JP2016080874A - Image forming method and image forming apparatus - Google Patents

Abstract

Generation of a blurred image due to an image density difference between a convex portion and a concave portion on the surface of a recording sheet P is suppressed.
Image forming means 10Y, 10C, 10M, 10K for forming Y, C, M, K toner images on the surfaces of photoconductors 1Y, 1C, 1M, 1K, and photoconductors 10Y, 10C, 10M, 10K In an image forming apparatus including a transfer unit that transfers the above Y, C, M, and K toner images to the intermediate transfer belt 6 and then transfers them to the recording sheet P, the optical sensor unit 140 controls the surface smoothness of the recording sheet P. Based on the detected result, the linear velocity difference between the photoreceptors 1Y, 1C, 1M, and 1K and the intermediate transfer belt 6 is adjusted.
[Selection] Figure 1

Description

  The present invention relates to an image forming method and an image forming apparatus.

  Conventionally, as an image forming apparatus of this type, a transfer unit that directly transfers a toner image on an image carrier from the image carrier to a recording medium or transfers the toner image from the image carrier to the recording medium via an intermediate transfer body. What is provided with is known.

  For example, the color printer described in Patent Document 1 uses a Y (Y) for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images by an electrophotographic process as an image carrier. , M, C, and K photoconductors. The following transfer unit is also provided. That is, the transfer unit has the Y, M, C, and K photoconductors in contact with the endless transfer belt to form the primary transfer nip for Y, M, C, and K, and the transfer belt. The recording sheet held on the surface is passed through the primary transfer nip for Y, M, C, and K as the belt moves endlessly. In this process, the Y toner image, the M toner image, the C toner image, and the K toner image on the Y, M, C, and K photoconductors are sequentially superimposed on the surface of the recording sheet that is a recording medium and are primarily transferred. In this way, a full color image is formed on the recording sheet by a direct transfer method in which each color toner image is directly transferred from the photosensitive member of each color to the recording sheet.

  In such a configuration, when a recording sheet having a high surface roughness such as Japanese paper is used, a minute amount is formed between the toner image on the surface of the photoreceptor and the concave portion on the surface of the recording sheet having a high surface roughness. Create a gap. Further, it is difficult to transfer a sufficient amount of toner to the inside of the concave portion of the surface of the recording sheet without applying an electrostatic force necessary to move the toner image in the minute gap. Become. This makes it easy to generate a blurred image having an image density difference between the convex and concave portions on the surface of the recording sheet.

  This problem is not limited to an image forming apparatus that forms a color image using a plurality of photoconductors as in the color printer described in Patent Document 1, and uses only one image carrier such as a photoconductor to produce a monochrome image. This can also occur in the image forming apparatus to be formed.

  Also, in the indirect transfer method in which the toner image on the image carrier is transferred to the intermediate transfer member and then transferred to the recording sheet, a minute gap is formed between the surface of the intermediate transfer member and the concave portion of the surface of the recording sheet. Therefore, a similar problem arises.

  In order to solve the above-described problems, the present invention provides an image forming unit that forms a toner image on a moving surface of an image carrier, and a toner image on the image carrier from the image carrier to a recording medium. In an image forming apparatus comprising a transfer unit that directly transfers or transfers from the image carrier to a recording medium via an intermediate transfer body, an information acquisition unit that acquires surface smoothness information of the recording medium; Based on the acquisition result of the information by the information acquisition means, the linear velocity difference between the image carrier and the recording medium when the toner image is transferred from the image carrier to the recording medium, or the toner image as the image carrier. And a control means for adjusting a linear velocity difference when transferring the toner image to the intermediate transfer member.

  According to the present invention, there is an excellent effect that it is possible to suppress the generation of a blurred image due to the difference in image density between the convex portion and the concave portion on the surface of the recording medium.

1 is a schematic configuration diagram illustrating a schematic configuration of a printer according to an embodiment. FIG. 2 is a block diagram showing a part of an electric circuit in the printer. FIG. 2 is an enlarged configuration diagram showing a light sensor unit mounted on the printer. 3 is a flowchart showing each step in a linear velocity difference adjustment process performed by the control unit of the printer. The schematic diagram for demonstrating the relationship between secondary transfer property, a secondary transfer current, and the difference in secondary transfer property in the recessed part and convex part of a sheet | seat surface. The graph which shows the relationship between the primary transfer rate clarified by the experiment conducted by the present inventors, the primary transfer current output target value (constant current control), and the linear velocity difference. 6 is a graph showing the relationship between toner transferability to a recess on the sheet surface (recess transferability), secondary transfer current output target value, and toner charge amount Q / M, which has been clarified by experiments conducted by the present inventors. The expanded block diagram which shows the optical sensor unit system applicable to the structure of a one pass system.

  Hereinafter, an embodiment of a color printer (hereinafter simply referred to as “printer”) that forms a color image will be described as an image forming apparatus to which the present invention is applied. The printer according to the embodiment shows an example of an image forming apparatus to which the present invention is applied, and the scope of application of the present invention is not limited to the printer.

First, a basic configuration of the printer according to the embodiment will be described.
FIG. 1 is a schematic configuration diagram illustrating a schematic configuration of a printer 100 according to the embodiment. The printer 100 is a tandem printer having four image forming devices 10Y, 10C, 10M, and 10K for yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) as image forming means. It is. Note that the subscripts Y, C, M, and K attached to the end of the symbol “10” indicate members for Y, C, M, and K. The same applies to the subscripts Y, C, M, and K attached to the end of other codes.

  In the vicinity of the center of the printer 100 housing, an endless intermediate transfer belt 6 as an intermediate transfer member, various rollers disposed in the loop, a belt cleaning device 7, a secondary transfer roller 8, and the like are provided. A transfer unit is provided.

