JPH07104543A - Color image forming device - Google Patents

Abstract

PURPOSE:To provide a color image forming device capable of preventing a temperature rising caused by overshooting of a fixing device, obtaining an image of high image quality free from gloss irregularities and prolonging the service life of the fixing device. CONSTITUTION:In accordance with the kinds of transfer material, that is, an ordinary transfer material or an OHT transfer material, the device carries out image formation by changing ordinary-rotation mode for carrying out fixing immediately after the transfer of a toner image in the final color or decelerated- rotation mode for making the driving speed of a transfer body 2 lower than the driving speed of the fixing device 5 after the transfer of the toner image in the final color, reducing the driving speed of the fixing device 5 to a speed almost equal to the driving speed of the transfer body, and, further, reducing the driving speed of the fixing device 5 to a speed almost equal to the driving speed of the decelerated transfer body 2 after a prescribed time has elapsed, then carrying out fixing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus,
In particular, the present invention relates to a color image forming apparatus that obtains a color image by superposing and transferring toner images of respective colors formed by using an electrophotographic method on the same transfer material.

[0002]

2. Description of the Related Art Conventionally, an electrostatic recording method using electrophotography has been widely used in color image forming apparatuses. As shown in FIG. 7, these image forming apparatuses include, for example, developing units 1Y, 1M containing color developers such as yellow (Y), magenta (M), cyan (C), and black (B).
A developing device 1 having 1C and 1B for developing an electrostatic latent image corresponding to an image of each color formed on the image carrier 3 uniformly charged by the primary charging roller 14, and the supplied transfer material 17 Is held by a transfer material holding means such as electrostatic adsorption or a gripper 16, and is generated from an exposure device having a transfer body 2 for transferring the toner image on the image carrier 3 onto the transfer material 17, and a light source 12 such as a laser. An image bearing member 3 that bears both the electrostatic latent image written by the optical signal 13 and the toner image obtained by developing the electrostatic latent image by the developing device 1, and the image bearing by transferring the toner image onto the transfer material 17. A color image obtained by superposing and transferring the toner images of the respective colors onto the cleaner 4 for cleaning the toner remaining on the body 3 and the transfer material 17 is transferred.
It is composed of a fixing device 5 for fixing to.

As shown in FIG. 8, the transfer body 2 in the above apparatus has a hollow drum casing 2a with a side surface cut out only in the transfer area, and a polyethylene terephthalate (P) is formed in the cutout portion.
ET), polyvinylidene fluoride (PVdF), fluorinated ethylene propylene copolymer (FEP), and other flexible sheets 2b are stretched. Also, FIG.
As shown in FIG. 2, the inside and outside of the transfer body 2 are attracting rollers 6 of means for electrostatically attracting the transfer material 17 to the flexible sheet 2b along the rotation direction thereof, and facing the attracting rollers 6. Adsorption charger 7 for charging the flexible sheet 2b by means of transfer, a transfer charger 8 for transferring the toner image formed on the image carrier 3 onto the transfer material 17, and transfer electrostatically attracted to the flexible sheet 2b. In order to initialize the separation charger 9 that separates the material 17, the separation claw 10 that assists the separation and guides the separated transfer material 17 to the transfer material conveying unit 15 to the fixing device 5, and the flexible sheet 2b. A sheet static eliminator 11 for erasing static electricity is arranged.

The color image forming process of the apparatus equipped with the above equipment will be described. First, the exposure 13 based on the image signal of the first color from the exposure apparatus having the light source 12.
By this, an electrostatic latent image of the first color is formed on the image carrier 3.
The electrostatic latent image is developed by a developing device 1Y containing a first color developer such as a yellow developer, and is visualized as a yellow toner image. In parallel with this step, the transfer body 2 holds the front end of the transfer material 17 supplied thereto by the gripper 16 or the like of the transfer material holding means, and then rotates the transfer material 17 onto the surface of the transfer body 2. Wrap it around. At this time, the transfer material 17 is sandwiched between the suction roller 6 and the flexible sheet 2b on the surface of the transfer body 2, and at the same time, electrostatically held on the surface of the flexible sheet 2b by charging by the suction charger 7. To be done. Subsequently, the transfer material 17 is conveyed to the image transfer portion Ptr located at a position facing the image carrier 3 as the transfer material 2 rotates, and the toner image formed on the image carrier 3 is transferred onto the transfer material 17. The image is transferred by being charged by a transfer charger 8 arranged so as to face the image carrier 3.

