JPH07128917A - Electrophotographic developer - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an electrophotographic developer having improved maintainability of charge amount when developing an electrostatic latent image having a low potential contrast of about 100 to 400V. Also provided is a multicolor image forming method for forming excellent image quality by a one-pass multicolor developing method. A developer for electrophotography comprising a magnetic powder-dispersed carrier and toner particles obtained by externally adding inorganic oxide fine particles, wherein conductive particles are externally added to the magnetic powder-dispersed carrier. Thus, 100 mg or more of the conductive fine particles strongly adhere to the carrier with respect to 100 g of the carrier. This electrophotographic developer is used in a multicolor image forming method having a step of developing an electrostatic latent image formed on a latent image holding member by using a plurality of developing devices, in which case at least one of the developing devices is used. It is preferably used in the second developing device, especially in the second developing device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to 100 to 400V.
The present invention relates to an electrophotographic developer for developing an electrostatic latent image having low potential contrast, and a multicolor image forming method using the same.

[0002]

2. Description of the Related Art Heretofore, a so-called microtoning carrier, which is a magnetic powder dispersion type carrier having a small particle size in which magnetic fine powder is dispersed in a binder resin, has been proposed and put into practical use.
Such a magnetic powder-dispersed carrier has a low true specific gravity, high insulation, and a small particle size, so the magnetic brush is denser and more uniform than conventional carriers, and has good concentration reproducibility and magnetic properties. There is an advantage that there is no noise such as brush eyes due to the brush and the image quality is improved. However, on the other hand, due to the high insulating property, there is a problem that charges are initially accumulated in the carrier and high charge is exhibited, and thus the toner concentration is high, or the specific gravity is small and the particle size is small. Therefore, there is a problem that the fluidity of the developer is deteriorated, the contact between the toner and the carrier is significantly deteriorated, the toners are charged with each other, the toner and the developing member are charged, and the image background portion is fogged. For the purpose of improving these problems, it has been proposed to add fine powder of a conductive substance to a carrier to prevent uneven charging. On the other hand, regarding the toner, various inorganic and organic fine powders are added as external additives in order to improve the fluidity, anti-caking property, fixing property, charging property, cleaning property, etc. and to have process compatibility. It is known to add, and it has been proposed to use, for example, silica, titanium dioxide, aluminum oxide, tin dioxide or the like. Further, a developer in which these toners are combined with the magnetic powder dispersion type carrier is also proposed. (For example, JP-A-60-136775 and JP-A-61-19661)

Various methods have also been proposed for obtaining a color image using these developers.
In recent years, a multi-color image forming method by a one-pass multi-color developing method has been often adopted in which development and transfer are repeated twice or more during one rotation of the photosensitive drum to obtain toner images of two or more colors. As a developer used in the one-pass multicolor development system, the development potential width per color is limited due to the sensitivity of the electrophotographic photosensitive member used, and it is necessary to charge the developer to a low potential. Further, the developer for that purpose is required to have a high charging speed and a good charge exchange property. Conventionally proposed developers, when used in the image forming method as described above, when many sheets are copied,
There is a problem that the distribution of the charge amount of the toner is widened, and as a result, the toner having the opposite polarity is generated, and image defects such as toner scattering and fogging occur. This tendency is particularly remarkable when copper phthalocyanine is used as a colorant.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the prior art. That is, it is an object of the present invention to provide an electrophotographic developer having an improved ability to maintain a charge amount when developing an electrostatic latent image having a low potential contrast of about 100 to 400V. Another object of the present invention is to provide a multicolor image forming method for forming excellent image quality by a one-pass multicolor developing method.

The electrophotographic developer of the present invention is a mixture of magnetic powder-dispersed carrier and toner particles to which inorganic oxide fine particles are externally added. Is added externally, 100 g of carrier
On the other hand, 100 mg or more of the conductive fine particles are strongly adhered to the carrier. Further, the multicolor image forming method of the present invention has a step of developing the electrostatic latent image formed on the photoconductor with a plurality of developing devices, wherein at least one of the developing devices is used for electrophotography. It is characterized by using a developer.

