JP2020154005A - Image formation apparatus - Google Patents

Abstract

To solve such a problem that the charge failure due to a strong transfer history occurs in a photoreceptor drum with the high transfer voltage applied at the high-resistance medium printing and causes strips and streaks at the printing.SOLUTION: An image formation apparatus comprises: a color toner image formation part which consists of an image formation unit 12K for black, an image formation unit 12Y for yellow, an image formation unit 12M for magenta, and an image formation unit 12C for cyan; a reception part 43 which inputs printing data; a medium setting control part 41a which determines the type of a recording medium; an image information creation part 41b which selectively generates a first image data group creating a toner image by the image formation parts for black and color, and a second image data group creating the toner image only by the color toner image formation part in accordance with the type of the recording medium on the basis of the printing data; and an image output part 41c which instructs the output of the first or second image data group and the operation of each image formation unit 12 in accordance with the output.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus such as a copier, a printer, and a fax machine using an electrophotographic method, and particularly to an improvement of a strong transfer history.

Conventionally, in this type of image forming apparatus, on the transfer rollers of a plurality of image forming portions arranged in series, an image forming on the downstream side is formed based on the transfer current of the transfer rollers of the image forming portions arranged on the upstream side. Some set the transfer voltage of the transfer roller of the unit (see, for example, Patent Document 1).

JP-A-2005-77598 (page 4, FIG. 1)

When printing a medium having a narrower paper-passing width and a higher volume resistance than plain paper (hereinafter referred to as a high-resistance medium), a transfer voltage higher than that during normal printing is applied, so that the medium is passed through the photoconductor drum. Outside the passing region of the medium facing the transfer roller, a transfer current strongly flows through the photoconductor drum, and the photoconductor drum may be charged with the opposite polarity (+). When this is repeated, the photoconductor drum becomes poorly charged, and the poorly charged portion does not improve even if left for several hours and remains as a history. When halftones are printed on a medium having a wider paper-passing width than the medium having a narrower paper-passing width in a state where the history remains, vertical black streaks called density steps and strong transfer history occur in places where charging is poor.

The image forming apparatus according to the present invention includes a black toner image forming unit that forms a black toner image, a toner image forming unit that forms a yellow toner image, a toner image forming unit that forms a magenta toner image, and a cyan toner image. Based on the color toner image forming unit including the toner image forming unit forming the above, the input unit into which print data is input from an external device, the medium determination unit for determining the type of recording medium to be printed, and the print data. Depending on the type of recording medium, only the first image data group consisting of image data for creating a toner image in the black toner image forming unit and the color toner image forming unit, and the color toner image forming unit only. An image data creation unit that selectively generates a second image data group composed of image data for creating a toner image, and an output of the first image data group or the second image data group. It is characterized by including an output unit for instructing the operation of the black toner image forming unit and the color toner image forming unit according to the output.

Another image forming apparatus according to the present invention has a plurality of image forming units for individually forming a plurality of color toner images on a recording medium, an input unit for inputting print data from an external device, and a type of recording medium for printing. It has a print control unit that discriminates and instructs the plurality of toner image forming units to print from the input print data.
The print control unit is characterized in that the number of the plurality of image forming units used when printing the print data is reduced according to the selected recording medium.

According to the present invention, the function of the black toner image forming unit can be stopped according to the type of the recording medium, so that the applied voltage as the required transfer voltage can be lowered, and a strong transfer history is generated. Can be suppressed.

FIG. 5 is a main part configuration diagram schematically showing a main part configuration when the image forming apparatus of the first embodiment according to the present invention is viewed from the front. It is a block diagram which shows the main part structure of the control system of the image forming apparatus mainly which concerns on this invention. It is a block diagram which shows typically the structure of the static elimination device. It is a flowchart which shows the flow of the printing process performed by the image forming apparatus of Embodiment 1. It is a flowchart which shows the flow of the printing process performed by the image forming apparatus of Embodiment 2.

Embodiment 1.
FIG. 1 is a main part configuration diagram schematically showing a main part configuration when the image forming apparatus 11 of the first embodiment according to the present invention is viewed from the front.

The image forming apparatus 11 has, for example, a configuration as an electrophotographic type direct transfer type color printer, and has four independent image forming units 12K, 12Y, 12M, and 12C (unless it is necessary to distinguish them, simply an image). (Sometimes referred to as a forming unit 12) are arranged in order from the upstream side along the conveying direction (arrow A direction) of the recording medium 30. The image forming unit 12K forms a black (K) toner image, the image forming unit 12Y forms a yellow (Y) toner image, and the image forming unit 12M forms a magenta (M) toner image to form an image. Unit 12C forms a toner image of cyan (C). As the recording medium 30, in addition to plain paper, water resistant paper (hereinafter referred to as coated paper), a recording medium made of a polyester film material, or the like can be used.

The image forming unit 12K corresponds to the black toner image forming unit, and the image forming unit 12Y, the image forming unit 12M, and the image forming unit 12C correspond to the color toner image forming unit.

In the present embodiment, the configurations of these image forming units 12K, 12Y, 12M, and 12C are the same, and only the color of the contained non-magnetic one component toner is different. Therefore, here, cyan (C) is used. Taking the image forming unit 12C as an example, the internal structure thereof will be described below.

The image forming unit 12C includes a photoconductor drum 13C as an image carrier (may be simply referred to as a photoconductor drum 13 when it is not necessary to distinguish them), and a charging means for uniformly charging the surface of the photoconductor drum 13C. Charging roller 14C (may be simply referred to as charging roller 14 when it is not necessary to distinguish), electrostatic latent image formed on the surface of the photoconductor drum 13C, and toner 25C for cyanide as a developing agent ( When it is not necessary to make a distinction, it may be simply referred to as toner 25. When it is simply referred to as a developing roller 16C as a toner carrier that forms a toner image (when it is not necessary to make a distinction, it is simply referred to as a developing roller 16). There is), and a supply roller 18C (which may be simply referred to as a supply roller 18 when it is not particularly necessary to distinguish) as a developer supply means that is pressure-contacted with the developing roller 16C.

