JPS6363063A - Two-color electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain a distinct image by maintaining a toner layer which has been thinly formed, in a non-contact state to an electrostatic latent image holding body. CONSTITUTION:A first electrostatic latent image (negative latent image) is brought to reversal development by a first developing device 4, and subsequently, a second electrostatic latent image (positive latent image) is brought normal development by a second developing device 6, the first development is executed by a two-component developing device 4 serving as the first developing device, and the second development is executed by maintaining a toner layer which has been thinly formed in a non-contact state to the electrostatic latent image holding body 1, and also, under an AC electric field by which a DC bias value has been set to a prescribed value. In this regard, when exposure part and non-exposure part latent image potentials, and an image part potential and a non-image part potential are denoted as Vl, Vd, and Vc1, Vc2, respectively, a DC portion Vdc of a bias voltage applied to the second developing device 6 is set so as to satisfy Vl+Vc2<=Vdc<=Vd$=Vc1, and Vd+Vc1<=Vdc<=Vl-Vc2, in case the latent image polarity is positive, and in case the latent image polarity is negative, respectively. In this way, a distinct image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-color electrophotographic apparatus that performs two-color printing, and in particular, to a uniformly charged electrostatic latent image carrier.
A negative latent image is formed as a first electrostatic latent image, this is reversely developed in a first developing device, a positive latent image is formed as a second static IfPPI image, and this is developed in a second developing device. The present invention relates to a two-color electrophotographic device that can carry out regular development in the device and perform two-color printing in one copy cycle.

-7. Currently, the electrostatic recording method using electrophotography is often applied to printers as terminal devices for information equipment such as computers, facsimiles, and CAD'X.

These printers use a laser beam, LE
A recorded image is obtained by the process of depositing an electrostatic latent image on an electrostatic latent image carrier, that is, a photosensitive drum, using an LCD, etc., converting it into a visible image using a developing device, and then transferring and fixing it onto transfer paper. In printers, the recorded image was of one color, for example, black.

However, recently, recorded images have become clearer and it has become easier to understand information. For example, the color of the format and the color of the calculated value or data value are expressed in different colors, or output using CAD. It is desirable to be able to distinguish between two colors, such as outputting a part of a printed drawing in a different color.

An example of an electrophotographic apparatus using such a two-color recording circuit is shown in FIG.

A drum-shaped electrophotographic photoreceptor 1 made of a photoconductive layer is rotatably provided on a conductive substrate E as an electrostatic latent image holder, and the photoreceptor drum 1 is uniformly charged by a charger 2. The first information signal is exposed by a light-emitting element such as a laser to form a first static image, and the first developing device 2! Thereafter, the second information signal 5 is similarly exposed to light using a light emitting element such as a laser to form a second latent image, which is visualized by the second developing device 6.

Next, the image is transferred to a transfer paper 9 via a post charger 7, and further fixed by a fixing device 10. Further, the transfer residual toner on the photosensitive drum IL is cleaned by a cleaning device 11.

Various WI image forming methods have been proposed as two-color electrophotographic methods for performing two-color printing using an electrophotographic apparatus having the above configuration, and representative methods are as follows.

The first method is disclosed in Japanese Patent Application Laid-Open No. 56-52760.

In other words, a uniformly charged photoreceptor is exposed to negative light as a first exposure to form a first electrostatic latent image (negative latent image), which is reversely developed by a first developing device and transferred to a first toner. Obtain an image and then take a second negative exposure to obtain a second static Tft? 19
This is a method in which an image (negative latent image) is formed and this is reversely developed in a second developing device to obtain a second toner image.

In this method, since the first negative latent image remains even after the first toner image is formed, not only the second negative latent image but also the first negative latent image is developed during the second development. However, there is a problem in that so-called color mixing is likely to occur.

The second method is JP-A-54-81855, JP-A-56-
87060, etc., a latent image is formed simultaneously or sequentially at three levels of potential, and the levels higher and lower than the intermediate level are developed with toners having different polarities to form a two-color image. This is the way to get it.

