JP3081653B2 - toner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention supplies a non-magnetic one-component developer to which an auxiliary agent is externally added as necessary, to a developing roller which is driven to rotate, and applies the developer to the surface of the developing roller. In the developing region where the latent image carrier and the developing roller face each other, the electrostatic latent image formed on the latent image carrier is visualized by the developer carried on the developing roller. The present invention relates to a toner for use in an image forming method.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electronic copier, a printer or a facsimile, which forms an electrostatic latent image on a latent image carrier and visualizes the latent image with a developer to obtain a recorded image, a powdery image is formed. Dry developing devices using a developer are widely used. As such a powdery developer, a two-component developer having a toner and a carrier and a one-component developer without a carrier are known, and two-component development using the former two-component developer is known. In the method, although a relatively stable and good recorded image is obtained, deterioration of the carrier and fluctuation of the mixing ratio of the toner and the carrier are apt to occur, maintenance of the apparatus is complicated, and the structure of the entire apparatus is easily enlarged. Has disadvantages. From such a viewpoint, a one-component developing method using a one-component developer which does not have the above-mentioned disadvantages has attracted attention. The one-component developer includes a toner composed of only a toner and a toner obtained by externally adding an auxiliary agent as needed and mixing the toner and the auxiliary agent. As the toner, there are a magnetic toner in which magnetic powder is kneaded into each toner particle itself, and a non-magnetic toner containing no magnetic material.

Here, since a magnetic material is generally opaque, if a color image including full-color or multi-color is formed with a magnetic toner, a developed visible image becomes unclear and a vivid color image cannot be obtained. .
Therefore, it is desirable to adopt a one-component developing method using a non-magnetic toner especially for color development. By the way, in a developing device employing a one-component developing method, a one-component developer is carried on a developing roller and conveyed. In a developing region where the developing roller and the latent image carrier face each other, the latent image carrier is The electrostatic latent image formed on the surface is visualized with a developer, but in order to form a high-quality visible image of a predetermined density, a large amount of sufficiently charged toner is conveyed to the developing area, and The latent image needs to be visualized with toner.

In the case where a magnetic toner is used, the one-component developer can be carried on the developing roller by utilizing the magnetic force of a magnet provided in the developing roller. Is possible. However, when a non-magnetic one-component developer is used, it cannot be carried on the developing roller by magnetic force, so that it is difficult to satisfy the above-mentioned requirements. Various countermeasures against this have been conventionally proposed.For example, JP-A-61-42672 discloses that a layer of a dielectric (insulator) is formed on the surface of a developing roller, and for this, for example, a sponge roller is used. A developer supply member composed of a non-magnetic toner having a polarity opposite to that of the dielectric material, and a non-magnetic toner charged to a polarity opposite to that of the dielectric material is electrostatically attached to the dielectric material. There has been proposed a method of transporting an agent to a developing area. However, even with this method, the strength of the electric field formed in the vicinity of the dielectric surface cannot be sufficiently increased, so that it is difficult to carry a large amount of toner on the surface of the developing roller, and the developing roller can be transported to the developing area. Insufficient amounts of the agent make it difficult to form a high-density visible image.

Further, between the developing roller and the developer supply member,
A configuration for applying an electric field in a direction in which the non-magnetic toner electrostatically moves to the developing roller side is also known. However, even if such a configuration is added, it is not possible to attach a sufficient amount of toner to the developing roller. difficult. Further, as the toner supply member, 10 ²
~ 10 ⁶ Ωcm conductive foam (JP 60-229057 A),
It has been proposed to use an elastic body with a skin layer (Japanese Patent Application Laid-Open No. 60-229060) and a fur brush (Japanese Patent Application Laid-Open No. 61-42672). Metal body (Japanese Patent Application Laid-Open No. 60-53976), insulative coated roller body (Japanese Patent Application Laid-Open No. 55-46768), medium resistance coated roller (Japanese Patent Application Laid-Open No. 58-13278), and having an insulator and a conductive surface An electrode roller (JP-A-53-36245) and the like are disclosed.

Further, in a developing device using a non-magnetic one-component developer, a sponge roller is disclosed in JP-A-60-229057, an elastic roller is disclosed in JP-A-62-229060,
In 52663, using a fur brush or the like, a charge is applied to the toner by frictional charging between the toner and the replenishing member, and further, by friction in contact with the developing roller, the toner is electrostatically attached to the developing roller, Further, the latent image on the photoreceptor is developed by controlling the toner layer using a layer thickness regulating member such as a blade. As the material of the developing roller, various materials such as an insulating material, a medium-resistance material, and a laminated material are used.