The supply roller 18C is a roller that supplies the cyan toner 25C contained in the toner accommodating portion 20C (may be simply referred to as the toner accommodating portion 20 when it is not particularly necessary to distinguish) to the corresponding developing roller 16C. A developing blade 19C (may be simply referred to as a developing blade 19 when it is not particularly necessary to distinguish) is pressure-welded to the developing roller 16C. The developing blade 19C thins the toner 25C for shearan supplied from the supply roller 18C on the developing roller 16C.

The cleaning device 27C (which may be simply referred to as a cleaning device 27 when it is not necessary to distinguish) includes a cleaning blade 27a that presses against the surface of the photoconductor drum 13C and remains on the photoconductor drum 13C after transfer described later. The cyan toner 25C (residual toner) is scraped off and stored inside.

The static eliminator 36C (which may be simply referred to as the static eliminator 36 when it is not necessary to distinguish between them) removes static electricity from the surface of the photoconductor drum 13C after the transfer is completed to eliminate the variation in the surface potential, and continues. Prepare for charging by the charging roller 14C. The static elimination device 36C will be described in detail later. The image forming unit 12C is formed by the above members.

In the positive direction of the Z-axis, which will be described later, of the photoconductor drum 13C, an exposure device 15C as an exposure means (may be simply referred to as an exposure device 15 when it is not particularly necessary to distinguish) faces the photoconductor drum 13C. It is arranged at the position. Similarly, the corresponding exposure devices 15M, 15Y, 15K are arranged on the other photoconductor drums 13M, 13Y, 13K, respectively. The exposure apparatus 15 selectively exposes the photoconductor drum 13 according to the image data of the corresponding color, and forms an electrostatic latent image on the surface thereof.

A transfer unit 21 is arranged below each photoconductor drum 13 of the four image forming units 12. The transfer unit 21 includes transfer rollers 17K, 17Y, 17M, 17C (sometimes referred to simply as transfer rollers 17 when it is not necessary to distinguish them), transfer belt drive rollers 21a, and transfer belt driven rollers 21b as transfer units. A transfer belt 26 as a medium transporting portion is provided so as to be able to travel in the direction of arrow A in FIG. 1 in a stretched state. The residual toner adhering to the transfer belt 26 is scraped off by the belt cleaning blade 34 and stored in the belt cleaner container 35.

Each transfer roller 17 is arranged by pressure contacting the corresponding photoconductor drum 13 via the transfer belt 26, and in the nip portion formed by the pressure contact, the recording medium 30 conveyed by the transfer belt 26 is reversed from the toner 25. Toner images of each color formed on the corresponding photoconductor drum 13 are sequentially superimposed on the recording medium 30 and transferred.

A paper feeding mechanism for supplying the recording medium 30 to the transfer belt 26 is provided below the transfer unit 21 of the image forming apparatus 11. The paper feed mechanism includes a paper feed tray 24 for storing the recording medium 30, a hopping roller 22 for taking out the recording medium 30 from the paper feed tray 24, and a registration roller pair 23 for transporting the recording medium 30 without skewing.

Further, a fixing device 28 is provided on the discharge side of the recording medium 30 by the transfer belt 26. The fixing device 28 has a heating roller 28a and a pressure roller 28b, and fixes the toner image transferred onto the recording medium 30 by pressurizing and heating the toner image. On the discharge side of the fuser 28, a paper guide portion 31, a discharge roller pair 32 arranged at the rear end of the paper guide portion 31, a paper stacker portion 29, and the like are provided. Here, the medium width of the image forming apparatus 11 in the printable main scanning direction is set to 297 mm (corresponding to the long side size of A4 paper) capable of horizontal printing of A4 size media.

The image forming apparatus 11 has a rotatable upper cover 39 centered on a rotating shaft 40 extending in the rotation axis direction of the photoconductor drum 13, and the upper cover 39 is opened to face the inside of the apparatus. be able to. Further, the upper cover 39 is provided with a touch panel 38 having a display function and a data input function described later.

The X, Y, and Z axes in FIG. 1 have X axes in the transport direction when the recording medium 30 passes through the image forming units 12K, 12Y, 12M, and 12C, and the photoconductor drums 13K, 13Y, The Y-axis is taken in the rotation axis direction of 13M and 13C, and the Z-axis is taken in the direction orthogonal to both of these axes. Further, here, it is assumed that the Z axis is arranged so as to be substantially in the vertical direction.

The configuration of each part will be further described.

The photoconductor drum 13 is provided with a charge generation layer having a thickness of 0.5 μm and a charge transport layer having a thickness of 20 μm on the surface of a conductive support of a metal pipe such as aluminum having a thickness of 0.75 mm and an outer diameter of 30 mm. The charging roller 14 has a structure in which a conductive elastic layer (rubber layer) such as epichlorohydrin is coated on the outer periphery of a conductor metal shaft made of SUS material. The exposure device 15 is a device for selectively exposing the surface of a uniformly charged photoconductor drum 13 to form a latent image pattern, and is a device for forming a latent image pattern, and is a light emitting element such as an LED, an LED driving element, and a lens eye for condensing light. Is provided at a position where the irradiation light from the LED element forms an image on the surface of the photoconductor drum 13.

The developing roller 16 has an elastic layer arranged in a roll shape on a conductive shaft (core metal) made of SUS material, and has a surface layer covering the elastic layer. Urethane rubber or silicone rubber was used for the elastic layer, and a surface layer treated with a urethane solution or coated with an acrylic resin or an acrylic-fluorine copolymer resin was used. Acrylic resin and acrylic-fluorine copolymer resin as the surface layer were blended with carbon black in order to impart conductivity.

The supply roller 18 is formed of a conductive shaft (core metal) made of SUS material and an elastic layer. This elastic layer is a conductive silicone rubber foam layer or a conductive urethane rubber foam layer. If the elastic layer has semiconductivity, acetylene black, carbon black, or the like is added. The developing blade 19 is made of SUS having a plate thickness of 0.08 mm, the contact portion with the developing roller 16 is bent, the radius of curvature R of the bent portion is 0.2 mm, and the linear pressure on the developing roller 16 is 30 gf /. It was set to cm. However, the radius of curvature R and the linear pressure of the developing blade 19 are not limited to these, and can be adjusted according to the amount of toner and the amount of toner charged on the developing roller 16.