This method has the advantage that color mixing is less likely to occur because it uses two types of toner with different polarities, but the intermediate level is considered to be the white background potential, and it is difficult to stably control this Φ level. However, since this intermediate level is approximately half of the high level, the contrast of each latent image is low, and an image with sufficiently high density cannot be obtained. Further, if a high potential is applied to obtain contrast, there is a problem that the photoreceptor is seriously damaged.

Furthermore, as a third method, there is a method disclosed in Japanese Patent Publication No. 59-2224. According to this method, after exposing an original image to a uniformly charged photoreceptor, a high-resistance white or light-colored toner is charged to the same polarity as the photoreceptor, and the exposed area is reversed and developed in the first step. ), the original image is then exposed to light through a color separation filter on the photoconductor, which still has a heavy weight on its surface, leaving a charge only in the area corresponding to the black image, which is then combined with the toner used in the previous process. Regular development is performed with a black insulating toner charged with a different polarity (different polarity than the photoreceptor) (second step), followed by secondary charging, or at the same time as secondary charging, the entire surface is exposed to light,
Then, a two-color image is obtained by reversal development (third step) with a toner of a different color from the toner used in the second step. Applications for forming two-color images by the method up to the second step of this method are described in JP-A-55-137538 and JP-A-57-2047. In terms of content, the difference is that black or chromatic toner is developed on the part where the charge has been erased in the first step.
The method is the same as the method up to the second step.

This JP-A-55-137538 and JP-A-57-2047
According to experiments conducted by the present inventors, the method described in 2.1 uses toners of different polarity and performs reversal development and regular development, respectively, so it is advantageous for color mixing, and it is also possible to improve latent image contrast during each development. Because it can be made large, there is no background fog and a toner image of sufficient density can be obtained.
It has been found that this method has many advantages, such as that it is easy to stabilize the potential of the white background area because an area with stable image potential characteristics is used as the white background area.

According to research experiments conducted by the present inventors, it has been found that when carrying out the method, the second developing device that visualizes the second latent image is a magnetic brush developing device. +9 Developing while rubbing the image surface! In jt71, when the toner image visualized in the first developing device passes through the second developing device, the first toner image is disturbed due to rubbing with the second developer, or a part of the toner image is The first toner that is scraped off may cause a decrease in image density, or even worse, the first toner that is scraped off is used in the second development! It has been found that a problem arises in that the particles get mixed into the A device and cause deterioration in color tone and image quality.

Furthermore, regarding the conventional technology related to a developing device used in a two-color image forming method, particularly a two-color electrophotographic method, an aerosol developing means as disclosed in Japanese Patent Publication No. 55-30620 is used as a second developing device. Forming a toner image without applying mechanical friction to the developing screen (electrostatic latent image holder surface) may disturb the first toner image during the development of the second latent image or damage the first toner image. This prevents the toner from being mixed into the second developer and impairing the color tone and image quality, and can be said to be an effective means for this purpose.

However, the aerosol developing means has a complicated structure, the equipment is large, and it is also expensive.
Furthermore, it is difficult to maintain stable image quality over a long period of time, and it cannot be said to be an excellent method.

On the other hand, Japanese Patent Application Laid-Open No. 54-43037 discloses a method in which a thin layer of toner is applied to the surface of a toner carrier disposed in an apparatus, and the surface of the electrostatic latent image carrier and the toner layer are developed in a non-contact state. A developing device constructed as follows is disclosed in Japanese Patent Application Laid-Open No. 126-1981.
50 uses such a developing device as a second developing device 2
A color electrophotographic developing and printing method is disclosed.

