JPH09269677A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which prevents image quality deterioration resulting from toner scattering during transfer and also prevents transfer density decrease and density irregularity from occurring when image formation is repeated. SOLUTION: This image forming device 110 is equipped with an image carrier 1 where toner images T are formed, an intermediate transfer body 2 where the toner image T are transferred, a corona discharger 9 for transferring the toner images T onto the intermediate transfer body 2 and a heat transfer roller 11 for transferring the toner images T, transferred to the surface of the intermediate transfer body 2, onto a recording medium 3. The device repeats a number of times the process of forming the toner images T onto the image carrier 1 and transferring them to the intermediate transfer body 2, and then transfers the plurality of toner image T, formed on the intermediate transfer body 3 by the transfer repeated a number of times, onto recording medium 3 all at once. In the case, the device is provided with a toner images heater 4 for applying heat to the toner images T, transferred to the surface of an intermediate transfer body 2, before the final transfer starts, thereby melting the surface of the toner images.

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 used in an electrophotographic copying machine, a laser printer or the like.

[0002]

2. Description of the Related Art Conventionally, as a color image forming method in an electrophotographic image forming apparatus of this type, an intermediate transfer method using an intermediate transfer body or a toner image is directly transferred to a recording medium without using the intermediate transfer body. The recording medium direct transfer method is widely known. The former intermediate transfer method is, for example, as disclosed in Japanese Patent Publication No. 49-209 and Japanese Patent Application Laid-Open No. 62-206567, a toner image is formed on a photosensitive drum and the toner image is transferred to a belt. By repeating, for example, four times the process of sequentially transferring the toner images onto the intermediate transfer body of a mold or a drum type, a multiple toner image of four colors is formed on the intermediate transfer body, and the multiple toner images are recorded on a recording medium such as paper. In the latter recording medium direct transfer method, the process of forming a toner image on the image bearing drum and transferring the toner image onto the recording medium is repeated, for example, four times, so that the recording medium is directly transferred onto the recording medium. In this method, a color image composed of four color toners is formed. Each of these two methods has advantages and disadvantages, and they are used properly according to the application.

The outline and problems of the intermediate transfer type image forming apparatus will be described below. FIG. 4 is a schematic configuration diagram of a conventional intermediate transfer type image forming apparatus. As shown in FIG. 4, the image forming apparatus 100 includes an image carrier drum 10 having a surface formed of a photoconductor and rotating in the direction of arrow A.
1, four developing devices 105 to 108 provided around the image carrier drum 101, an intermediate transfer belt 102 rotating in the direction of arrow B, and a corona discharger provided on the back side of the intermediate transfer belt 102. 109 and a bias roll 111 provided on the back surface side of the passage of the recording medium 103. The bias roll 111 is disposed so as to be able to come into contact with and separate from the intermediate transfer belt 102, and the toner image T of the final color is transferred from the image carrier drum 101 to the intermediate transfer belt 10.
It is separated from the intermediate transfer belt 102 until it is completely transferred to the second transfer belt 2. The image forming apparatus 100 is provided with means relating to electrostatic latent image formation, means relating to fixing, and other incidental equipment, which are not shown in FIG.

The four developing devices 105 to 108 are developing devices for the respective colors of black (Bk), yellow (Y), magenta (M), and cyan (C), and the image carrier drum 101 is one. Each time it rotates, four developing units 105-
Development is performed by one of the 108. The developed toner image T has a negative charge, and the toner image T is electrostatically transferred onto the intermediate transfer belt 102 by the positive charge supplied from the transfer corona discharger 109. When the image carrier drum 101 and the intermediate transfer belt 102 rotate four times, the developing process and the transferring process for forming one image are completed.

That is, the first developing device 10 at the first rotation.
5, a black toner image T is formed on the image carrier drum 101, the black toner image T is transferred onto the intermediate transfer belt 102, and the second developing device 106 forms an image at the next second rotation. A yellow toner image T is formed on the carrier drum 101, the yellow toner image T is transferred onto the black toner image on the intermediate transfer belt 102 in an overlapping manner, and at the next third and fourth rotations. Respectively, magenta and cyan toner images T are formed by the third and fourth developing devices 107 and 108, respectively, and these toner images are sequentially superposed and transferred onto the toner images on the intermediate transfer belt 102, and finally, A multiple toner image for four colors is formed on the intermediate transfer belt 102.

Next, the multi-color toner images of four colors formed on the intermediate transfer belt 102 are collectively transferred from the intermediate transfer belt 102 onto the recording medium 103 by the voltage applied to the bias roll 111, and are recorded. A desired color image is formed on the medium 103. In this image forming apparatus 100, transfer from the image carrier drum 101 to the intermediate transfer belt 102, and transfer from the intermediate transfer belt 102 to the recording medium 103.
The transfer is performed by the electrostatic transfer method. That is,
By applying a voltage having a polarity opposite to that of the toner to the corona discharger 109 or the bias roll 111 provided on the back side of the transfer target (the intermediate transfer belt 102 or the recording medium 103) at each transfer position, the toner image is obtained. T is the image carrier drum 101 to the intermediate transfer belt 102.
To or from the intermediate transfer belt 102 to the recording medium 103
Electrostatically transferred to.

