JP2009180890A - Electrostatic latent image developing toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an electrostatic latent image developing toner which suppresses dielectric breakdown, inhibits the deposition of a discharge product and toner components on a photoreceptor surface, prevents image deletion, and can stably form a good image. <P>SOLUTION: The electrostatic latent image developing toner includes toner base particles and conductive fine particles as an external additive, wherein the conductive fine particles have an average primary particle diameter of ≤90 nm and form aggregates having an average aggregated particle diameter of 0.5-2.0 μm and a BET specific surface area of ≥15 m<SP>2</SP>/g on surfaces of the toner base particles. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrostatic latent image developing toner suitably used in an electrophotographic image forming apparatus, particularly an image forming apparatus provided with an amorphous silicon photoreceptor.

In an image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine, or a complex machine of these, an image is formed on a transfer medium as follows.
The surface of the photoreceptor (image carrier) is uniformly charged by a charging unit.
An electrostatic latent image is formed by exposing the surface of the photosensitive member by exposure means.
The developing means attaches toner to the electrostatic latent image and develops it as a toner image.
The toner image is transferred from the photosensitive member to a transfer target (paper or the like) by a transfer unit.
The toner image is fixed on the transfer medium by fixing means to form an image.
The toner remaining on the surface of the photoconductor is removed by a cleaning unit to prepare for the next image formation.

As the photoconductor, an Se photoconductor, a CdS photoconductor, an OPC (organic photoconductor), an amorphous silicon photoconductor, and the like are known.
Se photoconductors are traditional photoconductors that have been used since the creation of electrophotographic technology. However, due to environmental considerations, selenium must be recovered at the time of disposal.
OPC is widely used as a photoreceptor at present because of its excellent environmental safety and low cost. However, it has problems of wear resistance and durability.
Amorphous silicon photoconductors are excellent in environmental safety and have a high surface hardness (Vickers hardness of 1500 to 2000). Therefore, a long life can be expected, and the printing durability is several times that of CdS photoconductors.

However, when a conventional toner is used in an image forming apparatus that includes an amorphous silicon photoconductor and a blade-type cleaning unit, an abnormal image is generated due to dielectric breakdown of the photoconductor. This is presumably because the amorphous silicon photoconductor is more susceptible to dielectric breakdown than OPC. The location where dielectric breakdown occurs is the blade ridge line portion (near the tip) where the photoreceptor is cleaned. The same toner (toner mother particles and external additive) that stays in the blade ridge part is excessively charged (overcharge) due to friction with the blade, and discharges at once when exceeding a certain upper limit. At that time, it is considered that the photoconductor is subjected to dielectric breakdown by discharging at one point toward the photoconductor (discharge to a very small area).
When the dielectric breakdown of the photosensitive member occurs, the photosensitive layer of the photosensitive member is broken, which is a problem that cannot be repaired, and a black dot appears remarkably on the image.

As the toner or image forming apparatus for suppressing the dielectric breakdown of the photoreceptor, the following has been proposed.
For example, Patent Document 1 discloses a toner containing free magnetic powder.
Patent Document 2 discloses a toner in which the surface of toner base particles is surface-treated with low-resistance titanium oxide fine particles. According to the toner described in Patent Document 2, the dielectric breakdown of the photoconductor is suppressed by suppressing the charge-up of the toner by adding titanium oxide having an average primary particle diameter of 100 nm or more to the toner base particles. .

By the way, in an image forming apparatus equipped with an amorphous silicon photoconductor, by using a repetitive device, the discharge product generated in the charging process and adhering to the surface of the photoconductor adsorbs moisture under high temperature and high humidity, and is clear. In some cases, an image defect called “image flow” occurs that prevents the formation of an electrostatic latent image.
In addition, the frictional resistance of the surface of the photoconductor increases due to the influence of the discharge products adhering to the surface of the photoconductor, so that the additive contained in the transfer target, the toner base particles, and the components constituting the toner base particles are amorphous silicon photosensitive. It may adhere to the body surface and cause image defects.

Therefore, for the purpose of suppressing the adhesion of discharge products and toner components to the surface of the amorphous silicon photoreceptor, particles (abrasive particles) functioning as an abrasive are added to the toner base particles, and the polishing is performed. There has been proposed a method in which the surface of an amorphous silicon photoreceptor is polished with an agent particle every time an image is formed, and is always maintained in an initial use state.
For example, Patent Document 3 discloses a toner in which titanium oxide that forms an aggregate having a primary particle size of 0.1 to 0.3 μm and a particle size of 0.5 μm or more on the surface of the toner base particles is added to the toner base particles. Is disclosed.

