JPS59162522A - Optical modulator - Google Patents

Abstract

PURPOSE:To improve the light transmittance in a shutter opening state by applying a voltage to plural one-side beltlike electrodes of a matrix electrodes as row electrodes, row by row, on time-division basis and operating liquid crystal, and forming a metallic mask in an area other than shutter opening parts. CONSTITUTION:Shutter opening parts 21 (21a, 21b...) are arrayed zigzag at intersections of row electrodes 22a, 22b and signal electrodes 23 (23a-23d...). A row electrode substrate for a shutter is formed by providing the metallic light-shield mask 25 on a substrate 24 (glass, plastic, etc.) at the area except areas 21' (21'a and 21'b) where the shutter opening parts 21 are formed, and the row electrodes 22a and 22b are arranged thereupon with an insulating film 26 interposed (provided that the electrostatic capacity between the row electrodes is held below 100PF). Consequently, the light transmittance in the shutter opening state is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical modulation device, particularly a liquid crystal-optical shutter, and more particularly to a liquid crystal-optical shutter suitable for a time-division driving method.

This liquid crystal-optical shutter utilizes the electro-optical modulation function of liquid crystal.The modulators are arranged in an array, illuminated with light, and the transmitted light is selectively extracted. A digital copy can be obtained by forming an optical signal corresponding to the image signal and irradiating the electrophotographic photoreceptor with this optical signal.

The advantages of this liquid crystal-optical shutter array are: 1. When used in an electrophotographic printer, the printer device can be made smaller; 2. It can be used in applications such as polygon scanners used in LBP (laser beam link). There are no mechanically driven parts, so there is no noise, and there is little requirement for strict mechanical precision. Although such advantages naturally lead to the possibility of improved reliability, weight reduction, and cost reduction, there are actually various problems.

FIG. 1 shows an example of a liquid crystal shutter array configuration that will be most easily understood.

As shown in FIG. 1, a shutter opening l is provided, and other hatched areas are usually masked to prevent leakage of light. The liquid crystal has signal electrodes 3 (3a, 3b) provided on the inner surface of the substrate 2.

3c, 3d, . . .) and a common electrode 4 disposed opposite to the signal electrode 3. However, in such a liquid crystal-optical shutter, the apertures are arranged in the format shown in Fig. 1, and the image density of the formed image is set to l Odot/m.
In order to design a shutter array with an A-4 size width of m, approximately 2000 signal electrodes would be required, and the number of drivers to drive each would also be 2.
00.0 pieces are required.

The number of driver ICs must be 40 if it is a 5o pin IC. This naturally limits the ability to reduce costs.

For this reason, it has been considered that by dividing the common electrode into multiple rows and making them correspond to the signal electrodes in a matrix, the shutter can be opened and closed in a time-sharing manner for each row of the common electrode. When used as a head of an electrophotographic copying machine, the row electrode is usually iC150t in the longitudinal direction.
rrm or more, and in particular, it is necessary that the length in the longitudinal direction of the row electrode be 210 haze or more in order to conform to the size of Japanese Industrial Standards A-4 size.

However, according to research conducted by the present inventor, multiple rows of long row electrodes are arranged in parallel on a single substrate, and there is no insulation between the row electrodes in order to prevent light from leaking through the gaps between the row electrodes. In a liquid crystal shutter array that uses an electrode plate with a light-shielding mask placed on it, a large capacitance is generated between the row electrodes, and this causes the light transmittance when the shutter is open to be as low as a few percent. It turned out that there was. Therefore, the contrast between when the shutter opens and when the shutter closes is small, making it difficult to design a photosensitive drum or process when this liquid crystal shutter array is attached to a printer head of an electrophotographic copying machine. In particular, it has been found that when a fluorescent lamp of about 30 W is used as a light source, a good image cannot be formed.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical modulation device, in particular a liquid crystal-optical shutter, which eliminates the above-mentioned drawbacks.

Another object of the present invention is to provide a liquid crystal-optical shutter suitable for time-division driving.

Another object of the present invention is to provide a liquid crystal-optical shutter with improved light transmittance when the shutter is open.

That is, the present invention has an electrode structure in which a plurality of band-shaped electrodes facing each other are crossed to form a matrix, and one of the plurality of band-shaped electrodes is used as a row electrode (common electrode) to time-divisionally apply a voltage to each row. The liquid crystal can be operated by a driving method that uses a drive method, and a light-shielding mask is formed over the entire area of the substrate forming the row electrodes except for the area that will become the shutter opening. The capacitance of is 1
It has a boiling characteristic that is maintained below 00 OPF (picofarads).

