JP4109975B2 - Double-sided transfer device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a double-sided transfer device that transfers an image onto both sides of a recording medium such as transfer paper by a so-called one-pass method, and an image forming apparatus including the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is known an image forming apparatus that employs a so-called switchback method as a double-sided transfer method for transferring a visible image such as a toner image onto both sides of a recording medium (for example, Patent Document 1). In the switchback method, the recording body is passed through the transfer means and the fixing means to fix the visible image on only one surface thereof, and then the recording body is reversed and switched back to the transfer means and the fixing means again. It is a method. In an image forming apparatus using such a switchback method, there is a problem that a complicated switchback mechanism for inverting and switching back the recording medium once passed through the fixing unit is expensive. Another problem is that it is difficult to increase the speed of double-sided transfer due to the switchback of the recording medium. Furthermore, the recording medium before the switchback is heated and curled in the fixing means, and it is easy to generate a jam at the time of switchback.
[0003]
In view of this, various image forming apparatuses that perform so-called one-pass double-sided transfer that transfers a visible image to both sides of a recording medium while passing the recording medium only once in an internal conveyance path have been proposed. According to such one-pass double-sided transfer, it is not necessary to switch back the recording medium, so that it is possible to eliminate the cost increase due to the addition of the switchback mechanism and jamming at the time of switchback. In addition, it is possible to eliminate the situation where the double-sided transfer is hindered by the switchback.
[0004]
As an image forming apparatus that performs the above-mentioned one-pass double-sided transfer, for example, the one described in Patent Document 2 is known. This image forming apparatus has a pre-stage transfer unit in which a photoconductor as an image carrier and an intermediate transfer belt as an intermediate transfer member are opposed to each other. In addition, the image forming apparatus also includes a rear transfer unit in which the intermediate transfer belt and the transfer charger are opposed to each other with a predetermined gap. Then, after the first toner image is electrostatically transferred from the photoconductor to the intermediate transfer belt in the pre-transfer portion, a second toner image is formed on the photoconductor. Next, the second toner image on the photosensitive member is electrostatically transferred to the second surface of the recording member fed to the preceding transfer portion, and the first toner image of the intermediate transfer belt is transferred to the first surface on the opposite side. Adhere. At this time, an electric field is applied to the first toner image in a direction away from the first surface and moving toward the belt. For this reason, the first toner image remains untransferred to the first surface. The recording material that has passed through the preceding transfer section is sent to the succeeding transfer section, and a charge having a polarity opposite to that of the toner is applied to the second surface by the transfer charger. Then, the first toner image that has not been transferred to the first surface of the recording medium is electrostatically transferred from the intermediate transfer belt to the first surface due to the influence of the charge.
[0005]
[Patent Document 1]
JP-A-5-61288
[Patent Document 2]
JP-A-10-142869
[0006]
[Problems to be solved by the invention]
However, the image forming apparatus described in Patent Document 2 has a problem that it is easy to generate spotted stains due to toner scattered around the image. In particular, when a configuration in which multiple images are formed by a so-called tandem method, this spot-like stain appears remarkably. The tandem system is a process in which a plurality of image carriers such as photoconductors are arranged, and a recording body held by a moving body is sequentially passed through a portion facing each image carrier, and each toner image is transferred to each tandem system. In this method, multiple images such as color images are formed by superposing and electrostatic transfer.
[0007]
Then, when the present inventors earnestly researched about the cause which produces the above-mentioned spot-like dirt, the following thing was found. That is, in the image forming apparatus described in Patent Document 2, when charge is applied to the second surface of the recording medium by the transfer charger in the latter transfer unit, the toner is removed from the second toner image on the second surface by impact. It becomes easy to scatter around. At this time, since the recording body cannot be strongly pressed from the second surface side toward the intermediate transfer belt, the first toner image interposed between the first surface of the recording body and the intermediate transfer belt can also be used. It becomes easy to scatter toner around. Furthermore, a phenomenon called so-called transfer dust occurs in the above-described pre-transfer portion. This is a phenomenon in which the toner in the toner image is scattered around due to the occurrence of a discharge or the formation of a weak electric field at the entrance or exit of the preceding transfer section. The toner scattering due to the transfer dust and the toner scattering in the subsequent transfer portion are accumulated, and the toner easily deteriorates to the extent that spot-like stains are visually recognized.
[0008]
On the other hand, not only the image forming apparatus described in Patent Document 2 described above, but one that performs one-pass double-sided transfer disturbs the toner image on the recording medium when the recording medium is transferred from the double-sided transfer apparatus to the fixing unit. It is easy to happen. When transporting the recording medium while guiding it with a guide member such as a guide plate, the unfixed toner image on the recording body is rubbed against the guide member in order to ensure delivery from the double-sided transfer device to the fixing means. It will be disturbed. In the image forming apparatus described in Patent Document 2, a guide member that guides toward a fixing unit while supporting a recording body with a rotatable star-shaped flat spur is used as a guide member in order to suppress such disturbance. Yes. By supporting the recording body with a star-shaped flat spur, the contact area with the recording body is reduced, and the spur is rotated following the movement of the recording body to suppress friction with the recording body. ing. However, if the spur does not rotate well, the toner image is disturbed at the contact portion between the spur and the recording medium.
[0009]
The present invention has been made in view of the above background, and an object of the present invention is to provide a double-sided transfer device and an image forming apparatus that can realize any of the items listed below.
(1) Eliminates spot-like stains around the image caused by applying a charge to the second surface of the recording medium by the transfer charger.
(2) Image disturbance caused by rubbing between the recording medium delivered from the double-sided transfer device to the fixing unit and the guide member is more reliably suppressed than before.