  The intermediate transfer belt 6 has a multilayer structure. The base layer, which is the base layer of the multilayer, is formed of, for example, a fluororesin, a PVDF (polyvinylidene fluoride) sheet, a polyimide resin, or the like that has little elongation. On the surface of the base layer, a coat layer having good smoothness such as a fluorine resin is coated. In the loop of the intermediate transfer belt 6, four support rollers (15, 16, 18, 19), primary transfer rollers 17Y, 17C, 17M, 17K and the like are arranged. The intermediate transfer belt 6 is endlessly moved in the counterclockwise direction in the drawing as one of the supporting rollers is rotated in the counterclockwise direction in the drawing while being tensioned by these rollers. .

  The four image forming devices 10Y, 10C, 10M, and 10K are arranged on the belt front surface at the stretched portion between the second support roller 16 and the third support roller 18 in the entire area of the intermediate transfer belt 6 in the circumferential direction. They are arranged so as to face each other in the belt moving direction while facing each other. Hereinafter, the tandem image forming unit 30 includes these four image forming devices 10Y, 10C, 10M, and 10K. Below the tandem image forming unit 30, a latent image writing exposure device 5 as a latent image forming unit is provided.

  The four image forming apparatuses 10Y, 10C, 10M, and 10K have the same structure. Specifically, the four image forming devices 10Y, 10C, 10M, and 10K include Y toner images, C toner images, M toner images, and photoconductors 1Y, 1C, 1M as image carriers that carry K toner images. 1K. Different colors of Y, C, M, and K toners are used, but other configurations are the same.

  Taking an image forming device 10Y for forming a Y toner image as an example, the image forming device 10Y includes a photoreceptor 1Y, a developing device 3Y, a charging device 2Y, a photoreceptor cleaning device 4Y, and the like. These are integrally attached to and detached from the housing of the printer 100 while being held by a common holding body as one unit.

  The charging device 2Y has a charging roller disposed so as to be in contact with or close to the photoreceptor 1Y, and the charging roller is rotationally driven by a driving unit (not shown). A predetermined charging bias is applied to the charging roller by a charging power source (not shown). Then, by generating a discharge between the charging roller and the photoreceptor 1Y, the surface of the photoreceptor 1Y is uniformly charged to the same polarity as the normal charging polarity of the toner. A scorotron charger or the like may be employed instead of such a charging device.

  The photoreceptor 1Y is a drum-like member having an organic photosensitive layer, and is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown). The surface of the photoreceptor 1Y uniformly charged by the charging device 2Y is exposed and scanned by a laser beam emitted from a latent image writing exposure device 5 described later to carry a Y electrostatic latent image.

  The developing device 3Y contains a developer (not shown) containing Y toner and a magnetic carrier. An opening is formed in the casing of the developing device 3Y, and a part of the peripheral surface of the cylindrical developing sleeve is exposed from the opening and faces the surface of the photoreceptor 1Y. The developing sleeve, which includes a magnet roller (not shown) so as not to be able to rotate, carries the developer in the casing by the magnetic force generated by the magnet roller. Then, the developer is transported to a developing area where the developer and the photoconductor 1Y face each other in accordance with the rotation driving of the developer. In the developing area, a developing potential for moving negatively charged Y toner from the developing sleeve side to the photosensitive member 1Y acts between the developing bias applied to the developing sleeve and the electrostatic latent image on the photosensitive member 1Y. In addition, a non-development potential that moves negative polarity Y toner from the photosensitive member side to the developing sleeve side acts between the developing sleeve and the non-image portion of the photosensitive member 1Y. The Y toner in the developer is transferred to the electrostatic latent image on the photoreceptor 1Y in the development region by the action of the development potential described above. As a result, the electrostatic latent image on the photoreceptor 1Y is developed into a Y toner image.

  Although the image forming apparatus 10Y for Y has been described in detail, the image forming apparatuses 10C, 10M, and 10K for other colors have the same configuration, and the C toner image and the M toner image are formed on the photoreceptors 1C, 1M, and 1K. , K toner images are formed.

  The latent image writing exposure apparatus 5 is a laser scanning exposure apparatus using, for example, a laser light source and a polygon mirror. Image data input from an input device such as an external personal computer or scanner is subjected to image processing and separated into image information of each color (Y, C, M, K), and then output to the latent image writing exposure device 5. The The latent image writing exposure device 5 irradiates laser light L emitted from each light source based on image information of each color from each light source, scans the uniformly charged surfaces of the photoreceptors 1Y, 1C, 1M, and 1K. Electrostatic latent images for C, M, and K are formed. As the latent image writing exposure apparatus 5, it is possible to use an apparatus that performs an optical scanning system using an LED array instead of such a system.

  The primary transfer rollers 17Y, 17C, 17M, and 17K disposed inside the loop of the intermediate transfer belt 6 sandwich the intermediate transfer belt 6 between the photoreceptors 1Y, 1C, 1M, and 1K. As a result, primary transfer nips for Y, C, M, and K in which the front surface of the intermediate transfer belt 6 and the photoreceptors 1Y, 1C, 1M, and 1K abut are formed. A primary transfer bias having a polarity opposite to the charging polarity of the toner is applied to the primary transfer rollers 17Y, 17C, 17M, and 17K by a primary transfer power source (not shown). As a result, a primary transfer electric field is formed in each primary transfer nip to draw the toner image on the photoreceptor 1 from the photoreceptor 1 side to the intermediate transfer belt 6 side. The intermediate transfer belt 6 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof, and a Y toner image on the photoreceptors 1Y, 1C, 1M, and 1K is formed on the surface thereof. , C toner image, M toner image, and K toner image are superposed in order and primarily transferred. As a result, a four-color superimposed toner image is formed on the intermediate transfer belt 6.

