JP2552833B2 - Image forming method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image forming method for forming a brush of a small amount of magnetic particles on a toner holding member by using a negatively chargeable developer and using the brush for development.

[Prior Art] Various methods have heretofore been proposed and put into practical use as dry development methods.

For example, in a developing method using a two-component developer, when the image portion of the latent image is developed by the developer applied on the developing roller, the toner in the developer is the toner applied on the developing roller. I use less than a few percent of them. This is extremely inefficient considering the developing device configuration. This is because it is necessary to apply a large amount of developer on the developing roller with a constant amount and a uniform toner concentration each time the developing roller rotates in order to obtain a predetermined sufficient developing concentration. For this reason, the structure of the developing device has become large and complicated. Of course, attempts have been made to improve the developing efficiency even in this type of developing method. For example, the present applicant has proposed and put into practical use Japanese Patent Application Laid-Open No. 55-32060, 55-133058, 56-70560. According to this, although the development density can be increased and the development efficiency can be increased, the development efficiency close to 100% cannot be achieved in the image area, and this type of development method still has room for improvement. Is left.

In terms of improving development efficiency, the one-component development method is two
Better than the component development method. Among them, in Japanese Patent Application Laid-Open No. 54-43037, which was previously filed by the applicant of the present invention, a toner thin layer of 200 μm or less is formed on the developing roller, and the toner applied on the sleeve is developed to almost 100% in the image area. Developing with efficiency. Therefore, it was possible to put the developing device into a compact and simple structure for practical use. This was achieved because a thin layer of 200 μm or less could be formed on the developing roller. However, it is extremely difficult to form a thin layer of a dry developer in either one-component development or two-component development. Therefore, even in the one-component development, a relatively thick layer is formed by anyone other than the applicant. Configure the device. From the viewpoint of image quality, at the present time, it is required to improve the sharpness and resolution of a developed image, and development of a thin layer forming method of a dry developer and its apparatus is indispensable.

By the way, the above-mentioned applicant's method relates to the formation of a thin layer of the magnetic toner. In order to give the magnetic toner magnetism, it is necessary to internally add a magnetic substance to the toner. This is because of poor fixability when thermally fixing a developed image transferred onto a transfer paper, and the magnetic substance is internally added to the toner itself. Therefore (the magnetic substance is usually black), there is a problem such as poor color when reproducing the color.

Therefore, as a method for forming a thin layer of non-magnetic toner, a soft brush such as beaver hair is made into a cylindrical brush, and toner is adhered and applied to the brush, or a developing roller whose surface is made of fiber such as velvet. There has been proposed a method of coating with a doctor blade or the like.

However, when an elastic blade is used as a doctor blade for the fiber brush, the amount of toner can be regulated, but uniform application is not performed, and the fiber of the brush is simply rubbed by rubbing the fiber brush on the developing roller. Since triboelectrification charges are not applied to the toner existing between them, there is a problem that fogging is likely to occur.

Further, magnetic toners can easily prevent the toner from scattering by utilizing magnetic force, but non-magnetic toners cannot utilize magnetic force, and the toners are easily scattered inside the machine. The inconveniences described above occur not only during copying but also when vibration or shock is applied during transportation of the apparatus.

The applicant of the present application uses a non-magnetic toner and magnetic particles as a developing device which is completely different from the above-mentioned conventional method, provides a magnetic particle restraining member facing the toner carrying member, and restrains the magnetic particle with respect to the moving direction of the surface of the holding member. A method has already been proposed in which a magnetic brush of magnetic particles is formed upstream of the member by the magnetic force of the magnetic field generating means, the magnetic brush is restricted by the magnetic particle restriction member, and a thin layer of non-magnetic toner is formed on the toner holding member. (JP-A-58-143360). According to this method, the gap between the latent image carrier and the toner carrier in the developing section is set wider than the toner layer thickness, and an alternating electric field is applied to obtain a non-magnetic toner developed image on the surface of the latent image carrier. It was put to practical use. As a result, the development efficiency is extremely high and the size is small.
It is now possible to obtain a color developed image with a simple developing device configuration. Particularly, in the two-component magnetic brush rubbing development, a good quality solid image was obtained without any rubbing marks generated in the solid image portion. However, there has been a demand for further improvement in development image quality, for example, development of a development system that further improves gradation.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned conventional circumstances, and is small in size and light in weight to obtain a developed image having extremely high developing efficiency and comparable to the conventional developing method. The purpose is to provide a simple color development system.

