JPH04294376A - Image printing device - Google Patents

Abstract

PURPOSE:To automatically fix a color toner image on a transparent printing sheet on a condition that it is suitable for projection without sacrificing the stable fixing characteristic of the toner image on plain paper. CONSTITUTION:An image color detection means for detecting whether the toner image is the color toner image and a sheet kind detection means for detecting whether a printing sheet is a transparent sheet are provided in a control means, and a carrying path switching means is controlled so that the printing sheet which passes a fixing means may be fed to a printing sheet recirculating feeding means when the toner image is the color toner image and the printing sheet is the transparent sheet, and the fixing means is controlled so that a rotating and driving speed for a thermal fixing roller pair at the time of fixing the image again may be set lower than that at the first time of fixing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image printing apparatus, and more particularly to an image printing apparatus capable of printing a color image for projection onto a transparent plastic printing sheet such as an OHP sheet using color toner.

0002

2. Description of the Related Art An image printing device that prints an image on a print sheet using an electrophotographic process exposes the outer peripheral surface of a uniformly charged photosensitive drum to image light to form an electrostatic latent image.
The electrostatic latent image is developed to form a toner image, the toner image is transferred to a print sheet, and the toner image is fixed on the print sheet and discharged. If you print on a white printing sheet using black toner, you can print a black and white image, if you print using color toner, you can print a color image, and if you print using multiple color toners, you can print a black and white image. Multicolor images can be printed by performing the electrophotographic process multiple times.

[0003] Also, double-sided printing can be achieved by reversing the printed sheet with printing on its surface and performing the electrophotographic process again.

The problem with such an image printing device is that when printing a color image for projection onto a transparent plastic printing sheet such as an OHP sheet, it is difficult to obtain a printed image that can project a clear color image. It is.

One of the reasons for this is that due to insufficient fixing, particulate toner remains inside the toner layer and reflects light diffusely, resulting in a decrease in light transmittance. In such a fixed state, although the color image on the print sheet appears clear, the projected image becomes dark.

In order to completely melt the toner particles during fixing, there are methods of increasing the fixing temperature of the fixing device or slowing down the fixing speed, but the conditions for fixing the toner image (toner particles) on plain paper and the plastic The fixing conditions for the toner image (toner particles) on the plastic printing sheet are different, and if the fixing conditions are set so that the color toner image is optimally fixed on the plastic printing sheet, it may become overheated and cause hot offset. This increases the amount of dirt on the heat fixing roller caused by the heat fixing process, which causes a problem that the period during which stable fixing characteristics can be maintained (the life of the fixing device) becomes shorter.

In order to solve this problem, a method has been proposed in which the process of fixing the toner image on the print sheet is repeated multiple times to increase the melting rate of the toner particles. It is disclosed in 63-296083 and JP-A-1-193884.

[0008]

[Problems to be Solved by the Invention] This type of image printing device is mainly used for single-sided printing or double-sided printing on an opaque printing sheet with a white background, such as plain paper, and for projection onto a transparent printing sheet. Printing of color images is an ancillary use. Therefore, in the image printing apparatus disclosed in Japanese Patent Application Laid-Open No. 63-296083, fixing conditions are set so that toner image fixation on plain paper is optimal, and when printing an image on a transparent printing sheet, Although the fixing process was repeated several times, the color toner could not be sufficiently melted and could not be fixed in a manner that would allow a clear color image to be projected. Also, JP-A-1-19
The image printing apparatus disclosed in Japanese Patent No. 3884 is equipped with a control means for switching the electrophotographic process execution means to a re-fixing mode and re-fixing when printing an image on a transparent print sheet. This required manual operation, which was troublesome.

[0009] Therefore, an object of the present invention is to provide a switching method that allows a color toner image to be fixed on a transparent printing sheet in an optimal state for projection without sacrificing the stable fixing characteristics of the fixing device. The idea is to make it easy to do.

