JP3029138B2 - 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 device for use in an image forming apparatus such as an electrophotographic copying machine, a printer or a facsimile. The present invention relates to a developing device that performs development by transporting the developing unit to a developing unit facing an 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. It is known that this problem can be solved by forming a relatively low-frequency alternating electric field in the developing section (for example, see Japanese Patent Publication No. Sho 64-1013). However, simply applying a low-frequency alternating electric field to the developing unit reduces the image density when the condition of the alternating electric field can improve the gradation, and conversely increases the image density when the condition of the alternating electric field is increased. In this case, there is a problem that the line portion of the image becomes thick. There is also a problem that image fog is deteriorated due to background fog. 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.

[0003]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the image density while maintaining the gradation and improve the image density without lowering the frequency of the alternating electric field applied to the developing section. It is an object of the present invention to provide a developing device capable of preventing thickening of a line portion and fogging of a background, thereby obtaining a high-quality image.

[0004]

In order to achieve the above object, the present invention provides an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer in a developing section. In a developing device in which a bias is applied by a voltage applying unit in the developing unit to perform development, a developing unit that forms a large number of minute electric fields on the surface is used as the developing unit, and the voltage applying unit is used as the voltage applying unit. A voltage applying means for forming an intermittent alternating electric field in the developing unit, a potential on the electrostatic latent image carrier, an electric field formed by the voltage applying means, and an electric field on the developer carrier. The movement of the developer is controlled by an electric field determined by the correlation with the above. As the developer carrying member, two types of portions having different resistances or dielectric constants are regularly or irregularly mixed and exposed, and at least a relatively high resistance portion or a relatively low dielectric portion of the two types of portions. A plurality of portions having different resistances are regularly or irregularly formed on a developer carrier, and a conductive substrate, in which a portion having a different ratio is charged with a polarity opposite to or the same as the polarity of the developer to form a large number of minute electric fields on the surface. At the same time that the developer is exposed in a mixed manner, at least the portion having a relatively high resistance is charged to a polarity opposite to or the same as the polarity of the developer to form a large number of minute electric fields on the surface. And a developer in which the surface layer on the conductive substrate is made of a conductive material in which insulating particles are dispersed, and at least an exposed portion on the surface of the insulating particles is charged to form a large number of minute electric fields on the surface. Carrier, The serial surface, the conductive portions,
The dielectric portion formed in the foam cell near the surface of the conductive foam layer, and mixed with a small area, at least,
The exposed portion on the surface of the dielectric is charged with a polarity opposite to or the same as the polarity of the developer to form a large number of minute electric fields on the surface, or the surface of the developer carrier is an insulating particle, preferably It is made of an elastic conductive material containing elastic insulating particles, and a conductive area and a dielectric part are mixed in a small area on the surface, and at least the dielectric part is charged to a predetermined polarity and the surface is charged. A developer carrier that forms a large number of minute electric fields can be used. In addition, as a developer carrier, a conductive portion having a conductive substrate exposed on the surface and a dielectric portion having a dielectric fixed on the substrate exposed on the surface are regularly or irregularly formed on the surface. It is also possible to use a developer carrier in which the dielectric portion is charged to a predetermined polarity and a large number of minute electric fields are formed on the surface while being mixed.

[0005]

