JP2005250516A - Electrostatic latent image developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrostatic latent image developer capable of stably forming an image and having a long life and a wide controlling range of the charge amount. <P>SOLUTION: The developer contains: (a) a magnetic resin-coated carrier comprising magnetic particles as the carrier core having the surface treated with a catalyst and coated with a polymeric polyethylene resin prepared by directly polymerizing ethylene monomers; (b) a magnetic powder carrier substantially comprising magnetic particles only; and (c) a polishing toner having abrasive fine particles fixed on the surface of the toner mother material, in a compounding ratio of 70:30:5 by weight. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is an electrostatic latent image developer used in electrophotographic methods, electrostatic recording methods, electrostatic printing methods and the like employed in copying machines and laser printers (sometimes simply referred to as a developer). About.

  Conventionally, magnetic powder particles such as iron, magnetite, or ferrite are usually used as a carrier for stably transporting toner in a developer used in the two-component development system. A carrier made of such magnetic powder particles (sometimes referred to as a magnetic powder carrier) has an advantage that the structure is simple, the magnetic force is excellent, and the cost is low.

Patent Document 1 discloses a developer containing a mixed carrier composed of a magnetic powder carrier and a magnetic resin carrier in which magnetic fine particles are dispersed in a binder resin.
Such a developer has a large volume resistance value and contains a magnetic resin carrier having a high charge amount, so that the charge imparting power to the toner is increased, and thus fog generation can be efficiently suppressed. There are advantages.

  Furthermore, in order to improve the durability of the carrier itself, Patent Document 2 proposes a magnetic resin-coated carrier. This magnetic resin-coated carrier is provided with a coating layer made of a high molecular weight polyethylene resin obtained by directly polymerizing ethylene monomer on the surface of the carrier core material using a catalyst supported on the surface of the carrier core material. Yes. Therefore, the obtained polyethylene coating layer has an excellent strength, and has an appropriate elastic force, and can absorb an impact force such as stirring, so that an excellent durability can be obtained.

However, the conventional magnetic powder carrier itself has a problem in that it has a small volume resistance value, has poor moisture resistance, and easily causes poor charging. In addition, since the magnetic powder carrier is heavy, the toner component adheres to the carrier due to the impact of agitation in the developing device and tends to cause spent, and as a result, the charging ability of the carrier is reduced and further charging failure occurs. There was a problem that it was easy.
Furthermore, once a charging failure occurs, it becomes difficult to stably convey the toner, and the toner is likely to be fogged into the apparatus and the white background portion of the visible image is stained, and the image density is reduced. There was a problem of adverse effects.

Moreover, although the developer disclosed in Patent Document 1 uses a magnetic powder carrier and a magnetic resin carrier in combination, the magnetic resin carrier has poor binding between the magnetic particles and the binder resin. Therefore, there has been a problem that the binder resin is easily peeled off when used for a long time. In addition, since the magnetic resin carrier has a small specific gravity and a large charge per unit weight (specific charge Q / M), there is a problem that carrier pulling easily occurs.
For this reason, in order to stably form an image and extend the life of the developer, the blending ratio of the magnetic resin carrier has to be lowered. Therefore, since the blending ratio of the magnetic powder carrier is increased, there has been a problem that the color developability of the obtained color image tends to be lowered when used in combination with the color toner. In other words, since the magnetic powder carrier has high blackness, when carrier pulling occurs when the blending ratio of the magnetic powder carrier is high, the carrier is noticeable or the color of the color image particularly in a color other than black. It became easy to become cloudy.

  Furthermore, since the magnetic resin-coated carrier itself disclosed in Patent Document 2 has low blackness, even when used in combination with a color toner, the color developability of the obtained image is rarely lowered, but the cost alone is low. It was relatively expensive and the resulting developer was likely to be expensive. In addition, the magnetic resin-coated carrier has a problem that the charge imparting power to the toner is slightly lower than that of the magnetic powder carrier.

Japanese Patent No. 2922050 JP-A-9-204075

  Therefore, it has been desired to adjust the mixing ratio of the mixed carrier in a wide range so that the charge amount of the mixed carrier can be adjusted more easily and a developer with less carrier pulling is desired. That is, the present invention has been made to solve the above-described problems, and a developer that can stably form an image, has a long lifetime, has a wide charge amount adjustment range, and has a small carrier pull. The purpose is to provide.

According to the electrostatic latent image developer of the present invention,
(A) a magnetic resin-coated carrier having a coating layer made of a high molecular weight polyethylene resin obtained by directly polymerizing an ethylene monomer;
(B) a magnetic powder carrier substantially consisting of the magnetic particles themselves;
(C) toner and
It is characterized by containing.

Thus, by combining (a) the magnetic resin-coated carrier and (b) the magnetic powder carrier into a mixed carrier, (a) the magnetic resin-coated carrier is more than the case of using a conventional magnetic resin carrier. Can be blended in a wide range. As a result, the necessary charge amount can be arbitrarily set and stably applied to the toner.
In addition, the magnetic force is higher and the specific gravity is lower than the magnetic resin carrier. (A) Since the magnetic resin-coated carrier is used, (b) the blending ratio of the magnetic powder carrier can be reduced and the carrier pulling is efficient. Can be prevented. Therefore, even when it is used in combination with color toner, it is less likely that the color developability of the obtained image is lowered.

In constructing the electrostatic latent image developer of the present invention, the mixing ratio (a) / (b) of (a) magnetic resin-coated carrier and (b) magnetic powder carrier is 85/15 by weight. A value in the range of ~ 45/55 is preferred.
By limiting to such a range of the blending ratio, excellent carrier fluidity can be obtained while securing an initial charge amount of a certain level or more.

In constituting the electrostatic latent image developer of the present invention, the volume resistance value of (a) the magnetic resin-coated carrier and (b) the magnetic powder carrier or one of the carriers is set to 1 × 10 ² to 1 A value within the range of × 10 ¹⁴ Ω · cm is preferable.
When the volume resistance value of the carrier is smaller than 1 × 10 ² Ω · cm, the image density may be lowered or the image quality may be deteriorated. On the other hand, the volume resistance value is lower than 1 × 10 ¹⁴ Ω · cm. This is because the carrier pulling and fogging are likely to occur when the value is larger.

In constructing the electrostatic latent image developer of the present invention, when (a) the volume resistance value of the magnetic resin-coated carrier is Va and (b) the volume resistance value of the magnetic powder carrier is Vb, The value of Va−Vb) is preferably set to a value in the range of 10 to 1 × 10 ³ Ω · cm.
The reason for this is that when two types of carriers are used, if there is an extreme resistance difference between the carriers, fogging or carrier pulling is likely to occur, and a development margin cannot be secured, and carriers with extremely low resistance. This is because, when these are mixed, a leakage current to the photoconductor flows and image defects may occur.
Accordingly, if the resistance difference between (a) the volume resistance value of the magnetic resin-coated carrier is Va and (b) the volume resistance value of the magnetic powder carrier is Vb, the toner is more stably conveyed. be able to.