According to the method disclosed in these documents , toner is adhered to the developing roller by friction between the toner replenishing member and the developing roller. Is difficult to obtain, resulting in insufficient toner adhesion. When comparing the color toner with the black toner, in order to obtain the required density, the black toner has an adhesion amount of about 0.4 to 0.5 mg / cm ² , whereas the color toner has a 1.5 to ² mg / cm ² of the black toner. Double the amount of adhesion is required. The need for a large amount of this adhesion also makes non-magnetic one-component development difficult. Further, Japanese Patent Application Laid-Open
As shown in JP-A-51841, etc., after scraping the one-component developer on the developing roller after passing through the developing area, the surface layer of the developing roller is subjected to corona discharge to discharge the electric charge. In addition, a technique has been proposed in which the non-magnetic toner is positively and electrostatically adhered to the developing roller by a developer supply member and then the developer carrying member on the surface of the developing roller. The amount cannot be increased, and a large amount of the developer cannot be transported to the development area.

Against this background, Japanese Patent Publication No. 41-947 discloses the use of a one-component toner having no magnetism.
Japanese Patent Application Laid-Open No. 5 (1999) -2005 proposes a method in which a toner member having a thin layer of toner on its surface is disposed close to a latent image forming body, and the toner flies only to the latent image portion while keeping them out of contact. Thus, in this proposal, retention of the toner is achieved by suctioning the toner onto a suitably tacky web or pre-charged film sheet. However, this method has a limited sheet and web length, and is not suitable for continuous copying and printing.

On the other hand, if the toner carrier is made endless so that it can be used repeatedly, the above-mentioned problem can be solved. No. 2,290,655. In this proposal, a thin layer is formed by bringing an elastic homogenizing member into contact with a developer carrying roller, and an AC and DC developing bias is applied to develop a latent image. However, in this method, the number of formed toner layers is almost one, and it is difficult to obtain high image density and high-quality images with clear contrast. Also, Japanese Patent Application Laid-Open
Japanese Patent Application Publication No. 30537 discloses a developing device using a pulse bias system, which is said to improve the image quality. However, even with this system, there is no effect of increasing the image density and clearing the contrast.

Further, Japanese Patent Application Laid-Open Nos. 47-12635 and 50-10143 disclose the structure of a developer carrier having an insulating and conductive fine pattern on the surface. These use a minute electric field to form peaks and valleys of the toner according to the minute pattern and attach toner corresponding to the potential level of the latent image. The manufacturing process is complicated and causes an increase in cost.

As a method for solving these problems, the present inventors have previously described "a one-component developer composed of a non-magnetic toner in which an auxiliary agent is externally added to a rotationally driven developing roller, if necessary." Is supplied, and the developer is carried on the surface of the developing roller and conveyed. The electrostatic latent image formed on the latent image carrier is developed in a developing area where the latent image carrier and the developing roller face each other. In the developing method of visualizing the image with the developer carried on the developing roller, a plurality of minute closed electric fields are formed in the vicinity of the developing roller surface by selectively holding electric charges on the surface of the developing roller body. Then, the charged toner is sucked by the closed electric field, the developer is adhered to the surface of the developing roller and carried, and an electrostatic latent image is visualized by the carried developer.

In this invention, since a large number of minute closed electric fields (microfields) are formed in the vicinity of the surface of the developing roller, the intensity of the electric field can be significantly increased as compared with the prior art, and a large amount of a sufficiently charged non-electric field can be obtained. It has many advantages such that the magnetic toner can be carried on the developing roller and transported to the developing area. However, according to the subsequent studies by the present inventors, in a developing method for forming such a minute closed electric field (microfield), when a conventionally known toner is directly used, the toner is formed on a developing roller. It is difficult to always stabilize the toner layer with two or more layers, and the toner layer becomes thinner, the amount of toner to be developed decreases, and the density of the image area becomes lower or the toner layer becomes non-uniform. It may cause unevenness, fogging, and reduced contrast.Furthermore, filming phenomenon often occurs on the developing roller, the microfield effect decreases, and the toner holding amount on the developing roller It has been found that there is a problem that it becomes difficult to sufficiently develop the toner on the latent image carrier.