In order to achieve the above object, the present invention provides an electrostatic latent image carrier for carrying an electrostatic latent image and a developer carrier for carrying a developer in a developing section. In a developing device in which a bias is applied by a voltage applying unit in the developing unit to perform development, a developing unit that forms a large number of minute electric fields on the surface is used as the developing unit, and the voltage applying unit is used as the voltage applying unit. A voltage applying means for forming an intermittent alternating electric field in the developing unit, a potential on the electrostatic latent image carrier, an electric field formed by the voltage applying means, and an electric field on the developer carrier. The movement of the developer is controlled by an electric field determined by the correlation with the above. The developer carrying member, the upper Symbol surface, a conductor portion, a dielectric portion formed in the foam cells in the vicinity of the surface of the conductive foam layer and is, together with the mixed in small area, at least, the exposed portions of the surface of the dielectric is charged to a polarity opposite polarity or the same polarity of the developer Ru using a developer carrying member for forming a plurality of micro-electric field on the surface.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view schematically showing an overall configuration of a developing device according to an embodiment of the present invention. Developing device 2
An opening for development is provided in a portion of the casing facing the photosensitive drum 3, and the developing roller 1 is rotatable into the casing while maintaining a predetermined gap between the photosensitive drum 3 through the opening. Is provided. This gap is 30 to 500 μm, preferably 50 to 25 μm, so that the developing roller 1 does not substantially contact the photosensitive drum 3.
The gap is set to 0 μm. Thereby, the developing roller 1
This eliminates the need for an excessive load as in the case of contacting the photosensitive drum 3 with the photosensitive drum 3 to develop an electrostatic latent image, and makes it possible to reduce the size of the drive motor. The developing roller 1 is driven to rotate in the direction of the arrow so as to have a linear velocity as described in detail later. An agitator 6 is provided in the toner tank 5 formed in the casing, and is driven to rotate clockwise as shown by an arrow to agitate the toner 7 with the resistance of the tip portion thereof and to the left developing roller 1 in the figure.
Move to the side. A toner supply roller 8 is provided on the right side of the developing roller 1 so as to be in contact therewith, and is driven to rotate in the direction of the arrow. The roller 8 is made of a sponge material made by foaming urethane rubber, or a brush made of polyester, tetrafluoroethylene resin, or the like as a fiber. The toner supply roller 8 supplies the toner 7 conveyed by the agitator 6 by rubbing the surface of the developing roller 1 in the forward or reverse direction, and also returns to the developing roller 1 without being used for development. It has the function of scraping off the toner 7 that has fallen. A blade member 4 for regulating the thickness of the toner layer carried and conveyed by the roller 1 is provided on the upper portion of the developing roller 1 so as to resiliently press against the toner layer. The thickness of the toner 7 supplied onto the developing roller 1 is regulated. The blade member 4 may be manufactured by attaching 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. The blade member 4 may be provided in the trailing direction as shown in the drawing with respect to the rotation direction of the developing roller 1, or may be provided in the leading direction opposite to the rotating direction. Instead of the blade member 4, a regulating roller or a regulating belt may be used. Incidentally, a developing bias applying means 9 is connected to the developing roller 1 and the toner supply roller 8. Further, the bias applying means 9 may be connected to the blade member 4. The bias applied to the developing row 1 will be described later in detail. Thus, the toner 7 in the toner tank 5
Is supplied to the vicinity of the toner supply roller 8 by the agitator 6, and the toner 7 itself is also charged by a frictional charging action generated by mutual friction between the toner supply roller 8 and the development roller 1, and electrostatically contacts the surface of the development roller 1. It is carried. The thickness of the photosensitive drum 3 and the developing roller 1 are conveyed by the rotation of the developing roller 1 and regulated by a blade member 4 which resiliently presses on the developing roller 1, and the photosensitive drum 3 and the developing roller 1 are conveyed to a developing unit. Then, in this developing section, a required amount of toner 7 is applied to the electrostatic latent image formed on the photosensitive drum 3 in accordance with the electrostatic latent image under application of a bias voltage.
And development is performed.

In the present embodiment, the developing roller 1 is configured such that two types of portions having different resistances or dielectric constants are regularly or irregularly exposed on the surface. FIG.
FIG. 2A is a perspective view showing the appearance of an example of such a developing roller 1, and FIG. 2B is an enlarged sectional view of a surface portion thereof. The developing roller 1 of this example is formed by subjecting a roller made of a conductive material, for example, a metal material such as aluminum or a conductive rubber or a conductive plastic 21 to a knurling process in a grid pattern, and applying a knurling process to polycarbonate, acrylic, polyester, A dielectric resin such as ethylene tetrafluoride is rubbed in and filled to form a grid-like insulating region surface 22, and the surface of the base roller is exposed to the grid portion to form a conductive region surface 21. doing. (A), (b), (c) of FIG.
Are formed on the surface by knurling to form streaks having an inclination angle of 45 ° with respect to the moving direction (circumferential direction) of the surface of the developing roller 1.
In this example, the pitch P of the knurl is set to 0.3 mm, and the width W of the insulating region surface 22 is set to W, respectively.
1 = 0.075 mm, W2 = 0.15 mm, W3 = 0.22
5 mm, pattern pitch 0.3 mm on the surface of the developing roller 1
Thus, the insulating region surface 22 and the conductive region surface 21 are mixed. The method for forming the fine conductive region surface 21 and the insulating region surface 22 is not limited to the above example, and various methods can be adopted. In the case where the insulating region surface 21 is formed in a lattice shape, the inclination angle with respect to the circumferential direction is not limited to 45 °, but can be preferably set in the range of 30 to 60 ° with respect to the circumferential direction. . The size of the insulating region surface 22 has an average diameter of 30 to 2000 μm, preferably 50 to 1000 μm. When the shape of the insulating region surface 22 is, for example, circular, the diameter D1 (see FIG. 3) is 30 to 2000 μm,
Preferably, it is set to about 100 to 400 μm, and the center distance P1 is appropriately set in a well-balanced manner. When the shape of the insulating region surface 22 is rectangular, the length of the shortest side is about 30 to 2000 μm. Similarly, when the shape of the insulating region surface 22 is an ellipse or an ellipse, the width on the minor axis side is about 30 to 2000 μm. Even when the shape of the insulating region surface 22 is another shape, the width is set to about 30 to 2000 μm according to these. The occupied area ratio may be 50 to 80%, preferably 65 to 75% of the surface area of the developing roller 1. With the structure of the developing roller 1, a sufficient amount of toner is charged on the surface of the developing roller 1 by charging the toner 7 by a frictional charging effect generated when the toner 7 is rubbed against the developing roller 1 by the toner supply roller 8. 7 can be carried.

