JP2010122442A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus using a non-magnetic one-component toner capable of maintaining high image quality even when environmental conditions are changed is high.
In an electrophotographic image forming apparatus, a developing unit includes a developer carrier provided with a gap from an image carrier, and the developer carrier is covered with an external additive. When developing an electrostatic latent image with the one-component developer, a DC developing bias potential is applied to the toner base particles, and a single-component developer composed of toner base particles having a volume average particle size of 8 to 12 μm is carried. Volume average particle diameter D (μm), toner base particle surface coverage S (%) by external additive, gap G (μm) between developer carrier and image carrier, and development bias potential V _B ( V) and the electrostatic latent image potential V _L (V) on the image carrier are as follows:

An image forming apparatus characterized by satisfying
[Selection] Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus using a one-component developer.

As a developer used in an electrophotographic image forming apparatus, a one-component developer composed only of toner is known. One-component developers are easier to handle than two-component developers.
As a one-component developer, a nonmagnetic toner is known. A one-component developer made of a non-magnetic toner is said to be excellent in terms of high image quality and color compatibility even in color electrophotographic image forming apparatuses that have become popular in recent years.

  By the way, in Patent Document 1, in a developing device that uses a non-magnetic one-component developer and develops a developer carrier and an electrostatic latent image carrier in a non-contact manner, a gap (gap) between the two carriers is provided. It is described that there is a problem that the development efficiency is reduced by the fluctuation of the image quality, and it is not always possible to obtain high-quality development.

Patent Document 1 discloses, as means for solving this problem, an electrostatic latent image carrier on which an electrostatic latent image is formed, and is arranged with a gap between the electrostatic latent image carrier and a non-magnetic one component. A developer is carried and conveyed toward the electrostatic latent image carrier, and a developer carrier for developing the electrostatic latent image on the electrostatic latent image carrier and an alternating voltage applied to the developer carrier. In the image forming apparatus provided with a developing device having a power supply means for applying, the magnetic one-component developer has a charge density ρ (C / m ³ ) of 1 ≦ | ρ | ≦ 3 on the developer carrier. The power supply means has a first peak value V _max (V) for forming an electric field for urging the developer in a direction from the developer carrying member toward the electrostatic latent image carrying member; a second peak value V _min (V) appear alternately to form an electric field for urging in a direction toward said developer carrying member from the electrostatic latent image bearing member The turn voltage is applied; also, the power supply means includes a time T ₁ for forming an electric field for urging the developer from said developer carrying member in a direction toward the electrostatic latent image bearing member, the electrostatic developer A time T ₂ for forming an electric field energizing in the direction from the electrostatic latent image carrier toward the developer carrier satisfies the relationship of T ₁ <T ₂ ; and the power supply means further includes the first peak value V _max , the charge density ρ, the developer layer thickness t (μm) on the developer carrier, and the electrostatic latent image potential V _L (V) on the electrostatic latent image carrier,
400 ≦ | (t ₀ / t) × [− (V _max −V _L ) / ρ] | ≦ 500
t ₀ = 40 μm
And a gap SD (μm) between the developer carrier and the electrostatic latent image carrier is
200 ≦ D ≦ 400
An image forming apparatus characterized by the above is proposed.

However, even in the image forming apparatus of Patent Document 1, it is impossible to always maintain a good image quality with high image quality and little fogging.
This is because there is a minute gap between the developer carrier and the image carrier, so that if the particle size of the developer is too small, the charge amount of the developer becomes large and it is difficult to move to the image carrier (that is, Therefore, it is necessary to make adjustments such as increasing the developing electric field and reducing the coverage of the toner base particle surface with the external additive. On the other hand, if the toner particle size is too large, the charge amount of the developer becomes low and the toner tends to shift to the image carrier (i.e., the developer shift amount is large), and fogging easily occurs. This is because it is necessary to increase the coverage of the toner base particle surface with the agent.

  Further, the image forming apparatus disclosed in Patent Document 1 needs to apply an alternating voltage, so that there is a problem that the power supply means becomes complicated and further miniaturization is difficult. This problem becomes prominent in a tandem color image forming apparatus in which multicolor image forming units are arranged side by side.

JP-A-5-241440

The present invention has been made in view of the above problems.
In an image forming apparatus including a non-contact type developing device using a non-magnetic one-component developer, the present inventors have added a toner particle size, an electric field strength, a gap between the developer carrier and the image carrier, and an external addition of the toner surface. By defining the relationship of the coverage with the agent and controlling it with a direct current electric field, it was found that it was possible to maintain good image quality with high image quality and low fogging, and in addition, it was possible to achieve further downsizing of the device. .

