JP4157611B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and in particular, at the time of a transfer process for transferring a toner image formed on a toner image carrier such as a photosensitive member or an intermediate transfer member to the next recording material. Image formation with improved transfer performanceapparatusAbout.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine, a printer, or a facsimile, for example, an electrophotographic image forming apparatus, a method for transferring a toner visible image formed on an image carrier, for example, a photosensitive member, to a transfer sheet as a recording material is Well known. In addition, another transfer process is included in the process of transferring from the photoconductor to the transfer paper. After the primary transfer from the photoconductor to the intermediate transfer body, the primary transfer image on the intermediate transfer body is secondary transferred to the transfer paper. An intermediate transfer method for obtaining a final image by transferring is already known. In particular, the intermediate transfer method is employed as a superposition transfer method for each color toner image in a full-color image forming apparatus that reproduces a color-separated document using subtractive color mixing with black, cyan, magenta, and yellow toners.
[0003]
By the way, one of the “abnormal images” generated in the transfer process in the electrophotographic image forming apparatus is a “hollow-out phenomenon” in which a part of the toner image is not transferred. This phenomenon occurs in a full-color image forming apparatus with a large total toner adhesion amount, and also tends to occur in a contact transfer system using a bias roller or the like, although it also occurs in a general non-contact transfer system using corona discharge.
[0004]
The cause of this “missing phenomenon” is that in the case of a full-color image, the toner layer becomes thicker, and the bias roller has a mechanical adhesion force that is a non-Coulomb force between the surface of the intermediate transfer member and the toner due to contact pressure. In the process of repeatedly executing the image forming process, a filming phenomenon occurs in which the toner adheres to the surface of the toner image carrier in the form of a film, and a strong adhesion force is generated between the surface and the toner. It is thought to be due to.
[0005]
The following two techniques have already been disclosed as means for avoiding such a “missing phenomenon”.
First technology: US Pat. No. 5,053,827 (METHODO AND APPARATUS FOR A TRANSFER BELT).
[0006]
In this US patent, a roller (conditioning mean) composed of a member made of a fluorine-based material having a surface energy smaller than the surface energy of an intermediate transfer belt as an intermediate transfer member is applied to the surface of the intermediate transfer belt. A technique is disclosed having a conditioning process that reduces the surface energy on the transfer belt.
[0007]
Japanese Patent Laid-Open No. 2-198476 is also disclosed as a similar technique. This open patent publication discloses a technique for reducing the surface energy of the intermediate transfer body itself by adding a substance that reduces wettability (that is, reducing the surface energy) to the intermediate transfer body.
[0008]
Second technique: JP-A-63-58387.
This open patent publication discloses a technique for reducing the “collapse phenomenon” during transfer by changing the linear velocity of the toner image support and the transfer paper.
[0009]
Further, similar techniques are also disclosed in the following published patent publications. JP-A-3-148680, JP-A-6-83212, JP-A-6-317992.
[0010]
The first technique and the second technique are techniques for avoiding a “hollow-out phenomenon” that occurs during the transfer process of the image forming apparatus. However, these techniques are insufficient, and sufficient effects cannot be obtained. There is. Hereinafter, problems to be solved by the present invention will be described.
[0011]
The following was found from the results of experiments conducted by the inventor in a color image forming apparatus (FIGS. 1 and 2) using an intermediate transfer belt system having a configuration shown in the embodiments described later.
1. The surface energy of the surface of the toner image carrier (the surface of the intermediate transfer belt 19 in the examples of FIGS. 1 and 2) is equal to or less than that of the recording material (transfer paper 24 in the examples of FIGS. 1 and 2). If zinc stearate is applied to the surface as a lubricant, and the toner can be easily released from the toner image carrier, the “collapse phenomenon” is improved, but the effect depends on the linear velocity difference between the toner image carrier and the recording material. Is different. Specifically, in the state where there is no difference in linear velocity between the toner image carrier and the transfer paper, it is difficult to completely eliminate the “collapse phenomenon” with this technology alone. Here, FIG. 3 shows the relationship between the linear speed ratio of the transfer paper and the intermediate transfer belt and the hollow rank. In FIG. 3, Δ: when zinc stearate is applied to the intermediate transfer belt, and ○: when not applied As is clear from the comparison, when there is no linear speed ratio, the “slip-out phenomenon” is improved by applying zinc stearate to the intermediate transfer belt, but when the linear speed ratio is 0, it should be completely eliminated. I can't. 3 is a rank 5 in which no “blank” portion is found by visual observation when an image is formed on the transfer paper using the apparatus shown in FIGS. It is difficult to determine the “missing” part, and it is difficult to find the “missing” part in Rank 4, and the “missing” part can be barely found by visual observation, and the “missing” part does not impair the image quality. The state is rank 3, the state in which the “void” part can be relatively easily found by visual observation is ranked 2, and the state in which the “hole” part can be found immediately even if anyone observes is rank 1. In order not to impair the image quality, rank 3 or higher is necessary.
