JPH0561306A - Two-color image forming method - Google Patents

Abstract

(57) [Summary] [Object] To provide an image forming method capable of stably forming a clear two-color image free from color mixture and color turbidity over a long period of time. A two-component developer containing a black toner is formed by forming a first electrostatic latent image on a photosensitive member 1 by a primary charger 2 and then forming a first electrostatic latent image on the photosensitive member 1. Reverse development is performed by the first developing device 4 used. Then, after being uniformly charged by the secondary charging device 5, a second electrostatic latent image is formed by the secondary exposure 6, and the reverse development is performed by the second developing device 7 using the one-component red toner. Transfer to toner image transfer paper. As the toner of the first developing device 4, the volume average particle diameter D _V is 7.40 μm and the number average particle diameter D _P is 6.9, in which the particle diameter distribution and the charge amount distribution are sharp.
2 μm (D _V / D _P = 1.07) black toner is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-color image forming method. More specifically, the first step of charging, exposing and developing an image carrier to form a first color toner image. In the state where the toner image of the first color is still carried, the second step of charging, exposing and developing is performed on the image carrying body to carry out the second step.
The present invention relates to an image forming method for forming a color toner image, and thereby forming a first color toner image and a second color toner image on the same image carrier.

[0002]

2. Description of the Related Art Conventionally, this type of image forming method basically comprises the following steps (a) to (f) (for example, JP-A-57-23952 and JP-A-58-58). 1
16553, JP-A-59-121349). (A) Primary charging: The surface of the image bearing member is uniformly charged with, for example, a negative polarity (see FIG. 6A). (B) Primary exposure: Image information corresponding to the toner image of the first color is exposed to form a first latent image (see FIG. 6B). (C) Primary development: The first latent image is reversely developed with a toner having a negative polarity to form a toner image of the first color (FIG. 6).
(See (c)). (D) Recharging: While the first color toner image is carried on the image carrier, the image carrier is recharged and the image carrier including the first color toner image is made to have a uniform potential (see FIG. )reference). (E) Secondary exposure: Image information corresponding to the second color toner image is exposed to form a second latent image (see FIG. 6E). (F) Secondary development: The second latent image is reversely developed with toner having the same polarity as the charge of the image carrier to form a second color toner image (see FIG. 6 (f)). When the above-mentioned series of steps are completed, 2
Toner images of colors are formed, and these toner images are transferred onto a transfer material such as transfer paper, and the toner images are fixed to form two-color images. In the second development (f), generally, a non-contact development method is used so as not to disturb the toner image of the first color on the image carrier. As a result, it is possible to obtain good 2
A color image is obtained.

[0003]

However, if such a two-color image is formed over a long period of time, the toner image of the second color gradually becomes clouded, resulting in a problem that the image quality is deteriorated. It was This is because the first-color toner image on the image carrier flies backward to the second-color developing device during the non-contact secondary development, and the first-color toner mixes into the second-color developing device. ..

The present invention has been made in view of the above problems, and an object thereof is an image capable of stably forming a clear two-color image free from color mixture and color turbidity for a long period of time. It is to provide a forming method.

[0005]

In order to achieve the above-mentioned object, a two-color image forming method according to a first aspect of the present invention is a method of forming a single image on an image carrier.
After the toner image of the first color is formed, the toner image of the second color is formed by the non-contact developing method, whereby the toner image of the first color and the toner image of the second color formed on the image carrier are simultaneously transferred to the transfer material. In the two-color image forming method, the ratio D _V / diameter D _P between the volume average particle diameter D _V and the number average particle diameter D _P of the first color toner is within the range of 1.00 or more and 1.20. Yes, and the volume average particle size D _V is 1.0 μm or more and 1
A two-color image forming method according to claim 2, characterized in that a toner within a range of 0.0 μm or less is used.
The two-color image forming method according to claim 1, wherein the absolute value of the charge amount per unit weight of the first-color toner on the image carrier before forming the second-color toner image is 10.0 μC / g or more and 80 or more. In the two-color image forming method according to claim 3, the toner image of the first color is formed on the image carrier, and thereafter the non-contact developing method is used. In a two-color image forming method, in which a second color toner image is formed and thereby the first color toner image and the second color toner image formed on the image carrier are simultaneously transferred to a transfer material,
The charge amount per unit weight of the first color toner on the image carrier before forming the second color toner image is at least twice the charge amount per unit weight of the second color toner on the developer carrier. According to the method for forming a two-color image of claim 4, after the toner image of the first color is formed on the image carrier, the toner image of the second color is formed by the non-contact developing method. In the two-color image forming method of simultaneously transferring the first-color toner image and the second-color toner image formed on the image carrier to the transfer material, the hydrophobic SiO in the first-color toner is
Than ₂ of content, and is characterized in that the 2/5 color hydrophobic SiO ₂ content ratio in the toner is greater.

