from the photosensitive layer. Photosensitive drum 40
The yellow toner image formed on the photosensitive layer is transferred to the transfer drum 50 at a position facing the corona charger transfer device 51. That is, positive polarity corona ions generated from the corona charger transfer device 51 accumulate on the side of the polyester film of the transfer drum 50 that faces the corona charger transfer device 51, and the toner image is transferred to the photosensitive layer by the electrostatic force generated by the corona ions. transferred to polyester film. At this time, the fur brush of the cleaner 53 and the roller of the roller transfer device 54 are operated until the completed color toner image is transferred from the polyester film of the transfer drum 50 to the recording paper so as not to scrape off the transferred toner image. Alternatively, they are separated until each color toner image is transferred. The photosensitive layer after the toner image is transferred is a clear layer.
After the remaining toner after transfer is removed by a step 47, the toner is reused.

Subsequently, in the same process as before, a magenta toner image is formed by the magenta toner two-component magnetic brush developer 44 in response to the recording signal corresponding to the magenta toner image. Similarly to the yellow toner image, the magenta toner image is also transferred onto the transfer drum 50 so as to be superimposed on the yellow toner image previously transferred. Similarly, the cyan toner image is formed by the cyan toner two-component magnetic brush developing device 45 in accordance with the recording signal corresponding to the cyan toner image, and the yellow toner image and magenta toner image that have been previously transferred to the transfer drum 50 are The images are superimposed and transferred. Further, if necessary, a black toner image formed by the two-component magnetic brush developing device 42 of black toner is superimposed and transferred in accordance with a recording signal corresponding to the black toner image. In this device, the black toner image is formed and transferred last.

Since the distance between the back surface of the polyester film of the transfer drum 50, which is a transfer electrode, and the toner image to be transferred increases depending on the number of times the toner images are superimposed, the distance between the transferred toner image and the corona charger 5 increases.
The corona ion generation voltage of No. 1 needs to be set higher in sequence.

After the color toner image is completed on the transfer drum 50, full-color printing paper 57, which has a smoother surface than the cassette 56, is transferred.
is conveyed to a transfer station consisting of a roller transfer device 54. The color toner image on the transfer drum 50 is then transferred onto a special paper 57 by a roller transfer device 54.

Next, using FIG. 2, the roller transfer device 54 in FIG.
The structure and transfer operation of this will be explained.

The roller transfer device 54 includes a transfer roller 58 and a power source 59 that supplies a transfer voltage. The transfer roller 58 has a flexible resistance layer 60. It consists of a conductive layer 61, a deformable elastic layer 62, and a metal shaft 63.

The metal shaft 63 and the conductive layer 61 are electrically connected by making a part of the elastic layer 62 conductive. As the transfer drum 50 rotates, the color toner image 64 is conveyed to a toner transfer section (B-C section), and the color toner image 64 is pressed against a recording paper (special paper) 57 at this toner transfer section.

A transfer voltage (+1.5 kV) having a polarity opposite to that of the toner is supplied to the metal shaft 63 from a power source 59, and the same potential is applied to the conductive layer 61 and the resistive layer 60.

The color toner image 64 is transferred to the recording paper 57 by the electrostatic force acting between the resistive layer 60 and the grounded conductive back roller 65 . In the toner transfer section, the elastic layer 6 of the transfer roller 58 can
Due to the elastic deformation of 2, the transfer pressure is also kept almost constant. As a result, "hollow spots" in the toner image that tend to occur with roller transfer devices (development where the toner in the center of the toner image is reversely transferred)
No image deterioration occurs.

An example of such a transfer device is Japanese Patent Application No. 104080/1983. In this transfer device, a resistive layer 60 and a conductive back roller 6
Since the toner is transferred by the electrostatic field that acts between the
It is not affected by the hygroscopicity of recording paper. Therefore, high temperature and humidity (35℃-80%R,) 1. ) Even in the environment, at room temperature,
The same transfer efficiency as in a normal humidity (20° C.-60% R5H) environment can be obtained. The color toner image 64 transferred to the recording paper 57 is fixed by a fixing device 55, and then the paper is discharged. The surface charge of the polyester film to which the color toner image has been transferred is removed by a pair of corona charger static eliminators 52 that generate corona ions of both positive and negative polarities, and the remaining toner after transfer is removed by a fur brush cleaner 53 for reuse. .