After that, the residual toner remaining on the image carrier 3 is removed by the cleaner 4, and an electrostatic latent image based on the image signal of the second color is formed again by the exposure device. The image is developed as a magenta toner image by developing with a developing device 1M containing a magenta developer of a color, for example. The toner image of the second color is similarly transferred onto the same transfer material 17 by the transfer charger 8 from the top of the toner image of the first color previously transferred.

The above steps are similarly performed for the third and fourth colors, for example, cyan and black, and the cyan toner image and the black toner image obtained by the development by the developing devices 1C and 1B are similarly performed. And transferred onto the transfer material 17 in an overlapping manner.
A color image can be obtained by superimposing color toner images and transferring them in multiple.

The transfer material 17 on which the toner images of four colors have been transferred as described above is rotated by the rotation of the transfer body 2, and a pair of separation chargers 9 are arranged so as to face the inside and the outside of the transfer body 2. The transfer device 17 is conveyed to that position, the electrostatic attraction force between the transfer material 17 and the flexible sheet 2b is removed by the separation charger 9, and the transfer material 2 is separated from the transfer body 2 by the separation claw 10. The separated transfer material 17 is guided to the fixing device 5 by the transfer material conveying means 15, and the toner image transferred onto the transfer material 17 is fixed by the fixing device 5. On the other hand, the transfer body 2 after the transfer material 17 is separated is electrically neutralized by discharging electricity by the sheet discharging charger 11.

The case where a color image is formed by the multiple transfer system by using the transfer body 2 having a cutout structure as a typical example of the transfer body has been described above. However, as shown in FIG. The flexible sheet 2 having the drum housing 2a ′ as described above
By the method of applying a bias voltage to the solid drum type transfer body 2 ′ having a structure covered with b, the same multi-transfer as the transfer body 2 having the cutout structure can be performed. In this solid drum type transfer body 2 ′, since the inside can be simplified as compared with the transfer body 2 having the cutout structure, the cost can be reduced and the flexible sheet 2b can be provided from the inside to the drum housing 2a ′.
Since it is supported as a whole, there is also an advantage that deformation and damage of the sheet 2b, which is a problem of the transfer body 2 having the cutout structure, can be reduced. Therefore, at present, a color image forming apparatus using the conductive solid drum type transfer body 2'having no cutout portion is drawing attention. The color image forming method in the apparatus using the solid drum type transfer body 2'is basically similar to the apparatus using the transfer body 2 having the cutout structure.

A color image forming method in the color image forming apparatus using the solid drum type transfer member 2'will be described below with reference to FIG. 10, members having the same functions as those in FIG. 7 are designated by the same reference numerals, and detailed description thereof will be omitted.

First, the transfer material 17 supplied to the solid drum type transfer body 2'is sandwiched between the transfer body 2'and the suction roller 6 by the suction roller 6 which comes in contact with and separates from the transfer body 2 '. At the same time, the transfer body 2 ′ sandwiched with the transfer material 17 and the suction roller 6 were connected to the drum housing 2 a ′ of the transfer body 2 ′ so that a potential difference required for adsorbing the transfer material 17 was generated. A predetermined attraction and transfer bias is applied from a transfer bias power source (not shown) and an attraction bias power source (not shown) connected to the attraction roller 6. The transfer material 17 is electrostatically adsorbed and held on the transfer body 2 ′ by the charges induced by the application of this bias.

Then, the transfer material 17 held on the transfer body 2 '.
Is conveyed to the image transfer portion Ptr by the rotation of the transfer body 2 ′, and the toner image of the first color formed on the image carrier 3 is transferred. Next, when the toner image of the second color is transferred, the bias voltage value of the above-mentioned transfer is changed, and the surface of the transfer material 17 on the transfer body 2 ′ lowered by transferring the toner image of the first color. The electric potential is corrected to be optimum for the transfer of the second color.

While the correction of the surface potential is also performed at the time of transferring the toner images of the third and fourth colors, the transfer member 2 '
The third sequentially formed on the image carrier 3 on the upper transfer material 17.
A color image is obtained on the transfer material 17 by superposing and transferring the toner images of the colors and the fourth colors. The transfer material 17 that has undergone such a multiple transfer process is destaticized by the separation charging device 9 to remove the electrostatic attraction force between the transfer material 17 and the transfer material 2 ′, and the transfer material 2 ′ via the separation claw 10. Separated from. Then, the transfer material 17 on which the toner images of four colors have been transferred is sent to the fixing device 5 by the conveying means 15, and the image is fixed there to be a permanent color image.

