JP2013152302A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a back side of a recording sheet from being contaminated with toner, in forming an image on the whole surface of the recording sheet.SOLUTION: An image forming device includes: an intermediate transfer belt 25 on which toner images on a photoreceptor drum 15 are transferred in an overlapped manner; a secondary transfer roll 33 for transferring the toner images on the intermediate transfer belt 25 to a recording sheet 34; a cleaning blade 51 and a brush 52 for removing toner adhered on the secondary transfer roll 33; and a CPU 51 that controls image formation so as to set a first peripheral speed of the secondary transfer roll 33 when a first image formation mode is selected to form an image with margins formed in the recording sheet 34, and to set a second peripheral speed lower than the first speed when a second image formation mode is selected to form an image on the whole surface of the recording sheet 34.

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus that forms an image, such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions, there is an apparatus that forms an image by applying an intermediate transfer method.

  In the intermediate transfer method, after a multi-color toner image (developer image) formed by a plurality of image forming units is primarily transferred by being superimposed on an intermediate transfer belt (intermediate transfer member) by a primary transfer roll (primary transfer means). In this system, the toner image on the intermediate transfer belt is batch-transferred (secondary transfer) onto a recording medium such as recording paper by a secondary transfer roll (secondary transfer means).

  On the other hand, there are two forms of the image formed on the recording paper: an aspect of forming an image by creating a margin on the recording paper and an aspect of forming an image using the entire surface of the recording paper.

  As an image forming apparatus that forms an image using the entire surface of a recording sheet, for example, those described in Patent Documents 1 to 3 are known.

Japanese Patent No. 4645357 Japanese Patent No. 4765825 JP 2009-282367 A

  The present invention provides an image forming apparatus capable of alleviating contamination on the back surface of a recording medium due to a developer transferred from an intermediate transfer member to a secondary transfer unit when an image is formed using the entire surface of the recording medium. For the purpose.

  In order to solve the above-described problem, an image forming apparatus according to the first aspect of the present invention includes a plurality of holding units that are provided corresponding to a plurality of colors and that hold an electrostatic latent image formed based on image information. A plurality of developing means provided corresponding to the plurality of holding means, and developing a latent image formed on the surface of each holding means using a developer to form a developer image; and A plurality of primary transfer means provided corresponding to the holding means and transferring the developer images on the holding means to the intermediate transfer member so as to be superimposed on each other; and the developer images on the intermediate transfer member are recorded on the recording medium A second transfer means for transferring to the image forming apparatus, a removing means for removing the developer attached to the secondary transfer means, a first image forming mode for forming an image by forming a margin on the recording medium, and the entire surface of the recording medium. The second image forming mode in which an image is formed using the The image forming mode is controlled as described above, and when the first image forming mode is selected, the image is formed at the first speed, and when the second image forming mode is selected, the first image forming mode is selected. Control means for controlling the image formation speed so that the image formation is executed at a second speed lower than the first speed.

  The invention according to claim 2 is the invention according to claim 1, wherein the peripheral speed of the secondary transfer means at the second speed is the peripheral speed of the secondary transfer means at the first speed. The speed is 70% or less.

  The invention according to claim 3 is the invention according to claim 1, wherein the peripheral speed of the secondary transfer means is 308 mm / sec at the first speed and 220 mm / sec at the second speed. It is characterized by being.

  According to the first aspect of the present invention, the developer transferred from the intermediate transfer member to the secondary transfer unit when the image is formed using the entire surface of the recording medium as compared with the case where the present invention is not adopted. Contamination on the back surface of the recording medium can be reduced.

  According to the second aspect of the present invention, an image can be formed using the entire surface of the recording medium without reducing the transfer efficiency of the developer from the intermediate transfer member to the recording medium as compared with the case where the present invention is not adopted. Contamination on the back surface of the recording medium during the recording can be reduced.

