JP2854317B2 - Electrophotographic color developer - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a color developer for electrophotography, and more particularly to an improvement in an electrophotographic carrier useful for full-color copying electrophotography.

[Prior Art] Conventionally, regarding electrophotography, US Pat. No. 2,297,
No. 691, JP-B-42-23910, JP-B-43-24748, etc., a uniform electrostatic charge is imparted to the photoconductive layer by corona discharge, and an The latent image is formed by exposing the exposed portion to eliminate the electric charge in the exposed portion. The development is carried out by adhering a fine powder test substance, so-called toner, on the obtained electrostatic latent image.
The toner is attracted to the electrostatic latent image according to the amount of charge on the photoconductive layer, and forms a toner image having a density. This toner image is transferred to a support surface such as paper or cloth as necessary, and is permanently fixed to the support surface by using appropriate fixing means such as heating, pressing, solvent treatment, or overcoating. If it is desired to omit the toner image transfer step, the toner image can be fixed on the photoconductive layer.

In the development of the electrostatic latent image, the toner is mixed with a carrier having relatively large particles and used as a developer for electrophotography. The composition of both the toner and the carrier are chosen such that the toner has a polarity opposite to the charge on the photoconductive layer due to mutual contact friction. As a result of the contact friction between the two, the carrier electrostatically attaches the toner to the surface, transports the developer as a developer in the developing device, and supplies the toner onto the photoconductive layer.

There are many known methods for developing a developer. Cascade developing method described in U.S. Pat.No. 2,618,552, magnetic brush method described in U.S. Pat.No. 2,874,063, U.S. Pat.
JP-A-62-63970 discloses a touch-down method described in JP-A No. 47-63970 and others, in which a bias electric field composed of an AC component and a DC component is applied between a developer carrier (developing sleeve) and a photoconductive layer to perform development. And the so-called J / B development method.

A typical method is a magnetic brush method. That is, magnetic particles such as steel and ferrite are used as the carrier, and the developer including the toner and the magnetic carrier is held by a magnet, and the developer is arranged in a brush shape by the magnetic field of the magnet. When the magnetic brush comes into contact with the electrostatic latent image surface on the photoconductive layer, only the toner is attracted from the brush to the electrostatic latent image to perform development.

When a large number of continuous copies are made with an electronic copying machine using a two-component developer, a clear image with good image quality can be obtained at the initial stage. The resulting image is poor in tonality and sharpness.

In color copying using chromatic toners, continuous tone is an important factor affecting image quality. Is greatly impaired. For example, a pseudo contour by an edge effect is formed in the vicinity of an actual contour, thereby deteriorating copy reproducibility including color reproducibility in color copying. Also, the image area used in conventional black-and-white copying is 10% or less, and the image is almost a line image portion such as a letter, a document, a report, etc., whereas in color copying, the image area is at least 20% or more, and solid images having gradation such as photographs, catalogs, maps, and paintings occupy a considerable frequency or area.

When continuous copying is performed using such a document having a large image area, a copy having a high image density is usually obtained in the initial stage, but the toner supply to the two-component developer cannot be completed in time, and the density decreases. When the toner is supplied or insufficiently charged, the replenishment toner and the carrier are mixed with each other to cause fogging, and the toner density (indicating the mixing ratio of the toner and the carrier) partially increases or decreases on the developing sleeve. There is a tendency that blurring of the resulting image and uniformity of density in the image cannot be obtained. This tendency is more remarkable when the diameter of the toner is reduced.

This is because the amount of toner included in the developer (that is, the toner concentration) is too low, or the rapid rise of triboelectric charging between the replenishment toner and the carrier in the two-component developer is poor, and the uncontrollability is insufficient. It is considered that such insufficient development and fogging occur due to the fact that the toner of the charge amount participates in the development. As a color developer, the ability to always output a high-quality image by continuous copying of a document having a large image area is essential. Conventionally, in order to cope with an original having a large image area and a very large amount of toner consumption, improvement of the developing device rather than improvement of the developer itself has been dealt with more. That is, in order to increase the chance of the developing sleeve contacting the electrostatic latent image, the peripheral speed of the developing sleeve is increased, or the size of the developing sleeve is increased.