The present invention will be described in detail below. The toner in the electrostatic latent image developer of the present invention is composed mainly of a binder resin and a colorant. The binder resin used is styrene such as styrene or chlorostyrene;
Mono-olefins such as ethylene, propylene, butylene, isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, butyl acrylate,
Octyl acrylate, dodecyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate,
Α-Methylene aliphatic monocarboxylic acid esters such as butyl methacrylate and dodecyl methacrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether; vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone, etc. Examples thereof include homopolymers and copolymers of vinyl ketones and the like, and particularly representative binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene- Acrylonitrile copolymer, styrene-butadiene copolymer,
Examples thereof include styrene-maleic anhydride copolymer, polyethylene and polypropylene. In addition, polyester, polyurethane, epoxy resin, silicone resin,
Examples thereof include polyamide, modified rosin and paraffin wax.

As the colorant, carbon black, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, copper phthalocyanine, malachite green oxalate, lamp black, rose bengal. , C.I. I. Pigment Red 4
8: 1, C.I. I. Pigment Red 122, C.I. I.
Pigment Red 57: 1, C.I. I. Pigment Yellow 97, C.I. I. Pigment Yellow 12, C.I.
I. Pigment Blue 15: 1, C.I. I. Pigment Blue 15: 3 etc. can be mentioned. Further, part or all of the coloring agent may be replaced with magnetic powder. In addition to the above components, the toner may further contain a charge control agent, a cleaning aid, a fluidity accelerator, etc., if necessary.

A preferable toner in the present invention is one using copper phthalocyanine as a colorant, and in this case, the charge amount is stable for a long period of time. The toner particle size is about 20 μm or less, preferably 2 to 20 μm
Those in the range of can be used.

Inorganic oxide fine particles are externally added to the toner. As the inorganic oxide fine particles, for example, Ti
O ₂ , Al ₂ O ₃ , Fe ₂ O ₃ , MnO, ZnO, Mg
O, CaO, K ₂ O, Na ₂ O, SnO ₂ , ZrO ₂ ,
Examples thereof include CaO.SiO ₂ , K ₂ O. (TiO ₂ ) _n, etc., but are not limited thereto.
These inorganic oxide fine particles may be used in combination with other inorganic oxide fine particles or organic fine particles. The surface of the inorganic oxide fine particles may be treated with an organic substance. The particle size of the inorganic oxide fine particles is 0.
The range of 005 to 0.2 μm is preferable. The amount of the inorganic oxide fine particles added is 100 parts by weight of the toner,
The range of 0.1 to 5.0 parts by weight is preferable.

On the other hand, the carrier used in the present invention is of a magnetic powder dispersion type and is composed mainly of resin and magnetic powder. As the resin, those exemplified as the binder resin for the toner particles can be used. Further, as the magnetic powder, it is possible to use fine particles of a ferromagnetic material that are usually used. Specific examples thereof include ferrosoferric oxide, γ-iron sesquioxide, various ferrites, chromium oxide, and various fine metal powders. Furthermore, if necessary, a charge control agent or the like can be included. The content of these magnetic powders is about 30 to 95% by weight, preferably 45 to 90% by weight, based on the whole carrier.

The carrier can be prepared by kneading, pulverizing and classifying the above components. Further, by adding the above components to a suitable solvent, or by heating to melt,
It can also be produced by spray drying or the like. The average particle size of the carrier is generally in the range of about 20 to 400 μm, preferably 30 to 100 μm. In the present invention, it is necessary for the above-mentioned carrier to have conductive fine particles previously mixed and adhered to the surface of the carrier with a V blender, a Henschel mixer, or the like. The conductive fine particles that can be used include TiO ₂ , SnO ₂ , and Al.
Examples include fine powders of ₂ O ₃ , MgO, ZnO and the like. These conductive fine particles have an average primary particle size of 0.005 to 0.2 μm.
Those in the range of m can be preferably used.

