JPH08334989A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device using an intermediate transfer system excellent in transfer efficiency between a photoreceptor/an intermediate transfer body(primary transfer), and the intermediate transfer body/transfer material(secondary transfer) and capable of suppressing a worm-eaten print. CONSTITUTION: In this image forming device of the intermediate transfer system, plural visible color developed images successively formed on an image carrier 1 are successively superposed on the endlessly traveling intermediate transfer body 7 and primarily transferred, and the primarily transferred image on the intermediate transfer body 7 is secondarily transferred altogether on the transfer material 13. The coefficient of dynamic friction of toner to be used to the image carrier 1, the intermediate transfer body 7 and the transfer material 13 in a real use state is expressed in such relation as the image carrier <=the intermediate transfer body <= the transfer material. By having such relation, the suppressing effect to a worm-eaten print characteristic is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a printer,
The present invention relates to an image forming apparatus using an electrophotographic method such as a facsimile, and more specifically, to an image forming apparatus using an intermediate transfer method in which primary and secondary transfer steps are performed with an intermediate transfer member such as an intermediate transfer belt interposed.

[0002]

2. Description of the Related Art In recent years, electrophotographic image forming apparatuses (color copying machines, color printers, color facsimiles, etc.) capable of forming multicolor images of two or more colors and full-color images have been put into practical use. In such an image forming apparatus,
For example, as a method of transferring a full-color image onto a transfer material, an image of toner of each color (cyan (C), magenta (M), yellow (Y), black (Bk)) is color-transferred onto an image carrier such as a photoconductor. The developed image of each color is sequentially superposed on the intermediate transfer member and primary-transferred to form a full-color image on the intermediate transfer member, and then the full-color toner image is collectively transferred to a transfer material such as recording paper. An intermediate transfer method in which secondary transfer is performed is known. The intermediate transfer body after the toner image transfer is prepared for the next transfer step by scraping off the toner remaining on the surface by a cleaning member such as a cleaning blade.

The present invention relates to the transferability of a color developed image in an electrophotographic image forming apparatus using the above-mentioned intermediate transfer member, and in particular, the transferability of the electrostatic transfer method is improved and the local transfer omission occurs. Although it relates to the improvement of (insect-eaten prints), the conventional technique for this problem is to use an elastomer for the intermediate transfer member and to regulate the surface roughness of the intermediate transfer member to improve the adhesion to the transfer material. Improving the transfer property and improving the insect biting print (JP-A-3-242667), regulating the surface roughness of the intermediate transfer member, improving the transfer property and improving the insect biting print. (JP-A-63-194274, JP-A-4-303869, JP-A-4-30
No. 3872, Japanese Patent Application Laid-Open No. 5-193020), the transfer nip pressure is specified to improve the transferability and improve the insect bite printing (Japanese Patent Application Laid-Open Nos. 1-177063 and 4-284479). In order to improve the transferability by regulating the linear velocity between transfer media and to improve the insect bite print (JP-A-2-213882), the surface of the intermediate transfer member is refreshed (filming polishing, etc.) to improve the transferability. With the aim of improving the insect bite prints during maintenance and aging (JP-A-5-273893 and JP-A-5-3)
No. 07344, JP-A-5-313526, and JP-A-5-323802), the material of the intermediate transfer member is specified (for example, the wettability of the surface of the intermediate transfer member that affects the adhesion of the toner is reduced). With improved transferability and improved bug-eaten print (Japanese Patent Laid-Open No. 2-19
No. 8476, Japanese Unexamined Patent Publication No. 2-212867), an intermediate transfer member having a multi-layered structure, and a material having excellent releasability as an outermost layer is used to improve transferability and improve insect biting prints ( JP-A-62-293270, JP-A-5
-204255, JP-A-5-204257, and JP-A-5-303293), a material having excellent releasability is supplied to the surface of the intermediate transfer member to improve transferability and insect worm print. Tamono (Japanese Patent Laid-Open No. 58
No. 187968), and the like.

[0004]

When the above-mentioned existing techniques are stratified, (1) reduction of the surface roughness of the intermediate transfer member, and (2)
Linear velocity difference setting between transfer media, (3) Reduction of transfer nip pressure,
(4) The surface energy of the intermediate transfer member is reduced, and (5) the toner filming layer on the surface of the intermediate transfer member is removed.

