JP5929793B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  As a prior art described in the publication, in an electrophotographic laser printer (image forming apparatus), as a charging device for charging a photosensitive member, a charging roller arranged in contact with the photosensitive member is used, and a DC voltage is applied to the charging roller. There is one in which a bias voltage superimposed with a voltage is applied (see Patent Document 1).

JP 2011-133686 A

  Here, an object of the present invention is to make inconsistent micro density unevenness due to noise in an output image in an image forming apparatus using a contact charging system.

According to a first aspect of the present invention, there is provided a rotating image carrier, and a contact charging unit that is arranged in contact with the image carrier and charges the image carrier using a charging bias in which an alternating current component is superimposed on a direct current component. And exposing the charged image holding member to form an electrostatic latent image, and developing the electrostatic latent image formed on the image holding member with toner using a supplied developing bias. The difference between the developing means, the recording means for recording the toner image formed on the image carrier on a recording material, and the potential of the developing bias and the image portion of the image carrier on which the toner is to be developed. The recording means is set so that the gloss of the toner image recorded on the recording material is lower when a certain flight potential difference is equal to or less than a predetermined threshold value, compared to when the flight potential difference exceeds the threshold value. and setting means only including, of toner A plurality of the developing means having different colors are provided, and the setting means sets the recording means based on the flying potential difference in the developing means using the toner having the lowest brightness among the plurality of developing means. An image forming apparatus characterized by the above.

According to a second aspect of the present invention, when the flying potential difference exceeds the threshold value, the setting means has a primary color glossiness X of a toner image recorded on the recording material by the recording means as 15 <X <40. 2. The image forming apparatus according to claim 1 , wherein when the flying potential difference is equal to or smaller than the threshold value, the recording unit is set so that the primary color glossiness X satisfies 10 <X <25. . (However, the primary color glossiness X is continuously 20 sheets by the recording means for a recording material having a basis weight of 127 gsm and a 60 ° glossiness (JISZ8741) 34 in an environment of a temperature of 22 ° C. and a humidity of 50%. (The glossiness is 60 ° in the 11th to 20th recording materials when a 100% toner image is recorded.)
According to a third aspect of the present invention, the recording unit heats the recording material to a transfer portion that transfers the toner image formed on the image carrier to the recording material, and the toner image transferred to the recording material. 3. The image forming apparatus according to claim 1 , wherein the setting unit sets an amount of heat applied to the recording material that passes through the fixing unit.

According to the first aspect of the present invention, in comparison with the case where the present configuration is not provided, in the image forming apparatus using the contact charging method , a micro color due to noise caused by a specific color in the output color image. Unevenness of high density can be made inconspicuous.
According to the second aspect of the present invention, it can be compared with the case not having this constitution, more properly, in the image output, inconspicuous unevenness of microscopic density due to noise.
According to the invention described in claim 3, it is possible to set the difference in gloss by a simpler method as compared with the case where the present configuration is not provided.

1 is a diagram illustrating an overall configuration example of an image forming apparatus according to an embodiment. 2 is a block diagram for explaining a configuration of a control system in the image forming apparatus. FIG. FIG. 4 is a diagram for explaining a relationship between a charging potential and an exposure potential on a photosensitive drum and a developing bias potential in a developing device. Difference in flight potential and visual image noise feeling when charging is performed by contact charging using a charging roll and by non-contact charging using scorotron, etc. It is a figure for demonstrating the relationship. 6 is a flowchart illustrating a procedure of fixing condition setting operation. It is a figure for demonstrating the content of the condition determination table used by the process which determines fixing conditions. FIG. 3 is an enlarged view of a printed matter output by the image forming apparatus according to the present embodiment. It is a figure for demonstrating the relationship between the image fixed on the paper and the paper, and the visual noise feeling. FIG. 6 is a diagram illustrating a relationship between the glossiness of a primary color image fixed on a sheet and the visual noise feeling of the primary color image. 6 is a diagram for explaining a relationship between fixing conditions and image glossiness. FIG.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment.
The image forming apparatus includes, for example, a plurality (four in the present embodiment) of image forming units 10 (specifically, 10Y, 10M, 10C, and 10K) that form toner images of each color by electrophotography, and image formation. An intermediate transfer belt 20 that transfers (primary transfer) and holds each color toner image formed by the unit 10; and a secondary transfer device 30 that secondary-transfers the superimposed toner image primarily transferred to the intermediate transfer belt 20 onto a sheet. The image forming apparatus includes a fixing device 50 that fixes the second-transferred image on a sheet, and a control device 100 that controls the operation of each unit constituting the image forming apparatus.

  Each image forming unit 10, that is, a yellow (Y) image forming unit 10Y, a magenta (M) image forming unit 10M, a cyan (C) image forming unit 10C, and a black (K) image forming unit 10K is used. Except for the color of the toner, they have a common configuration. Therefore, the yellow image forming unit 10Y will be described as an example.

  The yellow image forming unit 10Y includes a photosensitive drum 11 that is rotatably provided in the arrow A direction. Further, the yellow image forming unit 10Y has a charging roll 12, an exposure unit 13, a developing device 14, a primary transfer roll 15 and a drum cleaner 16 provided around the photosensitive drum 11 in the clockwise direction in the drawing. doing.