The transfer step has been described above with respect to the image forming method in the color image forming apparatus using the solid drum type transfer body 2 '. The developing step is the color image using the transfer body 2 having the cutout structure described above. It is the same as in the forming device.

[0014]

The transfer material 17 used in the color image forming apparatus described above is usually plain paper, but a special transfer material such as OHT (overhead transparency) is also used. To be done. In that case, in the fixing device 5 of the color image forming apparatus, since the toner of each color is melted to develop a color, the heat capacity of the transfer material 17 greatly affects the image quality after fixing. Particularly, the heat capacities of paper and special transfer material are significantly different.
When 7 is an OHT, the heat capacity is several times larger, and in order to obtain the transparency that can be used as an OHT, the amount of heat required is several times that of paper of the same thickness. Therefore, the transfer material 17 is
In the case of a special transfer material such as T, in the color image forming apparatus as described above, the transportation speed of the special transfer material 17 to the fixing device 5 by the transportation device 15 and the fixing speed of the fixing device 5 (specifically, The rotation time of the fixing roller and the like of the fixing device 5) is slowed down to lengthen the fixing time of the special transfer material 17 to obtain the amount of heat required for fixing.

However, in the above method, the special transfer material 17 separated from the transfer body 2'must be decelerated on the conveying means 15, and at least L1 of the conveying means 15 is used in the color image forming apparatus. It must be longer than the longest length L _{OHT of the} longest special transfer material 17. For this reason, this method has a drawback that a large space is required for the conveying means 15 and the color image forming apparatus becomes large. In addition, even when the transfer material is separated, the special transfer material 17 has a drawback that charge removal is apt to be insufficient due to its physical properties, resulting in image disturbance, that is, so-called scattering.

In order to solve this, a method of controlling the temperature of the fixing device 5 at a temperature at which the special transfer material 17 is appropriately fixed by making the conveying means 15 shorter than the above conditions, or a special transfer material is always used. A method of raising the fixing temperature only when the paper 17 is passed is used. When these methods are used, the fixing device 5
The temperature of the fixing roller 20 of the fixing device 5 becomes high.
For example, there is a drawback that the silicone rubber or the like constituting the above-mentioned components is easily deteriorated and the life of the fixing device 5 is significantly shortened.

There is also a method in which the image forming time of the above-mentioned color image forming apparatus, that is, the entire process speed is decelerated only to the speed at which the special transfer material 17 is appropriately fixed. In the case of the method, the throughput from sheet feeding to sheet discharging is slowed down, and the signal for writing the electrostatic latent image on the image carrier 3 and the timing of writing must be changed according to the process speed. Has the drawback of being complicated and expensive.

As a method for solving the drawbacks of these conventional methods, the present inventors have filed Japanese Patent Application No. 4-1124.
As shown by 31, the drive speed of at least the transfer member and the fixing device is variable, and at least when the special transfer material such as OHT is used, the transfer member and the fixing device are decelerated after the toner image transfer is completed, and the fixing is performed in the decelerated state A method has been proposed.

According to this method, when the transfer material is the special transfer material, the transfer body and the fixing device are driven after the transfer of the toner image of the final color onto the special transfer material is completed. The speed is reduced to a speed at which the special transfer material can be properly fixed by the fixing device, and the special transfer material can be separated from the transfer body and directly inserted into the fixing device under the decelerated state. Therefore, since it is not necessary to decelerate the transfer material by the transfer material transfer means to transfer the transfer material to the fixing device, the transfer material transfer means can be omitted, and therefore the color image forming apparatus can be made compact and inexpensive.

Further, since the method of separating the special transfer material after decelerating the transfer body is used, the special transfer material can be sufficiently discharged, and the scattering of the image at the time of separation which is likely to occur on the special transfer material can be reduced. You can

Furthermore, a charging means such as a charging device for electrostatically attracting the color image on the transfer material onto the transfer material can be provided. According to this, when the driving speed of the transfer body and the fixing device is decelerated. The color image on the transfer material has many advantages such as easy prevention of image disturbance that may occur due to reverse transfer on the image carrier.