  The secondary transfer roller 8 disposed outside the loop is in contact with the first support roller 15 in the circumferential direction of the intermediate transfer belt 6 from the belt front surface side, and the secondary transfer. A nip is formed. A secondary transfer bias is applied to one of the first support roller 15 and the secondary transfer roller 8, while the other is grounded. As a result, a secondary transfer electric field is formed in the secondary transfer nip to electrostatically move the four-color superimposed toner image on the intermediate transfer belt 6 from the belt side to the recording sheet P sandwiched in the nip. The On the recording sheet P fed into the secondary transfer nip so as to be synchronized with the four-color superimposed toner image, the four-color superimposed toner image on the belt is secondarily transferred by the action of the nip pressure and the secondary transfer electric field. The As a result, a full color toner image is formed on the recording sheet P.

  In addition, a belt cleaning device 7 disposed outside the loop is in contact with the fourth support roller 19 from the belt front surface side in the entire area in the circumferential direction of the intermediate transfer belt 6. The belt cleaning device 7 is for removing residual toner remaining on the front surface of the intermediate transfer belt 6.

  A fixing device 13 is provided above the secondary transfer nip. The fixing device 13 forms a fixing nip by contact between the fixing roller 13a and the pressure roller 13b. The recording sheet P fed into the fixing device 13 from the secondary transfer nip enters the fixing nip and is pressurized or heated by a heat source (halogen lamp) in the fixing roller 13a. A full-color toner image is fixed on the surface.

  A paper feed cassette 26 that stores a plurality of recording sheets P in a bundle of sheets is disposed at a lower portion of the housing of the printer 100. The uppermost recording sheet P in the sheet bundle in the sheet feeding cassette 26 is sent out toward the sheet feeding path 29 by the rotation driving of the sheet feeding roller 27. Then, the paper is sandwiched between the conveyance nips of the conveyance roller pair and is conveyed from the upstream side to the downstream side in the paper feed path 29. A registration roller pair 28 is disposed near the end of the paper feed path 29. The recording sheet P transported in the paper feed path 29 by the transport roller pair is temporarily stopped when the transport roller pair is stopped while the skew is corrected by abutting the leading end against the resist nip of the resist roller pair 28. Is done. Then, the conveyance is resumed by the start of driving of the registration roller pair 28 and fed into the secondary transfer nip.

  For example, the color image is formed in the printer 100 as follows. That is, when image data is sent from a personal computer (not shown), one of the four support rollers (15, 16, 18, 19) is rotationally driven by a driving means (not shown), whereby the intermediate transfer belt 6 is rotated. It can be moved endlessly. At the same time, the other support rollers are driven to rotate. Further, the image forming apparatuses 10Y, 10C, 10M, and 10K start to rotate the photoreceptors 1Y, 1C, 1M, and 1K, and start to form Y toner images, C toner images, M toner images, and K toner images. . Thereafter, the Y toner image, the C toner image, the M toner image, and the K toner image formed on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K are primarily transferred to be superimposed on the front surface of the intermediate transfer belt 6. As a result, a four-color superimposed toner image is obtained.

  On the other hand, the sheet feeding roller 27 starts to rotate at an appropriate timing and feeds the recording sheet P from the sheet feeding cassette 26. The fed recording sheet P enters the sheet feeding path 29 in a state of being separated into one sheet by a separation roller (not shown), and then abuts against the registration roller pair 28 and stops. Thereafter, the toner is fed into the secondary transfer nip by the rotational driving of the registration roller pair 28, and the four-color superimposed toner image on the intermediate transfer belt 6 is secondarily transferred.

  The recording sheet P having a full-color image formed on the surface in this manner is discharged from the secondary transfer nip and then fed into the fixing device 13 via the conveyance guide member. Then, in the process of passing through the fixing nip of the fixing device 13, the full color image is fixed by being heated and pressurized. Thereafter, the sheet is discharged outside the apparatus via the discharge roller pair 32 and stacked on the discharge tray 40.

  Untransferred toner that has not been secondarily transferred to the recording sheet P adheres to the front surface of the intermediate transfer belt 6 that has passed through the secondary transfer nip. This transfer residual toner is removed from the front surface of the intermediate transfer belt 6 by the belt cleaning device 7. Further, transfer residual toner that has not been primarily transferred onto the front surface of the intermediate transfer belt 6 is formed on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K that have passed through the primary transfer nips for Y, C, M, and K. It is attached. This transfer residual toner is removed from the surface of the photoreceptors 1Y, 1C, 1M, and 1K by the photoreceptor cleaning devices 4Y, 4C, 4M, and 4K.

  FIG. 2 is a block diagram illustrating a part of an electric circuit in the printer 100. In the figure, a control unit 110 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, etc. (not shown), and controls driving of various devices in the printer 100. And various arithmetic processes. The controller 110 is electrically connected to a color image forming motor 150, a K image forming motor 151, a belt drive motor 151, an optical sensor unit 140, a primary transfer power source 155, and the like.

  The color image forming motor 150 is a motor that is a drive source for the Y, C, and M image forming apparatuses 10Y, 10C, 10M, and 10K. The rotational driving force of the color image forming motor 150 is transmitted to the image forming apparatuses 10Y, 10C, and 10M via a drive transmission system (not shown). The rotational speed (linear speed) of the developing sleeves for the photoreceptors 1Y, 1C, 1M and Y, C, M in the image forming apparatuses 10Y, 10C, 10M depends on the rotational drive speed of the color image forming motor 150.

  The K image forming motor 151 is a motor that is a drive source of the K image forming apparatus 10K. The rotational driving force of the K image forming motor 151 is transmitted to the image forming apparatus 10K via a drive transmission system (not shown). The rotational speed (linear speed) of the photoreceptor 1K and the developing sleeve in the image forming apparatus 10K depends on the rotational drive speed of the K image forming motor 151.

  The belt drive motor 151 is a motor that is a drive source of any one of four support rollers (15, 16, 18, 19) disposed in the loop of the intermediate transfer belt 6. Hereinafter, the supporting roller is referred to as a belt driving roller. The rotational driving force of the belt drive motor 151 is transmitted to the belt drive roller via a drive transmission system (not shown). Since the belt drive roller moves the intermediate transfer belt 6 endlessly with its rotation, the endless moving speed (linear speed) of the intermediate transfer belt 6 depends on the rotational drive speed of the belt drive motor 151.