  In the present embodiment, the photosensitive drum 11 as an example of the image carrier is formed by forming an organic photosensitive layer (not shown) on the surface of a thin metal cylindrical drum. It is composed of a negatively charged material. The photosensitive drum 11 is grounded.

  The charging roll 12 as an example of the contact charging unit is rotatably disposed in contact with the photosensitive drum 11, and is rotated by the rotation of the photosensitive drum 11. The charging roll 12 is applied with a charging bias for charging the photosensitive drum 11 to a negative potential. Here, the surface of the charging roll 12 is made of a sponge material made of foamed polyurethane in which many holes are formed.

  The exposure unit 13 as an example of an exposure unit forms an electrostatic latent image by selectively performing light writing on the photosensitive drum 11 charged to a negative potential by the charging roll 12 using a laser beam or the like. . Here, the exposure unit 13 of the present embodiment irradiates light to a part (image part) that becomes a toner image (image) and does not irradiate light to a part (background part) that becomes a background. Exposure is performed by a so-called image portion exposure method. In addition to the laser light source, an LED (Light Emitting Diode) light source may be used as the light source in the exposure unit 13.

  The developing device 14 as an example of the developing unit includes a developing roll 14a that is rotatably disposed opposite to the photosensitive drum 11, and includes a corresponding color toner (yellow image forming unit 10Y). In this case, a developer containing yellow toner is accommodated. Here, in the developing device 14 of the present embodiment, a so-called developer includes a carrier having magnetism and toner colored in a predetermined color (yellow in the case of the yellow image forming unit 10Y). A two-component developer is used. In this developer, the carrier has a positive charging polarity, and the toner has a negative charging polarity. The developing roll 14a incorporates a magnet (not shown), and a carrier, that is, a developer to which toner is attached by electrostatic force, is held on the surface of the developing roll 14a by magnetic force. In the developing device 14, the electrostatic latent image on the photosensitive drum 11 is developed by a developer (toner) held on the developing roll 14a. The developing device 14 transfers a negatively charged toner to the negatively charged image portion of the electrostatic latent image by supplying a developing bias for setting the developing roll 14a to a negative potential. Development is performed by a so-called reversal development method.

The primary transfer roll 15 faces the photosensitive drum 11 with the intermediate transfer belt 20 interposed therebetween, is disposed in contact with the intermediate transfer belt 20, and rotates following the rotation of the intermediate transfer belt 20. The primary transfer roll 15 is applied with a primary transfer bias having a polarity (positive in this example) opposite to the charging polarity of the toner.
The drum cleaner 16 removes deposits (toner and the like) on the photosensitive drum 11 after the primary transfer and before charging.

  The intermediate transfer belt 20 is rotatably wound around a plurality of (six in the present embodiment) support rolls. Among the plurality of support rolls, the drive roll 21 stretches the intermediate transfer belt 20 and rotationally drives the intermediate transfer belt 20 in the arrow B direction. The driven rolls 22, 23, and 26 stretch the intermediate transfer belt 20 and rotate following the intermediate transfer belt 20 driven by the drive roll 21. The correction roll 24 stretches the intermediate transfer belt 20 and regulates the meandering in the width direction intersecting the conveyance direction of the intermediate transfer belt 20 (is disposed so as to be tiltable with one axial end as a fulcrum). Function as. Further, the backup roll 25 stretches the intermediate transfer belt 20 and functions as a constituent member of the secondary transfer device 30 described later. A belt cleaner 27 that removes deposits (toner and the like) on the intermediate transfer belt 20 after the secondary transfer is disposed at a portion facing the drive roll 21 with the intermediate transfer belt 20 interposed therebetween.

  The secondary transfer device 30 includes a secondary transfer roll 31 disposed in contact with the toner image transfer surface side of the intermediate transfer belt 20, and a counter electrode of the secondary transfer roll 31 disposed on the back surface side of the intermediate transfer belt 20. And a backup roll 25. A secondary transfer bias having the same polarity (negative polarity in this example) as the charging polarity of the toner is applied to the backup roll 25. On the other hand, the secondary transfer roll 31 is grounded.

  The image forming apparatus further includes a paper transport system that transports paper as an example of a recording material. The paper transport system includes a paper storage unit 40, a transport roll 41, a registration roll 42, a transport belt 43, and a discharge roll 44. In the paper transport system, the paper loaded in the paper storage unit 40 is transported by the transport roll 41, temporarily stopped by the registration roll 42, and then sent to the secondary transfer device 30 at a predetermined timing. Further, the sheet that has passed through the secondary transfer device 30 is conveyed to the fixing device 50 via the conveying belt 43, and the sheet discharged from the fixing device 50 is sent out to the outside by the discharge roll 44.

