JP2007011111A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of performing image formation at adequate image density even with a toner having degraded electrostatic charge characteristics after printing of a number of sheets is performed and providing an image of high sharpness even when the device is used in a low-temperature and low-humidity environment. <P>SOLUTION: The developing device 50 comprises using the toner T having a base particle and an external additive, having a developing roller 52 and a supply roller, using the toner reverse in the electrostatic charge characteristics as the toner T on the basis of the developing roller 52 between the base particle and the external additive, and having a controller 57 for controlling the voltage between the developing roller 52 and the supply roller 53. The controller 57 applies the voltage of the direction to attract the external additive toward the supply roller 53 between the developing roller 52 and the supply roller after the prescribed degree of use and successively intensifies the voltage of that direction on progression of the degree of use. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a developing device that is used in an electrophotographic image forming apparatus and develops an electrostatic latent image using toner. More specifically, the present invention relates to a one-component toner type developing device that does not use a carrier.

  Conventionally, in an electrophotographic image forming apparatus, an image is formed by developing an electrostatic latent image formed on a photoreceptor with toner. Here, in the developing device of the non-contact one-component developing method, a carrier is not used, and a one-component toner in which various external additives are attached to mother particles obtained by adding colored powder to a resin is used. In general, the one-component toner is triboelectrically charged between the developer carrying member and the developer regulating member. Then, a Coulomb force is received by the electric field applied between the developer carrying member and the image carrying member, and the coercive force is blown to the image carrying member.

Patent Document 1 discloses an image forming apparatus in which an appropriate voltage is applied to a developer regulating member. In the image forming apparatus described in this document, a voltage applying unit is connected to the regulating member and an alternating voltage is applied. As a result, the charging of the toner is further ensured, and it is said that the followability of the image quality can be improved without degrading the image quality.
JP 2000-98739 A

  However, in the above-described conventional developing device, since the toner is subjected to a physical pressure contact force when being charged, the charging characteristics of the toner gradually deteriorate as the same toner is continuously used. As a result, if the charge amount is too low, the response to an applied bias between the developer carrying member and the image carrying member is lowered. This causes a change in the flying amount of the developer due to the magnitude of the electric field strength caused by the shake between the developer carrier and the image carrier, which may cause image density unevenness.

  In addition, the charging characteristics of the toner change due to environmental changes. In general, charging characteristics are high at low temperatures and low humidity, and charging characteristics tend to decrease at high temperatures and high humidity. If the charge amount is too high, the mirror image force between the toner and the image carrier becomes too large, which may lead to transfer failure in the transfer portion. In particular, when a new toner is used in a low-temperature and low-humidity environment, there is a risk of causing such a deterioration in image quality.

  The present invention has been made to solve the problems of the conventional developing device and image forming apparatus. In other words, the problem is that even with toners whose charging characteristics have deteriorated after printing a large number of sheets, it is possible to form an image with an appropriate image density, and good image quality even when used in a low temperature and low humidity environment. It is an object of the present invention to provide a developing device that can obtain the image.

  In order to solve this problem, the developing device of the present invention uses a developer having base particles and an external additive, a developer carrying member that faces the image carrier while carrying the developer, and a developer. A developing device having a developer supply / recovery member in contact with the carrier, wherein the developer has charging characteristics based on the developer carrier as opposite to the mother particles and the external additive; An internal bias control unit that controls a voltage between the developer carrier and the developer supply / recovery member, and the internal bias control unit is configured so that the developer carrier and the developer supply / recovery member after a predetermined degree of use. In the meantime, a voltage in a direction to attract the external additive to the developer supply / recovery member is applied, and the voltage in that direction is strengthened as the use progresses.

  According to the developing device of the present invention, the developer is carried on the developer carrying member and is also in contact with the developer supply / recovery member. Here, after a predetermined degree of use, the internal bias controller applies a voltage in a direction that attracts the external additive to the developer supply / recovery member between the developer carrier and the developer supply / recovery member. Therefore, the external additive in the developer is attracted to the developer supply / recovery member. Furthermore, if the developer is one whose charging characteristics with respect to the developer carrier are opposite to those of the mother particles and the external additive, the remaining development in which the external additive is attracted to the developer supply / recovery member is used. The agent has improved charging characteristics. Therefore, an image can be formed with an appropriate image density even with toner whose charging characteristics have deteriorated after printing a large number of sheets.

  Further, the developing device of the present invention uses a developer having base particles and an external additive, a developer carrier that faces the image carrier while carrying the developer, and a developer supply that contacts the developer carrier. A developing device having a recovery member, and having an internal bias control unit that controls a voltage between the developer carrier and the developer supply and recovery member, and an environmental sensor that detects at least one of temperature and humidity The internal bias controller is configured to attract the external additive to the developer supply / recovery member between the developer carrier and the developer supply / recovery member when at least one of temperature and humidity is lower than a predetermined threshold. The voltage to be applied may be applied.

