JPH0364063B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an image forming method that includes a step of developing a latent image formed in electrophotography, electrostatic recording, electrostatic printing, etc. using a two-component developer. . [Prior Art] Currently, in order to form a visible image from certain image information, methods using electrostatic latent images or magnetic latent images, such as electrophotography, are widely used. For example, according to an example of electrophotography, an electrostatic latent image formed on a latent image carrier made of a photoconductive photoreceptor by a charging process and an exposure process is used as a developer made of electrodetectable colored particles called a toner. The toner image is usually transferred and fixed onto a transfer material to obtain a visible image. The developer used to develop such an electrostatic latent image or a magnetic latent image includes a so-called two-component developer consisting of a mixture of toner and a carrier, and a carrier consisting of a magnetic toner containing a magnetic substance. There is a so-called one-component developer that is used alone, but in a system that uses a two-component developer, the toner is triboelectrified by mechanically stirring the toner and carrier, so the carrier is By selecting characteristics, stirring conditions, etc., it is possible to control the charge polarity and charge amount of the toner to a considerable extent, and in this respect it is superior to two-component developers. Development methods using such a two-component developer include a magnetic brush method and a cascade method, among which the magnetic brush method is preferably used.
This magnetic brush method involves forming a developer layer consisting of spikes that stand up like a brush by magnetic force on a developer transporting carrier, and then rubbing this developer layer on the surface of the latent image carrier to remove the latent image toner. This is a method in which particles are attached and development is performed. Conventionally, the two-component developer used in such a magnetic brush method is generally composed of toner particles with an average particle size of about 10-odd μm and magnetic carrier particles with an average particle size of about 70 to 200 μm. It is. In such a two-component developer, only the toner is consumed as development progresses, so there is a problem that the toner concentration in the developer changes and the image quality deteriorates. It is necessary to replenish toner and control the toner concentration so that it is within a certain allowable range. However, in the above-mentioned two-component developer containing a carrier with a larger diameter than the toner, the allowable range of toner concentration is narrow and extremely sophisticated technology is required to control the toner concentration. The problem is that the device for controlling the toner concentration is expensive. Moreover, because the carrier has a large diameter, the bristles of the developer that stand up like a brush inevitably become rough, resulting in uneven latent image development and poor reproducibility, resulting in a high-quality image. There are some problems that are difficult to obtain. For this reason, a small-diameter carrier was developed in which fine magnetic powder was dispersed in a binder resin (Japanese Patent Application Laid-open No. 66134/1983). According to a two-component developer using such a carrier, the surface area of the entire carrier particles is significantly increased compared to the same amount of large-diameter carrier, so there is an increased chance of frictional contact between the toner particles and the carrier particles. Fluctuations in image quality due to changes in toner density are reduced, and the allowable range of toner density is correspondingly widened, making it easier to control toner density. Moreover, as the carrier particles become smaller in diameter, the spikes of developer that stand up like brushes become denser, making it difficult to form sharp images with no unevenness and excellent fine line reproducibility. There is a possibility that it can be done. However, a small diameter carrier made by dispersing fine magnetic powder in a binder resin as described above,