However, subsequent studies by the inventors of the present application have revealed that the following problems exist.

That is, after the transfer of the final color is completed, it is necessary to further rotate the transfer body once and then separate the transfer material, while the decelerated rotation is performed before the separation, preferably immediately after the transfer of the final color. However, since it is necessary from the viewpoint of preventing image disturbance, the temperature control of the fixing device is also performed in the decelerated rotation state, and as a result, there is a problem in that the temperature of the fixing device increases due to overshoot. The reason for this will be described in detail below.

FIG. 11 shows an example of the structure of the fixing device 5.
The fixing roller 20 has a single-layer or multi-layer release layer 25 made of silicone rubber, fluororubber or the like on the surface of a metal core metal 24 such as aluminum. A heater 23 is provided inside, and a constant temperature is maintained by appropriately turning on the heater 23 while monitoring the surface temperature with the temperature detecting element 22. The transfer material 17 is heated and pressure-fixed at the contact portion (nip portion) between the fixing roller 20 and the pressure roller 21. Here, the pressure roller 21 has the elastic layer 27 on the core metal 26, and the fixing roller 20 is deprived of heat at the contact portion by the heat capacity of the pressure roller 21.

In the case of fixing a color developer, a fixing roller 20 is provided with a coating roller 28 or a coating blade 30 for improving the releasability, and silicone oil 29 is applied to the surface thereof.
It is common to apply the above materials and the like. Further, a cleaning member 31 such as a cleaner web made of a non-woven fabric or the like is often used to remove stains such as toner, oil, and paper dust attached to the surface of the fixing roller 20.

As described above, when various contact members are used, heat is easily taken from the surface of the fixing roller 20. Therefore, as the fixing roller 20 rotates at a higher speed, the temperature gradient generated between the inside of the cored bar 24 and the surface of the release layer 25 increases. In other words, it was found that when the rotation speed of the fixing roller 20 was changed to a slower speed on the way, the amount of heat taken from the surface was decreased, and an overshoot as shown in FIG. 12 occurred temporarily. The occurrence of such overshoot has the following disadvantages. (1) Fixing roller 20 heated by overshoot
When the image is fixed on the surface of, the image has a strong toner gloss. On the other hand, at the time of overshoot, the thermosensitive element 2
Since the detected temperature of 2 also becomes high and the heater 23 is turned off, the temperature of the fixing roller 2 that has once risen as the transfer material 17 is fixed.
The surface of No. 0 is rapidly cooled, and as a result, the image of the transfer material 17 has a large glossiness at the front end and a weak gloss at the rear end and has a large gloss unevenness. Moreover, the high gloss tends to cause offset at the tip glossy portion. (2) When the overshoot is large, the release layer 25 on the surface of the fixing roller 20 when repeated durable printing is performed.
Deteriorates due to heat.

Therefore, an object of the present invention is to provide a color image forming apparatus capable of preventing a temperature rise due to overshoot of a fixing device.

[0028]

The above object can be achieved by a color image forming apparatus according to the present invention. In summary, the present invention relates to a transfer body that holds a transfer material and sequentially transfers toner images of a plurality of colors formed on an image carrier onto the transfer material, and a transfer body for each color. A color image obtained by the transfer of the toner image on the transfer material by heating and fixing the color image on the transfer material,
(I) a normal rotation mode in which the transfer material is immediately separated from the transfer member after the transfer of the toner image of the final color of the toner image is completed, and the fixing means fixes the toner image; After the transfer of the toner image of the final color among them, first, the linear velocity of the drive of the transfer member is decelerated so as to be lower than the linear velocity of the drive of the fixing unit, and after a predetermined time elapses, the fixing unit And a deceleration rotation mode in which the driving linear velocity is decelerated to a velocity substantially equal to the linear velocity of the driving of the transfer body after deceleration, and the transfer material separated from the transfer body is fixed by the fixing unit in the decelerated state, In the color image forming apparatus, the modes (i) and (ii) can be switched according to the type of the transfer material or the color type of the toner image to be printed.

It is preferable that the target value for adjusting the heating temperature by the fixing unit can be switched according to the type of the transfer material or the color of the toner image to be printed.

Further, preferably, a sensor for detecting the type of the transfer material is provided.