In constructing the electrostatic latent image developer of the present invention, when the bulk density of the magnetic resin-coated carrier (a) is ρa and (b) the bulk density of the magnetic powder carrier is ρb, ρb> It is preferable to satisfy the relationship of ρa.
With this configuration, (b) the magnetic powder carrier can attract the (a) magnetic resin-coated carrier, and the carrier pulling that the carrier adheres to the surface of the photoreceptor can be more efficiently suppressed.

In constituting the electrostatic latent image developer of the present invention, it is preferable that the ratio of the amount of toner added to the mixed carrier of (a) and (b) is set to a value in the range of 2 to 40% by weight.
In this way, by limiting the amount of toner added to a value of 2% by weight or more, it is possible to effectively suppress the toner charge amount from becoming excessively high and the image density from being lowered. Further, when the toner addition amount is set to a value of 40% by weight or less, it is possible to efficiently suppress toner scattering in the apparatus and fogging on a visible image due to insufficient toner charge amount.

In constituting the electrostatic latent image developer of the present invention, the toner is preferably a color toner.
With this configuration, even when the carrier is attached to the photosensitive member together with the toner by the carrier pulling and printed, the color developability of the color visible image is reduced.

In constructing the electrostatic latent image developer of the present invention, it is preferable to use an abrasive toner having abrasive fine particles fixed on its surface as the toner.
Thus, by using the abrasive toner, the surface of the carrier can be polished with the abrasive of the toner itself. Therefore, it is possible to further suppress the occurrence of spents in which toner accumulates and grows on the surface of the carrier with long-term use.
Further, by using an abrasive toner, the surface of the photoreceptor can be polished and cleaned with an appropriate force. Therefore, it is possible to suppress the occurrence of image flow due to the occurrence of leakage current.

In constituting the electrostatic latent image developer of the present invention, it is preferable that the abrasive fine particles are conductive titania.
By configuring in this way, the charge amount of the carrier increases, so that it is possible to efficiently prevent the carrier from transferring to the photosensitive member together with the toner.
Further, since conductive titania has high whiteness, even when the toner base material to which the abrasive is fixed is colored, it is possible to avoid the toner color becoming cloudy due to the color of the abrasive. In addition, since conductive titania is chemically stable, it can be combined with color toners having various color components. Furthermore, since conductive titania is stable against heat, it is suitable for fixing a developed visible image by heating.

According to the present invention, by using a mixed carrier comprising the magnetic resin-coated carrier (a) and the magnetic powder carrier (b), a long-lived electrostatic latent image capable of stably forming an image. An image developer is obtained. Furthermore, since the blending ratio can be changed in a wide range, the required charge amount can be set arbitrarily and can be stably applied to the toner. Also, when the developer contains an abrasive toner, The surface can be polished and cleaned with an appropriate force. As a result, it is possible to suppress the occurrence of image flow due to the occurrence of leakage current.
In addition, if the developer of the present invention containing an abrasive toner is used in an image forming apparatus equipped with an α-Si photoconductor that is inherently hard to wear and can be used for a long time, the photoconductor is used for a long time. become able to. As a result, it is possible to provide a long-life printer as well as a long developer life.

[First Embodiment]
The electrostatic latent image developer of the first embodiment is
(A) a magnetic resin-coated carrier having a coating layer made of a high molecular weight polyethylene resin obtained by directly polymerizing an ethylene monomer on the surface of magnetic particles as a carrier core;
(B) a magnetic powder carrier substantially consisting of the magnetic particles themselves;
(C) an abrasive toner having abrasive fine particles fixed on the surface of the toner base material;
Contains.

[I] Magnetic resin-coated carrier Carrier Core Material (1) Material As a material of the carrier core material used in the present invention, a known two-component carrier for electrophotography can be used, and specifically, the following types can be given.
(i) Ferrite, magnetite and metals such as iron, nickel and cobalt
(ii) Alloys or mixtures of the metals listed in (i) with metals such as copper, zinc, antimony, aluminum, lead, tin, bismuth, beryllium, manganese, magnesium, selenium, tungsten, zirconium, vanadium
(iii) Mixtures of metals and the like listed in (i) with metal oxides such as iron oxide, titanium oxide, and magnesium oxide, nitrides such as chromium nitride and vanadium nitride, and carbides such as silicon carbide and tungsten carbide
(iv) Ferromagnetic ferrite
(v) A mixture of (i) to (iv)

(2) Shape and particle size The shape of the carrier core material is not particularly limited, and may be any of a spherical shape and an indefinite shape. However, since it is easy to charge uniformly, a spherical shape is preferable.
Further, the average particle diameter of the carrier core material is preferably set to a value in the range of 20 to 120 μm, for example, and more preferably set to a value in the range of 25 to 80 μm.
This is because when the average particle size of the carrier core material is less than 20 μm, carrier adhesion (scattering) to the electrostatic latent image carrier (generally a photoreceptor) may occur. This is because, when the average particle size exceeds 120 μm, carrier streaks or the like are generated, which may cause deterioration of image quality characteristics (decrease in image density).

(3) Ratio of carrier core material The ratio of the carrier core material is preferably 90% by weight or more, more preferably 95% by weight or more when the entire carrier is 100% by weight. .
This is because when the ratio of the carrier core material is less than 90% by weight, the magnetic force is lowered and the toner transportability may be lowered. Further, the ratio of the carrier core material indirectly defines the thickness of the coating layer of the carrier. However, when the composition ratio of the carrier core material is less than 90% by weight, the coating layer has an excessively or non-uniform thickness. This is because there are cases where For this reason, when the carrier is applied to the developer, problems such as peeling of the coating layer and an increase in the charge amount may occur, or the durability and charge stability required for the developer may not be satisfied. Because there is. Furthermore, if the ratio of the carrier core material is less than 90% by weight, the fine line reproducibility is poor in terms of image quality, and the image density may decrease.

On the other hand, the upper limit of the composition ratio of the carrier core material is preferably such that the coating resin layer completely covers the carrier core material and the magnetic powder, and specifically, a value of 99.5% by weight or less. Preferably, the value is 99.0% by weight or less.
The preferable range of the ratio of the carrier core material may be slightly different depending on the physical properties of the carrier core material and the coating method.

(4) Conductive layer Prior to coating with high molecular weight polyethylene resin, a conductive layer having a volume resistance in the range of 1 × 10 ² to 1 × 10 ¹⁰ Ω · cm is provided on the carrier core particles. Is also preferable. By providing such a conductive layer, more excellent developability can be obtained, and an image with high image density and clear contrast can be obtained. This is presumably because the electric resistance of carriers is moderately reduced due to the presence of the conductive layer, and charge leakage and accumulation are performed in a well-balanced manner.

As the kind of the conductive layer, it is preferable to use a conductive layer in which conductive fine particles are dispersed in a suitable binder resin. Examples of such conductive fine particles include carbon black such as carbon black and acetylene black, carbide such as SiC, magnetic powder such as magnetite, SnO ₂ , and titanium black.
On the other hand, examples of the binder resin include polystyrene resins, poly (meth) acrylic resins, polyolefin resins, polyamide resins, polycarbonate resins, polyether resins, polysulfonic acid resins, polyester resins, and epoxy resins. Examples thereof include a single type of resin, a polybutyral resin, a urea resin, a urethane resin, a silicone resin, and a fluorine resin, or a combination of two or more. Furthermore, the mixture (polymer blend), copolymer, block polymer, graft polymer, etc. of these resin can also be mentioned.

