JPH05307308A - Multicolor image forming device - Google Patents

Abstract

PURPOSE:To always form an excellent image without color mixture even in the case that the electric charge quantity of first developing toner is not lowered by lowering the potential of a host writing part according to the lapse of time. CONSTITUTION:In a multicolor image forming device constituted by orderly arranging plural image forming units consisting of electrifiers 4 and 15, the writing parts 10 and 20 and developing devices 5 and 6 around a photosensitive body 1, the potential of the host wiring part 10 is lowered according to the lapse of time or adjusted according to humidity. That means, a humidity sensor 31 is fitted to the first developing device 5 and the potential of a latent image part is raised or lowered according to the value thereof. Besides, the second electrifier 15 is moved to the downstream side of the rotating direction of the body 1 according to the lapse of time or in the case that the humidity is high in order to increase the electrification quantity of the toner after second electrification. That means, the nearer the charger 15 is moved to the downstream side, the lower the potential before the second electrification becomes, whereby more current can be made to flow by the body 1 and the electrification quantity of the toner can be increased.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses an electrophotographic recording method. The present invention relates to a multicolor image forming apparatus such as a laser printer, a copying machine or a facsimile, which records a color image on a recording sheet.

[0002]

2. Description of the Related Art In a generally well-known electrophotographic recording method, a photoconductor is uniformly charged, a light image is formed on the photoconductor, and exposure is performed to form an electrostatic latent image. After that, the electrostatic latent image is developed to form a toner image corresponding to the electrostatic latent image, and the toner image is transferred to a recording sheet.

Various methods have been developed for recording a color image using such an electrophotographic recording method. Each has its own problems.

[0004]

Among them, FIG. 1 shows a schematic construction of an apparatus which employs a so-called over-developing method.

The apparatus as a two-color image forming apparatus includes
On the outer periphery of the photoconductor 1, the pre-clean contron 2, the cleaning device 3, the first charging device 4, the first developing device 5, the second charging device 15, the second developing device 6, the pre-transfer control device 14, and the transfer device 8 are provided. It is arranged.

A first writing section 10 is provided between the first charging device 4 and the first developing device 5, and a second charging device 15 is provided.
The second writing unit 20 is provided between the second developing unit 6 and the second developing unit 6.

In this apparatus, after the photosensitive member 1 is uniformly charged by the first charging device 4, an electrostatic latent image is formed by the first writing section 10, and the first developing device 5 causes, for example, black toner. And reverse development. Next, after the second developing device 15 and the first non-image area are recharged by the second charger 15, that is, the photoconductor 1 is uniformly charged again, the first writing portion
An electrostatic latent image is formed on the non-image area and is developed by the second developing device 6 using, for example, red toner. In this way, two-color toner images are formed on the photoconductor 1, and these toner images are transferred onto the recording paper 12 at once.

FIG. 2 shows a process in the conventional two-color image formation.

First, as shown in FIG. 2a, the first
The charger uniformly charges the photoconductor to V ₀ . Next, as shown in FIG. 2B, the first writing unit writes a latent image on the photoconductor. The potential of the latent image portion at this time is V _L0 . Then, the first latent image is developed by the first developing device. Potential after development of the latent image portion at this time, as shown in FIG. 2c, is higher than (V _L0 + α) becomes, V _L0. A second charge is then applied to uniformly recharge the photoreceptor as shown in Figure 2d. A scorotron is used for the second charging, and (V
_It plays the role of raising the potential of ( _L0 + α) to V ₀ .

In this method, by performing the second charging,
The second development is prevented from being performed in the first development section, and the charge amount of the toner in the first development section is increased to prevent the first development toner from mixing into the second development section. Further, there are advantages that the copying speed does not decrease and highly accurate registration is not required.

However, in the second developing device 6, the toner image already formed on the photoconductor 1 is disturbed, the developing density is lowered, or the toner is mixed in the second developing device 6, There is a drawback that it causes a problem such as a shortened life of the developer. Particularly, in the electrostatic latent image formed by the first writing unit 10, one having a latent image potential close to the background portion potential has a weak toner attracting force to the photoconductor 1, and the toner in the second developing device 6 is a developing brush. Is easily scraped by. Therefore, there is a drawback that image information is lost.