[0013]

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned technical background, and has as its object to stably and uniformly laminate two or more layers on a developing roller and to develop the developing roller. Filming is suppressed, the contrast is clear and the high density
A high-quality image can be given, and therefore, the developer carrier is charged by charging the surface of the developer carrier having a chargeable and photoconductive surface and then selectively irradiating the surface with light. A large number of micro-closed electric fields are formed in the vicinity of the surface, and a non-magnetic one-component developer composed of a toner externally added with an auxiliary agent is supplied onto the developer carrier as needed. An object of the present invention is to provide a toner that can be suitably used in an image forming method in which a developer is carried on a surface of a developer carrier and an electrostatic latent image is visualized by the carried developer.

[0014]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a toner containing a binder resin and a colorant and having a specific average particle size and a specific shape factor is suitable for the above purpose. And completed the present invention.

That is , according to the present invention, after the surface of a developer carrier having a chargeable and photoconductive surface is charged, the surface is selectively irradiated with light, whereby the developer carrier is charged. A large number of micro-closed electric fields are formed in the vicinity of the surface, and a non-magnetic one-component developer composed of a toner externally added with an auxiliary agent is supplied onto the developer carrier as needed. A toner used for an image forming method in which a developer is carried on a surface of a developer carrier and an electrostatic latent image is visualized by the carried developer, wherein the toner contains at least a binder resin and a colorant. And a toner having an average particle diameter of 3 to 20 μm and a shape factor of 40% or more.

The toner of the present invention contains a binder resin and a colorant as described above, has an average particle size of 3 to 20 μm, preferably 5 to 20 μm, and a shape factor of 40% or more, preferably 40 to 75 μm. %.

According to the study of the present inventors, when the average particle diameter and the shape factor of the toner are within the above-mentioned ranges, it becomes difficult for the toner to be pulverized on the developing roller and to make the toner particles uniform. It has been found that two or more layers can be stably stacked, and that filming on a developing roller and fog development during development are reduced.

Even if the average particle size of the toner is smaller or larger than the above range, it becomes difficult to prevent the pulverization on the developing roller or to stably laminate two or more layers. Can not achieve. The shape factor referred to in the present invention is defined by the following formula (I).

(Equation 1) Here, the specific surface area of the particles in (a) is calculated using a Coulter counter.
(TYPE TA = II), the specific surface area of the sphere having the same volume as the particles of (b) is an air-permeable specific surface area measuring device (manufactured by Shimadzu Corporation, powder specific surface area measuring device SS-100 type) Measured.

When the shape factor is 40% or more, the movement of the toner with respect to the microfield on the developing roller is smooth, and the toner can be uniformly and stably multilayered on the developing roller. Toner is easily developed. The shape factor of the toner is
If it is less than 40%, it is possible to multiply the toner on the developing roller, but the adhesive force between the developing roller and the toner is reduced, the toner is scattered, and the toner adheres to the background portion of the image Development tends to occur.

The binder resin used in the toner of the present invention comprises:
All of those that have been used as binders for toners can be applied. Specifically, polystyrene, styrene
-Acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylate copolymer, styrene-
Including styrenic resins such as methacrylic acid ester copolymers and styrene-butadiene copolymers, saturated polyester resins, unsaturated polyester resins, epoxy resins, phenolic resins, maleic resins, coumaronic resins, chlorinated paraffins, xylene resins , Vinyl chloride resins, polypropylene, polyethylene and the like. It goes without saying that two or more of these binder resins may be used as a mixture as appropriate. Among these, the use of polystyrene, styrene resin and epoxy resin is advantageous.

The toner of the present invention contains a colorant. As the colorant used in the toner of the present invention, all pigments and dyes conventionally used as colorants for toner are applied. Specifically, carbon black, lamp black, iron black, ultramarine, nigrosine dye, aniline blue, calco oil blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, phthalocyanine green, hansa yellow G, rhodamine 6C lake, Examples thereof include chrome yellow, quinacridone, benzidine yellow, malachite green, malachite green hexalate, oil black, azo oil black, rose bengal, monoazo dyes, disazo dyes, trisazo dyes and mixtures thereof.