[0010]
[Means for Solving the Problems]
  In order to achieve the above object, the invention according to claim 1 provides a path extending from the upstream side to the downstream side of the image bearing member carrying the visible image and the intermediate transfer member from the upstream side to the downstream side. The first visible image previously transferred from the image carrier to the intermediate transfer member is transferred to the first surface of the recording member that passes once, while the second possible image on the image carrier is transferred. In a double-sided transfer device that transfers a visual image to the second surface,Heat transfer means for heating and transferring the first visible image from the intermediate transfer body to the first surface on the upstream side in the path, and the recording body on which the first visible image is heated and transferred to the intermediate transfer A separation guide means for guiding toward the facing portion after separation from the body, and a cleaning means for cleaning the surface of the intermediate transfer body,From the image carrierTheIntermediate transferthe aboveWhile transfer to the second surface is performed by an electrostatic transfer method,TheTransfer from the intermediate transfer member to the first surface is performed by a heat transfer method.I didIt is characterized by.
MaClaim2The invention of claim1In the double-sided transfer apparatus, the cleaning means is disposed so as to clean the surface of the intermediate transfer body after passing through the recording member separation position by the separation guide means and before entering the facing portion. To do.
MaClaim3The invention of claim 1Or 2In the double-sided transfer apparatus, the intermediate transfer member having a surface roughness Rz of 5 [μm] or more and less than 20 [μm] is used.
  Claims4The invention comprises an image carrier that carries a visible image on the surface, a visible image forming means that forms a visible image on the image carrier, and a visible image on the image carrier on both sides of the recording medium. In the image forming apparatus comprising a double-sided transfer device that transfers the toner image to the both sides and a fixing unit that heat-fixes the visible image on both sides,1, 2 or 3It is characterized by using the thing.
  Claims5The invention of claim4In the image forming apparatus, the heating temperature by the heat transfer unit is lower than the heating temperature by the fixing unit.
  Claims6The invention of claim4Or5In the image forming apparatus, when a visible image is formed only on one side of the recording medium, the second visible image is formed as the visible image, and heating by the heating transfer unit is not performed. It is characterized by that.
[0011]
In these inventions, the transfer of the first visible image from the intermediate transfer member to the first surface of the recording member is performed not by the charge applying method by the transfer charger but by the heat transfer method not using the charge. For this reason, it is possible to eliminate the spot-like stains around the image due to the charge applied to the recording medium by the transfer charger.
Further, with respect to the first visible image that is heat-transferred to the first surface of the recording medium, the adhesion between the image forming substances (for example, toners) and between the image forming substance and the first surface of the recording medium is enhanced. The degree of increase in the adhesion force depends on the temperature at the time of heat transfer, but when heat transfer is performed at a relatively high temperature such as 100 ° C. or higher, the first visible image is almost fixed on the first surface. In addition, even if heat transfer is performed at a relatively low temperature such as 65 ° C., a state of so-called hypothetical wearing is obtained in which the adhesive force is increased to a level that does not cause disturbance as long as it is rubbed with the guide member. Therefore, for the first visible image after heat transfer, the disturbance due to rubbing with the guide member can be almost eliminated.
As a result, both of the items (1) and (2) described above can be realized.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an electrophotographic printer (hereinafter simply referred to as a printer) will be described as an embodiment of an image forming apparatus to which the present invention is applied.
First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the printer. In the figure, the printer 100 includes four process units 6Y, 6M, 6C, and 6K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). Yes. These use Y, M, C, and K toners, which are image forming materials of different colors, but otherwise have the same configuration and are replaced when the lifetime is reached. Taking a process unit 6Y for generating a Y toner image as an example, as shown in FIG. 2, a drum-shaped photoconductor 1Y, a drum cleaning device 2Y, a charge eliminating device 3Y, a charging device 4Y, a developing device 5Y and the like are provided. Yes. In the photoreceptor 1Y as an image carrier, a surface layer of an organic semiconductor which is a photoconductive substance is coated on an aluminum cylinder having a diameter of 30 to 100 [mm]. An amorphous silicon surface layer may be coated. Further, it may be a belt shape instead of a drum shape. The charging device 4Y uniformly charges the surface of the photoreceptor 1Y that is rotated clockwise in the drawing by a driving unit (not shown). The surface of the uniformly charged photoreceptor 1Y is exposed and scanned with a laser beam L emitted from an exposure device 7 described later, and carries a Y electrostatic latent image. The Y electrostatic latent image is developed into a Y toner image by the developing means 5Y using Y toner. Then, the toner image is primary-transferred electrostatically onto an intermediate transfer belt 8 described later or a second surface of the transfer paper P. The drum cleaning device 2Y removes the toner remaining on the surface of the photoreceptor 1Y after the primary transfer process. Further, the charge removing unit 3Y discharges the residual charge of the photoreceptor 1Y after cleaning. By this charge removal, the surface of the photoreceptor 1Y is initialized and prepared for the next image formation. In the other process units 6M, 6C, and 6K, M, C, and K toner images are similarly formed on the photoreceptors 1M, 1C, and 1K, and 1 is formed on the intermediate transfer belt 8 or the second surface of the transfer paper P. Next transferred. In such a configuration, a visible image forming unit that forms a toner image that is a visible image on a photoconductor as an image carrier is configured by a combination of an exposure device 7 and process units (6Y, M, C, K) described later. ing.
[0013]
In FIG. 1 described above, an exposure device 7 is disposed above the process units 6Y, 6M, 6C, and 6K. The exposure device 7 serving as a latent image forming unit irradiates the respective photoconductors in the process units 6Y, 6M, 6C, and 6K with a laser beam L emitted based on the image information. By this exposure, electrostatic latent images for Y, M, C, and K are formed on the photoreceptors 1Y, 1M, 1C, and 1K. The exposure device 7 irradiates the photoconductor with a laser beam (L) emitted from a light source through a plurality of optical lenses and mirrors while scanning with a polygon mirror rotated by a motor. Instead of the exposure apparatus 7 having such a configuration, an exposure unit that irradiates LED light from the LED array may be employed.
