KR20050105415A - Printing method of electrophotographic image forming apparatus - Google Patents

Abstract

The disclosed printing method is a printing method of an electrophotographic image forming apparatus which prints an image on paper by an electrophotographic method, comprising the steps of selecting the type of paper and the duplex / single-sided or color / mono print mode, and the double-sided reproduction paper. And reducing the transfer field difference between the image portion and the non-image portion during double-sided printing by reducing the amount of the developer developed by the photosensitive member to at least 80% of the reference amount when the color print mode is selected.

Description

Printing method of electrophotographic image forming apparatus

The present invention relates to a printing method of an electrophotographic image forming apparatus, and more particularly, to a printing method of an electrophotographic image forming apparatus capable of printing single-sided / double-sided printing of a single color / color image using a developer of four colors.

An electrophotographic image forming apparatus scans light on a photosensitive member charged at a uniform potential to form an electrostatic latent image corresponding to a desired image, and develops by supplying a developer to the electrostatic latent image, and developing on a photosensitive member An apparatus for forming an image by fixing the transferred image through an intermediate transfer medium or directly on a paper and then applying heat and pressure to the transferred image. In the case of printing a color image, yellow, magenta, cyan, and black developer are superimposed and fixed on the paper. In the case of double-sided printing, an image is printed on the first surface by the above-mentioned steps, and the paper exiting from the mounting machine is inverted and put again into the transfer process. During the inversion of the paper, the image forming apparatus performs the above-described charging-exposure-developing process. Then, the duplex printing is completed by transferring the developer to the second side of the paper and fixing it.

1 is a schematic diagram showing a transfer process in the case of double-sided printing.

1, the developer is transferred from the photosensitive member (or intermediate transfer medium) 3 to the second surface 2 of the paper P on which the image is printed on the first surface 1. Although not shown in the drawing on the first side 1 of the paper P, the opposite polarity (e.g., "-") of the toner is prevented by a corona discharger or a transfer roller to which a transfer bias is applied. Charge is supplied. The developer is transferred from the photosensitive member (or intermediate transfer medium) 3 to the paper by the transfer electric field formed thereby.

Good transfer quality can be obtained when the backside charge amount of the image portion is larger than the backside charge amount of the non-image portion. On the contrary, when the amount of backside charge of the image portion is less than or equal to the amount of backside charge of the non-image portion, the developer transferred to the paper is dragged or scattered toward the non-image portion to generate an image stain.

The larger the amount of the developer to be transferred, the larger the transfer electric field acting on the non-image portion than the image portion is, so that image staining is likely to occur. Since the color image transfers the developer of yellow (Y), magenta (M), and cyan (C) colors onto the paper, the amount of the developer transferred is larger than that in the case of printing a monochrome image. In the case of double-sided printing of a color image, the charge of the developer already attached to the first surface 1 of the paper P cancels the charge supplied from the corona discharger or the transfer roller to which the transfer bias is applied. Therefore, the transfer field of the image portion is lower than the transfer field of the non-image portion, and the developer transferred to the uppermost layer is scattered to generate an image stain.

If duplex printing is performed, after the image is printed on the first side 1 of the paper P, transfer of the image portion is performed if sufficient static elimination is performed in the process of inverting the sheet for printing the image on the second side 2. The fall of an electric field can be prevented to some extent. However, low quality recycled paper has high self-resistance of the paper P, making it difficult to eliminate static electricity. Therefore, image staining is most likely to occur when color duplex printing is performed using recycled paper.

SUMMARY OF THE INVENTION The present invention has been made in view of the above necessity, and an object thereof is to provide a printing method of an electrophotographic image forming apparatus that is improved to prevent image staining due to a change in a transfer electric field when double-sided printing is performed. .

A printing method of an electrophotographic image forming apparatus of the present invention for achieving the above object is a printing method of an electrophotographic image forming apparatus which prints an image on paper by an electrophotographic method, the method comprising: (a) a type of paper; Selecting a duplex / single-sided or color / mono print mode; (b) when the double-sided color printing mode of the recycled paper is selected, reducing the transfer field difference between the image portion and the non-image portion during double-sided printing by reducing the amount of the developer developed by the photosensitive member to a reference amount; do.

In one embodiment, the step (b) is performed by setting the maximum target value of the look-up table of the yellow, magenta, and cyan colors according to the color image information to a minimum of 80% in the printer driver.