The toner of the present invention may contain a charge control agent, a fluidizing agent, or a release agent, if necessary. As the charge control agent, there are nigrosine dyes, quaternary ammonium salts, basic dyes, amino acid-containing polymers and the like for imparting positive polarity to the toner, and chromium-containing monoazo dyes for imparting negative polarity. Chlorinated organic dyes, metal salts of salicylic acid derivatives, and the like.

Examples of the fluidizing agent include inorganic oxides such as SiO ₂ and TiO ₂ whose surfaces have been hydrophobized, inorganic fine particles such as SiC, and metal soaps such as zinc stearate.
Examples of the release agent include low molecular weight polyethylene, synthetic waxes such as polypropylene, plant waxes such as candelilla wax, carnauba wax, rice wax, wood wax, and hoboba oil; beeswax, lanolin,
Animal waxes such as whale wax; mineral waxes such as montan wax and ozokerite; oil-based waxes such as hardened castor oil, hydroxystearic acid, fatty acid amide, and phenol fatty acid ester.

In addition to the above components, the toner of the present invention may contain various plasticizers (dibutyl phthalate, phthalate, etc.) for the purpose of adjusting the thermal, electrical and physical properties of the toner as required.
It is also possible to add an auxiliary agent such as dioctyl phthalate or the like, a resistance adjusting agent (such as tin oxide, lead oxide or antimony oxide).

The toner of the present invention forms a large number of micro-closed electric fields near the surface of the developing roller by selectively holding electric charges on the surface of the developing roller. A non-magnetic one-component developer composed of a toner externally added with an auxiliary agent is supplied, and the developer is carried on the surface of a developing roller by the minute closed electric field, and the electrostatic latent image is visualized by the carried developer. Image forming method,
Useful.

Hereinafter, such an image forming method will be described. FIG. 1 shows an outline of a typical developing device useful for carrying out this image forming method, focusing on a developing roller portion. In FIG. 1, the toner 60 of the present invention contained in a toner tank 70 is forcibly brought to a toner supply member (a sponge roller or a fur brush) 40 by a stirring blade (toner supply auxiliary member) 50, and the toner 60 Is supplied to the toner supply member 40. On the other hand, the developing roller 20 that has completed the development rotates in the direction of the arrow (for example, 400 rpm) and reaches a contact portion with the toner supply member (sponge roller) 40. The toner supply member 40 rotates in the opposite direction to the developing roller 20 (for example, 300 rpm), and
20 and the toner 60, and the toner 60
To adhere. Further, the developing roller 20 rotates and the developing roller
The attached toner on the toner 20 is stabilized in charge while being controlled in thickness by the toner layer thickness regulating member (elastic blade) 30, and reaches the developing area 80. In the development area 80, the latent image is developed by contact or non-contact development. Here, if necessary, a bias such as direct current, alternating current, direct current superimposed alternating current, or pulse can be applied to the developing roller 20 and the toner supply member 40 to control an optimum image.

Next, the mechanism of toner adhesion to the developing roller 20 of this type (electrode type) will be described. Examples of the developing roller 20, for example as shown in FIG. 3, on the surface of the induction conductor section and the conductive portion is configured to mix a minute area. As for the size of the area, assuming that the shape is circular, minute areas having a diameter of 10 to 500 μm are dispersed randomly or according to a certain rule. As the area ratio, the area of the insulating portion is preferably in the range of 20 to 60%.

The toner adhesion is as follows. First, the developing roller 20 that has completed the development rotates in the direction of the arrow and comes into contact with the toner supply member 40. Here, the remaining toner in the non-image portion that has not been developed is mechanically and electrically scraped off by the toner supply member 40, and the dielectric portion is charged by friction. At this time, the charge of the developing roller 20 and the toner by the previous development is
It is stabilized and initialized by friction. Next, the supply member
The toner carried by 40 is charged by friction and electrostatically adheres to the dielectric portion of developing roller 20. At this time, the polarity of the toner is opposite to the charge on the photosensitive member , and the dielectric portion of the developing roller 20 has the same polarity. At this time, the electric field on the developing roller 20 becomes a microfield (closed electric field) as shown in FIG. 2, and becomes an electric field having a large electric field gradient, so that the toner can be attached to multiple layers. Further, since the adhered toner has a closed electric field, it is strongly pulled toward the developing roller 20 and is hardly separated. The toner layer thickness of the toner layer is further controlled by the toner layer thickness regulating member 30, so that the toner in the developing area 80 becomes an electric field that easily adheres to the photoreceptor, and development is performed.