  According to such a developing device, when at least one of temperature and humidity is lower than a predetermined threshold value, an external additive is placed between the developer carrier and the developer supply / recovery member by the internal bias controller. Since a voltage in the attracting direction is applied to the developer supply / recovery member, the external additive in the developer is attracted to the developer supply / recovery member. Therefore, the charging characteristics of the remaining developer are adjusted according to the environment.

Further, in the present invention, as the developer, the charging characteristics based on the developer carrier are the same in both the mother particle and the external additive, and the external additive is more charged than the mother particle. It is desirable to use one.
In such a case, the external additive is attracted to the developer supply / recovery member, whereby the charging of the developer as a whole is weakened. Accordingly, since the charge amount is prevented from excessively increasing in a low temperature and low humidity environment, an image with good image quality can be obtained even when used in a low temperature and low humidity environment.

  According to the developing device of the present invention, it is possible to form an image with an appropriate image density even with toner whose charging characteristics have deteriorated after printing a large number of sheets, and it is excellent even when used in a low temperature and low humidity environment. A high quality image is obtained.

"First form"
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to an electrophotographic color printer that uses a one-component toner developing type developing device.

  The color printer 1 of this embodiment has image forming units 10Y, 10M, 10C, and 10Bk for each color, an intermediate transfer belt 11, a secondary transfer device 12, and a belt cleaner 13, as schematically shown in FIG. Yes. The image forming units 10Y, 10M, 10C, and 10Bk for each color are arranged along the intermediate transfer belt 11 and form the toner images of the respective colors on the intermediate transfer belt 11. The superimposed toner images are transferred to the recording paper 14 by the secondary transfer device 12. Further, the toner remaining on the intermediate transfer belt 11 is scraped off by the belt cleaner 13. In the following description, the subscript YMCBk for each color is omitted when there is no need for distinction.

  Each color image forming unit 10 has the same configuration. As shown in FIG. 1, each image forming unit 10 has a charging device 30, an exposure device 40, a developing device 50, and a transfer device 60 around the photosensitive drum 20. In addition, a cleaner device or the like for scraping off the toner remaining on the photosensitive drum 20 after transfer may be provided.

  The developing device 50 according to this embodiment is of a non-contact one-component developing system. This is a developing system that does not use a carrier, and the toner used in the developing device 50 is a one-component toner. As shown in FIG. 2, the developing device 50 has a housing 51 in which toner T of each color is accommodated. The housing 51 is further provided with a developing roller 52, a supply roller 53, and a toner regulating member 54, respectively.

  The developing roller 52 is for supplying an appropriate amount of toner T to the photosensitive drum 20. The developing roller 52 faces the photosensitive drum 20 through the opening of the housing 51, but does not contact the photosensitive drum 20. A power source 55 is connected to the developing roller 52 and an appropriate bias voltage is applied. The supply roller 53 is rotated in contact with the developing roller 52 and supplies toner T to the developing roller 52. A power source 56 is connected to the supply roller 53 and an appropriate bias voltage is applied. Both the power supply 55 and the power supply 56 are controlled by the controller 57.

  Normally, the bias voltage applied to the developing roller 52 and the supply roller 53 is obtained by superimposing a rectangular wave AC component of Vpp = 1600V on a DC component of Vdc = −420V as shown in FIG. Here, since the negatively charged toner T is used, the toner T is blown from the developing roller 52 to the photosensitive drum 20 when a negative voltage is applied to the developing roller 52. The voltage in this direction is the development direction voltage. For example, in the waveform shown in FIG. 3, a voltage having a development direction duty = 35% is used.

  The toner regulating member 54 regulates the layer thickness of the toner T carried on the surface of the developing roller 52. In the developing device 50 of this embodiment, no voltage is applied to the toner regulating member 54. Further, in this embodiment, toner T is used in which various external additives are attached to mother particles obtained by adding colored powder to resin. The toner T is charged by friction between the developing roller 52 and the supply roller 53 or between the developing roller 52 and the toner regulating member 54, for example. In this embodiment, a negatively charged toner that negatively charges the mother particles is used.

  Here, as the external additive of the toner T, a type in which the base particles and the external additive have opposite charging characteristics with respect to the surface of the developing roller 52 is used. In such an external additive, when the mother particle is negatively charged with respect to the developing roller 52, the external additive is positively charged. For example, calcium stearate, strontium titanate, zinc stearate or the like is used as an external additive for polyester resin base particles.