Next, the recording operation during monochrome printing will be explained. The photosensitive layer of the photosensitive drum 40 is uniformly charged to, for example, -600V by a corona charger 41. The laser beam 49 is modulated according to monochromatic image information supplied from an image information source (not shown), and scans the uniformly charged photosensitive layer transported by the rotation of the photosensitive drum 40 by the laser beam scanning system 48. Expose. This lowers the surface potential of the exposed area to -150V, forming a monochromatic electrostatic latent image. The electrostatic latent image is reversely developed by a two-component magnetic brush developer 42 using monochrome toner of negative polarity to form a monochrome toner image. At this time, the magnetic brushes of the other developing devices 43 to 45 are separated from the photosensitive layer.

In this electrostatic printing device, the monochrome developer 42 is placed at the beginning of each developer in the rotational direction of the photosensitive drum 40; If placed last, the magnetic brushes of other developers may be in contact with the photosensitive layer. By controlling the timing, the leading edge of the monochromatic toner image reaches the transfer station of the corona charger transfer device 46.
6 feeds recording paper (plain paper) 67 to the transfer station of the corona charger transfer device 46. The monochrome toner image is transferred onto recording paper 67 at a position facing corona charger transfer device 46 . Positive corona ions generated from the corona charger transfer device 46 to which a DC voltage plus 8 kV is applied as the corona generation voltage accumulate on the side of the recording paper 67 facing the corona charger transfer device 46, and the electrostatic force generated by the corona ions As a result, the toner image on the photosensitive layer is transferred to recording paper (plain paper) 67. After the transfer, the recording paper 67 is conveyed to the fixing device 55 to fix the monochrome toner image thereon, and then is discharged.

As is clear from the above description, in the case of color printing in the electrostatic printing apparatus of this embodiment, the recording paper 57 is transferred to the transfer drum 50.
Since there is no need to fix the image to the printer, there are no unrecordable areas at the edges, and there is no need to consider image quality deterioration such as color shift or toner drop, allowing full-color printing with good reproducibility that is safe in humid environments. . In this case, the recording paper 57 is a special paper, but it may also be a "strong" one or a small one, and there is a wide range of usable recording papers.

In addition, in the case of monochrome printing, since the toner image is directly transferred from the photosensitive drum to the plain paper, in addition to the same effect as color printing, it has the advantage of being able to record images with sharp edges, especially for text images. .

Furthermore, in this embodiment, recording paper 57, 67 (dedicated paper and plain paper) suitable for each color printing and monochrome printing is automatically supplied, so that high-quality images can always be printed.

Next, a second embodiment of the electrostatic printing apparatus according to the present invention will be described with reference to FIG. This embodiment differs from the embodiment shown in FIG. 1 in that the recording paper is supplied between the toner carrier and the intermediate transfer member. A photosensitive drum 40 serving as a toner image carrier, a corona charger 41, and a two-component magnetic brush developer 42 for black toner are the same as those shown in FIG. As a developing device for yellow toner, magenta toner, and cyan toner, -component non-contact developing device 70.7
1 and 72 are used. In addition, in this embodiment, the first. In place of the second and third transfer means, corona charge transfer devices 46, 51 and roller transfer device 54, a corona charge transfer device 73 is used as a common transfer device. A blade cleaner 74 and a static elimination lamp 75 are further provided around the photosensitive drum 40. The laser beam scanning system 76 irradiates the photosensitive drum 40 with a laser beam 77 to perform scanning exposure.