  Further, the size and amount of the conductive fine particles are not particularly limited as long as various properties such as the electrical resistance of the finally obtained carrier are satisfied. The particle size is such that it can be uniformly dispersed in the resin solution. Specifically, the particle size is preferably in the range of 0.01 to 2.0 μm, more preferably in the range of 0.01 to 10 μm. Value is good.

  Further, the amount of the conductive fine particles to be added also varies depending on the type of the conductive fine particles, but is a value within the range of 0.1 to 60% by weight with respect to the binder resin of the conductive layer, preferably 0.1. A value within the range of ˜40% by weight is appropriate. In particular, when the carrier filling rate is as small as 90% by weight and the thickness of the coating layer is relatively thick, the reproducibility is reduced when continuous copying of fine lines is performed using such a carrier. May occur, but can be efficiently prevented by adding the above-mentioned conductive fine particles.

The method for forming the conductive layer is not particularly limited, but a solution in which conductive fine particles are dispersed in a binder resin is applied to the surface of the carrier core material by spray coating, dipping, or the like. Can be formed.
The conductive layer can also be formed by solution, kneading and pulverization of the carrier core material, conductive fine particles and binder resin. Further, it can be formed by directly polymerizing a polymerizable monomer on the surface of the carrier core material particle in the presence of conductive fine particles.
In addition, what a functional layer such as a conductive layer is formed on carrier core particles may be simply referred to as carrier core particles.

2. Coating layer made of high molecular weight polyethylene resin (1) High molecular weight polyethylene resin The high molecular weight polyethylene resin constituting the coating layer is usually simply called polyethylene, but in the present invention, the number average molecular weight is 10,000 or more as the molecular weight range. Or a thing with a weight average molecular weight of 50,000 or more is preferable, More preferably, it is a polyethylene resin with a number average molecular weight of 40,000 or more, or a weight average molecular weight of 200,000 or more.
The reason for this is that when the number average molecular weight is less than 10,000, the polyethylene resin becomes waxy, and after dissolving in hot toluene or the like, it can be coated by a normal infiltration method or spray method, but the mechanical strength is weak. For this reason, when used for a long time, it may be peeled off from the carrier core material due to a shearing force (share) in the developing device.
In addition, it is also preferable to add the functional resin which consists of 1 type individual, or 2 or more types of combinations, such as electroconductive fine particles and electric-resistant characteristic fine particles which have charge control ability, in the coating layer which consists of high molecular weight polyethylene resin.

(2) Coating layer
(i) Forming method of coating layer As a method for forming a coating layer made of high molecular weight polyethylene, it is preferable to employ a direct polymerization method, for example, a forming method such as a dipping method, a fluidized bed, a dry method, and a spray drying method. It is also preferable to combine them.
Here, the direct polymerization method refers to a method in which the surface of the carrier core material is previously treated with an ethylene polymerization catalyst, and then a polyethylene resin-coated carrier is produced while directly polymerizing (generating) ethylene on the surface. . That is, as an ethylene polymerization catalyst, a high-activity catalyst component and a carrier core material that contain titanium and / or zirconium and are soluble in a hydrocarbon solvent (for example, hexane, heptane, etc.) are obtained by contact treatment in advance. A method of forming a polyethylene resin coating layer by adding an organoaluminum compound to a solid product obtained, suspending it in a hydrocarbon solvent, supplying an ethylene monomer, and polymerizing it on the surface of the carrier core material Say.
According to this forming method, since the polyethylene coating layer is directly formed on the surface of the carrier core material, the resulting coating layer is thin, excellent in strength and elasticity, and excellent in carrier durability. Become.
Details of such a direct polymerization method are described in, for example, JP-A-60-106808 and JP-A-2-187770, and the same method can be mentioned.

  When fine particles having a charge imparting function or conductive fine particles are added to the coating layer, they may be added to the ethylene monomer and coexisting when the coating layer is formed. For example, if conductive fine particles or functional fine particles having charge control ability are dispersed in the polymerization system, the functional fine particles are taken in when the coating layer is polymerized to form functional fine particles. Etc. can be easily formed.

(ii) Coating amount When the coating amount of the high molecular weight polyethylene is represented by a weight ratio of [high molecular weight polyethylene resin coating] / [carrier core particle], it is within the range of 0.5 / 99.5 to 10/90. It is preferable to form so that it may become the value of this, and it is more preferable to set it as the value within the range of 1 / 99-5 / 95.
This is because when the weight ratio is larger than 10/90, the coating layer becomes relatively thick and the coating layer may be peeled off or the charge stability may not be satisfied. Further, in terms of image quality, there are cases where problems such as poor reproducibility of fine lines and a decrease in image density may occur. On the other hand, when the weight ratio is smaller than 0.5 / 99.5, the coating layer becomes relatively thin, and it may be difficult to completely cover the carrier core material and the magnetic powder.

(iii) Silica particles In addition, it is preferable to add silica particles having a positive charging characteristic or a negative charging characteristic after, for example, surface hydrophobization treatment in the coating layer.
By adding silica particles in this way, the chargeability of the carrier can be easily controlled, and the mechanical strength of the coating layer can be improved.
Moreover, it is preferable to make the average particle diameter of a silica particle into the value of 40 nm or less as a primary particle diameter, and it is more preferable to set it as the value within the range of 10-30 nm. The reason for this is that when the temporary particle diameter of the silica particles exceeds 40 nm, the gap between the silica particles becomes large, irregularities are generated on the carrier surface, and the fluidity may be lowered.
Examples of such commercially available silica particles include R812 and RY20 (trade name) manufactured by Nippon Aerosil Co., Ltd., 2000 and 2000/4 (trade name) manufactured by Wacker Chemicals, and the like as positively chargeable silica. .

  In addition, when increasing the charge amount of the positively charged toner, it is preferable to use silica particles having negative charge characteristics, and when increasing the charge amount of the negatively charged toner, it is preferable to add silica particles having positive charge characteristics. . In order to reduce the charge amount of the toner, it is preferable to use silica particles having the same polarity as the toner.

(iv) Functional fine particles Next, functional fine particles other than silica particles will be described. It is also preferable to modify the coating layer by adding conductive fine particles or charge characteristic particles having charge control ability alone or in combination of two or more. As such conductive fine particles, conventionally known fine particles can be used. For example, carbon black, carbide such as SiC, conductive powder such as magnetite, SnO ₂ , titanium black, or the like can be used. The average particle size of the conductive fine particles is preferably in the range of 0.01 to 2.0 μm.
Examples of the charge characteristic particles include the following negative charge characteristic resin (A) and positive charge characteristic resin (B).

(A) Negative charge characteristic resin Examples of the negative charge characteristic resin include fluorine resins (for example, vinylidene fluoride resin, tetrafluoroethylene resin, trifluorochloroethylene resin, tetrafluoroethylene to hexafluoroethylene). Polymer resin), vinyl chloride resin, celluloid) and the like.