[0012]
2. Even when the linear velocity difference between the toner image carrier and the transfer paper is given, the effect differs depending on the surface energy states of the toner image carrier surface and the recording material surface. Specifically, when the surface energy of the recording material is made smaller than that of the toner image carrier (for example, zinc stearate is applied to the recording material as a lubricant), the linear velocity difference between the toner image carrier and the transfer paper is increased. Regardless, the “missing phenomenon” is not improved at all. That is, in FIG. 3, Δ: when zinc stearate is applied to the intermediate transfer belt and □: when zinc stearate is applied to the transfer paper, as apparent from comparison between when zinc stearate is applied to the transfer paper In such a case, even if anyone observes, the “void” portion can be immediately found, and the image quality is greatly reduced.
[0013]
3. In an image forming apparatus having a transfer unit using a roller or a belt, the transfer sheet is conveyed by a frictional force with the transfer unit. It occurs that the linear velocity is different. Furthermore, because the frictional force generated varies depending on the type of transfer paper, the same linear velocity cannot be obtained for each transfer paper under the same transfer unit drive conditions, and the “slow-out phenomenon” varies depending on the transfer paper. is there.
[0014]
From the above results 1 to 3, what the inventor has considered for the “slow-out phenomenon” will be described below.
In the electrophotographic method, a toner image is transferred by forming a transfer electric field by a transfer means such as a corona charger, a bias roller, and a bias belt disposed on the back surface of the recording material, and the toner on the toner image carrier is recorded by the electrostatic force. In the actual transfer process, the force between the toner image carrier and the toner (hereinafter referred to as F1), the force between the toner and the toner (hereinafter referred to as F2), the toner and the recording material are used. The mechanical adhesion force, which is the force in between (hereinafter referred to as F3), is greatly affected.
[0015]
That is, if F1 is large, the toner in contact with the toner image carrier cannot move to the recording material side regardless of the action of the transfer electric field. Further, it is influenced by F2 which is uniformly generated between the toner layers by the transfer pressure, and the toner layer is separated at a portion where F2 is weak. However, the surface energy of the toner image carrier is equal to or less than the recording material surface energy (the releasability of the toner image carrier surface with respect to the toner is higher than the releasability of the recording material surface with respect to the toner). Since the influence of F1 is reduced, the toner can be easily moved to the recording material by the transfer electric field.
[0016]
Here, as shown in the model of “collapse phenomenon” in the case where there is no linear velocity difference between the toner image carrier and the recording material in FIG. 4, there is no linear velocity difference between the recording material 24 of the toner image carrier 19. F1 to F3, which are the forces in the vertical direction between the toner image carrier 19 and the recording material 24, are the main components. If F1 is not sufficiently small, the surface energy of the toner image carrier 19 is reduced with respect to the recording material surface energy. Even if it is equal to or less than that (FIG. 4B2), a part of the toner 39 in the toner layer 44 remains on the toner image carrier 19 side and a sufficient effect cannot be obtained.
[0017]
Further, when the linear velocity of the recording material 24 of the toner image carrier 19 is made different as shown in the model of “slow-out phenomenon” in the case where there is a linear velocity difference between the toner image carrier and the recording material in FIG. As shown in (b1), the surface energy of the toner image carrier 19 is made smaller than the surface energy of the recording material 24 (the releasability of the toner image carrier surface from the toner layer 44 is separated from the toner layer 44 on the surface of the recording material). When the F1 is small, a shear force caused by a shear strain caused by a speed difference is generated between the toner image carrier 19 and the toner 44 due to the small F1, and a uniform transfer without “spotting phenomenon” is obtained. . However, as shown in (b2), if the relationship between the surface energy (releasing properties with respect to the toner) is reversed, a shearing force due to shearing strain caused by the speed difference is generated between the toner 39 and the recording material 24, and “slow-out” In addition to the “phenomenon”, not only a uniform transfer was obtained, but also the toner image was disturbed.
[0018]
From the above, it can be understood that the above-described conventional technique is a necessary condition, but it is not possible to obtain a sufficient effect by itself, and an adverse effect is caused depending on the condition.
In order to solve such a problem, the present inventor makes the surface energy of the toner image carrier equal to or less than the surface energy of the recording material, and at least changes the linear velocity of the toner image carrier and the recording material in the transfer step. The application has been published as JP-A-9-106194.
[0019]
According to the invention described in this patent publication, a lubricant is periodically applied to prevent the surface energy of the toner image carrier from increasing with time and to keep a value smaller than the surface energy of the recording material. 3 and the linear velocity ratio between the toner image carrier and the recording material to be within a range of ± 1 to 3%. As indicated by “Δ” in the diagram showing the relationship, a hollow spot rank 5 is always obtained, and the occurrence of a “blank hole phenomenon” can be almost completely prevented.
[0020]
That is, the surface energy of the toner image carrier is made smaller than the surface energy of the recording material, and a shearing force caused by shear strain caused by the speed difference is generated between the toner image carrier and the toner. A uniform transfer without any problems can be obtained.
[0021]
[Problems to be solved by the invention]
Incidentally, an image forming apparatus such as a copying machine or a printer is well known that has a double-sided or composite function in which a single recording material undergoes two or more transfer processes. The technique disclosed in Japanese Patent Laid-Open No. 9-106194 is also applied to this type of apparatus. At this time, when the recording material is a transfer sheet, the toner image transferred in the first transfer process is “a void phenomenon”. In contrast, the toner image transferred in the second transfer process sometimes has a “blank phenomenon”. That is, there is a problem in that the first time is normal and the second time is lost even though the first time and the second time are transferred under the same conditions and on the same transfer paper.
