JPH0720722A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the cost of the developing head of a wet type developing device and to stabilize image quality. CONSTITUTION:The developing head 41 of the developing device 4 is hollow and has minute holes in a developer supply part 41a facing a photoreceptor 1. A development gap is made smaller than the amplitude of the vibration of the developing head 41 in the direction to the photoreceptor l. A reference toner image is formed on the photoreceptor 1 at the prescribed timing, and a control part (not illustrated) exerts control so that the frequency of a vibration exciter 42 varies based on the result of the detection of the P-sensor 11 for the image density of the reference toner image. The surface of the developer supply part 41a of the developing head 41 may be coated with a releasing material such as an oil repellent agent. Also, control may be carried out so that the development gap varies based on the result of the detection by the P-sensor 11 for the image density of the reference toner image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile and a printer, and more particularly, to a developing apparatus which visualizes a latent image formed on a latent image carrier with a liquid developer. The present invention relates to a provided image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, dry developing devices and wet developing devices are known as developing devices used in image forming apparatuses. Further, the wet type developing device using the liquid developer has an advantage that high resolution can be obtained because the toner particles are finer than the dry type developing device. As a wet developing device, for example, an oil-based developer in which a toner made of carbon black coated with a resin is dispersed in a liquid carrier made of a petroleum solvent such as Isopar (trade name) is used to form a latent electrostatic latent image. By flowing between the surface of the image bearing member and a counter electrode as a developer bearing member disposed at a constant interval on the surface to bring the oily developer into contact with the surface of the latent image bearing member, the toner charged by the liquid carrier A contact development type apparatus that develops an electrostatic latent image by utilizing an electrophoretic phenomenon is generally used. This oil-based developer is called a two-component liquid developer because it uses a liquid carrier for toner charging and toner transfer.

However, in a wet type developing device using a two-component liquid developer, the developer is brought into contact not only with the electrostatic latent image but also with the non-charged portion, so that the developer adhered to the latent image carrier is taken out. Since the amount is large, a means for removing the excess developer on the surface of the latent image carrier is required. Further, since the developer also contacts the non-charged portion, the residual charge of the non-charged portion causes the toner to adhere to the non-charged portion, which may cause a background stain on the image. Further, when the toner on the latent image carrier is transferred to a transfer material such as a transfer to obtain a final image, the developer adhered to the latent image carrier is transferred to the transfer material regardless of the image area and the non-image area. Therefore, the transfer material immediately after the transfer of the toner image is in a wet state with the developer, and it is necessary to evaporate the solvent at the time of fixing, for example, before discharging the transfer material out of the apparatus. The amount of heat for evaporating the solvent not only occupies a large part of the amount of heat used in the image forming apparatus, but also the vapor concentration of the organic liquid evaporated by drying becomes high around the image forming apparatus, which may cause discomfort. is there.

As a wet developing device for solving the above problems, a liquid developer in which a coloring material is dispersed or dissolved in a liquid is used, and the liquid developer on the developer carrier and the latent image carrier are used. There has been proposed a developing device for performing non-contact jumping development. This liquid developer is called a one-component liquid developer because the coloring material does not move in the liquid, the entire liquid behaves as a toner, and there is no liquid carrier equivalent to a two-component liquid developer. ing. In the non-contact jumping developing method using the one-component liquid developer, the film thickness of the liquid developer on the developer carrier must be thin and uniform, but the contact developing method using the two-component liquid developer. As described above, it is difficult to hold a predetermined amount of liquid developer necessary for development on a developer carrier having a flat surface of the developer supply portion facing the latent image carrier.
Therefore, recently, by forming minute irregularities on the surface of the developer supply portion, a predetermined amount of liquid developer required for development is held in the minute portions of the respective recesses, and jumping development is facilitated. It is under consideration.

[0005]

However, in the conventional wet type developing device using the one-component liquid developer, it is necessary to form fine irregularities on the surface of the developer supplying portion, and therefore the developer carrying member is formed. Cost will be high. Furthermore,
Since it uses a non-contact jumping development method,
Since the image quality is greatly affected by the variation in the developing gap between the developer carrying member and the latent image carrying member, it is necessary to strictly control the developing gap. As a result, the cost is further increased, and the variation in image quality is also increased due to the variation in parts.