(B) Positive charge characteristic resin Examples of the positive charge characteristic resin include acrylic resin, polyamide resin (for example, nylon-6, nylon-66, nylon-11, etc.), and styrene resin (for example, polystyrene, ABS, AS). , AAS, etc.), vinylidene chloride resins, polyester resins (eg, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyacrylate, polyoxybenzoyl, polycarbonate, etc.), polyether resins (eg, polyacetal, polyphenylene ether, etc.) And polyethylene resins (for example, EVE, EEA, EAA, EMAA, EAAM, EMMA, etc.).

3. Conductive characteristics Regarding the conductive characteristics of the magnetic resin-coated carrier, although the optimum value varies slightly depending on the developing system using the carrier, for example, the volume resistance value is within the range of 1 × 10 ² to 1 × 10 ¹⁴ Ω · cm. Are preferable, those showing a value in the range of 1 × 10 ³ to 1 × 10 ¹⁰ Ω · cm are more preferable, and values in the range of 1 × 10 ⁴ to 1 × 10 ⁹ Ω · cm are preferable. What is shown is more preferred.
The reason for this is that when the volume resistance value is less than 1 × 10 ² Ω · cm, it may be difficult to suppress carrier-drawing development and fogging. On the other hand, if the volume resistance value exceeds 1 × 10 ¹⁴ Ω · cm, it may be difficult to suppress degradation of image quality due to a decrease in image density.
The volume resistance value of the carrier is adjusted by adjusting the thickness of the upper and lower electrodes by sandwiching the carrier to be measured between the upper and lower electrodes (electrode area 5 cm ² ) and pressing it under the condition of a load of 1 kg. It can be calculated by applying a voltage of 1 to 500 V between them and measuring the flowing current value.

4). Average particle diameter Further, the average particle diameter of the magnetic resin-coated carrier is not particularly limited. For example, the average particle diameter is preferably set to a value in the range of 20 to 120 μm, and preferably 20 to 100 μm. A value within the range is more preferable, and a value within the range of 20 to 80 μm is even more preferable.
This is because when the average particle size of the carrier is less than 20 μm, carrier development or fogging may occur. On the other hand, when the average particle size exceeds 120 μm, the carrier transportability may be lowered.

5). Operation The above-described magnetic resin-coated carrier has both a true specific gravity and an apparent specific gravity smaller than that of the magnetic powder carrier. For this reason, the magnetic resin-coated carrier has a large surface area per unit weight, and has a charge imparting ability to toner particles even in a small amount.
In addition, this magnetic resin-coated carrier can reduce the occurrence of spent in a developing device of a small printer where a large shearing force is applied during mixing and stirring, and can also reduce the impact during stirring of the magnetic powder carrier. In addition, even if the magnetic resin-coated carrier is subjected to a surface treatment such as a surface coating, since the stress during stirring is relatively small, the surface coating material (surface treatment material) is not easily polished or peeled off by the abrasive toner. There is a feature.

[II] Magnetic powder carrier (1) Configuration
(i) Type As the magnetic powder carrier, for example, magnetic particles substantially made of magnetic powder such as iron, magnetite or ferrite can be used.
However, in order to improve moisture resistance, it is also preferable to form a resin film on the surface of the magnetic powder. Examples of resins that form such resin films include silicone resins, epoxy resins, polyester resins, acrylic resins, polyamide resins, styrene resins, vinylidene chloride resins, polyether resins, and polyethylene resins. It is done. Of these resins, silicone resins are particularly preferred because of their excellent moisture resistance and lubricity.
In addition, when forming a resin film in a magnetic powder carrier, it is preferable to make the resin film quantity into the value within the range of 0.01 to 1 weight% with respect to the whole quantity of a magnetic powder carrier.

(ii) Bulk density The bulk density of the magnetic powder carrier is desirably higher than the bulk density of the magnetic resin-coated carrier. For example, the bulk density of the magnetic resin carrier is preferably less than 2.3 g / cm ³ , whereas the bulk density of the magnetic powder carrier is preferably 2.3 g / cm ³ or more.
With this configuration, the magnetic powder carrier attracts the magnetic resin-coated carrier, and the carrier pulling that the carrier adheres to the surface of the photoreceptor can be more efficiently suppressed.

(iii) Average particle diameter The average particle diameter of the magnetic powder carrier is preferably set to a value within the range of 20 to 130 μm, more preferably set to a value within the range of 20 to 110 μm. It is more preferable to set the value within the range.
This is because, when the average particle size of the magnetic powder carrier is 20 μm, carrier pulling development or fogging may occur. On the other hand, if the average particle diameter exceeds 130 μm, the toner transportability by the magnetic powder carrier may be lowered.

(iv) Compounding ratio (b) The compounding ratio of the magnetic powder carrier and the above-mentioned (a) magnetic resin-coated carrier can be set widely. For example, the compounding ratio (a) / (b) is The ratio is preferably in the range of 85/15 to 45/55, more preferably in the range of 75/25 to 50/50, and in the range of 70/30 to 40/60. More preferably, it is a value.
The reason for this is that when the blending ratio (a) / (b) is smaller than 85/15, the defects of the magnetic resin-coated carrier of (a) can be sufficiently compensated by the magnetic powder carrier of (b). For example, by improving the toner transportability, it is possible to suppress a decrease in image density and a deterioration in dot reproducibility. Furthermore, it is possible to extend the life of the electrostatic latent image developer by suppressing an increase in the charge amount associated with use.
On the other hand, when the blending ratio (a) / (b) is larger than 45/55, the defects of the magnetic powder carrier of (b) can be sufficiently compensated by the magnetic resin-coated carrier of (a), Occurrence of fog due to defects can be suppressed. Further, deterioration of charging failure due to spent can be suppressed, and the life of the electrostatic latent image developer can be extended. Furthermore, if it is larger than 50/50, it can suppress more effectively.

  Further, when the electrostatic latent image developer is constituted by mixing the magnetic resin coated carrier, the magnetic powder carrier and the toner, the weight ratio is within the range of 60 to 80:40 to 20: 4 to 6, respectively. It is more preferable that

(2) Action As described above, by using the magnetic powder carrier in combination with the magnetic resin-coated carrier, the spike from the sleeve becomes the spike centering on the magnetic powder carrier having this high magnetic force. When leaving the development zone, the magnetic resin-coated carrier is attracted to the high magnetic force carrier. As a result, it is possible to prevent the occurrence of carrier pulling in which the magnetic resin-coated carrier moves to the photoreceptor together with the toner.
That is, when a magnetic resin-coated carrier is used alone without using a magnetic powder carrier, the magnetic resin-coated carrier has a small specific gravity, a large charge per unit weight (specific charge Q / M), and a relatively low magnetic force. This is because it is weak and carrier pulling easily occurs.
In order to prevent carrier pulling, it may be possible to set the average particle diameter of the magnetic resin-coated carrier (for example, a value exceeding 100 μm). However, when the image quality becomes rough and it is difficult to improve the toner density. There is.

Further, by using the magnetic resin-coated carrier and the magnetic powder carrier in combination, the magnetic powder carrier can remove an increase in the electric charge charged to the magnetic resin-coated carrier.
Therefore, the charge amount of the carrier and the toner at the time of development can be stabilized, and as a result, the toner charge holding force by the carrier is superior to the toner attracting force due to the potential difference on the electrostatic latent image of the photoreceptor. Can be avoided.
As a result, the toner conveyed by the carrier can be sufficiently adhered onto the electrostatic latent image, thereby preventing a decrease in image density and a deterioration in dot reproducibility and extending the life of the electrostatic latent image developer. be able to.

