JPH0749622A - Electrophotographic printer and printing method - Google Patents

Abstract

PURPOSE:To secure a sufficient heating time for a multicolor toner image while maintaining a fixing speed and to print a color image excellent in quality, at the time of transferring the multicolor toner image onto a recording medium. CONSTITUTION:This electrophotographic printer 1 provided with an exposing means 80 successively forming plural electrostatic latent images based on the printing information having the completion of color resolution on an electrostatic latent image carrier 10, a developing means 20 successively developing the electrostatic latent image with the toner of hue corresponding to the printing information having the completion of resolution the color to obtain a toner image, an intermediate transfer medium 31 on which the toner image is successively transferred to form the multicolor toner image, a carrying means 70 carrying the recording medium P on which the multicolor toner image is transferred/fixed and a transfer fixing means 50 press-contacting with the intermediate transfer medium 31 via the recording medium P and beating/fixing the multicolor toner image on the recording medium P and the electrophotographic printing method are provided. The transfer fixing means 50 has a heated endless belt 54 holding/carrying the recording medium P between the means 50 and the intermediate transfer medium 31 and transferring and simultaneously fixing the multicolor toner image onto the recording medium P.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic printer and an electrophotographic printing method.

[0002]

2. Description of the Related Art An electrophotographic printer is an electrostatic latent image carrier,
That is, the electrostatic latent image formed on the photosensitive drum is developed with toner, and this toner image is transferred by a heating roll or the like.
The fixing means heats and pressurizes the recording medium such as paper to fix it. Such electrophotographic printers include paper,
Some include an intermediate transfer unit such as a belt or a drum, which has an advantage of being able to transfer a toner image onto various recording media such as a plastic film or a metal thin plate. An electrophotographic printer provided with an intermediate transfer means is disclosed in, for example, Japanese Patent Laid-Open No.
No. 0-23234 and the electrophotographic toner transfer / melting device disclosed in Japanese Patent Publication No. 57-20632 are known. The former is a wet type using liquid toner, and the latter is the latter. Is a dry type using a dry toner. The latter uses a belt as an intermediate transfer means, and an electrophotographic printer disclosed in Japanese Patent Laid-Open No. 63-34573 is known as a wet type using a belt as an intermediate transfer means. Has been.

Here, a wet type electrophotographic printer using a liquid toner has an advantage that a high resolution and a sharp image can be obtained, as compared with a dry type, since fine toner particles of submicron order can be used. ing. When a color image is created in this electrophotographic printer, for example, an electrostatic latent image corresponding to a magenta hue is formed on a photosensitive drum, and the electrostatic latent image is developed with a magenta liquid toner. The magenta toner image is transferred to an intermediate transfer unit, for example, an intermediate transfer drum, which is pressed against the photosensitive drum. Similarly, the cyan and yellow toner images are sequentially layered and transferred to the intermediate transfer drum to form a multicolor toner image. Then, the heating roll is pressed against the intermediate transfer drum, and the multicolor toner images laminated and transferred onto the intermediate transfer drum are transferred and fixed on a recording medium such as paper to form a color image.

[0004]

By the way, the heating roll of the electrophotographic printer is different from the ordinary printer.
Since the recording medium such as paper is heated from the back side, it is difficult for the heat to be transferred by the amount of the recording medium and the heating efficiency is not always good.
Therefore, in the electrophotographic printer, the heating of the multicolor toner image becomes insufficient when the multicolor toner image in which a plurality of toner images are stacked is collectively transferred to the recording medium,
There is a problem that the image quality of the obtained color image may deteriorate.

If the heating for transferring the multicolor toner image to the recording medium is insufficient, the fixing speed is reduced to secure the heating time of the multicolor toner image. Therefore, in the above electrophotographic printer, the fixing speed cannot be increased, so that the electrophotographic printer cannot be operated at high speed, it takes time to form a color image, and there is a problem that the user's needs cannot be met.

The present invention has been made in view of the above points, and when transferring a multicolor toner image to a recording medium, a sufficient heating time of the multicolor toner image is ensured while maintaining the fixing speed, thereby ensuring quality. An object of the present invention is to provide an electrophotographic printer and an electrophotographic printing method capable of printing an excellent color image.