Another object of the present invention is to provide a clear color image forming apparatus which is free from image density fluctuation and fog even after repeated use.

[Means and Actions for Solving Problems] That is, the present invention relates to a latent image holding member for holding an electrostatic latent image, and a developing agent carrying member in a developing area of the developer carrying member facing the latent image holding member. In the image forming method of developing an electrostatic latent image with a non-magnetic toner while applying an alternating electric field between the electrostatic latent image and the latent image carrier, the true specific gravity is 6 or less, and the electrostatic latent image is covered with an electrically insulating resin. Magnetic particles (excluding the case of magnetic particles coated with an electrically insulating resin having substantially the same structure as the binder resin of non-magnetic toner) are used in the developing area of the developer carrier. A magnetic brush is formed so that the amount of particles is 5 to 100 mg / cm ^2, and the latent image carrier and the surface of the developer carrier and the latent image carrier are kept in contact with the magnetic brush in the developing area. Between the surface of the magnetic brush and the amount of tribo charge on the magnetic particles is −
The present invention relates to an image forming method characterized by developing an electrostatic latent image by positive development while reciprocating a non-magnetic toner of 2.0 μC / g to −20.0 μC / g.

The non-magnetic toner referred to here is an external magnetic field 5000e,
A toner that exhibits only magnetization of 10 emu / g or less and that cannot behave substantially as a magnetic toner.

The inventors of the present invention proposed the above-mentioned Japanese Patent Application Laid-Open No. 58-143360, and as a result of earnest research on its improvement, as a result, a clear developing magnetic pole was formed in the developing portion to perform locally concentrated development. In the one-component developing method, the triboelectric charge is imparted to the toner mainly between the surface of the sleeve and the surface area of the sleeve is substantially increased. It has been found that stabilization of the toner supply to the top and improvement of image quality such as gradation and uniformity are achieved. Further, the non-magnetic toner having a triboelectric charge amount of −2.0 μC / g to −20.0 μC / g with respect to the magnetic particles used in the present invention is a toner which is a feature of the main developing system when applied to the main developing system. It has been found that the flight development from both the carrier and the magnetic particles can be smoothly performed, and an extremely clear color image can be stably formed even in repeated development over a long period of time.

In other words, in the main developing method, a toner image is obtained so that a good image can be obtained without providing a complicated stirring mechanism for toner and magnetic particles and a precise toner concentration control mechanism like the conventional two-component magnetic brush developing. It is necessary to utilize the surfaces of both the carrier and the magnetic particles forming the magnetic brush to take in the toner, perform triboelectrification, and ensure smooth flight development. A combination of non-magnetic toner having a triboelectric charge amount of −2.0 μC / g to −20.0 μC / g with respect to magnetic particles used in the present invention and magnetic particles having a true specific gravity of 6 or less and coated with an electrically insulating resin. Found that they could achieve them very well.

Here, a method of measuring the triboelectric charge amount (triboelectric charge amount) of the toner in the present invention will be described in detail with reference to the drawings.

FIG. 4 is an explanatory view of an apparatus for measuring the triboelectric charge amount of toner. First, in a metal measuring container 60 having a 400-mesh screen 61 on the bottom, a mixture of toner and magnetic particles having a weight ratio of 1: 9 (ball,
(Mixed for 10 minutes in a mill) Approximately 4 g is put into the metal lid
62. At this time, weigh the entire measuring container 60 and W ₁
(G). Next, in the suction device 59 (at least the portion in contact with the measurement container 60 is an insulator), suction is performed from the suction port 65 to adjust the air volume control valve 64 to adjust the pressure of the vacuum gauge 63 to 70 mmHg. In this state, suction is sufficiently performed (for about 1 minute) to remove the toner by suction. The potential of the electrometer 67 at this time is V (volt). Here, 66 is a condenser, and the capacity is C
(ΜF). The weight of the entire measuring container after suction is weighed and is W ₂ (g). Tribo charge of this toner (μC
/ g) is calculated by the following formula.

However, the measurement conditions are 23 ° C and 50% RH.

