JPH0266559A - Image forming method - Google Patents

Abstract

PURPOSE:To improve the particle size distribution and surface characteristics of a magnetic toner by applying impact to particles obtd. from specified materials for a toner to practically sphere the resulting magnetic toner. CONSTITUTION:A resin binder, an electrostatic charge controller, a magnetic body and wax are kneaded and pulverized and/or classified and mechanical energy by impact is repeatedly applied to the resulting particles in a vapor phase to obtain a practically sphered magnetic toner forming a developer. Since the particles receive uniform impact, the particle size distribution of the magnetic toner is made uniform. The surface characteristics of the toner are also made uniform because the wax contained in the particles does not exude.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming method applied to electrophotography, electrostatic recording, electrostatic printing, etc., and particularly relates to an image forming method that uses spherical magnetic toner. The present invention relates to an image forming method.

[Technology background]

Generally, in electrophotography, a latent image carrier (hereinafter also referred to as "photoreceptor") has a photosensitive layer made of a photoconductive material.

), an electrostatic latent image is formed on the surface of the photoreceptor by imagewise exposure, and this electrostatic latent image is developed with a developer to form a toner image. . The obtained toner image is transferred to a transfer material such as paper and then fixed by heating or pressure to form a copy image.

A wet developing method and a dry developing method are known as methods for developing an electrostatic latent image, but the dry developing method is preferred from the viewpoint of high-speed copying.

The developers used in such dry development methods are generally two-component developers consisting of a non-magnetic toner that does not contain a magnetic substance and a magnetic carrier, and a magnetic toner that contains only a magnetic substance. Although so-called one-component developers are known, a one-component developer made of magnetic toner is preferred from the viewpoint of not requiring adjustment of toner concentration and simplifying the configuration of a developing device.

Such magnetic toner is normally transported to the development area while being supported on a developer carrier by magnetic force. However, when the magnetic toner has a so-called amorphous shape, its magnetization has directionality, which causes It becomes difficult to form a developer layer with uniform density and thickness on the developer carrier.

Moreover, if the magnetic toner has an amorphous shape, it has low fluidity, and as a result, the magnetic toner that is replenished from the top of the developing device stays at the top, creating a cavity inside, which is the so-called "kamakura" phenomenon, which reduces the toner's ability to withdraw. Becomes unstable.

Furthermore, if the magnetic toner is amorphous, the area of frictional contact with the surface of the developer transporting carrier will be reduced, resulting in a slow rise in frictional charging, and as a result, the proportion of weakly charged or oppositely polarized magnetic toner will increase. As a result, fog and fringe phenomena occur in the toner image on the photoreceptor, and fine line reproducibility in the fixed image deteriorates. Here, the term "fringe phenomenon" refers to a phenomenon in which toner of opposite polarity mainly adheres to a non-image area near an electrostatic latent image on a photoreceptor.

When such a fringe phenomenon occurs, toner consumption increases, making it difficult to form an economical image.In addition, since toner of opposite polarity tends to remain without being transferred, the burden of cleaning increases, resulting in poor cleaning. is likely to occur. Furthermore, the fine line reproducibility of the obtained image deteriorates.

In order to solve such problems, it is effective to make the magnetic toner spherical.

Conventionally, the following spheroidization techniques have been proposed.

(1) A technique in which the surface of the powder particles obtained through the steps of kneading, crushing, and classification is melted with hot air using a spray dryer to make them spherical (Japanese Patent Laid-Open No. 56-52758,
(See Japanese Unexamined Patent Publication No. 127662/1983).

(2> Technology for manufacturing toner and making it spherical by granulation polymerization method (see JP-A-56-121048).

(3) A technique in which particles obtained through the steps of kneading, pulverization, and classification are dispersed in a hot air stream and their surfaces are melted to make them spherical (see JP-A-58-134650).

(4) Technology for simultaneously pulverizing and spheroidizing the particles obtained by kneading and coarsely pulverizing the particles by controlling the temperature of the inflowing air (see JP-A No. 61-61627 f3@
).

[Problem to be solved by the invention]

However, in the techniques (1), (3), and (4) above, in order to thermally melt the surface of the powder particles to make them spherical, heat is applied evenly to all particles. It cannot be melted, and therefore the shape becomes irregular and the particle size distribution becomes wide, making it difficult to produce a magnetic toner with a desired particle size distribution at a high yield.

In order to improve the fixing properties, it is effective to include wax in the magnetic toner particles, but when the surface of the wax-containing particles is thermally melted to make them spherical, , the wax bleeds onto the surface of the particles and the surface properties tend to change. It is impossible to uniformly apply such a thermal effect to all particles. As a result, triboelectric charging properties become uneven, and the proportion of weakly charged or oppositely polarized magnetic toner increases.As a result, fringes occur, the cleaning burden increases, cleaning defects are more likely to occur, and from an image quality perspective, There is a problem that image density decreases and fine line reproducibility decreases.

