JP2009237207A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents dielectric breakdown. <P>SOLUTION: In the image forming apparatus 10 which includes an amorphous silicon photoreceptor 122 and a cleaning means 123 for cleaning the amorphous silicon photoreceptor 122 and forms images using toner containing conductive titanium oxide as an external additive, the toner has at least one peak within the range of a particle diameter of 0.6 to 2.0 μm in measurement by a flow type particle image analyzer, and the ratio (number% after printing/number% before printing) of the number% within the range of the particle diameter of 0.6 to 2.0 μm in measurement by the flow type particle image analyzer before printing and after 5,000 sheets printing is 0.4 to 0.7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

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), so a long life can be expected, and printing performance is several times that of CdS photoconductors.

However, when a conventional toner is used in an image forming apparatus having an amorphous silicon photoconductor and a blade-type cleaning unit, an abnormal image may be 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 photoreceptor is dielectrically broken by local discharge toward the photoreceptor (discharge to an extremely small area).
When the dielectric breakdown of the photosensitive member occurs, the photosensitive layer of the photosensitive member, which cannot be repaired, is broken, and black spots (black spots) appear 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. .
JP 2003-149857 A Japanese Patent Laid-Open No. 2005-17524

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, as described in Patent Document 2, the method of adding low-resistance titanium oxide fine particles has not always been sufficient to suppress dielectric breakdown.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that suppresses dielectric breakdown.

An image forming apparatus according to the present invention includes an amorphous silicon photoconductor and a cleaning unit that cleans the amorphous silicon photoconductor, and forms an image using toner containing conductive titanium oxide as an external additive. The toner has at least one peak in a particle diameter range of 0.6 to 2.0 μm as measured by a flow particle image analyzer, and the flow particle image before printing and after printing 5000 sheets. The ratio (number% after printing / number% before printing) of the number% in the range of the particle diameter of 0.6 to 2.0 μm measured by the analyzer is 0.4 to 0.7. Features.
The conductive titanium oxide is preferably surface-treated with silicone oil.

According to the image forming apparatus of the present invention, dielectric breakdown can be suppressed.
The image forming apparatus of the present invention is also suitable for full color printing.

Hereinafter, the present invention will be described in detail.
[Image forming apparatus]
The image forming apparatus of the present invention includes an amorphous silicon photoconductor (hereinafter referred to as “a-Si photoconductor”) and a cleaning unit for cleaning the a-Si photoconductor, and uses the toner described above.

Examples of the image forming apparatus include a laser printer, an electrostatic copying machine, a plain paper facsimile machine, and a complex machine thereof.
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. The image forming apparatus 10 of this example is an indirect copying tandem type color image forming apparatus, and an intermediate transfer belt 130 that runs while being stretched around rollers 131 to 135 is disposed in a housing 110. Four image forming units 120 are arranged on 130 in the order of toner image transfer (in order from the upstream side). In addition, a laser scanner unit (LSU) 140 and a paper feed cassette 150 are provided in the housing 110.

The image forming unit 120 includes a developing device 121, an a-Si photosensitive member 122, and a cleaning unit 123.
The developing device 121 is for developing the electrostatic latent image on the a-Si photosensitive member 122 to form a toner image. The developing device 121 includes a supply roller 121a, a developing roller 121b on which a toner thin layer is formed, a stirring mixer 121c that stirs and charges toner together with a carrier, and a developer supplied from the stirring mixer 121c while stirring the developer. A paddle mixer 121d for supplying to the supply roller 121a is provided.

As the a-Si photosensitive member 122, a known photosensitive member in which an amorphous silicon photosensitive layer is formed on the surface of a drum-like conductive substrate can be used.
Examples of the material for the photosensitive layer include amorphous silicon-based materials having photoconductivity such as a-Si, a-SiC, a-SiO, and a-SiON.
The photosensitive layer can be formed by a vapor phase growth method such as a glow discharge decomposition method, a sputtering method, an ECR method, or an evaporation method.