  The primary transfer power supply 155 individually outputs primary transfer biases to be applied to the primary transfer rollers 17Y, 17C, 17M, and 17K by constant current control. The primary transfer bias is applied to the primary transfer rollers 17Y, 17C, 17M, and 17K by constant current control. As a result, the primary transfer nip for Y, C, M, and K is supplied with a constant primary transfer current regardless of fluctuations in the electrical resistance of the intermediate transfer belt 6 and the primary transfer rollers 17Y, 17C, 17M, and 17K due to temperature and humidity fluctuations. And stable primary transfer performance can be obtained.

  In the printer 100 according to the embodiment, when a recording sheet P having a lot of surface irregularities such as Japanese paper is used, a toner image on the intermediate transfer belt 6 and a concave portion on the surface of the recording sheet P are used in the secondary transfer nip. A minute gap is formed between the two. Then, a sufficient amount of toner can be secondarily transferred to the inside of the concave portion of the surface of the recording sheet P without applying the electrostatic force necessary to move the toner image in the minute gap. This makes it difficult to produce a blurred image due to an image density difference between the convex portion and the concave portion.

Next, a characteristic configuration of the printer 100 according to the embodiment will be described.
The optical sensor unit 140 shown in FIG. 3 includes a light emitting unit 141 and a light receiving unit 142, and is shown in FIG. 1 in order to function as smoothness detecting means for detecting the surface smoothness of the recording sheet P. In this way, it is disposed on the side of the paper feed path 29. As shown in FIG. 3, the light emitted from the light emitting unit 141 is irradiated obliquely onto the surface of the recording sheet P being conveyed in the paper feed path. Some of the light reaching the surface of the recording sheet P is irregularly reflected on the surface of the sheet and then received by some of the plurality of light receiving elements in the light receiving unit 142. The light receiving unit 142 outputs a voltage corresponding to the amount of received light from each light receiving element.

  These voltage output values are converted from analog data to digital data by the data conversion circuit 145 shown in FIG. 2, and further converted into light reflection distribution curve data indicating the spread of reflected light, and then the control unit 110. Is input. The control unit 110 obtains a dispersion value of the light reflection distribution curve data. This dispersion value is a dispersion value of the light reflection distribution curve data derived from the amount of light received by the plurality of light receiving elements of the light receiving unit 142, and is correlated with the surface smoothness of the recording sheet P. Therefore, the control unit 110 calculates the surface smoothness (Beck smoothness) of the recording sheet P based on the obtained dispersion value.

  Upon receiving image data from a personal computer or the like, the control unit 110 adjusts the linear velocity difference between the photoreceptors 1Y, 1C, 1M, and 1K and the intermediate transfer belt 6 before starting a print job based on the image data. The linear velocity difference adjustment process is performed. FIG. 4 is a flowchart showing each step in the linear velocity difference adjustment process. When the linear velocity difference adjustment process is started, the control unit 110 first waits until it receives image data sent from a personal computer or the like (N in step 1; hereinafter, step is denoted as S). When the image data is received (Y in S1), paper feeding is started by starting driving of the paper feeding roller 27 and the conveying roller pair. At the same time, in the color print mode, the photosensitive drums 1Y, 1C, 1M, and 1K are driven to rotate by the color imaging motor 150 and the K imaging motor 151, and the belt driving motor 152 is driven to rotate. Starts the endless movement of the intermediate transfer belt 6. In the monochrome mode, the tension of the intermediate transfer belt 6 is changed by driving a solenoid (not shown) to separate the intermediate transfer belt 6 from the photoreceptors 1Y, 1C, 1M. Immediately after the separation, the rotation of the photosensitive member 1K by the rotation driving of the K image forming motor 151 and the endless movement of the intermediate transfer belt 6 by the rotation driving of the belt driving motor 152 are started. Regardless of the color mode or the monochrome mode, when the driving of the photosensitive member 1 and the intermediate transfer belt 6 performed almost simultaneously with paper feeding, the photosensitive member 1 and the intermediate transfer belt 6 are driven at the same linear velocity. . That is, the mutual driving is started with the mutual linear velocity difference being zero.

  The recording sheet P conveyed to the sheet feeding path 29 by the sheet feeding operation is detected at its leading end by a sheet detection sensor including a reflective photosensor (not shown) immediately before hitting the registration nip. As soon as the recording sheet P is detected by the sheet detection sensor, the control unit 110 stops the rotation driving of the paper feed roller 27 and the conveyance roller pair. Thus, the conveyance of the recording sheet P is temporarily stopped in a state where the leading end of the recording sheet P is abutted against the registration nip. However, if the recording sheet P is not detected by the sheet detection sensor even after a predetermined time has elapsed from the start of paper feeding by the paper feeding roller 27, the recording sheet P is not stored in the paper feeding cassette 26. Judgment is made (N in S3), and no sheet error processing is performed (S4). This no sheet error process is a process in which the user is prompted to replenish the recording sheet P to the sheet cassette 26 and then waits for the sheet cassette 26 to be attached to and detached from the housing. After the sheet no error process, the process flow is returned to S2 described above, and the paper feeding operation is performed again.

  When the recording sheet P is detected by the sheet detection sensor after the sheet feeding operation is started (Y in S3), the control unit 110 stops the rotation driving of the sheet feeding roller 27 and the conveying roller pair and removes the recording sheet P. Paper feeding is temporarily stopped in a state where it abuts against the registration nip (S5). In this state, the surface smoothness of the recording sheet P is detected by the optical sensor unit 140 (S6). Thereafter, when the detection result of the surface smoothness (Beck smoothness) is not less than 20 seconds, that is, when the surface smoothness is relatively high and the unevenness of the sheet surface is relatively small (N in S7), the photosensitive member 1 Then, the linear velocity difference from the intermediate transfer belt 6 is kept zero (S8). Then, the linear velocity difference adjustment process ends. On the other hand, when the detection result of the surface smoothness is less than 20 seconds, that is, when the surface smoothness is relatively low and the unevenness of the sheet surface is relatively large (Y in S7), the photoreceptor 1 and the intermediate transfer belt After adjusting the linear velocity difference with 6 to 0.5 [%], the linear velocity difference adjustment processing is terminated. When the linear velocity difference adjustment process is completed, the image forming process based on the image data is started, and then the conveyance of the recording sheet P is resumed at an appropriate timing and the recording sheet P is fed into the secondary transfer nip.

