JPH10301321A - Electrophotographic developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such a developer which gives sharp high quality images and causes little deterioration in images due to decrease in electrification property of the developer even after many sheets are continuously printed, by avoiding problems of aggregation by moisture which are intrinsic to a developer using a small particle carrier or a polymer carrier. SOLUTION: This developer contains toner particles and carrier particles and has such property that when the developer is left to stand for 10 hours in 30 deg.C and 80% RH environment and then subjected to mesh filter test, the amt. of the rough powder of >=200 mesh is <=20 wt.%, and the amt. of the fine powder of <=235 mesh is <=50 wt.%. The carrier particles may be magnetic material-coated carrier particles or polymer carrier particles. It is preferable that the toner particles and carrier particles show absorptivity for water of <=0.3% weight change rate between the weight after the particles are left to stand for 10 hours in an environment of 30 deg.C and 80% RH for the toner particles and carrier particles to be used, and the weight after the particles are further left to stand in an environment of 60 deg.C and 30% RH for 1 hour, and that both particles contain fine particles of >=60 hydrophobicity degree.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer suitable for an electrophotographic image forming apparatus that forms a toner image using an electrostatic latent image.

[0002]

2. Description of the Related Art As a developing method in electrophotography, a magnetic brush developing method is generally used. Among them, the magnetic brush developing method using a developer containing a toner and a carrier has characteristics that the toner is easily charged and the toner particles are hardly agglomerated. Widely used.

Conventionally, this developing method generally uses a carrier having an average particle size of 20 to 100 μm as disclosed in Japanese Patent Application Laid-Open No. 3-55562. The carrier material is generally made of a magnetic substance such as iron powder, ferrite, or the like, or has a surface coated with a resin.

[0004] Further, with the demand for higher image quality and longer life, further improvements have been made for such carriers. For example, when a carrier having a large particle diameter and magnetization is used, the formed magnetic brush becomes coarse, and stripe-like brush marks are likely to appear on a copy image due to a magnetic brush called a brush mark, and it is difficult to obtain a high-quality image. There was a problem. Further, when the carrier diameter is large, there is a problem that the toner carrying ability is reduced and the scattering of the toner to the non-image portion is increased. Therefore, in Japanese Patent Application Laid-Open No. 8-69131, high image quality is achieved by using a carrier having a 50% particle size of 15 to 60 μm and an average particle size of about 30 to 50 μm.

[0005] By the way, since such a carrier composed of a magnetic substance alone has a large specific gravity (4.0 g / cm ³ or more), the mixing of the developer in the developing device is efficiently performed, and the rise of the charge of the toner is increased. On the other hand, when the developer is mixed, the stress on the toner is also increased, and the life of the developer is shortened, and since the specific gravity is large, carrier scattering due to centrifugal force is likely to occur during development. However, when such a carrier made of a magnetic substance alone adheres to the electrostatic latent image carrier, the carrier particles are hard, and when the surface of the electrostatic latent image carrier is cleaned with a cleaning blade or the like, the electrostatic latent image carrier is In some cases, the body surface may be damaged.

As a means for solving the weak points of the carrier composed of a single magnetic substance, a polymer carrier in which fine particles of a magnetic substance are dispersed in a polymer matrix to form particles has been proposed in Japanese Patent Application Laid-Open No. 7-219278. . This type of polymer carrier has a lower magnetization than conventional carriers consisting of a single magnetic substance, so a soft and high-density magnetic brush can be formed, and high-quality images without streak-like brush marks can be obtained. Can be done. Further, since the specific gravity is smaller than that of a carrier made of a magnetic substance alone, carrier scattering due to centrifugal force during development is less likely to occur. In addition, since the carrier particles are mainly composed of the polymer, there is little risk of damaging the surface of the electrostatic latent image carrier when the carrier particles adhere to the electrostatic latent image carrier. Further, such a polymer carrier has a lower specific gravity (2 to 3 g /
(approx.cm ³ ), the rise of toner charge due to the mixing of the developer in the developing device is slightly disadvantageous compared to the carrier composed of a magnetic substance alone, but when the developer is mixed in the developing device, Since it has the advantage of reducing the stress on the toner and providing a developer having a long life, it is expected that its use will be further increased in the future.

However, the developer using such a small-diameter carrier or a polymer carrier has a problem in that an image with less fog and a lot of fog is generated under high humidity such as in summer. In particular, it has been found that such a problem is particularly likely to occur in the aforementioned polymer carrier. When the developer at this time was taken out of the developing device and examined, aggregation of the developer was observed.