It has a particle size that is not much different from that of toner and is easily scattered, and since it is not possible to contain a large amount of magnetic material in carrier particles, it is difficult to make the particles have large magnetic properties. Therefore, the holding force exerted by the magnetic sleeve for conveying the developer is small, and as a result, a considerable amount of carrier particles adhere to the latent image carrier together with toner particles during development. Problems arise, and in the end, it is not possible to fully obtain the benefits of reducing the diameter of the carrier. [Object of the Invention] The present invention has been made based on the above-mentioned circumstances, and its object is to use a two-component developer containing a small-diameter carrier to produce high density and clear images without fogging. An object of the present invention is to provide an image forming method that can stably form images for a long period of time. [Structure of the Invention] The above object is to form a developer layer of a two-component developer consisting of toner and carrier on a developer transport carrier, and to supply this developer layer to a development space where an oscillating electric field is generated. The image forming method includes a developing step of developing a latent image on a latent image carrier without the surface of a developer layer contacting the surface of the latent image carrier, wherein the carrier is The two-component developer is made by dispersing fine magnetic powder in a binder resin in a proportion of 55 to 80% by weight.The average particle diameter of the toner is r ₁ μm, and the average particle diameter of the carrier is r r ₂ μm, the true specific gravity of the toner is ρ ₁ , the true specific gravity of the carrier is ρ ₂ , and the content ratio of the toner to the carrier is
This is achieved by an image forming method characterized in that Tc (weight %) is within the range expressed by the following formula. 80 (r ₁ / r ₂ ) (ρ ₁ / ρ ₂ ) ≦T _C ≦140 (r ₁ / r ₂ ) (ρ ₁
/ρ ₂ ) However, 10≦r ₂ ≦50, 0.3≦r ₁ /r ₂ ≦0.6. The present invention will be explained in detail below. In the present invention, a developer transport carrier is disposed opposite to a latent image carrier carrying a latent image with a certain space in which development is performed, that is, a development space, and within this developer transport carrier, for example, developer is held. By the magnetic force of this magnet, a developer layer consisting of spikes of two-component developer containing a specific carrier, the details of which will be described later, is made to stand up like a brush on the surface of the developer transport carrier. The developer layer is formed in a state in which it is not in contact with the latent image carrier, that is, the height of the developer spike is smaller than the shortest distance between the latent image carrier and the developer transport carrier in the development space. On the other hand, an oscillating electric field is applied to the developing space, and the particles forming the ears of the developer are dispersed by vibration to form a gap between the latent image carrier and the developer transport carrier. This causes toner particles to adhere to the latent image carried on the latent image carrier, thereby performing development and forming a toner image. Next, the toner image is transferred to a transfer material such as paper, and the transferred image is fixed in a fixing device by a contact heating fixing method using a heating roller, for example.
This forms a visible image. Next, the two-component developer used in the method of the present invention will be explained. In the two-component developer used in the method of the present invention, the toner concentration T _C , that is, the content ratio (weight %) of the toner to the carrier, is larger than the average particle size of the toner.
If r ₁ μm, the average particle diameter of the carrier is r ₂ μm, the true specific gravity of the toner is ρ ₁ and the true specific gravity of the carrier is ρ ₂ , it is characterized in that it falls within the range expressed by the following formula (1). . 80 (r ₁ / r ₂ ) (ρ ₁ / ρ ₂ ) ≦T _C ≦140 (r ₁ / r ₂ ) (ρ ₁
/ρ ₂ )...(1) However, 10≦r ₂ ≦50, 0.3≦r ₁ /r ₂ ≦0.6. The above formula (1) was derived from research from the viewpoint that the surface area ratio between the toner and the carrier is an important factor in obtaining an appropriate charging state through contact between the carrier and the toner. In other words, although the details are omitted, formula (1) specifically indicates that 1/3 to 1/4 of the surface area of the carrier particles is occupied by the toner adhering to the surface of the carrier. It has been experimentally confirmed that under such conditions, frictional charging between the toner and the carrier can be performed well, and this finding was made based on this finding. The carrier is formed by dispersing fine magnetic powder in a binder resin, and the content ratio of the fine magnetic powder to the carrier is 55 to 80.
