JPS63294579A - Two-color image forming method - Google Patents

Abstract

PURPOSE:To prevent generation of a mixed color fogging by intrusion of different toners by determining the average grain size of the 2nd toner at the size larger than the average grain size of the 1st toner. CONSTITUTION:The average grain size of the 2nd toner is determined at the size larger than the average grain size of the 1st toner. Namely, the color mixed fogging is generated in the following manner: The 1st toner which intrudes into the 2nd toner and is charged to the polarity reverse from the polarity of the 2nd toner by the interaction with the 2nd toner forms the nucleus to cause the 2nd toner to be electrostatically attached on the surface of the 1st toner and these toners migrate integrally to a photosensitive body. The force to generate this migration depends on the absolute charge quantity of the 1st toner. The grain size of the 1st toner is, therefore, made smaller and the grain size of the 2nd toner is made larger. Then, even if the 1st toner is charged to the reverse polarity, the electrostatic charge quantity thereof decreases relatively with the 2nd toner. If the 2nd toner is electrostatically attracted thereto, the charge quantity is conversely affected by the electrostatic charge quantity of the 2nd toner and the migration of the toners to the photosensitive is forbidden. The mixed color fogging is thereby prevented.

Description

[Detailed description of the invention]

Industrial Application Field The present invention relates to a two-color image forming method in electrophotographic copying machines and printers, more specifically, to an image forming method using a two-component dry developer, in which color mixing fog occurs due to the contamination of different toners. This provides a method to prevent this. Traditionally, as a two-color phenomenon method, a first latent image is first developed using a first toner, and then a second latent image is developed using a second toner charged to the same polarity as the first toner. Two-color development methods are known. As shown in FIG. 1, this developing method performs the following steps: charging, first exposure, first development, second exposure, second development, and transfer, while one photoreceptor drum rotates once in the direction of the arrow. It is something to do. That is, the developing device includes a main charger (
11), first exposure device (12), second developing device (13L
Such a developing device is provided with a second charger (14), a second exposure device (15), a second developing device (16), a transfer charger (17), a cleaning blade (1B), an eraser lamp (19), etc. In order to form a two-color image using the above method, development is performed according to steps (a) to (g) of the conceptual diagram of the two-color image forming process shown in FIG. (a) The surface of the photoreceptor drum (10) is heated by the main charger (11). is charged with electricity. The normal range of voltage V0 is
For example, it is +500 to +100 OV. (b) Next, perform exposure by irradiating a laser beam etc.
Form a latent image. (c) Next, a first developing device performs reversal development by applying a bias voltage Va using a two-component magnetic developer containing a color toner and a carrier. (d) then using the second subcharger (14);
Make the surface potential uniform. (e) Further, a second exposure is performed using a laser beam or the like to form a second latent image. (f) Using a two-component magnetic developer containing black toner and carrier, a bias voltage VB is applied and reversal development is performed by the second developing device. (g) Transfer the finally obtained two-color image to a transfer charger (1
7), the image is transferred and fixed onto a recording medium such as paper. Such a developing method has the disadvantage that the toner used in the first development gradually mixes into the developer used in the second development, resulting in color turbidity as the number of copies increases. These drawbacks are particularly noticeable in magnetic brush development. That is, in this method, the first toner image previously formed on the surface of the photoreceptor by the first development is scraped off by the ears of the magnetic brush during the second development, and a portion of the first toner is transferred to the second development.
It gets mixed into the developer, causing color mixture and color mixture fog. Such color mixing occurs when the first toner and the second toner have complete compatibility (they are at the same position on the charging series, and the charging polarity and charge amount do not change due to interaction). Since the toner and the second toner remain charged to the same polarity and are not distinguished, and are developed equally to the second latent image, the first toner mixes into the image formed by the second toner, resulting in color mixture. On the other hand, mixed color fog occurs when the first toner and the second toner are completely incompatible (the positions on the charging series are far apart, and the charging polarity and the amount of charged charge change due to interaction). That is, the second toner is electrostatically attracted to the surface of the mixed first toner as a nucleus, and the second toner is attached to the non-image area of the photoreceptor as a whole. The first toner is charged to the opposite polarity due to frictional charging with the second toner and is not transferred, and only the second toner is transferred to the background of the transfer paper, causing fog. In order to prevent color mixing