Hereinafter, the main developing method will be described with reference to Examples. First
The figure is an embodiment according to the present invention. In FIG.
3 is a latent image holding member, 21 is a toner supply container, 22 is a non-magnetic sleeve, 23 is a fixed magnet, 24 is a non-magnetic blade, 26 is a magnetic particle circulation region limiting member, 27 is magnetic particles, 28 is non-magnetic toner, Reference numeral 29 is a developer collecting container portion, 30 is a scattering prevention member, 31 is a magnetic member, 32 is a developing region, and 34 is a bias power source. The sleeve 22 rotates in the b direction, and the magnetic particles 27 circulate in the c direction accordingly. Then, as described later, it is preferable that the upper limit of the circulation region of the magnetic particles 27 is regulated by the magnetic particle circulation region limiting member 26 provided in the developer supply container 21. This causes contact and rubbing between the sleeve surface and the magnetic particle layer to form a non-magnetic toner layer on the sleeve surface. Further, while the magnetic particles circulate in the c direction, a part of the magnetic particles is regulated to a predetermined amount by the gap between the nonmagnetic blade 24 and the sleeve 22, and is applied onto the nonmagnetic toner layer. That is, the non-magnetic toner is applied on both the surface of the sleeve and the surface of the magnetic particles, and the effect equivalent to that of substantially increasing the surface area of the sleeve is exhibited.

In the developing area 32, one of the magnetic poles of the fixed magnet 23 is opposed to the latent image surface to form a clear developing pole, and the alternating electric field causes the toner to fly and develop on the sleeve and from the magnetic particles. (This phenomenon will be described later.)
After development, the magnetic particles and the undeveloped toner are collected in the developing container as the sleeve rotates.

The sleeve 22 may be a paper cylinder or a synthetic resin cylinder, but if the surface of these cylinders is subjected to a conductive treatment or is made of a conductor such as aluminum, brass or stainless steel, it can be used as a developing electrode roller.

As the magnetic particles used in the present invention, in order to remove the discharge between the sleeve and the latent image carrier due to an alternating electric field, it is desirable that the magnetic particles have a high electrical resistance, and the surface of the magnetic particles is made of an electrically insulating resin. It is preferably partially covered. The electrical insulating property referred to here means 10 ⁸ Ω · cm or more.

Further, the magnetic particles used in the present invention preferably have a low specific gravity so that the magnetic brush constituted by the magnetic particles can behave smoothly by an alternating electric field, and specifically, the true specific gravity is preferably 6 or less.

The coating amount of the magnetic particles on the downstream sleeve surface of the non-magnetic blade 24 in the present invention is 5 to 100 mg / cm ² , preferably 10 to 80 mg / in order to sufficiently utilize both the magnetic brush and the surface of the sleeve 22. A small amount of cm ² is desirable. If the amount of magnetic particles present on the surface of the sleeve is too large, the regulation force by the non-magnetic blade 24 is weakened, the sliding force between the sleeve and the magnetic particles is reduced, and the toner can be smoothly charged. Can not. Further, there is a drawback that the magnetic particles also fly during the flight development of the toner and adhere to the latent image carrier 3. On the contrary, the development area of magnetic particles
If the amount of the sleeve surface present in 32 is too small, the amount of toner applied to the developing area will decrease, resulting in uneven density and image density reduction. The amount of magnetic particles present on the surface of the sleeve can be adjusted mainly by the gap with the sleeve 22, the position of the N ₁ pole of the fixed magnet 23, the magnetic density of the S ₁ pole, and the like.

The method for measuring the abundance of magnetic particles in the present invention is described below. First, a magnetic brush made of only magnetic particles was formed on the sleeve, magnetic particles in a portion corresponding to the developing area were sucked using a cylindrical filter as a filter, and the weight M (g) was measured. Next, the remaining magnetic particles on the sleeve after the magnetic particles were attracted were sampled with a transparent adhesive tape, and the occupied area S (cm ² ) of the attracted magnetic particles was determined. The abundance m (mg / cm ² ) of magnetic particles was calculated as follows.

m = M / S The developing area means an area of 10 mm in the front and back with the closest portion between the latent image holding member and the developer carrying member as the center.