The toner base particles used in the toner described in Patent Document 3 are easily transferred to the transfer target, but the aggregate of titanium oxide is difficult to transfer. For this reason, a large amount of aggregate remains on the surface of the amorphous silicon photosensitive member after the transfer. The surface of the amorphous silicon photoconductor can be polished by the aggregate remaining on the surface of the amorphous silicon photoconductor to remove discharge products and the like. In addition, since aggregates gather at the blade ridge line portion, discharge products and the like can be smoothly removed by the cleaning blade.
JP 2003-149857 A Japanese Patent Laid-Open No. 2005-17524 JP 2002-372800 A

However, in the toner described in Patent Document 1, it is difficult to adjust the amount of free magnetic powder added. In addition, when free magnetic powder is used, it may be difficult to develop color toner.
Further, in the toner described in Patent Document 2, since a relatively large titanium oxide having an average primary particle diameter of 100 nm or more is used, it is necessary to add a large amount of titanium oxide, which causes a decrease in toner fluidity. was there. Further, when developed on color toner, the color tone of the image after fixing may be affected.
In addition, the toner described in Patent Document 3 uses a relatively large titanium oxide having a primary particle size of 0.1 to 0.3 μm, and thus the polishing ability is not always sufficient.

  The present invention has been made in view of the above circumstances, suppresses dielectric breakdown, suppresses adhesion of discharge products and toner components to the surface of the photoreceptor, prevents image flow, and stably forms a good image. An object is to realize a toner for developing an electrostatic latent image.

The toner for developing an electrostatic latent image of the present invention is a toner for developing an electrostatic latent image containing toner base particles and conductive fine particles as an external additive, and the conductive fine particles have an average primary particle diameter of 90 nm or less. And an aggregate having an average aggregated particle size of 0.5 to 2.0 μm and a BET specific surface area of 15 m ² / g or more is formed on the surface of the toner base particles.
Here, the conductive fine particles are preferably titanium oxide.
The toner for developing an electrostatic latent image of the present invention is suitably used for an image forming apparatus provided with an amorphous silicon photoconductor and a cleaning blade for cleaning the amorphous silicon photoconductor.

According to the toner for developing an electrostatic latent image of the present invention, dielectric breakdown is suppressed, adhesion of discharge products and toner components to the surface of the photoreceptor is suppressed, image flow is prevented, and a stable and good image is obtained. Can be formed.
The electrostatic latent image developing toner of the present invention can also be used as a color toner.

Hereinafter, the present invention will be described in detail.
The electrostatic latent image developing toner of the present invention (hereinafter sometimes simply referred to as “toner”) includes toner base particles and conductive fine particles as an external additive added to the toner base particles.

[External additive]
<Agglomerates of conductive fine particles>
The conductive fine particles used in the present invention form an aggregate. The average primary particle diameter of the conductive fine particles forming the aggregate is 90 nm or less, and preferably 10 to 50 nm. Moreover, the average aggregate particle diameter of the aggregate is 0.5 to 2.0 μm, and preferably 0.8 to 1.5 μm. When the average primary particle diameter of the conductive fine particles is 90 nm or less and the average aggregate particle diameter of the aggregates is 0.5 μm or more, excellent polishing properties can be obtained, and adhesion of discharge products to the photoreceptor can be suppressed. Therefore, image flow can be prevented. Further, the aggregates are easily detached from the toner base particles, and the conductive fine particles are likely to remain on the photoreceptor. Therefore, for example, since the ratio of the conductive fine particles collected by the blade type cleaning means increases, overcharging of the toner at the blade ridge line portion is suppressed, and insulation breakdown can be prevented.
On the other hand, if the average aggregate particle size of the aggregate is 2.0 μm or less, it is possible to suppress the aggregate from being excessively detached from the toner base particles, so that the concentration of the conductive fine particles in the developing device is moderate. Thus, overcharging of the toner can be prevented and the image density can be improved.

The average primary particle size of the conductive fine particles is obtained by taking an enlarged photograph with an electron microscope or an optical microscope, and calculating the equivalent circle diameter from the projected area of the particles with an image analyzer to obtain the primary particle size. The particle size.
On the other hand, the average aggregate particle diameter of the aggregate is measured by taking an enlarged photograph with an electron microscope or an optical microscope and using an image analyzer. For the measurement, the maximum diameter of 50 or more aggregates is measured, and the average value is taken as the average aggregate particle diameter. In addition, a single aggregate may be used for the measurement, or it may be used in a state of being added to the toner base particles. In either case, the same measurement result can be obtained.
The primary particle diameter of the conductive fine particles may be calculated based on an enlarged photograph of the aggregate.