Here, the relationship between the existing technology and the insect-eating prints, which are defective in local transfer, will be slightly supplemented. If the surface energy of the intermediate transfer member is ideally reduced, toner filming does not occur, and the technique (5) is not necessary. In other words, (5) can be said to be a complementary technology to (4). Therefore, the existing technology is divided into four elements. The relationship between insect-eating woodblock prints will be described below for each element.

(1) Surface roughness of intermediate transfer member. From another perspective, toner transfer between the photoconductor / intermediate transfer member and between the intermediary transfer member / transfer material can be said to be a discharge phenomenon. Assuming that the surface of the intermediate transfer member has an extremely uneven surface roughness, the transfer electric field for the toner on the convex portion and the concave portion becomes as follows: convex portion transfer electric field> concave portion transfer electric field. It can be said that the toner is more easily transferred. Further, it can be said that the adhesive force of the toner located on the edge of the concave portion or the like to the intermediate transfer body is larger than that of the convex portion (when the toner shapes of both toners are regarded as the same), and in this respect also the concave portion is difficult to be transferred. I can say. From the above, the roughness of the surface of the intermediate transfer member must be suppressed to such a level that the above matters are not a problem. This is true for the photoconductor, but the surface roughness of the photoconductor is S
It is a well-known technique in the industry, dating back to the e-drum.

(2) A linear velocity difference is set between transfer media. The toner transfer between the photosensitive member and the intermediate transfer member will be described as an example. If the linear velocities of the two are the same, it is necessary to overcome the adhesion force between the photoconductor and the toner, which is represented by the van der Waals force acting between the photoconductor and the toner, only by the transfer electric field to transfer. On the other hand, when both have a linear velocity ratio, both the mechanical force due to the speed difference between the photoconductor and the intermediate transfer member and the transfer electric field can be applied. Therefore, it can be said that the latter is more excellent in transferability, and it is more advantageous to provide a linear velocity difference between the transfer media in view of the insect bite print as microscopic transferability.

(3) Reduction of transfer nip pressure. As in the previous section, toner transfer between the photoconductor / intermediate transfer member will be described as an example. At the time of transfer, the photoconductor and the intermediate transfer body are pressed by some force. That is, the toner interposed between the two is pressed. The Van der Waals force described above increases as the intermolecular distance approaches, and the toner intermolecular attractive force due to toner aggregation also increases. Based on the above reasons, it can be said that a lower transfer nip pressure is desirable from the viewpoint of transferability.

(4) Reduction of surface energy of the intermediate transfer member. It is a well known fact that the adhesive force between different kinds of substances is expressed as a function of surface tension (surface energy), and that the adhesive force increases as the surface tension increases. Therefore, it can be said that it is advantageous to suppress the surface tension of the intermediate transfer member to a low level and improve the releasability from the toner.

The above is the concept of the effect of countermeasures against insect-eating prints of the prior art. Here, it is clear that the above-mentioned conventional technologies are independent of each other, and the effect of the insect bite prints was confirmed by combining these measures, but the suppression effect on the insect bite print characteristics is not satisfactory. It was

The present invention has been made in view of the above circumstances and is excellent in transfer efficiency between a photoconductor / intermediate transfer member and between an intermediate transfer member / transfer material, and suppresses the occurrence of abnormal images such as insect bite prints. It is an object of the present invention to provide an image forming apparatus using an intermediate transfer system capable of performing the above.

[0012]

In order to achieve the above object, in the present invention, a plurality of visible color developed images sequentially formed on an image bearing member are sequentially superposed on an endlessly traveling intermediate transfer member. In an image forming apparatus of an intermediate transfer system in which the primary transfer image on the intermediate transfer member is collectively and secondarily transferred onto a transfer material, an image carrier, an intermediate transfer member, and a transfer material in an actually used state. The dynamic friction coefficient of the toner used with respect to is in the relationship of image carrier ≦ intermediate transfer member ≦ transfer material.