[0014]
In the lower part of the printer housing, paper supply means having a paper storage cassette 41, a paper supply roller 43 incorporated therein, a registration roller pair 45, and the like are disposed. The paper storage cassette 41 stores a plurality of transfer papers P as a recording body in a stack of paper sheets, and a paper feed roller 43 is in contact with the uppermost transfer paper P. When the paper feed roller 43 is rotated counterclockwise in the drawing by a driving means (not shown), the uppermost transfer paper P is fed toward the rollers of the registration roller pair 45. The registration roller pair 45 rotationally drives both rollers to sandwich the transfer paper P, but temporarily stops rotating immediately after sandwiching. Then, the transfer paper P is sent out toward a later-described heating transfer nip at an appropriate timing.
[0015]
Below the process units 6Y, 6M, 6C, and 6K, a double-sided transfer device 20 that moves the intermediate transfer belt 8 endlessly while stretching is disposed. In addition to the intermediate transfer belt 8, the double-side transfer device 20 includes a belt cleaning device 14, a heat transfer roller 15, a separation guide plate pair 16, and the like. Also, four primary transfer bias rollers 9Y, 9M, 9C, and 9K, an under roller 10, a middle roller 11, a tension roller 12, and a top roller 13 are provided. The intermediate transfer belt 8 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of at least one of the rollers while being stretched around these eight rollers. The four primary transfer bias rollers 9Y, 9M, 9C, and 9K hold the intermediate transfer belt 8 that is endlessly moved in this manner between the photoreceptors 1Y, 1M, 1C, and 1K, thereby forming primary transfer nips. is doing. Each of these four primary transfer nips is caused by a potential difference between the primary transfer bias rollers 9Y, 9M, 9C, and 9K to which a primary transfer bias is applied by a power source (not shown) and the photoreceptors 1Y, 1M, 1C, and 1K. A primary transfer electric field is formed. In the process of endless movement, the intermediate transfer belt 8 sequentially passes through the primary transfer nips for Y, M, C, and K where the primary transfer electric field is thus formed. Each of the four primary transfer rollers 9Y, 9M, 9C, and 9K is of a type in which a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 8. is there. Instead of this method, a charger method that discharges from an electrode may be used. Of the eight rollers that stretch the intermediate transfer belt 8, the remaining four rollers other than the primary transfer rollers 9Y, 9M, 9C, and 9K are all electrically grounded.
[0016]
This printer transfers the four-color first toner image and the four-color second toner image to the first surface and the second surface of the transfer paper P (the surfaces facing upward and downward, respectively, in a stack portion described later). . Of these toner images, monochromatic Y, M, C, and K toner images for forming a first four-color toner image are formed on the four photosensitive members 1Y, 1M, 1C, and 1K, respectively. These single-color Y, M, C, and K toner images are primarily transferred onto the intermediate transfer belt 8 by being influenced by the nip pressure and the primary transfer electric field in the primary transfer nip described above. A four-color first toner image is formed by superposing four-color toners. Before and after the superimposing primary transfer, the four photoreceptors 11Y, 11M, 11C, and 11K each have monochrome Y, M, C, and K toner images for forming a four-color second toner image. Begin to form.
[0017]
The heating roller 15 containing a heat source such as a halogen lamp (not shown) rotates while contacting the front surface of the intermediate transfer belt 8 to form a heating transfer nip. On the back side of the heat transfer nip, the under roller 10 contacts the back surface of the intermediate transfer belt 8 to back up the contact of the heat roller 15 with the belt front surface.
[0018]
The registration roller pair 45 feeds the transfer paper P sandwiched between the rollers toward the heating transfer nip at a predetermined timing. The predetermined timing is a timing at which the transfer paper P is synchronized with the four-color first toner image on the intermediate transfer belt 8 at the heating transfer nip. The transfer paper P fed into the heating transfer nip is heated while the first toner image of four colors on the intermediate transfer belt 8 is brought into close contact with the first surface thereof. The four-color first toner image on the intermediate transfer belt 8 passes through the heating transfer nip while being transferred to the first surface by the influence of the heating and the nip pressure. The four-color first toner image, which is heated and transferred to the first surface of the transfer paper P, is combined with the white color of the first surface to form a full-color image.
[0019]
In the vicinity of the outlet of the heating transfer nip, the above-described separation guide plate pair 16 is disposed, and the transfer paper P that has passed through the heating transfer nip is separated from the intermediate transfer belt 8. Then, the separated transfer paper P is guided toward the primary transfer nip for Y so as to make a detour larger than the belt track. In this way, the transfer sheet P guided to the primary transfer nip for Y is brought into close contact with the intermediate transfer belt 8 on the first surface, and the photoreceptor 1Y for Y is brought into close contact with the second surface. It is done. Then, the Y toner image on the Y photoconductor 1Y is electrostatically primarily transferred onto the second surface of the transfer paper P. Thereafter, every time the toner passes through the primary transfer nips for M, C, and K, the M, C, and K toner images are sequentially transferred onto the second surface of the transfer paper P and are primarily transferred to the first transfer paper P. A four-color second toner image is formed on the two surfaces. Since the four-color second toner image is directly transferred onto the white transfer paper P, it becomes a full-color image from the beginning.
[0020]
The belt cleaning device 14 is disposed so as to be sandwiched between the separation guide plate pair 16 and the intermediate transfer belt 8. Then, after the transfer paper P is separated after passing through the heating transfer nip, the transfer residual toner adhering to the belt portion before coming into close contact with the transfer paper P again in the Y primary transfer nip is cleaned. The belt cleaning device 14 is disposed so as to sandwich the cleaning roller with the middle roller 11. Then, the transfer residual toner on the front surface of the intermediate transfer belt 8 is transferred to the cleaning roller for cleaning. The transfer residual toner transferred onto the cleaning roller is scraped off by a scraping blade in the belt cleaning device 14 and then conveyed to a collecting unit (not shown). The cleaning roller is a roller whose surface roughness is rougher than that of the intermediate transfer belt 8. When it is difficult to transfer the transfer residual toner to the surface of the cleaning roller, a heat source may be provided inside the roller. In this case, copper or aluminum having good thermal conductivity can be used as the roller material. .
