JPH0786704B2 - Electrophotographic developer - Google Patents

Description

The present invention relates to a developer for developing an electrostatic charge image, and more particularly to a two-component developer in which a magnetic toner and a resin-coated magnetite carrier are mixed.

[Conventional technology]

A developer for developing an electrostatic image is roughly classified into a two-component developer formed by mixing a non-magnetic toner and a carrier,
It is well known that there is a one-component developer consisting only of magnetic toner.

Among them, the developing method using the two-component developer has the following problems as compared with the one-component system.

A toner concentration sensor is required to control the mixing ratio of toner and carrier.

The life of the developer is short.

Care must be taken when handling the developer agitation mechanism, and the size of the developing machine and other devices becomes large.

In addition, the following points can be cited as problems in the developing method using the one-component developer.

Since the charging member is a sleeve or a blade, the charging ability is weaker and the charging ability is weaker than that of the carrier.

The accuracy of the developing machine is required to uniformly form the magnetic brush.

Transferability, fixability, environmental dependence, and damage to the photoconductor are inferior to non-magnetic toner.

In order to overcome the problems of these two-component and one-component developing methods, various two-component developers using a magnetic toner and a magnetic carrier have recently been proposed and partially put into practical use with the following advantages. There is.

Wide tolerance range of toner density does not require precise density sensor.

Since a carrier is used, the triboelectric chargeability is good.

The magnetic brush is easy to form and does not require the precision of a developing machine as in a one-component system.

The content of the magnetic substance in the toner may be smaller than that of the one-component system, and the fixability, transferability and environmental characteristics can be made to the same level as those of the non-magnetic toner.

Since almost no stirring of the developer is required, the structure of the developing machine is simple and the design can be made compact as in the one-component system.

As a specific proposal of a two-component developer using such a magnetic toner, there is a developing method using a magnetic toner and a ferrite carrier, U.S. Pat. No. 4,640,880. There is a problem in that the carrier is electrostatically or mechanically attached to the photoconductor from the magnetized sleeve or spills out of the developing tank.

Further, since the triboelectric charge between the ferrite carrier and the magnetic toner is low, the developability is poor, and problems such as insufficient image density or background fog due to uncharged toner occur.

There is also a proposal U.S. Pat.No. 4,441,322 which uses a non-coated granulated magnetite carrier and a magnetic toner, but the carrier particles are fine and the carrier itself has a low volume resistivity, so that the carrier is significantly attached to the photoconductor. Problems such as adhesion to images and occurrence of scratches on the surface of the photoconductor have become problems. Further, in the non-coated granulated magnetite, the triboelectric charge with the toner was not sufficient like the above-mentioned ferrite carrier, and problems such as insufficient image density, background fog, scattered characters, and character bleeding occurred.

[Problems to be Solved by the Invention]

The present invention solves the problems of the conventional two-component developer using a magnetic toner, and provides an electrophotographic developer capable of obtaining high image quality with stable image accuracy and less background fog in various environments. Is.

[Means for Solving the Problems]

The present invention is a developer for electrophotography, which comprises a magnetic toner and a magnetic carrier in which a core material of granulated magnetite is coated with a resin, and the frictional electrification amount between the magnetic toner and the core material of granulated magnetite is Q. _1, the volume resistivity of the core material of granulated magnetite and R _1, the frictional charge amount of the granulated magnetite after the magnetic toner and a resin-coated Q _2, the volume resistivity of the granulated magnetite after resin coating and R ₂ In the case of the above, the developer for electrophotography is characterized by the following formula.

Hereinafter, the present invention will be described in detail.

[I] Magnetic Toner The magnetic toner of the present invention has an average particle size of 5 to 20 μm.
m, volume specific resistance is 10 ¹⁰ Ωm or more, and magnetic particles such as ferrite or magnetite, which is a mixture of metal oxide and iron oxide, are dispersed in a binder resin. Crystallographically, the magnetic particles have spinel, perovskite, hexagonal, garnet, and offsoferrite structures, and their constitutions are nickel, zinc, manganese, magnesium, copper, lithium, barium, vanadium, chrome,
It is a sintered body of oxide such as calcium and trivalent iron oxide.