[0007]

According to the electrophotographic printer of the present invention, there is provided an electrostatic latent image carrier,
Exposure means for sequentially forming a plurality of electrostatic latent images based on the color-separated print information on the electrostatic latent image carrier, and the electrostatic latent image formed on the electrostatic latent image carrier is color-separated. Developing means for sequentially developing with a toner having a hue corresponding to the print information to form a toner image, an intermediate transfer medium for sequentially transferring the toner images on the electrostatic latent image carrier to form a multicolor toner image, A transporting unit that transports a recording medium on which the multicolor toner image formed on the intermediate transfer medium is transferred and fixed, and the intermediate transfer medium are pressed against the intermediate transfer medium through the recording medium.
Transfer that heat-fixes the multicolor toner image on the recording medium
An electrophotographic printer including a fixing unit, wherein the transfer / fixing unit holds the recording medium between the intermediate transfer medium and conveys the recording medium, and transfers the multicolor toner image onto the recording medium. It is configured to have a heating endless belt for fixing at the same time.

Preferably, the heated endless belt is wound around at least two rollers, one of which is arranged on the upstream side in the conveying direction of the recording medium and the other of which is arranged on the downstream side. One is a heat roller. Further, preferably, the at least two rollers are arranged such that the pressure contact pressure of the heating endless belt is in pressure contact with the intermediate transfer medium, and the pressure contact pressure of a roller arranged on the downstream side in the transport direction of the recording medium is arranged on the upstream side. Set higher than the contact pressure of the roller.

More preferably, the at least two rollers cover at least the roller arranged on the downstream side in the transport direction of the recording medium with an elastic member. Preferably, the heating endless belt is a metal belt, a metal belt having a surface coated with a silicone resin or a fluororesin, or a resin belt made of a silicone resin or a fluororesin.

Further, according to the electrophotographic printing method of the present invention to achieve the above object, an exposure step of sequentially forming a plurality of electrostatic latent images based on the color-separated print information on the electrostatic latent image carrier. A developing step of sequentially developing the electrostatic latent image formed on the electrostatic latent image carrier with a toner having a hue corresponding to the color-separated print information to form a toner image, and the toner developed in the developing step The image forming apparatus includes an intermediate transfer step of sequentially transferring an image onto an intermediate transfer medium to form a multicolor toner image, and a transfer / fixing step of heating and fixing the multicolor toner image formed in the intermediate transfer step while being pressed against a recording medium. In the electrophotographic printing method, the transfer / fixing step is configured to fix the multicolor toner image onto a recording medium simultaneously with transfer.

Preferably, in the transfer / fixing step, the multicolor toner image is heat-fixed on the downstream side of the recording medium in the conveying direction while being in pressure contact with the recording medium at a pressure contact pressure higher than the upstream side.

[0012]

In the electrophotographic printer and electrophotographic printing method of the present invention, the recording medium is nipped and conveyed between the intermediate transfer medium and the endless heating belt, and the multicolor toner image is fixed onto the recording medium at the same time. . Therefore, when transferring and fixing the multicolor toner image to the recording medium, a sufficient heating time of the multicolor toner image is secured while maintaining the fixing speed.

At this time, if one of at least two rollers around which the heating endless belt is wound is a heat roller, the heating endless belt is heated by this heat roller. With respect to the pressure contact pressure of at least two rollers in pressure contact of the heated endless belt with the intermediate transfer medium, the pressure contact pressure of the roller arranged downstream in the transport direction of the recording medium is arranged on the upstream side. When the pressure is set to be equal to or higher than the contact pressure, the transferability of the multicolor toner image is improved.

Further, when at least two rollers, which are arranged at least on the downstream side in the transport direction of the recording medium, are covered with an elastic member, the width of the pressure contact pressure for contacting the heating endless belt with the intermediate transfer medium becomes wide. Granted. Further, when the heating endless belt is a metal belt, a metal belt having a surface coated with a silicone resin or a fluororesin, or a resin belt made of a silicone resin or a fluororesin, adhesion of a multicolor toner image to the heating endless belt is prevented. .

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the electrophotographic printer and electrophotographic printing method of the present invention will be described below with a main conveyance path for conveying a recording medium and a bypass conveyance path for reversing the recording medium and returning it to the main conveyance path. A detailed description will be given with reference to the accompanying drawings based on an electrophotographic printer including a carrying device.

As shown in FIG. 1, the electrophotographic printer 1 includes a photosensitive means 10, a developing means 20, an intermediate transfer means 30, and
A cleaning unit 40, a transfer unit 50, an auxiliary squeeze roller 60, a recording medium (transfer sheet P) conveyance device 70, and an exposure unit 80 for irradiating light for exposure from the direction of arrow A are provided. The means 30, the cleaning means 40, and the auxiliary squeeze roller 60 are integrated as one process unit UP as a whole and are pulled out to the front side in FIG. 1 along the guide rails 5 and 5.