  According to the third aspect of the present invention, compared with the case where the present invention is not adopted, image formation is performed using the entire surface of the recording medium without reducing the transfer efficiency of the developer from the intermediate transfer member to the recording medium. Contamination on the back surface of the recording medium during the recording can be reduced.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is an explanatory diagram showing toner images before and after secondary transfer in a second image forming mode in the image forming apparatus according to the embodiment of the present invention. FIG. 7 is an explanatory diagram showing toner transferred to a secondary transfer roll in a second image forming mode in the image forming apparatus according to the embodiment of the present invention. In the image forming apparatus according to an embodiment of the present invention, a graph showing the relationship between the transfer bias voltage and the backside contamination grade of the recording paper when the peripheral speed of the secondary transfer roll is 308 mm / sec and 220 mm / sec. It is. 6 is a table showing toner charge amount and adhesion when the peripheral speed of the secondary transfer roll is 308 mm / sec and 220 mm / sec in the image forming apparatus according to the embodiment of the present invention. 6 is a graph showing the relationship between toner charge distribution and adhesion when the peripheral speed of the secondary transfer roll is 308 mm / sec and 220 mm / sec in the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, an embodiment as an example of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.

  FIG. 1 shows a tandem type digital color copying machine as an image forming apparatus PR1 according to an embodiment of the present invention.

  At the upper part of one end side of the digital color copying machine PR1, there is provided a platen cover 3 that presses the document 2 against the platen glass 5, and an image reading device 4 that reads an image of the document 2 placed on the platen glass 5. It has been.

  The image reading device 4 illuminates a document 2 placed on a platen glass 5 with a light source 6, and reflects a reflected light image from the document 2 from a full-rate mirror 7, half-rate mirrors 8 and 9, and an imaging lens 10. The image reading element 11 made of a CCD or the like is scanned and exposed through a reduction optical system, and the color reading light image of the original 2 is read by the image reading element 11 at a preset dot density. Yes.

  The color material reflected light image of the document 2 read by the image reading device 4 is sent to the image processing device 12 as, for example, document reflectance data of three colors of red (R), green (G), and blue (B). In this image processing apparatus 12, the reflectance data of the document 2 is subjected to image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, and the like. .

  The image data that has been subjected to image processing by the image processing apparatus 12 is document color material gradation data (raster data) of four colors of yellow (Y), magenta (M), cyan (C), and black (K). As described below, the image forming units 13Y, 13M, 13C and 13K for the respective colors of yellow (Y), magenta (M), cyan (C) and black (K) are exposed to exposure devices 14Y, 14M and 14C. , 14K (an example of exposure means, hereinafter collectively referred to simply as “exposure device 14”), and these exposure devices 14 perform image exposure with laser light in accordance with the original color material gradation data. Is called.

  Inside the tandem type digital color copying machine PR1, as described above, four image forming units 13Y, 13M, 13C, and 13K of yellow (Y), magenta (M), cyan (C), and black (K) are provided. (Hereinafter collectively referred to simply as “image forming unit 13”) are arranged at intervals in the horizontal direction.

  The four image forming units 13Y, 13M, 13C, and 13K are all configured in the same manner, and a photosensitive drum 15 (an example of a holding unit) that rotates at a preset rotation speed along the arrow A direction, A charger 16 for primary charging (an example of a charging unit) that charges the surface of the photosensitive drum 15 and an exposure device that exposes an image corresponding to each color on the surface of the photosensitive drum 15 to form an electrostatic latent image. 14 and developing devices 17Y, 17M, 17C, and 17K (examples of developing means; examples of developing means) that develop the electrostatic latent image formed on the photosensitive drum 15 into toner images (examples of developer images). And a cleaning device 18 that removes the toner remaining on the photosensitive drum 15 after the toner image is transferred.

  The exposure device 14 modulates the semiconductor laser 19 according to the original color material gradation data, and emits a laser beam LB from the semiconductor laser 19 according to the gradation data. The laser beam LB emitted from the semiconductor laser 19 is deflected and scanned by the rotary polygon mirror 22 via the reflection mirrors 20 and 21, and again as a holding means via the reflection mirrors 20 and 21 and the plurality of reflection mirrors 23 and 24. The photosensitive drum 15 is scanned and exposed.