During the second charging, the current flowing from the second charger toward the photosensitive member flows into the photosensitive layer and the toner layer, so that not only the photosensitive layer but also the charge amount of the first developing toner is increased. .. Here, as shown in FIG. 3, the amount of increase in the charge amount of the toner is proportional to the value of the current flowing in, and the greater the amount of current flowing, the greater the amount of increase in the charge amount.

However, under normal image forming conditions, the charging potential V
_{Since 0} , the latent image potential V _L0 and the first developing bias V _B0 are determined, (V _L0 + α) on the photoconductor is limited. Therefore, the current flowing to the photoconductor side is V ₀ − (V _L0 + α)
It is limited by and is always constant. The constant current flowing to the photoconductor side means that the amount of increase in the charge amount is always constant.

However, the charge amount of the toner usually decreases with time or when the humidity is high. In such a case, the charge amount of the toner cannot be sufficiently increased, and the first development The toner is mixed in the second developing device.

Although the charge amount of the first developing toner can be increased by increasing the discharge current from the second charger, the charge in the first non-image area also increases,
The second writing section and developing conditions must be changed.

Therefore, in view of the above problems, the present invention provides a multicolor image forming apparatus capable of always forming a good image without color mixture even when the charge amount of the first developing toner is reduced. It is an issue.

[0017]

The present invention solves this problem by
In a multicolor image forming apparatus in which a plurality of image forming units including a charger, a writing unit and a developing unit are sequentially arranged around a photoconductor, the potential of a higher writing unit is lowered with time or adjusted according to humidity. By solving.

In the case of a two-color image forming apparatus, the original potential of the first writing section is V _L0 and the original first developing bias is V _L0 .
_B0 , the potential when the potential of the first writing unit is lowered is V _L1
And the corresponding reduced first bias V
The _BI, is set so that _{V B0 -V L0> V BI -V} L1, is suitable.

It is also preferable if the lower charger can be moved downstream in the direction of rotation of the photosensitive member.

It is also convenient to integrally configure the lower image forming units.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail as a two-color image forming apparatus according to an embodiment based on the drawings.

FIG. 4 shows changes in the latent image portion potential V _L0 and the charge amount Q ₀ of the developing toner with the passage of time when the latent image is written on the photosensitive member by the first writing unit.

In response to such a change, the latent image portion potential in the first writing portion is lowered with time to become V _L1 . As a result, as shown in FIG. 5, the value of (V _L1 + α) after the first development becomes low, and a large amount of current is required to raise it to V ₀ by the second charging. At this time, a large amount of current also flows into the toner layer, and the charge amount can be made higher than that when the latent image portion potential is V _L0 .

The decrease in the charge amount of the toner occurs not only over time but also when the humidity is high. FIG. 6 shows the relationship between humidity and the latent image portion potential. Therefore, as shown in FIG. 7, the first image forming unit, specifically, the first image forming unit
The temperature sensor 31 is attached to the developing device 5, and the latent image portion potential is increased or decreased according to the value.

Even when the toner charge amount is reduced, the first
If the development is performed without changing the development bias, the latent image portion potential is lowered, so that the toner adhesion amount may become too large. In order to prevent this, when the original potential of the first writing unit is V _L0 , the original first developing bias is V _B0 , and the potential when the potential of the first writing unit is lowered is V _L1 Developing bias V _B1 to V _B0 −V _L0
If the setting is such that> V _BI −V _L1 , the toner adhesion amount does not become too large. In the case of V _B0 -V _L0 = V _BI -V _L1 , the developing potential becomes the same as the original developing potential, but the potential is more decreased when the toner charge amount decreases. Toner will adhere.

Further, in order to increase the charge amount of the toner after the second charging, the second charger is moved to the downstream side in the rotation direction of the photoconductor with the passage of time or when the humidity is high. The potential of the photoconductor has a time constant, and the potential becomes lower than the initial potential as the time after the photoconductor is charged is longer.
That is, if the second charger is moved to the downstream side, the potential (V _Ln + α) before the second charging becomes lower as the second charger is moved. That is, the current value for setting V ₀ becomes large, and the charge amount of the toner can be increased. The amount of movement of the second charger may be determined by the amount of charge of the toner, and specifically, the amount of movement is controlled by the elapsed time, humidity and the like.