In the technique of 2) above, since the granulation polymerization method is adopted, the range of resins that can be selected as the binder resin is narrow, which is disadvantageous, and it is also difficult to uniformly disperse and contain magnetic fine particles in the resin particles. As a result, the magnetic properties of the magnetic toner obtained are uneven, resulting in toner scattering and
There are problems in that various problems such as uneven development occur.

On the other hand, there are two developing methods: a contact developing method in which the electrostatic latent image is developed by bringing the developer layer into direct contact with the photoconductor, and a contact development method in which the developer layer is conveyed to the developing area without contacting the photoconductor. A non-contact developing method is known in which an electrostatic latent image is developed by causing developer particles to fly in a developing area under the action of an alternating current bias electric field.

However, in the contact development method, when development is performed by bringing a magnetic toner containing a magnetic material into direct contact with a photoreceptor,
When a photoreceptor is subjected to a large abrasion force, particularly when the photoreceptor is an organic photoreceptor, there is a problem in that the surface of the photoreceptor is damaged early.

The present invention has been made based on the above-mentioned circumstances, and its purpose is to suppress the occurrence of fringing, provide a high transfer rate, sufficient image density, and excellent fine line reproducibility. An object of the present invention is to provide an image forming method capable of forming an image without causing early damage to a photoreceptor.

[Means to solve the problem]

In order to achieve the above object, the present invention transports a thin developer layer formed on a developer transport carrier to a developing area without contacting the latent image carrier, and generates an oscillating electric field in the developing area. In an image forming method including a developing step of developing an electrostatic latent image on a latent image carrier by causing developer particles to fly due to action, the toner constituting the developer contains a binder resin, a charge control agent, and a magnetic material. and wax, kneading process,
The magnetic toner is characterized in that it is made into particles through a pulverization process and/or a classification process, and is made substantially spherical by repeatedly applying mechanical energy by impact force to the particles in a gas phase.

Preferably, the developer transport carrier includes a rotating developing sleeve and a magnet fixedly disposed inside the developing sleeve.

Further, it is preferable that the latent image carrier is made of an organic photoreceptor.

[Effect]

Since magnetic toner is made into spherical particles by repeatedly applying mechanical energy through impact force to the particles by wiping them into a gas phase, the ml force applied to each particle is made uniform, and the particle size distribution of the magnetic toner is Furthermore, the wax contained in the particles does not ooze out, and the magnetic toner has uniform surface characteristics.

Since the magnetic toner is thus spherical and has a uniform particle size distribution and surface characteristics, it is possible for the magnetic toner to come into frictional contact with, for example, the surface of the developer transport carrier, the inner wall of the developer, the developer stirring member, etc. As a result, the magnetic toner is triboelectrically charged with one polarity specified by the charge control agent and with a charge amount within an appropriate range. Therefore, the ratio of the weakly charged magnetic toner to the magnetic toner of opposite polarity is significantly reduced.

In addition, spheroidization improves the fluidity of the magnetic toner, making it possible to form a thin developer layer with a uniform thickness on the developer transport carrier, and spheroidization eliminates the directionality of the magnetization of the magnetic toner particles. , a thin developer layer supported by magnetic force on the developer transport carrier is stably transported to the development area.

Therefore, when an electrostatic latent image is developed by wiping the developing area and causing magnetic toner to fly under the action of an oscillating electric field, a toner image with sufficient density and excellent fine line reproducibility is formed without causing the fringe phenomenon. .

Since the triboelectric charging properties of magnetic toner are stable, the magnetic toner particles constituting the toner image retain sufficient electric charge. Therefore, in the transfer process, the toner image is highly transferred by electrostatic transfer means. transferred to the transfer material at a certain rate.

As a result, the density and fine line reproducibility of the fixed image are sufficient, the amount of magnetic toner consumed is reduced, and the burden of cleaning is also reduced. Damage to the surface can be prevented.

Furthermore, during development, the thin developer layer is transported to the development area without coming into direct contact with the surface of the latent image carrier, which greatly reduces the abrasion force that the latent image carrier receives. This effectively prevents early damage to the latent image carrier. Therefore, it is possible to stably form images many times using an organic photoreceptor whose surface is particularly susceptible to damage.

In addition, since the triboelectricity of magnetic toner is stable, a simple developer transport carrier consisting of a rotating developing sleeve and a magnet fixedly placed inside the developing sleeve can be used to create a thin layer. The developer layer can be stably transported to the development area.