Although many types of developing device parts can be used, as shown in Table 1, when only the preferable materials are used from the viewpoint of releasability from toner and durability.

[0030]

[Table 1]

Further, in the induction conductor section and the conductive portion to produce a configured developing roller so as to mix in a small area on the surface, for example, firstly facilities grooving by iris low red machining or the like on the surface (In this case, the groove is 0.1 mm)
~ 0.5mm pitch, about 45 ° to roller longitudinal direction
(See FIG. 3 (a)), and then coat the grooved metal surface with, for example, a fluororesin (Lumiflon LF200; manufactured by Asahi Glass Co., Ltd.), and cure and dry at 100 ° C. for about 30 minutes. (The thickness of the coating should be such that the groove is completely filled.)
FIG. 3 (b)], and then the surface of the roller is cut or polished so that the conductive portion surface is mixed in a small area, and the conductive portion area is reduced to 20 to 60% [see FIG. c)] is adopted.

In the developing method in which a microfield electric field is formed on the developing roller, when conventionally known toner is used as it is, the toner layer on the developing roller is always stabilized by using two or more toner layers. Is difficult, the amount of toner to be developed is reduced due to the thinning of the toner layer, the density of the image area is reduced, and the unevenness of the toner layer causes uneven development and fogging. There is. Further, in the conventional toner, a filming phenomenon often occurs on the developing roller. However, when the filming is formed on the developing roller, the microfield effect decreases, and the amount of toner held on the developing roller decreases. This makes it difficult to sufficiently develop the toner on the latent image carrier.

However, when the toner of the present invention is used, pulverization of the toner on the developing roller is suppressed, and as a result, filming on the developing roller is suppressed.
A sufficient microfield effect is exhibited, and a high-density, high-quality image can be obtained over a long period of time by the toner of the present invention.

Further, in addition to the above components, various plasticizers (dibutyl phthalate, dioctyl phthalate) may be added to the toner used in the present invention in order to adjust the thermal, electrical and physical properties of the toner as required. ), And a resistance adjusting agent (such as tin oxide, lead oxide, and antimony oxide).

In the above example, the micro-feed on the developing roller
The field is composed of a dielectric part and a conductor part. Against this
Thus, in the present invention, having a chargeable and photoconductive surface
Charge the developer carrier and selectively irradiate it with light
The area where the charge has been dissipated due to light irradiation
And the remaining charge constitutes a microfield.
Is what it does. Therefore, toner on the developer carrier is
-The state of adhesion is composed of the above dielectric part and conductor part.
This is the same as in the case of the microfield.

Therefore, the toner of the present invention is
, Developer carrier having a chargeable and photoconductive surface
After charging the surface, the surface is selectively irradiated with light.
And a large number of small closed electric fields near the surface of the developer carrier
Is formed on the developer carrier, and if necessary,
Supply of non-magnetic one-component developer consisting of toner externally added
Then, the developer is caused to contact the developer carrier by the minute closed electric field.
Surface, and the electrostatic latent image is visualized by the developer.
The present invention is also useful in an image forming method.

Hereinafter, such an image forming method will be described. FIG. 4 shows a developer carrier (developing roller) having a chargeable and photoconductive surface useful for carrying out this image forming method.
1 schematically shows a developing device 102 provided with 101. In FIG. 1, a developing device 102 is disposed close to a photosensitive drum 103 that holds a latent image. A blade member 10 for regulating the thickness of the toner layer is provided around the developing roller 101.
4 is provided to be elastically pressed to the lower left of the developing roller 101 so that the toner 107 supplied from the toner tank 105 with the rotation of the agitator 106 is uniformly thinned. The agitator 106 moves the toner 107 in the clockwise direction indicated by the arrow due to the resistance of the tip. An elastic roller member 108 for supplying toner is disposed below and to the right of the developing roller 101. The toner supply roller 108 is made of a sponge material obtained by foaming urethane rubber, or a brush made of polyester, polytetrafluoroethylene, or the like. The toner supply roller 108 is connected to the developing roller 10 to which a charge has been given in advance by a method described later.
1 on the surface of the toner 107 moved by the agitator 106
It has the function of rubbing.