Moreover, aggregates of the conductive fine particles is a BET specific surface area of ^{15 m} 2 / g or more, preferably ^{15~40m 2 / g, 25~35m 2 /} g is more preferable. The BET specific surface area represents the unevenness of the aggregate surface, and the unevenness of the aggregate surface tends to become finer as the value of the BET specific surface area increases. Aggregates with moderately fine irregularities on the surface are easy to be detached from the toner base particles, and the abrasiveness is improved. When the BET specific surface area is 15 m ² / g or more, the aggregates are easily detached from the toner base particles, and the conductive fine particles are likely to remain on the photoreceptor. Therefore, for example, since the ratio of the conductive fine particles collected by the blade type cleaning means increases, overcharging of the toner at the blade ridge line portion is suppressed, and insulation breakdown can be prevented. In addition, sufficient polishing properties can be obtained, and adhesion of discharge products to the photoreceptor can be suppressed, so that image flow can be prevented.

The BET specific surface area of the aggregate can be adjusted by adjusting the average primary particle diameter of the conductive fine particles and the average aggregate particle diameter of the aggregate. For example, the BET specific surface area tends to increase as the average primary particle diameter of the conductive fine particles or the average aggregate particle diameter of the aggregates decreases, and the BET ratio increases as the average primary particle diameter or the average aggregate particle diameter of the aggregates increases. The surface area tends to be small.
Here, the BET specific surface area is an area calculated according to the nitrogen adsorption specific surface area method (BET method), and is determined from the amount of liquid nitrogen adsorbed on the surface of the aggregate.

By the way, the larger the BET specific surface area, that is, the finer the surface unevenness, the easier the aggregates are detached from the toner base particles, and the abrasiveness tends to be improved. However, when the BET specific surface area becomes larger than necessary, it means that the average aggregate particle diameter of the aggregate becomes smaller, and the surface irregularities tend to be too fine. On the other hand, the larger the particle diameter of the aggregate, the better the detachability of the aggregate. Therefore, when the BET specific surface area becomes larger than necessary, the detachability of the aggregate may be lowered. Therefore, in order to achieve both the detachability of the aggregate and the abrasiveness, it is preferable to adjust the particle diameter of the aggregate and the BET specific surface area to be appropriate values.
If the BET specific surface area is within the above range, the surface irregularities become moderately fine aggregates, so that the balance between the detachability of the aggregates and the abrasiveness becomes better.

  As the material of the conductive fine particles forming such an aggregate, inorganic particles represented by titanium oxide, silica, aluminum oxide, magnetite and the like can be used. Of these, titanium oxide is preferred because it is particularly excellent in abrasiveness. Titanium oxide is also suitable when the toner of the present invention is used as a color toner.

In the present invention, “conductive” means that the resistance value is 1.0 × 10 ⁵ Ω · cm or less.
In order to impart conductivity to the inorganic particles described above and to make conductive fine particles having a resistance value within the above range, for example, the inorganic particles may be coated with tin-antimony oxide or indium-tin oxide.

Here, an example of a method for producing an aggregate of conductive fine particles will be described taking titanium oxide as an example of inorganic particles.
First, a mixture of titanium tetrachloride and oxygen gas obtained by the chlorine method is introduced into a gas phase oxidation reactor and reacted at a temperature of 1000 ° C. in the gas phase to obtain a titanium oxide bulk. The obtained titanium oxide bulk is pulverized with a hammer mill or the like, then washed, dried at a temperature of 110 ° C., and then pulverized with a jet mill or the like to obtain titanium oxide fine particles.
In addition, the average primary particle diameter of the conductive titanium oxide fine particles (conductive fine particles) can be adjusted by changing the bulk pulverization conditions of titanium oxide by a hammer mill or the like.

Next, titanium oxide fine particles are dispersed in water so that the concentration is about 50 g / L, and sodium pyrophosphate is further added, and wet pulverization is performed with a sand mill or the like to prepare a water-soluble slurry.
Next, after heating the water-soluble slurry to 80 ° C., a mixed solution in which appropriate amounts of tin chloride (SnCl ₄ .5H ₂ O) and antimony chloride (SbCl ₃ ) were dissolved in 2N hydrochloric acid solution (300 mL) and 10 mass % Sodium hydroxide solution is added over 60 minutes while maintaining the pH at 6-9 to form a coating layer made of tin oxide and antimony oxide on the surface of the titanium oxide fine particles to form conductive titanium oxide fine particles. . In addition, since the obtained conductive titanium oxide fine particles are in a state where primary particles are aggregated, they are pulverized to a desired aggregated particle size by a jet mill to obtain aggregates.