[III] Abrasive Toner (1) Structure The structure of (c) the abrasive toner will be described with reference to FIG. FIG. 1 is a model diagram of the abrasive toner (c), and shows that the toner 11 has the abrasive fine particles 15 fixed on the surface of the toner base particles 13.
The fixing of the abrasive fine particles to the surface of the toner base particles may be performed by, for example, mixing the toner base particles and the abrasive fine particles uniformly, attaching the abrasive fine particles to the surface of the toner base particles, and then mechanically or thermally. This is performed by applying a small impact and driving the abrasive fine particles into the toner base particles. That is, it is preferable that the fine abrasive particles are not completely buried in the toner base particles but are fixed in a state in which a part thereof protrudes from the surface of the toner base particles.

(2) Manufacturing method Abrasive fine particle fixing devices are commercially available as surface modification devices and systems, and one example is as follows. Examples of the dry mechanochemical method include a mechanochemical (trade name) manufactured by Okada Seiko Co., Ltd. and a mechanofusion system (trade name) manufactured by Hosokawa Micron Corporation. Moreover, as a thing by the impact method in a high-speed air current, the hybridization system (brand name) by Nara Machinery Co., Ltd. and the kryptron system (brand name) by Kawasaki Heavy Industries, Ltd. can be mentioned.

Furthermore, as a thing by a wet method, the disperse coat (brand name) by Nisshin Flour Milling Co., Ltd. and the coat-mizer (brand name) by Freund Sangyo Co., Ltd. can be mentioned.
Examples of the heat treatment method include surfing (trade name) manufactured by Nippon Pneumatic Industry Co., Ltd.
In addition, examples of the fixing device by other methods include spray drying (trade name) manufactured by Okawara Chemical Corporation.

(3) Abrasive fine particles
(i) Type 1
Examples of the type of abrasive fine particles include fine particles having high hardness, for example, fine particles such as metal oxides such as alumina, zirconia, and titanium oxide (titania).
In particular, titanium oxide is preferable because it has a high whiteness, and therefore, even when the toner base material to which the abrasive is fixed is colored, it is possible to avoid a decrease in toner color development due to the color of the abrasive. Further, since titanium oxide is chemically stable, it can be combined with color toners having various color components. Furthermore, since titanium oxide is stable against heat, it is suitable for heat fixing a developed visible image.

(ii) Type 2
Moreover, it is preferable that the abrasive fine particles exhibit conductivity in a volume resistance range of 0.1 to 100 Ω · cm. The reason is that the use of conductive abrasive fine particles increases the charge amount of the carrier, so that the carrier can be efficiently prevented from moving to the photoreceptor together with the toner.
The conductive abrasive fine particles can be easily obtained by subjecting the electrically insulating abrasive fine particles to a conductive treatment such as tin oxide treatment or indium oxide treatment.

(iii) Hardness Considering application to an amorphous silicon photoconductor (α-Si photoconductor) having an amorphous-silicon carbide (SiC) layer as the surface protective layer 31 (see FIG. 3) of the photoconductor, an abrasive. It is preferable that the Mohs hardness of the fine particles is a value of 8 or more, preferably a value within the range of 8-9. That is, since the Mohs hardness of the SiC layer is about 8, an excellent polishing effect can be obtained by using abrasive fine particles having such hardness.

(iv) Average particle diameter Further, regarding the average particle diameter of the abrasive fine particles, the average particle diameter of the toner base particles is D, and the average particle diameter of the abrasive fine particles is d, the range of D / d = 10-50. It is preferable that the average particle diameter is within the range of D / d = 10-40.
This is because the abrasive fine particles are firmly fixed to the surface of the toner base particles, and the polishing effect by the abrasive fine particles is increased.
The surface of the abrasive fine particles may be subjected to a surface treatment for the purpose of charge adjustment or prevention. Further, other fine particles may be used in combination for the purpose of adjusting fluidity and the like.

(4) Toner Base Particles As toner base particles, those having the same structure as in conventional toners are used. For example, a binder resin, a colorant, a charge control agent, an offset preventing agent and the like can be blended. . Further, a magnetic material can be added to obtain a magnetic toner.
As such a binder resin, a vinyl resin such as a styrene-acrylic copolymer, a polyester resin, or the like is used. As the colorant, various pigments and dyes including carbon black are used. A color toner may be used by using a plurality of pigments. As the charge control agent, a quaternary ammonium compound, nigrosine, nigrosine base, crystal bio red, triphenylmethane compound or the like is used. Further, as the offset preventing agent and the fixing improving aid, olefin waxes such as low molecular weight polypropylene, low molecular weight polyethylene or modified products thereof can be used. Furthermore, magnetite, ferrite, etc. can be used as the magnetic material.

  The toner base particles can be obtained by a conventionally known method, for example, by melt-kneading each component with a twin screw extruder, kneader or the like, and then pulverizing and classifying with a jet mill or the like. In general, the average particle diameter of the toner is preferably 20 μm or less, and more preferably 15 μm or less.

(5) Operation When the above-described abrasive toner is used, the toner 11 polishes the surface of the magnetic powder carrier when the developer is stirred and mixed, and the spent material fused to the surface of the magnetic powder carrier is polished. Remove. Therefore, spent does not accumulate or grow more than a certain amount, and stable image quality can be obtained over a long period of time.
The spent amount is quantified as the spent amount for both the resistance value and the total carbonaceous carrier.

  In addition, when an electrostatic latent image is transferred and image formation is performed using an abrasive toner, when the toner contacts and rubs against the surface layer of the photoconductor, such as during development and cleaning of the photoconductor. The surface of the photoreceptor can be polished effectively. In particular, it is effective for an α-Si type photoreceptor having a SiC layer as a surface phase.

[Second Embodiment]
Next, an embodiment relating to an image forming method using the electrostatic latent image developer (developer) of the present invention will be described.

(1) Photoconductor First, the configuration of the photoconductor of the image forming apparatus to which the developer is applied will be described with reference to FIG.
FIG. 2 is a schematic cross-sectional view of an essential part for explaining the layer structure of the photosensitive layer of the photosensitive drum. As shown in FIG. 2, the photosensitive layer of the photoreceptor 21 includes a light-absorbing layer 25 made of Si: Ge: H, a carrier injection blocking layer made of Si: H: B: O, etc. on a conductive substrate 23. 27, a carrier excitation / transport layer 29 (photoconductive layer) made of Si: H or the like, and a surface protective layer 31 are sequentially formed.

This surface protective layer (sometimes referred to as a SiC layer) 31 is formed of, for example, SiC having a thickness of about 0.3 to 1 × 10 μm, more preferably α-SiC (amorphous-silicon carbide). Yes. The surface of this SiC layer is not smooth, and a large number of minute protrusions (cones) are present on the surface. Moreover, this SiC layer has strong hydrophilicity, and the ion product produced by corona discharge adheres.
For this reason, when continuous printing is performed or printing is started under high humidity conditions, toner adheres to the photosensitive drum and toner filming occurs, and adhesion of a hydrophilic compound such as ammonium nitrate as an ion product occurs. Occur. For this reason, the charge of the photoconductor leaks and a so-called “image flow” phenomenon occurs. In addition, these products tend to accumulate between the fine protrusions of the SiC layer, which is the surface protective layer 31, and thus image flow cannot be prevented by ordinary cleaning.