Although these countermeasures increase the developing ability, they cause contamination of the inside of the apparatus due to scattering of toner from the developing device, and significantly limit the life of the device due to overload on the driving of the developing device. In addition, in some cases, a large amount of developer is charged into the developing device to compensate for the lack of developing ability of the developer. However, these problems also increase costs due to an increase in the weight of the copier and an increase in the size of the device. As described above, this results in overload on the driving of the developing device, which is not very preferable.

Japanese Patent Application Laid-Open Nos. Sho 51-3238, 58-144839, and 61-204646 disclose the average particle size and particle size distribution of the carrier. JP-A-51-3238 refers to a rough particle size distribution. However, it does not specifically disclose the magnetic properties closely related to the developability of the developer and the transportability in the developing device. Furthermore, all the carriers in the examples are about 80% by weight of 250 mesh on.
The average particle size is also 60 μm or more.

Further, Japanese Patent Application Laid-Open No. 58-144839 discloses only the average particle size and mentions the amount of fine powder that affects the carrier adhesion to the photoreceptor and the amount of coarse powder that affects the sharpness of the image. The distribution is not described in detail in consideration of the characteristics of color copying. Furthermore, Japanese Patent Application Laid-Open No. 61-204646 discloses a combination of a copying machine and an appropriate developer as the gist of the invention, and does not specifically describe the particle size distribution and magnetic properties of the carrier. Furthermore, it does not even disclose why the developer is effective in the copying machine.

Also, JP-A-49-70630 describes the magnetic force of a carrier, but these are used as carrier materials.
This is for iron powder having a higher specific gravity than ferrite, and has high saturation magnetism. Conventionally, these iron powder carriers have been used in many cases. However, since the specific gravity is large, the copying apparatus is liable to increase in weight and the driving torque is overloaded, and the environment is highly dependent.

Further, the ferrite carrier described in Japanese Patent Application Laid-Open No. 58-23032 is based on a porous material having a large number of pores, and such a carrier tends to cause an edge effect and has poor durability. This has been found to be unsuitable as a color carrier.

Heretofore, there has been a long-awaited demand for a developer capable of continuously copying an image having a large image area with a small amount of developer and satisfying the characteristic characteristic of color copying in which an edge effect does not occur even after durability. Although studies are being made on developers and carriers, most of them have been proposed in consideration of black-and-white copying, and very few have been proposed for full-color copying. In addition, a carrier having the ability to continue copying an image having an image area of 20% or more, which is almost a solid image, to reduce the edge effect, and to maintain the uniformity of the image density in one copy is available. Long awaited.

[Problems to be Solved by the Invention] An object of the present invention is to provide a color developer for electrophotography which does not cause a decrease in image density and does not cause blurring even when a color original having a large image area is continuously copied.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrophotographic color developer capable of obtaining a color copy in which an edge effect is suppressed even after durability by repeated copying.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrophotographic color developer capable of obtaining a rapid rise in triboelectric charging between a toner and a carrier.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic color developer having little environmental dependency of triboelectric charging.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color developer for electrophotography having good transportability in a developing device.

Means and Action for Solving the Problems The inventors of the present invention have intensively studied the best carrier for color copying using a toner having a small particle diameter of 6 to 11 μm, and have reached the present invention.

Specifically, the present invention has an average particle size of 20 to 60 μm,
The amount of fine powder in the 350 mesh pass is 40% by weight or less, the amount of fine powder in the 400 mesh pass is 20% by weight or less, and the amount of ultrafine powder in the 500 mesh pass is 1 to 8% by weight. 11 μm or less is substantially 0,
The amount of coarse powder of 250 mesh on is 1.0 to 7% by weight and 3000
The saturation magnetization for the applied magnetic field of Oersted is 55 to 75 emu /
g, the residual magnetization is 10 emu / g or less, and the coercive force is 10
The magnetic particles of e or less are used as an electrophotographic carrier.

The electrophotographic carrier used in the present invention is different from a conventionally known carrier in that the average particle size is small and the amount of fine powder and the amount of coarse powder are controlled, so that the particle size distribution is very narrow and sharp cut. As a result, there is almost no ultrafine powder that adversely affects the carrier adhesion, and the carrier has a uniform particle size and uniform particle size. Therefore, the rise of the triboelectric charging property with the toner is also preferably improved. In addition, by being a uniform carrier with a small particle size,
The amount of toner having good chargeability that can be included in a carrier is much larger than that of a carrier having a broad particle diameter. When a broad carrier having a particle size is used, the fine powder carrier causes the carrier to adhere to the photoreceptor during development. Further, in many cases, the toner mixed with the coarse powder carrier has a charge amount that is too high in terms of charge, and is difficult to develop.