[0022]
Therefore, the present inventor conducted various experiments to investigate the cause, and found that the transfer paper that has undergone the first transfer process undergoes a fixing process to fix the toner image. That is, it has been found that after the fixing process of the transfer paper is finished, the surface property, particularly the friction coefficient, is changed, and the toner image transferred in the second transfer process is caused to be void due to the change.
[0023]
As a factor that changes the surface property of the transfer paper, first, oil as a release agent is attached. Generally, in order to secure the releasability of the fixing roller in the fixing device, silicone oil or the like as a release agent is applied, and this oil also adheres to the transfer paper that has passed through the fixing device. The transfer paper to which oil is attached has a reduced slip force due to a decrease in frictional force with the transfer bias roller, so that the surface property of the transfer paper changes. Another factor is that the surface property of the transfer paper changes because the transfer paper is pressed and held on the pair of fixing rollers to level the unevenness of the surface. Another factor is that the surface property of the transfer paper changes because the toner surface is mirror-finished when the toner is heat-fused. Note that the fixing device used in the full-color image forming apparatus uses a fixing roller having a smooth surface compared to a single-color device, so that the unevenness of the surface due to pressure is more even. Further, a full-color image forming apparatus has a larger amount of toner than a single-color image forming apparatus, and its surface is made to be a mirror surface, so that the surface property of the transfer paper tends to change more easily. Therefore, the problem that the first transfer is normal and the second transfer is lost is a problem even in a monochromatic image forming apparatus, but the problem is particularly serious in a full color image forming apparatus.
[0024]
  The present invention has been made in view of the above circumstances, and can form an image that can solve the problem of transfer failure such as “slow-out phenomenon” even if a single recording material undergoes a transfer process twice or more.apparatusThe purpose is to provide.
[0025]
[Means for Solving the Problems]
  To achieve the above object, the toner image is transferred to an image carrier that carries the toner image and a recording material that is sandwiched between the image carrier and the image carrier.forA transfer member and fixing means for fixing the toner image formed on the recording material to the recording material, each of the image carrier and the transfer member being driven to rotate,Of the transfer memberIn the image forming apparatus configured so that the rotation speed can be changed, when the recording material is plain paper, the first transfer process is performed after the first transfer process and then the second transfer process through the fixing process by the fixing unit. In the transfer step, the linear velocity of the image carrier and the linear velocity of the transfer member are respectivelyThe linear velocity of the transfer member is higher than the linear velocity of the image carrier.In the second transfer step, the linear velocity of the transfer member is increased without changing the linear velocity of the image carrier, and when the recording material is an OHP sheet, after the first transfer step When the second transfer process is performed after the fixing process by the fixing unit, the linear speed of the image carrier and the linear speed of the transfer member are set to the designed speeds in the first transfer process, respectively. In the process, an image forming apparatus is proposed in which the linear velocity of the image carrier and the linear velocity of the transfer member are not changed.
[0026]
  In the present invention,In the case where the recording material is an OHP sheet, it is more effective if the linear velocity of the transfer member in the first transfer process is higher than that in the case where the recording material is plain paper.
[0027]
  Furthermore, the present invention providesIn the case where the recording material is plain paper, the linear speed of the transfer member is set to 0.5% or more higher than that in the first transfer step in the second transfer step of the recording material.And effective.
[0028]
  Furthermore, the present invention provides:When the recording material is plain paper, the linear speed of the transfer member is set to be 0.6% or less higher than that in the first transfer step in the second transfer step of the recording material.And effective.
[0039]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a color image forming apparatus using an intermediate transfer belt system according to the present invention, and FIG. 2 is an enlarged view around a photoconductor and an intermediate transfer belt of the color image forming apparatus. The configuration and operation of the color image forming apparatus using the intermediate transfer belt system will be described below with reference to FIGS.
[0040]
A color image reading apparatus (hereinafter referred to as a color scanner) 1 forms an image of an original 3 on a color sensor 7 through an irradiation lamp 4, a mirror group 5 (−1, 2 and 3), and a lens 6. The color information of the document 3 is read for each color separation light of, for example, Blue, Green, Red (hereinafter abbreviated as B, G, R) and converted into an electrical image signal.
[0041]
In this example, the color sensor 7 includes B, G, and R color separation means and a photoelectric conversion element such as a CCD, and performs simultaneous reading of three colors. Then, color conversion processing is performed by an image processing unit (not shown) based on the intensity levels of the B, G, and R color separation image signals obtained by the color scanner 1, and Black, Cyan, Magenta, Yellow (hereinafter referred to as “black”). , Bk, C, M, and Y). A color image forming apparatus (hereinafter referred to as a color printer) 2 to be described below forms a visible image on the photoreceptor 9 as a toner image carrier using toners of Bk, C, M, and Y colors. A typical color image. The operation method of the color scanner 1 for obtaining the image data of Bk, C, M, and Y is a scanner start signal that takes the timing and operation of the color printer 2, and the illumination / mirror optical system faces left in FIG. The document is scanned in the direction of the arrow, and one color image data is obtained for each scan.
[0042]
Next, an outline of the color printer 2 will be described.
The writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 9. The writing optical unit 8 includes a laser light source (LD) 8-1 and its light emission drive control unit (not shown), a polygon mirror 8-2 and its rotation motor 8-3, an f / θ lens 8-4, and a reflection. It consists of a mirror 8-5 and the like.
[0043]
The photosensitive drum 9 rotates counterclockwise as indicated by an arrow in the figure, but around the photosensitive drum 9 is a photosensitive member cleaning unit (including a pre-cleaning static eliminator) 10, a static elimination lamp 11, a charger 12, and a potential sensor 13. , Bk developing unit 14, C developing unit 15, M developing unit 16, Y developing unit 17, development density pattern detector 18, intermediate transfer belt 19 and the like are arranged.
[0044]
Each of the developing devices 14, 15, 16, and 17 is a developing sleeve 14-1, 15-1, and 16-1 that rotates by contacting the ears of the developer with the surface of the photosensitive drum 9 in order to develop the electrostatic latent image. , 17-1, developing paddles 14-2, 15-2, 16-2, and 17-2 that rotate to draw up and stir the developer, and a toner concentration detection sensor 14-3 that detects the toner concentration of the developer 15-3, 16-3, 17-3, and the like.
[0045]
Now, in the standby state, all of the four developing devices 14, 15, 16, and 17 are in the spike-off state (development inoperative state) of the agent on the development sleeve. (Color image formation order) will be described using examples of Bk, C, M, and Y (however, the image formation order is not limited to this).
[0046]
When the copying operation is started, reading of the Bk development data is started at a predetermined timing by the color scanner 1, and optical writing and latent image formation by the laser beam from the writing optical unit 8 is started based on this image data. An electrostatic latent image based on the Bk image data is formed on the drum 9 (hereinafter, the electrostatic latent image based on the Bk image data is referred to as a Bk latent image. Similarly, the C latent image M Latent image, Y latent image).
[0047]
In order to enable development from the leading edge of the Bk latent image, before the leading edge of the latent image reaches the developing position of the Bk developing unit 14, the developing sleeve 14-1 is rotated to stand up the agent. Is developed with Bk toner. Thereafter, the developing operation of the Bk latent image area is continued. However, when the trailing edge of the latent image passes the Bk developing position, the material spikes on the Bk developing sleeve 14-1 are quickly cut off, and the development inoperative state is set. This is completed at least before the leading edge of the C latent image by the next C image data arrives.
[0048]
This is done by switching the direction of rotation of the spike cutting developing sleeve 14-1 to the opposite direction to that during the developing operation.
The Bk toner image formed on the photosensitive drum 9 is transferred by electrostatic force to the surface of an intermediate transfer belt 19 as an intermediate transfer member as a toner image carrier driven in the same direction as the photosensitive drum 9. (Hereinafter, toner image transfer from the photosensitive drum 9 to the intermediate transfer belt 19 is referred to as belt transfer).
[0049]
This belt transfer is performed by applying a predetermined bias power to the transfer bias roller 20 while the photosensitive drum 9 and the intermediate transfer belt 19 are in contact with each other.
The intermediate transfer belt 19 sequentially aligns the Bk, C, M, and Y toner images formed on the photosensitive drum 9 on the same surface to form a four-color superimposed belt transfer image. Perform batch transfer on transfer paper.
[0050]
The configuration and operation of this transfer belt unit will be described later.
By the way, on the photosensitive drum 9 side, after the Bk toner image formed in the Bk process is transferred to the intermediate transfer belt 19, cleaning and static elimination are performed, and the process proceeds to the next C process. Reading of C image data starts, and a C latent image is formed on the photosensitive drum 9 by laser beam writing of the writing optical unit 9 by the image data.
[0051]
The C developing device 15 starts rotating the developing sleeve 15-1 with respect to the developing position after the rear end of the previous Bk latent image has passed and before the front end of the C latent image has arrived. And the C latent image is developed with C toner. Thereafter, the development of the C latent image area is continued, but when the rear end of the latent image passes, the cutting on the C developing sleeve 15-1 is performed as in the case of the previous Bk developing device. This is also completed before the leading edge of the next M latent image arrives.
[0052]
Note that the operations of M and Y are the same as the above-described Bk and C, respectively, and the description of the image data reading / latent image forming / developing operations is omitted.
Next, the intermediate belt unit will be described.
[0053]
The intermediate transfer belt 19 is stretched around a drive roller 21, a belt transfer bias roller 20, and a driven roller group, and is driven and controlled as described later by a drive motor (not shown). The belt cleaning unit 22 includes an inlet seal 22-1, a rubber blade 11-2, a belt contact / separation mechanism 22-3, and the like, 2, 3, 4 after the first color Bk image is transferred to the belt. While the color is being transferred to the belt, the contact / separation mechanism 22-3 keeps it away from the belt surface.
[0054]
A transfer unit 23 for transferring the image on the intermediate transfer belt 19 to the transfer paper 24 is disposed at a position facing the driving roller 21 of the intermediate transfer belt 19. The transfer unit 23 serves as a charge applying unit. The transfer bias roller 23-1, the roller cleaning blade 23-2, and the contact / separation mechanism 23-3 from the intermediate transfer belt 19 are contact transfer members. The transfer bias roller 23-1 of the transfer unit 23 is normally separated from the surface of the intermediate transfer belt 19 by the contact / separation mechanism 23-3, but the four-color superimposed image formed on the surface of the intermediate transfer belt 19 is transferred to the transfer paper. At the time of batch transfer to 24, the timing is pressed by the contact / separation mechanism 23-3, and a predetermined bias voltage is applied to the roller 23-1 to perform transfer onto the transfer paper 24.
