JP2003263006A - Image forming method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an image from being degraded due to reverse transfer while preventing toner scattering before transfer in an image forming method (image forming apparatus) to form an electrostatic latent image on a latent image carrier, develop the electrostatic latent image so as to form a toner image and transfer the toner image to a final transfer medium so as to form a final image. <P>SOLUTION: A maximum potential difference V between the surface potential of the latent image carrier 1 in an area to which the toner image is transferred and the surface potential of a final transfer medium S at least in the case of transferring the toner images of second and succeeding colors to the final transfer medium S is set to satisfy a condition V<312+6.2×t when the thickness of the toner image held between the latent image carrier and the final transfer medium is defined as t [μm]. In the case of transferring the toner image from the latent image carrier 1 to the final transfer medium S, the toner image is transferred while eliminating the surface potential of the latent image carrier 1 at a transfer nip part NP by a destaticizing light source 8. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and an image forming method using an image forming process such as an electrostatic recording method or an electrophotographic method, which is applicable to a copying machine, a printer, a plotter, a facsimile, a printing apparatus and the like. The present invention relates to an apparatus, and more particularly, to a multicolor image forming method and an image forming apparatus which obtain a multicolor image by multiple transfer of toner images on a plurality of latent image carriers onto a final transfer medium.

[0002]

2. Description of the Related Art In recent years, a large amount of color documents have been handled even in offices, and there is a demand for higher speed full color printers and full color copying machines than ever before. In general, a color laser printer which has become popular in recent years has a plurality of developing devices each containing a developer of each color of yellow (Y), magenta (M), cyan (C), and black (Bk) for one photoconductor. Are arranged so that they can contact each other, a toner image of each color is created for each rotation of the photoconductor, and the image is sequentially transferred from the photoconductor to an intermediate transfer body or a paper held on a transfer drum or the like. The so-called one-drum system for forming a toner image is the mainstream. The toner images of a plurality of colors are superposed on the above-mentioned intermediate transfer body, and then,
There are an intermediate transfer method in which they are collectively transferred to paper, and a direct transfer method in which they are sequentially transferred to paper held on a transfer drum or the like to create a color toner image.

However, in any machine, in order to obtain a color image using four colors, the photoconductor must rotate four times,
The productivity did not go up. Therefore, in order to cope with the speedup, the number of photoreceptors is increased by the number of colors (usually 3 or 4),
Machines of so-called tandem system or in-line system, in which respective developing devices are arranged correspondingly and paper is continuously brought into contact with the photoconductor to obtain a color image, are commercially available. In Japanese Laid-Open Patent Publication No. 53-74037 (corresponding to US Pat. No. 4,162,843), a plurality of photoconductors are stacked for speeding up color image output, and a transfer material is conveyed by a belt-shaped conveying means. There has been proposed an image forming apparatus for sequentially transferring multiple toner images. In this case, if the 1-drum system and the outer peripheral speed of the photoconductor are constant, it is possible to print at a speed 4 times or more.

However, the following problems have been pointed out in the case of a color image forming method in which such toner images are multiple-transferred onto a transfer medium such as paper. For example, a photoreceptor as a latent image carrier, a primary charger as a charging unit,
Four image forming units having an image exposure device as a latent image forming device, a developing device as a developing device, and a transfer device are used for cyan toner, magenta toner, yellow toner, and black toner, and for each color toner on paper. In the full-color image forming apparatus that sequentially multiple-transfers toner images by the transfer unit of the image forming unit, the toner already transferred onto the paper at the time of multiple-transfer of the second and subsequent colors is
In some cases, so-called reverse transfer occurs in which the image is transferred to the photoreceptor and then returned.

When the above-mentioned reverse transfer occurs, when waste toner from the photoconductor drum cleaner is reused in the developing device, a problem of toner color mixing in the developing device occurs. The color mixture in the developing device is a serious problem in multicolor image formation. Further, occurrence of reverse transfer means that the toner image on the paper is disturbed, which causes deterioration of image quality.

In order to solve the same problem, Japanese Patent Application Laid-Open No. 9-146334 proposes to reduce the reverse transfer by setting the contact angle of the latent image carrier with water to 85 degrees or more. However, it seems that the problem has not been fully resolved.

[0007] As a result of the investigations made so far by the present inventors,
In the so-called negative-positive process, it has been found that in the transfer process from the photoconductor to the paper, the reverse transfer mainly returns the toner on the paper to the non-image portion on the photoconductor. Under the experimental conditions of the present inventors, the charging potential of the non-image portion of the photoconductor is −550V, whereas the potential difference of about −150V and 400V occurs in the image portion where the toner is developed. . The transfer bias for transferring the toner image onto the paper causes the surface of the paper to be about + 500V.

At this time, the potential difference between the image portion and the paper surface is about 650 V in the vicinity of the transfer nip, whereas the potential difference between the non-image portion and the paper surface is as large as about 1050 V. It has been confirmed that discharge easily occurs between the non-image area and the paper surface. These discharges are considered to be the cause of the reverse transfer, and it has been found that the reverse transfer largely contributes to the potential difference between the paper and the surface of the photoreceptor.

Japanese Unexamined Patent Publication No. 5-165383 proposes to reduce the potential difference between the image portion and the non-image portion by eliminating the charge on the surface of the photosensitive member before the transfer nip, thereby reducing the reverse transfer to the non-image portion. The results of experiments conducted by the present inventors are shown in FIG.
5 shows. FIG. 15A is an image when the surface of the photoconductor is not discharged before the transfer of the toner image, and FIG. 15B is an image when the surface of the photoconductor is discharged by light irradiation before the transfer of the toner image.

As described above, the electrostatic charge removal before transfer affects the image clarity. When the electrostatic charge on the surface of the photosensitive member is removed by light irradiation before the transfer of the toner image to eliminate the potential difference between the image and the non-image portion, the toner is removed. Since the image is a collection of charged particles of the same polarity, it is considered that the toners repel each other electrostatically, causing the toner to scatter before being transferred to paper, that is, so-called toner scattering. Normally, the toner particles are suppressed so as not to scatter at the height of the potential of the non-image portion with respect to the image portion on the photoconductor, but when the charge is removed, the deterrent force is reduced.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent toner scattering before transfer and prevent image deterioration due to reverse transfer. It is an object of the present invention to provide an image forming method and an image forming apparatus capable of obtaining an excellent image.

[0012]

The present invention employs the following image forming method and structure as means for solving the above problems. (1). An electrostatic latent image is formed on the latent image carrier, a toner image is formed by developing this electrostatic latent image, and the toner image on this latent image carrier is the same as that held on the transfer / transport member. In the image forming method for multi-color multiple transfer onto the final transfer medium to form a final multi-color image, at least when transferring the toner images of the second and subsequent colors onto the final transfer medium, the latent image in the area for transferring the toner image is used. When the maximum potential difference V between the surface potential of the image carrier and the surface potential on the final transfer medium is the thickness of the toner image sandwiched between the latent image carrier and the final transfer medium as t [μm] In addition, it was decided that the condition of V <312 + 6.2 × t should be satisfied (claim 1).

(2). In the image forming method according to (1), by using a light-transmitting member as the transfer / transport member, the surface potential of the latent image carrier is eliminated by irradiating light from the back surface of the transfer nip portion. The maximum potential difference in the transfer area is set within the specified range (claim 2). The following are specific means for removing electricity by irradiation with light. (2-1). In the image forming method described in (2), the surface potential of the latent image carrier is eliminated by irradiating light from the inside of the transfer conveying member upstream in the rotation direction of the transfer electric field applying means provided inside the transfer conveying member. To do so. (2-2). In the image forming method described in (2), the transfer electric field applying unit having a light transmitting property is used,
By irradiating light from the back side, the latent image carrier is photo-erased while the transfer electric field is applied. (2-3). In the image forming method described in (2-2),
A corona charger is used as the transfer electric field applying means. (2-4). In the image forming method described in (2-2),
A contact transfer member made of a light transmissive material is used as the transfer electric field applying means. (2-5). In the image forming method described in (2), a toner image on the latent image carrier is transferred to a transfer nip portion that transfers the toner image to the final transfer medium, a downstream side in a rotation direction of the latent image carrier, or the final transfer. The latent image carrier is discharged by irradiating light from the downstream side in the medium transport direction. (2-6). In the image forming method according to any one of (2-1) to (2-5), the latent image carrier is not discharged on the upstream side in the rotation direction of the latent image carrier with respect to the transfer nip portion. In addition, the light shielding means is provided.