Furthermore, since an oscillating electric field is formed in the development area during development, the image quality of line drawings is improved.

[Specific structure of the invention]

The present invention will be explained in detail below.

In the image forming method of the present invention, a developer made of a specific toner is used. That is, the toner constituting the developer is made into particles by a binder resin, a charge control agent, a magnetic material, and a wax through a kneading process, a crushing process, and/or a classification process, and the particles are subjected to an impact force in a gas phase. This is a magnetic toner that has been made into a spherical shape by repeatedly applying mechanical energy.

In this spheroidization process, the mechanical energy applied to the particles is, for example, about 115 to 1/10 of the mechanical energy normally required during pulverization. Specifically, although it varies depending on the characteristics of the binder resin and cannot be specified unconditionally, in the example, 1.59 Xl0-3 to 9 per particle.
．． 56 Xl0-'erg, preferably 1.2 [lX
Mechanical energy of 10-' to 1.60×10-'erg may be applied.

The average particle size of the magnetic toner is preferably 5 to 20 microns. According to the magnetic toner having such an average particle size,
Images with high resolution can be formed.

It is preferable that the particle size distribution of the magnetic toner is narrow, and specifically, it is preferable that 95% by weight or more of the magnetic toner particles are in a range of 0.5 to 2.0 times the average particle size of the magnetic toner.

The average particle size and particle size distribution of the magnetic toner were measured using a "Coulter Counter" (manufactured by Coulter Co., Ltd.), and the average particle size means that the cumulative weight is 50% by weight.
This refers to the particle size when

The binder resin constituting the magnetic toner is not particularly limited, and conventionally known resins can be used. Specifically, for example, styrene resin, styrene-acrylic resin, styrene-butadiene resin, polyester resin,
Epoxy resin, polyamide resin, polyurethane resin, etc. can be used.

The magnetic material constituting the magnetic toner includes materials that are strongly magnetized in the direction of magnetic fields, such as iron, ferrite, magnetite, and other ferromagnetic metals such as iron, nickel, and cobalt, or alloys containing these metals. Compounds, alloys that do not contain ferromagnetic elements but become ferromagnetic through appropriate heat treatment, such as alloys called Heusler alloys such as manganese-copper-aluminum or manganese-copper-aluminum, or chromium dioxide, etc. can be mentioned.

The magnetic material is preferably uniformly dispersed and contained in the binder resin in order to obtain uniform magnetic properties, and from this point of view, the average particle size is preferably 50 to 200 hII. Further, the content ratio of the magnetic material is 15 to 15% of the magnetic toner.
65% double soaking is preferred.

Various pigments or dyes can be used as the charge control agent contained in the magnetic toner. Specifically, nigrosine-based, azo-based, quaternary ammonium salt-based, thiourea-based pigments or dyes can be used. These charge control agents may be used in combination. The content ratio of the charge control agent is, for example, about 0.5 to 10 parts by weight, based on a total of 100 parts by weight of the binder resin and the magnetic material.

Examples of the waxes contained in the magnetic toner include polyolefins, fatty acid metal salts, fatty acid esters, partially saponified fatty acid esters, higher fatty acids, higher alcohols, liquid or solid paraffin waxes, amide waxes,
Polyhydric alcohol esters, silicone esters, aliphatic fluorocarbons, and the like can be used. In order to efficiently spheroidize the mother particles without crushing them using mechanical impact force, i
The wax contained as a toner component is preferably a polyolefin such as polyethylene or polypropylene, and one having a Rockwell hardness of R30 to R120, particularly preferably R80 to R120, as measured by JIS K7202. These waxes may be used in combination. The content ratio of wax is 1 in total of binder resin and magnetic material.
For example, it is ~ parts by weight per 00 parts by weight.

In magnetic toners, the magnetic material usually also functions as a black colorant, but if a chromatic toner is to be obtained, other colorants may be included. Such colorants include, for example, carbon black, phthalocyanine blue, benzidine yellow, nigrosine dye, aniline blue, calco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, malachite green offsalate, lamp. Dyes and pigments such as black and rose bengal can be used. These substances may be used alone or in combination.

The magnetic toner used in the present invention may further contain inorganic fine particles in order to improve fluidity. Examples of such inorganic fine particles include silica, alumina, titania, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, silica sand, sauce, mica, wollastonite, diatomaceous earth, chromium oxide, Examples include fine particles of cerium oxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, and the like.