In the present invention, the conductive fine particles are externally added in the range of 200 to 500 mg based on 100 parts by weight of the carrier, but 100 mg or more of the conductive fine particles adhere strongly to the carrier per 100 g of the carrier. It is necessary to have When the amount strongly adhered to the carrier surface is lower than 100 mg / 100 g carrier, when the electrostatic latent image of low potential contrast is developed, the charge amount distribution of the developer becomes wider when copying a large number of sheets,
The opposite polarity toner is generated. In the present invention, in order to strongly attach the conductive fine particles to the carrier, it depends on the blend scale and the charged amount, but when a V blender of 2 liters or more is used, 500 mg / 100 g of the carrier is charged at 40 rpm. Mixing for 5 minutes or more is required.

The amount of the conductive fine particles strongly adhered to the carrier surface in the present invention is the value obtained as follows. That is, after dispersing a carrier in which conductive fine particles are mixed in a solution containing a surfactant, an ultrasonic vibrator having an oscillation frequency of 20 kHz is immersed in the dispersion liquid,
It is the ratio of the amount of conductive fine particles adhering to the carrier after desorption for 30 minutes at an output of 60 W to the amount of conductive fine particles in the carrier before desorption.

The electrophotographic developer of the present invention is preferably prepared by mixing the above toner and carrier in a ratio of 1: 100 to 15: 100. The electrophotographic developer of the present invention is suitable for developing an electrostatic latent image having a low potential contrast of about 100 to 400V. Therefore, it can be used in a one-pass color developing method having a step of developing using a plurality of developing devices that repeat development and transfer twice or more during one rotation of the photosensitive drum to form toner images of two or more colors.

FIG. 1 is a schematic configuration diagram of an example of a multicolor image forming apparatus adopting the one-pass color developing system used in the present invention. In the figure, reference numeral 1 is a photosensitive drum, around which a charging device 2, a first exposing device 3, a first developing device 4, a second exposing device 5, and a second developing device 6 are sequentially provided. Further, the pre-transfer charger 7, the transfer charger 8, the static eliminator 9,
A cleaner 10 and a static elimination lamp 11 are provided. In addition, 12 is a recording paper.

The photosensitive drum 1 is rotating in the direction of the arrow. First, the charging device 2 uniformly charges the photosensitive layer on the surface of the photosensitive drum 1. Then, the first exposure device 3 performs light irradiation according to the image information corresponding to the first color,
An electrostatic latent image corresponding to the first color is formed on the photoconductor. Any exposure device can be selected. Then, the first developing device 4 supplies toner corresponding to the first color to the photosensitive layer having the first electrostatic latent image formed by the first exposing device to visualize the toner. At this time, the developing bias is selected depending on whether regular development or reverse development is performed. Subsequently, the second exposure unit 5 irradiates light according to the image information corresponding to the second color, and an electrostatic latent image corresponding to the second color is formed on the photosensitive layer. An arbitrary second exposure device is used. Then, the second developing device 6 supplies the toner corresponding to the second color to the photosensitive layer having the second electrostatic latent image formed by the second exposing device to visualize the photosensitive layer. At this time, the developing bias can also be arbitrarily selected. The first toner image and the second toner image formed on the photosensitive layer of the photosensitive drum are transferred to the recording paper 12 by the transfer charger 8, but may be transferred using a means other than electrostatic transfer. . The recording paper is then fixed by a fixing unit (not shown). Further, the photoconductor that has passed through the transfer portion is cleaned by the static eliminator 9, the cleaner 10 and the static elimination lamp 11 for reuse.

The first and second exposing means are composed of a light illuminating means, a document scanning means and an image forming optical system, which are used in an ordinary copying machine, but can be light-modulated according to image information. An optical writing device such as a laser writing device, a liquid crystal light valve including a uniform light source and a liquid crystal micro shutter, an LED array, an optical fiber, or the like can be used according to the purpose. In some cases,
A second charging unit may be provided before the second exposure unit.