On the other hand, the abrasive toner (c) uses the abrasive fine particles 15 to polish the vicinity of the tips of the microprojections on the SiC layer to smooth the surface of the SiC layer, and between the microprojections. The deposited ion products are removed to prevent image flow and contribute to ensuring development stability.
In addition, the abrasive toner does not exhibit excessive polishing power because abrasive particles are provided on the surface of the toner. Therefore, even when polished with a cleaning blade or a rubbing roller, the surface of the α-Si photosensitive member is not damaged.

(2) Image Forming Method Next, with reference to FIG. 3, a method for forming an image using the electrostatic latent image developer according to the present invention will be described together with a configuration example of an image forming apparatus.
FIG. 3 is a schematic diagram for explaining the configuration of the image forming apparatus.
This image forming apparatus is the same as a conventional general image forming apparatus except that a rubbing roller (pressing member) 49 is provided. In FIG. 3, the carrier is not shown.

Around the drum-shaped α-Si photosensitive member 21, a corona charger 41, an LED head 43 (exposure device), a developing roller 45, a transfer device 47, a rubbing roller 49, and a cleaning blade 51 are disposed. After uniform charging of the surface of the photosensitive member 21 by the corona charger 41 and formation of an electrostatic latent image by selective image exposure by the LED head 43, the developer 61 is supplied to the surface of the photosensitive member 21 by the developing roller 45, and toner is developed by development. A visible image consisting of 11 is formed. At this time, the surface of the photoreceptor 21 is rubbed by the toner 11 in the developer 61, and the SiC layer (not shown) on the surface is polished.
Further, since the abrasive fine particles 15 are firmly fixed to the toner base particles 13, they do not fall off and do not cause development defects or image defects.

Further, the toner 11 on the surface of the photosensitive member 21 is transferred to the paper 63 (a material to be transferred) by the transfer machine 47 and then fixed on the paper 63 by a fixing device (not shown).
In the transfer step, not all of the toner 11 on the surface of the photoreceptor 21 is transferred to the paper 63 but a part of the toner 11 (residual toner) remains on the photoreceptor 21. The residual toner 11 is pressed against the surface of the photoreceptor 21 by the rubbing roller 49 to polish the SiC layer on the surface, and the polishing effect of the toner 11 by the abrasive fine particles 15 is increased.

Next, the residual toner 11 on the photoconductor 21 is removed from the surface of the photoconductor 21 by the cleaning blade 51, and at this time, the residual toner 11 on the photoconductor 21 is removed between the cleaning blade 51 and the photoconductor 21. The SiC layer on the surface of the photoreceptor 21 is polished by the abrasive fine particles 15 of the toner 11 by a mechanical force applied between them.
Further, as the rubbing roller 49, an elastic roller is used, and the rubbing roller 49 is pressed against the surface of the photoconductor 21 and rotated so as to apply a shear stress to the photoconductor 21. The surface (not shown) of the body 21 is polished and cleaned.
Further, by attaching a heater to the inner surface of the photoconductor 21 and heating it, the effect of preventing image drift can be further improved.

Examples of the present invention will be described below.
(1) Manufacture of magnetic resin coated carrier
(i) Preparation of titanium-containing catalyst component In a 500-ml flask purged with argon, 200 ml of dehydrated n-heptane and 1.5 g (25 mmol) of magnesium stearate dehydrated at 120 ° C. under reduced pressure (266 kPa (2 mmHg)) at room temperature. ) To make a slurry. After dropwise addition of 0.44 g (2.3 mmol) of titanium tetrachloride with stirring, the heating was started and reacted for 1 hour under reflux to obtain a viscous transparent titanium-containing catalyst (active catalyst). .

(ii) Activity evaluation of titanium-containing catalyst component In an autoclave with an internal volume of 1 liter substituted with argon, 400 ml of dehydrated hexane, 0.8 mmol of triethylaluminum, 0.8 mmol of diethylaluminum chloride, and the above (i) were prepared. The titanium-containing catalyst was taken as 0.004 mmol of titanium atoms and charged, and the temperature was raised to 90 ° C. At this time, the internal pressure was 147 kPa (1.5 kg / cm ² G).
Subsequently, hydrogen is supplied into the autoclave and the pressure is increased to 539 kPa (5.5 kg / cm ² G), and then ethylene is continuously added so that the total pressure is maintained at 931 kPa (9.5 kg / cm ² G). Supplied to. In this state, ethylene was polymerized for 1 hour to obtain 70 g of polyethylene. The polymerization activity was 365 kg / g · Ti / Hr, and the obtained polyethylene had an MFR (melt flowability measured according to JIS K 7210 at 190 ° C. and 21.168 N (load 2.16 kg)) of 40 g. / Min.

(iii) Production of polyethylene-coated carrier 960 g of sintered ferrite powder F-2535 (trade name) (average particle size 65 μm, manufactured by Powdertech Co., Ltd.) was accommodated in an autoclave with an internal volume of 2 liters substituted with argon, up to 80 ° C. The temperature was raised, and drying under reduced pressure (1330 kPa (10 mmHg)) was performed for 1 hour. Thereafter, the temperature was lowered to 40 ° C., 800 ml of dehydrated hexane was accommodated, and stirring was started.
Subsequently, after adding 5.0 mmol of diethylaluminum chloride and 0.05 mmol of the titanium-containing catalyst component prepared in the above (i) as titanium atoms, the reaction was performed for 30 minutes, and the temperature was further raised to 90 ° C. 4 g was introduced. At this time, the internal pressure of the autoclave was 294 kPa (3.0 kg / cm ² G). Thereafter, hydrogen was supplied to increase the internal pressure to 313.6 kPa (3.2 kg / cm ² G), and 5.0 mmol of triethylaluminum was added to initiate the polymerization. The internal pressure was about 225. 5 minutes. It decreased to ⁴ kPa (2.3 kg / cm ² G) and stabilized.

Next, a slurry composed of 5.5 g of carbon black (manufactured by Mitsubishi Chemical Corporation, MA-100 (trade name)) and 100 ml of dehydrated hexane is introduced into the autoclave, and the internal pressure is 421.4 kPa (4.3 kg). / Cm ² G), while continuously supplying ethylene so as to supply 40 g of ethylene in the total amount into the system, the supply was stopped and polymerization was directly performed for 45 minutes. Thus, 1005.5 g of carbon black-containing polyethylene resin-coated ferrite was obtained.
The powder obtained by drying the obtained carbon black-containing polyethylene resin-coated ferrite had a uniform black color. From the electron micrograph, it was observed that the ferrite surface was thinly covered with polyethylene resin, and carbon black was uniformly dispersed in the polyethylene resin.
When the composition ratio of the carbon black-containing polyethylene resin-coated ferrite was measured by TGA (thermobalance), the composition ratio of ferrite: carbon black: polyethylene was 90.5: 0.5: 4.0 by weight. there were.
Further, the weight average molecular weight of the coated polyethylene in the obtained carbon black-containing polyethylene resin-coated ferrite was 206,000 as measured by GPC.

