JPH03263066A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the generation of ozone and to contrive the reduction in cost by providing a voltage applying means applying a bias voltage on both front and back surfaces of an image carrier. CONSTITUTION:The surface of a photosensitive drum 2 is rubbed by an electrifier 8 composed of a conductive brush on which the bias voltage is applied, and biased. On the other hand, an aluminum substrate 2a bias-applies a low voltage from the back surface by a high voltage power source 14. A photosensitive body 2b has high insulation in the dark, so that a current does not flow between the font and back surfaces, but a potential difference is uniformly formed among the layers of the photosensitive body 2b. Then, a light source 3 is tuned on/off, and optical writing is carried out from the surface of the photosensitive drum, so that a pair of carriers, that is, a hole and an electron are generated inside the photosensitive body 2b corresponding to a part irradiated with the light the electron passes through the aluminum substrate 2a and the high voltage power source 14, and the hole is moved in the vicinity of the surface of the photosensitive body 2b. And two types of potential patterns are formed on the surface. Thus, the generation of the ozone is eliminated and the reduction in cost is contrived.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that applies a bias voltage to an image carrier to perform charging and exposure.

<Prior Art> As a conventional image forming apparatus, one using an image forming process called the Carlson process as shown in FIG. 4 is generally known.

In the figure, 1 is a corona charger, and as shown in FIG. 7 in detail, a tungsten wire 11 with a diameter of several tens of μm
The wire 11 is stretched with a certain tension and is surrounded by a shield 12 made of a metal plate or the like.
A corona discharge is caused by applying a high DC voltage of 4 to 5 KV through a cable or the like. The corona ions generated near the surface of the wire 11 are located at a portion of the shield 12 that has a lower potential than the opening i2a, that is, the fourth
It moves toward the surface of an image carrier (hereinafter referred to as a photosensitive drum) 2 shown in the figure, and charges the surface of the photosensitive drum 2 to a desired potential. As described above, this corona charger 11 includes a corotron charger consisting of a wire 11 and a shield 12, and a mesh 13 stretched directly below the opening 12a of the shield 12 to control the corona current to the charged member. Two types of scorotron chargers are used depending on the discharge polarity. In the case of negative discharge, a scorotron charger is generally used to improve the non-uniformity of charging. As shown in FIG. 5, the photosensitive drum 2 has a photosensitive member 2b coated to a constant thickness on a highly conductive substrate 2a such as aluminum. Typical materials for this photoconductor include 5eSSe-TeSa-8i and OPC (organic photoconductor 0PGANICPH0TOC0NDUCTOR), which are highly insulating in the dark, but are highly insulating when irradiated with light of a specific wavelength. Hall 2C at the site
and electrons 2d generate electron pairs 2e (hereinafter referred to as carrier pairs), and as these carrier pairs 2e move in opposite directions according to the direction of the electric field, the area irradiated with light of a specific wavelength changes to have good conductivity. It has the property of

That is, when the surface of the photoreceptor 2b is negatively charged, the electrons 2d of the generated carrier pairs 2e pass through the aluminum base 2a and flow into the ground.
The holes 2C drift inside the photoreceptor 2b and reach the surface. The holes 2C that have reached the surface combine with negative charges to neutralize the surface charges and cause a decrease in surface potential. A normal image forming process is performed using this property. Here, there are two processes, one in which the surface of the photosensitive drum 2 is charged positively, and the other in which it is charged negatively, and although the principle is the same in both cases, it depends on the material of the photoreceptor 2b used. is selected.

Se, 5e-Te, and a-8t are electron transfer types and are used as positively charged materials, but recently, OPC, which is advantageous in terms of toxicity and productivity, is increasingly being used as a photoreceptor material. Since the hole transfer type OPC is in practical use, negative charging is used as the charging polarity. Therefore, as an example, the principle of a negative charging type image forming process is explained in FIGS. 4, 5, and 6.
This will be explained in more detail using figures.

The photosensitive drum 2 has an aluminum base 2a that is grounded, and rotates in the direction of arrow A in FIG. 4, and the following processes are sequentially performed.