  As described above, in the linear velocity difference adjustment process, the printer 100 has the photoreceptors 1Y, 1C, 1M, and 1K when the surface smoothness of the recording sheet P is relatively high, that is, when the occurrence of a blurred image is not a concern. And the linear velocity difference with the intermediate transfer belt 6 is made zero. On the other hand, when the surface smoothness of the recording sheet P is relatively low, that is, when the occurrence of a blurred image is concerned, the linear velocity difference between the photoreceptors 1Y, 1C, 1M, and 1K and the intermediate transfer belt 6 Is adjusted to 0.5 [%]. When such a linear velocity difference is provided, the adhesion of the Y toner layer, C toner layer, M toner layer, and K toner layer to the photoreceptors 1Y, 1C, 1M, and 1K in the primary transfer nip for Y, C, M, and K Generates a shear force that weakens This shearing force promotes the separation of the Y toner layer, C toner layer, M toner layer, and K toner layer from the surface of the photoreceptors 1Y, 1C, 1M, and 1K, so that a difference in linear velocity is not provided. Thus, more Y, C, M, and K toners are primarily transferred onto the intermediate transfer belt 6. Then, the layer thicknesses of the Y toner image, C toner image, M toner image, and K toner image that are primarily transferred to the intermediate transfer belt 6 are increased, and the respective color toner images on the intermediate transfer belt 6 in the secondary transfer nip. As a result, the minute gap with the concave portion on the surface of the recording sheet P is further reduced. Accordingly, by increasing the amount of toner transferred from the intermediate transfer belt 6 to the concave portion on the surface of the recording sheet P, the difference in image density between the convex portion and the concave portion on the sheet surface is reduced, thereby suppressing the generation of a blurred image. be able to. Further, as compared with the case where a linear velocity difference is always provided, the machine to the photoreceptors 1Y, 1C, 1M, 1K and the intermediate transfer belt 6 due to the sliding friction between the photoreceptors 1Y, 1C, 1M, and 1K and the intermediate transfer belt 6 is possible. Reduce the amount of load applied. As a result, it is possible to prevent the life of the photoreceptors 1Y, 1C, 1M, and 1K and the intermediate transfer belt 6 from being shortened due to a mechanical load.

  As a first example of another method for increasing the amount of toner transferred from the intermediate transfer belt 6 to the concave portion of the sheet surface (hereinafter referred to as another method 1), a Y toner image on the photoreceptors 1Y, 1C, 1M, 1K, C For example, the toner image, M toner image, and K toner image are developed with a larger layer thickness. However, when this alternative method 1 is adopted, a phenomenon called transfer dust that causes toner to scatter around the toner image on the belt is likely to occur at the exit of the primary transfer nip for Y, C, M, and K. . In contrast, in the printer 100 according to the embodiment, the Y toner image, the C toner image, the M toner image, and the K toner image are developed with a larger layer thickness to increase the layer thickness of each color toner image on the belt. Thus, the secondary transfer property to the recesses on the sheet surface is not increased. By providing the above linear velocity difference, the layer thickness of each color toner image on the belt is increased, thereby improving the secondary transfer property to the concave portion of the sheet surface. Thereby, it is possible to suppress the generation of a blurred image without promoting the generation of transfer dust.

  As a second example of another method for increasing the amount of toner transferred from the intermediate transfer belt 6 to the concave portion of the sheet surface (hereinafter referred to as another method 2), a larger amount of secondary transfer current is generated in the secondary transfer nip. Can be mentioned. However, as shown in FIG. 5, when the secondary transfer current is increased, the secondary transfer property of the toner to the concave portion on the sheet surface is improved, while the secondary transfer property of the toner to the convex portion on the sheet surface is improved. It will decrease. As a result, the blurred image may be deteriorated. Furthermore, it becomes easy to generate a discharge between the intermediate transfer belt 6 and the secondary transfer roller 8 due to an increase in the secondary transfer bias. When such a discharge occurs, the amount of toner charged on the belt is reduced, or the toner is reversely charged, so that white spots are easily generated. In the printer 100 according to the embodiment, the secondary transfer property from the intermediate transfer belt 6 to the concave portion of the sheet surface is improved by the linear velocity difference without increasing the secondary transfer current. As a result, it is possible to avoid the deterioration of the blurred image and the occurrence of the whiteout image due to the increase in the secondary transfer current.

  In the printer 100 according to the embodiment, the photosensitive members 1Y, 1C, 1M, and 1K, the intermediate transfer belt 6, and the photosensitive members 1Y, 1C, 1M, and 1K are increased by 0.5% faster than usual. A linear speed difference of 0.5% is provided between the two. Instead of making the linear speeds of the photoreceptors 1Y, 1C, 1M, and 1K faster than usual, the linear speed difference may be provided by making it slower than usual. When the linear velocity of the photoreceptors 1Y, 1C, 1M, and 1K is changed, the laser irradiation time per dot at the irradiation position of the laser beam on the photoreceptors 1Y, 1C, 1M, and 1K changes accordingly. As a result, the one-dot latent image written as a latent image expands and contracts in the sub-scanning direction (photoconductor surface movement direction). However, since this expansion / contraction can be offset by the reverse expansion / contraction of one dot after belt transfer due to the linear velocity difference at the primary transfer nip, even if the linear velocity of the photoreceptors 1Y, 1C, 1M, 1K is changed, The dot shape is not disturbed.