[0007]

When a line-shaped color image forming test is performed using the image forming apparatus 100 of the intermediate transfer type as described above, each color of the colors sequentially formed on the image carrier drum 101 is tested. The toner image T is transferred onto the intermediate transfer belt 1
02, the intermediate transfer belt 1
When the toner image of the next color is overlaid on the toner image already transferred on 02, the toner of the next color to be overlaid is not over the toner image of the previous color. It may be scattered to the peripheral portion, and normal image formation may not be possible.

The cause of the toner scattering is generally considered as follows. (1) Immediately before the contact between the image carrier drum 101 and the intermediate transfer belt 102 in the transfer pre-nip portion (the part immediately before the position where the toner image is transferred from the image carrier drum 101 to the intermediate transfer belt 102), The transfer electric field existing in the voids acts on the toner image to cause toner scattering.

(2) Occurrence between the image carrier drum and the intermediate transfer belt when the image carrier drum 101 and the intermediate transfer belt 102 move from the contact state to the state where they are separated from each other after passing the transfer position. Toner scattering occurs due to the discharge phenomenon. Conventionally, various remedies for these causes have been taken, but a sufficient improvement effect has not yet been obtained.

According to the research conducted by the present inventor, it is found that the toner scattering occurs remarkably when a semiconductor having an electric conductivity intermediate between a conductor and an insulator is used as the material of the intermediate transfer member. There is. When a semiconductor is used for the intermediate transfer body, one of the causes of the remarkable toner scattering is that, when the intermediate transfer body is a semiconductor, the transfer charge passes through the intermediate transfer body to the transfer pre-nip portion because the resistance is relatively low. This is considered to be because the transfer electric field acts on the toner image in the gap between the image carrier drum 101 and the intermediate transfer belt 102 as described in (1) above.

As another cause, it has been found that the phenomenon described below has a greater effect than the above causes. That is, in the image forming apparatus 100, the corona discharger 109 is connected to the intermediate transfer belt 1
A charge serving as a driving force for the transfer is supplied to 02, and the toner image T on the image carrier drum 101 is electrostatically transferred to the intermediate transfer belt 102 by the charge. Since the electric charge is gradually attenuated, the toner holding ability of the intermediate transfer belt 102 is reduced, and the toner is scattered due to the repulsion between the electric charges of the toner. Since the toner holding capacity of the intermediate transfer belt 102 is smaller as the toner in the upper layer is increased, when the charge is attenuated, the toner image of the color superimposed on the toner image is scattered more severely.

The behavior of the toner when the toner image is transferred onto the intermediate transfer belt 102 will be described in detail below with reference to FIGS. 5 and 6. FIG. 5 is a schematic diagram showing changes in the potential distribution and the electric field distribution in the gap between the image carrier drum and the intermediate transfer belt. In both FIGS. 5A and 5B, an image carrier drum is shown above, and an intermediate transfer belt is shown below. A gap is formed between the image carrier drum and the intermediate transfer belt. The toner layer transferred onto the intermediate transfer belt is shown. The potential distribution is displayed as contour lines, and the electric field distribution is displayed in the direction of the arrow. The arrows representing the electric field distribution are displayed only at the left and right end portions of the toner layer and the central portion of the toner layer.

In case 1 shown in FIG. 5A, immediately after the toner is transferred from the image carrier drum to the intermediate transfer belt,
FIG. 5B shows a state in which the image carrier drum and the intermediate transfer belt are close to each other. Case 2 shown in FIG. 5B is different from case 1 immediately after the toner is transferred to the intermediate transfer belt in comparison with the image carrier drum. And the intermediate transfer belt are separated from each other.

In case 1 immediately after the toner is transferred,
Since the electric charge supplied to the intermediate transfer belt by the transfer charger is sufficiently maintained, an upward electric field is formed at both the left and right end portions of the toner layer and the central portion of the toner layer, and toner having a negative charge is directed downward. Therefore, the toner is not scattered. On the other hand, in case 2, as compared with case 1, as the image carrier drum and the intermediate transfer belt move away from each other, the electric charge of the intermediate transfer belt gradually attenuates as time elapses, and as shown in FIG. In the central portion of the toner layer, a downward electric field is formed from the upper layer to the lower layer, and an oblique downward electric field is formed in the vicinity of the upper layer on both left and right ends of the toner layer. For this reason, the toner in the vicinity of the upper layer on both the left and right ends of the toner layer receives a diagonal upward force. When the upward force received by the toner exceeds a certain limit and becomes large, toner scattering occurs.