(3). In the image forming method according to (2) (or any one of (2-1) to (2-6)), the amount of light to be emitted for static elimination is changed according to the light transmittance of the final transfer medium. (Claim 3). That is, the light amount of the light irradiation for removing the charge of the latent image carrier is set to an appropriate value according to the light transmittance of the final transfer medium.

(4). In the image forming method according to any one of (1) to (3), the latent image carrier is destaticized only when the final transfer medium passes through the transfer nip (claim Item 4). That is, the latent image carrier is destaticized only in the image creation area.

(5). An electrostatic latent image is formed on each of a plurality of latent image bearing members, and these electrostatic latent images are developed by respective developing means provided for each latent image bearing member so that each latent image bearing member is developed. A toner image is formed on each of the toner images, and each of these toner images is sequentially superimposed and transferred onto the same final transfer medium to form a final image, while each of the toner images from each latent image carrier to the final transfer medium is formed. In the image forming method, the toner remaining on the latent image carrier without being transferred by each transfer unit is collected by each cleaning unit provided corresponding to each latent image carrier, and the image forming method described above (1) to ( The image forming method according to any one of 4) is applied, and the toner collected by each cleaning unit is returned to each developing unit for use (Claim 5).

(6). A latent image carrier for carrying an electrostatic latent image, a latent image forming means for forming an electrostatic latent image on the latent image carrier, and the electrostatic latent image developed with a toner which is a charged colored particle. A developing means for forming a toner image on the latent image carrier and a transfer means for transferring the toner image on the latent image carrier to the final transfer medium held on the transfer / transport member. In the image forming apparatus having one or more image forming units, the image forming method according to any one of (1) to (5) is used (claim 6).

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, an embodiment of the image forming method and apparatus according to (1) and (6) of the above-mentioned solving means will be described. The image forming apparatus according to this embodiment is
A latent image carrier for carrying an electrostatic latent image, a latent image forming means for forming an electrostatic latent image on the latent image carrier, and the electrostatic latent image developed with a toner which is a charged colored particle. A developing means for forming a toner image on the latent image carrier and a transfer means for transferring the toner image on the latent image carrier to the final transfer medium held on the transfer / transport member. An image forming apparatus having at least one image forming unit, which forms an electrostatic latent image on a latent image carrier, develops the electrostatic latent image to form a toner image, and the latent image carrier The above toner image is multi-transferred in multiple colors onto the same final transfer medium held on the transfer / transport member to form a final multi-color image. In such an image forming apparatus, the inventors of the present invention return the toner image once transferred onto the paper, which is the final transfer medium, to the photoreceptor as a latent image carrier at the time of transferring the next toner image. It was found that the reverse transfer phenomenon that would occur is caused by the discharge phenomenon in the toner layer in the transfer area. That is, when the potential difference between the surface potential of the photoconductor and the paper to which the transfer electric field is applied across the toner (potential difference generated in the thickness of the toner layer) exceeds a certain value, reverse transfer occurs. I found it. Paschen's law is known as a natural law of discharge in a void having a potential difference in the air, but it was found that discharge occurs in accordance with Paschen's law even in the toner layer in the transfer area. This is because the toner layer is not completely filled with toner particles and the discharge is occurring in the gap occupied by the air between the toners.

Therefore, the reverse transfer phenomenon can be prevented if the maximum potential difference applied to the toner layer in the transfer nip during the transfer is such that no discharge occurs. The maximum potential difference V that can be applied to the toner layer is correlated with the thickness of the toner layer, and when the thickness of the toner layer is t [μm], if the potential difference satisfies the condition of V <312 + 6.2 × t No internal discharge occurs.

This condition is particularly effective for the second and subsequent colors when obtaining a multicolor image. This is because in the normal reversal development method, the potential of the non-image area where the toner on the photoconductor is not developed is more than the potential of the image area where the toner on the photoconductor is developed and attached and the potential on the paper. This is because the potential difference with the paper becomes large. In most cases, the potential difference between the image area and the paper usually does not exceed the discharge limit potential difference. This is because the transfer rate itself deteriorates when discharge occurs. Therefore, even if there is no problem at the time of transferring the first first color image, there is no problem in transferring the second color toner image after the second color, but the first color toner image already transferred onto the paper is not transferred onto the photoconductor. Discharge occurs in the non-image portion of the image and reverse transfer occurs. Therefore, the main problem is the potential of the non-image area of the photoconductor. Here, from the viewpoint of development, it is difficult to reduce the potential of the non-image area of the photoconductor, so there is the idea that the non-image area potential on the photoconductor should be eliminated after development. The problem of toner dust occurs.

Therefore, in the present invention, at least when the toner images of the second and subsequent colors are transferred onto the paper which is the final transfer medium, the maximum of the surface potential of the photoconductor in the area where the toner image is transferred and the surface potential on the paper is the maximum. The potential difference V satisfies the condition of V <312 + 6.2 × t 2 when the thickness of the toner image sandwiched between the photoconductor and the paper is t [μm].

(Embodiment 2) Next, an embodiment of the image forming method and apparatus according to (2) and (6) of the above-mentioned solving means will be described. The present inventors form an electrostatic latent image as a latent image carrier, develop the electrostatic latent image to form a toner image, and transfer the toner image to a final transfer medium to form the final image. In the image forming method for forming, in the above-mentioned conventional technique, the transfer electric field after the development is completed and before reaching the transfer portion is not applied, and the surface of the photoconductor is exposed in the area where the toner image is exposed in the space. Focusing on the occurrence of toner scattering to eliminate static electricity, in order to achieve the above object,
On the other hand, after development, transfer is performed while removing the charge on the surface of the photoconductor in the area where the transfer electric field is generated or in the area where the final transfer medium and the toner image are in contact, so that the reverse transfer can be performed without causing toner scattering. It has been found that can be prevented.

The toner scattering acts on the developed toner so as to be trapped on the photoconductor due to the potential difference between the image portion and the non-image portion on the photoconductor, and the confinement action force is rapidly released by the charge removal. It occurs because of.

Therefore, after development, if the transfer is performed while removing the surface potential of the photoconductor in the area where the transfer electric field is generated or the area where the final transfer medium and the toner image are in contact with each other, toner scattering does not occur. For example, in the transfer nip portion, the photoconductor and the final transfer medium are in close contact with each other and the transfer electric field acts, and since the final transfer medium and the toner image are in contact with each other, both conditions are satisfied, and there is no space for scattering. No toner scattering occurs. This example corresponds to a superordinate concept of each example described below.

The means for removing electricity will be described below in various examples. FIG. 1 shows the relationship between “photoconductor surface potential and reverse transfer amount”. The horizontal axis represents the surface potential of the photoconductor in the non-image area immediately after passing through the transfer nip where the photoconductor and the final transfer medium (paper) are in close contact, and the vertical axis represents the amount of reverse transfer toner to the photoconductor. .

It can be seen from FIG. 1 that the reverse transfer can be suppressed more when the absolute value of the surface potential of the photoconductor in the non-image area is suppressed to a lower value. From the results of this experiment, it is understood that by suppressing the surface potential of the non-image portion of the photoconductor to preferably −200 V or less, it is possible to prevent reverse transfer and obtain a good image without disturbance. Since the photosensitive member surface potential of the image portion at this time was almost 0 V, it is desirable to prevent the reverse transfer by setting the potential difference between the toner image portion and the non-image portion on the photosensitive member within 200 V. The surface potential of the paper at this time was +200 V, and the toner image already transferred onto the paper had a thickness of about 15 μm with an adhesion amount of about 0.65 mg / cm ² . The allowable potential difference V according to the first embodiment (claim 1) is about 405.
Since it is V, the potential difference of 400 V is less than or equal to this potential difference, and it can be seen that the reverse transfer is eliminated by the discharge disappearing.

