JPH09218529A - Developer for electrostatic image and method for forming multicolor image - Google Patents

Abstract

(57) Abstract: [PROBLEMS] To provide a white developer for an electrostatic image in which the maintainability of the charge amount is improved when developing an electrostatic latent image of low potential contrast. Also provided is a multicolor image developing method for forming an excellent image by a one-pass multicolor developing method. A developer for an electrostatic charge image comprising toner particles composed of a binder resin and a white colorant, inorganic oxide fine particles, and a carrier provided with a resin coating layer, and comprising 60% by weight of the inorganic oxide. The above is strongly adhered to the surface of the toner particles.
In the multi-color image forming method of the one-pass multi-color development method, which includes the step of developing the electrostatic latent image developer with the electrostatic latent image on the latent image carrier, Supply to at least one of the developing devices accommodated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white developer for an electrostatic charge image for developing an electrostatic latent image having a low potential contrast of about 100 V to 400 V and a multicolor image forming method using the same.

[0002]

2. Description of the Related Art Conventionally, as a method of visualizing an electrostatic latent image formed on a photoconductive photosensitive member or the like by using a toner in an electrophotographic method, for example, US Pat. No. 2,874,063 has been used.
Magnetic brush method described in the specification, No. 2,61
The cascade method described in No. 8,552 and the powder cloud method described in No. 2,221,776 are known. Various methods have heretofore been proposed as methods for obtaining a color image by electrophotography. For example, a system of forming a color image on a transfer paper by repeating the steps of uniform charging, color separation image projection, dry development and transfer, and developing and transferring during one rotation of the photosensitive drum 2
There is known a one-pass multicolor color development system or the like in which toner images of two or more colors are obtained by repeating the process once or more times. As a developer used in the one-pass multicolor color developing 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, therefore, the developer is required to have a high charging speed and a good charge exchange property. In particular, when a toner having high conductivity such as titanium oxide is added to the toner, the charge is leaked so that the charge retention is insufficient and the charge amount is apt to decrease, resulting in toner scattering, fog, etc. The image quality defect is caused.

[0003]

Therefore, the present invention has been made in view of the above problems in the prior art. That is, an object of the present invention is to provide a white developer for an electrostatic charge image, in which the maintainability of the charge amount is improved when developing an electrostatic latent image having a low potential contrast. Another object of the present invention is to provide a multicolor image developing method for forming an excellent image by a one-pass multicolor developing method.

[0004]

The developer for electrostatic charge images of the present invention comprises toner particles composed of a binder resin and a white colorant, inorganic oxide fine particles, and a carrier provided with a resin coating layer. And 60% by weight or more of the inorganic oxide is strongly adhered to the surface of the toner particles.

The multicolor image forming method of the present invention is a one-pass multicolor image forming method having a step of developing an electrostatic latent image on a latent image carrier with a plurality of developers. The above-mentioned electrostatic latent image developer is supplied to at least one of the developing devices that contain the developer.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The toner particles, which are the constituent components of the developer for electrostatic images of the present invention, are composed mainly of a binder resin and a white colorant. The binder resin used is styrene, chlorostyrene, or the like. Mono-olefins such as styrenes, ethylene, propylene, butylene, isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate , Α-methylene aliphatic monocarboxylic acid esters such as dodecyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether, etc. Vinyl ethers; vinyl methyl ketone Examples thereof include homopolymers and copolymers of vinyl ketones such as vinyl hexyl ketone and vinyl isopropenyl ketone, and particularly representative binder resins include polystyrene, styrene-alkyl acrylate copolymer, and styrene- Examples thereof include an alkyl methacrylate copolymer, a styrene-acrylonitrile copolymer, a styrene-butadiene copolymer, a styrene-maleic anhydride copolymer, polyethylene and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide resin, modified rosin, paraffin wax and the like can be mentioned.

Examples of the white colorant include titanium oxide, silica, tin oxide, aluminum oxide, magnesium oxide and the like, and it is particularly preferable since titanium oxide has a great effect. As the titanium oxide, it is possible to use both rutile type and anatase type, but the anatase type has problems such as chalking, and is inferior to the rutile type in terms of concealability, so that the rutile type Those are preferable. Also, Al, Si, etc. added for the purpose of imparting light resistance to anatase type titanium,
There is no problem in use.

Although the content of the white colorant is appropriately set,
When titanium oxide is used, it is set in the range of 10% by weight to 40% by weight, preferably 20% by weight to 30% by weight, based on the toner particles. When the content of titanium oxide is 10% by weight or less, sufficient hiding property cannot be obtained and a thin image is formed. On the other hand, if the amount is more than 40% by weight, the fixing property is deteriorated, and particularly when the image is copied on a thick paper, the entire image comes off. In addition, particles having a particle diameter of 0.1 μm to 0.5 μm are generally preferably used. If it is smaller than 0.1 μm or larger than 0.5 μm, sufficient hiding property cannot be obtained.
There are two types of titanium oxide, one of which is based on the sulfuric acid method and the other of which is based on the chlorine method. The sulfuric acid method has a characteristic that it is slightly yellowed compared to the chlorine method.