[0021]
On the left side of the double-side transfer device 20 in the drawing, a fixing unit 61 having two fixing rollers 62 that are rotationally driven so as to move in the forward direction at the contact portion while abutting each other to form a fixing nip is disposed. It is installed. Each of these two fixing rollers 62 includes a heat source such as a halogen lamp (not shown). The transfer paper P on which full-color images are formed on both sides by the double-side transfer device 20 is conveyed toward the fixing unit 61 as the intermediate transfer belt 8 moves endlessly. Then, after being separated from the intermediate transfer belt 8 and delivered to the fixing means 61 at a belt stretching position by the top roller 13 of the double-sided transfer device 20, it is sandwiched between the fixing nips. Then, under the influence of heating and nip pressure by the two fixing rollers 62, full-color images are heated and fixed on both sides respectively.
[0022]
The transfer paper P that has passed through the fixing unit 61 enters between the plates of the reverse guide plate pair 50 and is then conveyed while being guided by the reverse guide plate pair 50 so as to be turned upside down. Then, after passing through the paper discharge roller pair 51, the paper is discharged toward the stack portion 65 formed on the upper surface of the printer housing.
[0023]
An exhaust fan F fixed to the printer housing is provided on the left side of the fixing unit 61 in the drawing, and plays a role of discharging heat generated from the fixing unit 61 together with air in the housing.
[0024]
As described above, the four-color first toner image is formed prior to the four-color second toner image, and is primarily transferred onto the intermediate transfer belt 8 and then heated and transferred to the first surface of the transfer paper P. And turn up at the stack 65. On the other hand, the four-color second toner image formed after the four-color first toner image is directly transferred directly to the second surface of the transfer paper P, and then faces downward at the stack portion 65. Therefore, the transfer paper P stacked on the stack unit 65 faces the previously formed four-color first toner image upward and the subsequent four-color second toner image facing downward. In this printer, in order to align the page numbers of the transfer sheets P stacked in this manner in order from the smallest, the four colors of the images with the larger page number are first printed for the images of two consecutive page numbers, odd and even. One toner image is formed. For example, the second page image is formed prior to the first page image. As a result, even when documents of several pages are continuously output, the page numbers can be aligned in order from the bottom in the stack unit 65. However, when executing the single-sided print mode in which an image is formed only on the second side of the transfer paper P, four-color second toner images are formed in order from the image with the smallest page number. As a result, even in the single-sided printing mode, the page numbers can be aligned in order from the bottom in the stack unit 65.
[0025]
On the four photoreceptors 1Y, 1M, 1C, and 1K, the single-color (Y, M, C, K) toner images for the four-color second toner images are respectively formed as mirror images. This is because the formed mirror image is changed to a non-mirror image (hereinafter referred to as a normal image) by being primarily transferred at the primary transfer nip. By forming a mirror image on the photoconductor, a normal image can be formed on the second surface of the transfer paper P. On the other hand, single-color (Y, M, C, K) toner images for the four-color first toner images are formed as normal images. This is because the formed normal image changes to a mirror image and a normal image through two transfer processes of primary transfer and heat transfer, and becomes a normal image on the first surface of the transfer paper P. Because it can.
[0026]
Next, a characteristic configuration of the printer will be described.
As described above, in this printer, the transfer from the photoreceptors 1Y, 1M, 1C, and 1K to the intermediate transfer belt 8 and the second surface of the transfer paper P is performed by the electrostatic transfer method, while the intermediate transfer belt. The transfer from 8 to the first surface of the transfer paper P is performed by a heat transfer method. In such a configuration, when the four-color first toner image is heated and transferred from the intermediate transfer belt 8 to the first surface of the transfer paper P, it is not necessary to apply a charge by the transfer charger to the second surface of the transfer paper P. Therefore, it is possible to eliminate spot-like stains around the image due to the application of charge. For the four-color first toner image, the adhesion force between the toner particles and between the toner and the first surface of the transfer paper P is increased to a level that does not cause any disturbance as long as it rubs against the guide member. Accordingly, it is possible to substantially eliminate the disturbance of the four-color first toner image due to the friction between the first surface of the transfer paper P transferred from the double-side transfer device 20 to the fixing unit 61 and the guide plate.
[0027]
In this printer, a heat transfer means is configured by a combination of a heat transfer roller 15 that forms a heat transfer nip and an under roller 10 that backs up the formation of the heat transfer nip from the back side of the intermediate transfer belt 8. . This heat transfer means is provided on the upstream side of the transfer sheet conveyance path from the facing portion between each of the photoreceptors 1Y, 1M, 1C, and 1K and the intermediate transfer belt 8. In this configuration, the four-color first toner image transferred onto the intermediate transfer belt 8 is heated and transferred onto the first surface of the transfer paper P prior to re-entering each primary transfer nip as the belt moves endlessly. By doing so, the adhesive force with the first surface can be increased in advance. As a result, the disturbance of the four-color first toner image caused by applying an electric field to the four-color first toner image reentering each primary transfer nip can be suppressed.
[0028]
The heat transfer roller 15 is a roller having an outer diameter of 20 to 40 [mm] in which an elastic layer such as an elastically deformable rubber layer is provided on the outer surface of a metal base tube made of aluminum or the like. The nip pressure at the heat transfer nip is 2 to 10 [N / cm.²The degree is good. Further, the heat transfer roller 15 and the middle roller 11 may be provided with their arrangement positions reversed. However, in this case, the amount of heat loss due to heat conduction to the intermediate transfer belt 8 is larger than when the transfer paper P is directly heated by the heat transfer roller 15. Therefore, energy saving can be achieved by disposing the heat transfer roller 15 so that the transfer paper P is heated by direct contact as shown in the figure.