[0055]
The transfer paper 24 is fed from a transfer paper cassette (for example, transfer paper cassette (A) 30) selected from a plurality of transfer paper cassettes 30, 31, and 33 by a paper feed roller (25), and is registered. The roller 26 feeds the leading end portion of the four-color superimposed image on the surface of the intermediate transfer belt 19 to the transfer position in accordance with the timing when it reaches the transfer position.
[0056]
The intermediate transfer belt 19 moves in the following manner depending on the image forming mode.
(1) Constant speed forward movement system.
This operation is performed in the image formation mode of only a uniform color such as Bk toner, and continues to move forward at a constant speed even after the belt transfer of the first toner image.
[0057]
The transfer bias roller 23-1 is brought into contact with the intermediate transfer belt 19 by the contact / separation mechanism 23-3 in time with the transfer paper 24 fed in time with the leading edge of the first toner image. Is transferred to the transfer paper 24.
[0058]
Thereafter, the toner images formed according to the number of repeats and transferred onto the intermediate transfer belt 19 are transferred to the transfer paper 24, respectively.
(2) Reciprocating (quick return) method.
This operation is performed in an image forming mode in which an image is formed with toner of two or more colors. When the transfer of the Bk toner image is completed, the intermediate transfer belt 19 is separated from the surface of the photosensitive drum 9, and the forward movement is performed. At the same time it is finished, it will return in the reverse direction at high speed. In return, the position of the leading edge of the image on the surface of the intermediate transfer belt 19 passes the belt transfer equivalent position in the reverse direction, and further, after moving a predetermined distance, is stopped and put into a standby state.
[0059]
Next, when the leading end of the C toner image on the surface of the photosensitive drum 9 reaches a predetermined position before the belt transfer position, the intermediate transfer belt 19 is started again in the forward movement direction. Further, the intermediate transfer belt 19 is brought into contact with the surface of the photosensitive drum 9 again. Also in this case, the belt image is transferred under the condition that the C image accurately overlaps the Bk image on the surface of the intermediate transfer belt 19.
[0060]
Thereafter, the same operation is followed to proceed to the M and Y image process, and a four-color superimposed belt transfer image is obtained.
Then, following the belt transfer process of the Y image of the fourth color, the transfer bias is made so that the four-color superimposed toner image on the surface of the intermediate transfer belt 19 is transferred to the transfer sheet 24 at a speed without returning. The roller 23-1 is brought into contact with the intermediate transfer belt 19 by the contact / separation mechanism 23-3 in time with the transfer paper 24 fed in time with the leading edge of the toner image, and the toner image is transferred to the transfer paper 24. Transcribed.
[0061]
The transfer paper 24 onto which the toner image is transferred from the surface of the intermediate transfer belt 19 is conveyed to a fixing device 28 by a paper conveyance unit 27, controlled to a predetermined temperature, and a fixing roller to which silicon oil as a release agent is applied. The toner image is melted and fixed on the transfer paper by 28-1 and the pressure roller 28-2. Then, the fixed transfer paper is discharged to the copy tray 29 to obtain a final copy image.
[0062]
Note that for each color image formation on the photosensitive drum 9, the photosensitive drum 9 after the belt transfer of the toner image is performed on the photosensitive member cleaning unit 10 (pre-cleaning static eliminator 10-1, brush roller 10-2, rubber blade). The surface is cleaned in 10-3) and the charge is uniformly removed by the charge removal lamp 11. Further, the cleaning unit 22 is pressed by the contact / separation mechanism 22-3 on the intermediate transfer belt 19 after the toner image is transferred to the transfer paper 24, and the belt surface is cleaned.
[0063]
At the time of repeat copying, the operation of the color scanner 1 and the image formation on the photosensitive drum 9 are the second Bk (first color) image at a predetermined timing following the first Y (fourth color) image process. Proceed to the process. In the intermediate transfer belt 19, the second Bk toner image is transferred onto the belt whose surface has been cleaned by the cleaning unit 22 following the batch transfer process of the first four-color image to the transfer paper 24. To be. Thereafter, the operation is the same as that of the first sheet.
[0064]
The transfer paper cassettes 30, 31 and 33 store transfer papers of various sizes, and take the timing from the size paper storage cassette designated on the operation panel (not shown) toward the registration roller 26. Paper is fed and transported. Reference numeral 34 denotes a manual paper feed tray used for feeding overhead projector (OHP) paper, cardboard, and the like. Further, reference numeral 32 denotes a double-sided transfer paper cassette for double-sided copying. When the double-side mode is selected on the operation unit, the fixed transfer paper is reversed by a reversing means (not shown) and stored in the double-sided transfer paper cassette 32. Is done. Then, transfer / fixing is performed in the same sequence as that for one side in accordance with image formation for both sides.
[0065]
Up to this point, the copy mode for obtaining a four-color full-color image has been described. In the case of the three-color copy mode or the two-color copy mode, the same operation as described above is performed for the designated color and number of times. It will be.