or color mixing fog that may occur during the second development, the surface potential of the photoreceptor drum before the second exposure is increased to increase the electrostatic attraction force of the first toner to the photoreceptor surface. A method has also been proposed for preventing the first toner from being scraped off by the ears of a magnetic brush during the second development. Problems to be Solved by the Invention However, even in this method, as the number of copies increases, the first toner gradually accumulates in the second developer, making it difficult to avoid color mixing or color mixing fog. An object of the present invention is to provide a two-color developing method that does not cause color mixing, color mixing fog, or defective color change during transfer even when two types of toner are mixed in a developing device. Means for solving the problem, that is, the present invention develops a first electrostatic latent image formed on the surface of an electrophotographic photoreceptor with a first toner, and further develops a second electrostatic latent image formed in an overlapping manner. In a two-color image forming method in which a latent image is developed with a second toner and then the toner image on the photoreceptor is transferred onto an image carrier, the average particle size of the second toner is the same as the average particle size of the first toner. The present invention provides an image forming method characterized by a larger image size. In the method of the present invention, an excellent two-color image can be formed using a conventional two-color development apparatus as shown in FIG. 1 and based on the same process as the conventional two-color development. The average particle size of the second toner used in the method of the present invention is larger than the average particle size of the first toner. The first toner preferably has an average particle size of 5 to 15 microns, and the second toner preferably has an average particle size of 6 to 16 microns. The first toner and the second toner have an average particle size of the first toner <
The average particle size of the second toner is adjusted. As for other components used in the first toner and the second toner, such as a binder resin, a colorant, and a charge control agent, any of those conventionally used as components of toners can be suitably used. That is, examples of the binder resin include conventionally known resins such as polystyrene, styrene-acrylic copolymers, polyesters, epoxy resins, polyolefin resins such as polyethylene and polypropylene, polyamide resins, maleic acid resins, and modified resins thereof. These may be used alone or in combination of two or more. Note that it is preferable to select binder resins for the first toner and the second toner that are close to each other on the charging series from those with the same charging polarity, and the first toner and the second toner are semi-compatible. have That is, the charging property of the first toner is set to change to a slightly opposite polarity side than that of the second toner due to the interaction between the first toner and the second toner. In this way, the amount of electrical charge (q) of the first toner mixed in the second developer is set to q=O1
Alternatively, the polarity may be slightly shifted to the opposite polarity side, thereby making it possible to separate the first toner mixed into the second toner to the outside of the system. Therefore,
The first toner (of q''=rO), which has lost its charge amount, turns into powder smoke and scatters outside the second developing device, and can be removed by air suction. The first toner (
Since q<0 or q>0) remains on the surface of the photoreceptor without being transferred, it is collected by a cleaner. In this way, since the first toner that comes into contact with the second toner does not adhere to the electrostatic latent image (image area) together with the second toner, it is possible to suppress the occurrence of color mixture. Further, as the coloring agent, carbon black, phthalocyanine-based organic pigments, xanthine-based organic pigments, dyes, etc. are used. Other known additives such as a charge control agent, a fluidizing agent, or a female molding agent may be added if necessary. The first and second toners used in the method of the present invention are produced by mixing the above-mentioned components and processing in a conventional manner. . It is assumed that the method of the present invention prevents the color mixture fog for the following reason. That is,
Mixed color fog occurs when the first toner mixes into the second toner and is charged to the opposite polarity to the second toner due to interaction with the second toner, which becomes a nucleus and the second toner is electrostatically attracted to the surface of the first toner and integrated. The toner then transfers to the photoreceptor, but the force that causes this transfer is thought to depend on the absolute amount of charge of the first toner. Therefore, by reducing the particle size of the first toner and increasing the particle size of the second toner, even if the first toner is charged to the opposite polarity, the amount of charge will be smaller relative to the second toner. It is thought that when the second toner is electrostatically attracted, it is adversely affected by the charge amount of the second toner, making it difficult to transfer to the photoreceptor, thereby preventing color mixture fog. EXAMPLES Next, the present invention will be explained in more detail with reference to Examples. Manufacturing example