FIG. 6 is a graph showing the state of the electric field in the gap between the image carrier drum and the intermediate transfer belt. FIG.
The horizontal axes of (a) and FIG. 6 (b) represent the horizontal position of FIG. 5 on the uppermost layer surface of the toner layer formed on the intermediate transfer belt of FIG. 5, and the vertical axis of FIG. 6 (a). The axis represents the strength of the electric field, and the vertical axis in FIG. 6B represents the direction of the electric field.

As shown in FIG. 6 (a), in case 2 compared to case 1, the electric field strength decreases as the charge of the intermediate transfer belt decays, and as shown in FIG. 6 (b), The direction of the electric field in Case 2 is opposite to that in Case 1. As described above, in the case 2, the electric field is applied to the toner in the direction in which toner scattering easily occurs. The hatched portion in FIG. 6B represents the direction of the electric field in which toner scattering occurs as a range.

From the above description, it is understood that the charge of the intermediate transfer belt should not be attenuated in order to prevent the toner scattering after the transfer. However, even if a material with low charge decay is used for the intermediate transfer belt,
As the toner layers are successively transferred onto the intermediate transfer belt in multiple layers and the layer thickness gradually increases, the ability of the intermediate transfer belt to hold the charges of the intermediate transfer belt decreases, so that the charge transfer of the intermediate transfer belt is prevented from decaying. It is not enough to solve the problem of toner scattering. In addition, when the toner image is secondarily transferred from the intermediate transfer belt to the recording medium, a high transfer electric field is necessary because the multiple-transferred high density toner images are secondarily transferred all at once, and the charge attenuation is small. When the intermediate transfer belt is used, discharge easily occurs between the intermediate transfer belt and the recording medium, which may cause image quality defects. In addition, when an intermediate transfer belt with a small amount of charge attenuation is used, electric charges may be accumulated on the intermediate transfer belt when image formation is repeated, resulting in a decrease in transfer density or uneven density.

By the way, for example, Japanese Patent Publication No. 46-4167.
No. 9, JP-B-48-22763, JP-B-57
JP-A-20632 discloses a method in which a toner image on an image carrier is adhesively transferred to an intermediate transfer member, and the toner image transferred to the intermediate transfer member is transferred and fixed to a recording medium by using heat or pressure. Has been done. This publication describes that it is possible to prevent toner scattering during transfer, which is a problem in electrostatic transfer. However, in this method, it is difficult to generate an adhesive force between a plurality of toner layers, and therefore it is not suitable for forming a color image by superposing toner images.

Further, in Japanese Patent Laid-Open No. 64-77077, the intermediate transfer belt is heated by energizing the intermediate transfer belt, and the heat on the intermediate transfer belt itself melts the toner on the image carrier drum to perform the intermediate transfer. A transfer method for welding and transferring to a belt is disclosed. However, in this method, since the image carrier drum comes into contact with the high temperature intermediate transfer belt,
The photoconductor on the surface of the image carrier drum may change its electrical characteristics or be damaged by heat.

Further, in Japanese Patent Laid-Open No. 5-249799, in a color image forming method of an intermediate transfer system, toner images transferred from an image carrier onto an intermediate transfer body are sequentially assumed to be attached, and toner images of plural colors are formed. On the intermediate transfer body, then the intermediate transfer body and the recording medium are overlapped and heated, and the cohesive force between the toners becomes larger than the adhesive force between the toner and the intermediate transfer body, and then the recording medium is peeled from the intermediate transfer body. An image forming method is disclosed. One of the objects and effects of the present invention is reduction of toner scattering. In this method, the toner image after being transferred onto the intermediate transfer body is assumedly attached and the toner is fixed onto the intermediate transfer body, which is effective in reducing the scattering of the toner after being once transferred onto the intermediate transfer body. However, when the toner image of the next color is transferred onto the already transferred toner image, it is not effective in reducing the scattering of the transferred toner image. It is not possible to prevent the deterioration of the image quality due to.

The problems in the case of the color image forming apparatus of the above-mentioned recording medium direct transfer system will be described. Also in this system, as the toner image is gradually transferred onto the recording medium, the toner layer thickness becomes thicker. The ability to retain the charge on the recording medium with respect to the toner image formed on the upper layer is reduced, and toner scattering similar to that in the case of the above-described intermediate transfer system occurs.

In view of the above circumstances, the present invention prevents the deterioration of the image quality due to the toner scattering at the time of transfer, and prevents the decrease of the transfer density and the occurrence of the density unevenness when the image formation is repeated. An object is to provide an image forming apparatus.

[0023]

In a first image forming apparatus of the present invention that achieves the above object, an image carrier on which a toner image is formed and a toner image formed on the image carrier are transferred. Intermediate transfer body, an electrostatic transfer means for electrostatically transferring the toner image on the image carrier onto the intermediate transfer body, and the toner image transferred on the intermediate transfer body to a predetermined recording from the intermediate transfer body. A secondary transfer means for secondary transfer onto the medium, and a process of forming a toner image on the image carrier and transferring it onto the intermediate transfer member is repeated a plurality of times, and then the intermediate transfer member is transferred by the plurality of times. In an image forming apparatus that collectively transfers a plurality of toner images formed on a recording medium onto a recording medium, the toner transferred onto the intermediate transfer body at the latest before the final transfer of a plurality of transfers. Image, for the toner image that is subsequently transferred onto the intermediate transfer member Characterized by comprising an adhesive applying means for applying a wear resistant.