In order to eliminate the surface potential of the photoconductor in the region where the transfer electric field acts, or in the region where the final transfer medium and the toner image on the photoconductor are in contact, light elimination by irradiating light is most effective. This is a simple means. Hereinafter, an example of the configuration of the image forming apparatus provided with a means for performing light elimination will be described.

FIG. 2 is a front view for explaining the structure of the main part of the image forming apparatus. In FIG. 2, reference numeral 1 denotes a drum-shaped photoconductor, and the charging roller 2 and the erase lamp 3 are arranged in the order of rotation indicated by arrows. A developing device 4, a drum-shaped paper transfer / conveying drum 5, a paper S which is a final transfer medium adsorbed and fixed on the drum, a cleaning device 6, a static eliminator 7, and the like are arranged. The writing light L emitted from an exposing device (not shown) is irradiated onto the photosensitive member between the charging roller 2 and the developing device 4. A region where the photoconductor 1 and the paper S are in contact with each other is referred to as a transfer nip portion and is indicated by a symbol NP.

The outline of the image forming process is as follows.
Thus, the peripheral surface of the photoconductor 1 is uniformly charged, and then the writing light L forms an electrostatic latent image. The electrostatic latent image is developed with toner in the developing device 4 to form a toner image, and the toner image is transferred to the final transfer medium such as the paper S on the paper transfer / conveying drum 5 to form the final image.

A transfer electric field is applied to the transfer nip portion NP by a bias voltage applied between the photoconductor 1 and the transfer / transport drum 5. Therefore, this transfer nip portion NP
Is a region where a transfer electric field is generated after development and a region where the paper transfer conveyance drum 5 and the toner image on the photoconductor are in contact with each other. By doing so, reverse transfer can be prevented without causing toner scattering.

In the usual method, it is difficult to irradiate the transfer nip portion NP where the photosensitive member 1 and the paper are in contact with each other, because the paper S and the photosensitive member 1 itself block the transfer nip portion NP. However, as in the example shown in FIG. 2, the paper S itself is almost white, and although it has different light transmittance depending on the thickness and the paper type, it has the light transmittance itself. Therefore, the charge can be removed from the back side of the transfer nip portion NP with respect to the photoconductor 1, that is, through the paper S, in the nip. In the example of FIG. 2, the paper S is held by the paper transfer / conveyance drum 5 for holding and conveying the paper and giving a transfer electric field. However, the transfer / conveyance drum 5 should be made of a light transmissive material. Accordingly, a charge eliminating light source 8 as an exposure device for eliminating the charge on the photoconductor is arranged therein, and the light from the charge eliminating light source 8 is applied to the transfer nip portion NP through the paper transfer conveyance drum 5 and the paper S. The surface potential of can be removed.

As the static elimination light source 8, a light emitting diode (L
ED: Light emitting diode (LD) and semiconductor laser (LD:
Laser diode), a xenon lamp, etc. can be used. It is possible to control the surface potential of the photoconductor to an arbitrary value by grasping the relationship between the current or applied voltage flowing through the LED or LD and the light emission (exposure) light amount in advance and adjusting the light emission light amount to control the charge removal amount. . Basically, as shown in FIG. 1, the lower the potential of the surface of the photoconductor 1 is, the less the reverse transfer is likely to occur. However, when the photoconductor 1 is irradiated with an excessively high light amount, the photoconductor 1 is damaged and the life is remarkably increased. There is a risk of contraction, so it is necessary to set it to an appropriate range.

Further, in addition to the configuration example of FIG. 2, as in another configuration example shown in FIG. 3, the drive roller 10 and the bias roller are used as a transfer transport member for transporting the paper S and applying a bias. An example using the stretched light-transmissive medium-resistance transfer transport belt 9 or without using such a paper transport member,
There is a method of directly generating an electric field on paper. In this case, the toner image is transferred by directly applying an electric charge to the back surface of the paper with a conductive roller or a corona charger.

The semiconductive resin or rubber used in the above-mentioned paper transfer carrier is black because pigments such as carbon black are dispersed in order to have conductivity. Although some of them have ionic conductivity themselves, most of them are also colored.

A paper transfer / conveyance member having a drum shape such as the paper transfer / conveyance drum 5 shown in FIG. 2 is generally made of aluminum (Al) or stainless steel (SUS) having a thickness of about 2 mm. The surface of the metal tube has a thickness of 0.
A material having a conductive rubber of about 5 to 3 mm is often used, but in this example, since it is necessary to expose the photoconductor 1 from the back surface of the transfer nip portion NP, the normal configuration is used. Is difficult to use.

Therefore, here, as an example, a transparent acrylic resin tube having a thickness of about 3 mm is used in place of the metal tube in order to take out the rigid body of the drum constituting the paper transfer / conveyance body.
A transparent metal film such as ITO is attached to the surface of the acrylic resin tube to form a bias applying electrode. Further, a transparent rubber such as polyurethane rubber in which metal oxide powder such as tin oxide is finely dispersed in order to impart conductivity is used as a surface rubber layer.

Further, not only in this embodiment but also in each of the following embodiments, in order to effectively eliminate the surface potential of the photosensitive member, the paper transfer / transport member, the transfer electric field applying means, and other members are It is necessary to make it with a light transmissive material. In that case, a resin or rubber, which is a material, is used as a light-transmitting material, and a metal oxide such as titanium oxide or tin oxide is finely dispersed and used as a filler for imparting conductivity. As a result, a light-transmitting semiconductive polymer can be produced.

(Embodiment 3) Next, an embodiment of the image forming method and apparatus according to (2), (2-1) and (6) of the above-mentioned solving means will be described. Although the configuration example in FIG. 2 is an example in which a drum-shaped member is used as the paper transfer / transport member, in the present embodiment, as shown in FIG. 4, a belt-shaped paper transfer / transport member (paper transfer / transport belt) is used. I'm using it.
As for the other constituent members, those having the common function are designated by the same reference numerals as those in FIG. 2, and the description thereof will be omitted. In FIG. 4, a belt-shaped paper transfer / transporting member (paper transfer / transporting belt) is denoted by reference numeral 12. This paper transfer conveyance member 1
In this example, the photosensitive member 1 is discharged by exposing from the back surface of 2.

Generally, a belt-shaped paper transfer / transport member 12
When using, the transfer electric field applying means 13 for applying a bias is used on the back side of the transfer nip portion NP of the paper transfer / transport member 12 with respect to the photoconductor 1. This transfer voltage applying means 1
No. 3 is mainly due to application of electric charges to the back surface of the belt by a corona charger (corotron, scorotron, etc.) or voltage application by contact with a conductive roller, a conductive brush, a conductive blade, or the like.

FIG. 4 shows an example in which the transfer roller 13 made of a conductive roller is used as an example of the transfer voltage applying means. Conventionally, not only the transfer roller 13 but also a member as the above-mentioned transfer electric field applying means, which has conventionally not been a light transmissive member, is exposed to the transfer nip portion NP from the inside of the paper transfer conveying member 12. Irradiation from the upstream side of the transfer electric field applying means in the rotational direction of the paper transfer conveying member is desirable. The transfer roller 13 is provided slightly offset to the downstream side of the transfer nip portion NP, and the static elimination light source 8 is arranged on the upstream side thereof so that the transfer nip portion NP is irradiated with light. .

In the present embodiment, as shown in FIG. 4, inside the paper transfer / transport member 12 on the upstream side in the rotational direction of the paper transfer / transport member 12 with respect to the transfer roller 13 provided inside the paper transfer / transport member 12. The surface potential of the photoconductor 1 is neutralized by passing through the transparent paper transfer / transport member 12 and the paper S which is the final transfer medium transported on the surface thereof by irradiation of light from the provided static elimination light source 8.

The belt having a light-transmitting property used for the paper transfer / transport member 12 and the like is, for example, a belt made of polyimide having high durability and a high Young's modulus, or PVD having excellent surface smoothness.
F (polyvinylidene fluoride) belt, other ETFE
(Ethylene-tetrafluoroethylene resin), PFA (tetrafluoro-perfluoroalkyl vinyl ether resin) and other fluoropolymers, polyethylene, polystyrene, PE
T (polyethylene terephthalate), nylon, vinyl chloride-containing vinyl chloride, vinyl acetate, vinyl acetylene, vinyl styrene, etc., polycarbonate,
Polyurethane resin, silicone resin and the like can be used as the paper transfer / conveyance belt.