% by weight, and consists of particulate powder with an average particle size of 10 to 50 μm, preferably 15 to 40 μm. Various binder resins can be used to constitute the carrier, including styrenes such as styrene, parachlorostyrene, and α-methylstyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, α-methylene resin group monocarboxylic acid esters such as 2-ethylhexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylxyl methacrylate, and phenyl methacrylate; acrylonitrile, methacrylate Vinyl nitriles such as nitrile;
Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; 2-vinylpyridine,
Pinylpyridines such as 4-vinylpyridine; N-
N-vinyl cyclic compounds such as vinylpyrrolidone;
Contains monomers such as vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and methyl isopropenyl ketone; unsaturated hydrocarbons such as propylene, ethylene, isoprene, and butadiene; and halogenated unsaturated hydrocarbons such as chloroprene. Polymers, copolymers of two or more of these monomers, mixtures thereof, non-vinyl condensation resins such as rosin-modified phenol-formalin resins, oil-modified epoxy resins, polyester resins, polyurethane resins, polyimide resins, etc. Examples include mixtures of the vinyl resin and the above-mentioned vinyl resin. The magnetic material used for the magnetic fine powder constituting the carrier includes ferrite, magnetite, iron, cobalt, nickel, and other ferromagnetic metals or alloys, compounds containing these elements, or ferromagnetic elements. alloys that do not contain manganese and copper but become ferromagnetic through appropriate heat treatment, such as alloys called Heusler alloys that contain manganese and copper, such as manganese-copper-aluminum, manganese-copper-tin, etc. or chromium dioxide, and others. The average particle size of the magnetic fine powder is preferably about 0.05 to 3 μm. Furthermore, if the magnetic fine powder is exposed in a bare state on the surface of the carrier particles, the triboelectric charging properties of the carrier particles may be adversely affected by the triboelectric charging properties of the magnetic fine powder. It is desirable to coat the surface of the magnetic fine powder with a resin or higher fatty acid before incorporating it into the binder resin. Examples of higher fatty acids that can be used for this purpose include stearic acid, palmitic acid, and oleic acid.
Coating can be easily carried out by immersing fine magnetic powder in a solution dissolved in an organic solvent such as dichloroethane. The carrier is preferably insulating and has a specific resistance of 10 ¹³ Ωcm or more. If the value of this specific resistance is low, when a bias voltage is applied to the developer transport carrier A, charges are injected into the carrier particles, making it easier for the carrier particles to adhere to the image bearing surface, or the bias voltage may break. This results in problems such as the possibility of a breakdown occurring more easily. The specific resistance was determined by placing carrier particles in a container with a cross-sectional area of 0.50 cm ² and tapping them, then applying a load of 1 Kg/cm ² on the packed particles, and applying 100 V/cm 2 between the load and the bottom electrode. This value is obtained by reading the current value when applying a voltage that produces an electric field of cm. The carrier may contain various property improvers as required, and the property improvers include:
Charge control agents, fluidity improvers, and other known agents can be used. As such a charge control agent, for example, fetish-wartz HBN having positive triboelectric charging properties as described in Japanese Patent Publication No. 41-2427.
(Fettschwarz HBN; CI No. 26150), alcohol-soluble Nigrosin (CI No. 50415),
Sudan Chief Shubarts BB (Sudan
tiefchwarz BB; Solvent Black 3; CINo.
26150), Brilliant Spirits Universal TN
(Brillantspritschwarz TN; manufactured by Bahia, Falben, Favriken), Brillantspritschwarz X
(Zaponschwarz
No.14645), Azo Oil Black (R)
-Black (R): National, manufactured by Aniline Co., Ltd.), Spiron Black TRH (manufactured by Hodogaya Chemical Co., Ltd.), Bontron S34 (manufactured by Orient Chemical Co., Ltd.), Nigrosine SO
(manufactured by Orient Chemical Co., Ltd.) and pigments such as phthalocyanine blue.
Furthermore, oxidized carbon black and resins having positive or negative charge control groups can be considered as a type of charge control agent. Furthermore, in order to improve the compatibility of these charge control agents with the resin component, they can be added in the form of salts formed with higher fatty acids, or a compatibility improver can be added separately. Furthermore, examples of the fluidity improver include inorganic powders such as silica and alumina. The carrier can be manufactured as follows. For example, a binder resin, magnetic fine powder, and other property improving agents added as necessary are premixed using a ball mill or the like, and uniformly mixed and dispersed. Next, the mixture is kneaded using heated rolls, and then cooled and pulverized. Next, in order to obtain carriers having a desired particle size, the particles are classified as necessary to produce carriers. Further, it is preferable that the carrier has a spherical shape because it can improve fluidity, and as a method for obtaining such a spherical carrier, for example, a pulverized carrier obtained according to the above-mentioned manufacturing method can be used. A suitable method is to further spray the carrier particles into hot air using, for example, a known spray dryer method, thereby instantaneously melting the surface of the carrier particles and making the carrier particles spherical due to surface tension. . Still another method for producing the carrier is a method in which a monomer component of a binder resin is polymerized in the presence of fine magnetic powder to form a polymer, and this method is industrially stable. This is preferable because it is easy to manufacture. Specifically, the following methods can be mentioned, for example. (a) A method in which ordinary bulk polymerization is carried out without a solvent at a temperature of 60 to 120°C under a nitrogen stream. (b) In water at a temperature of 60 to 120°C under a nitrogen stream, for example, gelatin, starch, polyvinyl alcohol, barium sulfate, calcium sulfate, barium carbonate, etc.