Examples of the above-mentioned adhesive resin include homopolymers of styrene and its substitution products such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymers, styrene-vinyltolylene copolymers, and copolymers thereof. Copolymers; copolymers of styrene and acrylic ester such as styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-n-butyl acrylate copolymer; styrene-methyl methacrylate copolymer Copolymers of styrene and methacrylic ester such as polymer, styrene-ethyl methacrylate copolymer, styrene-n-butyl methacrylate copolymer; multi-component copolymer of styrene and acrylic ester and methacrylic ester; other Styrene-acrylonitrile copolymer, styrene vinyl methyl ether Styrene-based copolymers of styrene and other vinyl-based monomers such as polymers, styrene-butadiene copolymers, styrene-vinyl methyl ketone copolymers, styrene-acrylonitrile-indene copolymers, styrene-maleic acid ester copolymers; Polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc., alone or mixed. Can be used.

If necessary, a charge control agent and a fluidity modifier may be added to the magnetic toner, and the charge control agent and the fluidity modifier may be used as a mixture (external addition) with the toner. Good. Examples of the charge control agent include synthetic metal dyes and nigrosine type dyes, and conventionally known dyes and pigments such as carbon black can be used as the colorant. Flowability modifiers include colloidal silica and fatty acid metal salts.

Further, in order to prevent the mutual aggregation of the toner particles and improve the fluidity thereof, a fluidity improver such as Teflon fine powder may be blended, and the purpose of improving the releasability at the time of heat roll fixing. It is also possible to add waxes such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax and sazol wax.

The magnetic toner is produced by a method in which the constituent materials are well kneaded by a heat kneader such as a hot roll, a kneader or an extruder, and then mechanically pulverized or classified, or the magnetic particles are dispersed in a binder resin solution. After that, a method of obtaining by spray-drying or a method of producing a magnetic toner by mixing a predetermined material with a monomer that constitutes an adhesive resin and then polymerizing this emulsion suspension Can be used.

[II] Magnetic Carrier The magnetic carrier of the present invention is a resin-coated carrier having granulated magnetite particles obtained by granulating fine magnetite (Fe ₃ O ₄ ) particles as a core material, and the surface of which is coated with a resin.

The reason why the granulated magnetite is applied to the magnetic carrier constituting the present invention is as follows.

That is, conventionally, a ferrite carrier has been used as a carrier for a two-component developer that uses a magnetic toner, but this ferrite carrier does not have sufficient magnetic force and is transferred from the developing sleeve to the photoreceptor (hereinafter, this phenomenon This is called "developing" or spillage from the developing tank occurs. This problem of carrier development is particularly serious in reversal development type developing machines used in laser printers and the like. The stronger the magnetic force of the carrier is, the more advantageous it is for this carrier development. Table 1 shows general magnetic properties of iron, granulated ferrite, and granulated magnetite used as carriers for the two-component developer.

From the above magnetic characteristics, it can be understood that iron has the highest saturation magnetization, and iron powder is effective for reducing carrier development. However, since the torque of the developing sleeve when passing through the doctor blade increases in proportion to the saturation magnetization, the torque of the developer using iron powder as the carrier is the highest. There is a correlation between this torque and the life of the developer, and the larger the torque, the shorter the life of the developer. Therefore, the iron powder carrier is disadvantageous in this respect.

On the other hand, in the case of granulated ferrite and granulated magnetite, since a substantially spherical particle can be obtained by a manufacturing method of firing after granulation by a spray drying method or the like, it is easy to control the shape, and depending on the spherical particle morphology. Due to the good and flexible formation of the magnetic brush, the image quality is good when the electrostatic charge image is developed. As described above, granulated ferrite and granulated magnetite are more advantageous than iron powder in terms of the life of the developer and the image quality.

Further, comparing the granulated ferrite with the granulated magnetite, the granulated magnetite is advantageous in carrier development because it has a larger saturation magnetization. Further, comparing the volume resistivity of each core material, the range is as shown in Table 2.

The core material of the granulated magnetite has a lower volume resistivity than the granulated ferrite, and when used as a developer, the volume resistivity of the developer is low. Therefore, the developing electrode effect is increased, and the amount of toner adhered to the transfer medium is large, which is advantageous for the image density. When coating the core material with resin,
Since granulated magnetite has a low volume resistivity, it can be coated with a large amount of resin, and the volume resistivity can be controlled widely depending on the amount of resin. On the other hand, in the case of granulated ferrite, the volume resistivity increases even with a small amount of resin coating, the developing electrode effect decreases, and the image density becomes insufficient.