The ultrafine powder of the 500 mesh pass is 1 to 8% by weight, preferably 2 to 6% by weight. When the amount exceeds 8% by weight, carrier adhesion and smooth triboelectric charging with the toner are hindered, and the edge effect tends to be promoted. If the amount is less than 1% by weight, the magnetic brush becomes sparse, the rise of the toner charge becomes poor, and toner scattering and fogging are caused.

Further, the amount of coarse powder showing a carrier amount of 250 mesh-on is closely correlated with the sharpness of an image, and needs to be 1 to 7% by weight. If the amount is more than 7% by weight, the toner carrying ability of the carrier is reduced, the scattering of the toner to the non-image is increased, and the resolution of the image is reduced and the roughness is likely to become apparent. Therefore, the content of 250 mesh-on is preferably 7% by weight or less, and more preferably 5% by weight or less. On the other hand, when the content is less than 1% by weight, the fluidity of the developer is deteriorated, and the bias of the developer in the developing device is caused, so that it is difficult to obtain a stable image.

The average particle size of the carrier is preferably from 20 to 60 μm, more preferably from 30 to 56 μm. When the average particle diameter is less than 20 μm, the carrier adhesion to the photoreceptor increases drastically, and when the average particle diameter exceeds 60 μm, the highlight reproducibility of color copying deteriorates.

The magnetic characteristics of the carrier are affected by the magnet roller built into the developing sleeve, and greatly affect the developing characteristics and transportability of the developer.

In the present invention, on a developing sleeve having a built-in magnet roller, the magnet roller is fixed and the developing sleeve is rotated by itself, and a two-component developer composed of magnetic particles and an insulating color toner is circulated and conveyed. When developing an electrostatic latent image carried on the surface of the electrostatic latent image carrier with a developer, the developing sleeve has an outer diameter of 32 mm, and the magnet roller has a 5-pole configuration having repulsive poles,
The magnetic flux density in the development area is 600-1200 gauss,
When the carrier has a saturation magnetization of 75 emu to 55 emu, color uniformity is excellent in image uniformity and gradation reproducibility.

If the saturation magnetization exceeds 75 emu / g (for an applied magnetic field of 3000 Oersted), a brush-like spike composed of a carrier and toner on a developing sleeve facing the electrostatic latent image on the photoreceptor during development Standing tightly tightened,
Gradation and reproduction of halftones deteriorate. On the other hand, if it is less than 55 emu / g, it becomes difficult to hold the toner and the carrier on the developing sleeve satisfactorily, and the problem that the adhesion of the carrier and the scattering of the toner are deteriorated easily occurs. Further, if the residual magnetization and coercive force of the carrier are too high, good transportability of the developer in the developing device is hindered, and image defects are likely to occur such as blurring and uneven density in a solid image,
The developing ability is reduced. Therefore, unlike ordinary black-and-white copying, in order to maintain developability in color copying, the residual magnetization is 10 emu / g or less, preferably 5 emu / g or less.
u / g or less, more preferably substantially 0, and the coercive force is 10
It is important that it is less than or equal to e (3000 Oe, relative to the applied magnetic field), preferably less than or equal to 6.0 e and more preferably substantially zero.

Next, an example of the developing device according to the present invention will be described with reference to FIG.

The latent image carrier 1 is a photosensitive drum having a photoconductive insulating material layer such as a-Si, Cds, ZnO ₂ , OPC, a-Se. The latent image carrier 21 is rotated in the direction of arrow a by a driving device (not shown). twenty two
Reference numeral denotes a developing sleeve which is close to or in contact with the latent image carrier 21, and is made of a non-magnetic material such as aluminum or SUS316. The developing sleeve 22 has a horizontally long opening formed in the longitudinal direction of the container on the lower left wall of the developing container 36, with a substantially right half circumferential surface protruding into the container 36, and a left substantially half circumferential surface being exposed outside the container to be rotatably supported. It is provided horizontally and is driven to rotate in the direction of arrow b.

