JPH07121026A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain high image quality by means of an image forming method having a development method using a small, high erformance device and, a transfer process using a roller. CONSTITUTION:The image forming method consists of a development method in which a photosensitive drum 101 with a fixed magnet 102 inside is used and toner in a non-image part is recovered by a nonmagnetic electrode roller 108 after the formation of an electrostatic latent image, and a transfer method in which a transfer roller 120 composed of a conductive elastic body is used. The surface of magnetic toner to be used, is modified by hot air in dispersion state, a magnetic body is coated and the toner is sphered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner used in copying machines, printers and facsimiles, and an image forming method.

[0002]

2. Description of the Related Art In recent years, electrophotographic apparatuses are shifting from the purpose of office use to personal use, and there is a demand for a technology for realizing downsizing and maintenance free.
Therefore, conditions such as maintainability such as recycling of waste toner and less ozone exhaust are required.

The printing process of an electrophotographic copying machine or printer will be described. First, the photoreceptor is charged to form an image. As a charging method, a conventionally used corona charger is used, and in recent years, a contact type charging method in which a conductive roller is directly pressed against the photoreceptor to reduce the amount of ozone generation is used. Charge the surface uniformly. After the photoconductor is charged, in the case of a copying machine, the copy original is irradiated with light and the reflected light is applied to the photoconductor through a lens system. Or, if it is a printer, send an image signal to a light emitting diode or laser diode as an exposure light source,
A latent image is formed on the photoconductor by turning the light on and off.

When a latent image (high or low surface potential) is formed on the photoconductor, the photoconductor is a toner which is a pre-charged colored powder.
(The diameter is about 5 μm to 15 μm) and visualized. The toner adheres to the surface of the photoconductor according to the level of the surface potential of the photoconductor, and is electrically transferred to the copy paper. That is, the toner is charged positively or negatively in advance, and a charge having a polarity opposite to the polarity of the toner is applied from the back surface of the copy sheet and is electrically attracted.

Up to now, a corona discharger has been widely used as the charge applying method like the charging method, but in recent years, a transfer device using a conductive roller has been put into practical use in order to reduce the ozone generation amount. There is. At the time of transfer, not all the toner on the photoconductor is transferred to the copy sheet, but a part of the toner remains on the photoconductor. This residual toner is scraped off by a cleaning blade or the like in the cleaning section to become waste toner.

Conventionally, as a developing method for visualizing an electrostatic latent image by an image forming method, there are a cascade developing method, a touchdown developing method, a jumping developing method and the like. Among them, a cascade developing method shown in US Pat. No. 3,105,770 is known as a developing method in which a developer is directly sprinkled with a developer. The cascade developing method is an image forming method and a developing method used for the first practical copying machine. Further, there is US Pat. No. 3,866,574 as a method of applying an AC bias to the developing roller to fly and develop the one-component toner. According to the present invention, the AC bias applied to the developing roller is used for the purpose of activating the movement of the toner, and the toner flies to the image portion and returns to the middle in the non-image portion.

Further, as a modification of the technique for applying the AC bias, there is a jumping developing method disclosed in JP-B-63-42256. In this jumping development method, toner is carried on a toner carrier, and a rigid or elastic regulating blade is installed on the toner carrier with a minute gap from the carrier. Then, the regulation blade regulates the toner in a thin layer, conveys the toner to a developing portion, and attaches the toner to the image portion of the photoconductor by an AC bias there. The technical idea of the Japanese Patent Publication No. 63-42256 differs from the above-mentioned US Pat. No. 3,866,574 in that the toner reciprocates in the image portion and the non-image portion.

As is well known, the toner for electrostatic charge development used in these developing methods is generally composed of a coloring component consisting of a resin component, a pigment or a dye and an additive component such as a plasticizer and a charge control agent. Has been done. As the resin component, natural or synthetic resins are used alone or in a proper mixture.

FIG. 8 is a schematic diagram showing the structure of a toner image transfer device disclosed in Japanese Patent Application Laid-Open No. 48-69524, US Pat. No. 2,807,233, Japanese Patent Application Laid-Open No. 3-155584. . In FIG. 8, 200 is a transfer roller which is made of foamed or solid rubber and has a medium resistance adjusted to about 10 ⁷ Ω.
01 is a power source for applying a voltage to the transfer roller, 202 is a photoconductor, 203 is image receiving paper (copy paper), and 204 is toner. The operation of the transfer device configured as described above will be described.

On the surface of the photoconductor 202, the above-mentioned toner image is formed. Now, the normal development in which the polarity of the photoconductor 202 is negative and the polarity of the toner 204 is positive is defined. Transfer roller 2
00 is in contact with the photoconductor 202 with a predetermined pressing force. Image receiving paper 203
Is pressed against the photoconductor 202 and comes into contact with the toner 204. A negative voltage opposite to the polarity of the toner 204 is applied to the transfer roller 200 by the power source 20.
Since the toner is applied from 1, the toner 204 is transferred to the image receiving paper 203. Since the transfer roller 200 is in contact with the image receiving paper 203, the voltage applied from the power source 201 can be as low as several hundred to 3000V. The image receiving paper 203 passes through the contact point between the photoconductor 202 and the transfer roller 200, and is conveyed to a fixing unit (not shown). With such a transfer method, harmful ozone generation can be suppressed to an extremely low level as compared with the conventional corona discharger.