As a constitution, not only the resin belt but also a rubber layer such as polyurethane rubber or polyurea rubber on the resin belt layer, and a coat layer containing a fluorine component on the rubber layer, the surface has an elastic multilayer structure. Belts are also used. Particularly, since the surface of the polyurethane multilayer structure belt has elasticity, it has good adhesion to the surface of the photoconductor and the surface of paper and excellent transferability. Further, there is also one constituted by rubber itself, such as NBR, polyurethane rubber, polyurea rubber, EPDM rubber, CR rubber, silicone rubber, and hydrin rubber.

The electric resistance of each of the belts is adjusted by adding a metal oxide or an ionic conductor.
^It has a volume resistance of about ¹⁰ to 10 ¹² Ω · cm, and the surface resistance of the portion on which the toner is placed has a characteristic value of 10 ¹² Ω / □ or more, which is excellent in transferability. Depending on the type of high-molecular polymer used as the base, there may be some milky white or brown color, but 650n for removing charge from the surface of the photoconductor
Red to near-infrared light having a wavelength of about m to 780 nm can be sufficiently transmitted.

(Embodiment 4) Next, an embodiment of an image forming method and apparatus according to (2), (2-1), (2-6), and (6) of the above-mentioned solving means will be described. As in the example shown in FIG. 4, a belt-shaped, light-transmissive paper transfer / transport member 12 is used, and the upstream direction of rotation of the paper transfer / transport member 12 indicated by an arrow is indicated as compared with the transfer roller 13 as a transfer charge applying unit. When the transfer nip portion NP is irradiated with light from the inner side by the static elimination light source 8, there is a possibility that the surface of the photosensitive member before entering the transfer nip portion NP may also be neutralized through the light transmissive paper transfer conveying member 12 and the paper S. . If the surface of the photoconductor is neutralized at a position on the upstream side in the rotation direction of the photoconductor 1 with respect to the transfer nip portion NP, the toner scatters as described above and the image remarkably deteriorates.

Therefore, in order to prevent this from happening, in this embodiment, as shown in FIG. 5, it is located upstream of the transfer nip portion NP in the rotational direction of the paper transfer conveying member 12 (upstream side in the rotational direction of the photoconductor 1). ) So that the photoconductor 1 is not neutralized,
A shielding plate 14 as a shielding means for shielding the light from the static elimination light source 8 is additionally provided to avoid light irradiation to a region which should not be irradiated. In this embodiment, the shielding plate 14 is the static elimination light source 8
However, the present invention is not limited to this and can be provided on an appropriate immovable member.

(Embodiment 5) Next, the above-mentioned solving means (2), (2-1), (2-5), (2-6), (6).
Embodiments of the image forming method and apparatus according to the present invention will be described. FIG. 6 shows an example of a color image forming apparatus according to the present invention.
FIG. 1 is a diagram showing an entire configuration of a full color printer Ipsio8000 manufactured by Ricoh Co., Ltd. In the drawing, reference numeral 101 is an optical unit as an exposure unit for image writing, 102 is a polygon motor, 103 is a photoconductor unit (PCU), 104 Is a developing unit, 105 is a paper transfer conveyance belt, 106 is a P sensor, 107 is a registration roller, 108 is a manual paper feed tray, 109 is a first paper feed tray, 110 is a second paper feed tray, 111 is a double-sided conveyance unit, 112 is a double-sided reversing unit, 113 is a fixing belt, 114 is a pressure roller, 11
5 is a toner bottle, and 116 is a waste toner bottle.

This full-color printer Ipsio8000 has a structure in which four image forming units having a photoconductor unit 104, a developing unit 104, and a transfer unit are arranged side by side, and four photoconductors are provided, and the photoconductor is formed on paper as a final recording medium. It is a so-called direct transfer tandem system in which the paper is directly transferred from, and the paper transfer / conveying belt 105 is used for conveying the paper. A characteristic point of the layout is that the paper conveyance path is inclined in order to reduce the machine size, and the photoconductor unit 103 and the developing unit 104 are designed accordingly. Further, although the four image forming units (photoreceptor unit 103 and developing unit 104) arranged in parallel have the same configuration, the toner colors of the two-component developer accommodated in each developing unit 104 are different from each other. In the example, the image forming unit forms images of yellow (Y), magenta (M), cyan (C), and black (B) from the upstream side to the downstream side in the paper transport direction.

FIG. 7 is a diagram showing an example of the structure of one image forming section, showing the structure around the photosensitive member and the transfer section. In FIG. 7, reference numeral 121 is a drum-shaped photosensitive member, 122 is a charging roller, 123 is a developing roller, 124 is a conveying screw (right), 125 is a conveying screw (left), 126 is a developing doctor, 127 is an agent cartridge, 128. Is a toner concentration sensor, 129 is a transfer bias roller, 130 is a belt holding roller, 131 is a cleaning brush roller, 13
2 is a cleaning blade, and 133 is a discharge lamp (QL) which is a discharge light source. For image formation on the photoconductor, after charging the photoconductor 121 by the charging roller 122, the writing light L corresponding to the image data of each color is exposed from the optical unit 101 to form an electrostatic latent image on the photoconductor 121. Then, the electrostatic latent image is developed by the toner of the two-component developer carried on the developing roller 123 of the developing unit 104 to be visualized, which is a normal electrophotographic image formation. The image formed on the photoconductor 121 is the paper transfer and transport belt 1.
It is transferred to the paper S conveyed by 05.

This full-color printer Ipsio8000 uses a substantially transparent PVDF belt having a thickness of 150 μm and a volume resistance of about 3 × 10 ¹² Ω · cm as the paper transfer / conveying belt 105, and uses the first paper feeding bank shown in FIG. Tray 10
9 or the paper S fed from the second paper feed tray 110 is electrostatically adsorbed on the paper transfer / conveyance belt 105 and is conveyed to the transfer portion. Further, as shown in FIG. 7, when the paper S on the paper transfer / conveyance belt 105 is conveyed to a position relative to the photoconductor 121, the toner is removed by the transfer bias roller 129 installed on the inner surface of the paper transfer / conveyance belt 105. An electric field that moves to the surface of the paper is generated, and the toner on the photoconductor is transferred onto the paper. Then, in the configuration of FIG. 6, by repeating this process four times in four image forming units, the images of four colors are superimposed and transferred onto the paper to obtain a full-color image.

By the way, when a color image is formed through the above-described transfer process, as described above, when the toner transferred from the first photosensitive member is transferred to the second color, the third color and the fourth color, There is a reverse transfer phenomenon of returning to the photoconductor. Therefore, in the example of FIG. 7, the static elimination lamps (for example, LEDs) 133 are evenly arranged over the entire width direction on the inner surface of the paper transfer conveyance belt 105 upstream of the transfer bias roller 129 in the belt moving direction, and the transfer bias roller 129 is disposed. The light was irradiated between the photoconductor 121 and the photoconductor 121. As aforementioned,
The PVDF forming the paper transfer / conveying belt 105 has a light-transmitting property, and the paper S is also white but has a light-transmitting property. Therefore, the photoconductor 121 is neutralized in the transfer nip region NP, and there is no reverse transfer. A good image with less toner scattering could be obtained.

Next, FIGS. 8 and 9 show an example of an image forming unit having the same structure as that of FIG. 7, in which the position of the static elimination lamp 133 is changed, and FIG. 8 shows the transfer of the inner surface of the paper transfer / conveying belt 105. Discharging lamps (for example, LEDs) 133 are evenly arranged over the entire width direction on the downstream side of the bias roller 129 in the belt moving direction, and the transfer bias roller 129 and the photoconductor 12 are provided.
This is an example of irradiating the light between 1 and 1. In addition, FIG.
Is a static elimination lamp (for example LE
D) 133 is evenly arranged over the entire width direction, and light is emitted toward the transfer nip portion NP between the photoconductor 121 and the paper S.