The cleaning means 123 includes a roll-shaped rubbing member 123a and a cleaning blade (not shown).
The rubbing member 123 a rotates by rubbing against the a-Si photosensitive member 122, thereby polishing the surface of the a-Si photosensitive member 122 by the rubbing contact and removing water adhering to the surface. Examples of the material of the rubbing member 123a include urethane sponge and ethylene-propylene rubber.
The cleaning blade removes toner (developer) remaining on the surface of the a-Si photosensitive member 122. Examples of the cleaning blade include a rubber blade made of polyurethane or the like.
The toner removed by the cleaning unit 123 is collected, returned to the developing device 121 as needed, and reused.

Here, the image forming method will be described with reference to FIG.
First, the surface of the a-Si photosensitive member 122 is charged by the charging unit 124 (charging process).
Next, the surface of the a-Si photosensitive member 122 is exposed by exposure means (not shown) to form an electrostatic latent image (exposure process).
Next, the developing means (developing device 121) causes the toner to be carried on the surface of the supply roller 121a to form a magnetic brush, and the toner is transferred from the magnetic brush to the surface of the developing roller 121b so as to adhere to the surface of the developing roller 121b. A thin toner layer is formed. Next, the toner is ejected from the toner thin layer of the developing roller 121b, and the toner is attached to the electrostatic latent image of the a-Si photosensitive member 122 to develop it as a toner image (developing step).
Next, after the toner image is transferred to the intermediate transfer belt 130 in order from the upstream a-Si photosensitive member 122 in the image forming unit 120 by the transfer unit, the toner image transferred to the intermediate transfer belt 130 is transferred to the transfer roller 136. The image is transferred to a transfer medium (paper or the like) supplied from the paper feed cassette 150 (transfer process).
Next, the toner image transferred to the transfer medium is fixed by fixing means 160 having a pair of fixing rollers 161 to form an image (fixing step), and is discharged above the housing 110.
Next, the toner remaining on the surface of the a-Si photosensitive member 122 is removed by the cleaning unit 123 to prepare for the next image formation.
The above steps are repeated.

As a result of intensive studies, the inventors of the present invention positively caused the conductive titanium oxide to fly (develop) from the developing device to the photosensitive member, thereby increasing the proportion of the conductive titanium oxide on the photosensitive member. As a result, it has been found that since the proportion of the conductive titanium oxide recovered by the blade type cleaning means is increased, the toner is prevented from being overcharged at the blade ridge line portion and the dielectric breakdown is prevented.
And, compared with the proportion of conductive titanium oxide in the toner before printing, the proportion of conductive titanium oxide in the toner after printing 5000 sheets is reduced within a specific range, thereby preventing dielectric breakdown. It has been found that a sufficient amount of conductive titanium oxide can be a measure of flying from the developing device. Further, the ratio of the number% in the range of the particle diameter of 0.6 to 2.0 μm obtained by measuring the toner before and after printing 5000 sheets with a flow type particle image analyzer is before and after printing 5000 sheets. As a result, the present invention has been completed.
In the present invention, “number%” refers to the number ratio of particles having a particle diameter in the range of 0.6 to 2.0 μm with respect to the whole toner.

  That is, the image forming apparatus of the present invention is a ratio (number printing) in which the particle diameter is within a range of 0.6 to 2.0 μm as measured by a flow type particle image analyzer before printing and after printing 5000 sheets. The subsequent number% / number% before printing) is 0.4 to 0.7. If the ratio by number% is 0.4 or more, the amount of conductive titanium oxide flying from the developing unit to the photoconductor is sufficient, and the ratio of conductive titanium oxide in the toner in the developing unit is also sufficiently secured. Therefore, it is possible to suppress overcharging of the toner and prevent a decrease in image density. On the other hand, if the ratio by number% is 0.7 or less, the amount of conductive titanium oxide flying from the developing device to the photoreceptor is sufficient, so that dielectric breakdown can be suppressed and black spots can be prevented from being generated.