The transfer roller 17 is made of, for example, a conductive foamable elastic body, and the cleaning device 27 is provided with a cleaning blade 27a using, for example, urethane rubber, so that the tip of the cleaning blade 27a is brought into contact with the surface of the photoconductor drum 13. It is located in. The fuser 28 includes a heating roller 28a and a pressurizing roller 28b. The heating roller 28a has an elastic layer of silicone rubber arranged on an iron tube having an outer diameter of 28 mm, and is provided with a PFA tube as a toner peeling layer so as to cover the elastic layer. On the other hand, the pressure roller 28b has no elastic layer and is provided with a PFA tube on an iron raw tube. The heating roller 28a includes a halogen lamp (not shown) inside the raw tube as a heat source.

The toner 25 contains polyester as a binder resin, carbon black as a colorant, a copper phthalocyanine pigment (CI Pigment Blue15), a quinacridone pigment (CI Pigment Red122), and C.I. I. It is a non-magnetic one-component negatively charged toner using Pigment Yellow 185 or the like. The specific surface area is 3.15 m ² / g, the toner sphericity is 0.95, the volume average particle size is 5.8 μm, and additives such as silica and titanium oxide are added externally for the purpose of controlling the fluidity and chargeability. are doing.

FIG. 3 is a configuration diagram schematically showing the configuration of the static elimination device 36.

As shown in FIG. 3, the static eliminator 36 is composed of a static eliminator 36a extending in the longitudinal direction and a plurality of LED elements 36b linearly arranged on the static eliminator 36a at substantially equal intervals along the longitudinal direction. Therefore, it is electrically connected to a voltage control unit 47 (see FIG. 2) described later via a voltage supply line 36c, and is driven by the voltage control unit 47 to emit light at a predetermined timing and light emission amount.

As shown in FIG. 1, the static elimination device 36 is located near the surface of the photoconductor drum 13 of each image forming unit 12 of the image forming device 11, and its longitudinal direction is the rotation axis direction (Y-axis direction) of the photoconductor drum 13. : Main scanning direction), and each LED element 36b is arranged so as to vertically irradiate the surface of the opposing photoconductor drum 13. Further, a plurality of LED elements 36b are arranged so that the required irradiation can be performed over the entire printable area in the main scanning direction.

FIG. 2 is a block diagram showing a main configuration of a control system of the image forming apparatus 11 mainly according to the present invention.

The image forming apparatus 11 includes a control unit 41, a receiving unit 43, a medium setting unit 42, a medium setting control unit 41a, an image information creation unit 41b, an image output unit 41c, a fixing control unit 45, an exposure control unit 46, and a voltage control unit 47. , Drive control unit 44, drum motor 49, belt motor 48, fuser 28, exposure device 15, charging roller 14, developing roller 16, supply roller 18, developing blade 19, transfer roller 17, and static elimination device 36. ..

When the image forming apparatus 11 receives a print instruction (including print data) from the host device by the receiving unit 43 as an input unit, the image forming apparatus 11 sends it to the control unit 41. The control unit 41 is composed of a microprocessor, ROM, RAM, input / output port, timer, etc., and when functionally grasped, the media setting control unit 41a as a medium determination unit and the image information creation unit as an image data creation unit. A 41b and an image output unit 41c as an output unit are provided, and the entire image forming apparatus 11 is sequence-controlled to perform a printing operation.

The medium setting control unit 41a sets the printing speed and the voltage value at the time of printing according to the medium setting set by the medium setting unit 42 or the host device. The control unit 41 creates image data in the image information creation unit 41b based on the print instruction sent from the reception unit 43 and the medium setting set in the medium setting control unit 41a, and sends the image data to the image output unit 41c. The image output unit 41c issues a printing operation instruction to the fixing control unit 45, the exposure control unit 46, the voltage control unit 47, and the drive control unit 44 according to the transmitted image data and its form.

Here, as will be described later, when the recording medium 30 to be printed is a high resistance medium, the image information creation unit 41b uses three colors of yellow (Y), magenta (M), and cyan (C) from the print data. When the recording medium for creating and printing image data is a low resistance medium, image data in four colors of black (K), yellow (Y), magenta (M), and cyan (C) is created from the print data. To do.

The medium setting unit 42 displays the type of the medium by the display function of the touch panel 38 described above, and transmits the medium setting information selected by the user to the control unit 41 by the input function.

Upon receiving an instruction from the control unit 41, the drive control unit 44 rotates the drum motor 49 and the belt motor 48, and rotates the photoconductor drum 13 and the transfer belt drive roller 21a in the directions of the arrows shown in FIG. Upon receiving an instruction from the control unit 41, the voltage control unit 47 controls the voltage applied to the charging roller 14, the developing roller 16, the supply roller 18, the developing blade 19, the transfer roller 17, and the static elimination device 36.

When the image forming apparatus 11 is operated in a normal temperature and humidity environment using a negatively charged toner, the voltage control unit 47 applies a constant voltage (-1050V (direct current)) to, for example, the charging roller 14 and sets it to the developing roller 16. A voltage (-200V (direct current)) is applied, a constant voltage (-300V (direct current)) is applied to the supply roller 18 and the developing blade 19, and a predetermined constant voltage (direct current) described later is applied to the transfer roller 17. Further, a constant voltage (+ 24V (direct current)) is applied to the static eliminator 36 (see FIG. 3).

The exposure control unit 46 controls the light emission of the exposure device 15 according to an instruction from the control unit 41. That is, the exposure control unit 46 is the exposure device 15 of (K), (Y), (M), (C) or (Y), (M), (C), as will be described later, based on the image data. FIG. 1 shows that the surfaces of the charged photoconductor drums 13 facing each other are irradiated with light to control the formation of an electrostatic latent image. Upon receiving an instruction from the control unit 41, the fixing control unit 45 drives and controls a halogen lamp (not shown) to control the temperature of the fixing device 28.