A method in which suspension polymerization is carried out by conventional methods in the presence of a dispersant such as magnesium carbonate, calcium phosphate, talc, clay, silicic acid, or metal oxide powder. (c) Using an aqueous polymerization initiator in the presence of a surfactant such as sodium dodecylbenzene sulfonate, an alkyl sulfate type anion emulsifier, or sodium dodecyl sulfonate under a nitrogen stream at a temperature of 40°C.
A method of carrying out emulsion polymerization using a conventional method at ~90°C. (d) A method in which solution polymerization is carried out by a conventional method under a nitrogen stream at a temperature of 60 to 120°C, diluted with an appropriate solvent (for example, benzene, xylene, ethanol, methyl ethyl ketone). The toner that constitutes the two-component developer together with the carrier described above is made by dispersing toner components such as colorants in a binder resin.
Various thermoplastic resins are used as the binder resin here. Specific examples include styrenes such as styrene, parachlorostyrene, and α-methylstyrene; methyl acrylate;
Ethyl acrylate, n-propyl acrylate, lauryl acrylate, 2-ethylxyl acrylate, methyl methacrylate, ethyl methacrylate,
α- such as n-butyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.
Methylene fatty acid monocarboxylic acid esters; Vinyl nitriles such as acrylonitrile and methacrylonitrile; Vinyl pyridines such as 2-vinylpyridine and 4-vinylpyridine; Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; Vinyl methyl ketone, vinyl Vinyl ketones such as ethyl ketone and methyl isopropenyl ketone; unsaturated hydrocarbons such as ethylene, propylene, isoprene, butadiene and their halides; polymers of monomers such as halogenated unsaturated hydrocarbons such as chloroprene; , a copolymer obtained by combining two or more of these monomers, and a mixture thereof, or
Examples include non-vinyl condensation resins such as rosin-modified phenol formalin resin, oil-modified epoxy resin, polyester resin, polyurethane resin, polyimide resin, cellulose resin, and polyether resin, or mixtures of these and the vinyl resins. Examples of colorants include carbon black, nigrosine dye, aniline blue,
Mention may be made of calco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue or mixtures thereof. Toner components other than the colorant include a charge control agent, an anti-offset agent, a fluidity improver and the like, and if necessary, fine magnetic powder may be contained. Such toner can be obtained by a conventionally known toner manufacturing method, and has an average particle size of 25 μm or less,
Particularly preferred is a toner having a diameter of 10 to 16 μm. The two-component developer used in the method of the present invention has been described above.Next, a specific developing process for developing, for example, an electrostatic image using such a developer will be described. The developer transport carrier for supplying the developer to the development space can be the same as the conventional one to which a bias voltage can be applied. A structure in which a rotating magnet body having magnetic poles is provided can be preferably used. In such a developer transport carrier, the developer layer carried on the surface of the sleeve moves in an undulating manner due to the rotation of the rotating magnet, so new developer is supplied one after another. Moreover, even if there is some unevenness in the thickness of the developer layer on the surface of the sleeve, the above-mentioned wave-like undulations sufficiently cover the effect so that it does not become a problem in practice. It is preferable that the developer conveying speed due to the rotation of the rotating magnet or the rotation of the sleeve is almost the same as or faster than the moving speed of the electrostatic image carrier. Further, it is preferable that the rotation of the rotating magnet and the rotation of the sleeve are carried in the same direction. Image reproducibility is better in the same direction than in the opposite direction. However, it is not limited to these. Further, it is preferable that the developer layer supported on the developer transport carrier has a uniform thickness. For example, the developer adhering to the developer transport carrier is sufficiently scraped with a blade that regulates the thickness. It is preferable to drop it to form a uniform layer. The gap between the developer transport carrier and the electrostatic charge image carrier is preferably several tens to 2000 μm, and if the gap between the developer transport carrier and the electrostatic charge image carrier becomes narrower than several tens of μm, it will be uniform in the developing space. It becomes difficult to form the ears of the magnetic brush that acts on the developing space, and it also becomes impossible to supply a sufficient amount of toner particles to the developing space, making it difficult to perform stable development.