Among these, silica is particularly preferred. As this silica, generally known colloidal silica can be used, and silica that has been hydrophobized is particularly preferred. Commercial products of colloidal silica fine particles include, for example, "Aerosil 200", "Aerosil 300", [Aerosil 13
0J (The above examples include Nippon Aerosil Co., Ltd.).In addition, examples of hydrophobically treated products include [Aerosil R-972J, "Aerosil R-812
J, “Aerosil R-805J, etc.

The average particle size of the primary particles of these inorganic fine particles is, for example, 5
A value of about 11μ to 2μ is preferable. Further, the addition ratio of the inorganic fine particles is, for example, 0. It is preferably about 5% by weight.

The magnetic toner used in the present invention may further contain a lubricant for the purpose of improving cleaning properties. Examples of such lubricants include zinc stearate, lithium stearate, stearic acid, IJ chromium stearate, and others. The addition ratio of these lubricants is, for example, 0.01 to 1% by weight of the magnetic toner.
degree is preferred.

Next, a method for manufacturing magnetic toner will be explained.

First, binder resin, magnetic material, charge control agent, wax, and other additives used as necessary are prepared.
The mixture is premixed and then kneaded while being melted using, for example, an extruder. Thereafter, it is cooled, then coarsely ground using, for example, a hammer mill or Willey type grinder, and further finely ground using, for example, a jet mill, and then classified to obtain particles of a desired particle size.

Next, by repeatedly applying mechanical energy through impact force to the particles in the gas phase using a surface treatment device that is an improved version of an impact crusher, the particles are essentially spheroidized and magnetically Get toner. Further, if necessary, external additives such as inorganic fine particles and lubricants are further added and mixed to obtain a magnetic toner with improved characteristics.

FIG. 1 is an explanatory diagram showing another example of the surface treatment apparatus,
In the figure, 31 is a powder official valve, 32 is a powder official chute, 33 is a circulation circuit, 34 is a casing, 35 is a rotary disk, 36 is a blade, 37 is a stator, 38 is a cooling or heating jacket, 39 is powder discharge chute, 4
0 is a powder discharge valve. Note that the arrow represents the locus of the powder.

When the rotary disk 35 having the blades 36 is rotated at high speed,
The centrifugal force acts on the internal air by the blades 36, so that the outside of the rotary disk 35 is pressurized, and the center of the rotary disk 35 is under negative pressure.

Since the outside and center of the rotary disk 35 are connected by the circulation circuit 33, the pressurized air outside the rotary disk 35 moves to the center of the rotary disk 35 via the circulation circuit 63. A reflux of air is formed.

Of air like this? In the state in which Ti reflux is formed, the powder input unit 3 provided in the middle of the circulation circuit 33
When particles are introduced from step 2, the particles are circulated through the circulation circuit 33 along with the circulation flow, and during this circulation process, the particles collide with the blade 36 and receive an impact force, which causes the particles to becomes spherical. After performing this circulation process for a certain period of time, the powder discharge valve 40 is opened to discharge the processed particles by centrifugal force, thereby obtaining spherical particles.

In such a circulation process, the circulation circuit 33 and the powder input chute 39 may be cooled or heated by the jacket 38 provided on the stator 67 side in order to control the temperature inside the apparatus.

Next, the photoreceptor will be explained.

Conventionally, known photoreceptors include selenium photoreceptors, zinc oxide photoreceptors, cadmium sulfide photoreceptors, organic photoreceptors, amorphous silicon photoreceptors, etc. Among these, organic photoreceptors include: Compared to selenium photoreceptors, oxidized Ng photoreceptors, cadmium sulfide photoreceptors, amorphous silicon photoreceptors, etc., it exhibits particularly excellent functions in terms of sensitivity, heat resistance, resolution, durability, etc.

However, organic photoreceptors have a relatively soft surface and are easily damaged. Early damage to the body occurs.

However, since the present invention uses a non-contact development method,
The surface of the photoreceptor is not excessively rubbed by the magnetic toner. Therefore, in the present invention, organic photoreceptors can be preferably used.

An organic photoreceptor is constructed by laminating an organic photosensitive layer containing an organic photoconductive substance dispersed in a binder resin, for example, on a conductive support made of aluminum, stainless steel, or the like.

As an organic, phosphorescent layer, especially from the viewpoint of increasing durability,
For example, a carrier-generating substance that absorbs image exposure light and generates a charged ↓ I37, such as an anthanthrone type compound, perylene type TL, bisazo type compound, phthalonanine type compound, etc., can be used, for example, a styrene-methyl methacrylate copolymer, A carrier generation layer configured by dispersing and containing a carrier generation layer in a binder resin such as a polycarbonate resin or a silicone resin, and an oxadiazole derivative, for example) IJ 71
J + A carrier transport substance that transports carriers generated in the carrier generation layer, such as a ruamine transparent conductor, a polyarylalkane derivative, a hydrazone derivative, a stilbene derivative, or a styryl triarylamine transparent conductor, is dispersed and contained in the same binder resin as above. It is preferable to use a functionally separated type photosensitive layer formed by combining the photosensitive layer with a carrier transport layer having the following structure.