The resistance value of the conductive fine particles can be adjusted by controlling the thickness of the coating layer, and the resistance value tends to decrease as the thickness of the coating layer is increased. Moreover, when a coating layer consists of a tin oxide and an antimony oxide, resistance value can be adjusted also by changing the ratio of these oxides. For example, when the proportion of antimony oxide is increased, the resistance value tends to decrease. In the present invention, the resistance value of the conductive fine particles is preferably 1.0 × 10 ³ Ω · cm or less. When the resistance value of the conductive fine particles is within the above range, the toner can be prevented from being highly charged.
The resistance value of the conductive fine particles can be obtained by, for example, using “R8340A HIGH REISTANCE METER” manufactured by ADVANTEST, applying a load of 1 kg, and applying a voltage of DC 10 V and measuring.

  The conductive fine particles may be subjected to a surface treatment with a coupling agent or the like for the purpose of improving hydrophobicity.

  Since the average primary particle diameter of the above-mentioned conductive fine particles is as small as 90 nm or less, the aggregate has a larger BET specific surface area than a normal aggregate having the same average aggregate particle diameter. Therefore, it is extremely excellent in abrasiveness and can suppress the adhesion of discharge products that easily adhere to the photoconductor, so that it prevents image flow and also prevents the adhesion of toner components, etc. Can be formed.

  In the present invention, in addition to the above-described conductive fine particles, other external additives may be used in combination as the external additive. Examples of other external additives include silica, alumina, and metal soaps of various fatty acids (such as zinc stearate).

[Toner mother particles]
As the toner base particles constituting the toner of the present invention, known toner base particles can be used. Specific examples include those obtained by dispersing a colorant and other additives as required in the binder resin.

<Binder resin>
Examples of the binder resin include polyester resins, styrene resins, acrylic resins, styrene-acrylic copolymer resins, olefin resins (polyethylene, polypropylene, etc.), vinyl chloride resins, polyamide resins, and polyurethane resins. Thermoplastic resins such as resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, styrene-butadiene resins; epoxy resins (bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, poly Alkylene ether type epoxy resin, cycloaliphatic type epoxy resin, etc.), and thermosetting resins such as cyanate resin.

<Colorant>
As the colorant, black pigments such as carbon black, acetylene black, lamp black, aniline black; yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Yellow pigments such as Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, etc .; Orange pigments such as Rembrilliant Orange GK; Bengala, Cadmium Red, Lead Dan, Mercury Cadmium Sulfide, Permanent Red 4R, Risor Red, Pyrazolone Red, Red pigments such as hatching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B; purple pigments such as manganese purple, fast violet B, methyl violet lake; bitumen, cobalt Blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, indanthrene blue BC and other blue pigments; chrome green, chromium oxide, pigment green B, malachite green lake , Green pigments such as final yellow green G; white pigments such as zinc white, titanium oxide, antimony white, zinc sulfide; barite powder, barium carbonate, clay, silica White carbon, talc, extender pigments such as alumina white and the like.
2-15 mass parts is preferable with respect to 100 mass parts of binder resin, and, as for the quantity of a coloring agent, 3-10 mass parts is more preferable.

When used as a toner (magnetic toner) used in the magnetic one-component development method, a magnetic component is contained instead of the colorant described above or together with the colorant. As a magnetic component, a metal exhibiting ferromagnetism, such as iron, cobalt, nickel, or an alloy thereof, a compound containing these elements, or a ferromagnetic element that does not contain a ferromagnetic element, but exhibits ferromagnetism when subjected to an appropriate heat treatment. Examples thereof include magnetic powders such as alloys and chromium dioxide, among which magnetic powders such as ferrite and magnetite are preferable.
The amount of magnetic powder added is preferably 50 to 100 parts by mass with respect to 100 parts by mass of the binder resin.

<Other additives>
Examples of additives other than the colorant include a release agent and a charge control agent.

(Release agent)
Examples of the release agent include waxes and low molecular weight olefin resins. Examples of waxes include polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylene bis fatty acid amide compounds, natural waxes, and the like.
1-15 mass parts is preferable with respect to 100 mass parts of binder resin, and, as for the quantity of a mold release agent, 2-10 mass parts is more preferable.

The charge control agent is for controlling the triboelectric charging characteristics of the toner, and a charge control agent for positive charge control and / or negative charge control is used according to the charge polarity of the toner.
Examples of positive charge control agents include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5- Triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4- Tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline, quinoxaline, etc. Azine Fast Red FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azine Fast Red FC Direct dyes composed of azine compounds such as Nylon Brown GR, azine dark green BH / C, azine deep black EW, azine deep black 3RL; nigrosine compounds such as nigrosine, nigrosine salt, nigrosine derivatives; nigrosine BK, nigrosine NB, nigrosine Z, etc. An acid dye comprising a nigrosine compound of the following: a metal salt of naphthenic acid or higher fatty acid; an alkoxylated amine; an alkylamide; a quaternary ammonium salt such as benzylmethylhexyldecylammonium or decyltrimethylammonium chlorid; Examples include oligomers; resins or oligomers having a carboxylate; resins or oligomers having a carboxyl group.