  The image processing device 12 sequentially outputs image data (raster data) of each color to the exposure device 14 of the image forming unit 13 for each color of yellow (Y), magenta (M), cyan (C), and black (K). The laser beams LB emitted according to the image data from these exposure devices 14 are scanned and exposed on the surfaces of the respective photosensitive drums 15 to form electrostatic latent images.

  The electrostatic latent image formed on each photosensitive drum 15 is developed as a toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) by the developing device 17.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photoconductive drums 15 of the image forming units 13 are image forming units 13Y and 13M. , 13C, and 13K on the intermediate transfer belt 25 (an example of an intermediate transfer member) disposed on the intermediate transfer belt 25 so as to be superimposed on each other by primary transfer rolls 26Y, 26M, 26C, and 26K (an example of a primary transfer unit). That is, it is transferred in multiple.

  The intermediate transfer belt 25 includes a belt drive roll 27 (an example of an intermediate transfer body support member), a tension roll 28 (an example of an intermediate transfer body support member), a tensioner 29 (an example of an intermediate transfer body support member), an idle A roll 30 (an example of an intermediate transfer member support member), a backup roll 31 (an example of an intermediate transfer member support member), and an idle roll 32 (an example of an intermediate transfer member support member) are wound around and supported. Yes. Then, in a state in which a predetermined tension is applied by the tensioner 29, the belt is rotated in the circumferential direction indicated by an arrow A by a belt driving roll 27 driven and rotated by a driving force transmission roll that is rotated by a driving motor (not shown). It is like that.

  As the intermediate transfer belt 25, for example, a synthetic resin film such as polyamideimide having flexibility is formed in a band shape, and both ends of the synthetic resin film formed in a band shape are connected by means such as welding, thereby being endless. What was formed in the shape is used.

  A toner image made up of yellow (Y), magenta (M), cyan (C), and black (K) toners transferred onto the intermediate transfer belt 25 in multiple layers is a secondary transfer roll 33 (in contact with the backup roll 31). The secondary transfer means) is secondarily transferred collectively onto a recording sheet 34 as a recording medium by a pressure contact force and an electrostatic force, and the recording sheet 34 on which the toner images of the respective colors are transferred is transferred to two continuous belts 35. , 36 to a fixing device 37 (an example of fixing means).

  The recording paper 34 onto which the toner images of the respective colors have been transferred undergoes a fixing process with heat and pressure by a fixing device 37 and is discharged onto a discharge tray 38 provided outside the digital color copying machine PR1.

  As shown in FIG. 1, the recording paper 34 includes a paper feed roller 42 and recording paper transport roller pairs 43, 44, 45 from any one of a plurality of paper feed trays 39, 40, 41. It is once transported to the registration roll 47 via the recording paper transport path 46.

  The recording paper 34 supplied from any of the paper feed trays 39, 40, 41 is sent onto the intermediate transfer belt 25 by a registration roll 47 that is rotationally driven at a predetermined timing.

  In the four image forming units 13Y, 13M, 13C, and 13K of black, yellow, magenta, and cyan, as described above, toner images of black, yellow, magenta, and cyan are sequentially formed, respectively. .

  Such a digital color copying machine PR1 is provided with a power source 49 (an example of a voltage applying unit), and the rotating elements (for example, the photosensitive drum 15, the belt driving roll 27, the primary transfer rolls 26Y and 26M, 26C, 26K, secondary transfer roll 33, etc.) for supplying electric power to a motor (not shown), applying a transfer bias of the toner image to the primary transfer rolls 26Y, 26M, 26C, 26K and the secondary transfer roll 33, etc. Done.

  Further, the digital color copying machine PR1 is provided with a CPU (Central Processing Unit) 51 (an example of control means), and the operation of the apparatus related to image formation by the digital color copying machine PR1 (that is, the series of images described above). Control).

  After the toner image transfer process is completed, the photosensitive drum 15 is prepared for the next image forming process by removing residual toner, paper dust, and the like by the cleaning device 18. Further, residual toner is removed from the intermediate transfer belt 25 by a belt cleaner 48. Further, the toner attached to the secondary transfer roll 33 via the intermediate transfer belt 25 is removed by a cleaning blade 51 (an example of a removing unit).