[0066]
In the case of the single color copy mode, only the developing unit for that color is in a developing operation (spreading) state until the predetermined number of sheets is completed, and the intermediate transfer belt 19 remains in contact with the surface of the photosensitive drum 9. The belt cleaning unit 22 is driven at a constant speed in the forward movement direction, and the belt cleaning unit 22 performs a copying operation while being in contact with the intermediate transfer belt 19.
[0067]
Also,
Here, specific examples of the main configuration and image forming conditions of the image forming apparatus in the present embodiment are shown below.
Photoconductor drum: OPC.
・ Intermediate transfer belt:
Carbon-dispersed fluororesin ETFE (ethylene / tetrafluoro / ethylene),
Volume resistivity 10^TenΩcm,
Surface resistivity 10⁹Ωcm².
・ Transfer bias roller:
Cover the hydrin rubber roller with a PFE tube,
Volume resistivity 10⁹Ωcm.
・ Toner:
Polyol is the main resin, black (Bk) is colored with carbon, cyan (C), magenta (M), and yellow (Y) with each pigment.
[0068]
Silica is externally added as a fluidity-imparting material.
・ Developer characteristics:
Toner concentration: 4 to 6 (wt%) for each color,
Toner charge amount: each color -15 to -25 (C / g).
・ Photoreceptor potential:
Image portion (LD data “255” portion) −80 to −130 (V),
Non-image part (LD data “0” part) −500 to −700 (V),
・ Process speed: 180mm /_sec,
・ Belt transfer bias voltage:
1C: 1200 (v), 2C: 1300 (v),
3C: 1400 (v), 4C: 1500 (v),
Transfer bias voltage: 1300 (v).
[0069]
The configuration and operation of the image forming apparatus according to the present invention has been described above.
In the present embodiment, the recording material is conveyed under a conveying condition such that a shearing force is generated between the toner image carrier and the recording material at the time of transfer. Specifically, the drive roller 21 that drives the intermediate transfer belt 19 is driven so that the linear velocity of the intermediate transfer belt 19 becomes Vb, and the transfer bias roller 23-1 that conveys the transfer paper 24 by the frictional force generated. Is driven so that the linear velocity of the transfer paper 24 becomes Vp. At this time, the speeds of Vb and Vp are basically designed so that Vp> Vb.
[0070]
Furthermore, in order to prevent the belt surface energy of the intermediate transfer belt 19 from increasing with time and maintain a value smaller than the surface energy of the transfer paper 24, by providing a coating device 36 that periodically applies a lubricant, It is possible to always obtain the hollow spot rank 5, and it can be set so as to prevent the occurrence of the “blank hole phenomenon” almost completely.
[0071]
By the way, even if the transfer paper transport speed is set so as to prevent the occurrence of the “bloom phenomenon” as described above, the transfer paper is transferred again to the transfer paper. I found out. Then, it has been found that this shift in the transfer speed of the transfer paper causes a “slow-out phenomenon” in the second and subsequent transfer steps.
[0072]
In order to prevent the occurrence of such a “missing phenomenon”, the present invention is configured as follows.
When the double-sided or composite function is selected, the linear velocity of the transfer bias roller 23-1 is made higher in the first transfer process than in the case of single-sided copying by comparing the linear velocity of the intermediate transfer belt 19 with the linear velocity. By providing a difference, the rank of the void is very good at “5” as indicated by a circle in FIG. Here, when the transfer paper is in the second transfer process, the surface speed of the transfer paper after the fixing process changes, and more specifically, because the frictional force of the transfer paper decreases and the slip ratio increases, it is “slow”. Deviation in direction. For this reason, the hollow rank deteriorates from “5”, which is very good, to “3”.
[0073]
Therefore, in order to correct this deviation, the transfer bias roller 23-1 is provided with an adjusting means so that the conveying force can be varied. This speed adjustment method can be performed by changing the fundamental frequency if the drive motor that drives the transfer bias roller 23-1 is, for example, a brushless motor.
[0074]
Thus, when the speed of the transfer bias roller in the second transfer process is shifted in the direction of “fastening” in both sides or in the synthesis, the “hollow-out phenomenon” shifts in a direction in which it becomes favorable according to the amount. According to the experiment using the apparatus shown in FIG. 1 of the present inventor, as shown in FIG. 6, when the speed is increased by “+0.5 to 0.6%” with respect to the first transfer process, the first transfer process is performed. The same hollow rank as that of time “5” was obtained, and the effect was confirmed. Further, the linear speed of the transfer paper itself in the second transfer process at this time was almost the same as that in the first transfer process.
[0075]
Next, in the image forming apparatus according to the present embodiment, it is possible to select transfer paper, which is mainly plain paper, and an OHP sheet as the type of recording material. When an OHP sheet is selected, the image forming apparatus needs to recognize the OHP. This is because the fixing condition of the OHP sheet is different from that of the plain paper in order to satisfy the fixability of the OHP sheet from the forming material (OHP is the main material). As a method for recognizing that the apparatus uses an OHP sheet, the operation unit (not shown) is provided with a selection key for setting the OHP mode, or a special mark is provided on the OHP sheet, and the apparatus has it. It is detected by the sensor that is.