Examples of the negative charge control agent include organometallic complexes or chelate compounds, such as aluminum acetylacetonate, iron (II) acetylacetonate, chromium 3,5-ditertiary butylsalicylate, and the like, and acetylacetone metal complexes. A salicylic acid metal complex or salt is preferred.
The amount of the charge control agent is preferably 0.1 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the binder resin.

<Production method>
The toner base particles can be produced by a known melt-kneading / pulverization method, polymerization method, melt granulation method, spray granulation method, spinning method or the like. For example, if it is a melt-kneading and pulverizing method, it is manufactured by the following procedure. Necessary raw materials such as a binder resin and a colorant are mixed with a mixer such as a Henschel mixer, melt-kneaded with a twin screw extruder or the like, and then pulverized with a pulverizer such as a turbo mill. Thereafter, the toner base particles are classified by a classifier such as an airflow classifier.

[toner]
The toner of the present invention can be obtained by adding an external additive to the toner base particles described above. The amount of the external additive added is preferably 0.1 to 8.0 parts by mass, more preferably 0.5 to 5.0 parts by mass with respect to 100 parts by mass of the toner base particles.

The toner of the present invention may be used as it is as a one-component developer, or may be used as a two-component developer in combination with a carrier.
Examples of the carrier include magnetic particles or resin particles in which a magnetic material is dispersed in a binder resin.
The proportion of the toner of the present invention in the two-component developer is preferably 2 to 20% by mass and more preferably 3 to 15% by mass in the two-component developer (100% by mass).

[Image forming apparatus]
The toner of the present invention can be suitably used in a general electrophotographic image forming apparatus. Due to its characteristics, the amorphous silicon photoconductor (hereinafter referred to as “a-Si photoconductor”) and the a-Si photoconductor are used. It is particularly suitable for use in an image forming apparatus having a cleaning means for cleaning a body.

<Amorphous silicon photoconductor>
Examples of the a-Si photosensitive member include those in which an amorphous silicon photosensitive layer (a-Si photosensitive layer) is formed on the surface of a conductive substrate formed in a predetermined shape such as a drum shape. In particular, it is preferable to have a thin film type a-Si photosensitive layer having a thickness of 30 μm or less in view of excellent productivity and formation of an image with high resolution. The a-Si photosensitive layer may have a carrier blocking layer, a surface protective layer, or the like in addition to a single layer or two or more layers that actually function as a photosensitive layer. However, when it has a plurality of layers, it is preferable that the total layer thickness is 30 μm or less.

  Moreover, you may form as a-Si photosensitive layer the thing containing H, a halogen element, and the elements containing elements, such as C, N, and O, on the surface of an electroconductive base | substrate. Specific examples include a-Si, a-SiC, a-SiO, and a-SiON.

When a magnetic toner is used as the toner, a carrier blocking layer is preferably interposed between the a-Si photosensitive layer and the conductive substrate. The carrier blocking layer prevents carrier injection from the conductive substrate to the a-Si photosensitive layer when the surface of the a-Si photosensitive layer is in contact with the magnetic toner while a bias voltage is applied during development. Thus, the electrostatic contrast between the exposed portion and the non-exposed portion is increased, the image density is improved, and the background fogging is reduced.
Examples of such a carrier blocking layer include inorganic insulating layers formed of a-SiC, a-SiO, a-SiN, a-SiON, a-SiCON, polyethylene terephthalate, parylene (registered trademark), polytetrafluoride. It is preferable to use an organic insulating layer formed of ethylene, polyimide, polyfluorinated ethylene propylene, polyurethane, epoxy resin, polyester, polycarbonate, cellulose acetate resin, or the like.
The thickness of the carrier blocking layer is preferably from 0.01 to 5 μm, more preferably from 0.1 to 3 μm.

The surface protective layer is formed on the surface of the a-Si photosensitive layer, and the surface of the a-Si photosensitive layer is oxidized and easily adsorbs discharge products, water molecules, and the like during discharge by a charging means or the like. Formation of an oxide film can be prevented. Further, by covering the a-Si photosensitive layer with the surface protective layer, it is possible to improve the withstand voltage or improve the wear resistance when repeatedly used.
As such a surface protective layer, an organic or inorganic insulating material is preferable, and among them, an inorganic insulating layer formed of a-SiC, a-SiO, a-SiN, a-SiON, a-SiCO or the like is preferable. These can be formed by the same thin film forming method as that for the a-Si photosensitive layer, and it is particularly preferable that they be formed by a-SiC.