In one embodiment, the print mode is input through an input device provided in the image forming apparatus or a user interface provided in a host.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram showing an example of an electrophotographic image forming apparatus to which a printing method according to the present invention is applied.

2, the photosensitive drum 11 (photosensitive member) is a photoconductive layer formed on the outer periphery of a cylindrical drum. Instead of the photosensitive drum 11, a belt-shaped photosensitive belt may be used. The charging roller 12 is an example of a charger for charging the photosensitive drum 11 to a uniform potential. The charging bias Vc is applied to the charging roller 12. The charging roller 12 supplies electric charge while rotating in contact or non-contact state with the outer circumferential surface of the photosensitive drum 61 so that the outer circumferential surface of the photosensitive drum 11 has a uniform electric potential. As the charger, a corona discharger (not shown) may be used instead of the charging roller 12. The exposure machine 13 scans the light corresponding to the image information to the photosensitive drum 11 to form an electrostatic latent image. As the exposure machine 13, a laser scanning unit (LSU) using a laser diode as a light source is generally used.

Four developing devices 14C, 14M, 14Y, and 14K are provided along the outer circumference of the photosensitive drum 11. Developers 14C, 14M, 14Y, and 14K contain yellow (Y), magenta (M), cyan (C), and black (K) colors, respectively. The developing devices 14C, 14M, 14Y, and 14K include a developing roller 19 for supplying the developer contained therein to the outer circumferential surface of the photosensitive drum 11. The developing roller 19 is rotated in contact with the outer circumferential surface of the photosensitive drum 11 when the contact developing method is adopted, and is spaced apart by the developing gap from the outer circumferential surface of the photosensitive drum 11 when the non-developing developing method is adopted. . The developing gap is preferably about tens to hundreds of microns. A developing bias Vd for supplying a developer to the electrostatic latent image formed on the photosensitive drum 11 is applied to the developing roller 19.

The intermediate transfer belt 15 is for temporarily receiving a developer attached to the photosensitive drum 11. Instead of the intermediate transfer belt 15, an intermediate transfer drum (not shown) in the form of a drum may be used. The first transfer roller 16 is applied with a first transfer bias Vt1 for transferring the developer attached to the photosensitive drum 11 to the intermediate transfer belt 15.

A second transfer bias Vt2 for transferring the developer attached to the intermediate transfer belt 15 to the paper P is applied to the second transfer roller 17. The fixing unit 18 is such that a pair of rollers are engaged with each other at a predetermined pressure to rotate. At least one of the pair of rollers is provided with a heating means (not shown). The fixing unit 18 applies heat and pressure to the developer transferred to the paper P to fix the paper P to the paper P.

Looking at the image forming process by such a configuration as follows. When the charging bias Vc is applied to the charging roller 12, the outer circumferential surface of the photosensitive drum 11 is charged to a uniform electric potential. When the optical signal corresponding to, for example, yellow (Y) image information is scanned by the exposure machine 13 to the rotating photosensitive drum 11, the portion where the light is scanned is attached to the outer peripheral surface of the photosensitive drum 11 while the resistance decreases. Charge is released. Therefore, a potential difference occurs between a portion where light is scanned and a portion where it is not, thereby forming an electrostatic latent image on the outer circumferential surface of the photosensitive drum 11. When the developing bias Vd is applied to the developing roller 19, the developer contained in the developing unit 14Y is attached to the electrostatic latent image. The developer is transferred to the intermediate transfer belt 15 by the electric field of the first transfer bias Vt1 applied to the first transfer roller 16. Next, the developer of magenta (M), yellow (Y), and black (K) colors is sequentially transferred to the intermediate transfer belt 15 through the above-described process.

The paper P drawn out from the paper feeding means (not shown) is drawn into the transfer nip in which the intermediate transfer belt 15 and the second transfer roller 17 face each other. When the second transfer bias Vt2 is applied to the second transfer roller 17, the developer is transferred to the paper P. FIG. As the paper P passes through the fixing unit 18, the developer adheres to the paper P by heat and pressure, thereby completing printing of the image. In the case of duplex printing, the paper P passing through the fixing unit 18 is supplied to the transfer nip through the reverse path 20 again. In this process, the developer of four colors is overlaid and transferred to the intermediate transfer belt 15 by the above-described charging-exposure-developing-transfer process, and the developer is transferred and fixed on the paper P, thereby completing duplex printing.

