JPH08227255A - Electrophotographic recorder - Google Patents

Abstract

PURPOSE: To always print an excellent image without any soiling by providing toner moved to a brush with the same polarity even when the toner is rubbed with the brush at the time of cleaning a photoreceptor and an intermediate transfer body. CONSTITUTION: A cleaning means is provided with the brush 1, metallic roll 2, a blade 3, a screw 4, M toner 5 and C toner 6. Then, toners 5 and 6 remaining on the photoreceptor after the toner image is transferred onto a recording medium, is recovered by the brush 1 being cleaning means to which bias voltage is applied. At this time, the brush 1 is triboelectrified by the friction since the toner 5, 6 are rubbed with the toner. Since the triboelectrification series of the brush 1 and the toner 5, 6 is the same as that of every toner 5 and 6, the polarity of the toner 5, 6 is hardly inverted. Thus, the toner 5, 6 stuck on the brush 1 surface are prevented from returning to the photoreceptor surface or the intermediate transfer body surface, and therefore the excellent image is always obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic recording apparatus such as a printer, a copying machine or a FAX which records an image by an electrophotographic method, and a cleaning means in the apparatus.

[0002]

2. Description of the Related Art Electrophotographic recording devices such as copiers and printers that obtain color images by electrophotography are widely used. The printing method of an image by this recording apparatus is to form an electrostatic latent image consisting of a printing level and a non-printing level by exposing a uniformly charged surface of a photoreceptor based on image information, A method of developing a latent image to obtain an image (two-level printing method) is generally used. In order to obtain a full-color image by this printing method, it is necessary to repeat charging, exposure and development four times.

For the purpose of further increasing the printing speed and making the recording device smaller than this method,
US Pat. No. 4,078,929 discloses a method (three-level printing method) of forming an electrostatic latent image consisting of two printing potential levels and a non-printing potential level by one exposure and developing two colors. ing. According to this method, the surface of the photoconductor is uniformly charged by a charger, and then the photoconductor is irradiated with light modulated based on image information to form an electrostatic latent image having three potential levels. . The potential of the electrostatic latent image is the part where the initial charging potential is maintained without being exposed by the exposure device, the part where the surface potential of the photoconductor is lowered due to strong exposure, and the part where the surface potential of the photoconductor is exposed due to weak exposure. It consists of a part that is approximately the middle value of the potential. This electrostatic latent image is stored in one developing device that contains positively charged toner, and in the other developing device that contains negatively charged toner, an appropriate developing bias voltage is applied to the developing roll. By applying, the electrostatic latent image is developed to obtain a color image. The portion where the surface potential of the photoconductor is weakly exposed and has an intermediate value of the initial charging potential is a portion (background portion) to which neither toner adheres. After the toner image is formed on the photosensitive member, the polarities of the toner are aligned by the charging device, and the toner image is transferred onto the recording medium (cut paper, continuous paper, OHP sheet, etc.) by the transfer device.
After that, the toner image is fused on the recording medium by heat in the fixing device. In this way, two-color printed images are obtained on the recording medium.

[0004]

The feature of the three-level printing system is that a latent image for two colors can be formed by one exposure, so that there is no displacement at the same printing speed as a one-color machine. Two-color printing is possible. On the other hand, since development is performed using two color toners having polarities different from each other, it is necessary to make the charging polarities of the toners uniform before transferring the toner image to the recording medium. It is possible to reverse the charge polarity of the toner on the photoconductor by applying a charge to the toner by corona discharge. When the toner on the photoconductor having a uniform charging polarity is transferred onto the recording medium, not all the toner on the photoconductor is transferred onto the recording medium, and a slight amount of toner remains on the photoconductor. As a means for removing the toner, a cleaning means for removing the toner by rubbing an electrically biased brush on the surface of the photoconductor is often used. This cleaning means is composed of a brush, a metal roll and a blade. The toner adsorbed on the brush is adsorbed on the surface of the metal roll when the metal roll to which the bias voltage is applied comes into contact with the brush, and is scraped off by a blade arranged at a position in contact with the surface of the metal roll.