<Cleaning means>
As a cleaning means for removing the toner remaining on the surface of the a-Si photosensitive layer of the a-Si photosensitive member, an elastic blade (cleaning blade) brought into pressure contact with the surface of the a-Si photosensitive layer can be used. . As the cleaning blade, a known elastic blade made of rubber or soft resin can be used. Specific examples include a cleaning blade made of silicone rubber, fluoro rubber, urethane rubber, urethane resin, or the like.
The cleaning blade removes the toner satisfactorily and suppresses the formation of pressure marks on the surface of the a-Si photosensitive layer at a linear pressure of 10 to 50 g / cm. It is preferable to press the surface.

  By using the toner of the present invention, such an image forming apparatus can always maintain the surface of the a-Si photosensitive member in a fresh state, and can obtain a good image over a long period of time.

  By the way, when the surface of the a-Si photosensitive member is cleaned by a cleaning means such as a cleaning blade, the toner blocked by the cleaning blade is caused by friction with the cleaning blade at the blade ridge portion (near the tip) of the cleaning blade. It is easy to accumulate electric charge by overcharging. Therefore, the charge accumulated in the toner in the vicinity of the cleaning blade is suddenly discharged and becomes a leak current, and discharges at one point toward the surface of the a-Si photosensitive member (discharges to a very small area), thereby insulating the photosensitive member. There was a phenomenon of destruction. When the dielectric breakdown of the photosensitive member occurs, there is a problem that the photosensitive layer of the photosensitive member is broken due to an irreparable defect, and a leak black spot is easily generated on the image.

However, according to the toner of the present invention, an aggregate having an average primary particle size as small as 90 nm or less, an average aggregate particle size of 0.5 to 2.0 μm, and a BET specific surface area of 15 m ² / g or more on the toner base particles. Since the conductive fine particles forming the toner are added, the aggregates are easily detached from the toner base particles, and only the toner base particles are easily transferred by the transfer means, and the conductive fine particles remain on the a-Si photosensitive member. It becomes easy. Therefore, since the ratio of the conductive fine particles collected by the cleaning blade increases, the abundance ratio of the conductive fine particles in the cleaning blade increases. As a result, the toner can be prevented from being overcharged at the blade ridge line portion, so that the dielectric breakdown of the photoconductor can be prevented even when an a-Si photoconductor is used as the image carrier. Therefore, a stable image free from image defects (leak black spots) can be formed.

  Further, since the specific conductive fine particles used in the toner of the present invention have a uniform uniform particle size as small as 90 nm or less, the BET specific surface area of the aggregate formed on the toner base particles has the same average aggregate particle size. It is larger than the ordinary agglomerates. Therefore, it is extremely excellent in abrasiveness and can suppress the adhesion of discharge products that easily adhere to the photoconductor, so that it prevents image flow and also prevents the adhesion of toner components, etc. Can be formed.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to a following example.
[Preparation of conductive fine particles and aggregates]
<Titanium oxide a>
First, a mixture of titanium tetrachloride obtained by the chlorine method and oxygen gas was introduced into a gas phase oxidation reactor and reacted at a temperature of 1000 ° C. in the gas phase to obtain a titanium oxide bulk. The obtained titanium oxide bulk was pulverized with a hammer mill, washed, dried at a temperature of 110 ° C., and then pulverized with a jet mill to obtain titanium oxide fine particles.
Next, titanium oxide fine particles were dispersed in water so that the concentration was about 50 g / L, sodium pyrophosphate was further added, and wet grinding was performed with a sand mill to prepare a water-soluble slurry.
Next, after heating the water-soluble slurry to 80 ° C., a mixed solution in which appropriate amounts of tin chloride (SnCl ₄ .5H ₂ O) and antimony chloride (SbCl ₃ ) were dissolved in 2N hydrochloric acid solution (300 mL) and 10 mass % Sodium hydroxide solution is added over 60 minutes while maintaining the pH at 6-9 to form a coating layer composed of tin oxide and antimony oxide on the anatase-type titanium oxide surface. Titanium a) was obtained. Since the obtained titanium oxide a was in a state where primary particles were aggregated, it was crushed by a jet mill and then treated with a titanate coupling agent to obtain an aggregate of titanium oxide a.

The average primary particle diameter and resistance value of the obtained titanium oxide a, and the average aggregate particle diameter and BET specific surface area of the aggregate were measured. The results are shown in Table 1.
The average primary particle size is obtained by taking an enlarged photograph of the aggregate of titanium oxide a with an electron microscope, and calculating the equivalent circle diameter from the projected area of the primary particles by an image analyzer to obtain the primary particle size. Was the average primary particle size.
The resistance value was measured using “R8340A HIGH REISTANCE METER” manufactured by ADVANTEST, applying a load of 1 kg, and applying a voltage of DC 10V.
The average aggregated particle diameter of the aggregates was measured with an image analyzer for 50 aggregates taken with an electron microscope, and the average value was defined as the average aggregated particle diameter.
The BET specific surface area of the aggregate was calculated from the amount of liquid nitrogen adsorbed on the surface of the aggregate based on the nitrogen adsorption specific surface area method (BET method).