That is, the present invention provides an image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for irradiating the image carrier with light to form an electrostatic latent image, and the electrostatic latent image. An electrophotographic image forming apparatus comprising: a developing unit that visualizes with a developer to form a toner image; and a transfer unit that deposits the toner image on a transfer material, wherein the developing unit includes the image carrier. And a developer carrying member that carries a one-component developer, and a developing bias potential applied to the developer carrying member is a DC potential V _B (V). In the image forming apparatus,
The one-component developer is composed of toner base particles having a volume average particle diameter D (μm; 8 ≦ D ≦ 12) coated with an external additive, and the surface coverage of the toner base particles by the external additive S ( %) Is the following relation:
(Where V _L is the electrostatic latent image potential (V) on the image carrier)
An image forming apparatus characterized by satisfying the above is provided.

According to the image forming apparatus of the present invention, it is possible to maintain high image quality, low fogging, and good image quality even when environmental conditions change.
In the image forming apparatus of the present invention, since the developing electric field is DC-controlled, the developing electric field generating power supply means is simplified and a low-cost mechanism can be achieved.

The image forming apparatus of the present invention comprises an image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for irradiating the image carrier with light to form an electrostatic latent image, and the electrostatic latent unit. An electrophotographic image forming apparatus comprising: a developing unit that visualizes an image with a developer to form a toner image; and a transfer unit that adheres the toner image onto a transfer material, the developing unit including the image A developer carrying body provided with a carrier G and a gap G (μm) and carrying a one-component developer, and a developing bias potential applied to the developer carrying body is a DC potential V _B (V) In an image forming apparatus,
The one-component developer is composed of toner base particles having a volume average particle diameter D (μm; 8 ≦ D ≦ 12) coated with an external additive, and the surface coverage of the toner base particles by the external additive S ( %) Is the following relation:
(Where V _L is the electrostatic latent image potential (V) on the image carrier)
It is characterized by satisfying.

In the present invention, the developing means includes at least a developer carrying member (for example, a developing roller or a developing sleeve) that is provided with a gap from an image carrier (for example, a photosensitive drum) and carries a one-component developer. Prepare.
The developer carrying member conveys the carried one-component developer to a position facing the image carrying member, and the electrostatic developer on the image carrying member is electrostatically driven by a DC developing vial potential applied thereto (that is, in a non-contact manner). Supply to the electrostatic latent image.

In the present invention, the coverage S of the toner base particle surface by the external additive means a value calculated by the following formula:
here,
D: average volume particle size (μm) of toner base particles;
d: average volume particle diameter (μm) of fine particles used as an external additive;
ρt: True specific gravity (g / cc) of toner base particles;
ρi: True specific gravity (g / cc) of fine particles used as an external additive;
C: The weight ratio (%) of fine particles / toner base particles used as an external additive.

The coverage S defined by the above formula can take a value exceeding 100%.
Moreover, when using 2 or more types of microparticles | fine-particles as an external additive, let a coverage be the sum total of the coverage calculated about each microparticles | fine-particles. That is, for example, when three types of fine particles A, B, and C are used as external additives, the coverage S is the coverage S _A for the fine particles A, the coverage SB for the fine particles _B, and the coating for the fine particles A. The sum S _A + S _B + S _C with the rate S _C is obtained.

  In the present invention, the average volume particle size of the toner base particles and the fine particles for the external additive is determined according to JIS Z8703 under standard environmental conditions by Multisizer III manufactured by Beckman Coulter, temperature is standard condition class 3 (20 ± 5 ° C.), humidity Is a value obtained under the condition of standard humidity condition class 2 (65 ± 5%).

The coverage S is, for example, 140 to 205%, preferably 150 to 195%, and more preferably 160 to 180%.
The gap G between the developer carrier and the image carrier is, for example, 150 to 300 μm, preferably 160 to 250 μm, and more preferably 165 to 220 μm.
The development bias potential V _B is, for example, −750 to −300 V, preferably −700 to −350 V, and more preferably −650 to −400 V.
The electrostatic latent image potential V _L is, for example, −200 to −50 V, preferably −180 to −70 V, and more preferably −150 to −80 V.
The potential difference | V _B −V _L | is, for example, 200 to 700 V, preferably 300 to 650 V, and more preferably 350 to 600 V.

In one embodiment, the external additives are silica fine particles and titanium oxide fine particles, and in the relational expression (I), S = (coverage ratio S ₁ of the toner base particles by silica fine particles) + (by titanium oxide fine particles) The toner base particle surface coverage S ₂ ).
According to this embodiment, it is possible to achieve fluidity control due to external addition of silica fine particles and resistance control due to external addition of titanium oxide fine particles.

In a specific embodiment, the silica fine particles and the titanium oxide fine particles have the following relational formula:
5% ≦ S ₂ / S ₁ × 100 ≦ 20% (III)
Is externally added to the surface of the toner base particles.
According to this specific embodiment, it becomes possible to keep the charging property of the developer better and constant, and as a result, a satisfactory image can be obtained even under a high temperature and high humidity environment condition, and the image solid portion has a rough surface. A non-image forming apparatus can be realized.