Here, the intermediate transfer member has a volume resistivity of 1
0 ¹² Ω · cm or less, and surface resistivity and backside resistivity 1
It is preferable to have electrical characteristics of 0 ¹² to 10 ¹⁵ Ω / □. The second aspect of the present invention that achieves the above object
The image forming apparatus includes an image carrier on which a toner image is formed,
Recording medium conveying means for carrying and conveying a predetermined recording medium, electrostatic transfer means for electrostatically transferring the toner image on the image carrier onto the recording medium conveyed by the recording medium conveying means, and recording A fixing means for fixing the toner image transferred onto the medium onto the recording medium, and after repeating the process of forming the toner image on the image carrier and transferring onto the recording medium a plurality of times,
In an image forming apparatus that collectively fixes a plurality of toner images formed on a recording medium by these multiple transfers,
A tackiness imparting unit that imparts tackiness to the toner image transferred onto the recording medium before the final transfer of the plurality of transfers at the latest is attached to the toner image transferred next to the recording medium. It is characterized by having.

Here, it is preferable that the tackiness imparting means imparts tackiness by heating the transferred toner image to melt the surface of the toner image.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a schematic configuration diagram showing an embodiment of a first image forming apparatus of the present invention. The image forming apparatus 110 shown in FIG. 1 is an example in which the present invention is applied to a color image forming apparatus.

As shown in FIG. 1, the image forming apparatus 11
0 is provided with an image carrier drum 1 which rotates in the direction of arrow A and whose surface is a photoconductor. The image carrier drum 1 has an electrostatic latent image corresponding to image information by a well-known electrophotographic process. An electrostatic latent image forming means (not shown) for forming the image is provided. Around the image carrier drum 1, developing devices 5 to 8 corresponding to each color of black (Bk), yellow (Y), magenta (M), and cyan (C) are provided, and the image carrier drum 1 is provided. The electrostatic latent image formed above is developed by any one developing device to form a toner image T.
Therefore, the electrostatic latent image written on the image carrier drum 1 is
For example, if the electrostatic latent image corresponds to yellow image information, the electrostatic latent image is developed by a developing device 6 containing yellow (Y) toner, and a yellow toner image T is formed on the image carrier drum 1. To be done.

An intermediate transfer belt 2 which is stretched by a plurality of rolls and rotates in the direction of arrow B is provided at a position close to the image carrier drum 1. The intermediate transfer belt 2 is
At the first transfer position P1, it is arranged close to the image carrier drum 1 with a slight gap. An electrostatic transfer unit is provided at the first transfer position P1. That is, the first
The corona discharger 9 and the transfer baffle 10 are provided on the back surface side of the intermediate transfer belt 2 at the transfer position P1 of 1., and when a voltage having a polarity opposite to the charging polarity of the toner is applied to the corona discharger 9, the image is formed. The unfixed toner image T formed on the carrier drum 1 is electrostatically transferred to the intermediate transfer belt 2. The transfer baffle 10 prevents the transfer pre-nip portion (a position slightly upstream of the first transfer position P1 in the moving direction of the image carrier drum 1 and the intermediate transfer belt 2) from being charged.

The image forming apparatus 110 of this embodiment employs an intermediate transfer system, and the electrostatic transfer means transfers the image from the image carrier drum 1 to the intermediate transfer belt 2.
This is equivalent to so-called primary transfer, and the subsequent transfer from the intermediate transfer belt 2 to the recording medium 3 is equivalent to secondary transfer. In the present invention, the reason why the electrostatic transfer method is used for the primary transfer is
This is because the primary transfer of the heat transfer method or the heat / pressure transfer method may damage the photoconductor forming the surface of the image carrier drum 1. Incidentally, when the primary transfer by the heat transfer method is adopted, the unfixed toner image T
Since it is necessary to add a sufficient amount of heat to melt the whole,
The heat may be directly transmitted to the photoconductor on the image carrier drum 1, and the temperature of the photoconductor may reach a high temperature of 150 ° C to 200 ° C.

A toner image heater 4 is provided facing the surface of the intermediate transfer belt 2 upstream of the first transfer position P1 where the unfixed toner image T is primarily transferred onto the intermediate transfer belt 2. There is. The toner image heater 4 applies the toner image transferred next to the intermediate transfer belt 2 to the surface of the unfixed toner image transferred from the image carrier drum 1 to the intermediate transfer belt 2 at the first transfer position P1. It is a tackifier that imparts tackiness.

