JPH0248683A - Image forming device - Google Patents

Abstract

PURPOSE:To improve the efficiency of removal of remaining toner by a cleaning means by reducing the extent of electrification of two kinds of remaining toner on a latent image carrier after the transfer process and weakening the electrostatic attraction between toner and the carrier. CONSTITUTION:After a charging corotron 12 is used to uniformly electrify a negative charge type photosensitive drum 11, it is irradiated with beam from a first laser 13 in accordance with image information to form a first negative image on the drum 11. Thereafter, a first developing device 14 to which a proper developing bias is applied is used to develop the negative image with red toner, thus obtaining a first toner image. After a second positive latent image is formed on the drum 11 by a second laser 15, a second developing device 16 is used to develop the second positive latent image with positive-polarity different color toner, thus obtaining a second toner image. Thereafter, polarities of respective toner images are equalized, for example, to the positive polarity by a transfer corotron 17 and they are transferred to a storage sheet 19, and thus, remaining toner is surely removed by a cleaner 21 because negative- polarity remaining toner remains on the drum 11 with a large extent of electrification and positive-polarity remaining toner remains there with neutral electric charge.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus such as a copying machine or a printer that forms two images using electrostatic latent images, and particularly relates to an image forming apparatus such as a copying machine or a printer that forms two images using electrostatic latent images. The present invention relates to an improvement in an image forming apparatus in which two dove images are formed by using a dovetail image, and these images are electrostatically transferred all at once to a transfer medium.

[Prior Art] Conventionally, as this type of image forming apparatus, for example, Japanese Patent Application Laid-open No. 1986-
The one published in Publication No. 1.37538 is known.

This involves uniformly charging the surface of the photoreceptor, then projecting a negative image, performing reversal development using toner of the same polarity as the photoreceptor on the static-eliminating area of the photoreceptor, and then creating a positive image. The residual charge on the surface of the photoreceptor other than the positive image projection area is neutralized, and the residual charge on the positive projection area is subjected to regular development using toner of a different polarity than the photoreceptor, thereby producing negative and positive images. A toner image is formed on the same photoreceptor, and after the polarity of the negative and positive toner images is aligned, they are simultaneously transferred to a transfer medium.

[Problem to be Solved by the Invention 1] Incidentally, in this type of image forming apparatus, in order to repeat the image forming cycle, residual toner on the photoreceptor is removed by a cleaning means after the transfer process. However, the removal of residual toner by the cleaning means tends to be insufficient, and there is a risk that the quality of the reproduced image will be impaired due to poor cleaning or toner filming on the photoreceptor.

In this case, the above-mentioned prior art discloses a configuration in which a static eliminator is provided before the cleaning process to remove residual charges on the surface of the photoreceptor. Even if the residual toner is obtained, it is unclear how to configure the above-mentioned static eliminator to remove the two systems of residual toner charges, since two systems of different polarity are mixed together as residual toner. This is insufficient as a means to fundamentally solve the above problems.

This invention was made in view of the above problems, and is based on a type that forms two systems of images using toners of different polarities, and improves the cleaning efficiency of residual toner by a cleaning means. Thus, an image forming apparatus capable of reproducing images with good image quality is provided.

[Means for Solving the Problems] The present inventors analyzed the above-mentioned prior art as follows and came up with the present invention.

Specifically, in the transfer pretreatment step, as shown in FIG. 2(a)
As shown, two systems of 1 to ner images T1 with different polarities
(for example, negative polarity) and T2 (for example, positive polarity), each toner image TI formed on the latent image carrier 1 such as a photoconductor , T2.

At this time, toner of the same polarity as the one you want to align @T2
As shown in FIG. 2(b), the amount of charge gradually increases while maintaining the same polarity, while the upper layer of toner 9T1 with a polarity different from the polarity to be aligned A phenomenon was observed in which the charge of the toner in the lower layer portion 10a was gradually neutralized and finally reached a state where the polarity was reversed, but the polarity of the toner in the lower layer portion 10b remained partially unchanged without being reversed.