First, as shown in FIG. 5, the surface of the photosensitive drum 2 is set to a predetermined initial surface potential by the corona charger 1 in the dark.
Uniformly charged to Vo (V). Next, a light source 3 such as a laser beam or an LED light having a wavelength suitable for the photosensitivity of the photoreceptor 2b is irradiated with a light beam by performing 0N10FF based on the data signal sent by the lighting drive circuit. The photosensitive drum 2 is scanned in a pattern to provide a portion of the photosensitive drum 2 that is irradiated with light and a portion that is not irradiated with light.

(This is called optical writing or fog light.) As mentioned above, carrier pairs 2e are generated inside the photoreceptor 2b in the portion irradiated with light, and the electrons pass through the aluminum substrate 2a. The holes also drift toward the surface of the photoreceptor 2b, neutralizing the negative charges on the surface. As a result, the area irradiated with light has an initial surface potential of -V.

(v) to the latent image potential -Vi (V) (called optical attenuation). On the other hand, the portion that is not irradiated with light maintains the initial surface potential, but in reality, the initial surface potential -Vo (V) changes to -Vs (V) due to a slight potential decrease called dark decay. As a result, as shown in FIG. 6, two types of potentials, -Vs (V) and -Vi (V), called electrostatic latent images, are formed into a pattern on the surface of the photosensitive drum 2 by optical writing. It is formed. Since the electrostatic latent image formed in this way is a pattern of charges and is invisible to the naked eye, the average particle size of the particles enclosed in the developing device 4 is approximately 10 μm.
The image is visualized by colored fine powder particles (hereinafter referred to as toner) 10 of a certain degree. This toner 10 is a composite material in which styrene or the like is used as a main binder and magnetic powder, a plasticizer, a charge control agent, a fluidizing agent, etc. are dispersed therein. This toner 10 can be produced as both a negatively charged toner and a positively charged toner by selecting the type of charge control agent. Further, this toner 10 has properties such as obtaining a triboelectric charge of a predetermined polarity through contact and separation, and being held by a magnetic material and oriented according to the magnetic field. FIG. 8 shows a typical developing device 4 using such toner. The main structure of this developing device 4 is a non-magnetic cylindrical roll 4.
1a and a magnet roll 41b magnetized with an N pole or an S pole therein, and the cylindrical roll 41a and the magnet roll 41b are rotatable independently.
1, a doctor blade 42 that regulates the thickness and conveyance fee of the toner 10 held on the developing roll 41, a paddle 43 that stirs and frictionally charges the toner 10, and a level sensor 44 that detects the remaining amount of the toner 10. and toner 10
It consists of a toner hopper 45 etc. that stores toner. Developer device 7
As the paddle 43 rotates, the toner 10 inside the toner 10 repeatedly collides with and separates from other toner particles, the surface of the developing roll 41, and the housing material 46, thereby obtaining a predetermined triboelectric charge. Thereafter, the developing roll 4 is held on the surface of the developing roll 41.
By rotating the toner 1, the thickness of the toner layer is kept constant by a doctor blade 42, and the toner is conveyed to a position facing the developing area of the photosensitive drum 2. Here, the toner 10 charged to a predetermined polarity adheres to the photosensitive drum 2 according to the electrostatic latent image due to the relationship between the electrostatic latent image on the photosensitive drum 2 and the developing bias voltage applied to the developing roll 41. . This relationship will be schematically explained using FIG. 6. With respect to the electrostatic latent image formed on the photosensitive drum 2 at a surface potential of -Vs (V) and a latent image potential of -Vi (V), a voltage of -vb (v) is applied to the developing device 7.
), the negatively charged toner 10 is applied a Coulomb force from the developing roll 41 in the direction of the latent image potential -Vi (V) and adheres to the photosensitive drum 2.