The liquid crystal-optical shutter of the present invention has, for example, the embodiment shown in FIG. 2(a), and the row electrode (common electrode) substrate used therein has the embodiment shown in FIG. 2(b).

The shutter shown in FIG. 21 has a shutter opening 21 (21
a, 2. lb,...) are arranged in a zigzag pattern, and the row electrodes 22a and 22b and the signal electrode 2
3 (23a, 23b, 23c, 23d, ---
) is located at the intersection of The row electrode substrate used for this shutter has an area 21'(21'
A metal light-shielding mask 25 is formed in the area except for the areas 21'a and 21'b), and the row electrode 2 is formed on the metal light-shielding mask 25 through an insulating film 26.
2a and 22b are arranged. This aspect is made clear in FIG.

In FIG. 3, the row electrode substrate used for this shutter is
An area 21'(21'a, 2
A metal light-shielding mask 25 is formed on the row electrodes 22a and 22b in the area except 1'b). Furthermore, a light-shielding mask 2 having insulation properties is provided between the row electrodes 22a and 22b.
6 is placed.

Further, numeral 27 in the figure indicates an insulating film made of resin or the like.

An example of the process of forming the row electrode substrate shown in FIG. 3 will be described.

In FIG. 3, it is assumed that electrode row electrodes 22a and 22b made of transparent conductive thin films and a metal light-shielding mask 25 are formed on the inner surface side of the glass substrate 24, and a polyvinyl alcohol (PVA) film is formed thereon as an alignment film. form t;
4゜PVA is Gohsenol (Nippon Gosei Kagaku Kogyo) EG-
Using a 10% aqueous solution of 05, ammonium dichromate was added to the photosensitive adhesive side at a ratio of 5% to the solid content of the PVA (6QQQrpm, IQ
) and then heated at 60°C for 15 minutes to form the insulating film 27. Next, with the peripheral edges covered with a mask, the P and VA films (insulating film 27) were exposed for 10 to 15 seconds, and then exposed to light using pure water. Develop for 30 seconds to remove unexposed areas. Next, after blow-drying with N gas and heating and drying at 80° C. for 5 minutes, the surface of the PVA film is subjected to an alignment treatment by rubbing.

Next, a photoresist (PPP⇠=l(800)) was spin-coated (2000 rpm, lO'') and heated at 80°C for 5 minutes to form a photoresist layer.
7. Apply a layer of photoresist with a mask covering the area.
After exposure to light for a second, the photoresist layer was developed in a developer to remove the photoresist layer in 26 areas in the figure.

Next, the PVA film is immersed in a dye solution for 5 minutes to dye the PVA film, thereby forming an insulating light-shielding mask 26. The dye is 8um
ifix Black EN8 (Sumitomo Chemical), 8o1
opheny INGL (f Bageiggy), C1bac
etGreyNH (Ciba Geigy) NH,O
It may be used after being dissolved in a 2% aqueous solution of H(7), and the desired concentration may be obtained by sequentially immersing it in two or three types of dyes. Next, after rinsing with pure water, removing the remainder of the photoresist layer (with methyl ethyl ketone), rinsing with Inglobil alcohol, drying with Freon paper, and baking (180°C, 15'), the row electrodes 2
A light shielding mask 26 in which the gap between 2a and 22b is opaquely dyed is completed.

Further, an example of the process of forming the row electrode substrate shown in FIG. 4 will be explained. In FIG. 4, it is assumed that row electrodes 22a and 22b made of transparent conductive thin films and a metal light shielding mask 25 are formed on the inner surface of a glass substrate 24, and a polyvinyl alcohol (PVA) film is formed thereon. For the PVA, a 10% aqueous solution of Gohsenol (Nippon Gosei Kagaku Kogyo) no-os was used, and as the photosensitive adhesive side, ammonium dichromate was added at a ratio of 5% to the solid content of the PVA, which was spin-coated (6000 rpm). , 10″) after 60℃
Heat for 15 minutes.

Next, with the mask aligned so that light hits only the gap between the metal light-shielding mask 25, a PVA film of 10~1
The film was exposed for 5 seconds and developed with pure water for 930 seconds to remove the unexposed areas. Next, it is blown dry with N2 gas and then heated and dried at 80° C. for 5 minutes.