In another specific embodiment, the titanium oxide fine particles comprise rutile type titanium oxide fine particles and anatase type titanium oxide fine particles.
According to this specific embodiment, acicular or spindle-shaped rutile titanium fine particles are fixed so as to partially pierce the toner base particles (core particles) to realize resistance control, and anatase-type oxidation excellent in fluidity Resistance control and fluidity can be secured by using titanium.

In yet another specific embodiment, the one-component developer externally adds rutile type titanium oxide fine particles and silica fine particles to toner base particles, and then anatase type titanium oxide fine particles and silica fine particles or only anatase type titanium oxide fine particles. It is manufactured by external addition.
According to this specific embodiment, in the initial stage of use, resistance control of toner base particles is realized by anatase-type titanium oxide fine particles, and fluidity is realized by anatase-type titanium oxide fine particles, or by anatase-type titanium oxide fine particles and silica fine particles. For long-term use, resistance control is realized by rutile titanium fine particles, and fluidity is realized by silica fine particles. Therefore, resistance control and fluidity can be ensured over a long period of time, and good image quality can be maintained.

In another embodiment, an image forming apparatus including a plurality of developing units is provided. In the apparatus, the transfer unit collectively attaches a plurality of toner images developed by the plurality of developing units onto a transfer material. .
According to this embodiment, the tandem color image forming apparatus can be reduced in size and cost.

From another viewpoint, the present invention also provides an image carrier, charging means for charging the surface of the image carrier, exposure means for irradiating the image carrier with light to form an electrostatic latent image, and the static An electrophotographic image forming apparatus comprising: a developing unit that visualizes an electrostatic latent image with a one-component developer to form a toner image; and a transfer unit that adheres the toner image onto a transfer material. In the image forming apparatus, the developer is composed of toner base particles having a volume average particle diameter D (μm; 8 ≦ D ≦ 12) coated with an external additive at a coverage ratio S (%).
The developing means includes a developer carrier provided with a gap G (μm) from the image carrier, and a DC developing bias potential V _B (V) applied to the developer carrier and a gap G Is the following relation:
(Where V _L is the electrostatic latent image potential (V) on the image carrier)
An image forming apparatus characterized by satisfying the above is provided.

  The image forming apparatus of the present invention can be various printers, copiers, facsimiles, multifunction peripherals, etc. using an electrophotographic process regardless of monochrome or color.

The present invention will be described below with reference to the drawings.
<Image forming apparatus>
FIG. 1 is a schematic cross-sectional view of one embodiment of an image forming apparatus of the present invention.
The image carrier 1 has a surface of a photoconductive material provided on the outer periphery of a conductive substrate (for example, a photosensitive drum), and the conductive substrate is grounded and rotated in the direction of the arrow.

  Around the image carrier 1, from the upstream side to the downstream side in the rotational direction, the charger 2 as a charging means for charging the surface of the image carrier, and the image carrier is irradiated with light according to the image information to correspond to the image information An exposure device 3 as an exposure means for forming an electrostatic latent image, a developing cartridge 4 as a developing means for visualizing the electrostatic latent image with a developer to form a toner image, and a transfer means for adhering the toner image onto a transfer material A transfer roller 6 is disposed.

  As it rotates, the surface of the image carrier 1 is uniformly charged by the charger 2 and exposed by laser light or LED light emitted from the exposure device 3. By exposure, an electrostatic latent image corresponding to the image signal is formed on the surface of the image carrier 1.

Next, the electrostatic latent image on the surface of the image carrier 1 is visualized (developed) as a toner image by the developing cartridge 4.
The developing cartridge 4 includes a developing roller 5 (developer carrier) that faces the image carrier at a predetermined interval. Here, in the developing cartridge 4, the gap G (developing gap) between the developing roller 5 and the image carrier 1 is set to a predetermined interval, for example, 150 to 300 μm, by bringing the frame of the image forming apparatus into contact with the frame of the developing cartridge 4. Retained.

  The developing roller 5 carries and conveys a one-component developer on its peripheral surface and is driven to rotate in the direction of the arrow. The one-component developer (toner) carried on the developing roller is regulated to a thin layer by a layer regulating member (for example, a blade plate) to be a thin layer and charged, and is opposed to the image carrier 1 (development). Area). In the developing area, a DC developing bias potential is applied to the developing roller 5 by a DC power source (not shown), and the one-component developer is transferred from the developing roller 5 to the image by an electric field generated between the developing roller and the image carrier. The electrostatic latent image on the surface of the carrier 1 is supplied in a non-contact manner, and the electrostatic latent image is developed to be visualized as a toner image.

This toner image is transferred to a recording member (transfer material) 10 by a transfer roller 6, then conveyed to a fixing device 7, heated and melted, and fixed on the recording member.
On the other hand, the toner remaining on the surface of the image carrier 1 after the transfer is removed and collected by the cleaner device 9. Thereafter, the charge remaining on the surface of the image carrier 1 is uniformly discharged by the charge removing lamp 8, and a series of image forming processes is completed.