The fixing device 50 incorporates a heating source 51 a such as a halogen lamp, and is disposed so as to be rotatable in contact with the heating roll 51 and driven by rotation of the heating roll 51. And a pressure roll 52 that applies pressure to the heating roll 51. Here, the heating roll 51 is disposed on the side of the paper facing the toner image transfer surface, and the pressure roll 52 is disposed on the side of the paper opposite to the toner image transfer surface.
In this embodiment, the primary transfer roll 15, the intermediate transfer belt 20, and the secondary transfer device 30 as an example of a transfer unit, and the fixing device 50 as an example of a fixing unit have a function as a recording unit. doing.

FIG. 2 is a block diagram for explaining the configuration of the control system in the image forming apparatus of the present embodiment.
The control device 100 according to the present embodiment includes a CPU (Central Processing Unit) 101 that reads and executes a program, and a ROM 102 (Read Only Memory) that stores a program executed by the CPU 101 and data used when the program is executed. RAM 103 (Random Access Memory) that stores data temporarily generated when the program is executed, and data used when the program is executed, and the contents can be rewritten. , An EEPROM (Electrically Erasable Programmable Read-Only Memory) 104 capable of retaining the stored contents without supplying power.

  The control device 100 as an example of a setting unit includes a drum driving unit 111 that rotationally drives the photosensitive drum 11, a charging power source 112 that supplies a charging bias to the charging roll 12, and a light source driving that drives a light source provided in the exposure unit 13. A control signal is output to each of the units 113. The control device 100 also includes a developing power source 114a that supplies a developing bias to the developing roll 14a provided in the developing unit 14, a developing driving unit 114b that rotationally drives the developing roll 14a, and a toner that replenishes the developing unit 14 with toner. Control signals are respectively output to the replenishing unit 114c. Further, the control device 100 includes a primary transfer power source 115 that supplies a primary transfer bias to the primary transfer roll 15, a belt drive unit 120 that rotationally drives the intermediate transfer belt 20, and a secondary to the backup roll 25 of the secondary transfer device 30. A control signal is output to each secondary transfer power supply 130 that supplies a transfer bias. In addition, the control device 100 includes a conveyance power supply unit 140 a that supplies heating power to the conveyance roller 41, the registration roll 42, the conveyance belt 43, and the discharge roller 44. Then, control signals are respectively output to the fixing driving unit 150b that rotationally drives the heating roll 51 of the fixing device 50. The control device 100 receives a photoconductor potential detection signal from a photoconductor potential detection unit 160 that detects the potential of the organic photosensitive layer in the photoconductor drum 11.

  The drum driving unit 111, the charging power source 112, the light source driving unit 113, the developing power source 114a, the developing driving unit 114b, the toner replenishing unit 114c, the primary transfer power source 115, and the photosensitive member potential detecting unit 160 are the yellow image forming unit 10Y, It is provided in each of the magenta image forming unit 10M, the cyan image forming unit 10C, and the black image forming unit 10K.

  In this example, each charging power source 112 supplies a charging bias obtained by superimposing an AC component (rectangular wave) on a DC component set to a negative value to the corresponding charging roll 12. In the following description, the DC component in the charging bias is called a DC charging bias, and the AC component in the charging bias is called an AC charging bias. Here, the DC charging bias is for charging the organic photosensitive layer provided on the photosensitive drum 11 to a target potential (referred to as a charging potential), and the AC charging bias is an organic photosensitive layer based on a DC charging bias. For assisting charging of the layer.

  Each developing power supply 114a supplies a developing bias obtained by superimposing an alternating current component (rectangular wave) on a direct current component set to a negative value to the corresponding developing roll 14a. In the following description, the DC component in the developing bias is called a DC developing bias, and the AC component in the developing bias is called an AC developing bias. Here, the DC developing bias is for transferring the toner from the developing roll 14a to the organic photosensitive layer (more specifically, the image portion) provided on the photosensitive drum 11, and the AC developing bias is a DC developing bias. This assists the transfer of toner from the developing roll 14a to the organic photosensitive layer by the developing bias.

  In this embodiment, the control device 100 performs constant current control on the primary transfer bias supplied from the primary transfer power supply 115 to the primary transfer roll 15, and the secondary transfer power supply 130 supplies the secondary transfer device 30 (more Specifically, the secondary transfer bias supplied to the backup roll 25) is controlled at a constant voltage.

Next, an image forming operation using the image forming apparatus shown in FIG. 1 will be described. The image forming operation described below is executed under the control of the control device 100.
With the start of the image forming operation, driving of each photosensitive drum 11 and driving of the intermediate transfer belt 20 via the driving roll 21 are started. Each photosensitive drum 11 is in the direction of arrow A, and the intermediate transfer belt 20 is moved to arrow B. Start rotating in each direction. Further, the driving of the developing roll 14a provided in each developing device 14 is started, and each developing roll 14a starts to rotate. Furthermore, supply of the charging bias to each charging roll 12 and supply of the developing bias to each developing roll 14a are started. Furthermore, driving of the heating roll 51 and power supply to the heating source 51 a in the fixing device 50 are started, the heating roll 51 starts to rotate in the direction of arrow C, and the pressure roll 52 rotates following the heating roll 51. Begin to. The heating roll 51 is driven to rotate at a predetermined speed (fixing speed) and is heated to a predetermined temperature (fixing temperature) by the heating source 51a, and thereafter the fixing temperature is maintained. Controlled.