Then, when the transfer medium is charged with a polarity opposite to the polarity with which the toner images TI and T2 are to be aligned using a transfer charger such as a corotron, the toners @T1 and T2 are basically The second toner image T2 is electrostatically attracted and transferred to the transfer medium, but since the second toner image T2 has a considerable charge, the transfer efficiency is lower than that of the first toner (I).
Since the ITI cannot be made sufficiently high compared to the ITI, and since there is toner whose polarity is not reversed for the first toner image T1, as shown in FIG. is the toner R1 of the first toner image T1 whose polarity has not been reversed and a portion of the toner R of the second toner image T2.
2 remains without being transferred to the transfer medium.

In this state, residual toner R1, R on the latent image carrier
2 is charged with a negative charge e in this example by the transfer electric field, as shown in FIG. 2(C), and the negative residual toner R1 whose polarity has not been reversed is further negatively charged. As a result, the residual toner R2 is charged neutrally or slightly positively. Therefore, in particular, the amount of charge of the residual toner R1 whose polarity was not reversed in the pre-transfer treatment process becomes considerably large, so that this residual toner R1 is
This results in strong electrostatic adsorption to the I image carrier, making it difficult to remove by cleaning means.

Based on the above analysis, the inventors of the present invention have found that in order to improve cleaning efficiency, it is possible to suppress the increase in the residual toner charge and remove the charge of the residual toner whose polarity is not aligned in the pre-transfer treatment process. They discovered that this was necessary and came up with this invention.

That is, the present invention, as shown in FIG. a first developing means 3 for developing the formed first latent image with a first toner of either positive or negative polarity; and a second latent image formed by the latent image forming means 2. a second developing means 4 for developing with a second toner having a polarity different from that of the first toner; a transfer pretreatment means 5 for aligning the polarities of both toner images on the latent image carrier 1; It is assumed that the image forming apparatus is equipped with a transfer means 7 that electrostatically transfers both toner images to the transfer medium 6 at once, and a cleaning means 8 that removes residual toner from the transfer process, , a charge eliminating means 9 is provided to which charge having the same polarity as the transfer pretreatment means 5 is biased toward the residual toner having a polarity different from that of the transfer pretreatment means 5.

In such technical means, the latent image carrier 1 may be appropriately selected from a photoreceptor, dielectric, etc. as long as it can form a latent image by the latent image forming means 2, and the specific Regarding the configuration, it does not matter whether it is drum-shaped or bell mill-shaped.

Further, as for the latent image forming means 2, if it is capable of forming two systems of latent images on the latent image carrier 1, the two systems of latent images may be formed in advance before the developing step, or It may be selected as appropriate, such as forming each latent image before each developing step. Further, as a specific latent image forming method of the latent image forming means 2, the latent image carrier 1 is charged in advance, and a portion corresponding to an image or a non-image portion is adjusted to a predetermined level with light or ions. Alternatively, the design may be changed as appropriate, such as one in which a latent image of a predetermined level is formed using ions without charging the latent image carrier 1 in advance. In this case, in order to form a latent image with light, an optical writing means such as a so-called optical imaging system using a mirror or lens system, a laser diode, a light emitting diode array, a liquid crystal shutter array, a fluorescent display element array, etc. should be used. In order to form a latent image with ions, a discharge head such as a multi-stylus, ion flow modulation, etc. may be used.

Furthermore, regarding the first and second developing means 3.4, the developing agent used may be used as long as it performs normal development or reversal development with toners of different polarity corresponding to the first and second electrostatic latent images. , development method, etc. may be selected as appropriate, but at least the second developing means 4 must be designed so as not to disturb the first toner image. For example, the second developing means 4
When using the magnetic brush development method, low-density Ki1? is used as the developer. Use a magnetic brush to the extent that the developing capacity can be secured, such as by using a magnetic brush that uses a rear roller, by forming a repelling magnetic field in the developing nip area, or by lowering the moving speed of the magnetic brush relative to the rotational moving speed of the latent image carrier. It is preferable to reduce the sliding force.