<Single component developer>
The one-component developer used in the image forming apparatus of the present invention is composed of toner base particles (colored resin particles) having an average volume particle diameter of 8 to 12 μm and coated with an external additive.

(Toner base particles)
The toner base particles include at least a binder resin material and a colorant.
The binder resin material used for the toner base particles is not particularly limited, and a known binder resin material for black toner or color toner can be used. Examples of the binder resin material include styrene resins such as polystyrene or polystyrene-acrylic acid ester copolymer, vinyl chloride resin, phenol resin, epoxy resin, polyester resin, polyether polyol resin, polyurethane resin, or polyvinyl butyral resin. One or two or more selected from the group may be used. Further, the binder resin material may be one in which crystalline surname waxes or incompatible substances are finely dispersed in advance from the synthesis stage. Among the binder resin materials described above, the polyester resin or the polyether polyol resin is preferably used for the binder resin material because it is excellent in thermal properties such as resin elasticity.

  The glass transition temperature (Tg) of the polyester resin or polyether polyol resin is suitably in the range of 50 to 90 ° C. from the viewpoints of toner thermal fixability and storage stability. The number average molecular weight (Mn) of the polyester resin or polyether polyol resin is suitably in the range of 3,000 to 100,000. When Mn is less than 3,000, particle formation may be difficult, and when it is 100,000 or more, it becomes high viscosity during phase inversion emulsification and affects particle size and distribution control. May give.

The colorant used for the toner base particles is not particularly limited as long as it is various dyes and pigments commonly used in the field, and examples thereof include various organic or inorganic dyes as shown below. And pigments can be used.
Examples of the black colorant include carbon black, copper oxide, manganese dioxide, aniline / black, activated carbon, nonmagnetic ferrite, magnetic ferrite, and magnetite.

  Yellow colorants include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, nablue yellow, naphthol yellow S, Hansa yellow G, Hansa yellow ... 10G, benzidine yellow G, benzidine Examples of the compound include yellow GR, quinoline yellow lake, permanent yellow NCG, and tartrazine lake.

  Examples of the orange colorant include compounds such as red chrome yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, indanthrene brilliant orange RK, benzidine orange G or indanthrene brilliant orange GK.

  Examples of red colorants include bengara, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, risor red, virazolone red, watch red, calcium salt, lake red C, lake red D, brilliant carmine 6B, Examples include eosin lake, rhodamine lake B, alizarin lake or brilliant carmine 3B.

Examples of purple colorants include compounds such as manganese purple, fast violet B, and methyl violet lake.
Examples of the blue colorant include compounds such as bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, and induslen blue BC.

Examples of the green colorant include compounds such as chromium green, chromium oxide, pigment green B, micalite green lake, and final yellow green G.
Examples of the white colorant include compounds such as zinc white, titanium oxide, antimony white, or zinc sulfide.

  In addition to the above materials, the toner base particles can also contain components such as magnetic powders such as magnetite, hematite or various ferrites, an anti-offset agent, or a charge control agent as required.

  The anti-offset agent used for the purpose of improving the fixing property of the toner is not particularly limited as long as it can be used as a toner material, and the following can be used. For example, petroleum wax such as paraffin wax, oxidized paraffin wax or microcrystalline wax, mineral wax such as montan wax, animal and plant wax such as beeswax or carnauba wax, or polyolefin wax (such as polyethylene or polypropylene), Examples thereof include synthetic waxes such as oxidized polyolefin wax or Fischer-Tropsch wax. These may be used alone or in combination of two or more.

  As the charge control agent, various substances from low molecular weight compounds to high molecular weight compounds can be used. For example, quaternary ammonium salt compounds, nigrosine compounds, organometallic complexes, chelate compounds, and monomers having amino groups are homopolymerized or copolymerized. Examples thereof include polymerized polymer compounds.

As a method for producing toner base particles, a so-called pulverization method in which a binder resin material, a colorant, and, if necessary, other additives are melt-kneaded and then pulverized and classified is generally used.
In addition, a toner manufacturing method called a wet method has been proposed, and this wet method is a method in which a monomer (monomer) of a binder resin material in which a colorant and necessary additives are dispersed is present in the presence of a dispersion stabilizer. In addition, there are a suspension polymerization method, an emulsion polymerization method, a phase inversion emulsification method, and the like for polymerization in an aqueous medium.

(External additive)
The external additive is not particularly limited as long as it is used in the field, but inorganic fine particles are preferably used.
Examples of the inorganic fine particles include silica (silicon oxide), titanium oxide, silicon carbide, aluminum oxide, barium titanate, and the like.