Reference numeral 23 denotes a fixed permanent magnet (magnet) serving as a fixed magnetic field generating means inserted into the developing sleeve 22 and positioned and held in the position and orientation shown in the figure. Even when the developing sleeve 22 is driven to rotate, this magnet 23 is It is fixed and held as it is in the posture. The magnet 23 has four magnetic poles, an N-pole 23a, an S-pole 23b, an N-pole 23c, and an S-pole 23d. The magnet 23 may be provided with an electromagnet instead of the permanent magnet.

Reference numeral 24 denotes a developer supply device provided with a developing sleeve 22 and a base fixed to the side wall of the container on the upper edge side of the developer supply opening. A non-magnetic blade as a developer regulating member
For example, SUS316 is bent into a cross-sectionally curved shape.

Reference numeral 26 denotes a magnetic particle limiting member whose upper surface is in contact with the lower surface of the non-magnetic blade 24 and whose front end surface is a developer guide surface 261.
The portion constituted by the non-magnetic blade 24 and the magnetic particle limiting member 26 and the like is a regulating portion.

27 is a magnetic particle having a resistance of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more (maximum magnetization 55 to 75 emu /
g) 0.05 to 10% by weight of electrically insulating resin coating
A value of from ⁹ Ωcm to 10 ¹⁴ Ωcm may be used.

The measurement of the resistance value of the magnetic particles was performed using a measurement electrode area of 4 cm ² ,
Using a sandwich type cell with an electrode spacing of 0.4 cm,
A method is adopted in which an applied voltage E (V / cm) between both electrodes is applied to one electrode under a pressure of 1 kg weight, and the resistance value of the magnetic particles is obtained from the current flowing in the circuit.

 37 is a non-magnetic toner.

Numeral 40 denotes a sealing member for sealing the toner accumulated in the lower portion of the developing container 36, which has elasticity and is bent in the rotation direction of the sleeve 22, and elastically presses the surface side of the sleeve 22.
The seal member 40 has an end on the downstream side in the sleeve rotation direction in a contact area with the sleeve so as to allow the developer to enter the inside of the container.

Reference numeral 60 denotes a toner replenishing roller that operates according to an output obtained by a toner density detection sensor (not shown).
Examples of the sensor include a volume detection method of a developer, a piezoelectric element, an inductance change detection element, an antenna method using an alternating bias, and a method of detecting optical density. The non-magnetic toner 37 is supplied by stopping the rotation of the roller. The fresh developer supplied with the toner 37 is mixed and stirred while being conveyed by the screw 61. Accordingly, a tribo is applied to the replenished toner during this conveyance. Reference numeral 63 denotes a partition plate which is cut out at both ends in the longitudinal direction of the developing device. At this portion, the fresh developer conveyed by the screw 61 is delivered to the screw 62.

The S magnetic pole 23d is a transport pole. The collected developer after the development is collected in the container, and the developer in the container is further transported to the regulating section.

In the vicinity of 23d, the fresh developer conveyed by the screw 62 provided near the sleeve and the recovered developer after development are exchanged.

Numeral 64 denotes a conveying screw for uniformizing the amount of developer in the developing sleeve axial direction.

This configuration is also effective when magnetic particles and non-magnetic or weak magnetic toner are mixed in the developer container.

The distance d ₂ between the end portion of the non-magnetic blade 24 and the developing sleeve 22 surface is 300 to 1000, preferably 400～900Myuemu. If this distance is smaller than 300 μm, the magnetic particles described later are clogged in the meantime, and the developer layer is likely to be uneven, and the developer required for good development cannot be applied, and the density of the developed image is low and uneven. There is a disadvantage that can only be obtained. d ₂ is 40 in order to prevent non-uniform application (so-called blade jam) due to unnecessary particles mixed during development.
0 μm or more is preferred. On the other hand, if the thickness is larger than 1000 μm, the amount of the developer applied on the developing sleeve 22 increases, so that a predetermined developer layer thickness cannot be regulated, the magnetic particles adhere to the latent image carrier and the developer circulation described later increases. , Developer limited member
There is a drawback that the development regulation by Step 26 is weakened and the toner tribo is insufficient and fogging easily occurs.

The angle θ1 is −5 ° to 35 °, preferably 0 ° to 25 °. When θ1 <−5 °, the developer thin layer formed by the magnetic force, mirroring force, cohesive force, etc. acting on the developer becomes sparse and uneven, and when θ> 35 °, the non-magnetic blade is The amount of developer applied increases, and it is difficult to obtain a predetermined amount of developer.