The developing device disclosed in Japanese Patent Application Laid-Open No. 54-43037 has a simple structure, can be easily miniaturized, is inexpensive, and is also advantageous in terms of stabilizing image quality over a long period of time. In the above method using the developing G2 device, development is performed by forming only a DC electric field due to a DC bias between the electrostatic latent image holder and the toner carrier, resulting in poor development reproducibility and a clear two-color image. It is disadvantageous to obtain

1: Japanese Patent Laid-Open No. 55-18659 discloses a method of improving the developing device to obtain sharp images with high development reproducibility. This is a method in which an electrostatic latent image holder and a toner carrier of a developing device coated with toner in the ≠λ layer are separated by a distance greater than the thickness of the toner layer, and an alternating electric field is applied to this gap to perform development. It is. Is this method interchangeable? By applying an electric field to the developing section, toner particles move back and forth between the latent image and the toner carrier, and in the process they are loosened into individual particles, causing the toner to become dense in the electrostatic latent image area. The adhesion to the surface makes it possible to obtain a flexible f-distance, resulting in excellent reproducibility and sharpness.

JP-A-56-144452 discloses a two-color image forming apparatus to which the above-mentioned developing method is applied.

In this way, by applying the developing method disclosed in JP-A-55-18659 to a two-color image forming apparatus, it is possible to perform the second development without disturbing the first toner image, and it is possible to perform the second development without disturbing the first toner image. In order to improve the reproducibility and clarity of the second toner image, an alternating current electric field is applied to the first toner image.
Even though the toner polarity and the second toner polarity are opposite to each other, a force that pulls the first toner toward the second toner carrier is exerted in 1 copy cycle, and in 1.1 However, the toner may gradually get mixed into the second developer, and this causes the amount of mixed toner in the second developer to increase as the number of times the device is used increases. A problem arises in that the tone and image quality of the toner image deteriorate.

As a result of numerous research experiments on conventional developing systems and two-color electrophotographic devices as described above, the present inventors have determined that the development method of JP-A-55-18659, which is considered to be extremely preferable, can be used in conventional two-color electrophotographic devices. It has been found that it is not possible to obtain two-color images of excellent image quality simply by applying the method as is.

The present invention has been made based on this new knowledge.

The purpose of the present invention is to eliminate the drawbacks of conventional devices and to obtain clear images without background fog, sufficient purulence, and color mixing in each developing device. The object of the present invention is to provide a two-color electrophotographic device that can perform the following steps.

, iLj+old - The above object is achieved by a two-color electrophotographic apparatus according to the present invention. To summarize, the present invention forms a negative latent image as a first electrostatic latent image on a uniformly charged electrostatic latent image holder, reversely develops this in a first developing device, and then develops the negative latent image in a first developing device. In a two-color electrophotographic apparatus in which a positive latent image is formed as an electrostatic latent image of 2, and this is regularly developed by a second developing device, the first developing device is a 2-color electrophotographic imager containing magnetic particles and non-magnetic toner. The second developing device is a component developing device, and the second developing station forms a thin layer of l component magnetic toner, which is charged to a polarity opposite to that of the first non-magnetic toner, on a toner carrier provided in the device. The toner layer is maintained in a non-contact state with the electrostatic latent image carrier, and an alternating current electric field is formed between the toner carrier and the electrostatic latent image carrier, and development is performed by the alternating current electric field. This is a two-color electrophotographic device characterized by:

Next, the two-color electrophotographic device according to the present invention will be explained in more detail with reference to the drawings.

FIG. 1 shows an embodiment of a two-color electrophotographic apparatus according to the present invention, the overall configuration of which is the same as that of FIG. In the example, the electrostatic latent image holding member 1 is an electrophotographic photosensitive drum in which a photoconductive layer such as OPC is coated on a drum-shaped conductive substrate, and is supported rotatably in the direction of the arrow. The photosensitive drum l is uniformly negatively charged to a potential Vd by a primary charger 2,
The charged photosensitive drum l is scanned and exposed by a laser beam 3 modulated by first image information. In the present invention, the laser beam 3 as the first exposure is a negative exposure that eliminates the charge in the image area. As a result, the first latent image is formed as a negative latent image.

This latent image of ilj'Sl is developed by the first developing device 4. To explain further, the first developing device 4 includes a sleeve 41 containing non-magnetic toner and a toner carrier for supporting the toner, that is, a magnet 43 in this embodiment, and a sleeve 41 that includes a magnet 43 therein. The non-magnetic toner of a chromatic color such as red, which is charged to the same polarity as the latent image polarity (negative), is carried together with magnetic particles and conveyed to the photosensitive drum l side. The first latent image is reversely developed by the first developing device.