[0008] Such agglomeration of the developer occurs when the developer absorbs moisture. In a normal electrophotographic apparatus, although measures against moisture absorption by heat are taken by using a heat source such as a driving device, an exposure device, and a fixing device, or by providing a dedicated heat generating device, a normal electrophotographic device is used. Even in an office environment, if air conditioning is stopped in summer, the temperature around the developing unit in the apparatus may reach 30 ° C. or more and the humidity may reach 80% or more. Examination of the state of occurrence of developer agglomeration in summer reveals that, when the temperature inside the developing device becomes 30 ° C. or more and the humidity becomes 70%, the occurrence of agglomeration is observed, and particularly, the humidity inside the developing device becomes 80%. It was confirmed that a large amount of agglomeration of the developer occurred when the pressure was approaching.

As described above, when the agglomeration of the developer occurs in the developing device, the chargeability of the developer is reduced because the effective charge area of the carrier is reduced, and the toner is removed while continuously taking a print sample. The carrier is subjected to development without being sufficiently charged by the carrier, and as a result, the image becomes fogged with lack of sharpness. In particular, in the case of a color image, a solid image having gradation such as a photograph, a painting, and a map occupies the mainstream, and the image area is wider than that of a line-mainstream black-and-white image. Such a tendency becomes more remarkable because the toner is supplied.

[0010]

In the case where the carrier particles have a large mass, such as a carrier having a large diameter and a magnetic substance alone, as in the prior art, the developer agglomerates due to its own weight by mixing in the developing unit. Is relatively easy to loosen, but in the case of a small-diameter carrier or a polymer-based carrier that can achieve good image quality, aggregation occurs once because the mass of carrier particles is smaller than that of a conventional carrier consisting of a large-diameter magnetic substance alone. Agglomeration is less likely to be loosened, and the occurrence of such aggregation due to moisture of the developer becomes a problem.

An object of the present invention is to avoid the problem of aggregation due to moisture inherent in a developer using such a small-diameter carrier or a polymer-based carrier, thereby obtaining a clear high-quality image and a large number of continuous images. An object of the present invention is to provide a developer that does not deteriorate an image due to a decrease in chargeability of the developer even when printed.

[0012]

The above object has been achieved by an electrophotographic developer having the following characteristics.

The electrophotographic developer of the present invention is a developer containing toner particles and carrier particles.
When a mesh filtration test was performed after leaving the mixture in an environment of 0 ° C. and 80% RH for 10 hours, the amount of coarse powder of 200 mesh or more was 20% by weight or less, and the amount of fine powder of 325 mesh or less was 50% by weight. It is characterized by the following.

In the electrophotographic developer, the carrier particles may be a magnetic carrier obtained by coating a resin layer on a magnetic substance alone, or a polymer formed by mixing magnetic fine particles and a polymer resin to form particles. It is a carrier.

In this electrophotographic developer, the weight of the toner particles after standing for 10 hours in an environment of 30 ° C. and 80% RH, and then for 1 hour in an environment of 60 ° C. and 30% RH The rate of change in weight with the weight after standing is 0.3
%, Indicating that the carrier particles are within
The change in weight between the weight after leaving for 10 hours in an environment of 30 ° C. and 80% RH and the weight after leaving for 1 hour in an environment of 60 ° C. and 30% RH is within 0.3%. It is preferable that the toner particles contain fine particles having a degree of hydrophobicity of 60 or more, and that the carrier particles contain fine particles having a degree of hydrophobicity of 60 or more.

The electrophotographic developer of the present invention (hereinafter referred to as
(Referred to as developer) is exposed to a high-temperature, high-humidity environment in the developing unit of the electrophotographic apparatus, and the aggregation state of the developer due to moisture is defined in the above range, so that the initial image quality is good. In addition, the problem of image quality deterioration at the time of continuous printing of many sheets has been solved. More specifically, in the present invention, more excellent effects can be obtained by defining the water absorption and the degree of hydrophobicity of each of the toner particles and the carrier particles of the two-component developer in the above ranges.

The sieving conditions in the present invention are as follows. 1. Weigh 2 g of sample to the nearest 0.1 g.

2. The sieve uses a standard sieve of 200 to 325 mesh, and 200, 285, 32 from the top.
Stack the samples in the order of 5 meshes, place a saucer on the bottom surface that receives 325 meshes, put the sample in the top sieve and cover it. In addition, what is used here is a standard sieve conforming to the Japanese Industrial Standards. The sieve opening size of each mesh is 77, 53, and 44 μm in the order of 200, 285, and 325 mesh.