Further, it is preferable to complete the deceleration of the driving speed of the transfer member within the time when the portion where the transfer material is not held and the image bearing member face each other.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A color image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. The same members as those of the conventional image forming apparatus described with reference to FIG. 7 are designated by the same reference numerals, and detailed description thereof will be omitted.

Embodiment 1 A first embodiment of the color image forming apparatus according to the present invention will be described with reference to FIGS.

In the color image forming apparatus shown in FIG. 1, the distance L2 between the transfer material separating position P _sep of the transfer body 2 having a notch structure provided _therein and the entrance of the fixing device 5 is as shown in FIG.
Unlike the conventional image forming apparatus, the length L _{OHT of the} longest special transfer material 17 that can be used in this apparatus is set shorter. Further, in this apparatus, a driving device 41 for driving the fixing roller 20, a transfer drum 2, and photosensitive drums 3 and 1
A drive device 42 for driving the next charging roller 14 is attached.

The color image forming process in this embodiment will be described below. The OHT (overhead transparency) of the transfer material 17 is applied to the color image forming apparatus of the present invention.
When a special transfer material such as the above is used, the special transfer material 17 is first conveyed to the transfer body 2 by a conveying means (not shown), and is held on the transfer body 2 by a holding means such as a gripper 16 as in the conventional case. The toner image of the first color is transferred during the first rotation of the transfer body 2 (therefore also during the first rotation of the transfer material 17. The same applies to the second and subsequent rotations of the transfer body 2). It 2nd rotation, 3
Toner images of different colors are transferred on each rotation.
In the 4th rotation, which is the final color transfer process,
The transfer material 17 is not separated from the transfer body 2 until the entire fourth color toner image is transferred onto the special transfer material 17.

At the time when the entire toner image of the fourth color has been transferred, the driving speed which is the rotation speed of the transfer body 2 (therefore, the rotation speed of the special transfer material 17) and subsequently the fixing device 5
The drive speed, which is the paper-passing speed, is sequentially reduced from the speed during normal image formation to the speed at which the special transfer material 17 slower than this is properly fixed by the fixing device in accordance with the sequence described later.

After the deceleration process is completed, the special transfer material 1
7 is separated by the transfer separation unit P _sep and carried into the fixing device 5 as in the conventional case. At this time, according to the present invention, the fixing device 5 matches the drive speed of the transfer body 2 as described above. Since the speed is reduced to the above speed, it is not necessary to provide a conveying means and reduce the speed of the transfer material 17 on the conveying means as in the conventional case. Therefore, the device can be downsized.

For switching the special transfer material 17 to the image forming process, it is desirable to provide a switch for selecting the image forming process, but as shown in FIG. 2, the transfer path of the transfer material 17 to the transfer body 2 is provided. Transfer material 17 on top of the optical or mechanical
If a sensor 18 for determining the type of the transfer material is provided, and a processing unit for determining the type of the transfer material 17 based on a detection signal from the sensor 18 is the special transfer material or the normal transfer material, the operation is performed. Is more preferable than the above-mentioned method because it simplifies.

Next, a method for preventing thermal overshoot of the fixing device 5 will be described with reference to the timing chart of FIG.

First, when a normal transfer material is passed, the transfer drum 2, the photosensitive drum 3, the fixing roller 20, and the primary charging roller 14 are turned on by the driving devices 41 and 42 shown in FIG. To do. Then, after sequentially transferring the first to fourth colors, a separation step is performed, and after the transfer material has finished fixing and is discharged out of the apparatus, the rotation of the transfer drum 2 and the fixing roller 20 is turned off.

Next, a case where a special transfer material such as OHT is passed will be described. In this case as well, the transfer process up to the fourth color is similar to the case of plain paper, but after the transfer of the fourth color is completed, the driving device 42 decelerates the transfer drum 2 and the photosensitive drum 3. From the viewpoint of avoiding the image shift between the photosensitive drum 3 and the transfer material due to the shock at the time of deceleration, immediately after the completion of the transfer of the fourth color, the transfer material 17 is not interposed between the photosensitive drum 3 and the transfer roller 2. It is desirable to finish the deceleration immediately. Then, when the transfer drum 2 is rotated at a reduced speed, in order to prevent the toner image on the transfer material 17 from being retransferred to the photosensitive drum 3 when coming into contact with the photosensitive drum 3, the transfer bias is equal to or larger than the transfer bias at the fourth rotation. A retransfer prevention bias is applied. Next, after the transfer material 17 is separated from the transfer drum 2 by the separating claw 10, the driving device 41 drives the fixing roller 2
Decelerate and rotate 0.