[0018]

[Operation] When conductive fine particles are externally added to the carrier,
When this carrier is used in combination with a color toner, especially a toner containing copper phthalocyanine, the conductive fine particles are detached from the carrier surface, and the charge exchange property of the developer itself is deteriorated. As a result, fogging occurs. However, in the electrophotographic developer of the present invention, a sufficient amount of conductive fine particles, that is, conductive fine particles of 100 mg / 100 g carrier or more, which impart charge exchangeability, are strongly adhered to the carrier surface in advance. Therefore, the conductive fine particles are not desorbed by stirring in the developing machine and the charge exchange property of the developer is not deteriorated. Therefore, the electrophotographic developer of the present invention has a good maintainability of the charge amount.

[0019]

EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following description, all "parts" mean "parts by weight". Example 1 (Toner) Styrene-n-butyl acrylate (80:20) copolymer 100 parts (Tg: 63 ° C., Mw: 300,000) Copper phthalocyanine 5 parts Low molecular weight polypropylene (660 p, manufactured by Sanyo Kasei Co., Ltd.) 5 parts Charge control agent (Bontron P-51, manufactured by Orient Chemical Co., Ltd.) 1 part The above components were melted, kneaded, pulverized and classified to obtain toner particles having an average particle diameter of 11 μm. Obtained toner particles 10
To 0 parts, 2 parts by weight of titanium oxide fine particles having an average particle size of 0.03 μm were added and mixed with a Henschel mixer. (Carrier) Styrene-n-butyl methacrylate (80:20) copolymer 24 parts (Tg: 80 ° C., Mw: 100,000) Magnetite (EPT-1000, manufactured by Toda Kogyo Co., Ltd.) 70 parts Fluororesin (Kynar 201, pen) (Walt Co., Ltd.) 6 parts The above components were melt-kneaded with a pressure kneader, pulverized, and classified to obtain carrier particles having an average particle size of 40 μm. To 100 parts of the carrier particles, 0.5 part of titanium oxide fine powder (average primary particle diameter 0.03 μm) was added as conductive particles and mixed by a V blender to adhere the conductive particles to the surface. Got a career. The mixing by the V blender at this time was performed at 40 rpm for 35 minutes. The amount of conductive material strongly adhered to the surface is 300 mg / 10
It was a 0 g carrier. (Developer) The above toner and carrier are mixed at 10: 100.
To prepare a developer.

Example 2 The conditions for adding the conductive fine particles externally added to the carrier were set to 4
A developer was prepared in the same manner as in Example 1 except that stirring was carried out at 0 rpm for 5 minutes. In this case, the amount of the conductive fine particles strongly adhered to the carrier surface was 100 mg / 100 g carrier.

Comparative Example 1 The amount of conductive fine particles externally added to the carrier was 0.2.
A developer was prepared in the same manner as in Example 1 except that part of the developer was added. In this case, the amount of the conductive fine particles strongly adhered to the carrier surface was 80 mg / 100 g carrier. Comparative Example 2 The amount of conductive fine particles externally added to the carrier was 0.2.
A developer was prepared in the same manner as in Example 2 except that a part was added. In this case, the amount of the conductive fine particles strongly adhered to the carrier surface was 35 mg / 100 g carrier.

Regarding the developers obtained in Examples 1 and 2 and the developers obtained in Comparative Examples 1 and 2, a copying machine (Able
Using a modified 1301 machine, manufactured by Fuji Xerox Co., Ltd., 20
000 sheets were continuously copied, and the degree of initial fog after 24 hours was evaluated. The evaluation results are shown in Table 1. The fog in Table 1 is 5 from G1 (good) to G5 (bad).
It was determined by comparison with a sample of stages, G1 indicates no fog, G4 indicates high fog, and G5 indicates extremely fog.