3. The sieve on which the sample is placed is sieved by a vibrator at an amplitude of 0.5 mm and the number of vibrations at 300 times per minute for 1 minute. 4. After sieving, calculate the weight% of each sieve and the sample in the pan, and pass the sample remaining on the sieve without passing through the 200-mesh sieve through the coarse powder and the 325-mesh sieve. The sample present in the sample was taken as fine powder.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the operation and effect of each element of the present invention will be described below.

As the developer of the present invention, a two-component developer containing a toner and a carrier is preferably used. The carrier may be a metal particle-coated carrier in which ordinary metal particles are coated with a resin, or a magnetic powder may be a polymer. Any of polymer carriers dispersed in a resin to form particles can be used.

Among them, a polymer carrier obtained by mixing magnetic fine particles with a polymer will be described. As described above, the polymer carrier has a lower magnetization than a conventional carrier made of a magnetic substance alone, so that a soft and high-density magnetic brush can be formed. Can be obtained. Further, since there is an advantage that the possibility of damaging the surface of the electrostatic latent image carrier when adhered to the electrostatic latent image carrier is small, it can be suitably used in the developer of the present invention.

In order for such a polymer carrier to bind the magnetic powder and maintain the shape as a carrier, the upper limit of the content of the magnetic powder to the binder resin is 80% by weight. If the amount is increased, the material becomes brittle and cannot function as a carrier. On the other hand, when the content of the magnetic powder is small, the magnetic force of the carrier is reduced, so that a phenomenon that the carrier adheres to the latent image carrier occurs. For these reasons, the content of the magnetic powder in the polymer carrier used in the present invention is preferably about 60 to 80% by weight.

Regarding the magnetic characteristics of the carrier, regardless of the type of the carrier, from the viewpoint of the shape of the magnetic brush and the adhesion of the carrier on the electrostatic latent image carrier, the magnetization at an applied magnetic field of 1000 Oe is 20 or more and 60 emu. / g or less is desirable. If it is less than 20 emu / g, the binding force of the carrier due to magnetism may be weakened and the carrier may adhere to the electrostatic latent image carrier. If it exceeds 60 emu / g, the brush of the magnetic brush becomes coarse and brush marks appear on the printed image. Can be seen.

As the binder resin of the polymer carrier,
Various things can be mentioned, for example, styrene resin, acrylic resin, styrene-acrylic copolymer resin, polyester resin, epoxy resin and the like,
These may be used alone or in combination as necessary. The physical properties of these binder resins include:
Number average molecular weight is 10,000 or more, 50,000 or less, and
Those having a weight average molecular weight of 50,000 or more and 30,000 or less are preferably used. If a polymer having a molecular weight lower than the above range is used, the carrier itself is deformed by heat during continuous printing, and thermal aggregation of the developer is likely to occur. Further, when a polymer having a higher molecular weight than this range is used, it becomes difficult to produce a carrier, and both are not preferable.

The magnetic fine particles used in the polymer carrier include known magnetic particles such as magnetite fine particles and ferrite fine particles. As for the size of the magnetic fine particles, the average particle diameter is set at 0.
About 1 to 0.5 μm is preferable.

There are various methods for producing a polymer carrier. For example, a polymer and a magnetic powder are melt-kneaded by a Banbury mixer, a kneader, an extruder or the like, cooled, pulverized and classified, or And a spray drying method in which a magnetic powder is mixed and dispersed in a polymer solution, followed by spray drying. A suspension polymerization method in which a monomer constituting a polymer and a predetermined material are dispersed in an appropriate solvent and the suspension is polymerized to obtain a desired carrier can also be used.

In both the magnetic material-coated carrier and the polymer carrier, the particle size of the carrier particles is desirably small in order to form a soft and high-density magnetic brush. The binding force of the carrier is weakened, and the carrier adheres to the electrostatic latent image carrier. In consideration of these, the average particle size of the carrier is preferably about 36 to 60 μm, and the actual particle size distribution is such that the carrier particles themselves have a coarse powder amount of 200 mesh or more and 20% by weight or less, and A powder having a fine powder content of 325 mesh or less and 50% by weight or less is suitable.

When the average particle size exceeds 60 μm, or when the amount of coarse powder of 200 mesh or more exceeds 20% by weight, the brush of the magnetic brush becomes coarse and brush marks can be seen on the printed image. become. When the average particle size is less than 0.1 μm, or when the amount of fine powder of 325 mesh or less exceeds 50% by weight,
Since the presence of the fine powder carrier having a small magnetizing force is increased, there is a possibility that the carrier is significantly attached to the electrostatic latent image carrier.