This point will be described in more detail. The insulating region surface 22 of the developing roller 1 is charged to a positive polarity opposite to the charging polarity of the toner 7 by friction with the toner supply roller 6. On the other hand, the toner 7 conveyed to the developing roller 1 while being in contact with the peripheral surface of the toner supply roller 8 is
Is negatively charged by friction with the developing roller 1
At this time, the toner is further frictionally charged to the negative polarity by friction with the developing roller 1, particularly its insulating region surface 22, and is electrostatically attached to the peripheral surface of the developing roller 1. At this time, each insulating region surface 22 of the developing roller 1 is frictionally charged to a positive polarity, and the conductive region surface 21 is in contact with each insulating region surface 22. The positive charge is selectively applied only to the insulating region surface 22 of FIG. As a result, as shown in FIG. 3, a closed electric field is formed between each positively charged insulating region surface 22 and the conductive region surface 21 in contact therewith, and countless minute electric fields are formed near the surface of the developing roller 1. A closed electric field (microfield) is formed. That is, when considering the lines of electric force indicating the state of the electric field, the space near the surface of the developing roller 1 exits from the developing roller 1 as shown by a number of arc-shaped lines in FIG. 1 is formed, and a closed electric field is formed between each insulating region surface 22 and the conductive region surface 21. Since the area of each insulating region surface 22 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 7 is strongly attracted to the insulating area surface 22 and is held on the roller 1 in a state where it is hard to separate. Further, when the layer thickness of the toner 7 held on the developing roller 1 is regulated by the blade member 4, the toner 7 having a sufficient charge is strongly held on the surface of the developing roller 1 by the minute closed electric field. The small toner 7 is removed by the contact pressure with the blade member 4, so that only the toner 7 having a large charge amount, for example, the toner 7 charged to about 5 to 20 (preferably 10 to 15) μC / g, is developed. Transported to the department.

In the developing section, the intermittent alternating electric field applied by the developing bias applying means 9 causes the conductive area surface 21 and the insulating area surface 2 existing on the surface of the developing roller 1.
It is considered that this acts on the minute electric field between the toner image 2 and the charged toner 7 to provide dynamic energy suitable for developing the electrostatic latent image. That is, the surface potential of the developing roller 1 is
Since the insulating region surface 22 holds the charges as described above, while the conductive region surface 21 does not hold such charges, the respective regions are different. Specifically, the surface potential of the insulating region surface 22 becomes a potential deviated by a predetermined amount by the charge held by the voltage applied by the developing bias applying unit 9, while the surface potential of the conductive region surface 21 becomes the developing potential. It becomes the applied voltage itself by the bias applying means 9. Therefore, the electric field between the surface of the developing roller 1 and the photosensitive drum 3 not only corresponds to the image portion or the non-image portion of the photosensitive drum 3 but also the insulating region surface 22 of the developing roller 1 surface. And the conductive region surface 21. The electric charge held on the insulating region surface 22 acts on the toner 7 existing on the insulating region surface 22, and excessive toner adhesion is suppressed. On the other hand, the toner existing on the conductive region surface 21 is relatively easily transferred to the photosensitive drum 3 side. or,
Since this portion is conductive, it acts to suppress the edge effect and make the image density uniform. As a result, although the image density is low, the developing roller 1 is excellent in the reproducibility and the gradation of the diagram, but when the density is increased as it is, the reproducibility and the gradation of the diagram are deteriorated. The characteristics of the developing roller, whose surface is insulated, and its electrode effect make it possible to obtain a high density image with excellent uniformity of the solid part, but the surface is poor in the reproducibility of the diagram and the gradation. It has the features of the conductive developing roller at the same time. The conductive region surface 21 and the insulating region surface 22 are formed on the surface of the developing roller 1.
Are mixed, the charge-up of the developing roller 1 and the toner supply roller 8 is prevented. It is considered that the reason is that the toner is charged on the insulating region surface 22 and the toner supply roller is discharged on the conductive region surface 21 to maintain a well-balanced charged state as a whole.

Next, the intermittent alternating electric field applied to the developing section will be described. This intermittent alternating electric field, for example,
May be formed by applying a pulse voltage as shown in FIG. 9 with a pause interval T _1, it may be formed by applying with a pause interval T ₁ a sinusoidal alternating. The frequency is desirably 500 to 2000 Hz, and the ratio of the pause interval T ₁ to the application time T ₂ is 1: 2 to 10
A one-to-one range is desirable.