Although the tackiness imparting means is constituted by a heater such as a ceramic heater or a halogen lamp in this embodiment, it is not limited to such a heater and the transferred unfixed toner is not limited thereto. Any means can be used as long as it can provide the surface of the image with adhesiveness to the toner image to be transferred next. For example, the surface of the unfixed toner image is reacted with the toner and adhered to the toner. Means such as spraying a liquid that imparts the property may be used.

However, a heating means, such as a ceramic heater or a halogen lamp, which can be arranged in a non-contact manner so as to face the surface of the intermediate transfer belt 2, effectively melts only the surface of the unfixed toner image T and is adhesive. Is preferable because it can be added. When the toner image heater 4 is used as the tackiness imparting means, the heat amount of the toner image heater 4 may be a heat amount necessary and sufficient for the surface of the unfixed toner image T after transfer to be partially melted. It is preferable that the entire toner image T is melted and not fixed on the intermediate transfer belt 2. Therefore, when such an amount of heat is applied, the surface temperature of the intermediate transfer belt 2 remains at about 40 ° C. to 60 ° C. and does not rise to a higher temperature. Although the surface temperature of the image carrier drum 1 slightly rises due to the influence of the toner image heater 4, the surface temperature of the image carrier drum 1 becomes lower than the surface temperature of the intermediate transfer belt 2, so a special cooling device is used. However, since the temperature of the photoconductor on the surface of the image carrier drum 1 can be suppressed to about 40 ° C. or less, there is no possibility that the photoconductor of the image carrier drum 1 is damaged by heat.

The operation of the tackiness imparting means when a four-color image is formed will be described. First, the first color (black) unfixed toner image primarily transferred onto the intermediate transfer belt 2 is an intermediate image. When the toner image heating device 4 reaches the position as the transfer belt 2 rotates, the surface of the black unfixed toner image is heated by the toner image heating device 4, and the toner image surface is melted and is in a state of being highly adhesive. Become. The black unfixed toner image becomes the first as the intermediate transfer belt 2 rotates.
When the transfer position P1 is reached, the second color (yellow) unfixed toner image is primarily transferred onto the black unfixed toner image. Since the surface of the black unfixed toner image is melted and has adhesiveness, the yellow unfixed toner image adheres to the surface of the black toner image, and the charge on the intermediate transfer belt 2 increases with time after the primary transfer. Even if is attenuated, the adhesion between the black and yellow toners is maintained, so that the yellow unfixed toner image is prevented from scattering. The same process is repeated for the third and subsequent colors (magenta and cyan), and black, yellow, and
The unfixed toner images of magenta and cyan are formed without being scattered, respectively.

Since the toner image to be heated and melted does not exist on the intermediate transfer belt 2 until the first black toner image is primarily transferred, heating by the toner image heater 4 is not necessary. Further, the heating by the toner image heater 4 does not necessarily have to be performed for all color toner images except the final color toner image, and only the second color and the third color where the toner scattering increases, or only the third color. May be performed.

Each time the intermediate transfer belt 2 makes one revolution, the toner images are superposed on the intermediate transfer belt 2. When the primary transfer process is completed by superposing the four color toner images in this way, the intermediate transfer belt 2 is completed. The unfixed toner image T carried on 2 is conveyed to the second transfer position P 2 facing the conveyance path of the recording medium 3 as the intermediate transfer belt 2 rotates. At the second transfer position P2, a heat transfer roller 11 that is in contact with the intermediate transfer belt 2 and rotates in the direction of arrow C is provided and constitutes a secondary transfer unit. Heat transfer roller 1
Reference numeral 1 contains a heat source such as a ceramic heater or a halogen lamp, and the surface of the heat transfer roller 11 is coated with fluororesin. In addition, the second transfer position P2
On the back surface side of the intermediate transfer belt 2 in FIG.
2 are deployed. Like the heat transfer roller 11, the backup roll 12 has a built-in heat source. A voltage can be applied between the heat transfer roller 11 and the backup roll 12.

The recording medium 3 carried out from the tray 14 by the feed roller 13 at a predetermined timing is supplied to the second transfer position P2, and is sandwiched between the heat transfer roller 11 and the intermediate transfer belt 2. The unfixed toner image carried on the intermediate transfer belt 2 is secondarily transferred onto the recording medium 3 at the second transfer position P2. In the secondary transfer, the toner image is melted and transferred by the heating unit and the pressure unit, so that discharge occurs between the intermediate transfer belt 2 and the recording medium 3 even if an intermediate transfer belt with small charge attenuation is used. There is no risk of causing image quality defects. When an intermediate transfer member having a large charge attenuation is used as the intermediate transfer belt 2, a bias roller may be used instead of the heat transfer roller 11.

Then, the recording medium 3 to which the unfixed toner image is transferred is separated from the intermediate transfer belt 2 by the separating claw 15 and sent to a fixing device (not shown) by the conveyor belt 16 to fix the unfixed toner image. Processing is performed. It should be noted that the secondary transfer means (heat transfer roller 11 and backup roll 12) may also serve as fixing without using an independent fixing device, but in order to obtain sufficient color fixing property, independent fixing is possible. It is better to use a bowl.