The electrophotographic printer 1 shown in FIG. 1 is viewed from the front. In the following description, the illustrated side is referred to as the front side, and the back side corresponding to the back side of the drawing is referred to as the back side. In addition, each arrow shown in FIG. 1 indicates the rotation direction of each member and the conveyance direction of the recording medium. Photosensitive means 10
Has a photosensitive drum 11, a static eliminator 12 for removing the residual charges of the photosensitive drum 11, and a charger 13 for uniformly charging the photosensitive drum 11. Prior to the removal of the residual charges, the cleaning unit 40 cleans the surface of the surface. To be cleaned. These cleaning means 40, static eliminator 12 and charger 1
3 is arranged between the intermediate transfer means 30 and the developing means 20 in this order along the rotation direction of the photosensitive drum 11.

The photosensitive drum 11 has a photosensitive layer formed of an organic photoelectric material (OPC) on the surface of a cylindrical drum. The material for the photosensitive layer is O
Other than PC, for example, selenium (Se) system, amorphous silicon (α-Si), or the like can be used. The static eliminator 12 is an LED
An array or a small incandescent lamp irradiates the surface of the photosensitive drum 11 with light to erase the residual latent image. The charger 13 uniformly charges the photosensitive drum 11 with the ions generated by the corona discharge.

The developing means 20 includes a first developing unit 21 to a fourth developing unit 24 formed on an upper portion of the housing 210, and a developing unit 21 to a left and right direction which is a tangential direction of the photosensitive drum 11 as indicated by an arrow in the figure. Drive unit 25 for moving the unit 24 horizontally and the developing units 21 and 2
4 is provided with a toner cartridge 26 that is detachably attached to each of the developing units 21 to 24. The drive means 25 has a ball screw 25a and a drive motor 25b. The first developing unit 21 has a liquid toner liquid tank 211 formed in an upper portion of a housing 210, and a toner cartridge 26 containing liquid toner of each hue in a lower portion thereof. The liquid tank 211 has a developing roller and a developing roller, respectively. Squeeze rollers (both not shown) are arranged in parallel at a predetermined interval. The other developing units 22 to 24 have the same structure as the first developing unit 21.

The developing means 20 includes the developing units 21-2.
4 are provided with toner cartridges 26 containing yellow, magenta, cyan, and black liquid toners, respectively. At the initial position before the start of development, the photosensitive drum 11 is placed.
It is located to the right of. Then, the developing units 21 to
The developing device 24 is sequentially moved to the photosensitive device 10 side in this order by the driving device 25 during development, and each electrostatic latent image formed based on the color-separated print information is sequentially developed.
As the liquid toner, a liquid carrier in which toner particles such as yellow, magenta, and cyan are dispersed is used.

The intermediate transfer means 30 comprises an intermediate transfer drum 31.
And a charger 32 arranged along the rotation direction of the intermediate transfer drum 31, and the toner images developed by the developing units 21 to 24 of the developing means 20 are sequentially laminated on the intermediate transfer drum 31. Transcribed. Intermediate transfer drum 31
Is a cylindrical metal drum on which a thin silicone resin layer having an insulating property is formed, or a conductive substrate on which a silicone resin layer is formed and which is wound around a metal drum. Good transferability can be obtained by providing an appropriate cushion layer under the resin layer. The intermediate transfer drum 31 is brought into pressure contact with the photosensitive drum 11, and each time a toner image of each hue is developed by the developing device 20, the toner images are sequentially transferred in layers.

The intermediate transfer drum 31 may have an appropriate diameter depending on the size of the recording medium, and when the recording medium is large, the photosensitive drum 11 as shown in FIG.
Larger in diameter. The charger 32 is a photosensitive unit 10.
The intermediate transfer drum 31 is charged according to the same principle as that of the charger 13 in order to cancel the influence of the previous toner image so that the next toner image having a different hue transferred from the photosensitive drum 11 is easily transferred. This is to prevent the toner image already transferred onto the intermediate transfer drum 31 from returning to the photosensitive drum 11.

Then, in the intermediate transfer means 30, the toner images developed on the photosensitive drum 11 are sequentially transferred to the intermediate transfer drum 31 while being charged by the charger 32. At the time of this transfer, a small amount of toner image or liquid toner not transferred to the intermediate transfer drum 31 remains on the photosensitive drum 11, but these are cleaned by the cleaning means 40.