Hereinafter, a more specific example of this embodiment will be described. In this specific example, the photosensitive drum 3 is OP
4C, the developing roller 1 having the surface shape shown in FIG. 4B was set to a surface potential of −900 V and a potential of the exposed portion to −100 V, and the developing roller 1 having the surface shape shown in FIG.
The photosensitive drum 3 and the developing roller 1 are driven in the directions indicated by arrows to perform reversal development. The insulative area surface 22 on the surface of the developing roller 1 holds an amount of electric charge that is rubbed by the toner supply roller 8 so that the electric potential with respect to the ground becomes +200 V, whereby the negatively charged toner 7 is removed. 1.0-1.2m
g / cm ² . Then, as shown in FIG. 9, a peak-to-peak 1000 V, a maximum potential 0 V, and a frequency 500 H are applied to the developing roller 1 by a developing bias applying means 9.
z, was applied by wave T ₂ by the duty ratio of 50% of the pulse voltage with a pause interval T ₁ of the 2 msec.

The image thus obtained was high in density and excellent in gradation and reproducibility of the diagram without occurrence of background fog. Although the above example uses the developing roller 1 having the surface shape shown in FIG. 4B, the developing roller 1 having the surface shape shown in FIGS. 4A and 4C is used.
And development was carried out under the same conditions as in the above example. As a result, it was possible to obtain an image having no background fog and excellent in high-density gradation and line diagram reproducibility.

Next, referring to FIG. 5, a description will be given of a developing device using a modified example of the developing roller 1 for forming a large number of minute electric fields on the surface. This developing device has basically the same configuration as the developing device according to the above-described embodiment except that the configuration of the developing roller is different from that of the above-described embodiment. As shown schematically in FIG. 5A, the developing roller 1 of the present embodiment has a dielectric part and a conductive part mixed in a very small area on the surface thereof, and the dielectric part is conductive. It is formed in a foam cell near the surface of the foam layer. The size of the minute area is, when the shape is circular, a size of 10 to 500 μm in diameter,
These minute areas are dispersed randomly or according to a certain rule. As the area ratio, the area of the conductor portion is 20
A range of ６０60% is preferred. 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 a material having a volume resistivity of 10 ¹⁰ Ωcm or more, particularly 10 ¹⁴ Ωcm or more is preferable. Examples of such an insulating material include organic polymers such as a polystyrene resin, a polyethylene resin, an acrylic resin, a resin material, and a rubber material. In the present embodiment, those mainly composed of an aliphatic fluorinated compound or silicone resin are preferably 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.

To manufacture the developing roller 1 of the present embodiment,
For example, (i) an elastic foam layer is formed by extruding a conductive foam composition comprising rubbers, a conductivity-imparting agent, a foaming agent and other additives on the outer periphery of the core metal, and then grinding the surface. To expose the foam cell to form a concave portion for burying the dielectric portion. Then, the dielectric material is buried in the concave portion by a method such as spraying or dipping.
(Hardening) (baking) for (time) (the thickness of the coating film is such that the concave portion is completely filled) (see FIG. 5 (b)), (ii) the surface is subsequently cut or polished to form a conductive surface and a dielectric. The surface is cut so as to be mixed with a very small area, and the conductive part area is 20 to
A method of cutting to 60% (see FIG. 5C) is employed.

In the developing roller 1 of the present embodiment, the surface portion of the developing roller 1 after the development is brought into contact with the toner supply roller 8 by the rotation of the developing roller 1 in the direction of the arrow,
Here, the remaining toner of the non-image portion that has not been developed is mechanically and electrically scraped off by the toner supply roller 8, and the dielectric portion is charged by friction. At this time, the charge of the developing roller 1 and the toner by the previous development is fixed by friction,
Initialized. Next, the toner carried by the toner supply roller 8 is charged by friction and electrostatically adheres to the dielectric portion of the developing roller 1. Further, the electric field on the developing roller 1 at this time becomes a microfield (closed electric field) as shown in FIG. 5A, and becomes an electric field with a large electric field gradient, so that the toner can be attached to multiple layers. Become. Further, since the adhered toner has a closed electric field, it is strongly pulled toward the developing roller 1 and hardly separated. And
Similarly to the developing roller 1 in the above-described embodiment, a dielectric portion holding electric charges and a conductor portion holding almost no electric charges include:
Different developing electric fields can be formed between the photosensitive drum 3 and the developing electric field.

Hereinafter, a specific example of the developing roller 1 will be described. Parts are by weight. The following conductive foam composition was extruded around the core treated in advance with a primer, and was temporarily vulcanized in a mold at 170 ° C. for 20 minutes.
Secondary vulcanization at 00 ° C for 2 hours and volume resistivity of 10 ¹¹ Ωc
m, specific gravity 0.57, foam cell size is 30-50 μm
A developer carrier having a conductive foam layer was prepared. Conductive foam composition diorganopolysiloxane (average degree of polymerization 2000 or more) 100 parts [Product name: KF901FU-U (manufactured by Shin-Etsu Chemical Co., Ltd.)] 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 1 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%.