The control unit 41 also includes a transport motor that rotationally drives the registration roller pair 23, a discharge motor that rotationally drives the discharge roller pair 32, a hopping motor that rotationally drives the hopping roller 22, and the like via the drive control unit 44. The entire image forming apparatus 11 is sequence-controlled by controlling the rotation of the image forming apparatus 11.

The printing operation of the image forming apparatus 11 configured as described above will be described with reference to FIGS. 1 to 3.

First, the recording media 30 in which a plurality of sheets are stacked in the paper feed tray 24 are sequentially fed from the uppermost one by the hopping roller 22 whose rotation is controlled in the direction of the arrow by the control unit 41, and along the paper guide 33. It is sent to the resist roller pair 23 to correct the skew, and then sent from the resist roller pair 23 to the transfer belt 26 and mounted on the transfer belt 26 to the image forming units 12K, 12Y, 12M, 12C. It is transported in sequence.

On the other hand, in each image forming unit 12, the surface of the photoconductor drum 13 whose rotation is controlled in the direction of the arrow by the drive control unit 44 and the drum motor 49 is a charging roller to which a DC voltage (-1050V) is applied by the voltage control unit 47. It is uniformly charged by 14 and exposed by the corresponding exposure device 15. At this time, the exposure apparatus 15 irradiates the surface of the photoconductor drum 13 with light whose exposure amount is adjusted based on the image data created by the image information creation unit 41b, and forms an electrostatic latent image on this surface.

The surface of the photoconductor drum 13 is charged when a charging voltage equal to or higher than a predetermined value is applied to the charging roller 14, and the surface potential changes in proportion to the applied charging voltage. Here, when −1050 V (charging voltage) is applied to the charging roller 14, the surface potential of the photoconductor drum 13 is charged to about −500 V, and the latent image potential of the latent image pattern formed by exposure by the exposure apparatus 15 is The voltage becomes about −50 V, and the toner is reverse-developed from the developing roller 16 in the latent image pattern, and in the case of positively charged toner, the sign of the voltage is reversed.

Toner 25 thinned on the developing roller 16 is electrostatically adhered to the portion where the electrostatic latent image is formed, and a toner image of the corresponding color is formed. At this time, the developing roller 16 and the supply roller 18 rotate in a direction different from that of the photoconductor drum 13 while maintaining a predetermined peripheral speed ratio as the photoconductor drum 13 rotates in the direction of the arrow.

In FIG. 1, the toner 25 contained in the toner accommodating portion 20 is held in the cells in the supply roller 18 and is rubbed between the supply roller 18 and the developing roller 16 to carry a negative electrode charge. Further, the toner 25 carries the electric charge that moves between the members to which the voltage is applied by moving to the toner 25. Then, the toner 25 carrying the electric charge adheres to the developing roller 16 due to the electric field generated by the potential difference between the supply roller 18 and the developing roller 16.

The toner 25 on the developing roller 16 is regulated to a uniform toner layer thickness by the developing blade 19, and is triboelectrically charged by being rubbed by the developing blade 19 and the developing roller 16. The toner 25 on the developing roller 16 is conveyed to the electrostatic latent image on the photoconductor drum 13 and adheres to the electrostatic latent image due to the potential difference between the electrostatic latent image and the developing roller 16 to develop the electrostatic latent image. The toner 25 on the undeveloped developing roller 16 is scraped off by the supply roller 18.

The toner image formed on each photoconductor drum 13 by the development is transferred to the recording medium 30 by the corresponding transfer roller 17 to which the bias voltage (direct current) is applied by the transfer voltage generating unit 51. This transfer is executed in a sequential manner at the timing when the recording medium 30 is conveyed to the transfer belt 26 and reaches each transfer portion (nip portion between the photoconductor drum 13 and the transfer roller 17), whereby the transfer medium 30 is executed on the recording medium 30. A color toner image is formed in. After the transfer, the toner 25 (residual toner) remaining on each photoconductor drum 13 is removed by a cleaning device 27 provided with a cleaning blade 27a.

The static elimination device 36 irradiates the surface of the photoconductor drum 13 with static elimination light from the LED element 36b by applying a DC voltage of 24V to the plurality of LED elements 36b (FIG. 3) by the voltage control unit 47. This exposure resets the surface potential of the photoconductor drum 13 after transfer.

The recording medium 30 on which the color toner image is formed by the transfer is sent to the fixing device 28. By the heating / pressurizing treatment in the fixing device 28, the color toner image is fixed on the recording medium 30 and a color image is formed. The recording medium 30 on which the color image is formed is conveyed along the paper guide portion 31, and is ejected to the paper stacker portion 29 by the ejection roller pair 32.

Through the above process, a color image is formed on the recording medium 30. The residual toner adhering to the transfer belt 26 is scraped off by the belt cleaning blade 34 and stored in the belt cleaner container 35.

The recording medium 30 includes plain paper, slightly thick paper, gloss paper, thick paper and the like as low resistance media, and as a specific example, excellent white paper (manufactured by Oki Data, volume resistance 9. 64 x 10 ⁹ Ω / cm ³ ), P-thick paper as a slightly thick paper (manufactured by Fuji Xerox, volume resistance 1.36 x 10 ¹¹ Ω / cm ³ ), gloss text (manufactured by Future Laser, volume resistance) The rate is 2.02 × 10 ¹¹ Ω / cm ³ ), and the thick paper is LABEL33up paper (manufactured by Xerox, volumetric resistance 3.85 × 10 ¹² Ω / cm ³ ).

Further, as a high resistance medium, there are a film medium using polyester or the like, coated paper, and the like. As a specific example, the film medium is laser peach paper (manufactured by Daio Postal Chemical Co., Ltd., volumetric resistance 5.05 × 10 ¹⁴ Ω / cm ³ ), Lami-free paper (manufactured by Nakagawa Seisakusho, volumetric resistance 3.72 x 10 ¹⁵ Ω / cm ³ ), Kaleka paper (manufactured by Mitsubishi Chemical Media, volumetric resistance) as coated paper coated with paper to give smoothness. A rate of 1.36 × 10 ¹⁶ Ω / cm ³ ) can be mentioned.