A transfer belt 78 made of a polyester film as an intermediate transfer body is provided with a part of the front surface facing the photosensitive drum 40, and the above-mentioned corona charger transfer device 73 is disposed on the back surface of the transfer belt 78. The circumferential length of the transfer belt 78 is slightly longer than the vertical length of an A3 size sheet. The corona charger transfer device 73 performs two functions: directly transferring the toner image on the photosensitive drum 40 onto the recording paper 84, transferring the toner image on the photosensitive drum 40 onto the transfer belt 78, and transferring the toner image on the transfer belt 78. Recording paper 8
For this purpose, positive and negative high voltage power sources 79A and 79B, which are first and second power sources, are connected via a switch 80 as a switching means.

81 is a transfer belt cleaner, and 82 is a fixing device consisting of a pair of heat rollers.

First, the recording operation during color printing will be explained. The photosensitive layer on the photosensitive drum is uniformly charged to -600V by a corona charger 41. Image information source (
The laser beam 77 modulated according to the yellow image information supplied from a device (not shown) scans and exposes the uniformly charged photosensitive layer transported by the rotation of the photosensitive drum 40 by the laser beam scanning system 76. Reduce the surface potential of the exposed area to minus 150
V to form a yellow electrostatic latent image. The electrostatic latent image is reversely developed by a one-component non-contact developer 70 using negative polarity yellow toner to form a yellow toner image. At this time, the magnetic brush of the black toner developer 72 is separated from the photosensitive layer. The yellow toner image is transferred to the transfer belt 78 at a position facing the corona charger transfer device 73. The corona charger transfer device 73 is connected via a switch 80 to a positive high voltage power source 79A, which is a first power source. As a result, the positive corona ions generated from the corona charger transfer device 73 accumulate on the side of the polyester film of the transfer belt 78 facing the corona charger transfer device 73, and the electrostatic force generated by the corona ions causes the toner on the photosensitive layer to The image is transferred to polyester film.

At this time, the blade of the cleaner 81 is operated until the completed color toner image is transferred from the polynisteri film of the transfer belt 78 to the recording paper, or until each color toner image is transferred, so as not to scrape off the transferred toner image. It is kept separate until it is done. After the toner image is transferred to the transfer belt 78, the photosensitive layer is reused after the remaining toner is removed by the cleaner 74.

Subsequently, in the same process as before, a magenta toner image is formed by the magenta toner one-component non-contact developer 71 in response to the recording signal corresponding to the magenta toner image.

Similarly to the yellow toner image, the magenta toner image is also transferred onto the transfer belt 78 so as to be superimposed on the yellow toner image previously transferred. Similarly to the above, the cyan toner image is also formed by the cyan toner one-component non-contact developer 72 in accordance with the recording signal corresponding to the cyan toner image, and the cyan toner image is formed by the yellow toner which has been previously transferred onto the transfer belt 78. image, which is superimposed on the magenta toner image and transferred.

Further, if necessary, a black toner image formed by the two-component magnetic brush developing device 42 of black toner is superimposed and transferred in accordance with a recording signal corresponding to the black toner image. As the distance between the back surface of the polyester film of the transfer belt 78, which is a transfer electrode, and the toner image to be transferred increases depending on the number of times the toner images are superimposed, the corona ion generation voltage of the corona charger transfer device 73 gradually increases. Must be set high.

After the color toner image is completed on the transfer belt 78, the recording paper 84 is conveyed from the cassette 83 between the corona charger transfer device 73 and the photosensitive drum 40. At this time, the corona charger transfer device 73 is connected to the negative high voltage power source 79B, which is the second power source, by the switch 80. The color toner image formed on the transfer belt 78 is transferred onto the recording paper 84 by electrostatic force generated by negative corona ions generated from the corona charger transfer device 73. The color toner image transferred to the recording paper 84 is fixed by the fixing device 82, and then the paper is discharged. After the color toner image is transferred to the recording paper 84, the polyester film is reused after the remaining toner is removed by the cleaner 81.