The present invention has been made in view of the above problems, and an object thereof is to provide a developing device for visualizing a latent image formed on a latent image carrier with a liquid developer. In an image forming apparatus, it is possible to reduce the cost of the developer carrier and to stabilize the image quality.

[0007]

In order to achieve the above object, the invention of claim 1 is provided with a developing device for visualizing a latent image formed on a latent image carrier with a liquid developer. In an image forming apparatus, the developing device is hollow, and a developer carrier having a large number of minute holes in a developer supply portion facing the latent image carrier, and the developer carrier are vibrated. It has a vibrating means.

Further, in the image forming apparatus according to claim 1,
According to a second aspect of the present invention, the developing gap between the developer supply section and the latent image carrier is PG, and the amplitude of vibration of the developer carrier in the direction facing the latent image carrier is a. When I did
The present invention is characterized in that the relation of PG> a is satisfied, and the invention of claim 3 is characterized in that a film of a releasing material is provided on the surface of the developer supply section. According to the invention of claim 4, a reference image forming means for forming an image of a reference density pattern on the latent image carrier, an image density detecting means for detecting the image density of the reference image, Control means for changing the frequency or the amplitude of the vibrating means based on the detection result of the image density of the reference image is provided, and the invention according to claim 5 is characterized in that: Gap adjusting means for adjusting the developing gap between the image forming section and the latent image carrier, a reference image forming means for forming an image of a reference density pattern on the latent image carrier, and a reference image of the reference image. Image density detecting means for detecting image density and image density of the reference image In which characterized in that a control means for controlling the developing gap adjusting unit to adjust the developing gap based on the detection result.

According to a sixth aspect of the invention, in the image forming apparatus according to the fifth aspect, the developing gap adjusting means is:
A piezoelectric element fixed between the developer bearing member and the latent image bearing member is used.

[0010]

According to the first aspect of the invention, the liquid developer is substantially filled in the hollow developer carrier, and when the developer carrier is vibrated by the vibrating means in this state, the liquid developer is the only one. It projects so as to rise due to the surface tension from each of a large number of minute holes in the developer supply portion of the developer carrying member which is an outlet. This protruding liquid developer is in an unstable state,
Development is performed by flying toward the latent image according to the potential of the latent image on the latent image carrier. This makes it possible to supply the amount of liquid developer required for non-contact development such as jumping development from the developer supply section without forming irregularities on the surface of the developer supply section. Further, it becomes possible to perform development using a one-component liquid developer that does not require a solvent, and there is no need for a concentration control means for controlling the toner concentration in the liquid developer as in a developing device using a two-component liquid developer.

According to the second aspect of the present invention, the development gap of the developer carrying member facing the latent image carrying member is the development gap PG between the developer supplying portion of the developer carrying member and the latent image carrying member. By setting the amplitude of vibration to be larger than the amplitude a, even if the developer carrying member is vibrated by the vibrating means, the developer supplying portion does not come into contact with the latent image carrying member, and the vibration of the developer carrying member is caused by vibration. Can be prevented from reaching.

According to the third aspect of the present invention, by providing a film of the releasable material on the surface of the developer supply portion of the developer carrier, the liquid developer is likely to protrude from the fine holes of the developer supply portion. .

In the invention of claim 4, the image density of the visible image of the reference density pattern formed on the latent image carrier by the reference image forming means is detected by the image density detecting means, and the detection result is obtained. Based on this, the control means controls so as to change the frequency or the amplitude of the vibrating means. For example,
When the image density of the visible image is low, the frequency is increased or the amplitude is increased, thereby activating the liquid developer in the developer carrying body, and the liquid developer is reduced to a minute amount in the developer supply section. It is possible to easily project from the holes and increase the image density, while the frequency is decreased or the amplitude is decreased when the image density of the visible image is high, whereby the liquid developer is supplied to the developer. The image density can be lowered by making it difficult to project from the minute holes of the portion.

In the invention of claim 5, the image density of the visible image of the reference density pattern formed on the latent image carrier by the reference image forming means is detected by the image density detecting means, and the detection result is obtained. Based on the above, the control means controls the developing gap adjusting means so as to adjust the developing gap between the developer supply section and the latent image carrier. For example,
When the image density of the visible image is low, the developing gap is narrowed, which makes it possible to increase the image density. On the other hand, when the image density of the visualized image is high, the developing gap is widened, whereby the image density can be lowered.