One or more kinds of fine particles may be used as the external additive. Among these, a combination of silica fine particles capable of imparting good fluidity and titanium oxide capable of satisfactorily controlling resistance is preferable.
As the titanium oxide fine particles, it is preferable to use rutile type titanium oxide fine particles and anatase type titanium oxide fine particles in combination. Since the rutile titanium fine particles are needle-shaped or spindle-shaped, the resistance of the toner base particles can be efficiently controlled by fixing them so as to partially pierce the toner base particles. On the other hand, since anatase type titanium oxide is excellent in fluidity, the fluidity can be secured while controlling the resistance of the toner base particles. More preferably, the rutile titanium fine particles are mixed and added together with the silica fine particles.

The volume average particle diameter of the external additive is, for example, 10 to 100 nm, preferably 15 to 90 nm, and more preferably 20 to 80 nm.
The volume average particle diameter of the silica fine particles is, for example, 10 to 60 nm, preferably 15 to 55 nm, and more preferably 20 to 50 nm.
The volume average particle diameter of the titanium oxide fine particles is, for example, 20 to 100 nm, preferably 30 to 90 nm, and more preferably 35 to 60 nm.

  External additives include silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oils, silane coupling agents, silane coupling agents having functional groups, and other organosilicon compounds for hydrophobicity and chargeability adjustment It may be treated with one kind or two or more kinds of treating agents.

The external additive is added to the toner base particles at a weight ratio of inorganic fine particles (external additive) / toner base particles satisfying the relational expression (I).
When silica fine particles and titanium oxide fine particles are used as the external additive, the relation S _{1 of the} surface of the toner base particles with the silica fine particles and the coverage S _{2 of the} surface of the toner base particles with the titanium oxide fine particles are related. : It is preferable to externally add to the toner base particles so as to satisfy 5% ≦ S ₂ / S ₁ × 100 ≦ 20%. The chargeability and fluidity of the developer can be kept better and constant.

The coating of the toner base particles with the external additive can be performed by a method known in the art, for example, stirring and mixing in an airflow mixer (for example, a Henschel mixer).
For example, when silica fine particles and rutile type and anatase type titanium oxide fine particles are used as external additives, the toner base particles are first externally coated with rutile type titanium oxide fine particles and silica fine particles, and then the anatase type oxidation particles. Only titanium fine particles and silica fine particles or anatase-type titanium oxide fine particles can be externally coated. In the one-component developer thus produced, appropriate resistance control and fluidity are ensured over a longer period.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to these.

[Example 1]
Manufacture of one-component developer In the manufacture of toner base particles, the following materials were used in the weight ratios shown.
-Binder resin material: Polyester resin (acid value: 21 mgKOH / g) 87.5 parts by weight
Aromatic alcohol components: PO-BPA (bisphenol A propylene oxide adduct) and EP-BPA (bisphenol A ethylene oxide adduct)
Acid component: fumaric acid and melitric acid anhydride Colorant: CI Pigment Blue 15: 1 5.0 parts by weight Wax: non-polar paraffin wax 6.0 parts by weight
(DSC peak 75 ° C)
・ Charge control agent: 1.5 parts by weight of zinc compound of salicylic acid

  The above raw materials were mixed for 10 minutes with a Henschel mixer (trade name, manufactured by Mitsui Mining Co., Ltd.), and this raw material mixture was melt-kneaded with a twin-screw extrusion kneader (trade name: PCM65, manufactured by Ikekai Co., Ltd.). The obtained melt-kneaded product was coarsely pulverized with a cutting mill (trade name: VM-16, manufactured by Orient Chemical Industries, Ltd.). Subsequently, the obtained coarsely pulverized product was finely pulverized by a counter jet mill, and then the excessively pulverized product was classified and removed by a rotary classifier to prepare toner base particles 1 having a volume average particle diameter of 9 μm.

To the obtained toner base particles 1, the following silica fine particles 1 and titanium fine particles 1 were mixed and added as external additives to prepare a one-component developer 1.
Toner base particles 1 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R976, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 7 nm) 0.75 parts by weight Titanium oxide fine particles 1 (trade name: STT) -30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 2.0 parts by weight

The coverage S of the obtained one-component developer 1 was found to be 180.9% from the calculation formula (II). At this time, (the coverage S ₂ of the toner base particles with titanium oxide) / (the coverage S ₁ of the toner base particles with silica) × 100 = 20.7 (%).
For the calculation of the coverage, the values of ρt = 1.1, ρi = 1.95 (silica) and 4.4 (titanium oxide) were used (the same values were used for the calculation in the following examples and comparative examples) ).

The one-component developer 1 is filled in the developing cartridge 4 of the monochrome type image forming apparatus in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 180 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, good image quality was obtained.

In relational expression (I),
Then, A = 27.1 for this example.