Next, the recording operation during monochrome printing will be explained. The photosensitive layer of the photosensitive drum 40 is uniformly charged to negative aoov by the corona charger 41. Image information source (
A laser beam 77 modulated according to monochromatic image information supplied from a device (not shown) scans and exposes the uniformly charged photosensitive layer transported by the rotation of the photosensitive drum 40 by a laser beam scanning system 76. The surface potential of the exposed area is lowered to -150V to form a monochromatic electrostatic latent image. The electrostatic latent image is produced by a two-component magnetic brush developer 42 using monochromatic toner of negative polarity.
to form a monochromatic toner image. The recording paper 84 is fed from the cassette 83 to the transfer station of the corona charge transfer device 73 by controlling the timing before the leading edge of the monochrome toner image reaches the transfer station of the corona charge transfer device 73 . The corona charger transfer device 73 is connected to the positive high voltage power supply 79A by a switch 80. Therefore, the positive corona ions generated from the corona charger transfer device 73 accumulate on the side of the polyester film of the transfer belt 78 that faces the corona charger transfer device 73, and the monochromatic toner image is transferred to the photosensitive layer by the electrostatic force generated by the corona ions. The image is then transferred onto the recording paper 84. The monochromatic toner image transferred to the recording paper 84 is fixed by the fixing device 82, and then the paper is discharged. After the monochromatic toner image has been transferred to the recording paper 84, the photosensitive drum 40 is
After the toner remaining after transfer is removed by a cleaner 74, it is reused. Further, although the transfer belt 78 does not come into direct contact with toner, it is cleaned by a cleaner 81 to remove paper dust and the like.

In the electrostatic printing apparatus of this embodiment, in the case of color printing, there is no unrecordable area and full color recording with good reproducibility is possible, and in the case of monochrome printing, the toner image is directly transferred to the photosensitive drum 4.
Since the image is transferred onto the recording paper 84, an image with sharp edges can be recorded. Further, the toner image is transferred from the photosensitive drum 4o to the transfer belt 78, and the toner image is transferred from the transfer belt 78 to the recording paper 8.
Since the transfer of the toner image to the photosensitive drum 4 and the transfer from the photosensitive drum to the recording paper 84 are performed using one transfer device 73,
The device configuration is simplified and at the same time, the reliability of the device is improved.

Next, a third embodiment of the electrostatic printing apparatus according to the present invention will be described with reference to FIG. In this embodiment, the recording paper is supplied between the toner carrier and the intermediate transfer member, and a roller transfer device is provided as the transfer means.

The electrostatic printing device of this embodiment is different from the electrostatic printing device shown in FIG. 3 in the intermediate transfer body and transfer means, or the other parts are the same, so those parts are designated by the same numbers as in FIG. 3. The description will be omitted.

As the intermediate transfer body, a transfer belt 85 made of a polyester film provided with a thin aluminum film is used. The circumferential length of this transfer belt 85 is slightly longer than the vertical length of an A3 size sheet. Further, as a transfer means, a roller transfer device 86 including an elastic roller having a conductive layer on its surface is used. A positive high voltage power source 87 as a first power source and a negative high voltage power source 89 as a second power source are switches for switching and connecting the roller transfer device 86 and power sources 87 and 88.

First, the recording operation for color printing will be explained. Similar to the apparatus shown in FIG. 3, a yellow toner image is first transferred to the photosensitive drum 40.
to form. The toner image forming operation is the same as that of the apparatus shown in FIG. 3, so a description thereof will be omitted. The yellow toner image formed on the photosensitive drum 40 is transferred to the transfer belt 85 at a position facing the roller transfer device 86.