As an example of the cleaning means used in an apparatus for obtaining an image by using toners having different charging polarities, there is an example disclosed in Japanese Patent Laid-Open No. 3-181982. This shows an electrophotographic recording apparatus provided with cleaning means for positively charged toner and negatively charged toner. In this example, voltages of different polarities are applied to the two cleaning means to clean the surface of the photoconductor. If the toner is sufficiently charged before the transfer, the polarity of the toner remaining on the surface of the photoconductor after the transfer is uniform, and it should be possible to clean the toner with one cleaning unit. However, the contact between the brush and the metal roll is 1
Even if the toner is charged only once, not all of the toner adhered to the brush during cleaning is adsorbed on the surface of the metal roll during cleaning, and a small amount of toner remains adhered to the brush. Even so, when the brush comes into contact with the metal roll 2-3 times, the toner attached to the brush is adsorbed on the surface of the metal roll. When toners with different charging polarities are used during development, the toner whose polarity has been reversed due to pre-transfer charging is frictionally charged with the brush before all the toner is adsorbed on the metal roll surface, and the charging polarity becomes the polarity during development. And may return to the surface of the photoconductor. If there are two cleaning means as in the above publication, the toner returned to the surface of the photoconductor is collected by the second cleaning means. Since the amount of toner existing on the photoconductor before the cleaning by the second cleaning unit is small, even if the contact between the metal roll and the brush is made only once, all the toner is collected by the cleaning unit. However, having two cleaning means has a problem that the volume of the electrophotographic recording apparatus increases and the cost increases.

An object of the present invention is to provide a cleaning means for surely collecting the toner remaining on the surface of the photoconductor after transferring the toner image from the surface of the photoconductor, and preventing the toner from returning to the surface of the photoconductor. It is in.

Further, in the electrophotographic recording apparatus of the type in which the toner image on the surface of the photoconductor is transferred onto the intermediate transfer member, and then the toner image on the intermediate transfer member is transferred onto the recording medium, the same means as the cleaning means is used. When cleaning the intermediary transfer member using, be sure to collect the toner remaining on the intermediary transfer member,
It is an object of the present invention to provide a cleaning unit that prevents the toner from returning to the surface of the intermediate transfer member.

[0008]

In order to obtain a color image by the two-level printing method which is the mainstream at present, since the developing performance of each color needs to be uniform, the charge train between toner particles is equal to zero. . Therefore, if the brush of the conventional cleaning means is used, the charging polarity of the toner is not reversed even if the brush and the toner of a plurality of colors rub. When a color image is obtained by the three-level printing method, a plurality of color toners having positive and negative charging polarities are used during development, so that there is a charge train between the toners. The brush of the cleaning means and the toner are charged by friction with each other. In that case, the brush needs to have a property of being charged with the same polarity regardless of which toner is rubbed.

Therefore, in order to provide a cleaning means for surely collecting the toner remaining on the photoconductor after the transfer, the brush is so charged as to have the same polarity no matter which toner the brush rubs against. The surface-treated product is used.

[0010]

The toner remaining on the photoconductor after the toner image is transferred onto the recording medium is collected by the brush of the cleaning means to which the bias voltage is applied. At that time, the brush rubs the toner, so that the brush is charged by friction. Since the triboelectric series of brushes and toner is the same for all toners, the charging polarity of the toner is never reversed. Therefore, the toner attached to the surface of the brush does not return to the surface of the photoconductor or the surface of the intermediate transfer body, and a good image can always be obtained.

[0011]

Embodiments of the present invention will be described below with reference to FIGS.

When a full-color image is printed by the electrophotographic recording device, image information for each pixel is transmitted from the host computer to the electrophotographic device to form the entire image. Each print pixel has eight types of white (W), magenta (M), red (R), green (G), cyan (C), blue (B), yellow (Y), and black (K). Printed in color. Intermediate colors can be expressed by setting an appropriate toner mixing ratio among M, C, and Y.

FIG. 4 is an example of an explanatory view of an electrophotographic apparatus according to the present invention.

Around the first photosensitive member 10 along the rotation direction, a first charging device 11, a first main exposure device 12, a first developing device 13, a second developing device 14, and a first toner adhesion amount sensor 15 are provided. An auxiliary exposure unit 16, a first pre-transfer charging unit 17, a first charge eliminating unit 18, and a first cleaning unit 19 are arranged.

Similarly, around the second photoconductor 20, the second charging means 21, the second main exposure means 22, and the third developing means 2 are provided.
3, a fourth developing means 24, a second toner adhesion amount sensor 25,
A second pre-transfer charging means 27, a second charge eliminating means 28, and a second cleaning means 29 are arranged.