[0011]

However, as is well known in the art for the developing method having the above-mentioned structure, the cascade developing method is not good at reproducing solid images. Further, there is a problem that the device becomes large and complicated. Further, the developing device of U.S. Pat. No. 3,866,574 has a drawback that the device requires high precision, is complicated, and is expensive. In the jumping development method, it was essential to form a very uniform thin layer on a toner carrier carrying a toner layer. Further, in this method, a so-called sleeve ghost phenomenon occurs in which the history of the previous image remains in the thin toner layer on the toner carrier and an afterimage appears in the image. Further, there is a drawback that the device is complicated and the cost is high.

Therefore, the present inventor has proposed an image forming method (Japanese Patent Application Laid-Open No. 5-72890) capable of realizing the downsizing and high performance of the developing device. The developing device of this image forming method includes a photosensitive member containing a fixed magnet, and a toner recovery electrode roller (hereinafter, referred to as an electrode roller) having a magnet facing the photosensitive member with a predetermined gap provided therebetween. Is a structure for removing. Therefore, this developing device faithfully reproduces a solid image, does not cause the sleeve ghost phenomenon, and is a method that enables further downsizing, simplification, and cost reduction of the apparatus.

However, in order to improve the image quality by using this developing device, higher performance toner characteristics are required. Since this developing device does not use a regulating blade for regulating the toner in a thin layer, the toner is not regulated in the layer and is conveyed to the developing field which is a narrow gap space between the photoconductor and the electrode roller. Therefore, there are few places and spaces required for the toner to be triboelectrically charged to obtain a desired charge amount, and the toner requires higher charging characteristics than ever before. The fluidity and surface resistance of the toner affect the high charging property of the toner. Therefore, the toner requires the following two characteristics more than ever before.

(1) High powder fluidity (2) High charging characteristics By the way, the fluidity of the toner can be defined by the static bulk density, and the surface resistance can be defined by the dielectric loss.

At the level of fluidity of the toner used in the conventional one-component developing method and two-component developing method, unevenness occurs in the solid black image area and the halftone image area, and the background fog occurs in the non-image area. Will increase. This phenomenon remarkably appears in the toner having low fluidity. The reason for this is that a toner having a low fluidity has a low contact probability with the developing member, so that a satisfactory triboelectric charge amount cannot be obtained. Further, the triboelectric chargeability varies among the toners, and uniform toner chargeability cannot be obtained. However, it is considered that a toner having a high fluidity has a uniform contact property with the developing member, a high charge amount can be obtained, and a high-quality image can be obtained.

In order to improve the fluidity of the toner, conventionally, a measure has been taken to increase the addition amount of an external additive such as silica which is a fluidity imparting agent. However, if the amount of the external additive such as silica is increased, the fluidity is improved to some extent with the addition amount, but there is a limit. In addition, suspended matter of silica increases, and this silica serves as nuclei, and the silica is struck by the pressing force of the cleaning blade to cause scratches. Then, filming occurs in which silica or toner is fixed on the photoconductor. In addition, the suspended matter of silica adheres to the solid black image portion to generate white spots.
As described above, increasing the amount of silica has many adverse effects and cannot solve the problem.

In the conventional magnetic toner, the magnetic material is internally added to the binder resin. The toner is crushed into fine particles. At this time, a magnetic material having a resistance lower than that of the binder resin is exposed on the surface of the toner, so that the electric charge obtained by the triboelectric charging easily leaks, and it is difficult to obtain a high charge amount in the magnetic toner. Further, this magnetic material has a drawback that it tends to generate a reverse polarity toner when it comes into contact with a binder resin.

Further, the transfer method using the transfer roller of the conductive elastic body has the following three problems.

(1) Missing characters and lines (2) Scattering of toner around characters (3) Scratches on the photoconductor by magnetic powder added to the toner When the image is transferred onto the image receiving paper by the transfer roller, the transfer roller is in contact with the photoconductor at a predetermined pressure. For this reason, characters and lines are edge-developed, where the amount of toner is large and where toner is concentrated, the pressure is higher than in areas where there is no toner, causing aggregation of toner due to pressure, It causes so-called "blank" that is not transferred to the image receiving paper. Remarkably appears in low-fluidity toner. Further, in the case of a magnetic toner, the electric charge obtained by the triboelectric charging in the developing process easily leaks before reaching the transferring process, and the charge amount of the toner decreases, which further promotes the hollow defect.

The transfer of the toner onto the photoreceptor to the image receiving paper is
This is performed by the attraction of the electrostatic charge of the toner and the electric charge opposite to the electrostatic charge of the toner applied from the outside. If the toner charge amount is low, the toner easily scatters around the characters where no toner exists. This is noticeable in low-charged toner.

When the toner on the photoconductor is transferred to the image receiving paper by using the transfer roller, the transfer roller is in contact with the photoconductor at a predetermined pressure. For this reason, the magnetic particles exposed on the toner surface are likely to damage the photoconductor by this pressure.

In view of the above problems, the present invention provides a developing method capable of further downsizing, simplification, and cost reduction of the apparatus, in order to realize high image density and high image quality such as low background fog, high flow rate. An object of the present invention is to provide an image forming method using a magnetic toner having high charging property and high charging property.

It is another object of the present invention to provide an image forming method using a magnetic toner which can prevent hollow defects and scattering during transfer in a low ozone process using a transfer roller.

Another object of the present invention is to provide an image forming method using a magnetic toner capable of preventing the photoconductor from being scratched by a magnetic substance and further preventing filming on the photoconductor.