[Example 2]
A toner base particle 2 having a volume average particle diameter of 10.5 μm was prepared in the same manner as in Example 1. The resulting toner base particles 2 were externally mixed with the following silica fine particles 1 and titanium fine particles 1 as external additives to prepare a one-component developer 2.
Toner base particle 2 100.0 parts by weight Silica fine particles 1 (trade name: Hydrophobized silica; R972, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 16 nm) 1.5 parts by weight Titanium oxide fine particles 1 (trade name: STT) -30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 2.0 parts by weight

The coverage S of the obtained one-component developer 2 was found to be 189.3% from the calculation formula (II). Further, S ₂ / S ₁ × 100 = 20.2 (%) was obtained.

The one-component developer 2 is filled in the developing cartridge 4 of the image forming apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 180 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, the fog was kept constant and good image quality was obtained.
For this example, A = 26.3.

Example 3
To the same toner base particles 2 as in Example 2, the following silica fine particles 1 and titanium fine particles 1 were mixed and added as external additives to prepare a one-component developer 3.
Toner base particles 2 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R976, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 7 nm) 0.75 parts by weight Titanium oxide fine particles 1 (trade name: STT) -30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 0.5 parts by weight

The coverage S of the obtained one-component developer 3 was found to be 183.9% from the calculation formula (II). At this time, it was S ₂ / S ₁ × 100 = 5.1 (%).

The one-component developer 2 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1, and an electrostatic latent image is formed on the image carrier surface 1. The distance between the developer carrier and the image carrier is 180 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, the fog was kept constant and good image quality was obtained.
For this example, A = 25.5.

Example 4
To the same toner base particles 2 as in Example 2, the following silica fine particles 1 and 2 and titanium fine particles 1 were mixed and added as external additives to prepare a one-component developer 4.
Toner base particle 2 100.0 parts by weight Silica fine particle 1 (hydrophobized silica; trade name: R972, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 16 nm) 1.25 parts by weight Silica fine particle 2 (hydrophobized silica; product Name: RX50, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 40 nm) 0.2 parts by weight Titanium oxide fine particles 1 (trade name: STT-30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 1.5 parts by weight

The coverage S of the obtained one-component developer 4 was found to be 162.9% from the calculation formula (II). At this time, it was S ₂ / S ₁ × 100 = 20.0 (%).

The one-component developer 4 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 170 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, the fog was kept constant and good image quality was obtained.
For this example, A = 21.4.

Example 5
First, the following silica fine particles 1 and titanium fine particles 1 are mixed and externally added as external additives to the toner base particles 1 having the same volume average particle diameter of 9.0 μm as in Example 1, and then the following silica fine particles 2 and titanium fine particles 2 are added. A one-component developer 5 was prepared by external addition of the mixture.
Toner base particle 1 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R976, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 7 nm) 0.75 parts by weight Silica fine particles 2 (hydrophobized silica; product Name: RX50, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 40 nm) 0.2 parts by weight Titanium oxide fine particles 1 (rutile titanium oxide; trade name: MT-500SA, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 0 .75 parts by weight Titanium oxide fine particles 2 (anatase type titanium oxide; trade name: STT-30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 0.5 parts by weight

The coverage S of the obtained one-component developer 5 was found to be 176.3% from the calculation formula (II). At this time, it was S ₂ / S ₁ × 100 = 12.4 (%).
The electron beam image revealed that the titanium oxide fine particles were dispersed on the surface of the toner base particles.

A one-component developer 5 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 180 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, the fog was kept constant and good image quality was obtained.
For this example, A = 26.5.

(Comparative Example 1)
A comparative one-component developer 1 was prepared by externally adding the following silica fine particles 1 and titanium fine particles 1 as external additives to the toner base particles 1 having the same volume average particle diameter of 9.0 μm as in Example 1.
Toner base particles 1 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R976, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 7 nm) 1.00 parts by weight Titanium oxide fine particles 1 (trade name: STT) -30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 0.45 parts by weight

The coverage S of the comparative component one-component developer 1 thus obtained was found to be 206.9% from the calculation formula (II). At this time, S ₂ / S ₁ × 100 = 3.5 (%).

The comparative one-component developer 1 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 180 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, the charge amount increased and satisfactory image quality could not be obtained.
For this example, A = 31.0.

[Comparative Example 2]
A comparative one-component developer 2 was prepared by externally adding the following silica fine particles 1 and titanium fine particles 1 as external additives to the toner base particles 1 having the same volume average particle diameter of 9.0 μm as in Example 1.
Toner base particles 1 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R972, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 16 nm) 1.25 parts by weight Titanium oxide fine particles 1 (trade name: STT) -30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 1.5 parts by weight

The coverage S of the comparative component one-component developer 2 obtained was found to be 132.6% from the calculation formula (II). At this time, it was S ₂ / S ₁ × 100 = 21.3 (%).

A comparative one-component developer 2 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 180 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, the charge amount decreased and satisfactory image quality could not be obtained.
For this example, A = 19.9.