[0013]

According to the present invention, in the intermediate transfer type image forming apparatus, the image carrier, the intermediate transfer member, and
When the dynamic friction coefficient of the toner used with respect to the transfer material has a relationship of image carrier ≦ intermediate transfer member ≦ transfer material, an effect of suppressing insect bite printing characteristics can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. First, an example of an image forming apparatus using an intermediate transfer system to which the present invention is applied will be shown, and its configuration and operation will be described. FIG. 1 is a schematic configuration diagram showing a full-color image forming apparatus using an intermediate transfer system. It should be noted that only the configuration of the image forming unit (printer unit) is shown in the figure, and when the image forming apparatus is a copying machine, a known image reading apparatus (scanner unit) for reading a document is provided. Here, taking a full-color copying machine as an example, an image reading device (not shown) reads color image information of a document for each color separation of red (R), green (G), and blue (B), and the color image information is read. Is converted into an image signal. And
Based on the intensity levels of the R, G, B color separation image signals,
Color conversion processing is performed in the image processing unit of the image reading apparatus, and converted into color image data of cyan (C), magenta (M), yellow (Y), and black (Bk). Then, based on this color image data, the printer unit having the configuration shown in FIG. 1 forms an image using four color toners of cyan (C), magenta (M), yellow (Y), and black (Bk). Done. When used as a printer such as a personal computer or a workstation, color image data is transmitted from these devices to the printer unit.

Next, the structure and image forming operation of the printer section shown in FIG. 1 will be described. Reference numeral 3 in the drawing is a writing optical unit 3, and the writing optical unit 3 is a unit that converts color image data from an image reading unit or the like into an optical signal and performs optical writing corresponding to an original image or the like. As the writing optical unit 3, for example, a laser beam from a laser light source is deflected and scanned through a rotary polygon mirror, and f
There is an optical scanning device that guides scanning light to the photosensitive drum 1 via a constant velocity scanning optical system such as a θ lens to form an electrostatic latent image. In addition to this, there are an optical writing device using an LED array and an optical writing device using a liquid crystal shutter array.

The photosensitive drum 1, which is an image bearing member, rotates counterclockwise as indicated by an arrow, and around it, a charger 2, a potential sensor 4, a developing section 5, a developing density pattern detector (P sensor). ) 6, endless belt-shaped intermediate transfer member 7, pre-cleaning static eliminator (Pcc) 9, photoconductor drum cleaning device (cleaning brush 10a, cleaning blade 10b) 10, static eliminator 11 and other image forming processes by electrophotography. Equipment for execution is arranged. The developing unit 5 includes a Bk developing device 5a and a C developing device 5
b, M developing device 5c, and Y developing device 5d are arranged, and a two-component developer composed of toner of each color and carrier is used as the developer of each developing device. In addition, each developing device holds a developing sleeve 51a, 51 that carries and rotates a developer so as to face the photosensitive drum 1 in order to develop the electrostatic latent image.
b, 51c, 51d, and developing paddles 52a, 52b, 52c, 52 that rotate to draw up and agitate the developer.
d, and toner concentration detection sensors 53a, 53b, 53c, 53d for detecting the toner concentration of the developer. It should be noted that the toner replenishing unit and the like for each developing unit are not shown.

In FIG. 1, when the image forming process is started, the photosensitive drum 1 is charged by the charger 2 and
Optical writing is performed by the writing optical unit 3 based on the image data of the color (for example, Bk image data), and the latent image of the Bk image of the first color is formed. Then, in the developing unit 5, the latent image is visualized by the toner of the Bk developing device 5a and Bk is developed.
A toner image is formed. B formed on the photosensitive drum 1
The k toner image is transferred onto the surface of the intermediate transfer member 7 at the contact portion between the photosensitive member and the intermediate transfer member 7 which is driven at a constant speed.
The transfer here is called primary transfer. The residual toner on the photoconductor drum 1 after transfer is removed by the pre-cleaning charge remover 9 and the photoconductor drum cleaning device 10, and the charge is removed by the charge removal lamp 11. Then, the image forming process of the next color is executed, and in the case of full color image forming,
The latent image formation, development, and primary transfer processes described above are sequentially repeated for the C, M, and Y images of the second and subsequent colors, and a full-color image is formed on the intermediate transfer belt 7. Incidentally, in the case of full-color image formation, it may be performed with three colors of C, M and Y.