The volumetric resistance value is measured in an RT environment (26 ° C., using a digital ultra-high resistance / micro ammeter (R8340, ADC Co., Ltd.) and a digital electrometer (R12702A, ADC Co., Ltd.). Humidity 37%) and applied voltage 500V.

In this embodiment, as the recording medium 30, as plain paper having a low resistance medium using excellent white paper (made by Oki Data, volume resistivity ^{9.64 × 10 9 Ω / cm 3} ), high resistance medium coat Lami-free paper (manufactured by Nakagawa Seisakusho, volume resistivity 3.72 × 10 ¹⁵ Ω / cm ³ ) is used as the paper, and laser peach (manufactured by Daio Postal Chemical, volume resistivity 5) is used as the film medium of the high resistance medium. .05 × 10 ¹⁴ Ω / cm ³ ) was used.

Further, as a method of distinguishing between a low resistance medium and a high resistance medium, between a low resistivity medium in which a history (concentration step) described later does not occur and a high resistivity medium in which a history (concentration step) described later occurs. Boundary values may be set. Specifically, a value between the volume resistivity of the thick paper and the film medium may be set as a boundary value, and for example, the boundary value may be defined as 5.00 × 10 ¹³ Ω / cm ³ .

Here, the transfer voltage applied to each transfer roller 17 by the transfer voltage generating unit 51 will be considered.

Coated paper, film medium, etc. (hereinafter referred to as high resistance medium), which have a higher volume resistance value than plain paper (low resistance medium), have a toner image when the same transfer voltage as plain paper is applied to the transfer roller 17 during transfer. Is not transferred to the high resistance medium, and transfer blurring occurs. Therefore, when transferring to a high resistance medium, it is necessary to apply a higher transfer voltage to the transfer roller 17 than when transferring to plain paper.

Further, in the transfer step, a transfer voltage having a polarity opposite to the charge polarity of the toner is applied, but at this time, the medium itself is charged. Since the charging of the recording medium 30 increases by repeating the transfer process from the upstream to the downstream, in order to prevent transfer blurring, the recording medium 30 is arranged downstream in order to overcome the charging of the recording medium 30. It is necessary to apply a transfer voltage as high as the transfer roller 17.

By the way, in the transfer step, when the transfer current flows into the photoconductor drum 13 outside the passing region of the recording medium 30, positive charges are accumulated in the photoconductor drum 13 and the photoconductor drum 13 becomes opposite polarity (positive polarity). It is charged. If this is repeated, the photoconductor drum 13 becomes poorly charged. The surface potential of the photoconductor drum 13 after the charging voltage is applied by the charging roller 14 at the portion where the charging defect occurs is lower than the surface potential at the portion where the charging defect does not occur. Even if the portion that has become poorly charged is left for several hours, it does not improve and a concentration difference occurs. The poor charging that does not improve even after being left for several hours is referred to as a strong transfer history here.

When a halftone image is printed in a state where this strong transfer history is generated, the density becomes high at the place where the charging defect occurs, and the printing defect of streaks and bands occurs. This printing defect does not appear on the print as long as the recording medium 30 having the same print width is printed in the same passing area, because the defective charging portion exists outside the passing area of the recording medium 30. If the wide recording medium 30 is printed after printing the narrow printing medium 30, charging defects will occur in the print area of the wide recording medium 30, and the effect will appear on the print. ..

Table 1 shows the test results in Test 1 in which 20 sheets of plain paper, coated paper, and film medium were printed by A4 vertical feed printing and then halftone images were printed by A4 horizontal feed, and printing defects were shown. The level of is represented by color. In the table, ○, △, and × indicate the image quality evaluation of streaks and bands at the time of printing. If there is no problem with both, it is judged as ○, and if the streaks and bands can be slightly confirmed, it is judged as △. If the streaks and bands can be clearly seen, it is marked as x. In either case, the judgment is visual.

Further, the apparatus used in this test 1 has the same configuration as the image forming apparatus 11, and the applied voltage to each part was also applied by applying the voltage described above. However, the transfer voltage differs depending on the type of the recording medium 30, and is set higher than that of the transfer roller 17 facing the photoconductor drum 13 arranged downstream.

In the apparatus used here, similarly to the image forming apparatus 11 of the present embodiment shown in FIG. 1, the image forming unit 12K for black (K), yellow, in order from the upstream side in the paper transport direction (arrow A direction). The image forming unit 12Y for (Y), the image forming unit 12M for magenta (M), and the image forming unit 12C for cyan (C) are arranged side by side.

As shown in Table 1, in the coated paper, a slight streak band was generated in cyan (C), and in the film medium, a streak band was clearly generated in cyan (C). From this, it can be seen that the streak band due to poor charging is generated in the most downstream cyan (C) that requires a higher transfer voltage when printing a medium having a high volume resistance that requires a high transfer voltage. ..

The evaluation test result here is to apply an appropriate transfer voltage to each medium, and this appropriate transfer voltage applies not only to the resistivity of the medium but also to the surface properties and dielectric constant. Because it is affected, for example, a medium with a certain resistivity may have a higher suitable transfer voltage than a medium with a higher resistivity.

The image forming apparatus 11 of the present embodiment has the following features in order to prevent streaks and bands generated due to poor charging due to strong transfer history generated after printing on a high resistance medium.
(1) When printing on a high-resistance medium, printing is performed in three colors of yellow (Y), magenta (M), and cyan (C) without using the black (K) image forming unit 12K. The high-resistance medium defined here is a medium having a volume resistivity of 5.00 × 10 ¹³ Ω / cm ³ or more as described above.
(2) The black (K) image forming unit 12K drives the photoconductor drum 13K in contact with the transfer belt 26 in the same manner as during normal printing in order to stably convey the recording medium 30, and charges the image forming unit 12K. The development and supply voltages are applied in the same manner as during normal printing.
The term "normal printing" as used herein refers to a state in which a low-resistance medium such as plain paper is printed.
(3) When the black (K) image forming unit 12K is arranged in the uppermost stream, the transfer voltage applied to the black (K) transfer roller 17K is turned off (here, 0V), and yellow (Y), The absolute value of the transfer voltage applied to each of the magenta (M) and cyan (C) transfer rollers 17 is set smaller than that in the case of printing in four colors (see Table 2-1).
(4) When the black (K) image forming unit 12K is arranged at the most downstream, the transfer voltage applied to each of the yellow (Y), magenta (M), and cyan (C) transfer rollers 17 is printed in four colors. The settings are the same as at the time, and the transfer voltage applied to the black (K) transfer roller 17K is set to be equal to or less than the absolute value of the transfer voltage applied to the transfer roller 17 (here, cyan (C)) one upstream (here). See Table 2-2).