  Instead of changing the linear speeds of the photoreceptors 1Y, 1C, 1M, and 1K, the linear speed difference may be provided by changing the linear speed of the intermediate transfer belt 6. However, in this case, the shape of one dot after belt transfer is expanded or contracted in the sub-scanning direction due to a difference in linear velocity at the primary transfer nip. In order to suppress the distortion of the dot shape due to the expansion and contraction, the main scanning speed (polygon mirror rotation speed) in the laser beam scanning and the laser irradiation time per dot are changed, so that one-dot latent image is sub-scanned in advance. It is desirable to generate direction expansion and contraction. This is because the dot shape disturbance can be suppressed by canceling the expansion and contraction of the one-dot latent image on the photosensitive member by the expansion and contraction of the one dot in the primary transfer nip. When the above linear velocity difference is provided by changing the linear velocity of the intermediate transfer belt 6, a linear velocity difference is also generated between the recording sheet P and the intermediate transfer belt 6 in the secondary transfer nip, so that the secondary transfer is performed. There is also an advantage that the efficiency can be further improved.

  In the printer 100 according to the embodiment, the linear velocity difference is provided only when the surface smoothness is less than 20 seconds. However, the linear velocity difference is changed continuously or stepwise according to the size of the surface smoothness. You may make it make it.

  Next, printers according to each example in which a more characteristic configuration is added to the printer 100 according to the embodiment will be described. Unless otherwise specified below, the configuration of the printer 100 according to each example is the same as that of the embodiment.

[First embodiment]
FIG. 6 is a graph showing the relationship between the primary transfer rate, the primary transfer current output target value (constant current control), and the linear velocity difference, which has been clarified by experiments conducted by the present inventors. In the figure, when the primary transfer rate is y [%] or more, a sufficient amount of toner is secondarily transferred to the concave portions on the surface of the recording sheet P rich in surface irregularities, so that no blurred image is generated. The small linear velocity difference graph in the figure shows the relationship between the primary transfer rate and the primary transfer current target value when the linear velocity difference is actually set to zero. Further, the graph of the large linear velocity difference shows that the primary transfer rate and the primary transfer current target value when the linear velocity of the photoreceptor 1 is actually set to a value 0.5 [%] faster than the intermediate transfer belt 6. Showing the relationship. As shown in the figure, under the condition that the primary transfer current output target value is set to A ₂ [μA], when the linear velocity difference is set small, the primary transfer rate becomes lower than the target y [%], whereas If the speed difference is set to a large value, the primary transfer rate becomes higher than the target y [%]. This suppresses the generation of a blurred image. However, if the linear velocity difference is set large, the primary transfer rate can be set even if the primary transfer current output target value is set to A ₁ lower than A ₂ as shown in the figure. Can be maintained higher than the target y [%].

  FIG. 7 shows the relationship between the toner transferability (concave transferability) to the concave portion of the sheet surface, the secondary transfer current output target value, and the toner charge amount Q / M, which has been clarified by experiments conducted by the present inventors. It is a graph to show. In this experiment, a secondary transfer power source that outputs the secondary transfer bias is one that outputs the secondary transfer bias by constant current control. In addition, the toner charge amount Q / M in the figure represents the charge amount of the toner secondarily transferred onto the intermediate transfer belt 6, not the charge amount of the toner accommodated in the developing device. When the primary transfer bias is output by constant current control, as the primary transfer current output target value is increased, the charge amount Q / M of toner on the belt after secondary transfer to the intermediate transfer belt 6 is increased. I know. As shown in the figure, it can be seen that as the charge amount Q / M of the toner on the belt increases, the recess transferability deteriorates. This is because as the charge amount Q / M increases, the electrostatic adhesion between the toner and the intermediate transfer belt 6 increases, and the toner is less easily transferred onto the recording sheet P.

As described with reference to FIG. 6, when the linear velocity difference is set to a relatively small value, the primary transfer current output target value is set to a relatively high value (A ₂ ). The target primary transfer rate (y%) cannot be obtained. On the other hand, when the linear velocity difference is set to a relatively large value, the target primary transfer rate (A ₁ ) is set despite the primary transfer current output target value being set to a relatively low value (A ₁ ). y%) can be obtained. When the primary transfer current output target value is made smaller, the recessed portion transferability can be further improved as described with reference to FIG. In other words, when the linear velocity difference is changed to a larger value, it is possible to change the primary transfer current output target value to a smaller value, further improving the recess transferability and more reliably generating a blurred image. It will be able to be suppressed to.

  Therefore, in the printer 100 according to the first embodiment, when the detection result of the surface smoothness of the recording sheet P is less than 20 sec in the linear speed difference adjustment process, the linear speed difference is set to 0.5 [%]. In addition to the adjustment, the primary transfer current output target value for each color is set to a smaller value. As a result, it is possible to more reliably suppress the occurrence of a blurred image by further improving the toner recess transferability at the secondary transfer nip.

[Second Example]
In the printer 100 according to the second embodiment, a switchback device (not shown) is provided as an option to realize double-sided printing. The switchback device is a switching claw that switches the conveyance path of the recording sheet P on which the full color image is fixed on the first surface through the fixing device 13 from the direction toward the discharge roller pair 32 to the direction toward the switchback device main body. It has. When the recording sheet P is received by the switchback device main body, the recording sheet P is retransmitted to the registration nip of the registration roller pair 28 while the upper and lower surfaces thereof are reversed. The recording sheet P that has reached the registration nip is in a posture in which the second surface is brought into close contact with the intermediate transfer belt 6 at the secondary transfer nip. When the registration roller pair 28 feeds the recording sheet P to the secondary transfer nip in time, the four-color superimposed toner image is secondarily transferred to the second surface of the recording sheet P to form a full color image. Thereafter, the recording sheet P is sent to the fixing device 13 to fix the full-color image on the second surface, and then discharged to the outside through the discharge roller pair 32. In this way, the printer 100 according to the second embodiment can form images on both sides of the recording sheet P.