  For example, in the yellow image forming unit 10 </ b> Y, the photosensitive drum 11 rotating in the direction of arrow A is charged to a charging potential by a charging bias supplied to the charging roll 12 that is in contact therewith. Next, exposure by the exposure unit 13 is started, and the photosensitive drum 11 that rotates in the direction of arrow A while being charged to the charging potential is selectively exposed to the image portion by the light emitted from the exposure unit 13. . As a result, an electrostatic latent image for yellow is formed in the organic photosensitive layer that has been charged and exposed, with the background portion being charged and the image portion being exposed.

  Subsequently, the electrostatic latent image for yellow formed on the photosensitive drum 11 is opposed to the developing roll 14a provided in the developing unit 14 as the photosensitive drum 11 rotates in the arrow A direction ( Hereinafter, it will be referred to as a development area). At this time, the developing roll 14a rotates in a state where a developer containing a carrier and toner (two-component developer) is held on the surface, and a developing bias is supplied to the developing roll 14a. For this reason, the toner is selectively transferred from the developing roll 14a to the photosensitive drum 11 to the image portion at the exposure potential of the yellow electrostatic latent image. As a result, a yellow toner image corresponding to the electrostatic latent image is developed on the photosensitive drum 11 that has passed through the development area.

  Then, the yellow toner image developed on the photosensitive drum 11 is moved to a primary transfer position facing the primary transfer roll 15 with the intermediate transfer belt 20 interposed therebetween as the photosensitive drum 11 rotates in the direction of arrow A. To reach. At this time, when the primary transfer bias is supplied to the primary transfer roll 15, the yellow toner image formed on the photosensitive drum 11 rotating in the arrow A direction is transferred onto the intermediate transfer belt 20 rotating in the arrow B direction. Primary transfer (electrostatic transfer). The adhering matter such as the toner remaining on the photosensitive drum 11 after the primary transfer reaches the portion facing the drum cleaner 16 as the photosensitive drum 11 further rotates in the A direction, and is cleaned by the drum cleaner 16. Is done.

  In the other magenta image forming unit 10M, cyan image forming unit 10C, and black image forming unit 10K, charging, exposure, development, primary transfer, and cleaning are performed similarly to the yellow image forming unit 10Y. At this time, by shifting the image formation timing in each, a superimposed toner image is formed on the intermediate transfer belt 20 by superimposing these yellow, magenta, cyan and black color toner images.

The superposed toner image primarily transferred onto the intermediate transfer belt 20 in this way is rotated with the intermediate transfer belt 20 in the direction of the arrow B, and the secondary transfer roll 31 and the backup roll 25 sandwich the intermediate transfer belt 20 therebetween. To the opposite secondary transfer position.
On the other hand, the paper taken out from the paper storage unit 40 is moved to the secondary transfer position by the transport roll 41 and the registration roll 42 in accordance with the timing at which the superimposed toner image on the intermediate transfer belt 20 reaches the secondary transfer position. It is conveyed.

  At this time, at the secondary transfer position, a secondary transfer bias is supplied to the backup roll 25 constituting the secondary transfer device 30. Then, at the secondary transfer position, the superimposed toner image on the intermediate transfer belt 20 is secondarily transferred (electrostatically) to the paper by the action of the secondary transfer electric field formed between the secondary transfer roll 31 and the backup roll 25. Transferred).

  Thereafter, the sheet on which the superimposed toner image is secondarily transferred is conveyed to the fixing device 50 by the conveying belt 43. The superimposed toner image on the paper is heated and pressurized and fixed by the heat supplied from the heating roll 51 of the fixing device 50 and the pressure received from the heating roll 51 and the pressure roll 52, and image formation is performed by the discharge roll 44. It is discharged out of the machine. In addition, adhering matters such as toner remaining on the intermediate transfer belt 20 after the secondary transfer reach a portion facing the belt cleaner 27 as the intermediate transfer belt 20 further rotates in the B direction. To be cleaned.

  FIG. 3 is a diagram for explaining the relationship between the charging potential VH and the exposure potential VL in the photosensitive drum 11 and the developing bias potential VB in the developing device 14 (more specifically, the developing roll 14a). The horizontal axis in FIG. 3 is the position on the photosensitive drum 11, and the vertical axis in FIG. 3 is the potential (where the lower side is the ground (GND), and the upper side has a higher negative potential). Here, the charging potential VH is determined by the above-described charging bias (DC charging bias and AC charging bias), and the exposure potential VL is determined by the charging bias and the exposure energy by the exposure unit 13. The development bias potential VB is determined by the magnitude of the DC development bias in the above-described development bias (DC development bias and AC development bias).

  In this embodiment, the charging potential VH and the exposure potential VL are both negative, but the magnitude of the exposure potential VL is an absolute value smaller than the charging potential VH (| VL | <| VH |). The value of the developing bias potential VB, that is, the DC developing bias in the present embodiment is negative, and the absolute value is set to a magnitude between the charging potential VH and the exposure potential VL (| VL | <| VB | <| VH |).