Here, the difference between the image data created when the image information creation unit 41b performs four-color printing and the image data created when performing three-color printing will be described.
When performing four-color printing, the image information creation unit 41b creates four image data for black (K), yellow (Y), magenta (M), and cyan (C), and the four image forming units 12 create four image data. A desired color image is formed by creating a toner image based on the image data of each corresponding color and sequentially superimposing and transferring these toner images on the recording medium 30.

On the other hand, when performing three-color printing, the image information creation unit 41b corresponds to a black toner image formed by the image forming unit 12K for black (K) based on the image data for black (K) during four-color printing. The image to be printed is formed by black (hereinafter, may be referred to as process black) formed by three color toners of yellow (Y), magenta (M), and cyan (C). Therefore, the three image data for yellow (Y), magenta (M), and cyan (C) at the time of three-color printing form a black image by process black on the image data of each color at the time of four-color printing. The data for process black for this is added.

At this time, except for the image data (image data formed by process black) corresponding to the black toner image formed by the three color toners of yellow, magenta, and cyan, it may be appropriately formed according to the print pattern. That is, the image data of yellow single color, magenta single color, and cyan single color may not be created depending on the print pattern.

Based on the characteristics of the image forming apparatus 11 of (1) to (4) described above, the transfer voltage at the time of printing on a high resistance medium by the image forming apparatus 11 of the first embodiment will be further described. Further, here, a case where a film medium is printed as a high resistance medium will be described.

Table 2-1 shows the case where the image forming unit 12K for black (K) is arranged in the most upstream direction of the recording medium 30 in the transport direction (FIG. 1, arrow A direction) among the four image forming units 12. , The transfer voltage value applied to the transfer roller 17 facing the photoconductor drum 13 of each color is shown. As shown in the table, here, four image forming units 12 are arranged in the order of black (K), yellow (Y), magenta (M), and cyan (C) from the upstream side, and face each other. The transfer voltage is turned off (0V is set here) for the transfer roller 17K, 1.8 kV is applied to the transfer roller 17Y, 2.0 kV is applied to the transfer roller 17M, and the transfer roller 17C is applied. On the other hand, 2.7 kV is applied.

As shown in Table 2-1 when the image forming unit 12K for black (K) is arranged at the uppermost stream in the transport direction (arrow A direction) of the recording medium 30, the transfer roller corresponding to black (K) The transfer voltage applied to 17K can be turned off. As a result, the transfer voltage corresponding to yellow (Y) is changed from 2.0 kV to 1.8 kV, the transfer voltage corresponding to magenta (M) is changed from 2.7 kV to 2.0 kV, and the transfer voltage corresponding to cyan (C) is changed. Can be set as low as 3.3 kV to 2.7 kV, respectively. If the maximum value of the transfer voltage can be suppressed to 2.7 kV in this way, as confirmed in Test 1, deterioration of print quality (generation of streaks and bands) due to poor charging can be prevented.

The transfer voltage applied to the transfer roller 17K corresponding to the black (K) image forming unit 12K arranged at the uppermost stream is set to such that the photoconductor drum 13 on the downstream side does not have a charge defect. It suffices, and it can be adjusted appropriately within a setting range equal to or lower than that at the time of normal printing.

Table 2-2 shows the case where the image forming unit 12K for black (K) is arranged at the most downstream side of the recording medium 30 in the transport direction (FIG. 1, arrow A direction) among the four image forming units 12. , The transfer voltage value applied to the transfer roller 17 facing the photoconductor drum 13 of each color is shown. As shown in the table, here, four image forming units 12 are arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side, and face each other. 1.8 kV is applied to the transfer roller 17Y, 2.0 kV is applied to the transfer roller 17M, 2.7 kV is applied to the transfer roller 17C, and 2.7 kV is applied to the transfer roller 17K. It is being applied.

As shown in Table 2-2, when the image forming unit 12K for black (K) is arranged at the most downstream of the transport direction (arrow A direction) of the recording medium 30, the transfer roller corresponding to black (K) The transfer voltage applied to 17K was set to be the same as the transfer voltage applied to the transfer roller 17C corresponding to the cyan (C) on the upstream side. This setting does not need to transfer the toner on the black (K) photoconductor drum 13K, but does not move the toner image formed on the recording medium on the upstream side to the black (K) photoconductor drum 13K. Therefore (to prevent reverse transfer), this is done to apply an electrical force to the toner on the recording medium in the transfer direction, which is the most preferable setting here, the transfer roller corresponding to cyan (C). The same voltage as 17C is applied.

Here, too, the maximum value of the transfer voltage can be suppressed to 2.7 kV, so that it is possible to prevent deterioration of print quality (generation of streaks and bands) due to poor charging, as confirmed in Test 1.

If the transfer voltage applied to the transfer roller 17K corresponding to the image forming unit 12K for black (K) arranged at the most downstream side is set so as not to disturb the toner image formed on the recording medium on the upstream side. Therefore, the transfer voltage is not limited to the same as that of the transfer roller 17C corresponding to cyan (C), and can be appropriately adjusted within a range equal to or less than the absolute value of the transfer voltage.

Here, the four image forming units 12 are arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side, but yellow (Y) and magenta (M). ) And cyan (C) can be freely set as appropriate. However, the method of applying the transfer voltage to each transfer roller 17 in which the downstream side is sequentially set to be high is not changed.

FIG. 4 is a flowchart showing the flow of printing processing performed by the image forming apparatus 11 of the first embodiment. Hereinafter, the printing operation of the image forming apparatus 11 will be described with reference to this flowchart.