In this example, the surface of the photoconductor 121 is neutralized at the transfer nip portion NP where the transfer electric field is generated.
In addition, the transfer bias roller 129 and the belt holding roller 1
A static elimination lamp (for example, LED) 1 having a static elimination light source 30
It serves as a shielding unit that shields the light from 33, and the transfer is performed by a composite action such as removing the charge on the photoconductor 121 during the application of the transfer electric field, and not performing the charge removal on the photoconductor other than the transfer region. The image deterioration due to reverse transfer is prevented while preventing the previous toner scattering. In addition, like the example of FIGS.
Here, a static elimination light source (a static elimination lamp (Q
Although an example of the arrangement of (L)) is also shown, all show good results in preventing reverse transfer.

(Embodiment 6) Next, an embodiment of an image forming method and apparatus according to (2), (2-2), (2-4) and (6) of the above-mentioned solving means will be described. In the examples so far, the photosensitive member was large and there was a room inside the paper transfer / conveying belt, so it was possible to install a charge removal light source, a shielding means, etc. In many cases, there is not enough room in the layout due to the layout.

Therefore, in this embodiment, the transfer roller 1 having the structure shown in FIG. 4 is used as in the structure shown in FIG.
3 is replaced with a light-transmissive transfer roller 13 ', and the static elimination light source 8 is positioned on the back side of the light-transmissive transfer roller 13' to expose the photoconductor 1.
In this embodiment, a slightly opalescent roller in which titanium oxide is dispersed in conductive urethane rubber is used as the light transmitting transfer roller 13 '. In this case, although it is milky white, there is some scattering, but light can be sufficiently transmitted.

In addition to the transfer roller, a contact transfer member such as a transparent conductive brush or a transparent conductive blade is used as a transfer electric field applying means, and the transparent conductive blade or the transparent conductive brush is used. It is also possible to design the image forming apparatus in a smaller size by performing the exposure from the back side.

(Embodiment 7) Next, the above-mentioned solving means (2), (2-2), (2-3), (2-6), (6).
Embodiments of the image forming method and apparatus according to the present invention will be described. In this embodiment, as shown in FIG. 11, instead of the transfer roller 13 ′ shown in FIG. 10 as the transfer electric field applying means, the corona charger 15 is arranged toward the transfer nip portion NP. The corona charger 15 has a configuration in which a wire is contained in a metal case, and it is easier to form the corona charger 15 as a light transmission type than a transfer roller. That is, if a part of the case forming the corona charger 15 is in a mesh shape or in an open state and the light of the charge eliminating light source 8 is irradiated from there, the exposure at the transfer nip portion NP can be easily performed. it can. When a non-contact type transfer electric field applying unit such as the corona charger 15 is used, the paper transfer / conveying belt 12 and the corona charger 15 are used.
There is a possibility that a gap is generated between the two and the light from the charge eliminating light source 8 is irradiated onto the surface of the photoconductor before transfer. Therefore, in the configuration example of FIG. 11, the shield plate 14 is installed on the upstream side of the corona charger 15 in the belt moving direction to prevent the surface of the photoreceptor before transfer from being irradiated with light.

(Embodiment 8) Next, an embodiment of the image forming method and apparatus according to (2), (2-5) and (6) of the above-mentioned solving means will be described. Other than the above-described method of making the paper transfer / conveying belt light-transmissive and performing static elimination in the transfer nip from the back side, the effect is slightly diminished, but as in the example shown in FIG. By irradiating the transfer nip portion NP with light from the downstream side in the rotation direction of the paper transfer / conveying belt 105 and the photosensitive member 121 with respect to the portion NP, the photosensitive member 121 can be neutralized in the transfer nip portion NP. .

A static elimination light source such as an LED is provided in a space position between the paper transfer / transport belt 105 and the paper S and the photoconductor 121 on the downstream side in the rotation direction of the paper transfer / transport belt 105 and the photoconductor 121 from the transfer nip portion NP. 133 is arranged, and the light emitted toward the downstream of the transfer nip portion NP is applied to the photoconductor 121.
Since the photosensitive layer has a light-transmitting property, it also enters the transfer nip portion NP, and the transfer bias roller 129 erases the surface of the photosensitive member in the transfer nip portion NP area where the transfer electric field is acting.

In the case of this embodiment, the paper transfer / conveyance belt 1
Since the photosensitive member 121 is not exposed through 05 and the paper S, it is possible to use an opaque paper transfer / transport belt instead of the transparent paper transfer / transport belt. Also,
This is effective for colored paper and other paper that does not pass the wavelength of static elimination light. However, if a paper transfer / transport belt having a light-transmitting property is used, or if the paper transfer / transport belt having a light-reflecting property on the surface is used, the static elimination effect is further enhanced.

(Embodiment 9) Next, another embodiment of the image forming method and apparatus according to (2), (2-5) and (6) of the above-mentioned solving means will be described. When a light-transmissive paper transfer / conveyance belt is used, as in the configuration example of the main part of the image forming apparatus shown in FIG. Transfer transport belt 12
The static elimination light source 8 may be arranged on the downstream side in the transport direction of to irradiate the light toward the transfer nip portion NP. By irradiating the light from the downstream side of the transfer nip portion NP in this way, it is possible to reliably prevent the charge removal of the photoconductor 1 due to the wraparound of the light to the upstream side of the transfer nip portion, and to prevent the image deterioration due to the toner scattering. .

(Embodiment 10) Next, an embodiment of the image forming method and apparatus according to (3) and (6) of the above-mentioned solving means will be described. The thickness of the paper, the degree of whiteness, etc., in the case where the static elimination is performed at the transfer nip portion as in the examples shown in Examples 2 to 9, and especially when the static elimination is performed through the paper or the paper transfer / conveying belt from the back side. The light transmittance of the paper itself differs depending on the type of paper, and there is a case where the amount of static elimination is not appropriate with a constant light irradiation intensity. Therefore, by changing the light irradiation light amount according to the characteristics (light transmittance) of the paper to be printed, it is possible to perform static elimination without excess or deficiency.

The light amount is adjusted by adjusting the voltage or the amount of current applied to the charge eliminating light source. When the amount of light is changed according to the paper used, a mechanism for detecting the light transmittance of the paper is required. The light transmissivity may be detected with high accuracy by actually detecting the light transmissivity. Specifically, it is preferable to measure the light transmittance with a combination of a light emitting element and a light receiving element so that the paper is sandwiched in the paper transport path. This detection device does not need to have a dedicated one and can use existing sensors for paper detection. For example, an image forming apparatus such as a copying machine or a printer has a photo interrupter for detecting the position of the leading edge of the paper in order to perform registration in the paper advancing direction, or a size detection photo for detecting the size of the manually fed paper. Since an interrupter or the like is usually provided, the cost can be reduced and a function can be added by utilizing this element. In addition, in a system using a transfer / conveyance belt, there is a system for forming a toner image on the belt and measuring the reflection density thereof with a P sensor to adjust the toner density and position. It is also possible to use.

The position of the light transmissivity detection sensor for the paper is also important. It is desirable that the detection unit be located in the center of the direction (width direction) perpendicular to the traveling direction of the conveyance path so that it can be used for small paper.
Since it has a bypass tray to accommodate a small number of paper feeds,
Instead of the transport path immediately after the paper is pulled out from the paper feed bank,
It is desirable to provide it in a common transport path from the manual feed tray and the paper feed bank.

When a transfer / transport belt is used, the transfer / transport belt is incorporated in the machine and its light transmittance does not change as frequently as paper. Therefore, basically, a combination of the paper type and the paper transfer / transport belt is used. There is no need to change the amount of light unless it changes. However, there is a case where the paper transfer / conveying belt is scratched or soiled over time, and the light transmittance is deteriorated.
Therefore, in this case, it is better to change the light amount according to the change in the light transmittance of the paper transfer / conveyance belt. In this case, the light transmission sensor, with the paper held on the paper transfer and transport belt,
It is desirable to attach it to a place where the transmittance of the paper and the paper transfer / conveyance belt can be measured at the same time. In this case, when the paper comes
Since the light transmittance of the belt alone can be detected independently,
In order to prevent light fatigue, which will be described later, it is also effective to change the amount of light when the paper comes and when only the belt is used. Needless to say, it is desirable that the wavelength of the light used for the measurement is also the same as the wavelength for performing the light elimination.