  Next, the carbon black-containing polyethylene resin-coated ferrite was classified with a 125 μm sieve to remove large particle diameters of 125 μm or more. The carbon black-containing polyethylene resin-coated ferrite after classification is placed in a fluidized bed type air classifier having a tower diameter of 14 cm and heated so that the linear velocity of the classifier body becomes 20 (cm / s) (115 ° C.) Was introduced, and the carbon black-containing polyethylene resin-coated ferrite was allowed to flow for 10 hours to obtain a primary carrier.

  10 kg of the primary carrier thus obtained is accommodated in a 20-liter Henschel mixer (FM20C / I type (trade name) manufactured by Mitsui Miike Chemical Co., Ltd.), and hot water is supplied to a jacket provided around the Henschel mixer. By flowing in, the temperature (treatment temperature) in the Henschel mixer was set to 70 ° C. While maintaining the temperature at 70 ° C., the surface of the primary carrier was smoothed by stirring for 2.0 hours and applying a mechanical impact.

After that, in order to completely remove the fine powder and agglomerated powder generated by the Henschel mixer, sieving (# 125 mesh) and classification (using a fluidized bed type air classifier, linear speed 20 cm / s, 2 hours) are performed. Thus, a magnetic resin-coated carrier (sometimes referred to as a secondary carrier) was obtained.
When the surface of the obtained magnetic resin-coated carrier was observed with a scanning electron microscope (SEM), it was confirmed that a polyethylene coating layer was formed on the surface, the surface was extremely smooth, and was nearly spherical as a whole. did.
The properties of the obtained magnetic resin-coated carrier are as shown in Table 1, column A. The average particle size is 75 μm, the volume resistance is 1 × 10 ¹⁰ Ω · cm, and the bulk density is 2.1 g / cm ^3. The saturation magnetization was 62 emu / g (130.2 emu / cm ³ ).
In addition, since the magnetic resin-coated carrier used in the present invention is coated with polyethylene, the bulk density as a carrier is a normal carrier bulk density (for example, 2.7-3. 3 g / cm ³ or so) lower than the magnetic properties between Thus the photosensitive member and the developing roller tends to decrease. However, since a general saturation magnetization value of 62 emu / g was obtained as described above, there is no practical problem.

In the Table 1 above, the column of the volume resistivity, conveniently a "1 × 10 ^10" is represented as "1E + 10", the "1 × 10 ^8" is represented as "1E + 08", "1 × 10 ¹⁵ ”is expressed as“ 1E + 15 ”.
In Table 1 above, “cm ³ ” is represented as “cm ^ 3” for convenience.

(2) Production of Magnetic Powder Carrier In this example, Fe ₂ O ₃ and CuO · ZnO-based composite ferrite were used for production of the magnetic powder carrier.
The properties of the obtained uncoated magnetic powder carrier are as shown in the column B of Table 1 above, with an average particle diameter of 90 μm, a volume resistance value of 1 × 10 ⁸ Ω · cm, and a bulk density of 2 .7g / cm ^3, the saturation magnetization was ^{64emu / g (172.8emu / cm 3} ).

(3) Production of Abrasive Toner In this example, the following materials were sufficiently kneaded and pulverized by a high-speed mixer and classified in the production of the abrasive toner to obtain toner base particles having an average particle diameter of 10 μm.
90 parts by weight of styrene-n-butyl acrylate copolymer (copolymerization ratio 80/20)
5 parts by weight of carbon black (manufactured by Mitsubishi Chemical Industries, Ltd., MA-100 (trade name))
Polypropylene wax 3 parts by weight (manufactured by Sanyo Chemical Industries, Ltd., Biscol (trade name))
Charge control agent 2 parts by weight (manufactured by Hoechst, copy blue PR (trade name))

To the toner base particles, 1.5% by weight of conductive titania (TiO ₂ ) having an anatase crystal structure was added as abrasive fine particles. The primary particle diameter of the abrasive fine particles is in the range of 0.1 to 0.5 μm, and the volume resistance value is in the range of 10 to 1 × 10 ³ Ω · cm. Hydrophobization treatment (in this example, titanate treatment) ). Further, the amount of the abrasive fine particles added to the toner base particles was in the range of 0.5 to 3% by weight.
The characteristics of the obtained abrasive toner are as shown in column C of Table 1. The average particle size is 90 μm, the volume resistivity is 1 × 10 ⁸ Ω · cm, the bulk density is 2.7 g / cm ³ , The saturation magnetization was 64 emu / g (172.8 emu / cm ³ ).

Next, the magnetic coated resin carrier (a), magnetic powder carrier (b) and abrasive toner (c) produced as described above were mixed at different weight ratios of A: B: C, respectively. The electrostatic latent image developers of Examples 1 to 4 and the first and second comparative examples were prepared.
First, in the first embodiment, the mixing ratio of the developer was A: B: C = 80: 20: 5.
In the second embodiment, the mixing ratio of the developer is A: B: C = 60: 40: 5.
Further, in the third example, the mixing ratio of the developer was A: B: C = 40: 60: 5.
In the fourth embodiment, the mixing ratio of the developer is A: B: C = 20: 10: 5.
In the first comparative example, the blending ratio of the developer was A: B: C = 100: 0: 5.
In the second comparative example, the mixing ratio of the developer was A: B: C = 0: 100: 5.

  And the charge amount and fluidity | liquidity were measured about the developer in the compounding ratio of said each Example and each comparative example, respectively. The charge amount was measured by a QM meter method manufactured by Trek. The fluidity was measured according to JIS Z-2502 method. The measurement results are shown in Table 2 below.

Further, the measurement results are shown in the graph of FIG. On the horizontal axis of the graph of FIG. 4, the above six mixing ratios are given, the left vertical axis represents the charge amount (μC / g), and the right vertical axis represents the fluidity (fall time: seconds). .
A curve I in the graph is obtained by connecting white circle plots of the measurement results of the charge amount. Curve II is obtained by connecting white square plots of the measurement results of fluidity.
As shown by the curve I in the graph of FIG. 4, the charge amount tends to increase as the proportion of the magnetic resin-coated carrier in (a) increases. On the other hand, as shown in the curve II, the fluidity tends to increase as the proportion of the magnetic powder carrier (b) increases.
In order to perform stable image formation, it is necessary to ensure a certain amount of charge and fluidity for the developer.

  As a range satisfying such conditions, it is desirable that the value of (a) / (b) is in the range of 85/15 to 45/55, as judged from the curves I and II. In particular, if the value of (a) / (b) is in the range of 75/25 to 50/50, it is possible to secure a charge amount of 15 μC / g or more and to secure fluidity of 35 seconds or less. Understand. Furthermore, it can be seen that when the value of (a) / (b) is around 70/30, a charge amount of 16 μC / g or more and fluidity of 34 seconds or less can be secured.