0010

[Means for Solving the Problems] In order to achieve this object, the present invention provides means for forming a black toner image and a color toner image on the surface of a photoreceptor, and a printing sheet for conveying a printing sheet to which the toner images are to be transferred. A conveying means, a transfer means for transferring the toner image on the surface of the photoreceptor to the print sheet conveyed by the print sheet conveyance means, and a pair of heat fixing rollers rotationally driven by a drive device. A fixing device heats and fixes the toner image on a print sheet passing between a pair of fixing rollers, a paper ejecting device ejects the print sheet that has passed through the fixing device, and a paper ejecting device that ejects the print sheet that has passed through the fixing device. a print sheet circulation conveyance means that conveys the print sheet through a path longer than the sheet length and feeds it again to the fixing means to be re-fixed; and a print sheet that has passed through the fixing means is selectively sent to the paper discharge means or the print sheet circulation conveyance means. In the image printing apparatus, the image printing apparatus includes a conveyance path switching means for feeding the toner image, and a control means for controlling the driving device of the fixing means and the conveyance path switching means, wherein the control means includes an image color control means for detecting whether the toner image is a color toner image. A detection means and a sheet type detection means for detecting whether the printed sheet is a transparent sheet are provided, and when the toner image is a color toner image and the printed sheet is a transparent sheet, the printed sheet that has passed through the fixing means is fixed to the printed sheet. The conveyance path switching means is controlled so as to feed the heat fixing roller to the circulation conveyance means, and the rotational drive speed of the heat fixing roller during re-fixing is slower than the rotational drive speed of the heat fixing roller during the first fixing. It is characterized by controlling the means.

[0011]

[Operation] The control device automatically adjusts the conveyance path and conveyance speed of the print sheet depending on whether the print sheet is plain paper or a transparent print sheet, and whether the image to be printed is black and white or color. control to increase the fixation (melting rate) of the color toner image on the transparent printing sheet.

0012

[Embodiment] The present invention is best applied to a laser beam printer that reproduces information images created by an information processing device such as a personal computer or a word processor onto a print sheet. explain.

FIG. 2 is a longitudinal sectional side view of the laser beam printer. A charger 12, an exposure device 13, and a first developing device 1 are arranged opposite to the outer peripheral surface of a photosensitive drum 11 that is rotatably provided.
4, a second developing device 15, a transfer device 16, a cleaner 17, and an eraser 18 are provided to constitute electrophotographic process execution means. The photosensitive drum 11 is rotationally driven at a predetermined speed in the direction of the arrow by a main drive motor, which will be described later. The charger 12 is a corona discharge type charger, and the photosensitive drum 1
Corona discharge is controlled according to the rotational speed so that the outer circumferential surface of 1 is uniformly charged. The exposure device 13 deflects a laser beam emitted from a semiconductor laser diode with an electric rotating mirror 13a, and scans and exposes the outer peripheral surface of the photosensitive drum by irradiating the laser beam through an Fθ lens 13b and folding mirrors 13c and 13d. form an image. The first developing device 14 is a developing device that uses color toner as a developer,
The second developing device 15 is a developing device using black toner as a developer, and is selectively operated to develop the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum by exposure by the exposure device 13. controlled by the state.

The transfer device 16 includes a transfer belt 1 wrapped around a driving roller 16a and driven rollers 16b and 16c.
At step 6d, the printing sheet is conveyed so as to come into contact with the outer circumferential surface of the photosensitive drum, and a charge for transfer is applied by the charger 16e, thereby transferring the toner image on the outer circumferential surface of the photosensitive drum onto the printing sheet. The belt cleaner 16f removes toner attached to the transfer belt 16d. Further, the transfer belt 16d is configured to be able to move toward and away from the outer peripheral surface of the photosensitive drum, and the conveyance speed can also be adjusted in two stages.

The cleaner 17 removes toner remaining on the outer circumferential surface of the photosensitive drum after transfer, and in the process of forming toner images of multiple colors on the outer circumferential surface of the photosensitive drum, the cleaner 17 moves away from the outer circumferential surface of the photosensitive drum and stops the cleaning action. configured to do so.