The toner 107 rubbed by the toner supply roller 108 is stably charged with the effect of the frictional charging effect generated by the mutual friction between the toner supply roller 108 and the developing roller 101. The roller 101 is stably held in spite of a relatively large number of toner layers on the surface. And the toner 10
Reference numeral 7 denotes a developing roller 101 by a blade member 104 provided by being elastically pressed to the lower left of the developing roller 101.
The film is uniformly thinned with the rotation of, and supplied to the developing area. As the blade member 104, a material having a toner charging property such as urethane rubber may be attached to an elastic cylindrical leaf spring, or an elastic member may be used as it is.

The development of the latent image on the photosensitive drum 103 is performed by transferring a desired amount of toner according to the latent image by a developing bias unit 109 connected to the developing roller 101 and the toner supply roller 108. It has become. The developing roller 101 has a relationship of 30 to 500 μm, preferably 50 μm, so as not to substantially contact the photosensitive drum 103.
They are arranged at intervals of up to 250 μm. As a result, an excessive load such as when a developing roller is brought into contact with a photoreceptor to develop a latent image is not required, and the drive motor can be replaced with a small one. If the photosensitive member is formed into a flexible belt shape, the relationship may be such that the developing roller 101 essentially contacts the photosensitive member. In this case, the developing roller 1
The thickness of the toner layer held on the surface of No. 01 has a relationship separating them. If the peripheral speed of the photosensitive drum 1033 and the peripheral speed of the developing roller 101 are set to be substantially equal, the driving torque can be further reduced.

In this connection, if the developing bias applying means 109 is provided, a desired amount of toner can be transferred to the photosensitive drum 103. It goes without saying that the level and polarity of the bias potential are changed between the normal development and the reversal development. As the developing bias, an AC electric field can be used in combination with a DC electric field. As the AC electric field, a square-wave pulse electric field was
00 Hz, preferably in the range of 500 to 1,500 Hertz, and when used in a waveform having a different ratio between the time of the high potential portion and the time of the low potential portion, the sharpness of the low latent image potential portion is also improved. As a result, it is possible to obtain an excellent developed image in which the image density in the high latent image potential portion is high and the background is less stained. As the ratio (duty ratio), the optimum ratio is different depending on the polarity of the latent image and the polarity of the toner.For example, when reversal development is performed on a negative latent image with a negative toner, a high potential portion (-100 V or more) is used. Time and low potential time (-800
V or less) may be 5-18: 2-8. In the case of regular development, if this ratio is reversed, the sharpness of the same low latent image potential portion is good, the image density of the high latent image potential portion is high, and the background is less stained. Images can be obtained.

Above the developing roller 101, a developing roller charging member 110 is arranged in contact. Charging member 110
Are made of a conductive sponge material obtained by foaming urethane rubber, or a brush made of a material obtained by dispersing a conductive substance in polyester, polytetrafluoroethylene, or the like, into fibers. Then, the charging member 110
Removes toner from the surface of the developing roller 101 and
1 provides an effect of giving a charged charge to the same surface by applying a voltage. The removed toner is collected by the scraper 112 and used again. The charging member 110 may be any device as long as it can supply a charge to the developing roller 1, and may be a normal corona charging device. The power supply 111 may be configured to superimpose alternating current in addition to direct current. In the example shown in FIG. 4, the potential applied to the developing roller 101 is 50 to 500 V, preferably 100 to 300 V, and the voltage at which the power supply 111 operates is 300
To 2,000 V, preferably 500 to 1,000 V
It is.

On the right side of the developing roller 101, a light irradiating member 1 composed of, for example, an LED array element is provided as a minute point light source.
13 are arranged to erase the charged charges of the developing roller 101 in a desired pattern. As a result, on the surface of the developing roller 101, an infinite number of minute portions having a charged charge and an infinite number of minute portions having no such charge are generated, and an infinite number of minute electric fields are formed therebetween. Since these electric fields cause a phenomenon well known as an “edge effect” over the entire surface of the developing roller 101, the toner adhesion force is significantly increased as compared with the case of a uniform and uniform electric field. Generally, the rate of increase reaches 1.5 to 2 times,
The toner adhesion amount also increases at this rate. Through the above operation steps, the toner 107 moved by the agitator 6 acts on the suction and attraction of the charged charges held by the developing roller 101 and the frictional charging effect generated by the mutual friction between the toner supply roller 8 and the developing roller 101. In addition, since the charging of the toner is stabilized, the toner is stably held on the surface of the developing roller 101 despite a relatively large number of toner layers. In general, the non-magnetic toner is called a thin layer,
0.2 to 0.4 mg / cm ² , and the state called multilayer is about 0.5 mg / cm ² or more, usually 0.8 to 1.2 mg / cm ^2.
It means that an amount of cm ² is present on the developing roller.