<Titanium oxide b to k>
Based on the preparation method of titanium oxide a, the conditions were changed to prepare titanium oxides b to k having physical properties shown in Table 1. Each physical property was adjusted by changing the following conditions.
Average primary particle size: Titanium oxide bulk grinding condition by hammer mill.
Resistance value: Amount of tin chloride and antimony chloride added.
Average agglomerated particle diameter and BET specific surface area: Crushing conditions by jet mill.

[Example 1]
<Manufacture of toner and developer>
100 parts by mass of a polyester resin (acid value: 5.6 mg KOH / g, melting point: 120 ° C.) as a binder resin, 4 parts by mass of a copper phthalocyanine pigment (CI Pigment Blue 15: 3) as a colorant, and as a release agent 5 parts by weight of wax (Carnauba wax WAX) and 1 part by weight of a charge control agent (manufactured by Clariant, “P51”) were mixed in a Henschel mixer (manufactured by Mitsui Miike Kogyo Co., Ltd.), and an extruder (manufactured by Ikekai, PCM-30). ) And pulverization with a turbo mill (manufactured by Turbo Kogyo Co., Ltd.), followed by classification with an elbow jet classifier (manufactured by Nippon Steel Mining Co., Ltd.) to obtain toner base particles having an average particle size of 7.8 μm.
To 100 parts by mass of toner base particles, 1.5 parts by mass of an aggregate of conductive fine particles (titanium oxide a) and 1.0 part by mass of silica fine particles (“RA200H” manufactured by Nippon Aerosil Co., Ltd.) are added as external additives. And a Henschel mixer (Mitsui Miike Kogyo Co., Ltd.) to obtain a toner.
The toner and the carrier (“Ferrite Carrier”, manufactured by Powdertech Co., Ltd., average particle size: 45 μm) are mixed with a rocking mixer for 30 minutes so that the ratio of the toner is 12.0% by mass. Obtained.

<Evaluation>
A two-component developer is installed in a color copier (KM-C3232 (32 sheets machine) manufactured by Kyocera Mita Co., Ltd.) equipped with an amorphous silicon photoreceptor, and is in a high temperature and low humidity environment (temperature: 32.5 ° C., relative humidity 20%) ), 10,000 intermittent printings were performed. Incidentally, toner charge-up tends to occur in a low humidity environment. Further, in a high temperature environment and intermittent printing, the toner is rapidly deteriorated and the fluidity of the toner is deteriorated, so that the toner tends to accumulate in the cleaning means. As described above, in a high-temperature and low-humidity environment and intermittent printing durability, dielectric breakdown of the photoconductor is likely to occur, and a toner component or the like is likely to adhere to the photoconductor to cause image defects.

(1) Evaluation of image density A two-component developer was mounted on a color copying machine, the color copying machine was turned on, and an image immediately after stabilization was output, which was used as an initial image.
Next, a Macbeth reflection densitometer (manufactured by Gretag Macbeth Co., Ltd., “RD-”) was used for an image obtained when 10,000 sheets of intermittent printing were performed in a high temperature and low humidity environment (temperature: 32.5 ° C., relative humidity 20%). 914 ") to measure the image density (ID). The judgment criteria are as follows. The results are shown in Table 2.
Excellent: ID is 1.40 or more.
Good: ID is 1.30 or more and less than 1.40.
Possible: ID is 1.20 or more and less than 1.30.
Impossible: ID is less than 1.20.

(2) Evaluation of black spot generation In the same manner as the evaluation of the image density in evaluation (1), the presence or absence of black spot generation was visually determined for an image when 10,000 sheets were intermittently printed. The judgment criteria are as follows. The results are shown in Table 2.
○: After printing 10,000 sheets, no black spots are seen in the image.
Δ: 1 to 5 black spots are seen in the image after 10,000 sheets have been printed.
X: After printing 10,000 sheets, 6 or more black spots are seen in the image.

(3) Evaluation of adhesion of photoconductor In the same manner as the evaluation of image density in Evaluation (1), the presence or absence of toner adhesion was visually determined for 10,000 photoconductors after intermittent printing durability. The judgment criteria are as follows. The results are shown in Table 2.
○: After 10,000 sheets were printed, no deposits were seen on the photoreceptor, and the obtained image was free of defects.
Δ: 1 to 5 deposits can be seen on the photoreceptor after printing 10,000 sheets.
X: After printing 10,000 sheets, 6 or more deposits are seen on the photoreceptor.