When the diameter greatly exceeds 2000 μm, the counter electrode effect decreases, making it impossible to obtain sufficient image density, and the edge effect, in which more toner adheres to the contours than the center of the electrostatic charge image, becomes significant. Become. In addition, the gap and the thickness of the developer layer should be set so that the ears of the magnetic brush do not come into contact with the surface of the electrostatic image carrier and are as close as possible to the surface of the electrostatic image carrier when no oscillating electric field is applied. Particularly preferred. This is because it is possible to prevent scratches and fog from occurring on the toner image due to the rubbing of the magnetic brush. Preferably, the oscillating electric field is created by applying an oscillating bias voltage to the sleeve of the developer transport carrier. Further, as the bias voltage, it is preferable to use a voltage obtained by superimposing a DC voltage, which prevents toner particles from adhering to non-image areas, with an AC voltage, which makes it easier for the toner particles to separate from the carrier particles. However, the present invention is not limited to these methods. An example of a specific apparatus that can be used to carry out the developing step in the method of the present invention is shown in FIG. In FIG. 1, 1 is a drum-shaped electrostatic charge image carrier made of a photoreceptor such as Se, which rotates in the direction of the arrow, and an electrostatic charge image is formed on its surface by a charging exposure device (not shown). . 2 is a sleeve made of non-magnetic material such as aluminum; 3 is a sleeve 2;
The sleeve 2 and the magnet 3 constitute a developer transport carrier. These sleeves 2
and the magnet body 3 are relatively rotatable, and in the illustrated example, the sleeve 2 is rotated in the direction of the arrow, and the magnet body 3
is fixed. The N and S magnetic poles of magnet body 3 are usually
It is magnetized to a magnetic flux density of 500 to 1500 Gauss,
Due to the magnetic force, a layer of developer D consisting of spikes standing up like a brush, ie, a magnetic brush, is formed on the surface of the sleeve 2. 4. A regulating blade made of magnetic or non-magnetic material that regulates the height and amount of the magnetic brush;
A cleaning plate 5 removes the magnetic brush that has passed through the developing space A from above the sleeve 2.
The surface of the sleeve 2 comes into contact with the developer D in the developer reservoir 6, thereby supplying the developer D, and 7 stirs the developer D in the developer reservoir 6 to make the components uniform. This is a stirring screw. Since toner particles of the developer D in the developer reservoir 6 are consumed when development is performed, toner particles T in the toner hopper 8 are replenished as appropriate. Reference numeral 9 denotes a supply roller having a concave portion on its surface that drops the toner particles T into the developer reservoir 6 . A bias power supply 10 applies a bias voltage to the sleeve 2 via a protective resistor 11. A via voltage having an oscillating alternating current component is applied by the bias power supply 10 between the base 1a of the electrostatic image carrier 1 and the sleeve 2, which are grounded. This bias voltage is, for example, a superimposed voltage of a DC voltage and an AC voltage.The DC component prevents fogging, and the AC component vibrates the magnetic brush to improve the developing effect. For this DC voltage component, a voltage of, for example, 50 to 600 V, which is approximately equal to or higher than the potential of the non-image area, is usually used.