Next, the key steps of the image forming method of the present invention will be specifically explained.

(Developing Step) A thin developer layer is formed on a developer transport carrier using a one-component developer made of a specific magnetic toner as described above.

The width of this thin developer layer is the minimum gap Ds in the development area.
It is necessary that it be smaller than d. Then, this thin developer layer is transported to a developing area without contacting the photoreceptor, and in the developing area, developer particles, that is, magnetic toner particles, are caused to fly by the action of an oscillating electric field, and are caused to fly onto the photoreceptor. Develop the electrostatic latent image. The oscillating U electric field can be formed by applying an alternating current bias voltage or an alternating current and direct current bias voltage to the developing sleeve. The minimum gap Dscl in the development area is preferably about 50 to 5 DOux.

The developer transport carrier for transporting the thin developer layer to the development area is not particularly limited, but for example, one having the same structure as the conventional one to which a bias voltage can be applied can be used. In particular, a structure in which a magnet having a plurality of magnetic keys is fixedly disposed within a rotating cylindrical developing sleeve is preferable because of its simple structure.

The means for forming a thin developer layer is not particularly limited, but for example, a means for forming a thin developer layer by using a regulation blade whose tip is placed close to the surface of the developer transport carrier, such as an elastic The developer layer is formed by placing a plate-shaped thin layer forming member having an elastic pressure on the surface of the developer transporting carrier, and passing the developer between the thin layer forming member and the developer transporting carrier. A method of forming a thin layer can be used. When a thin layer forming member is used, it is preferably an elastic plate that is pressed against the developer transport carrier such that its tip faces upstream in the rotational direction of the developer transport carrier.

By making the developer layer thin, the minimum gap Dsd in the development area can be made sufficiently small, and a sufficient bias effect can be exerted even with a very small bias voltage. Therefore, toner scattering, bias voltage leakage, etc. can be effectively prevented. Also, the minimum gap Ds
By decreasing d, the electric field strength formed in the development area increases, and furthermore, the contrast of the electrostatic latent image increases, so that the resolution and fine line reproducibility are generally improved.

However, if the developer layer conveyed to the development area is thin, the amount of toner conveyed generally decreases, leading to a risk of insufficient image density. For this reason, conventionally, the insufficient amount of toner to be conveyed has been compensated for by rotating a magnet disposed within the developing sleeve. This is because conventional magnetic toner has unstable triboelectric charging properties, so there is a considerable amount of weakly charged or oppositely polarized magnetic toner in the magnetic toner that makes up the thin developer layer. This is because the proportion of magnetic toner used for development is low.

In contrast, in the present invention, the magnetic toner is spherical and has high fluidity, and has a narrow particle size distribution and uniform triboelectric charging properties. Most of them are in a state where they can be sufficiently developed under the action of an alternating current bias electric field. Therefore, even when the magnet disposed inside the developing sleeve is fixed, a sufficient amount of toner can be transported to the developing area. Therefore, it is possible to simplify the configuration of the device.

(Transfer step) The toner image formed on the photoreceptor by development is transferred to a transfer material such as paper.

In this transfer step, an electrostatic transfer method can be preferably used. Specifically, for example, a transfer device that generates a DC corona discharge is placed so as to face the latent image carrier through the transfer material, and the DC corona discharge is applied to the transfer material from the back side of the photoreceptor. The toner carried on the surface is transferred to the surface of the transfer material.

In this transfer step, since most of the magnetic toner particles constituting the toner image on the photoreceptor have sufficient triboelectric charge, it is possible to transfer the toner image at a high transfer rate using an electrostatic transfer method.

(Cleaning Step) The cleaning means is not particularly limited, but for example, a cleaning blade placed in contact with the surface of the photoreceptor can be preferably used. According to this cleaning blade, magnetic toner remaining on the surface of the photoreceptor without being transferred is scraped off. In addition, in the present invention, since the transfer rate of the toner image in the transfer step is high, the burden of cleaning is considerably reduced.

Note that, in the first stage of the cleaning process, it is preferable to add a static elimination process for eliminating static electricity from the surface of the photoreceptor in order to facilitate cleaning. This static elimination step can be performed, for example, using a static eliminator that generates AC corona discharge.

(Fixing process) The transfer material onto which the toner image has been transferred in the transfer process is subjected to a fixing process using a heat fixing device, a pressure fixing device, etc.
A fixed image is thereby formed.