It is another object of the present invention to provide an image forming method using a magnetic toner which can extend the life of the magnetic toner.

[0026]

SUMMARY OF THE INVENTION In order to solve the above problems and to achieve the object, the present invention includes an electrostatic latent image holding member that moves by containing a fixed magnet, a toner hopper, and the electrostatic latent image holding member. Has a toner collecting electrode roller having a magnet inside thereof at a position having a predetermined gap from the surface of the toner, and is positioned in the toner hopper after forming an electrostatic latent image on the electrostatic latent image holder. The magnetic toner is magnetically attracted to the surface of the electrostatic latent image carrier, the magnetic toner is carried on the surface of the electrostatic latent image carrier, and the electrostatic latent image carrier is moved to move the toner. A developing process in which toner is left in the image portion of the electrostatic latent image holding member so as to face the collecting electrode roller, and toner in the non-image portion is collected by the toner collecting electrode roller; The conductive elastic transfer roller that abuts and biases An electrostatic latent image on the electrostatic latent image holding member and having a transfer step of transferring the magnetic toner visualized on the image receiving sheet.

In the magnetic toner used in the present invention, the magnetic toner is composed of at least a binder resin, a magnetic substance, and an external additive, and the binder resin, the magnetic substance, and other additives used as necessary. The toner base particles that have been subjected to at least kneading treatment, pulverizing treatment and, if necessary, classification treatment, are subjected to surface modification treatment with hot air in a dispersed state.

[0028]

In the image forming method according to the present invention, an electrostatic latent image holder containing a fixed magnet is used, and toner is sprinkled and magnetically attached to the electrostatic latent image holder on which the electrostatic latent image is formed, and the electrode roller It is configured such that the toner is carried and conveyed to another portion, an AC bias is applied to the electrode roller, and the non-image portion toner of the electrostatic latent image holding member is removed by electrostatic force and magnetic force.

That is, the image forming method presented in the present invention is a cascade developing method in which a magnet is installed inside the electrostatic latent image holding member and an AC voltage is applied to the electrodes to further reduce the size and improve the performance.

In the present invention, the development is almost completed when the toner is first sprinkled on the electrostatic latent image carrier. The electrode roller part circulates the toner in the toner hopper and at the same time collects the toner in the non-image part of the electrostatic latent image. That is, it is the electrostatic latent image carrier that carries and carries the toner from the toner hopper to the developing section. A bare surface of the electrode roller that does not carry the toner layer faces the electrostatic latent image holding member. The electrode roller and the electrostatic latent image carrier rotate in opposite directions.

In the image forming method according to the present invention, the transfer means is composed of a conductive elastic roller. Examples of the elastic body of the roller include CR rubber, NBR, Si rubber, and fluororubber, and urethane foam is preferable. Carbon black and lithium salts such as Li ₂ O are preferable materials as the conductivity-imparting agent for imparting conductivity.

Further, since the developing method in the image forming method according to the present invention has a simple structure, there are few toner charging opportunities and it is difficult to obtain high charging characteristics. Therefore, when combined with a conductive elastic transfer roller as the transfer means,
In order to prevent voids at the time of transfer and scattering around the characters, the magnetic toner is required to have higher fluidity, higher chargeability, and higher surface resistance than ever before.

When the charge amount of the toner is reduced, the mirror image force with the electrostatic latent image holding member is weakened, the toner attached to the electrostatic latent image holding member is easily removed by the magnetic force, and the image density is lowered. Further, the toner scattering around the characters increases, and the sharpness of the image decreases.

The magnetic toner used in the image forming method of the present invention will be described below.

The toner is mixed, kneaded, pulverized, externally added, and if necessary classified. Other methods such as a polymerization method may also be used.

The mixing treatment is a treatment in which the binder resin, the magnetic substance and other internal additives such as a charge control agent, a release agent and a pigment, which are added if necessary, are uniformly dispersed by a mixer equipped with a stirring blade. A known processing method is used.

In the kneading process, the mixed material is heated to disperse the internal additive in the binder resin by shearing force. The kneading at this time can be performed using a known heating kneader. As the heating and kneading machine, it is possible to use an apparatus for heating a kneaded material such as a three-roll type, a single screw type, a twin screw type, a Banbury mixer type, and applying a shearing force to knead the mixture. The mass obtained by the kneading process is roughly crushed with a cutter mill or the like.

In the crushing process, the crusher is finely crushed by a jet mill crusher or the like. Further, in the classification treatment, if necessary, fine powder particles are cut by an airflow classifier to obtain a desired particle size distribution. At this time, mechanical crushing and classification are also possible. For example, there is a method in which toner is charged into a minute gap between a fixed stator and a rotating roller and pulverized. Also in classification, there is a method of classifying by centrifugal force with a rotating rotor. Known methods are used in both cases.

The magnetic toner used in the present invention is pulverized, or if necessary, the magnetic toner base particles, which have been classified, are surface-modified with hot air. The surface modification treatment is performed by dispersing and ejecting the magnetic toner base particles by compressed air from a dispersion nozzle which is a dispersion spraying means, and radiating hot air heated by a heater which is a hot air generating means thereto.

Conventionally, there is an example in which the surface treatment of the toner is carried out, but in the method of making the toner spherical by mechanical impact, noise and vibration etc. occur due to the fusion of the toner particles on the rotating shaft and the presence of the rotating body. Moreover, only the spheroidizing is performed, and the coating treatment of the magnetic material cannot be appropriately performed.