The core material of granulated ferrite or granulated magnetite is
Changes due to the environment, especially humidity, are apt to be affected by humidity, and changes in volume specific resistance due to humidity cause changes in triboelectrification characteristics and eventually changes in image density, which is not preferable. Therefore, in the present invention, by coating the surface of the core material of the granulated magnetite with a resin, the change in volume resistivity due to environmental conditions is reduced and the environmental dependence of image density is improved.

The fine magnetite particles used in the magnetic carrier according to the present invention preferably have a particle size of 5 μm or less and a purity of 95% or more, and have an average particle size of 30 to 100 μm and a saturation magnetization of 70 to 95 emu / g. It is preferable to granulate.

The preferred method for producing the granulated magnetite constituting the magnetic carrier according to the present invention is as follows, but the method is not necessarily limited thereto.

That is, magnetite (Fe ₃ O ₄ ) that has been made finer in advance has a solid content concentration measured by a ball mill or an attritor.
After mixing with stirring in a suitable solvent at 40-70%, the magnetite slurry is spray-dried with a spray drier.
Approximately 100 μm spherical particles. Then, the spherical particles are heat-treated at a temperature of 1000 ° C. or higher in a nitrogen atmosphere by an electric furnace or the like so as to have sufficient mechanical strength, and then the particles are formed on the surface of the particles by a known method such as a fluidized bed coating apparatus. A magnetic carrier can be obtained by coating with a resin.

In the present invention, the resin that coats the surface of the core material of the granulated magnetite is preferably a resin that enhances the chargeability of the magnetic toner, and the following can be used.

That is, a thermoplastic resin containing polyolefin, such as polyethylene, polypropylene, chlorinated polyethylene,
And chlorosulfonated polyethylene; polyvinyl and polyvinylidene such as polystyrene, polymethylmethacrylate, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinylcarbazole, polyvinyl ethers and polyvinyl ketones; vinyl chloride-vinyl acetate polymers. , Styrene-acrylic copolymers, silicone resins; fluorocarbons such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyamide resins; polyesters such as polyethylene terephthalate; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde; Epoxy resin etc. are mentioned.

Further, a material having a chargeability opposite to that of the magnetic toner may be added to these resins. Examples of the material include pigments and dyes used as charge control agents for toners, and amine-based resins for negatively-chargeable toners and acid-copolymerized resins such as acid-copolymerized resins for positively-chargeable toners. You may use.

The charging characteristics and coating amount of the resin coating the core material constituting the magnetic carrier of the present invention must be selected so that the following characteristics can be obtained.

That is, the triboelectric charge amount between the magnetic toner and the granulated magnetite core material was Q ₁ (μc / g), and the triboelectric charge amount between the magnetic toner and the resin-coated granulated magnetite was Q ₂ (μc / g). In this case, a resin that satisfies the following formula is used.

At this time, the triboelectric charge amount is measured by the magnet blow-off method described in Japanese Patent Application No. 62-18490 (Japanese Patent Application Laid-Open No. 63-187163).

In the above formula, When the value is less than 1.2, the amount of magnetic toner adhering to the transfer medium is small and the image density is insufficient, or uncharged and low charged magnetic toner is generated, which causes background fog. Further, due to these uncharged and low-charged magnetic toners, there are problems such as blurred characters and toner scattering.

Further, the coating amount of the resin is represented by the following formula when the volume resistivity of the core material of the granulated magnetite is R ₁ and the volume resistivity of the granulated magnetite after resin coating is R ₂ . Determine the coverage.

At this time, the volume resistivity was measured using an apparatus as shown in FIG. That is, in the insulating cylinder 2 having the main electrode 1 (Cu-Zn) (polytetrafluoroethylene)
A small amount (several 10 mg) of granulated magnetite 3 is installed on top of which an upper electrode 4 (Cu-Zn) is placed, and a load 5 (4200 g) is placed on the upper electrode 4 and a DC voltage of 100V is applied. Is applied and the current flowing through the granulated magnetite is stable, and the current value is measured by a micro-current meter (KEITHLEY 616 DIGITAL ELE
Calculated by reading with CTROMETER).

Small coating amount of the resin, the resin on the surface of the core material of granulated magnetite is not uniformly coated R ₂ / R ₁ is smaller than 100, not be sufficiently exhibited resin charging capability case, and environmental characteristics Causes a problem that the image density is insufficient due to a large change in the volume resistivity under a high temperature and high humidity environment.

