JP2890727B2 - Development method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developing method for developing an electrostatic image formed by an electrophotographic method, an electrostatic recording method, or the like using a two-component developer.

[Conventional technology]

As a developer used for developing an electrostatic latent image formed on a photoreceptor by an electrophotographic method or the like, a two-component developer in which a toner and a carrier are mixed, and a toner alone such as a magnetic toner are used. There is a one-component developer. The two-component developer is provided with functions such as stirring / conveying / charging by a carrier. Therefore, since it is separated in function as a developer, it has characteristics such as good controllability and is widely used at present. In particular, when a carrier coated with a resin is used, the charge controllability is improved, and the environment dependency and the stability over time tend to be improved. As a developing method, a cascade method or the like has been used in the past, but the mainstream of the developing method currently used is a magnetic brush method using a magnetic roll as a developer carrier.

[Problems to be solved by the invention]

The problems with the magnetic brush method using such a carrier include the occurrence of background contamination due to toner adhering to the non-image area, image roughness and carrier consumption due to the carrier adhering to the image area, and the resulting image density. Occurrence of unevenness,
Further, the image density is lowered due to the deterioration of the charge of the developer, and the background is significantly stained.

Usually, as a feature of the two-component magnetic brush developing method, when the moving direction of the photoconductor and the developer is the same, the generation of the toner on the non-image area is relatively small, but the generation of the carrier on the image area is somewhat avoided. Can not do. Conversely, when the photoconductor and the developer move in opposite directions, the carrier adhesion is relatively good, but the background stain is slightly improved by the development bias, etc. There is.

The present invention has been made in view of the above problems.

Accordingly, an object of the present invention is to improve the problems of the developing method by the magnetic brush method using the two-component developer. That is, it is an object of the present invention to provide a developing method capable of obtaining a high-quality image free of background stains and image roughness and realizing stable maintenance with less carrier consumption.

[Means for solving the problem]

The present inventors have conducted intensive studies on a developing method in which the moving direction of the photosensitive member and the developer is the same as the initial image quality with respect to the background stain, and as a result, a carrier having a specific carrier physical property under predetermined developing conditions. By using, a developing method capable of controlling carrier adhesion and realizing good maintainability was found, and the present invention was completed.

According to a first aspect of the present invention, a developer comprising a toner and a resin-coated carrier is carried on a magnetic roll disposed opposite to a photoreceptor, and a developing bias potential is applied to the magnetic roll. In the developing method of moving the developer in the same direction as the moving direction of the photoreceptor to convey the developer and developing the electrostatic latent image formed on the photoreceptor, the maximum development electric field at the developing site is used as the resin-coated carrier. Wherein the V _I image portion maximum potential of the photosensitive member in the developing region (V), the V _B developing bias potential (volt), D denotes a gap (cm) between the photosensitive member and the magnetic roll. ], Characterized by using a material having a specific resistance of 10 ⁹ Ω · cm or more.

According to a second aspect of the present invention, a developer composed of a toner and a resin-coated carrier is carried on a magnetic roll disposed opposite to a photoconductor, and a developing bias potential is applied to the magnetic roll. In the developing method of moving the developer by moving in the same direction as the moving direction of the photoreceptor and developing the electrostatic latent image formed on the photoreceptor, as the resin-coated carrier, at 10 ³ V / cm It is characterized by using a material having a specific resistance of 10 ⁹ Ω · cm or more and a dielectric breakdown voltage satisfying a condition represented by the following equation.

[Where _EB is the breakdown voltage of the carrier (volts), V _I
The image portion maximum potential of the photosensitive member in the developing region (V), the V _B developing bias potential (volt), D denotes a gap (cm) between the photosensitive member and the magnetic roll. Carrier adherence to the image portion of the electrostatic latent image formed on the photoreceptor occurs because charge is injected into the carrier in the developer against the image portion charge, thereby causing carrier development. Can be considered. This carrier development can be prevented by increasing the resistance of the developer and eliminating a sharp decrease in the resistance of the developer (dielectric breakdown). Is consumed, the resistance of the developer may be controlled by controlling the resistance of the carrier or the dielectric breakdown voltage. Further, after deterioration with the passage of time, the toner concentration is usually maintained at an extremely low concentration, so that the resistance of the carrier may be controlled. In addition, since carrier adhesion occurs due to partial dielectric breakdown, it is sufficient to control the dielectric breakdown resistance of the carrier. In this case, the relationship between the maximum potential at the development site, the development bias potential, and the gap between the photoconductor and the magnetic roll is determined. Very important.