The image signal sent from the host computer consists of eight kinds of basic color data and halftone data.
Halftone data is data that represents the amount of toner attached,
This is data that determines the electrostatic latent image potential during exposure. The electrostatic latent image potential is determined by changing the exposure amount during exposure. The relationship between the exposure dose and the electrostatic latent image potential after exposure is
It is measured in advance using a photoconductor and an optical system to be used, and is stored in the exposure amount calculation means in the first main exposure means 12 and the second exposure means 22.

FIG. 3 shows a potential diagram of an electrostatic latent image in the case where image data for two colors is recorded on a photoconductor by one exposure. On the surface of the photoconductor, a portion where the initial charging potential V1 is maintained, a portion where the surface potential becomes V2 due to weak exposure,
There is a portion exposed to strong exposure and having a surface potential of V3. Development is performed by setting appropriate developing bias potentials Vb1 and Vb2 to obtain a toner image. The portion where the surface potential after exposure is V2 becomes the background portion of the image to which toner does not adhere. The toner adheres most to the areas where the surface potential after exposure is V1 and V3. When printing an image in full color, the exposure amount at the time of exposing the surfaces of the first photoconductor 10 and the second photoconductor 20 is changed to set the surface potential of the photoconductor to the range of V1 to V3.
An image is obtained by depositing an appropriate amount of toner on the photoconductor by the developing means.

First developing means 1 in the vicinity of the first photoconductor 10.
3 and the toner contained in the second developing means 14 are
Any one of M, C, and Y, one of which is a positively charged toner, and the other of which is a negatively charged toner. In this embodiment, the first developing means 13 contains a developer containing positively charged M toner, and the second developing means 14 contains negatively charged C.
It contains a developer containing toner. The developer may be a conventionally used one-component developer or a two-component developer. If the toner amount is detected by the first toner adhesion amount sensor 15, the image quality can be controlled based on the result.

In this method, since two kinds of toner (C, M) cannot be attached to the same pixel, blue (B)
Cannot be expressed. However, since the two types of toner have different charging polarities from each other, the two types of toner are attached to the adjacent pixels, and then the charges on the surface of the first photoconductor 10 are appropriately removed (or reduced). It can be mixed by the electrostatic force of its own charge. As a method thereof, light is emitted from the first photoconductor 1 by using the auxiliary exposure means 16.
A method of expressing blue (B) by irradiating the 0 surface to remove (or reduce) the charge on the photoconductor and mixing two types of toner is considered.

As the auxiliary exposure means 16, similar to the first main exposure means 12, an optical system including a laser light source, a lens system, a polygon motor, an LED array and the like can be mentioned.

After the auxiliary exposure, the charging polarities of the two types of toner are aligned to one polarity by the pre-transfer belt means 17, and the toner is transferred onto the intermediate transfer body 40 by electrostatic force using the corona charger 34. Changing the charge polarity of the toner before the transfer to the intermediate transfer member 40 can be achieved by corona discharging the toner on the photosensitive member. Corona discharge includes direct current corona discharge and alternating current corona discharge. In order to give an electric charge to the toner by electric discharge, DC corona discharge is indispensable. Although it is possible to sufficiently reverse the charging polarity of the toner only with the direct current, the charging polarity of the toner can be more efficiently reversed with the corona discharge in which the alternating current is superposed on the direct current.

After transferring the toner image to the intermediate transfer member 40,
The surface of the first photoconductor 10 is neutralized by the first static eliminator 18.
It is cleaned by the first cleaning means 19.

FIG. 1 shows a sectional view of the first cleaning means 19. 1 is a brush, 2 is a metal roll, 3 is a blade, 4
Is a screw, 5 is an M toner, and 6 is a C toner. In this embodiment, the case where the charging polarity of the M toner 5 is inverted from positive to negative will be described. After the toner image is transferred to the intermediate transfer body 40, a small amount of M toner 5 and C toner 6 remains on the surface of the first photoconductor 10. In order to improve the efficiency of collecting toner to the cleaning unit, the brush 1 is rotated in the direction opposite to the traveling direction of the first photoconductor 10. The brush 1 is biased by a voltage source so as to have a potential that is more positive than the surface potential of the first photoconductor 10. First photoconductor 10
The M toner 5 and the C toner 6 remaining on the surface are adsorbed to the brush 1, and the surface of the first photoconductor 10 is cleaned. The brush 1 is in contact with the rotating metal roll 2, and the metal roll 2 is biased to a potential that is more positive than that of the brush 1. The toner adsorbed on the brush 1 is adsorbed on the surface of the metal roll 2 and conveyed. Then, the toner is scraped off by the blade 3 which is in contact with the metal roll 2. The scraped toner is conveyed by the rotation of the screw 4, and is stored in a waste toner reservoir (not shown).