The flow type particle image analyzer can measure up to about 0.6 μm particle size and can measure by particle size, so that the conductive titanium oxide has a relatively small particle size relative to the whole toner. Can be measured more accurately. Therefore, this is a suitable method for prescribing the decreasing rate of conductive titanium oxide before and after printing.
As a flow type particle image analyzer, “FPIA-2100” manufactured by Sysmex Corporation can be used.
Below, an example of a measuring method is shown.

First, 0.05 g of toner is put in a 50 mL beaker, and a dispersion (Wako Pure Chemical Industries, “Contaminone-N”) is added until the internal volume becomes 0.5 g, and dispersed for 60 seconds with an ultrasonic cleaner. Let Then, a nonionic surfactant (manufactured by Sysmex Corporation, “Particle Sheath”) is added until the internal volume becomes 50 g, and further dispersed for 60 seconds with an ultrasonic cleaner. The obtained test solution is set in a flow type particle image analyzer (manufactured by Sysmex Corporation, “FPIA-2100”), and the particle size is measured under the conditions of analysis standard: number standard, measurement range: 0.6 μm to 400 μm. Then, the value of the number% in the range of the particle diameter of 0.6 to 2.0 μm is read.
Next, the toner after printing 5000 sheets is collected from the inside of the developing device, the test solution is prepared in the same manner, the particle size is measured with a flow type particle image analyzer, and the particle size is 0.6 to Read the value of number% in the range of 2.0 μm.
The ratio of the number% is calculated from the values of the number% before printing and the number% after printing.
In addition, when mixing a carrier with toner and using it as a two-component developer, the developer is sieved using a mesh or the like, the toner is separated from the developer, a test solution is prepared, and a flow particle image analyzer Measure the particle size at.

  In the present invention, in order to make the ratio of the number% in the particle diameter range of 0.6 to 2.0 μm within the above-described range, for example, each component contained in the toner used in the image forming apparatus, particularly the external additive What is necessary is just to adjust the kind, addition amount, etc. of the conductive titanium oxide which is an agent.

[toner]
The toner used in the image forming apparatus of the present invention includes toner base particles and conductive titanium oxide as an example of an external additive added to the toner base particles.

<External additive>
(Conductive titanium oxide)
The conductive titanium oxide used in the present invention forms an aggregate. The average primary particle diameter of the conductive titanium oxide forming the aggregate is preferably 90 nm or less, and more preferably 10 to 50 nm. The average aggregate particle diameter of the aggregate is preferably 0.6 to 2.0 μm, and more preferably 0.8 to 1.5 μm.
If the average primary particle diameter of the conductive titanium oxide is 90 nm or less, or the average aggregate particle diameter of the aggregate is 0.5 μm or more, the aggregate is easily detached from the toner base particles, and on the photoreceptor. Conductive titanium oxide tends to remain. Therefore, for example, the proportion of titanium oxide recovered by the blade type cleaning means increases, so that 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 diameter of the aggregate is 2.0 μm or less, the aggregate can be prevented from excessively desorbing from the toner base particles, so that the concentration of conductive titanium oxide in the developing device is moderate. Therefore, the toner can be prevented from being overcharged and the image density can be improved.

The average primary particle diameter of the conductive titanium oxide is taken as an enlarged photograph with an electron microscope or an optical microscope, and the equivalent particle diameter is calculated from the projected area of the particles by an image analyzer to obtain the primary particle diameter. The primary 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.
In addition, you may calculate the average primary particle diameter of electroconductive titanium oxide based on the enlarged photograph of an aggregate.

In the present invention, “conductive” means that the resistance value is 1.0 × 10 ⁵ Ω · cm or less.
Conductive titanium oxide is obtained by imparting conductivity to titanium oxide. In order to obtain conductive titanium oxide having a resistance value within the above range, for example, titanium oxide may be coated with tin-antimony oxide or indium-tin oxide. Here, a specific method for imparting conductivity to titanium oxide will be described.