In a sixth aspect of the present invention, a piezoelectric element fixed between the developer carrying member and the latent image carrying member is used as the developing gap adjusting means, and the voltage applied to the piezoelectric element is applied. By changing the size, the size of the piezoelectric element is changed, and the distance between the developer carrier and the latent image carrier, which are fixed so as to sandwich the piezoelectric element, can be precisely adjusted.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) which is an image forming apparatus will be described below. FIG. 1 is a front view showing a schematic configuration of a copying machine according to this embodiment. At the time of copying, the drum-shaped photoconductor 1 serving as a latent image carrier is rotationally driven in a fixed direction (the direction of the arrow in FIG. 1) by a driving device (not shown), and is uniformly charged by the charging charger 2 and then not shown. The document image L is projected by the exposure device to form an electrostatic latent image. In addition,
The eraser 3 eliminates the charge on the portion of the photoconductor 1 other than the image area. The electrostatic latent image on the photoconductor 1 is developed by the wet developing device 4 and then transferred to the intermediate transfer belt 5,
The image is transferred by a transfer roller 8 onto a transfer sheet serving as a transfer material that is fed from a sheet feeding device (not shown) via the transport roller 6 and the registration roller 7. This transfer paper is discharged to the outside of the device after the toner is fixed by a fixing device (not shown). On the other hand, the photosensitive member 1 is prepared for the next copying after the residual toner is removed by the cleaning device 9 after the transfer to the intermediate transfer belt 5 and the residual charge is removed by the static elimination lamp 10. In addition, instead of the drum-shaped photoreceptor 1,
A belt-shaped photoreceptor may be used.

The wet developing device 4 of the present embodiment develops an electrostatic latent image on a photoconductor using a conductive one-component liquid developer (hereinafter referred to as a developing solution). This developing solution is formed by mixing an oily or aqueous solvent with a binder and a pigment or dye. If necessary, various special agents may be added to exert a special function. Note that a gel-like developer can also be used as this developer.

The wet developing device 4 includes a developing head 41 as a developer carrying member, a shaker 42 as a vibrating means for vibrating the developing head 41, and a replenishing tank for replenishing the developing head 41 with a developing solution. 43, developer pump 44
Etc. The developing head 41 is hollow, and the developing solution 45 is substantially filled therein. The liquid level of the developing solution 45 in the developing head 41 is detected by a liquid level sensor (not shown), and the developing solution pump 44 is driven based on the detection result of the liquid level sensor. It can be controlled by driving a piezoelectric element (not shown) that pressurizes the developing solution 45. When the developing head 41 and the replenishment tank 43 are communicated with each other without providing the developer pump 44, the replenishment tank 4
The float level switch 3 may be used for liquid level control.
Here, the liquid surface of the developing solution 45 does not necessarily have to come into contact with the inner surface of the developer supply unit 41a in a state where the vibration is not generated by the vibration generator 42. The liquid may come into contact with the inner surface of the developer supply section 41a. Further, in the developer supply section 41a facing the photoconductor 1, a large number of minute holes 41b for supplying the developing solution 45 to the photoconductor 1 side.
Are formed.

Further, in this embodiment, as shown in FIG.
A developing gap PG, which is a gap between the developer supply unit 41a of the developing head 41 and the photoconductor 1, has a vibration amplitude a in a direction of the developing head 41 facing the photoconductor 1 (direction of arrow A in FIG. 2).
The development gap PG or the shaker 4
The driving force of 2 is set.

In this embodiment, the toner image of the reference density pattern of the predetermined density is formed on the photosensitive member 1 at a predetermined timing by the charging charger 2, the eraser 3 as the reference image forming means, the wet developing device 4, and the like. (Hereinafter referred to as a reference toner image) is formed, and the image density of the reference toner image is detected by a light reflection type density sensor (hereinafter referred to as P sensor) 11 as an image density detecting means, and based on the detection result, The vibration frequency of the vibrator 42 is controlled by a control unit (not shown) as a control unit including, for example, a CPU, a RAM, a ROM, an I / O unit and the like. Specifically, the frequency between the vibration frequency of the shaker 42 and the image density is as shown in FIG.
4 has a relationship as shown in FIG. 4, when the image density of the reference toner image detected by the P sensor 11 is low, the area B in FIG.
The vibration frequency of the shaker 42 within the range of
The developing solution 45 in the inside is activated, and the developing solution 45 becomes fine holes 41b.
The image density is increased so that it easily protrudes from the image.
On the other hand, when the image density of the reference toner image detected by the P sensor 11 is high, the vibration frequency of the vibration exciter 42 is lowered within the range of the area B in FIG. 4 so that the developer 45 does not easily project from the minute hole 41b. Reduce the image density.