In addition to the above components, the toner particles may further contain a charge control agent, a cleaning aid, and a fluidity accelerator, if necessary. The particle size of the toner particles is set to about 20 μm or less, preferably 3 to 20.
.mu.m, more preferably 5 to 15 .mu.m is used.

Inorganic oxide fine particles are added to the toner particles in the present invention, and 60% by weight or more of the added inorganic oxide fine particles must be strongly adhered to the surface of the toner particles. If the amount of the inorganic oxide fine particles strongly adhered to the surface of the toner particles is less than 60% by weight, mutual charging occurs with the added toner particles to generate a toner of opposite polarity, and dirt or fog occurs.

In the present invention, it is necessary that 60% by weight or more of the added inorganic oxide fine particles are strongly adhered to the toner surface for the following reason. For example, toner particles in which titanium oxide is internally added in an amount of 10% by weight or more have high conductivity and are hardly charged unless an external additive is added. However, when the relatively insulative inorganic oxide fine particles are externally added, the influence of the charge of the internally added titanium oxide is almost eliminated, and the chargeability of the inorganic oxide fine particles added to the outside is governed. By the way, when the inorganic oxide fine particles adhere weakly, the surface area increases and the charging level increases. When the inorganic oxide particles adhere strongly, the surface area decreases and the charging level decreases. When the toner which is relatively weakly adhered is used, the external additive is gradually strongly embedded by being stirred together with the carrier in the developing unit, and the mutual charge level difference between the additional toner and the additional toner is caused. It becomes charged and causes fog and dirt. Therefore, in order to suppress the mutual charging, 60% by weight or more of the inorganic oxide fine particles must strongly adhere to the surface of the toner particles.

The amount of the inorganic oxide fine particles strongly adhered to the surface of the toner particles in the present invention is a value determined as follows. That is, after dispersing toner particles in which fine particles of inorganic oxide are mixed in a solution containing a surfactant, an ultrasonic vibrator having an oscillation frequency of 20 kHz is dipped in the dispersion liquid and desorbed at an output of 60 W for 30 minutes. After that, the amount of the inorganic oxide fine particles adhering to the toner is measured, the ratio to the amount of the inorganic oxide fine particles in the toner particles before desorption is calculated, and the value is strongly adhered to the toner particle surface. The amount of the inorganic oxide fine particles is

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 inorganic oxide fine particles may have the surface thereof treated with an organic substance. As these fine particles, those having an average primary particle diameter in the range of 0.005 to 0.20 μm can be used.

On the other hand, as the carrier, one made of magnetic particles having a resin coating on the surface is used. As the magnetic particles, any known particles such as ferric tetroxide, γ-iron sesquioxide and various ferrites can be used. As the resin used for coating, styrene resin, epoxy resin, fluorine resin, silicone resin, etc. are preferably used. The thickness of the coating layer of the carrier is 0.005 to 5 μm, more preferably 0.05 to 0.
It is set in the range of 5 μm. The particle size of the carrier is generally set in the range of about 20 to 400 μm.

In the developer for electrostatic charge image of the present invention, the mixing ratio of the above-mentioned toner and carrier can be set arbitrarily, and it is generally used by mixing in a weight ratio of 1: 100 to 15: 100.

The electrostatic image developer of the present invention is suitable for developing an electrostatic latent image having a low potential contrast of 100 to 400V. Therefore, it can be used in a one-pass color developing system 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 to perform regular development or reversal development.

Subsequently, the second exposure device 5 irradiates light according to the image information corresponding to the second color to form an electrostatic latent image corresponding to the second color 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 be arbitrarily selected.

The first formed on the photosensitive layer of the photosensitive drum
The toner image and the second toner image are transferred onto 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). In addition, the photoconductor that has passed through the transfer portion has a static eliminator 9, a cleaner 10 and a static eliminator 1 for reuse.
1, the cleaning is performed.

Although the first and second exposure means are composed of a light illuminating means, a document scanning means and an image forming optical system as used in a normal copying machine, they can be optically modulated according to image information. A light writing device, for example, a laser writing device, a liquid crystal light valve including a uniform light source-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.

The above-mentioned white electrostatic image developer of the present invention is supplied to the above-mentioned first developing device or second developing device.
Other colored developers can be used in the developing device that does not supply the white developer.

