JPH0816792B2 - Image forming method - Google Patents

Description

The present invention relates to a novel image forming method having a magnetic brush cleaning mechanism.

[Prior Art] As one of electrophotographic copying methods, an electrostatic latent image is formed on a photoreceptor by charging and exposure, and the electrostatic latent image is developed by a magnetic brush method, and a developed toner image is formed on a plain paper or the like. The so-called PP that transfers the image to the transfer sheet of and then fixes it to obtain the final image
The C method is well known. As the photoconductor, a photoconductor such as Se, ZnO, CdS coated with Mylar, or an organic photoconductor such as polyvinylcarbazole or poly-N-vinylcarbazole is generally used.

In the copying system described above, a two-component type developer consisting of a magnetic carrier such as iron powder or ferrite powder and a colored resin powder called toner has been used as a developer, which constitutes such a developer. It is common to add silica to the surface of the toner to improve the fluidity. However, silica easily absorbs moisture in the air, and in an environment with high humidity, the amount of triboelectricity of the toner to which silica is attached decreases, resulting in toner scattering, image quality deterioration, increased background fog, and toner consumption. This caused problems such as an increase in quantity. Further, in an environment where the humidity is low, there is a problem that the electric charge is accumulated in the toner and the image density is lowered due to the increase of the triboelectric charge amount.

Therefore, it has been proposed that, in addition to silica, a conductive surface treatment agent such as titanium oxide be attached to the surface of the toner to prevent the accumulation of electric charges in the toner and suppress the change in image density due to environmental changes.

However, when titanium oxide is attached to the surface of the toner, the toner is likely to be fused to the surface of the photoconductor, and there is a problem of so-called filming phenomenon in which the toner is attached to the surface of the photoconductor.

In particular, a copying method in which development and cleaning are performed with the same magnetic brush, and one copy can be obtained while the photosensitive drum makes two rotations (hereinafter simply referred to as two-rotation one-copy method).
In the image forming apparatus described in Japanese Patent Application Laid-Open No. 64-84280, which simultaneously performs development and cleaning, toner having transfer failure remains on the photoconductor due to lack of a cleaning blade, and filming occurs on the photoconductor surface. It had the problem of being easy.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a novel image forming method having a magnetic brush cleaning mechanism without toner filming on the surface of a photoconductor. is there.

[Means for Solving the Problems] In the image forming method of the present invention, a magnetic brush is formed by magnetically adhering a developer consisting of toner and carrier to a photoconductor having an electrostatic latent image on its surface. In the method of disposing a developing roller, rubbing the surface of the photoconductor with the magnetic brush to visualize the electrostatic latent image, and cleaning the residual toner on the photoconductor, magnetic powder as the toner,
An image forming method is characterized in that a toner having a surface on which a composite external additive composed of silica and titanium oxide is adhered is used.

 Hereinafter, details of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram for explaining a two-rotation, one-copy type copying system which is an example of an image forming method having a magnetic brush cleaning mechanism.

In FIG. 1, the photosensitive drum 1 is rotating in the direction of the arrow in the figure, and the corona charger 2, the optical system 3, and the
A developing device 4, a corona transfer device 5, and a charge eliminating means 9 are arranged. First, the surface of the photoconductor drum 1 is corona charger 2
Are uniformly charged and then exposed by the optical system 3 to form an electrostatic latent image (not shown). Next, the electrostatic latent image is visualized by the developing device 4 to obtain a developed toner image 6. The transfer sheet 7 is superposed on the obtained toner image 6, and a transfer electric field is applied from the back surface of the transfer sheet 7 by the corona transfer device 5 to transfer the toner image 6 onto the transfer sheet 7, and then is fixed by the fixing device 8. The final image is obtained. After the transfer, the surface of the photosensitive drum 1 is rubbed and cleaned by the magnetic brush formed by the developing device 4 during the second rotation. In an ordinary copying machine, an AC corona charger and / or a discharging means 9 such as a lamp is provided between the corona transfer device 5 and the corona charger 2 in order to improve the cleaning property.

In the above copying system, as a result of various studies by the present inventors, by adhering silica and titanium oxide together with magnetic powder on the toner surface, toner filming on the photosensitive member can be obtained and good cleaning property can be obtained, and Environmental dependence has been eliminated. This result is considered to be because titanium oxide stabilizes the triboelectric charge amount of the toner, and the filming problem due to titanium oxide is caused by the magnetic powder scraping off the toner adhering to the drum.

 Next, the toner constituting the present invention will be described.

The toner of the present invention is prepared by mixing a binder resin, a colorant, a charge control agent, etc., melt-kneading, and pulverizing and classifying the toner to prepare a toner, which is a composite of the magnetic powder, silica, and titanium oxide described below. The external additive is agitated by a general agitator such as a turbine type agitator, a Henschel mixer, a super mixer and the like, so that the magnetic powder, silica and titanium oxide are attached to the surface of the toner.