The gap distance d between the tip of the non-magnetic blade 24 and the surface of the developing sleeve 22 at the point 25 is 50 to 500 μm, preferably 100 to 400 μm. If the distance d is less than 50 μm, the magnetic particles are likely to be clogged and the sleeve is easily damaged. If it is larger than 500 μm, a large amount of non-magnetic toner and magnetic particles are likely to leak out, and it is difficult to form a thin layer.

In FIG. 1, reference numeral 26 is a magnetic particle circulation region limiting member whose lower surface is in contact with the upper surface side of the non-magnetic blade 24 and whose front end surface is an undercut surface.

Denoted at 27 and 28 are magnetic particles and non-magnetic toner that are sequentially accommodated in the toner supply container 21.

The bottom plate of the toner supply container 21 is extended below the developing sleeve 22, which is a toner holding member, to prevent the toner from leaking to the outside. In order to further prevent the leakage of this toner to the outside, a leakage toner collection container portion 29 that receives and restrains the leakage toner and a scattering toner along the length of the tip edge of the extension bottom plate are provided on the upper surface of the extension bottom plate. Prevention member
30 is provided. A voltage described later is applied to this member 30.

The magnetic particles 27 generally have an average particle size of 30 to 100 μm, preferably 40 to 80 μm. Each magnetic particle may be composed of only a magnetic material, a combination of a magnetic material and a non-magnetic material, or a mixture of two or more kinds of magnetic particles. Then, by first inserting the magnetic particles 27 into the toner supply container 21, the magnetic particles 27 from the toner supply container 21 in which the magnetic particles 27 face the inside of the container 21, that is, the sleeve 22 are arranged. Alternatively, the magnetic particle layer in the sleeve 22 is attracted and held by each magnetic field by the magnet 23 in the sleeve 22 in each part of the sleeve surface area from the magnetic member 31 for preventing the leakage of the toner to the tip of the non-magnetic blade 24 which is the magnetic particle restraining member. The entire surface area is covered. The non-magnetic toner 28 is charged into the container 21 after the magnetic particles 27 are charged therein, so that a large amount of the non-magnetic toner 28 is stored outside the magnetic particle layer as the first layer with respect to the sleeve 22 and exists as the second layer.

It is preferable that the magnetic particles 27 to be initially charged contain about 2 to 70% (weight) of the non-magnetic toner 28 based on the magnetic particles, but the magnetic particles may be magnetic particles only. Further, once the magnetic particles 27 are adsorbed and held as a magnetic particle layer on the sleeve surface area, they do not substantially flow to one side even if the apparatus is vibrated or the apparatus is tilted to a large extent. The overall covered state is retained.

Thus, in the state where the magnetic particles 27 and the non-magnetic toner 28 are sequentially charged and accommodated in the container 21 as described above, the magnetic particle layer portion near the sleeve surface corresponding to the magnetic pole S ₂ position of the magnet 23 is A magnetic brush of magnetic particles is formed by a magnetic field having a strong magnetic pole.

Further, the magnetic particle layer portion near the tip of the non-magnetic blade 24, which is a magnetic particle regulating member, is regulated based on the effect of gravity and magnetic force and the presence of the non-magnetic blade 24 even if the sleeve 22 is driven to rotate in the direction of arrow b. Due to the balance between the force and the conveying force of the sleeve 22 in the moving direction, the force accumulates at a point 25 on the surface of the sleeve 22 and forms a stationary layer which can move a little but dwell.

When the sleeve 22 is rotated in the direction of the arrow b, the magnetic brush can be moved near the magnetic pole S ₂ by appropriately selecting the position of the magnetic pole and the fluidity and magnetic characteristics of the magnetic particles 27.
Circulating in the direction to form a circulating layer. In the circulation layer,
The magnetic particles that are relatively close to the sleeve 22 rise up from the vicinity of the magnetic pole S ₂ onto the stationary layer on the downstream side of the rotation of the sleeve as the sleeve 22 rotates. That is, it receives the force of pushing it up. The magnetic particles pushed up are provided with a magnetic particle circulation region limiting member 26 provided on the non-magnetic blade 24.
Therefore, since the upper limit of the circulation region is determined, it does not ride on the non-magnetic plate 24, falls by gravity, and returns to the vicinity of the magnetic pole S ₂ again. In this case, the magnetic particles having a small push-up force, such as being located far from the sleeve surface, may fall before reaching the magnetic particle circulation region limiting member 26. That is, in the circulation layer, the magnetic brush of magnetic particles is circulated as indicated by an arrow c due to the magnetic force and frictional force due to gravity and magnetic poles and the fluidity (viscosity) of the magnetic particles. The non-magnetic toner 28 is successively taken in from the toner layer on the upper side and returned to the lower part in the developer supply container 21, and this circulation is repeated as the sleeve 22 is driven to rotate.