[0006]

As described above, the cause of the color turbidity is that the toner image of the first color formed on the image carrier flies backward to the developing device of the second color. That is, the first color is, for example, the negatively charged toner, the potential difference between the second-color charging potential V _D2 and the second color developing bias _{V B2 (V D2 -V B2)} , the second color developing device from the image bearing member This is because the toner is attracted to the developer carrying member such as the developing roller and mixed in the toner of the first color in the developing device. As a result of detailed examination of this reverse flight phenomenon, the following facts (1) to (5) were found. (1) The toner having a relatively large particle size in the particle size distribution of the first color toner is more likely to fly backward. (2) The lower the charge amount of the toner of the first color is, the easier the backward flight is. (3) The smaller the adhesion of the first color toner to the image carrier, the easier it is for the reverse flight. (4) The larger the above potential difference (V _D2 −V _B2 ) is, the easier it is for reverse flight. (5) The smaller the gap between the image bearing member and the developer bearing member at the time of development with the second color toner, the easier the backward flight. Of these, the gap between the potential difference (V _D2 −V _B2 ) of (4) and the gap of (5) is a condition related to the image quality of the second color toner image alone, and therefore the selectable range is narrow. Therefore, the present invention is based on the facts (1) to (3) described above to prevent the reverse flight of the toner of the first color.

The two-color image forming method according to claim 1 or 2
As the color toner, the volume average particle diameter D _V is in the range of 1.0 μm or more and 10.0 μm or less, and the ratio of the volume average particle diameter D _V and the number average particle diameter D _P is D _V / diameter D. _P is 1.
It is in the range of 00 or more and 1.20, and therefore, the toner particle size distribution is relatively sharp and does not include toner having a relatively large particle size, and the charge amount distribution is also sharp and the toner amount is relatively low. In order to prevent the reverse flight of the toner of the first color. In addition, claim 3
In the two-color image forming method, the charge amount per unit weight of the toner of the first color on the image carrier before forming the toner image of the second color is the unit weight of the toner of the second color on the developer carrier. It should be more than twice the amount of charge per
The adhesion of the first color toner to the image carrier at the time of the second development is made relatively strong to prevent the reverse flight of the first color toner. Furthermore, the two-color image forming method of claim 4 is
Than the content of hydrophobic SiO ₂ in the toner of the color, to increase towards the second color hydrophobic SiO ₂ content ratio of the toner in,
As a result, the toner of the first color is less likely to fly than the toner of the second color, and the first color toner does not fly backward at a developing bias V _B2 for flying the toner of the second color during the second development. To do.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram of a copying machine capable of carrying out the two-color image forming method according to this embodiment. This copying machine uses a photoconductor 1 which is negatively charged and has photosensitivity. The primary charger 2 uniformly covers the photosensitive member 1 by about minus 8.
It is charged to 00 V (V _D1 ). Next, the primary exposure (laser beam) 3 corresponding to the black image is performed to optically attenuate the image portion potential to about −100 V (V _L1 ), thereby forming the first electrostatic latent image. The first electrostatic latent image is reversely developed by the first developing device 4 using black toner to form a black toner image on the photoconductor 1. The developing bias at this time is −600 V (V _B1 ), and the negatively charged black toner adheres to the image portion due to the potential difference (VL ₁ −V _B1 ) between this and the image portion potential. Further, the first developing device 4 forms a magnetic brush of a two-component developer composed of carrier and toner on the developing roller. Photoconductor 1 after this black toner development
The surface potential of the upper toner layer rises to about −300V, but it is insufficient to prevent color mixing, so the secondary charger 5 continues to uniformly set it to about −900V including the black toner developing area. Get charged. Then the second corresponding to the red image
Next exposure (laser beam) 6 is performed, and similarly, the potential of the image area is optically attenuated to approximately −120 V (V _L2 ) to form a second electrostatic latent image. This second electrostatic latent image is reversely developed by the second developing device 7 using red toner, and as a result, the second color toner image of the black toner image and the red toner image is obtained on the photoconductor 1. In the second developing device, the gap between the photoconductor 1 and the developing roller is set to about 150 μm, and the non-magnetic one-component developer (toner) charged with the negative polarity flies from the surface of the developing roller toward the surface of the photoconductor 1. Non-contact development is performed. This development bias is minus 750V
(V _B2 ), the potential difference between this and the image portion potential (V _L2 −
The red toner, which is negatively charged by V _B2 ), adheres to the image area. At this time, as described above, this potential difference (V _L2 −
The negatively charged toner on the surface layer of the toner image of the first color already formed on the photoconductor 1 by V _B2 ) is attracted to the second developing device 7 side. Next, for the second color toner image on the photoconductor 1, the pre-transfer charger 8 makes the charge amount of the second color toner image uniform, and the transfer paper on the transfer belt 9 whose back surface is charged by the transfer charger 10 is used. Make them adhere closely. As a result, the toner image of the second color on the photoconductor 1 is transferred by the electric field generated by the charged transfer belt 9, and the fixing device 11 heat-fixes and fixes the toner image on the transfer paper. On the other hand, the photoreceptor 1 after transfer is charged by the pre-cleaning charger 12 to make the charge polarity of the residual toner uniform again, and the surface of the photoreceptor 1 is cleaned by the cleaner 13. Further, the residual charges are photo-erased by the static eliminator 14 to initialize the photoconductor 1 and prepare for the next image formation.