By decelerating the speed of the fixing roller 20 just before the fixing is actually performed (strictly, with a slight margin as described later), the surface temperature of the fixing roller 20 is reduced. It can prevent overshoot. In contrast to the overshoot mechanism in which the temperature gradient between the inner surface of the fixing roller 20 and the surface of the fixing roller 20 becomes small due to a decrease in the degree of heat of the surface of the fixing roller 20 being taken away by surrounding members due to deceleration, the present invention By passing the transfer material 17 immediately after deceleration like
Heat is taken from the surface of the fixing roller 20, and as a result, overshoot can be prevented. In the above example, when the experiment was performed at a speed that is approximately 1/2 of the normal speed (= full speed) as the deceleration speed, good results were obtained and uneven glossiness may occur on the image as shown in FIG. There wasn't.

As a deceleration timing of the fixing roller 20, a timer may be used with the clock of the main body as a reference, and an on / off signal of the separation claw 10 or a signal of a separation sensor (not shown) near the separation claw. May be used as a reference.

It is needless to say that the fixing roller 20 may be driven by another driving source without using an independent driving source and may be turned on / off by a spring clutch or the like.

The timing of decelerating the fixing roller 20 is preferably immediately before the transfer material 17 reaches the fixing roller 20, but the fixing roller 20 is stably decelerated, and the fixing roller 20 is decelerated. It is desirable to switch to deceleration rotation at least one rotation earlier than when the transfer material 17 reaches the fixing roller 20 in consideration of smoothing the unevenness of oil application on the surface.

In this embodiment, the transfer member is the transfer member 2 having a typical notch structure, but the solid drum described in the prior art section with reference to FIGS. 9 and 10. It goes without saying that the present invention may be applied to the type of transfer body 2 '.

Embodiment 2 Next, a second embodiment of the color image forming apparatus according to the present invention will be described with reference to FIGS.

In the above-described first embodiment, the method of preventing the overshoot of the fixing roller 20 by delaying the deceleration timing of the fixing roller 20 relative to the transfer drum 2 has been described. At this time, the thermistor 22 and the heater are used. You may change the target value of the temperature control performed by 23. FIG. 5 is an overall configuration diagram of a color image forming apparatus showing this example.

In FIG. 5, the color image forming apparatus includes a microcomputer 43, a driver circuit 44 for the driving devices 41 and 42, and a halogen heater 2 for heating the fixing roller 20.
The driver circuit 45 of No. 3 and the thermistor 22 for measuring the surface temperature of the fixing roller 20 are provided. Then, according to the detection result of the transfer material detecting unit 18, the driving devices 41, 4
The control of No. 2 and switching of the temperature control target value of the fixing roller 20 are performed.

Specifically, when the special paper is passed through the timing chart of FIG. 3, the temperature is adjusted so that the temperature detected by the thermistor 22 becomes the target T ₁ = 175 ° C. during the first to fourth rotations. After that, the temperature control target value is once switched to a value of T ₂ <T ₁ . Immediately before the transfer material reaches the fixing roller 20, the temperature control target value is switched from T ₂ to T ₁ again. Actually, T ₂ = 170 ° C. while T ₁ = 175 ° C.
As an experiment, At this time, the timing for lowering the temperature control target value T ₁ → T ₂ is set to be traced back to the fixing roller deceleration timing for t ₁ seconds, and good results were obtained at t ₁ = 1 to 3 seconds (Fig. 6). Although the surface temperature of the fixing roller 20 sharply drops due to the passage of paper, a good fixing state can be maintained by setting the temperature control target value T ₂ → T ₁ when the fixing is started.

Embodiment 3 In the first and second embodiments, the case where color printing of four colors is mainly performed has been described. However, when printing only the first color, the fixing roller 20 is rotated at a decelerating speed. In some cases, it is not necessary to let them do. In particular, in the case where only black is printed, color development is not required even when fixing to the OHT, so deceleration rotation is not necessary. In such a case, the throughput can be accelerated by performing the rotation at the same speed as the normal paper during OHT printing and printing at full speed. Further, in the case of the color monochromatic printing and the case of the first embodiment, the color developability may be obtained without decelerating to the 1/2 speed as in the full color printing. Therefore, as an example, when the present invention was carried out according to the following cases when the special paper was passed, the throughput for the single color was improved for the special paper, and good results were obtained.