[0023]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. In the following explanation, all "parts" are "weight parts"
Means Example 1 (Toner) Styrene-n-butyl acrylate (80:20) copolymer 100 parts (Tg: 63 ° C., Mw: 300,000) Titanium oxide (average particle diameter: 0.21 μm, trade name: CR60) , 30 parts Ishihara Sangyo Co., Ltd.) Charge control agent (Bontron E84, manufactured by Orient Chemical Co., Ltd.) 0.5 part Polypropylene (660P) 5.0 parts The above components are kneaded by a twin-screw kneader, and subsequently pulverized and classified. As a result, toner particles having a volume average particle diameter of 11 μm were obtained. To 100 parts of the toner particles, 1 part of silica fine particles having an average primary particle diameter of 0.016 μm was added and mixed with a Henschel mixer. At this time, the ratio of strongly adhered silica fine particles was 80%. (Carrier) Cu-Zn-Fe core (100 μm) 100 parts Fluorine-containing acrylic polymer (perfluorooctyl 2.0 parts ethyl methacrylate copolymer) The above components were mixed in a kneader and dried to obtain a volume average particle diameter. A carrier of 100 μm was obtained. (Developer) The above toner and carrier were mixed at a weight ratio of 10: 100 to prepare a developer.

Example 2 As a white colorant, titanium oxide fine particles (average particle size:
0.40 μm, product name: KR380, manufactured by Titanium Industry Co., Ltd.)
A developer was prepared in the same manner as in Example 1 except that was used. At this time, the ratio of strongly adhered silica fine particles is 7
It was 0%.

Example 3 As a white colorant, titanium oxide fine particles (average particle size:
0.15 μm, trade name: JA-4, manufactured by Teika Co., Ltd.) was used, and a developer was prepared in the same manner as in Example 1 except that the ratio of strongly adhered silica fine particles was 60%.

Comparative Example 1 A developer was prepared in the same manner as in Example 1 except that the ratio of strongly adhered silica fine particles was 40%.

Comparative Example 2 A developer was prepared in the same manner as in Example 2 except that the ratio of strongly adhered silica fine particles was 55%.

Comparative Example 3 A developer was prepared in the same manner as in Example 3, except that the ratio of strongly adhered silica fine particles was 20%.

(Test) The developers prepared in the above-mentioned examples and comparative examples were put in a copying machine (ABLE1301α, manufactured by Fuji Xerox Co., Ltd.) and copying operation was carried out to obtain initial and 5000.
The amount of electrification and fog at the time of sheet copying were evaluated. The results are shown in Table 1.

[0030]

[Table 1] The evaluation criteria for fogging in the table are from G1 (good) to G
It was decided by comparing it with a sample of 5 grades up to 5 (bad), and G2 is a level that does not bother you with fog but G
From 3 onward, the level is noticeable. As is clear from the above results, the developer of the example has an excellent effect on the fog as compared with the developer of the comparative example.

Next, in the image forming apparatus shown in FIG.
Specific conditions for using the white developer for an electrostatic image of the present invention will be described. In carrying out the present invention, the white developer described in Example 1 was supplied to the first developing device, and the commercially available red developer was supplied to the second developing device 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 unexposed portion becomes −1000 V, and then the semiconductor from the first exposure device 3 is charged. Reverse exposure is performed with laser light, and the exposed portion potential -4 on the surface of the photosensitive drum.
A first electrostatic latent image having a potential of 1000V at the non-exposed portion of 00V was formed. Then, a bias voltage of −700 V was applied, and development was performed by the first developing device 4 to form a white first toner image. Subsequently, a positive image exposure is performed by the second exposure device 5 to form an electrostatic latent image of -200V on the exposed portion and -900V on the non-exposed portion, and the developing bias voltage is set to -400V.
Then, development was performed by the second developing device 6 to form a red toner image. As a result, two color toner images of red and white were formed on the photosensitive drum. This toner image was transferred onto the black recording paper 12 by the transfer charger 8 and fixed by an appropriate 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 5000 times. From the beginning, clear white and red two-color images without fog, mixed color fog, and image distortion could be obtained. Further, the electrostatic charge image developer of the present invention has a sharp charge distribution, and the presence of a toner having an opposite polarity was not observed.

[0032]

EFFECT OF THE INVENTION Since the developer for electrostatic charge image of the present invention has the above-mentioned constitution, it is a white developer having an improved ability to maintain the charge amount when developing an electrostatic latent image of low potential contrast. Can be used. By using this developer for electrostatic charge images in the one-pass multicolor image forming method of the present invention, it is possible to form a multicolor image including white with excellent image quality.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus for carrying out 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 .

Claims (2)

[Claims] 1. An electrostatic charge image developer comprising toner particles composed of a binder resin and a white colorant, inorganic oxide fine particles, and a carrier provided with a resin coating layer, and 60% by weight of the inorganic oxide. The above is strongly adhered to the surface of the toner particles, and the developer for electrostatic charge images is characterized. 2. A multicolor image forming method comprising a step of developing an electrostatic latent image on a latent image carrier with a plurality of developers, wherein at least one of the developing devices containing the plurality of developers comprises: A multicolor image forming method comprising supplying the electrostatic latent image developer according to claim 1.