A first embodiment of the present invention will be described.
As the first color toner, the volume average particle diameter D _V is 7.40 μ.
m, the number average particle diameter D _P is 6.92 μm (D _V / D _P = 1.
The negatively chargeable black toner manufactured by the dispersion polymerization method of No. 07) was used. This dispersion polymerization method is a method in which a polymer dispersant is dissolved in a hydrophilic organic solution, but the resulting polymer is swollen or almost dissolved by the hydrophilic organic solution. Resin particles (hereinafter referred to as resin particles A) are produced by adding and polymerizing one or two or more vinyl weights, and dispersing the resin particles A in an organic solvent that does not dissolve the resin particles A, Before or after the dispersion, the dye is dissolved to allow the dye to permeate the resin particles A, and thereafter the organic solvent is removed to produce a toner. And, as a carrier, the particle size is 10
A 0 μm ferrite particle coated with a silicone resin in a thickness of 1 μm was used, and the black toner was mixed with this carrier at a ratio of 3.0% by weight to form a developer.

As a result of investigating the above-mentioned reverse flight using this developer in the above copying machine, there is no back-flying toner at all, and the result of measuring the charge amount of the toner on the photoconductor 1 immediately before the second development. , Minus 43 μC / g. As is well known in the art, this charge amount is connected to an electrometer after the photoconductor 1 is exposed to light on its entire surface and sufficiently attenuated.
In addition, the suction device with a filter for capturing toner in the nozzle absorbs the toner on the photoconductor, and the ratio of the total current flowing at this time measured by the electrometer to the total weight of the toner adhering to the filter. I asked from. In addition, the reverse flight characteristics are
The amount of toner that flies back to the second developing device 7 when the image forming process was performed in the same manner without adding toner to the second developing device 7 was measured, and this toner amount was used as an evaluation value. As a result of forming a two-color image using this black developer, a clear image was obtained, and even after the same image formation was performed on 5,000 sheets, an image without color mixing and color turbidity was obtained.

Next, a second embodiment of the present invention will be described. This embodiment is different from the first embodiment in that the black toner has a volume average particle diameter D _V of 5.02 μm and a number average particle diameter D _P of 4.35 μm (D _V / D _P = 1.15). Only the point of using the negatively chargeable toner is used, and other points are the same as those of the first embodiment. Also in this embodiment, as a result of examining the backward flight characteristics, there is no backward flight toner, and the toner charge amount on the photoconductor 1 is −65 μC / g. Similarly, even after 5,000 sheets of two-color images were formed, an image without color mixture and color turbidity was obtained.