The present invention has been made from such a viewpoint. The present inventors have confirmed that no carrier adhesion occurs when the specific resistance of the carrier under the developing conditions is 10 ⁹ Ω · cm or more. Furthermore, at 1000 V / cm, 10
If a carrier having a resistance of ⁹ Ωcm or more and a dielectric breakdown voltage of 1/2 or more of the developing electric field defined by the image portion maximum potential and the developing bias potential and the gap between the photoreceptor and the magnetic roll is used, the carrier can be used. It was confirmed experimentally that no adhesion occurred, and the present invention was completed.

 Hereinafter, the present invention will be described in detail.

FIG. 1 is a schematic configuration diagram of a developing device for carrying out the present invention. Reference numeral 1 denotes a photosensitive drum having a photoconductive layer, which carries an electrostatic latent image and rotates in the direction of the arrow. The photoconductive layer has the ability to retain an image portion maximum potential V _I. Numeral 2 denotes a magnetic roll, which has a sleeve 21 made of a nonmagnetic material such as aluminum which rotates on the surface in the direction of the arrow, and has a structure in which a magnet is provided inside. This magnetic roll has
The bias power source 3, the developing bias potential V _B is applied. A gap D is formed between the photosensitive drum 1 and the magnetic roll 2.
Are opposed to each other. Reference numeral 4 denotes a developer, and reference numeral 5 denotes a layer regulating member.

In the above-described developing device, the electrostatic latent image formed on the photoconductive layer of the photosensitive drum reaches the developing site by rotating the photosensitive drum in the direction of the arrow. On the other hand, developer 4
Is supplied on the sleeve of the magnetic roll 2 by the layer regulating member 5, and is conveyed to the developing site by rotating the magnetic roll in the direction of the arrow. A development electric field is formed at the development site, and the developer conveyed on the sleeve forms a magnetic brush to develop the electrostatic latent image. In the present invention, it is preferable that the development is performed with the ratio of the peripheral speed of the photosensitive drum to the peripheral speed of the magnetic roll being in the range of 1: 1.5 to 4.0.

The developer used in the present invention is composed of a toner and a carrier, and the carrier is composed of a resin-coated magnetic core material, and has a specific resistivity or a dielectric breakdown voltage defined as described above. Use what you have. That is, in the first case, it is the maximum developing electric field at the developing site.

The one having a specific resistance of 10 ⁹ Ω · cm or more measured under the following conditions is used.

In the second case, the specific resistance at 10 ³ V / cm is 10 ⁹
And the Omega · cm or more and a dielectric breakdown voltage E _B is used which satisfies the condition represented by the following formula.

Known as the magnetic core material of the carrier, for example,
Iron, cobalt, and alloys exhibiting ferromagnetism such as _{nickel, Fe 3 O 4, γ-} Fe 2 O 3, metal oxides such as cobalt added iron oxide, MnZn ferrite, various ferrites such as NiZn ferrite, Magnetite, hematite, etc., or alloys that do not contain ferromagnetic elements but become ferromagnetic when subjected to appropriate heat treatment, such as Mn-Cu-Al, Mn-
What is called a Heusler alloy containing Mn and Cu, such as Cu-Sn, or chromium dioxide can be used. However, in consideration of stability over time, it is preferable to use ferrite. The particle size of the core material is 30 μm to 200 μm,
Preferably, those having a range of 50 μm to 120 μm can be used.

