JPH03225350A - Electrophotographic developer - Google Patents

Abstract

PURPOSE:To obtain high image quality by specifying relationships among a triboelectrifiability between a magnetic toner and a core material, the volume resistivity of the core material, the triboelectrifiability between the magnetic toner and a resin-coated granulated magnetite, and the volume resistivity of said magnetite. CONSTITUTION:The triboelectrification amount between the magnetic toner and the core material of the granulated magnetite is designated by Q1, the volume resistivity of the core material is designated by R1, the triboelectrification amount between the magnetic toner and the resin-coated granulated magnetite is designated by Q2, and the volume resistivity of the resin-coated granulated magnetite is designated by R2. High image quality is obtained by satisfying the relationships of expressions I. If ¦Q2/Q1¦ < 1.2, an amount of magnetic toner to be attached to a transfer medium becomes small and image density is made insufficient, resulting in causing problems, such as bleeding of characters and scattering of the toner. When the resin coating amount is small, and the surfaces of the core material is not uniformly coated, R2/R1 is made smaller than 100, resulting in exhibiting insufficient triboelectrifiability of the resin, increasing variation of the volume resistivity under environments of high temperature and high humidity, and dropping the image density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developer for developing electrostatic images, and more particularly to a two-component developer in which a magnetic toner and a resin-coated magnetite carrier are mixed.

[Conventional technology]

Developers for developing electrostatic images can be roughly divided into two-component developers formed by mixing non-magnetic toner and carrier;
It is well known that there is a one-component developer consisting only of magnetic toner.

Among these, the developing method using a two-component developer has the following problems compared to a one-component developer.

■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 stirring mechanism, and equipment such as the developing machine becomes large.

Furthermore, problems with the developing method using a -component developer include the following points.

■Charging member is a gas sleeve or blade, and compared to carriers, charging stability and charging ability are weaker.

■The precision of the developing machine is necessary to uniformly form the magnetic brush.

■ Transferability, fixability, environmental dependence, and damage to photoreceptors are inferior to non-magnetic toners.

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

■Wide range of toner density tolerance (does not require a precise density sensor).

■Good triboelectric charging properties when using a carrier.

■It is easy to form a magnetic brush, and it does not require the precision of a developing machine unlike one-component systems.

■The content of magnetic material in the toner is smaller than that of a one-component type, and the fixability, transferability, and environmental characteristics can be at the same level as non-magnetic toners.

■Since there is almost no need to stir the developer, the structure of the developing machine is simple and compact, similar to the one-component system.

A specific proposal for a two-component developer using magnetic toner is US Pat. No. 4,640,880, which uses a magnetic toner and a ferrite carrier. There is a problem that the carrier may electrostatically or mechanically adhere to the photoreceptor from the magnetized sleeve or may spill out of the developing tank.

Furthermore, the low frictional electrification between the ferrite carrier and the magnetic toner results in poor developability, resulting in problems such as insufficient image density and blur due to uncharged toner.

In addition, there is a proposal in US Pat. No. 4,414,322 that uses a non-coated granulated magnetite carrier and magnetic toner, but since the carrier particles are fine and the carrier itself has a low volume resistivity, the carrier adheres to the photoreceptor significantly, resulting in copying. Problems include adhesion to images and scratches on the surface of the photoreceptor. Furthermore, like the ferrite carrier mentioned above, 77-unit granulated magnetite does not have sufficient frictional charging with the toner, resulting in insufficient image density, blurring, and scattering of characters.
Problems such as blurring of characters occurred.

[Problem to be solved by the invention]

The present invention solves the problems of conventional two-component developers using magnetic toner, and provides an electrophotographic developer that can provide stable image density, less ground blur, and high image quality in various environments. [Means for Solving the Problems] The present invention provides an electrophotographic developer comprising a magnetic toner and a magnetic carrier in which a core material of granulated magnetite is coated with a resin. Q1 is the amount of frictional charge between the magnetite core material, R is the volume resistivity of the core material of granulated magnetite, Q2 is the amount of frictional charge between the magnetic toner and the granulated magnetite after resin coating, and Q2 is the amount of frictional charge between the magnetic toner and the granulated magnetite after resin coating. This is an electrophotographic developer characterized by a relationship expressed by the following formula, where R2 is the volume resistivity of grained magnetite.

