JP3049620B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method and an apparatus used in an image forming apparatus such as an electrophotographic copying machine, a printer or a facsimile, and more particularly to a developing method in which a developer is carried on a developer carrier. The present invention relates to a developing method and an apparatus for performing development by transporting the developer to a developing unit facing an electrostatic latent image carrier.

[0002]

2. Description of the Related Art In a developing device of this type, a developer carrier having a thin layer of developer formed on a surface thereof and an electrostatic latent image carrier are opposed to each other in a developing section. 2. Description of the Related Art There is known an image forming apparatus which forms an electric field capable of transferring a developer on a body to an electrostatic latent image carrier and develops the electrostatic latent image on the electrostatic latent image carrier. In this developing device, there is a threshold value for transferring the developer from the developer carrier to the electrostatic latent image carrier, and the developer adheres to an image portion having a surface potential exceeding the threshold value. On the other hand, since the developer hardly adheres to an image portion having a surface potential equal to or lower than the threshold value, there is a problem that an image having a so-called γ and poor gradation is formed. However, it is known that this problem can be solved by forming an alternating electric field having a relatively low frequency in the developing section (for example, see Japanese Patent Publication No. 64-1013).

However, simply applying a low-frequency alternating electric field to the developing section lowers the image density if the condition of the alternating electric field is such that the gradation property can be improved. However, there is a problem that the line portion of the image becomes thicker when the value is increased. Further, in this type of developing device, particularly when a non-magnetic toner is used as a developer, when a reciprocating motion of the non-magnetic toner is caused, the toner is turned into a powder cloud and the image density is significantly reduced. (See, for example, Japanese Patent Publication No. 2-14706). In recent years, along with diversification of output information of an image created by an image forming apparatus, higher image quality than ever has been desired. Accordingly, the present applicant has previously described, in a developing device that carries a developer on a developer carrier and performs development in a developing unit where the developer carrier and the electrostatic latent image carrier are opposed to each other, A developer carrier having a large number of electric field arrangements formed on its surface as an agent carrier, and a voltage applying means for forming an electric field in the developing section, and a potential on the electrostatic latent image carrier, A developing device characterized in that the movement of the developer is controlled by an electric field determined by the correlation between the electric potential on the developer carrier and the electric field formed by the voltage applying means. Such a developing device forms a large number of electric field arrangements on a surface as a developer carrying member, and a potential on the electrostatic latent image carrying member, a potential on the developer carrying member, and an electric field formed by the voltage applying means. The movement of the developer is controlled by the electric field determined by the correlation between the toner and the developer, whereby an appropriate amount of the developer is attached to the electrostatic latent image on the electrostatic latent image carrier. There is an advantage that a developed image having excellent reproducibility and gradation can be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention is a further improvement of the developing device described above, and its object is to provide a high image density and a high reproducibility and gradation of a diagram. In addition to obtaining an excellent developed image, a member for forming a thin layer of the developer on the surface of the developer carrying member can be constituted by a rigid body, thereby forming a thin layer of the developer for a long time. Is to provide a developing device capable of stably performing the developing.

[0005]

In order to achieve the above object, the present invention is directed to an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer. In a developing device which is opposed in a developing section and performs development by applying a bias by a voltage applying means in the developing section, a developer to which silica particles are externally added is used as the developer, and a surface of the developer carrier is used as the developer carrier. The conductive part and the dielectric part are mixed in a small area, and the dielectric part is formed in a foam cell near the surface of the conductive foam layer, and at least the dielectric part is a developer. Using a developer carrying member charged with a polarity opposite to or the same as the polarity of the developer to form a large number of small electric fields on the surface, and as the voltage applying means, the conductive portion and the electrostatic latent image carrying member Between the non-image portion and the developer to the electrostatic latent image carrier And 1V / [mu] m or more of the intensity of the cell facing the electric field, the orientation of 1V to direct the developer to the surface / mu
m, using a voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of at least m, and a potential on the electrostatic latent image carrier,
The movement of the developer is controlled by an electric field determined by a correlation between an electric field formed by the voltage applying unit and an electric field on the developer carrier. Claim 2
In the invention , the electrostatic latent image carrier that carries the electrostatic latent image and the developer carrier that carries the developer are opposed to each other in the developing unit,
In a developing device in which a bias is applied by a voltage applying means in the developing section to perform development, a developer having silica particles externally added is used as the developer, and a conductive portion and a dielectric are provided on the surface as the developer carrier. The body part is mixed with a small area and the dielectric part is formed in a foam cell near the surface of the conductive foam layer, and at least the dielectric part has a polarity opposite to the polarity of the developer or Using a developer carrier that is charged to the same polarity and a number of minute electric fields are formed on the surface,
As the voltage applying means, between the dielectric part and the image part on the electrostatic latent image carrier, the developer having an intensity of 1 V / μm or more in a direction for directing the developer toward the electrostatic latent image carrier. Using a voltage applying means for applying a voltage capable of alternately forming an electric field and an electric field having an intensity of 1 V / μm or more in a direction in which the developer is directed to the surface, the potential on the electrostatic latent image carrier and The movement of the developer is controlled by an electric field determined by a correlation between an electric field formed by the voltage applying means and an electric field on the developer carrier. The invention of claim 3 is claim
Item 1. In the developing device according to Item 1 or 2, the minute electric field is a closed electric field.
It is characterized by being. The invention of claim 4
The developing device according to claim 1, 2 or 3, wherein
Friction charging means for frictionally charging the body to a predetermined polarity is provided.
It is characterized by the following. The invention of claim 5 is claim
Item 4. In the developing device according to Item 4, the developer carried on the developer carrier
Layer thickness that regulates the layer thickness of the developer conveyed to the developing section
Regulating means, wherein said frictional charging means is provided with said layer thickness regulating means.
Upstream of the developer transport direction, and
Also located downstream of the developer transport direction.
It is.