Furthermore, the transfer pretreatment means 5 may be appropriately selected from a charger such as a corotron as long as it applies a charge of one polarity to equalize the polarity of the two systems of toner images having different polarities.

Furthermore, the design of the transfer means 7 may be changed as appropriate as long as it charges the transfer medium 6 to a polarity opposite to that of the toner image whose polarity is aligned, and allows the toner image to be electrostatically attracted to the transfer medium 6. do not have.

Further, the cleaning means 8 includes various types such as blade and brush cleaning.

Further, as for the static eliminating means 9, if it is capable of intensively removing residual toner charges having a polarity different from that to be aligned by the transfer pretreatment means 5, the residual toner charges may be neutralized by a charger such as a corotron. Alternatively, the residual toner charge can be released to other parts using a static eliminating brush or the like, or the design can be changed as appropriate, but at least - an increase in the residual toner charge having the same polarity as the transfer pretreatment means 5 is prevented. It is necessary to design it in such a way.

One mode of using a charger such as a corotron as the static eliminating means 9 is to use an AC corona charger to which an AC operating voltage with the same polarity as the transfer pretreatment means 5 and a predetermined level of DC bias is applied. This can be mentioned.

[Operation] According to the technical means described above, the two systems of toner images formed with toners of different polarities are basically made to have the same polarity (for example, positive polarity) in the process by the transfer pretreatment means 5. The images are aligned and transferred onto the transfer medium 6 in a step by the transfer means 7.

At this time, the latent image bearing member 1 after the transfer process has the following properties as shown in FIG.
), residual toner R1 with a different polarity from the transfer pretreatment means 5 (with a large charge l) and residual toner R2 with the same polarity as the transfer pretreatment means 5 (with a coatral or small amount of charge) remain. are doing.

In this state, when the residual toners R1 and R2 undergo a process by the static eliminating means 9, as shown in FIG. 2(d),
The positive charge e+ is intensively supplied to the residual toner R1 of one polarity, the charge of the residual toner R1 of one polarity is almost removed, and the charge of the residual toner R2 of the other polarity is almost unchanged. do not. Therefore, the charges of both residual toners R1 and R2 are neutral or suppressed to a very small amount, and both residual i-toners R1 and R2 and the latent image carrier 1
There is almost no electrostatic attraction between the two. Therefore, this type of residual toner R1 and R2 can be easily scraped off by the cleaning means 8.

[Embodiments] Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.

FIG. 3 shows the invention applied to a two-color printer.

In the figure, 11 is a negatively charged photosensitive drum as a latent image carrier whose periphery is a photoconductive layer 11a, 12 is a charging corotron that charges the photosensitive drum 11 in advance, and 13 is a first latent image on the photosensitive drum 11. The first laser for forming,
14 is a first developing device using a magnetic brush development method using negatively charged red toner; 15 is a second laser for forming a second latent image on the photosensitive drum 11; 17 is a pre-transfer corotron that aligns the charging polarity of toner images of different polarities on the photosensitive drum 11 to, for example, positive polarity before the transfer process; The recording sheet 19 has a polarity opposite to that of the toner image aligned by the corotron 17 before transfer.
20 is a charge removal corotron which removes the residual toner charge on the photosensitive drum 11 after the transfer step, and 21 is a charge removal corotron which removes the residual toner charge after the charge removal step. 22 is a static eliminating lamp that removes the surface potential of the photosensitive drum 11 after the cleaning process; 23 is a sheet supply cassette in which the recording sheet 19 is stored in advance; 24 is a transport path for the recording sheet 19; The guiding plate 25 is a fixing device that fixes the transferred image on the recording sheet 19 after the transfer process.