Printed sheets are supplied to the electrophotographic process execution means using removable paper feed cassettes 20a and 20b.
This is configured to be performed from the manual paper feed port 21. Plain papers 22a and 22b are stored in paper feed cassettes 20a and 20b, extracted by paper feed rollers 23a and 23b, and transferred one by one to the registration roller 2 in cooperation with separation pads 24a and 24b.
Feed paper up to 5. Plastic transparent printing sheet 26
is supplied from the manual paper feed port 21, and the paper feed rollers 27a, 2
7b, it is conveyed to the registration rollers 25.

A sheet type detector 28 is provided between the registration roller 25 and the transfer device 16, and includes a light emitting element 28a and a light receiving element 28b facing each other across the printing sheet path.

The transfer device 16 sends the print sheet 22a, 22b or 26 onto which the toner image has been transferred to a fixing device 30 equipped with a pair of heat fixing rollers. The rotational speed (fixing speed) of the pair of heat fixing rollers of the fixing device 30 is configured to be adjustable in two stages.

The conveyance roller 31 conveys the print sheet 22a, 22b or 26 sent out from the fixing device 30.

The first conveyance path switching lever 32 is configured to switch the print sheets 22a, 2 sent out from the conveyance roller 31.
2b or 26 is the direction of the face-down paper ejection passage 34 that ejects the paper to the face-down paper ejection tray 33 provided on the top surface of the apparatus, or the direction of the paper ejection roller 36 that ejects the paper to the face-up paper ejection tray 35 provided on the side surface of the apparatus. switch direction.

The second conveyance path switching lever 37 is disposed between the first conveyance path switching lever 32 and the paper discharge roller 36, and is used to control the print sheet 22a conveyed from the conveyance roller 31 toward the paper discharge roller 36. , 22b or 26 is switched to the direction of the print sheet circulation conveyance path 40.

The print sheet circulation conveyance path 40 carries the sent print sheets 22a, 22b or 26 as they are.
Alternatively, the sheet is turned upside down and circulated to the registration rollers 25. The conveyance path that circulates and conveys the fed transparent print sheet 26 as it is to the registration rollers 25 includes a conveyance roller 41, a third conveyance path switching lever 42, and conveyance rollers 43a, 43b, 43c, 43d, and 43e. and has a path length longer than the length of the usable print sheet. Printed sheet 22a, 2 like plain paper
2b is turned upside down and circulated to the registration rollers 25, the conveyance path is connected to a fourth conveyance path switching lever 44 and a conveyance roller 45a arranged in a path branched from the conveyance path by the third conveyance path switching lever 42. ,45b
and an intermediate tray 46, the print sheet branched from the conveyance path is reversed in its traveling direction and returned to the conveyance path, thereby turning the circulating print sheet inside out.

The rotation of the transfer device, fixing device, and various conveyance rollers is performed by a main drive motor, which will be described later, in synchronization with the photosensitive drum.

The control device 100 executes an electrophotographic process for forming a toner image on the outer peripheral surface of the photosensitive drum 11;
Extraction and conveyance of print sheet, transfer and fixation of toner image, setting of print sheet conveyance path (operation of conveyance path switching lever and control of rotation timing and rotation direction of conveyance roller), speed control, and communication with information processing equipment described later etc.

FIG. 3 shows the configuration of the control device 100 and the information processing device 200.

The control device 100 is configured around a CPU 101, and includes a clock signal generation circuit 102, a program ROM 103, and a RAM 1 connected to the CPU 101.
04, an input port 105, an output port 106, a communication circuit 107, and a laser control circuit 114.

[0027] The CPU 101 has a program ROM1.
03 is executed in synchronization with the clock signal supplied from the clock signal generation circuit 102. The print control program sets the photosensitive drum rotation speed, print sheet conveyance speed, and fixing speed depending on whether the color of the image to be printed is black and white or color, and whether the print sheet is plain paper or a transparent sheet. , the charger control voltage is set, the developing device to be used is selected, and the print sheet conveyance path is selected.

The input port 105 mediates the input of detection signals from various sensors, and one of them is the output signal of the comparator 108 that determines the level of the output signal of the light receiving element 28b of the sheet type detector 28. input and CPU1
01.