The electrophotographic developer of the present invention is prepared by mixing the above-mentioned magnetic toner and magnetic carrier. The mixing ratio at that time is not particularly limited, but it is preferable to use magnetic toner: magnetic carrier = 10: 90 to 90:10. If the mixing ratio of the magnetic toner exceeds 90%, the frequency of triboelectric charging with the magnetic carrier decreases, and a sufficient triboelectric charge amount cannot be obtained, and the magnetic toner cannot be sufficiently conveyed by the magnetic carrier.
Moreover, it becomes impossible to form enough ears by the magnetic carrier,
Problems such as image density uniformity, background fog, and toner scattering occur. On the other hand, if the mixing ratio of the magnetic toner is less than 10%, the triboelectric charge amount of the magnetic toner becomes too large, the developability deteriorates, and the image density becomes insufficient. The magnetic toner and the magnetic carrier are mixed by a known dry blending method such as a V blender or a ball mill.

〔Example〕

Hereinafter, the present invention will be described based on examples. In addition, the part in an Example shows a weight part.

Example 1 The above materials are melt-kneaded by a roll mill, allowed to cool, and then roughly crushed by a cutter mill to have a size of 2 mm or less. Then, after finely pulverizing with an air crushing type jet mill, classifying with an air flow type classifier, average particle diameter 12 μm, volume resistivity 10 ¹¹ Ω
cm magnetic toner was obtained.

Also, using a fluidized coating device, a core material of granulated magnetite (average particle size: 46 μm, saturation magnetization: 88 emu / g)
The surface of was spray-coated with a methyl methacrylate / isocyanate resin to obtain a magnetic carrier.

Next, 30 parts of the magnetic toner and 70 parts of the magnetic carrier are mixed with V
Mixing was performed using a blender to obtain the electrophotographic developer of the present invention.

Example 2 Using a fluidized coating device, an amine-modified silicone resin was spray-coated on the surface of a core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization: 88 emu / g) to obtain a magnetic carrier.

Next, 70 parts of this magnetic carrier and the magnetic toner 30 of Example 1 are used.
Parts were mixed using a V blender to obtain the electrophotographic developer of the present invention.

Example 3 A styrene / methyl methacrylate / dimethylaminoethyl acrylate copolymer resin was spray-coated on the surface of a core material (average particle size: 46 μm, saturation magnetization: 88 emu / g) of granulated magnetite using a fluidized coating device. To obtain a magnetic carrier.

Next, 70 parts of this magnetic carrier and the magnetic toner 30 of Example 1 are used.
Parts were mixed using a V blender to obtain the electrophotographic developer of the present invention.

Example 4 A styrene / quaternary ammonium salt group copolymer resin was spray-coated on the surface of a granulated magnetite core material (average particle diameter: 46 μm, saturation magnetization: 88 emu / g) using a fluidized coating device to obtain magnetic properties. Got a career.

Next, 70 parts of this magnetic carrier and the magnetic toner 30 of Example 1 are used.
Parts were mixed using a V blender to obtain the electrophotographic developer of the present invention.

Example 5 Using a fluidized coating device, 97 parts of methyl methacrylate / isocyanate resin and nigrosine dye (Orient Chemical Co., Ltd.) Pontron NO
4) A resin mixed with 3 parts was spray-coated to obtain a magnetic carrier.

Next, 70 parts of this magnetic carrier and the magnetic toner 30 of Example 1 are used.
Parts were mixed using a V blender to obtain the electrophotographic developer of the present invention.

Example 6 Using a fluidized coating apparatus, the same styrene / methylmethacrylate / as in Example 3 was formed on the surface of the core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization: 88 emu / g).
A small amount of dimethylaminoethyl acrylate copolymer resin was spray-coated as compared with Example 3, and a magnetic carrier having a reduced volume resistivity was obtained as in Example 3.

Next, 70 parts of this magnetic carrier, Example 1 and magnetic toner 30
Parts were mixed using a V blender to obtain the electrophotographic developer of the present invention.

Example 7 The above materials are melt-kneaded by a roll mill, allowed to cool, and then roughly crushed by a cutter mill to have a size of 2 mm or less. Then, after finely pulverizing with an air crushing type jet mill, classifying with an air flow type classifier, average particle diameter 12 μm, volume resistivity 10 ¹¹ Ω
cm magnetic toner was obtained.