The electric resistance of the carrier is 10⁸Ω
・ Cm or more is preferable. Resistance value is 10 ⁸Less than Ωcm
In this case, electric charges are injected into the carrier particles and the latent image carrier
Carrier adheres to the top and leakage of the developing bias occurs.
Be frightened. The measurement of the resistance value of the carrier in the present invention
The following method is used. Transfer 10g of carrier into a cylindrical 40mm diameter
Put it in a molding container, put it between the electrodes and apply 1 ton of pressure
The current value is measured by changing the voltage while the
Plot the electric field-volume resistance curve from the thickness at 1000 V / cm
Is adopted.

Next, the toner used in the developer of the present invention will be described. The particle size of the toner particles greatly affects the image quality, and the larger the particle size, the coarser the image. Although there is no practical problem with toner having an average particle diameter of about 20 μm, it is desirable that the toner has an average particle diameter of 10 μm or less from the viewpoint of fine line resolution. On the other hand, when the toner diameter becomes smaller, the adhesive force such as van der Waals force acting between the toner and the carrier becomes dominant, and the developability is reduced. In addition, when the toner diameter is small, aggregation of the toner is likely to occur, which causes a problem in handling. From the above viewpoints, in the present invention, a toner having an average particle size of 5 to 10 μm is suitably used.

The following are used as the main binder resin for the toner. For example, polystyrene, styrene
Propylene copolymer, styrene-butadiene copolymer,
Styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer, polyester resin, polyurethane resin, etc. A plurality of binder resins are used in combination. In particular, in the case of a color toner, since different color toners need to be fused and fixed satisfactorily at the time of fixing, a polymer having a number average molecular weight of 10,000 or less is used as the binder resin for the toner used, and preferably a number average molecular weight. It is a polymer with a molecular weight of 5,000 or less. However, when the number average molecular weight is less than 2,000, the toner itself is deformed by heat due to the temperature rise in the developing device during continuous printing, and the toner surface is thermally deformed and the toner surface is thermally deformed. Since the problems such as deterioration of the chargeability and developability of the toner occur, the number average molecular weight of the binder resin for the toner is 2,2.
It is desirable that it be 000 or more.

From the viewpoint of increasing the releasability from the roll during heat roll fixing and preventing toner offset, an olefin homopolymer or copolymer such as ethylene or propylene may be added as a wax component. At this time, the addition amount of the wax component is 0.5 to 1 with respect to the toner.
0% by weight is desirable. If the amount is less than this, the effect of the wax component is not obtained. On the other hand, if the addition amount is larger than this, the toner is likely to be deformed by heat, and aggregation of the developer is likely to occur.

In the toner particles according to the present invention, the high molecular weight of 100.000 or more has a weight average molecular weight of 100.000 or more in order to increase the mechanical strength of the toner or to increase the cohesive force of the toner at the time of heat roll fixing to prevent toner offset. A polymer or a crosslinked polymer may be contained. The content of these high molecular weight polymers and crosslinked polymers is desirably 20% by weight or less based on the toner. If the content is more than this, the different color toners will not be fused and fixed satisfactorily at the time of fixing, causing a problem in color reproducibility.

As for the colorant used in the toner, carbon black, nigrosine, graphite and the like are used as the black type.

The chromatic color system varies depending on the hue, but the following known colorants are used. (Yellow or orange pigment) CI Pigment Orange
31, CI Pigment Orange 43, CI Pigment Yellow 12, CI Pigment Yellow 14, CI Pigment Yellow 17, CI Pigment Yellow 93, CI Pigment Yellow 94, CI Pigment Yellow 138, CI Pigment Yellow 174 and the like. (Magenta or red pigment) CI Pigment Red 5
, CI Pigment Red 48: 1, CI Pigment Red 5
3: 1, CI Pigment Red 57: 1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178 , CI Pigment Red 222 and the like. (Sian or green pigment) CI Pigment Green
7, CI Pigment Blue 15, CI Pigment Blue 1
5: 2, CI Pigment Blue 15: 3, CI Pigment Blue 60, etc.

It is desirable that the content of the toner colorant is 0.5% by weight or more and 20% by weight or less based on the toner. If the content is less than 0.5% by weight, the color developability is not sufficient and clear image quality cannot be obtained. If the content is more than 20% by weight, unevenness in image quality occurs due to poor dispersion of the colorant in the toner.

Considering the hygroscopicity of these developers, it is desirable that the carrier also has low hygroscopicity, and the surface of the carrier may be coated with a highly hydrophobic resin such as a fluororesin or a silicone resin. Further, fine particles having a high degree of hydrophobicity may be attached to the carrier surface.