The intermediate transfer belt 2 after the secondary transfer is moved in the direction of arrow B, and the cleaner 17 removes the toner remaining on the intermediate transfer belt 2. When the residual charge remains on the intermediate transfer belt 2, a rotary conductive brush (not shown) or the like is provided near the cleaner 17 to remove the charge on the intermediate transfer belt 2. The conductive brush may be grounded or an alternating voltage may be applied. By removing the charge with a conductive brush or the like so that the charges are not accumulated on the intermediate transfer belt 2, it is possible to maintain a good image quality even when image formation is repeated.

The heat transfer roller 11, the peeling claw 15,
The cleaner 17 and a charge removing member (not shown) are arranged so that they can come into contact with and separate from the intermediate transfer belt 2, and these members are intermediate until the unfixed toner image T of the final color is primarily transferred to the intermediate transfer belt 2. It is separated from the transfer belt 2. The intermediate transfer belt 2 in the present embodiment is configured by laminating a fluororesin, a silicone rubber, a fluororubber or the like having a good toner releasing property on the surface of a polyimide resin, an aramid resin or the like having excellent heat resistance, or a fluororesin. It is made of a material having good heat resistance and toner releasability such as resin, silicone rubber, and fluororubber.

The volume resistivity of the intermediate transfer belt 2 is set to an appropriate amount of an antistatic agent such as carbon black so as not to cause a decrease in transfer density or uneven density due to charge accumulation when image formation is repeated. 1 by including
It is adjusted to 0 ¹² Ω · cm or less. This is because if the volume resistivity is 10 ¹² Ω · cm or less, the time constant of charge decay is 1 second or less, and the charge sufficiently leaks during one rotation of the intermediate transfer belt 2.

Further, in order to prevent charge diffusion to the transfer pre-nip portion, it is preferable to adjust the surface resistivity and back surface resistivity of the intermediate transfer belt 2 to 10 ¹² to 10 ¹⁵ Ω / port.
The surface resistivity and the backside resistivity of the intermediate transfer belt 2 are 10 ¹⁶
If it is Ω / port or more, electric discharge is generated when the image carrier and the intermediate transfer belt 2 are separated, and the toner image is scattered. Table 1
6 is a table showing the relationship between the electric resistance value of the intermediate transfer belt and toner scattering.

[0042]

[Table 1]

As shown in Table 1, by setting the volume resistivity of the intermediate transfer belt 2 to 10 ¹² Ω · cm or less, and the surface resistivity and the back surface resistivity of 10 ¹² to 10 ¹⁵ Ω / hole, A toner image is prevented from scattering and a high quality image can be obtained. The results in parentheses shown in the bottom row of Table 1 show the toner image scattering condition when the heating by the toner image heater shown in the above embodiment is not performed.

By setting the volume resistivity of the intermediate transfer belt 2 to 10 ¹³ Ω · cm or more in order to prevent charge decay after the primary transfer, toner image scattering is further suppressed and a high quality image can be obtained. However, in that case, it is necessary to install a static eliminator having good performance so as not to accumulate the charges of the intermediate transfer belt 2. To measure the electrical resistivity of the intermediate transfer belt 2, a high resistivity meter (HIRESTA IP, manufactured by Mitsubishi Yuka) and an HR100 probe (inner electrode diameter 50
mm, ring electrode inner diameter 53 mm, manufactured by Mitsubishi Petrochemical Co., Ltd.), a voltage of 500 V is applied between the electrodes, and the measured value after 1 minute has elapsed is used. Instead of using the high resistance resistivity meter, the above probe may be used and the constant voltage power supply may be used under the same conditions as above to convert the measured value from the minute ammeter to obtain the value.

Next, an embodiment of the second image forming apparatus of the present invention will be described. In the above-described first embodiment (see FIG. 1), an example in which the intermediate transfer type image forming apparatus is provided with the tackiness imparting means (toner image heater 4) has been described. The image scattering prevention can be similarly applied to the image forming apparatus of the recording medium direct transfer system described above.

FIG. 2 is a schematic block diagram of an embodiment of such a second image forming apparatus of the present invention. The image forming apparatus 200 shown in FIG. 2 is an image forming apparatus of a recording medium direct transfer system, unlike the intermediate transfer system of the image forming apparatus 110 (see FIG. 1) in the embodiment of FIG. 1) is used instead of the transfer drum 21.

As in the first embodiment shown in FIG. 1, the unfixed toner image T corresponding to each color image information is rotated in the direction of arrow A by the four color developing devices 5-8.
Are sequentially formed on top. The transfer drum 21 rotating in the direction of arrow B has a toner image heater 4 similar to that of the embodiment of FIG.
An electrostatic transfer means including a corona discharger 9 and a transfer baffle 10, a static elimination corotron 22 for removing residual charges on the surface of the transfer drum 21, and a sheet suction for adsorbing the recording medium 3 on the surface of the transfer drum 21. Corotron 23,
A paper peeling corotron 24 for peeling the recording medium 3 from the surface of the transfer drum 21 is provided. Further, in the vicinity of the transfer drum 21, the conveyor belt 16 and the fixing unit 1 are provided.
And 8 are provided. The image carrier drum 1 is provided with an electrostatic latent image forming means (not shown) for forming an electrostatic latent image according to image information by a well-known electrophotographic process. In the second embodiment, the toner image T is multiple-transferred directly from the image carrier drum 1 to the recording medium 3 without passing through the intermediate transfer member, so that the second transfer device does not exist in the second embodiment. .