Example 6
The following silica fine particles 1 and 2 and titanium fine particles 1 as external additives were mixed and externally added to the toner base particles 2 having the same volume average particle diameter of 10.5 μm as in Example 2 to prepare a one-component developer 6.
Toner base particle 2 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R976, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 7 nm) 0.75 parts by weight Silica fine particles 2 (hydrophobized silica; product Name: RX50, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 40 nm) 0.5 part by weight ・ Titanium oxide fine particles 1 (trade name: STT-30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 0.5 part by weight

The coverage S of the obtained one-component developer 6 was found to be 204.3% from the calculation formula (II). At this time, S ₂ / S ₁ × 100 = 4.6 (%).

The one-component developer 6 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer carrier and the image carrier is 170 μm, the development bias potential V _B is −500 V, and the electrostatic latent image potential V _L is −100 V (that is, the potential difference | V _B −V _L | = 400 V). At that time, good image quality equivalent to that of Examples 1 and 2 was obtained.
For this example, A = 26.8.

Example 7
To the toner base particles 2 having the same volume average particle diameter of 10.5 μm as in Example 2, the following silica fine particles 1 and titanium fine particles 1 were mixed and added as external additives to prepare a one-component developer 7.
Toner base particles 2 100.0 parts by weight Silica fine particles 1 (hydrophobized silica; trade name: R972, manufactured by Nippon Aerosil Co., Ltd .; primary particle size 16 nm) 1.25 parts by weight Titanium oxide fine particles 1 (trade name: STT) -30, manufactured by Titanium Industry Co., Ltd .; primary particle size 40 nm) 1.6 parts by weight

The coverage S of the obtained one-component developer 7 was found to be 156.5% from the calculation formula (II). At this time, it was S ₂ / S ₁ × 100 = 22.6 (%).

The one-component developer 7 is filled in the developing cartridge 4 of the apparatus shown in FIG. 1 to form an electrostatic latent image on the image carrier surface 1. The distance between the developer bearing member and the image bearing member is 180 μm, the developing bias potential V _B is −450 V, and the electrostatic latent image potential V _L is −100 V (that is, potential difference | V _B −V _L | = 350 V). At that time, good image quality equivalent to that of Examples 1 and 2 was obtained.
For this example, A = 24.8.

  Volume average particle size and blending amount of toner base particles used in one-component developers used in Examples and Comparative Examples, type of fine particles used as external additive, volume average particle size and blending amount, according to formula (II) Table 1 summarizes the calculated coverage of the toner base particle surface by the external additive (for each fine particle and the total) and the ratio of the coverage by titanium oxide to the coverage by silica.

Table 2 shows each parameter in the relational formula (I) (coverage S, volume average particle diameter D of toner base particles, developer carrier and image carrier for Examples 1 to 7 and Comparative Examples 1 and 2. G and G values of development bias potential V _B and electrostatic latent image potential V _L ) and A value (= (S / √D) × G / | V _B −V _L |) are collectively shown.

  Table 3 summarizes evaluations related to image quality of images formed by the image forming apparatuses of Examples 1 to 7 and Comparative Examples 1 and 2.

Evaluation of high image quality was performed for gradation. A 16 gradation chart (256 batch images; FIG. 2) was output, and it was confirmed how many gradations could be reproduced in the output document.
“X” if only 10 gradations or less can be reproduced, “Δ” if 11 gradations, 11 “12”, “◯” if 13-15 gradations, “◎” if all 16 gradations can be reproduced. ".

For evaluation of fogging stability, the image density of the non-image area was measured before and after continuous output of 2,000 sheets using a whiteness meter (Z-Σ90 COLOR MEASURING SYSTEM: manufactured by Nippon Denshoku Industries Co., Ltd.) The fogging degree was obtained.
When the change in fogging was 0.3 or more, it was evaluated as “X”, when it was 0.1 or more and less than 0.3, “◯”, and when it was less than 0.1, “◎”.

For evaluation of image quality stability, the toner charge amount was measured before and after continuous output of 2,000 sheets using a suction type small charge amount measuring device (210HS-2A: manufactured by Trek Japan Co., Ltd.).
The charge amount change Δ (μc / g) after continuous output of 2,000 sheets relative to the initial value was determined.
When the change in charge amount was 3 μc / g or more, “X” was evaluated, and “◯” was evaluated when it was 2 μc / g or more and less than 3 μc / g, and “◎” when it was less than 2 μc / g.

For evaluation of environmental stability, a reflection densitometer (Macbeth: RD918) was used before and after continuous output of 2,000 sheets in a high-temperature and high-humidity environment of 35 ° C / 85%. Measured.
The change in the image density of the solid portion after continuous output of 2,000 sheets relative to the initial environment of 35 ° C./85% was determined.
When the image density change was 0.3 or more, it was evaluated as “×”, when it was 0.1 or more and less than 0.3, “◯”, and when it was less than 0.1, “◎”.