The output port 106 is connected to the main drive motor 4.
Corona discharge necessary for uniformly charging the outer circumferential surface of the photosensitive drum 11 to a predetermined potential is generated from the charger 12 by mediating the setting of a control target speed for the main motor control circuit 109 that controls the rotation speed of the photosensitive drum 11. The control target value of the first high voltage generation circuit 110 that controls the charger 12 is set in accordance with the rotation speed of the photosensitive drum 11 so that the rotation of the electric rotating mirror 13a in the exposure device 13 is controlled. The second controller mediates the transmission of a control signal to the mirror drive circuit 111 that controls the mirror drive circuit 111, and controls the transfer device 16 so that the timing of releasing the transfer charge by the charger 16e of the transfer device 16 is synchronized with the conveyance of the print sheet.
Mediates the transmission of timing control signals that control the high voltage generation circuit 112 of
An operation drive circuit 1 that drives an electromagnetic device 48 that performs the direction setting operation of the transfer device 16, the operation of moving the transfer device 16 toward and away from the photosensitive drum 11, and the operation of switching forward and reverse rotation of the conveying rollers 45a and 45b.
Mediates the transmission of operation signals to 13.

[0030] The communication circuit 107 is connected to the CPU 101.
and a laser control circuit 114 and information processing device 20, which will be described later.
Mediates communication between 0 and 0.

The laser control circuit 114 is connected to the exposure apparatus 1.
The blinking of the laser beam emitted from the semiconductor laser diode 13e in 3 is controlled according to the dot data given from the communication circuit 107 or the command from the CPU 101, and the laser beam reflected from the electric rotating mirror 13a is placed at the scanning reference position. The signal detected by the detector 13f is transmitted to the communication circuit 107 as a horizontal synchronization signal.

The information processing device 200 is configured around a CPU 201, and processes black and white or color document data in accordance with function commands input from a keyboard 203 connected via a key control circuit 202, as well as character information and graphic information. (image information), develops the document data into dot data, stores it in the bitmap memory 204, reads out the dot data by the CRT control circuit 205, and outputs the dot data to the CRT.
It is displayed on the display 206, read out by the printer control circuit 207 in synchronization with the horizontal synchronization signal, and sent to the control device 100.

In the above configuration, the operator operates the keyboard 203 of the information processing device 200 to create document data. When printing the document data, a print command is input from the keyboard 203. The CPU 201 is
When a print command is input, one page of document data to be printed is divided into black dots and color dots, developed, and stored in the bitmap memory 204. When the expansion is completed, a print request signal is sent via the printer control circuit 207. The print request signal includes image color discrimination information for specifying the color of the information image to be printed, printing surface specification information for single-sided printing or double-sided printing, information for specifying the paper feeding method, and the like.

When the CPU 101 of the control device 100 receives the print request signal via the communication circuit 107, it checks the color and print surface of the image to be printed according to the print control program stored in the program ROM 103, and prints the image. After setting the print processing mode and setting BUSYN to low level,
The electric rotating mirror 13a and the main drive motor 47 are activated, and the charger 12 starts uniformly charging the outer peripheral surface of the photosensitive drum 11. The rotational speed of the main drive motor 47 at this time is
Optimal printing processing (conveyance) when the printing sheet is plain paper
set to speed. After preparing to execute the electrophotographic process in this way, if paper is fed from the paper feed cassette 20a (20b), the paper feed roller 23a or 23b is rotated to extract the plain paper 22a (22b). It is conveyed to the registration rollers 25.

[0035] After completing such printing preparation, the CP
U101 controls the communication circuit 107 to send out a vertical synchronization signal indicating the start of printing and a horizontal synchronization signal indicating the start of transmission of dot data.

Upon receiving the vertical synchronization signal, the CPU 201 reads out the dot data of the specified color from the bitmap memory 204 in synchronization with the horizontal synchronization signal and sends it to the control device 10.
controlling the printer control circuit 207 to transmit to 0;
Sends out dot data that constitutes the information image to be printed.

Laser control circuit 1 receiving dot data
14 controls the semiconductor laser diode 13e to blink in accordance with the received dot data, and exposes the outer peripheral surface of the photosensitive drum 11 to form an electrostatic latent image. If the electrostatic latent image corresponds to a black and white image, the second developing device 15 is activated to develop the electrostatic latent image with black toner, and if the electrostatic latent image corresponds to a color image, the first developing device 15 is activated. The developing device 14 is put into operation and the electrostatic latent image is developed with color toner.