  In this embodiment, when the number of printed sheets with the same toner T exceeds a predetermined value, the bias voltage applied to the developing roller 52 is changed. That is, as shown in FIG. 4, the peak voltage in the developing direction of the bias applied to the developing roller 52 is slightly reduced under the control of the controller 57. Thereby, a difference ΔV is provided between the voltage applied to the developing roller 52 and the voltage applied to the supply roller 53. Further, as shown in FIG. 5, the difference ΔV is gradually increased as the use proceeds. Here, every time 1000 sheets are printed, the difference ΔV is increased by 50V.

  As described above, when a difference ΔV is provided between the bias voltage applied to the developing roller 52 and the bias voltage applied to the supply roller 53, a part of the external additive charged to the positive side with respect to the mother particles. Is attracted to the supply roller 53. This is because the external additive that has been peeled off from the mother particles and floated in the toner T and the external additive that has weakened the adsorption force with the mother particles gather to the supply roller 53 side due to the difference ΔV. Moreover, as the difference ΔV is increased, the amount of external additive adsorbed increases.

  The result of verifying this situation is shown in FIG. Since the external additive is white, the content of the external additive in the toner T can be estimated by measuring the color L * of the toner T using black particles as base particles. As shown in FIG. 6, although the color L * = 14.5 in the initial state, the color L * becomes smaller as the difference ΔV is increased. This is because the amount of the external additive contained in the toner T that is adsorbed by the supply roller 53 is increased, so that the amount of the external additive contained in the remaining toner T is reduced, and the color of the toner T becomes blackish as a whole. It represents that. That is, by increasing the difference ΔV between the bias voltages applied to the developing roller 52 and the supply roller 53, the amount of the external additive in the toner T can be reduced. The charge amount can be increased to the negative side.

  As shown by the solid line in FIG. 7, the degree of decrease in the average charge amount of the toner T by this processing was greatly suppressed. In addition, in this figure, the change in the charge amount when the same bias is continuously applied without performing such bias control is indicated by a two-dot chain line. With normal bias, the charge amount surely decreased with use. From these comparisons, it was found that the effect of this embodiment appeared when printing 2000 sheets or more, and the effect became clear as the number of printed sheets increased. When the image quality of the images formed by these controls was compared, as shown in FIG. 8, if the processing of this embodiment was performed, an image with good image quality was obtained even after printing 5000 sheets.

  As described above in detail, according to the color printer 1 of the present invention, the developing device 50 of the non-contact one-component developing system has the bias voltage applied to the developing roller 52 and the bias voltage applied to the supply roller 53. A difference ΔV is provided depending on the situation. When the charging characteristics of the toner T have deteriorated due to the durability of the toner T, the peak voltage in the developing direction of the bias applied to the developing roller 52 is slightly reduced. Further, as the external additive of the toner T, a type that is positively charged when the mother particles are negatively charged is used. As a result, the external additive is adsorbed to the supply roller 53, and the charge amount of the toner T as a whole is appropriately adjusted. Therefore, an image can be formed with an appropriate image density even with toner whose charging characteristics have deteriorated after printing a large number of sheets.

"Second form"
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to an electrophotographic color printer that uses a one-component toner developing type developing device.

  The color printer 2 of this embodiment is different from the color printer 1 of the first embodiment only in that it has an environmental sensor 70, and the other members are the same, so that the same reference numerals are given. Description is omitted. The environment sensor 70 is a general temperature / humidity sensor. This embodiment is a countermeasure against an excessive increase in the charge amount of the toner T when placed in a low temperature and low humidity environment.

  In this embodiment, as the external additive of the toner T, a toner having a charge series that is negatively charged more strongly than the mother particles when the mother particles are negatively charged is used. That is, from the negative side of the charge series, the order of external additive <base particle <developing roller 52 is applied. Examples of such external additives include silica particles surface-treated with a silane coupling agent that is N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, and a silane cup that is 3-aminopropyltriethoxysilane. Silica particles surface-treated with a ring agent can be used.

  In this embodiment, when the surrounding environment is detected by the environment sensor 70 and it is determined that the environment is a low temperature and low humidity environment, as shown in FIG. 10, the peak developing direction peak voltage applied to the developing roller 52 is slightly increased. . In particular, when the toner T is new, this is preferable. Thus, a difference ΔV is provided between the voltage applied to the developing roller 52 and the voltage applied to the supply roller 53 on the developing side. This difference ΔV may be adjusted according to the degree of the environment. A part of the external additive as described above is adsorbed to the supply roller 53. As a result, the charge amount of the toner T as a whole can be slightly reduced, and the occurrence of transfer defects caused by the charge amount being too high can be prevented.