  When the charging potential VH, the exposure potential VL, and the developing bias potential VB have the relationship described above, the toner (negative polarity) on the developing roll 14a that passes through the developing area where the photosensitive drum 11 and the developing roll 14a face each other. Is easily transferred (flyed) to the region of the exposure potential VL (image portion), which is a relatively positive potential on the photosensitive drum 11, while being relatively negative on the photosensitive drum 11. It becomes difficult to transfer (fly) to the region of the charging potential VH (background portion) that becomes the potential. Further, the carrier (charged positively) on the developing roller 14a passing through the developing region is an area of the exposure potential VL (image portion) that is a relatively positive potential on the photosensitive drum 11, contrary to the toner. However, it is difficult to transfer (fly) to the region of the charging potential VH (background portion) that is a relatively negative potential on the photosensitive drum 11. However, since the carrier in the developer is magnetically held by the developing roll 14a, practically no carrier transfer occurs. In the following description, the ease of toner flying is considered as a reference, and the difference between the exposure potential VL based on the exposure potential VL and the developing bias potential VB is called a flying potential difference Vdev, and the developing bias potential VB is used as a reference. The difference between the developing bias potential VB and the charging potential VH is called a reverse flight potential difference Vcln. Further, the difference between the exposure potential VL and the charging potential VH with the exposure potential VL as a reference may be referred to as a latent image potential difference VI. This latent image potential difference VI can also be expressed as the sum of the flying potential difference Vdev and the reverse flying potential difference Vcln.

  In this embodiment, a charging bias obtained by superimposing a DC charging bias and an AC charging bias is supplied to the charging roll 12 in order to charge the photosensitive drum 11. For this reason, the actual charging potential VH includes noise of an applied AC frequency component as shown in FIG. Further, the photosensitive drum 11 is charged to the charging potential VH by the charging roll 12, and then the exposure potential VL is formed by the exposure unit 13. The exposure potential VL is influenced by the original charging potential VH. As a result, the actual exposure potential VL includes not only a direct current component but also an alternating current component as shown in FIG.

  Here, in the present embodiment, the material and composition of the charging roll 12 differ depending on the type, but since there are micro surface irregularities and resistance unevenness, slight discharge unevenness occurs, and the charging potential VH and the exposure potential VL are AC. It is one of the causes that contain ingredients.

  In the following description, the AC component in the charging potential VH serving as the background portion is referred to as background portion noise NH. In the following description, an alternating current component at the exposure potential VL serving as an image portion is referred to as image portion noise NL. Both the background noise NH and the image noise NL include a plurality of frequency components.

  When an electrostatic latent image (image portion) in which an image portion noise NL made of an AC component is superimposed on a target exposure potential VL (DC value) as shown in FIG. 3 is developed using toner. In the obtained toner image, variation in density due to the image portion noise NL occurs. Here, when the magnitude of the image part noise NL is sufficiently small with respect to the magnitude of the flight potential difference Vdev, that is, when the SN ratio between the flight potential difference Vdev (signal) and the image part noise NL (noise) is large (good). The variation in density due to the image portion noise NL becomes inconspicuous. On the other hand, when the image portion noise NL is so large that it cannot be ignored with respect to the magnitude of the flight potential difference Vdev, that is, when the SN ratio between the flight potential difference Vdev (signal) and the image portion noise NL (noise) is small (bad), Variations in density due to the image portion noise NL are conspicuous. In particular, when the image portion noise NL includes a specific frequency component, the density variation (more specifically, “noise feeling”, It becomes easy to be recognized as "roughness" or "moyatsu").

  In the image forming apparatus according to the present embodiment, for example, at the timing of the startup operation after turning on the power, or after a predetermined time has elapsed after the startup operation is completed, the charging potential VH, the exposure potential VL, and the like. An adjustment operation for adjusting the developing bias potential VB and the like to maintain the density of the obtained image at a constant level is performed. In this adjustment operation, the charging potential VH, the exposure potential VL, and the development bias potential VB are adjusted so that the flying potential difference Vdev and the reverse flying potential difference Vcln fall within a predetermined range according to changes in environmental conditions and the like. Done. Accordingly, the values of the charging potential VH, the exposure potential VL, and the developing bias potential VB are not always constant, and change according to the situation when the adjustment operation is performed. For this reason, the flight potential difference Vdev can vary within a predetermined range.

  FIG. 4 shows an image obtained as a flying potential difference Vdev when charging is performed by the contact charging method using the charging roll 12 and when charging is performed by the non-contact charging method using scorotron or the like. FIG. 6 is a diagram for explaining a relationship with a visual noise feeling of a (toner image transferred and fixed on a sheet).

  From FIG. 4, it can be seen that in both the contact charging method and the non-contact charging method, the visual noise sensation is maintained at a substantially constant level when the flying potential difference Vdev exceeds a certain magnitude. Here, in the case of using the non-contact charging method, the visual noise feeling is almost constant from when the flying potential difference Vdev exceeds 240V. However, in the case of using the contact charging method, the flying potential difference The visual noise sensation is almost constant when Vdev exceeds 300V. That is, when the contact charging method is adopted, the visual noise feeling is not stabilized unless the flying potential difference Vdev is increased as compared with the case where the non-contact charging method is adopted. In the image forming apparatus according to the present embodiment, the flight potential difference Vdev may be set to 300V or less.