On the other hand, when the surface potential is -Vs (V), no Coulomb force is generated, so the toner 10 does not adhere to the photosensitive drum 2. Therefore, the toner 10 selectively adheres only to the portions irradiated with light, and the electrostatic latent image becomes a visible image. Note that in reality, several percent of counter toner (positively charged toner in this example) charged to the opposite polarity to the desired polarity is generated in the developing device 4, and this is located at a potential area of −Vs (V) that is not irradiated with light. It may adhere to the surface and stain the background of non-image areas (fogging), but in practice, this can be prevented by setting the development bias potential -vb (v) almost the same as the surface potential -Vs (V). . Note that the above example is a method called reversal development in which the toner 10 is selectively attached only to the areas irradiated with light (FIG. 6(a)), but on the contrary,
A method called regular development in which toner is selectively attached to areas that are not irradiated with light has also been put into practical use, and in this case, as shown in Figure 6(b), the development bias potential -Vb
(V) is set to approximately the same potential as the latent image potential -Vi (V),
By using a positively charged toner, an electrostatic latent image can also be visualized using the same principle.

Next, the toner 10 attached to the photosensitive drum 2 is electrostatically transferred in the transfer area. 5 in Fig. 4 is a corona transfer device,
It has almost the same configuration as corona charger 1. That is, it consists of a tungsten wire, a shield, etc., and a high voltage is applied similarly to the corona charger 1. However, in order to electrostatically transfer the negatively charged toner on the photosensitive drum 2 to the recording medium 9, a positive voltage is applied, and the corona charger 1
The polarity is opposite to that of . The recording medium 9 onto which the toner image has been transferred from the photosensitive drum 2 is conveyed as is to the fixing device 7. As shown in FIG. 10, the fixing device 7 includes a heat roll 71, a halogen lamp 72, and a backup rubber roll 7.
It is comprised of a peeling claw 74, a pressure spring 75, a temperature sensor 76, a control circuit 77, and the like. Usually, a halogen lamp 72 is held on the central axis of a hollow heat roll 71, and a predetermined voltage is applied to the halogen lamp 72 to heat the heat roll 71. The surface temperature of the heat roll 71 is fed back to the control circuit 77 by the temperature sensor 76.
By repeating 0N10FF of voltage application, it is controlled to always be constant. This heat roll 71
The backup rubber roll 73 is pressed with a constant tension by a pressure spring 75, and the backup rubber roll 73 is configured to rotate in synchronization with the rotation of the heat roll 71. The recording medium 9 holding the toner 10 is conveyed to the contact area between the heat roll 71 and the rubber roll 73 and heated. The heated toner 10 is softened and at the same time is permanently fixed on the recording medium 9 by pressure, forming the final image.

On the other hand, toner 1 remaining on the photosensitive drum 2 without being transferred
0 is collected as waste toner by a cleaning device 6, and the surface of the photosensitive drum 2 is cleaned. Then, by irradiating the entire surface of the photosensitive drum 2 from which the residual toner has been collected and removed with light hν, the surface potential of the photosensitive member 2b is removed, and the process from the above-mentioned charging step is repeated again.
Continuous image formation becomes possible.

The cleaning device 6 includes a peeling member 61 made of urethane rubber, a rubber holder 62, and a rubber holder 62, as shown in FIG.
It consists of a collected toner box 63 and the like, and a peeling member 6
1 is pressed against a sightseeing drum 2 under a certain tension, and the blade cleaning method is mechanically peeled off. While rotating the brush roll 64, frictional electrification is generated with the residual toner on the surface of the photoreceptor 2b, and electrostatic separation is performed using the charged charge of the toner, and the toner is removed from the brush by the stirring blade 65 and collected in the toner box 63. A brush cleaning method that collects the waste has also been put into practical use.

In addition to the method of irradiating the entire surface with light, there is also known a method of removing static electricity from the surface of the photosensitive drum using a discharging means such as a corona charger (not shown).

The optical writing method, development method, transfer method, fixing method, cleaning method, and static elimination method described above each have advantages and disadvantages, and the optimal method is selected based on the lifespan, cost, dimensions, etc. of the device.

<Problem to be solved by the invention> However, in such a conventional image forming apparatus,
Since the initial charging of the photosensitive drum 2 was performed by corona discharge, there were the following problems.

1) Normally, a high voltage of 4 to 5 KV, which is higher than the discharge starting voltage, must be applied to the tungsten wire 11.
Due to the high degree of danger, it is necessary to never touch the human body, and protective parts are costly.
The equipment becomes larger due to design constraints. Furthermore, as the output performance of the high-voltage power supply increases, the size and cost increase.