Examples of the resin for coating the core material include styrenes such as styrene, p-chrome styrene and α-methyl styrene; vinyl halides such as vinyl chloride, vinyl bromide and vinyl fluoride; vinyl acetate, vinyl propionate and benzoate. Vinyl esters such as vinyl acrylate and vinyl butyrate; methyl acrylate, ethyl acrylate, acryl-guided n-butyl, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 3-chloroethyl acrylate, phenyl acrylate, α Esters of α-methylene aliphatic monocarboxylic acids such as chloroacrylmethyl, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate;
Vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl ethers such as vinyl methyl ether, vinyl isopropyl ether and vinyl ethyl ether;
Vinyl methyl ketone, vinyl hexyl ketone, phonopolymer or copolymer obtained by polymerizing monomers such as vinyl ketones such as methyl isopropenyl ketone, and other resins, epoxy resin, rosin-modified phenol-formalin resin, Resins such as a cellulose resin, a polyether resin, a pyrivinylbutyral resin, a polyester resin, a styrene-butadiene resin, a polyvinyl formal resin, a polycarbonate resin, and a fluororesin can be used alone or in combination.

Among these, fluororesins, vinyl chloride-vinyl acetate resins, polyester resins, and the like are preferable, and fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, polyfluoroacrylate, and polyfluoromethacrylate are particularly preferable.

As the coating means, various commonly used methods such as a dip coating method, a spray coating method and a fluidized bed method can be used.

In order to set the carrier resistance and the dielectric breakdown voltage to predetermined values, the thickness of the resin coating may be increased and the resin may be uniformly coated, or a core material having a high resistance may be used. In consideration of stability over time, ferrite is preferably used as the core material.

The toner constituting the developer used in the present invention includes:
As a main component, it consists of a binder resin and a colorant dispersed therein.

Various thermoplastic resins can be used as the binder resin. Specific examples thereof include styrenes such as styrene, p-chlorostyrene and α-methylstyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, acrylic acid Α such as 2-ethylhexyl, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.
-Methylene aliphatic monocarboxylic esters; vinyl nitriles such as acrylonitrile and methacrylonitrile; 2
Vinyl pyridines such as vinyl pyridine and 4-vinyl pyridine; vinyl ethers such as vinyl methyl ether and vinyl isopropyl ether; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; ethylene, propylene, isoprene and butadiene And polymers or copolymers comprising one or more monomers such as unsaturated hydrocarbons such as chloroprene and halogenated unsaturated hydrocarbons such as chloroprene, and mixtures thereof. Further, for example, rosin-modified phenol-formalin resin, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, polyether resin and the like, or a mixture of these with the above-mentioned vinyl resin can also be used.

Examples of the colorant include carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue, and a mixture thereof. Examples of the toner component other than the colorant include a charge control agent, an anti-offset agent, and a fluidity improver. If necessary, a magnetic fine powder may be contained.

The specific resistance and dielectric breakdown voltage of the carrier were measured as follows. FIG. 2 is an explanatory diagram illustrating a measurement state. First, the measurement sample 11 is filled between the lower electrode 12 and the upper electrode 13, and the filling height H (cm) is measured by the dial gauge 14. Next, a voltage is applied between the lower electrode and the upper electrode, the voltage is increased in steps of 100 V up to 2000 V, and the resistance value R (Ω) of the sample is read by the high-voltage resistance meter 15, and the following formula is used. The specific resistance (Ω · cm) at each electric field strength is obtained.
The voltage at the point where the resistance value sharply decreases by increasing the voltage is defined as the breakdown voltage.

Specific resistance = R × S / H (S represents an electrode area (cm ² )) Electric field intensity (V / cm) = applied voltage / filling height H [Examples] Hereinafter, the present invention will be described by Examples and Comparative Examples. This will be described in detail.

Example 1 Ferrite particles having an average particle size of 80 μm were used as a core material, and a polymethyl methacrylate or vinylidene fluoride-6-propylene propylene copolymer (copolymer molar ratio: 80: 2) was used.
0) to prepare a carrier. The coating was performed, for example, as a solution of dimethylformamide by a fluidized bed method. Table 1 shows the obtained coated state and specific resistance of the carrier.