For the AC voltage component, a voltage of 100 V to 5 KV is used with a frequency of 100 Hz to 10 kHz, preferably 1 to 5 kHz. Note that when the toner particles contain a magnetic material, the DC voltage component may be lower than the non-image area potential. If the AC voltage component frequency is too low, the effect of imparting vibration will be reduced; if it is too high, the developer will be unable to follow the vibrations of the electric field, resulting in a decrease in image density and the inability to obtain clear, high-quality images. appears. In addition, the voltage of the AC voltage component is also related to the frequency, but the higher the voltage, the more the magnetic brush will vibrate and the more effective it will be, but if it is too high, it will easily cause fogging, and insulation problems such as lightning strikes will occur. This is not preferable since it also tends to cause destruction. In the above-described apparatus, the gap between the sleeve 2 and the electrostatic image carrier 1 is set to be in the range of several tens to 2000 μm, and the electrostatic image on the electrostatic image carrier 1 is developed. As the magnetic flux density on the surface of the sleeve 2 changes as the sleeve 2 rotates, the magnetic brush formed on the surface of the sleeve 2 moves on the sleeve 2 while vibrating, thereby creating an electrostatic charge image. It stably and smoothly passes through the gap between the electrostatic charge image carrier 1 and imparts a uniform developing effect to the surface of the electrostatic image carrier 1, making it possible to stably develop images with high image density. do. Although an example of the apparatus that can be used in the method of the present invention has been described above with reference to FIG. 1, the present invention is not limited thereto. For example, several electrode wires may be stretched around the developing area between the developer transport carrier and the electrostatic image carrier, and an oscillating voltage may be applied to them to vibrate the magnetic brush and produce a developing effect. can be improved. In that case as well, a DC bias voltage may be applied to the developer transport carrier, or oscillating voltages of different frequencies may be applied. Furthermore, the method of the present invention can be similarly applied to reversal development and the like. In that case, the DC voltage component is set to a voltage approximately equal to the receiving potential in the non-image background portion of the electrostatic image carrier. Furthermore, the method of the present invention can be applied even when the image to be developed is a magnetic latent image. [Operations and Effects of the Invention] In the image forming method of the present invention, by applying an oscillating electric field to the development space in the development step, even if a small-diameter carrier is used as the carrier constituting the developer, the carrier's latent image carrier can be It is possible to suppress adhesion to the film and achieve good development.
That is, by applying an oscillating electric field to the developing space, particles constituting the developer fly between the developer layer and the latent image carrier in the state of unit particles as the electric field changes. Therefore, toner particles can be made to selectively adhere to the electrostatic latent image based on strictly defined Coulomb attraction, so that adhesion of carrier particles to the latent image carrier is suppressed. As a result, the effect of making the carrier smaller in diameter is that the allowable range of toner concentration in the two-component developer is wide, making toner replenishment easier, and the brush-like ears in the developer layer have a high density. It is possible to fully exhibit effects such as being able to obtain high-quality images without unevenness. Furthermore, in the image forming method of the present invention, since the developer used has a toner concentration within a specific range defined by the average particle diameter and true specific gravity of the carrier and toner, the toner The frictional contact between the toner and the carrier is maintained in a good condition, and the toner can obtain an appropriate charging state. As a result, as is clear from the examples described below, a clear toner with no fog and a high density can be obtained. Images can be formed. [Embodiments of the Invention] Examples of the present invention will be described below, but the present invention is not limited thereto. In addition, “department”
represents parts by weight. <Manufacture of carrier> 1) Carrier A Styrene-acrylic resin (monomer composition ratio of styrene, butyl methacrylate and methyl methacrylate 500:20:30, softening point 133°C) 40 parts magnetite "BL-100" (Titan Kogyo Co., Ltd.) made)
70 parts Charge control agent "Spiron Black TRH" (manufactured by Hodogaya Chemical Co., Ltd.) 2 parts The above substances were mixed in a ball mill, further kneaded with two rolls, then crushed and classified, with an average particle size of 20.4 μm, A microcarrier with a true specific gravity of 1.92 was obtained. This will be referred to as "Carrier A." 2) Carrier B Change the average particle size of Carrier A from 20.4μm to 40μm.
