JP2003131496A - Transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transfer device in which residue toner quantity on an image carrier after transferring is reduced and the toner can be efficiently used and to obtain the transfer device in which the image quality is not greatly deteriorated even when the toner recovered from the image carrier is reused. SOLUTION: In the transfer device 5 transferring the toner held on the image carrier 1 to recording material 7, current value 'It' fed to a transferring machine 51 is stipulated to be a value more than the current value when transferring efficiency Y is made maximum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer device for transferring toner held on an image carrier onto a recording material.

[0002]

2. Description of the Related Art A toner used in an image forming apparatus typified by a laser printer or a copying machine is a resin such as styrene-acryl or polyester containing a colorant (in the case of a black toner, carbon black is mainly used as a color toner). In the case of toner, pigments and dyes are used) and a charge control agent for adjusting the charge amount of toner is mixed.

When manufacturing such a toner, a resin,
The colorant and the charge control agent are melt-kneaded, pulverized into a fine powder with a pulverizer such as a jet mill, and a classifier provides an extremely small particle size so that a desired particle size (for example, a particle size of about 10 μm) becomes main. (For example, 4 μm or less) or large particle size (for example, 20 μm)
m or more) is excluded. Then, fine powder such as silica is externally added to obtain a toner that can be used as a developer.

On the other hand, in the image forming apparatus, the photoconductor is charged, and then the charged photoconductor is subjected to scanning exposure according to image data to form an electrostatic latent image on the photoconductor. By developing the image, it appears on the photoreceptor as a visible toner image. After that, the toner image is transferred from the photoconductor to a recording material such as paper, and the toner image is fixed on the recording material by subsequent thermal fixing.

When the toner on the photoconductor is transferred to the recording material,
It is difficult to transfer all the toner on the photoconductor to the recording material, and some toner remains on the photoconductor without being transferred to the recording material. Generally, the weight of the toner transferred to the recording material,
The ratio to the toner weight on the photoconductor before transfer is called transfer efficiency, and the lower the transfer efficiency, the more toner remains on the photoconductor.

Therefore, if the image forming process with such a low transfer efficiency is continued, the toner image formed in the next process is overlapped and the image quality is deteriorated.
After the transfer, the surface of the photoconductor is cleaned to remove the residual toner. The toner removed from the photoconductor by this cleaning may be discarded without being used as it is, or may be returned to the developing machine and reused.

[0007]

However, the toner removed from the surface of the photoconductor in the cleaning step is used for development once and is subjected to mechanical stress when being removed from the surface of the photoconductor. , It is deteriorated compared to the new condition. For example, it has been confirmed from an observation image of a scanning electron microscope that fine powder such as silica disappears from the toner surface as compared with a new toner.

The silica externally added to the toner is necessary for improving the fluidity of the toner (the ease of flow as a powder, the difficulty of forming lumps), and the toner having a small amount of silica has poor fluidity. The print quality is also poor.

Therefore, when the toner removed by cleaning is to be reused, a large amount of low-fluidity toner is contained in the developer, and therefore all development is performed using new unused toner. The image quality will be lower than that of the case.

Further, when the toner removed by cleaning is discarded, the toner corresponding to that amount does not contribute to the image formation, which causes waste and increases the cost required for image formation. Further, since waste is generated, the treatment cost is required, which is not preferable for the environment.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a transfer device capable of reducing the amount of toner remaining on the image carrier and effectively utilizing the toner.

Another object of the present invention is to provide a transfer device which does not significantly deteriorate the image quality even when the toner collected from the image carrier is reused in the developing process.

[0013]

SUMMARY OF THE INVENTION In the transfer device for transferring the toner held on the image carrier to the recording material, the above-mentioned object is to control the current value supplied to the transfer device when the transfer efficiency is maximized. This is achieved by specifying a value larger than the current value.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, the image forming process in the image forming apparatus will be described with reference to FIG.

In FIG. 1, reference numeral 1 is a photoconductor which is exemplified as one form of the image carrier. The surface of the photoconductor 1 rotating in the clockwise direction is uniformly charged by the charger 2, the light of the exposure device 3 blinks according to the image data, and the light-irradiated portion of the photoconductor 1 becomes conductive. The surface charge disappears.

The developing device 4 holds a two-component developer consisting of toner and carrier, and the developer is conveyed to a region facing the photoconductor 1 as the developing roller 41 having a magnet inside rotates. To be done. A bias voltage (not shown) is applied to the developing roller 41, and the toner having the same charging polarity as that of the photoconductor adheres to the portion of the surface of the photoconductor where the electric charge disappears due to the electric field action between the photoconductor and the developing roller. The toner image formed on the photoconductor 1 by the development is transferred to the recording material 7 by the transfer device 5.