[Toner adjustment]

(a) Black toner I Composition Heavy! ! Part polyester resin 100 (acid value: 2-15) Styrene amino acrylic resin 3 (amine value:
l 50-200 KOH-mg/g) Carbon black MA#8 3.5 (manufactured by Mitsubishi Chemical Industries, Ltd.) Manufactured by Orient Chemical Industries, Ltd.) After thoroughly mixing the above components in a mixer, twin-screw extrusion was performed. The mixture was melted and kneaded using a machine. After cooling, it is finely pulverized using a jet mill, and then classified using a rotary wind classifier to obtain an average particle size of 14.
A black toner I with 2μ debris was obtained. (b) Black toner ■ Treated in the same manner as the above toner (1), with an average particle size of 12
．． A black toner ■ with a weight of 2μ was obtained. (c) Color toner ■ (red) Composition 1 part polyester resin 100 (acid value: 15-22) Lakerad C (manufactured by Dainippon Ink) 5 The above acid content was treated in the same manner as in the case of toner (I). Average particle size 13
．． A color toner (■) with a shoulder size of 1μ was obtained. (d) Color Toner ■ (Blue) Same as Color Toner I except that Lake Rad C was replaced with Cu-phthalocyanine, average particle size! A color toner (■) with a shoulder size of 3.0μ was obtained. (e) Color Toner ■ (Green) Same as Color Toner R except that Lake Rad C was replaced with Cu-phthalocyanine green, with an average particle size of 13.
1 μl of color toner ■ was obtained.

[Career adjustment]

Magnetic powder (Mabico Black BL-500200 manufactured by Titanium Industries) Carbon black M A # 100 4 (
(manufactured by Mitsubishi Chemical Industries, Ltd.) The above components were thoroughly mixed in a ball mill and melt-kneaded using a three-roll mill. After cooling, it is crushed and classified to an average particle size of 35.
A binder-type microcarrier with μ shoulders was obtained. Example 1 Developer using black toner (■) (average particle size 14.2 μJI) (6 parts by weight of black toner (I), Microcarrier 94
parts by weight) in the second developing device (16 parts by weight) of the two-color image forming device.
), on the other hand, a developer using color toner (■) (
6 parts by weight of color toner (■) and 94 parts by weight of microcarrier) were added to the first developing device (13), and 5,000 pages of two-color image formation was performed. No color mixing fog was observed in the obtained image. Examples 2 and 3 Images were formed in the same manner as in Example 1, using color toners (II) and (II[) instead of color toner (I). Similar to Example 1, no color mixing fog was observed in the obtained image. Comparative Examples 1 to 3 Black toner (■) (average particle size 12.2 μm) was used as the black toner, and the color toner (1) was used as the color toner.
An image was formed in the same manner as in Example 1 using ~(I[[). Clear color mixing fog was observed in the obtained image. Effects of the Invention According to the method of the present invention, no color mixing fog occurred even after long-term image formation, and good images were stably obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a two-color developing method, and FIG. 2 is a conceptual diagram showing a two-color image forming process.

Claims (1)

[Claims] (1) A first electrostatic latent image formed on the surface of an electrophotographic photoreceptor is developed with a first toner, and a second
In a two-color image forming method in which an electrostatic latent image is developed with a second toner, and then the toner image on the photoreceptor is transferred onto an image carrier, the average particle size of the second toner is equal to that of the first toner. An image forming method characterized in that the particle size is larger than the average particle size.