JPS6358379A - Time-division driven liquid crystal optical switch array for printer - Google Patents

Abstract

PURPOSE:To obtain a print of high quality which is free from blurring and fogging at a high speed by forming an insulating light-absorptive film on a substrate and eliminating light leakage originating from the space between adjacent row electrodes. CONSTITUTION:A color filter layer 6 are provided between row electrodes 4a and 4b of a row electrode substrate. A color filter which is used in combination with a black color filter and an optical switch array and absorbs the light emission spectrum of a light source i.e. color filter layer of complementary color to the light emission spectrum color is usable as the color filter layer 6. The color filter layer 6 which absorbs the light of the light source is formed on the electrode substrate which constitutes the optical switch array, so light is transmitted only through the optical switch part.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal optical switch array, and particularly to an optical switch array suitable for high-speed, high-resolution optical printers.

[Conventional technology]

Electrophotographic printers that can print on plain paper with non-impact, high speed, and high image quality are attracting attention. In this method, a photoreceptor drum whose surface is uniformly charged is irradiated with a light pattern created in response to a print signal from a computer, etc. to create a latent image, and this is transferred to paper using toner. .

Two methods are used to create a light pattern: one is to mechanically scan laser light using a polygon mirror, and the other is to line up optical switches that control the amount of light transmitted according to electrical signals (
There is a method of converting light from fluorescent lamps etc. into a light pattern using an optical switch array (optical switch array). The latter has the advantage that it is highly reliable because it has no moving parts, and that the optical system can be made smaller because the optical path length is short.

FIG. 2 shows a method using an optical switch array 10 using liquid crystal. Light from a fluorescent lamp 8 (usually a color fluorescent lamp such as green is used) is irradiated onto the liquid crystal optical switch array 10 by a Rondo lens 9. The incident light is converted into a light pattern according to the printing signal by the optical switch array 10, and an image is formed on the surface of the photoreceptor drum 12 by the convergent optical fiber array 11.

Liquid crystal optical switch arrays require high-speed response and high resolution. Conventional optical switch arrays for printers using nematic liquid crystals are described in JP-A-57-120468 and JP-A-58-115414.

Figure 3 shows the electrode pattern of the 1/2 duty time division section-movement panel shown in the above patent; Figure 3(a)
3(b) shows a row electrode substrate, and FIG. 3(b) shows a signal electrode substrate. Both substrates have a transparent conductive film (InzOs) 2 on a glass plate 1.
is patterned, and an opaque conductive film 3 is formed in the area other than the optical switch section 5. A metal film of Ni or Cr can be used as the opaque conductive film. FIG. 3(c) shows an optical switch array made up of elements using a signal electrode substrate and a row electrode substrate, an optical switch column Uty U21.
ua.

... and D 1 g D z p D a ... are arranged in a staggered manner.

There are also regions 14 above and below which have no electrodes. In a printing method using a panel having such an array of optical switches, the photoreceptor is first exposed to light by the array of optical switches Ut, Us, Us, etc., and then the drum rotates (the drum rotation direction is 15). Then, the light is exposed by the optical switch array of Dl*DQtDa, thereby completing one line of print exposure. In this case, the amount of light transmitted through the region 14 is always based on the molecular arrangement in a state where no voltage is applied.

In the conventional method using nematic liquid crystal, liquid crystal molecules take a TN (twisted nematic) orientation, which is a twisted structure twisted by 90 degrees between both substrates. The light transmission characteristics of the optical switch section in this case are as shown in FIG. If the polarization axes of the polarizing plates 16a and 16b arranged on the outside of the liquid crystal panel substrate are set at right angles to each other (normally closed), light is blocked when no AC voltage is applied, and the threshold voltage Vth
When a higher voltage is applied, light is transmitted. Therefore, if the polarizing plate arrangement of the optical switch array is set to normally closed, there will be no leakage of light from the region 14.

Prints with high dispersion can be made based on the opening and closing of the optical switch section.

However, when ferroelectric liquid crystal is used as the liquid crystal material, the light is not blocked even in the normally closed state.
Conventional electrode configurations pose a problem with light leakage. That is,
The conventional structure is effective only in the case of a TN-oriented nematic liquid crystal element, and cannot be applied in the case of a ferroelectric liquid crystal.