The toner image transferred to the recording material 7 is melted by being heated by a fixing device (not shown) and is fixed on the recording material 7. After that, the toner remaining on the surface of the photoconductor 1 is removed by the cleaning device 6, and thereafter, the same image forming process is repeated.

A transport path (not shown) is formed between the cleaner 6 and the toner hopper 42, and the cleaner 6 is provided.
The toner collected by is sent to the toner hopper 42 and used again for development.

Here, in the image forming apparatus of FIG. 1, a corona charging type transfer device 51 is provided inside the circulating member (endless belt) 52 as the transfer device 5, and the recording material 7 is placed on the belt 52.
A belt transfer device that transfers the toner on the photoconductor 1 to the recording material 7 side by causing the transfer device 51 to carry the toner while the discharge polarity of the transfer device 51 is opposite to that of the toner is used. There is.

The transfer efficiency is a value obtained by dividing the toner weight per unit area transferred onto the recording material by the toner weight per unit area on the photosensitive member before transfer and expressing it as a percentage.

FIG. 2 shows the relationship between the transfer efficiency Y and the current It supplied from the power source 53 to the transfer device 51 (hereinafter referred to as the transfer current) in the image forming apparatus shown in FIG. There is. In FIG. 2, the two curves have different recording materials, the curve 13 is a sheet having a thickness of about 80 μm, and the curve 14 is a sheet having a thickness of about 180 μm. is there.

The transfer current It is a relative value where the maximum transfer efficiency when using thin paper is 1. The transfer current characteristics of the transfer efficiency are characteristics in which the transfer current once takes a maximum value and then decreases with an increase in the transfer current. The transfer efficiency may be low regardless of whether the transfer current is small or large, but there is the following difference in image quality depending on whether the current is the maximum transfer efficiency or not.

When the transfer current value is smaller than that at the maximum transfer efficiency, a partial transfer failure occurs in a relatively wide range of the image, and a black background is cut off white or a line drawing is interrupted within a range of several millimeters. Further, in this case, the fluctuation of the transfer efficiency is large with respect to the fluctuation of the transfer current, and the decrease of the transfer efficiency is large especially when the transfer current is decreased.

When the transfer current value is larger than that at the maximum transfer efficiency, transfer defects such as white spots and breaks in a wide range do not occur, but transfer defects occur in a narrow range (around 0.1 mm), or transfer defects occur. Images tend to scatter. In particular, when the transfer current value increases, the toner of the line image is disturbed, and the image density of the line decreases with the naked eye, and the line width appears thick.

From the above reasons, it is preferable from the viewpoint of image quality that the transfer current is set to a value at the maximum transfer efficiency. However, as shown in FIG. 2, the transfer current value at which the maximum transfer efficiency is obtained differs depending on the thickness of the recording material used. In addition, in reality, it is difficult to set the maximum transfer efficiency point because it changes depending on the charge amount of the toner, the water content of the recording material, and environmental conditions (particularly humidity) in addition to the thickness of the recording material.

Therefore, the transfer current value is set to a value larger than that at the maximum transfer efficiency, which is relatively insensitive to the fluctuations of these external factors and has a small decrease in the transfer efficiency with respect to the fluctuations of the transfer current. Further, the transfer condition is set in accordance with the case where the recording material is thick so that the transfer efficiency does not drop extremely. Therefore, in the case of thin paper, the transfer efficiency is lower than the maximum and the amount of toner remaining on the photoconductor is large.

In the actual use of the image forming apparatus, the amount of thin paper used is larger than that of thick paper. Therefore, the large amount of residual toner means that the image quality of an image forming apparatus that reuses the toner deteriorates the print quality and The image forming apparatus which is not used has a high printing cost per page.

The present inventor investigated the relationship between the transfer current and the transfer efficiency shown in FIG. 2 and found that below the transfer current at which the transfer efficiency is maximized, the charge polarity of the toner remaining on the photosensitive member is the charge before transfer. It was the same as the polarity, but it was discovered that the charging polarity of the toner remaining on the photoconductor was opposite to the original polarity at the transfer current or higher at which the transfer efficiency was maximized.

In the range where the transfer current is lower than the maximum transfer efficiency, the increase of the transfer current tends to strengthen the transfer electric field, and thus the transfer efficiency also increases with the increase of the transfer current. The reason why the transfer efficiency decreases once the transfer efficiency reaches the maximum after the transfer current exceeds the maximum value is that the toner is charged in the opposite polarity and cannot be moved to the recording material side by the transfer electric field. It is thought to be because. Therefore, as shown in FIG. 2, after the transfer efficiency once reaches the maximum value with respect to the transfer current,
It was thought that the transfer efficiency would decrease with a transfer current higher than that.