[0029]
In this printer, the intermediate transfer belt 8 is stretched in a horizontally long shape that takes a space in the horizontal direction rather than in the vertical direction, and the photoreceptors 1Y, 1M, 1C, and 1K are opposed to the belt stretch portion in the lateral direction. Thus, a so-called horizontal double-sided transfer device 20 that forms each primary transfer nip is employed. In such a horizontal type, the transfer paper P must be supplied from the side to each primary transfer nip. However, if the paper cassette 41 is disposed on the side of the double-sided transfer device 20 that takes a space in the horizontal direction, the plane size of the printer main body becomes very large, which is not suitable for the actual situation. In order to avoid such an increase in the planar size, it is desirable to adopt the following layout in the case of the horizontal type. That is, as shown in the drawing, a paper cassette 41 is disposed immediately below the double-side transfer device 20, and the transfer paper P discharged therefrom is first transported in the vertical direction, and then the transport direction is changed to the horizontal direction. In this layout, transfer paper is supplied to the upper surface of the intermediate transfer belt 8. However, for the transfer paper P in which the transport direction is sequentially changed from vertical to horizontal as described above, the four-color first toner image is brought into close contact with the intermediate transfer belt 8 before reaching each primary transfer nip. It is necessary to perform the heat transfer. Such heat transfer is very difficult. The transfer paper P, which is brought into close contact with the side surface of the intermediate transfer belt 8 for heat transfer, cannot follow the intermediate transfer belt 8 that changes its traveling direction abruptly according to the curvature of the middle roller 11, but from the belt surface. This is because they will leave. Therefore, in this printer, the transfer paper P brought into close contact with the side surface of the intermediate transfer belt 8 at the heating transfer nip is positively separated from the belt surface by the separation guide plate pair 16. Then, after being guided to each primary transfer nip while largely detouring from the belt trajectory, it is brought into close contact with the intermediate transfer belt 8 again. By adopting such a configuration, the paper cassette 41 is disposed directly under the horizontal double-sided transfer device 20 to suppress the enlargement of the installation plane area of the printer body, and the transfer paper P is heated and transferred to the nip and each primary transfer. The nip can be sequentially entered.
[0030]
Transfer residual toner adheres to the surface of the intermediate transfer belt 8 separated from the transfer paper P after passing through the heating transfer nip. If the transfer residual toner and the transfer paper P are brought into close contact with each other at the primary transfer nip, the four-color first toner image on the first surface of the transfer paper P will be stained. If the relative position between the untransferred toner and the four-color first toner image does not change at all, it does not become dirty, but the relative position of the transfer paper P greatly changes when it is separated from the belt and largely detoured. Because. Therefore, in this printer, a belt cleaning device 14 as a cleaning means for cleaning the transfer residual toner on the intermediate transfer belt 8 is arranged as follows. That is, it is disposed at a position where the surface of the intermediate transfer belt 8 is cleaned after passing through the paper separation position by the separation guide plate pair 16 and before entering each primary transfer nip. As a result, the cleaned intermediate transfer belt 8 can be brought into close contact with the first surface of the transfer paper P at the primary transfer nip, and contamination of the first surface of the transfer paper P due to adhesion of transfer residual toner is eliminated. can do.
[0031]
The transfer direction of the toner image in the heat transfer depends on the difference in surface properties between the two members sandwiching the toner image in the heating nip. Specifically, for example, it is assumed that the two members A and B are moving in the forward direction while being in contact with each other in the heat transfer nip. The toner image heated while being sandwiched between these members A and B and heated to a glass transition point or higher is transferred to the member having the larger surface roughness when the members A and B are separated. This is because the member having the larger surface roughness has a larger contact area with the toner image due to the unevenness of the surface, making it difficult to exhibit toner releasability. Therefore, if the surface roughness is “member A> member B”, the toner image is transferred to the member A.
[0032]
In such a heat transfer, the conditions required for the intermediate transfer belt 8 which is the transfer destination of the four-color first toner image are as listed below.
・ Extension rate due to heat is extremely low
A resistance value (surface resistance value and volume resistance value) suitable for realizing primary transfer of a toner image from the photoreceptors 1Y, 1M, 1C, and 1K to a belt or transfer paper.
The surface roughness is smaller than that of the transfer paper P (the surface roughness Rz of the general transfer paper P is about 20 to 40 [μm]).
In the printer 100, the intermediate transfer belt 8 described below is used to satisfy these conditions. That is, a surface layer of 20 to 100 [μm] in thickness is coated with ETFE (ethylene / tetrafluoroethylene copolymer) on the front surface of a seamless polyimide belt having a thickness of 20 to 50 [μm]. The surface roughness Rz of this surface layer is adjusted to less than 20 [μm]. The general surface roughness Rz of the transfer paper P is about 20 to 40 [μm]. Therefore, as long as the most frequently used transfer paper P is generally used as the recording medium, there is insufficient heat transfer due to not satisfying the condition of “surface roughness of the second intermediate transfer belt <surface roughness of the recording medium”. Can be suppressed.