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 electroconductive titanium oxide can be adjusted by changing the bulk grinding | pulverization conditions of the titanium oxide by a hammer mill etc.

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 titanium oxide 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 titanium oxide is preferably 1.0 × 10 ³ Ω · cm or less. When the resistance value of the conductive titanium oxide is within the above range, the toner can be prevented from being highly charged.
The resistance value of the conductive titanium oxide can be obtained, for example, by 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 titanium oxide is preferably subjected to a surface treatment. By performing the surface treatment, the adhesion between the toner and titanium oxide can be reduced, and the detachability of the titanium oxide from the toner surface can be adjusted. Thereby, the ratio of the number% can be easily adjusted within the above range. For the surface treatment, it is preferable to use silicone oil, titanate coupling agent or the like. In particular, if the surface of the conductive titanium oxide is treated with a silicone oil that can further reduce the adhesive force, the range of the primary particle diameter and the aggregate particle diameter of the aggregate that can be used is widened.
As a surface treatment method, a known method can be used. Specifically, in the case of a titanate coupling agent, isopropyl triisostearoyl titanate is applied to titanium oxide particles at a temperature of 130 ° C. with a Henschel mixer. The surface treatment can be performed by adding and mixing to 2.6 wt%, causing a coupling reaction, drying and crushing.

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

<Toner base particles>
As the toner base particles constituting the toner, 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.

(Coloring agent)
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.

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. Examples of the low molecular weight olefin resin include polypropylene, polyethylene, propylene-ethylene copolymer and the like having a number average molecular weight in the range of 1000 to 10000, preferably 2000 to 6000, and low molecular weight polypropylene is preferable.
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 of toner base particles)
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 manufacturing method>
The toner used in the present invention can be obtained by adding conductive titanium oxide as an external additive to the toner base particles described above and mixing with a mixer such as a Henschel mixer. The amount of the conductive titanium oxide added is preferably 0.5 to 4.0 parts by mass, more preferably 1.0 to 3.0 parts by mass with respect to 100 parts by mass of the toner base particles. When other external additives other than conductive titanium oxide are used in combination, the amount of other external additives added is preferably 0.1 to 8.0 parts by mass with respect to 100 parts by mass of toner base particles. More preferably, it is 5 to 5.0 parts by mass.

The toner used in 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).

The toner thus obtained has at least one peak in the particle diameter range of 0.6 to 2.0 μm as measured by a flow particle image analyzer.
The toner used in the present invention usually has an average particle size of 5.0 to 10.0 μm. On the other hand, as for the particle diameter of the conductive titanium oxide which is an external additive, it is preferable that the average primary particle diameter is 10 to 50 nm and the average aggregate particle diameter of the aggregate is 0.6 to 2.0 μm as described above.
Therefore, a peak derived from conductive titanium oxide is mainly observed within a particle diameter range of 0.6 to 2.0 μm as measured by a flow type particle image analyzer. Therefore, by measuring the particle diameter with a flow type particle image analyzer, the degree of reduction of conductive titanium oxide in the toner before and after printing 5000 sheets becomes clear.

  As described above, according to the image forming apparatus of the present invention, the particle diameter is in the range of 0.6 to 2.0 μm as measured by the flow type particle image analyzer before printing and after printing 5000 sheets. The ratio (number% after printing / number% before printing) is 0.4 to 0.7, so that the electrically conductive titanium oxide in the toner actively flies from the developing device to the photoreceptor. . As a result, the proportion of conductive titanium oxide on the photoconductor increases, and the proportion of conductive titanium oxide recovered by the cleaning means also increases, so that overcharging of the toner at the blade ridge is suppressed and dielectric breakdown occurs. Can be prevented.

  Furthermore, according to the present invention, since the dielectric breakdown is suppressed by positively flying the conductive titanium oxide in the toner from the developing device to the photoconductor, the present invention is not limited to monochrome printing, and can be applied to full color printing.