When the second charger is moved, if the distance between the second writing unit and the second developing unit is not accurately kept constant, the potential after the second charging will be different, and The latent image process cannot be made constant. Therefore, as shown in FIG. 7, the second charger, the second writing unit, and the second developing unit are integrated. As a result, the second charger can be moved as the second image forming unit when moved to the downstream side in the rotation direction of the photoconductor with the passage of time or when the humidity is high, and a uniform latent image is formed at all times. , Can be visualized. FIG. 8 shows the overall control configuration of each image forming unit.

[0028]

According to the multicolor image forming apparatus of the first aspect, the potential of the upper writing section is lowered with time. In the multicolor image forming apparatus of the second aspect, the potential is adjusted according to the humidity. Therefore, a larger amount of current can be passed to the photoconductor, and the toner charge amount can be increased.

In the two-color image forming apparatus of claim 3,
When the toner charge amount is reduced and the potential of the first writing unit is reduced, the original potential of the first writing unit is V _L0 , the original first developing bias is V _B0 , and the potential of the first writing unit is reduced. When the potential when the voltage is set to V _L1 is set, the corresponding reduced first bias V _BI is set so that V _B0 −V _L0 > V _BI −V _L1, and therefore the first developing bias is set to the first This is more than the amount of reduction in the writing section, and an unnecessarily large amount of adhered development is always avoided.

In the multicolor image forming apparatus of the fourth aspect,
Since the lower charger is movable to the downstream side in the rotation direction of the photoconductor, the toner charge amount after recharging can be increased when the toner charge amount decreases.

In the multicolor image forming apparatus of the fifth aspect,
Since the lower image forming unit is configured integrally,
Even when the lower-order charger is moved to the downstream side, the distance between the charger, the writing unit, and the developing unit does not change, and it is not necessary to change the latent image condition at that position.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a known two-color image forming apparatus.

FIG. 2 is a diagram showing a process in a conventional two-color image formation.

FIG. 3 is a diagram showing the relationship between the amount of increase in the toner charge amount and the amount of current flowing in.

FIG. 4 is a graph showing changes in the latent image portion potential and the charge amount of developing toner over time.

FIG. 5 is a diagram showing a process in two-color image formation according to the present invention.

FIG. 6 is a graph showing the relationship between humidity and the latent image portion potential.

FIG. 7 is a schematic diagram showing a relative relationship between an image forming unit including a humidity sensor according to the present invention, a movable lower image forming unit, and a photoconductor.

FIG. 8 is a conceptual diagram showing an overall control configuration for each image forming unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 4 1st charging device 5 1st developing device 6 2nd developing device 10 1st writing part 15 2nd charging device 20 2nd writing part 31 Humidity sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G03G 15/06 101 H04N 1/29 G 9186-5C

Claims (5)

[Claims] 1. A multi-color image forming apparatus comprising a plurality of image forming units, each comprising a charger, a writing section and a developing section, which are sequentially arranged around a photoconductor to lower the potential of the upper writing section with time. Characteristic multicolor image forming apparatus. 2. In a multicolor image forming apparatus in which a plurality of image forming units including a charger, a writing unit and a developing unit are sequentially arranged around a photoconductor, the potential of a higher writing unit can be adjusted according to humidity. Characteristic multicolor image forming apparatus. 3. A two-color image forming apparatus, wherein the original potential of the first writing unit is V _L0 , the original first developing bias is V _B0 , and the potential when the potential of the first writing unit is lowered is V _L0 .
_{When L1} is set, the corresponding reduced first bias V _BI
Is set so that V _B0 −V _L0 > V _BI −V _L1 . 3. The multicolor image forming apparatus according to claim 1, wherein 4. The multicolor image forming apparatus according to claim 1, wherein the lower charger is movable downstream in the rotation direction of the photoconductor. 5. The multicolor image forming apparatus according to claim 4, wherein lower image forming units are integrally formed.