Carrier was obtained in the same manner as Carrier A, except for the following. This will be referred to as "Carrier B." 3) Carrier C Styrene-acrylic resin (monomer composition ratio of styrene, butyl methacrylate and methyl methacrylate 50:20:30) 25 parts magnetite "EPT-1000" (manufactured by Toda Kogyo Co., Ltd.)
70 parts Charge control agent "Spiron Black TRH" 2 parts Using the above substances, a carrier having an average particle diameter of 24.6 μm and a true specific gravity of 2.02 was obtained in the same manner as in the case of carrier A. This will be referred to as "Carrier C."<Manufacture of toner> 1) Toner a Styrene-acrylic resin (monomers of styrene, butyl acrylate and methyl methacrylate, composition ratio 75:15:10, weight average molecular weight Mw/number average molecular number M _N = 10.1, softening point 128 ℃) 100 parts carbon black "Mogul L" (manufactured by Kayabot Co., Ltd.) 10 parts polypropylene "660P" (manufactured by Sanyo Chemical Co., Ltd.) 3 parts charge control agent "Nigrosine SO" (manufactured by Orient Chemical Co., Ltd.) 2 parts Put the above substances into a ball mill. The mixture was mixed, further kneaded with two rolls, and then crushed and classified to obtain a non-magnetic toner powder having an average particle size of 11.0 μm and a true specific gravity of 1.06. Hydrophobic silica fine powder "R-972" corresponding to 0.2% by weight was added to this toner powder.
(manufactured by Nippon Airosil Co., Ltd.) was added and mixed to prepare a toner. This is referred to as "toner a". 2) Average particle size of toner powder in toner b and toner a
A toner was obtained in the same manner as toner a except that the thickness was changed from 11.0 μm to 16.5 μm. This is referred to as "toner b". Examples 1 and 2 and Comparative Examples 1 and 2 Carrier A and toner a were used, and the toner content ratio (weight %) Tc to the carrier was set to the value shown in Table 1, and two types were used for the examples and two types were used for the comparative examples. A total of four types of developers were prepared. In the developer composed of carrier A and toner a, the content ratio Tc of the toner satisfying the above-mentioned formula (1) ranges from approximately 20 to 42.

[Table] A photographic test was conducted using the apparatus shown in FIG. 1 using each of the above-mentioned developers, and the following evaluation items were examined. The results are shown in Table 1. <Evaluation Items> (1) Fog Fog, that is, occurrence of toner adhesion to background areas other than image areas to which toner should be attached, was visually observed. The evaluation was rated as "○" if there was almost no fogging, "△" if there was some fogging, and "x" if there was significant fogging. (2) Carrier adhesion The carrier adhesion of the transferred image was visually observed. The evaluation was given as "○" if there was almost no carrier adhesion, "△" if there was some carrier adhesion, and "x" if there was significant carrier adhesion. (3) Image defects Image defects were determined by visually observing the transferred images. The evaluation was ``〇'' if the image density was sufficient and practical, ``△'' if the image density was slightly low and an edge effect was observed, and ``x'' if the image density was low and the edge effect was noticeable. . The equipment used for the live-action test had the following conditions. That is, the electrostatic charge image carrier 1 is an organic photoconductive (OPC) photoreceptor, its circumferential speed is 150 mm/sec, and the highest potential of the electrostatic image formed on the electrostatic charge image carrier 1 is -
500V, outer diameter of sleeve 2 30mm, rotation speed
100 rpm, magnetic flux density of N and S magnetic poles of magnet body 3 is 500
Gauss, the rotation speed is 1000 rpm, the thickness of the developer layer in the developing space A is 0.2 mm, the gap between the sleeve 2 and the electrostatic image carrier 1 is 0.3 mm, that is, 300 μm, and the sleeve 2
The bias voltage applied to is the DC voltage component -250V,
The AC voltage component was 1.5kHz and 400V. For fixing, a heat roller fixing device with a heat roller surface temperature of 180° C. was used. Examples 3 to 5 and Comparative Example 3 Carrier A and toner b were used, and the toner content ratio (weight %) to the carrier was the value shown in Table 2, three types for Examples and one type for Comparative Example. A total of four types of developers were prepared. In addition,
In the developer composed of carrier A and toner b, the content ratio Tc of the toner satisfying the above-mentioned formula (1) ranges from approximately 36 to 63. For each of these developers, an actual photographic test was conducted using the apparatus described above. The results are shown in Table 2.