When the developing roller 1 of this embodiment is placed in contact with the photosensitive drum 3 and the same pulse voltage as that of the above-described embodiment is applied to perform the contact development, the developing roller 1 The transfer rate of the toner was 90% or more, and an image having high density, excellent gradation and reproducibility of a line diagram could be obtained without occurrence of background fog.

Next, referring to FIG. 6, a description will be given of a developing device using still another modification of the developing roller 1 for forming a large number of minute electric fields on the surface. This developing device has basically the same configuration as the developing device according to the above-described embodiment except that the configuration of the developing roller is different from that of the above-described embodiment. As shown schematically in FIG. 6, the developing roller 1 of the present embodiment has a conductor part and a dielectric part mixed at least on its surface, and these materials are made of elastic insulating particles. And an elastic conductive material containing the same. 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). (A value measured using a machine A) is 50 degrees or less, preferably 40 degrees or less. 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. As the elastic conductive material, a material having a volume resistivity of 10 ¹² Ωcm or less, preferably 10 ⁸ Ωcm or less is good, and an effective rubber hardness (described above) is 50 degrees or less, preferably 40 degrees or less. What added a filler 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.

In order to manufacture the developing roller 1, for example, (i) a conductive primer is applied on a metal core,
(Ii) forming a compound obtained by mixing an appropriate amount of insulating particles into a conductive material on a core metal by an extrusion molding method or the like;
By applying temperature and pressure by mold molding vulcanization, steam vulcanization, etc., an elastic roller is formed on the core metal, and (ii)
i) Then, a method of smoothing the surface of the elastic roller by a method such as grinding or cutting so that the conductive portion and the insulating portion are mixed on the surface may be adopted.

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.

When the developing roller 1 of this embodiment is disposed in contact with the photosensitive drum 3 and the same pulse voltage as in the specific example according to the above embodiment is applied to perform the contact development, the developing roller 1 The toner transfer rate is 90 to 95%,
An image having high density, excellent gradation and reproducibility of a diagram could be obtained without occurrence of background fog. When the developing roller 1 is used, the linear velocity ratio of the roller 1 to the photosensitive drum 3 is desirably set to 1: 1.08 to 1: 1.1, and the applied bias is set to two wavelengths. those having a minute pause interval T ₁ between 1 and application time T ₂ of the wavelengths, or pause interval T ₁ of the one wavelength and the things fogging prevention and a application time T ₂ of the two wavelengths particularly good Results were obtained.

Next, with reference to FIG. 7, a description will be given of a developing device using a further modified example of the developing roller 1 for forming a large number of minute electric fields on the surface. This developing device has basically the same configuration as the developing device according to the above-described embodiment except that the configuration of the developing roller is different from that of the above-described embodiment.
An example in which the toner is charged to a positive polarity will be described. As shown schematically in FIG. 7A, the developing roller 1 according to this embodiment is enlarged.
Is composed of a base made of a conductive roller 10 made of a metal such as Al, Fe, Cu, and the like, and a surface layer made up of a medium resistance body 12 and a high resistance body 11 fixed to the peripheral surface thereof. FIG. 7B is a plan view of the developing roller schematically showing each dielectric material in an enlarged scale, FIG. 7C is a cross-sectional view taken along line IV-IV of FIG. 7B, and FIG. FIG. 4 is an explanatory diagram showing electric lines of force of a minute closed electric field formed. Medium resistor 1
2 is higher than the resistivity of the conductive substrate surface (the conductive roller 10 in this example), for example, 10 ³ to 10 ⁸ Ωcm.
The resistivity of the high-resistance element 11 is set to about
2 higher than the resistivity, for example, 10 ³ to 10 ¹⁵ Ωc
It is set to about m. Both resistors 11 and 12 are made of a dielectric material having such a resistivity.
In FIG. 7B, a horizontal line is shown with respect to the high-resistance body 11 in order to make it easy to distinguish the two resistance bodies 11 and 12 (the same applies to FIGS. 11A to 11D). As can be seen from this figure and FIGS. 7 (a) and 7 (c), the high resistance body 11 and the medium resistance body 12 are arranged regularly (or may be in an irregular state). It is exposed on the surface of the developing roller 1. The shape of each of the middle resistor 12 and the high resistor 11 can be set as appropriate. When the surface shape is rectangular as illustrated in FIG. 7B, the lengths D1 and D2 of each side are, for example, 10 to 500 μm. It can be set to an appropriate value of the degree. The values relating to the sizes of the resistors 11 and 12 and the resistivity thereof are appropriately selected so that the intensity of a closed electric field described later can be increased and an optimal amount of toner can be carried on the developing roller 1. You. In this embodiment, the high resistance element 11 and the medium resistance element 12 are made of a material having a polarity opposite to the charging polarity of the toner, that is, a material that is frictionally charged to a negative polarity. When the toner carrier comprises a belt, a medium resistor and a high resistor are laminated and fixed on the surface of the conductive base of the belt in the above-described state. On the other hand, the toner supply roller 8 in contact with the developing roller 1
Is made of a material that comes into contact with the high-resistance element 11 and the medium-resistance element 12 and frictionally charges them to a polarity (negative polarity) opposite to the charging polarity of the toner. In the example shown in FIG. 7A, the toner supply roller 8 is made up of a conductor core member 14 and a cylindrical foam (for example, polyurethane foam) 15 laminated therearound, and the foam 15 is elastic. When the toner supply roller 8 is used while being pressed against the developing roller 1 while being deformed, the foam 15 may be made of a material that frictionally charges the resistors 11 and 12 to the negative polarity as described above. Good. Instead of the foam 15, a known material such as a fur brush may be used.