(1) Magnetic toner The magnetic toner in the present invention has an average particle diameter of 5 to 20 μm.
m, the volume resistivity is 10111 Ωcm 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 a spinel, perovskite, hexagonal, garnet, orthoferrite structure, and are composed of nickel, zinc, manganese, magnesium, copper, lithium, barium, vanadium, chromium, and calcium. It is a sintered body of oxides such as iron oxide and trivalent iron oxide.

The above-mentioned binder resins include homopolymers of styrene and its substituted products, such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, and styrene-vinyltoluene copolymer, and copolymers thereof. Coalescence: Copolymers of styrene and acrylic esters such as styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-n-butyl acrylate copolymer; Styrene-methyl methacrylate copolymer Coalescence, styrene-ethyl methacrylate copolymer, styrene-
Copolymers of styrene and methacrylic esters such as n-butyl methacrylate copolymers; multi-component copolymers of styrene and acrylic esters and methacrylic esters; other styrene-acrylonitrile copolymers, styrene vinyl methyl ether copolymers Styrenic copolymers of styrene and other vinyl monomers, such as styrene butadiene copolymers, styrene vinyl methyl ketone copolymers, styrene acrylonitrile indene copolymers, and styrene maleic acid ester copolymers; methyl methacrylate,
Polybutyl methacrylate, polyvinyl acetate polyester, polyamide, epoxy resin, polyvinyl plaal,
Polyacrylic acid phenol resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc. can be used alone or in combination.

Furthermore, a charge control agent and a fluidity modifier may be added to the magnetic toner as necessary, and the charge control agent and fluidity modifier may be mixed (externally added) with the toner. good. Examples of the charge control agent include metal-containing dyes and nigrosine dyes, and as the colorant, conventionally known dyes and pigments such as carbon black can be used. Examples of fluidity modifiers include colloidal silica and fatty acid metal salts.

Furthermore, in order to prevent mutual agglomeration of toner particles and improve their fluidity, a fluidity improver such as Teflon fine powder may be added, and the purpose is to improve releasability during hot roll fixing. It is also possible to add waxes such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, and Sasol wax.

Magnetic toner can be produced by kneading the constituent materials using a thermal kneader such as a hot roll or kneader-extruder, followed by mechanical crushing or classification, or by adding magnetic particles in a binder resin solution. A toner manufacturing method is a method in which a magnetic toner is obtained by spray drying after dispersion, or a polymerization method in which a magnetic toner is obtained by mixing a predetermined material with a monomer to constitute a binder resin and then polymerizing the emulsified suspension. etc. can be used.

(n) Magnetic carrier The magnetic carrier in the present invention is a fine magnetite)
This is a resin-coated carrier in which the core material is granulated magnetite particles obtained by granulating (FeiO4) particles, and the surface thereof is coated with a resin.

The reason for applying granulated magnetite to the magnetic carrier constituting the present invention is as follows.

In other words, ferrite carriers have conventionally been used as carriers for two-component developers using magnetic toner, but these ferrite carriers do not have sufficient magnetic force and transfer from the developing sleeve to the photoreceptor (hereinafter, this phenomenon is referred to as carrier (referred to as development) or spillage from the developer tank.

This problem of carrier development is especially serious in reversal development type developing machines used in laser printers and the like.

The stronger the magnetic force of the carrier, the more advantageous it is to this carrier development. Table 1 shows general magnetic properties of iron, granulated ferrite, and granulated magnetite used as carriers for two-component developers.

From the above magnetic properties, iron has the highest saturation magnetization, and it can be understood that iron powder is effective in 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 a carrier is the highest. There is a correlation between this torque and the lifespan of the developer, and the greater the torque, the shorter the lifespan of the developer. Therefore, iron powder carriers are disadvantageous in this respect.

On the other hand, in the case of granulated ferrite and granulated magnetite, nearly spherical particles can be obtained by a manufacturing method such as spray drying, which involves granulation and then firing, making it easy to control the shape. Since the magnetic brush is well formed and flexible, the image quality is good when developing an electrostatic charge image. As described above, granulated ferrite and granulated magnetite are advantageous compared to iron powder in terms of developer life and image quality.