However, according to the surface modification treatment, since it is of a continuous type, the production efficiency is improved. Further, since the surface modification is performed in a dispersed state, particles are not fused with each other and coarse particles are not generated. In addition, it has a very simple structure and is compact. There is no rise in the machine wall temperature and the product recovery rate is high. Since it is an open type, there is almost no possibility of dust explosion. Since the treatment is performed with hot air instantaneously, the toner particles are not aggregated with each other and the entire toner particles are uniformly treated. Since the corners of the particles generated by pulverization are cleanly taken and spherical, the fluidity is dramatically improved.

Further, by this treatment, the surface of the binder resin of the magnetic toner base particles is melted, and the surface tension of the magnetic substance exposed on the surface of the toner base particles by the binder resin is also spherical. It is possible to perform the processing simultaneously and instantaneously.

The hot air temperature of the treatment at this time is 100 to 600
Degree is preferred. If it is less than 100 degrees, the effect of the surface modification treatment cannot be obtained. If the temperature is higher than 600 degrees, aggregation of toner particles is likely to occur, which is not suitable. Further, by using the dispersion nozzle, the dispersibility of the toner can be further improved.

In the magnetic toner used in the present invention, an external additive is externally added to the toner fine powder obtained by the surface modification treatment. A known stirring method such as a mixer is used for the external addition treatment.

The magnetic toner used in the present invention is preferably an insulating one-component toner. When the one-component toner is used, the mixing and stirring mechanism of the carrier and the toner, which is necessary for the two-component development, and the toner concentration control are unnecessary, so that the apparatus configuration can be simplified.

In the magnetic toner used in the present invention, since the magnetic material exposed on the surface can be coated with the binder resin, a high charge amount can be obtained. Therefore, a high image density can be obtained, and a clear image can be obtained without scattering of toner around the characters. Further, since the surface resistance of the toner is high, the electric charge obtained by the triboelectric charging is retained until the transfer step, the occurrence of hollow defects can be prevented, and the effectiveness is extremely high.

It was also found that the generation of reverse polarity toner was suppressed to a very low level during development. This is because the magnetic particles that affect the generation of the opposite polarity toner are coated. The dielectric loss of the magnetic toner used in the present invention is 4.5.
It is preferably × 10 to ³ or less. Dielectric loss is 4.5 × 10 ~
^When it is ³ or less, the amount of magnetic material exposed on the surface of the magnetic toner is small, and the surface resistance of the magnetic toner is increased, so that the leakage of the charge obtained by the triboelectric charging can be suppressed and the high charge amount is maintained. A magnetic toner can be realized.

The dielectric loss was measured by molding a magnetic toner into a pellet of 12 mmφ under a pressure of 100 kg / Q ² and using a LCR meter at a frequency of 1 kHz.

If the fluidity of the toner is low, the toner in the non-image area adheres strongly to the electrostatic latent image holder and cannot be removed, resulting in background fog and degrading the image. It was also found that unevenness was generated in the solid black image area. When the amount of external additive silica is increased to improve the fluidity of the toner, the non-electrostatic adhesion of the toner to the electrostatic latent image holding member is reduced, the background fog is reduced, the image density is increased, and a solid black image is obtained. The unevenness of parts tends to be eliminated. However, problems such as filming of silica on the photoconductor and adhesion of white spots on the solid black image portion of silica aggregates have occurred.

Further, in the image forming method according to the present invention, since the toner is attached to the entire surface of the photosensitive member during development, the toner and the photosensitive member are in contact with each other longer than in the conventional one-component developing method. Therefore, when a magnetic toner whose magnetic material is exposed on the surface is used, the surface of the photoreceptor is easily scratched. Further, since the transfer means is an elastic roller, which is in contact with the photoconductor, the photoconductor is more easily scratched.

If a large amount of silica as an external additive is added to improve the fluidity of the toner, floating silica is generated and the filming of the toner on the photosensitive member is likely to occur.

However, in the magnetic toner used in the present invention, a high fluidity can be imparted to the toner with the minimum amount of silica which has been subjected to the hydrophobic treatment by the surface modification treatment. Further, since the toner is spheroidized, silica can be uniformly adhered to the toner during the external addition treatment, and the amount of floating silica is extremely smaller than that of the conventional toner that is not spheronized. Therefore, there is no occurrence of scratches or filming on the photoconductor due to the floating silica.

Therefore, with the magnetic toner having the high fluidity, the obtained copy image has a high image density and is a high-quality image with no background fog. Further, in the transfer of the elastic roller, where toner such as characters and lines is concentrated, even if the transfer is performed with a predetermined pressing force, the toners are unlikely to aggregate with each other, and a clear image with no voids can be obtained.

Further, since the magnetic material is coated with the binder resin, no scratch is generated on the surface of the photoconductor by the magnetic material in the developing process and the transferring process.

The amount of silica added is preferably 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the magnetic toner. It is necessary to add 0.1 parts by weight or more to prevent the toner particles from coagulating, and 5.0 parts by weight or more increases floating silica. Although hydrophobic silica is used as the external additive, other known inorganic or organic fine powder external additives may be used.