(Embodiment 11) Next, an embodiment of an image forming method and apparatus according to (4) and (6) of the above-mentioned solving means will be described. In the image forming method and apparatus described in Embodiments 2 to 10, the charge removal of the photoconductor 1 (121) is performed at the transfer nip portion NP, but the charge removal light source 8 (133) is continuously discharged during the operation of the image forming apparatus. It is known that if the light is irradiated more, the control is easier, but as mentioned above, it is known that the photoconductor causes light fatigue and the charging characteristics are deteriorated if it is overexposed. Deterioration of the photoconductor by erasing light by irradiating only the image creation area without irradiating light in areas where no image is created, such as the area between papers during continuous printing at the time of finishing or at the time of continuous printing. Can be prevented.

(Embodiment 12) Next, an embodiment of the image forming method and apparatus according to (5) and (6) of the above-mentioned solving means will be described. In the image forming apparatus capable of achieving good transfer with less reverse transfer as described in Examples 1 to 11, it is possible to reuse the transfer residual toner, that is, to recycle toner.

As an example of an image forming method (apparatus) for performing such toner recycling, an electrostatic latent image is formed on each of a plurality of latent image carriers, and these electrostatic latent images are formed on each latent image carrier. The latent image bearing member is developed by each developing means provided for the image bearing member to form a toner image on each latent image bearing member, and these toner images are sequentially superimposed and transferred onto the same final transfer medium to form a final image. On the other hand, the toner remaining on each latent image carrier without being transferred at each transfer portion of each toner image from each latent image carrier to the final transfer medium is formed on each latent image carrier. In the case of a so-called tandem type image forming method (apparatus) in which one photoconductor is provided for each color, such as collecting by each cleaning means provided correspondingly, it is input to each cleaning apparatus. If there is no reverse transfer, the toner is only the color developed by the photoconductor corresponding to the cleaning device, so the toner collected by each cleaning device is directly transferred to the developing device provided for the photoconductor. It is possible to return it, and it is possible to provide a good image that has both small toner scattering and small reverse transfer,
Toner can be easily recycled.

As an example of the image forming apparatus of this embodiment, a configuration example of a tandem type color image forming apparatus will be described. The image forming apparatus main body is provided with an image for forming a color image by a conventionally known electrophotographic method. It is composed of a reading unit, an image writing unit, an image forming unit, a paper feeding unit, a paper discharging unit, and the like. Here, FIG. 13 shows an image writing unit 23 in a color printer which is an example of the color image forming apparatus of the present embodiment.
FIG. 3 is an enlarged view showing the image forming unit 20 and the like. FIG. 14 is an enlarged view showing the structure around the photoconductor of the color printer.

The operation of forming an image will be described with reference to these figures. First, an image processing unit (not shown) performs image processing on the basis of an image signal to generate black (Bk) for image formation,
The image signals are converted into yellow (Y), magenta (M), and cyan (C) color signals, and the image signals are transmitted to the image writing unit 23. Although the internal configuration of the image writing unit 23 is well known, illustration thereof is omitted, but a laser scanning optical system including a laser light source, a deflector such as a rotating polygon mirror, a scanning imaging optical system, and a mirror group, or It is composed of an LED array in which a large number of LEDs are arranged one-dimensionally or two-dimensionally, an LED writing system including an imaging optical system, and the like, and has four optical paths corresponding to the image signals of the respective colors, and image formation is performed. Image writing is performed by irradiating the photosensitive drums 1Bk, 1Y, 1M, and 1C provided for each color of the unit 20 with the writing light L corresponding to each color signal.

The image forming section 20 is provided with four image forming sections (image forming units) for black (Bk) and yellow (Y).
1B for magenta (M) and cyan (C)
It is equipped with k, 1Y, 1M and 1C. An OPC photoconductor is usually used as the photoconductor for each of these colors. Around the photosensitive members 1Bk, 1Y, 1M, 1C, the charging roller 2,
An exposure unit, which is an irradiation unit of the writing light L from the image writing unit 23 by a laser or the like on the photoconductor, a developing device 4 provided corresponding to each photoconductor, a transfer bias roller 13 for transfer,
A cleaning device 6, a static eliminator 7, etc. are provided.
The developing device 4 uses a two-component magnetic brush developing system.

Since the image forming process for each of the photoconductors 1Bk, 1Y, 1M, 1C is common, the photoconductor 1Bk
The surrounding image forming process will be described as a representative.
Before writing an image, the surface of the photoconductor is charged to about -700V by the charging roller 2 provided upstream of the exposed portion on the photoconductor 1Bk in the rotational direction. In the embodiment, a conductive rubber roller is used as the charging roller 2, and the charging roller 2 is placed in a non-contact manner with a distance of about 50 μm from the photoconductor 1Bk.

The charging roller 2 has a frequency of about 1 kHz,
An AC voltage having a peak-to-peak voltage of 2 kV is applied, and its center value is set to about -800V. As a result, the photoconductor 1Bk is uniformly charged to about -700V.
The charging means is not limited to the charging roller 2, but contact charging in which a conductive rubber roller is charged so as to contact the photosensitive member 1Bk, AC + DC charging, or only DC bias of about -1400 V is applied without applying AC bias. Photoconductor 1
It is also possible to employ a DC bias roller charging method for charging Bk, a corona charging method using a corotron or a scorotron, which has been often used conventionally, and a brush charging method. Writing is performed on the charged photoconductors 1Bk, 1Y, 1M, and 1C by the writing light L from the image writing unit 23, and after the electrostatic latent image is formed, the electrostatic latent image is formed by the developing process by the developing device 4. The image is developed.

In FIG. 14, the developing device 4 is the developing roller 4
a, doctor blade 4b, two screws 4c, 4
d, a toner density sensor 4e and an outer case 4f. Regarding the positional relationship between the developing roller 4a and the screws 4c and 4d, the screw 4c is located obliquely downward from the developing roller 4a, and the two screws 4c and 4d are arranged in parallel in the horizontal direction. Two screws 4 on the outer case 4f
A partition plate 4g is provided to divide c and 4d into two chambers. The back side and front side of this partition plate 4g perpendicular to the paper surface are
A two-component developer composed of non-magnetic toner and carrier is cut out so as to circulate between these two screws 4c and 4d. In addition, the outer case 4f is the photoconductor 1Bk.
A portion facing the is opened, and a part of the developing roller 3a is exposed from this opening. As shown in FIG. 14, the outer case 4f has a slightly larger space above the screw 4c beside the developing roller 4a, so that the developing roller 4a, the screws 4c and 4d, the doctor blade 4 are formed.
It encloses b.

The developing roller 4a comprises a rotatable non-magnetic developing sleeve 4a1 and a magnet 4a2 which is a magnetic field generating means fixed inside. Screw 4c,
The rotation of 4d conveys the developer in opposite directions. The developer is conveyed while being agitated by screws 4c and 4d having opposite feed directions, and constantly circulates in two chambers partitioned by a partition plate 4g. The developer that has been agitated and conveyed and circulated is supplied to the developing sleeve 4a1 by the screw 4c, and is supplied to the magnet 4a2.
Is held on the surface in the form of a magnetic brush by the magnetic force of and is drawn up in the rotating direction of the developing sleeve 4a1. The developer drawn on the magnetic brush is cut into a proper amount by the doctor blade 4b and sent to the developing unit facing the photoconductor 1Bk. On the other hand, the developer remaining after being cut off by the doctor blade 4b drops by gravity on the magnetic brush-shaped outer side of the surface of the developing sleeve 4a1 and is returned to the screw 4c, and the screw 4 from the notch on the back side of the partition plate 4g.
The process shifts to d, returns to the screw 4c from the notch on the front side of the partition plate 4g, and is supplied again to the developing sleeve 4a1 while being stirred and conveyed again.

The developer sent to the developing portion, which is the peripheral surface portion of the photoconductor 1Bk facing the developing sleeve 4a1, is visualized by transferring the toner to the electrostatic latent image on the photoconductor 1Bk.
The frequency on the developing sleeve 4a1 is 2.25 kHz,
AC voltage with a peak-to-peak voltage of about 1 kV has a center value of -50
It is applied as 0V. With this development bias,
The toner is transferred due to the potential difference from the exposed area (charge potential of about −150 V) on the photoconductor 1Bk. In addition, the developer not used for visualization returns to the inside of the outer case 4f and the magnet 4
The portion a2 where the magnetic force does not work is separated from the developing sleeve 4a1 and collected by the screw 4c.