Therefore, if it is possible to prevent the toner from being charged to the opposite polarity when the transfer current is large, it is possible to maintain a high transfer efficiency in the range where the transfer current is large and to set the thin paper even when the transfer condition is set to thick paper. The transfer efficiency can also be maintained at a high level, the amount of toner remaining on the photoconductor after transfer can be reduced, deterioration of print quality can be prevented, and printing costs can be reduced.

The reason why the toner is charged in the opposite polarity when the transfer current is large is that the insulation of the toner is destroyed by the high electric field acting at the time of transfer and the charge of the opposite polarity is injected. To prevent the injection of charges, the resistance of the toner may be increased. Several kinds of negatively charged toners were made as prototypes and the relationship between their resistance and transfer efficiency characteristics was investigated.

<Toner A> A low acid value polyester resin, carbon black as a colorant, a metal complex charge control agent, and wax as a release agent were used.

<Toner B> A styrene acrylic resin, carbon black as a colorant, a metal complex charge control agent, and wax as a release agent were used.

<Toner C> The amount of wax is larger than that of Toner B.

The materials of the respective toners were mixed, kneaded, pulverized, and classified to an average particle size of 9.5 μm.

FIG. 3 shows characteristics of transfer efficiency with respect to transfer current in the case of thin paper. In FIG. 3, curve 11 is based on toner A, curve 12 is based on toner B, and curve 13 is based on toner C. Next, the toner resistance measuring device will be described with reference to FIG.

FIG. 4 is a schematic explanatory view of a measuring device for measuring the resistivity of toner in a powder state. Resistance measuring jig 84
Is provided with a disk-shaped electrode 81 in the center thereof,
It is grounded via an ammeter 83. A guard electrode 82 is electrically insulated from the periphery of the electrode 81 and is grounded. The toner 30 is placed on the electrode 81 and the guard electrode 82.
To fill. A high voltage power supply 21 is directed toward the surface of this toner.
When a high voltage is applied to the corona discharge wire 22 from the above, a corona discharge is generated between the corona discharge wire 22 and the shield 23, a part of the generated corona is applied to the toner 30, and the current flowing through the toner 30 is measured by the ammeter 83. .

When the voltage of the power source 21 is set to about 4000 V, the discharge from the corona discharge wire 22 starts, and the current starts flowing through the toner. When the voltage of the power supply 21 exceeds 7000 V, some toner is partially discharged. The polarity of the voltage applied to the corona discharge wire 22 is such that the charge around the toner at the time of transfer is the charged charge of the photoconductor, and in this embodiment, since the negatively charged organic photoconductor is used, the negative corona is A correlation with the transfer efficiency was obtained when a negative voltage was applied so as to occur.

When a positive voltage was used, there was no correlation between the transfer efficiency and the resistance. It is presumed that this is because the toner itself and the charge around the toner at the time of transfer are negative, and the positive charge in such a situation is related to the decrease in transfer efficiency.

The calculation of the resistivity R is such that the toner 30 has a thickness of 2
Since the distance between the surface of the toner 30 and the corona discharge wire 22 is 7 mm, the voltage applied to the toner 30 is set to 2/9 of the voltage applied to the corona discharge wire 22 and the current flowing through the ammeter 83 is set. It was divided by to obtain a resistance value, which was multiplied by the area of the electrode 81 and divided by the thickness of the toner 30 to obtain the resistivity. As a result, the toner A has a resistivity of 5.7 × 10 ¹⁴ Ω · cm, and the toner B has a resistivity of 4.6 × 10 ¹⁴
Ω · cm, and toner C was 3.0 × 10 ¹⁴ Ω · cm.

From this result, as the transfer current increases,
It has been found that the toner whose transfer efficiency does not decrease has high resistance. Next, the resistance of this toner was examined further by changing the composition.

<Toner A1> Medium acid value polyester resin,
Carbon black as a colorant, a metal complex charge control agent,
Wax was used as a release agent.

<Toner B1> With respect to Toner B, 60% of Toner B was used as carbon black.

<Toner B2> With respect to Toner B, carbon black was 70% of Toner B.

<Toner B3> Toner B2 was changed to a charge control agent having a weak negative chargeability.