The binder resin of the magnetic toner used in the present invention is
A vinyl polymer obtained by polymerizing or copolymerizing a vinyl monomer. Examples of the monomer styrene constituting the binder resin include styrene and its substitution products such as styrene, α-methylstyrene, and P-chlorostyrene, and examples of the acrylic acid alkyl ester include acrylic acid, methyl acrylate, and Examples of ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, isobutyl acrylate, hexyl acrylate, and alkyl methacrylate include, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, methacrylic acid. Examples include monocarboxylic acids having a double bond such as isobutyl, dodecyl methacrylate, and hexyl methacrylate, and their substitution products.

As a method for producing these copolymers, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization are adopted.

The copolymer used in the magnetic toner used in the present invention preferably contains a styrene component as a component in an amount of 50 to 95% by weight. If the proportion of styrene is less than 50% by weight, the melting property of the toner will be poor, the fixability will be insufficient, and the pulverizability will be poor.

The magnetic toner used in the present invention has the binder resin as a main component as described above, but other known polymers or copolymers may be used as necessary in addition to the main component. . For example, polyester resin,
Epoxy resin, polyurethane resin, etc. are available.

If necessary, other known external additives may be added to the magnetic toner used in the present invention. As a preferable material for the external additive, known inorganic fine powder materials such as hydrophobic silica, titania, alumina, zirconia are used. For example, in the case of hydrophobic silica, hydrophilic silica obtained by treating silicon tetrachloride is further surface-treated to obtain hydrophobic silica. However, as a treating agent, dimethyldichlorosilane in consideration of negative electrification and hydrophobicity, Hexamethylene disilazane,
Known treatment agents such as dimethyl siloxane are effective materials for hydrophobicity and negative charging.

If necessary, the magnetic toner used in the present invention may be mixed with a suitable pigment or dye for the purpose of controlling coloring and charge. Examples of such pigments or dyes include carbon black, iron black, graphite, nigrosine, metal complexes of azo dyes, phthalocyanine blue, DuPont oil red, aniline blue, benzine yellow, rose bengal, and mixtures thereof. The amount required for coloring is blended.

Further, the magnetic toner used in the present invention may further contain a release agent such as WAX if necessary. Further, other types of additives can be blended if necessary. For example, it is a polishing agent such as tin oxide, strontium titanate, or tungsten carbide. Fine powder of an organic material is also added as needed for the purpose of fluidity aid, charging aid, cleaning aid and the like.

Further, the magnetic toner used in the present invention contains a magnetic material. Magnetic powders include metal powders of iron, manganese, nickel, cobalt, etc., iron, manganese, nickel,
There are ferrites such as cobalt and zinc. The average particle size of the powder is preferably 1 μm or less, particularly preferably 0.6 μm or less.
The addition amount is preferably 20 to 60% by weight. When the addition amount is 20% by weight or less, the toner scattering tends to increase, and when the addition amount is 60% by weight or more, the toner charge amount tends to decrease, and the image quality tends to deteriorate.

With the above-described structure, by using the magnetic toner having a high charge amount and a high fluidity obtained by the surface modification treatment, a developing method which enables further downsizing, simplification and cost reduction of the apparatus can be realized. High image quality with high density and low ground fog can be realized. Even with the transfer means using an elastic roller, a high-quality image free from scattering of characters and voids can be obtained. Furthermore, since the waste toner to be recycled can maintain high fluidity and high chargeability, it is possible to recycle the waste toner, and it is a magnetic toner that enables the prevention of global environmental pollution and the reuse of resources by recycling without waste. .

[0065]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic toner according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing the construction of a main part of an electrophotographic apparatus used in an image forming method according to an embodiment of the present invention. This developing method uses a one-component developing method. 101
Is an organic photoconductor drum in which phthalocyanine is dispersed in a polyester binder resin (hereinafter referred to as a photoconductor), 102 is a magnet fixed coaxially with the photoconductor 101, 103 is a corona charger for negatively charging the photoconductor 101, 104 Is a grid electrode for controlling the charging potential of the photoconductor 101, and 105 is signal light. The developing device for visualizing the latent image after exposure comprises the following parts. That is, 106 is a toner hopper that supplies the magnetic toner 107 to the surface of the photoconductor 101, 108 is a nonmagnetic electrode roller (hereinafter referred to as an electrode roller) set with a gap between the photoconductor 101, and 109 is inside the electrode roller 108. The installed magnet, 110 is an AC high-voltage power supply that applies a voltage to the electrode roller 108, and 111 is a scraper made of a polyester film that scrapes off the toner on the electrode roller 108.
8 collects excess toner in the non-image area.

Reference numeral 113 is a damper for smoothing the flow of the toner in the toner hopper 106 and for preventing the toner from being crushed by its own weight and clogged between the photoreceptor 101 and the electrode roller 108. is there.

Reference numeral 120 denotes a transfer roller for transferring the toner image on the photoconductor to the paper, which is set so as to contact the photoconductor 101. The transfer roller 120 is an elastic roller in which a conductive elastic member is provided around a shaft made of a conductive metal. Photoconductor
The pressing force to 101 is 0 per transfer roller (about 216 mm)
2000 g, preferably 500 to 1000 g. This was measured from the product of the spring coefficient and the amount of contraction of the spring for pressing the transfer roller 120 to the photoconductor 101. The contact width with the photoconductor 101 is about 0.5
mm to 5 mm.