At this time, among the liquid toners of yellow (Y), magenta (M), cyan (C) and black (Bk), the hue of the toner image first developed on the photosensitive drum 11 is yellow (Y). ), The yellow toner image is fixed to the uppermost layer on the transfer paper P. Therefore, since the yellow toner has a higher light transmittance than the toners of other hues, the obtained color image becomes clear and the image quality is improved.

Moreover, the yellow toner image is located at the bottom of the toner images transferred and laminated on the intermediate transfer drum 31, and can remain on the intermediate transfer drum 31 without being transferred onto the transfer paper P. The highest. However, since the yellow toner image is less noticeable than the toner images of other hues, even if it remains on the intermediate transfer drum 31, it has little influence on the color image to be printed next and needs to be cleaned. Absent.

The cleaning means 40 is the cartridge 4
Cleaning roller 4 in contact with photosensitive drum 11 in 1
2 etc. are provided. This cleaning means 40 is
The cleaning roller 4 removes the toner image and the liquid toner residue remaining on the photosensitive drum 11 after the transfer to the intermediate transfer drum 31.
2 is electrostatically adsorbed and collected, and is scraped by a rubber blade made of urethane rubber or the like and collected in a toner collecting container.

The transfer means 50 has heat rollers 51 and 52, a tension roller 53, a heating endless belt 54, and a pressing mechanism described later. The heat rollers 51 and 52 are metal rollers having a built-in heater (not shown) for heating the heating endless belt 54. As shown in FIG. 2, the heat roller 51 is the same as the heat roller 51 on the upstream side in the conveyance direction of the transfer sheet P. Heat roller 5 on the downstream side
2 are heating endless belts 5 on the intermediate transfer drum 31, respectively.
4 are abutted on each other. Heat rollers 51, 52
Is driven integrally with the tension roller 53 by the pressing mechanism at the time of heat fixing of the multicolor toner image on the transfer paper P, and the heating endless belt 54 is brought into pressure contact with the intermediate transfer drum 31 to be transferred to the intermediate transfer drum 31. The multicolor toner images transferred in layers are heated and pressed to be fixed on the transfer paper P.

The tension roller 53 applies tension to the heated endless belt 54 and prevents the transfer sheet P being conveyed from meandering. This roller 53 is the heat roller 5
1, 52 are arranged obliquely above and parallel to the intermediate transfer drum 31, and the rotation axes of these rollers 51 to 53 are arranged in a substantially equilateral triangle shape. The heating endless belt 54 is a thin metal belt made of nickel or stainless steel having a thickness of 60 μm and wound around the heat rollers 51, 52 and the tension roller 53.

Here, with respect to the pressure contact pressure of the heat rollers 51 and 52 for pressing the heated endless belt 54 against the intermediate transfer drum 31, the pressure contact pressure of the heat roller 52 arranged on the downstream side in the transport direction of the transfer paper P is upstream. Side heat roller 51
It is set higher than the contact pressure of. With this setting, the heating roller 52 applies a pressure contact pressure while the toner is sufficiently heated and melted, so that the toner can penetrate deeper into the transfer paper P. Therefore, the multicolor toner image is reliably transferred and fixed on the transfer paper P nipped between the heated endless belt 54 and the intermediate transfer drum 31.

When the toner image is transferred from the photosensitive drum 11 to the intermediate transfer drum 31, the pressing mechanism is
The heat rollers 51 and 52 are separated from the intermediate transfer drum 31 together with the heating endless belt 54. Then, by the pressing mechanism, the heat rollers 51 and 52 come into contact with the intermediate transfer drum 31 with a predetermined pressure by the pressing mechanism by the time the last toner image of the four types of toner images on the intermediate transfer drum 31 is reached. It is pressed by force. As a result, the heating endless belt 54 pressurizes and heats the multicolor toner images stacked and transferred onto the intermediate transfer drum 31 to transfer and fix the multicolor toner images onto the transfer paper P conveyed by the conveying device 70.

Here, the pressing mechanism is constructed as shown in FIG. 3 and has an arm member 55, a support arm 56 and a cam member 57. The right end side of the arm member 55 is rotatably supported by the rotating shaft 55a, and the left end side of the arm member 55 is urged downward by a pressing spring 58 provided between the arm member 55 and the housing H of the electrophotographic printer 1. Also, the arm member 55
Supports the heat roller 52 and the tension roller 53 rotatably, and also supports the support arm 56.