Regarding the hygroscopicity of the carrier, the carrier 1
00g is allowed to stand in an environment of 30 ° C. and 80% RH for 10 hours, and then is allowed to stand in an environment of 60 ° C. and 30% RH for 1 hour.

The application of the fine particles having a high degree of hydrophobicity to a toner or a carrier can be achieved by mixing and stirring the toner or the carrier and the fine particles. The manner in which the particles are contained in the toner and carrier varies depending on the mixing or stirring conditions, and various conditions such as a state in which the particles are attached to the toner surface and a state in which the particles are embedded in the toner surface Are used under desired conditions in consideration of chargeability and fluidity as a developer.

Examples of the fine particles to be contained in the toner and the carrier include inorganic fine particles such as titanium oxide, alumina and silica, and acrylic organic fine particles such as polyacrylate, polymethacrylate and polymethyl methacrylate. The fine particles contained in these toners act not only as an anti-agglomeration agent but also as a fluidity improver and a charge control agent. In consideration of environmental stability, these fine particles need to be hydrophobic, and for this purpose, highly hydrophobic fine particles having a degree of hydrophobicity of 60 or more are used.

The definition of the degree of hydrophobicity in the present invention will be described. The degree of hydrophobicity in the present invention is as follows.
Add 2 g, stir with a stirrer, titrate with methanol, and determine the methanol titer when all the fine particles are suspended in the solvent by T
cc. The degree of hydrophobicity (M) at this time is defined by the following equation.

[0043]

## EQU1 ## Degree of hydrophobicity (M) = [T / (50 + T)] × 10
0 (vol.%) In particular, in the case of inorganic fine particles having hygroscopicity, such as titanium oxide, alumina, and silica, those subjected to a hydrophobic treatment are used. The hydrophobic treatment of these inorganic fine particles is performed, for example, by subjecting the fine particles to a silane coupling agent such as a dialkyl dihalogenated silane, a trialkyl halogenated silane, an alkyl trihalogenated silane, or a hydrophobizing agent such as dimethyl silicon oil at a high temperature. The reaction can be performed under the following conditions.

The particle size of these fine particles is 20 to 100 nm.
The particle size of If the particle size is less than 20 nm, the external additive will be buried in the toner during long-term use, and the function will not be fulfilled. If the particle size exceeds 100 nm, the external additive will be easily peeled off from the toner or the carrier surface and used for a long time. May not function.

The amount of the fine particles to be added is preferably 20% or more, and
80% or more. If the coverage is less than 20%, it is insufficient to impart stable fluidity and chargeability to the toner. From the viewpoint of fluidity and hydrophobicity, the coverage is preferably 80% or more, and 100%, that is, the surface of the toner or carrier particles may be entirely covered with the fine particles.

Here, the coverage on the surface of the toner and carrier particles is determined from a scanning electron micrograph. As a magnification, 15 photographs were taken at random at a magnification of 100,000 times in order to clearly grasp the presence state of fine particles of the order of 10 nm, and an average of 10 photographs were selected, and the covering area was determined. Then, the coverage is calculated.

These fine particles may be used alone or in combination of two or more in order to impart desired fluidity and chargeability as a toner. In addition, as long as it does not cause a problem due to moisture absorption, it can be used in combination with fine particles having a low hydrophobicity.

In the present invention, fine particles are contained, that is,
The hygroscopicity of the toner or carrier after adhering to the surface was determined by measuring the weight after standing for 10 hours in an environment of 30 ° C. and 80% RH, and the weight for 1 hour in an environment of 60 ° C. and 30% RH. After that, those having a weight change ratio of 0.3% by weight or less from the weight measured are used. In the case where toner or carrier particles having a weight change of more than 0.3% by weight are used, aggregation of the developer under high temperature and high humidity becomes a problem.

The charge amount of the toner when it is used as a developer is too high. If the charge amount is too high, a phenomenon that the toner is not developed because the adhesive force of the toner to the carrier becomes too high occurs. On the other hand, if the charge amount of the toner is too low, the adhesion of the toner to the carrier becomes too weak, and a toner cloud due to free toner is generated, which causes a problem of fogging in printing. In consideration of these, if the charge amount of the toner in the developer is defined from the viewpoint of suitably developing the toner, the charge amount is in an absolute value of 5 to 50 μC / g, preferably 10 to 40 μC / g. Is desirable.