If the information image to be printed is monochromatic, the conveyance of the print sheet 22a is restarted so that it matches the toner image, and the transfer device 16 moves the print sheet 22a so that it matches the toner image. 22a is conveyed while being in contact with the outer peripheral surface of the photosensitive drum. The transfer device 16 contacts the outer circumferential surface of the photosensitive drum while rotating the transfer belt 16d on which the printing sheet 22a is placed, and contacts the outer circumferential surface of the photosensitive drum in an area before the toner image reaches, and then transfers the printing sheet 22a to the outer circumferential surface of the photosensitive drum. It is desirable that 22a reach the contact area in conformity with the toner image. When the print sheet conveyance is restarted, the output signal of the sheet type detector 28 is checked to confirm whether the print sheet is transparent (transparent print sheet made of plastic) or opaque (plain paper). At the same time, the charger 16e is operated to transfer the toner image on the outer peripheral surface of the photosensitive drum onto the print sheet 22a, and the print sheet 22a with the toner image transferred thereon is sent toward the fixing device 30.

When the information image to be printed is in multiple colors, the transfer device 16 and cleaner 17 are kept separated from the outer peripheral surface of the photosensitive drum, and the photosensitive drum 11 on which the black toner image has been formed is further rotated. Then, the toner image forming area is exposed again by the exposure device 13 to form an electrostatic latent image corresponding to another color. This electrostatic latent image is developed by the first developing device 14 to complete the formation of a plurality of color toner images on the outer peripheral surface of the photosensitive drum. Thereafter, conveyance of the print sheet 22a is restarted so as to be aligned with the toner image, and the print sheet 22a is conveyed by the transfer device 16 while being brought into contact with the outer peripheral surface of the photosensitive drum so that the print sheet 22a is aligned with the toner image. At the same time, the charger 16e is operated to transfer the toner image on the outer peripheral surface of the photosensitive drum onto the print sheet 22a, and the print sheet 22a with the toner image transferred thereon is sent toward the fixing device 30.

After the toner image is transferred, a cleaner 17 is pressed against the outer peripheral surface of the photosensitive drum to remove toner remaining on the outer peripheral surface of the photosensitive drum, and an eraser 18 is turned on to erase the remaining electrostatic latent image.

The fixing device 30 heats and melts the toner particles and fixes them on the print sheet 22a while the print sheet 22a sent out from the transfer device 16 is conveyed while being held between a pair of heat fixing rollers. Printed sheet 22a fed out after fixing
In single-sided printing, after passing through the conveyance rollers 31, the conveyance path switching lever 32 selects the direction of the face-down paper discharge path 34 to discharge the paper to the face-down paper discharge tray 33 or the direction of the paper discharge to the face-up paper discharge tray 35. It is sent out in the direction of roller 36.

FIG. 4 shows the print sheet conveyance path when printing such image information.

In the case of double-sided printing, the conveyance path switching lever 32 is set so as to guide the printed sheet 22a with an image printed on the surface as described above in the direction of the paper discharge roller 36, and the printed sheet is The conveyance path switching lever 37 is set so as to guide the printing sheet 22a in the direction of the print sheet circulation conveyance path 40. Then, the conveyance path switching lever 42 is set so as to guide the incoming print sheet 22a toward the conveyance roller 45a, and the print sheet 22a with the image printed on its surface is conveyed to the intermediate tray 46. In this carrying-in, the rear end of the print sheet 22a is placed on the conveyor roller 4.
5b, and then the conveying rollers 45a and 45b are reversely rotated so that the printed sheet 22a is conveyed out of the intermediate tray 46, and the conveyed printed sheet 22a is guided in the direction of the conveying roller 43a. The conveyance path switching lever 44 is set so as to. As a result, the registration rollers 25 are moved by the transport rollers 43a to 43e.
The print sheet 22a, which has been circulated until it reaches the standby state, has its front and back reversed.