As the developing bias voltage 34, an alternating voltage having the same peak voltage on the positive side and the negative side or a DC voltage superimposed on this alternating voltage can be used. For example, with respect to an electrostatic latent image having a dark portion latent image potential of +600 V and a bright portion latent image potential of +200 V, as an example, a DC voltage of +330 V is superimposed on the sleeve 22, and a peak voltage V _{pp of} 300 to 2000 V and a frequency of 200 to 3000 Hz are applied. An alternating voltage selected within the range is applied to hold the photosensitive drum 3 at the installation potential. Generally, the electric resistance of the magnetic brush is relatively high (greater than 10 ⁸ Ωcm), in which case the peak voltage width V _pp of the developing bias should be high (for example, 800 V or higher) and the frequency is 600 Hz or higher, preferably 800 Hz or higher. Preferably 1kHz
As described above, the higher the quality, the better the image quality with sufficient density. However, even if only V _pp is high, if the frequency is low, the density is low and it is difficult to obtain good image quality. In any case, the upper limit of V _pp is determined by the gap discharge limit value of the developing section, and the lower limit thereof is determined by the toner flight limit value on the sleeve and the magnetic particles.

In the comparatively high resistance developing brush, the peak value of the alternating electric field is set by appropriately selecting the frequency of the alternating electric field to be applied and the time constant of the developing brush itself so that the gap voltage does not reach the discharge start voltage. It is preferable.

Incidentally, the resistance value of the magnetic particles and the magnetic brush described in the present invention means the developing sleeve 22 by the developing device shown in FIG.
A magnetic brush of 50 mg / cm ² magnetic particles is formed on the top, a developing sleeve and a metal drum with a gap of about 5 mm are provided opposite to this, and a DC circuit is connected to a resistance of about 1 MΩ in series with these. It is calculated and calculated from the value of the current that flows when a voltage of 200 V is applied.

The phenomenon in the developing section 32 will be described below regarding the developing method according to the present invention.

2 and 3 are enlarged explanatory views of the developing section in the developing method according to the present invention. 50 is the latent image charge in the dark area on the latent image carrier. 28 is a non-magnetic toner. 34 is an alternating voltage power supply on which a DC component is superimposed. 2 shows the case where a plus waveform component of the alternating voltage is added to the sleeve 22, and FIG. 3 shows the case where a minus waveform component of the alternating voltage is added. The polarity of the latent image charge is shown as positive and the polarity of the developer is shown as negative.

Since the resistance of the developing brush 51 is relatively large (greater than about 10 ⁸ Ωcm), the developing brush 51 depends on the charging / discharging time constant of the charge due to the material of the developing brush 51 itself, etc. Alternatively, there is a charge injected by the mirror charge, the latent image electric field on the latent image carrier 3 and the alternating electric field between the latent image carrier 3 and the sleeve 22.

When the electric field due to the latent image charge 50 in the dark portion on the latent image carrier 3 and the electric field due to the alternating electric field coincide with each other, the developing brush 51 is in the maximum sagging state in the sleeve 22 direction.

When the direction of the electric field due to the latent image charge on the latent image carrier 3 and the direction of the electric field due to the alternating electric field do not match, the yielding of the developing brush 51 becomes small.

In any case, as described above, the developing brush is generated by the alternating electric field.
51 is in a fine but violent vibration state, and the fog toner excessively attached to the latent image holding member is rubbed by the developing brush, removed from the latent image holding member 3, and pulled back onto the brush. Further, due to the vibration of the brush, the toner is easily separated from the brush 51 and is easily supplied to the latent image holding member 3, so that the image density is also improved. Also brush 51
The above-mentioned vibration loosens the toner in the brush 51, which contributes to improvement of image density and prevention of ghost. further,
When this vibrating state is severe, a part of the magnetic brush separates from the brush or the sleeve and reciprocates between the latent image carrier and the sleeve surface. The kinetic energy of this reciprocating brush is large and efficient, and the effect of the above-mentioned vibration is expected. The above behavior of the magnetic particles in the developing section is a phenomenon observed as a result of high-speed photography of 8000 frames per second with a high-speed camera.