  The result of verifying the influence on the image quality by this processing is shown in FIGS. FIG. 11 shows the results of using N-2 (aminoethyl) 3-aminopropyltrimethoxysilane as an external additive, and FIG. 12 shows the results of using 3-aminopropyltriethoxysilane as an external additive. In addition, all of these were tested using a new toner T.

  For example, in an example in which an external additive is not attached to the supply roller 53 in a low temperature and low humidity environment with a temperature of 10 ° C. and a humidity of 10%, the “environment” is “low temperature and low humidity” and the “supply roller state” is “external additive adhesion”. As shown in the column “No”, the toner T has an excessively high charge amount, and transfer failure has occurred. On the other hand, in an example in which an external additive is attached to the supply roller 53 even in the same low temperature and low humidity environment, the “environment” is “low temperature and low humidity” and the “supply roller state” is shown in the column “external additive is present”. As described above, the charge amount of the toner T can be suppressed and a good image can be obtained. On the other hand, in a high-temperature and high-humidity environment where the temperature is 30 ° C. and the humidity is 65%, better results were obtained when the external additive was not attached to the supply roller 53. Therefore, in this embodiment, it was found that an image with better image quality can be obtained by changing the difference ΔV according to the result of the environment sensor 70.

  As described above in detail, according to the color printer 2 of the present invention, the developing device 50 of the non-contact one-component developing system is provided, and the bias voltage applied to the developing roller 52 and the supply thereof according to the result of the environmental sensor 70. A difference ΔV is provided for the bias voltage applied to the roller 53. When placed in a low-temperature and low-humidity environment, the development direction peak voltage of the bias applied to the developing roller 52 is slightly increased. Further, as the external additive of the toner T, a type that is more strongly negatively charged when the mother particle is negatively charged is used. As a result, the external additive is adsorbed to the supply roller 53 according to the bias condition, and the charge amount of the toner T as a whole is adjusted appropriately. Therefore, even when used in a low-temperature and low-humidity environment, image formation can be performed with an appropriate image density.

In addition, this form is only a mere illustration and does not limit this invention at all. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
For example, the developing bias voltage value is an example, and is not limited to this value. The type of each external additive is also given as an example.
Further, for example, the present invention can be applied not only to a color printer but also to an image forming apparatus such as a monochrome printer, a copier, and a FAX.

1 is a schematic configuration diagram illustrating a color printer according to a first embodiment. It is sectional drawing which shows the inside of a developing device. It is explanatory drawing which shows the bias voltage applied to a developing roller and a supply roller. It is explanatory drawing which shows the bias voltage applied to a developing roller and a supply roller. It is explanatory drawing which shows the control method of a bias voltage. It is explanatory drawing which shows the change of the amount of external additives by control of a bias voltage. It is explanatory drawing which shows the change of the charge amount by control of a bias voltage. It is explanatory drawing which shows the change of the image quality by control of a bias voltage. It is a schematic block diagram which shows the color printer which concerns on a 2nd form. It is explanatory drawing which shows the control method of a bias voltage. It is explanatory drawing which shows the change of an image quality by the environment and the presence or absence of adhesion of the external additive to a supply roller. It is explanatory drawing which shows the change of an image quality by the environment and the presence or absence of adhesion of the external additive to a supply roller.

Explanation of symbols

50 Developing Device 52 Developing Roller (Developer Carrier)
53 Supply roller (developer supply / recovery member)
57 Controller (Internal bias control unit)
70 Environmental Sensor T Toner (Developer)

Claims (3)

A developing device using a developer having base particles and an external additive, having a developer carrying member that faces the image carrier while carrying the developer, and a developer supply and recovery member that contacts the developer carrying member In
As the developer, a developer whose charging characteristics with respect to the developer carrier are opposite to those of the mother particle and the external additive is used.
An internal bias controller for controlling a voltage between the developer carrier and the developer supply / recovery member;
The internal bias controller is
After a predetermined degree of use, a voltage is applied between the developer carrier and the developer supply / recovery member in a direction that attracts the external additive to the developer supply / recovery member,
A developing device characterized in that the voltage in the direction increases with the progress of use. A developing device using a developer having base particles and an external additive, having a developer carrying member that faces the image carrier while carrying the developer, and a developer supply and recovery member that contacts the developer carrying member In
An internal bias controller for controlling a voltage between the developer carrier and the developer supply / recovery member;
An environmental sensor for detecting at least one of temperature and humidity;
When at least one of temperature and humidity is lower than a predetermined threshold, the internal bias control unit supplies an external additive to the developer supply / recovery member between the developer carrier and the developer supply / recovery member. A developing device for applying a voltage in a direction attracting the toner. The developing device according to claim 2,
As the developer, use a developer whose charging characteristics are based on the developer carrier in the same direction as the base particle and the external additive, and that the external additive has a higher degree of charge than the base particle. A developing device.

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