[0006]

According to the present invention, as a developer carrier, a conductive portion and a dielectric portion are mixed in a small area on the surface, and the dielectric portion is provided in a foam cell near the surface of the conductive foam layer. While being formed, at least the dielectric portion is charged to a polarity opposite to or the same as the polarity of the developer and a developer carrier on which a large number of minute electric fields are formed on the surface, or a conductor portion on the surface. The dielectric portion is mixed with a small area and these are made of an elastic conductive material containing insulating particles, and at least the dielectric portion is charged to the opposite polarity or the same polarity as the polarity of the developer. A developer carrying member having a large number of minute electric fields formed on its surface is used, whereby the potential on the electrostatic latent image carrying member, the potential on the developer carrying member, and the voltage applying means are formed. The movement of the developer is controlled by the electric field determined by the correlation with the electric field. To, to deposit a suitable amount of the developer to the electrostatic latent image on the electrostatic latent image bearing member. Further, the developer carrier is provided with elasticity, so that a member that contacts the surface of the developer carrier and forms a thin layer of the developer can be formed of a rigid body having excellent durability. Further, a developer to which silica particles are externally added is used as the developer, thereby reducing friction between the developer carrier and a member forming a thin layer of the developer.
Further, as a voltage applying means for applying a bias to the developing unit,
Between the conductor portion and the non-image portion on the electrostatic latent image carrier,
1 V / of the direction in which the developer is directed to the electrostatic latent image carrier.
voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of not less than 1 μm and an electric field having an intensity of not less than 1 V / μm for directing the developer toward the surface. An electric field having an intensity of 1 V / μm or more in a direction for directing the developer toward the electrostatic latent image carrier between the image portion on the electrostatic latent image carrier and the developer toward the surface; Direction 1V /
A voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of μm or more is used, so that even when the shape of the developer carrying member varies, stable developing characteristics can be obtained. To

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing the overall configuration of an embodiment of the developing device according to the present invention. The casing 70 of the developing device is provided with an opening for development at a portion facing the photosensitive drum 10, and the developing roller 20, which is a developer carrying member, has a predetermined gap between the photosensitive drum 10 through this opening. It is held and rotatably provided in the casing. An opposing portion between the developing roller 20 and the photosensitive drum 10 is a developing unit 80. Above the developing roller 20, a blade member 3 for regulating the thickness of the toner layer carried and conveyed by the roller 20 is provided.
0 is provided so as to be resiliently pressed, whereby the layer thickness of the toner 60 supplied from the toner tank formed in the casing with the rotation of the agitator 50 and the toner supply roller 40 is regulated. ing. The blade member 30 may be manufactured by bonding a material having a toner charging property such as urethane rubber to an elastic leaf spring, or may use an elastic member as it is. Further, since the developing roller 20 has elasticity as described later, the developing roller 20 can be formed of a rigid body having excellent durability.
Further, in the present embodiment, the toner 60 to which silica is externally added is used, whereby the friction between the blade member 30 and the developing roller 20 can be reduced, and the durability of the blade member 30 can be improved. ing. The blade member 30 may be provided in the trailing direction with respect to the rotation direction of the developing roller 20 as shown in the drawing, or may be provided in the leading direction opposite to the rotation direction. Instead of the blade member 30, a regulating roller or a regulating belt may be used. The agitator 50 rotates clockwise as indicated by the arrow, and agitates the toner 60 by the resistance of the tip thereof and moves the toner 60 to the left in the figure. The toner supply roller 40 is made of, for example, a sponge material made by foaming urethane rubber, or a brush made of polyester, tetrafluoroethylene resin or the like as a fiber. This toner supply roller 4
Numeral 0 indicates that the toner 60 conveyed by the agitator 50 is rubbed in the forward or reverse direction on the surface of the developing roller 20 and supplied, and the toner 60 remaining on the developing roller 20 without being used for development is returned. It acts to scrape off. The toner 60 supplied to the surface of the developing roller 20 by the toner supply roller 40 is also charged by the frictional charging action generated by the mutual friction with the toner supply roller 40 or the developing roller 20, and the toner 60 itself is charged on the surface of the developing roller 20. It is carried electrostatically. Thus, the toner 60 carried and transported by the developing roller 20 is
The layer thickness of the photosensitive drum 10 and the developing roller 20 are conveyed to the developing section where the layer thickness is regulated by the blade member 30 which resiliently presses above the zero. Each of the developing roller 20 and the toner supply roller 40 is connected to a power source, and a bias is applied. Further, a bias may be applied to the blade member 30. In developing the electrostatic latent image formed on the photosensitive drum 10, a required amount of toner 60 is transferred from the developing roller 20 to the electrostatic latent image according to the electrostatic latent image while applying a bias voltage to the developing roller 20. This is done by letting
The developing roller 20 has a positional relationship of 30 to 500 μm, preferably 50 to 500 μm, which does not substantially contact the photosensitive drum 10.
They are arranged with a gap of 250 μm. As a result, an excessive load such as that required when the developing roller 20 is brought into contact with the photosensitive drum 10 to develop an electrostatic latent image is not required, and the drive motor can be reduced in size. If the peripheral speed of the photosensitive drum 10 and the peripheral speed of the developing roller 20 are substantially equal, the driving torque can be further reduced. As a developing bias applied to the developing roller 20, an AC electric field can be used in combination with a DC electric field. As the alternating electric field, a rectangular pulse electric field is set at a frequency of 300 to 2000 Hz, preferably 500 to 1500 Hz, and the ratio of the time of the high voltage portion to the time of the low voltage portion to the time of one cycle is set. By using the waveforms having different ratios, it is possible to obtain an excellent developed image having good sharpness in the low voltage portion, high image density in the high voltage portion, and less background smear. The ratio (duty ratio) between the time of the high voltage portion and the time of the low voltage portion has an optimum ratio depending on the polarity of the electrostatic latent image and the polarity of the toner 60. Is developed with the negative polarity toner 60, the ratio of the time of the high voltage part (for example, −100 V or more) to the time of the low voltage part (for example, −800 V or less) is 5
18: 2 to 8 may be set. In the case of normal development, if this ratio is generally reversed, an excellent developed image can be obtained in which similar low-potential portions have good sharpness, high-potential portions have high image density, and less background smear.