The PVA film is then dyed by immersion in the dye for 5 minutes. The dye is 8umifix Black ENS (Sumitomo Chemical)
, 5olopheny INGL (Ciba Geigy),
Either C1bacetGrey NH (Ciba Geigy) may be used after being dissolved in a 2% aqueous solution of NH4OH, and the desired concentration may be obtained by sequentially immersing it in two or three types of dyes. The PVA film is dyed to form an insulating light-shielding mask 26.

Next, after rinsing with pure water, rinse with isopropyl alcohol, dry with Fron paper, and bake (180℃).
, 15'), etc., to complete the light-shielding mask 26 in which the gap portions are opaquely dyed.

Then, polyimide resin (Sf'- manufactured by Toshi ■) was applied to the surface of the polyimide resin.
510) using a 2.5×NMP solution (3000 rpm, 60 seconds), and then heated at 300° C. for 30 minutes to form an insulating film 27.

After removing the polyimide film on the seal and electrode terminal portions (etching for 10 minutes at a temperature of 60° C. using a 10% aqueous alkali U solution), the alignment direction of the liquid crystal molecules is determined by rubbing.

The metal light-shielding mask 25 can be formed by forming a film of a reflective metal such as chromium, aluminum, or silver by vapor deposition or plating, and then employing a photolithography process. When the metal light-shielding mask 25 is made of chromium, it has a film thickness of about 300 to 2000 layers. or,
The insulating film 27 has a thickness sufficient to provide insulation (approximately 0.5 to
The row electrodes 22 and the signal electrodes 23 can be formed using indium oxide, tin oxide, or other insulating materials such as Sin or polyimide (about 3.0μ) by vapor deposition, sputtering, or coating. It can be formed from a transparent conductive material such as an alloy of. 8i0. on the row electrode 22 and signal electrode 23. An alignment control film made of polyimide, polyparaxylylene, or the like can be disposed, and by performing a treatment such as rubbing on the alignment control film, the liquid crystal can be aligned according to the rubbing direction.

FIG. 5 is a plan view showing a portion of the liquid crystal-optical shutter array of the present invention.

In a specific example of the present invention, a liquid crystal-optical shutter array having a 1/2 time-division drive electrode structure shown in FIG. 5 can be used. The array shown in FIG.
Row electrodes 22a and 22b (indicated by dotted lines in the figure) are arranged, and these are 23C, 23d...
) are placed. Since the row electrodes 22a and 22b and the signal electrode 23 can each be referred to as an opening in a ray, they will be referred to as openings hereinafter.

Such a liquid crystal-optical shutter array is subjected to a rubbing treatment or the like so that the P-type liquid crystal sandwiched between the first groups is initially oriented in the direction of the arrow (approximately 45 degrees to the polarization direction of the polarizing plate). A highly homogeneous alignment process has been applied.

In order to simplify the following explanation, we will focus on openings A1 and A2 corresponding to the row electrode 22a and ta openings A: and A; corresponding to the row electrode 22b, and these openings A, ,
A2. The operations in A1' and A2' will be explained as an example.

FIG. 6 shows a time chart used in the driving method of the present invention. Time T, , rl11', T, Jr.
・Song... is the time when the openings corresponding to the row electrodes 22a operate, and all the openings corresponding to the row electrodes 22b stop operating. Time 'r21 T2','
r2"... is the time during which the openings corresponding to the row electrodes 22b operate, and the openings corresponding to the row electrodes 22a stop operating. That is, time TI.

``r, r, T:r,'', the signals S1 and 82 applied to the signal electrodes 23b and 23c must not affect the operation of the openings AI' and A2', and the time T2° In T2p, , it..., the signals S and S must not affect the operation of the apertures A and A.

First, time '111 'r,', TI''...
The operation of each opening in will be explained. As shown in the time chart of FIG.
Apply voltages C and C' to K, respectively. At this time, the voltage C is
The phase is opposite to voltage C'. On the other hand, by applying a voltage to the signal electrodes 23b and 23C that is in phase with the voltage C applied to the addressing row electrode 22H, or by keeping it at a certain voltage level, it is possible to determine whether the shutter is on or off. At the time T shown in FIG. 6, the opening A.

