JPS6344222B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-stylus electrostatic recording method used as a multi-color recording device such as a facsimile printer.

Conventional methods for obtaining multicolor recorded images with electrostatic recording involve forming charge images of different polarities on a recording medium such as electrostatic recording paper, and using toner resins of different colors that adhere only to the charge images of each polarity. It is known to develop and fix this to obtain a two-color image.

First, the structure of the multi-stylus electrostatic recording head and its charge image forming method will be briefly explained. In FIG. 1, 1 is a multi-stylus electrostatic recording head of the same plane control type, 2 is a recording electrode, and 3 is a control electrode. FIG. 2 shows a recording control block diagram of the electrostatic recording head 1 of FIG. Recording electrode needle 2
As shown in the figure, the electrodes are divided into a plurality of needles, and are generally grouped into two groups, A and B, and the control electrodes 3 are arranged astride each recording electrode needle group. 4,5 more
6 is a voltage amplification circuit that generates a high voltage in accordance with a recording signal to each recording electrode needle, and 6 is a voltage amplification circuit that generates a high voltage in accordance with a control signal. The charge image is formed by matching the pulse voltages applied to the recording electrode 2 and the control electrode 3, and applying a pulse voltage of about -300 V to multiple recording electrode needles simultaneously according to the recording signal for each group of recording electrode needles. Furthermore, a pulse voltage of approximately +300 V is applied to the control electrode of a predetermined portion to be recorded at the same time, and is formed on the recording medium 7 such as electrostatic recording paper. In this case, the charge image formed is of negative polarity, and the positive charge image is obtained by applying to the recording electrode 2 and the control electrode 3 a pulse voltage corresponding to the opposite polarity when forming the negative charge image. The pulse voltages for forming charge images of each polarity are shown in FIG. 3, with FIG. 3a showing negative polarity and FIG. 3b showing positive polarity.
Note that Vcn and -Vcp are positive and negative control electrode voltages, respectively, and -Vnn and Vnp are negative and positive recording electrode voltages, respectively. As shown in Fig. 4, scanning to obtain positive and negative charge images to obtain a two-color image is as follows.
A recording scan is performed in synchronization with the input recording signal _S1 , and the recording period signal _S2 is separated into two scanning stages: a scan for forming a positive charge image and a scan for forming a negative charge image. During this two-step scanning, the two scanning lines are generally arranged to overlap on the recording medium.

A two-color electrostatic recording device was manufactured using the recording scanning method described above, and recording experiments were conducted, and the following results were obtained.

When a recording scan is performed and a bipolar charge image is developed with black toner, the optical reflection density of this image is lower than that of a recorded image of a negative polarity, as shown in Figure 5. . This is because the discharge mechanism differs depending on the polarity, and positive polarity recording dots are formed smaller. Furthermore, it was found that missing recorded dots occur in positive polarity recorded images. At present, the cause of this has not been elucidated in detail, but as shown in Figure 6, the recording voltage is the sum of the control voltage Vcp and the recording electrode voltage Vnp.
I know that I am dependent on VR. α is the charge image formation probability, and the higher the recording voltage Vr is, the fewer missing recording dots occur. Therefore, from Figures 5 and 6, when recording a positive charge image, the recording voltage should be set as low as possible.
It can be seen that the higher the Vr, the higher the quality of the image.

by the way. , there is an upper limit to the recording voltage Vr, and especially when electrostatic recording paper is used as the recording medium, if the recording voltage Vr increases beyond a certain value, traces of recording will remain in the half-selected area other than the recorded area, and the image will deteriorate. It may reduce quality. For this reason, it is known that the maximum value of the recording voltage |Vr| is about 650V. In general, a recording voltage |Vr| for forming a negative charge image is in the range of 550 to 600 V due to the characteristics of negative discharge to obtain a clear image with sufficiently high contrast. Since the conventional two-color electrostatic recording apparatus has the above-described configuration, a fatal phenomenon in two-color electrostatic recording using positive and negative charge images is that the formed charge image disappears.

This charge disappearance phenomenon occurs because when positive and negative charge images are formed on the same scanning line on a recording medium such as electrostatic recording paper, the optical reflection density of the previously formed recording dots becomes the same as that of the recording dots during unipolar scanning. In other words, the density of the recorded dots may be lower than that of the recorded dots, or they may not be reproduced as recorded dots. If a negative charge image is formed first in the recording scanning period tr, the area around the recording dot will be left blank, and if a positive charge image is formed first, the entire recording dot will be left blank. tends to disappear.