[0033]
In the present invention, the intermediate transfer member is elastically deformed at the time of heat transfer to improve the adhesion with the transfer paper P, and at least the surface is elastic from the viewpoint of suppressing heat transfer defects due to poor adhesion. It is desirable to be made of a material. On the other hand, for elastic materials such as rubber, it is generally difficult to process the surface roughness to less than 5 [μm] with the current manufacturing technology. For this reason, if the design value of the surface roughness of the second intermediate transfer member is set to less than 5 [μm], it is necessary to use an expensive second intermediate transfer member having a low yield, resulting in an increase in cost. Therefore, in the present printer, the intermediate transfer belt 8 whose surface roughness is adjusted to 5 [μm] or more is used. In such a configuration, the surface of the intermediate transfer belt 8 is elastically deformed satisfactorily to suppress the heat transfer failure due to the poor adhesion between the belt and the transfer paper P, and the cost is increased by using the expensive intermediate transfer belt 8 having a low yield. Can be resolved.
[0034]
In this printer, the heating temperature (65 to 68 ° C.) by the heat transfer roller 15 is set lower than the heating and fixing temperature (160 to 200 ° C.) by the fixing means 61. This is for the reason explained below. That is, the present inventors have conducted intensive research and can transfer a toner image by heating it to a temperature higher than the glass transition point of the toner, whereas the toner image can be fixed more than the glass transition point. It has been found that it is necessary to raise the temperature to above the softening temperature of the high toner. It is possible to heat and transfer the four-color first toner image by heating using the heat transfer roller 15, and at the same time, the four-color second toner image is present on the second surface of the transfer paper P. Therefore, the fixing process for the four-color second toner image cannot be performed. Therefore, even if the four-color first toner image is fixed by the heat transfer roller 15, the four-color second toner image needs to be fixed by another fixing means. Therefore, in this printer, the four-color first toner image is merely heated and transferred at the heating transfer nip for the time being, and finally the fixing unit 61 performs the heat-fixing process together with the four-color second toner image. I have to. Then, the heating temperature by the heat transfer roller 15 can be made lower than the temperature necessary for fixing, thereby saving energy.
[0035]
The fixing unit 61 fixes the toner image on each side while heating the transfer paper P from both sides. With such a configuration, it is possible to eliminate the difference in fixability between both sides caused by heating the transfer paper P from only one side. One fixing roller 62 in the fixing unit 61 heats the first surface of the transfer paper P by a contact method. The other fixing roller 62 heats the second surface of the transfer paper P by a contact method. Accordingly, the fixing device 61 performs contact-type heating on both sides of the transfer paper P. The two fixing rollers 62 have the same configuration. This is a roller in which an elastic layer such as a silicone rubber layer is provided on the outer surface of a cored bar containing a heat source. On the elastic layer, a release promoting layer made of a material having good release properties such as Teflon (registered trademark) may be provided. Generally, a toner image is glossy when subjected to heat fixing processing while being pressed against a heating member, but this glossiness is influenced by the degree of elasticity and double-sided roughness of the heating member. Therefore, if the two fixing rollers 62 having different surface materials are used, there is a difference in glossiness between the fixing toner images on both sides of the transfer paper P. Therefore, in this printer, two fixing rollers 62 having the same configuration are used. In such a configuration, the glossiness of the fixed toner image differs on both surfaces of the transfer paper P due to the difference in the surface materials of the two heating members that respectively contact the both surfaces of the transfer paper P and perform the heat treatment. The situation can be resolved.
[0036]
When the single-side mode in which an image is formed on only one side of the transfer paper P is selected, the printer forms the image as a four-color second toner image and directly transfers the image onto the second side of the transfer paper P directly. It is like that. At this time, power supply to the heat source of the heat transfer roller 15 is stopped so that heating by the heat transfer means is not performed. With such a configuration, it is possible to avoid wasteful energy consumption due to the heat source of the heat transfer means generating heat even in the single-side mode where heat transfer is not required.
[0037]
As the toner of each color, it is desirable to use a toner whose average circularity is adjusted to 0.90 to 0.99. When toner having a relatively large error from the true sphere and an average circularity of less than 0.90 is used, the transfer rate (post-transfer weight / pre-transfer weight) in electrostatic transfer is abruptly deteriorated to obtain a high-quality image. This is because it becomes difficult. In addition, when toner close to a true sphere having an average circularity exceeding 0.99 is used, transfer dust is easily generated due to its high fluidity. The average circularity of the toner can be obtained as follows. That is, the circumference of an equivalent circle having the same projected area is obtained in an optical detection zone in which a suspension containing toner particles is passed through an imaging zone detection zone on a flat plate and a particle image is optically detected by a CCD camera. Is obtained on the basis of the value obtained by dividing by the perimeter of the actual particle. Specifically, for example, first, 0.1 to 0.5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant in 100 to 150 ml of water from which impure solids have been removed in advance. About 0.1 to 0.5 g of a measurement sample is added. Then, the suspension in which the sample is dispersed is subjected to dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes to obtain a test solution having a dispersion concentration of 3000 to 10,000 / μl. This test solution can be analyzed with a flow type particle image analyzer FPIA-2100 (manufactured by Toa Medical Electronics Co., Ltd.) to determine the average circularity.
[0038]
Further, as the toner of each color, it is desirable to use a toner having a shape factor SF-1 of 120 to 180 and a shape factor SF-2 of 120 to 190. This is because a toner having a shape factor SF-1 or SF-2 of less than 120 and approaching a perfect sphere is likely to be generated rapidly from transfer dust due to its high fluidity. In addition, the toner with a relatively large error from the true sphere due to the shape factor SF-1 exceeding 180 or SF-2 exceeding 190, the transfer rate in electrostatic transfer suddenly deteriorates. This makes it difficult to obtain high-quality images.
[0039]
The shape factor SF-1 referred to here is a value indicating the ratio of the roundness of the shape of the spherical substance. It is represented by a value obtained by dividing the square of the maximum length MXLNG of an elliptical figure formed by projecting a spherical substance on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4. That is, the shape factor SF-1 is defined by the following equation.
[Expression 1]
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4)
When the value of SF-1 is 100, the shape of the substance becomes a true sphere, and as the value of SF-1 increases, the shape of the substance becomes indefinite.