  In such a digital color copying machine PR1 of the intermediate transfer system, a recording mode (hereinafter, referred to as “first image forming mode”) in which a margin is formed on the recording paper 34 and an image is formed. The CPU 51 controls such that a formation mode (second image formation mode) called borderless printing in which an image is formed using the entire surface is selectively executed.

  As shown in FIG. 2A, in the second image forming mode, a toner image larger than the recording paper 34 is formed on the intermediate transfer belt 25. Therefore, as shown in FIG. 2B, an extra toner image corresponding to four vertical and horizontal sides that have not been transferred to the recording paper 34 remains on the intermediate transfer belt 34 after the secondary transfer.

  Here, the configuration around the secondary transfer roll 33 is shown in FIG.

  As shown in the drawing, the cleaning blade 51 described above is provided such that the tip is in contact with the secondary transfer roll 33. Therefore, the toner adhering to the secondary transfer roll 33 is removed by being scraped off by the cleaning blade 51.

  Further, the brush 52 (an example of a removing unit) is brought into contact with the secondary transfer roll 33 on the downstream side in the rotation direction of the secondary transfer roll 33 with respect to the contact position between the cleaning blade 51 and the secondary transfer roll 33. Has been placed. The brush 52 includes a shaft portion 52a and a brush portion 52b provided around the shaft portion 52a, and rotates around the shaft portion 52a while bringing the brush portion 52b into contact with the secondary transfer roll 33. It is like that. Therefore, the minute toner on the secondary transfer roll 33 that could not be removed by the cleaning blade 51 is removed by the rotation of the brush 52.

  Further, a lubricant 53 made of zinc stearate (ZnSt) is disposed so as to come into contact with the brush 52. The lubricant 53 is applied to the secondary transfer roll 33 by the rotation of the brush 52, and the friction between the secondary transfer roll 33 and the intermediate transfer belt 25 is alleviated.

  In such a configuration, when the second image forming mode is executed, the excessive toner image (toner) on the intermediate transfer belt 25 described above is opposed to the backup roll 31 as shown in FIG. The toner image is directly transferred from the intermediate transfer belt 25 to the secondary transfer roll 33 at the secondary transfer position. Specifically, the extra toner images for four sides in the vertical and horizontal directions that have not been transferred to the recording paper 34 have a maximum density of 300% (total density of the four color toners) from the intermediate transfer belt 25 to the secondary transfer roll 33. Is transcribed.

  As shown in FIG. 1, yellow, magenta, cyan, and black toner images are transferred to the intermediate transfer belt 25 in this order to form a four-layer superimposed toner image. Magenta and cyan toner images are stacked as the lowermost layer, and the black toner image is the uppermost layer. On the other hand, when transferred to the secondary transfer roll 33, the black toner image is the lowermost layer, the cyan and magenta toner images are laminated, and the yellow toner image is the uppermost layer.

  The four-layer toner transferred to the rotating secondary transfer roll 33 is removed by the cleaning blade 51 and the brush 52, but is not completely removed as shown in FIG. When the toner that has not been removed remains on the secondary transfer roll 33 and circulates and reaches the secondary transfer position, the back surface of the recording paper 34 (more precisely, the back surface on the downstream side in the conveyance direction of the recording paper 34). Is contaminated. The toner that is not removed is often black or cyan toner located in the lower layer of the secondary transfer roll 33.

  Here, the toner on the secondary transfer roll 33 located on the vertical side with respect to the conveyance direction of the recording paper 34 in the excess toner images for the four sides in the vertical and horizontal directions protrudes from the width of the recording paper 34. Therefore, it is difficult to transfer to the recording paper 34. In addition, the toner on the secondary transfer roll 33 that has been positioned downstream with respect to the conveyance direction of the recording paper 34 is transferred to the secondary transfer roll 33 before the next recording paper 34 reaches the secondary transfer position. Along with the rotation, it is cleaned by the cleaning blade 51 a plurality of times and almost removed. However, the toner on the secondary transfer roll 33 positioned upstream with respect to the conveyance direction of the recording paper 34 reaches the secondary transfer position with the rotation of the secondary transfer roll 33 during the secondary transfer. As a result, the back surface of the recording paper 34 is contaminated.