The toner coating magnetic particles used in the present invention include:
A true specific gravity of 6 g / cm ³ or less is used, and for example, surface-oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, metals such as rare earths, and alloys or oxides thereof can be used, but preferably Metal oxides, more preferably ferrite particles, can be used. Further, there is no particular limitation as a manufacturing method thereof.

Further, as a method of coating the surface of the magnetic particles with a resin or the like, a method of dissolving or suspending a coating material of a resin or the like in a solvent and applying it and adhering it to a carrier, a method of simply mixing with a powder, etc. Any known method can be applied.

The coating resin for the carrier surface varies depending on the toner material, but examples include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, styrene resin, acrylic resin, polyamide, polyvinyl butyral, amino. It is suitable to use one or more acrylate resins, but it is not necessarily limited thereto.

The amount of the above compound to be treated may be appropriately determined so that the carrier satisfies the above conditions, but in general, the total amount is preferably 0.1 to 30% by weight (preferably 0.5 to 20% by weight) based on the carrier of the present invention.

On the other hand, as the binder resin for the toner used in the present invention, a homopolymer of styrene such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene and the like, or a substituted polymer thereof;
Styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-
Methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer Coalesce, styrene-butyl methacrylate copolymer,
Styrene-acryl-amino acrylic copolymer, styrene-amino acrylic copolymer, styrene-α-methyl methyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl Ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acryloylitol-indene copolymer, styrene-maleic acid copolymer, styrene- Styrene-based copolymers such as maleic acid ester copolymers; polymethylmethacrylate, polybutylmethacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyrers , Polyacrylic acid resins, rosin-modified rosin, terpene resins, phenol resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffin, and paraffin wax may be used alone or in combination.

In the toner, any suitable pigment or dye can be used as a colorant. For example, there are known dyes and pigments such as carbon black, iron black, phthalocyanine blue, ultramarine, quinacridone, and benzidine yellow.

Further, as a charge control agent, an organic dye, a metal-containing dye, a salicylic acid metal-containing compound or the like may be added. Further, magnetic powder may be added to the extent that the effects of the present invention are not impaired.

The above toner composition may be used for a toner by a commonly used mixing-pulverizing method, or may be used for a wall material or a core material of a microcapsule toner or both.

EXAMPLES The present invention will be described in more detail with reference to examples. Parts shown in the examples are parts by weight.

 As the developing device, the one shown in FIG. 1 was used.

In the apparatus of the embodiment, the photosensitive drum 3 is 60
It rotates at a peripheral speed of mm / sec. 22 is a stainless steel with an outer diameter of 32 mm and a thickness of 0.8 mm that rotates at a peripheral speed of 66 mm / sec in the direction of arrow b (S
US304) sleeve, the surface of which was subjected to irregular sandblasting using ^# 600 alundum abrasive grains so that the surface roughness in the circumferential direction was 0.8 μm (R _Z =).

On the other hand, a ferrite sintered type magnet 23 is fixedly arranged in the rotating sleeve 22, and the magnetic pole arrangement is such that the maximum value of the surface magnetic flux density is about 800 gauss as shown in FIG.

The non-magnetic blade 24 was made of non-magnetic stainless steel having a thickness of 1.2 mm. The blade sleeve gap was 400 μm.

On the surface of the photosensitive drum 3 facing the sleeve 22,
As an electrostatic latent image, an electrostatic latent image of + 600V in the dark portion was formed at + 600V in the dark portion, and the distance from the sleeve surface was set to 300 μm. And the frequency of 1,800H is applied to the sleeve by the power supply 34.
z, peak-to-peak value was 1.4 kV, and center value was +330 V, and a voltage was applied to develop.

Example 1 To 100 parts of green particles having an average particle size of 12.5 μm, 0.6 part of hydrophobic colloidal silica was externally added to obtain a toner.