In this embodiment, the static eliminating corotron 20 has a fourth
As shown in the figure, it consists of a discharge wire 20a and a U-shaped shield 20b surrounding the discharge wire 20a. An operating voltage Vf is applied.

Next, the image forming operation of the two-color printer according to this embodiment will be explained.

First, the negatively charged photosensitive drum 11 is uniformly charged by the charging corotron 12 (FIG. 5(a)), and then the first laser 13 is irradiated with light according to the image information, so that the photosensitive drum 11 is charged with light. Form a first negative latent image Z1 (fifth
Figure (b)). Thereafter, in the first developer 14 to which an appropriate developing bias vB1 is applied, the first negative latent mz
i is developed with a red toner of negative polarity to form a first toner image T1.
(Fig. 5(C)).

Subsequently, the second laser 15 irradiates light according to the image information to form a second positive latent image Z on the photosensitive drum 11.
2 (FIG. 5(d)), the second positive latent image Z2 is developed with positive polarity black toner in the second developing device 16 to which an appropriate developing bias VB2 is applied, A second toner (llT2) is formed (FIG. 5(e)).

After this, each toner image 1 is transferred by the pre-transfer corotron 17.
．． For example, the polarity of T2 is set to positive polarity (Fig. 5 (f))
After that, the transfer corotron 18 transfers each toner image 1. T2
was transferred onto the recording sheet 19. At this time, on the photosensitive drum 11 after the transfer process, the negative residual toner R1 remains with a relatively high charge, and the positive residual toner R2 remains with a neutral or slight charge ( Figure 5(g)).

Subsequently, when the static eliminating corotron 20 operates, most of the charge of the negative residual toner R1 is removed, while the amount of charge of the positive residual toner R2 is maintained as it is without substantially increasing. Therefore, the electric charge of both residual toners R1 and R2 is neutral or almost eliminated, and almost no electrostatic attraction force acts between the residual toners R1 and R2 and the photosensitive drum 11 (Fig. 5 (h)).
).

In this state, when the residual toners R1 and R2 enter the cleaning area, the residual toners R1 and R2 are reliably removed by the brush cleaner 21.

In order to confirm such an operation process, the current flowing into the photosensitive drum 11 is changed using the DC bias VS of the rotron 20 as a variable parameter, and the first toner image TI is
, an experiment was conducted to measure the residual toner density of the second toner image T2.

When conducting experiments, ☆Photosensitive drum・OPC (Organic Photo Condu
ctor) Process speed: 160s/sec ☆First developer two-component system (negative polarity red toner) Styrene-〇-butyl methacrylate copolymer 30ff
A carrier having an average particle diameter of 80 μm obtained by melt-mixing pulverization and classification of 1 part of i and 70 parts by weight of cubic magnetite.

Average particle diameter 12 μm obtained by melt-kneading, pulverizing, and classifying 90 parts by weight of styrene-n-butyl methacrylate copolymer and 10 parts by weight of red pigment Lysol Scalt (manufactured by BASF).
consisting of toner.

☆Second developer Two-component system (positive polarity black toner) Ferrite carrier with an average particle size of 100 μm.

A toner having an average particle diameter of 10 μm obtained by melt-kneading, crushing, and classifying 90 parts by weight of a styrene-n-butyl methacrylate copolymer, 9 parts by weight of carbon black, and 1 part by weight of a charge control agent.

☆Charging corotron DC-6.0KV ☆Pre-transfer corotron・AC frequency 400Hz, Vl)-1) 8.5KV・
DC+1.5KV ☆Transfer corotron-AC frequency 400Hz, Vp-p 10KV-DC
-2,5KV ☆ Static elimination corotron - AC frequency 400H2, vp-p 10KV-DC+
The condition was that r was variable in the range 2.0 to -2.0 KV (7).