Next, the developing roller 20 will be described. As shown in FIG. 2A, the developing roller 20 according to the present embodiment has a dielectric area (dielectric part) and a conductive area (conductive part) mixed on a small area on its surface, and The body is formed in a foam cell near the surface of the conductive foam layer. As for the size of this minute area, assuming that the shape is a circle, the diameter is 10 to 500 μm, and the minute area is dispersed randomly or according to a certain rule. As for the area ratio, the area of the conductor portion is 20 to 60%.
Is preferable. As the material used for the dielectric portion formed in the foam cell, any material can be used as long as it has insulating properties, but the volume resistivity is 10 ¹⁰ Ωcm or more, particularly 10 ¹⁴ Ω.
cm or more is preferred. As such an insulating material, for example, polystyrene resin, polyethylene resin,
Organic polymers such as acrylic resins, resin materials, and rubber materials are exemplified. In this embodiment, preferably,
Those mainly composed of an aliphatic fluorinated compound or a silicone resin are used. Further, the conductor portion in this embodiment is formed of a conductive foam layer, and various organic polymers can be used as the resin material forming the foam.
Examples of the conductivity-imparting agent include metal powder, carbon black, conductive oxide, electroless plating, graphite, metal fiber, and carbon fiber. As the foaming agent, any of conventionally known organic or inorganic foaming agents can be used.

In order to manufacture the developing roller 20 of this embodiment, for example, (i) a conductive foam composition comprising rubber, a conductivity-imparting agent, a foaming agent, and other additives is extruded around the core metal. Forming to provide an elastic foam layer, then grinding the surface to expose the foam cells, forming a recess for embedding a dielectric portion, and then spraying the dielectric material into the recess,
Embedded by a method such as dipping, and cured (fired) under predetermined conditions (temperature and time) (the thickness of the applied film is such that the concave portion is completely filled) (see FIG. 2 (b));
(Ii) Then, the surface is cut or polished so that the conductive surface and the dielectric surface are mixed in a small area, and the conductive portion area is reduced to 20 to 60% (see FIG. 2).
The method (c)) is adopted.

Hereinafter, specific examples will be described. Parts are by weight. The following conductive foam composition is extruded around a core metal previously treated with a primer,
After temporarily vulcanizing in a mold for 0 minutes, secondary vulcanization is performed at 200 ° C. for 2 hours to obtain a volume resistivity of 10 ¹¹ Ωcm, a specific gravity of 0.57,
A developer carrier having a conductive foam layer having a foam cell size of 30 to 50 μm was prepared. Conductive foaming composition diorganopolysiloxane (average degree of polymerization 2000 or more) 100 parts [Product name: KF901FU-U (manufactured by Shin-Etsu Kagaku)] Furnace black 10 parts [Product name: Ketjen Black EC (manufactured by Lion Akzo) Dicumyl peroxide 2 parts Azobisisobutyronitrile 2 parts Next, the surface of the obtained developer carrier was ground to expose the foam cells, and concave portions for embedding the dielectric were formed. Next, the concave portion was coated with 150 parts of the fluororesin composition (Lumiflon LF601-C (made by Asahi Glass Co., Ltd.) as a main component) as the dielectric, and the concave portion of the foam cell was completely filled. Crosslinked and cured. Subsequently, the developing roller 20 was manufactured by cutting or polishing the surface so that the conductor portion and the dielectric portion were mixed so that the conductor portion area was 50%.

In the developing roller 20 of this embodiment, the insulator on the surface is charged to a positive polarity opposite to the charging polarity of the toner 60 by friction with the toner supply roller 6. On the other hand, the toner 60 carried to the developing roller 20 while being in contact with the peripheral surface of the toner supply roller 40 is
The toner is supplied to the developing roller 20 by friction with the negative polarity due to friction with 0. At this time, the developing roller 20 is further frictionally charged to a negative polarity by friction with the insulator portion, and the developing roller 20 is charged. Electrostatically adheres to the peripheral surface. At this time, each insulator portion of the developing roller 20 is triboelectrically charged to a positive polarity, and a conductor portion exists in contact with each insulator portion. Therefore, the surface of the developing roller 20 has a large number of insulator portions. Only the positively charged state is selectively provided. As a result, as shown in FIG. 2A, a closed electric field is formed between each positively charged insulator portion and the conductor portion in contact with the insulator portion, and countless minute electric fields are formed near the surface of the developing roller 20. A closed electric field (microfield) is formed. That is,
Considering the lines of electric force representing the state of the electric field, the developing roller 2
In the space in the vicinity of the surface of the developing roller 20, the same developing roller 2 that exits from the developing roller 20 as shown by a number of arc-shaped lines in FIG.
The lines of electric force returning to zero are formed, and a closed electric field is formed between each insulator part and the conductor part. Since the area of each insulator portion is minute as described above, the intensity of each closed electric field is greatly increased by the fringing effect (peripheral electric field effect). Due to such a closed electric field, the negatively charged toner 60 is strongly attracted to the insulator portion and is held on the roller 1 in a state where it is hard to separate. In addition, when the layer thickness of the toner 60 held on the developing roller 20 is regulated by the blade member 30, the toner 60 with sufficient charge is strongly held on the surface of the developing roller 20 by the minute closed electric field. The small toner 60 is removed by the contact pressure with the blade member 30, so that only the toner 60 having a large charge amount is carried to the developing unit 80.

In the present developing device, the developing roller 2
By mixing the conductor portion and the insulator portion on the surface of 0, the charge-up of the developing roller 20 and the toner supply roller 40 is prevented. It is considered that the reason is that the toner is charged in the insulator portion, and the toner supply roller is destaticized in the conductor portion, so that a well-balanced charged state is maintained as a whole. Here, a rectangular-wave pulse electric field applied as a developing bias acts on a minute electric field between a conductor portion and an insulator portion present on the surface of the developing roller 20 and the charged toner, and is suitable for developing an electrostatic latent image. It is thought to provide mechanical energy.