Next, 100 ferrite particles with a particle size of 250-300 mesh
Part surface styrene-methyl methacrylate copolymer 0.
Coated with 5 parts, magnetic particles were obtained (true specific gravity: 5.2). When 15 parts of the above toner and 100 parts of magnetic particles were mixed and charged into the developing device shown in FIG. 1 and a magnetic brush of about 40 g / cm ² was formed in the developing area, a clear green image without fog was obtained. . When the state at the time of development was photographed with a high-speed camera, it was possible to observe that the flight development was smoothly performed from both the sleeve and the magnetic brush. The triboelectric charge amount of the mixture of the toner and the magnetic particles of 1: 9 was measured and found to be −2.0 μC / g.

Example 2 In Example 1, 10 parts of phthalocyanine green pigment was added.
The same good results were obtained as in Example 1 except that CI Pigment Yellow 151 was changed to 15 parts. The triboelectric charge of the 1: 9 mixture of this toner and magnetic particles was measured and found to be −20.0 μC / g.

Example 3 1 part of hydrophobic colloidal silica was externally added to 100 parts of red particles having an average particle size of 9.5 μm to obtain a toner.

Next, 100 ferrite particles with a particle size of 250-300 mesh
The surface of each part was coated with 1.5 parts of epoxy resin to obtain magnetic particles (true specific gravity: 5.8). When 10 parts of the above toner and 100 parts of magnetic particles were mixed and the same procedure as in Example 1 was carried out, good results were obtained. The triboelectric charge amount of the 1: 9 mixture of the toner and the magnetic particles was measured and found to be −7.7 μC / g.

[Effects of the Invention] As described above, according to the present invention, in a developing device using magnetic particles having a simple structure, a non-magnetic toner having a triboelectric charge amount of −2.0 to −20.0 μC / g with respect to the magnetic particles. By using, it was possible to obtain good image quality with no background fog, good gradation, and no negative characteristics.

Further, by effectively distributing the toner that contributes to the development on the sleeve and the magnetic particles and performing the flight development from both of them, it was possible to achieve a development efficiency of nearly 100% in an alternating electric field. This is a compact developing device configuration.
This enables simplification.

Further, the brush of magnetic particles according to the present invention was brought into contact with the latent image carrier and vibrated by at least an alternating electric field, whereby the ground fog toner adhering to the latent image carrier could be removed.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view of a developing device according to the developing method according to the present invention, FIGS. 2 and 3 are enlarged explanatory views of a developing portion by the developing method according to the present invention, and FIG. 4 is measurement of triboelectric charge amount of toner. It is a device. 1 ... Electrostatic latent image holder, 3 ... Latent image holding member, 21 ... Developer supply container, 22 ... Non-magnetic sleeve, 23 ... Fixed magnet, 24 ... Non-magnetic blade, 26 ... Magnetic Particle circulation area limiting member, 27 ... Magnetic particles, 28 ... Non-magnetic toner, 29 ... Developer collecting container section, 30 ... Scatter prevention member, 31 ... Magnetic member, 32 ... Development area, 34 ... … Bias power supply, 50… Electrostatic latent image, 51… Magnetic brush, 59… Suction machine, 60… Measuring container, 61… Screen, 62… Lid, 63… Vacuum gauge, 64
...... Air flow control valve, 65 …… Suction port, 66 …… Condenser,
67 …… Electrometer.

Claims (2)

(57) [Claims] 1. A latent image holder for holding an electrostatic latent image,
In the image forming method of developing an electrostatic latent image with a non-magnetic toner while applying an alternating electric field between the developer carrying member and the latent image holding member in the developing area of the developer carrying member facing this, the true specific gravity is Of 6 or less and coated with an electrically insulating resin (provided that the magnetic particles coated with the electrically insulating resin having substantially the same structure as the binder resin of the non-magnetic toner are (Excluding the case), a magnetic brush is formed in the developing area of the developer carrier so that the amount of the magnetic particles present is 5 to 100 mg / cm ^2, and in the developing area, the latent image carrier and the magnetic brush are While contacting the surface of the latent image carrier and the surface of the developer bearing member and the surface of the magnetic brush, the amount of tribo charge on the magnetic particles is -2.
An image forming method comprising developing an electrostatic latent image by positive development while reciprocating a non-magnetic toner of 0 μC / g to −20.0 μC / g. 2. The image forming method according to claim 1, wherein the upper limit of the magnetic particle circulation region is regulated by a magnetic particle circulation region limiting member provided in the developer supply container.