[0076]
By the way, the OHP sheet originally has surface smoothness, and the surface property hardly changes even after the fixing process. In addition, there may naturally be a case where an OHP sheet is selected and both sides or a synthesis function is selected. At this time, even when the speed of the transfer bias roller 23-1 was increased during the second transfer step as in the above-described method, the rank of the “missing phenomenon” did not change substantially.
[0077]
Therefore, when the double-sided or composite function using plain paper is selected, the speed of the transfer bias roller in the second transfer process is set to be higher than that in the first transfer process, but the double-sided or composite function using the OHP sheet is selected. When the transfer is performed, the speed of the transfer bias roller in the second transfer process is controlled to be the same as that in the first transfer process.
[0078]
By controlling in this way, a transfer without a “blank phenomenon” can be obtained in the toner image in the second transfer step, regardless of whether the recording material is plain paper or an OHP sheet.
FIG. 7 is a flowchart showing the flow of the control described above. First, it is determined whether the duplex function or the composite function is selected (step 1). Next, it is determined whether the user has turned on the OHP mode selection key (step 2). When the user does not press the OHP mode selection key, it is determined whether or not the manual feed tray 34 that can use the OHP sheet is used (step 3). If the manual feed tray 34 is used, it is placed on the manual feed tray 34. It is determined whether the recorded material is an OHP sheet (step 4). In step 4, when the OHP sheet is used and when the OHP mode is selected in step 2, the speed of the transfer bias roller in the second transfer process is set to the same speed as in the first transfer process. (Step 5).
[0079]
When the manual feed tray 34 is not used in step 3 and when the recording material placed on the manual feed tray 34 is not an OHP sheet in step 4, transfer paper is used, so that the second transfer process is performed. The speed of the transfer bias roller is increased (step 6).
[0080]
By the way, although the OHP sheet has a smaller frictional force than that of plain paper, if the linear velocity of the transfer bias roller 23-1 is constant regardless of the type of the recording material, the speed of the recording material is different. Even if the paper blank rank is good, the rank of the OHP sheet may deteriorate.
[0081]
Therefore, when an OHP sheet is selected, the transfer bias roller 23-1 capable of adjusting the speed is used to shift the speed during the transfer process in the direction of “faster” than that for plain paper. As a result, it is possible to shift the “hollow-out phenomenon” of the OHP sheet in a favorable direction. Therefore, when the OHP sheet is selected and the double-sided or composite function is selected, as described above, the speed of the transfer bias roller in the first transfer process is increased, and in the second transfer process, the speed is the same as the first. You can do it.
[0082]
Next, when functions such as double-sided / compositing are provided as “automatic” in the image forming apparatus, as shown in the block diagram of FIG. The CPU 41 automatically determines the time of the second transfer process, sends each speed value data stored in a ROM or RAM (memory) 42 as a preset storage medium to the motor control circuit 45, and according to the data The motor 40 is rotated to drive the transfer bias roller 23-1.
[0083]
In addition, when the image forming apparatus is provided with “manual” functions such as double-sided / compositing, the user can select the “double-sided” or “composite” button provided on the operation unit 43 from the user. Each speed value data stored in the ROM or RAM 42 preset by the CPU 41 according to the input information is sent to the motor control circuit 45, and the motor 40 is rotated according to the data to drive the transfer bias roller 23-1. . If the drive motor 40 is a brushless motor, the speed value data sent to the motor control circuit 45 is sent as a PWM value, for example.
[0084]
Thus, the speed control of the transfer bias roller 23-1 can be realized in each case according to both sides / combination and the type of recording material.
The ROM or RAM 42 has a program for controlling the linear speed of the transfer bias roller 23-1 to be higher in the second transfer process than in the first transfer process when the double-sided or combined process using the transfer paper is selected. By storing and attaching it to an existing image forming apparatus, the existing apparatus can perform the control described above.
[0085]
Furthermore, the ROM or RAM 42 selects the double-sided or combined by using the OHP sheet when the double-sided or combined by transfer paper is selected, and the linear speed of the transfer bias roller 23-1 is higher in the second transfer process than in the first transfer process. When this is done, a program for controlling the linear velocity of the transfer bias roller 23-1 to be the same in the first transfer process and the second transfer process is stored.
[0086]
With this configuration, the ROM or RAM 42 is attached to an existing image forming apparatus, so that the existing apparatus can perform the above-described control.
[0087]
FIG. 9 is an explanatory view showing another embodiment of the present invention. In this example, the toner image carrier is an intermediate transfer roller 51, and the charge applying means is a transfer bias wound around the belt wheels 53 and 54. The belt 52 is configured. In this case, the belt wheel 53 is on the drive side, and by controlling the rotation of the belt wheel 53, the linear velocity of the transfer bias belt 52 can be controlled in the same manner as the transfer bias roller 23-1. In the present invention, the toner image carrier may be an intermediate transfer drum. The present invention can also be applied to an image forming apparatus that does not include an intermediate transfer member. In this case, the toner image carrier is not an intermediate transfer member but a photosensitive member.
[0088]
Furthermore, although the embodiment shows that zinc stearate is periodically applied as a means for lowering the surface energy of the intermediate transfer belt 19 that is a toner image carrier, as described in the prior art, a fluorine-based member. It is well known that there are also means for applying the belt and forming the belt with a silicon or fluorine-based material.