Next, initial image characteristics and durability test results were conducted for the blending ratio when only the charge amount was high, when both the charge amount and fluidity were high, and when only the fluidity was high.
As an example in which only the charge amount is high and the fluidity is low, in the fifth example, the blending ratio of the developer was A: B: C = 90: 10: 5.
Further, as an example in which both the charge amount and the fluidity are high, in the sixth example, the blending ratio of the developer was A: B: C = 70: 30: 5.
Furthermore, as an example where the charge amount is low and only the fluidity is high, the blending ratio of 40: 60: 5 of the third embodiment described above was adopted.

Table 3 shows the test results of the initial image characteristics and durability of the developers having the blending ratios of the fifth, sixth and third examples.
In the test, a modified machine of FS-3500 (trade name) manufactured by Kyocera Corporation was used as an evaluation machine. In this modified machine, the gap between the photosensitive member and the sleeve is set to 0.6 mm, the gap between the developer regulating blade and the sleeve is set to 0.6 mm, and the white background (non-static) of the photosensitive member is set. The potential of the electrostatic latent image portion) is 500V, the potential of the photosensitive member after exposure (electrostatic latent image portion) is 15V, the sleeve applied voltage is 350V, and the peripheral speed ratio between the photosensitive member and the sleeve is 2.0 times. It was.

As shown in Table 3, the initial image characteristic test was performed under the following environmental conditions for image density, dot reproducibility, and white background fogging.
Room temperature and normal humidity (25 ° C-60%, sometimes referred to as NN environment)
Low temperature and low humidity (10 ° C-20%, sometimes referred to as LL environment)
High temperature and high humidity (33 ° C-85%, sometimes referred to as HH environment)

In measuring the dot reproducibility, actual printing was performed using A4 paper in a state where 400 g of the evaluated developer was accommodated in the printer and fixed at a surface potential of 400 V and a bias voltage of 300 V. The dot reproducibility was evaluated according to the following criteria.
○: No image defect occurs Δ: Image defect is slightly observed ×: Image defect occurs

The white background fogging was evaluated according to the following criteria.
○: No fogging occurred Δ: Slight fogging was observed ×: Fog was clearly recognized

  As shown in Table 3, the image density and the dot reproducibility tend to improve as the blending ratio of (b) magnetic powder carrier increases. On the other hand, the white background fogging property tends to improve as the blending ratio of the magnetic resin-coated carrier (a) increases. In particular, in the case of the third example in which the blending ratio of the magnetic powder carrier was high, fogging was observed in a high-temperature and high-humidity environment (HH environment) because the moisture resistance of the magnetic powder carrier was low.

In the durability test, 300,000 (300k) continuous prints were performed, and the results of evaluation of image density transition and charge amount transition according to the following criteria are shown in Table 3.
In measuring the image density, the image density of the solid portion of the developed image was measured periodically with a Macbeth densitometer, and the transition of the image density was evaluated according to the following criteria.
○: A constant image density is maintained even after continuous printing of 300,000 sheets. Δ: The image density gradually decreases. X: The image density decreases rapidly.

In measuring the charge amount, the charge amount was measured with a blow-off charge measuring device. The charge amount was evaluated according to the following criteria.
○: Charge amount changes within an appropriate range Δ: Charge amount changes within an appropriate range ×: Charge amount becomes too high or too low

  As shown in Table 3 above, in the case of the sixth embodiment having a blending ratio A: B: C = 70: 30: 5, both the image density transition and the charge amount transition are good. However, in the fifth embodiment where A is excessive and in the third embodiment where B is excessive, the transition of the image density and the charge amount tends to deteriorate and the life tends to be shortened. Particularly, in the case of the fifth embodiment in which A is excessive, the charge amount of the carrier is excessive and charge up occurs.

  Therefore, the value of A / B = (a) / (b) including A: B: C = 70: 30: 5 is in the range of 85/15 to 45/55, more preferably 75/25 to 50 /. If it is within the range of 50, it can be seen that a long-life electrostatic latent image developer capable of stable image formation can be obtained.

As described above in detail, according to the present invention, it is possible to stably form an image by using the mixed carrier comprising the magnetic resin-coated carrier (a) and the magnetic powder carrier (b). A long-lived electrostatic latent image developer is obtained. Furthermore, since the blending ratio can be changed in a wide range, the required charge amount can be set arbitrarily and can be stably applied to the toner. Also, when the developer contains an abrasive toner, The surface can be polished and cleaned with an appropriate force. As a result, it is possible to suppress the occurrence of image flow due to the occurrence of leakage current.
In addition, if the developer of the present invention containing an abrasive toner is used in an image forming apparatus equipped with an α-Si photoconductor that is inherently hard to wear and can be used for a long time, the photoconductor is used for a long time. become able to. As a result, it is possible to provide a long-life printer as well as a long developer life.

It is a schematic diagram for explaining an abrasive toner according to an embodiment. It is a principal part cross-sectional schematic diagram of a photoreceptor. 1 is a schematic diagram for explaining a configuration of an image forming apparatus. It is a figure which shows the measurement result of the charge amount and fluidity | liquidity by the composition ratio of the electrostatic latent image developer of an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Toner 13 Toner mother particle 15 Abrasive fine particle 21 Photoconductor 23 Conductive substrate 25 Light absorption layer 27 Carrier injection blocking layer 29 Carrier excitation / transport layer 31 Surface protective layer 41 Corona charger 43 LED head 45 Developing roller 47 Transfer device 49 Rub roller 51 Cleaning blade 61 Developer 63 Paper

Claims (9)

(A) a magnetic resin-coated carrier having a coating layer made of a high molecular weight polyethylene resin obtained by direct polymerization;
(B) a magnetic powder carrier substantially consisting of magnetic particles;
(C) toner and
An electrostatic latent image developer, comprising:   The blending ratio ((a) / (b)) of the (a) magnetic resin-coated carrier and (b) magnetic powder carrier is set to a value within the range of 85/15 to 45/55 by weight ratio. The electrostatic latent image developer according to claim 1. The volume resistance value of (a) the magnetic resin-coated carrier and (b) the magnetic powder carrier or any one of the carriers is set to a value within the range of 1 × 10 ² to 1 × 10 ¹⁴ Ω · cm. The electrostatic latent image developer according to claim 1 or 2. When (a) the volume resistance value of the magnetic resin-coated carrier is Va and (b) the volume resistance value of the magnetic powder carrier is Vb, the value of (Va−Vb) is 10 to 1 × 10 ³ Ω. 4. The electrostatic latent image developer according to claim 1, wherein the electrostatic latent image developer has a value in a range of cm.   2. The relationship of [rho] b> [rho] a is satisfied, where (b) the bulk density of the magnetic powder carrier is [rho] b and the bulk density of the magnetic resin-coated carrier of (a) is [rho] a. 2. The electrostatic latent image developer according to 2, 3, or 4.   6. The ratio of the added amount of the toner to the mixed carrier (a) and (b) is set to a value in the range of 2 to 40% by weight. Electrostatic latent image developer.   The electrostatic latent image developer according to claim 1, wherein the toner is a color toner.   8. The electrostatic latent image development according to claim 1, wherein the toner is an abrasive toner having abrasive fine particles fixed on the surface of a toner base material. Agent.   9. The electrostatic latent image developer according to claim 8, wherein the abrasive fine particles are conductive titania.

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