Here, the tension roller 53 is
The arm member 55 is movably supported along the long hole 55b, and the long hole 55b is formed in a direction substantially orthogonal to a line connecting the axial centers of the heat rollers 51 and 52. One end of the support arm 56 is supported by the arm member 55 around the rotation center of the heat roller 52 as a rotation center, and the other end rotatably supports the heat roller 51. In addition, the support arm 56
The other end side is biased toward the intermediate transfer drum 31 side by a pressing spring 59 provided between the arm member 55 and the arm member 55. Therefore, in the support arm 56, the heat roller 51 side is the heat roller 5 side.
Although it rotates in the vertical direction in FIG. 3 with the rotation center of 2 as the rotation center, the rotation of the end portion on the heat roller 52 side is restricted by the pin 55c in the upward direction.

The cam member 57 moves the left end of the arm member 55 up and down against the urging force of the push spring 58 to rotate the left end side of the arm member 55 about the rotating shaft 55a. Therefore, in the pressing mechanism, the intermediate transfer drum 3
When the multicolor toner images laminated and transferred to 1 are transferred and fixed on the transfer paper P by pressurizing and heating, the heat roller 51 is pressed by the biasing force of the spring 59 and the heat roller 52 is pressed by the spring 58. The urging force presses the intermediate transfer drum 31 respectively, and thereby the heated endless belt 54 between the rollers 51 and 52 is pressed against the surface of the intermediate transfer drum 31.

When the pressure contact of the heated endless belt 54 with the intermediate transfer drum 31 is released, the cam member 57 is used.
Is rotated 180 ° as shown in FIG. Then, the left end of the arm member 55 is pushed by the cam member 57.
It is pushed up against the urging force of 8, and rotates clockwise around the rotation shaft 55a, and the pressing of the heat rollers 51 and 52 to the intermediate transfer drum 31 is released.

At this time, the support arm 56 also rotates around the rotation center of the heat roller 52 as the arm member 55 rotates, but the rotation of the heat roller 52 side is restricted by the pin 55c. The heat roller 51 side rotates clockwise, and the pressing of the heat roller 51 on the intermediate transfer drum 31 is quickly released. Thus, in the pressing mechanism,
The heating rollers 51, 52 and the heating endless belt 54 can be pressed against the intermediate transfer drum 31 by a single cam member 57, and a supporting arm 56 for supporting the heating roller 51.
Since the center of rotation of is matched with the center of rotation of the heat roller 52, the pressing mechanism is downsized. Further, the push springs 58, 5
9 is the heat roller 5 by appropriately selecting the spring constant.
The pressing force for pressing 1, 52 against the intermediate transfer drum 31 can be individually adjusted.

Here, the photosensitive drum 11, the intermediate transfer drum 31, and the heat rollers 51 and 52 are the same as the photosensitive drum 1.
The axis line passing through the center of the rotation shaft of the intermediate transfer drum 31 and the intermediate transfer drum 31 and the action line of the resultant force of the pressure contact forces of the heat rollers 51 and 52 to the intermediate transfer drum 31 are substantially orthogonal to each other. With this arrangement, when the heat rollers 51 and 52 are brought into pressure contact with the intermediate transfer drum 31 by the pressing mechanism, the intermediate transfer drum has a pressure contact force acting from the heat rollers 51 and 52 toward the center of the rotation axis of the intermediate transfer drum 31. The component force from the rotation axis center of 31 to the rotation axis center of the photosensitive drum 11 becomes zero.

Therefore, when the heat rollers 51 and 52 are pressed against the intermediate transfer drum 31, a stress that changes the pressing force of the intermediate transfer drum 31 pressed against the photosensitive drum 11 does not act on the intermediate transfer drum 31. Absent. Therefore, the intermediate transfer drum 31 is always pressed against the photosensitive drum 11 with a constant pressing force, and there is no adverse effect on the transfer of the toner image developed on the photosensitive drum 11 to the intermediate transfer drum 31. A color image with high image quality can be obtained.

The auxiliary squeeze roller 60 is the photosensitive drum 1
1 is disposed between the developing unit 20 and the intermediate transfer unit 30 with a gap of 30 μm, for example, and rotates in the same direction as the photosensitive drum 11 to develop the toner image. To remove excess liquid toner, especially liquid carrier, beyond this interval. The same effect can be obtained by using a squeeze corona using a charging device instead of the auxiliary squeeze roller 60.