The following toner was used. That is, in the case of a carrier coated with polymethyl methacrylate, a styrene-n-butyl methacrylate copolymer (Mn = 8,000, M
w = 100,000), carbon black (BP1300, manufactured by Degussa) was added at 10% by weight based on the total weight of the toner, and a toner having an average particle diameter of 10 μm obtained by a kneading and pulverizing method was used. In the case of a carrier coated with a vinylidene fluoride-6-propylene copolymer, a styrene-n-butyl methacrylate copolymer (Mn = 8,000, Mw = 100,000) and carbon black (R330, manufactured by Degussa Co., Ltd.) 10% by weight and 1% by weight of nigrosine (Bontron No. 4, manufactured by Orient) were added, and a toner having an average particle diameter of 10 μm obtained by a kneading and pulverizing method was used.

The above carrier and toner are mixed at a weight ratio of 97: 3 to make a developer, and a copy operation is performed using an electrophotographic copying machine (FX5870, manufactured by Fuji Xerox Co., Ltd.) and a copying machine modified for reversal development. Was done. The development condition is the peripheral speed of the photosensitive drum.
Is rotated at a moving speed of 270 mm / sec, the peripheral speed ratio between the photosensitive drum and the magnetic roll 1: 2.5 is set to the gap D between the photosensitive drum and the magnetic roll, the image portion the maximum potential V _I and the developing bias voltage the V _B was performed by setting the values shown in table 1.

With respect to the obtained copy image, the initial image quality and the image quality after 10,000 copies were evaluated. Table 1 shows the results. In Table 1, .largecircle. Indicates that there is no background stain, no line roughness, and there is no density unevenness in the image, and x indicates that the background stain is remarkable, the line roughness is remarkable, or the density is low. This shows the case where unevenness occurs.

Example 2 A carrier was prepared as in Example 1. However, the specific resistance and breakdown voltage at 10 ³ V / cm
Resin coating was performed so as to obtain the values shown in the table.

Using the same toner as in Example 1, a copy operation was performed under the same conditions. Table 2 shows the results.

[Effect of the Invention] The developing method of the present invention uses the resin-coated carrier having the specific physical properties as described above, and performs development by moving the developer in the same direction as the photoconductor, so that carrier contamination is less likely to occur. Therefore, it is possible to obtain a high-quality image free from background stains and image roughness. In addition, when used for a long time, stable maintenance with less carrier consumption can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a developing device embodying the present invention, and FIG. 2 is an explanatory diagram illustrating a measurement direction of a specific resistance and a dielectric breakdown voltage. DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Magnetic roll, 21 ... Sleeve, 3
... bias power supply, 4 ... developer, 5 ... layer regulating member, 11 ... measurement sample, 12 ... lower electrode, 13 ... upper electrode, 14 ... dial gauge, 15 ... high voltage resistance meter.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-159664 (JP, A) JP-A-60-125868 (JP, A) JP-A-2-83 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) G03G 15/06-15/09 G03G 9/10

Claims (2)

(57) [Claims] 1. A developer comprising a toner and a resin-coated carrier is carried on a magnetic roll disposed opposite to a photoreceptor, and the photoreceptor moves while applying a developing bias potential to the magnetic roll. In the developing method of transporting the developer while moving the developer in the same direction as the direction of development and developing the electrostatic latent image formed on the photoreceptor, the maximum development electric field at the development site is used as the resin-coated carrier. Wherein the V _I image portion maximum potential of the photosensitive member in the developing region (V), the V _B developing bias potential (volt), D denotes a gap (cm) between the photosensitive member and the magnetic roll. ], Wherein the specific resistance of the developing method is 10 ⁹ Ω · cm or more. 2. A developer comprising a toner and a resin-coated carrier is carried on a magnetic roll disposed opposite to a photoreceptor, and the photoreceptor is moved while applying a developing bias potential to the magnetic roll. In the developing method in which the developer is transported while being moved in the same direction as the direction, and the electrostatic latent image formed on the photoreceptor is developed, 10 ³ V is applied as the resin-coated carrier.
A developing method characterized by using a material having a specific resistance of 10 ⁹ Ω · cm or more at / cm and a dielectric breakdown voltage satisfying a condition represented by the following formula. Wherein, E _B is the breakdown voltage of the carrier (V), V _I is the image portion the maximum potential of the photosensitive member in the developing region (V),
V _B means a developing bias potential (volt), and D means a gap (cm) between the photoconductor and the magnetic roll. ]