FIG. 2 is an explanatory diagram showing an example of an image forming apparatus that can be used to implement the present invention. In the figure, 50 is a photoreceptor, 51 is a charger, 52 is an exposure optical system, 53 is a developer, 54 is a static elimination lamp, 55 is a transfer electrode, 56 is a separation electrode, 57 is a static elimination electrode, and 58 is a cleaning device. , 59 is a cleaning blade, 60 is a fixing device, and 61 is a document table. This apparatus is of a type in which an exposure optical system 52 is fixedly arranged and a document table 61 is moved.

The surface of the photoreceptor 50 is uniformly charged by the charger 51,
The surface of the charged photoreceptor 50 is imagewise exposed by the exposure optical system 52, and an electrostatic latent image corresponding to the original is formed on the photoreceptor 50. This electrostatic latent image is developed by a developing device 53 to form a toner image.

After the toner image thus obtained is neutralized by the static eliminating lamp 54 and is in a state where it is easily transferred, the toner image is transferred to the transfer electrode 5.
5, the image is transferred onto the transfer paper P. Transfer paper P is separated electrode 5
6 and is separated from the photoreceptor 50 and subjected to fixing processing in a fixing device 60, thereby forming a fixed image. On the other hand, the photoreceptor 50 is neutralized by the charge eliminating electrode 57, and the residual toner remaining on the photoreceptor 50 without being transferred is scraped off by the cleaning device 58.

Details of the developing device 53 are shown in FIG. In the same ward, 71
is a developing sleeve, and 72 is a magnet, and these developing sleeve 71 and magnet 72 constitute a developer transport carrier. The magnet 72 has a structure in which N poles and S poles are alternately arranged along the circumference, and
The position is fixed relative to 3. 74 is a thin layer forming member, 75 is a first stirring member, 76 is a second stirring member, 77
78 is a toner supply container, 78 is a toner supply roller, 79 is a developer reservoir, 80 is a bias power supply for applying alternating current and direct current bias voltages, and 81 is a developing area. Note that the first stirring member 75 and the second stirring member 76 are
As shown by the arrows, the stirring areas are rotated in opposite directions so that they overlap without colliding with each other.

In this developing device 53, when the magnetic toner in the developer reservoir 79 is stirred by the stirring members 75 and 76, it is triboelectrically charged due to frictional contact with the stirring members 75 and 76, the developing sleeve 71, the inner wall of the developing device 53, etc. be done. The frictionally charged magnetic toner is carried by the magnetic force of a magnet 72 fixed to the surface of the developing sleeve 71 rotating in the direction of the arrow.

The magnetic toner layer supported on the surface of the developing sleeve 71 is
The thin layer is formed by a plate-shaped thin layer forming member 74 made of an elastic body and placed in pressure contact with the surface of the virtual sleeve 71.

This thin layer forming member 74 is fixed at one end by a fixing member and is made of, for example, magnetic or non-magnetic metal, metal compound, plastic, rubber, etc., and is imparted with elasticity.
It is preferable that the thickness is extremely thin, and it is preferable that the thickness is uniform. Specifically, its thickness is 5
A 0-500μ layer is preferred.

The thin layer forming member 74 is elastically pressed against the developing sleeve 71 on one side near its tip, and the developer is allowed to pass little by little between the thin layer forming member 74 and the developing sleeve 71. The amount of developer withdrawn is regulated.

Impurities, aggregates, etc. in the developer are prevented from entering the developing area 81 by the thin layer forming member 74.
The developer layer transported is thin, and its thickness is uniform and stable. Furthermore, the amount of toner conveyed to the developing area 81 can be sufficiently controlled by changing the pressing force and contact angle of the thin filling member 74 against the developing sleeve 71.

The developer layer formed into a thin layer by the thin layer forming member 74 is conveyed to the developing area 81 by the developing sleeve 71 without contacting the surface of the photoreceptor 5o rotating in the direction of the arrow, and in this developing area 81, Due to the action of the oscillating electric field formed by the bias power source 8°, the magnetic toner flies and adheres to the electrostatic latent image on the photoreceptor 50, and development is performed to form a toner image.

The frequency of the AC bias voltage applied to the developing sleeve 71 to form this oscillating electric field is 0.5 to 3.
kHz, voltage is 0.3 to 1.5 kVp-p (
Peak-to-peak value) is sufficient.

Further, during development, it is preferable to further apply a DC bias voltage from the bias power supply 8o, so that the image quality of the line drawing can be improved.

Note that the thickness of the thin developer layer formed on the developing sleeve 71 is determined by using, for example, a "Nikon Profile Projector" (manufactured by Nippon Kogaku Co., Ltd.).
The thickness of the developer layer can be determined by comparing the positions of the projected image onto the screen and the projected image onto the screen with a thin developer layer formed on the developing sleeve 71.