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 titanium oxide]
<Conductive 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 surface of titanium oxide, and conductive titanium oxide fine particles (titanium oxide a ) Since the obtained titanium oxide a was in a state where primary particles were aggregated, it was crushed by a jet mill and then subjected to titanate coupling treatment to obtain an aggregate of titanium oxide a.

The average primary particle diameter and resistance value of the obtained conductive titanium oxide a, and the average aggregate particle diameter of the aggregate were measured. The results are shown in Table 1.
The average primary particle size was obtained by taking an enlarged photograph with an electron microscope, calculating the equivalent circle diameter from the projected area of the particles with an image analysis device to obtain the primary particle size, and setting the average value as 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 aggregate particle diameter of the aggregates was obtained by taking an enlarged photograph of the 50 particles with an electron microscope in a state where the particles were dispersed, and measuring the average aggregate particle diameter with an image analyzer.

<Conductive titanium oxide b to e>
Based on the preparation method of titanium oxide a, the conditions were changed to prepare titanium oxides b to e having physical properties shown in Table 1. Each physical property was adjusted by changing the following conditions. Further, the conductive titanium oxide b was subjected to a silicone oil treatment as a surface treatment.
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 size: 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 conductive titanium oxide a as an external additive, and 1.0 of silica fine particles (“RA200H” manufactured by Nippon Aerosil Co., Ltd., average particle size: 0.017 μm) Part by mass was added and mixed with a Henschel mixer (manufactured by 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.

<Measurement / Evaluation>
A two-component developer is installed in a color copying machine (KM-C3232 (32 sheets machine) manufactured by Kyocera Mita Co., Ltd.) equipped with an amorphous silicon photoconductor, and is in a high temperature and low humidity environment (temperature: 32.5 ° C., relative humidity 20%). ) Below, intermittent printing of 5000 sheets and 10,000 sheets was performed at a printing rate of 5% (A4 size). Incidentally, toner charge-up tends to occur in a low humidity environment. Further, in high temperature environments and intermittent printing, the toner deteriorates quickly and the fluidity of the toner deteriorates, so that the toner tends to accumulate in the cleaning means. As described above, the dielectric breakdown of the photoconductor tends to occur in a high-temperature and low-humidity environment and intermittent printing.

(1) Measurement of ratio of number% First, a part of the two-component developer was collected, and the two-component developer was sieved using a mesh (aperture 23 μm) to separate the toner from the two-component developer. Add 0.05 g of this toner into a 50 mL beaker, add a dispersion (“Contaminone-N” manufactured by Wako Pure Chemical Industries, Ltd.) until the internal volume becomes 0.5 g, and disperse with an ultrasonic cleaner for 60 seconds. It was. Next, a nonionic surfactant (manufactured by Sysmex Corporation, “Particle Sheath”) was added until the internal volume reached 50 g, and the mixture was further dispersed for 60 seconds with an ultrasonic cleaner. The obtained test solution is set in a flow type particle image analyzer (manufactured by Sysmex Corporation, “FPIA-2100”), and the particle size is measured under the conditions of analysis standard: number standard, measurement range: 0.6 μm to 400 μm. The value of number% in the range of particle diameter of 0.6 to 2.0 μm was read.
Next, the two-component developer is mounted on a color copying machine, and after intermittent printing of 5000 sheets in a high-temperature and low-humidity environment (temperature: 32.5 ° C., relative humidity 20%), the two-component developer in the developing device A part was taken from within the developer. Further, after intermittent printing of 50 million sheets (after a total of 10,000 sheets of intermittent printing), a part of the two-component developer in the developing device was collected from the developing device. For the two-component developer collected after intermittent printing of 5000 sheets and 10,000 sheets, a test solution is prepared in the same manner as described above, and the particle size is measured with a flow type particle image analyzer. The value of number% in the range of 0.6 to 2.0 μm was read.
The ratio of the number% (number% after printing 5000 sheets or 10,000 sheets / number% before printing) was calculated from the values of the number% before printing and the number% after printing of each number of sheets. The results are shown in Table 2.