The intermediate transfer member 7 is composed of an endless belt member (referred to as an intermediate transfer belt), is stretched around a drive roller 18, a belt transfer bias roller 17, a transfer earth roller 19 and a driven roller group, and a drive motor (not shown). Is rotated in the direction of the arrow in the figure by applying a predetermined bias voltage to the belt transfer bias roller 17 when the photosensitive drum 1 and the intermediate transfer member 7 are in contact with each other. Primary transfer of the image is performed. Also,
Around the intermediate transfer member 7, a sweeper brush 8 and a transfer device (paper transfer bias roller 14a, etc.) 1 for transferring the transfer material 13 are provided.
4, a belt cleaning device (brush roller 12a, cleaning blade 12b, etc.) 12 is arranged. These members are contacted and separated from the intermediate transfer member 7 (1).
5, 12c) are provided so that during the formation of a full-color image, they can be separated from the surface of the intermediate transfer body 7 while the first to fourth colors (or the first to third colors) are being transferred. There is.

When a full-color image is formed on the intermediate transfer body 7 through the above-described process, the paper transfer bias roller 14a of the transfer device 14 is brought into contact with the intermediate transfer body 7 by the contact / separation mechanism 15, and at the contact portion. Images are collectively transferred onto a transfer material (recording paper or the like) 13. The transfer here is called secondary transfer.
Then, the transfer material 13 on which the image has been transferred is separated from the intermediate transfer member 7, and is sent to a known fixing device (not shown) by the conveyor belt 16 to output a full-color image through a fixing process. On the other hand, the belt cleaning device 12 and the sweeper brush 8 are brought into contact with the intermediate transfer body 7 after the secondary transfer by a contacting / separating mechanism, and the surface of the intermediate transfer body is cleaned and discharged.

The structure and operation of the intermediate transfer type image forming apparatus have been briefly described above. In the secondary transfer step of the above process, the formed image is transferred from the intermediate transfer body 7 to the transfer material 13. However, in order to obtain a sufficient image density, the transfer efficiency here needs to be 90% or more. Further, even if 90% or more of the toner is transferred, the toner may not be transferred in a pinpoint manner and may remain on the intermediate transfer member, resulting in an abnormal image called an insect bite print.

As a means for solving this problem, the present inventors have found that the dynamic friction coefficient of the toner used with respect to the image carrier, the intermediate transfer member and the transfer material in the actual use condition is: image carrier ≦ intermediate transfer member ≦ It was found that the relationship of the transfer material was effective. Less than,
A more specific example will be shown and the effect thereof will be described including the examination result.

[0022] First, the intermediate transfer member surface roughness: 0.6 to 0.9, the transfer medium between linear velocity difference: photoconductor linear velocity (V _P) / intermediate transfer member linear velocity (V _B) ratio ... 1 1., intermediate transfer member linear velocity (V _B ) / transfer material linear velocity (V _P ) ratio: 0.91, transfer nip pressure: photoconductor / intermediate transfer member nip pressure: 125 g / cm ² , intermediate Transfer body / transfer material nip pressure: 250 g / cm ² , photoconductor: made by Ricoh, photoconductor for PRETER550 (coated with lubricant (lead stearate)), developer: made by Ricoh, type E developer As a fixed condition, an evaluation experiment of insect-eating prints was carried out by using the dynamic friction coefficient of toner of the intermediate transfer member as a parameter. Table 1 below shows the evaluation results of the insect bite prints and the experimental results of the insect bite print generation locations (primary transfer or secondary transfer). Each of the intermediate transfer members used in the experiments was prepared by dispersing carbon in the resin material shown in the table below and adjusting the resistance to 10 ¹¹ to 10 ¹² Ω · cm. Further, the image forming apparatus for evaluation is a full-color copying machine (manufactured by Ricoh: PR) having the configuration shown in FIG.
ETER550) was used.

The insect bite prints were evaluated by a visual test in 5 grades (rank 5: best ← → rank 1: worst).
As an example of the evaluation in this case, the evaluation of each rank is set as follows. Rank 5: A state in which almost no insect-eating part can be found by observing with the naked eye, Rank 4: A state in which the insect-eating part can be barely found so much that it is difficult to determine the insect-eating part by observing with the naked eye, Rank 3: You can barely find the insect-eating part with the naked eye, and the insect-eating part does not impair the image quality. Rank 2: You can find the insect-eating part with the naked eye and count the number. Rank 1: Who observes However, there are many things that are obviously large enough to find the insect-eating part immediately. Instead of such an observation, it is also possible to evaluate the insect-eating print by using image pattern analysis or the like.