  Therefore, in the present embodiment, it is caused by adopting the contact charging method by adjusting a specific image forming condition in the image forming operation, more specifically, a fixing condition in the fixing device 50. Variations in image density (toner image) on paper (visual “noise”, “roughness” and / or “haze”) are made inconspicuous.

  FIG. 5 is a flowchart showing the procedure of the fixing condition setting operation in the present embodiment. The setting operation described below is executed under the control of the control device 100 shown in FIG.

  With the start of the setting operation, first, the potential of the photosensitive drum 11 is measured using the photosensitive member potential detector 160 (step 101). In step 101, the photosensitive drum 11 is rotationally driven using the drum driving unit 111, and a charging bias (DC charging bias and AC charging bias) is supplied to the charging roll 12 using the charging power source 112, so A portion of the organic photosensitive layer of the photosensitive drum 11 charged to the charging potential VH is obtained by charging the organic photosensitive layer of the drum 11 to the charging potential VH and further performing exposure using the light source driving unit 113 and the exposure unit 13. Is set to the exposure potential VL. At this time, the magnitude of the charging bias (DC charging bias and AC charging bias) supplied to the charging roll 12 and the magnitude of the exposure energy by the exposure unit 13 are, for example, a predetermined set value or the previous image. This is the current setting value used in the forming operation. In step 101, the photoreceptor potential detection unit 160 detects the charging potential VH and the exposure potential VL and outputs them to the control device 100.

  Next, the control device 100 acquires the magnitude of the DC development bias of the development bias (DC development bias and AC development bias) from the development power supply 114a (step 102). Here, the magnitude of the acquired DC developing bias is a predetermined setting value or a current setting value used in the previous image forming operation. In this example, since the magnitude of the DC developing bias is equal to the developing bias potential VB, in step 102, the developing bias potential VB is actually acquired.

  Subsequently, the control device 100 uses the charging potential VH and exposure potential VL acquired in step 101 and the developing bias potential VB acquired in step 102 to use the fixing conditions in the fixing device 50 used in the next image forming operation. Is determined (step 103). In step 103, the fixing condition is actually determined based on the flying potential difference Vdev obtained as the difference between the exposure potential VL and the developing bias potential VB. The details of the specific processing will be described later. .

  Next, the control device 100 determines whether or not the new fixing condition determined in step 103 has been changed from the current fixing condition (step 104).

  When an affirmative determination (YES) is made in step 104, the control device 100 adjusts the fixing conditions in the fixing device 50 based on the new fixing conditions determined in step 103 (step 105), and a series of steps. Complete the setting operation. On the other hand, when a negative determination (NO) is made in step 104, the control device 100 completes a series of setting operations without adjusting the fixing conditions.

Now, the procedure for determining the fixing condition in step 103 will be specifically described.
FIG. 6 is a diagram for explaining the contents of the condition determination table used in the process of determining the fixing condition in step 103. Here, FIG. 6A shows a condition determination table used when the fixing speed Sp is used as the fixing condition, and FIG. 6B shows a condition determination table used when the fixing temperature Temp is used as the fixing condition.

  The condition determination table shown in FIG. 6A is a table in which the fixing speed Sp is associated with the flying potential difference Vdev obtained based on the exposure potential VL acquired in step 101 and the developing bias potential VB acquired in step 102. It has become. In this condition determination table, the threshold value Vth is set for the flying potential difference Vdev, and when the flying potential difference Vdev exceeds the threshold value Vth (Vdev> Vth), the first fixing speed Sp1 is set as the fixing speed Sp. When the flying potential difference Vdev is equal to or less than the threshold value Vth (Vdev ≦ Vth), the second fixing speed Sp2 (Sp1 <Sp2) faster than the first fixing speed Sp1 is selected as the fixing speed Sp.

In the condition determination table shown in FIG. 6B, the fixing temperature Temp is associated with the flying potential difference Vdev obtained based on the exposure potential VL acquired in step 101 and the developing bias potential VB acquired in step 102. It has become. In this condition determination table, the threshold value Vth is set for the flying potential difference Vdev, and when the flying potential difference Vdev exceeds the threshold value Vth (Vdev> Vth), the first fixing temperature Temp1 is set as the fixing temperature Temp. If the flying potential difference Vdev is equal to or lower than the threshold value Vth (Vdev ≦ Vth), the second fixing temperature Temp2 (Temp1> Temp2) lower than the first fixing temperature Temp1 is selected as the fixing temperature Temp.
In this example, the threshold value Vth is set to 300 V, for example (see FIG. 4).