An example was given in which only the shutter is in a shutter-on state (a state in which irradiated light is transmitted). However, in this example, a time τ is provided at the end of the time for addressing one row to ensure that a signal prompting the off state is input. To explain that at time T1, the corresponding fold openings A,' and A' of the row electrode 22b are in a shutter-off state (a state where irradiation light is blocked).The operation of the liquid crystal at 80' is caused by the voltage C' and the signal It is determined by the electric field caused by S. Since C' and 81 are voltage signals with opposite phases to each other, the liquid crystal layer at 80' is not subjected to a strong electric field and is in a state where no light is transmitted (off state) as explained in the prior art example above. It is. On the other hand, A2 is determined by C' and 82, and since S2 is maintained at a certain constant voltage level, a relatively strong electric field is applied to the liquid crystal layer at fi A2' due to the voltage C', resulting in an off state. On the other hand, A2 is determined by the signal S2 and the voltage C, and since %l is a constant signal level, a relatively strong electric field acts on the liquid crystal layer at the voltage CK, so it is in the off state.However, at A1, C and However, since Sl is a voltage signal in the same phase as C, IC-8 is used in the liquid crystal layer in AI.
When a voltage with an absolute value of 11 is applied, this produces a zero or relatively weak electric field, creating a state (on state) through which light is transmitted.

Similarly, at the time T,' when addressing the row formed by the row electrode 22a, both AI and A are in the on state, and A,' and A2' are S, , S, and C', respectively.
It is in the off state due to a relatively strong electric field determined by . To summarize the above, at the time of addressing the row formed by the row electrode 22a, regardless of the states of the signals S and 82,
The folded opening of the row electrode 22b is always reliably in the OFF state.

Next, the time T for addressing the row formed by the row electrode 22b,
, T,', T,''... will be explained.

An example has been given in which only A1' is in the on state in Saima T2, and only A1' is in the on state at T and'. T2. T,
', T211..., the voltage C' is in opposite phase to C. On the other hand, the signal voltage SI and 8
2 is in phase with C', or whether it is kept at a certain voltage level. r, I Tl'v '11''・・・・・・・・・
As explained above, a relatively strong electric field always acts on AI', A, and 7, so that the off state is maintained. On the other hand, time 'r, s Tt'*T2'...
A1' and A2' in ... are '111 'r, ', 'I'1'' depending on the signals S and S2.
As explained for A and A2 in , on or off states can be selected.

Here T, + Tt * TI' * 'r, ', 'r
, "I T2" ......... is provided at the end of each time to uniformly turn off all the apertures), which is the same as the signal S1. This is done by setting voltage 82 at a constant level. By applying this erase signal, it is possible to block light transmission to the opening that should be in the OFF state next time.

In the operation mode that utilizes the retardation of the liquid crystal described above, a voltage is always applied between the row electrode 22 and the signal electrode 230 in order to maintain the light shielding state (off), and the voltage is always applied to the selected shutter and ivy opening. 21 to be in the open state (on), the selected signal electrode 23 is synchronized with the row electrode 22 and zero voltage or a low voltage below the threshold is applied to the liquid crystal, thereby converting the alignment mode of the liquid crystal. In other words, in order to obtain the shutter open state as shown in FIG. ) However, as mentioned above, since capacitive coupling occurs between the row electrodes on the row electrode substrate side, when operating the open state, This causes a situation in which sufficient light transmittance cannot be obtained in the open state.

Moreover, this capacitance is C=ε・S/d (where 1C is the capacitance, ε is the dielectric constant, S is the surface M of the opposing part between the row electrodes, and d is the distance between the row electrodes. For example, in order to apply a liquid crystal-optical shutter to the head of an electrophotographic printer, a length equivalent to the short side of Japanese Industrial Standard A4 size or Doujin 3 size is required, and this type of shutter is determined by In the case of a shutter, S' in the above equation becomes large. For this reason, a long liquid crystal-optical shutter array cannot obtain a sufficient amount of transmitted light when the shutter is opened, so it is necessary to increase the amount of light from the light emitting source, or to use a low-speed printer that rotates the photosensitive drum at a relatively low speed. It was necessary to do so.

In a preferred embodiment of the invention, the aforementioned capacitance it is equal to t,
, ooopp (picofarad) or less, preferably 50
It can be set to 0PF or less, particularly preferably 250PF or less.

Figure 7(a) to (d) are each 100OPF, 4
70PF% Expresses the transmittance when the shutter opening is turned on by applying a Σ voltage having the drive waveform shown in figure AG6 to a liquid crystal-optical shutter using a row electrode substrate with 220PF and QPF static capacitance. There is.

According to FIGS. 7(a) to (d), the capacitance between the row electrodes'
When f1000Pl;' is set, the transmission when the shutter is open is about 5%, when it is 470PF, the transmission when the shutter is open is about 13%, and when it is 220PF, the transmission when the shutter is open is about 22%. A light-shielding mask 26 having insulating properties
It can be seen that in the OFF mode where the use of is omitted, the transmittance when the shutter is open is approximately 24%.