(4) Evaluation of image flow In the same manner as the evaluation of the image density in Evaluation (1), 10,000 sheets of intermittent printing were performed. Thereafter, the environment was changed to a high-temperature and high-humidity environment (temperature: 32.5 ° C., relative humidity 80%), and the image was output after being left in that state for 24 hours, and the presence or absence of image flow was judged visually. The judgment criteria are as follows. The results are shown in Table 2. Incidentally, the discharge product easily adheres to the photoconductor as the number of printed sheets increases, and when the discharge product adheres to the photoconductor, image flow is likely to occur in a high-temperature and high-humidity environment.
○: There is no image flow and the image content can be recognized without any problem.
Δ: Some image flow occurs, but the image content can be recognized, and the image flow disappears after several printings.
×: Image flow occurs and the image content cannot be recognized.

[Examples 2 to 7]
A toner and a developer were produced and evaluated in the same manner as in Example 1 except that each titanium oxide shown in Table 2 was used as the conductive fine particles. The results are shown in Table 2.

[Comparative Examples 1-4]
A toner and a developer were produced and evaluated in the same manner as in Example 1 except that each titanium oxide shown in Table 2 was used as the conductive fine particles. The results are shown in Table 2.

As is clear from Table 2, the toner obtained in the examples had good image density before and after printing. In particular, in Examples 1 to 6, since no black spot was generated, it became clear that the dielectric breakdown of the photoreceptor could be suppressed. Further, since the occurrence of image flow could be reduced, it became clear that the adhesion of the discharge product to the photoreceptor could be suppressed by the excellent abrasiveness. Further, since adhesion of toner components and the like to the photosensitive member could be suppressed, a good image could be stably formed over a long period of time.
The toner obtained in Example 7 had a BET specific surface area of 45 m ² / g, and the surface irregularities were finer than in the other examples, and therefore the agglomerate detachability slightly decreased. Therefore, the evaluation result of black spot generation was inferior to other examples. In addition, since the abrasiveness was slightly lowered, the evaluation results of the photoreceptor adhesion and image flow were inferior to those of the other examples.

On the other hand, the toner obtained in Comparative Example 1 had an average primary particle size of conductive fine particles as large as 150 nm, so that the abrasiveness was inferior to that of Examples, and the suppression of discharge product adhesion was not sufficient, and the image flow was poor. It was easy to occur. In addition, toner components and the like are easily attached to the photoreceptor, and streaks are generated in the obtained image. Furthermore, since the BET specific surface area of the aggregate was as small as 10 m ² / g, the aggregate was not easily detached from the toner base particles, and the proportion of the conductive fine particles recovered by the cleaning means was small compared to the examples. Inhibition of toner overcharging at the blade ridge was insufficient, causing dielectric breakdown in the photoreceptor and black spots.

In the toner obtained in Comparative Example 2, the average aggregate particle diameter of the aggregate was as small as 0.3 μm, so that the aggregate was difficult to be detached from the toner base particles. As a result, the toner was insulated with the photoconductor as in Comparative Example 1. Destruction occurred and black spots occurred. Further, since the abrasiveness was inferior to that of the example, an image flow occurred, and the toner component or the like was likely to adhere to the photoreceptor.
In the toner obtained in Comparative Example 3, the average aggregated particle size of the aggregates was as large as 2.5 μm. Therefore, the aggregates were excessively detached from the toner base particles, and the concentration of the conductive fine particles in the developing device was high. The toner was excessively charged and the toner was overcharged. As a result, the image density after printing for 10,000 sheets decreased.

Since the toner obtained in Comparative Example 4 had a small BET specific surface area of 13 m ² / g, the abradability was inferior to that in Examples, and the suppression of the adhesion of discharge products was not sufficient, and the image flow was poor. It was easy to occur. In addition, toner components and the like are easily attached to the photoreceptor, and streaks are generated in the obtained image. However, since the average aggregate particle diameter of the aggregates was an appropriate size of 2.0 μm, the aggregates were appropriately detached from the toner base particles, and generation of black spots could be suppressed.

Claims (3)

An electrostatic latent image developing toner comprising toner base particles and conductive fine particles as an external additive,
The conductive fine particles have an average primary particle diameter of 90 nm or less, an average aggregated particle diameter of 0.5 to 2.0 μm, and a BET specific surface area of 15 m ² / g or more on the surface of the toner base particles. A toner for developing an electrostatic latent image, characterized by forming a collection.   The electrostatic latent image developing toner according to claim 1, wherein the conductive fine particles are titanium oxide.   The electrostatic latent image developing toner according to claim 1, wherein the toner is used for an image forming apparatus including an amorphous silicon photoreceptor and a cleaning blade for cleaning the amorphous silicon photoreceptor.