2) Since the discharge state is greatly affected by the environment such as atmospheric pressure, temperature, and humidity, especially relative humidity, the long-term stability of the surface potential is unreliable. In addition, in order to control the surface potential within a certain range, it is necessary to change the wire current value or applied voltage value, for example, based on the output of a humidity sensor.
This leads to an increase in costs associated with the control.

3) If a part of the tungsten wire 11 becomes partially dirty due to atmospheric dust or toner adhering to it, the corona discharge current from that part decreases, causing charging failure or uneven charging on the photosensitive drum 2. This results in image deterioration. For this reason, although the wire 11 is regularly cleaned using special paper, cloth, brush, etc., there is a risk that the wire 11 may be cut during cleaning.

4) When OPC is used as the photoreceptor 2b, negative corona discharge is used as a charger because OPC is negatively chargeable, but due to its charging mechanism, negative corona discharge has less uniform charging than positive corona discharge. Inferior, partial charging failure is likely to occur. Therefore, like the scorotron charger mentioned above,
Since the opening of the mesh is designed to be smaller and the total current is increased, the total current consumption becomes larger than the current required to charge the photoreceptor, and as a result, the charging efficiency decreases. Furthermore, the number of parts such as the mesh and the power supply and electrodes applied to the mesh increases, leading to an increase in cost.

5) In the case of negative corona discharge, a larger amount of ozone is generated than in positive corona discharge. Since ozone is extremely harmful to the human body, multiple ozone filters are required to adsorb and decompose the generated ozone, which increases costs. Furthermore, since the ozone filter also has a limited lifespan, its ozone decomposition performance gradually deteriorates. Furthermore, since ozone is a gas,
It is basically impossible for a filter to absorb and decompose all of the generated ozone, and human health is always at risk.

As mentioned above, there are major problems in using corona discharge for charging. Recently, the following two contact charging methods have been proposed in order to eliminate such drawbacks of corona discharge. For example, there is a brush charging method in which a brush roll made of polymeric fiber used as a cleaning brush is rotated at high speed and frictionally charged by sliding it on a photosensitive drum, but the brush's electrical resistance changes significantly due to environmental changes. This method has many problems such as poor charging due to poor contact of the brush, abrasion of the photoreceptor, and design of the rotation mechanism, and it has not yet been put into practical use. A roller charging method has also been proposed in which a bias-applied conductive rubber roller is rotated in contact with the photosensitive drum to charge the photosensitive drum, but like the brush charging method, the relative speed between the photosensitive drum and the brush can be set arbitrarily. However, the circumferential speeds of the roller and the photosensitive drum must be set to be the same in order to avoid scratches on the surface of the photosensitive drum. However, when rotating at the same speed, the charging part of the photosensitive drum and the charge supplying part of the roller have a one-to-one correspondence. There is a drawback that defects occur.

As described above, charging methods that eliminate the generation of ozone have been proposed as a replacement for discharging means such as corona chargers, but many problems still remain.

The present invention was made in view of these conventional problems.
Without using a discharge phenomenon as a charging method or applying high voltage, ozone generation is completely eliminated, and the charging efficiency is reduced to almost 1.
00%, and the purpose is to provide an image forming apparatus that can significantly reduce costs compared to the case where a conventional corona charger is used.

Means for Solving the Problems> In order to achieve the above object, the present invention includes an image carrier, a charging means for charging the image carrier, and a writing means for optically writing on the image carrier. , an image forming apparatus comprising: a developing means for visualizing the electrostatic latent image formed on the image carrier; a transfer means for transferring the developed image to a recording medium; and a cleaning means and a static eliminating means for the image carrier. The image carrier is characterized in that voltage applying means for applying a bias voltage to the front surface and the back surface of the image carrier, respectively, are provided.

Effect〉 The measures described above operate as follows.

A high voltage bias is applied to the back surface of the photosensitive drum, which has highly insulating properties in the dark, on the side of a highly conductive substrate made of aluminum or the like, and a conductive member to which a high voltage has been applied is brought into contact with the surface of the photosensitive drum. This biases the surface of the photosensitive drum and provides a constant electric field strength across the layers of the photosensitive drum. Furthermore, carrier pairs of holes and electrons are generated by performing image exposure using a normal optical writing means, and each moves to the substrate side or the surface side of the photosensitive drum according to the electric field inside the photosensitive drum, thereby forming an electrostatic latent image. Form. This electrostatic latent image is recorded on a recording medium by ordinary developing means and transfer means, and is permanently fixed by fixing means to obtain a final image.