(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, in the high temperature and low humidity environment (temperature: 32.5 ° C., relative humidity 20%), an image obtained by intermittently printing 5000 sheets and 10,000 sheets at a printing rate of 5% (A4 size), and an initial image, Image density (ID) was measured using a Macbeth reflection densitometer ("RD-914", manufactured by Gretag Macbeth). 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 generation of black spots In the same manner as the evaluation of image density in evaluation (1), the presence or absence of black spots was visually determined for the images when 5000 sheets and 10,000 sheets were intermittently printed. The judgment criteria are as follows. The results are shown in Table 2.
○: Black spots are not seen in the image in both 5000 sheets and 10,000 sheets of intermittent printing.
X: A black spot is seen in the image after intermittent printing of 5000 sheets.

[Example 2]
Except that the conductive titanium oxide shown in Table 2 was used, a toner and a two-component developer were produced in the same manner as in Example 1, and the obtained two-component developer was mounted on a color copying machine. Each measurement and evaluation was performed. The results are shown in Table 2.

[Comparative Examples 1-3]
Except that the conductive titanium oxide shown in Table 2 was used, a toner and a two-component developer were produced in the same manner as in Example 1, and the obtained two-component developer was mounted on a color copying machine. Each measurement and evaluation was performed. The results are shown in Table 2.

  As is apparent from Table 2, in the example using the toner in which the ratio of the number% within the range of the particle diameter of 0.6 to 2.0 μm before and after printing 5000 sheets is 0.4 to 0.7. The ratio of the conductive titanium oxide in the developing device was appropriate, and the charging of the toner was stable. Therefore, the image density was good before and after printing 5000 sheets and 10,000 sheets. Further, since the aggregate (conductive titanium oxide) was appropriately detached from the toner base particles and flew from the developing unit to the photosensitive member, dielectric breakdown could be suppressed and generation of black spots could be prevented.

On the other hand, Comparative Example 1 using a toner in which the ratio of the number% in the range of 0.6 to 2.0 μm before and after printing 5000 sheets is 0.37 is an aggregate (conductive titanium oxide). Was unnecessarily detached from the toner base particles and flew from the developing unit to the photosensitive member, so that the ratio of the conductive titanium oxide in the developing unit was reduced too much and the concentration could not be secured. As a result, the toner was overcharged and the image density was lowered.
In Comparative Example 2 using a toner in which the ratio of the number% in the range of 0.6 to 2.0 μm before and after printing 5000 sheets is 0.78, the aggregate (conductive titanium oxide) is a toner. Since it was difficult to detach from the mother particles, the amount of conductive titanium oxide flying from the developing device to the photoreceptor was insufficient. As a result, it was difficult to suppress dielectric breakdown, and black spots were easily generated.
In Comparative Example 3, since the average aggregate particle diameter of the aggregate was as small as 0.2 μm, no peak was observed within the range of the particle diameter of 0.6 to 2.0 μm. Further, since the aggregate (conductive titanium oxide) was not easily detached from the toner base particles, the amount of conductive titanium oxide flying from the developing device to the photoconductor was insufficient. As a result, it was difficult to suppress dielectric breakdown, and black spots were easily generated.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention.

Explanation of symbols

10: Image forming apparatus, 121: Developer, 122: Amorphous silicon photoreceptor, 123: Cleaning means

Claims (2)

In an image forming apparatus that includes an amorphous silicon photoconductor and a cleaning unit that cleans the amorphous silicon photoconductor, and forms an image using a toner containing conductive titanium oxide as an external additive.
The toner has at least one peak in a particle diameter range of 0.6 to 2.0 μm as measured by a flow particle image analyzer.
The ratio of the number% in the range of particle diameter of 0.6 to 2.0 μm measured by a flow type particle image analyzer before printing and after printing 5000 sheets (number% after printing / number% before printing) ) Is 0.4 to 0.7.   The image forming apparatus according to claim 1, wherein the conductive titanium oxide is surface-treated with silicone oil.

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