The reason for this charge disappearance phenomenon is that the potential difference between the potential of the charge image initially formed during the recording scan period tr and the half-selected pulse voltage applied to the recording electrode needle during the next scan causes the recording electrode to When the discharge threshold voltage Vth between the needle and the recording medium is exceeded, the initially formed charge image causes re-discharge and becomes a low potential, making it difficult to develop. Figure 7 shows a schematic potential distribution of the charge image, and Figures 7a and b
are positive and negative charge images, respectively. Vp and −
VN is the potential of positive and negative charge images, respectively, and its absolute value is generally about 80 to 110V. This potential is a value calculated from the average surface potential of multiple charge images and the density, or area occupancy, of the recording dots of the charge images, and there is no problem using this approximate measurement method. It is. Also, the discharge threshold voltage
It is known that Vth is approximately 360V from the bottom curve of FIG. 8, which shows the relationship between the discharge starting voltage and the distance between the discharge electrodes. Therefore, in the case of a positive charge image, Vp+Vnn>Vth=360, and in the case of a negative charge image, if VN+Vmp>Vth, the charge image starts to discharge again and its potential attenuates.
This potential attenuation becomes more noticeable as the difference between Vp+Vnn and VN+Vnp and the discharge threshold voltage Vth increases, and becomes as shown by the broken line in the potential distribution of the charge image in FIG. 7. Therefore, when a re-discharged charge image is developed with toner, the positive charge image is hardly developed, and the negative charge image becomes hollow recorded dots, resulting in a very unclear recorded image.

The present invention aims to eliminate the above-mentioned drawbacks and provides a multi-stylus electrostatic recording method capable of producing clear multicolor recorded images with no risk of charge image disappearance.

The recording method of this invention is as shown in FIG.
As shown in Fig. 9, first the high recording voltage Vr
Scanning is performed to form a positive charge image that requires , and then negative charge image formation is performed. Furthermore, when the potential of the positive charge image is Vp, the recording electrode needle voltage during formation of the negative charge image is set so that Vnn<360-Vp. Forming a positive charge image first in this way means that the recording electrode voltage Vnp and the control voltage
It is possible to increase Vcp, and the optical reflection density shown in Figure 5 can be increased, making it possible to obtain clear images.Furthermore, the frequency of recording dot omissions shown in Figure 6 can be reduced by increasing the recording voltage Vr. By doing so, it can be reduced to a completely negligible level. When forming a negative charge image that provides high contrast without applying a large recording voltage Vr, the recording electrode voltage is set such that |Vnn|<360−Vp with respect to the positive charge image voltage Vp. By applying -Vnn, it is possible to prevent the positive charge image potential from attenuating and disappearing.

Furthermore, as shown in FIG. 9, the scanning for forming positive and negative charge images does not need to be performed immediately after the scanning for forming positive charge images. Furthermore, in a general multi-stylus electrostatic recording head, there is only one row of recording electrode needles.
Although the present invention is arranged in a row, it is clearly effective even in the case of a plurality of rows, regardless of the shape or machine of the electrostatic recording head. In addition, although the main text describes an electrostatic recording device using a same-side control method, the present invention is also effective in an electrostatic recording device using a back-side control method.

In the main text, the discharge threshold voltage Vth is set to 360V from the Patsien curve in Figure 8, but in the case of electrostatic recording paper,
This is thought to be due to the gap length between the electrostatic recording paper and the recording electrode needle, but as a result of actual recording experiments,
It has been found that the development of image disappearance due to re-discharge of the charge image begins to occur when the value of Vth is set larger than 370V and the recording needle voltage -Vnn during negative charge image formation is set. Therefore, the discharge threshold voltage referred to in the text is 370V.

As described above, if positive and negative charge images are formed according to the multi-stylus electrostatic recording method of the present invention, it is possible to obtain clear recorded images of two or more colors with high contrast.

[Brief explanation of the drawing]

Figure 1 is an external view of the multi-stylus electrostatic recording head, Figure 2 is a recording control block diagram of the electrostatic recording head, and Figure 3 is the voltage applied to the recording electrode needle and control electrode during formation of positive and negative charge images. FIG. 4 is a recording timing diagram showing the recording scanning period tr and the moving position of the recording medium. FIG. 5 is a characteristic diagram showing the recording voltage dependence of the recorded image density of positive and negative polarity charges. , Fig. 6 is a characteristic diagram showing the recording voltage dependence of recording dot dropout peculiar to positive polarity recording, Fig. 7 is a potential distribution diagram showing the state of potential distribution of positive and negative charge images, and Fig. 8 is a flat electrode FIG. 9 is a graph showing the discharge starting voltage with respect to the gap length, and FIG. 9 is a recording timing chart showing the recording scan timing according to an embodiment of the present invention. In the figure, 1 is a multi-stylus electrostatic recording head;
2 is a recording electrode needle, and 3 is a control electrode. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. Pulse voltages of different polarities, positive and negative, are applied to the recording electrode needle of the multi-stylus electrostatic recording head and its control electrode, respectively, to generate positive and negative pulse voltages on the recording medium according to the input signal. and a multi-stylus electrostatic recording method in which a negative charge image is scanned and formed, in which the positive charge image is formed in the first half of each scanning period of the input signal, and the negative charge image is formed in the second half. The electrode needle voltage (absolute value) applied to the recording electrode needle when forming a negative charge image is the discharge start threshold voltage (370 V) between the recording electrode needle and the recording medium.
A multi-stylus electrostatic recording method characterized in that the voltage value is set to be slightly smaller than the voltage value obtained by subtracting the potential (absolute value) of the positive charge image formed on the recording medium from the above.