The transfer device 70 enables double-sided printing of the transfer paper P, and pulls out the transfer paper P from one of the drawers D ₁ and D ₂ arranged in the upper and lower two stages and transfers it to the intermediate transfer drum 31. A main conveyance path 71 and a bypass conveyance path 72 that reverses the transfer paper P and returns it to the main conveyance path 71 are provided. The main transport path 71 serves as a transporting means for the transfer paper P, and includes a plurality of reversible rollers 71a that can rotate forward and backward on the drawer D ₁ and D ₂ sides.
However, a plurality of normal rotation rollers 71b are respectively provided from the intermediate transfer drum 31 side to the discharge side. A guide plate 71c for guiding the transfer of the transfer paper P is provided in the main transfer path 71.

On the other hand, the bypass conveyance path 72 is the main conveyance path 7
1, a switching claw 72a for switching the transport direction of the transported transfer paper on the entrance side located on the intermediate transfer drum 31 side, a plurality of transport rollers 72b for transporting the transfer paper in the middle, and a main transport. Guide members 72c for guiding the conveyance of the transfer paper are respectively provided on the exit side where they rejoin the path 71.

Here, the main transport path 71 extends from the drawers D ₁ and D ₂ to the bypass transport path 72 in the transfer sheet transport direction.
The length to the guide member 72c on the outlet side is set to be at least the length in the transport direction of the transfer paper.
As a result, during double-sided printing, the transfer paper that has been reversed by the switching claw 72a is reliably transported from the bypass transport path 72 to the main transport path 71 again. At this time, the main transport path 71 is
Before the transfer sheet returns from the bypass conveyance path 72 to the main conveyance path 71, the conveyance direction of the reversible roller 71a is reversed. As a result, in double-sided printing, switching of the transfer direction of the transfer paper from the bypass transfer path 72 to the main transfer path 71 due to the reversal of the transfer paper becomes smooth.

The exposure unit 80 is a laser optical system for forming an electrostatic latent image on the surface of the photosensitive drum 11 based on the color-separated print information, and is arranged immediately below the developing unit 20, and includes a laser light source, a liquid crystal shutter, and the like. Have Exposure means 80
Irradiates the photosensitive drum 11 with laser light from the direction of arrow A based on the print information corresponding to each hue of the color original, and forms an electrostatic latent image corresponding to each print information on the surface. Further, an LED array may be used as an exposure unit that irradiates the photosensitive drum 11 with print information.

The electrophotographic printer 1 of the present invention is constructed as described above, and produces a color image by the electrophotographic printing method described below. First, the cleaning means 40
Residual charges are removed from the surface of the photosensitive drum 11 cleaned in step 1 by the static eliminator 12 and uniformly charged by the charger 13. Next, laser light is irradiated as indicated by an arrow A in the figure to form an electrostatic latent image based on the color-separated print information on the photosensitive drum 11.
Are sequentially formed on the surface of. The electrostatic latent image by the irradiation of the laser light is formed four times in total corresponding to the hues of yellow, magenta, cyan and black.

Next, the ball screw 25a is attached to the drive motor 2
5b, the developing means 20 disposed on the right side of the photosensitive drum 11 in the drawing is horizontally moved to the photosensitive drum 11 side, and the yellow toner image is transferred from the first developing unit 21 to the second developing unit 22. The magenta toner image and the cyan and black toner images are successively developed in the same manner. In this way, the toner image developed by each developing unit is sequentially transferred to the intermediate transfer drum 31, and a multicolor toner image in which toner images of four colors are stacked is formed on the intermediate transfer drum 31.

Then, in parallel with the transfer of the toner image developed by the fourth developing unit 24 to the intermediate transfer drum 31,
Alternatively, after the transfer is completed, the heating endless belt 54 wound around the heat rollers 51 and 52 and the tension roller 53 is pressed against the intermediate transfer drum 31 by the pressing mechanism. As a result, the multicolor toner images that have been layer-transferred onto the intermediate transfer drum 31 are heated and pressed onto the transfer paper P conveyed through the main conveyance path 71 of the conveyance device 70 and are collectively fixed, and the transfer paper is transferred. One step of forming a color image on the surface of P is completed.

At this time, the multicolor toner image on the intermediate transfer drum 31 is heated and pressed by the nip with the heated endless belt 54 heated by the heat rollers 51 and 52 to be heat-fixed on the transfer paper P. However, the transfer paper P has the heat rollers 51 and 52.
The heating endless belt 54 in between presses against the intermediate transfer drum 31 to secure a sufficient heating region, and thus a sufficient heating time of the multicolor toner image. In addition, the heat rollers 51, 52
Is set so that the pressure contact pressure of the heat roller 52 is equal to or higher than the pressure contact pressure of the heat roller 51 arranged on the upstream side.