The rubber hardness of the transfer roller 120 is measured by Asker C measurement (measurement using a block piece, not the roller shape).
It is 80 degrees or less, preferably 30 to 40 degrees. In this embodiment, the transfer roller 120 has a conductive urethane elastomer in which a foaming lithium salt is internally added around a shaft having a diameter of 6 mm and has a resistance value of 10 ⁷ Ω (electrodes are provided on the shaft and the surface, and 500 V is applied to both electrodes). The one used was. The outer diameter of the entire transfer roller 120 was 16.4 mm, and the hardness of Asker C was 40 degrees. The transfer roller 120 was brought into contact with the photoconductor 101 by pressing the shaft of the transfer roller 120 with a metal spring. The pressing force was about 1000 g. The present invention is not limited to this material.

Reference numeral 121 is a thrust guide made of a conductive member for introducing the image receiving paper to the transfer roller 120, and reference numeral 122 is a conveyance guide in which the surface of the conductive member is covered with insulation. The plunge guide 121 and the transport guide 122 are grounded directly or via a resistor. Reference numeral 123 is an image receiving paper, and 124 is a voltage generating power source for applying a voltage to the transfer roller 120.

The magnetic flux density on the surface of the photoconductor 101 is 600 Gs. The magnetic force inside the electrode roller 108 was made stronger to improve the transportability. The magnetic pole angle θ of the magnet 102 shown in the figure was set to 15 degrees. The photoconductor 101 has a diameter of 30 mm and a peripheral speed of 60 mm / s.
Was used by rotating in the direction of the arrow in the figure. Electrode roller 108
Has a diameter of 16 mm, and is rotated at a peripheral speed of 40 mm / s in the direction opposite to the traveling direction of the photoconductor 101 (the direction of the arrow in the figure). Photoconductor
The gap between 101 and the electrode roller 108 was set to 300 μm.

The photoconductor 101 is connected to the corona charger 103 (applied voltage −
It was charged to -500 V at 4.5 kV and the voltage of the grid electrode 104 of -500 V). The photoconductor 101 was irradiated with the signal light 105 to form an electrostatic latent image. At this time, the exposure potential of the photoconductor 101 is -90V.
Met. Magnetic toner 107 was attached to the surface of the photoconductor 101 by a magnet in the toner hopper 106. Next, the photoconductor 101 was passed in front of the electrode roller 108. When passing through the uncharged area of the photoconductor 101, an AC high voltage power supply 110 applies to the electrode roller 108 an AC voltage of 750 V 0-p (peak to peak 1.5 kV) superposed with a DC voltage of 0 V (frequency 1 kHz). did. After that, when passing through the photoconductor 101 charged to −500V and having the electrostatic latent image written therein, the electrode roller 108 is superposed with a DC voltage of −350V by the AC high-voltage power supply 110 at 750V0.
-p (peak-to-peak 1.5kV) AC voltage (frequency 1k
Hz) was applied. Then, the magnetic toner 107 attached to the charged portion of the photoconductor 101 is collected by the electrode roller 108, and
A negative-positive inverted toner image of only the image portion remained on the upper portion. The magnetic toner 107 attached to the electrode roller 108 rotating in the direction of the arrow was scraped off by the scraper 111, returned to the inside of the toner hopper 106, and used for the next image formation. The toner image thus obtained on the photoconductor 101 is transferred onto the image receiving paper 123 by the transfer roller 120, and then thermally fixed by a fixing device (not shown) to obtain a copied image.

Here, an example of the material composition of the magnetic toner used in the present image forming method is shown in (Table 1), which is composed of at least a mixture of a binder resin, a magnetic material and an external additive, and in addition to the above, a small amount Charge control part and a release agent.

[0074]

[Table 1]

The mixture shown in (Table 1) is mixed with a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.). The mixture is kneaded by heating with a twin-screw kneading extruder PCM30 (made by Ikegai Tekko Co., Ltd.). The kneaded product is finely pulverized with a jet mill pulverizer IDS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.). Air flow classifier DS2 type (made by Nippon Pneumatic Mfg. Co.)
Cut the fine powder at. Average particle size of 8μ
m particles were obtained.

The surface modification treatment apparatus shown in FIG. 2 was used for treatment at a hot air temperature of 300 degrees. Then, inorganic fine powder of hydrophobic silica was mixed with Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.) and externally added.

In FIG. 2, the magnetic toner base particles 22 are fed from a constant quantity feeder 21 and are sent by compressed air 23 to a dispersion nozzle 24 which is a toner dispersion means, and are ejected in the direction of about 45 degrees. Two dispersion nozzles 24 are arranged at symmetrical positions. This is because the toner can be processed more uniformly by ejecting the toner from a plurality of nozzles. Since hot air is emitted to the magnetic toner base particles 22 ejected from the dispersion nozzle 24, hot air 26 is emitted from the hot air generator 25. Here, a heater is used. The device is not limited as long as it can generate hot air. The magnetic toner base particles 22 pass while being dispersed in the hot air 26, and the surface modification treatment is performed there. Surface-modified magnetic toner is a hood
It is taken into 28 and collected in a cyclone (not shown) at the tip of arrow 29.

FIG. 3 shows a sectional view of the magnetic toner used in the present invention. Reference numeral 1 is a binder resin, 2 is magnetic particles, 3 is a charge control agent, 4 is a release agent, and 5 is hydrophobic silica.

FIG. 4 shows the entire surface observation image of the magnetic toner used in the present invention by a scanning electron microscope. The magnification is 3000 times.

FIG. 5 shows a local surface observation image of the magnetic toner used in the present invention by a scanning electron microscope. The magnification is 30,000 times.