This transfer operation will be explained using FIG. 5. The transfer roller 90 provided in the roller transfer device 86 includes a conductive layer 91, a sponge layer 92 which is a deformable elastic layer, and a metal shaft 93. The metal shaft 93 and the conductive layer 91 are electrically connected by making a part of the sponge layer 92 conductive (not shown). If a conductive sponge layer is used, the conductive layer may not be provided. The thickness of the transfer belt 85 is 25
It consists of a dielectric layer 94 made of a 0 μm polyester film and a conductive layer 95 made of a 2 μm thick aluminum thin film provided thereon.
It is arranged so as to be in contact with the conductive layer 91 of. As the photosensitive drum 40 rotates, the yellow toner image 96 is transported to the toner transfer area. Yellow toner image 9 in the toner transfer area
6 is pressed against the dielectric layer 94 of the transfer belt 85. A power supply 8 connected to the metal shaft 93 by a switch 89
A transfer voltage plus 1.5 kV having a polarity opposite to that of the toner is supplied from 7, and the same potential is applied to the conductive layer 91 and the conductive layer 95 of the transfer belt 85 in contact with the conductive layer 91. The yellow toner image 96 is attached to the conductive layer 95 and the photosensitive drum 40 which is grounded.
The image is transferred to the dielectric layer 94 of the transfer belt 78 by electrostatic force acting between the conductive layers (not shown). conductive layer 95
By continuing to supply power to the photosensitive drum 40 until a series of toner transfers from the photosensitive drum 40 to the transfer belt 85 is completed,
The transferred toner image is held on the transfer belt 85 by electrostatic force acting between the conductive layer 95 and the toner. Also,
The blades of the cleaner 81 are kept apart until a series of toner transfers is completed. The reuse operation of the photosensitive drum 40 after toner transfer is the same as that of the electrostatic printing apparatus shown in FIG. 3, and therefore the explanation thereof will be omitted.

A magenta toner image, a cyan toner image, and a black toner image are also formed in the same manner, and are sequentially superimposed on the transfer belt 85 to form a color toner image.

The transfer voltage may be fixed, but may be increased as the toner images are superimposed, if necessary. As the toner images are superimposed, the toner layer of the color toner image on the transfer belt 85 becomes thicker, and the thickness of the toner layer also differs in some areas, and in roller transfer, the toner image deteriorates due to the above-mentioned "hollowness". Although easy to transfer, by using the transfer roller 90 having sufficient elasticity, "hollow spots" in the toner image do not occur, similar to the transfer to the recording paper described above. Transfer belt 8
After the color toner image is completed in step 5, the recording paper 84 is conveyed from the cassette 83 between the transfer roller 90 of the roller transfer device 86 and the photosensitive drum 40. Color toner image recording paper 8
4, the roller transfer device 86 switches the switch 89.
is connected to a negative power supply 88 which is a second power supply. The color toner images of negative polarity formed by the toner images of each color are collectively transferred onto the recording paper 84 by electrostatic force generated by a DC voltage of −1.5 kV applied to the conductive layer 95 of the transfer belt 85. The color toner image transferred to the recording paper 84 is fixed by a fixing device 82,
Paper is ejected. After the color toner image has been transferred to the recording paper 84, the transfer belt 85 removes the remaining toner from the cleaner 8.
1 to be removed and reused.

Next, the recording operation during monochrome printing will be explained. The operation of forming a monochromatic toner image is the same as that of the apparatus shown in FIG. 3, so a description thereof will be omitted. By controlling the timing before the leading edge of the monochrome toner image reaches the transfer station of the roller transfer device 86, the recording paper 84 is conveyed from the cassette 83 between the transfer roller 90 of the roller transfer device 86 and the photosensitive drum 40. Ru. Prior to this, or at the same time, the transfer roller 90 is connected to the positive power source 87 by the switch 89, and the conductive layer 95 of the transfer belt 85 is connected to the positive voltage of 1.5 kV.
DC voltage is applied. Due to the electrostatic force generated by this, the monochromatic toner image is transferred onto the recording paper 84 and further fixed by the fixing device 82 . Thereafter, the recording paper 84 is ejected. After the monochromatic toner image has been transferred to the recording paper 84, the photosensitive drum 40 is reused after the remaining toner is removed by the cleaner 74. Furthermore, although the transfer belt 85 does not come into direct contact with toner, it is cleaned by a cleaner 81 to remove paper dust and the like.