Thereafter, a toner image corresponding to the image to be printed on the back side of the printing sheet 22a is formed on the outer circumferential surface of the photosensitive drum, transferred and fixed in the same manner as described above, and then discharged.

FIG. 5 shows a printing sheet conveyance path when printing such image information.

Next, switching control of fixing toner images on the plain paper 22a, 22b and the transparent plastic print sheet 26 will be explained. CPU1 for printing the image
FIG. 1 shows the control processing executed by 01.

Processing 301 is an image printing processing mode setting process, in which the image color is changed to print only a black image or print including a color image, depending on the image color distinction information included in the print request signal from the information processing device 200. Configure information C. The image color information C is set to C=0 for printing only a black image, and C=1 for printing including a color image.

Process 302 is a toner image forming process in which the outer peripheral surface of the photosensitive drum 11 is uniformly charged while rotating, dot data is received from the information processing device 200, and the outer peripheral surface of the photosensitive drum is formed according to the dot data. It is exposed to light to form an electrostatic latent image, and the electrostatic latent image is developed to form a toner image.

Process 303 is a paper feed control process in which the printing sheets 22a, 22 to which the toner images on the outer peripheral surface of the photosensitive drum are transferred are
b or 26 paper feed.

Process 304 is a sheet type detection process in which the detection signal output from the sheet type detector 28 is checked to determine whether the fed print sheet is opaque plain paper 22a or 2.
2b or the plastic transparent printing sheet 26.

In process 305, image color information is checked,
In processes 306 and 307, fixing control information X is set according to the image color information. For printing on plain paper or printing only a black image, set X=0, and for printing including a color image on a transparent print sheet, set X=1.

Process 308 is a transfer control process in which the transfer device 1
6 to convey the print sheet 22a, 22b or 26, and transfer the toner image on the outer peripheral surface of the photosensitive drum to the print sheet 2.
2a, 22b or 26.

Process 309 is a fixing process in which the passage of the print sheet 22a, 22b or 26 to which the toner image has been transferred is confirmed, and in process 310 the value of fixing control information X is checked.

Process 311 is a paper discharge control process performed when the fixing process is completed, and the process 311 is a paper discharge control process that is performed when the fixing process is completed.
Control is performed to set the conveyance path switching levers 32 and 37 so that the sheet b or 26 is conveyed in the direction of the paper discharge tray 33 or 35.

When the fixing control information X is X=1 and the fixing process is not completed, in step 312, the fixing control information
A conveyance path switching lever setting operation control process 313 is performed to circulate the print sheet 26 via the print sheet circulation conveyance path 40, and in a conveyance roller control process 314, the print sheet 26 is transferred to the conveyance rollers 41, 43a, 43b, 43c, 43d, 43
These transport rollers are controlled to be in a rotating state so that the paper is transported along the direction e.

Process 315 is a print sheet stop control process,
Control is performed to temporarily stop the conveyance of the print sheet 26 when the leading edge of the print sheet 26 has circulated to the registration rollers 25.

Process 316 is a speed switching control process, and even if the conveying speed of the print sheet 26 to be re-fed is fast, it is 50 mm/s.
A control target speed for reducing the rotation speed of the main drive motor 47 is set in the main motor control circuit 109 as follows.

Process 317 is a white print control process in which toner adheres to the outer peripheral surface of the photosensitive drum during the process of conveying the print sheet 26 stopped at the position of the registration roller 25 to the fixing device 30 again. The electrophotographic process execution means and the transfer device 1
6 is set to perform control to restart conveyance of the print sheet 26. When the electrophotographic process employs reversal development, the corona discharge of the charger 12 is weakened as the rotation speed decreases so that the charging potential on the outer peripheral surface of the photosensitive drum rotating at a low speed becomes a predetermined value. Control is performed to prevent charging, stop the exposure action of the exposure device 13, stop the development action of the developing devices 14 and 15, and stop the transfer action of the transfer device 16.

After the process 317, the process returns to the fixing process 309, but the fixing speed has also decreased in the same way as the conveying speed. Therefore, the heating time for the toner image on the print sheet 26 passing through the fixing device 30 becomes longer, and the toner can be completely melted (in a state suitable for projection).