In this way, the developer is supplied and collected in the developing sleeve 4a1 while being circulated while being stirred and conveyed by the screw 4c and the screw 4d. When the image is repeatedly output, the toner density becomes low, so the toner density sensor 4e
The toner is replenished from a toner bottle (not shown) or the like so that the density becomes constant while being detected in step 1.

As the paper transfer / transport belt 12 for transporting the paper S which is the final transfer medium, a transparent belt-shaped one is used, and the transfer roller 13 and each photoconductor having the same structure as described in FIG. 5 are used. 1Bk, 1Y, 1M, and 1C, and the static elimination light source 8 and the shielding plate 14 having the same configuration as described in FIG. 5 are provided on the back side of the paper transfer / conveying belt 12 with respect to the transfer nip portion NP. It is located in.

The toner images of the respective colors formed on the photoconductors 1Bk, 1Y, 1M and 1C are the paper S which is the final transfer medium.
Are sequentially superposed and transferred while passing through the transfer nip portion NP, and when passing through the transfer portion of the last photoconductor 1C, a full-color superposed transfer image is carried by combining toner images on the respective photoconductors. As a method of paper transfer, a transfer roller 13 as a transfer charge adding unit, which is provided to face the photoconductors 1Bk, 1Y, 1M, and 1C so as to sandwich the paper S with a belt-shaped paper transfer conveyance belt 12, is provided. It is electrostatically transferred by generating a transfer electric field. In the figure, conductive urethane rubber (rubber hardness JIS-A 40
The transfer electric field is generated by applying a voltage of about 1.5 kV to the transfer roller 13 having a volume resistance of 10 ⁸ Ωcm).

As the paper transfer / conveyance belt 12, a PVDF (polyvinyl denfluoride) belt having a thickness of 150 μm and excellent in surface smoothness is used. The electrical resistance is adjusted by adding a metal oxide such as tin oxide to PVDF, which has a volume resistance of about 10 ¹⁰ to 10 ¹² Ωcm,
The surface resistance of the portion on which the toner is placed has a characteristic value of 10 ¹² Ω / □ or more, and the transferability is excellent. In addition, it has a slightly milky white color and some scattering,
Allows sufficient light transmission.

Sixteen LEDs constituting the charge eliminating light source 8 are arranged at regular intervals in the axial direction of the photoconductor 1Bk (direction penetrating the paper surface in FIG. 14). A diffusing plate (not shown) is provided on the surface in order to make the light irradiation amount constant. Further, a shield plate 14 is also provided so that light is not irradiated to unnecessary areas.

As shown in FIG. 13, the paper transfer / conveyance belt 1
2 is supported by a plurality of rollers 16, 17, 18, 19 and is driven by one of them, and some of the rollers are biased by elastic means in the tension direction in order to control the tension. It is assumed that When the paper S, which is the final transfer medium, is introduced from the paper feed unit onto the paper transfer / transport belt 12 by the paper feeder 21, electric charges are applied by the paper suction roller 22 provided in contact with the paper transfer / transport belt 12. Then, the paper S is electrostatically adsorbed to the paper transfer / transport belt 12. Then, after transferring the image on the paper S at each transfer section of the four image forming stations, the paper S is discharged by the separation charger 24, loses the adsorption charge, and is separated from the transfer conveyance belt 12 by the rigidity of the paper S. The paper is ejected, fixed by the fixing device 26, and ejected by a paper ejection roller 27 to a paper ejection unit (not shown). On the other hand, after the transfer onto the paper S, the transfer-transfer cleaning belt 25 provided downstream of the transfer unit removes the transfer residual toner, and the transfer unit forms the next image again.

In this embodiment, the belt-shaped paper transfer / conveyance belt 12 is used as an example.
From the required accuracy and size, the drum-shaped transfer / conveyance method as described in FIG. 2 may be adopted.

Next, the cleaning device 6 will be described. In this case as well, the cleaning device 6 includes
Although provided in each of 1Y, 1M, and 1C, the interiors are the same, so only the cleaning device 6 for the black photoconductor 1Bk will be described. The cleaning device 6 removes the toner remaining on the photoconductor 1Bk after the transfer, and may be an elastic cleaning blade, a fur brush, or a combination thereof. In this embodiment, the cleaning blade 6a made of an elastic material such as polyurethane rubber, the fur brush 6b, and the electric field roller 6c arranged in contact with the fur brush 6b.
And the scraper 6d of the electric field roller 6c, and the recovery screw 6e having a length in the direction of penetrating the paper surface in FIG.
Etc. The fur brush 6b is conductive and the electric field roller 6c is metal.

As for the operation, first, the fur brush 6 rotated by the counter in the direction opposite to the rotation direction of the photoconductor 1Bk.
At b, the residual toner on the photoconductor 1Bk is scraped off. The toner attached to the fur brush 6b is removed by the electric field roller 6c rotating with a counter with respect to the fur brush 6b. The electric field roller 6c is cleaned by the scraper 6d. At this time, a bias is applied to the electric field roller 6c, and the residual toner moves from the photoconductor 1Bk to the fur brush 6b and from the fur brush 6b to the electric field roller 6c by electrostatic force, and is finally scraped off by the scraper 6d. It is returned to the developing device 4 by the recovery screw 6e and reused. Alternatively, it may be collected in a waste toner bottle (not shown).

Here, a structure which can be returned to the developing device 4 and reused will be described. As for the positional relationship between the cleaning device 6 and the developing device 4 with respect to the same photosensitive member, for example, the photosensitive member 1Bk, the conveying duct 6f surrounding the recovery screw 6e of the cleaning device 6 has an outer case above the screw 4d of the developing device 4. It is configured to communicate with 4f on the upper side. A conveying screw is provided inside the conveying duct 4f, and the toner scraped off by the scraper 4d is collected by the screw 4d of the developing device 4.

In the image forming method (apparatus) according to the present invention described above, there is little reverse transfer with the photoconductor, and a good image can be formed at high speed without disturbing the toner image. This can be achieved without deteriorating the property, and the residual toner on the photoconductor can be recovered by a cleaning device and reused.

[0088]

As described above, according to the first aspect of the invention, when the toner images of the second and subsequent colors are transferred onto at least the final transfer medium, the latent image carrier in the area where the toner images are transferred. The maximum potential difference V between the surface potential of the latent image carrier and the surface potential on the final transfer medium is t [μ
m], by satisfying the condition of V <312 + 6.2 × t, it is possible to prevent toner scattering before transfer and prevent image deterioration due to reverse transfer. Obtainable.

According to the second aspect of the invention, in the image forming method according to the first aspect, the transfer / conveyance member having a light-transmitting property is used, and the latent image is formed by irradiating light from the rear surface of the transfer nip portion. By eliminating the surface potential of the carrier, the maximum potential difference in the transfer area was kept within the specified range, so it is difficult to eliminate the charge because it is blocked by the transfer transport member and the latent image carrier itself. For the transfer nip part, which is a part, it is possible to easily remove the surface potential of the photoconductor, and it is possible to prevent toner scattering before transfer and prevent image deterioration due to reverse transfer, and obtain a good image. You can

In the image forming method according to the second aspect of the present invention, the transfer electric field applying means is a material having optical transparency (or the transfer electric field applying means is a contact transfer member made of a light transmissive material). ), By irradiating light from the back side of the latent image carrier while applying the transfer electric field, the area on which the transfer bias is applied can be directly irradiated with light to remove the charge. The occurrence of reverse transfer can be effectively prevented, and the size of the image forming apparatus can be reduced. Further, in the image forming method according to the second aspect, if the corona charger is used as the transfer electric field applying means, the transfer nip area can be easily neutralized without using a new transfer electric field applying means. The image forming method according to claim 2, further comprising: a transfer nip portion for transferring the toner image on the latent image carrier to the final transfer medium, a downstream side in a rotation direction of the latent image carrier, or If the latent image carrier is discharged by irradiating light from the downstream side in the conveying direction of the final transfer medium, it is possible to reliably prevent the charge removal due to the wraparound of the light to the upstream side of the transfer nip, and image deterioration due to toner scattering. Can be prevented. In addition, if the light shielding means is provided so as not to eliminate the charge on the latent image carrier on the upstream side in the rotation direction of the latent image carrier with respect to the transfer nip portion, the latent image carrier is not used before the transfer. Static electricity can be prevented.