As the binder resin, styrene resin, styrene-acrylic resin, styrene-butadiene resin, epoxy resin, polyester resin and the like can be used. Carbon black, aniline blue, chrome yellow, ultramarine blue, malachite green oxalate and the like can be used as the colorant. As the charge control agent, for example, a positively charged nigrosine dye or a negatively charged metal-containing dye can be used. Further, a low molecular weight polypropylene or the like as a fixing aid may be contained.

The magnetic powder of the present invention includes iron, cobalt, nickel,
Compounds such as manganese and zinc such as magnetite, maghemite, ferrite, etc., specifically EPT-500
(Made by Toda Kogyo), KBN-400 (made by Kanto Denka Kogyo), etc. Further, the shape of the magnetic powder is preferably an octahedron so that the photosensitive member is not damaged when the magnetic powder is separated from the toner. The amount of magnetic powder added to the surface of the toner is
To effectively remove the filming on the photoconductor and to prevent the magnetic powder from separating from the surface of the toner, the toner
The magnetic powder is preferably 0.01 to 3 parts by weight per 100 parts by weight.
Hydrophobic silica fine powder is suitable as the silica, and specific examples thereof include Aerosil R-972 (manufactured by Nippon Aerosil Co., Ltd.) and Taranox 500 (manufactured by Degussa). As the titanium oxide, hydrophobic titanium oxide such as MT-600BS (manufactured by Teika) is preferable.

As the carrier constituting the present invention, those generally used as a carrier for toner can be used, and specifically, an iron powder type carrier and a ferrite type carrier can both be used, and a polyester type carrier using these as a core substance. It is also possible to use a resin-coated carrier whose surface is coated with a resin, a fluorine-based resin, an acrylic resin, a silicone-based resin or the like, or a so-called resin carrier in which iron powder or ferrite is kneaded into a binder resin and granulated.

[Examples] Examples of the present invention will be described below.

Styrene-acrylic copolymer resin 85 parts by weight (SANYO Kasei Co., Ltd. TB-1000) Carbon black 10 parts by weight (Degussa PRINTEX-L) Chromium metal dye 2 parts by weight (Orient Chemical Co., Ltd. Bontron S-34) Polypropylene wax 3 parts by weight (Viscole 330P, manufactured by Sanyo Kasei Co., Ltd.) The above materials were melt-kneaded and then pulverized and classified to obtain an average particle size.
A toner of 10 μm was obtained. To 100 parts by weight of this toner, a composite external additive composed of magnetic powder, silica and titanium oxide as shown in Table 1 was mixed using a Henschel mixer and made to adhere to the toner surface. EPT-500 (made by Toda Kogyo Co., Ltd.) in Table 1 has an octahedral structure, and KBN-400 (made by Kanto Denka Kogyo Co., Ltd.) has a needle-shaped structure.

Next, 3 parts of each of the toners and 97 parts of non-coated ferrite carrier are mixed to prepare a developer, which is installed in a copying machine having a two-rotation, one-copy type copying system, and the temperature and humidity are low (10 ° C, 10% RH). ) And high temperature and high humidity (30 ° C., 85% RH) environment, copying evaluation was performed up to 10,000 sheets. The evaluation results after 10,000 sheets are shown in Table 2. The image densities shown in Table 2 were measured with a Macbeth reflection densitometer, and filming was performed by visually observing the photoconductor after copying 20,000 low-temperature low-humidity 10,000 sheets and high-temperature high-humidity 10,000 sheets. In addition, Table 2 shows the items comprehensively evaluated from the evaluation results of the image density and the filming.

As is clear from the second evaluation result, Examples 1 to 6 based on the image forming method of the present invention have a stable image density in a low temperature and low humidity environment and a high temperature and high humidity environment, and filming on the photoconductor is also possible. It did not occur. On the other hand, in Comparative Example 1, Comparative Example 2 and Comparative Example 6, the image density in the low temperature and low humidity environment was significantly reduced. Further, in Comparative Examples 3 to 5, filming on the photoconductor occurred, which was a problem in practical use.

EFFECTS OF THE INVENTION As described above, according to the present invention, the toner having the composite external additive composed of magnetic powder, silica and titanium oxide adhered to the surface thereof is used in the copying system having the magnetic brush cleaning mechanism. It is possible to provide a stable image density and an image forming method free from the problem of filming regardless of the above.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a two-rotation one-copy type copying system. 1 ... Photosensitive drum, 4 ... Developing device, 7 ... Transfer sheet, 8 ... Fixing device.

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Claims (3)

[Claims] 1. A developing roll having a magnetic brush formed by magnetically adhering a developer consisting of toner and a carrier is arranged facing a photoconductor having an electrostatic latent image on the surface thereof, and the magnetic brush is used for the photosensitization. In the method of rubbing the body surface to visualize the electrostatic latent image and cleaning the residual toner on the photoreceptor, a composite external additive composed of magnetic powder, silica and titanium oxide is attached to the surface as the toner. An image forming method, characterized in that the used toner is used. 2. The image forming method according to claim 1, wherein the magnetic powder has an octahedral structure. 3. The amount of the magnetic powder added is 0.01 to 3 parts by weight with respect to 100 parts by weight of the toner.
The image forming method described.