[Table] Examples 6 and 7 and Comparative Examples 4 and 5 Comparison of two types of Examples using carrier B and toner a, with the toner content ratio (weight %) to the carrier being the value shown in Table 3. Example 2
A total of four types of developers were prepared, two types for each. In the developer composed of carrier B and toner a, the content ratio Tc of toner satisfying the above-mentioned formula (1) ranges from approximately 12 to 22. For each of these developers, an actual photographic test was conducted using the apparatus described above. The results are shown in Table 3.

[Table] Examples 8 and 9 and Comparative Examples 6 and 7 Example 2 in which carrier B and toner b were used and the toner content ratio (weight %) to the carrier was the value shown in Table 4. A total of four types of developers, two types of which were used as a seed and a comparative example, were prepared. In the developer composed of carrier B and toner b, the content ratio Tc of toner satisfying the above-mentioned formula (1) ranges from approximately 18 to 32. For each of these developers, an actual photographic test was conducted using the apparatus described above. The results are shown in Table 4.

[Table] Examples 10 and 11 and Comparative Examples 8 and 9 Comparison of two types of Examples using Carrier C and Toner A, where the content ratio (wt%) of toner to carrier is the value shown in Table 5. A total of four developers were prepared, two types for each example. In addition,
In the developer composed of carrier C and toner a, the content ratio Tc of the toner satisfying the above-mentioned formula (1) ranges from approximately 19 to 33. For each of these developers, an actual photographic test was conducted using the apparatus described above. The results are shown in Table 5.

[Table] From the above results, in the examples of the present invention,
In all cases, it was confirmed that the toner concentration was within an appropriate range, and it was possible to obtain high-quality visible images with good reproducibility and no fogging, carrier adhesion, or image distortion. On the other hand, the comparative example was inferior in all evaluation items; if the toner density is too low, carrier adhesion and image distortion occur significantly, and if the toner density is too high, fogging occurs significantly. It has been found.

[Brief explanation of drawings]

FIG. 1 is an explanatory cross-sectional view schematically showing an example of a developing device that can be used to perform a developing step in carrying out the method of the present invention. 1... Electrostatic image carrier, 2... Sleeve, 3...
... Magnet, 4 ... Regulation blade, 5 ... Cleaning blade, 6 ... Developer reservoir, 7 ... Stirring screw, 8 ... Toner hopper, 9 ... Supply roller, 10 ... Bias power supply, 11 ... Protection Resistance, A...development space, D...developer, T...toner particles, N, S...magnetic poles.

Claims (1)

[Scope of Claims] 1. A developer layer of a two-component developer consisting of toner and carrier is formed on a developer transport carrier, and this developer layer is supplied to a development space where an oscillating electric field is generated to develop a latent An image forming method comprising a developing step of developing a latent image on an image carrier without the surface of a developer layer coming into contact with the surface of the latent image carrier, wherein the carrier is 55 to 50% of the carrier. 80
The two-component developer is made by dispersing fine magnetic powder in a proportion of % by weight in a binder resin.The average particle size of the toner is r ₁ μm, the average particle size of the carrier is r ₂ μm, When the true specific gravity of toner is ρ ₁ and the true specific gravity of carrier is ρ ₂ , the content ratio of toner to carrier
An image forming method characterized in that Tc (weight %) is within the range expressed by the following formula. 80 (r ₁ / r ₂ ) (ρ ₁ / ρ ₂ ) ≦T _C ≦140 (r ₁ r ₂ ) (ρ ₁ /
ρ ₂ ) However, 10≦r ₂ ≦50, 0.3≦r ₁ /r ₂ ≦0.6.