Therefore, the multicolor toner image is transferred and fixed on the transfer paper P in a completely melted state, and a high quality color image is obtained. Moreover, since the electrophotographic printer 1 can secure a sufficient heating time for the multicolor toner image between the heat rollers 51 and 52, the multicolor toner image can be transferred and fixed onto the transfer paper P at a higher speed. This makes it possible to increase the number of color image prints per unit time.

Furthermore, since the heating endless belt 54 is a metal belt, the multicolor toner image on the intermediate transfer drum 31 transferred and fixed to the transfer paper P is applied to the heat rollers 51 and 52.
The heat energy from can be efficiently supplied, and the transferability of the multicolor toner image onto the transfer paper P is further improved. Also,
When a color image is also printed on the back surface of the transfer paper P, the transfer pawl P on which the multicolor toner image is fixed on the front surface of the transfer paper P is bypassed by flipping the switching claw 72a upward.
Guide to and flip the inside out. As a result, the transfer paper P on the surface of which the color image has been formed is conveyed through the bypass conveyance path 72 by the plurality of conveyance rollers 72b, and the guide member 72c.
And is conveyed again to the main conveyance path 71.

At this time, in the main transport path 71, before the transfer sheet P returns from the bypass transport path 72 to the main transport path 71, the transport direction of the reversible roller 71a is reversed, and the transfer sheet P whose front and back sides are reversed is: The reversible rollers 71a are temporarily accommodated in a transfer paper conveyance path. Next, in the same manner as described above, the electrostatic latent images formed on the photosensitive drum 11 based on the color-separated print information are sequentially developed by the developing device 20, and are transferred in layers on the intermediate transfer drum 31. When the color toner image is transferred to the back surface of the transfer paper P, the transfer paper P
Is again conveyed from the transfer sheet conveyance path that is temporarily accommodated to the intermediate transfer drum 31 through the main conveyance path 71, and is nipped between the endless heating belt 54 and the multicolor toner image on the back surface. Is fixed.

Next, the switching claw 72 of the bypass conveyance path 72
After a is switched to the lower side, the transfer paper P on which the multicolor toner images are printed on both sides is the guide plate 71 of the main conveyance path 71.
The electrophotographic printer 1 is guided by c and is indicated by the arrow.
It is discharged to the outside of the printer and stored in a paper discharge tray or the like. Here, in the above-described embodiment, the heat rollers 51 and 52 are metal rollers. However, if the heat roller 52 disposed at least on the downstream side in the transport direction of the transfer paper P is covered with an elastic member such as silicone rubber, the heating is performed. It is possible to impart a width within a predetermined range to the contact pressure for contacting the endless belt 54 with the intermediate transfer drum 31.

As the heating endless belt 54, the metal belt of the above-mentioned embodiment coated with a silicone resin or a fluororesin, or a resin belt formed by molding a silicone resin or a fluororesin into a ring shape may be used. . Thus, the presence of silicone resin or fluororesin on the surface of the heated endless belt can prevent the heated endless belt from being stained due to the adhesion of toner, and in particular, at the time of double-sided printing, the multicolor image already fixed on the surface of the transfer paper can be used. The toner image does not adhere to the heated endless belt when the multicolor toner image is transferred and fixed on the back surface of the transfer paper, and the deterioration of the image quality of the obtained color image can be prevented.

[0052]

As is apparent from the above description, according to the electrophotographic printer and the electrophotographic printing method of the present invention, when transferring a multicolor toner image to a recording medium, the multicolor toner is maintained while maintaining the fixing speed. It is possible to print a color image with excellent quality while ensuring a sufficient heating time of the image.

Therefore, when transferring / fixing the multicolor toner image to the recording medium, a sufficient heating time of the multicolor toner image is secured, and the fixing speed, and hence the printing time of the color image is shortened and the high speed is achieved. Transfer multicolor toner image to transfer paper
It is possible to fix the color image, and it is possible to increase the number of color image prints per unit time. Further, when one of at least two rollers around which the heating endless belt is wound is a heating roller, the heating endless belt can be heated by this heating roller, and heating efficiency is improved.

Further, regarding the contact pressure of at least two rollers for contacting the heated endless belt with the intermediate transfer medium, the contact pressure of the roller arranged downstream in the conveying direction of the recording medium is arranged upstream. If the pressure is set higher than the contact pressure of the roller, the transferability of the multicolor toner image is improved. Further, when at least two rollers, which are arranged at least on the downstream side in the transport direction of the recording medium, are covered with the elastic member, a width is given to the range of the pressure contact pressure for contacting the heating endless belt with the intermediate transfer medium. You can

If the heating endless belt is a metal belt or a metal belt whose surface is coated with a silicone resin or a fluororesin, or a resin belt made of a silicone resin or a fluororesin, a multicolor toner image is attached to the heating endless belt. And improves the image quality of the resulting color image.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of an electrophotographic printer to which an electrophotographic printing method of the present invention is applied.