Here, reversal development is a development method in which the portion where the charge has been attenuated is developed with toner having the same polarity as the latent image polarity.

Further, in the developing interval 2t4, a sleeve 4, which is a toner carrier, is provided.
1 to connect to AC power supply 44. A direct current R source 45 is provided, and development is carried out under an alternating current electric field. As a result, a chromatic first toner image is formed on the photosensitive drum l.

Next, a laser beam 5 modulated by the second image information is applied to the photosensitive drum l, which still has charge remaining in areas other than the toner image area, to remove the charge in the non-image area (white background area). Exposure is performed, thereby forming a second latent image as a positive latent image.

Thereafter, a second latent image is developed in a second development station 6. The second developing chamber 216 has a sleeve 61 containing one-component magnetic toner and a carrier for carrying the toner, that is, a magnet 63, and is supported on the sleeve 61. The one-component magnetic toner charged with the opposite polarity (positive) to the first toner is applied to the sleeve 61 in a thin layer by the regulation blade 62, and is not in contact with the surface of the static image carrier l. maintained in condition. Further, an alternating current electric field is formed between the surface of the latent image holder and the sleeve 61 by an alternating current power source 64 and a direct current power source 65 to perform development. Here, the height of the toner thin layer is 30-500 mm, preferably 30-100 mm, and the gap between the sleeve 61 and the photosensitive drum 1 is 100-600 mm, preferably 200-400 mm.
．． setting is suitable for obtaining an excellent toner image.

As described above, a thin layer of black one-component magnetic toner charged with a polarity (positive) different from the discharge polarity (negative) of the primary charger 2 is formed in the second developing device 6 and the photosensitive drum 1. is placed in a non-contact manner and is developed by an alternating current electric field. However, due to the action of the alternating current electric field, a small amount of a portion of the first toner image formed on the photosensitive drum l is transferred to the second developer*2t6. It gets mixed into.

However, according to the present invention, it is possible to obtain a large latent image contrast even during the second development, and for this purpose, by appropriately setting the second development bias value, positively charged black Sufficient density can be obtained in the visible image area with the one-component magnetic toner, and at the same time, the mixed red one-component non-magnetic toner can be flown to the non-image area and separated and removed from the second developing device 6. It is made up of 對.

Next, with reference to FIG. 3, a more specific explanation will be given with numerical values.

First, the bias voltage of the second developing device will be explained.

DC component V of the bias voltage applied to the second developing device
dc is the exposed area latent image potential 7, the non-exposed area latent image potential Vd,
Contrast Vc with respect to the minimum required image area potential to develop an image with sufficient density 1. Assuming that the contrast Vc2 is the minimum required non-image area potential in order to separate and remove mixed toner without background fog, development can be performed without background fog and the first toner mixed in the second toner can fly, and, In order to develop the image area with sufficient density, when the latent image polarity is positive, Vl+Vc2≦Vdc≦Vd-Vcl, and when the latent image polarity is negative, Vd+Vc l≦Vdc≦VJI-Vc2. You need to set it to your satisfaction.

According to this embodiment, the photosensitive drum 1 is charged to a surface potential of -700V by the primary charging by the charger 2, and the charge in the image area is attenuated by the first exposure, and the exposed area becomes -100V (see Fig. 3). a)) Next, the negatively charged chromatic toner is reversely developed to form a first toner image, but due to the negative charge of the toner, a potential of approximately toov is generated, and the toner image has a surface potential of -200V. (Figure 3(b))
).

Next, a second exposure is performed and the potential of the non-image area is attenuated to -toov in the same way as the first exposure (see Figure iS3(
c)) After that, a second development is performed, but the positively charged black toner is normally developed in the image area (Fig. 3(d)'), and the mixed chromatic toner is reversely developed in the non-image area. Ru. At this time, according to experiments, the direct wave component Vdc of the developing bias increases the contrast Vcl with respect to the image area potential by 250 cm or more.
When the contrast Vc2 for the non-image area potential is set to 150V or more, the above-mentioned effect can be obtained. Therefore -100
-150≦Vdc≦-700+250-250≦Vdc
By setting ≦-450, sufficient black image density and separation and removal of mixed toner can be achieved.