[0040]
The shape factor SF-2 is a numerical value indicating the ratio of the unevenness of the material shape, and the square of the perimeter PERI of the figure formed by projecting the spherical substance on the two-dimensional plane is divided by the figure area AREA to obtain 100. It is expressed as a value when multiplied by / 4π. That is, the shape factor SF-2 is defined by the following equation.
[Expression 2]
SF-2 = {(PERI) 2 / AREA} × (100 / 4π)
When the SF-2 value is 100, there is no unevenness on the surface of the substance, and as the SF-2 value increases, the unevenness on the surface of the substance becomes more prominent.
[0041]
Specific examples of methods for measuring these shape factors SF-1 and SF-2 include the following. That is, the spherical material is photographed with an FE-SEM (S-800) manufactured by Hitachi, Ltd., and is randomly sampled 100 times as an image. Then, these images are introduced into an image analysis apparatus (LUSEX 3) manufactured by Nireco Corporation, analyzed, and calculated based on the formula shown above.
[0042]
Each color toner has a volume average particle size (Dv) of 4 to 8 [μm] and a particle size distribution (volume average particle size Dv / number average particle size Dn) of 1.05 to 1.30. It is desirable to use one. This is for the reason explained below. In other words, among toner powders having a particle size distribution in the range of 1.05-1.30, toner particles having a particle size suitable for the pattern of the electrostatic latent image contribute to development in preference to other toners. Since such a phenomenon tends to proceed, images of various patterns can be stably formed. In addition, when the apparatus adopts a configuration in which toner remaining on an image carrier such as a photoreceptor is collected and recycled, a large amount of small-size toner particles that are difficult to be transferred are recycled. When such a recycle having a relatively large particle size distribution is used, the variation in the particle size from the new toner supply to the next toner supply becomes large, which adversely affects the development performance. Further, in the case of a toner having a volume average particle diameter (Dv) smaller than the above range, when used as a two-component developer, the toner is fused to the surface of the carrier during a long period of stirring in the developing device, and the charging ability of the carrier is increased. Reduce. When used as a one-component developer, toner filming on the developing roller and toner fusion to a member such as a blade for thinning the toner are likely to occur. On the contrary, if the volume average particle system (Dv) is larger than the above range, it becomes difficult to obtain a high-resolution and high-quality image, and when the balance of the toner in the developer is performed, The variation in the particle size often increases.
[0043]
The particle size distribution of the toner can be measured by a measuring device using a Coulter counter method, for example, a Coulter counter TA-II or Coulter Multisizer II (both manufactured by Coulter). Specifically, first, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution. As the electrolytic aqueous solution, approximately 1% NaCl aqueous solution is prepared using primary sodium chloride, and for example, ISOTON-II (manufactured by Coulter) can be used. Further, 2 to 20 mg of a measurement sample is added to the obtained solution. Then, the solution is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toner particles or toner are measured with the above-described measuring apparatus using a 100 μm aperture as the aperture. Calculate the distribution. From the obtained distribution, the volume average particle diameter (Dv) and the number average particle diameter (Dn) of the toner can be obtained.
[0044]
In view of the toner properties as described above, in this printer, the user is instructed to use toner powder set in the main body that satisfies the following conditions.
(1) The average circularity is 0.90 to 0.99.
(2) The shape factor SF-1 is 120 to 180, and the shape factor SF-2 is 120 to 190. (3) The particle size distribution is 1.05 to 1.30.
[0045]
The designation to the user is performed, for example, by setting and shipping toner powder satisfying the above-described conditions in the printer main body, or packaging and shipping together with the printer main body. In addition, for example, in the printer body or the instruction manual attached to it, the toner powder product number or product name applicable to the printer body is described as the toner powder satisfying the above conditions. By doing. Further, for example, a printer body manufacturer or a distributor performs the distribution of information in which the product number or product name is associated with the product number or product name of the printer body using text or electronic data.
[0046]
Next, a modified apparatus of the printer having the above configuration will be described. The configuration of this modified example apparatus is the same as that of the printer according to the embodiment except for the items described below.
FIG. 3 is a schematic configuration diagram showing the modified apparatus. In this modified apparatus, the heat transfer means is provided on the downstream side of each primary transfer nip in the paper conveyance path. Specifically, the heat transfer roller 15 is not the middle roller 11 disposed near the downstream side of the Y primary transfer nip, but the top roller disposed near the upstream side of the K primary transfer nip. The intermediate transfer belt 8 is sandwiched between the intermediate transfer belt 8 and the intermediate transfer belt 8. In this modified apparatus, instead of the middle roller 11, the top roller 13 constitutes a part of the heat transfer means.
[0047]
In the heat transfer nip, not only the transfer paper P but also the intermediate transfer belt 8 is heated. If the heated intermediate transfer belt 8 enters each primary transfer nip without being sufficiently cooled and warms each photoreceptor 1Y, M, C, K, the image forming performance on the photoreceptor is adversely affected. There is a fear. Therefore, in this printer, the heat transfer unit is provided downstream of the primary transfer nip. In such a configuration, the intermediate transfer belt 8 can be naturally cooled by being moved endlessly by a distance close to one round before being heated into the primary transfer nip after being heated by the heating transfer means. Therefore, it is possible to suppress deterioration in image quality due to heat conduction from the intermediate transfer belt 8 to each of the photoreceptors 1Y, 1M, 1C, and 1K without providing a cooling unit for cooling the intermediate transfer belt 8.