As mentioned above, in a liquid crystal-optical shutter that employs a time-division drive system, a gap is created between the row electrodes, and the light leaking from there is irradiated onto a photosensitive drum provided in a printer head as shown in FIG. 8, for example. Situations such as malfunctions or the formation of unnecessary images may occur, so a transparent mask is required between the row electrodes.The capacitance formed between the row electrodes is preferably 100 OPF or less, taking into account the transmittance when the shutter is open. is 500P
The spacing between the row electrodes and the length in the longitudinal direction can be determined so as to be set to less than F, particularly preferably less than 250 P'F. In particular, in order to match the length in the longitudinal direction to 150 Orm or more, especially the length in the short direction of A4 size paper, the length should be 21 Orm.
It can be maintained at a distance of s or more.

In addition, as a comparative experiment, the length μ in the longitudinal direction of the row electrodes was set to 210wn, and a row electrode substrate with two row electrodes with the interval between the row electrodes maintained at a distance of 10% m was used. When a liquid crystal-optical shutter was prepared and operated by applying a voltage having the drive waveform shown in Fig. 6, the capacitance between the row electrodes was 100 OPF or more, and the light transmittance when the shutter was open was as follows. On the other hand, in the present invention, the spacing between the row electrodes is 3o/:,
. Ya□yo tso, eh, 8a, wow. Between.

The capacitance could be reduced to 500PF or less, and the light transmittance when the shutter was open was approximately 15%.

Figure 8 shows a schematic configuration for applying an optical signal to a photoreceptor using a liquid crystal shutter array. 84 is a light source (i-light amount, etc.), and 84 is a Selfolafre printer that is more compact than a conventional LBP. Can be summarized.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a conventional liquid crystal-optical shutter. FIG. 2 is a plan view of the liquid crystal-optical shutter of the present invention, and FIGS. 3 and 4 are sectional views taken along line AA of the row electrode substrate. FIG. 5 is a plan view of the row electrodes and signal electrodes of the present invention. FIG. 6 is an explanatory diagram showing a time chart when operating the liquid crystal-optical shutter of the present invention. Figure 7 (a
), FIG. 7(b), FIG. 7(C), and FIG. 7(d) are explanatory diagrams showing the transmission group at the shutter opening when the liquid crystal-optical shutter of the present invention is operated. Figure 8 shows
1 is a schematic perspective view of a printer head using a liquid crystal-optical shutter of the present invention. 21 (21a, 21b...)...
- Shirt opening 22 (22a, 22b...
)... Row electrode (common electrode) 23 (23
a, 23b...)...Signal electrode 2
4... Substrate 25... Gold I14 light-shielding mask 26... Light-shielding mask 27 having insulation properties.
... Insulating film 34, 35 ... Polarization direction 36 ... Rubbing direction 81 ... Shutter array 82 ... Photosensitive drum 83 ... Light source 84 --- Selfoc lens 85 --- Concentrating cover d --- Distance between row electrodes Patent developer Canon Co., Ltd.

Claims (9)

[Claims] (1) A time-division drive optical system comprising an electrode structure in which a plurality of signal electrodes and a plurality of row electrodes arranged opposite to the signal electrodes are arranged in a matrix, and a liquid crystal arranged between the signal electrodes and the row electrodes. An optical modulation device, characterized in that the capacitance between the plurality of row electrodes is 100 OPF (picofarad) or less. (2) The optical modulation device according to claim 1, wherein the capacitance between the plurality of row electrodes is 500 PF (picofarad) or less. (3) The optical modulation device according to claim 2, wherein the capacitance between the plurality of row electrodes is 250 PF (picofarad) or less. μ (4) The optical modulation device according to claim 1, wherein the distance between the plurality of row electrodes is maintained at a distance of 15% m to 100% m. (5) The spacing between the plurality of row electrodes is 2-Q% m~
The optical modulation device according to claim 4, wherein the optical modulation device is maintained at a distance of 50% m. (6) The optical modulation device according to claim 5, wherein the plurality of row electrodes have a length of 150 mm or more in the longitudinal direction. μ (7) The optical modulation device according to claim 6, wherein the distance between the plurality of row electrodes is maintained at a distance of 25 m to 40 m. (8) The optical modulation device according to claim 1, wherein a metal light-shielding mask is disposed in an area of the substrate having the plurality of row electrodes excluding at least an area serving as a shutter opening. (9) The optical modulation device according to claim 1, wherein an insulating light shielding mask is disposed between the plurality of row electrodes.