  The recording sheet P retransmitted from the fixing device 13 to the position of the registration roller pair 28 by the switchback device to transfer the full-color image to the second surface is detected by the optical sensor unit 140 for the surface smoothness of the second surface. . Based on the detection result, the control unit 110 selects whether to adjust the linear velocity difference to zero or to adjust the linear velocity difference to 0.5 [%]. With such a configuration, it is possible to suppress the generation of a blurred image even on the second surface of the recording sheet P.

  The printer 100 according to the second embodiment performs double-sided printing by a so-called switchback method, but an image forming apparatus that performs double-sided printing by a so-called one-pass method is also known. In the one-pass method, the recording sheet P is not retransmitted to the registration roller pair 32, and the transfer of the toner image to the first surface and the transfer of the toner image to the second surface are performed simultaneously or continuously, and then fixed. The fixing process of the first side and the second side is simultaneously performed by the apparatus. In such a one-pass method, there is only one opportunity to detect the surface smoothness of the sheet upstream of the registration roller pair 32 in the sheet conveyance direction. Thus, as shown in FIG. 8, in addition to the optical sensor unit 140 for detecting the surface smoothness of the first surface, an optical sensor unit 150 for detecting the surface smoothness of the second surface is provided. The surface smoothness of the first surface and the second surface may be detected.

  Although the printer has been described as an example of the image forming apparatus to which the present invention is applied, the present invention can also be applied to an image forming apparatus such as a copying machine, a facsimile machine, or a plotter.

  Further, the printer having a configuration in which the toner image on the photoreceptor 1 is transferred to the recording sheet P via the intermediate transfer belt 6 has been described. However, an image of a system in which the toner image on the photoreceptor 1 is directly transferred to the recording sheet P is described. The present invention can also be applied to a forming apparatus. In this case, if the linear velocity difference between the transfer roller, the sheet conveying belt, or the like that contacts the photosensitive member 1 to form the transfer nip and the photosensitive member 1 is adjusted according to the detection result of the surface smoothness of the recording sheet P. Good.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
[Aspect A]
In the aspect A, the image forming means for forming a toner image on the moving surface of the image carrier (for example, the photoreceptors 1Y, 1C, 1M, and 1K), and the toner image on the image carrier from the image carrier In the image forming apparatus comprising: a transfer unit that directly transfers to a recording medium (for example, the recording sheet P) or transfers the recording medium to the recording medium via an intermediate transfer body (for example, the intermediate transfer belt 6). Information acquisition means for acquiring surface smoothness information of the medium, and the image carrier and recording when transferring a toner image from the image carrier to a recording medium based on the information acquisition result by the information acquisition means Control means for adjusting a linear velocity difference with the medium or a linear velocity difference between the image carrier and the intermediate transfer member when the toner image is transferred from the image carrier to the intermediate transfer member is provided. It is characterized by

  In the present invention having such a configuration, when the surface smoothness of the recording medium is relatively low, that is, when the generation of a blurred image is concerned, the image carrier and the recording medium are compared with the case where the surface smoothness is relatively high. Or the linear velocity difference between the image carrier and the intermediate transfer member is increased. When such a linear velocity difference is provided, the shear that weakens the adhesion force of the toner image to the image carrier at the contact portion between the image carrier and the recording medium or the contact portion between the image carrier and the intermediate transfer member. Generate power. This shearing force promotes the separation of the toner image from the surface of the image carrier. Then, in the configuration in which the toner image is transferred from the image carrier to the recording medium, the toner transfer amount from the image carrier to the surface concave portion of the recording medium is increased to the concave portion as compared with the case where the linear velocity difference is not increased. This reduces toner transfer defects. Further, in the configuration in which the toner image is transferred from the image carrier to the recording medium via the intermediate transfer member, the layer thickness of the toner image transferred to the intermediate transfer member is increased as compared with the case where the linear velocity difference is not increased. As a result, when transferring the toner image from the intermediate transfer member to the recording medium, the fine gap between the toner image on the intermediate transfer member and the concave portion on the surface of the recording medium is made smaller, and the toner from the intermediate transfer member to the concave portion is reduced. Reduce transfer defects. In other words, in both the configuration in which the toner image is directly transferred from the image carrier to the recording medium and the configuration in which the toner image is transferred from the image carrier to the recording medium via the intermediate transfer body, the toner is poorly transferred to the concave portion on the surface of the recording medium Reduce. Thereby, the occurrence of a blurred image can be suppressed by reducing the difference in image density between the surface convex portion and the surface concave portion of the recording medium.

[Aspect B]
Aspect B is characterized in that, in aspect A, the transfer means is a means for transferring a toner image on the image carrier to the intermediate transfer member and then transferring it to a recording medium. In such a configuration, by increasing the linear velocity difference, the thickness of the toner image transferred from the image carrier to the intermediate transfer member is increased, and toner transfer defects from the intermediate transfer member to the surface recesses of the recording medium are suppressed. be able to.

[Aspect C]
Aspect C is a current output target from a transfer power source (for example, a primary transfer power source 155) that controls a transfer bias for forming a transfer electric field between the image carrier and the intermediate transfer member by constant current control. The control means is configured to perform a process of changing a value based on the acquisition result. In such a configuration, as the surface smoothness of the recording medium deteriorates, the current output target value is changed to a smaller value to reduce the charge amount of toner transferred from the image carrier to the intermediate transfer member. As a result, the worse the surface smoothness of the recording medium, the weaker the electrostatic adhesion between the intermediate transfer member and the toner and the higher the toner transferability from the intermediate transfer member to the surface recess of the recording medium. Occurrence can be suppressed more reliably.

[Aspect D]
In the aspect D, in the aspect C, when the acquisition result indicates that the surface smoothness is relatively low, the image carrier and the intermediate are compared with the case where the acquisition result indicates that the surface smoothness is relatively high. An image forming apparatus, wherein the control means is configured to perform a process of increasing a linear velocity difference with a transfer body and decreasing the current output target value.