As described above, according to the present embodiment, the developing solution 45 is substantially filled in the hollow developing head 41, and when the developing head 41 is vibrated by the shaker 42 in this state, as shown in FIG.
As shown in (a), the developing solution 45 in the developing head 41 has a large number of minute holes 41b in the developer supply section 41a which is the only outlet.
From each, it projects so as to rise due to surface tension. The projecting developer 45 is further raised and is in an unstable state as compared with the conventional uneven surface, and the developer 45 flies toward the photoconductor 1 according to the potential of the electrostatic latent image on the photoconductor 1. Then, non-contact development, for example jumping development, is performed. As a result, the developer 45 necessary for non-contact development such as jumping development can be supplied from the developer supply unit 41a, and thus the developer supply unit 41 as in the conventional case.
Since it is not necessary to form irregularities on the surface of a, the cost of the developing head 41 can be reduced. Also, development using a one-component liquid developer that does not require a solvent is possible,
Like the developing device using the two-component liquid developer, the developing solution 45
Since a concentration control means for controlling the concentration of is also unnecessary, the structure of the device can be simplified as compared with the conventional one, and the cost of the device can be reduced.

Further, according to this embodiment, the developing head 41
By setting the development gap PG between the developer supply portion 41a of the developer head 41 and the photoconductor 1 to be larger than the amplitude a of the vibration of the developer head 41 in the direction facing the photoconductor 1,
Even if the developing head 41 is vibrated by the
Does not contact the photoconductor 1 and the vibration of the developing head 41 is not transmitted to the photoconductor 1. Therefore, it is possible to prevent the vibration from adversely affecting the image.

According to the present embodiment, the image density is changed by changing the frequency of the vibrator 42 based on the detection result of the image density of the toner image of the reference density pattern detected by the P sensor 11. Since it can be controlled to be constant,
The image quality can be optimally maintained even when the development conditions such as the environment and the toner viscosity change. Here, while changing the frequency of the vibrator 42, or instead of changing the frequency, the amplitude of the vibration by the vibrator 42 may be changed. For example, when the image density of the reference toner image detected by the P sensor 11 is low, the vibration amplitude of the vibrator 42 is increased to activate the developing solution 45 in the developing head 41, so that the developing solution 45 becomes fine holes 41b. The image density is increased so that it easily protrudes from the image. On the other hand, when the image density of the reference toner image detected by the P sensor 11 is high, the amplitude of the vibration by the shaker 42 is reduced and the developer 4
The image density is lowered by making 5 difficult to project from the minute hole 41b.

In the above embodiment, the developing head 4
The releasable film 46 may be formed by coating a releasable material such as an oil repellent agent on the surface of the first developer supply section 41a. In this case, as shown in FIG. 3B, the developer 45 is likely to project from the minute holes 41b of the developer supply unit 41a, so that reliable and efficient development can be performed, and a clear image can be obtained. Can be

In the above embodiment, the vibration frequency of the vibrator 42 is controlled based on the detection result of the P sensor. However, instead of or in addition to this, the P sensor is used. Based on the detection result, the development gap P
You may control by a control part (not shown) so that G may be changed. Specifically, as the developing gap adjusting means, as shown in FIG. 5, for example, bearings 12 at both ends of the rotation shaft of the photoconductor 1 are provided.
Between the piezoelectric element 13 and the developer supply section 41a of the developing head 41, a piezoelectric element 13 and a voltage variable power source (not shown) for applying a voltage to the piezoelectric element 13 are provided, and as shown in FIG.
When the image density of the reference toner image detected in 1 is low, a voltage that narrows the development gap PG is applied to the piezoelectric element 13 to increase the image density. On the other hand, when the image density of the reference toner image detected by the P sensor 11 is high, a voltage that widens the development gap PG is applied to the piezoelectric element 13 to reduce the image density. By the above control, even when the development conditions such as the environment and the toner viscosity change, the optimum development gap PG can be always maintained, and the image quality can be maintained optimum. Further, it is not necessary to rely on the processing accuracy of the parts, and the stability of the device is increased.