  Here, in the present embodiment, among the yellow, magenta, cyan, and black colors, the flying potential difference Vdev in the black image forming unit 10K that is easily noticeable due to the lowest brightness in an image with a density of 100%. Judgment is made based on this. From a different perspective, this means that among yellow, magenta, cyan, and black colors, black is the color in which the variation in density is most noticeable. However, the present invention is not limited to this, and the determination may be made based on the average value of the flight potential difference Vdev in each of the image forming units 10Y, 10M, 10C, and 10K of each color of yellow, magenta, cyan, and black.

FIG. 7 shows an enlarged view of a printed matter output by the image forming apparatus of the present embodiment.
The image forming apparatus of the present embodiment forms an image using a so-called area gradation method, and an image (toner image) composed of a plurality of dot images D is fixed on the paper P. . Here, when a halftone image is formed on the paper P, the dot images D having the same area are theoretically arranged vertically and horizontally, but actually, as shown in FIG. Variations occur in the area. In particular, in the situation where the flying potential difference Vdev is equal to or less than the threshold value Vth, the variation in the area of each dot image D becomes significant.

  FIG. 8 is a diagram for explaining the relationship between the sheet P and the image (toner image) fixed on the sheet P and the visual noise feeling. Here, FIG. 8A schematically shows the relationship between the variation (standard deviation) of the image area (referred to as dot image area) of each dot image D and the visual noise feeling. FIG. 8B schematically shows the relationship between the contrast between the brightness of each dot image D and the brightness of the paper P serving as the background (referred to as brightness contrast) and visual noise.

  As shown in FIG. 8A, the visual noise feeling deteriorates as the dot image area variation increases, and the visual noise feeling improves as the dot image area variation decreases. On the other hand, as shown in FIG. 8B, the greater the lightness contrast between the dot image D and the paper P, the worse the visual noise, and the smaller the lightness contrast between the dot image D and the paper P. Visual noise is improved.

  Therefore, by reducing the brightness contrast between the dot image D and the paper P when the variation in the dot image area is large, and increasing the brightness contrast between the dot image D and the paper P when the variation in the dot image area is small, The visual noise is leveled and becomes less noticeable.

  Here, the lightness of the dot image, that is, the lightness of the toner image after fixing has a correlation with the glossiness (gloss) of the toner image after fixing. More specifically, the higher the glossiness of the toner image, the higher the brightness, and the lower the glossiness of the toner image, the lower the brightness.

FIG. 9 shows the relationship between the glossiness of a single color image fixed on the paper P, that is, the primary color image (referred to as primary color glossiness), and the visual noise feeling of the primary color image. FIG. Here, FIG. 9 illustrates the case of magenta (M), cyan (C), and black (K) as the primary color image.
The primary color glossiness shown in FIG. 9 is continuous for 20 sheets using an image forming apparatus for paper P having a basis weight of 127 gsm and a 60 ° glossiness of 34 in an environment of a temperature of 22 ° C. and a humidity of 50%. The 60 ° glossiness (JIS Z8741) of the 11th to 20th recording materials when a 100% toner image is recorded.

  As shown in FIG. 9, the higher the primary color glossiness, the worse the visual noise feeling, and the lower the primary color glossiness, the better the visual noise feeling. In this embodiment, when the flight potential difference Vdev exceeds the threshold value Vth, the primary color glossiness X is 15 <X <40, and when the flight potential difference Vdev exceeds the threshold value Vth, the primary color glossiness X Is set such that 10 <X <25.

  FIG. 10 is a diagram showing the relationship between the fixing conditions and the glossiness of the image. Here, FIG. 10A shows the relationship between fixing speed and glossiness as an example of fixing conditions, and FIG. 10B shows the relationship between fixing temperature and glossiness as an example of fixing conditions. Is shown. In FIG. 10A, the horizontal axis represents the number of sheets passing through the unit time (ppm) as a measure of the fixing speed, and the vertical axis represents the 60 ° gloss (JISZ8741). In FIG. 10B, the horizontal axis is the fixing temperature (° C.), and the vertical axis is the 60 ° glossiness (JISZ8741). Here, FIG. 10A illustrates the case of magenta (M), and FIG. 10B illustrates the case of magenta (M) and cyan (C).

  In this embodiment, for example, the condition determination table shown in FIG. 6A is used, and when the flying potential difference Vdev exceeds the threshold value Vth (300 V in this example), the fixing speed Sp is set to the first fixing speed Sp1 (this example). In this case, the fixing speed Sp is set to a second fixing speed Sp2 (100 ppm in this example) faster than the first fixing speed Sp1. Here, as apparent from FIG. 10A, the 60 ° gloss value is smaller at the second fixing speed Sp2 than at the first fixing speed Sp1, and at the time of the first fixing speed Sp1. The 60 ° glossiness is more than 15 and less than 40, and the 60 ° glossiness at the second fixing speed Sp2 is more than 10 and less than 25, respectively.