<Example> The present invention will be explained below based on the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, the charger 8 has a structure in which a conductive polymer fiber brush 8 is inserted into a conductive metal plate 8, and a high voltage of 0 (V) is applied by a high voltage power source 13. . Like the conventional example, the photosensitive drum 2 is a cylindrical base made of a highly conductive material such as aluminum and coated with a photosensitive material to a thickness of several tens of μm. A carrier pair 2e of a hole 2C and an electron 2d is generated within the layer, and has the property of drifting in opposite directions according to the direction of the electric field. In the developing device 4, a constant voltage +vb (v) is applied to the developing roll 41 from a power source 15. The toner 10 held on the developing roll 41 is negatively charged by frictional charging or the like.
Q (μC/g) is obtained, selectively adheres to the photosensitive drum 2 according to the electrostatic latent image formed on the photosensitive drum 2 by Coulomb force, and becomes a visible image. The transfer device 5 electrostatically transfers the toner image on the photosensitive drum 2 onto the recording paper 9 by charging the recording paper 9 with corona discharge from a wire applied to Vt (V) by the high voltage power supply 16 .

The toner transferred onto the recording paper 9 is heated by the fixing device 7 and is softened by applying a certain pressure to the recording paper 9.
permanently affixed to the top. On the other hand, it is not transferred to the recording paper 9,
The toner remaining on the photosensitive drum 2 is removed by a cleaning device 6.
The photosensitive drum 2 is peeled off from the top of the photosensitive drum 2, and the surface of the photosensitive drum 2 is cleaned.

Finally, the entire surface of the photosensitive drum 2 is irradiated with light hv to neutralize the charges in the photosensitive layer 2b of the photosensitive drum 2, and the process cycle is completed.

Here, the charging process and the formation of an electrostatic latent image generated by optical writing will be explained in more detail with reference to FIGS. 2 and 3. As shown in FIG. 2, the surface of the photosensitive drum 2 is biased to Vo (V) by being rubbed by a charger 8 consisting of a conductive brush to which a bias voltage is applied. On the other hand, a low voltage of +VD (V) is applied as a bias from the back side to the aluminum base 2a by the high voltage power supply 14. As mentioned above, since the photoreceptor 2b has high insulation properties in the dark, no current flows between the front surface and the back surface, and VD -V occurs between the layers of the photoreceptor 2b.

(v) A uniform potential difference is formed. Next, the light source is adjusted so that the desired image area is irradiated with light and the non-image area is not irradiated with light.
0N10FF, and optical writing is performed from the surface of the photosensitive drum 2. Carrier pairs of holes and electrons are generated inside the photoreceptor 2b corresponding to the portion irradiated with light, and the electrons are transferred to the aluminum base 2a and the high voltage power supply 14.
The holes move near the surface of the photoreceptor 2b.

As a result, as shown in Figure 3, the potential changes from Vo (V) to +Vi (V) in the irradiated area due to the movement of the holes, and is maintained at Vo (V) in the non-irradiated area. Two types of potential patterns, Vo (V) and +Vi (V), ie, electrostatic latent images, are formed on the surface of the photoreceptor 2b. Third
Figure (a) shows a reversal development method in which toner is attached in accordance with the formed electrostatic latent image, and the development bias potential is adjusted to Vo of the surface potential of the photoreceptor 2b using negatively charged toner.
By setting +VB (V) near (V), +
Toner can be electrostatically attached to a portion having a potential of Vi(v). In addition, the same figure (b) shows the case of regular development in which toner is attached to areas that are not irradiated with light, and using positively charged toner, the development bias potential is set to around the potential of the area that is irradiated with light, 10 Vi (V). By setting, toner is electrostatically attached to a portion having a potential of +Vo (V).