The cleaning device 58 includes a cleaning blade 59. The cleaning blade 59 is made of an elastic material such as hard urethane rubber with a thickness of 1 to 3 mm, and is width of the photoreceptor 50 (in the direction perpendicular to the plane of the paper in FIG. 2).
blade holder (not shown)
is held so as to be switchable between a pressure contact position and a pressure release position.

〔Example〕

Examples of the present invention will be specifically described below, but the present invention is not limited to these Examples.

(Making a magnetic toner!!) (1) Magnetic toner Tl (for the present invention) - Styrene/methyl methacrylate/butyl acrylate copolymer resin (composition ratio = 75: 10: 15 glass transition point Tg = 59°C) 50 parts Part 1: Magnetic material (BL
50 parts by weight of charge control agent (Bontron E-82. manufactured by Orient Chemical Industry Co., Ltd., negatively chargeable) 1 part by weight of wax (
Polypropylene with Rockwell hardness R110
The materials having triple bond parts or more were premixed using a V-type blender, and then kneaded at 120°C using an extruder. After kneading, the mixture was cooled, coarsely pulverized, finely pulverized using a jet mill, and classified using a zigzag classifier to obtain amorphous particles A having an average particle size I)so of 11.5 μm.

Next, the irregularly shaped particles were transferred to the impact-type surface modification device shown in Fig. 1, and in the gas phase, the impact blades were rotated at 8000 rpm for 3 minutes to form spherical particles without heating. The spherical particles B were obtained by the spherical treatment.

The average particle size of the spherical particles B is. is 11.3μ
It was trash.

In addition to these spherical particles, hydrophobic silica fine particles (R-
972, manufactured by Nippon Aerosil Co., Ltd.) and zinc stearate were added and mixed from the outside in a ratio of 0.4% by weight and 0.4% by weight to obtain magnetic toner T1.

The static bulk density of this magnetic toner T1 is 0.82 g/cm3
Met.

(2) Magnetic toner tl (for comparison) In the production of magnetic toner T1, the amorphous particles A were not subjected to spheroidization treatment, and hydrophobic silica fine particles and zinc stearate were added to the particles A as in the case of magnetic toner T1. were added and mixed to obtain a comparative magnetic toner t1. The static bulk density of this magnetic toner t1 was 0.57 g/cm3.

(3) Magnetic toner t2 (for comparison) In the production of magnetic toner Tl, irregularly shaped particles are melted with hot air using a spray dryer to make them spherical.
Particles C were obtained through the classification process again.

The average particle size of this particle C is. was 11.4μ debris.

Hydrophobic warp fine particles and zinc stearate were added to and mixed with the spherical particles C to obtain a comparative magnetic toner t2 in the same manner as in the case of the magnetic toner T1. The static bulk density of this magnetic toner t2 was 0.80 g/cm'.

Actual photocopying test 1 (Non-contact developing method) An electrophotographic copying machine 1''U-Bix 1200J (:l= A live photo test was conducted to form a copy image using a modified machine (manufactured by Ka@), and the following items were evaluated.

The organic photoreceptor has a negatively charged two-layer organic photosensitive layer composed of an anthanthrone pigment as a carrier-generating substance and a styryl-triphenylamine derivative as a carrier-transporting substance, in the form of a rotating drum. It is constructed by laminating on a conductive support made of aluminum.

Further, in the above-mentioned modified machine, the main developing conditions are as follows.

・Minimum gap Dsd in the developing area: 0.3Qmm ・Developer layer thickness regulating member: An elastic plate made of a urethane rubber plate lined with a phosphor bronze plate, one side of which is placed in pressure contact with the developing sleeve ・A photosensitive member Surface potential Vs (exposed area) knee 50V, AC bias voltage VAC: 1 kHz, 0.5 kVp-
p・DC bias voltage Voc: 450V・Magnet: Fixed・Peripheral speed of developing sleeve: 220mm/S・Transfer device: Electrostatic transfer device (evaluation) (1) Image density A solid black copy image is formed and this The density of the copied image was visually determined. In the table, "○" indicates that the density is sufficient, "△" indicates that the density is slightly insufficient but can withstand practical use, and "X" indicates that the density is significantly insufficient.

(2) Fringe phenomenon This was determined by visually observing the toner image on the photoreceptor before being transferred after development. In the table, "○" indicates that the fringe phenomenon hardly occurred, "Δ" indicates that the fringe phenomenon occurred slightly, and "x" indicates that the fringe phenomenon occurred significantly.