Hereinafter, more specific embodiments of the present invention will be described. In this example, an OPC is used as the photosensitive drum 10.
And the developing roller 20 is set to the photosensitive drum 1 by setting the surface potential of the background portion to −900 V and the potential of the exposed portion to −100 V.
In this case, reversal development was carried out by opposing the surface of No. 0 with a gap of 100 μm. The insulator portion on the surface of the developing roller 20 holds an amount of charge that is rubbed by the toner supply roller 40 and has an electric potential of +200 V with respect to the ground.
Thereby, the toner 60 charged to the negative polarity is reduced to about 1.0 to
1.2 mg / cm ^{2 was} carried. Then, a pulse voltage having a peak-to-peak (hereinafter referred to as PP) 1000 V, a maximum potential of 0 V, a frequency of 500 Hz, and a duty ratio of 30% (T ₂ / T ₁ ) is applied to the developing roller 20 by a developing bias power supply. did.

FIGS. 4A and 4B show the change over time of the surface potential of the developing roller 20 with respect to the ground. FIG. 4A shows the surface potential of the insulator portion, and FIG. 4B shows the surface potential of the conductor portion. Is shown. In these figures, the level (−900 V) of the surface potential of the background portion on the surface of the photosensitive drum 10 is shown.
And the level (-100 V) of the surface potential of the exposed portion is shown as a horizontal line. 4A, the surface potential of the insulator portion deviates by +200 V with the charge held by the voltage applied by the developing bias power source, as can be seen from the continuous rectangular line showing the temporal change in the surface potential of the insulator portion in FIG. Potential. On the other hand, the surface potential of the conductor portion is the voltage applied by the developing bias power supply itself, as can be seen from a continuous rectangular line indicating the temporal change of the surface potential of the conductor portion in FIG.

Next, an electric field between the surface of the developing roller 20 and the photosensitive drum 10 when the potential of the surface of the developing roller 20 changes as described above will be described. The electric field depends on whether the electric field is on the insulator portion or the conductor portion on the surface of the developing roller 20. Further, for each of the insulator portion and the conductor portion, any one of the image portion and the background portion of the photosensitive drum 10 is used. It depends on whether it is facing.

FIG. 5 is a view for explaining an electric field on the conductor portion which causes a temporal change in the surface potential as shown in FIG. 4B, and FIG. FIG. 5B shows a temporal change of a potential difference between the body part and the image part (exposure part) of the photosensitive drum 10 when the body part faces the image part (exposure part). 5 shows a temporal change of a potential difference between the two when facing the (unexposed portion). FIG. 6 is a view for explaining an electric field on the insulator portion which causes a temporal change in the surface potential as shown in FIG. 4 (a). FIG. Drum 1
FIG. 6B shows a temporal change of the potential difference between the non-image portion (unexposed portion) of the photosensitive drum 10 and the potential difference between the two when the image portion (exposed portion) is opposed to the non-image portion (exposed portion). 5 shows a temporal change in a potential difference between the two when they face each other.

In these figures, since the electric field exerts an electrostatic force on the toner 60 carried on the surface of the developing roller 20 or the toner 60 carried on the surface of the photosensitive drum 10, the direction of the electrostatic force is The potential difference corresponding to the electric field in the direction of the toner 60 toward the photosensitive drum 10 is expressed as positive, and the potential difference corresponding to the electric field in the direction of the developing roller 20 is expressed as negative. Also, the level of the above-mentioned potential difference threshold +100 V at which the toner 60 on the developing roller 20 transfers to the photosensitive drum 10 and the electric field at which the toner 60 on the photosensitive drum 10 transfers to the developing roller 20 have been confirmed by experiments. Threshold-1
The level of 00V is indicated by a horizontal line, and a portion corresponding to an electric field exceeding the threshold value and contributing to the transfer of the toner 60 is indicated by an oblique line.

In the above experiment, the gap between the developing roller 20 and the photosensitive drum 10 was set to 100 μm,
The transfer of the toner was observed while applying a DC voltage to 0 and changing the value of the DC voltage. In this example, it was found that the threshold value of the developing electric field was 1 V / μm. Further, the charge amount of the toner 60 used at this time was examined.
It was 0 μC / g.

When the toner 60 existing on the conductive portion of the developing roller 20 faces the image portion of the photosensitive drum 10, the toner 60 has a voltage of +900 V as shown by a hatched portion in FIG.
Electric field (hereinafter referred to as the electric field)
It is considered that the transfer is made in the direction of the photoconductor drum 10 at the time when the voltage of the photoconductor drum 10 is changed, and when the surface of the photoconductor drum 10 is opposed to the background portion, as shown by the shaded portion in FIG.
It is considered that when the developing electric field reaches the developing electric field, it is shifted in the direction of the developing roller 20.

Similarly, the toner 60 existing on the insulator portion of the developing roller 20 is charged at +200 V from the insulator portion. As shown by the hatched portion in FIG.
A negative electric field of 00V and a positive electric field of + 700V appear alternately,
In the case of a positive electric field, the developing roller 20 and the photosensitive drum 10
To the developing roller 2 from the photosensitive drum 10 in the case of a negative electric field.
It is considered that it has shifted to 0. Further, when the photosensitive drum 10 is opposed to the background portion of the photosensitive drum 10, as shown by a hatched portion in FIG. 6B, the photosensitive drum 10 is transferred from the photosensitive drum 10 to the developing roller 20 by a negative electric field of -1100V, and alternately. It is not expected to transfer.

As described above, the transfer of the toner 60 carried on the developing roller 20 is selectively controlled by the electric field formed on the surface of the developing roller 20. The image thus obtained was compared with an image developed using only the developing electric field as shown in FIGS. 5A and 5B using the developing roller 20 whose surface is all aluminum.
An image with high density was obtained without background contamination, and the reproducibility of the diagram was excellent. In addition, an attempt was made to obtain the same reproducibility of the diagram as in this example by using a developing roller whose surface is entirely made of aluminum, but the image density was reduced.

According to this embodiment, a region where a different developing bias acts locally is provided on the surface of the developing roller 20. Therefore, the photosensitive drum 10 having an electrostatic latent image and the toner are carried on the surface. When a bias is applied between the developing roller 20 and the developing roller 20 to perform development, the transfer of toner can be selectively controlled by the developing roller 20 having electric charges selectively held on the surface. It is considered possible. That is, the toner 6 existing on the insulator portion
As shown in FIG. 6 (a), a positive and negative electric field exceeding the threshold value acts on 0, and excessive toner adhesion is suppressed. On the other hand, the toner existing on the conductor portion is As shown in FIG. 5A, the electric field has a higher developing ability of the toner 60 than that of the insulator. Further, since this portion is conductive, it acts to suppress the edge effect and make the image density uniform. More specifically, although the image density is low, the reproducibility and gradation of the diagram are excellent, but if the density is directly increased, the reproducibility and gradation of the diagram are impaired. Due to the characteristics of the insulative developing roller and its electrode effect, it is possible to obtain high-density images with excellent uniformity of the solid part, but the reproducibility of the diagram and the gradation are poor. The developing roller 3 according to this embodiment has the features of the developing roller at the same time.