Furthermore, when granulated ferrite and granulated magnetite are compared, granulated magnetite has a larger saturation magnetization and is therefore more advantageous in terms of carrier development. Further, when comparing the volume resistivity of each core material, the range is as shown in Table 2.

The core material of granulated magnetite in Table 2 has a lower volume resistivity than granulated ferrite, and when used as a developer, the volume resistivity of the developer is low. Therefore, the developing electrode effect becomes large, and a large amount of toner adheres to the transfer medium, which is advantageous for the density of the image. In addition, when coating the core material with resin,
Granulated magnetite has a low volume resistivity, so it can be coated with a large amount of resin, and the volume resistivity can be controlled over a wide range by changing the amount of resin. On the other hand, in the case of granulated ferrite, even a small amount of resin coating increases the volume resistivity, reduces the developing electrode effect, and causes insufficient image density.

In addition, the core material of granulated ferrite and granulated magnetite is
It is easily influenced by environmental changes, especially humidity, and changes in volume resistivity due to humidity undesirably cause changes in triboelectric charging characteristics and, in turn, changes in image density. Therefore, in the present invention, the surface of the core material of granulated magnetite is coated with a resin to reduce changes in volume resistivity due to environmental conditions and improve the environmental dependence of image density.

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 are manufactured to 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 it.

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

That is, magnetite (Fe30a) that has been refined in advance
After stirring and mixing in a suitable solvent with a solid content concentration of 40 to 70% using a ball mill or attritor, the magnetite slurry is spray-dried using a spray dryer to form spherical particles of 30 to 100 μm. Next, the spherical particles are heated at 1000°C in a nitrogen atmosphere using an electric furnace or the like.
After heat treating the particles at the above temperature to provide sufficient mechanical strength, the surfaces of the particles are coated with a resin using a known method such as a fluidized bed coating device to obtain a magnetic carrier.

In the present invention, the resin to be coated on the surface of the core material of granulated magnetite is preferably a resin that enhances the charging property of the magnetic toner, and the following resins can be used.

That is, thermoplastic resins containing polyolefins, such as polyethylene, polypropylene, chlorinated polyethylene,
and chlorosulfonated polyethylene; polyvinyl and polyvinylidene, such as polystyrene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polyvinyl ketone; vinyl chloride-vinyl acetate polymers , styrene-acrylic copolymers, silicone resins; fluorocarbons such as polytetrafluoroethylene, polyvinyl fluoride, polyvinyldene fluoride, polychlorotrifluoroethylene; polyamide resins; polyesters such as polyethylene terephthalate; polyurethanes;
Polycarbonate; amino resin such as urea-bormaldehyde; epoxy resin and the like.

Furthermore, a material having a chargeability of opposite polarity to that of the magnetic toner may be added to these resins. In addition to pigments and dyes used as charge control agents in toners, these materials include resins copolymerized with polar groups, such as amine-based for negatively chargeable toners and acid copolymer resins for positively chargeable toners. May be used.

The charging characteristics and coating amount of the resin to be coated on the core material constituting the magnetic carrier of the present invention must be selected so as to obtain the following characteristics.

That is, the amount of frictional electrification between the magnetic toner and the core material of granulated magnetite is Q2 (μc/gL), and the amount of frictional electrification between the magnetic toner and the granulated magnetite coated with resin is Q2 (μc/g
), a resin that satisfies the following formula is used.

The method for measuring the amount of triboelectric charge in this case is disclosed in Japanese Patent Application No. 62-1849.
It is measured by the magnetic pull-off method described in No. 0 (Japanese Unexamined Patent Publication No. 187163/1988).

If it is small, the amount of magnetic toner adhering to the transfer medium will be small, resulting in insufficient image density, or uncharged or low-charged magnetic toner will be produced, resulting in blurring. Furthermore, these uncharged and low-charge magnetic toners cause problems such as blurring of characters and toner scattering.

In addition, the amount of resin coating is determined by the following formula, where R is the volume resistivity of the core material of the granulated magnetite, and R2 is the volume resistivity of the granulated magnetite after resin coating. Determine the amount.