(3) Stability of Image Quality Copied images were visually observed to check for image defects due to damage to the surface of the photoreceptor.

(4) Fine line reproducibility The fixed image was determined visually. In the table, "○" indicates that the fine line reproducibility is sufficient, "To the mouth" indicates that skipped letters occur and is slightly inferior, and "x" indicates that skipped letters and blurring are significant.

The above results are shown in Table 1 below.

Live-action test 2 (Contact development method; for comparison) For comparison,
A photo test was conducted in which a copy image was formed in the same manner as in the photo test 1, except that the developing conditions were changed to a contact development method, and evaluation was made.

The changes in the development conditions are as follows.

- Minimum gap Dsd in developing area: 0.15 mm - Direct current bias voltage Voc: 350 V or more The results are shown in Table 2 below.

As can be understood from the results in Tables 1 and 2, according to the image forming method of the present invention, the occurrence of fringing is suppressed, the transfer rate is high, the image density is sufficient, and fine line reproducibility is reduced. Furthermore, image defects due to damage to the surface of the photoreceptor do not occur.

On the other hand, even if a non-contact development method is applied, the image density is slightly insufficient when using the comparative magnetic toner t1, and the fringe phenomenon occurs when using the comparative magnetic toner t2. This occurs significantly, and the image density is significantly insufficient.

On the other hand, a comparative image forming method using a contact development method (
According to the actual photographic test 2), even when the magnetic toner T1 of the present invention was used, image defects caused by damage to the surface of the photoreceptor occurred early.

〔Effect of the invention〕

As explained in detail above, according to the present invention, magnetic toner is obtained by applying TFL force to particles obtained from a specific toner material to make them substantially spherical, so that particle size distribution and surface The properties are uniform, the triboelectricity of the magnetic toner is stabilized, and the proportion of magnetic toner with opposite polarity or weak charge is significantly reduced. Furthermore, since the spherical shape eliminates the directionality of the magnetization of the magnetic toner particles, the thin developer layer supported on the developer transport carrier can be stably transported to the development area.

Therefore, this thin developer layer is conveyed to the development area without contacting the latent image carrier, and in the development area, the developer particles are caused to fly by the action of the oscillating electric field and are placed on the latent image carrier. When an electrostatic latent image is developed, a toner image with sufficient image density can be formed without causing early damage to the surface of the latent image carrier, without causing fringing. In the transfer process, since the magnetic toner particles that make up the toner image have sufficient charge, they are efficiently transferred due to electrostatic attraction, making it possible to form an image with high image density. .

In addition, since the triboelectric charging property of the magnetic toner is stable in this way, a developer transport carrier having a simple structure consisting of a rotating developing sleeve and a magnet fixedly disposed inside the developing sleeve can be used. Accordingly, the thin developer layer can be stably transported to the development area.

Furthermore, by forming an oscillating electric field in the development area, the image quality of line drawings can be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a surface treatment device that can be applied to spheroidizing magnetic toner, FIG. 2 is an explanatory diagram showing an example of an image forming apparatus, and FIG. 3 is an explanatory diagram showing details of a developing device. be. 31...Powder official valve 32...Powder input valve
--To 33...Circulation circuit 34...Casing 35...Rotary disk 36...Blade 37...Stator 38...Jacket 3
9...Powder discharge chute 40...Powder discharge valve 50.
... Photoreceptor 51 ... Charger 52 ... Exposure optical system 53 ... Developing device 54 ... Static elimination lamp 55 ... Transfer electrode 56 ... Separation electrode
57... Static elimination electrode 60... Fixing device
61... Document table 58... Cleaning device 59... Cleaning blade 71... Developing sleeve 72... Magnet 7
4... Thin layer forming member 75. 76... Stirring member 77... Toner supply container 78... Toner supply roller 79... Developer reservoir 80... Bias power supply 81... Development area 10 Illustrated spear + diagram

Claims (3)

[Claims] (1) A thin developer layer formed on a developer transport carrier is transported to a development area without contacting the latent image carrier, and developer particles are caused to fly in the development area by the action of an oscillating electric field. In the image forming method, the toner constituting the developer is mixed with a binder resin, a charge control agent, a magnetic substance, and a wax through a kneading process and a pulverization process. Image formation characterized in that the magnetic toner is formed into particles through a process and/or a classification process, and is made into substantially spherical magnetic toner by repeatedly applying mechanical energy by impact force to the particles in a gas phase. Method. (2) a developing sleeve in which the developer transport carrier is rotated;
The image forming method according to claim 1, further comprising a magnet fixedly disposed inside the developing sleeve. (3) The image forming method according to claim 1 or 2, wherein the latent image carrier is an organic photoreceptor.