[0026]

According to the present invention, the amount of liquid development required for non-contact development such as jumping development can be achieved without forming irregularities on the surface of the developer supply portion of the developer carrying member. Since the developer can be supplied from the developer supply section, it is possible to reduce the cost of the developer carrier and to stabilize the image quality. Further, since it becomes possible to develop using a one-component liquid developer that does not require a solvent, the generation of solvent gas as in the past is eliminated, and further, a concentration control means for controlling the concentration of the liquid developer is not necessary. The structure of the device can be simplified as compared with the conventional one, and the cost of the device can be reduced.

In particular, according to the second aspect of the invention, even if the developer carrying member is vibrated by the vibrating means, the developer supplying portion of the developer carrying member does not come into contact with the latent image carrying member, so that the developer is carried out. Since it is possible to prevent the vibration of the carrier from being transmitted to the latent image carrier, it is possible to prevent an adverse effect of the vibration on the image and to stabilize the image quality.

According to the third aspect of the present invention, by providing a film of the releasable material on the surface of the developer supplying portion of the developer carrying member, the liquid developer can be discharged from the fine holes of the developer supplying portion. Since the protrusion easily occurs, reliable and efficient development can be performed, an image can be made clear, and the image quality can be stabilized.

Further, according to the invention of claim 4, based on the detection result of the image density of the visible image of the reference density pattern,
Since the image density can be controlled to be constant by changing the frequency or the amplitude of the vibrating means, the image quality can be optimally maintained even when the developing conditions such as the environment and the toner viscosity change. There is an effect.

Further, according to the invention of claim 5 or 6, based on the detection result of the image density of the visible image of the reference density pattern, the development gap between the developer supply section and the latent image carrier is obtained. Can be precisely adjusted to control the image density to be constant, so that the optimum development gap can always be maintained even when the development conditions such as environment and toner viscosity change. Therefore, the image quality can be maintained optimally, and it is not necessary to rely on the processing accuracy of the parts, and the stability of the device is increased.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of a copying machine according to an embodiment.

FIG. 2 is an enlarged view of a developing head facing the photoconductor 1.

FIG. 3A is an explanatory diagram showing a protruding state of a developing solution 45.
FIG. 6B is an explanatory view showing a protruding state of the developing solution 45 when the release film 46 is formed on the surface of the developer supply unit 41.

FIG. 4 is a characteristic diagram showing the relationship between the frequency of the shaker and the image density. .

FIG. 5 is a perspective view of a developing head 41 and a photoconductor 1 according to a modification.

FIG. 6 is a characteristic diagram showing the relationship between the development gap PG and image density.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Wet developing device 11 P sensor 13 Piezoelectric element 41 Development head 41a Developer supply part 41b Micropore 42 Vibrator 45 Developer solution 46 Releasable film

Claims (6)

[Claims] 1. An image forming apparatus comprising a developing device for visualizing a latent image formed on a latent image carrier with a liquid developer, wherein the developing device is hollow and the latent image is formed. An image forming apparatus comprising: a developer carrier having a large number of minute holes in a developer supply section facing the carrier; and a vibrating unit for vibrating the developer carrier. 2. A developing gap between the developer supply section and the latent image carrier is PG, and an amplitude of vibration of the developer carrier in a direction facing the latent image carrier is a. , PG>
The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to satisfy the relationship of a. 3. The image forming apparatus according to claim 1, wherein a film of a releasable material is provided on the surface of the developer supply section. 4. A reference image forming means for forming an image of a reference density pattern on the latent image carrier, an image density detecting means for detecting an image density of the reference image, and an image of the reference image. The image forming apparatus according to claim 1, further comprising a control unit that changes a vibration frequency or an amplitude of the vibrating unit based on a detection result of the density. 5. A development gap adjusting means for adjusting a development gap between the developer supply section and the latent image carrier, and a reference image for forming a visible image of a reference density pattern on the latent image carrier. Forming means, image density detecting means for detecting the image density of the reference image, and control for controlling the developing gap adjusting means so as to adjust the developing gap based on the detection result of the image density of the reference image. The image forming apparatus according to claim 1, further comprising: 6. The image forming apparatus according to claim 6, wherein a piezoelectric element fixed between the developer carrying member and the latent image carrying member is used as the developing gap adjusting means.