When forming a full-color image of four colors, the transfer drum 21 that has adsorbed the recording medium 3 rotates four times in the direction of arrow A. Each time the transfer drum 21 makes one rotation, an unfixed toner image T of one color is sequentially transferred from the image carrier drum 1 to the recording medium 3.
Electrostatically transferred. The unfixed toner image T transferred is shown in FIG.
The surface of the unfixed toner image T of each color excluding the unfixed toner image T of the final color is heated and melted by the toner image heater 4 similar to that of the above embodiment, and then the unfixed toner image T is formed on the recording medium 3 Adhesiveness is imparted to the transferred unfixed toner image T, and toner scattering is prevented.

When the electrostatic transfer process to the recording medium 3 is completed, the recording medium 3 is peeled from the transfer drum 21 by the paper peeling corotron 24 and sent to the fixing means 18 by the conveyor belt 16 to be subjected to the fixing process, and a series of steps is performed. The image forming process is completed. FIG. 3 is a schematic configuration diagram of another embodiment of the second image forming apparatus of the present invention. The image forming apparatus 300 shown in FIG. 3 is still another example in which the present invention is applied to a color image forming apparatus, as in the embodiment shown in FIGS. 1 and 2.

The image forming apparatus 200 is an image forming apparatus of the recording medium direct transfer system as in the embodiment of FIG. 2 and is not provided with an intermediate transfer member. Then, the image forming apparatus 2
In 00, a transfer belt is used instead of the transfer drum 21 in the embodiment of FIG. As shown in FIG. 3, the image forming apparatus 300 includes a transfer belt 32, four image carrier drums 31a, 31b, 31c, and 31d.
Electrostatic transfer means consisting of four sets of corona discharger 9 and transfer baffle 10, three toner image heaters 4a, 4b and 4c for heating the electrostatically transferred unfixed toner image T and transfer belt 32 surface. A static elimination corotron 22 for removing residual charges, a paper adsorption corotron 23 for adsorbing the recording medium 3 on the surface of the transfer belt 32, and a paper peeling corotron 2 for exfoliating the recording medium 3 from the surface of the transfer belt 32.
4, a conveyor belt 16 and a fixing unit 18. Four image carrier drums 31a, 31b, 31c,
Reference numeral 31d is an image carrier dedicated to each color of black, yellow, magenta, and cyan, and includes dedicated developing devices 31a, 31b, 31c, and 31d.
The four image carrier drums 31a, 31b, 31c,
In addition to the above-mentioned developing device, 31d is provided with electrostatic latent image forming means (not shown) for forming an electrostatic latent image according to image information by a well-known electrophotographic process.

The recording medium 3 is supplied onto the transfer belt 32 rotating in the direction of the arrow A, and the recording medium 3 is adsorbed on the surface of the transfer belt 32 by the paper adsorption corotron 23, and the recording medium 3 is placed at the position of the image carrier drum 31a. When conveyed, first, the black unfixed toner image T of the first color is electrostatically transferred from the image carrier drum 31a onto the recording medium 3. When the recording medium 3 reaches the position of the toner image heater 4a due to the rotation of the transfer belt 32, the surface of the black unfixed toner image T transferred onto the recording medium 3 is heated and melted by the toner image heater 4a, so that the black The recording medium 3 is formed on the unfixed toner image T.
Adhesiveness is imparted to the second color yellow unfixed toner image T transferred next. When the recording medium 3 reaches the position of the image carrier drum 31b by the rotation of the transfer belt 32, the yellow unfixed toner image T of the second color is electrostatically transferred onto the black unfixed toner image T on the recording medium 3. To be done. Since the surface of the black unfixed toner image T on the recording medium 3 has adhesiveness due to the toner image heater 4a,
The yellow unfixed toner image T adheres onto the black unfixed toner image T and does not scatter. Next, when the recording medium 3 reaches the position of the toner image heater 4b by the rotation of the transfer belt 32, the surface of the yellow unfixed toner image T transferred onto the recording medium 3 is heated and melted by the toner image heater 4b. , The yellow unfixed toner image T is provided with adhesiveness to the third color magenta unfixed toner image T to be subsequently transferred onto the recording medium 3. The same process is repeated thereafter, and finally, when the cyan unfixed toner image T of the final color is electrostatically transferred from the image carrier drum 31d onto the recording medium 3, the recording medium 3 is separated by the paper peeling corotron 24. It is separated from the surface of the transfer belt 32 and is sent to the fixing means 18 by the conveyor belt 16, where the fixing process is performed and a series of image forming steps is completed.