Similar to the electrostatic printing device shown in FIG. 3, the electrostatic printing device of this embodiment can perform full-color printing with good reproducibility without producing unrecordable areas in the case of color printing, and can perform monochrome printing. Since the toner image is directly transferred from the photosensitive drum to the recording paper, images with sharp edges can be recorded. Further, since the transfer from the photosensitive drum 40 to the transfer belt 85, the transfer from the transfer belt 85 to the recording paper 84, and the transfer from the photosensitive drum 40 to the recording paper 84 are performed by a single transfer device 86, the device configuration is simplified. At the same time, the reliability of the device also improves.

Furthermore, since a roller transfer device is used as the transfer device 84, it is possible to perform printing with excellent print quality regardless of changes in the surrounding environment, whether in color printing or monochrome printing.

FIG. 6 shows the structure of a fourth embodiment of an electrostatic printing apparatus according to the present invention. Components in FIG. 6 that are the same as those of the apparatus in FIG. 4 are designated by the same numbers. This electrostatic printing device has a different paper feeding device from the device shown in FIG. 4, and includes a cassette 98 that stores color printing paper 97 as recording paper and a cassette 100 that stores plain paper 99. There is.

Regarding the recording operation, only the parts that are different from the apparatus shown in FIG. 4 will be explained, and the explanation of other parts will be omitted. In the case of color printing, the cassette 98 is selected by a color print signal from a CPU (not shown) that controls the printing operation of the device or by a set signal from the operator's color print selection, and the special paper 97 is moved along the conveyance path 101. Paper is fed through the printer to obtain color prints. For single color printing,
As before, when the cassette 100 is selected by CPU control or operator selection, plain paper 99 is fed through the conveyance path 102 to obtain a monochrome printed matter.

The apparatus of this embodiment not only provides the same effects as the previous embodiment, but also automatically selects and feeds the appropriate recording paper according to the printing conditions, so that printing always meets the purpose. It has the advantage that it can be done.

It should be noted that the specific configuration of the electrostatic printing apparatus according to the present invention is not limited to the embodiments shown above, and it goes without saying that various modifications can be made without departing from the spirit of the invention.

[Effects of the Invention] As explained above, according to the present invention, the following effects can be obtained.

(1) In monochrome printing where many character images are printed, the toner image transfer process only needs to be carried out once, so it is possible to print characters with excellent edge sharpness and quality similar to that of type.

(2) During color printing, the toner images of each color are superimposed on the intermediate transfer member and then transferred to the recording medium, which reduces the areas that cannot be recorded at the edges of the recording paper and improves the color overlay accuracy of each color. This enables printing with excellent color reproduction stability. Furthermore, since it is necessary to fix the recording paper to the transfer sleeve, the range of recording paper that can be used is expanded.

(3) Since an intermediate transfer member is not used in monochrome printing, which is performed frequently, the life of the intermediate transfer member or device can be substantially extended.

(4) A single transfer device can handle two different toner image transfer conditions (from a photosensitive drum or intermediate transfer member to recording paper, and from a photosensitive drum to an intermediate transfer member), simplifying the device configuration. Maintenance becomes easier.

(5) If an intermediate transfer body is provided between the recording paper and the transfer device, even if a corona charger transfer device is used, corona ions will not act directly on the recording paper, improving the transfer efficiency and increasing the Get quality images.

(6) By using an intermediate transfer body having a conductive layer,
During the overlapping of toner images, an electrostatic force is applied between the intermediate transfer body and the toner image to ensure that the overlaid toner images are retained on the intermediate transfer body.
It is possible to eliminate disturbances in toner images and obtain high-quality images.