2 ≧ 100 R.

The volume resistivity was measured using an apparatus as shown in FIG. That is, the main electrode 1 (Cu-Z
A small amount (several tens of square meters) of granulated magnetite 3 is placed in an insulating cylinder 2 (polytetrafluoroethylene) having a A load 5 (4200 g) was placed on the plate, a DC voltage of 100 V was applied, and when the current flowing through the granulated magnetite was stable, the current value was measured using a microcurrent meter (KEIT).
Manufactured by HLEY 616DIGITAL ELECTRO
Calculated by reading with METER).

The amount of resin coating is small, and the amount of granulated magnetite is small. If the resin is not evenly coated on the surface of the material, it will be R.

is less than 100, in which case the charging ability of the resin is not fully exhibited, and the environmental characteristics deteriorate, resulting in large changes in volume resistivity under high-temperature environments, resulting in a problem of insufficient image density.

The electrophotographic developer of the present invention is prepared by mixing the above-described magnetic toner and magnetic carrier. Although the mixing ratio at that time is not particularly limited, it is preferable to use magnetic toner:magnetic carrier=10:90 to 90:10. When the mixing ratio of magnetic toner exceeds 90%, the frequency of frictional charging with the magnetic carrier decreases, and a sufficient amount of frictional charging cannot be obtained, and the magnetic toner cannot be sufficiently transported by the magnetic carrier, and the magnetic toner cannot be sufficiently transported by the magnetic carrier. It becomes impossible to form a sharp panicle, and problems such as image density uniformity, ground braking, and toner scattering occur. Also, the mixing ratio of magnetic toner is 10
%, the amount of triboelectric charging of the magnetic toner is too large, resulting in poor developability and insufficient image density. The magnetic toner and the magnetic carrier are mixed by a well-known dry blending method such as a V-blender or a ball mill.

〔Example〕

Hereinafter, the present invention will be explained based on Examples. In addition, parts in Examples indicate parts by weight.

Example 1 The above materials were melt-kneaded using a roll mill, allowed to cool, and then coarsely ground using a cutter mill to give a powder of 2 an or less.

The particles were then finely pulverized using an air pulverizing jet mill and then classified using an air classifier to obtain a magnetic toner having an average particle diameter of 12 μm and a volume resistivity of IQIIΩcm.

In addition, a magnetic carrier was obtained by spray coating methyl methacrylate/isocyanate resin on the surface of a granulated magnetite core material (average particle diameter: 46 μm, saturation magnetization: 88 parts mu/g) using a fluid coating device. .

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.

Example 2 A core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization: 88 parts mu
/g) was spray coated with an amine-modified silicone resin to obtain a magnetic carrier.

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

Example 3 A core material of granulated magnetite (average particle diameter: 46 μm5 saturation magnetization: 88 parts mu/
A magnetic carrier was obtained by spray-coating a styrene/methyl methacrylate/dimethylaminoethyl acrylate copolymer resin on the surface of g).

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

Example 4 A core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization: 88 parts mu/
A magnetic carrier was obtained by spray coating the surface of g) with a styrene/quaternary ammonium base copolymer resin.

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

Example 5 A core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization: 88 parts mu/
A magnetic carrier was obtained by spray coating the surface of the sample g) with a mixture of 97 parts of methyl methacrylate/isocyanate resin and 3 parts of nigrosine dye (Bontron N04 manufactured by Orient Chemical Co., Ltd.).

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

Example 6 A core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization = 88 emu/
g) The same styrene/methyl methacrylate/dimethylaminoethyl acrylate copolymer resin as in Example 3 was spray-coated on the surface in a smaller amount than in Example 3 to obtain a magnetic carrier with a lower volume resistivity than in Example 3.

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

Example 7 The above-mentioned materials are melt-kneaded using a roll mill, allowed to cool, and then coarsely ground using a cutter mill to give a particle size of 2 mm or less.

The particles were then finely pulverized using an air pulverizing jet mill and then classified using an air classifier to obtain a magnetic toner having an average particle diameter of 12 μm and a volume resistivity of 10″ΩC.