Also, using a fluidized coating device, a core material of granulated magnetite (average particle size: 46 μm, saturation magnetization: 88 emu / g)
A magnetic carrier was obtained by spray-coating the surface of 4 with a 4-Fuccaethylene / 6-Fuccapropylene copolymer resin.

Next, 30 parts of the magnetic toner and 70 parts of the magnetic carrier were mixed using a V blender to obtain an electrophotographic developer of the present invention.

Comparative Example 1 30 parts of the magnetic toner of Example 1 and 70 parts of a non-coated ferrite carrier (average particle size: 44 μm, saturation magnetization: 61 emu / g) were mixed using a V blender to obtain a comparative developer.

Comparative Example 2 30 parts of the magnetic toner of Example 1 and the core material of the granulated magnetite used in Example 1 (average particle size: 46 μm, saturation magnetization: 88 em)
70 parts of u / g) was mixed using a blender to obtain a developer for comparison.

Comparative Example 3 Using a fluidized coating device, a small amount of methylmethacrylate / isocyanate-based resin was spray-coated on the surface of a granulated magnetite core material (average particle size: 46 μm, saturation magnetization: 88 emu / g) to obtain a magnetic carrier. It was

Next, 70 parts of this magnetic carrier and the magnetic toner 30 of Example 1 are used.
And parts were mixed using a V blender to obtain a comparative developer.

Q ₁ , Q ₂ and Q ₂ / Q _{1 of} the developers obtained in the above Examples and Comparative Examples
And R ₁ , R ₂ and R ₂ / R ₁ are shown in Table 3.

Next, the developers obtained in the examples and comparative examples were placed in copiers A and B having the following developing conditions, and were kept at room temperature and normal humidity (22 ° C / 60 ° C).
% RH), high temperature high humidity (35 ℃ / 85% RH), low temperature low humidity (10 ℃ /
A copy test up to 30,000 sheets was performed under each environmental condition (20% RH). However, in Examples 1 to 6 and Comparative Examples 1 to 3, the copy test was performed by the copying machine A, and in Example 7, the copy test was performed by the copying machine B. The results are shown in Table 4. The conditions of the copying machines A and B are as follows.

[Copier A]

Organic photoconductor: N type, outer diameter = 80 mmφ, peripheral speed = 120 mm / sec, developing sleeve: outer diameter = 30 mmφ, 100 rpm Mag roll: 8 poles, 800 gauss, 1000 rpm Rotates in the opposite direction.

[Copier B]

Organic photoconductor: N type, outer diameter = 80 mmφ, peripheral speed = 120 mm / sec, developing sleeve: outer diameter = 30 mmφ, 100 rpm Mag roll: 8 poles, 800 gauss, 1000 rpm Rotates in the opposite direction.

Development method: regular development The image density (ID) in Table 4 was measured with a Macbeth reflection densitometer, and the background fog (BG) was measured with a Hunter whiteness meter in the non-image area. The image quality and carrier drop were evaluated according to the following criteria.

image quality Career drop As is clear from the results shown in Table 4, it was confirmed that the electrophotographic developer of the present invention can obtain a stable image density and a copy image with less background fog under various environmental conditions.
On the other hand, the developer of Comparative Example 1 had a low image density after 30,000 sheets, especially the image density at high temperature and high humidity, as compared with the example. Further, the developers of Comparative Examples 2 and 3 had a lot of background fog in each environment from the initial stage, and the image quality was poor, which was a problem in practical use.

〔The invention's effect〕

According to the present invention, a two-sheet developer using a magnetic toner can be used to obtain a stable and high image density without being affected by environmental conditions, and to reduce background fog and obtain a high image quality.

[Brief description of drawings]

FIG. 1 is a view showing an apparatus for measuring the volume resistivity of granulated magnetite. 1 ... main electrode, 2 ... in an insulating cylinder, 3 ... granulated magnetite, 4 ... upper electrode, 5 ... load.

Claims (1)

[Claims] 1. A developer for electrophotography comprising a magnetic toner and a magnetic carrier in which a core material of granulated magnetite is coated with a resin, the frictional electrification amount between the magnetic toner and the core material of granulated magnetite. Q _1, the volume resistivity of the core material of the granulated magnetite and R _1, magnetic toner and a granulated magnetite frictional charge amount after the resin-coated Q _2, the volume resistivity of the granulated magnetite after resin-coated R _A developer for electrophotography, characterized in that the relation of the following formula is satisfied when the value is ₂ .