JPH054226B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printing apparatus including an optical signal generating section using a liquid crystal light valve.

In recent years, optical printing devices using liquid crystal light valves have been realized as high-speed, high-quality, and low-cost non-impact printers.

As a method for realizing an optical printing device using a liquid crystal light valve, there is a method described in Japanese Patent Application No. 141085/1985. First, the configuration of a printing apparatus using the above method and the characteristics of a liquid crystal light valve will be described.

FIG. 1 shows the configuration of the printing apparatus described above. By the optical signal generating section 101 using a liquid crystal light valve,
Light is written on the photosensitive drum 102. At this time, the photosensitive drum 102 is connected to the corona charger 110.
It is pre-charged with electricity. At this time, when printing characters, the optical signal is usually such that light is generated corresponding to the character part. This forms an electrostatic latent image, which is developed with toner by a magnetic brush developer 103. The developing method at this time is usually reversal development. Thereafter, the toner is transferred onto plain paper 104 by a transfer corona discharger 105 and fixed by a fixing device 106. The toner remaining on the photosensitive drum after transfer is removed by a blade 108, and the electrostatic latent image is neutralized by a static elimination lamp 109, and the process ends. FIG. 2 shows the configuration of the optical signal generator. The optical signal generating section consists of a light source 111 such as a fluorescent lamp, a liquid crystal light valve, and an imaging lens 115.
It consists of a substrate 114 on which a liquid crystal panel 112 and a liquid crystal drive circuit 113 are mounted. The light emitted from the light source is modulated by a liquid crystal light valve. This optical signal 11
6 is imaged onto the photosensitive drum 102 by the imaging lens 115. An established image can be obtained by using a focusing optical fiber array as the imaging lens. FIGS. 3 and 4 show the structure of the liquid crystal panel. The liquid crystal panel has common signal electrodes 119 and 12
0, and a signal electrode 121.
and 122, and a liquid crystal composition 125 is sealed between a glass substrate 118 and a spacer 126, and polarizing plates 123 and 12 are placed on both sides of the glass substrate.
It consists of 4. The common signal electrode is a transparent electrode 11
9 and an optically opaque metal electrode 120, and the signal electrodes 121 and 122 are transparent electrodes. The polarizing plates 123 and 124 are arranged so that their polarization planes are orthogonal to each other. The light is transmitted through the transparent part 11 of the common electrode.
The signal is modulated at the microshutter portion formed by the signal electrode 9 and the signal electrode. Patent application for liquid crystal composition
55-141085 Optically active substance 4-(2-methylbulyl)-4′-Cyamo-biphenyls in the nematic liquid crystal in Table 1
A high-speed liquid crystal light valve can be obtained by using a long-period cholesteric liquid crystal obtained by adding 3% by weight of . FIG. 5 shows the frequency characteristics of the dielectric anisotropy of this liquid crystal. The frequency at which the dielectric anisotropy is zero is called the crossover frequency and is represented by c. c
This is where the lower frequency is _L and the higher frequency is h.
The liquid crystal light valve is operated by applying signals at frequencies _L and h to each signal electrode. 6th
Figure b shows the application of the applied signal and the light transmitted through the liquid crystal light valve a.

A signal at time h indicated by T2 and a signal at time _L at T3 are applied. T1 is called the writing period, T2 is called the opening time, and T3 is called the non-opening time. The liquid crystal light valve opens by applying the h signal, and closes by _{the L} signal. By the method described above, we were able to obtain a revolutionary high-speed liquid crystal light valve.

By the way, as mentioned above, when performing optical writing using the electrophotographic process, light leakage when the microshutter is closed when using a liquid crystal light valve is not only a problem of reduced contrast between light and dark, but also a problem. , the following process problems occur: That is, when the photosensitive drum is charged with a charger, the surface potential attenuates gently at the edges. In order to ensure a charging width corresponding to the effective writing width, the edge portion must be made wider than at least the effective writing width. Furthermore, in order to accurately match the charging width to the effective writing width, the optical writing signal generating section and the charger must be assembled with high precision. From these demands,
Usually, the photosensitive drum is charged with a width larger than the effective writing width. For this reason, when the photosensitive drum is charged with a width larger than the effective writing width, as shown in FIG. Since it is larger than the writing width,
The electrostatic latent image after optical writing takes on three voltage levels as shown in the figure. The vertical axis of the figure corresponds to the surface potential, and the horizontal axis corresponds to the model diagram above. The area 133 where the liquid crystal micro shutter is open is
The surface potential drops to V _ON , but the closed part 1
32 also drops to V _OFF due to light leakage. However, in the area 131 that is not exposed to any light, the surface potential is higher than V _OFF only due to the decrease due to the dark decay characteristics of the photoreceptor.
It becomes V _O. When this latent image is reversely developed, if the bias potential applied to the developer is V _B , the positively charged toner is attracted by the electric field determined by the potential difference (V _B - V _ON ) and selectively adheres to the bright area 133. do. The bias potential is usually adjusted to prevent background smudges on the printed sample.
It is assumed that V _B <V _OFF , but at this time, if the potential V _O of the part 131 that is not exposed to any light due to light leakage when the microshutter is closed is relatively high compared to V _OFF , then (V _O -V _B ) The electric field determined by the potential difference causes carrier adhesion and toner scattering. As a result, dirt will adhere to both edges of the printed paper, greatly reducing the quality.

The present invention prevents background smudges on the paper caused by incomplete light blocking of the liquid crystal light valve when printing using a liquid crystal light valve, and prevents the paper from being smudged while printing using the liquid crystal light valve. An object of the present invention is to provide a printing device capable of making clear printing without stains on parts other than printing parts.