Even when the magnetic particle layer is driven to rotate in the direction of arrow b, the movement of the magnetic particle layer becomes slower as the distance from the sleeve surface increases due to the balance between the magnetic force and the restraining force based on gravity and the conveying force in the moving direction of the sleeve 22. . Of course, some fall under the influence of gravity.

Therefore, by appropriately selecting the arrangement positions of the magnetic poles 23a and 23d and the fluidity and magnetic characteristics of the magnetic particles 27, the magnetic particle layer is conveyed toward the magnetic pole 23a closer to the sleeve to form a moving layer.
Due to the movement of the magnetic particles, the magnetic particles are conveyed to the developing area with the rotation of the sleeve 22 and used for development.

As the binder resin for toner of the toner used with the carrier of the present invention, the following can be used. For example, polystyrene, chloropolystyrene, poly-
α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer , Styrene-acrylate copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer,
Styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, etc.), styrene-methacrylic ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methacrylic) Styrene resin (styrene or styrene-substituted product) such as butyl acrylate copolymer, styrene-phenyl methacrylate copolymer, styrene-α-methyl methacrylate copolymer, styrene-acrylonitrile-acrylate copolymer, etc. , A styrene-vinyl acetate copolymer, a rosin-modified maleic resin, a phenolic resin, an epoxy resin, a polyester resin, a low-molecular-weight polyethylene,
There are low molecular weight polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral resin and the like. In the practice of the present invention, particularly preferred resins are styrene-acrylate resins,
There is a polyester resin.

In particular, (Wherein R is an ethylene or propylene group, x,
y is an integer of 1 or more, and x + y has an average value of 2 to 10. A) a carboxylic acid component composed of a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof, such as fumaric acid, maleic acid,
A polyester resin obtained by at least co-condensation polymerization of maleic anhydride, phthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid and the like has sharp melting characteristics, and is therefore more preferable for a color toner.

As the carrier used in the present invention, known materials can be used without departing from the scope of the present invention. For example, surface-oxidized or unoxidized iron, nickel, copper, zinc, cobalt, manganese, chromium, rare earth elements And their alloys or oxides and ferrites. Preferably, ferrite selected from metals of zinc, copper, nickel, and cobalt can be preferably used in terms of magnetic properties.
The method of controlling the particle size distribution may be any method as long as it satisfies the above-mentioned particle size distribution. Preferably, the coarse powder side is controlled by a mesh and the fine powder side is controlled by air flow classification.

It is also possible to coat the surface of the carrier with a resin or the like. As the method, any of a method of dissolving or suspending a coating material such as a resin in a solvent, coating and attaching the coating material to a carrier, and a method of simply mixing with a powder can be applied.

The fixing substance on the carrier surface varies depending on the toner material, for example, polytetrafluoroethylene, monochlorotrifluoroethylene polymer, poly (vinylidene fluoride), silicone resin, polyester resin, metal complex of ditersharry butylsalicylic acid, styrene resin,
Acrylic resin, polyacid, polyvinyl butyral,
It is appropriate to use nigrosine, amino acrylate resin, basic dyes and lakes thereof, fine silica powder, fine alumina powder or the like alone or in combination.

The amount of the compound to be treated may be appropriately determined so that the carrier satisfies the above-mentioned conditions, but is generally desirably 0.1 to 30% by weight (preferably 0.2 to 20% by weight) based on the carrier of the present invention.

In the present invention, as a particularly preferred embodiment, a combination of styrene-2-ethylhexyl acrylate-methyl methacrylate (20 to 60: 5 to 30:10 to 50) is exemplified.

As the ferrite, a ternary ferrite of Cu-Zn-Fe is particularly preferable.

When a two-component developer is prepared by mixing with the 6 to 11 μm color toner used in the present invention, the mixing ratio is 2.0% to 12% by weight, preferably 3.0% to 10% by weight, as the toner concentration in the developer. Good results are usually obtained with a percentage by weight. If the toner concentration is less than 2.0%, the image density is low and it is difficult to use the image. easy.

As a colorant used when constituting a color developer together with the carrier of the present invention, as a dye, for example, CI Direct Red 1, CI Direct Red 4,
CI Acid Red 1, CI Basic Red 1, CI
Modant Red 30, CI Direct Blue 1, CI Direct Blue 2, CI Acid Blue 9, CI Acid Blue 15, CI Basic Blue 3, CI Basic Blue 5, CI Modern Blue 7, and the like.