In the above configuration, the high resistance element 11 and the medium resistance element 12 of the developing roller 1 come into contact with the toner supply roller 8 and are charged to the negative polarity opposite to the charging polarity of the toner by the friction. At this time, even if an electrostatic residual image due to the effect of the electrostatic latent image on the photoconductor 3 remains on the resistors 11 and 12 on the peripheral surface of the developing roller passing through the developing unit, the toner supply roller 8
Because the resistors 11 and 12 are charged to a substantially saturated state due to the friction between the developing roller and the developing roller 1, the developing roller 1 is initialized. On the other hand, the toner 4 conveyed to the developing roller 1 while being in contact with the peripheral surface of the toner supply roller 8 is frictionally charged to a positive polarity by friction with the toner supply roller 8 as schematically shown in FIG. Is supplied to the developing roller 1,
At this time, the toner is further frictionally charged to a more positive polarity due to the friction with the developing roller 1, and electrostatically adheres to the peripheral surface of the developing roller 1. At this time, the high resistance element 11 and the medium resistance element 12 of the developing roller 1 are triboelectrically charged to the negative polarity. However, since their resistivity is different from each other, as shown schematically in FIG. The amount of charge of the resistor 11 is larger than the amount of charge of the middle resistor 11, and a difference occurs between the surface potentials of the two. Therefore, a closed electric field is formed between the two resistors 11 and 12.
Since a large number of high resistance elements 11 and medium resistance elements 12 are alternately located on the surface of the conductive roller 10 so as to be countless, countless minute closed electric fields (micro fields) are developed on the surface of the developing roller 1. It is formed in a state of being uniformly distributed on the roller surface. That is, in consideration of the lines of electric force representing the state of the electric field, the space near the surface of the developing roller 1 has the configuration shown in FIG.
An electric force positive E is formed as shown by a large number of arc-shaped lines, and the electric force lines exit from the developing roller 1 and return to the same developing roller 1, and a number of closed lines are formed near the surface of the roller 5. An electric field is created. Thus, an electric field having a large electric field gradient is formed near the surface of the developing roller. High resistance 11
Since the surface size of the intermediate resistor 12 is very small as described above, each closed electric field is also very small. As a result, the intensity of each closed electric field is reduced by the so-called edge effect or fringing effect (peripheral electric field effect). Very strong. The toner positively charged by such a high-intensity closed electric field is not charged as shown in FIG.
As shown schematically in FIG. 5A, the high resistance body 11 is strongly pulled on the surface of the high resistance body 11 and is held on the developing roller 1 in a state where it is difficult to separate a large amount. That is, the charged toner is given a strong binding force inside the closed electric field, and the developing roller 1 is moved along the line of electric force.
It is kept above. The layer thickness is regulated by a doctor blade 4 made of, for example, urethane. In the vicinity of the surface of the developing roller 1, only a small closed electric field is formed over the entire surface as schematically shown in FIG. In any case, since a closed electric field is present, the intensity is increased and a large amount of toner can be carried. As described above, a large amount of sufficiently charged toner is carried on the developing roller 1 and transported to the developing area, where it can be used for development. The resistor 12 and the high resistor 11 are arranged, and the conductive surface of the conductive roller is not exposed on the surface of the developing roller 1. For this reason, in the developing section, the leakage of electric charge between the photoconductor 3 and the developing roller 1 can be reliably suppressed, and the problem that the electrostatic latent image formed on the photoconductor 3 is disturbed can be effectively suppressed. Thus, a high quality visible image can be formed.

In this embodiment, the high resistance element 11 and the medium resistance element 12 are charged to the opposite polarity to the toner. However, both the resistance elements 11 and 12 are charged to the same polarity as the charging polarity of the toner. A large amount of toner can be deposited on the surface of the resistor 12. Further, it is also possible to adopt a configuration in which the medium resistor 12 is not substantially charged, and only the high resistor 11 is charged to a predetermined polarity, and a closed electric field is formed between these members to carry the toner. It is sufficient to charge at least the high-resistance element of the high-resistance element and the medium-resistance element, and form a closed electric field based on the difference in surface potential to carry the toner.

When the developing roller 1 of this embodiment is arranged in contact with the photosensitive drum 3 and the same pulse voltage as in the specific example according to the above embodiment is applied to perform the contact development, the developing roller 1 The transfer rate of the toner was 80% or more, and an image having high density, excellent gradation and reproducibility of a diagram could be obtained without occurrence of background fogging.