(7) If the configuration is such that recording paper suitable for each printing condition is automatically selected and fed, printing can always be performed in accordance with the purpose.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of an electrostatic printing device according to a first embodiment of the present invention, FIG. 2 is a diagram illustrating a schematic configuration and transfer operation of a roller transfer device in FIG. 1, 3 is a diagram showing a schematic configuration of an electrostatic printing device according to a second embodiment of the present invention, FIG. 4 is a diagram showing a schematic configuration of an electrostatic printing device according to a third embodiment of the present invention, FIG. 5 is a diagram for explaining the schematic configuration and transfer operation of the roller transfer device and intermediate transfer body in FIG. 4, and FIG. 6 is a schematic configuration of an electrostatic printing device according to a fourth embodiment of the present invention. , FIG. 7, and FIG. 8 are diagrams showing a schematic configuration of a conventional electrostatic printing device. 40... Photosensitive drum (toner image carrier), 42° 4B
, 44, 45. 70, 71. ．． 72...Developer, 46
...Corona charger transfer device (first transfer means), 5
1...Corona charger transfer device (second transfer means),
50...Transfer drum (intermediate transfer body), 54...Roller transfer device (third transfer means), 57...Special color printing paper (recording body) 67...Plain paper (recording body), 73...
-Corona charger transfer device (transfer means) 78...transfer belt (intermediate transfer body), 79A, 79B...first
and second power source, 80... switch (switching means), 84... recording paper (recording body), 85... transfer belt (intermediate transfer body), 86... roller transfer device (transfer means), 87°88...first and second power supply, 89...
・Switch (switching means), 90...photosensitive drum (
toner image carrier), 97... color printing paper (recording body) 99... plain paper (recording body), 98,100...
- Cassette (holding body), 101, 102... Conveyance path (first and second conveyance means).

Claims (1)

[Claims] (1) In an electrostatic printing method that selectively performs color printing and monochrome printing, during color printing, monochrome toner images of different colors sequentially formed on a toner image carrier are sequentially transferred to an intermediate transfer member. A color toner image is formed on the intermediate transfer body by transferring and overlapping, and this color toner image is transferred to a recording body to obtain a color printed matter. When printing in monochrome, the monochrome toner image on the toner image carrier is transferred to the recording body. An electrostatic printing method characterized by obtaining monochromatic prints by direct transfer to. (2) In an electrostatic printing device that selectively performs color printing and monochrome printing, a toner image carrier that carries a toner image obtained by developing an electrostatic latent image, and a part of the toner image carrier an intermediate transfer member facing the toner image carrier, a first transfer unit that directly transfers the toner image on the toner image carrier to the recording member, and a second transfer unit that transfers the toner image on the toner image carrier to the intermediate transfer member. An electrostatic printing device comprising: means for transferring the toner image on the intermediate transfer member to the recording member. (3) In an electrostatic printing device that selectively performs color printing and monochrome printing, a toner image carrier that carries a toner image obtained by developing an electrostatic latent image; An intermediate transfer body whose portions are opposed to each other, and an intermediate transfer body provided on the back side of the intermediate transfer body, which transfers the toner image on the toner image carrier to the intermediate transfer body, and transfers the toner image on the intermediate transfer body between the toner carrier and the intermediate transfer body. A static image forming apparatus comprising a transfer means that selectively performs an operation of transferring a toner image to a recording body inserted between the toner image carrier and an operation of directly transferring a toner image on a toner image carrier to a recording body. Electric printing equipment. (4) In an electrostatic printing device that selectively performs color printing and monochrome printing, a toner image carrier that carries a toner image obtained by developing an electrostatic latent image; An intermediate transfer body whose portions are opposed to each other, and an intermediate transfer body provided on the back side of the intermediate transfer body, which transfers the toner image on the toner image carrier to the intermediate transfer body, and transfers the toner image on the intermediate transfer body between the toner carrier and the intermediate transfer body. a transfer means that selectively performs an operation of transferring to a recording body inserted between the toner image carrier and an operation of directly transferring the toner image on the toner image carrier to the recording body; When transferring the toner image on the toner image carrier to an intermediate transfer member or a recording member inserted between the toner image carrier and the intermediate transfer member, a first power supply is connected to the transfer means. An electrostatic printing apparatus comprising: switching means for connecting a second power source to the transfer means when the toner image on the intermediate transfer member is transferred to the recording member. (5) A first storage medium that holds recording media with different recording characteristics.
and a second holding body, and first and second conveying means for conveying the recording medium held by the first and second holding bodies during color printing and monochrome printing, respectively. The electrostatic printing device according to claim 2, 3 or 4.