As the pigment, naphthol yellow S, Hansa yellow G, permanent yellow NCG, permanent orange GTR, pyrazolone orange, benzidine orange G,
Permanent Red 4R, Watching Red Calcium Salt, Brilliant Carmine 3B, Fast Violet B, Methyl Violet Lake, Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue BC
Etc.

Preferably, disazo yellow, insoluble azo and copper phthalocyanine are suitable as pigments, and basic dyes and oil-soluble dyes are suitable as dyes.

Particularly preferably, CI Pigment Yellow 17, CI Pigment Yellow 15, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 12, CI
Pigment Red 5, CI Pigment Red 3, CI Pigment Red 2, CI Pigment Red 6, CI Pigment Red 7, CI Pigment Blue 15, CI Pigment Blue 16, and 2 to 2 carboxybenzamide methyl groups.
A copper phthalocyanine pigment having three phthalocyanine pigments or a Ba salt having a structural formula (1) shown below and having a phthalocyanine skeleton substituted with two or three carboxybenzamide methyl groups.

[Where X _{1 to} X ₄ are Or -H, and R and R 'represent an alkylene group having 1 to 5 carbon atoms. However, except in the case all of the X ₁ ~X ₄ is -H. Examples of dyes include CI Solvent Red 49, CI Solvent Red 52, CI Solvent Red 109, CI Basic Red 12, CI Basic Red 1, and CI Basic Red 3b.

The method for measuring the particle size distribution in the present invention is as follows.

1. Measure about 100 g of the sample to the nearest 0.1 g.

2. Standard sieve of 100 Mesh to 400 Mesh (hereinafter referred to as sieve)
And stack them in order of size 100, 145, 200, 250, 350, 400 from the top, place a saucer on the bottom, put the sample in the top sieve and cover it.

3. This is shaken by a vibrator at 285 ± 6 horizontal revolutions per minute and 150 ± 10 impulse revolutions per minute for 15 minutes.

4. After sieving, measure the iron powder in each sieve and tray to the nearest 0.1 g.

5. Calculate to the second decimal place by weight percentage and round to the first decimal place according to JIS-Z8401.

However, the size of the sieve frame is 200 mm inside diameter above the sieve surface,
The depth from the top surface to the sieve surface is 45mm.

The sum of the weights of iron powder in each part shall not be less than 99% of the mass of the starting sample.

The average particle size is determined from the above measured particle size distribution according to the following equation.

The amount of 500 mesh pass of the carrier is 50 g and the sample amount is 500
It is put on a mesh standard sieve, sucked from below, and calculated from the weight loss.

The BHU-60 is used to measure the magnetic properties of carriers.
Type magnetization measurement device (manufactured by RIKEN) is used.

About 1.0 g of a measurement sample is weighed, packed in a cell having an inner diameter of 7 mmφ and a height of 10 mm, and set in the above-mentioned apparatus.

In the measurement, an applied magnetic field is gradually applied to change up to 3,000 Oe. Next, the applied magnetic field is decreased, and finally a hysteresis curve of the sample is obtained on the recording paper. From this, the saturation magnetization, residual magnetization, and coercive force are obtained.

[Examples] Hereinafter, the present invention will be described in detail with reference to Examples.
"Parts" means parts by weight.

Example 1 To 100 parts of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid, a yellow toner, a magenta toner, a cyan toner, and a black toner were respectively added in the amounts shown in Table 1 using a coloring agent and a charge control agent. Obtained.

The production method is that the above-mentioned formulation amounts are sufficiently preliminarily mixed with a Henschel mixer, melt-kneaded at least twice with a three-roll mill, cooled, roughly crushed using a hammer mill to about 1-2 mm, and then air-cooled. It was pulverized to a particle size of 30 μm or less by a jet-type pulverizer. Further, the obtained finely pulverized product was classified, 2 to 12 μm was selected so as to have the particle size distribution of the present invention, and a silica fine powder treated with hexamethyldisilazane as a flow improver was added to 100 parts of each classified product for 0.5 part. Parts and 0.3 parts of alumina were externally added to obtain a color toner. The volume average particle size of this toner was 7.8 μm.

To 4 to 6 parts of these color toners, the carriers shown in Table 2 were mixed to a total amount of 100 parts to prepare a developer.
This carrier was a coated ferrite carrier coated with a styrene-2-ethylhexyl acrylate-methyl methacrylate (st-2EHA-MMA) copolymer (copolymerization ratio: 45:20:35) to a thickness of about 0.5 μm.