[0052]

[Table 1]

The deceleration rate at the time of deceleration is the ratio of the speed at the fifth or second rotation of the transfer drum to the normal rotation, and the deceleration rate at the time of deceleration of the fixing roller 20 is also the same. Further, the rotational speed refers to the rotational speed (rounding up) from the start of transfer to the end of separation.

Of course, in the case of executing a mode of only two colors (or only three colors), similar cases may be divided. However, for two or more colors, the deceleration rate is 4
A value similar to the case of color is an appropriate value.

[0055]

As is apparent from the above description, in the color image forming apparatus according to the present invention, the transfer material is immediately separated from the transfer member after the transfer of the toner image of the final color among the toner images is completed, and the fixing means is provided. After the normal rotation mode for fixing the toner image and the transfer of the toner image of the final color of the toner image are completed, first, the linear velocity of the drive of the transfer member is reduced to be lower than the linear velocity of the drive of the fixing unit. After further elapse of a predetermined time, the driving linear velocity of the fixing unit is reduced to a velocity substantially equal to the linear velocity of the transfer member after deceleration, and the transfer material separated from the transfer member is fixed by the fixing unit in the decelerated state. With rotation mode,
The normal rotation mode and the deceleration rotation mode can be switched according to the type of the transfer material or the color of the toner image to be printed. It is possible to obtain a high-quality image without unevenness, prevent thermal deterioration of the fixing unit, and achieve a long life.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing a first embodiment of a color image forming apparatus according to the present invention.

FIG. 2 is an overall configuration diagram of a color image forming apparatus showing a modification of the first embodiment.

FIG. 3 is a timing chart relatively showing an image forming process of a normal transfer material and a special transfer material.

FIG. 4 is a time series graph showing changes in the surface temperature of the fixing roller in the first embodiment.

FIG. 5 is an overall configuration diagram showing a second embodiment of a color image forming apparatus according to the present invention.

FIG. 6 is a graph showing a change in surface temperature of a fixing roller in a second example in a time series.

FIG. 7 is an overall configuration diagram of a conventional color image forming apparatus.

FIG. 8 is a perspective view showing a transfer body having a notch structure.

FIG. 9 is a perspective view showing a solid drum type transfer body.

FIG. 10 is an overall configuration diagram of a conventional color image forming apparatus including a solid drum type transfer body.

FIG. 11 is a configuration diagram showing an example of a fixing device.

12 is a graph showing changes in surface temperature of a fixing roller of the fixing device of FIG. 11 in time series.

[Explanation of symbols]

 2 transfer body 3 image carrier 5 fixing means 17 transfer material 18 transfer material type discrimination sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takehiko Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A transfer member, which holds a transfer material, and sequentially transfers toner images of a plurality of colors formed on an image carrier on the transfer material, and a toner image of each color on the transfer material. A color image forming apparatus having a fixing means for heating and fixing the color image obtained by the transfer of (1) onto the transfer material, (i) immediately after the transfer of the final color toner image among the toner images is completed. A normal rotation mode in which the material is separated from the transfer body and fixed by the fixing means, and (ii) after the transfer of the toner image of the final color of the toner image is completed, first, the linear velocity of the drive of the transfer body. Is decelerated so as to be lower than the linear velocity of the drive of the fixing unit, and after a predetermined time has elapsed, the linear velocity of the drive of the fixing unit is reduced to a velocity substantially equal to the linear velocity of the drive of the transfer body after the deceleration. Transfer separated from the transfer body And a decelerating rotation mode for fixing by means of the fixing means in a decelerating state, and the modes (i) and (ii) can be switched according to the type of the transfer material or the color type of the toner image to be printed. And a color image forming apparatus. 2. The color image forming method according to claim 1, wherein the target value for adjusting the heating temperature by the fixing unit can be switched according to the type of the transfer material or the type of color of the toner image to be printed. apparatus. 3. The color image forming apparatus according to claim 1, further comprising a sensor that detects the type of the transfer material. 4. The deceleration of the driving speed of the transfer member is completed within a time period in which a portion where the transfer material is not held and the image carrier face each other. 1 to 3, a color image forming apparatus.