  Here, the ability to remove the toner attached to the secondary transfer roll 33 by the cleaning blade 51 and the brush 52 was examined. Here, it is possible to review the shapes of the cleaning blade 51 and the brush 52 to increase the contact area with the secondary transfer roll 33, but there is a concern that the shape becomes complicated and the cost increases. As a result of various studies, it has been found that the toner removal capability is improved if the rotation speed of the secondary transfer roll 33 is decreased. That is, it was found that the contamination of the back surface of the recording paper 34 by the toner transferred from the intermediate transfer belt 25 to the secondary transfer roll 33 is alleviated.

  However, simply slowing the rotation of the secondary transfer roll 33 results in a slow image forming speed, which is against the demand for high-speed processing and is not desirable. Therefore, the relationship between the transfer bias voltage of the secondary transfer roll 33 and the backside contamination grade of the recording paper 34 when the peripheral speed of the secondary transfer roll 33 is varied was examined. As a result, the peripheral speed of the secondary transfer roll 33 is 220 mm / sec with respect to 308 mm / sec (an example of the first speed) that is the peripheral speed of the general secondary transfer roll 33 in the first image forming mode. It has been found that good results can be obtained when sec (an example of the second speed) is set, that is, when the peripheral speed of the secondary transfer roll 33 is reduced to about 70%. Thus, it was found that the peripheral speed of the secondary transfer roll 33 in the second image forming mode should be about 70% or less of the peripheral speed of the secondary transfer roll 33 in the first image forming mode.

  Here, FIG. 4 shows the relationship between the transfer bias voltage of the secondary transfer roll 33 and the back surface contamination grade of the recording paper 34 when the peripheral speed of the secondary transfer roll 33 is 308 mm / sec and 220 mm / sec. .

In FIG. 4, the numerical value of the back surface stain grade is an ideal stain value by visual judgment on the back surface of the recording paper 34 when 15 g of toner per 1 m ² is transferred to the secondary transfer roll 33. It shows that the dirt grade gets worse. Further, the target value is a limit value of a level at which the majority of people will feel the backside contamination of the recording paper 34 within an allowable range.

  As shown in FIG. 4, when the peripheral speed of the secondary transfer roll 33 is 308 mm / sec, when the transfer bias voltage of the secondary transfer roll 33 becomes 0.1 kV, the backside contamination grade is deteriorated from the target value as soon as possible. End up. On the other hand, when the peripheral speed of the secondary transfer roll 33 is 220 mm / sec, the back surface contamination grade is within the target value until the transfer bias voltage of the secondary transfer roll 33 is 1.15 kV. Since the general transfer bias voltage is 0.6 to 1 kV, if the peripheral speed of the secondary transfer roll 33 is 220 mm / sec or less (that is, about 70% or less of 308 mm / sec), the transfer is performed. Contamination of the back surface of the recording paper 34 is alleviated without lowering the bias voltage, in other words, without reducing the toner transfer efficiency from the intermediate transfer belt 25 to the recording paper 34.

  Therefore, in the digital color copying machine PR1, when the first image forming mode is selected, the image forming is executed at the peripheral speed of the secondary transfer roll 33 of 308 mm / sec, and the second image forming mode is selected. The image forming speed is controlled by the CPU 51 described above so that the image formation is executed at 220 mm / sec, which is slower than that.

  Here, numerical values of the toner charge amount and the adhesion force when the peripheral speed of the secondary transfer roll 33 is 308 mm / sec and 220 mm / sec are shown in the table of FIG. The graph of FIG. 6 shows the relationship between the toner charge distribution and the adhesive force when the peripheral speed of the secondary transfer roll 33 is 308 mm / sec and 220 mm / sec.