The method for measuring the dynamic friction coefficient of toner was as follows. Toner dynamic friction coefficient measurement method. Measuring device: Friction Analyzer DF.PM-SS (Kyowa Interface Chemistry). Indenter: Toner pellet (prepared by melt-molding toner into a cylindrical shape of φ10). Load: 100g. Stroke length: 20 mm. Stroke speed length: 1 mm / sec. Table 1 shows the above experimental results.

[0025]

[Table 1]

The resin materials in Table 1 are ETFE:
Ethylene-tetrafluoroethylene copolymer, PVd
F: polyvinylidene fluoride, PET: polyethylene terephthalate, PC: polycarbonate, ABS: acrylonitrile-butadiene-styrene copolymer.

Table 2 below summarizes the above results from the viewpoint of the coefficient of dynamic friction of the toner and the insect bite print.

[0028]

[Table 2]

From Table 2, it can be seen that if the toner dynamic friction coefficient of the intermediate transfer body is small, the local transferability (insect-eaten printing characteristics) is not necessarily good. Next, Table 3 is a table in which the toner dynamic friction coefficient is sorted according to the insect bite print generation location (primary transfer / secondary transfer).

[0030]

[Table 3]

From Table 3, the toner dynamic friction coefficient "small" ... 1
Insect-eating prints are generated by the next transfer, and the toner dynamic friction coefficient is "large" ...
It can be seen that the insect transfer prints are generated by the secondary transfer. Also,
It can also be seen that the insect bite print is not generated in the toner dynamic friction coefficient of the intermediate transfer body located between the large and small toner dynamic friction coefficients.

Here, the toner dynamic friction coefficient between the photoconductor used in the experiment and the transfer paper was measured, and the photoconductor (manufactured by Ricoh:
Photoreceptor for PRETER550) 0.29, transfer paper (manufactured by Ricoh: transfer paper for PRETER550) 0.5
It was 9. Corresponding this result with the result in Table 3, the toner dynamic friction coefficient of the photoconductor is 1 at the place where the insect-eating print is generated.
Positioned between the next transfer and the coefficient of dynamic friction of toner on the intermediate transfer belt that has not been generated.
It can be seen that it is located between the next transfer and the toner dynamic friction coefficient of the untransferred intermediate transfer belt.

From the above, the fact that the toner dynamic friction coefficient of the member relating to transfer according to claim 1 of the present invention is in the relationship of image carrier ≦ intermediate transfer member ≦ transfer material includes insect bite printing characteristics. It was concluded that this is an essential requirement for improving transferability.

[0034]

As described above, according to the present invention, in the image forming apparatus using the intermediate transfer system, the dynamic friction coefficient of the toner used with respect to the image carrier, the intermediate transfer body and the transfer material in the actual use state. However, when the relationship of image carrier ≦ intermediate transfer member ≦ transfer material is satisfied, the effect of suppressing insect-giving print characteristics can be obtained more than before, and the photoconductor / intermediate transfer member (primary transfer), intermediate transfer member / It is possible to provide an image forming apparatus that is excellent in transfer efficiency between transfer materials (secondary transfer) and can suppress the occurrence of insect biting prints.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a configuration example of an image forming apparatus using an intermediate transfer system in which the present invention is implemented.

[Explanation of symbols]

 1: Image bearing member (photosensitive drum) 2: Charging device 3: Writing optical system 5: Developing unit 5a to 5d: Developing device for each color 7: Intermediate transfer member (intermediate transfer belt) 10: Photosensitive drum cleaning device 11: Static elimination lamp 12: Belt cleaning device 13: Transfer material 14: Transfer device 17: Belt transfer bias roller

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Jun Aoto 1-3-6 Nakamagome, Ota-ku, Tokyo, Ricoh Co., Ltd. (72) Masahide Yamashita 1-3-6 Nakamagome, Ota-ku, Tokyo・ Inside Ricoh Co., Ltd.

Claims (1)

[Claims] 1. A plurality of visible color-developed images sequentially formed on an image bearing member are sequentially superposed and primary-transferred on an endlessly traveling intermediate transfer member, and the primary transfer on the intermediate transfer member is performed. In an image forming apparatus of an intermediate transfer system that secondarily transfers an image to a transfer material at a time, the dynamic friction coefficient of the toner used for the image carrier, the intermediate transfer member, and the transfer material in an actual use state is An image forming apparatus having a relationship of intermediate transfer body ≦ transfer material.