[0050]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Example 1 Preparation of Toner Polyester (number average molecular weight: 3,300, weight average molecular weight:
9,800, Tg = 60 ° C.) 93% by weight and 7% by weight of carbon black are kneaded and pulverized to obtain a base toner having an average particle diameter of 7 μm, and the base toner is subjected to hydrophobic treatment with hexamethylene disilazane. Chemical degree 60, average particle size 20n
m TiO ₂ fine particles were externally added so as to have a coverage of 50, 60, 70, and 80% so that the coverage on the toner surface was different to obtain four types of negatively chargeable toners having different hygroscopicity. The toners are referred to as toners 1, 2, 3, and 4 in descending order of coverage, that is, in descending order of hydrophobicity. The water absorption of each toner was determined by the method described above, that is, 100 g was added at 30 ° C., 8
After being left for 10 hours in an environment of 0% RH, the weight is measured,
Thereafter, the weight when left for 1 hour in an environment of 60 ° C. and 30% RH is measured, and the result of measurement by a method of determining the rate of change in the weight is also shown.

Toner 1: (80% hydrophobic fine particle coverage: 0.2 water absorption)
%) Toner 2: (70% coverage of hydrophobic fine particles: 0.3% water absorption)
%) Toner 3: (60% hydrophobic fine particle coverage: 0.4 water absorption)
%) Toner 4: (50% hydrophobic fine particle coverage: 0.5 water absorption)
%) Preparation of carrier Styrene-acrylic copolymer (number average molecular weight: 23,000,
Weight average molecular weight: 98,000, Tg = 78 ° C.) 30% by weight, granular magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) 70
The base carrier having an average particle size of 45 μm was manufactured by kneading, pulverizing and classifying the weight%. When the magnetic characteristics of these base carriers were measured, the saturation magnetization was 55 emu / g.

Further, for these base carriers,
SiO ₂ fine particles having a hydrophobicity of 60 and an average particle diameter of 20 nm, which have been subjected to a hydrophobizing treatment with hexamethylene disilazane, are externally added to the base carrier so that the coverage ratio on the base carrier surface is different from 50, 60, 70, and 80%. , Four types of positively chargeable carriers 1, 2, 3, and 4. The results obtained by measuring the water absorption of each carrier in the same manner as for the toner are also shown.

Carrier 1: (80% coverage of hydrophobic fine particles: 0% water absorption)
Carrier 2: (70% coverage of hydrophobic fine particles: 0% water absorption)
Carrier 3: (hydrophobic fine particle coverage: 60%: water absorption: 0.3%)
Carrier 4: (50% coverage of hydrophobic fine particles: 0% water absorption)
5%) Adjustment and Evaluation of Developer A developer was prepared by combining the above toner and carrier. The obtained developer was subjected to a print test using an electrophotographic image forming apparatus. All toner concentrations of the developer were 10% by weight.

Table 1 shows the combination of each toner and carrier and the characteristics of the developer. The characteristics of the developer are as follows: when the developer is left in an environment of 60 ° C. and 30% RH for 10 hours,
It is a value represented by the weight% of the amount of coarse powder of 00 mesh or more and the amount of fine powder passing through 325 mesh.

[0055]

[Table 1]

The developers shown in Table 1 were evaluated by the following electrophotographic apparatus. FIG. 1 is a schematic view of a developing section of the electrophotographic apparatus used for evaluating the developer.

This developing device comprises a developing sleeve 2 rotatably disposed with a small gap between the OPC photosensitive member 1 and the surface thereof, and a seven-electrode fixed inside the developing sleeve 2 coaxially therewith. , A bucket roller 4 that mixes the developer to frictionally charge the toner and the carrier and supplies the developer to the peripheral surface of the developing sleeve 2, and regulates the thickness of the developer layer on the developing sleeve 2. It is composed of a layer thickness regulating member 5. The photoconductor 1, the sleeve 2, and the bucket roller 4 rotate in the direction of the arrow. The development conditions are as follows. (Development conditions) Photoreceptor OPC (φ84) ROS LED (400dpi) Process speed 300mm / s Latent image potential Background part = -600V, image part = -100V Development roll Magnet fixed, sleeve rotation method Magnet magnetic flux density = 500G (on sleeve) ) Sleeve diameter = φ25 Sleeve rotation speed = 600mm / s Distance between photoconductor and development roll 0.5mm Developer layer thickness 0.4mm Development bias DC component = -550V AC component = 1.5kVP -P (8kHz) With these developers in mind, 30
A continuous print test was performed in an environment of 80 ° C. and 80% RH. Here, the occurrence of fog when 10,000 sheets were continuously printed was examined. In this continuous printing, one cycle is to provide a pause time of 30 seconds after continuous printing of 100 sheets, and this cycle is repeated 100 times. Before running the continuous print test, apply 30% of each developer.
It was left for 12 hours in an environment of 80 ° C. and 80% RH.