[0048]
In this modified apparatus, the belt cleaning device 14 is also disposed not on the upstream side of the paper conveyance path but on the downstream side. Specifically, the intermediate transfer belt 8 is disposed between the heat transfer roller 15 and the top roller 13 on the downstream side. When the four-color first toner image is transferred to the transfer paper P downstream of the primary transfer nips as in this modified example, cleaning of the transfer residual toner becomes a problem. This is because if the cleaning roller of the belt cleaning device 14 is always in contact with the intermediate transfer belt 8, the four-color first toner image superimposed and transferred on the belt is also cleaned. Therefore, the belt cleaning device 14 is configured to move the cleaning roller in contact with and away from the intermediate transfer belt 8 by swinging in the direction of the arrow in the figure about the swing shaft 14a by a swing mechanism (not shown). . The cleaning roller is separated from the intermediate transfer belt 8 at least while the four-color first toner image passes through the opposite position, thereby avoiding cleaning of the four-color first toner image.
[0049]
Up to this point, an example in which a drum-shaped photoconductor is used as the image carrier has been described. However, other types such as a belt-shaped photoconductor may be used. The present invention can also be applied to an image forming apparatus that uses a liquid developer containing toner and a liquid carrier instead of a powder toner.
[0050]
As described above, in the printer according to the embodiment, since the heating transfer unit is provided on the upstream side of the paper conveyance path, an electric field is applied to the four-color first toner image reentering each primary transfer nip. Disturbance of the four-color first toner image can be suppressed.
Further, after separating the transfer sheet on which the four-color first toner images are heated and transferred from the intermediate transfer body belt 8, a separation guide plate pair 16 is provided to guide the transfer sheet to each primary transfer nip. Makes it possible. That is, the paper cassette 41 is disposed immediately below the horizontal double-sided transfer device 20, and the transfer paper P is sequentially entered into the heating transfer nip and each primary transfer nip while suppressing an increase in installation area of the printer body. Can do.
Further, a belt cleaning device 14 serving as a cleaning unit is provided so as to clean the surface of the intermediate transfer belt 8 after passing through the paper separation position by the separation guide plate pair 16 and before entering each primary transfer nip. In such a configuration, the cleaned intermediate transfer belt 8 is brought into close contact with the first surface of the transfer paper P at the primary transfer nip, and contamination of the first surface of the transfer paper P due to the adhesion of transfer residual toner can be eliminated. .
[0051]
Further, in the modified apparatus, since the heat transfer means is provided on the downstream side of the paper conveyance path, each photoconductor 1Y from the intermediate transfer belt 8 can be provided without providing a cooling means for cooling the intermediate transfer belt 8. , M, C, and K can be prevented from being deteriorated in image quality.
[0052]
In the printer and the modification apparatus according to the embodiment, the intermediate transfer belt 8 having a surface roughness Rz of 5 [μm] or more and less than 20 [μm] is used. In such a configuration, as long as the most frequently used transfer paper P is generally used as a recording medium, heat transfer by not satisfying the condition of “surface roughness of the second intermediate transfer belt <surface roughness of the recording medium” Shortage can be suppressed.
Further, since the heating temperature by the heat transfer unit is set lower than the heat fixing temperature by the fixing unit 61, energy saving can be achieved as compared with the case where the same temperature is set.
In addition, when executing the single-side mode, the second toner image is formed as an image and heating by the heat transfer unit is not performed. It is possible to avoid wasteful energy consumption due to heating of the heat source of the thermal transfer means.
[0053]
【The invention's effect】
  Claims 1 to6According to the invention, there is an excellent effect that the above-described items (1) and (2) can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a printer according to an embodiment.
FIG. 2 is an enlarged configuration diagram showing a process unit for Y of the printer.
FIG. 3 is a schematic configuration diagram showing a modified apparatus.
[Explanation of symbols]
1Y, M, C, K photoconductor (image carrier)
6Y, M, C, K process unit (part of visible image forming means)
7 Exposure equipment (part of visible image forming means)
8 Intermediate transfer belt (intermediate transfer member)
9Y, M, C, K Primary transfer bias roller (electrostatic transfer means)
15 Heat transfer roller (part of heat transfer means)
61 Fixing means
P Transfer paper (recording medium)

Claims (6)

An image carrier that carries a visible image and a recording medium that passes once through a path extending from the upstream side to the downstream side of the intermediate transfer member from the upstream side of the intermediate transfer body. In the double-sided transfer device for transferring the first visible image transferred to the intermediate transfer member to the first surface, and transferring the second visible image on the image carrier to the second surface,
Heat transfer means for heating and transferring the first visible image from the intermediate transfer body to the first surface on the upstream side in the path, and the recording body on which the first visible image is heated and transferred to the intermediate transfer A separation guide means for guiding toward the facing portion after separation from the body, and a cleaning means for cleaning the surface of the intermediate transfer body,
For transfer from the image carrier to said intermediate transfer member and the second surface while performing electrostatic transfer method and the transfer from the intermediate transfer member to said first surface to perform the heating transfer method A double-sided transfer device. The double-sided transfer device according to claim 1 .
A double-sided transfer device, wherein the cleaning unit is disposed so as to clean the surface of the intermediate transfer member after passing through the recording member separation position by the separation guide unit and before entering the facing portion. The double-sided transfer device according to claim 1 or 2 ,
A double-sided transfer device using a surface roughness Rz of 5 [μm] or more and less than 20 [μm] as the intermediate transfer member. An image carrier that carries a visible image on the surface, a visible image forming means that forms a visible image on the image carrier, and both sides that transfer the visible image on the image carrier to both sides of the recording medium In an image forming apparatus comprising: a transfer device; and a fixing unit that heat-fixes a visible image on both sides.
4. An image forming apparatus according to claim 1, wherein the double-sided transfer device is the one of claim 1, 2, or 3 . The image forming apparatus according to claim 4 .
An image forming apparatus, wherein a heating temperature by the heating transfer unit is lower than a heating temperature by the fixing unit. The image forming apparatus according to claim 4 or 5 ,
When a visible image is formed only on one side of the recording medium, the second visible image is formed as the visible image, and heating by the heating transfer unit is not performed. Image forming apparatus.

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