The toner adsorbed on the brush 1 from the surface of the first photosensitive member 10 moves from the brush 1 to the surface of the metal roll 2 when the brush 1 and the metal roll 2 come into contact with each other while rotating. The toner is charged by rubbing against the brush 1,
Since it is attracted to the brush 1 by electrostatic force, all the toner does not move from the brush 1 to the metal roll 2 in one contact. A small amount of toner remaining on the surface of the brush 1 is rubbed with the brush 1 to be charged. In this embodiment, since the M toner 5 and the C toner 6 having different charging polarities at the time of development are used, frictional charging between the toners also exists. Although the M toner 5 is negatively charged by the pre-transfer charging, the negative charge is reduced due to friction with the negatively charged C toner 6 during cleaning, and the M toner 5 is less likely to be attracted to the metal roll 2. Therefore, brush 1 and M
It is necessary to prevent the negative charge of the M toner 5 from decreasing due to the friction of the toner 5. For that purpose, it is necessary to give the brush 1 a property having a stronger positive charging property than the conventional one. Conventionally used brushes include acrylic and nylon threads, but recently, many have used rayon threads. Since the rayon yarn itself has a low triboelectric chargeability, the chargeability of the rayon yarn can be improved by coating the surface of the rayon yarn with a resin or a charge control agent. Generally, substances containing substituents such as oxygen and basic nitrogen are likely to be positively charged. Nigrosine dye, fatty acid metal salt, etc. are mixed with acrylic resin, dissolved in an appropriate solvent (acetone, dichloromethane, etc.) and sprayed onto the rayon yarn surface to coat. When the cleaning means having such a brush is used, the brush 1 is positively charged and the toner is negatively charged when the surface of the first photoconductor 10 is cleaned.

In this way, the M toner 5 remains in the negatively charged state, so that it does not return from the brush 1 to the first photoconductor 10. Here, if the electric resistance of the brush is too large, the electrostatic force acting between the toner and the brush becomes strong, and even if a bias voltage is applied between the brush 1 and the metal roll 2, the toner will not be transferred to the metal roll. It becomes difficult to move to 2. On the other hand, when the electric resistance is too small, the electric charge of the brush 1 is lost and the toner is scattered, or the electric discharge is generated between the brush 1 and the metal roll 2 to which a potential difference is applied, so that the electric resistance value is increased. Is best about 10 ⁷ to 10 ¹⁰ Ωcm. Changing the electric resistance value can be easily carried out by changing the amount of carbon contained in the rayon yarn and the amount of resin on the surface of the rayon yarn.

Although the rayon yarn is used for the brush 1 as described above, a soft metal such as aluminum or a metal compound may be used for coating the surface of the brush with a resin.

Further, as a method of improving the transfer rate of the toner from the brush 1 to the metal roll 2, there is a method of grounding the metal roll 2. When a substance having a charge comes into contact with the grounded metal roll, an imaging charge is generated in the metal roll, and the charged substance is adsorbed on the surface of the metal roll. When the metal roll 2 is grounded, it is necessary to apply a negative bias voltage to the brush 1, the first photoconductor 10, and the like. For example,
The brush 1 is -300V and the base of the first photoconductor 10 is -60.
Set to 0V. In accordance with these, the first developing means 1
3, the potential applied to the second developing means 14 and the corona charger 34 is determined.

Also around the second photoconductor 20, as with the first photoconductor 10, the second photoconductor 2 is charged by the second main charging means 21.
The surface of No. 0 is uniformly charged, and the second main exposure unit 22 exposes the surface with a preset exposure amount. The toner contained in the third developing means 23 and the fourth developing means 24 is
A combination of black (K) toner and yellow (Y) toner,
Since these do not need to be mixed with each other, auxiliary exposure means is not required around the second photoconductor 20. If the charging polarities of the K toner and the Y toner are different from each other, the color of the toner contained in the third developing means 23 and the fourth developing means 24 may be either. The operation and action of the second toner adhesion amount sensor are the same as those of the first toner adhesion amount sensor 15.