As a result, the developers (1-A), (1-B), (1-C), (1-E),
For (1-F) and (1-I), fog did not occur even when continuous printing was performed, but developers (1-D), (1-G) and (1-G) outside the scope of the present invention were used. H), (1-J),
(1-K), (1-L), (1-M), (1-N),
Fog occurred in (1-O) and (1-P). The occurrence of fog can be reduced to 10 ° C under an environment of 30 ° C and 80% RH.
It can be seen that the amount of coarse powder of 200 mesh or more after being left for a long time is remarkable. Examination of the chargeability of the developer at this time confirmed the presence of the opposite polarity toner. The cause of the fog was presumed to be a decrease in the chargeability of the developer due to the aggregation of the developer. Example 2 Preparation of Toner Polyester (number average molecular weight: 3,300, weight average molecular weight:
(9,800, Tg = 60 ° C.) 93% by weight of carbon black and 7% by weight of carbon black were kneaded and pulverized to obtain particles having an average particle diameter of 7 μm. This spherical base toner was subjected to a hydrophobic treatment with methyltrichlorosilane, dimethyldichlorosilane, hexamethyldisilazane, and silicone oil, respectively.
TiO ₂ fine particles of 0 nm were externally added so as to have a coverage of 80% on the surface of the base toner to obtain four types of negatively chargeable toners having different hygroscopicity. At this time, the degree of hydrophobicity of the TiO ₂ fine particles was M = 45 for the product treated with methyltrichlorosilane, M = 50 for the product treated with dimethyldichlorosilane, M = 60 for the product treated with hexamethyldisilazane, and M = 60 for the product treated with silicone oil. 70. The number of the toner is as follows: The treating agent of the TiO ₂ fine particles used is toner 8 treated with methyltrichlorosilane, toner 7 treated with dimethyldichlorosilane, toner 6 treated with hexamethyldisilazane, and toner treated with silicone oil. 5 is assumed.

Toner 5: (using fine particles treated with silicone oil: water absorption 0.2%) Toner 6: (using fine particles treated with hexamethyldisilazane:
Toner 7: (using fine particles treated with dimethyldichlorosilane):
Toner 8: (using methyltrichlorosilane-treated fine particles)
Preparation of Carrier Ferrite particles having an average particle size of 45 μm were coated with polymethyl methacrylate to produce a ferrite base carrier having an average particle size of 45 μm. When the magnetic properties were measured, the saturation magnetization was 65 emu / g.

Further, for these base carriers,
SiO ₂ fine particles having an average particle diameter of 30 nm, each of which has been subjected to a hydrophobizing treatment with methyltrichlorosilane, dimethyldichlorosilane, hexamethyldisilazane, and silicone oil, are externally added so as to have a coverage of 80% on the base carrier surface. And four types of positively chargeable carriers having different hygroscopicity. At this time, the degree of hydrophobicity of the SiO ₂ fine particles was M = 45 for the product treated with methyltrichlorosilane, M = 50 for the product treated with dimethyldichlorosilane, M = 60 for the product treated with hexamethyldisilazane, and M = 60 for the product treated with silicone oil. 70.

The number of the carrier is as follows: the treating agent for the SiO ₂ fine particles used is methyl trichlorosilane-treated product;
Carrier 7 is treated with dimethyldichlorosilane, carrier 6 is treated with hexamethyldisilazane, and carrier 5 is treated with silicone oil.

Carrier 5: (using silicone oil-treated fine particles: water absorption)
Carrier 6: (using hexamethyldisilazane-treated fine particles)
Carrier 7: (using fine particles treated with dimethyldichlorosilane)
Carrier 8: (using fine particles treated with methyltrichlorosilane)
(For water absorption 0.5%) Adjustment and evaluation of developer The toner and carrier are combined to form a developer,
As in the first embodiment, the image forming apparatus using an electrophotographic method
A lint test was performed. The toner concentration of the developer is 10
% By weight. The combination of each toner and carrier
The characteristics of the developer are shown in the table. In the toner and carrier columns
The water absorption in the sample was measured in the same manner as in Example 1.

Table 1 shows the combination of each toner and carrier and the characteristics of the developer. The characteristics of the developer are as follows: when the developer is left in an environment of 60 ° C. and 30% RH for 10 hours,
It is a value represented by the weight% of the amount of coarse powder of 00 mesh or more and the amount of fine powder passing through 325 mesh.