In the next process 310, the fixing control information X=0, so in the paper discharge process 311, the paper discharge control process is executed. The setting of which of the face-down paper discharge tray 33 and the face-up paper discharge tray 35 to discharge paper to is determined by the direction setting of the conveyance path switching levers 32 and 37 that determine the conveyance direction.

FIG. 6 shows the print sheet conveyance path when printing such image information.

The relationship between fixing (melting) of a toner image on a transparent plastic printing sheet and light transmittance will now be explained. FIG. 7 shows the light transmittance of color toner images fixed by setting several fixing temperatures and varying the fixing speed.

When a fixed color toner image is projected onto a transparent printing sheet, the projected image becomes dark if the fixed state has a light transmittance of 50% or less. Incidentally, a satisfactory fixing state of a black toner image or a color toner image not used for projection depends on the light transmittance of the toner material itself, but
This corresponds to a fixed state in which a light transmittance of about 10% is obtained.

When the fixing temperature is set to 140° C. or 160° C., a satisfactory fixing state of a black toner image or a color toner image not used for projection is 40 mm/s or 80 mm/s.
can be obtained at a fixing speed of However, at this fixing temperature, it is not possible to fix a color toner image in a state suitable for projection within a practical fixing speed range.

When the fixing temperature is set at 180° C., satisfactory fixing of black toner images and color toner images not used for projection can be achieved at a fixing speed of 125 mm/s. Then, when the fixing speed is lowered and set to 50 mm/s,
A color toner image can be fixed in a state suitable for projection. Incidentally, at the same fixing speed, even if re-fixing is repeated, the light transmittance is only slightly improved, and it is not practical to repeat the fixing process until the color toner image is in a state suitable for projection.

[0066] When the fixing temperature is set to 200°C, the
Color toner images can be fixed in a state suitable for projection at a high fixing speed of m/s, but this fixing condition also has a high possibility of generating high temperature offset, and under these conditions, it is difficult to fix toner images on plain paper. Fixing an image or fixing a black toner image on a transparent print sheet is not a good idea from the viewpoint of maintaining stable fixing characteristics of the fixing device.

Considering the above characteristics, fixing of toner images on plain paper and fixing of black toner images on transparent printing sheets requires a fixing temperature of 180°C and a fixing speed of 125 mm/s.
The fixation of the color toner image on the transparent printing sheet was carried out by setting the fixing speed to 5°C while maintaining the fixing temperature of 180°C.
It is best to set it to 0 mm/s. However, the fixing speed is linked to the execution speed of the electrophotographic process that forms the toner image on the outer peripheral surface of the photosensitive drum, and changing the electrophotographic process execution speed is disadvantageous to stable toner image formation. The electrophotographic process execution speed for formation was unified at 125 mm/s, and the fixing speed was 50 mm/s.
It is preferable that the fixing step is carried out by circulating the fixed printed sheet.

In particular, an image printing device capable of double-sided printing is equipped with a print sheet circulation conveyance path for reversing the print sheet with an image printed on the front side and printing on the back side. If utilized, a print sheet circulation path for re-fixing color toner images on a transparent print sheet can be easily constructed.

[0069]

As described above, the present invention automatically fixes a color toner image on a transparent printing sheet in a state suitable for projection without sacrificing the stable fixation characteristics of the toner image on plain paper. It can be realized.

[Brief explanation of drawings]

FIG. 1 is a flowchart of an image printing control process executed by a CPU of a control device in a laser beam printer according to the present invention.

FIG. 2 is a longitudinal sectional side view of a laser beam printer according to the present invention.

FIG. 3 is an electric circuit diagram showing the configuration of a control device and an information processing device in a laser beam printer according to the present invention.

FIG. 4 is an operational explanatory diagram showing a print sheet conveyance path during single-sided printing in the laser beam printer according to the present invention.

FIG. 5 is an operation explanatory diagram showing a print sheet conveyance path during double-sided printing in the laser beam printer according to the present invention.

FIG. 6 is an operation explanatory diagram showing a print sheet conveyance path when printing a color image for projection onto a transparent print sheet in the laser beam printer according to the present invention.