This flow starts, for example, when the power of the image forming apparatus 11 is turned on. When the receiving unit 43 receives the print data from the host device, it transmits the print data to the control unit 41 (step S101), and the medium setting control unit 41a is the medium setting unit. 42 or the medium setting information set by the host device, that is, the medium information of the recording medium to be printed is acquired (step S102).

The medium setting control unit 41a determines from the acquired information whether or not the medium setting is printing of a high resistance medium (step S103). Here, when the medium information is plain paper, it is determined to be a low resistivity medium, and when it is a coated paper or a film medium, it is determined to be a high resistivity medium, but the volume resistivity of the medium is used as a reference. For example, a medium having a volume resistivity of 5.00 × 10 ¹³ Ω / cm ³ or more can be determined as a high-resistive medium.

In the case of a high resistance medium (step S103, Yes), the image information creation unit 41b uses three colors of yellow (Y), magenta (M), and cyan (C) based on the print data sent to the control unit 41. The image data to which the process black data of the above is added is generated and sent to the image output unit 41c (step S104).

The voltage control unit 47 sets the transfer voltage for the high resistance medium (step S105). That is, when the image forming unit 12K for black (K) is arranged at the uppermost stream in the transport direction (FIG. 1, arrow A direction) of the recording medium 30, the transfer voltage shown in Table 2-1 is applied. When the image forming unit 12K for black (K) applied to each transfer roller 17 is arranged at the most downstream side in the transport direction (arrow A direction) of the recording medium 30, it is shown in Table 2-2. A transfer voltage is applied to each transfer roller 17 to execute printing (step S108).

On the other hand, when the determination in step S103 indicates that the medium is not a high resistance medium (step S103, No), the image information creation unit 41b is a normal black (K), based on the print data sent to the control unit 41. Image data excluding the process black data in the four colors of yellow (Y), magenta (M), and cyan (C) is created and sent to the image output unit 41c (step S106).

The voltage control unit 47 sets the transfer voltage for normal printing (step S107). That is, regardless of the arrangement of the image forming unit 12K for black (K), for example, the transfer voltage corresponding to plain paper shown in Table 1, 1.6 kV, 1.7 kV, 1.9 kV, 2.0 kV in order from the upstream side. Is applied and printing is executed (step S108).

In this embodiment, a medium having a volume resistivity of 5.00 × 10 ¹³ Ω / cm ³ or more, including film paper and coated paper, is defined as a high resistance medium, and the medium is selected by selecting the type of medium. Whether or not it was decided, but it is not limited to this, and it can be defined by the resistance value of the medium and the thickness of the medium.

As described above, according to the image forming apparatus 11 of the present embodiment, when the recording medium 30 to be printed is a high resistance medium, the toner image is not formed by the black (K) image forming unit 12K. Since printing is performed for 4 colors including process black with 3 colors of yellow (Y), magenta (M), and cyan (C), the applied voltage as the required transfer voltage can be reduced, and it is strong. It is possible to suppress deterioration of print quality due to the generation of transfer history.

Embodiment 2.
FIG. 5 is a flowchart showing the flow of printing processing performed by the image forming apparatus of the second embodiment.

The image forming apparatus of the second embodiment is different from the image forming apparatus 11 of the first embodiment in the black (K) image forming unit 12K which does not form an image at the time of printing on a high resistance medium. It is characterized in that the absolute value of the voltage difference is made smaller than that at the time of normal printing. Table 3 shows the charging voltage applied to the charging roller 14K of the black (K) image forming unit 12K and the developing voltage applied to the developing roller 16K at this time, together with the voltage values at the time of normal printing.

Here, the image forming unit 12, the exposure apparatus 15, and the transfer roller 17 correspond to the image forming unit, and the control unit 41 corresponds to the print control unit.

As shown in the table, the charging voltage is -1050V and the developing voltage is -200V during normal printing, but the charging voltage is -900V and the developing voltage is -200V during printing on a high resistance medium, and the difference between the charging voltage and the developing voltage is set. The absolute value of is reduced. As a result, the low-charged toner and the back-charged toner can move to the surface of the photoconductor drum 13K where the electrostatic latent image is not formed, and can suppress "fog" adhering to the non-image area, resulting in improved image quality. improves. Reducing the difference between the charging voltage and the developing voltage affects the image density and color gradation, but since the black (K) development forming unit 12K is not used when printing on a high-resistance medium, such an applied voltage is used. It can be set.

The printing operation of the image forming apparatus according to the present embodiment will be described with reference to the flowchart of FIG.

As is clear from the comparison with the flowchart of FIG. 4 showing the flow of the printing process performed by the image forming apparatus 11 of the first embodiment, in the printing process performed by the image forming apparatus of the present embodiment, the first embodiment The only difference from the printing process performed by the image forming apparatus 11 is that step S105-1 is added to the flowchart of FIG. Therefore, the description of steps S101 to S108 will be omitted, and only the added step S105-1 will be described.

The voltage control unit 47 sets the transfer voltage for the high resistance medium in step 105, sets the charging voltage for the high resistance medium shown in Table 3 in step S105-1, and then executes printing in step S10. Is what you do.

Here, the set value of the charging voltage was changed in order to reduce the absolute value of the difference between the charging voltage and the developing voltage, but the setting value is not limited to this, and a method of reducing the difference by increasing the developing voltage or , A method of changing both the charging voltage and the developing voltage may be used.

As described above, according to the image forming apparatus of the present embodiment, it is possible to suppress the deterioration of print quality due to the generation of strong transfer history, and also to suppress the fog phenomenon in the black (K) image forming unit 12K. Therefore, the print quality can be further improved accordingly.

In addition, in the description of the scope of claims and the embodiment described above, the terms "top", "bottom", "left", "right", "front", and "rear" are used, but these are for convenience. However, it does not limit the absolute positional relationship in the state where the image forming apparatus is arranged.

In the present embodiment, a tandem color printer provided with a plurality of development units as an image forming apparatus has been described as an example, but in addition to the color printer, a copier, a fax machine, or an MFP that combines the functions of these devices ( It is also useful for an image forming apparatus such as a MultiFunction Peripheral). It is also useful for a monochrome image forming apparatus using one image forming unit.