In addition, a roller having elasticity, such as the developing roller 20 in the present embodiment, is difficult to process and form with high precision, and generally has variations in outer dimensions (variations between products, and / or the circumference of the rollers). (A variation in the position in the direction), and this variation leads to a variation in the development characteristics due to a variation in the development gap, especially in a case where non-contact development is performed as in this example. Since a predetermined alternating electric field is formed in the developing region 80 as described above, such a variation in the developing characteristics can be prevented. In the case of performing contact development,
By applying such a developing bias, it is possible to prevent variations in development characteristics due to variations in the contact width between the photosensitive drum 10 and the developing roller 20.

Next, a second specific example will be described. In this example, the peak-to-peak 900 V, the maximum potential minus 200 V,
Frequency 500 Hz, a duty ratio _{30% (T 2 / T 1} )
Are applied. Other points are the same as those of the first specific example.

FIG. 7 shows the change over time of the surface potential of the developing roller 1 with respect to the ground, as in FIG. 4 for the first specific example. (B) shows the surface potential of the conductor portion. In these figures, the surface potential level (−900 V) of the non-image portion on the surface of the photosensitive drum 10 and the surface potential level (−100 V) of the image portion are shown as horizontal lines, respectively. 7A, the surface potential of the insulator portion is deflected by +200 V by the charge held by the voltage applied by the developing bias power supply, as can be seen from the continuous rectangular line showing the temporal change in the surface potential of the insulator portion in FIG. Potential. On the other hand, the surface potential of the conductor portion can be understood from the continuous sinusoidal line showing the temporal change of the surface potential of the conductor portion in FIG.
It becomes the applied voltage itself by the developing bias power supply.

Next, when the potential of the surface of the developing roller 1 changes as described above, the surface of the developing roller 1 and the photosensitive drum 10 are changed.
The electric field between them will be described. This electric field further depends on whether the surface of the developing roller 1 is on the insulator portion or on the conductor portion, as in the first specific example, and furthermore, the photoconductor drum for each of the conductor portion and the insulator portion. It differs depending on which of the image section and the non-image section is facing. FIG.
Among these, the electric field on the conductor which causes a temporal change of the surface potential as shown in FIG. 7B is described. FIG. 8B shows a temporal change in the potential difference between the two when the image portion (exposed portion) faces the non-image portion (unexposed portion) of the photosensitive drum 10. 5 shows a temporal change of the potential difference between the two. FIG. 9 shows FIG.
FIG. 9A is for explaining an electric field on an insulator portion which causes a temporal change of a surface potential as shown in FIG.
Indicates that the insulator portion is an image portion (exposure portion) of the photosensitive drum 10
FIG. 9B shows a temporal change in the potential difference between the two when the insulator portion faces the non-image portion (unexposed portion) of the photosensitive drum 10. 5 shows a temporal change of a potential difference.

In these figures, an electric field is applied to the toner 60 or the photosensitive drum 1 carried on the surface of the developing roller 1.
Since the toner exerts an electrostatic force on the toner 60 carried on the surface of the toner 60, the toner 60 is used to distinguish the direction of the electrostatic force, as in FIGS. 5 and 6 according to the first specific example. The potential difference corresponding to the electric field toward the photosensitive drum 10 is expressed as positive, and the potential difference corresponding to the electric field toward the developing roller 1 is expressed as negative. In addition, the level of the potential difference + 100V at which the toner 60 on the developing roller 1 is transferred to the photosensitive drum 10 and the level of the toner 60 on the photosensitive drum 10 were confirmed by the same experiment as in the first specific example. The threshold value of the electric field transferred to the developing roller 1 and the level of −100 V are indicated by a horizontal line, and a portion corresponding to the electric field exceeding the threshold value and contributing to the transfer of the toner 60 is indicated by oblique lines. Also in this example, the threshold value of the developing electric field was 1 V / μm.

When the toner 60 present on the conductive portion of the developing roller 1 is opposed to the image portion of the photosensitive drum 10, as shown by the hatched portion in FIG.
When the positive electric field is reached, the toner is transferred in the direction of the photoconductor drum 10. When the non-image portion of the photoconductor drum 10 is opposed to the non-image portion, the toner is transferred as shown by a hatched portion in FIG. A negative electric field of -700 V and a positive electric field of +200 V appear alternately as an electric field contributing to the transfer of the photoconductor drum 10 from the developing roller 1 when the electric field is positive, and from the photoconductive drum 10 to the developing roller when the electric field is negative. The transfer period from the photosensitive drum 10 to the developing roller 1 due to the negative electric field is sufficiently longer and the transfer force is large, so that the toner 60 transferred to the photosensitive drum by the positive electric field is transferred. Even if it occurs, it is considered that the toner is transferred to the developing roller 1 again.

Similarly, when the toner 60 present on the insulator portion of the developing roller 1 is opposed to the image portion of the photosensitive drum 10, the toner 60 is +8 as shown by the hatched portion in FIG.
When a positive electric field of 00 V is applied, the transfer from the developing roller 1 to the photosensitive drum 10 occurs.
Since the toner is charged to 0 V, the transfer force is considered to be smaller than the toner 60 existing on the conductive positive conductor. When the non-image portion of the photosensitive drum 10 is opposed to the non-image portion, as shown by a hatched portion in FIG. 9B, only a negative electric field of -900 V appears as an electric field contributing to toner transfer. It is not considered to transfer to.