FIG. 5 shows another method of erasing the charged charge of the developing roller 101 in a desired pattern. In this method, uniform irradiation light from the cold cathode tube light source 121 is applied to a transparent film 122 on which a minute electric field pattern is printed. The light is emitted in synchronism with the rotation of the developing roller 101. Since the pattern is printed in a staggered pattern on the transparent film 122, a charge pattern is also formed in the staggered pattern on the surface of the developing roller 101.

FIG. 6 shows still another method of erasing the charged charge of the developing roller 101 in a desired pattern. After a light beam 132 emitted from a semiconductor laser light source 131 is made to a predetermined beam diameter by a collimator lens 133, The direction is changed by the rotating polygon mirror 134, and the reflecting mirror 1 such as a prism is added.
At 35, the surface of the developing roller 101 is scanned. An arbitrary minute electric field can be formed on the developing roller 101 by the light emission pattern of the laser beam.

The surface of the developing roller 101 is made of a chargeable and photoconductive material. As such a material, any material that can be generally used as an electrophotographic photosensitive member can be used. Anything can be used.
For example, Se, Pb, Cd, Zn, Si-based inorganic photoconductive material and its compound alone or dispersed in a binder material,
Carbocyclic compounds, heterocyclic compounds, pigment dyes, azo-based, phthalocyanine-based, arylamine / arylmethane-based organic photoconductive material, or polyvinyl carbazole-based polymer photoconductive material, A photoconductor may be used alone or in combination. It is preferable to use an amorphous silicon-based material from the point of abrasion durability, and to use zinc oxide which is an organic photoreceptor or a dispersion type inorganic photoreceptor from the viewpoint of cost performance. When the structure of the developing roller 101 is configured as described above, a sufficient amount of toner having a stable charge amount is electrically and stably maintained on the surface of the developing roller. Even when used in relation to speed, the image density does not decrease.

As is apparent from the above description, according to the image forming method described later, the surface of the developer carrier is made of a material having both chargeability and photoconductivity, so that the structure of the carrier can be simplified. Thus, the cost can be reduced, and a sufficient amount of toner having a stable charge amount is held on the surface. Then, a rectangular wave pulse electric field applied as a developing bias acts on a sufficient amount of toner having a stable charge amount to give dynamic energy suitable for developing a latent image, so that sharpness of a low potential portion is also improved. Thus, an excellent developed image can be obtained in which the image density of the high potential portion is high and the background is less stained. Further, by making the structure of the developer carrying member in this manner, the photosensitive member and the developer carrying member can be used at a constant speed, so that the developer carrying member can be used without lowering the image density. It is useful for reducing the rotational load and stabilizing the image quality. Since the load on the toner is reduced by these effects, it is possible to obtain the effect of extending the life of the toner.

However, in the developing method in which a large number of minute closed electric fields (microfields) are formed in the vicinity of the surface of the developer carrying member, a conventionally known toner is directly used as in the former method. In this case, it is difficult to always stabilize the toner layer on the developer carrier as two or more layers, and the toner layer becomes thinner, the amount of toner to be developed is reduced, and the density of the image portion is reduced, The toner layer becomes non-uniform and development unevenness occurs, and the density of the image part becomes non-uniform, or the toner on the developer carrier becomes reverse polarity, and the toner adheres to the non-image part and fog occurs. Sometimes. However, when the toner having the specific average particle diameter and the shape coefficient described above is used, a stable multilayer of the toner can be formed on the developer carrying member,
A high-quality image can be obtained with a high image density and no background stains or bleeding of characters.

[0048]

The present invention will be described in more detail with reference to the following examples. Parts represent parts by weight.

Example 1 Binder resin Styrene-acrylic polymer 95 parts Release agent Low molecular weight polypropylene 5 parts Coloring agent carbon black 10 parts Charge control agent Chromium-containing azo dye 4 parts The mixture having the above composition was melt-kneaded and cooled. Thereafter, coarse pulverization was performed using a hammer mill, and then fine pulverization was performed using a fine pulverizer using an air jet method. The obtained finely pulverized product was classified to have an average particle size of 11 μm. 0.15 parts of silica fine powder was added to and mixed with 100 parts of the present particles to obtain a toner of the present invention. The shape factor of the obtained toner was 68%. Next, this toner was loaded into the developing device shown in FIG. 4 equipped with a developing roller as shown in FIG. 5, and the developing roller and the photosensitive member were rotated at a constant speed to perform reversal development. In addition, a clear image free of background stain and fog was obtained. (The charged portion of the photoconductor is -800 V, the exposed portion is -100 V, and the toner is developed in the exposed portion.)