[0064]

[Table 2]

The developers shown in Table 2 were evaluated in the same electrophotographic apparatus as in Example 1 under the same conditions. As a result, the developers (2-A), (2-B), (2-
C), (2-E), (2-F) and (2-I) did not cause fogging even when continuous printing was performed, but other developers (2-D) and (2-G) ), (2-H), (2-
J), (2-K), (2-L), (2-M), (2-
Fog occurred in N), (2-O) and (2-P).
It can be seen that generation of fog is remarkable when the developer is left in an environment of 30 ° C. and 80% RH for 10 hours and the amount of coarse powder of 200 mesh or more is large. Examination of the chargeability of the developer at this time confirmed the presence of the opposite polarity toner. The cause of the fog was presumed to be a decrease in the chargeability of the developer due to the aggregation of the developer. Comparative Example 1 A base carrier having an average particle diameter of 33 μm was manufactured in the same manner as in Example 1. This base carrier was subjected to the same hydrophobic treatment as that of the carrier 1. (Water absorption:
0.2%) A developer was prepared by combining this carrier with toners 1, 2, 3, and 4, and evaluated using the same electrophotographic apparatus as in Example 1 under the same conditions.

As a result, with this developer, carrier adhesion to the image area was observed immediately after the start of printing. Observation of the photoreceptor surface at this time confirmed that the fine powder carrier had adhered to the photoreceptor surface.

When a mesh filtration test was performed on this developer, the amount of fine powder of 325 mesh or less exceeded 50% by weight based on the total amount of the developer. From this, in a developer in which the amount of fine powder of 325 mesh or less as an initial state of the developer exceeds 50% by weight with respect to the total amount of the developer,
All of the obtained developers, including those used in combination with the toners 1 and 2 having a favorable water absorption, are not practical due to the presence of many fine powder carriers having a weak magnetic binding force, resulting in carrier adhesion problems. It can be said that.

From the above results, when the mesh filtration test was performed after leaving the sample in an environment of 30 ° C. and 80% RH for 10 hours, the amount of coarse powder of 200 mesh or more was 20% by weight or less and 325 mesh The following fine powder content is 50% by weight
It was confirmed that by using the following developer, the problem of aggregation of the developer due to moisture can be avoided, and clear and high image quality can be obtained even when a large number of sheets are continuously printed. As described above, such a developer could be easily obtained by controlling the particle diameters of the base toner particles and carrier particles and the water absorption and hydrophobicity thereof.

[0069]

According to the developer for electrophotography of the present invention, a clear high-quality image can be obtained even under high humidity such as in summer. Further, even when a large number of sheets are printed, a long-life developer free from deterioration in image quality due to a decrease in the chargeability of the developer can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an image forming apparatus to which an electrophotographic developer of the present invention can be applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 OPC photosensitive body (electrostatic latent image carrier) 2 Charger 3 LED 4 Developing unit 5 Developing roll 6 Transfer pre-processing unit 7 Transfer unit 8 Cleaner 9 Static eliminator 10 Transfer material carrying-in port 11 Transfer material carrying member

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI G03G 9/10 351

Claims (7)

[Claims] 1. A developer containing toner particles and carrier particles, wherein the developer is left in an environment of 30 ° C. and 80% RH for 10 hours and then subjected to a mesh filtration test.
The amount of coarse powder of 200 mesh or more is 20% by weight or less;
An electrophotographic developer, wherein the amount of fine powder having a size of 325 mesh or less is 50% by weight or less. 2. The electrophotographic developer according to claim 1, wherein the carrier particles are a magnetic carrier obtained by coating a resin layer on a magnetic substance alone. 3. The electrophotographic developer according to claim 1, wherein the carrier particles are polymer carriers formed by mixing magnetic fine particles and a polymer resin to form particles. 4. The method according to claim 1, wherein the toner particles have a temperature of 30 ° C. and a relative humidity of 80%.
Weight after being left for 10 hours in an environment of
2. The electrophotographic developer according to claim 1, wherein the developer exhibits a water absorbency in which a weight change ratio with respect to a weight after being left for 1 hour in an environment of 30 ° C. and 30% RH is within 0.3%. . 5. The method according to claim 1, wherein the carrier particles are at 30 ° C. and 80% R.
H after being left for 10 hours in an environment of H
2. The electrophotographic development according to claim 1, wherein the toner exhibits water absorbency with a weight change rate within 0.3% of the weight after being left for 1 hour in an environment of 0 ° C. and 30% RH. Agent. 6. The electrophotographic developer according to claim 1, wherein the toner particles include fine particles having a hydrophobicity of 60 or more. 7. The electrophotographic developer according to claim 1, wherein the carrier particles include fine particles having a hydrophobicity of 60 or more.