As described above, the transfer of the toner 60 carried on the developing roller 1 is selectively controlled by the electric field formed on the surface of the developing roller 1. In this example,
Compared to the case where the same sine-wave voltage is applied to the developing roller 1 using the developing roller 1 whose surface is entirely made of aluminum, a high-density image with no background contamination can be obtained, and the reproducibility of the diagram is excellent. I was Also in this example, the above effect is obtained because the conductor portion and the insulator portion are mixed on the surface of the developing roller. Transfer from the developing roller 5 to the photoreceptor 1 and from the photoreceptor 1 to the developing roller 5, the image density is improved while the gradation is maintained, and the line portion of the image is prevented from being thickened. It is considered that a high-quality image can be obtained.

Next, a third specific example will be described. In this example, instead of the applied bias in the first specific example,
Peak-to-peak 1000V, maximum potential minus 1
00V, frequency 500Hz, duty ratio 30% (T
₂ / T ₁ ). Other points are the same as those of the first specific example.

FIG. 10 shows the change over time of the surface potential of the developing roller 1 with respect to the ground, as in FIG. 4 for the first specific example. (B) shows the surface potential of the conductor portion. In these figures, the surface potential level (−900 V) of the non-image portion on the surface of the photosensitive drum 10 and the surface potential level (−100 V) of the image portion are shown as horizontal lines, respectively. 10A, the surface potential of the insulator portion is deflected by +200 V by the charge held by the voltage applied by the developing bias power supply, as can be seen from the continuous rectangular line showing the temporal change in the surface potential of the insulator portion in FIG. Potential. on the other hand,
The surface potential of the conductor portion is the voltage applied by the developing bias power supply itself, as can be seen from the continuous sinusoidal line indicating the temporal change of the surface potential of the conductor portion in FIG.

Next, when the potential of the surface of the developing roller 1 changes as described above, the surface of the developing roller 1 and the photosensitive drum 10 are changed.
The electric field between them will be described. This electric field further depends on whether the surface of the developing roller 1 is on the insulator portion or the conductor portion, as in the first specific example, and furthermore, the photosensitive drum for each of the conductor portion and the insulator portion. It differs depending on which of the image section and the non-image section is facing. FIG.
FIG. 11A is a view for explaining an electric field on a conductor portion which causes a temporal change in the surface potential as shown in FIG. 10B, and FIG. FIG. 11B shows a temporal change of a potential difference between the photosensitive drum 10 and the non-image part (unexposed part) of the photosensitive drum 10 when the potential difference between the two parts is opposed to the image part (exposed part) of the drum 10. 5 shows a temporal change of the potential difference between the two when the electric field is opposed to the above. FIG. 12 is a view for explaining an electric field on the insulator portion which causes a temporal change in the surface potential as shown in FIG. 10A. FIG. FIG. 12B shows a temporal change in the potential difference between the image portion (exposed portion) when the image portion (exposed portion) of the photosensitive drum 10 is not exposed (non-exposed portion). 5 shows a temporal change of the potential difference between the two when the electric field is opposed to the above.

In these figures, as in FIGS. 5 and 6 according to the first embodiment, the potential difference corresponding to the electric field in the direction in which the toner 60 travels toward the photosensitive drum 10 is positive and the developing roller 1 The potential difference corresponding to the electric field in the direction of the direction is expressed as negative. Further, the level of the potential difference + 100V at which the toner 60 on the developing roller 1 is transferred to the photosensitive drum 10 and the level of the toner 6 on the photosensitive drum 10 confirmed by the same experiment as the first specific example.
0 is the threshold value of the electric field which shifts toward the developing roller 1 -100V
And the portion corresponding to the electric field exceeding the threshold value and contributing to the transfer of the toner 60 is indicated by oblique lines. Also in this example, the threshold value of the developing electric field is 1 V /
μm.

When the toner 60 present on the conductive portion of the developing roller 1 is opposed to the image portion of the photosensitive drum 10, as shown by the hatched portion in FIG.
When a positive electric field of V is applied, it is considered that the transition occurs in the direction of the photosensitive drum 10. When the electric field is opposed to the non-image portion of the photosensitive drum 10, as shown by a hatched portion in FIG. As an electric field contributing to toner transfer, a negative electric field of -800 V and a positive electric field of +200 V appear alternately. When the electric field is a positive electric field, the developing roller 1 moves to the photosensitive drum 10. Transfer to Roller 1,
Since the period during which the transfer from the photosensitive drum 10 to the developing roller 1 is caused by the negative electric field is sufficiently longer and the transfer force is large, the toner 60 transferred to the photosensitive drum by the positive electric field is used.
It is considered that the transfer to the developing roller 1 occurs again even if the image occurs.

Similarly, when the toner 60 present on the insulator portion of the developing roller 1 is opposed to the image portion of the photosensitive drum 10, the toner 60 as shown by the hatched portion in FIG. As the electric field contributing to the transition, a positive electric field of +800 V and a negative electric field of -200 V appear alternately. In the case of the positive electric field, the developing roller 1 moves to the photosensitive drum 10. However, since the period during which the transfer from the developing roller 1 to the photosensitive drum 10 occurs due to the positive electric field is sufficiently longer and the transfer force is large, sufficient toner can be transferred from the developing roller 1 to the photosensitive member by the positive electric field. It is considered that the transfer to the drum 10 has occurred. In the case where the photosensitive drum 10 faces the non-image portion of the photosensitive drum 10, FIG.
As shown by the hatched portion in FIG. 3B, since only a negative electric field of −1000 V appears as an electric field contributing to toner transfer, it is considered that the transfer does not occur alternately.

As described above, the transfer of the toner 60 carried on the developing roller 1 is selectively controlled by the electric field formed on the surface of the developing roller 1. In this example,
Compared with the case where the same pulse voltage is applied to the developing roller 1 using the developing roller 1 whose surface is all aluminum,
An image with high density was obtained without background contamination, and the reproducibility of the diagram was excellent. Further, in this example, more excellent results were obtained than in the first and second specific examples. Also in this example, the above effect is obtained because the conductor portion and the insulator portion are mixed on the developing roller surface,
Further, the toner on the insulator portion transfers from the developing roller 1 to the photosensitive member 1 and the toner from the photosensitive member 3 to the developing roller 1 with respect to the image portion on the photosensitive member. The toner on the conductor portion transfers from the developing roller 5 to the photoconductor 1 and from the photoconductor 1 to the developing roller 5 with respect to the portion, so that the image density can be improved while maintaining the gradation and It is considered that thickening of the line portion of the image can be prevented, and a high-quality image can be obtained.