When the resistivity of the toner was measured in the same manner as in the above case, the toner A1 was 4.5 × 10 ¹⁴ Ω · cm,
Toner B1 is 5.0 × 10 ¹⁴ Ω · cm, Toner B2 is 4.7 × 10 ¹⁴ Ω · cm, and Toner B3 is 2.7 × 10.
It was ¹⁴ Ω · cm.

Regarding carbon black, since carbon is a conductive material, its resistance can be increased by reducing it. Regarding the polyester resin, the resistance can be changed depending on the acid value (the amount of the site where electrons are easily incorporated in the molecule). Also, the resistance can be changed by using a charge control agent. As described above, the toner resistance can be controlled by the combination of resin, carbon black, and charge control agent.

Regarding the transfer current characteristics of the transfer efficiency, the toner A1 and the toner B2 have almost the same characteristics as the curve 12 in FIG. Toner B3 has characteristics close to curve 13. Toner B1 had a characteristic midway between curves 11 and 12.

In FIG. 2, in order to cope with thick paper as the transfer current, the transfer efficiency is 90% or more if it is about 2 to 3 times as large as the transfer current that maximizes the transfer efficiency in the case of thin paper. A value of 90% as the transfer efficiency is an acceptable value from the viewpoint of reuse of residual toner and cost.
It is a value that has been confirmed by conventional experience.

From FIG. 3, in order to obtain a transfer efficiency of 90% on thin paper, a curve 11 of toner A and a curve 12 of toner B are used.
It is considered that the resistivity of the toner may be slightly closer to the toner B, so that the resistivity of the toner may be about 5 × 10 ¹⁴ Ω · cm or more.

From the above results, the resistivity is about 5 × 10 ¹⁴
By using a toner of Ω · cm or more, the transfer efficiency can be maintained high. As an effect, the toner remaining without being transferred is reduced. Therefore, when the toner is reused in the development, the quantitative ratio of the reused toner in the developer is relatively reduced, so that the image quality is improved. The decline is less.

Further, by using such a toner, it becomes possible to set the transfer current larger than a value at which the maximum transfer efficiency is obtained. As described above, this makes it possible to make the setting of the transfer current the same even for recording materials having different thicknesses, eliminating the need for adjustment for each recording material, which is advantageous in terms of the apparatus configuration.

In this embodiment, the belt transfer type transfer device has been described as the transfer device, but a corona transfer device in which the transfer device is directly opposed to the photoconductor without the circulation member may be used. . Further, the same effect can be obtained not only by using a corona discharger but also by a roller transfer device.

[0054]

As described above, according to the present invention, it is possible to realize a transfer device capable of reducing the amount of toner remaining on the image carrier and effectively utilizing the toner.

Further, it is possible to provide a transfer device in which image quality deterioration is small even when the toner collected from the image carrier is reused in the developing process.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus to which the present invention is applied.

FIG. 2 is an explanatory diagram showing the relationship between transfer efficiency and transfer current.

FIG. 3 is an explanatory diagram showing the relationship between transfer efficiency and transfer current.

FIG. 4 is a schematic configuration diagram of a powder toner resistance measuring device.

[Explanation of symbols]

1 Image carrier (photoreceptor) 2 charger 3 exposure equipment 4 developing machine 5 Transfer device 6 cleaning machine 7 Recording material (paper) 41 developing roller 51 transcription device 52 Circulator (endless belt) 53 power supply

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Claims (4)

[Claims] 1. A transfer device for transferring toner held on an image carrier onto a recording material, wherein the current value supplied to the transfer device is set to a value larger than the current value at which the transfer efficiency is maximized. A transfer device characterized by the above. 2. The transfer device according to claim 1, wherein an electric resistivity of the toner powder is 5 × 10 ¹⁴ Ω · cm or more. 3. An image bearing member, a circulating member provided so as to face the image bearing member, and a circulating member provided inside the circulating member and having a predetermined polarity to the image bearing member side through the circulating member. A transfer device that supplies the toner held on the image carrier to a recording material that is conveyed between the image carrier and the circulating member, and supplies the toner to the transfer device. A transfer device characterized in that the current value is defined to be a value larger than the current value when the transfer efficiency is maximized. 4. An image carrier, a circulating member provided so as to face the image carrier, an inner side of the circulating member, and a charge of a predetermined polarity is provided to the image carrier side through the circulating member. In a transfer device that includes a transfer device that supplies the toner, the toner held on the image carrier is transferred to a recording material that is conveyed between the image carrier and the circulation body, and the powder is used as the toner. Toner having an electric resistivity of 5 × 10 ¹⁴ Ω · cm or more is used, and the current value supplied to the transfer device is defined to be a value larger than the current value when the transfer efficiency is maximized. Transfer device.