The user may use the input device 70 provided in the image forming apparatus or the user interface 60 provided in the host to determine the type of the paper P (for example, the size of the paper, whether it is recycled paper, etc.) and the printing mode (for example, For example, monochrome / calenar printing, single-sided / duplex printing) can be selected.

As described above, when double-sided / color printing is performed using recycled paper, the transfer field of the image portion and the non-image portion may be reversed to generate an image spot. In order to prevent this, the printing method according to the present invention, when the color / duplex printing mode of the recycled paper is selected, the developer to be transferred to the paper (P) by reducing the developing amount of the developer developed by the photosensitive drum 11 than the reference amount It is characterized by reducing the difference between the transfer field of the image portion and the non-image portion by reducing the amount of. The reference amount refers to the amount of the developer to be developed in order to print the input image information.

As a method of reducing the developing amount, a method of adjusting the developing bias Vd applied to the developing roller 19 may be considered. To this end, a hardware device for adjusting the development bias Vd should be further provided.

The printer driver 50 generates a control signal according to the image information input from the host and transfers it to the controller 40. The control unit 40 drives the printing unit 30 in accordance with the input control signal to print an image on the paper (P). The printer driver 50 has a look-up table in which information for mixing yellow (Y), magenta (M), and cyan (C) colors is recorded according to the color image information input from the host. do. The printing method according to the present embodiment reduces the amount of development by reducing the maximum target value of the look-up table. Since the maximum target value is almost proportional to the developing amount, the developing amount can be reduced without additional hardware. For example, when the color / duplex printing mode of the recycled paper is selected, the printer driver 50 reduces the maximum target value of the look-up table from 100% to 90%, for example. How much to reduce the maximum target value can be determined by experiment. However, it is desirable that the maximum target value is not reduced below 80%.

In this manner, when the color image is printed on both sides, the amount of the developer already attached to the first surface 1 of the paper P is reduced, so that the charge supplied from the second transfer roller 17 is reduced. As the amount of offset is reduced, the difference between the transfer field of the image portion and the non-image portion is reduced. Therefore, the amount of the developer scattered from the image portion to the non-image portion is reduced or no scattering occurs.

The electrophotographic image forming apparatus shown in FIG. 1 is a multi-pass image forming apparatus for printing a color image by repeating the charge-exposure-development-intermediate transfer process four times. The printing method according to the present invention can also be applied to an image forming apparatus of a tandem method (single pass method), which forms a color image by sequentially transferring and transferring four color developer onto a paper P at a predetermined time interval.

According to the printing method of the electrophotographic image forming apparatus according to the present invention as described above, stable image quality can be obtained by preventing the occurrence of image staining during color duplex printing on reproduction paper.

It is to be understood that the invention is not limited to that described above and illustrated in the drawings, and that more modifications and variations are possible within the scope of the following claims.

1 is a schematic diagram showing a transfer process in the case of double-sided printing.

2 is a configuration diagram showing an example of an electrophotographic image forming apparatus to which a printing method according to the present invention is applied.

<Description of the symbols for the main parts of the drawings>

11 ...... Photosensitive drum 12 ...... Anti-electric roller

13 ...... Exposure 14 ...... Developer

15 ...... Intermediate transfer belt 16 ...... 1st transfer roller

17 ...... Second Transfer Roller 18 ...... Fixing Machine

19 ...... Draw roller 20 ...... Reverse path

40 ...... Control section 50 ...... Printer driver

60 ...... User interface 70 ...... Input device

Claims (4)

A printing method of an electrophotographic image forming apparatus for printing an image on a paper by an electrophotographic method, (a) selecting a type of paper and a duplex / single-sided or color / mono print mode; (b) when the double-sided color printing mode of the recycled paper is selected, reducing the transfer field difference between the image portion and the non-image portion during double-sided printing by reducing the amount of the developer developed by the photosensitive member to a reference amount; A printing method of an electrophotographic image forming apparatus. The method of claim 1, The step (b) is performed by setting the maximum target value of the look-up table of the yellow, magenta, and cyan colors according to the color image information to a minimum of 80% in the printer driver. How to print. The method of claim 1, And the printing mode is input through an input device provided in the image forming apparatus. The method of claim 1, And the print mode is input through a user interface provided in a host.