In FIG. 4, it can be seen that the entire shape of the toner is spherical. In the further enlarged FIG. 5, the image of the magnetic substance on the surface is blurred, and it can be seen that the magnetic substance is covered. White dots in FIGS. 4 and 5 represent magnetic particles.

The physical properties of the magnetic toner A are shown in (Table 2).

[0083]

[Table 2]

The hot air temperature of the surface modification treatment is taken as a parameter. Magnetic toner A1 is hot air temperature 300 ℃, A2
Is 350 ° C and A3 is 400 ° C. As a comparative example, the physical property values of the magnetic toner B not subjected to the surface modification treatment are also shown. Flowability was defined as static bulk density. For the measurement, a powder tester manufactured by Hosokawa Micron was used. The charge amount was measured by the blow-off method. The measurement conditions were such that a non-coated ferrite carrier was mixed at a toner concentration of 10%, put in a 100 ml polyethylene bottle, and stirred at a rotation speed of 60 rpm for 10 minutes.

It can be seen that the magnetic toner A clearly exhibits high fluidity, high chargeability and low dielectric loss.

Using the image forming method of the present invention shown in FIG. 1, a copy test was conducted with the magnetic toner A which was surface-modified in FIG. The image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, there is no horizontal line distortion, magnetic toner scattering, hollow characters, etc., and a solid black image is uniform, and even 16 lines / mm with a density of 1.4 are reproduced with extremely high resolution and high image quality. Was given. A high density image with an image density of 1.4 or more was obtained. No background fog has occurred in the non-image area.

Then, a long-term copying test of 10,000 sheets was conducted. The fluidity of the magnetic toner after 10,000 sheets did not decrease, a high charge amount was maintained, and filming did not occur on the photoconductor. High density comparable to the initial image,
A low-fog copy image was obtained.

FIG. 6 shows magnetic toner A to which silica is externally added.
3 is a scanning electron microscope image of the above, showing an observation image of the initial state of silica adhesion. FIG. 7 is a scanning electron microscope of the magnetic toner A, and shows an observation image of the adhered state of silica after a long-term copying test of 10,000 sheets. The magnification is 50,000 times.
Large white dots are magnetic particles and small fine dots are silica particles.

It can be seen that the particles of the silica can be clearly seen both in the initial stage and after the copying test, and that the silica maintains a uniform adhered state.

Table 3 shows the fluidity of the toner and the image density at the initial stage and after the 10,000-sheet copying test.

[0091]

[Table 3]

It can be seen that the magnetic toner A1 shows stable characteristics with little change in fluidity (static bulk density) and image density. Although omitted in Table 3, other magnetic toner A
2 and A3 show the same tendency.

(Comparative Example 1) A magnetic toner B was manufactured as a trial with the same composition and formulation as the magnetic toner A except that the surface modification treatment was not performed.

It can be seen that the magnetic toner B exhibits low fluidity, low charge amount and low dielectric loss.

FIG. 9 shows the entire surface observation image of the conventional magnetic toner B by a scanning electron microscope. Magnification ratio is 30
It is 00 times.

FIG. 10 shows a local surface observation image of the conventional magnetic toner B by a scanning electron microscope. The magnification is
It is 30,000 times.

In FIG. 9, it can be seen that the overall shape of the magnetic toner B is irregular. In the enlarged view of FIG. 10, the image of the magnetic material on the surface can be clearly observed, and it can be seen that the magnetic material is exposed. White dots in FIGS. 9 and 10 represent magnetic particles.

Using this image forming method, a copy test was conducted with magnetic toner B. The image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, a large amount of toner was scattered, hollow characters were generated, unevenness was generated in a solid black image portion, and a low image density and a large amount of background fog were not obtained.

In the long-term copying test, the fluidity of the toner was remarkably lowered, the image density was lowered, and the background fog in the non-image area was increased. In addition, the occurrence of scratches on the photoreceptor is significant,
In addition, filming also occurred, and a practical image could not be obtained.

FIG. 11 is a scanning electron microscope image of the conventional magnetic toner B, showing an observation image of the initial state of silica adhesion. FIG. 12 shows a conventional magnetic toner B using a scanning electron microscope.
The observation image of the adhesion state of silica after a long-term copying test of 10,000 sheets is shown. The magnification is 50,000 times.

In the initial state, silica particles can be seen, but they are attached in a partially agglomerated state, which is inhomogeneous as compared with the magnetic toner A. Almost no particles of silica can be observed after the copy test,
It can be seen that the toner is buried in the magnetic toner B. This is the reason for the decline in liquidity.

The fluidity and the image density of the toner in the initial stage and after the 10,000-sheet copying test are shown in Table 3. It can be seen that both fluidity and image density have deteriorated.

(Comparative Example 2) A magnetic toner having the same composition as the magnetic toner A except that the hot air temperature was set to 50 degrees was manufactured as a trial. It showed almost the same characteristics as magnetic toner B, and practical characteristics could not be obtained.

(Comparative Example 3) When the hot air temperature was set to 650 ° C, a large amount of aggregation of magnetic toners occurred. Moreover, thermal damage is beginning to appear in other additives. Power consumption is high and not practical.