Since the mixed toner is separated and removed every copy cycle, the amount of toner tA that adheres at one time is small, and the toner that adheres to non-image areas is not noticeable.

In the present invention, the second developing device;! It is effective to make the toner layer 16 thin. In other words, the toner mixed in by forming a thin layer is exposed near the surface layer of the toner layer, so it is easy to fly away during development.On the other hand, even in a non-contact state, the toner layer is thick as in brush development. Once formed, the contaminants are trapped in the toner layer, making it difficult for them to fly away during development, and gradually remaining in the second developing device, resulting in color mixing.

Furthermore, regarding the AC bias applied to the second developing device, in this embodiment it was set to 1600 Hz and 1300 Vp-p, but it is better to set the frequency to a relatively high frequency of 1000 to 2000 Hz, so that the effect of loosening the toners each other during development is more effective. It is advantageous to separate the mixed toner from the black toner, and setting the voltage to a high value of 1100 to taoovp-p is advantageous because the reverse electric field that makes the mixed toner fly becomes stronger.

The two-color toner images obtained in the steps described above have charges of different polarities, positive and negative, so after the charges are aligned to one polarity by the post charger 7, they are charged by the transfer charger. The image is transferred to a transfer paper 9 and then fixed by a fixing device 1O, thereby obtaining a two-color image.

Although the present invention has been described with respect to a digital type two-negative electrophotography ye'a using a light emitting element such as a laser beam, it goes without saying that it is also applicable to an analog type two-color electrophotography apparatus.

As explained above, the two-color electrophotographic apparatus according to the present invention forms a negative latent image as the first electrostatic latent image, reversely develops this in the first developing device, and then A positive latent image is formed as a second electrostatic Ns image, and this is regularly developed with a second developer 'A21.The first development is performed with a two-component developing device, and the second development is P! Since the toner layer formed on the j layer is maintained in a non-contact state with the electrostatic latent image holder and development is performed under an alternating current electric field with the direct current bias value set to a predetermined value, j′! ! ! It is possible to obtain clear two-color images with no fog, sufficient density, and no color mixture even after long-term use in one copy cycle.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view of a two-color electrophotographic apparatus according to the present invention. FIG. 2 is a schematic cross-sectional view of an electrophotographic apparatus in which the present invention can be implemented. FIG. 3 is a diagram illustrating an image forming process performed in the two-color electrophotographic apparatus according to the present invention. l: Static electricity? PI image holder 3: First exposure means 4: First developing device 5: Second ``A light means 6: Second developing device Agent Patent attorney Akira Kura Tachibana;,,,)2i1.
+'. Figure 1

Claims (1)

[Claims] 1) Form a negative latent image as a first electrostatic latent image on a uniformly charged electrostatic latent image holder, reversely develop this in a first developing device, and then forming a positive latent image as a second electrostatic latent image;
In a two-color electrophotographic apparatus that regularly develops the toner in a second developing device, the first developing device is a two-component developing device containing magnetic particles and non-magnetic toner, and the second developing device A thin layer of one-component magnetic toner that is charged with a polarity opposite to that of the first non-magnetic toner is formed on a toner carrier provided in the apparatus, and the toner layer is in a non-contact state with the electrostatic latent image carrier. 2. A two-color electrophotographic apparatus, further comprising forming an alternating current electric field between the toner carrier and the electrostatic latent image holding member, and performing development under the alternating current electric field. 2) The DC component Vdc of the bias voltage applied to the second developing device is the exposed area latent image potential Vl and the non-exposed area latent image potential Vd.
, the contrast for the image area potential is Vc1, and the contrast for the non-image area potential is Vc2. When the latent image polarity is positive, Vl+Vc2≦Vdc≦Vd−Vc1. Also, when the latent image polarity is negative, Vd+Vc1≦Vdc≦ A two-color electrophotographic apparatus according to claim 1, which is set to satisfy Vl-Vc2.