  As shown in FIGS. 5 and 6, when the peripheral speed of the secondary transfer roll 33 is 308 mm / sec and when it is 220 mm / sec, the charge amount of the toner is smaller at 220 mm / sec. It can be seen that the adhesive force is also reduced, that is, the toner is easily peeled off from the secondary transfer roll 33 (it is easily removed).

  Therefore, when the peripheral speed of the secondary transfer roll 33 is decreased, the charge amount of the toner is reduced and the adhesion force to the secondary transfer roll 33 is reduced. As a result, the secondary transfer by the cleaning blade 51 and the brush 52 is performed. It can be said that the toner removing ability with respect to the roll 33 is improved, and the contamination of the back surface of the recording paper 34 is reduced as described above.

  Although the invention made by the present inventor has been specifically described based on the embodiment, the embodiment disclosed in this specification is an example in all respects and is limited to the disclosed technology. Should not be considered. That is, the technical scope of the present invention should not be construed restrictively based on the description in the above-described embodiment, but should be construed according to the description of the scope of claims. All modifications are included without departing from the technical scope equivalent to the described technique and the gist of the claims.

  For example, although a cleaning blade and a brush are used as the removing means of the present embodiment, both of these or any one of the removing means of the present invention may be used. Alternatively, any member other than these members may be used as long as the toner (developer) attached to the secondary transfer roll (secondary transfer unit) is removed.

  Further, the peripheral speed of the secondary transfer roll (secondary transfer means) described above is merely an example. Therefore, the present invention is not limited to these peripheral speeds.

  Furthermore, in the present embodiment, the first speed and the second speed are defined by the peripheral speed of the secondary transfer roll (secondary transfer means), but the image forming speed (the rotational speed of the photosensitive drum, The first speed and the second speed may be captured by the rotation speed of the intermediate transfer belt, the conveyance speed of the recording paper as the recording medium, and the like.

  If the peripheral speed of the secondary transfer roll 33 is slow, contamination of the back surface of the recording paper 34 is expected to be reduced. Therefore, it is sufficient that the second speed is slower than the first speed, which is about 70% of the first speed. Need not be. However, it should be noted that if the second speed is extremely slow, a phenomenon such as excessive supply of toner (developer) to the photosensitive drum during development occurs and image quality deteriorates.

  The image forming apparatus of the present invention is applied to various image forming apparatuses of an image recording system using an intermediate transfer member, and the number of colors and types of developer used are not limited. The recording medium is not limited to recording paper, and various media such as a film on which a developer is fixed are applied.

14 Exposure device 15 Photosensitive drum 17 Developing device 25 Intermediate transfer belts 26Y, 26M, 26C, 26K Primary transfer roll 27 Belt drive roll 28 Tension roll 29 Tensioner 30 Idle roll 31 Backup roll 32 Idle roll 33 Secondary transfer roll 34 Recording paper 37 Fixer PR1 Digital color copier

Claims (3)

A plurality of holding means provided corresponding to a plurality of colors and holding an electrostatic latent image formed on the basis of image information;
A plurality of developing means provided corresponding to the plurality of holding means, and developing a latent electrostatic image formed on the surface of each holding means using a developer to form a developer image;
A plurality of primary transfer means provided corresponding to the plurality of holding means, and transferring the developer images on the holding means to an intermediate transfer member so as to be superimposed on each other;
Secondary transfer means for transferring the developer image on the intermediate transfer member to a recording medium;
Removing means for removing the developer adhering to the secondary transfer means;
Image forming mode in which a first image forming mode in which a margin is formed on a recording medium and an image is formed and a second image forming mode in which an image is formed using the entire surface of the recording medium are selectively executed When the first image forming mode is selected, image formation is executed at the first speed, and when the second image forming mode is selected, the second speed slower than the first speed is selected. Control means for controlling the image formation speed so that the image formation is executed at a speed of
An image forming apparatus comprising: The peripheral speed of the secondary transfer means at the second speed is 70% or less of the peripheral speed of the secondary transfer means at the first speed.
The image forming apparatus according to claim 1. The peripheral speed of the secondary transfer means is 308 mm / sec at the first speed, and 220 mm / sec at the second speed.
The image forming apparatus according to claim 1.