Under these conditions, a solid image of 20 x 20 m is used as the input image, and the residual toner density d (refer to Fig. 3, select the downstream part A of the brush cleaner 21 of the photosensitive drum 11 as the fixed part 11), To measure the toner concentration, transfer the residual toner onto a transparent cellophane tape.
After pasting it on the recording paper, as for the black toner,
For red toner, use a green filter (Wratte).
Using a densitometer (Macbeth RD-914) that measures optical density through a densitometer (Macbeth RD-914), the current flowing into the photosensitive drum 11 of the static eliminating corotron 20 and the residual toner concentration (white circles:
The relationship with red toner (black circle: black toner) is shown in FIG.

In the same figure, the optical density is 0.08 at the base 81 of the recording paper.
Therefore, if the permissible level of bipolar residual toner concentration is optical density 0.1 or less, static elimination corotron 20
It is confirmed that the optimal range m of the DC component of is Q<m<+20 (μA), and more preferably +10≦m≦+15 (μA). In addition, the DC of static elimination corotron 20
When the components were set in the optimum range m described above, when we examined the residual toner charges after passing through the static eliminating corotron 20, it was confirmed that they were not very neutral, and the corotron 17 before transfer This proves that when an AC operating voltage with the same polarity and a predetermined level of DC bias is applied to the static eliminating corotron 20, the amount of charge of residual toner of both polarities can be suppressed as a result.

[Effects of the Invention] As described above, according to the image forming apparatus according to claims 1 and 2, it is possible to suppress the two systems of residual toner charges ω on the latent image carrier after the transfer process. The electrostatic adsorption force between the residual toner and the latent image carrier can be weakened, and the efficiency of removing the residual toner by the cleaning means can be improved. Therefore, deterioration in image quality due to poor cleaning or toner filming on the latent image carrier can be effectively prevented.

Furthermore, according to the image forming apparatus according to the second aspect of the present invention, the static elimination step (a) above can be achieved by simply superimposing a DC bias of a predetermined polarity on the operating voltage of the existing AC corona charger. There is no concern that the equipment-configuration will become unnecessarily complex.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing the image forming apparatus according to the present invention, FIGS. 2(a) to d) are explanatory diagrams schematically showing the operation process of the image forming apparatus according to the present invention, and FIG. 4 is an explanatory diagram showing an embodiment of the image forming apparatus according to the present invention.
The figure is an explanatory diagram showing the details of the static eliminating corotron used in the example, FIGS. 5(a) to h) are explanatory diagrams showing the operation process of the image forming apparatus according to the example, and FIG. FIG. 2 is a graph diagram showing the relationship between the current flowing into the photosensitive drum of the static eliminating corotron and the residual toner density after the cleaning process of both toner images. [Description of symbols] 1...Latent image carrier 2...Latent image forming means 3...First developing means 4...Second developing means 5...Transfer pretreatment means 6...・Transfer medium 7... Transfer means 8... Cleaning means 9... Static elimination means Fig. 2

Claims (1)

[Claims] 1) A latent image carrier (1), a latent image forming means (2) for forming two latent images on the latent image carrier (1), and this latent image forming means (2). a first developing means (3) for developing a first latent image formed by the first toner with a first toner of either positive or negative polarity; a second developing means (4) for developing the latent image with a second toner having a polarity different from that of the first toner; and a transfer pretreatment means (4) for aligning the polarities of both toner images on the latent image carrier (1). 5), a transfer means (7) that electrostatically transfers both toner images with the same polarity to the transfer medium (6) at once, and a transfer means (7) that transfers the toner images remaining on the latent image carrier (1) after the transfer process. In an image forming apparatus equipped with a cleaning means (8) for removing, an electric charge having the same polarity as that of the transfer pretreatment means (5) is placed before the cleaning means (8). An image forming apparatus characterized by being provided with a static eliminator (9) that supplies residual toner of different polarity in a biased manner. 2) In the device according to claim 1, the static eliminating means (9)
An image forming apparatus characterized in that it is an AC corona charger to which an AC operating voltage with a DC bias superimposed having the same polarity as that of the transfer pretreatment means (5) is applied.