[Aspect E]
Aspect E is characterized in that, in any one of Aspects A to D, a smoothness detecting means (for example, an optical sensor unit) for detecting the surface smoothness of the recording medium is provided as the information acquisition means. . With such a configuration, the smoothness information can be acquired without having the user input information about the surface smoothness of the recording medium.

[Aspect F]
Aspect F is the linear speed between the image carrier and the recording medium when transferring the toner image from the image carrier to the recording medium by adjusting the linear velocity of the image carrier in any of the aspects A to E. The control means is configured to perform a process of adjusting a difference or a linear velocity difference between the image carrier and the intermediate transfer member when transferring a toner image from the image carrier to the intermediate transfer member. It is characterized by that. In such a configuration, the image carrier that is expanded or contracted in the moving direction of the image carrier surface of the toner image on the image carrier due to a change in the linear velocity of the image carrier is generated when the toner image is transferred from the image carrier to the intermediate transfer member. This is offset by the expansion and contraction of the toner image due to the linear velocity between the body and the intermediate transfer body. Thereby, it is possible to suppress the occurrence of toner image disturbance due to the provision of the linear velocity difference.

[Aspect G]
Aspect G is the linear speed between the image carrier and the recording medium when the toner image is transferred from the image carrier to the recording medium by adjusting the linear speed of the intermediate transfer member in any of the aspects A to E. The control means is configured to perform a process for adjusting a difference or a linear velocity difference when transferring a toner image from the image carrier to the intermediate transfer member. In such a configuration, in addition to increasing the thickness of the toner image transferred from the image bearing member to the intermediate transfer member due to the difference in linear velocity, the toner transferability from the intermediate transfer member to the recording medium is improved. Increase the amount of toner transferred to the concave portion of the surface of the medium. Thereby, generation | occurrence | production of a blurred image can be suppressed more reliably.

[Aspect H]
In the aspect H, a toner image is formed on the moving surface of the image carrier, and the toner image on the image carrier is directly transferred from the image carrier to a recording medium or recorded from the image carrier. An image forming method including a step of transferring to a medium via an intermediate transfer body, a step of obtaining information on surface smoothness of the recording medium, and a toner image from the image carrier based on the information. The linear velocity difference between the image carrier and the recording medium when transferring to the recording medium, or the linear velocity between the image carrier and the intermediate transfer member when transferring the toner image from the image carrier to the intermediate transfer member And a step of adjusting the difference. In such a configuration, the occurrence of a blurred image can be suppressed by the same operation as in the aspect A.

1Y, 1C, 1M, 1K: photoconductor (image carrier)
10Y, 10C, 10M, 19K: Image forming unit (image forming means)
100: Printer (image forming apparatus)
110: Control unit (control means)
140: Optical sensor unit (information acquisition means, smoothness detection means)
155: Primary transfer power supply (transfer power supply)

JP-A-2005-234301

Claims (8)

Image forming means for forming a toner image on the moving surface of the image carrier, and the toner image on the image carrier is directly transferred from the image carrier to a recording medium, or from the image carrier to the recording medium. In an image forming apparatus comprising a transfer means for transferring to an intermediate transfer member,
Information acquisition means for acquiring surface smoothness information of the recording medium, and the image carrier when transferring a toner image from the image carrier to the recording medium based on the acquisition result of the information by the information acquisition means An image forming apparatus comprising: a control unit that adjusts a difference in linear velocity between the recording medium and a recording medium or a linear velocity difference when transferring a toner image from the image carrier to the intermediate transfer member. The image forming apparatus according to claim 1.
An image forming apparatus comprising: a transfer unit that transfers a toner image on the image bearing member to a recording medium after the toner image is transferred to the intermediate transfer member. The image forming apparatus according to claim 2.
A process of changing a current output target value from a transfer power source for controlling a transfer bias for forming a transfer electric field between the image carrier and the intermediate transfer member by constant current control based on the acquisition result is performed. An image forming apparatus comprising the control means. The image forming apparatus according to claim 3.
When the acquisition result indicates that the surface smoothness is relatively low, the linear velocity difference between the image carrier and the intermediate transfer member is smaller than when the acquisition result indicates a relatively high value. An image forming apparatus, wherein the control unit is configured to perform a process of increasing the current output target value and increasing the current output target value. The image forming apparatus according to any one of claims 1 to 4,
An image forming apparatus comprising a smoothness detecting means for detecting the surface smoothness of the recording medium as the information acquisition means. The image forming apparatus according to claim 1,
By adjusting the linear velocity of the image carrier, the linear velocity difference between the image carrier and the recording medium when the toner image is transferred from the image carrier to the recording medium, or the toner image is transferred from the image carrier to the recording medium. An image forming apparatus, wherein the control means is configured to perform a process of adjusting a linear velocity difference between the image carrier and the intermediate transfer member when transferring to an intermediate transfer member. The image forming apparatus according to claim 1,
By adjusting the linear velocity of the intermediate transfer member, the linear velocity difference between the image carrier and the recording medium when the toner image is transferred from the image carrier to the recording medium, or the toner image is transferred from the image carrier to the recording medium. An image forming apparatus, wherein the control means is configured to perform a process of adjusting a linear velocity difference between the image carrier and the intermediate transfer member when transferring to an intermediate transfer member. A step of forming a toner image on a moving surface of the image carrier, and a toner image on the image carrier is directly transferred from the image carrier to a recording medium or an intermediate transfer from the image carrier to the recording medium; An image forming method comprising a step of transferring through a body,
Obtaining a surface smoothness information of the recording medium, and a linear velocity difference between the image carrier and the recording medium when transferring a toner image from the image carrier to the recording medium based on the information; or And a step of adjusting a linear velocity difference between the image carrier and the intermediate transfer member when the toner image is transferred from the image carrier to the intermediate transfer member.

Images