In the above embodiment, a high voltage is applied to the charger 8 made of a conductive brush for charging, and the surface of the photosensitive drum 2 is heated to Vo (V
), but in other embodiments, if you want to simplify the device or reduce costs, you can lower the surface potential of the photosensitive drum 2 by grounding the conductive brush 8a and erasing the surface charge. It is also possible to bias to 0 (v), and in this case, the high voltage power source can be simplified to three: the high voltage power source 14 for the rear surface, the high voltage power source 15 for development, and the high voltage power source 16 for transfer. Furthermore, in the case of reversal development, the development bias potential is +VB (V) and the surface potential of the part of the photosensitive drum that is not irradiated with light, that is, O (V).
, it is also possible to connect the developing roll to ground. In this case, only two high-voltage power supplies, the high-voltage power supply 14 for the back side and the high-voltage power supply 16 for transfer, are required, and the apparatus can be significantly simplified and costs can be reduced.

<Effects of the Invention> As described above, according to the present invention, an image carrier, a charging means for charging the image carrier, a writing means for optically writing on the image carrier, and an image carrier for the image carrier are provided. In the image forming apparatus, the image forming apparatus includes a developing means for making the formed electrostatic latent image visible, a transfer means for transferring the developed image onto a recording medium, and a cleaning means and a static eliminating means for the image carrying member. By providing a voltage application means for applying a bias voltage to the front and back surfaces of the image carrier, a uniform and constant potential difference is generated in the thickness direction of the image carrier, and the optical writing means utilizes the photosensitive characteristics of the image carrier. Since an electrostatic latent image is formed by optical writing, it is possible to form an image without using a discharge phenomenon. For this reason, the high voltage power supply can be reduced without applying high voltage, resulting in miniaturization and cost reduction.
It is possible to control the surface potential at a constant level without being affected by the environment such as temperature and humidity. Furthermore, charging defects and uneven charging of the photosensitive drum caused by dust, dust, toner, etc. in the atmosphere do not occur, and partial charging defects, which are a major problem in negative corona discharge, are also improved. Furthermore, since no ozone is generated, an ozone filter is not required, which not only reduces costs, but also provides the great effect of being harmless and safe for the human body.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is an overall configuration diagram of an image forming apparatus showing an embodiment of the present invention, and Fig. 2 illustrates a movement model of a carrier pair inside a photoreceptor and light attenuation in the present invention. Conceptual diagram, Figure 3 (a
) is a conceptual diagram illustrating the potential model of an electrostatic latent image and toner adhesion when reversal development is used in the present invention, and FIG. 3(b) is a conceptual diagram illustrating the electrostatic latent image when regular development is used in the present invention. Therefore, a conceptual diagram explaining the potential model and toner adhesion, Fig. 4 is an overall configuration diagram of an image forming apparatus showing a conventional example, and Fig. 5 shows a movement model of carrier pairs inside a photoconductor and light attenuation in a conventional example. Fig. 6(a) is a conceptual diagram illustrating the electrostatic latent image potential model and toner adhesion when conventional reversal development is used, and Fig. 6(b) is a conventional normal image. A conceptual diagram explaining the electrostatic latent image potential model and toner adhesion when using development; Figure 7 is an overall diagram of a general corona discharger; Figure 8
The figure shows an overall view of a general developing device, and Fig. 9 shows an overall view of a general linning device. Fig. 9 (a) shows a blade cleaning method. Fig. 9 (b) shows a brush cleaning method. FIG. 2 is an overall diagram of a general fixing device. 1...Corona charger 2...Photosensitive drum 3...Light source 4-...Developer 5...Transfer device 6...
・Cleaning device 7... Fixing device 8... Charging brush 10... Toner 14... High voltage power source for charging 15... High voltage power source for back side 16... High voltage power source for developing 17... For transfer high voltage power supply

Claims (1)

[Claims] an image carrier; a charging means for charging the image carrier;
writing means for optically writing on the image carrier;
An image forming apparatus comprising: a developing means for making an electrostatic latent image formed on the image bearing member visible; a transfer means for transferring the developed image onto a recording medium; and a cleaning means and a static eliminating means for the image bearing member. . An image forming apparatus, further comprising voltage applying means for applying a bias voltage to the front surface and the back surface of the image carrier, respectively.