 The 500 mesh pass rate was 3.7%.

It was confirmed by Microtrack that the content of the magnetic particles having a size of 11 μm or less was substantially 0.

The developer concentration of each color toner is 4%, 4%, 5
% And 6%.

Using the above-mentioned developer, a commercially available Canon color copier (CLC-1) was modified to incorporate a 5-pole magnet roller with a developing main pole of 980 Gauss in a developing sleeve with a sleeve diameter of 32 mm. 280 mm sleeve speed
sec, and the test was performed using a document having an image area of about 40% in the full color mode.

As a result, a full-color image faithfully reproducing the original color chart with little edge effect was obtained even after printing of 15,000 sheets. Further, an image without blurring or density reduction was obtained even during continuous copying, and the conveyance in the copying machine and the detection of the developer density were good and stable. Further, a full-color image with excellent color was obtained even in an environment of low temperature and low humidity (15 ° C., 10% RH) and high temperature and high humidity (35 ° C., 85% RH). Even when an OHP film was used, the transparency of the toner was very favorable.

Example 2 Coloring agent for magenta was CI Basic Red 12,0.8 parts,
A magenta toner single color durability test was carried out using the carriers shown in Table 2 instead of 31 and 0.2 parts of CI Disperse Violet. Even after 20 000 copies, a good image density was obtained and a clear image was obtained. At this time, the 500 mesh pass ratio of the carrier was 2.9%.

Example 3 Using the carriers shown in Table 2, the colorant for cyan was changed to 6.0 parts of CI Pigment Blue 15, and the colorant for yellow was changed.
2.3 parts of CI Disperse Yellow 54, image area 50
The test was conducted in a high-temperature and high-humidity environment (32.5 ° C., 85% RH) in the same manner as in Example 1 except that the original was used. 1 was slightly inferior to 1. The 500 mesh pass ratio at this time was 2%.

Comparative Example 1 An image was formed in the same manner as in Example 2 except that the carriers shown in Table 2 were used. As a result, the decrease in image density under low temperature and low humidity was larger than that in Example 1 by 0.1.

The 500 mesh pass ratio of the carrier at this time was 7.3%.

Comparative Example 2 A test was performed in the same manner as in Example 2 except that the carrier was changed to the carrier shown in Table 2. However, during continuous copying, the image density gradually decreased, and the gradation reproducibility was sharper than that of the example. It became.

 At this time, the 500 mesh pass ratio was 0.2%.

Comparative Example 3 A test was conducted in the same manner as in Example 2 except that the carrier was thoroughly cut so that the 250 mesh-on became substantially 0, and changed to the carrier shown in Table 2. As a result, a very good image was initially obtained. However, when continuous copying was performed with a small consumption chart having an image area of about 6% under low temperature and low humidity, image density unevenness occurred, and the developer in the developing container was biased.

At this time, the 500 mesh pass ratio of the carrier was 5.2%.

[Effects of the Invention] The present invention uses magnetic particles having a specific particle size, particle size distribution and magnetic properties as a carrier for a small particle size toner of 6 to 11 μm, so that a copy excellent in image quality can be obtained even by repeated copying. The product is obtained, and the transportability in the developing device is good.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of the developing device according to the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinobu Baba 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-63-170660 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G03G 9/10

Claims (1)

(57) [Claims] 1. A two-component electrophotographic color developer containing at least magnetic particles and an insulating color toner is circulated and conveyed by fixing a magnet roller included in the developing sleeve and rotating the developing sleeve. An electrophotographic color developer used in a method of developing an electrostatic latent image carried on the surface of an electrostatic latent image carrier with the two-component developer, wherein (a) the insulating color toner Volume average particle size of 6 ~ 11μ
(b) the weight average particle size of the magnetic particles is 20 to 60 μm;
The amount of fine powder in the 350 mesh pass is 40% by weight or less, the amount of fine powder in the 400 mesh pass is 20% by weight or less, and the amount of ultrafine powder in the 500 mesh pass is 1 to 8% by weight. In an amount of 1.0 to 7% by weight,
Saturation magnetization of 55 to 75 emu for an applied magnetic field of 0 Oe
/ g, a residual magnetization of 10 emu / g or less, and a coercive force of 10 e or less.