In each of the above embodiments, the insulator portion is charged to the polarity opposite to the polarity of the toner. However, the surface material of the toner supply roller 40 is appropriately selected and the friction is set to the same polarity as the charge polarity of the toner. It may be charged. Also in this case, a minute closed electric field can be similarly formed by the potential difference between the insulator portion and the conductor portion. In this case, the toner mainly adheres to the conductor portion.

Next, a modified example of the developing roller 20 will be described. As shown in FIG. 3, for example, the developing roller 20 of this example has a conductive part and a dielectric part mixed at least on its surface, and these forming materials are made of an elastic conductive material containing elastic insulating particles. It is made of material. The elastic insulating particles constituting the dielectric portion are those having a volume resistivity of at least 10 ¹³ Ωcm, preferably at least 10 ¹⁴ Ωcm, and have an effective rubber hardness (a spring-type hardness test which determines the shape of the developer carrier according to JIS K6301). (Measured using A-type machine)
However, those having a temperature of 50 degrees or less, preferably 40 degrees or less are used. Examples of such a material include silicone-modified ethylene propylene rubber. The average particle size is 5 μm or more, preferably 10 μm or more. If it is less than 5 μm, it is difficult to form a microfield, and stable toner adhesion and charging cannot be obtained. Further, the particle shape may be either a regular shape or an irregular shape. The elastic conductive material has a volume resistivity of 10 ¹² Ωcm or less, preferably 10 ⁸ Ωc
m or less, and the effective rubber hardness (as described above) is 50
A rubber having a degree of not more than 40 degrees and a conductive filler added thereto is used. Examples of rubbers include silicone-modified ethylene-propylene rubber, and examples of conductive fillers include metal powder. Further, for various purposes, an inorganic filler, a crosslinking agent, a heat stabilizer and the like can be added.

The developing roller 20 is manufactured by, for example, (i) applying a conductive primer onto a metal core, and then extruding a compound obtained by mixing an appropriate amount of insulating particles into the conductive material. By molding on the core metal, etc.
(Ii) Molding vulcanization, steam vulcanization, etc., apply temperature and pressure to form an elastic roller on the core metal,
(Iii) Next, a method may be adopted in which the surface of the elastic roller is smoothed by a method such as grinding or cutting so that the conductive portion and the insulating portion are mixed on the surface.

Hereinafter, specific examples will be described. Parts are by weight. Method for producing elastic insulating particles Silicone-modified ethylene-propylene rubber: trade name SEP1421-U (manufactured by Shin-Etsu Chemical Co., Ltd.) 100.0 parts by weight Vulcanizing agent: trade name C-12 (manufactured by Shin-Etsu Chemical Co., Ltd.) 2.0 parts by weight were kneaded using two rollers so as to be sufficiently uniform, and then vulcanized under the conditions of press curing at 170 ° C. for 10 minutes and 50 kg / cm ² to form a sheet having a thickness of 2 mm. Molded. Then one
Cure was performed at 50 ° C. for 2 hours. The formed rubber sheet was pulverized by being passed through two rollers (to reduce the distance between the rollers) a plurality of times. Then pass through a sieve 100-200μ
m of elastic insulating particles were obtained. Production of elastic conductive compound containing elastic insulating particles Silicone-modified ethylene-propylene rubber: trade name SEP1421-U (manufactured by Shin-Etsu Chemical Co., Ltd.) 100.0 parts by weight carbon black: trade name Black Pearls L (Cabot Corporation) 8.0 parts by weight Vulcanizing agent: trade name C-12 (manufactured by Shin-Etsu Chemical Co., Ltd.) 4.0 parts by weight hydrocarbon-based synthetic oil: trade name Lucant (manufactured by Mitsui Petrochemical Co., Ltd.) 0 parts by weight was kneaded using two rollers so as to be sufficiently uniform.
To the kneaded compound was added 30.0 parts by weight of the previously produced elastic insulating particles. The mixture was again kneaded using two rollers so as to be sufficiently uniform to obtain an elastic conductive compound. Next, a conductive compound containing the elastic insulating particles is provided by extrusion molding on a core metal on which a conductive primer has been applied in advance, and then press cure is performed for 170/10 minutes at 50 kg / cm ² by a mold molding vulcanization method. After vulcanizing under the conditions and forming the elastic layer to a thickness of 7 mm and an outer diameter of the roller of 20 mmφ (core: 6 mmφ made of stainless steel), 150 ° C./2
Time cure was performed. The surface of the obtained elastic roller is adjusted to a finished roller outer diameter of 18 by a method such as grinding or cutting.
With a diameter of mm, the conductor portion and the insulator portion were mixed on the surface, and a developer carrier (effective rubber hardness: 38 degrees) having a smooth surface was obtained. Next, the obtained developer carrier was mounted on the developing device shown in FIG. 1, and the charge amount of the toner, the amount of the toner adhered, and the contact width (mm / kg of pressure) with the photoreceptor were measured. As a result, the toner charge amount was 12.3 μC / g, and the toner adhesion amount was 1.06 m.
g / cm ² and the contact width with the photoconductor (latent image carrier) is 0.8
mm / 500 g, 1.1 mm / 800 g, 1.6 mm / 1.1 kg.

Similarly, in the developing roller 20 of this embodiment, an effect based on the elasticity of the developing roller, an effect based on the formation of a minute closed electric field on the surface, and the like are exhibited.
Although elastic insulating particles are used as insulating particles constituting the dielectric portion on the surface of the developing roller, insulating particles having no elasticity may be used.