In addition, a core material of granulated magnetite (average particle diameter: 46 μm, saturation magnetization: 88
A magnetic carrier was obtained by spray-coating a 4-foot ethylene/6-foot propylene copolymer resin on the surface of the sample (mu 7 g).

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

Comparative Example 1 30 parts of the magnetic toner of Example 1 and non-coated ferrite carrier (average particle diameter: 44 μm, saturation magnetization: 61 parts m)
A comparative developer was obtained by mixing 70 parts of 7g) using a blender.

Comparative Example 2 30 parts of the magnetic toner of Example 1 and 70 parts of the granulated magnetite core material used in Example 1 (average particle diameter: 46 parts m, saturation magnetization: 88 en + u 7 g) were mixed using a V blender. A developer for comparison was obtained.

Comparative Example 3 Using a fluid coating device, a core material of granulated magnetite (average particle diameter: 46 μm, flllll and other magnetization 8 parts m
A small amount of methyl methacrylate/isocyanate resin was spray coated on the surface of the magnetic carrier (u/g) to obtain a magnetic carrier.

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

Table 3 shows Q+, Qz and Q2/Q, and R,, Rz and R2/RI of the developers obtained in the above Examples and Comparative Examples.

Next, the developers obtained in Examples and Comparative Examples were placed in copying machines A and B having the following development conditions, and the developer was placed at room temperature (22℃/
3 under each environmental condition of high temperature (35℃/85%RH), low temperature and low humidity (10℃/20%RH)
A copy test was conducted on up to 10,000 copies. However, Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to a copy test using copying machine A, and Example 7 was subjected to a copying test using copying machine B, and the results are shown in Table 4. The conditions for copying machines A and B are as follows.

[Copy machine A]

Organic photoreceptor = N type, outer diameter = 80tmφ, circumferential speed = 120
ass/sec.

Developing sleeve; outer diameter = 30 φ, 100 rpa + mag roll: 8 poles, 800 gauss, 11000 rp The photoreceptor and sleeve rotate in the same direction, and the sleeve and built-in mag roll rotate in opposite directions.

Development method Two-reversal development [Copy machine B] Organic photoreceptor type 2N, outer diameter = 80WMφ, circumferential speed = 1 20
tm/sec.

Developing sleeve: Outer diameter = 30 mφ, 1100 rpm Mag roll: 8 poles, 800 Gauss, 10000 rpm The phosphor and the sleeve rotate in the same direction, and the sleeve and the built-in mag roll rotate in opposite directions.

Development method: Regular development Image density (ID) in Table 4 was measured with a Macbeth reflection densitometer, and BG was measured in non-image areas with a Hunter whiteness needle. In addition, image quality and carrier dropout were evaluated using the following criteria.

Image Quality Carrier Falloff As is clear from the results in Table 4, the electrophotographic developer of the present invention was found to be capable of obtaining copy images with stable image density and less blurring under various environmental conditions. On the other hand, the developer of Comparative Example 1 had a lower image density after 30,000 copies than that of the example, and the image density was particularly low at high temperature and high humidity. Further, in each environment, the developers of Comparative Examples 2 and 3 had a lot of ground blur from the beginning and the image quality was poor, which caused problems in practical use.

〔Effect of the invention〕

According to the present invention, by using a two-component developer using magnetic toner, a stable high image density can be obtained without being affected by environmental conditions, and high image quality can be obtained with less ground force.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an apparatus for measuring the volume resistivity of granulated magnetite. l... Main electrode, 2... Insulating cylinder interior, 3... Granulated magnetite, 4... Upper electrode, 5... Load. Diagram

Claims (1)

[Scope of Claims] An electrophotographic developer comprising a magnetic toner and a magnetic carrier in which a core material of granulated magnetite is coated with a resin, the amount of frictional charging between the magnetic toner and the core material of granulated magnetite is Q_1, the volume resistivity of the core material of the granulated magnetite is R_1, the amount of frictional charge between the magnetic toner and the granulated magnetite after resin coating is Q_2, and the volume resistivity of the granulated magnetite after resin coating is R_2. An electrophotographic developer characterized by having the following relationship: ▲There are mathematical formulas, chemical formulas, tables, etc.▼, ▲Mathematical formulas, chemical formulas,
There are tables etc.▼