After the development, the toner image on the second photoconductor 20 is transferred onto the surface of the intermediate transfer body 40 by the corona charger 35 without displacement. The toner image on the intermediate transfer member 40 is transferred by a transfer roll 41 to which a voltage is applied on the surface of the recording medium 31 (cut paper, continuous paper, OHP sheet, or the like) that is transported by the transport unit 32. After that, the recording medium 3
1 is conveyed to the fixing unit 37, and the toner image is fixed on the surface of the recording medium 31 by heat and pressure to complete a full-color image. On the other hand, the toner remaining on the second photoconductor 20 and the intermediate transfer member 40 is cleaned by the second cleaning unit 29 and the intermediate transfer member cleaning unit 42, respectively.

Second cleaning means 29, intermediate transfer member cleaning means 4
The structure of 2 is similar to the first cleaning means. Therefore,
The materials of the brushes of the second cleaning unit 29 and the intermediate transfer member cleaning unit 42 have the same properties as the brush 1 of the first cleaning unit.

Here, as a condition of the brush 1 used for the cleaning means, it is necessary that the charging sequence of the brush 1 is the same for all toners, that is, the brush is positively charged for all toners. Is. FIG. 2 shows a charging train of the brush 1 and the toner. In this recording apparatus, two types of positively charged toner (toner a and toner b) and two types of negatively charged toner (toner c and toner d) are used. Toner a and toner b
Is almost the same, and the toner c and the toner d are almost the same. Therefore, the relationship of the charge train can be expressed as shown in FIG.

[0032]

Even in an electrophotographic recording apparatus that prints using a plurality of toners having different electrical characteristics, even if the toner that has moved to the brush when cleaning the photoconductor or the intermediate transfer body rubs against the brush. Since it always has the same polarity, it does not return to the photosensitive member or the intermediate transfer member. As a result, the photoconductor and the intermediate transfer member are not contaminated, and it is possible to always print a good image without stains.

[Brief description of drawings]

FIG. 1 is a sectional view of a cleaning means of the present invention.

FIG. 2 is an explanatory diagram showing a charging sequence of a brush used as a cleaning unit and a toner used in the recording apparatus.

FIG. 3 is a surface potential distribution diagram of the photoconductor after exposure.

FIG. 4 is an explanatory diagram of an electrophotographic recording apparatus.

[Explanation of symbols]

1 ... Brush, 2 ... Metal roll, 3 ... Blade, 4 ... Screw, 5, 6 ... Toner.

Claims (6)

[Claims] 1. A means for uniformly charging the surface of a photoconductor, an exposure means capable of forming at least three latent image potential levels on the surface of the photoconductor according to image information, and an electrostatic means formed on the surface of the photoconductor. Developing means for developing a latent image by using toners having different charging polarities to form a toner image, an intermediate transfer body for transferring the toner image on the photoconductor, and a toner image on the intermediate transfer body on a recording medium. In an electrophotographic recording apparatus having a transfer unit for transferring to a sheet, the cleaning unit electrically cleans the toner remaining on the photoconductor after the toner image is transferred onto the intermediate transfer body by rubbing with a brush. An electrophotographic recording apparatus provided with cleaning means having a brush that is charged with the same polarity for all toners used. 2. A means for uniformly charging the surface of the photoconductor, an exposure means capable of forming at least three latent image potential levels on the surface of the photoconductor according to image information, and an electrostatic means formed on the surface of the photoconductor. Developing means for developing a latent image by using toners having different charging polarities to form a toner image, an intermediate transfer body for transferring the toner image on the photoconductor, and the toner image on the intermediate transfer body on a recording medium. In an electrophotographic recording apparatus having a transfer means for transferring, by a cleaning means for electrically cleaning the toner image on the intermediate transfer body after transferring the toner image on the intermediate transfer onto a recording medium while rubbing the toner remaining on the intermediate transfer body with a brush. An electrophotographic recording apparatus is provided with a cleaning unit having a brush that is charged with the same polarity for all toners used. 3. The cleaning means according to claim 1, wherein the cleaning means is a brush, a metal roll for adsorbing the toner attached to the brush, a blade for scraping off the toner adsorbed on the metal roll, and the scraped off toner. An electrophotographic recording device consisting of a screw that conveys while rotating. 4. The electrophotographic recording apparatus according to claim 1, 2 or 3, wherein the electric resistance of the brush of the cleaning means is in the range of 10 ⁷ to 10 ¹⁰ Ωcm. 5. The electronic device according to claim 1, 2, 3 or 4, wherein the brushes of the cleaning means and the photoconductor, and the brushes of the cleaning means and the intermediate transfer member are in contact with each other in opposite traveling directions. Photo recording device. 6. The electrophotographic recording apparatus according to claim 1, wherein the metal roll forming the cleaning means is grounded.