Next, a developing device using a modified example of the developing roller 1 for forming a large number of minute electric fields on the surface will be described with reference to FIG. This developing device has basically the same configuration as the developing device according to the above-described embodiment except that the configuration of the developing roller is different from that of the above-described embodiment. As schematically shown in FIG. 8 as a schematic enlarged view, the developing roller 1 of the present embodiment employs a conductive substrate on which a surface layer made of a conductive material in which insulating particles are dispersed is formed. The surface has a conductor portion made of a conductive material mixed with an insulator portion in which insulating particles are exposed. The toner adhesion is as follows. First, the surface portion of the developing roller 1 which has completed the development comes into contact with the toner supply roller 8 by the rotation of the developing roller 1 in the direction of the arrow. Here, the remaining toner of the non-image portion which has not been developed is mechanically and electrically scraped off by the toner supply roller 8, and the insulator portion is frictionally charged to a polarity opposite to the polarity of the toner. At this time, the charges of the developing roller 1 and the toner by the previous development are fixed by friction and initialized. Next, the toner carried by the toner supply roller 8 is charged by friction and adheres mainly to the insulator portion of the developing roller 1 electrostatically. The electric field on the developing roller 1 at this time is as shown in FIG.
As shown in (b), a microfield (small closed electric field) is generated, and the electric field has a large electric field gradient, so that the toner can be adhered in multiple layers. Further, since the adhered toner has a closed electric field, it is strongly pulled toward the developing roller 1 and hardly separated. In the present embodiment, 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 so that the toner is charged to the triboelectric charge polarity. May be. Also in this case, a microfield can be similarly formed by the potential difference between the insulator and the conductor, and in this case, the toner mainly adheres to the conductor.
The toner layer further includes a toner layer thickness regulating member 3.
0 controls the toner layer thickness and reaches the developing section. Electric field between the developing roller 1 and the photoconductor 3 in the developing section (see FIG. 1)
In this case, the electrode effect is increased, and the toner on the developing roller 1 becomes an electric field that easily adheres to the photoconductor 3, so that the development is performed.

The developing roller 1 of this embodiment will be described in more detail. As described above, in the developing roller 1 of this embodiment, a surface layer made of a conductive material in which insulating particles are dispersed is formed on a conductive substrate. As the conductive material, 10 ¹² Ωcm
Below, preferably 10 ⁸ Ωcm or less can be used.
To be specific, there may be mentioned those obtained by adding a conductivity-imparting agent to organic polymers. In this case, the organic polymers include a resin material (plastomer) and a rubber material (elastomer). Examples of the conductivity-imparting agent include metal powder, carbon black, conductive oxide, electroless plating, graphite, metal fiber, and carbon fiber. still,
When an elastomer is used in the organic polymers as the conductive material, the surface layer of the developing roller becomes elastic, and the contact with the rigid drum-shaped photoreceptor becomes easy, so that the contact development becomes very The use of conductive elastomers is particularly preferred, as this makes it easier. On the other hand, as the insulating particle material, a material having a resistivity of 10 ¹³ Ωcm or more, preferably 10 ¹⁴ Ωcm or more is used. The average particle size is preferably 5 μm or more. If it is less than 5 μm, it is difficult to form a minute electric field,
Stable toner application and electrification cannot be obtained. In addition, fixed form,
Irrespective of irregular shape. Specifically, inorganic particles such as alumina and organic particles such as epoxy resin are exemplified. When the conductive elastomer is used as the conductive material, it is desirable to use the elastomer as the insulating particles in order to further promote the low hardness. In order to produce the insulating elastomer particles, known methods such as a method of freezing the elastomer with dry ice or the like, pulverizing and pulverizing, forming an aqueous emulsion using a surfactant or the like, and then hardening the emulsion. Is adopted. The amount of the insulating particles to be added to the conductive material is appropriately selected in the range of 10 to 200 parts by weight based on 100 parts by weight of the conductive material. The cost of the developer carrier is 20 to 6
The range of 0% is preferable, and the amount of the insulating particles added is appropriately adjusted so as to be within this range after the preparation of the carrier.

In order to manufacture the developing roller 20 of this embodiment, for example, the insulating particles are added to the conductive material based on a normal dispersion method such as ball milling or kneading, and then the mixed material is added. Injection molding, extrusion molding, spray coating, dipping, etc.
It is manufactured by molding on a conductive substrate typified by a metal roller of S, iron, Al or the like, and then polishing the surface so as to be smooth. Note that a plastomer can be used in order to improve the adhesion between the conductive material and the conductive substrate. In this case, the plastomer is preferably conductive.