Example 2 Binder Resin Styrene-acrylic polymer 95 parts Release agent Low molecular weight polypropylene 5 parts Coloring agent carbon black 10 parts Charge control agent Nigrosine dye 3 parts The mixture having the above composition was melt-kneaded and cooled. Coarse pulverization was performed using a hammer mill, and then pulverization was performed using a pulverizer using an air jet method. The obtained finely pulverized product was classified to have an average particle size of 9 μm. 0.2 parts of titanium oxide fine powder was added to and mixed with 100 parts of the present particles to obtain a toner of the present invention. The shape factor of the obtained toner was about 65 to 70%. Next,
This toner was loaded into the developing device of FIG. 4 equipped with a developing roller as shown in FIG. 5, and the developing roller and the photoconductor were rotated at a constant speed to perform reversal development. A clear image free of fogging was obtained. (The charged portion of the photoreceptor is -800 V, and the exposed portion is -100.
V, and the toner is developed in the exposed portion. )

[0051]

According to the present invention, the toner of the present invention is charged by charging the surface of a developer carrying member having a chargeable and photoconductive surface and then selectively irradiating the surface with the light. When used in an image forming method for forming a large number of micro-closed electric fields near the surface of the body, stable non-magnetic
It is possible to form a multi-layered one-component developer, and to obtain a high-quality image with a high image density and no generation of background smear, bleeding of characters and the like.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an example of a developing device in which a microfield electric field is formed on a developing roller, centering on a developing roller unit.

FIG. 2 is a schematic cross-sectional view for explaining a state in which a closed electric field is generated by a microfield on a developing roller in the apparatus shown in FIG.

FIGS. 3A to 3C are schematic cross-sectional views showing surface states in a process of manufacturing a developing roller used in a developing device of the type shown in FIG.

FIG. 4 is a schematic cross-sectional view of a developing device including a developer carrier (developing roller) having a chargeable and photoconductive surface, which is useful for implementing the present invention.

FIG. 5 is a schematic cross-sectional view showing a system using a cold-cathode tube light source for erasing a charged charge of the developing roller in a desired pattern.

FIG. 6 is a schematic perspective view showing a system using a semiconductor laser light source for erasing a charged charge of a developing roller in a desired pattern as in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 electrostatic latent image carrier 20 toner transport member 30 toner layer thickness regulating member 40 toner supply member 50 stirring blade 60 toner 70 toner tank 80 developing area 101 developer carrier (developing roller) 102 developing device 103 photosensitive drum 104 toner Layer thickness regulating blade member 105 Toner tank 106 Agitator 107 Toner 108 Toner supply roller 109 Developing bias applying means 110 Charging member 111 Power supply 112 Scraper 113 Light irradiation member 121 Cold cathode tube light source 122 Transparent film 131 Semiconductor laser light source 132 Light beam 133 Collimator lens 134 rotating polygon mirror 135 reflecting mirror

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masami Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company Limited (72) Inventor Koichi Kato 1-3-6 Nakamagome, Ota-ku, Tokyo (56) References JP-A-1-101557 (JP, A) JP-A-53-36245 (JP, A) JP-A-64-15756 (JP, A) (58) Fields investigated Int.Cl. ⁷ , DB name) G03G 9/08 G03G 13/08

Claims (1)

(57) [Claims] 1. A method according to claim 1, further comprising the step of charging the surface of the developer carrying member having a chargeable and photoconductive surface and selectively irradiating the surface with light, thereby providing a large number of minute particles near the surface of the developer carrying member. A closed electric field is formed, and a non-magnetic one-component developer composed of a toner to which an auxiliary agent is externally added as necessary is supplied onto the developer carrier, and the developer is carried by the minute closed electric field. A toner to be carried on a body surface and used for an image forming method for visualizing an electrostatic latent image by the carried developer, wherein the toner contains at least a binder resin and a colorant,
A toner having an average particle diameter of 3 to 20 μm and a shape factor of 40% or more.