Next, a comparative example will be described. This comparative example is different from the first embodiment in that the black toner has a volume average particle diameter D _V of 12.57 μm and a number average particle diameter D _P of 7.75 μm (D _V / D _P = 1.62). Only the point of using the negatively chargeable toner is used, and other points are the same as those of the first embodiment. As a result of investigating the reverse flight characteristics, it was found that 0.1% by weight of the black toner on the photoconductor 1 flies backward. In addition, the charge amount of the toner on the photoconductor 1 at this time was −23 μC / g. Observation of this backward flying toner revealed that a large number of coarse toner particles having a toner diameter of about 20 μm were included. It is presumed that this coarse toner flew backward due to the low charge amount. Furthermore, as a result of continuously performing two-color image formation, a clear two-color image was obtained in the initial stage.
The red image portion gradually began to become turbid, and after 1,000 sheets, the brightness of the red image was remarkably reduced, and it was unusable for practical use.
The charge amount distribution of the developer of the first embodiment is shown in FIG.
In addition, the charge amount distribution of the developer of this comparative example is shown in FIG.
It shows in (b). As a measuring instrument of these charge amount distribution,
An E-SPART analyzer (trademark) manufactured by Hosokawa Micron was used. As can be seen from this figure, the distribution of the charge amount of the developer of the first embodiment is sharper. FIG. 3 is a characteristic diagram showing the relationship between the ratio D _V / D _P of the volume average particle diameter D _V and the number average particle diameter D _P and the amount of the backward flying toner. As can be seen from this figure, the above ratio D _V / D _P is 1.2.
If it is larger than the above value, reverse flight occurs unless the toner charge amount is very large. This is considered to be because when the ratio D _V / D _P is such a large value, the toner charge amount distribution spreads along with the toner particle size distribution, and low-charged toner is generated. Here, if the toner charge amount for preventing the reverse flight is made extremely large, a problem such as a decrease in image density due to a transfer failure may occur. Therefore, the above ratio D _V / D _P is 1.2
The following is desirable. Further, even if the ratio D _V / D _P is 1.2 or less, if the toner charge amount is very small, reverse flight occurs. This is because the toner having a lower charge amount is more likely to fly backward. Therefore, it is desirable to maintain a predetermined toner charge amount.

Next, a third embodiment of the present invention will be described. In the non-contact development, there is a close relation between the charge amount of the toner and the developing characteristic (toner flying characteristic). Figure 4
FIG. 6 is a characteristic diagram showing the relationship between the toner charge amount and the developing characteristic, with the horizontal axis representing the development potential difference and the vertical axis representing the developing toner amount, with the toner charge amount as a parameter. This relationship is affected by the physical property of the toner other than the gap between the photoconductor 1 and the developing roller and the charge amount, but has the following tendency. That is, when the charge amount is low, the development starts with a small development potential difference, the inclination is large, and the development amount is large.
On the contrary, when the charge amount is high, development (flying) does not start unless the difference in development potential is large, the inclination is small, and the development amount is small. The reverse flight characteristics also tend to be similar to this. Therefore, in this embodiment, the charge amount of the developer of the first color is minus 23 μC / g, and the photoconductor 1 immediately before the second development is used.
A black toner having an electric charge of −37 μC / g was used, and a red toner having an electric charge of −12 μC / g on the developing roller was used as the second color toner. Here, the ratio of the charging amount of the black toner on the photosensitive drum 1 immediately before the second development and the charging amount of the red toner on the developing roller is
(-37) / (-12) = 3.08. Then, the gap between the developing roller of the second developing device and the photosensitive drum 1 is set to 1
When a two-color image was formed by setting the thickness to 80 μm, a good image was obtained for a long period of time.

Next, a fourth embodiment will be described. When the hydrophobic SiO ₂ is added to the toner, the hydrophobic SiO ₂
There is also a close relationship between the amount (% by weight) and the developing characteristics (toner flying characteristics). In FIG. 5, the horizontal axis represents the development potential difference, and the vertical axis represents the amount of developing toner.
Hydrophobic Si using the amount of iO ₂ (wt%) as a parameter
FIG. 4 is a characteristic diagram showing the relationship between the amount of O ₂ and development characteristics. As can be seen from this characteristic diagram, the greater the amount of hydrophobic SiO ₂ , the greater the amount of development and the more likely the toner is to fly.
The reverse flight characteristics also tend to be similar to this. Therefore, in the present embodiment, the hydrophobic SiO is applied to the second color toner so that the second color toner is more likely to fly than the first color toner. _{2 The} amount of addition was increased. Specifically, a black toner to which 0.5 wt% of hydrophobic SiO ₂ (R-972 (trademark, manufactured by Nippon Aerosil Co., Ltd.) is added is used as the first color toner, and the same hydrophobic SiO is used as the second color toner. A red toner containing 1.0% by weight of ₂ was used. The charge amount at this time is about minus 15 μC / both.
It was g. When the gap between the developing roller of the second developing device and the photosensitive drum 1 was set to 200 μm and a two-color image was formed, a good image was obtained for a long period of time.