Hereinafter, specific examples will be described. Parts are by weight. Conductive paint 100 parts [Product name: Electrodag 440 (manufactured by Acheson Japan) (solid content 70%; acrylic resin containing Ni particles)] Acrylic resin 50 parts (average particle size 80 μm) Diluent 200 parts [(trade name SB- 1 (manufactured by Acheson Japan Co., Ltd.)] The coating solution having the above formulation is applied to a SUS metal roller by spray coating, dried at 80 ° C. for 1 hour, polished, and developed with a surface layer having a thickness of 100 μm. A roller was made.

The developing roller 1 of this embodiment is disposed opposite to the photosensitive drum 3 with a gap of 100 to 150 μm, and the same pulse voltage as in the specific example according to the above-described embodiment is applied. Is performed, the transfer rate of the toner from the developing roller 1 is 70% or more, an image with high density, excellent gradation and reproducibility of a diagram can be obtained without occurrence of background fog. Was. In addition, since the insulating particles were irregularly exposed, a uniform solid density could be obtained without causing any pattern on the image due to the potential distribution pattern on the surface of the developing roller 1.

[0031]

According to the present invention, a developer carrier for forming a large number of small electric fields on its surface is used as a developer carrier for carrying a developer, and the developer carrier and the electrostatic latent image carrier are applied by a voltage applying means. The body forms an intermittent alternating electric field in a developing section opposed to each other, and the electric field formed on the electrostatic latent image carrier, the potential on the developer carrier, and the electric field formed by the voltage applying means are changed. The movement of the developer is controlled by the electric field determined by the relationship, whereby an appropriate amount of the developer is attached in accordance with the electrostatic latent image on the electrostatic latent image carrier, so that the image quality is maintained while maintaining the gradation. It is possible to improve the density and to prevent thickening of the line portion of the image and fogging of the background, thereby providing an excellent effect that a high quality image can be obtained.

[Brief description of the drawings]

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

FIG. 2A is a perspective view showing an appearance of an example of the developing roller, and FIG. 2B is an enlarged sectional view of an outer layer portion thereof.

FIG. 3 is an explanatory diagram showing electric lines of force of a minute closed electric field formed near the surface of an insulating region.

FIGS. 4A to 4C are diagrams illustrating an enlarged view of the surfaces of three developing rollers having insulating region surfaces having different widths from each other.

FIG. 5 illustrates another modification of the developing roller.
(A) is an explanatory diagram schematically showing each dielectric and toner particles of the developing roller in an enlarged scale, and (b) and (c) are explanatory diagrams of the manufacturing process.

FIG. 6 is an explanatory diagram schematically showing enlarged dielectrics and toner particles of a developing roller according to still another modification.

FIGS. 7A and 7B show a modified example of the developing roller, and FIG.
FIG. 3 is an explanatory diagram schematically showing enlarged dielectrics and toner particles of the developing roller, FIG. 4B is a plan view schematically showing enlarged dielectrics of the developing roller, and FIG. ) Is IV of (b)
FIG. 4D is a cross-sectional view taken along line IV, and FIG. 4D is an explanatory diagram showing electric lines of force of a minute closed electric field formed near the surface of the developing roller.

FIG. 8 is a partial sectional view of a surface of a developing roller according to still another modification.

FIG. 9 is a waveform chart showing an example of a developing bias.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Development roller, 2 Developing device 3 Photoconductor drum, 4 Blade member 5 Toner tank, 6 Agitator 7 Toner, 8 Toner supply roller 9 Developing bias application means, 10 Conductive roller 11 High resistance element 12 Medium resistance element, 21 Conductivity Area plane 22 Insulating area plane

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigekazu Enoki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Junko Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo No. Ricoh Co., Ltd. (56) References JP-A-55-62469 (JP, A) JP-A-60-37563 (JP, A) JP-A-61-198170 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/08-15/09 G03G 9/00

Claims (4)

(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. In the developing device, a conductive portion and a conductive foam are formed on the surface as the developing carrier.
A dielectric part formed in a foam cell near the surface of the body layer;
Are mixed in a small area, and at least the dielectric
The exposed portion on the surface of the developer has a polarity opposite to that of the developer or
Using a developer bearing member is charged with the same polarity to form a large number of fine field to the surface, as the voltage application means, using a voltage application means for forming an intermittent alternating electric field to the developing unit, the electrostatic The movement of the developer is controlled by an electric field determined by a correlation between an electric potential on the latent image carrier, an electric field formed by the voltage applying means, and an electric field on the developer carrier. Developing device. 2. The method according to claim 1, wherein the minute electric field is a closed electric field.
The developing device according to claim 1, wherein 3. The frictional charging of the dielectric portion to a predetermined polarity.
3. The method according to claim 1, wherein a frictional charging unit is provided.
Developing device. 4. The developing unit supported by the developer carrier
Is provided to regulate the layer thickness of the developer conveyed to the
Ke The frictional charging means is transported more developer than the layer thickness regulating means.
Direction upstream side and the developer transport direction relative to the developing section.
4. The developing device according to claim 3, wherein the developing device is located downstream.