[Problem that the invention seeks to solve]

When using liquid crystals for optical switch arrays for printers, responsiveness becomes a problem. In the conventional method, a response time of 0.5 to 1.0 ms has been obtained by using a nematic liquid crystal and improving the driving conditions (dual frequency driving method), but there are limitations as long as a nematic liquid crystal is used.

There is a method of using a ferroelectric liquid crystal as a method for increasing the speed (Japanese Patent Laid-Open No. 123305/1983). Using a ferroelectric liquid crystal makes it possible to achieve a high-speed response of 0.1 ms or less. On the other hand, the electric field response of ferroelectric liquid crystal molecules is different from that of conventional nematic liquid crystal molecules. FIG. 5 shows this. When no electric field is applied (E=O), the liquid crystal molecules 17 have a "twisted structure" around the helical axis 18, and spontaneous polarization 19 occurs in the short axis direction of the liquid crystal molecules. This is a feature of this liquid crystal. When an electric field Ec greater than a critical electric field Ec determined by the physical properties of spontaneous polarization and twist viscosity of the liquid crystal is applied to the liquid crystal molecules in a direction perpendicular to the helical axis 18, the liquid crystal molecules 17 will move the direction of the spontaneous polarization 19 in the direction of the electric field E. In order to arrange them so that they are aligned, they are oriented in a negative direction at an angle θt (tilt angle) with respect to the helical axis, as shown in FIGS. 5(a) and 5(c). By utilizing such electric field responsiveness of the liquid crystal molecules 17, an optical switch capable of transmitting and blocking light can be obtained. One is a birefringent method that uses two polarizing plates, and the other is a guest-host method that uses one polarizing plate and mixes dichroic dye into the liquid crystal material.

FIG. 6 shows the light transmission characteristics of an optical switch element using ferroelectric liquid crystal. Depending on the arrangement conditions of the polarizing plate, it can be placed in either a light transmitting state or a light blocking state by applying a positive voltage. However, when no voltage is applied, the liquid crystal molecules do not align uniformly (helical structure) as shown in Figure 5(b), so light passes through, and the amount of light transmitted is equal to the amount of light transmitted when the switch is open. Therefore, when ferroelectric liquid crystal is used in a time-division drive liquid crystal optical switch array as shown in FIG.
In the region 14 where no voltage is applied, approximately 50% of the amount of light transmitted when the optical switch is open is transmitted. Therefore, when such an optical switch array is applied to a printer,
Since the photoreceptor is exposed to light due to the amount of leaked light in the area 14, print quality deteriorates due to occurrence of "bleeding" or "fogging" in the printed text.

,,' An object of the present invention is to provide a time-division drive liquid crystal optical switch array that prevents light transmission in the region 14 and enables high-speed, high-quality printing without "bleeding" or "fogging." .

[Means for solving problems]

The above purpose is to form an insulating light-absorbing film on the substrate (electrode side) corresponding to the area 14 in Figure 3(c) in order to prevent light leakage due to the space between adjacent row electrodes. This is achieved by

This is shown in FIG. 1, where (a) shows the row electrode 4 of the row electrode substrate.
A color filter layer is provided between a and 4b. As the color filter layer, a black color filter or a color filter that absorbs the emission spectrum of the light wX8 used in combination with the optical switch array, that is, a color filter layer 6 of a complementary color to the emission spectrum color can be used. In the figure (b), a color filter layer 6 is similarly provided on the electrode of the signal electrode substrate in a region corresponding to the gap between the row electrodes at the time of device assembly.

Such an insulating light absorption film may be provided on both the signal electrode substrate and the row electrode substrate, or may be provided on only one of them.
The effect will be greater if it is provided on both sides.

[Effect]

As shown in FIG. 2, the light from a light source 8 such as a fluorescent lamp enters a liquid crystal optical switch array 10.A color filter layer that absorbs the light from the light source is formed on the electrode substrate that constitutes the 6-optical switch array. , region 1 in FIG. 3(c)
There is no leakage of light from the optical switch section U1.4, and light transmission occurs through the optical switch section U1.
Us..., Dl.

Limited to Dz, Da... only. As a result, printing can be performed without deterioration in resolution even when time-division driving is performed.

〔Example〕

(Example 1) An example of the present invention will be described with reference to FIG. glass plate 1
An indium oxide film 2 (thickness: 400 mm) was formed on the surface of the film, and patterned by etching.