  Comprehensive evaluation is “X” when one item is “×” for each evaluation item, “△” when two items or more are set as “△”, and “○” when two items or more are set. “○” in the case of “” and “◎” in the case of “◎” in three or more items.

As understood from Tables 2 and 3, all of the image forming apparatuses of Examples satisfying the relational expression (I) had a comprehensive evaluation of “◯” or more.
On the other hand, the image forming apparatus of the comparative example that does not satisfy the relational expression (I) was “x” in the comprehensive evaluation.

  In Comparative Example 1, it is considered that the developer (toner) is difficult to fly in the gap between the developer carrier and the image carrier as a result of the high coverage S on the surface of the toner base particles by the external additive and the increase in the charge amount. It is done. In Comparative Example 2, the coverage S was low and the charge amount decreased. As a result, the developer (toner) easily flew in the gap between the developer carrier and the image carrier (therefore, the image density of the solid portion was It is thought that it became too dark and the fog rose).

Even in Examples satisfying the relational expression (I), when Examples 1, 2, 6, and 7 and Examples 3 to 5 are compared, (the coverage S ₂ of the toner base particle surface with titanium oxide) / (silica) It is understood that if the coverage S ₁ ) × 100 on the surface of the toner base particles is 5% or more and 20% or less, an image forming apparatus that is further excellent in terms of gradation and charging stability can be obtained.

  Further, from the results of Example 5, while satisfying the relational formula (I), using rutile type titanium oxide and silica for the first external addition, and using anatase type titanium oxide and silica for the second external addition, It is understood that resistance control and fluidity can be ensured over a long period of time, and good image quality can be maintained.

  As mentioned above, although preferred embodiment and the Example of this invention were described, it cannot be overemphasized that this invention is not limited to these described embodiment and Example. It will be apparent to those skilled in the art that various changes and modifications can be easily understood within the scope of the claims, and these naturally belong to the technical scope of the present invention.

1 is a schematic cross-sectional view of an image forming apparatus which is an embodiment of the present invention. 16 gradation pattern used for image quality evaluation in the embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image carrier 2 ... Charger 3 ... Exposure apparatus 4 ... Developing cartridge 5 ... Developing roller 6 ... Transfer roller 7 ... Fixing device 8 ... Static elimination lamp 9 ... Cleaner device 10 ... Recording member

Claims (7)

An image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for irradiating the image carrier with light to form an electrostatic latent image, and the electrostatic latent image is visualized by a developer. An electrophotographic image forming apparatus having a developing means for forming a toner image and a transfer means for adhering the toner image onto a transfer material, wherein the developing means and the image carrier and a gap G (μm) In the image forming apparatus, the developing bias potential applied to the developer bearing member is a DC potential V _B (V).
The one-component developer is composed of toner base particles having a volume average particle diameter D (μm; 8 ≦ D ≦ 12) coated with an external additive, and the surface coverage of the toner base particles by the external additive S ( %) Is the following relation:
(Where V _L is the electrostatic latent image potential (V) on the image carrier)
An image forming apparatus satisfying the requirements. The external additives are silica fine particles and titanium oxide fine particles. In the relational formula (I), S = (coverage ratio S ₁ of the toner base particle surfaces by silica fine particles) + (surface of the toner base particles by titanium oxide fine particles) The image forming apparatus according to claim 1, which has a coverage ratio S ₂ ). Relational expression:
5% ≦ S ₂ / S ₁ × 100 ≦ 20%
The image forming apparatus according to claim 2, wherein:   The image forming apparatus according to claim 2, wherein the titanium oxide fine particles include rutile type titanium oxide fine particles and anatase type titanium oxide fine particles.   The one-component developer externally adds the rutile type titanium oxide fine particles and the silica fine particles to the toner base particles, and then externally adds only the anatase type titanium oxide fine particles and the silica fine particles or the anatase type titanium oxide fine particles. The image forming apparatus according to claim 4, wherein the image forming apparatus is manufactured. An image carrier, a charging unit that charges the surface of the image carrier, an exposure unit that irradiates the image carrier with light to form an electrostatic latent image, and the electrostatic latent image is visualized by a one-component developer. An electrophotographic image forming apparatus having a developing unit for forming a toner image and a transfer unit for adhering the toner image onto a transfer material, wherein the one-component developer is covered with an external additive. In an image forming apparatus comprising toner base particles having a volume average particle diameter D (μm; 8 ≦ D ≦ 12) coated with (%),
The developing means includes a developer carrier provided with a gap G (μm) from the image carrier, and a DC developing bias potential V _B (V) applied to the developer carrier and a gap G Is the following relation:
(Where V _L is the electrostatic latent image potential (V) on the image carrier)
An image forming apparatus satisfying the requirements.   The image according to claim 1, further comprising a plurality of the developing units, wherein the transfer unit collectively attaches a plurality of toner images developed by the plurality of developing units onto the transfer material. Forming equipment.