[0105]

As described above, according to the image forming method of the present invention, an electrostatic latent image holding member that contains a fixed magnet and moves,
A developing process including an electrode roller having an electrode roller having a magnet inside, which is installed at a position having a predetermined gap from the surface of the electrostatic latent image carrier, and a conductive process in which the electrostatic latent image carrier is brought into contact with and biased. An image forming method including a transfer step including a transfer roller of a flexible elastic body, wherein the magnetic toner used is subjected to surface modification treatment by hot air. As a result, high fluidity and high charging characteristics can be obtained by the spherical treatment of the toner and the coating treatment of the magnetic material, and high density, high image quality such as low background fog can be realized in a high-performance, compact, low-cost developing method.

Further, in the transfer roller, the character missing
It is possible to realize an image without scattering.

Further, it is possible to provide a magnetic toner and an image forming method in which the image density is not lowered even when the waste toner is recycled, the filming of the photosensitive member does not occur, and the life is extended.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view showing a main part of an electrophotographic apparatus in which an image forming method according to an exemplary embodiment of the present invention is used.

FIG. 2 is a schematic view showing a main part of a surface modifying apparatus for a magnetic toner used in the present invention.

FIG. 3 is a schematic cross-sectional view showing the structure of a magnetic toner used in the present invention.

FIG. 4 is an overall surface observation image of a magnetic toner used in the present invention with a scanning electron microscope.

FIG. 5 is a local surface observation image of a magnetic toner used in the present invention with a scanning electron microscope.

FIG. 6 is a scanning electron microscope image of a magnetic toner used in the present invention, which is an observation image of an initial silica adhesion state.

FIG. 7 is an observation image of a silica adhesion state after a long-term copying test of 10,000 sheets with a scanning electron microscope of the magnetic toner used in the present invention.

FIG. 8 is a schematic diagram showing a configuration of a conventional transfer device.

FIG. 9 is an overall surface observation image of a conventional magnetic toner with a scanning electron microscope.

FIG. 10 is a local surface observation image of a conventional magnetic toner with a scanning electron microscope.

FIG. 11 is a scanning electron microscope image of a conventional magnetic toner,
It is an observation image of the initial state of silica adhesion.

FIG. 12: Scanning electron microscope of conventional magnetic toner
It is an observation image of the adhesion state of silica after a long-term copying test of 000 sheets.

[Explanation of symbols]

1 ... Binder resin, 2 ... Magnetic particles, 3 ... Charge control agent,
4 ... Release agent, 5 ... Hydrophobic silica, 21 ... Quantitative feeder, 22 ... Magnetic toner base particles, 23 ... Compressed air,
24 ... Dispersion nozzle, 25 ... Hot air generator, 26 ... Hot air,
28 ... Hood, 101 ... Photosensitive drum, 102 ... Fixed magnet contained in photoconductor, 103 ... Corona charger, 104 ... Grid electrode, 106 ... Toner hopper, 107 ... Magnetic toner, 108 ... Non-magnetic electrode roller, 109 ... Magnet installed inside the electrode roller, 111 ... Scraper, 120 ... Transfer roller, 123 ... Image receiving paper.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location G03G 9/083 9/087 13/09 15/16 103 // G03G 15/09 101 (72) Invention Person Hideki Tatematsu 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (9)

[Claims] 1. An electrostatic latent image holder that contains a fixed magnet and moves, a toner hopper, and a toner recovery device that has a magnet inside at a position with a predetermined gap from the surface of the electrostatic latent image holder. An electrode roller is provided, and after forming an electrostatic latent image on the electrostatic latent image holder, the magnetic toner is magnetically attracted to the surface of the electrostatic latent image holder located in the toner hopper. , The magnetic toner is carried on the surface of the electrostatic latent image holder, the electrostatic latent image holder is moved to face the toner recovery electrode roller, and toner is applied to the image portion of the electrostatic latent image holder. And the toner in the non-image area is collected by the toner collecting electrode roller, and the electrostatic latent image holding member is contacted with the electrostatic latent image holding member by a biased conductive elastic body roller. Receiving the magnetic toner by visualizing the electrostatic latent image on top Image forming method characterized by having a transfer step of transferring to. 2. The magnetic toner, wherein the magnetic toner is composed of at least a binder resin, a magnetic substance, and an external additive, the binder resin, the magnetic substance, and other additives used as necessary. 2. A magnetic toner formed by subjecting toner base particles that have been subjected to at least kneading treatment, pulverization treatment and, if necessary, classification treatment to a surface modification treatment with hot air in a dispersed state, is used. Image forming method. 3. A surface modification treatment of toner base particles,
2. The image forming method according to claim 1, wherein a magnetic toner is used, which is a coating treatment of a magnetic substance with a binder resin and a spherical treatment of the toner base particles. 4. The image forming method according to claim 1, wherein the magnetic toner has a dielectric loss of 4.5 × 10 ³ to ³ or less. 5. The surface modification treatment is carried out by a surface modification device comprising a dispersing means for dispersing and jetting toner base particles, and a hot air generating means for applying hot air to the toner base particles jetted from the dispersing means. The image forming method according to claim 1, wherein a magnetic toner is used. 6. The image forming method according to claim 1, wherein a magnetic toner having a hot air temperature of 100 to 600 degrees is used for surface-modifying the magnetic toner base particles. 7. The image forming method according to claim 1, wherein the magnetic toner is a one-component toner. 8. The image forming method according to claim 1, wherein in the transferring step, the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added. 9. The image forming method according to claim 1, wherein the conductivity imparting agent dispersedly added to the urethane foam in the transfer step is a lithium salt.