FIG. 7 is a fixing characteristic curve diagram.

[Explanation of symbols]

301 Image print processing mode setting process 304 Sheet type detection process 305 Image color information check process 308 Fixing control information check process 311 Conveyance path switching lever setting operation control process 31
2 Conveyance roller control process 314 Speed switching control process

Claims (5)

[Claims] 1. Means for forming a black toner image and a color toner image on the surface of a photoreceptor, a print sheet conveyance means for conveying a print sheet to which the toner image is to be transferred, and a print sheet conveyed by the print sheet conveyance means. a transfer means for transferring the toner image on the surface of the photoreceptor onto the printing sheet; and a pair of thermal fixing rollers rotationally driven by a drive device, the toner on the printing sheet passing between the pair of thermal fixing rollers. a fixing device that heats and fixes the image; a paper ejecting device that ejects the print sheet that has passed through the fixing device; and a sheet discharging device that transports the print sheet that has passed through the fixing device through a path longer than the length of the print sheet and fixes the image again. a circulation conveyance means for feeding the print sheet into the fixing means and re-fixing it; a conveyance path switching means for selectively sending the print sheet that has passed through the fixing means to the paper discharge means or the print sheet circulation conveyance means; and a drive device for the fixing means. and a control means for controlling a conveyance path switching means, wherein the control means includes an image color detection means for detecting whether the toner image is a color toner image, and whether the printing sheet is a transparent sheet or not. a sheet type detection means for detecting the toner image, and when the toner image is a color toner image and the print sheet is a transparent sheet, the conveyance path switching means is configured to send the print sheet that has passed through the fixing means to the print sheet circulation conveyance means. and controlling the fixing means so that the rotational driving speed of the thermal fixing roller during re-fixing is slower than the rotational driving speed of the thermal fixing roller during initial fixing. Printing device. 2. The image printing apparatus according to claim 1, wherein the rotational driving speed of the heat fixing roller during the refixing is set to 50 mm/s or less. 3. Means for forming a black toner image and a color toner image on the surface of the photoconductor, a print sheet conveyance means for conveying a print sheet to which the toner image is to be transferred, and a print sheet conveyed by the print sheet conveyance means. a transfer means for transferring the toner image on the surface of the photoreceptor onto the printing sheet; and a pair of thermal fixing rollers rotationally driven by a drive device, the toner on the printing sheet passing between the pair of thermal fixing rollers. a fixing device that heats and fixes the image; a paper ejecting device that ejects the print sheet that has passed through the fixing device; and a sheet discharging device that transports the print sheet that has passed through the fixing device through a path longer than the length of the print sheet and performs the printing again. A print sheet circulation conveyance means that sends the print sheet to the sheet conveyance means, and a print sheet provided in the middle of the paper conveyance path of the print sheet circulation conveyance means, which branches the print sheet conveyed through the paper conveyance path, reverses it inside out, and returns it to the paper conveyance path. a paper reversing means for returning, a conveyance path switching means for selectively feeding the print sheet that has passed through the fixing means to the paper discharge means or the print sheet circulation conveyance means, a driving device for the fixing means, a conveyance path switching means, and a paper reversal unit. In the image printing apparatus, the control means includes an image color detection means for detecting whether the toner image is a color toner image, and an image color detection means for detecting whether the printing sheet is a transparent sheet. a sheet type detection means is provided, and when the toner image is a color toner image and the print sheet is a transparent sheet, the conveyance path switching means is controlled so as to send the print sheet that has passed through the fixing means to the print sheet circulation conveyance means; The paper reversing means is controlled to be inactive, and the fixing means is controlled so that the rotational driving speed of the thermal fixing roller during re-fixing is slower than the rotational driving speed of the thermal fixing roller during initial fixing. An image printing device characterized by: 4. The image printing apparatus according to claim 3, wherein the rotational driving speed of the heat fixing roller during the refixing is set to 50 mm/s or less. 5. The image printing apparatus according to claim 1, wherein the color toner image is formed of polyester toner having a softening point of 130 degrees Celsius or less.