According to the third aspect of the invention, in the image forming method according to the second aspect, the amount of light to be emitted for static elimination is changed according to the light transmittance of the final transfer medium, so printing is performed. Even when the type of paper is different, it is possible to reliably perform the appropriate amount of static elimination, and it is possible to prevent image deterioration due to reverse transfer and toner scattering. According to the invention of claim 4, in the image forming method according to any one of claims 1 to 3, the latent image carrier is neutralized by passing a final transfer medium through a transfer nip. Since it was decided to perform it only for the case where it is present, it can be used for a long time by preventing the deterioration of the photoreceptor due to photo-elimination. Further, according to the invention described in claim 5, the image forming method according to any one of claims 1 to 4 is applied, and the toner collected by the cleaning means is returned to each developing means for use. Since the reverse transfer can be efficiently prevented, it is possible to prevent color mixture in the cleaning / collecting unit and recycle the toner.

According to the invention of claim 6, a latent image carrier for carrying an electrostatic latent image, a latent image forming means for forming an electrostatic latent image on the latent image carrier, and A developing unit for developing the electrostatic latent image with toner that is charged colored particles to form a toner image on the latent image carrier, and a toner image on the latent image carrier are held on a transfer / transport member. The image forming method according to any one of claims 1 to 5 is used in an image forming apparatus including one or more image forming units having a transfer unit for transferring to a final transfer medium. While preventing the toner scattering before the transfer, it is possible to prevent the image deterioration due to the reverse transfer, and it is possible to obtain a good image.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the surface potential of a photoconductor and the amount of reverse transfer toner.

FIG. 2 is a diagram showing an embodiment of the present invention and is a front view illustrating the configuration of the main part of the image forming apparatus.

FIG. 3 is a view showing another embodiment of the present invention and is a front view illustrating the configuration of the main part of the image forming apparatus.

FIG. 4 is a view showing another embodiment of the present invention and is a front view for explaining the main configuration of the image forming apparatus.

FIG. 5 is a view showing another embodiment of the present invention and is a front view illustrating the configuration of the main part of the image forming apparatus.

FIG. 6 is a view showing another embodiment of the present invention and is a front view illustrating the overall configuration of the image forming apparatus.

7 is a front view illustrating a configuration example of an image forming unit of the image forming apparatus illustrated in FIG.

FIG. 8 is a front view illustrating another configuration example of the image forming unit of the image forming apparatus illustrated in FIG.

9 is a front view illustrating another configuration example of the image forming unit of the image forming apparatus illustrated in FIG.

FIG. 10 is a view showing another embodiment of the present invention and is a front view illustrating the configuration of the main part of the image forming apparatus.

FIG. 11 is a view showing another embodiment of the present invention and is a front view illustrating the configuration of the main part of the image forming apparatus.

FIG. 12 is a view showing another embodiment of the present invention and is a front view illustrating the configuration of the main part of the image forming apparatus.

FIG. 13 is a view showing another embodiment of the present invention and is a front view illustrating the configuration of a main part of a color printer.

FIG. 14 is a front view illustrating the main configuration of the color printer shown in FIG.

FIG. 15A is a photograph of an image when the surface of the photoconductor is not discharged before the transfer of the toner image to the final transfer medium, and FIG. 15B is the image before the transfer of the toner image to the final transfer medium. It is the figure which image | photographed the image at the time of destaticizing the body surface by light irradiation.

[Explanation of symbols]

1 Photoconductor (latent image carrier) 2 charging roller 3 erase lamp 4 Developing device (developing means) 5 Paper transfer transport drum (transfer transport member) 6 Cleaning device (cleaning means) 7 Static eliminator 8 Static elimination light source (exposure device for static elimination of photoconductor) 9 Paper transfer conveyor belt (transfer conveyor member) 12 Paper transfer conveyor belt (transfer conveyor member) 13 transfer roller (transfer electric field applying means) 14 Shielding plate (light shielding means) 15 Corona charger (transfer electric field applying means)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/08 G03G 15/08 507D 2H200 21/10 21/00 342 F term (reference) 2H030 AA04 AB02 AD02 AD03 AD17 BB34 BB43 BB46 BB55 BB58 2H035 AA09 AB01 AC02 2H077 AA37 AB02 AC02 AC12 AC16 AD06 AD13 AD36 DA10 DA42 EA03 GA13 2H134 GA01 GB02 HA01 HB12 HB13 HB15 FA12 FA15 FA22 FA15 FA01 FA19 K01 FA24 K17 FA01 K19 FA01 K19 H01 FA19 KH FAHK FAH KFAH KFAH FA17 KH FAH KFAH KFAH KFAH KH FAH KFAH KH FAH KH FAH KFAH KH FAH KFAH KH FAH KFAH KH KH FAH KH FAH KH FAH KH FAH KH FAH KH FAH KH FAH KH FAH KH FAH KH QA03 QA08 QB02 QB03 QB04 QB10 QB15 QB32 QB50 QC03 QC05 QC14 QC22 QC23 QC29 QC32 SA13 SA32 TA17 TB04 UA03 UA04 UA07 UA22 WA02 WA05 WA07 WA08 WA09 WA10 2H200 FA16 GA23 GA34 GA45 GA47 GA57 GB02 GB12 GB13 GB25 HA02 HB03 HB07 HB12 HB22 HB28 HB45 HB48 JA02 JA25 JA27 JA28 JB06 JB10 JB16 JB24 JB45 JB46 MA03 MA04 MA12 MB04 MB06 NA02 NA06

Claims (6)

[Claims] 1. An electrostatic latent image is formed on a latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner image on the latent image carrier is transferred onto a transfer / transport member. An image forming method for forming a final multi-color image by multiple-transferring a plurality of colors onto the same final transfer medium held by the above, at least when transferring the toner images of the second and subsequent colors onto the final transfer medium. The maximum potential difference V between the surface potential of the latent image carrier and the surface potential on the final transfer medium in the area to be filled represents the thickness of the toner image sandwiched between the latent image carrier and the final transfer medium by t [ [μm], the image forming method is characterized in that the condition of V <312 + 6.2 × t is satisfied. 2. The image forming method according to claim 1, wherein the transfer / conveyance member having a light-transmitting property is used,
An image forming method characterized in that the maximum potential difference in the transfer region is kept within a prescribed range by erasing light from the back surface of the transfer nip portion to eliminate the surface potential of the latent image carrier. 3. The image forming method according to claim 2, wherein the amount of light irradiated for static elimination is changed according to the light transmittance of the final transfer medium. 4. The image forming method according to claim 1, wherein the latent image bearing member is neutralized only when the final transfer medium passes through the transfer nip. A characteristic image forming method. 5. An electrostatic latent image is formed on each of a plurality of latent image carriers, and these electrostatic latent images are developed by respective developing means provided for each latent image carrier. Toner images are respectively formed on the latent image carriers, and the respective toner images are successively transferred and transferred onto the same final transfer medium to form a final image, while the latent images are transferred from the latent image carriers to the final transfer medium. An image forming method, wherein the toner remaining on each latent image carrier without being transferred at each transfer portion of each toner image is collected by each cleaning unit provided corresponding to each latent image carrier. Item 5. An image forming method, wherein the image forming method described in any one of Items 1 to 4 is applied, and the toner collected by each cleaning unit is returned to each developing unit and used again. 6. A latent image carrier for carrying an electrostatic latent image,
A latent image forming means for forming an electrostatic latent image on the latent image carrier, and developing the electrostatic latent image with toner which is a charged colored particle,
A developing unit for forming a toner image on the latent image carrier, and a transfer unit for transferring the toner image on the latent image carrier to a final transfer medium held on a transfer / transport member. An image forming apparatus comprising one or more image units, wherein the image forming method according to any one of claims 1 to 5 is used.