[0089]
【The invention's effect】
As described above, according to the present invention, with respect to a recording material that has undergone two or more transfer processes, the conveyance condition of the recording material is set in the second and subsequent transfer processes to prevent the occurrence of the “blowing phenomenon”. Can be prevented.
[0090]
Furthermore, according to the present invention, the recording material transport conditions in the second and subsequent transfer steps are set according to the type of the recording material for the recording material that has undergone two or more transfer steps, and the recording material It is possible to prevent the occurrence of the “missing phenomenon” regardless of the type.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a color image forming apparatus using an intermediate transfer belt system according to the present invention.
FIG. 2 is an enlarged view around a photoconductor and an intermediate transfer belt of the color image forming apparatus shown in FIG.
FIG. 3 is a diagram illustrating a relationship between a linear speed ratio between a transfer sheet and an intermediate transfer belt and a hollow rank.
FIG. 4 is an explanatory diagram of a model of “collapse phenomenon” when there is no speed difference between the toner image carrier and the transfer material.
FIG. 5 is an explanatory diagram of a model of “slow-out phenomenon” when there is a speed difference between a toner image carrier and a transfer material.
FIG. 6 is a diagram illustrating a relationship between a speed increase rate of a transfer bias roller and a hollow rank in a second transfer process.
FIG. 7 is a flowchart showing one control example of the present invention.
FIG. 8 is a block diagram illustrating a schematic configuration of a drive control system of a transfer bias roller.
FIG. 9 is a schematic view of an image forming apparatus to which the present invention is applied.
[Explanation of symbols]
1 Color image reading device (color scanner)
2 Color image recording device (color printer)
3 Manuscript
4 Lighting lamp
5 mirrors
6 Lens
7 Photoelectric conversion device (CCD)
8 Writing optical unit
8-1 Laser light source (LD)
8-2 Polygon mirror
8-3 Polygon motor
8-4 f / θ lens
8-5 Reflection mirror
9 Photosensitive drum
10 Photoconductor cleaning unit
10-1 Charger before cleaning
10-2 Brush roller
10-3 Rubber blade
11 Static elimination lamp
12 Charger
13 Potential sensor
14 Black (Bk) developer
14-1 Development sleeve for Bk
14-2 Bk development paddle
14-3 Bk toner density sensor
15 Cyan (C) developer
15-1 Development sleeve for C
15-2 Development paddle for C
15-3 C toner concentration sensor
16 Magenta (M) developer
16-1 Development sleeve for M
16-2 Development paddle for M
16-3 M toner density sensor
17 Yellow (Y) developer
17-1 Development sleeve for Y
17-2 Development paddle for Y
17-3 Y toner density sensor
18 Development density pattern detector
19 Intermediate transfer belt
20 Belt transfer bias roller
21 Belt drive roller
22 Belt cleaning unit
22-1 Brush roller
22-2 Rubber blade
22-3 Contact / separation mechanism
23 Transfer unit
23-1 Transfer bias roller
23-2 Rubber blade
23-3 Contact / separation mechanism
24 Transfer paper
25 Paper feed roller
26 Registration Roller
27 Paper transport unit
28 Fixing device
28-1 Fixing roller
28-2 Pressure roller
29 Copy tray
30 Transfer paper cassette (A)
31 Transfer paper cassette (B)
32 Double-sided transfer paper cassette (C)
33 Transfer paper cassette (D)
34 Bypass tray
35 Laura
36 Coating equipment
37 Lubricant
38 brushes
39 Toner
40 motor
41 Control unit (CPU)
42 Memory (RAM, ROM)
43 Operation unit
44 Toner layer
45 Motor drive circuit

Claims (4)

Fixing for fixing the image bearing member for bearing a toner image, a transfer member for transferring the toner image on the recording material is sandwiched between the image bearing member, a toner image formed on the recording material to the recording material Means,
In the image forming apparatus configured such that each of the image carrier and the transfer member is rotationally driven and the rotational speed of the transfer member can be changed.
When the recording material is plain paper, when the second transfer process is performed after the first transfer process and the fixing process by the fixing unit, the linear speed of the image carrier and the transfer are performed in the first transfer process. the linear speed of the linear velocity of the member to each of said transfer member and designed speed becomes faster than the linear velocity of the image bearing member, a second transfer step the transfer without changing the linear velocity of the image bearing member Increase the linear speed of the member,
When the recording material is an OHP sheet, when the second transfer process is performed after the first transfer process and the fixing process by the fixing unit, the linear speed of the image carrier and the transfer are performed in the first transfer process. An image forming apparatus, wherein the linear velocity of each member is set to a designed velocity, and the linear velocity of the image carrier and the linear velocity of the transfer member are not changed in the second transfer process. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the linear velocity of the transfer member during the first transfer step is higher when the recording material is an OHP sheet than when the recording material is plain paper.   3. The image forming apparatus according to claim 1, wherein when the recording material is plain paper, the linear velocity of the transfer member is set to be higher than that in the first transfer step in the second transfer step of the recording material. An image forming apparatus characterized in that the speed is 0.5% or more.   4. The image forming apparatus according to claim 1, wherein when the recording material is plain paper, the linear speed of the transfer member is set to the first transfer in the second transfer step of the recording material. An image forming apparatus characterized in that the speed is 0.6% or less from that in the process.

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