Although an example using a corona discharger has been described as the electrostatic transfer means in each of the above-mentioned embodiments, the electrostatic transfer means is not limited to the corona discharger, and for example, a voltage is applied. Any type may be used as long as it uses electrostatic force, such as a conductive roll or a conductive brush. Further, as the image bearing member in each of the above-described embodiments, an example of a drum type image bearing member has been described, but the image bearing member is not limited to the drum type and may be a belt type or a discontinuous type. It may be of the type.

Although an example of a belt type intermediate transfer body has been described as the intermediate transfer body in the embodiment of the intermediate transfer system, the intermediate transfer body is not limited to the belt type and may be a drum type. A non-continuous type may be used. Further, an example using a transfer drum and a transfer belt as means for conveying the recording medium to a predetermined transfer position in the embodiment of the direct transfer system has been described, but the means for conveying to the transfer position is not limited to these. ,
Other types of transportation means or discontinuous movement means may be used.

[0054]

As described above, the toner image transferred from the image carrier to the intermediate transfer member is transferred to the intermediate transfer member by the tackiness imparting means provided in the first image forming apparatus of the present invention. To the toner image to be transferred next, the toner image to be transferred next is attached to the surface of the toner image that has already been transferred by the adhesive force. Even if the toner carrying ability of the toner is lowered, the toner image can be prevented from scattering.

As described above, since the toner images are carried by the adhesive force between the toner images, there is no need to rely on the toner image carrying force based on the charge of the intermediate transfer member, and therefore the intermediate transfer member having a low electric resistance is used. Therefore, even if the image formation is repeated, no charge is accumulated in the intermediate transfer member,
It is possible to prevent a decrease in transfer density and the occurrence of density unevenness.

The toner image transferred from the image carrier onto the recording medium by the tackiness imparting means provided in the second image forming apparatus of the present invention and the toner image next transferred onto the recording medium. The toner image to be transferred next is attached to the surface of the already transferred toner image by the adhesive force, so that the toner image can be prevented from scattering.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a first image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram of an embodiment of a second image forming apparatus of the present invention.

FIG. 3 is a schematic configuration diagram of another embodiment of the second image forming apparatus of the present invention.

FIG. 4 is a schematic configuration diagram of a conventional intermediate transfer type image forming apparatus.

FIG. 5 is a schematic diagram showing changes in potential distribution and electric field distribution in a gap between an image carrier drum and an intermediate transfer belt.

FIG. 6 is a graph showing a state of an electric field in a gap between an image carrier drum and an intermediate transfer belt.

[Explanation of symbols]

 1 image carrier drum 2 intermediate transfer belt 3 recording medium 4 toner image heater 9 corona discharger 10 transfer baffle 11 heating transfer roller 12 backup roll 18 fixing means 21 transfer drum 32 transfer belt

Claims (4)

[Claims] 1. An image carrier on which a toner image is formed, an intermediate transfer member on which the toner image formed on the image carrier is transferred, and a toner image on the image carrier on the intermediate transfer member. Electrostatic transfer means for electrostatically transferring the toner image onto the intermediate transfer body, and secondary transfer means for secondarily transferring the toner image transferred onto the intermediate transfer body onto a predetermined recording medium. After the process of forming a toner image on the image carrier and transferring it onto the intermediate transfer member is repeated a plurality of times, the plurality of toner images formed on the intermediate transfer member by the plurality of times of transfer are recorded on the recording medium. In an image forming apparatus that collectively transfers to a medium, a toner image transferred onto the intermediate transfer member is transferred to the intermediate transfer member before the final transfer of the plurality of transfers at the latest. Adhesion-imparting hand that imparts adhesion to the toner image transferred to the An image forming apparatus comprising the. 2. The intermediate transfer member has a volume resistivity of 10 ¹² Ω.
-Cm or less, and surface resistivity and back surface resistivity 10 ¹² ~
The image forming apparatus according to claim 1, wherein the image forming apparatus has an electric characteristic of 10 ¹⁵ Ω / □. 3. An image carrier on which a toner image is formed, a recording medium carrying means for carrying and carrying a predetermined recording medium, and a toner image on the image carrier is carried by the recording medium carrying means. An electrostatic transfer means for electrostatically transferring the toner image onto the recording medium, and a fixing means for fixing the toner image transferred onto the recording medium onto the recording medium. An image forming apparatus that collectively fixes a plurality of toner images formed on the recording medium by the plurality of times of transfer after repeating a process of forming and transferring the plurality of toner images onto the recording medium, A tackifier is provided for tacking the toner image transferred onto the recording medium before the final transfer of the transfer times to the toner image transferred next onto the recording medium. Image characterized by Forming apparatus. 4. The adhesiveness imparting means imparts adhesiveness by heating the transferred toner image and melting the surface of the toner image. The image forming apparatus according to claim 1.