[0023]

[Table 1] As is clear from Table 1, the developers of Examples 1 and 2 have an excellent effect on fog at the initial stage of copying.

Next, specific conditions will be shown when the electrostatic image developer of the present invention is used in the multicolor image forming apparatus shown in FIG. In carrying out the present invention, a commercially available black developer (a toner for FX5039 manufactured by Fuji Xerox Co., Ltd.) is supplied as a developer to the first developing device, and the developer described in Example 1 is supplied to the second developing device. It was supplied to perform color image recording. First, the surface of the photosensitive drum having a photosensitive layer made of an organic photoconductive material is uniformly charged by the charger 1 so that the potential of the non-exposed portion is −1000 V, and then the first exposure device 3
Reverse exposure is carried out by the semiconductor laser light from the above, and the potential of exposed portion is −400 V and the potential of unexposed portion is −1 on the surface of the photosensitive drum.
A first electrostatic latent image of 000V was formed. Then, -7
A bias voltage of 00 V was applied, and development was performed by the first developing device 4 to form a black first toner image. continue,
Positive image exposure is performed by the second exposure device 5, and the exposure unit-20
An electrostatic latent image of 0 V and an unexposed portion of -900 V was formed, and the development bias voltage was set to -400 V for development by the second developing device 6 to form a blue toner image. As a result, two color toner images of blue and black were formed on the photosensitive drum. This toner image is transferred onto the recording paper 12 and the charging device 8
And transferred by a suitable fixing means (not shown). The photoconductor drum that passed through the transfer portion was cleaned by a static eliminator, a cleaner and a static eliminator lamp for reuse. This operation was repeated 5,000 times. From the beginning, clear two-color images free from fog, mixed color fog, and image distortion could be obtained. In addition, the developer of the present invention has a sharp charge distribution, and the presence of a toner having an opposite polarity was not seen.

[0025]

INDUSTRIAL APPLICABILITY The electrophotographic developer of the present invention has an improved ability to maintain the charge amount and is suitable for developing an electrostatic latent image having a low potential contrast of about 100 to 400V.
Therefore, the electrophotographic developer of the present invention is a multicolor image forming method using a one-pass multicolor development method in which development and transfer are repeated twice or more during one rotation of the photosensitive drum to obtain toner images of two or more colors. When used in, it is possible to stably obtain a good multicolor image for a long period of time. In particular, in the multi-color image forming method using the one-pass multi-color developing method, when used as a developer in the second development, the magnetic brush is soft, so that there is an advantage that color mixture fog and image disturbance can be prevented. .

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus used in the present invention.

[Explanation of symbols]

1 ... Photosensitive drum, 2 ... Charging device, 3 ... First exposure device, 4 ...
1st developing device, 5 ... 2nd exposure device, 6 ... 2nd developing device, 7 ... Pre-transfer charging device, 8 ... Transfer charging device, 9 ... Static eliminator, 10 ... Cleaner, 11 ... Static elimination lamp, 12 ... Recording paper .

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G03G 15/01 J G03G 9/10 (72) Inventor Suiko Sakai 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture Fuji Zero (72) Inventor Eimi Takahashi 1600 Takematsu, Minamiashigara City, Kanagawa Fuji Xerox Co., Ltd.

Claims (2)

[Claims] 1. A developer for electrophotography comprising a mixture of a magnetic powder-dispersed carrier and toner particles to which inorganic oxide fine particles are externally added, wherein conductive particles are externally added to the magnetic powder-dispersed carrier, An electrophotographic developer, characterized in that 100 mg or more of the conductive fine particles are strongly adhered to the carrier with respect to 100 g of the carrier. 2. The electrophotographic image forming apparatus according to claim 1, wherein at least one of the developing devices is a multicolor image forming method having a step of developing the electrostatic latent image formed on the photoconductor with a plurality of developing devices. A multicolor image forming method characterized by using a developer.