The printing device of the present invention includes a liquid crystal panel provided with microshutters for printing and writing, and a liquid crystal panel that moves relatively in a direction intersecting the arrangement direction of the microshatters to correspond to the light transmitted through the microshatters. In a printing device having a photosensitive drum for forming a latent image, and a developing means for developing the latent image on the photosensitive drum, the arrangement direction of the microshutters for printing and writing on the liquid crystal panel is extended. The part is provided with an exposure means that exposes a photoreceptor portion where the microshutter for printing and writing is not provided and approximates the surface potential of the photoreceptor to the surface potential of the microshutter when the light is blocked. It is characterized by

Examples are shown below.

The general configuration of the printing apparatus of the present invention is the same as that shown in FIG. That is, optical writing is performed on the photosensitive drum by an optical signal generator using a liquid crystal light valve. This photosensitive drum is previously charged with a corona charger. At this time, when printing characters, optical signals are usually generated corresponding to the character parts. This forms an electrostatic latent image, which is developed with toner using a magnetic brush developer. The developing method at this time is usually reversal development. Thereafter, the toner is transferred to plain paper by a transfer corona discharger and fixed by a fixing device. The toner remaining on the photosensitive drum after transfer is removed by a blade.
The electrostatic latent image is neutralized by a static eliminating lamp. Note that the optical signal generator and the liquid crystal panel are the same as those described above.
It is based on what is shown in Figures 3 and 4. Similarly, the frequency characteristic of the dielectric anisotropy of the liquid crystal material sandwiched between the liquid crystal panels is as shown in FIG. The response characteristics of the liquid crystal material and the driving signals at that time are shown in FIG.

<Example 1> As shown in Figure 8, LED 14 is placed outside the effective printing width.
0 and adjust the light intensity of the microshutter.
When adjusted to the OFF level (the level when the microshutter is closed and in a light-blocking state), as shown at the bottom of Figure 8, recording is made at the outer part of the effective printing width of the photosensitive drum shown at 131. The surface potential of the part where the toner image will be formed on the paper is now equal to V _OFF .

At this time, it is of course possible to use a device other than LED as long as it can be exposed to light.

Embodiment 2 In this embodiment, the exposure means outside the effective writing width is formed by a microshutter of the liquid crystal light valve itself. FIG. 9 shows a conceptual diagram of a liquid crystal panel used in Example 2. This liquid crystal panel has a glass substrate 117 provided with a common electrode 120.
and a glass substrate 118 provided with a signal electrode 121. The glass substrate 118 is provided with an exposure electrode 151 outside the effective writing width, and together with the common electrode 120, an exposure microshutter 153 is formed. As an extension of the microshutter 152 for writing, it is arranged outside the effective printing width.

Now, the common electrode signal 161 which is a combination of high frequency h and low frequency shown in FIG.
20, when the low frequency signal 162 with the opposite phase is applied to the exposure electrode 151, the signal applied to the liquid crystal becomes as shown by the symbol 163, and at this time, the microshutter 152 is in the closed state. Close in exactly the same condition. Therefore, similar to Example 1,
This means that the exposure section (means) is provided outside the effective writing width, and there is no need to adjust the amount of light at all.

According to the above-described printing apparatus of the present invention, when printing using a liquid crystal light valve, it is possible to prevent background smudges on the paper caused by incomplete light blocking of the liquid crystal light valve, and Although it is a print, it is possible to make a clear print without stains on parts other than the original print part.

[Brief explanation of drawings]

Figure 1 is a diagram showing the principle of a general liquid crystal printer configured using a liquid crystal microshutter in the optical writing signal section. FIG. 2 is a diagram showing an optical write signal generating section used in the printer of FIG. 1. 3 and 4 are diagrams showing the structure of a liquid crystal panel used in the optical write signal generation section of FIG. 2, respectively. FIG. 5 is a diagram showing the frequency characteristics of dielectric anisotropy of the liquid crystal material used in the present invention. FIG. 6 is a diagram showing the response characteristics of the liquid crystal material used in the present invention and the driving signals at that time. FIG. 7 is a diagram showing the distribution of surface potential on a photosensitive drum according to the prior art. FIG. 8 is an explanatory diagram of an embodiment of the present invention showing the effect of using an LED as an exposure means. FIG. 9 is an explanatory diagram of an embodiment of the present invention in which a part of the liquid crystal panel is used as an exposure means. FIG. 10 is a diagram showing a signal waveform applied to the exposure electrode of the liquid crystal panel of FIG. 9. 101... Optical writing signal generation unit, 102... Photosensitive drum, 103... Developer, 110... Charger,
111...Light source, 112...Liquid crystal panel, 113
...Drive circuit, 117,118...Glass substrate,
120... Common electrode, 121... Signal electrode, 12
3,124...Polarizing plate, 125...Liquid crystal, 151
...Exposure electrode, 152...Writing microshutter, 153...Exposure microshutter.

Claims (1)

[Scope of Claims] 1. A liquid crystal panel provided with micro-shutters for printing and writing, and a liquid crystal panel that moves relatively in a direction intersecting the arrangement direction of the micro-shutters and is hidden in response to the light transmitted through the micro-shutters. In a printing device having a photosensitive drum for forming an image and a developing means for developing the latent image on the photosensitive drum, an extension in the arrangement direction of the microshutter for printing and writing of the liquid crystal panel; Further, an exposure means is provided which exposes the photoreceptor portion where the microshutter for printing and writing is not provided and approximates the surface potential of the photoreceptor to the surface potential of the microshutter when the light is blocked. Characteristic printing device.