  In this embodiment, for example, the condition determination table shown in FIG. 6B is used. When the flying potential difference Vdev exceeds the threshold value Vth (300 V in this example), the fixing temperature Temp is set to the first fixing temperature Temp1 ( In this example, the fixing temperature Temp is set to a second fixing temperature Temp2 (160 ° C. in this example) lower than the first fixing temperature Temp1 when the flying potential difference Vdev is equal to or less than the threshold value Vth. Yes. Here, as is apparent from FIG. 10B, the 60 ° gloss value is smaller at the second fixing temperature Temp2 than at the first fixing temperature Temp1, and at the time of the first fixing temperature Temp1. The 60 ° glossiness is more than 15 and less than 40, and the 60 ° glossiness at the second fixing temperature Temp2 is more than 10 and less than 25, respectively.

  In this embodiment, the case where either the fixing speed Sp or the fixing temperature Temp is adjusted as the fixing condition has been described as an example. However, both the fixing speed Sp and the fixing temperature Temp are adjusted. It doesn't matter.

  In this embodiment, the amount of heat supplied by the fixing device 50 is set to adjust the glossiness of the obtained image. However, the present invention is not limited to this. For example, when a cooling device that cools an image on a sheet is provided downstream of the fixing device 50 in the sheet conveyance direction and the image is glossed by cooling with the cooling device, the cooling device By setting the cooling condition, the glossiness of the obtained image may be adjusted.

  Furthermore, in this embodiment, the case where the charging roll 12 is used as the contact charging unit has been described as an example, but the configuration of the contact charging unit is not limited thereto. As the contact charging means, for example, a brush-like or film-like one may be used. In the first to third embodiments, the charging roll 12 as the contact charging unit is rotatably provided. However, the present invention is not limited to this, and is fixedly attached to the photosensitive drum 11. It doesn't matter.

  Furthermore, in this embodiment, the electrostatic latent image is formed using a so-called image portion exposure method, but the exposure method is not limited to this. For example, the exposure method may be applied to the case where an electrostatic latent image is formed using a so-called background exposure method in which light is applied to the background portion and light is not applied to the image portion. In this case, the charging potential VH is an image portion, and the exposure potential VL is a background portion.

  In the present embodiment, the electrostatic latent image is developed using the reversal development method, but the development method is not limited to this. The developing method may be applied to the case where an electrostatic latent image is developed using a so-called regular developing method in which the charging polarity of the image portion to be developed is different from the charging polarity of the toner.

  In this embodiment, a so-called two-component developer including toner and carrier is used. However, the present invention is not limited to this, and a so-called one-component developer that includes toner but does not include a carrier may be used. Good.

10 (10K, 10Y, 10M, 10C) ... image forming unit, 11 ... photosensitive drum, 12 ... charging roll, 13 ... exposure section, 14 ... developing device, 14a ... developing roll, 15 ... primary transfer roll, 16 ... drum Cleaner 20 ... Intermediate transfer belt 25 ... Backup roll 30 ... Secondary transfer device 31 ... Secondary transfer roll 50 ... Fixing device 51 ... Heating roll 51a ... Heat source 52 ... Pressure roll 100 ... Control unit 111. Drum drive unit 112. Charge power source 113. Light source drive unit 114 a Development power source 114 b Development drive unit 114 c Toner replenishment unit 115 Primary transfer power source 120 Belt drive unit 130 ... Secondary transfer power supply 140 ... Conveyance drive unit 150a ... Fixing power supply 150b ... Fixing drive unit 160 ... Photoconductor potential detection unit VH ... Charge potential, VL ... dew Potential, VB ... developing bias potential, Vdeve ... flying potential, Vcln ... reverse flying potential, NH ... background noise, NL ... image unit noise

Claims (3)

A rotating image carrier;
Contact charging means arranged in contact with the image carrier and charging the image carrier using a charging bias in which an alternating current component is superimposed on a direct current component;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image formed on the image carrier with toner using a supplied developing bias;
Recording means for recording the toner image formed on the image carrier on a recording material;
The flying potential difference exceeds the threshold when the flying potential difference, which is the difference between the developing bias and the potential of the image portion of the image carrier that develops the toner, is equal to or less than a predetermined threshold. compared to, look including the setting means gloss of the toner image to be recorded on the recording material is set to the recording device to decrease,
A plurality of the developing means having different toner colors;
The image forming apparatus according to claim 1, wherein the setting unit sets the recording unit based on the flying potential difference in the developing unit that uses toner having the lowest brightness among the plurality of developing units. The setting means has a primary color glossiness X of a toner image recorded on the recording material by the recording means of 15 <X <40 when the flying potential difference exceeds the threshold value, and the flying potential difference is equal to or less than the threshold value. The image forming apparatus according to claim 1 , wherein the recording unit is set so that the primary color glossiness X satisfies 10 <X <25. (However, the primary color glossiness X is continuously 20 sheets by the recording means for a recording material having a basis weight of 127 gsm and a 60 ° glossiness (JISZ8741) 34 in an environment of a temperature of 22 ° C. and a humidity of 50%. (The glossiness is 60 ° in the 11th to 20th recording materials when a 100% toner image is recorded.) The recording unit includes a transfer unit that transfers a toner image formed on the image carrier to the recording material, and a fixing unit that heats and fixes the toner image transferred to the recording material to the recording material. ,
3. The image forming apparatus according to claim 1 , wherein the setting unit sets an amount of heat applied to the recording material that passes through the fixing unit.

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