FIG. 2 is a front view showing a transfer / fixing unit used in the electrophotographic printer of FIG. 1 together with a photosensitive drum and an intermediate transfer drum.

FIG. 3 is a front view showing a configuration of a pressing mechanism of a transfer / transfer means.

FIG. 4 is a front view showing a state in which the heating mechanism releases the heating endless belt against the intermediate transfer drum in the pressing mechanism of FIG. 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electrophotographic printer 5 Guide rail 10 Photosensitive means 11 Photosensitive drum (electrostatic latent image carrier) 12 Static eliminator 13 Charger 20 Developing means 21-24 Developing unit 25 Driving means 25a Ball screw 25b Driving motor 26 Toner cartridge 210 Housing 211 Liquid Tank 30 Intermediate transfer means 31 Intermediate transfer drum (intermediate transfer medium) 32 Charger 40 Cleaning means 41 Cartridge 42 Cleaning roller 43 Collection roller 50 Transfer means (transfer / fixing means) 51, 52 Heat roller 53 Tension roller 54 Heated endless belt 60 Auxiliary squeeze roller 70 Transport device 71 Main transport path 71a Reversible roller 71b Transport roller 71c Guide plate 72 Bypass transport path 72a Switching claw 72b Transport roller 72c Guide member 80 Exposure means P Transfer paper (recording) Medium) D ₁ , D ₂ drawer

Claims (7)

[Claims] 1. An electrostatic latent image carrier, exposure means for sequentially forming a plurality of electrostatic latent images on the electrostatic latent image carrier based on color-separated print information, and the electrostatic latent image carrier. Developing means for sequentially developing the electrostatic latent image formed on the electrostatic latent image with a toner having a hue corresponding to the color-separated print information to form a toner image; An intermediate transfer medium on which a color toner image is formed, a conveying means for conveying a recording medium on which the multicolor toner image formed on the intermediate transfer medium is transferred and fixed, and the intermediate transfer medium via the recording medium. An electrophotographic printer provided with a transfer / fixing unit that is pressed against and heat-fixes the multicolor toner image on the recording medium, wherein the transfer / fixing unit sandwiches the recording medium with the intermediate transfer medium. And then transport the Electrophotographic printer being characterized in that a toner image by a heating endless belt at the same time fixing the transferred onto the recording medium. 2. The heating endless belt is wound around at least two rollers, one on the upstream side in the conveying direction of the recording medium and the other on the downstream side, and at least one of the two rollers is wound around the heating endless belt. The electrophotographic printer of claim 1, wherein the book is a heat roller. 3. The pressure contact pressure of the at least two rollers for pressing the heating endless belt against the intermediate transfer medium, wherein the pressure contact pressure of a roller arranged on the downstream side in the conveyance direction of the recording medium is on the upstream side. The electrophotographic printer according to claim 2, wherein the pressure is set higher than the contact pressure of the rollers arranged. 4. The electrophotographic printer according to claim 2, wherein the at least two rollers have at least a roller arranged on the downstream side in the transport direction of the recording medium covered with an elastic member. 5. The electrophotographic printer according to claim 1, wherein the heating endless belt is a metal belt, a metal belt having a surface coated with a silicone resin or a fluororesin, or a resin belt made of a silicone resin or a fluororesin. . 6. An exposure step of sequentially forming a plurality of electrostatic latent images based on color-separated print information on an electrostatic latent image carrier, the electrostatic latent image formed on the electrostatic latent image carrier. Developing step with toner having a hue corresponding to the color-separated print information to form a toner image. The toner images developed in the developing step are sequentially transferred onto an intermediate transfer medium to form a multicolor toner image. An electrophotographic printing method comprising a transfer / fixing step in which the multicolor toner image formed in the intermediate transfer step is heated and fixed while being pressed against a recording medium, wherein the transfer / fixing step comprises: An electrophotographic printing method characterized in that a multicolor toner image is transferred onto a recording medium and fixed at the same time. 7. The transfer / fixing step heat-fixes the multicolor toner image on the downstream side in the transport direction of the recording medium while pressing the multicolor toner image onto the recording medium at a pressure contact pressure not lower than the upstream side. Electrophotographic printing method.