JPH0140347B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic recording device, and particularly to two
The present invention relates to a recording device capable of color recording.

Color electrophotographic devices have been developed that copy multicolor originals in natural colors. However, this requires separating the colors of the original into three primary colors and exposing and developing the photoreceptor at least three times, making the apparatus complicated and expensive. Furthermore, documents used for office purposes are rarely recorded in natural colors, and in many cases recording in two colors (for example, red and black) is sufficient.

FIG. 1 shows the configuration of a two-color recording device previously proposed by the present inventors. Further, FIG. 2 shows the potential state. First, the photoreceptor S of the rotating drum D is uniformly charged by the charger _C1 , and the potential is set to V _S.
(Figure 2a). The polarity of charging is positive if the photoreceptor S is a P-type semiconductor, and negative if it is an N-type semiconductor. Next, a form document _M1 such as a positive image such as a crease line is exposed in the first exposure section _P1 ,
The potential of the exposed part of the photoreceptor S is as shown in Fig. 2b.
A latent image is formed that is about 1/2 of V _S (indicated by V _L ). Next, positive development is performed using a two-component toner of A color having a negative charge. At this time, power supply B ₁ is connected to developer G ₁ .
When the applied bias voltage V _B1 is set to a potential slightly higher than V _L , the negative toner of color A adheres to the positively exposed unexposed area R ₁ as shown in FIG. 2c. Furthermore, when the second exposure section P ₂ exposes print data such as negative images of characters in the margins of the form document M ₁ to the document M ₂ , the potential V _LL of the exposure section R ₂ becomes approximately 0V, and the second A latent image as shown in FIG. 2d is formed. The document M ₂ also includes writing of an image using modulated laser light or the like. Next, it has a positive charge, B
Perform reversal development using two-component toner. At this time, if the bias voltage V _B2 applied to the developing device G ₂ is set to a potential slightly lower than V _L , the positive toner of B color will adhere to the exposed area R ₂ of the negative exposure, as shown in FIG. Two color toner images with different polarities are formed. Thereafter, the polarity of the toner is adjusted to be positive or negative by the pre-charger _C2 , and the toner image is further transferred onto the recording paper K by the transfer device T. Next, as in the normal electrophotographic process, the toner image is fixed and a static eliminator is installed.
C ₃ , static elimination by the static elimination lamp L, and cleaning process by the cleaner F, and one process is completed. This method made it possible to perform two-color form overlay recording, which was the initial goal.
The density of a color image may not always be said to be sufficiently uniform. This is because, according to research conducted by the present inventors, two-color toner images are not transferred uniformly.

The reason for this will be discussed below. Figure 3 shows the toner specific charge Q/m (Q: charge amount of one toner particle, m: charge amount of one toner particle, mass)
This shows the change in When positive pre-charging is applied, the specific charge of negative toner of color A is -18μC/g.
It can be changed up to about 18μC/g. Also, the specific charge of B color positive toner is from 19μC/g.
It will be about 27μC/g. By applying positive pre-charging in this manner, the polarity of both toners can be made positive, but the specific charge values of both toners are not the same. For this reason, the transfer efficiency of both toners is not the same, and the positive toner (B color) can achieve a transfer efficiency of about 80%, but the negative toner (A color) should have a transfer efficiency of 60%.
Only a moderate transfer efficiency can be obtained.

This is because in the conventional method described above, in order to balance the recording densities of both toner images, attention is paid to the developing process, and toners whose specific charges are almost the same in absolute value are often used. Further, when the pre-charging amount is further increased, the specific charges of positive and negative toners become equal in areas where the toner specific charges are large. However, according to research conducted by the present inventors, when the toner specific charge exceeds 40 μC/g, the electrostatic force between the toner and the recording medium becomes strong, making transfer difficult, and recording density decreases. For example, with a toner specific charge of 50 μC/g, a transfer efficiency of only 30% can be obtained.
Therefore, the specific charge of the toner must be 40 μC/g or less.

In view of the above-mentioned conventional problems, an object of the present invention is to
It is an object of the present invention to provide a recording device capable of obtaining a two-color toner image with uniform recording density on recording paper.

The purpose of this is to provide an image forming section that forms a two-color toner image of positive polarity toner and negative polarity toner on the recording medium, and to align the charging polarity of the two-color toner on the recording medium to one of the polarities. A recording device comprising: a charger; and a transfer device for transferring two-color toner with uniform polarity onto a recording medium, the positive polarity toner and negative polarity toner before being charged by the charger; The specific charge is such that the absolute value of the specific charge after charging by the charger is 40μC/
The absolute value of the specific charge before the charging of the toner whose charge polarity is reversed by charging by the charger is such that the specific charge becomes the same value in the range of 1.5 g or less. This is achieved by a recording apparatus characterized in that the absolute value of the specific charge before charging of the toner whose polarity is not reversed is set to a smaller value.