11 Image forming device, 12 Image forming unit, 13 Photoreceptor drum, 14 Charging roller, 15 Exposure device, 16 Development roller, 17 Transfer roller, 18 Supply roller, 19 Development blade, 20 Toner container, 21 Transfer unit, 21a Transfer Belt drive roller, 21b Transfer belt driven roller, 22 Hopping roller, 23 Resist roller pair, 24 Paper feed tray, 25 Toner, 26 Transfer belt, 27 Cleaning device, 28 Fixer, 28a Heating roller, 28b Pressurizing roller, 29 Paper Stacker, 30 Recording medium, 31 Paper guide, 32 Discharge roller pair, 33 Paper guide, 34 Belt cleaning blade, 35 Belt cleaner container, 36 Static eliminator, 38 Touch panel, 39 Upper cover, 40 Rotating shaft, 41 Control , 41a Media setting control unit, 41b Image information creation unit, 41c Image output unit, 42 Media setting unit, 43 Receiver unit, 44 Drive control unit, 45 Fixing control unit, 46 Exposure control unit, 47 Voltage control unit, 48 Belt motor , 49 Drum motor.

Claims (11)

A black toner image forming unit that forms a black toner image,
A color toner image forming part consisting of a toner image forming part for forming a yellow toner image, a toner image forming part for forming a magenta toner image, and a toner image forming part for forming a cyan toner image.
An input unit where print data is input from an external device,
A medium determination unit that determines the type of recording medium to be printed,
Based on the print data, a first image data group including image data for creating a toner image in the black toner image forming unit and the color toner image forming unit, respectively, according to the type of the recording medium, and An image data creation unit that selectively generates a second image data group consisting of image data for creating a toner image only by the color toner image formation unit, and an image data creation unit.
It is characterized by including an output of the first image data group or the second image data group, and an output unit for instructing the operation of the black toner image forming unit and the color toner image forming unit according to the output. Image forming apparatus. When the image data creating unit generates the second image data group, when the black toner image forming unit and the color toner image forming unit each create a toner image based on the first image data group. The second image data group is generated so that an image corresponding to the black toner image created by the black toner image forming unit is formed by three types of toners of yellow, magenta, and cyan. The image forming apparatus according to claim 1. The medium determination unit determines whether or not the recording medium to be printed is a high resistance medium.
When the recording medium to be printed is the high resistance medium, the image data creation unit generates the second image data group.
The image forming apparatus according to claim 1 or 2, wherein the output unit outputs the second image data group to the color toner image forming unit. A medium transport unit that transports the recording medium and
A black transfer unit arranged at a position facing the black toner image forming unit via the medium transport unit, and a black transfer unit.
The transfer unit for yellow, which is arranged via the medium transfer unit at a position facing the toner image forming unit that forms the yellow toner image, and the medium transfer unit that faces the toner image forming unit that forms the toner image of magenta. A magenta transfer unit arranged via the unit, a color transfer unit composed of a cyan transfer unit arranged via the medium transport unit at a position facing the toner image forming unit forming a cyan toner image, and a color transfer unit.
A voltage control unit that sets the applied voltage applied to each of the four transfer units in response to an instruction from the output unit.
With
The output unit is the absolute value of the applied voltage applied from the upstream side to the downstream side with respect to the black transfer unit and the color transfer unit arranged in order from the upstream side in the transport direction of the recording medium. The image forming apparatus according to claim 3, wherein the image forming apparatus is set to be large or equivalent. When the black toner image forming portion is arranged upstream of the color toner image forming portion in the transport direction of the recording medium,
The image forming apparatus according to claim 4, wherein the output unit sets the applied voltage applied to the black transfer unit to off when the recording medium to be printed is the high resistance medium. When the black toner image forming portion is arranged on the downstream side of the color toner image forming portion in the transport direction of the recording medium.
When the recording medium to be printed is the high resistance medium, the output unit may be used.
The feature is that the applied voltage applied to the black transfer unit is set to be equal to or lower than the applied voltage applied to the transfer unit facing the toner image forming unit located at the most downstream side of the color toner image forming unit. The image forming apparatus according to claim 4. The black toner image forming unit is
Image carrier and
A charging means for charging the surface of the image carrier to a predetermined potential,
A toner carrier that develops an electrostatic latent image of the image carrier, and
Have,
The voltage control unit receives an instruction from the output unit and sets a charging voltage applied to the charging means and a developing voltage applied to the toner carrier.
In the output unit, the difference between the absolute value of the development voltage and the absolute value of the development voltage, which is set when the recording medium to be printed is the high resistance medium, is set as the first voltage difference, and the recording medium to be printed is When the difference between the absolute value of the development voltage and the absolute value of the development voltage, which is set when the medium is not the high resistance medium, is the second voltage difference.
The image forming apparatus according to claim 5 or 6, wherein the first voltage difference is set to be less than the second voltage difference. The image forming apparatus according to claim 7, wherein the output unit changes the charging voltage and / and the developing voltage when the recording medium to be printed is the high resistance medium. A plurality of image forming portions that individually form toner images of multiple colors on a recording medium,
An input unit for inputting print data from an external device,
It has a print control unit that determines the type of recording medium to be printed and instructs the plurality of toner image forming units to print from the input print data.
The print control unit is an image forming apparatus that reduces the number of the plurality of image forming units used when printing the print data according to the selected recording medium. The print control unit 41 is characterized in that a low resistance medium or a high resistance medium can be selected, and when the high resistance medium is selected, the number of the plurality of image forming units used for printing is reduced. Item 9. The image forming apparatus according to item 9. The plurality of image forming portions
A black image forming unit that forms a black toner image on a recording medium,
A yellow image forming unit that forms a yellow toner image on a recording medium,
A magenta image forming unit that forms a magenta toner image on a recording medium,
It has a cyan image forming portion that forms a cyan toner image on a recording medium, and has a cyan image forming portion.
The image forming apparatus according to claim 10, wherein the print control unit does not instruct the black image forming unit to print when printing the print data when a high resistance medium is selected.

Images