[0015]

According to the two-color image forming method of the first or second aspect, the toner of the first color does not include a toner having a relatively sharp toner particle size distribution and a relatively large particle size, and a charge amount. A predetermined toner that has a sharp distribution and does not generate a toner with a relatively low charge amount is used to prevent the reverse flight of the toner of the first color. Therefore, a clear two-color image free from color mixture and color turbidity for a long period of time. Can be obtained. Further, since a predetermined toner having a sharp charge distribution and a toner having a relatively low charge amount is not used as the first color toner, a sharp image without toner dust can be obtained. The two-color image forming method according to claim 3, wherein the charge amount per unit weight of the toner of the first color on the image carrier before forming the toner image of the second color is the developer carrier of the toner of the second color. The amount of electric charge per unit weight is set to be twice or more, so that the adhesion of the toner of the first color to the image carrier at the time of the second development is made relatively strong and the reverse of the toner of the first color. Since flying is prevented, a clear two-color image free from color mixture and color turbidity can be obtained for a long period of time. Further, two-color image forming method according to claim 4, than hydrophobic SiO ₂ content ratio of the toner of the first color, increasing towards the second color hydrophobic SiO ₂ of content in the toner, thereby, By making the first color toner less likely to fly than the second color toner,
Since the toner of the first color is prevented from flying backward by the developing bias V _B2 for flying the toner of the color, it is possible to obtain a clear two-color image free from color mixture and color turbidity for a long period of time.

[Brief description of drawings]

FIG. 1 is a front view showing a schematic configuration of an electrophotographic copying machine that carries out a two-color image forming method according to an embodiment.

2A is a distribution diagram showing a charge amount distribution of a toner used in the first embodiment, and FIG. 2B is a distribution diagram showing a charge amount distribution of a toner used in a comparative example.

[Fig. 3] Ratio D _{V of} volume average particle diameter D _V and number average particle diameter D _P
FIG. 6 is a characteristic diagram showing the relationship between / D _P and the amount of backward flying toner.

FIG. 4 is a characteristic diagram showing a relationship between a toner charge amount and developing characteristics.

FIG. 5 is a characteristic diagram showing the relationship between the amount of hydrophobic SiO ₂ and developing characteristics.

FIG. 6 is a process diagram showing a basic process of a two-color image forming method.

[Explanation of symbols]

1 photoconductor, 2 charger 3 primary exposure laser beam, 4 first
Developing device 5 Secondary charger, 6 2nd
Next exposure laser beam 7 Second developing device, 8 Pre-transfer charger 9 Transfer belt, 10 Transfer charger 11 Fixer, 12 Pre-cleaning charger 13 Cleaning device, 14 Static eliminator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location G03G 15/08 7810-2H

Claims (4)

[Claims] 1. A first color toner image is formed on an image bearing member, and then a second color toner image is formed by a non-contact developing method. In a two-color image forming method in which a toner image of a color is transferred onto a transfer material at the same time, the ratio D _V / diameter D _P of the volume average particle diameter D _V and the number average particle diameter D _P is 1 as the toner of the first color. 0.000 or more and 1.20
And the volume average particle diameter D _V is 1.0 μm.
A two-color image forming apparatus, characterized in that a toner within the range of 10.0 μm or more is used. 2. The absolute value of the charge amount per unit weight of the toner of the first color on the image carrier before forming the toner image of the second color is 10.0 μC / g or more and 80.0 μC / g or less. The two-color image forming apparatus according to claim 1, wherein the two-color image forming apparatus is within the range. 3. A first-color toner image is formed on the image carrier, and then a second-color toner image is formed by a non-contact developing method. In the two-color image forming method of simultaneously transferring the toner image of the second color onto the transfer material, the charge amount per unit weight of the toner of the first color on the image carrier before forming the toner image of the second color is the second color. A two-color image forming apparatus, characterized in that the charge amount of the toner per unit weight on the developer carrying member is twice or more. 4. A first color toner image is formed on the image bearing member, and then a second color toner image is formed by a non-contact developing method. in two-color image forming method for transferring simultaneously the transfer material and a toner image of color, from the hydrophobic SiO ₂ content ratio of the toner of the first color, the 2/5 color hydrophobic SiO ₂ content ratio of the toner in A two-color image forming method characterized by being large.