Furthermore, after forming a chromium vapor deposited film 3 with a thickness of 2000 mm on this, etching is performed to obtain an electrode substrate consisting of an optical switch portion made of a transparent electrode and an opaque chromium vapor deposited film region formed to surround it. A color filter layer 6 is provided as the primary color filter layer 6. Possible methods for this include dyeing using photolithography technology, vapor deposition using electroplating technology, electrodeposition using electroplating technology, and low-cost printing methods. . In the case of an optical switch array, the width I2g of the filter layer is extremely narrow, about 50 to 300 μm, so a dyeing method using photolithography technology is suitable, and this was used. After forming the electrode pattern, a dyeable negative photoresist film is applied on the electrode surface using a spinner, and then exposed to light with a width of Qg to form a filter layer, and the unexposed areas are removed using a rinsing liquid. The substrate on which the dyeable resist film remains is inseminated with a red dye solution (for example, Suminol Fast Red B dye solution at 60°C) to dye the resist film red, and then aqueous solutions of tannic acid and potassium antimonyl tartrate are inseminated. A fixing process was carried out at , and a red filter layer 6 was obtained. Using the signal electrode substrate and the row electrode substrate provided with the red filter layer, a polyimide rubbing alignment film was formed on the substrate surface, and then devices were formed and ferroelectric liquid crystal was sealed to obtain a liquid crystal optical switch array.

When we investigated the light transmission characteristics by combining a green fluorescent lamp (wavelength: 543 nm) 8 as a light source with the above optical switch array, we found that a red filter layer was formed in the region 14 of FIG. The light from the lamp was absorbed and did not pass through the optical switch array, and the light was transmitted only through the optical switch section, resulting in high resolution.

(Example 2) In Example 1, a red filter layer was used, but a black filter layer may also be used. Note that when a red fluorescent lamp is used as a light source, the same effect as in Example 1 can be obtained by using a green color filter.

〔Effect of the invention〕

According to the present invention, the only light that passes through the time-division drive liquid crystal optical switch array is the optical switch section that opens and closes in response to electrical signals, making it possible to print at high resolution without "bleeding" or "fogging" using ferroelectric liquid crystals. This has the effect of making it possible to obtain an optical switch array.

[Brief explanation of the drawing]

Fig. 1 shows an embodiment of the present invention, Fig. 2 shows the structure of a printer head using a liquid crystal optical switch array, Fig. 3 shows a conventional example, and Fig. 4 shows a printer head using a nematic liquid crystal. FIG. 5 is a diagram showing the electric field response of ferroelectric liquid crystal molecules, and FIG. 6 is a diagram showing the light transmission characteristics of the ferroelectric liquid crystal element.

Claims (1)

[Claims] 1. A ferroelectric liquid crystal is provided between a signal electrode substrate provided with a plurality of signal electrodes and a row electrode substrate provided with a plurality of row electrodes, and a plurality of row electrodes are sequentially selected. In an electrode substrate of a time-division drive optical switch array for a printer that sequentially operates optical switch rows to expose a photoreceptor drum with light from a light source, at least one electrode substrate has a part or all of the area other than the optical switch section. 1. A time-division drive liquid crystal optical switch array for a printer, characterized in that a color filter layer is formed in a region to absorb light in the wavelength range to which a photoreceptor is sensitive. 2. For use in a printer according to claim 1, wherein the light source is a monochromatic light source having a spectrum in the high-sensitivity wavelength region of the photoreceptor, and the color filter layer has a complementary color relationship to the light source color. Split drive liquid crystal optical switch array. 3. In the row electrode substrate, the row electrode is composed of a transparent conductive film in the part that becomes the optical switch part and an opaque conductive film in the other part, and the above-mentioned color filter layer is formed in the gap between the row electrodes. A time-division drive liquid crystal optical switch array for a printer according to claim 1. 4. In the signal electrode substrate, the signal electrode is composed of a transparent conductive film in the part that becomes the optical switch part and an opaque conductive film in the other part, and the color filter layer is formed between the optical switch rows. A time-division drive liquid crystal switch array for a printer according to claim 1, characterized in that: 5. The time-division drive liquid crystal optical switch array for a printer according to claim 1, wherein the ferroelectric liquid crystal is a material exhibiting a chiral smectic C phase or a chiral smectic H phase.