The present invention will be described in detail below. Figure 4 shows the change in toner specific charge when positive and negative toners are pre-charged, and shows the case where a positive toner (B color) with a toner specific charge of 19 μC/g is used. state

As shown in FIG. 4, when a negative toner with a specific charge of -11 μC/g, which is smaller than the specific charge value of -18 μC/g in the conventional method described above, is used, by applying positive precharging, the toner has a specific charge of is 23μC/
The specific charge becomes about g, which is quite similar to the specific charge of positive toner. If the specific charge of the negative toner is even smaller, the specific charges of the positive and negative toners will match more, but according to the research of the present inventors, if it is smaller than -5 μC/g, the electrostatic force between the toner and the carrier becomes weaker. The rotation of the developing device's magnetic roller causes toner to scatter from the developing device and cause back brand stains, so it cannot be lower than -5 μC/g. In this way, by making the absolute value of the specific charge of the toner whose polarity is reversed in the pre-charging process before charging smaller than the absolute value of the specific charge of the other toner, the specific charges of both toners can be made almost equal. It is possible,
The toner image can be transferred uniformly. As mentioned earlier, the toner specific charge is
If it exceeds 40 μC/g, transfer becomes difficult, so even if pre-charging is performed, it is necessary to use the specific charge at 40 μC/g or less.

Examples of the present invention will be described below. A charger _C1 is placed on a rotating drum D using Se-Te as the photoreceptor S.
After initial charging of 1200V, the first photosensitive area P ₁
Perform positive exposure on a form original and set the potential of the exposed area to 750V. Next, the developing bias voltage from the power source B ₁ is set to 750 V, and positive development is performed using negative polarity blue toner in the developing device G ₁ . Furthermore, the second exposure part P ₂
Negative exposure, which is print data, is performed at , the potential of the exposed area is set to approximately 0V, and the developing bias voltage from power supply P ₂ is set to 450V, and reversal development is performed using positive polarity black toner in developer G ₂ . At this time, the toner specific charge of black toner is 19 μC/g, and the toner specific charge of blue toner is −11 μC/g. Then, when a pre-charge of about 130nC/cm ² is applied with the pre-charger C ₂ ,
The toner specific charge of both toners is 27μC/g, respectively.
The result is 20 μC/g, which is a good match.
Therefore, when negative corona transfer was performed on both toners using the transfer device T, the transfer efficiency was 80% or more, and a good two-color recorded image could be obtained on the recording paper.

The present invention can also be applied to the case of developing a three-level latent image having positive and negative potentials as shown in FIG. 5, and the same effect can be obtained.

In FIG. 5, V ₁ and V ₂ are potential levels formed corresponding to the exposure pattern.

As is clear from the above description, the multicolor recording device according to the present invention makes the absolute value of the specific charge of the toner whose polarity is reversed before being charged smaller than the absolute value of the specific charge of the other toner. After recharging, the specific charges of both toners are made to have approximately the same value within a range that does not exceed 40 μC/g, so the transfer efficiency of both toners is approximately equal, resulting in a clear reproduced image. It has the advantage of being

[Brief explanation of drawings]

Figure 1 is a configuration diagram of the recording device, Figure 2 is an explanatory diagram of its operation, Figures 3 and 4 are relationship diagrams between toner specific charge and pre-charge amount, and Figure 5 shows a three-level latent image. It is a diagram. D...Rotating drum, S...Photoconductor, _C1 , _C2 ...
... Charger, C ₃ ... Static eliminator, P ₁ ... First photosensitive section,
P ₂ ... second photosensitive section, G ₁ ... first developing device, G ₂
...Second developing device, T...Transfer device.

Claims (1)

[Scope of Claims] 1. An image forming unit that forms a two-color toner image of positive polarity toner and negative polarity toner on a recording medium, and aligning the charge polarity of the two-color toner on the recording medium to one of the polarities. A recording device comprising: a charger for transferring the two-color toner having the same polarity onto a recording medium; The specific charge of the toner is such that the absolute value of the specific charge after charging by the charger has a similar value within a range of 40 μC/g or less, and the toner whose charge polarity is reversed by charging by the charger The absolute value of the specific charge before the charging of the toner is set to a smaller value than the absolute value of the specific charge before the charging of the toner whose charging polarity is not reversed by charging by the charger. Recording device.