[0043]

According to the present invention, the electric field determined by the correlation between the electric potential on the electrostatic latent image carrier, the electric potential on the developer carrier and the electric field formed by the voltage applying means. By controlling the movement of the developer, an appropriate amount of the developer is attached to the electrostatic latent image on the electrostatic latent image carrier, so that the image density is high and the reproducibility and gradation of the diagram are improved. Excellent developed images can be obtained. Further, an elastic developer carrier is used as the developer carrier, whereby a member that contacts the surface of the developer carrier to form a thin layer of the developer can be constituted by a rigid body having excellent durability. Therefore, a thin layer of the developer can be stably formed over a long period of time. Furthermore, a developer to which silica particles are externally added is used as the developer, thereby reducing friction between the developer carrier and a member forming a thin layer of the developer, thereby improving the durability of the member. Thus, it is possible to form a stable thin layer of the developer over a long period of time. In addition, as a voltage applying means for applying a bias to the developing unit, a means capable of forming a predetermined bias is used, whereby a stable developing characteristic can be obtained even when there is a variation in the shape of the developer carrier. Can be

[Brief description of the drawings]

FIG. 1 is a side cross-sectional view schematically showing an entire developing device according to an embodiment of the present invention.

FIG. 2A is a schematic partial cross-sectional view of a surface of a developing roller of the developing device, and FIGS. 2B and 2C are explanatory diagrams of a manufacturing process of the developing roller.

FIG. 3 is a schematic partial sectional view of a surface of a developing roller according to a modification.

FIGS. 4A and 4B show a temporal change in the surface potential of the developing roller when a developing bias according to a first specific example is applied, and FIG. 4A shows a change in the potential of an insulator portion;
(B) shows a change in potential of the conductor portion.

5A and 5B are explanatory diagrams of a developing electric field on a conductor portion in the specific example, where FIG. 5A shows a temporal change when facing an image portion on the photosensitive drum, and FIG. 3 shows a temporal change in the case of facing a non-image portion.

6A and 6B are explanatory diagrams of a developing electric field on an insulator portion in the specific example, where FIG. 6A shows a temporal change when facing an image portion on a photoconductor, and FIG. It shows a temporal change when facing an image part.

FIGS. 7A and 7B show a temporal change in a surface potential of a developing roller when a developing bias according to a second specific example is applied, and FIG. 7A shows a change in the potential of an insulator portion;
(B) shows a change in potential of the conductor portion.

8A and 8B are explanatory diagrams of a developing electric field on a conductor portion in the specific example, where FIG. 8A shows a temporal change when facing an image portion on the photosensitive drum, and FIG. 3 shows a temporal change in the case of facing a non-image portion.

9A and 9B are explanatory diagrams of a developing electric field on an insulator portion in the specific example, where FIG. 9A shows a temporal change when facing an image portion on the photoconductor, and FIG. It shows a temporal change when facing an image part.

10A and 10B show a temporal change in the surface potential of the developing roller when a developing bias according to a third specific example is applied, and FIG. 10A shows a change in the potential of the insulator portion;
(B) shows a change in potential of the conductor portion.

FIGS. 11A and 11B are explanatory diagrams of a developing electric field on a conductor portion in the specific example, where FIG. 11A shows a temporal change when facing an image portion on the photoconductor drum, and FIG. 3 shows a temporal change in the case of facing a non-image portion.

12A and 12B are explanatory diagrams of a developing electric field on an insulator portion in the specific example, where FIG. 12A shows a temporal change when facing an image portion on a photoconductor, and FIG. It shows a temporal change when facing an image part.

[Explanation of symbols]

Reference Signs List 10 photoreceptor drum, 20 developing roller 30 blade member, 40 toner supply roller 50 agitator, 60 toner 70 casing, 80 developing unit

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Ueno 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Junko Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (56) References JP-A-55-62469 (JP, A) JP-A-58-211769 (JP, A) JP-A-2-296268 (JP, A) JP-A-60-61774 ( JP, A) JP-A-3-39980 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08-15/095 G03G 9/00

Claims (5)

(57) [Claims] An electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer are opposed to each other in a developing section, and a bias is applied by a voltage applying means in the developing section to perform development. A developer to which silica particles are externally added as the developer, and as a developer carrier, a conductor portion and a dielectric portion are mixed on a surface with a small area on the surface and the dielectric The body portion is formed in a foam cell near the surface of the conductive foam layer, and at least the dielectric portion is charged to a polarity opposite to or the same as the polarity of the developer, and a large number of minute electric fields are generated on the surface. Using the developer carrier formed, as the voltage applying means, the developer is applied to the electrostatic latent image carrier between the conductor portion and the non-image portion on the electrostatic latent image carrier. An electric field having a strength of 1 V / μm or more in the direction of turning, and the developer is applied to the surface. A voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more in an overturning direction is used, and a potential on the electrostatic latent image carrier and an electric field formed by the voltage applying means are used. A developing device for controlling movement of the developer by an electric field determined by a correlation with an electric field on the developer carrier . 2. An electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier carrying a developer are opposed to each other in a developing section, and a bias is applied by a voltage applying means in the developing section to perform development. A developer to which silica particles are externally added as the developer, and as a developer carrier, a conductor portion and a dielectric portion are mixed on a surface with a small area on the surface and the dielectric The body portion is formed in a foam cell near the surface of the conductive foam layer, and at least the dielectric portion is charged to a polarity opposite to or the same as the polarity of the developer, and a large number of minute electric fields are generated on the surface. Using the developer carrier to be formed, as the voltage applying means, the developer is directed to the electrostatic latent image carrier between the dielectric portion and the image portion on the electrostatic latent image carrier. An electric field having an intensity of 1 V / μm or more in a direction of fluctuating, and A voltage applying means for applying a voltage capable of alternately forming an electric field having an intensity of 1 V / μm or more in a direction in which the electric field is applied, and a potential on the electrostatic latent image carrier and an electric field formed by the voltage applying means. Wherein the movement of the developer is controlled by an electric field determined by a correlation between the electric field and the electric field on the developer carrier. 3. The method according to claim 2, wherein the small electric field is a closed electric field.
The developing device according to claim 1, wherein 4. A frictionally charging said dielectric portion to a predetermined polarity.
3. A device according to claim 1, further comprising a frictional charging means.
Is a developing device of 3. 5. The developing unit supported by the developer carrier and the developing unit
Is provided to regulate the layer thickness of the developer conveyed to the
In addition, the frictional charging means is more conveyed with the developer than the layer thickness regulating means.
Direction upstream side and the developer transport direction relative to the developing section.
5. The developing device according to claim 4, wherein the developing device is located downstream.